Design basis for flare system.pdf

JGC Job Code Doc. No.

0-5361-20-0000 S-PM-S330-1222-0001<6>

Project Management Services for Rabigh Phase II Petrochemical Project

DESIGN BASIS FOR FLARE SYSTEM

Project Management Services for Rabigh Phase II Petrochemical Project DESIGN BASIS FOR FLARE SYSTEM

JGC Job Code: 0-5361-20-0000 Doc. No.: S-PM-S330-1222-0001<6>

1.

INTRODUCTION ......................................................................................................................................... 3

2.

PROCESSING OBJECTIVES...................................................................................................................... 3

3.

REFERENCE DOCUMENT.......................................................................................................................... 3 3.1 3.2 3.3

4.

Project Specifications............................................................................................................................ 3 Saudi Aramco Standards ...................................................................................................................... 3 International Standards ......................................................................................................................... 3

UNIT CAPACITY......................................................................................................................................... 4 4.1 4.2

Design Relief Case ............................................................................................................................... 4 Design Relief Load................................................................................................................................ 4

4.2.1

HP Flare ....................................................................................................................................... 5

4.2.2

LP Flare........................................................................................................................................ 6

5.

PROCESS DESCRIPTION WITH CONTROL PHILOSOPHY....................................................................... 8

6.

DESIGN CONSIDERATION......................................................................................................................... 9 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10

Maximum Back Pressure ...................................................................................................................... 9 High Integrity Protection systems .......................................................................................................... 9 Emergency Purge System................................................................................................................... 10 Design Temperature ........................................................................................................................... 11 Design Pressure ................................................................................................................................. 11 Main Knockout Drum........................................................................................................................... 11 Intermediate Knockout Drum............................................................................................................... 11 On-plot Knockout Drum....................................................................................................................... 12 Capacity of KO Drum Pumps .............................................................................................................. 12 Vacu Leg in the Liquid Seal D 12


1.


INTRODUCTION This document covers the basis of design for a new stand-alone flare system serving the new process, utilities and off-sites facilities which comprise the Rabigh Phase-II Petrochemical Project.

2.

PROCESSING OBJECTIVES In Rabigh Phase-II Petrochemical Project, there are two types of flare system as follows: (i) (ii)

High Pressure Flare (HP Flare) Low Pressure Flare (LP Flare)

Each of the above flare systems is designed for safe disposing the relieving hydrocarbons and other gasses during normal start-up, emergencies and process upset conditions. Hydrocarbons relieved loads from various process units are handled in either high pressure flare system or low pressure flare system depending upon the set po int of pressure relief valves (PRV) and relief sources. In general, the high pressure flare system shall dispose of hydrocarbon releases from relief valves with a nominal set pressure of 9.5 kg/cm2G and higher, and the low pressure flare system shall dispose it with a set pressure below 9.5 kg/cm2G.



Process Industries

4.

UNIT CAPACITY

4.1

Design Relief Case The following potential cases as applicable are considered to determine the relieving duties of the Pressure Relief Valves. (1)Utility Failure - General/Single/Partial Power Failure (A) General power failure when all electrical equipment becomes simultaneously inactive in the entire facility. (B) Single power failure when one piece of equipment is not in operation due to loss of power. (C) Partial power failure when a group of electrical equipment is not in operation due to loss of power in any distribution center, motor control center or any bus. - General/Local Steam Failure



stack should be located far away from process units, requiring a large flare system and corresponding plot area. In early phase of FFED, allowable maximum relief load has been studied considering available plot plan and HSE. In order to set-up the relief load, HIPS (High Integrity Protection Systems) has been considered and dynamic simulation has also been conducted. Design relief loads for the flare systems are described below.

4.2.1

HP Flare Total relief load in general power failure case is summarized in Table-1a. Table-1a Total Relief Load in General Power Failure (HP Flare) Original Relief Load Design Relief Load (Without HIPS) (With HIPS) Unit No. Unit Relief Load MW Temp. Relief Load MW Temp. o [kg/h] [-] [ C] [kg/h] [-] [oC] R410 Naphtha 1,621,434 76.8 256 900,000 58.7 236 /R420 /Aromatics P240 Cumene 0 0 P270 Cyclohexanone 0 0 P410 Acrylic Acid 0 0 S220 T k 0 0



Table-1b. Relief Load in the Largest Single Failure Case Unit Relief Load(*1) MW Temp Unit Failure Case No. [kg/h] [-] [oC] R410/ Naphtha/ R420-T-2411 2,077,147 (*2) 106 267 R420 Aromatics Reflux Failure Fire P240 Cumene 30,300 78.6 289 Blocked Outlet P270 Cyclohexanone 14,727 44.1 69 Blocked Outlet P410 Acrylic Acid 7,100 42.1 32 Fire S220 Tankage 90,634 28.1 5 Note: (*1) The largest volumetric relief load case in each unit is listed above. (*2) This relief load will be mitigated by application of HIPS. As a result, the largest single relief will be 620,749 kg/h (MW: 75.7, Temp.: 170 oC) in R410-D-1201 Gas Blow-by Case.

4.2.2

LP Flare Total relief load in general power failure case is summarized in Table-2a Table-2a Total Relief Load in General Power Failure (LP Flare) Original Relief Load Design Relief Load (Without HIPS) (With HIPS) Unit No. Unit Relief Load MW Temp. Relief Load MW Temp.



the relief loads in this case. For detailed relief loads in other cases, refer to Study Report for Flare System (T-FE-S330-1222-0001). The design basis for LP flare system is as f ollows: A) Main Flare Mass flow: Mol. Weight:

1,024,061kg/h 53.0

B) Purge Flare Mass flow: Mol. Weight:

51,203 kg/h (5% of design load for main flare) 53.0

The largest relief load in single failure case from each process unit is summarized in Table-2b. Table-2b. Relief Load in the Largest Single Failure Case Unit Relief Load(*1) MW Unit No. [kg/h] [-] R410/ Naphtha/ 1,338,876(*3) 106 R420 Aromatics MTBE / P210 125,565 56.1 Isobutylene

Temp [oC] 210 78.2

Failure Case R420-T-2431 Reflux Failure P210-T-1170 Max Heat Duty P220-T-2301


5.


PROCESS DESCRIPTION WITH CONTROL PHILOSOPHY Considering the characteristics of the relief, set point and the configuration of the plot plan, two types of flare systems, i.e. LP and HP Flare systems, are provided. In LP and HP flare system, the relief fluids from various sources are routed to the on-plot knock out drum which is provided for each single process unit or a group of units to eliminate any potential liquid slugging in the header. The vapor outlet from the drum is routed to the main flare knock out drum via main flare header. The condensate produced by cooling due to ambient temperature during or after flaring in the main flare header is collected in the intermediate knockout drums or the main knockout drums. The exit vapor from the main flare knock out drum, which separates the entrained liquids from the vapor, is routed to the purge flare or the main flare via each seal drum. The vapor flow is normally routed to the purge flare stack because of lower liquid seal height in the purge flare seal drum than that in the main flare seal drum. In case of large release, back pressure across the purge flare system is increased, then the liquid seal in the main flare seal drum is broken and the vapor is routed to the main flare system. Smokeless operation is performed up to 15% of the design relief load. Flow rate of MP steam injected is automatically controlled by the ratio control with the relief load. Liquid seal drums are provided to prevent air ingress into the system. Utility water is continuously injected to the seal drum to ensure the liquid level and sweep any hydrocarbon on the liquid surface. When the liquid seal is broken due to hot and large relieving, fire water will be injected automatically to reestablish the seal within 5


6.

DESIGN CONSIDERATION

6.1

Maximum Back Pressure


Relief lines shall be sized to ensure that back pressure developed during flaring do not affect the flowing capacity of safety relief valves, depressuring valves or control valves that discharge into a flare system. The offsite flare headers are sized based on the allowable maximum back pressure at the process battery limits as follows: LP Flare: 1.0 kg/cm2G HP Flare: 3.2 kg/cm2G

6.2

High Integrity Protection systems In order to mitigate some key flare loads, HIPS (High Integrity Protection Systems) should be provided. The services for which HIPS should be applied are summarized in Table-3a and 3b. For detailed requirements in the system, refer to Flare Design Philosophy (S-PM-G000-1222-0609), General Specification for Flare System (S-PM-G000-1357-0001). Table-3a Systems with HIPS Application (LP Flare) Unit

Relief Load

Relief Load (With HIPS),



P220-T-2301

Deethylenizer

183,341

0

P220-T-2302

Depropylenizer

188,565

2,080

Table-3b Systems with HIPS Application (HP Flare) Unit No.

Item No.

Service

Relief Load (Without HIPS) [kg/h]

Relief Load (With HIPS) Note-1 [kg/h]

Remarks

428,995

(Note-2)

To mitigate the relief load in General Power Failure Case R420

R420-T-2111

Xylene Rerun Column

1,151,429

To mitigate the relief load in Single Failure Case (Reflux Failure Case) R420

R420-T-2111

Xylene Rerun Column

2,077,147

0

Note: 1. The mitigated relief load should be verified by the detailed engineering contractor. 2. Dynamic simulation has been done.

(Note-2)


6.4


Design Temperature The design temperature of OSBL flare system shall be based on the maximum relieving temperature from each unit as follows: LP Flare: HP Flare:

6.5

355 oC (for whole system) 400 oC (for Sub-header from Cumene unit) 300 oC (for main flare header and downstream facilities)

Design Pressure The design pressure of a flare system shall be based on the maximum back pressure developed during flaring. Design pressure for OSBL flare system is as follows: LP Flare: 3.5 kg/cm2G HP Flare: 5.0 kg/cm2G (for headers upstream of the main KO drum) 3.5 kg/cm2G (for facilities downstream of the main KO drum) Half vacuum condition should be considered for whole flare system, including ISBL system, considering potential vacuum condition after hot release. For ISBL flare system, EPC contractor shall finalize the design pressure considering the maximum back pressure in the unit.


LP Flare HP Flare


Estimated Condensate Volume (in 20 minutes) [m3] 105 47

EPC contractor shall verify the condensate volume based on the actual piping layout of the flare system.

6.8

On-plot Knockout Drum On-plot knockout drums shall be provided to eliminate significant quantities of liquid discharge to the flare system, resulting in elimination of potential slugging in the header. They have sufficient capacity to hold the volume of the liquid for a release of 20 minutes with no pump-out and to ensure residence time in excess of particle drop-out time based on the drop-out velocity required to remove particles larger than 1000 microns. The maximum design liquid level of the drum diameter for the horizontal knockout drums is 50% of drum diameter.

6.9

Capacity of KO Drum Pumps



-

MTBE/Isobuthylene (P210)

-

Cumene (P240)

-

Phenol (P250)

-

Acetone Recycle (P260)

-

Cyclohexanone (P270)

-

Caprolactam (P280)

-

EPR (P340)

-

LDPE/EVA (P360)

-

MMA (P370)

-

Acrylic Acid (P410)

-

Utility (C295)

-

Offsite (S220)

(Note)

(Note)

Note: No information for the condensate recovery system in this unit was available in FEED phase. EPC contractor shall verify it.


S330-P-3311A/B S330-P-3320A/B S330-P-3321A/B S330-E-3330 S330-Z-3310 S330-Z-3320


HP Flare Intermediate KO Drum Pumps LP Flare KO Drum Pumps LP Flare Intermediate KO Drum Pumps Slop Oil Air Cooler HP Flare Ignition Control Package LP Flare Ignition Control Package



UNIT S220 TANKAGE

UNIT R410 (NAPHTHA REFORMING

UNIT R420 (AROMA COMPLEX)

UNIT P370 (MMA) UNIT P240 (CUMENE)

UNIT P210 (MTBE/ISOBU TYLENE)

UNIT P220 (METATHESIS)

UNIT P250 (PHENOL) UNIT P410 (ACRYLIC ACID)

UNIT P280 (CAPROLACT AM) UTILITY FUEL GAS SYSTEM UNIT P270 (CYCLOHEX ANONE)

UNIT P260 (ACETONE RECYCLE)

UNIT P360 (LDPE/EVA)

UNIT P340 (EPR)

SLOP

(FOR FUTURE)

SLOP

Design basis for flare system.pdf

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