S07 Demethanizer

GL1.Z COMPLEX - SONATRACH

PROCESS OPERATING MANUAL MA NUAL

FRACTIONATION SYSTEM

« DEMETHANISER SECTION »

SECTION N o.07 ~ REVISION N o. 2

GL1.Z RENOVATION PROJECT

TABLE OF CONTENTS

1.0 GENERAL

1

1.1 Preamble.............................. Preamble..................................................... .............................................. .............................................. ....................................1 .............1 1.2 Introduction..................................... Introduction............................................................ .............................................. ............................................. ........................3 ..3 1.3 Location of the System in the Train..................................................... Train.......................................................................3 ..................3 1.4 Major Equipment in the Demethaniser System.....................................................3 2.0 SYSTEM DESCRIPTION

4

2.1 Process Description.................................... Description........................................................... .............................................. ....................................4 .............4 2.2 System Configuration ( Line by Line Description)........................ Description)................................................6 ........................6 3.0 PREPARATION FOR START-UP

23

3.1 Normal Start-up Preparation............................... Preparation.............................................................................. ............................................... 25 3.2 Nitrogen Purging.............................. Purging..................................................... .............................................. ............................................27 .....................27 3.2.1 Purging of the Process Side......................................... Side.................................................................... ........................... 28 3.2.2 Purging the MCR Refrigerant Side.........................................................30 Side.........................................................30 3.3 Deriming................................... Deriming.......................................................... .............................................. ....................................................32 .............................32 3.3.1 Deriming the Process Side of the Demethaniser System........................33 3.3.2 Deriming the MCR Refrigerant Side................................................ Side.......................................................38 .......38 4.0 NORMAL START-UP

41

5.0 NORMAL OPERATION

45

5.1 Normal Operating Parameters............................ Parameters................................................... ................................................45 .........................45 5.2 Feed Stream Composition............................................... Composition.......................................................................... ........................... .........47 ......... 47 5.3 Product Stream Composition............................... Composition...................................................... .............................................. .........................48 ..48 6.0 OPERATING VARIABLES

49

6.1 Internal Variables.............................. Variables..................................................... .............................................. ...........................................49 ....................49 6.1.1 Methane Refrigerant Production............................................................ Production............................................................ 49 6.2 External Variables................................ Variables....................................................... .............................................. ........................................50 .................50 6.2.1 Site Temperature........................................................ Temperature..................................................................................... ............................. 50 6.2.2 Feed Gas Composition................................. Composition........................................................ ...........................................50 ....................50 6.2.3 Butane Recycle.......................... Recycle................................................. .............................................. .......................................50 ................50

7.0 PROCESS CONTROL

51

7.1 Demethaniser Column Pressure............................ Pressure................................................... ............................................. .......................51 .51 7.2 Demethaniser Column Temperature................................. Temperature.................................................... .................................. ............... 52 7.3 Demethaniser Column Level........................................... Level...................................................................... ........................... .........52 ......... 52 7.4 Flow Control.................................... Control........................................................... .............................................. .............................................52 ......................52 7.5 Demethaniser Column Bottom Flow....................................... Flow..................................................... ............................ .............. 53 7.6 Reflux Drum Level................................................................. Level...............................................................................................53 ..............................53 7.7 MCR Vapour Back Pressure............................... Pressure...................................................... .............................................. .........................53 ..53 7.8 Process Control, Alarms, and Safety Relief Valves Set Points...........................54 8.0 NORMAL SHUTDOWN

55

8.1 Emptying of the System.......................................................................................55 8.2 Displacement of Hydrocarbons with Nitrogen........................... Nitrogen....................................................56 .........................56 9.0 SHORT TERM SHUTDOWN / START-UP

56

10.0 QUALITY CONTROL

57

11.0 PROTECTIVE SYSTEMS / EMERGENCY SHUTDOWN

59

11.1 Trip Systems and Shutdown Matrices................................. Matrices........................................................ ...............................60 ........60 11.1.1 Trip System......................................... System................................................................ ...................................................61 ............................61 11.1.2 Primary Protection System........................................ System............................................................... ............................61 .....61 12.0 SAFETY HAZARDS

62

12.1 General..................................... General............................................................ .............................................. .................................................. ........................... 62 12.2 Safety Precautions............................... Precautions...................................................... .............................................. ..................................... ................63 ..63 12.2.1 Combustible Mixtures........................................................................... Mixtures........................................................................... 64 12.2.2 Ventilation and Cleaning of Vessels and Lines.....................................64 Lines.....................................64 13.0 FIRE AND GAS DETECTION SYSTEM

65

14.0 FAILURES

65

14.1 Loss of Feed / Rundown.................................. Rundown.................................................................................. ................................................ ..66 14.2 Loss of Internal Equipment............................................................................... Equipment............................................................................... 66 14.3 Demethaniser Reflux Ref lux Pumps............................... Pumps...................................................... ...............................................67 ........................67 14.4 Loss of Utility Systems........................................... Systems.................................................................. ............................................67 .....................67 14.4.1 Power Failure................................. Failure........................................................ .............................................. ................................67 .........67 14.4.2 Instrument Air Failure..........................................................................67 14.4.3 Steam Failure................................. Failure........................................................ .......................................................69 ................................69

15.0 TROUBLE SHOOTING

70

16.0 EQUIPMENT LIST

72

16.1 Demethaniser Column X07-F-07.21................................. X07-F-07.21...................................................... ................................ ...........72 72 16.2 Demethaniser Column Condenser X07-E-07.22............................................ X07-E-07.22...............................................73 ...73 16.3 Demethaniser Reboiler X07-E-07.23................................................................ X07-E-07.23................................................................ 74 16.4 Demethaniser Bottoms Cooler X07-E-07.30.....................................................75 X07-E-07.30.....................................................75 16.5 Demethaniser Reflux Drum X07-G-07.24........................................... X07-G-07.24......................................................... .............. 76 16.6 Demethaniser MCR Separator X07-G-07.26.................................................... X07-G-07.26.................................................... 76 16.7 Demethaniser Reflux Pumps X07-J-07.25 & X07-J-07.27................................77 X07-J-07.27................................77 17.0 APPENDICES

77

17.1 DCS Print-Outs:............................................................. Print-Outs:................................................................................................ ................................... 77 17.2 Process Flow Diagrams - PFDs................................ PFDs....................................................... ........................................ ................. 77 17.3 Process and Instruments Diagrams - P&IDs.................... P&IDs.............................................. .......................... ......78 17.4 Cause and Effect Effe ct Charts - C&E Chart Chart .............................................................78 .............................................................78

DEMETHANISER SECTION

1.0

PROCESS OPERATING MANUAL

GENERAL 1.1

Preamble

The Fractionation System comprises the following four sub-systems: Section No.7:

Demethaniser System

Section No.8:

De-ethaniser System

Section No.9:

Depropaniser System

Section No.10:

Debutaniser System

These four sub-systems are arranged in series and handle the feed from one LNG Train. The liquid bottom product from the Scrub Tower X04-F-07.11 forms the feed to the Demethaniser Column X07-F-07.21. The liquid bottom product from the Demethaniser Column X07-F07.21 forms the feed to the De-ethaniser Column X08-F-07.31. The liquid bottom product from the De-ethaniser Column X08-F07.31 forms the feed to the Depropaniser Column X09-F-07.41. The liquid bottom product from the Depropaniser Column X09-F07.41 forms the feed to the Debutaniser Column X10-F-07.51. The liquid bottom product from the Debutaniser Column X10-F07.51 is the gasoline product, which after cooling in the Gasoline Cooler X10-E-07.58, is routed to the Gasoline Sphere for storage and eventual export. The purposes of the Fractionation System are as follows: a) To produce the components necessary for the normal MCR make up to the LNG Train Refrigeration Systems (methane, ethane, and propane). b) To produce liquid propane refrigerant to a high purity as make up to the Propane Refrigeration System. c)

SECTION No. 07

Route, as required, the ethane, propane, and butane to be:

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Reinjected into the feed gas at the inlet to the Main Exchanger for controlling / improving the LNG heating value. Or: Recycled back to the Scrub Tower X04-E-07.11 overheads • vapour stream. •

d)

To separate the gasoline from the LPG Stream.

e) To reprocess low purity propane refrigerant for improved purity. It is essential is to maintain the quality of the products produced in the system and to avoid routing butanes recycle / re-injection with heavier hydrocarbon components (C 5+) which would freeze in the Main Exchanger, causing plugging and subsequent loss of LNG production. The purposes from the Fractionation System are as follows: 1. Methane, which is used as MCR component make-up, as required, for increasing the pressure in the MCR Refrigeration System. 2. Ethane and propane vapour, which are used as components make up in the MCR Refrigeration Systems as required. 3. High purity liquid propane for use in the Propane Refrigeration System. 4. Ethane, propane, and butane for recycle into the Scrub Tower overhead vapour stream, as necessary. 5. Excess ethane, propane, and butane for re-injection into the feed gas at the inlet to the Main Exchanger for controlling / improving the LNG product heating value (PCS). 6. Gasoline product, which is routed to the Gasoline Sphere for storage prior to export. The purity of the products depends on the operating parameters and operation stability. This Operating Manual covers the Demethaniser System, Section No. 7.

The other Fractionation Systems are covered separately as follows: •

SECTION No. 07

Section No. 8:

De-ethaniser System

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1.2


•

Section No. 9:

Depropaniser System

•

Section No.10:

Debutaniser System.

Introduction

The main purpose of the Demethaniser System is to process the liquid product coming from the Scrub Tower X04-F-07.11 bottom in order to remove the light hydrocarbons (mainly methane) and produce liquid product (ethane and heavier hydrocarbons) for further processing in the downstream fractionation subsystems. The noncondensable vapours can either be routed to the Fuel Gas System and / or to the MCR Refrigeration System as MCR make-up, as required. The Demethaniser bottom liquid product is routed to the De-ethaniser Column X08-F-07.31 for further processing.

1.3

Location of the System in the Train

The Demethaniser System is not related to the natural gas feed flow path. However, the system is placed such that it receives the liquid product from the Scrub Tower X04-F-07.11 bottom for processing. It is the first system in the Fractionation System.

1.4

Major Equipment in the Demethaniser System • • • • • • •

SECTION No. 07

X07-F-07.21 X07-E-07.22 X07-E-07.23 X07-G-07.24 X07-G-07.26 X07-J-07.25/27 X07-E-07.30

Demethaniser Column Demethaniser Column Condenser Demethaniser Reboiler Demethaniser Reflux Drum Demethaniser MCR Separator Demethaniser Reflux Pumps Demethaniser Bottoms Cooler

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2.0 2.0

SYST SYSTEM EM DESC DESCRI RIPT PTIO ION N 2.1

Process Description

The feed to the Demethan Demethaniser iser Column Column X07-F-07.21 X07-F-07.21 is the Scrub Towe Towerr X04X04-FF-07 07.1 .11 1 botto bottom m prod produc uctt whic which h flow flowss unde underr flow flow controller FIC-X04-49. The saturated stream flashes across the flow control valve FV-X04-49 resulting in a two-phase flow in the line to the Demethaniser Column. To reduce the impact of any damage that the two-phase flow may cause, the line size is reduced from 4" to 3" downstream the FV and it is further reduced to 2" for the vertical pipe section along the Demethaniser Demethaniser Column. Column. The feed enters the Column on tray 9. The products from the Demethaniser Demethaniser System are: •

Methane vapour overhead stream, which can be routed to the Fuel Gas System or alternatively used as make up component to the MCR Refrigeration System.

•

Bottoms product, which is routed to the De-ethaniser System for further processing. See Section No.8 for details. The Demethaniser is a distillation Column, has 17 actual distillation trays each tray having one one pass. These trays are located as follows:

•

9 trays are located in the stripping (lower) section. •

8 trays are located in the rectifying rectifying (top) section. sec tion.

The tray numbering is from the top of the Column to the bottom. The Demethaniser Column normally operates at about 30.0 barg at the feed entry tray no. 9. The normal operating parameters are as follows:

Temperature, o C Pressure, barg Flow, KG/HR

Inlet 31.5

Overheads -57.9

Bottoms 91.3

30.4 19064 (H) 5084 (L)

29.7 3771 (H) 1026 (L)

30.4 18045 (H) 4805 (L)

The light hydrocarbons are separated from the feed stream and pass to the top of the Column flowing counter current to the reflux flow, cascading down the distillation trays in the Column.

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The overhead vapour stream from the Demethaniser Column flows to the Demetha Demethanis niser er Column Column Condenser Condenser X07-E-07.22 X07-E-07.22 where the overhead overhead vapour vapour is partially partially condensed condensed against against MCR Refriger Refrigerant ant Cooling. The MCR used for cooling is the high pressure MCR liquid withdrawn from upstream the warm Joule-Thomson Valve FV-X0615 located at the cold end of the warm bundle in the Main Exchanger X06-E-05.20 X06-E-05.20.. This This liquid liquid MCR is fed under level level controller controller LICX07-17 into the Demethaniser MCR Separator X07-G-07.26. The purpose of this level is to control the level in the Demethaniser Demethaniser Refl Reflux ux Drum Drum X07-G X07-G-07 -07.24 .24 by control controlli ling ng the amou amount nt of MCR Refrige Refrigerant rant passing passing through through X07-E-07.22 X07-E-07.22 and consequen consequently tly the amount of overhead condensate produced. The high-pressure MCR liquid flashes across the level valve LVX07-17 due to a pressure drop of about 35.8 bar, causing about 5.8 o C drop in its temperature (Auto-Refrigeration). The MCR vapour and and liqu liquid id are are sepa separa rated ted in X07-G X07-G-0 -07. 7.26 26 and and are are then then route routed d separately to the Demethaniser Column Condenser X07-E-07.22 to provide the necessary cooling and condensation of the Demethaniser Demethaniser Column overhead stream. The warm low pressure MCR vapour out of X07-E-07.22 is returned back to t o the Main Exchanger Exchanger downstream the warm Joule-Thomson Valve FV-X06-15. The two-phase overhead process stream out of X07-E-07.22 then flows to the Demethaniser Reflux Drum X07-G-07.24. The pressure in the Demethaniser Column is controlled by controlling the back pressure in the the Reflux Drum via via PIC-X07-03. The non-cond non-condensa ensabl blee vapours vapours because because of flashi flashing ng in the Reflux Reflux Drum are normally routed under pressure controller PIC-X07-03 via PV-X PV-X07 07-03 -03 to the the Fuel Fuel Gas Gas Mixe Mixerr Vapo Vapori rise serr X02X02-G-3 G-304 04 and and subsequently used as fuel gas make-up. Part of this stream may be routed under under flow flow controller controller FIC-X07-04 FIC-X07-04 via FV-X07-04 FV-X07-04A A to the st MCR 1 Stage Suction Drum X05-G-07.88, as necessary, for use as MCR component make-up or for increasing the pressure in the MCR Refrigeration System. Liqu Liquid id metha methane ne is pump pumped ed out of the Refl Reflux ux Drum under under flow flow controller controller FIC-X07-13 FIC-X07-13 by either either of the two Demetha Demethanis niser er Reflux Reflux Pump Pumpss X07-JX07-J-07 07.25 .25/27 /27 and is returne returned d to the top tray tray 1 of the Demethaniser Column as reflux. A total draw-off tray 17 in the bottom of the Demethaniser Column directs the liquid to the kettle type Demethaniser Reboiler X07-E07.23 07.23 where where it is heated heated and and partia partiall lly y vapour vapourise ised d again against st low pressure steam flowing flowing in the tube-side of the Reboiler. Reboiler. The hydrocarbon vapour is returned to the Column under the bottom tray 17 and passes passes back to the Column Column flowin flowing g upwards stripping stripping the

SECTION No. 07

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lighter lighter components from the liquid liquid flowing flowing down the Column. Column. The saturated liquid in the Reboiler overflows a baffle in the Reboiler and then flows under gravity flow back to the bottom of the Column. The The reboi reboile led d bottom bottom produc productt from from the Colu Column mn is cooled cooled again against st seawater in the Demethaniser Bottom Cooler X07-E-07.30 and is then routed under flow controller FIC-X07-15 to the De-ethaniser Column X08-F-07.31 for further processing. The flow controller is reset by the level controller LIC-X07-09, which senses the level in the Demethaniser Column Bottom.

2.2 2.2

Syst System em Conf Config igur urat atio ion n ( Line Line by Line Line Desc Descri ript ptio ion) n)

Refer to the Process and Instrument Diagrams listed below. These are applicable to all the six Process Trains. P&ID No

Title

85-X04-10.1 85-X06-10.1 85-X07-10 85-X08-10 85-X00-21.3

Scrub Tower System Main Exchanger - Sheet 1 Demethaniser De-ethaniser Steam and Condensate System - Sheet 3 of 3

Feed from the Scrub Tower to the Demethaniser Column The reboiled bottom product from the Scrub Tower X04-F-07.11 is route routed d to the the Deme Demeth than anis iser er Colu Colum mn X07X07-FF-07 07.2 .21 1 for for furt furthe her r processing. It leaves the Scrub Tower under flow control via line line 4"PTR-X0415-904. The following valves, instrumentations, and protective devices are installed in this 4" line: Temperature element TE-X04-108, that provides an output signal to temperature indicator TI-X04-108 on the DCS.

•

Flow element FE-X04-49 and 1½" flow control valve FV-X04-49 with a 3" upstream and a 3" downstream normally opened isolation valves and a 2" normally closed globe type bypass valve. The flow indicator controller FIC-X04-49 actuates the flow valve FV-X04-49 to control the flow but this FIC is reset by the Scrub Tower bottoms level indicator controller LIC-X04-17, which senses the level in the Scrub Tower Bottom. There is also a ¾" sample connection with double globe type valves, and a ¾" globe vent valve. Downstream the flow flow valv valves es arrang arrangem ement ent,, the flow flow is norma normall lly y routed routed to the •

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Demethaniser Column via line 3"-PTR-X0416-904 but can also be routed to the Liquid Disposal Drum X08-G-201 via the ESD Valve XV-X04-151 located in line 2"-PTR-X04212-904 by turning to the open position the hand switch HS-X04-151 via the DCS in the CCR. On instrument air failure, the XV valve fails in the open position. Downstream FV-X04-49, the line size reduces from 4" to 3" and its designation changes to 3"-PTR-X0416-904. There is a ¾" vent conn connec ecti tion on whic which h is norm normal ally ly used used duri during ng nitro nitroge gen n purg purgin ing g operation. •

•

A normally open gate isolation valve.

A derime gas supply tie-in line 2"-DR-7X004-904. This line is provided with a spectacle blind and a globe type isolation valve, which are normally kept in the closed position.

•

Ball type emergency isolation (ESD) valve XV-X04-133, which is pneumaticall pneumatically y operated by solenoid valve XY-X04-133. During norm normal al oper operat atio ions ns,, the the XV is kept kept in the the open open posi positi tion on.. On instrument air failure, the XV fails in the closed position. The XV position is indicated indicated on the DCS by ZLO-X04-133 ZLO-X04-133 (open) and ZLCX04-133 (closed). There is an input signal from the shutdown logic to the XY solenoid valve which in turn causes the XV to close and subsequently causes a process shutdown by any of the following: •

♦

PSHH-X PSHH-X07 07-12 -122 2 high pressure

Demet Demetha hani niser ser Colu Column mn high high

LSHH-X07-119 high level

Demethaniser Reflux Drum high

♦

♦

XS-X XS-X00 00-2 -27 79

Proce rocess ss Trai rain Fire or Gas Gas Dete Detect ctio ion n

The XV valve can also be closed manually via the following hand switches: ♦

HS-X HS-X07 07-12 -123A 3A

Deme Demeth than anis iser er Dep Depre ressu ssuri risa sati tion on (LCR (LCR))

♦

HS-X HS-X07 07-12 -123B 3B

Deme Demeth than anis iser er Depr Depres essu suri risa sati tion on (CCR (CCR))

♦

HS-X HS-X01 01-2 -227 27A A

Proc Proces esss Tra Train in Shut Shutdo down wn (LCR (LCR))

♦

HS-X HS-X01 01-2 -227 27B B

Proc Proces esss Tra Train in Shut Shutdo down wn (CCR (CCR))

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The XV valve can be opened and closed by hand switch HS-X04133 via the DCS. The shutdown logic ESD signal overrides hand switch HS-X04-133 operation. The 3" line reduces to 2" in size in the vertical segment along the Demethaniser Column. This is to reduce the impact of the two-phase flow and to prevent any damage to the line that could result due to possible hammering effect of the two-phase flow. The line size increases to 3" just before entry into the Demethaniser Column on the 9th tray. This 3" segment of the line is provided with temperature element TE-X07-101, which conveys an input signal to TI-X07-101 on the DCS.

Demethaniser Column overheads and Reflux Drum The vapour leaving the Demethaniser Column X07-F-07.21 overhead is routed via line 4"-M-X0701-1940 to the Demethaniser Column Condenser X07-E-07.22. This is a plate-fin type heat exchanger made of brazed aluminium and therefore, it is necessary to follow the manufacturer’s instruction regarding operation and maintenance of this exchanger to avoid any damage due to thermal shock or due to mal-operation. The following valves, instrumentations, and protective devices are installed in this 4" overhead line: •

Local pressure gauge PI-X07-12.

A 1" high point normally closed vent valve relieving to the atmosphere. •

High high pressure switch PSHH-X07-122 which provides an input signal to high high pressure alarm PAHH-X07-122 on the DCS and also provides an input signal to the shutdown logic. In the event of high high pressure in the Demethaniser Column, this will cause a process shutdown by closing ESD valve XV-X04-133 (feed inlet) and closing FV-X00-123 (low pressure steam to the Demethaniser Reboiler). •

Temperature element TE-X07-107, which provides an input signal to the temperature indicator TI-X07-107 on theDCS. •

•

A connection for a portable pressure gauge.

3"-M-X07203-1940. This line has a 2" depressurisation (ESD) valve XV-X07-113 which is normally kept in the closed position. This valve is actuated by two solenoid valves XY-X07-113A/B that receive an input signal from the shutdown logic or from hand switch •

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HS-X07-113 on the DCS. The XV position is indicated on the DCS by ZLO-X07-113 (open) and ZLC-X07-113 (closed). Downstream the XV, the line is routed to the Cold Flare and its size increases to 8". Its designation changes to 8"-FLRG-X00202-1938. This line is provided with a ½" normally closed vent connection and an 8" isolation valve which should always be kept in the open position. On power or instrument air failure, the XV valve fails in its last position prior to the failure. The shutdown logic receives input signals from the hand switches listed below which cause the XV valve to open and depressurise the Column: ♦

HS-X07-123ADemethaniser Depressurisation (LCR)

♦

HS-X07-123B Demethaniser Depressurisation (CCR)

The XV can also be opened and closed by hand switch HS-X07-113 on the DCS. Note that the shutdown logic ESD signal overrides hand switch HS-X07-113. A 1" vent connection with a normally closed gate type isolation valve. •

Take-off line 2"-FLRG-X0707-1940 on which 2" x 3" pressure safety relief valve PSV-X07-02 is mounted. The PSV is set at 34.5 barg and has a 1" globe type bypass valve, which is normally kept in the closed position. This bypass valve can be used during nitrogen purging and deriming operations. •

The overhead vapours enter the Demethaniser Column Condenser X07-E-07.22 and after cooling down against MCR Refrigerant vapour and liquid flow, the vapours are partially condensed and the two phase flow is routed by gravity via line 3"-M-X0702-1940 to the Demethaniser Reflux Drum X07-G-07.24 where the liquid and the non-condensable vapours are separated.

MCR Line from the Main Exchanger to the Demethaniser MCR Separator MCR Refrigerant used for cooling and partially condensing the Demethaniser overhead vapours is withdrawn via line 3"-MCRX0623-1940 from the high pressure MCR liquid line upstream the warm Joule-Thomson Valve FV-X06-15 located at the cold end of the warm bundle in the Main Exchanger X06-E-05.20. This line is provided with the following: •

Local flow indicator FI-X06-69.

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1" level control valve LV-X07-17 with an upstream and downstream 2" isolation valves, which are normally kept in the open position and a 1" globe type isolation valve which is normally kept in the closed position. The LV is a globe type control valve and fails in the closed position on instrument air failure. It is pneumatically actuated via an input signal from the I/P converter LY-X07-17, which receives an input signal from LIC-X07-17 on the DCS controlling the level in the Demethaniser Reflux Drum. •

The high pressure MCR liquid flashes across the LV as the pressure is dropped from 40 barg to 5.2 barg. This causes its temperature to drop from -109.4 oC to -115.2 oC (Auto-Refrigeration). The two phase low pressure MCR flow at the outlet of the LV is routed via line no. 3"-MCR-X0706-1939 to the Demethaniser MCR Separator X07-G-07.26 where the vapour and liquid phases are separated then routed to the Demethaniser Column Condenser providing cooling and partial condensation of the Demethaniser overhead vapours. See item below. Demethaniser MCR Separator to the Demethaniser Column Condenser After the high pressure MCR Refrigerant liquid flashing across the level control valve LV-X07-17 as mentioned in item no. 3.0 above, the two-phase flow is separated in the Demethaniser MCR Separator X07-G-07.26. The MCR vapour and the MCR liquid are routed separately to the Demethaniser Column Condenser X07-E-07.22 as follows: A.

MCR Vapour Flow

The low pressure MCR vapour leaves at the top of the Demethaniser MCR Separator and is routed via line 4"-MCR-X0707-1939 to the Demethaniser Column Condenser bottom inlet. This line is provided with the following: 4" x 6" pressure relief valve PSV-X07-28 set at 6.2 barg and relieving to the Liquid Disposal System via line 6"-FLRG-X07021938. This PSV is provided with a globe type bypass isolation valve, which is normally kept in the closed position. This bypass can be used during nitrogen purging and deriming operations. •

Local pressure indicator transmitter PIT-X07-00, which provides an input signal to PI-X07-00 on the DCS. •

Temperature element TE-X07-108, which provides an input signal to TI-X07-108 on the DCS. •

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A normally open globe type isolation valve which can be used to isolate the system during certain operations, e.g. during deriming of X07-E-07.22. •

1"-D-X0706-1938 routed to the Liquid Disposal. This line is normally used for draining the Condenser and during deriming operations. The line is provided with a normally closed 1" globe type isolation valve and a normally closed ¾" globe type valve releasing to the atmosphere. •

B.

MCR Liquid Flow

The low pressure MCR liquid leaves at the bottom of the Demethaniser MCR Separator via line 4"-MCR-X0708-1939. This 4" line then splits into two 3" lines feeding the Demethaniser Column Condenser bottom inlet at two opposite sides. These two 3" lines are identified as 3"-MCR-X07206-1939 and 3"-MCR-X07208-1939. The 4" line is provided with the following: Take-off line 1"-D-X0701-1938 with a normally closed globe type isolation valve. This line is routed to the Liquid Disposal and is used during emptying the Demethaniser MCR Separator. •

An in-line strainer to protect the Demethaniser Column Condenser from plugging due to foreign particles in the Liquid MCR Refrigerant. •

There are two connections for a portable pressure gauge located upstream and downstream the in-line strainer to enable reading the pressure upstream and downstream the in-line strainer and subsequently, the pressure drop across the strainer can be calculated. •

MCR from the Demethaniser Column Condenser to the Main Exchanger The MCR liquid and vapour, after providing refrigeration to the Demethaniser overhead vapours, leave the top of the Demethaniser Column Condenser as low pressure MCR vapour and is returned to the Main Exchanger downstream the warm Joule-Thomson Valve FV-X06-15. The low pressure MCR vapour leaves the Condenser via line 6"MCR-X07202-1939 which is provided with the following: Temperature element TE-X07-109 which provides an input signal to TI-X07-109 on the DCS. •

SECTION No. 07

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Pressure transmitter PT-X07-114 which provides an input signal to PIC-X07-114 on the DCS for controlling the back-pressure in the Condenser. The PIC provides an output signal to the I/P converter PY-X07-114 which in turn actuates PV-X07-114 accordingly. The PV is a 4" butterfly type control valve and it fails in the open position on instrument air failure. It is provided with an upstream and a downstream normally open gate type isolation valves and a 4" butterfly type bypass valve which is normally kept in the closed position. •

Downstream PV-X07-114, the 6" line decreases in size to 4" and its designation changes to 4"-MCR-X0709-1939. This line is provided with the following: Tie-in line 1½"-DR-X07201-1939 which is used to supply derime gas during deriming operations. This 1½" derime line originates from line no. 1"-DR-7X012-904 coming from the Derime Heaters and is provided with a spectacle blind and a globe type isolation valve which are normally kept in the closed position. •

•

A normally open 4" gate type isolation valve.

Take-off line 1"-D-X0707-1938 routed to the Liquid Disposal. This line is provided with a 1" normally closed globe type isolation valve. •

Overhead Line from the Demethaniser Reflux Drum The non-condensable vapours leave the Reflux Drum X07-G-07.24 via 3"-M-X0708-1940 and are routed either to the Fuel Gas System or to the MCR Refrigeration System as MCR components make-up as required. The following valves, instrumentation, and protective devices are installed in this 3" overhead line: 2" connection that forms one leg of the level bridle on which LSHH-X07-119 and LSLL-X07-120 are mounted. This leg of the level bridle has a 2" gate type isolation valve, which is normally kept in the open position. •

A 1½" take-off line on which 1½" X 2" pressure relief valve PSVX07-22 is mounted. The PSV is set at 34.5 barg and has a bypass with a normally closed globe type isolation valve. The discharge from the PSV is routed to the Cold Flare via 3"-FLRG-X0701-1938. •

The vapour outlet line 3"-M-X0708-1940 decreases to 1" to accommodate the ESD Valve XV-X07-117 then increases in size to

SECTION No. 07

Rev. 2

May 2001

Page 12 of 78



4" downstream of the ESD Valve and its designation changes to 4"M-X07205-1940. The following valves, instrumentation, and protective devices are installed in this overhead line from the Reflux Drum: 1" ball type ESD Valve XV-X07-117 which is normally kept in the open position. This valve is actuated by a single solenoid valve XYX07-117 that receives an input signal from the shutdown logic. The XV position is indicated on the DCS by ZLO-X07-117 (open) and ZLC-X07-117 (closed). Downstream the XV, the line increases to 4" and its designation changes to 4"-M-X07205-1940. This 4" line routes part of the overhead vapours via the ¾" on-line sample point AP-X07-115-1A for composition analysis by the on-line analyser AT-X07-115 which is common to the Demethaniser, De-ethaniser, Depropaniser, and Debutaniser overhead vapours. •

On instrument air failure, the XV valve fails in the closed position. The shutdown logic receives input signals from the switches listed below which cause the XV valve to close and isolate the Column: ♦

LSHH-X07-119

Demethaniser Reflux Drum high high level

♦

HS-X07-123A

Demethaniser Depressurisation (LCR).

♦

HS-X07-123B

Demethaniser Depressurisation (CCR)

♦

HS-X00-279

Process Train Fire or Gas Detection

♦

HS-X01-227A

Process Train Shutdown (LCR)

♦

HS-X01-227B

Process Train Shutdown (CCR)

The 4" line segment decreases in size to 1" downstream the sample point take-off and the line designation changes to 1"-M-X07111940. The following valves, instrumentation, and protective devices are installed in this 1" overhead line: Take-off line 1"-FG-X0727-1939 routed to the Fuel Gas Mixer X02-G-304. This line is provided with pressure control valve PVX07-03 controlling the pressure in the Demethaniser Reflux Drum •

SECTION No. 07

Rev. 2

May 2001

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via PIC-X07-03 on the DCS. The PIC provides an output signal to the I/P converter PY-X07-03 for actuating the PV to maintain the desired pressure in the Reflux Drum. The PV fails in the closed position on instrument air failure. There is a 1" globe type bypass valve around the PV, which is normally kept in the closed position. Upstream of the PV, there is sample connection SC-13, which is provided with a gate type and a globe type block valves that are normally kept in the closed position. Downstream of the PV, there is take-off line 1"-FG-X0729-1938 which is provided with a normally closed gate type isolation valve. This line is routed to the Cold Flare and is normally used during start-up only. The normal routing of the 1"-FG-X0727-1939 line is to the Fuel Gas Mixer Vapouriser X02-G-304. This line is provided with a normally open gate type isolation valve. Downstream this valve, the 1" line joins line 3"-FG-X0816-1939 coming from the De-ethaniser Column X08-F-07.31 overhead. The combined stream flows via line 3"-FGX0728-1939 to the Fuel Gas Mixer Vapouriser. A normally open gate type isolation valve and a check valve to prevent back flow from the Scrub Tower Separator X04-G-07.14 into the Reflux Drum. •

Tie-in line 1½"-PRG-X0437-1940 coming from the Scrub Tower Separator X04-G-07.14. This line is used to supply cold treated feed gas as MCR component make-up during start-up and when the Demethaniser Section is down. •

A 1½" spool piece accommodating flow element FE-X07-04 and flow transmitter FT-X07-04. The flow transmitter provides an out put signal to the flow controller FIC-X07-04. This flow controller also receives an input signal via a serial link from the DCS MCR components ratio control loop FY-X07-04B for controlling the ratio of methane to ethane in the MCR Refrigeration System. The FICX07-04 provides an output signal to the I/P converter FY-X07-04A for actuating the flow control valve FV-X07-04 accordingly. •

Downstream the 1½" spool piece, the line again becomes 1" in size and is provided with a flow control valve FV-X07-04 with an upstream and a downstream normally open gate type isolation valve. There is also a bypass arrangement with a 1" globe type and a 1" gate type isolation valves in series which are normally kept in the closed position. The control valve FV-X07-04 is a globe type valve and on instrument air failure, fails in the closed position. •

SECTION No. 07

Rev. 2

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Downstream the FV, the line 1"-M-X0711-1939 is routed to the MCR 1st Stage Suction Drum X05-G-07.88 for supplying methane as MCR components make-up or to raise the pressure in the MCR Refrigeration System.

SECTION No. 07

Rev. 2

May 2001

Page 15 of 78



Demethaniser Reflux Drum to the Demethaniser Reflux Pumps After the two phase flow flashing in the Demethaniser Reflux Drum X07-G-07.24, the non-condensable vapours are routed overhead to either the Fuel Gas System or the MCR Refrigeration System as MCR components make-up as described in item above. The liquid is collected in the Demethaniser Reflux Drum and flows via a common suction header to either or both of the two Demethaniser Reflux Pumps X07-J-07.25/27. This common suction header has no line designation. The Reflux Drum is provided with the following instrumentation: Temperature element TE-X07-110 which provides an input signal to TI-X07-110 on the DCS with an integrated low temperature alarm and logging facilities. •

•

Level gauge LG-X07-19.

Pressure transmitter PT-X07-03 which provides an input signal to PIC-X07-03 on the DCS. This PIC provides an output signal to the I/P converter PY-X07-03 which actuates the pressure control valve PV-X07-03 accordingly. There is also local pressure indicator PIX07-29. •

Level transmitter LT-X07-17 which provides an input signal to LIC-X07-17 on the DCS with integrated high and low level alarms. This LIC provides an output signal to I/P converter LY-X07-17 which actuates the level control valve LV-X07-17 to regulate the MCR Refrigerant flow. See Chapter No. 7 for Process Control Description. •

The following valves, instrumentation and protective devices are installed in the common suction header: A 2" take-off connection that forms the second leg of the level bridle on which LSHH-X07-119 and LSLL-X07-120 are mounted. This leg of the level bridle has a 2" gate type isolation valve, which, is normally kept in the open position. •

Ball type ESD Valve XV-X07-116, which is normally kept in the open position. This valve is actuated by a single solenoid valve XY-X07-116 that receives an input signal via the shutdown logic initiated by LSLL-X07.120. The XV position is indicated on the DCS by ZLO-X07-116 (open) and ZLC-X07-116 (closed). •

On instrument air failure, the XV valve fails in the closed position.

SECTION No. 07

Rev. 2

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The shutdown logic receives input signals from the switches listed below which cause the XV valve to close and isolate the Reflux Drum bottom outlet: •

HS-X01-227A Process Train Shutdown (LCR)

•

HS-X01-227B

•

HS-X00-279

•

LSLL-X07.120 Low Level Reflux Drum

Process Train Shutdown (CCR) Process Train Fire Gas Detection

This common suction header then splits into two 3" suction lines to each of the two Reflux Pumps. On each suction line, there is a normally open gate type isolation valve and a strainer. The suction line no. 3"-M-X0703-1940 feeds Reflux Pump X07-J-07.25 and line no. 3"-M-X0712-1940 feeds Reflux Pump X07-J-07.27. There is a derime gas supply line 1"-DR-7X003-904 which is provided with a spectacle blind that is normally kept in the closed position. This line then splits into two 1" derime lines to each of the two Reflux Pumps. On each derime line, there is a normally closed globe type isolation valve, a spectacle blind that is normally kept in the closed position, and a hose connection with a 1" normally closed globe type isolation valve. Line 1"-DR-X0701-1940 supplies derime gas to Pump X07-J-07.25 and line 1"-DR-X0702-1940 supplies derime gas to Pump X07-J-07.27. Note that the two reflux pumps are in-line vertical type and each is rated at 9.55 m³/h at 56.5 m differential head equivalent to a differential pressure of about 1.9 bar. Each pump is provided with an auto-start facility should the duty pump trip. There is a local pressure indicator on the casing of each pump, which can be monitored to indicate hydrocarbon leak into the casing. PI-X07-34 for Pump X07J-07.25 and PI-X07-35 for Pump X07-J-07.27. The casings are normally filled with methanol which acts as anti-freeze in the seal.

SECTION No. 07

Rev. 2

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Demethaniser Reflux Pumps to the Demethaniser Column During normal operations, only one of the two Reflux Pumps X07-J07.25 / 27 is on duty and the second pump is on auto-standby. The duty Reflux Pump returns the liquid from the Reflux Drum as reflux back to the top tray in the Demethaniser Column under flow control. Reflux Pump X07-J-07.25 discharge line 2"-M-X0704-1940 has a locally mounted pressure indicator PI-X07-34 with a normally open ¾" isolation valve in the instrument tubing, a check valve and a normally open globe type isolation valve. Between the check valve and the isolation valve, the following are provided: Start-up vent line 1"-M-X0705-1940 with a normally closed globe type isolation valve. Start-up line 1"-M-X0713-1940 from the discharge of Pump X07-J-07.27 ties into this line and the common line is routed back to the Reflux Drum. •

¾" x 1" thermal expansion safety relief valve TSV-X07-32 set at 48.3 barg and relieves back to the Reflux Drum. •

Drain line 1"-D-X0704-1938 with a normally closed globe type isolation valve and a globe type vent. This line is routed to the Liquid Disposal Surge Drum X08-G-201 located at the north end of the train. The drain line from the discharge of Pump X07-J-07.27 ties into this line. •

Reflux Pump X07-J-07.27 discharge line 2"-M-X0714-1938 ties into the discharge line from Pump X07-J-07.25 and also has a locally mounted pressure indicator PI-X07-35 with a normally open ¾" isolation valve in the instrument tubing, a check valve and a normally open globe type isolation valve. Between the check valve and the isolation valve, the following are provided: Start-up vent line 1"-M-X0713-1940 with a normally closed globe type isolation valve. This line ties into line 1"-M-X0705-1940 from the discharge of Pump X07-J-07.25 and the common line is routed back to the Reflux Drum. •

¾" x 1" thermal expansion safety relief valve TSV-X07-33 set at 48.3 barg and relieves via line 1"-M-X0707-1940 into the discharge •

SECTION No. 07

Rev. 2

May 2001

Page 18 of 78



line from TSV-X07-32. The common discharge line is then routed back to the Reflux Drum. Drain line 1"-D-X0705-1938 with a normally closed globe type isolation valve and a globe type vent. This line ties into the drain line from Pump X07-J-07.25 downstream the isolation valve. The common line is then routed to the Liquid Disposal Surge Drum X08G-201 located at the north end of the train. •

The common discharge header from both reflux pumps, line 2"-MX0704-1940, is routed back to the top of tray no.1 in the Demethaniser Column to provide reflux. This common discharge header is provided with flow element FE-X07-13 and flow transmitter FT-X07-13, which provides an input signal to FIC-X0713 on the DCS. This FIC is provided with a low flow alarm on the DCS. It provides an output signal to the I/P converter FY-X07-13. This in turn provides an input signal to actuate the flow control valve FV-X07-13 accordingly. The FV valve is a 1½" globe type control valve and has an upstream and a downstream normally open 2" gate type isolation valves. On instrument air failure, the FV fails in the open position. There is a bypass around the FV with a normally closed 2" globe type isolation valve. Upstream the FV, there is sample connection SC-12 with a ¾" gate type and globe type block valves which are normally kept in the closed position. Demethaniser Column to the Demethaniser Reboiler Total draw-off tray 17 in the stripping (lower) section of the Demethaniser Column directs the liquid via line 6"-PTR-X0701-904 to the kettle type Demethaniser Reboiler X07-E-07.23 where it is heated and partially vaporised against low pressure steam flowing in the tube-side of the Reboiler. This line is provided with the following: Drain line 2"-D-X0703-904 with a normally closed globe type isolation valve. This drain line is normally used whenever it is required to drain the shell side of the reboiler back to the Demethaniser bottom. •


SECTION No. 07

Rev. 2

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Page 19 of 78


•



The hydrocarbon vapour is returned via line 4"-PTR-X0702-904 to the Column under the bottom tray and passes back the Column flowing upwards stripping the lighter components from the liquid flowing down the Column. This line is provided with the following: •



The saturated liquid in the Reboiler overflows a baffle in the Reboiler and then flows under gravity flow via line 4"-PTR-X0706-904 back to the bottom of the Column. This line is provided with nitrogen connection comprising a 1" normally closed gate type valve and a threated connection. The 2" drain line 2"-D-X0703-904 from the feed line to the Reboiler line 6"-PTR-X0701-904 feeds into this 4" line. Demethaniser Column Bottom Product to the De-ethaniser Column The reboiled bottom product from the Demethaniser Column is fed under gravity flow via line 4"-PTR-X0703-904 to the Demethaniser Bottoms Cooler X07-E-07.30 where it is cooled down against seawater cooling medium flowing in the tube-side of the Cooler. The line is provided with a locally mounted temperature indicator TIX07-31. The outlet from the Cooler is routed via line 3"-PTRX0704-904 under flow controller FIC-X07-15 to the De-ethaniser Column X08-F-07.31 for further processing. The following valves, instrumentation and protective devices are installed in this 3" line: Temperature element TE-X07-111, which provides an input signal to TI-X07-111 on the DCS. This TI is provided with integral high temperature alarm. •

Ball type ESD Valve XV-X07-118, which is normally kept in the open position. This valve is actuated by a single solenoid valve XYX07-118 that receives an input signal from the shutdown logic. On instrument air failure, the XV valve fails in the closed position. The XV position is indicated on the DCS by ZLO-X07-118 (open) and ZLC-X07-118 (closed). •

The shutdown logic receives input signals from the switches listed below which cause the XV valve to close and isolate the Demethaniser Column bottoms product outlet: ♦

SECTION No. 07

Demethaniser

HS-X07-123A

Rev. 2

May 2001

Page 20 of 78



depressurisation (LCR). ♦

HS-X07-123B

Demethaniser depressurisation (CCR)

♦

HS-X01-227A

Process Train Shutdown (LCR)

♦

HS-X01-227B

Process Train Shutdown (CCR)

♦

HS-X00-279

Process Fire or Detection

♦

PSHH-X08-112

De-ethaniser high high pressure.

♦

HS-X08-115A

De-ethaniser Depressurisation (LCR)

♦

HS-X08-115B

De-ethaniser Depressurisation (CCR)

♦

PSHH-X09-124

Depropaniser high high pressure.

♦

LSHH-X09-125

♦

PSHH-X10-119

Depropaniser Reflux Drum high high level. Debutaniser high high pressure. Debutaniser high high level

•

LSHH-X10-118

Train Gas

The XV can also be opened and closed by hand switch HS-X07-118 on the DCS. Note that the shutdown logic ESD signal overrides hand switch HS-X07-118. Flow element FE-X07-15 and flow transmitter FT-X07-15 which provides an input signal to the flow controller FIC-X07-15. The FIC is reset by an input signal via the serial link from the level controller LIC-X07-09 which controls the liquid level in the Demethaniser Column Bottom. The LIC is provided with a high level and low level alarms on the DCS. •

SECTION No. 07

Rev. 2

May 2001

Page 21 of 78



Downstream FE-X07-15, the line size reduces to 2" and then to 1½" to accommodate the flow control valve FV-X07-15. It is a 1½" globe type control valve and is provided with a 2" upstream and 2" downstream isolation valves which are normally kept in the open position. It is also provided with a 1½" bypass with a normally closed globe type valve. Upstream the FV, there is sample connection SC-11 which is provided with a normally closed gate type and a globe type isolation valves. •

FIC-X07-15 provides an output signal to the I/P converter FY-X0715 which actuates the FV valve accordingly. The LIC (the Master Controller) resets the FIC (the Slave Controller) in order to maintain the liquid level in the Demethaniser Column at a pre-set level. Downstream the flow control valve arrangement, the line designation changes to 3"-PTR-X0705-904 and is routed to the De-ethaniser Column. Demethaniser Column There are three drain/vent lines, each is provided with a normally closed isolation valve but all of them have the same tag no. ¾"FLRG-X0704-1938. These lines originate from distillation trays number 2,3, and 4 in the Demethaniser Column and feed into a common header, line 1"-FLRG-X0705-1938 which is routed to the Cold Flare. There also three vent valves located in the rectifying (top) section of the Column and two vent valves located in the stripping (lower) section of the Column. All the five vent valves relieve to the atmosphere. The instrumentation listed below are provided on the Column. Note that the trays numbering is from the top of the Column to the bottom. Pressure differential transmitter PDT-X07-06 which transmits a signal to PDI-X07-06 on the DCS. The PDT measures the pressure drop across the Demethaniser Column trays. The transmitter is mounted on a bridle. One leg of the bridle is located above the top tray no.1 and the second leg is located below tray no. 16 in the lower suction of the Column. Both legs are provided with gate type isolation valves. •

Above tray 4: TE-X07-102, which provides an input signal to TIX07-102 on the DCS. This TI is provided with logging facilities. •

SECTION No. 07

Rev. 2

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Above tray 13: TE-X07-104, which provides an input signal to TIX07-104 on the DCS. •

Above tray 16: TE-X07-05, which provides an input signal to TICX07-05 on the DCS. This TIC provides an output signal via the serial link which resets FIC-X00-123 controlling the low pressure steam flow to the Demethaniser Reboiler X07-E-07.23 and consequently the temperature on tray 16 is controlled accordingly. •

Two level gauges LG-X07-10A/B with normally open block valves mounted on level bridles on the lower part of the Column. •

A level bridle mounted on the lower part of the Column, which is provided with two isolation valves that should normally be kept in the open position. •

On this bridle, the following instrumentation are mounted: D/P type level transmitter LT-X07-09 with two isolation valves which should always be kept in the open position. This LT transmits an output signal to the level controller LIC-X0709 located in the DCS. This LIC is provided with a low level alarm and a high level alarm. The LIC provides an output signal which reset the flow controller FIC-X07-15 that controls the Demethaniser Bottom product flow to the De-ethaniser. ♦

The LIC is considered as the “MASTER" controller and the FIC as the “SLAVE" controller. A secondary bridle on which LSLL-X07-121 is mounted. This LSLL is provided with two isolation valves which should normally be kept in the open position. The LSLL provides an output signal to low low level alarm LALL-X07-121 located on the DCS. ♦

3.0

PREPARATION FOR START-UP

Depending upon the reason for a shutdown, the system can be shut down to any one of a number of levels. Hence a start up can equally commence from any one of these levels. Some examples of the possible types of shutdowns / start-ups are listed below: 1. The entire Demethaniser System is shutdown, emptied, gas freed, and opened up.

SECTION No. 07

Rev. 2

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2. Hydrocarbon liquid inventory removed but left under gas pressure. 3.

Single item of equipment out of service.

4. Short-term shortage of feed stock, LNG storage capacity limitation due to shipping delays, or minor maintenance required on a vital piece of equipment. Only two of the above mentioned types of shutdowns / start-ups will be described in this Operating Manual: Normal Shutdown / Start- up, and Short Duration Shutdown / Start-up. Normal Shutdown / Start-up The shutdown of the system to be opened up for inspection / maintenance and the subsequent start-up. Short duration shutdown / start-up The shutdown of the unit to the standby state and the start-up to normal stable operations. The remaining types of shutdowns can be described by starting at an appropriate point in the normal shutdown / start-up procedure.

SECTION No. 07

Rev. 2

May 2001

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Order of Start-up / Shutdown Start-up Summary 1.

Cleanliness inspection prior to closing.

2.

Closing inspection.

3.

Removal of Vessel, Column and Equipment Blinds.

4. Pressure testing of the unit with air. Be aware of normal operating pressure limitations.

3.1

5.

Inerting of the System with nitrogen.

6.

Pre-start-up Checks.

7.

Removal of Battery Limit Blinds.

8.

Deriming of the System.

Normal Start-up Preparation

The following procedure is based on the assumption that the system was down for a prolonged period for inspection and maintenance work. If this is not the case, then part of this procedure may not be applicable. This section provides detailed guidelines to the preparatory steps required to progress a normal start-up of the Demethaniser System. It should be noted that certain items will require further detail depending on the site operating philosophy at that time. 1. Equipment Cleanliness Before any equipment is closed, it is the responsibility of the assigned Operations Personnel to ensure that all piping, vessels, Columns, and other equipment are free of debris. Debris can cause invalidation of safety systems, catastrophic failure of rotating equipment, serious fouling or damage to demister pads or Columns trays, etc. Final checks prior to closing are to be carried out by Operation Personnel. 2. Post Box-up Check

SECTION No. 07

Rev. 2

May 2001

Page 25 of 78



A full check of the system should be carried out to ensure that all flanges and man-ways have been remade with new gaskets installed. All instrumentation should have been reconnected and all block valves, control valves reinstated. 3.

Removal of Vessels, Column, and Equipment Blinds

When vessels, Columns, and equipment are boxed-up and the appropriate Work Permit have been signed off, then Blind Removal can proceed. As the Blinds are removed, they will be checked off the relevant blinds list, which should be held in the shutdown file in the Shift Engineer’s Office. 4.

Pressure Testing with Air

Prior to commencing inerting of the system, a full air pressure test should be performed. Leak testing of flanges and man-ways should be carried out at this point and suitable pressure gauges installed to enable a pressure drop test to be made. Acceptable pressure loss should be of the order of 0.20 bar per hour, bearing in mind the effect of changes in ambient temperature. The system should be depressurised to about 0.50 barg when the pressure testing is complete. 5.

Inerting

Prior to the introduction of hydrocarbons into the system, all equipment, all vessels, and pipe work will be purged with nitrogen to atmosphere until the oxygen concentration is less than 1%. Inerting can be achieved in two ways: either by slow continues purging or by the pressuring / depressurisation method. Note that the introduction of nitrogen to a unit means that a pressure source is now present. Unfortunately, none of the pressure relief devices are available as all Flare and Liquid Disposal lines are still blinded at the battery limit. They cannot be deblinded as the unit still contains oxygen. 6.

Pre-Start-up Checks

It is essential that all trip systems should be tested prior to start-up.

SECTION No. 07

Rev. 2

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Before the battery limit blinds are opened, the following checks should be carried out: 1.

All Hot Work Permits have been signed off.

2. The appropriate Relief Valves are on line and their block valves are locked open, with appropriate keys returned to the CCR. 3. All Emergency Depressurisation Valves have been function checked and all valves reset. 4. The Emergency Shutdown System has been function checked and all valves reset. 5. All Fire Detection and Fire Protection Systems are available and ready for use. 6. All non-permanent nitrogen removed and correct rating blinds fitted. 7.

connections

have

been

Removal of Battery Limit Blinds

The Demethaniser System is now inert, tightness and function checked ready to receive hydrocarbons after removal of battery limit blinds. The order should be Flare and Liquid Disposal lines first, followed by the feed product rundown line.

3.2

Nitrogen Purging It is necessary to inert the system after each shutdown that includes opening of an equipment containing hydrocarbon for inspection and maintenance work. Inerting is carried out by purging with nitrogen, utilising the pressurising and depressurising method. Refer to the P&IDs listed below. These are applicable to all the six Process Trains. P&ID No.

Title

85-504-10.1 85-507-10 85-508-10

Scrub Tower Section Demethaniser De-ethaniser

Purging the Demethaniser System covers the equipment listed below and their interconnecting piping and fittings: 1. X07-F-07.21

SECTION No. 07

Demethaniser Column

Rev. 2

May 2001

Page 27 of 78



2. 3. 4. 5. 6. 7.

X07-E-07.22 X07-E-07.23 X07-G-07.24 X07-G-07.26 X07-J-07.25/27 X07-E-07.30

Demethaniser Column Condenser Demethaniser Reboiler (Shell Side) Demethaniser Reflux Drum Demethaniser MCR Separator Demethaniser Reflux Pumps Demethaniser Bottoms Cooler

Purging of the Demethaniser System is divided into two parts: 1. Purging the Process Side. 2. Purging the MCR Refrigerant Side. These are covered in details as follows:

3.2.1

Purging of the Process Side

A. Carry out the following steps: 1.

Place all control systems in the circuit on manual.

2. Fully open all the isolation valves and all the control valves in the interconnecting lines within the Demethaniser System but excluding all battery limit isolation valves. 3. Ensure the closure of the isolation valve downstream FV-X0715 and the bypass valve around the FV. 4. Ensure the closure of the following battery limit isolation valves including those in the lines to the Cold Flare and to the Liquid Disposal and those from or to the other Process Units. a) The 3" gate type isolation valve upstream XV-X04-133 in the feed line to the Demethaniser Column. Keep the XV in the open position. b) The 8" gate type isolation valve downstream XV-X07-113 in the line to the Cold Flare. Keep the XV in the open position. c) The 1" gate type isolation valve in the start-up line 1"-FGX0729-1938 from the top of the Reflux Drum to the Cold Flare. d) The 1" gate type isolation valve in the line 1"-FG-X0727-1939 downstream PV-X07-03, which ties into the line from the Deethaniser Column that is routed to the Fuel Gas Mixer Vapouriser X02-G-304.

SECTION No. 07

Rev. 2

May 2001

Page 28 of 78



e) The 1" gate type isolation valve located downstream FV-X07-04 and the 1" isolation valve downstream the FV bypass valve in the line 1"-M-X0711-1939 to the MCR 1 st Stage Suction Drum. Keep the globe type bypass in the open position. f) The 1" globe type isolation valve in the drain lines downstream the Reflux Pumps and feeding into line 1"-D-X0704-1938 routed to the Liquid Disposal System. g) All the ¾" drain / vent valves in the Demethaniser Column.

B. Connect nitrogen hoses to the system at the following locations: 1. The 1" nitrogen connection on the Reboiler X07-E-07.23 liquid bottom outlet to the Demethaniser Column, line 4"PTR-X0706-904. 2. The two 1" hose connections downstream the isolation valves in the derime supply lines to the Reflux Pumps X07-J-07.25/27. C. Open the nitrogen supply and raise the pressure to 2 barg and block-in the nitrogen supply. Open slightly all the vent and drain valves in the system to release any trapped liquid. Briefly open the bypass valve around the Pressure Safety Valves then close. D. Depressurise the system slowly to approximately 0.50 barg via the vent and drain valves, and via the sample connections to the atmosphere. E. Repeat steps C and D above two more times or until the oxygen content of less than 1.0% is reached. At the end of the last and final depressurisation, slowly open for a short period then close the vent and drain valves in the instrument piping on level glasses, level and pressure transmitters. F. Test for oxygen content in the system after the third depressurisation. As a minimum, test at the following points: 1. Sample connection SC-11 in the bottom product line upstream FV-X07-15 to the De-ethaniser. 2. Sample connection SC-12 in the pumps common discharge (reflux) line upstream FV-X07-13. 3. Sample connection SC-13 in line 1"-FG-X07271939 to the Fuel Gas Mixer Vapouriser X02-G-304 upstream PVX07-03.

SECTION No. 07

Rev. 2

May 2001

Page 29 of 78



4. The vent valve upstream FV-X07-04 in the line to st the MCR 1 Stage Suction Drum. G. If the oxygen content is still above 1.0% continue purging the system as per steps C and D above until the 1.0% level is reached. Once this level is reached, close all vent and drain valves and all PSV’s bypass valves. Keep the system under about 0.50 barg nitrogen pressure when the final cycle is completed then close the nitrogen supply and remove the hoses.

3.2.2

Purging the MCR Refrigerant Side

During initial start-up, the nitrogen purging of the MCR Refrigerant Side within the Demethaniser System can be performed as part of the MCR Refrigeration System when purging the Main Exchanger X06E-05.20 or can be purged separately as shown below. The following procedure applies for purging the MCR Refrigerant side system independent of the MCR Refrigeration System.

SECTION No. 07

Rev. 2

May 2001

Page 30 of 78


A.


Ensure the Closure of the following valves:

1. The isolation valve upstream LV-X07-17 in the MCR line 3"-MCR-X0623-1940 in the MCR line from the Main Exchanger. Also close the bypass valve around the LV. 2. The 1" globe type isolation valve in the drain line 1"-DX0701-1938 from the bottom of the Demethaniser MCR Separator X07-G-07.26 to the Liquid Disposal. 3. The 1" globe type isolation valve in the drain line 1"-DX0706-1938 from the bottom of the Demethaniser Column Condenser X07-E-07.22 to the Liquid Disposal. 4. The bypass globe type valve around PSV-X07-28 on top of the MCR vapour outlet line from X07-G-07.26. 5. The isolation valve in the MCR vapour return line 4"MCR-X0709-1939 downstream PV-X07-114. Close the bypass valve around the PV. B. Connect a nitrogen hose to the ¾" drain connection located upstream the pressure control valve PV-X07-114 in the MCR vapour outlet line from the Demethaniser Column Condenser X07-E-07.22 and slowly commence pressurisation this part of the MCR System to 3.0 barg. Slowly depressurise the system to 0.50 barg via the following connections: 1. The ¾" drain valve located off the line 1"-D-X0706-1938 from the bottom of X07-E-07.22 to the Liquid Disposal. 2. The ¾" drain valve located upstream the level control valve LV-X07-17. Ensure that the LV and its downstream isolation valve are open. Keep the LV bypass valve in the closed position. 3. 1938.

Briefly open the 1" isolation valve in the line 1"-D-X0706-

4. close.

Briefly open the bypass valve around PSV-X07-28 then

C. Repeat the pressurisation / depressurisation until the oxygen content of less than 1.0% is reached. At the end of the last pressurisation, slowly open then close the block valves located in the tubing for portable pressure gauges upstream

SECTION No. 07

Rev. 2

May 2001

Page 31 of 78



and downstream the temporary strainer. Also briefly open then close the bypass valve around PSV-X07-28. Test for oxygen content as follows: 1. The ¾" drain connection off the line 1"-D-X0706-1938 from the bottom of X07-E-07.22 to the Liquid Disposal. 2.

The ¾" drain valve located upstream LV-X07-17.

If the oxygen content is still above 1.0% continue purging the system until the 1.0% level or less is achieved. Once this level is reached, close all vent and drain points, close the nitrogen supply and remove the hose. Keep the system under 0.50 barg nitrogen pressure.

3.3 Deriming Deriming is defined as the process of removing moisture or frost from a system that is normally operated at temperatures below 0 oC in order to prevent icing (frost formation) in the system which would affect its efficiency and performance. The medium used for deriming is usually dry natural gas feed but dry nitrogen may be used in certain circumstances. Deriming operations normally follow nitrogen purging and system inerting operations but can also take place after system’s shutdown due to suspected frost (ice) formation. Ensure that all relief valves and the emergency ESD valves are commissioned and the system has been inerted. Ensure that all hydrocarbon lines are still isolated at the battery limit. The common derime header pressure should be controlled at 5.0 barg and set the temperature controller at 65 oC maximum at the outlet of the Derime Heaters. Ensure that the derime gas pressure in the system to be derimed is always greater than the back pressure of the operational flare so that forward flow is established at all times. A stream is considered dry when the dew point of the gas is -50 oC or better. Refer to the P&IDs listed below. These are applicable to all the six Process Trains. P&ID No. 85-X00-25 85-X02-10.2

SECTION No. 07

Title Derime System Drier Section - Sheet 2

Rev. 2

May 2001

Page 32 of 78


85-X04-10.4 85-X07-10


MCR and Feed Chilling - Sheet 3 Demethaniser

A slip stream of dry gas from downstream the Mercury Removal Vessel X02-R-03.12 is routed to the Derime Heaters X02-E15.50/51 where it is heated and its temperature is controlled so that the hot derime gas to the system is supplied at 65 oC. Deriming of the Demethaniser System is divided into two parts: 1. 2.

Deriming the Process Side Deriming the MCR Refrigerant Side 3.3.1

Deriming the Process Side of the Demethaniser System

Derime gas is supplied from the Derime Heaters to the Process Side of the Demethaniser System at the following locations: Via line 2"-DR-7X004-904 to the Demethaniser feed inlet line 3"PRT-X0416-904 upstream the ESD valve XV-X04-133. •

Via line 1"-DR-7X003-904 to the Demethaniser Reflux Pumps X07-J-07.25/27 suction lines 3"-M-0703-1940 and 3"-M-X07121940 respectively. •

To proceed with deriming, carry out the following steps: A. Place the control systems listed below on manual and open all the relevant control valves:

SECTION No. 07

1. PIC-X07-03

Demethaniser Reflux Pressure Control.

2. FIC-X07-04

Methane Flow make-up).

3. LIC-X07-09

Demethaniser Column bottom level control.

4. FIC-X07-13

Demethaniser Reflux Flow Control.

5. FIC-X07-15

Demethaniser Bottom product flow control.

Rev. 2

May 2001

Control

Drum

(MCR

Page 33 of 78



Close the isolation valves downstream the above control valves except the isolation valve downstream FV-0X07-15. Keep all the upstream isolation valves in the open position. Close the bypass valves around the above control valves except the bypass valve around FV-X07-13. 1. XV-X04-133

Demethaniser Column feed inlet

2. XV-X07-113

Demethaniser Column overhead to the Cold Flare.

3. XV-X07-117

Demethaniser overhead outlet.

4. XV-X07-118

Demethaniser product to Column.

Reflux

Drum

Column bottom the De-ethaniser

Close the XV-X07-116, ESD valve in the Demethaniser Reflux Drum liquid outlet line. Close the isolation valves downstream the ESD valves except downstream XV-X07-117. C. Ensure the status of the following valves in the position shown below: 1. The closure of all the isolation valves in the lines to Liquid Disposal and to the Cold Flare. 2. and TSVs.

The closure of all bypass valves around the PSVs

3. The closure of the drain valve in line 2"-D-X0703904 off the Demethaniser Column Bottom feed line to the Demethaniser Reboiler. 4. The closure of all vent and drain valves relieving to the atmosphere. 5. The opening of all isolation valves in the interconnecting piping and on the instrument connections except those relieving to the atmosphere. 6. The closure of the isolation valve in the alternative feed gas supply as MCR make-up, line 1½"-PRG-X0437-1940 off the feed gas supply line downstream JV-X04-125.

SECTION No. 07

Rev. 2

May 2001

Page 34 of 78



D. During initial start-ups when all the Fractionation Sections need to be derimed, it is possible to achieve successful deriming by partly routing the derime gas from the bottom of the Distillation Column of one system to the next downstream Distillation Column and by routing the remaining derime gas to the Cold Flare. However, during subsequent start-ups and when it is necessary to derime just this Section of the Fractionation System, the deriming of the Demethaniser stripping (lower) Section is difficult to achieve successfully since there are no low drain points relieving to the Liquid Disposal or to the Cold Flare in this lower section of the Column. In this case, it is recommended that a hard pipe connection is installed as indicated in the procedure below. If this is not available then the use of suitable flexible hose that withstands the shut-off pressure of the derime gas under strict supervision may be necessary, although the utilisation of portable hoses is not recommended for hydrocarbon services. Note that incomplete deriming will lead to a progressive frost formation and consequent plugging of the overhead system and could possibly cause damages to parts of the overhead system e.g. the Demethaniser Column Condenser X07-E-07.22. The deriming of this part of the Demethaniser Section can be carried out in segments as follows: 1. Derime of the Overhead Section and the Reflux System Reflux Pump X07-J-07.25 or X07-J-07.27: a)

Close the isolation valves on both suction lines.

b)

Open the isolation valve on both discharge lines.

c) Close the isolation valves on the drain line off the discharge lines to liquid drain. d) Open the isolation valves on the derime gas supply line to both pumps. e) Ensure the opening of FV-X07-13, its upstream and downstream isolation valves and the bypass valve. f) Ensure the opening of XV-X07-113 and the downstream block valve. g) Ensure the upstream Demethanizer feed line is closed.

SECTION No. 07

Rev. 2

block

valve

May 2001

on

XV-X04-133

Page 35 of 78


h)


Ensure XV-X04-133 is open.

To commence deriming, proceed as follows: a) Turn to the open position the spectacle blinds in the derime gas supply lines to Demethaniser Column inlet, line 2"-DR-7X004904 and 1"-DR-7X003-904, reflux pumps. b) Commission the Derime Heaters X02-E-15.50/51 and admit gas to this Section of the Demethaniser System and pressurise to about 2.5 barg utilising the isolation valves in the above mentioned derime lines in item “a" above. c) Keep the system pressure at about 2.5 barg by ensuring continuous sufficient derime gas flow and at the same time by adjusting the opening of the following valves: The 1" globe type bypass valve around the PSV-X07-02 located off the Demethaniser Column overhead vapours line. ∗

∗

The start-up line 1"-FG-X0729-1938 to the Cold Flare.

∗

The globe type bypass valve around PSV-X07-22.

∗

The upstream block valve on XV-X07-113.

d) In order to prevent thermal shock damage to the Demethaniser Column Condenser X07-E-07.22, care should be exercised during start-up, upset, or other instances of unstable operation to limit the local metal temperature difference to 50 oF (27.8 oC) or less as recommended by ALTEC, the vendor. Also ensure that the derime gas supply temperature does not exceed 60 oC at the inlet to X07-E-07.22. This is to protect the brazed aluminium heat exchanger against damage due to high temperature. e) Although the release of hydrocarbon vapours to the atmosphere is a safety concern, it is necessary to open for a short duration at the end of this operation the drain and vent valves in all instrumentation piping on level glasses, level and pressure transmitters. This is to release any trapped liquid and moisture. This operation is to be carried out under strict supervision and with minimum release of hydrocarbons to the atmosphere. f) When the dew point of -50 oC is reached, switch deriming to the Demethaniser Reflux drum section as indicated following.

SECTION No. 07

Rev. 2

May 2001

Page 36 of 78



g) Close the discharge valves on both reflux pumps. h) Open the suction valves on both reflux pumps. i) Close the derime gas supply to the Demethanizer feed line and the bypass around PSV X07-02. j) Open XV-X07-116 on the Demethanizer reflux drum. Open XVX07-117 k) Derime through the pump suctions to the bypass around PSV X07 22 until a dewpoint of –50 °C is reached. As a minimum, test for dew point at the following locations: Sample Connection SC-12 off the Reflux line back to the Demethaniser Column upstream FV-X07-13. ∗

Sample Connection SC-13 off the Demethaniser Reflux Drum overhead line to the Fuel Gas Mixer Vapouriser upstream PVX07-03 in line 1"-FG-X0727-1939. ∗

g) If the dew point is still above -50 oC, continue deriming this part of the system until the -50 oC level or better is achieved. Once this level is achieved, continue the derime gas flow and switch the deriming operation to the remaining part of the system (Process Side) as described in Item No. 2 below. 2. Deriming the Demethaniser Column Bottom Section: a)

Close the suction isolation valves on both reflux pumps.

b)

Close the discharge isolation valves on both reflux pumps.

c) Close the valve in the derime gas supply line to both reflux pumps. d)

Close XV-X07-113/116/117.

e) turn).

Keep the PSV-X07-02 bypass valve slightly open (one

f)Open XV-07-118, upstream/downstream block valves on FV-X0715 and the bypass. g) Derime via line 2"-DR-7X004-904 into the Demethaniser feed inlet line, and out the bottom of the column to the Deethanizer

SECTION No. 07

Rev. 2

May 2001

Page 37 of 78



and out the deethanizer overhead line to the hot flare, (PSV X08 01 bypass). Most of the derime gas flow will now be diverted downwards the Column and out through the bottom to the deethanizer. When a dew point of -50 oC is reached, the deriming is deemed complete. As a minimum, test for dew point at the following locations: 1. Sample Connection SC-11 off the Demethaniser Column bottom product line upstream FV-X07-15. 2. The Nitrogen Connection off the Demethaniser Reboiler liquid return line to the Demethaniser Column. If the dew point is still above -50 oC, continue deriming this part of the system until the -50 oC level or better is achieved. Once this level is achieved, leave the system under about 1.0 barg pressure then stop the derime gas flow and decommission the Derime Heaters. Turn the spectacle blinds in the derime supply lines to the closed position. Close the valves in the drain lines and close PSV-X07-02 bypass valve. Close all drains and vents in the system.

3.3.2

Deriming the MCR Refrigerant Side

MCR Refrigerant is supplied from upstream the warm JouleThomson Valve FV-X06-15 to the Demethaniser MCR Separator X07-G-07.26 then to the Demethaniser Column Condenser X07-E07.22. During initial and subsequent train start-up, deriming this part of the MCR System can be carried out successfully as part of the MCR Refrigeration System deriming. However, when it is required to derime just this part of the MCR Refrigeration System, it is possible to derime it seperately as detailed below. Derime gas is supplied from the Derime Heaters to the MCR Refrigerant Side within the Demethaniser System via line no. 1"-DRX07201-1939 which ties-in upstream the pressure control valve PVX07-114. To proceed with deriming this part of the system, carry out the following steps:

SECTION No. 07

Rev. 2

May 2001

Page 38 of 78



A. On manual, open the level control valve LV-X07-17, its downstream isolation valve and its bypass globe type valve. Keep the upstream valve in the closed position. B. Put PIC-X07-114 on automatic control to control the derime gas pressure in the system at about 3.0 barg. Keep the PVX07-114 upstream and downstream isolation valves in the open position. Keep the bypass valve slightly open (½ turn). Also close the 4" gate type isolation valve in the line 4"-MCR-X0709-904-1938. C. Keep closed the globe type isolation valve in the drain line 1"-D-X0706-1938 and the globe type isolation valve in line 4"MCR-X0707-1939, the MCR vapour line from the Demethaniser MCR Separator X07-G-07.26.

SECTION No. 07

Rev. 2

May 2001

Page 39 of 78



D. Turn to the open position the spectacle blind in the derime gas supply line 1"-DR-X07201-1939, very slowly open the globe type isolation valve and pressurise the system to about 3.0 barg utilising PIC-X07-114. Avoid thermal shock in the Demethaniser Column Condenser X07-E-07.22. E. Open the globe type bypass valve around the pressure relief valve PSV-X07-28 and route the wet derime gas to the Liquid Disposal. Maintain the derime gas pressure at about 3.0 barg. F. Ensure that the derime gas supply temperature does not exceed 60 oC at the inlet to the MCR part of the Demethaniser System. This is to protect the brazed aluminium heat exchanger, Demethaniser Column Condenser X07-E-07.22 against possible damage due to elevated temperature. G. Once a temperature of about 55 oC is reached as read on TI-X07109, open one turn the isolation valve in the drain line 1"-D-X07061938 and the isolation valve in the MCR line 4"-MCR-X0707-1939 and route the wet gas to the Liquid Disposal. Increase the derime gas flow as necessary to maintain the 3.0 barg pressure in the system. Also open briefly then close the isolation valve in the drain line 1"-D0701-1938 from the bottom outlet of X07-G-07.26 to the Liquid Disposal. H. Under strict supervision, briefly open then close the low point drain valve upstream LV-X07-17, downstream PV-X07-114, and the drain valve off the drain line 1"-D-X0706-1938. This is to release any trapped liquid and moisture. I. When dew point of -50 oC is reached, deriming is deemed complete and the system is ready for service. As a minimum, test for dew point at the following locations: The connection for a portable pressure gauge either side of the strainer in the bottom outlet line from X07-G-07.26. ♦

♦

The drain valve upstream LV-X07-17.

♦

The drain valve off the drain line 1"-D-X0706-1938.

J. If the dew point is still above -50 oC, continue deriming until the -50 oC temperature or better is achieved. Once this temperature is achieved, deriming is complete and the system is ready to be put in service. Leave the system under about 1.0 barg pressure then stop the derime gas flow and decommission the Derime Heaters if they are no longer required for deriming other systems. Turn the to the

SECTION No. 07

Rev. 2

May 2001

Page 40 of 78



closed position the spectacle blind in the derime gas supply line. Close the drain and vent valves that were open during deriming and the bypass valve around PSV-X07-02

4.0

NORMAL START-UP

It is assumed that all pre-commissioning activities have been completed satisfactorily and that the following systems are operational: • • • •

MEA-CO 2 Removal. Gas Drying and Mercury Removal. Propane Refrigeration. Feed Chilling and Separation.

The De-ethaniser, Depropaniser, and Debutaniser are ready for service. Utilities and Auxiliary Systems are in service. If inerting and deriming of the system are necessary then these should be carried out and completed prior to starting up the system. Refer to the P&IDs listed below. These are applicable to all the six Process Trains. P&ID No.

Title

85-X04-10.1 85-X05-10.1 85-X06-10.1 85-X07-10 85-X08-10 85-X00-21.3

Scrub Tower Section MCR Compression - 1 st Stage Main Exchanger Demethaniser De-ethaniser Steam and Condensate System - Sheet 3 of 3

During initial start-up of the process train, the Demethaniser Column Condenser X07-E-07.22 will not be available since it depends on MCR Refrigerant as the cooling medium and this will only be available once the Main Exchanger final pre-cooldown is underway. In this case, the Demethaniser Column overhead vapours will not be partially condensed and will have to be routed to the Cold Flare via the start-up line 1"-FG-X0729-1938. The feed to the Demethaniser System is the bottoms product from the Scrub Tower X04-F-07.11 feeding the Demethaniser Column on distillation tray 9.

SECTION No. 07

Rev. 2

May 2001

Page 41 of 78



Prior to introducing feed into the Demethaniser Column check the following: 1.0 The ESD valves listed below should be kept in the position indicated: ♦ ♦ ♦ ♦ ♦

XV-X04-133: XV-X07-116: XV-X07-117: XV-X07-118: XV-X07-113:

Open Open Open Open Closed

2.0 Ensure that the Demethaniser Reflux Pumps X07-J-07.25/27 are properly lubricated and ready for service. 3.0 Ensure that all battery limit valves are in the closed position and all the spectacle blinds, except those in the derime gas supply lines, are in the open position. 4.0 Ensure that all safety valves are in place and that all instrumentation have been calibrated and are in place ready for service. 5.0 Place the following control valves in automatic mode with their set points as indicated in Chapter No. 7 below: ♦ ♦ ♦

PIC-X07-03 LIC-X07-09 LIC-X07-17

Demethaniser Reflux Drum Demethaniser Column Bottom Demethaniser Reflux Drum

6.0 All the remaining control valves should be kept in the closed position in manual with their block valves open and their bypass valves closed. 7.0 Commission the steam line to the Demethaniser Reboiler X07E-07.23 by slowly introducing low pressure steam in the tube side then put the Reboiler in service. Steam flow can be controlled via FIC-X00-123 on the DCS. This FIC is rest by TIC-X07-05, distillation tray 16 temperature controller. Avoid water hammer in the steam condensate line during initial start-up. 8.0 Open the isolation valve upstream the ESD Valve XV-X04133. 9.0 Slowly open the bypass globe type valve around FV-X04-49 and introduce feed to the Demethaniser Column. Pressurise the Demethaniser Column and its overheads system to about 30 barg.

SECTION No. 07

Rev. 2

May 2001

Page 42 of 78



Once this is achieved, gradually open the flow control valve FVX04-49 via FIC-X04-49. Note that if any part of the system has been opened for inspection and maintenance, the System’s pressurisation should be carried out gradually in steps of 7 barg each until reaching the normal operating pressure. At the end of each step, close the bypass valve and check the system for leaks and rectify as necessary. 10.0 Since the Demethaniser Column Condenser X07-E-07.22 is not ready for service during initial start-up, the overheads vapours will be routed via the start-up line 1"-FG-X0729-1938 to the Cold Flare. However, during subsequent start-ups and when the MCR System is operational, X07-E-07.22 will be in service and in this case, the overheads vapour will be partially condensed. The non-condensable vapours will be routed to either the Fuel Gas System and / or to the MCR Refrigeration System as MCR make-up as required. The condensed liquid will be accumulated in the Demethaniser Reflux Drum X07-G-07.24 and is then returned via the Demethaniser Reflux Pumps X07-J-07.25/27 back to the top distillation tray no.1 in the Demethaniser Column as a reflux. 11.0 As soon as a level is indicated in the downcomer from tray 17 in the Column as indicated by the level glass LG-X07-10A, increase the steam flow to the Reboiler and at the same time increase the feed flow to maintain bottoms level at about 70% as indicated via LICX07-09. Continue to increase the Column Bottoms heat input towards the normal operating set point of 91.3 oC. At this point, it is preferable to operate with a temperature slightly higher than normal in order to ensure that methane is boiled off from the liquid in the bottom of X07-F-07.21 and to prevent methane from entering the De-ethaniser Column X07-F-07.31.

SECTION No. 07

Rev. 2

May 2001

Page 43 of 78



12.0 Once high pressure MCR liquid is available from upstream the warm Joule-Thomson Valve FV-X06-15, crack open the 4" bypass valve around LV-X07-17 and start slowly cooling down the Demethaniser MCR Separator X07-G-07.26 and the Demethaniser Column Condenser X07-E-07.22. Avoid thermal shock to X07-E07.22. In order to prevent thermal shock damage to the Demethaniser Column Condenser X07-E-07.22, care should be exercised during start-up, upset, or other instances of unstable operation to limit the local metal temperature difference to 50 oF (27.8 oC) or less as recommended by ALTEC, the vendor.

Ensure that the isolation valve in line 4"-MCR-X0707-1939 is open and the drain valve in line 1"-D-X0706-1938 is closed. Also ensure that PIC-X07-114 is in automatic control and its upstream and downstream isolation valves are open and the bypass valve is closed. The isolation valve in line 4"-MCR-X0709-1938 downstream PVX07-114 should be in the open position. The design calls for this valve to be locked open. 13.0 After X07-G-07.26 and X07-E-07.22 have been slowly cooled down to about -115 oC, slowly open LV-X07-17 and introduce MCR into X07-G-07.26 and X07-E-07.22. Attention must be paid not to disturb the Main Exchanger operations. 14.0 As the Demethaniser Column overhead vapour rate increased, condensation will occur in X07-E-07.22 and a level will build up in the Reflux Drum. 15.0 Cool down both Reflux Pumps X07-J-07.25 / 27 by slightly opening (½ turn) the suction valves and bleeding the flow via the pumps discharge lines to the Liquid Disposal and routing the vapour back to the Reflux Drum. 16.0 Once normal liquid level is built up in the Reflux Drum, put either of the two Reflux Pumps on full recycle to the Reflux Drum via the start-up line. Slowly open the reflux flow control valve FVX07-13 via FIC-X07-13 on manual and commence reflux flow to the Demethaniser Column. Level Controller LIC-X07-17 will maintain the normal level in the Reflux Drum by adjusting the MCR Refrigerant liquid flow necessary for cooling and partially condensing the Demethaniser Column overheads vapour.

SECTION No. 07

Rev. 2

May 2001

Page 44 of 78



17.0 Continue to increase slowly the steam flow to the reboiler and gradually increase the reflux flow as necessary to improve fractionation. 18.0 As the Demethaniser Column temperature profile approaches design conditions, place TIC-X07-05 into cascade mode with FIC-X00-123 to maintain distillation tray 16 temperature of approximately 91.3o C. 19.0 Once the Demethaniser overheads vapour composition is satisfactorily as analysed via the in-line gas chromatograph analyser AT-X07-04, supply of methane make up to the MCR Refrigerant System can be commenced as necessary. 20.0 At this stage, ensure that all controllers within the system, except LIC-X07-09 and FIC-X07-15, are in automatic mode. 21.0 Before feeding bottoms liquid product via the Demethaniser Bottoms Cooler X07-E-07.30 to the De-ethaniser Column, ensure that Column X08-F-07.31 is ready to be put in service and is pressurised to about 19 barg via the bypass around FV-X07-15. Ensure that there is a steam flow through the De-ethaniser Reboiler X08-E-07.33 prior to admitting feed to the De-ethaniser Column.

5.0

NORMAL OPERATION

This section covers the normally required operations expected in the Demethaniser Section. These operations include those necessary to react to changes in the Operating Variables in Chapter No. 6 below. Operator actions include the normal control of the following: 1. The Demethaniser Column and its associated Reboiler and Condenser System including the control of the reflux flow. 2. The control of the high pressure MCR liquid flow from upstream of the warm Joule-Thomson Valve FV-X06-15 in the Main Exchanger. 3.

5.1

Methane make-up to the MCR Refrigeration System.

Normal Operating Parameters

SECTION No. 07

Rev. 2

May 2001

Page 45 of 78



Typical operating parameters for the Demethaniser System are listed below and these mainly depend on the feed gas flow rate and composition. Refer to the Process Flow Diagram No. 85-X07-PF-10B. All data listed below is based on 100% design capacity. Temperature, oC L.F.C H.F.C

Pressure, barg L.F.C H.F.C

31.3

31.2

30.02

30.02

Demethaniser Column Overhead Vapour

-59.5

-57.6

29.67

29.67

Reflux Stream

-86.9

-86.1

29.33

29.33

Demethaniser Bottoms (hot)

90.2

87.4

30.36

30.36

Demethaniser Bottoms Product

41.0

41.0

28.92

28.92

MCR Refrigeration to X07-E-07.22

-115.0

-114.9

4.16

4.16

MCR Refrigeration ex X07-E-07.22

-102.3

-102.3

2.44

2.44

Stream

Feed to the Demethaniser Column

Flow Rates Unit

L.F.C.

H.F.C

Feed to the Demethaniser Column

kg/h

4,869

17,827

Demethaniser Column Overhead Vapour

kg/h

1,009

3,660

Reflux Stream

kg/h

737

2,694

Demethaniser Bottoms Product

kg/h

4,596

16,861

MCR Vapour to X07-E-07.22

kg/h

157

591

MCR Liquid to X07-E-07.22

kg/h

3,265

12,365

MCR Refrigeration ex X07-E-07.22

kg/h

3,422

12,956

During normal operations, the flow rates are most likely to be at some points between the two possible cases shown above. Notes: L.F.C.:

SECTION No. 07

Light Feed Gas Case

Rev. 2

May 2001

Page 46 of 78



H.F.C.: 5.2

Heavy Feed Gas Case Feed Stream Composition

The feed entering the Demethaniser Column is withdrawn from the Scrub Tower Bottom and its composition depends on whether the feed gas to the train is lean or rich. However, during normal operations, the feed gas composition is most likely to be at the some point between the two possible feed gas compositions shown below.

Components

Formula

Nitrogen

N2

Methane

L.F.C.

H.F.C.

Mole %

Mole %

0.08

0.04

CH4

15.37

15.01

Ethane

C2H6

18.05

19.51

Propane

C3H8

20.64

22.12

Iso-Butane

iC4H10

9.55

10.44

Normal Butane

nC4H10

21.77

17.78

Iso-Pentane

iC5H12

7.20

4.69

Normal Pentane

nC5H12

7.34

4.79

Hexanes and Heavier

C6+

0.00

5.62

100.00

100.00

Total

SECTION No. 07

Rev. 2

May 2001

Page 47 of 78



5.3

Product Stream Composition

The non-condensable overhead vapour is rich in methane and is normally routed to the Fuel Gas System or alternatively, part of this vapour is used as MCR Refrigerant Make-up. The Demethaniser Bottoms Product is rich in ethane and heavier hydrocarbons and is routed to the De-ethaniser Column for further processing. Its composition depends on the feed gas composition entering the train. However, during normal operations, the composition is most likely to be at some point between the two possible compositions shown below:

Components

Formula

L.F.C.

H.F.C.

Mole %

Mole %

Methane

CH4

0.35

0.35

Ethane

C2H6

20.89

22.50

Propane

C3H8

24.45

26.08

Iso-Butane

iC4H10

11.31

12.30

Normal Butane

nC4H10

25.78

20.96

Iso-Pentane

iC5H12

8.53

5.53

Normal Pentane

nC5H12

8.69

5.65

Hexanes and Heavier

C6+

0.00

6.63

100.00

100.00

Total

SECTION No. 07

Rev. 2

May 2001

Page 48 of 78


6.0


OPERATING VARIABLES

The main responsibility of the DCS Panel Operator regarding the Demethaniser Section Operation is to maintain the quality of the products leaving this section. This is normally accomplished by the automatic controls described in Chapter No. 7 below, but requires the Operator to monitor the process variables and to intervene as necessary: When changes occur that would cause the product qualities to vary outside the allowable range. •

An understanding of the process is necessary to permit the Operator to anticipate the operating changes required due to changes in the Process Variables and thereby avoiding production of off specifications product. •

The operator is confronted with three types of Process Variables: 1. Observable Variables: Pressure, Temperature, Level, Flow, Stream Composition. 2. Internal Variables to this Section: These variables are dependent on special or alternate modes of operation within the system and which the Operator has control over, e.g. MCR Refrigerant Flow and Reflux Flow Rates. 3. External Variables to this Section: These variables are beyond the Operator control, e.g. Feed Gas Composition, Ambient Temperature, etc. Changes in each type of variables require the Operator to react in a particular way.

6.1

Internal Variables 6.1.1

Methane Refrigerant Production

To produce methane for use as MCR Refrigerant Make-up at design rates, the Demethaniser Column Overheads Vapour needs to be cooled down at minimum temperatures and providing maximum reflux flow. At temperatures above -80 oC in the Reflux Drum, methane can be produced but not at design rates and may be contaminated with ethane. However, methane make-up which contains small amounts of ethane to the MCR Refrigeration System

SECTION No. 07

Rev. 2

May 2001

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should not be a problem because the MCR Refrigerant contains both components. The Operator should take care not to withdraw excessive MCR Refrigerant from upstream the warm Joule-Thomson Valve FV-X06-15, which could upset the Main Exchanger operations.

6.2

External Variables 6.2.1

Site Temperature

Site temperature variations have no major effect on the operation of this system.

6.2.2

Feed Gas Composition

The light feed gas case and the heavy feed gas case compositions result in changes in the product splits and composition from the Fractionation Systems. Changes in the feed gas composition cause the distribution of the product to change and may require adjustments to the Demethaniser Column Reflux flow rate and steam flow to the Reboiler X07-E-07.23. The variation in the flow rate and composition of the bottom products from Scrub Tower X04-F-07.11 due to changes in the feed gas composition will produce large disturbances in the operation of this system.

6.2.3

Butane Recycle

When butane is recycled back to the Scrub Tower X04-F-07.11 from the Debutaniser Section, and depending on the amount recycled, it could cause a build up of the butane content in the feed stream from the Scrub Tower to the Demethaniser Column. In this case, the Operator needs to adjust the operating parameters within the system accordingly to maintain product specification.

SECTION No. 07

Rev. 2

May 2001

Page 50 of 78


7.0


PROCESS CONTROL

The following DCS Control Loops are associated with the Demethaniser System: 1. Pressure:

Regulates the vapour outflow.

2. Temperature:

Regulates the reboiler rate.

3. Level:

Regulates the liquid outflow.

4. Flow:

Regulates the reflux flow rate back to the Column.

5. Product Flow:

Regulates the Demethaniser Column Bottoms product flow.

6. Reflux Drum Level:

Regulates the level in the Reflux Drum by controlling the MCR Refrigerant to the Demethaniser Column Condenser X07-E07.22.

7. MCR Pressure:

Regulates the MCR vapour back pressure in X07-E-07.22.

7.1

Demethaniser Column Pressure

The pressure in the Demethaniser Column X07-F-07.21 is controlled by PIC-X07-03, which provides an output signal to the I/P converter that actuates the pressure control valve PV-X07-03 accordingly. An increase in the pressure results in the control valve opening and a corresponding increase in the vapour outflow from the Reflux Drum X07-G-07.24 to the Fuel Gas System. A decrease in the pressure works in the reverse direction. The vapour flow rate out the Reflux Drum should be steady during normal operation. However, changes in the feed flow rate to the Demethaniser Column, Feed Composition, MCR Refrigerant flow rate, or any other change that results in an increase or decrease in the Column operating pressure will immediately cause a change in the vapour flow rate out of the Reflux Drum.

SECTION No. 07

Rev. 2

May 2001

Page 51 of 78


7.2


Demethaniser Column Temperature

The temperature on tray 16 is very sensitive to changes in the methane and ethane content and so is used to control the heat input into the Column. This is accomplished by cascading the temperature controller TIC-X07-05 with flow controller FIC-X00-123 controlling the low-pressure steam flow to the Reboiler X07-E07.23. An increase in the temperature indicates a decrease in the methane content on tray 16, which could lead to a high ethane content in the overhead vapour stream. A decrease in temperature indicates an increase in the methane content, which could lead to high methane in the bottom product. The low-pressure steam flow to the Reboiler is increased when the temperature is low and decreased when the temperature is high.

7.3

Demethaniser Column Level

The level in the bottom of the Column and in the product side of the baffle in the Reboiler X07-E-07.23 is controlled by LIC-X07-09. This LIC provides an output signal, which resets the flow controller FIC-X07-15. The FIC provides an output signal to the I/P converter FY-X07-15, which actuates the flow control valve FV-X07-15 located in the bottom product line that feeds the De-ethaniser Column. The LIC is considered as the “MASTER" Controller and the FIC as the “SLAVE" Controller.

7.4

Flow Control

A. Feed Flow Rate The inlet flow rate to the Demethaniser Column is determined by the throughput to the Scrub Tower X04-F-07.11. The flow rate is controlled via FIC-X04-49 in the Feed Chilling and Separation System and not via any controller in the Demethaniser System. B. Reflux Flow Rate The reflux flow is controlled by FIC-X07-13 and should be adjusted with changes in the feed rate or composition to maintain the quality of the product streams.

SECTION No. 07

Rev. 2

May 2001

Page 52 of 78



Changing the reflux flow affects the overhead control system if it results in a change in level in the Reflux Drum. If the reflux is decreased and the level in the Reflux Drum builds-up, the level controller LIC-X07-17 will provide an input signal to the I/P converter LY-X07-17 which in turn provides a pneumatic signal to LV-X07-17 to slightly close and thus decrease the MCR Refrigerant flow. This will result in a decrease in the overheads vapour condensation rate and consequently, a decrease in the inflow of condensed liquid into the Reflux Drum.

7.5

Demethaniser Column Bottom Flow

The net product from the Demethaniser Column Bottom is drawn from the overflow section in the Reboiler X07-E-07.23 under gravity flow. This liquid, after cooling against seawater flow in the Demethaniser Bottoms Cooler X07-E-07.30 is then fed to the Deethaniser Column X08-F-07.31 on flow control by FIC-X07-15 reset by level controller LIC-X07-09. 7.6

Reflux Drum Level

The flow of liquid out of the Reflux Drum is controlled by flow controller FIC-X07-13, reflux flow to the Demethaniser Column. The level in the Reflux Drum is maintained by adjusting the MCR Refrigeration flow into X07-E-07.22 thereby controlling the fraction of Demethaniser Column Overheads condensed. This is accomplished by adjusting the MCR Refrigerant supplied via LVX07-17 to the Demethaniser MCR Separator X07-G-07.26 and consequently regulating the MCR flow through the Condenser X07E-07.22. The overhead vapour stream from the Demethaniser Column is saturated (at its dew point temperature) and contains both methane (about 85 mole%) and ethane (about 15 mole%) with negligible amounts of nitrogen and propane. Therefore, the amount of liquid condensed from this stream varies with temperature at a constant operating pressure. Hence, by varying the MCR flow, the outlet temperature from X07-E-07.22 and the condensed liquid flow into the Reflux Drum will vary. 7.7

MCR Vapour Back Pressure

The MCR vapour back pressure in the Demethaniser Column Condenser is controlled by PIC-X07-114 on the DCS which provides an output signal to the I/P converter PY-X07-114 that actuates the control valve PV-X07-114 accordingly. The PIC is to keep the

SECTION No. 07

Rev. 2

May 2001

Page 53 of 78



pressure at the outlet of the Condenser at a preset point so that the pressure downstream the control valve is sufficient to enable the MCR vapour return to the Main Exchanger downstream the warm Joule-Thomson Valve FV-X06-15 without causing any disturbance to the Main Exchanger operations.

7.8

Process Control, Alarms, and Safety Relief Valves Set Points

P&ID No. 85-507-10.0

85-500-21.3

Tag No.

Set Point

Unit

As required 225 0 740 550 4,600

kg/h kg/h kg/h kg/h kg/h kg/h

C1 make-up

PIC-X07-03 PIC-X07-114 PAHH-X07-122

29.4 3.14 32.7

barg barg barg

Overheads pressure MCR back pressure Causes process shutdown

LAH-X07-01 LAL-X07-01 LIC-X07-09 LAH-X07-09 LAL-X07-09 LIC-X07-17 LAH-X07-17 LAL-X07-17 LAHH-X07-119 LALL-X07-120 LALL-X07-121

75 20 70 75 25 50 75 25 75 25 25

% % % % % % % % % % %

MCR level in X07-G-07.26

FIC-X07-04 FAH-X07-04 FAL-X07-04 FIC-X07-13 FAL-X07-13 FIC-X07-15

Remarks

Reflux flow Product bottoms flow

Level in X07-F-07.21

Level in X07-G-07.24

Causes process shutdown Causes process shutdown Causes process shutdown

TIC-X07-05 TAL-X07-103 TAL-X07-110 TAH-X07-111

90 -17.5 -100 56

o

PSV-X07-02 PSV-X07-22 PSV-X07-28 TSV-X07-32 TSV-X07-33

34.48 34.48 6.2 48.3 48.3

barg barg barg barg barg

Tray 16 temperature Tray 3 temperature Temperature in G-07.24 Bottom Product Temperature X07-F-07.21 Overhead X07-G-07.24 Overhead X07-G-07.26 Overhead X07-J-07.25 Discharge X07-J-07.27 Discharge

kg/h

Steam flow to X07-E-

FIC-X00-123

SECTION No. 07

1,760

Rev. 2

C C o C o C o

May 2001

Page 54 of 78



07.23

8.0

NORMAL SHUTDOWN

The following procedure is used for a normal shutdown of the system. Variations to this procedure may be issued prior to the shutdown depending on other known conditions at the time. This procedure covers all aspects involved in bringing this Fractionation Section to a gas free state and ready for vessel entry. It can be used to cover any level of shutdown. Whenever positive isolation is necessary, e.g. to enable vessel entry, the relevant part of the system requires blinding.

8.1

Emptying of the System

1. Gradually reduce the feed flow, the reflux flow, the steam flow to the reboiler, and the MCR Refrigerant flow until the overheads liquid production ceases. Once this occurs, stop the reflux pumps and ensure that neither of the reflux pumps runs dry with loss of suction. 2. Allow the Demethaniser Column t o empty to the Deethaniser Column X08-F-07.31 until a low level alarm state is achieved then close LIC-X07-09 and isolate the level control valve LV-X07-09. Ensure that the opening of the globe type drain valve in line no. 2"-D-X0703-904 off the reboiler feed line to the reboiled liquid return line back to the Demethaniser Column. This is to drain the Reboiler. Maintain a small steam flow through the reboiler until the reboiler is drained. 3. Route all the overheads vapour to the Cold Flare via the start-up line 1"-FG-X0729-1938. 4. When the Column is empty, turn to the open position the spectacle blind in the derime gas supply lines 2"-D-7X004-904 and 1"-DR-7X003-904 then crack open the isolation valves and gas sweep the feed line to the De-ethaniser Column. This will assist in purging the reflux lines and in the disposal of any liquid in the system. Stop the derime gas after the above is completed. 5. Open the block valves in the drain lines off the Reflux Pumps discharge and drain both pumps to the Liquid Disposal via line no. 1"-D-X0704-1938. Once this is completed, close the block valves.

SECTION No. 07

Rev. 2

May 2001

Page 55 of 78



6. The Condenser X07-E-07.22 can also be freed of any remaining liquid by sweeping it with derime gas via line no. 1"-DR-X072011939 after turning the spectacle blind in this line to the open position. This should be carried out very carefully and avoid thermal shock. In order to prevent thermal shock damage to the Demethaniser Column Condenser X07-E-07.22, care should be exercised during start-up, upset, or other instances of unstable operation to limit the local metal temperature difference to 50 oF (27.8 oC) or less as recommended by ALTEC, the vendor.

7. Once the Column is drained off, depressurise the Column and ensure that the steam flow was stopped to the Reboiler X07-E07.23.

8.2

Displacement of Hydrocarbons with Nitrogen

1. With the exception of the Cold Flare and Liquid Disposal, all battery limit lines should be isolated by closing the relevant isolation valves. 2. Open all control valves with the exception of PV-X07-03. Keep all ESD valves in the system open with the exception of XVX07-113 which should be kept in the closed position. 3. Connect suitable flexible hose to the nitrogen connection off the reboiled liquid line between the Reboiler and the Column and pressurise the system slowly with nitrogen to 3.0 barg then depressurise to the Cold Flare and to the Liquid Disposal via every possible line including via the PSV’s bypass. 4. Repeat pressurisation and depressurisation t until the system is hydrocarbon free.

9.0

SHORT TERM SHUTDOWN / START-UP

The Demethaniser Section may be shut down for a short duration as a result of: 1. Trip of equipment within the train. 2. Maintenance being required on a vital piece of equipment within the train affecting the feed supply to this Section. In either of these cases, the Demethaniser Column could be placed into total reflux mode. However, if complete shutdown of this

SECTION No. 07

Rev. 2

May 2001

Page 56 of 78



section is necessary, then follow the procedure given in Chapter No. 8.0 above. The system should be restarted following the applicable procedure when the source of the trip has been rectified. The duration of a shutdown involving maintenance will depend on the complexity of the repairs. Subsequent start up should follow the relevant sections of the procedure given elsewhere in this Operating Manual.

10.0 QUALITY CONTROL

The Reflux Drum overheads vapour stream is continuously monitored for quality by the on-line analyser AT-X07-115 via the sampling point AP-X07-115A, which is located downstream the ESD Valve XV-X07-117. This stream is normally routed to the Fuel Gas System as Fuel Gas Make-up and / or to the MCR Refrigeration System, as required, as MCR Make-up. The analyser measures the content of methane, ethane, and propane, if any, in the stream (Composition Analysis). The composition specification for the methane make-up is set so that when added to the MCR Refrigerant, it will increase the methane content relative to the other components (methane to ethane ratio). The composition specifications of the overheads vapour are maintained by controlling the operation of the Demethaniser Column. If the correct operating parameters (pressure, temperature, reflux flow, and MCR Refrigerant flow) are maintained, the overheads vapour from the Reflux Drum will be to specification. A reduction in the operating pressure, an increase in the operating temperature, or a decrease in the reflux flow will cause an increase in the ethane content. This occurs because a decrease in pressure without an associated increase in the reflux flow rate enhances the stripping action in the Column and a shift in the product composition, i.e. more overheads vapour produced. The bottom product from the Column is not continuously monitored by the on-line analyser as this stream is routed to the De-ethaniser Section for further processing. For regular laboratory analysis, the following sampling points are provided: •

SC-11:

SECTION No. 07

Bottom product to the De-ethaniser Column.

Rev. 2

May 2001

Page 57 of 78



•

SC-12:

Reflux flow to the Demethaniser Column.

•

SC-13:

Overheads vapour flow to the Fuel Gas / MCR Systems.

Laboratory analysis of the samples taken via the SC-13 can also be used to verify the accuracy of the on-line analyser AT-X07-115. In addition to the regular samples, additional samples should be taken whenever the quality of a product stream is in question. The composition (mole %) of the above streams have the following restrictions:

SECTION No. 07

Rev. 2

May 2001

Page 58 of 78



Component

Formula

Overhead Vapour

Reflux Flow

Bottom Product

Nitrogen

N2

L.F.C 0.23

Methane

CH4

85.62

84.56

80.86

79.47

0.35

0.35

Ethane

C2H6

14.12

15.27

18.97

20.41

20.89

22.50

Propane

C3H8

0.03

0.04

0.05

0.06

24.45

26.08

Iso-Butane

iC4H10

0.00

0.00

0.00

0.00

11.31

12.30

Normal Butane

nC4H10

0.00

0.00

0.00

0.00

25.78

20.96

Iso-Pentane

iC5H12

0.00

0.00

0.00

0.00

8.53

5.53

Normal Pentane

nC5H12

0.00

0.00

0.00

0.00

8.69

5.65

C6+

0.00

0.00

0.00

0.00

0.00

6.63

100.00

100.00

100.00

100.00

100.00

100.00

Hexanes & Heavier

Total

H.F.C 0.13

L.F.C 0.12

H.F.C 0.06

L.F.C. 0.00

H.F.C 0.00

11.0 PROTECTIVE SYSTEMS / EMERGENCY SHUTDOWN

There are three levels of protection: 1. Tertiary Protection: This protection is represented by the control valves (PCVs, FCVs, TSVs, and LVs). During normal operation, these control valves when operating satisfactorily will keep the system within the specified operating parameters and hence keep the system under safe conditions. 2. Secondary Protection: This protection is represented by the emergency shutdown valves (XVs) which either close or open to keep the system under safe operating conditions in the event of control valves failures, maloperation or in an emergency situation. The system is provided with depressurisation valves (ED) for use in an emergency. The use of these valves is usually preceded by an ESD initiation.

SECTION No. 07

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The ED valves cannot be positioned. They are either open or closed. The ED valves are provided with secured air supply which will permit the opening and closing of the valves three times in the event of an instrument air failure. Activation switches are located in the CCR. If all the ED valves contained within one LNG Train were opened simultaneously, the vapours released would most likely exceed the design capacity and hence the pressure rating of the LNG Emergency Flare System. 3. Primary Protection: This is the ultimate protection and is presented by the safety relief valves: PSVs and TSVs. In this case, when the secondary and / or the tertiary protection fail to keep the system under safe operating conditions, the relief valves open.

11.1

Trip Systems and Shutdown Matrices

The Demethaniser System has been provided with a number of trip systems to protect equipment and personnel and prevent hazardous operating conditions from occurring. These systems, which are activated in the CCR, can be separated into two areas as follows: 1. 2.

The overall emergency shutdown system. Individual equipment emergency shutdown.

A number of these trips are simple and self-explanatory and therefore require no further explanation. However, there are a number of trips that are more complicated and require some clarification. Refer to the following Cause and Effect Charts: C&E Chart No. CE-85-X07-02

SECTION No. 07

Rev. 2

Demethaniser Section

May 2001

Page 60 of 78



11.1.1 Trip System

The Demethaniser System is provided with the following trip systems: A. PSHH-X07-122, which provides an output signal to alarm PAHH-X07-122 on the DCS and also to the shutdown logic. On initiation of this signal, the shutdown logic will cause the following: Close the ESD Valve XV-X04-133 and thus stops the feed from the Scrub Tower X04-F-07.11 to the Demethaniser Column. •

Close FV-X00-123 and thus stop the low-pressure steam supply to the Demethaniser Reboiler X07-E-07.23. •

B. LSHH-X07-119, which provides an output signal to alarm LAHH-X07-119 on the DCS and to the shutdown logic. On initiation of this signal, the shutdown logic will cause the following: Close the ESD Valve XV-X04-133 and thus stop the feed from the Scrub Tower X04-F-07.11 to the Demethaniser Column. •

Close the ESD Valve XV-X07-117 and thus isolate the Reflux Drum overheads to prevent the risk of liquid carry over. •

C. LSLL-X07-120, which provides an output signal to alarm LALLX07-120 on the DCS and also to the shutdown logic. On initiation of this signal, the shutdown logic will cause the following; Stop the duty Reflux Pump(s) X07-J-07.25/27.

•

11.1.2 Primary Protection System

The following safety devices provide the ultimate protection of the System: 1. PSV-X07-02 set at 34.5 barg and is located off the Demethaniser Column overhead vapour outlet line. It discharges to the Cold Flare. A hand operated bypass globe valve (1") is also installed around this PSV. The valve can be used during deriming operations.

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2. PSV-X07-22 set at 34.5 barg and is located off the Reflux Drum overhead vapour outlet line. It discharges to the Cold Flare. A hand operated bypass globe valve (1") is also installed around this PSV. The valve can be used during deriming operations. 3. PSV-X07-28 set at 6.2 barg and is located off the Demethaniser MCR Separator overhead vapour line. It relieves to the Liquid Disposal System. A hand operated bypass globe valve (1") is also installed around this PSV. The valve can be used during deriming operations. 4. TSV-X07-32 set at 48.3 barg and is located off Reflux Pump X07-J-07.25 discharge line. It discharges back to the Reflux Drum. 5. TSV-X07-33 set at 48.3 barg and is located off Reflux Pump X07-J-07.27 discharge line. It discharges back to the Reflux Drum. 6. PSE-X00-145 set at 20.3 barg and is located off the steam inlet line to the Demethaniser Reboiler. This is a rupture disc safety device installed to protect the steam and condensate systems in case of a reboiler tube rupture. Upon reaching the set point pressure, it relieves to atmosphere. There is an isolation valve located upstream of the PSE. In the event of disk rupture, it can be isolated by closing this valve and replacing the disc.

12.0 SAFETY HAZARDS 12.1

General

The role of the Demethaniser System is to produce methane rich overheads vapour, ethane and heavier bottoms product for further processing in the downstream Fractionation Units. The methane rich overheads vapour is lighter than air and will rise and dissipate when discharged into the atmosphere. Ethane and heavier bottom product stream is a colourless transparent liquid with a gaseous smell and is almost insoluble in water but soluble in alcohol and ether. This liquid is electrically non-conductive but can accumulate a static charge while flowing or in the event of leakage. This in turn will bring about a danger of fire due to a spark discharge. To prevent this from occurring, all equipment should be grounded.

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12.2


Safety Precautions

Except for methane which is lighter than air and will rise and dissipate when discharged into the atmosphere. Ethane, propane, butanes and heavier hydrocarbons have the same or higher density as air and therefore, any leakage or spillage will concentrate and accumulate at low points such as drains, ditches, etc., spreading at ground level to form a combustible mixture with air. In this context, all the leaks and spills should be stopped, contained and dispersed quickly so that fire and explosion risks are prevented or minimised. Great care should be taken to see that all pumps and motors are well lubricated and maintained to ensure that mechanical defects do not become sources of ignition. Any maintenance work in the near vicinity of a leak should be stopped, as there is the danger of tools creating sparks unless special non-sparking tools are being used. High vapour concentrations of all components will cause oxygen deficiency while lower concentrations will have an anaesthetic effect. Personnel must not enter an area suspected to be deficient of oxygen until the vapours and their causes have been cleared and the appropriate gas test shows the oxygen content will sustain life, i.e. about 20% oxygen. The atmosphere should also be tested for toxic material. If an inert atmosphere must be maintained, personnel must be equipped with self contained breathing apparatus and enter the area using the appropriate safety code for such work, e.g. standby personnel with extra breathing apparatus sets, belt and safety line to effect a rescue in case of an emergency. There are potential cold hazards due to the low processing temperature of the treated gas, propane and the MCR circuits. Any contact of the skin can cause severe burn type injuries. If such a contact occurs, immediately flush the affected area with tepid (slightly warm) water for approximately five minutes but DO NOT RUB OR TOUCH THE INJURED AREA. After flushing with tepid water, seek medical attention for the injury. Personnel working in areas of low temperature fluids to minimise the risk of injury should always wear protective clothing and gloves.

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12.2.1 Combustible Mixtures

1. Never admit flammable vapours or liquids into a circuit containing air or vise versa until you have purged the circuit or vessel with nitrogen and carried out tests to ensure that the level of air is down to a safe level, less than 1% O2. 2. When shutdown, always keep a slight positive pressure inside the circuits or vessels to avoid the ingress of air or vapours unless the shutdown was for inspection and maintenance reasons. In this case, purge the system concerned with nitrogen first prior to admitting air. 3. Do not vent large amount of cold hydrocarbon vapours through atmospheric vents as cold vapours are generally denser than air and could form low points pockets of flammable gas. Also avoid venting large amounts of air into flammable gas vents as this could form an explosive atmospheric inside the pipe.

12.2.2 Ventilation and Cleaning of Vessels and Lines

1. When vessels and lines are opened for inspection, repairs or cleaning, the system must first be purged with an inert gas (N2) to remove the combustible mixture. After the system is inert, air is introduced to prepare the system for inspection. 2. Proper ventilation will minimise the danger of forming flammable gas pockets or a toxic atmosphere. This can be achieved by opening top and bottom man-ways and lines in vessels and aiding the movement of air by using an air mover. Under no circumstances are personnel allowed in vessels and piping unless the atmosphere is between 20.0 – 21.5% O2. 3. Before using any cleaning agents, refer to supplier’s instructions and check for toxicity that could occur by breathing of the vapours and absorption through the skin. Wear the protective safety gear and follow the special handling and safety precautions as recommended by the chemical register for the particular agent that is being used.

SECTION No. 07

Rev. 2

May 2001

Page 64 of 78



13.0 FIRE AND GAS DETECTION SYSTEM

There are two types of Detection Systems installed in each train. These are as follows: 1. 2.

Explosive Gas Detectors, and Flame Detectors.

In addition to the above, there are two pairs Open Path Way Gas Detectors. The Detectors utilise either Infra Red (I.R.) rays or both Ultra Violet and Infra Red (U.V. / I.R. ) rays. When gas release or flames are detected, an alarm will be given in the C.C.R. When any one fire (flame) and / or any 3 gas detectors are initiated, these will cause a unit shutdown. There are no detectors installed in the Demethaniser System but there are a number of detectors installed in the adjacent Feed Chilling and Separation System and the De-ethaniser System. Full description of the system is covered in a separate Operating Manual detailing the Fire and Gas Detection System for the entire Complex (Trains, Utilities, and Offsite Facilities).

14.0 FAILURES

Factors affecting the operations of the unit fall into three broad categories: 1.

Loss of Feed or Unit to which the products are supplied.

2.

Loss of Internal Auxiliary Systems.

3.

Loss of Utilities Systems.

SECTION No. 07

Rev. 2

May 2001

Page 65 of 78


14.1


Loss of Feed / Rundown

In the event of an upset in the Feed Chilling and Separation (Scrub Tower and its associated equipment) System resulting in loss of the feed to the Demethaniser Column, carry out the following: A.

Isolate the system and put it on total reflux.

B. Should the upset in the Feed Chilling and Separation System prove to be of extended duration then isolate the Demethaniser System with maximum liquid inventory, shutdown the MCR Refrigeration supply to the Demethaniser MCR Separator, and stop the steam supply to the Demethaniser Reboiler. Also shutdown the duty Reflux Pump(s) X07-J-07.25/27. The loss of feed to the Demethaniser System will cause the shutdown of the downstream Fractionation Systems. Loss of the Demethaniser System will not normally necessitate routing the Scrub Tower Bottoms to the Liquid Disposal as the Deethaniser System can handle the bottoms product from the Scrub Tower. However, if the Demethaniser System is down and the Demethaniser Column is not available for use as a flow path, it is then not possible to route the Scrub Tower Bottoms to the Deethaniser Column via the Demethaniser Column. In this case, C 4 recycle to the Scrub Tower and LPG injection into the feed gas at the inlet to the Main Exchanger for PCS high heating value control will not be available from the downstream Fractionation Systems. Furthermore, propane from the Depropaniser Section to the Propane Refrigeration System and MCR Components make-up will not be available. If this scenario lasts for an extended period of time then it may be necessary to shutdown the entire train.

14.2

Loss of Internal Equipment

The loss of either the Propane Compressor or the MCR Compressors will result in an Emergency Shutdown. Prompt Operator action is needed to follow the established procedure for safe shutdown. Feed flow through the LNG Train will stop and depending on the cause of the trip, there could be a time delay for the closure of TVX06-12 and cessation of LNG production. Feed from the Scrub Tower to the Demethaniser Column and MCR Refrigerant flow will stop and the Demethaniser Section may have to be either shutdown or the system is boxed-in and put on total reflux.

SECTION No. 07

Rev. 2

May 2001

Page 66 of 78



14.3

Demethaniser Reflux Pumps

If both Reflux Pumps X07-J-07.25/27 fail for any reason, there will not be any reflux to the Demethaniser Column. This will necessitate steam shutoff to the Demethaniser Reboiler and routing the overheads vapour to the Fuel Gas System or to the Cold Flare. Bottom flow from the Demethaniser Column will continue to be routed to the De-ethaniser Column.

14.4

Loss of Utility Systems 14.4.1 Power Failure

On power failure within the train, all pumps and compressors will stop resulting in initiation of various equipment trips. In this case, contain the system pressure via PV-X07-03 to control the pressure in the system. Shut off the steam supply to the Demethaniser Reboiler and box-in the Demethaniser System. In the event of power failure, the following valves fail in the last position prior to the power failure: •

XV-X07-113 Demethaniser Column Overhead (normally closed)

14.4.2 Instrument Air Failure

On instrument air failure, the valves listed below will fail in their “fail safe" condition and the following will occur: 1. The Feed Stream and the MCR supply will be isolated. 2. The Product Stream will be isolated. 3. The Steam supply to the Reboiler will be isolated. In this case, the excess system pressure can only be relieved via the PSV-X07-02, PSV-X07-22, and PSV-X07-28 A. In the event of instrument air failure, the following valves fail in the CLOSED position: Valve

SECTION No. 07

Rev. 2

Location

May 2001

Page 67 of 78



•

XV-X04-133

Demethaniser Column Feed

•

XV-X07-116

Reflux Drum Liquid Outlet

•

XV-X07-117

Reflux Drum Vapour Outlet

•

XV-X07-118

Demethaniser Bottoms Liquid Product

•

PV-X07-03

Reflux Vapour

•

FV-X07-04

Methane make-up to the MCR Refrigeration System

•

FV-X07-15

Demethaniser Bottoms Liquid Product

•

LV-X07-17

Reflux Drum Level Control: MCR inlet to X07-G-07.26

•

FV-X00-123

Steam supply to Demethaniser Reboiler

Drum

Overheads

the

B. In the event of instrument air failure, the following valves fail in the OPEN position: •

FV-X07-13

Reflux Flow

C. In the event of instrument air failure, the following valves fail in the LAST position prior to the instrument air failure: •

SECTION No. 07

XV-X07-113

Rev. 2

Demethaniser Column Overhead (normally closed).

May 2001

Page 68 of 78



14.4.3 Steam Failure

On loss of the steam supply within the system, heat required to the Demethaniser Reboiler will be lost. This will affect the Demethaniser Column Operation. If the loss of steam is local to this system only then it is possible to continue operating the downstream Fractionation Units by passing the feed gas through the Demethaniser Section without being processed. This, however, will slightly affect the De-ethaniser Section Operating Parameters, which need to be adjusted accordingly. If the loss of steam is for a short duration and is common within the train, carry out the following: 1. Stop feed to the Demethaniser System by closing the feed control valve FV-X04-49. 2. Maintain level in the Demethaniser Column by closing the bottoms product flow control valve FV-X07-15. 3. Shutdown the duty Reflux Pump after vapour generation is reduced, i.e. when the Column conditions are stable. 4. Control the Column pressure by venting via the pressure control valve PV-X07-03. 5. Stop the MCR Refrigerant supply t o X07-G-07.26 by closing valve LV-X07-17. 6. Maintain the system in this condition until steam supply is re-established. Steam supply failure within the train due to loss of Process Boilers, 440t/h Boilers, or for any other reason will cause various automatic trips and in this case, the Operator needs to follow the relevant shutdown and restart-up procedures.

SECTION No. 07

Rev. 2

May 2001

Page 69 of 78



15.0 TROUBLE SHOOTING

Also refer to Cause and Effect Chart CE-85-X07-02 for additional information.

Effect

Check list & Immediate Action

Eventual Effect

Check: High high pressure in X07F-07.21. PAHH-X07-122

1. Operation of PIC-X0703. 2.Column temperatures are normal.

3. Reflux Flow.

Poor fractionation resulting in lifting the Pressure Relief Valve PSV-X07-02 and offspecifications product.

4. Reboiler Operation including cascade operation of TIC-X0705 and FIC-X00-123.

Check: Low low level in the Reflux Drum X07-G-07.24. LALL-X07-120.

1. Temperature and pressure in X07-F07.21 are normal. 2. Reflux Operation.

Pumps

Loss of suction to the Reflux Pumps with resultant loss of Fractionation Column X07-F07.21.

3. Operation of LIC-X0717 and PIC-X07-114.

SECTION No. 07

Rev. 2

May 2001

Page 70 of 78


Effect

High high level in the Reflux Drum X07-G-07.24. LAHH-X07-119


Check list & Immediate Action Check: 1. Temperature and pressure in X07-F07.21. 2. Reflux Operations.

Pumps

3. Operation of LIC-X0717 and PIC-X07-114.

Eventual Effect

1. Level could rise above feed inlet to the Reflux Drum causing back pressure and pressure increase in X07-F-07.21 resulting in poor fractionation. 2. Liquid carry over in the overheads vapour. 3. Process shutdown

Low low level in the Demethaniser Column X07-F07.21. LSLL-X07-121.

Check: 1. LIC-X07-09 operation. 2. FIC-X07-15 operation. 3. Correct operation.

Loss of feed to the De-ethaniser Column X08-F07.31.

Column

4. Reboiler Operation. 5. Drain is closed in the line from the Demethaniser Column to the Reboiler. 6. Column differential pressure which would indicate liquid hold-up. 7. Reduce steam flow to the Reboiler.

SECTION No. 07

Rev. 2

May 2001

Page 71 of 78



16.0 EQUIPMENT LIST

16.1

Demethaniser Column X07-F-07.21

Material of Construction:

Shell & Heads

SA-353 (9% Ni)

Trays:

TP 304 SS

Layout

Vertical

Design Pressure:

barg

34.5

Working Temperature

o

-90 to +94

C

Dimensions: •

Internal Diameter:

mm

1,067

•

Tan to Tan:

mm

16,256

No. of Trays:

17

Type of Trays:

Valves

No. of Passes:

1

SECTION No. 07

Rev. 2

May 2001

Page 72 of 78


16.2


Demethaniser Column Condenser X07-E-07.22

Vendor:

ALTEC International, Inc.

Type:

Plate-Fin Heat Exchanger


Brazed Aluminium

Heat Duty:

347 kW

Description

Unit

Stream

Pass No.1

Pass No.2

Pass No. 3

Pass No.4

DeC1 O/H in

DeC1 O/H out

MCR in

MCR out

Design vapour flow

kg/h

3,766

1,019

608

2,160

Design liquid flow

kg/h

0

2,747

13,918

12,366

Operating Temp.

o

C

-58.0

-86.2

-114.2

-100.0

Operating Pressure

barg

29.4

29.13

4.16

3.68

SECTION No. 07

Rev. 2

May 2001

Page 73 of 78



16.3

Demethaniser Reboiler X07-E-07.23

Type:

Kettle (U-Tube: B.K.U.)

Surface Area

45.9 m²

Shell Side

Tube Side

Stream:

Hydrocarbon

Steam


Carbon Steel

Carbon Steel A-214

Size:

I.D. 30" (762 mm)

83 U Tubes, I.D. ¾" 14 BWG Thickness: 1.9 mm Length: 4,572 mm

Design Flow Rate:

kg/h

26,428

1,398

Inlet Operating Temperature:

o

72.6

147.2

Outlet Operating Temperature:

o

C

98.2

147.2

Operating Pressure:

barg

30.4

3.47

Allowable Pressure Drop:

bar

0.034

0.345

SECTION No. 07

C

Rev. 2

May 2001

Page 74 of 78



16.4

Demethaniser Bottoms Cooler X07-E-07.30

Type:

Shell and Tube (AES)

Surface Area

43.7 m²

Shell Side

Tube Side

Stream:

Hydrocarbon

Seawater


SA-333 Grade 6

70/30 Cu Ni

Size:

I.D. 348 mm

152 tubes, O.D. 19.05 mm Thickness: 1.24 mm Length: 4.88 m

Design Flow Rate:

kg/h

18,036

48,096

Inlet Operating Temperature:

o

90.0

24.0

Outlet Operating Temperature:

o

C

41.0

38.0

Operating Pressure:

barg

30.4

1.4

Allowable Pressure Drop:

bar

1.0

0.7

SECTION No. 07

C

Rev. 2

May 2001

Page 75 of 78


16.5


Demethaniser Reflux Drum X07-G-07.24


Shell & Heads

SA-240 Grade 304

Layout:

Horizontal

Dimensions: •

Internal Diameter

mm

1,067

•

Tan to Tan

mm

1,753

barg

34.5

Design Pressure:

o

Design Temperature:

16.6

C

-115 to +66

Demethaniser MCR Separator X07-G-07.26


Shell & Heads

SA-240 Grade 304

Layout:

Vertical

Dimensions: •

Internal Diameter

•

Tan to Tan

mm

Design Pressure:

SECTION No. 07

mm

2,590

barg

6.2

o

Design Temperature:

C

Rev. 2

448

-157 to +66

May 2001

Page 76 of 78



16.7

Demethaniser Reflux Pumps X07-J-07.25 & X07-J-07.27

Manufacturer:

Union Pump Co.

Type:

Vertical in Line

Fluid Pumped:

Hydrocarbon Liquid

Design Capacity:

m³/h

9.55

Design Differential Pressure:

bar

1.9

Flow Temperature:

o

C

-90.5

Hydraulic Power:

kW

2.24

Motor Speed:

rpm

2,900

17.0

17.1

APPENDICES

DCS Print-Outs: • •

17.2

Figure No. 1: Figure No. 2:

Demethaniser I Demethaniser II

Process Flow Diagrams - PFDs

85-X07-PF-10A 85-X07-PF-10B

SECTION No. 07

Rev. 2

May 2001

Page 77 of 78

S07 Demethanizer

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