Norma Pdvsa K-337

PDVSA ENGINEERING DESIGN MANUAL VOLUME 9–II ENGINEERING SPECIFICATION SPECIFICATION

PDVSA N

°

TITLE

FURNACE AND BOILER INSTRUMENTATION

K–337

2

DIC.99

GENERAL REVISION

26

Y.K.

A.A.

J.E.R.

1

AUG.96

APPROVED

27

L.T.

E.J.

A.N

0

AUG.94

FOR APPROVAL

21

L.T.

E.J.

A.N.

PAG.

REV.

APPD.

APPD.

DATE

DIC.99

REV.

DATE

APPD.BY Alexis Arévalo

E

PDVSA, 1983

DESCRIPTION DATE

DIC.99

APPD.BY Jesús E. Rojas

ESPECIALISTAS

ENGINEERING SPECIFICATION

PDVSA


PDVSA K –337 REVISION

DATE

2

DIC.99

Page Menú Principal

Indice manual

Indice volumen

1

Indice norma

Index 1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

2 CODES, STANDARDS AND PRACTICES . . . . . . . . . . . . . . . . . . . . .

2

3 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

4 FIRED HEATERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

4.1 4.2 4.3 4.4 4.5 4.6

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fuel systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burner Management System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alarms and Shut–down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 BOILERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 5.2 5.3 5.4 5.5 5.6

4 5 6 9 9 12

14

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fuel System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burner Management System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alarms and Shut–down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14 14 15 17 17 19

6 FLAME DETECTION / BURNER MANAGEMENT SYSTEM . . . . .

21

7 PROTECTION SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23

8 INSTALLATION AND COMMISSIONING . . . . . . . . . . . . . . . . . . . . . .

24

9 QUALITY ASSURANCE / QUALITY CONTROL . . . . . . . . . . . . . . .

25

10 APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26


PDVSA



DATE

2

DIC.99

Page Menú Men ú Principal

1

Indice manual

Indice volumen

2

Indice norma

SCOPE This document covers minimum PDVSA instrumentation requirements for the design, specification, installation and commissioning of fired heaters and boilers located at petroleum refineries and production facilities. This standard applies to all fired heaters and boilers and is based on NFPA NFPA 8502, ASME CSD – 1 and API 556. The user of this standard must recognize the complexity of firing fuel with regard to the type of equipment and the characteristics of the fuel. It is intended that the designer shall be capable of applying a rigorous analysis to special or unusual problems. The validity of the design shall be approved by PDVSA. This specification does not cover the following: S S S

2

Steam control systems used for purging natural draft process fired heaters prior to burner light off. Pilot gas system supplies (filters and LPG vaporizers). Instrumentation systems for inert gas generators, incinerators, pulverized fuel and sulfur furnaces.

CODE CODES, S, STAN STANDA DARD RDS S AND AND PRA RACT CTIICE CES S NFPA 8502 NFPA 8501 API RP – 551, 55 552 API 555 API Std 560 API RP – 556 556 ASME CSD – 1 ANSI Z83.3 PDVSA B – 201 201 – PR PR PDVSA K – 300 300 PDVSA K – 303 303 PDVSA K – 334 334 PDVSA K – 335 335 PDVSA K – 336 336 PDVSA – – K K – 369 369 PDVSA IR – E – 01 01

Standard for the Prevention of Furnace Explosions/Implosions in Multiple Burner – Burner – Boilers. Boilers. Standard for Single Burner Boiler Operation. Process Me Measurement In Instrumentation Process Analyzers Fired Heaters for General Refinery Services Instrumentation and Control System for Fired Heaters and Steam Generators. Controls and Safety Devices for Automatically Fired Boilers. Gas Fired Boilers Calentadores de Fuego Directo Introduction Level Instrumentation Instrumentation and Thermocouple Extension Cables Packaged Unit Instrumentation Safety Instrumented Systems Instrumentation QA/QC Clasificació Clasificaci ón de Areas


PDVSA


DATE

2

DIC.99



Indice manual

Indice volumen

3

Indice norma

PDVSA IR – M – 01 01 PDVSA IR – P – 01 01

Separació Separaci ón entre Equipos e Instalaciones Sistemas de Parada de Emergencia, Bloqueo, Despresurizació Despresurizaci ón y Venteo de Equipos y Plantas PDVSA IR – S – 01 01 Filosofí Filosof ía de Diseñ Diseño Seguro PDVSA N – 201 201 Obras Elé Eléctricas Even though the NFPA 8502 standard scope does not cover process heaters, this standard (PDVSA K – 337) 337) considers that, from the security point of view, the principal purpose of both standards “contribute to operating safety and to prevent furnace explosions and implosions ” is the same and the premises of the NFPA 8502 shall be followed for the design, installation, operation, and maintenance of fired heaters and boilers and their fuel burning systems. NOTE: This document originated as a compilation of the PDVSA K – K – 337 337 “Furnace Instrumentation” Instrumentation ” Rev – 1, 1, Aug.1996 and PDVSA K – K – 338 338 “Boiler and Instrumentation” Instrumentation ” Rev – 1, 1, Aug. 1996 standards.

3

DEFINITIONS The following definitions are included to understand this standard. Continuous pilot An igniter applied to the fuel input through the burner and to support ignition under any burner light – – off off or operating conditions. This pilot burns throughout the entire period perio d the unit is in service whether or not the main burner is firing. This type of pilot requires a reliable gas source. This term is equivalent to igniter, class 1 according to NFPA 8502. Intermittent pilot An Igniter applied to the fuel input through the burner under prescribed light – – off off condition. This pilot is automatically lighted each time there is a call for heat. It burns during the entire period the main burner is firing. This term is equivalent to igniter, class 2 according to NFPA 8502. Interrupted pilot The pilot is automatically lighted each time there is a call for heat. The pilot fuel is cut off automatically at the end of the main burner flame – flame – establishing establishing period. This term is equivalent to igniter, class 3 according to NFPA 8502. Reliable gas source A pilot gas source that meets all of the following conditions: S

Separate from the main fuel gas supply such that both supplies will not be simultaneously interrupted by a single contingency such as power or instrument air failure or inadverted valve closing.


PDVSA


DATE

2

DIC.99


Page Menú Men ú Principal S S

Indice manual

Indice volumen

4

Indice norma

Available during startup. Liquefied petroleum gas vaporizers are not considered a reliable source.

Supervised Manual System A system in which a trained operator has primary responsibility for the proper start – – up, up, operation and normal shut – – down down of a heater or boiler with interlocks to ensure that the operation follows established procedures. See Section 6 – 6 – 8 and figures A.6.8.1.1 (a) and (b) on NFPA 8502. Furnace The portion of the heater or boiler enclosure within which the combustion process takes place and wherein heat transfer occurs predominantly by radiation. Blowdown Control The primary purpose of blowdown is to maintain the dissolved solids concentration and silica content of the water in the steam generator within acceptable limits. Proper blowdown control will limit scale formation on heat transfer surfaces, limit the solids content of the steam drum, and assure maximum benefit from water treatment chemicals. Note: For further definitions on Heater And Boiler instrumentation refer to NFPA 8502, Chapter 3, Definitions.

4

FIRED HEATERS

4.1

General

4.1.1 4.1 .1

All fired fired heater heaters s ha have ve the the follow following ing function functional al requi requireme rements: nts: S

Process control.

S

Burner Management System.

S

Decoking systems for plugged tubes, if applicable (process flow).

4.1.2 4.1 .2

The instru instrument mentatio ation n system system shall shall ensure ensure the the safe operatio operation n of the the heater heater and and include a control system to ensure optimum heat transfer at maximum, normal, and minimum loads.

4.1.3 4.1 .3

Electri Electrical cal equipme equipment nt or instrum instruments ents shall shall be speci specified fied and and installe installed d accordin according g to the intended service (fuel, gas, etc.) and the area classification. Special care shall be taken to position the local control panel and push button station in a safe area to be operated under und er emergency and harsh environment conditions according to PDVSA IR – P – 01 01 and HAZOP study results.

4.1. 4.1.4 4

The The m mai ain n fue fuell hea heate terr saf safety ety shut – – off off valves shall shall be located at a safe distance from the furnace, according to t o PDVSA IR – P – 01 01 and HAZOP study results.


PDVSA



DATE

2

DIC.99


4.1.5

4.2 4.2

Indice manual

Indice volumen

5

Indice norma

For cable routing, see specificatio n PDVSA K – 334. 334. an and d PDVSA N – 201. 201.

Fuel Fuel sy syst stem ems s

4.2.1 4.2 .1

The fuel for pilot pilot burners burners (igniter (igniters) s) shall shall be natur natural al gas. gas.

4.2.2

A self – – operated operated pressure regulator shall be installed in parallel with the main gas flow control valve to ensure safer light off and reduce the occurrence of flame out. For multiple burner heaters, this self – self – operated operated pressure regulator shall be able to handle light off requirements for any amount of operating burners in the unit. A mechanical stop on the flow control valve is not recommended.

4.2.3

Safety sh shut – – off off valves (for igniters and main burners) shall be fail safe and not readily bypassed or blocked open and shall not be used as modulating control valves. Modifications to this requirement shall be supported by cost – cost – benefit benefit and risk analysis, considering equipment dimensions, operation site, operating conditions, etc.

4.2.4

The main shut – – off off valve shall be tight shut – shut – off off and either fire safe or located in a fire safe area. Valve closure time shall not exceed 10 seconds. The main shut – shut – off off valve shall be manually and locally re – re – set. set. The valves shall be class VI tight shut – – off off and of a fail – – close close design. Vent valve shall be fail – – open. open.

4.2. 4.2.5 5

Main fuel Main fuel cont contro roll val valve ve shal shalll fai faill – – closed closed and shall have a closed position switch to be monitored by the BMS. This control valve shall be sized and arranged to ensure a fuel flow adequate for all operating requirements of the units.

4.2.6 4.2 .6

The fuel fuel gas syste system m arrange arrangement ment for for pilots pilots and and burner burner shall shall be in in accordan accordance ce to NFPA 8502, Part 6.3 “System Requirements” Requirements ” and 7.3 for fuel oil system.

4.2.7 4.2 .7

Any modific modificatio ation n in existing existing heater heaters s (i.e. revamp revamping ing)) shall consid consider er as first first option option to design the fuel gas system arrangement for pilots and burner recommended by NFPA 8502, Part 6.3. As a second option for existing heaters with few burners, a Supervised Manual System (NFPA 8502, Part 6.8, Figures A.6.8.1.1 (a) and (b)) shall be considered. Modifications to this arrangement shall be supported by cost – – benefit benefit and risk analysis, considering equipment dimensions, operation site, operating conditions, etc.

4.2. 4.2.8 8

All All ind indiv ividu idual al bu burne rnerr safet safety y shu shutt – – off off valves shall be located as close to the burner as practical, to minimize the volume of fuel left downstream of the burner valves in the burner lines.

4.2.9

The double double b bloc lock k and vent vent arra arrange ngemen mentt shall shall consi consist st of two two (2) (2) shut shut – off off valves and one (1) vent valve, each one independent from the others. An integral type valve might be considered and shall be approved by PDVSA.


PDVSA



DATE

2

DIC.99


Indice manual

Indice volumen

6

Indice norma

4.2.10 4.2 .10

Prov Provisi ision on shou should ld be ma made de to leak leak – test test the individual shut – – off off valves. On dual fuel units with combination burners, leak tests may be done on one fuel system while unit is operated with the other.

4.2.1 4.2. 11

On for force ced d draf draftt hea heater ter au autom tomati atic c shut shut – – off off for the combustion air, isolating dampers shall be provided. This damper shall close when the main flame is not alight. Provision shall be made to open these dampers during furnace purging, burner light – – off, off, and post – – purging purging if required.

4.2.12 4.2. 12

Furnace Furnaces s with a large large numbe numberr of small small burners burners,, making making pilots pilots impra impractic ctical, al, and and a constant firing rate, shall have a Main Fuel Low Pressure Indicator with a Main Fuel Low Pressure Alarm for shut – shut – off off of fuel to all burners on main fuel low pressure.

4.3 4.3

Meas Me asur urem emen ent t Typical measurements used to maintain automatic control or to actuate alarm devices are discussed below. below. Sensors and instruments shall be accessible for reading and maintenance. Certain local check measurements measuremen ts at the source are necess nec essary. ary. Refer to API RP 551 and an d PDVSA MID, Volume 9, for installation details. Modifications to this requirement shall be supported by cost – cost – benefit benefit and risk analysis, considering equipment dimensions, operation site, operating conditions, etc.

4.3.1

Temperature Temperature measuring elements complete with thermowells shall be provided at, but not limited to, the following locations: locations :

d.

Radiant se section.

e.

Con onv vectio tion S Se ectio tion.

f.

Flue Flue gas stac stack, k, before before the the damper damper,, at approx approximat imately ely 2 diame diameters ters from stack stack entrance, and preferably near the sampling point for flue gas analysis.

g.

At inle inlett and and outle outlett mani manifol folds ds of of proc process ess fluid. fluid.

h.

On multiple – pass pass furnaces, each individual tube process outlet temperature shall be measured by the installation of thermocouples or temperature indicators.

i.

On furnaces furnaces with high risk of cokin coking, g, tube skin temperat temperature ure measurem measurement ent on radiant coil tubes shall be considered. Measurement points shall be within two or three tube diameters of the outlet, but may be best selected by considering the expected temperature profile. It is important that the temperature be determined at or near the highest section of the temperature profile. Multiple skin thermocouples distributed along the potential coking area should also be considered.


PDVSA



DATE

2

DIC.99


Indice manual

Indice volumen

7

Indice norma

j.

Radiant Radiant coil coil tube tube skin skin metal metal thermocou thermocouples ples shall shall be installed installed according according to Figures Figures 2 and 3 on API RP 556. 556 . The thermocouples must be in direct contact with the tube. All scale and oxide must be cleaned from the tubes before attaching the thermocouple sheath or block. Consult the fired heater manufacturer for recommended location for tube skin temperature measurement points

k.

Where steam – air air decoking is specified, to prevent damage from spalling, the thermowells shall be located downstream of swing bends. To measure decoking effluent temperature, additional thermowells with thermocouples shall be located in decoking outlet lines. Where reverse steam – air air decoking is specified, additional skin thermocouples shall be installed in each pass, on one of the shock tubes.

l.

m.

4.3. 4.3.2 2

Where Where prov provis isio ion n is mad made e for for futu future re rev rever erse se ste steam am – – air air decoking, a thermowell with thermocouple shall be installed at the normal inlet end of each individual pass which will become an outlet outlet during decoking. This thermowell shall be located in the decoking piping, not the process piping, on the side of the swing bend away from the heater. In the the liqu liquid id fue fuell mani manifo fold ld,, as clos close e to the burners as possible.

Pres Pressu sure re The pressure shall be measured at, but not limited to, the following points:

a.

Fuel gas and liquid fuel: – Main supply line downstream of control valve. – Individual heater fuel supply downstream of control valve. – At burner manifold. – Across filters to measure pressure drop.

b.

Pilot gas: – Main supply line, when it is independent of main burner supply line. – On the pilot manifold. – Across filters to measure pressure drop.

c.

Atomizing steam: – Downstream of pressure control valve.

d.

Process: – At process fluid in inlet manifold. – At process fluid in Convection section outlet. – At process fluid in inlet to each pass, downstream of the regulating valve. – At process fluid in outlet manifold.


PDVSA



DATE

2

DIC.99


Indice manual

Indice volumen

8

Indice norma

– Pressure tapings only shall be provided in each crossover on all vaporizing duty furnaces. e.

Draft: – Pressure measurements should be made at the outlet of the forced – forced – draft draft fan, across the air pre – heater, heater, in the preheated air duct before the burners, in the firebox (near the burners and at the top of the radiant section), and across the dampers. – At firebox in natural draft burners. – On induced draft fired heater fitted with natural draft burners, if natural draft backup is not inherent in the fired heater design, the heater shall be shut – shut – down down on loss of the induced draft fan(s). In any case loss of the induced draft fan(s) shall be alarmed. – Plugged draft connection for test purposes shall be provided in the furnace firebox at different positions. – At outlet of the convection section.

4.3. 4.3.3 3

Flow Flow The flow shall be measured at, but not limited to, the following points:

a.

Combustion ai air flow in forced draft heaters locating the primary element (for example, venturi, averaging pitot, etc) in the forced draft duct system.

b.

Fuel Fuel gas and oil flow flow in the the main main line line locat located ed upst upstrea ream m of the the fuel fuel cont control rol valv valves. es.

c.

An ad addi diti tion onal al flow flow elem elemen entt for for pilot fuel gas if it is piped independently of the main gas supply.

d.

Flow meter meter locat located ed upstre upstream am of the the hea heater ter coil; coil; if the the proce process ss fluid fluid is divid divided ed into into two or more streams through the heater the flow in each pass shall be measured, if practical.

4.3. 4.3.4 4

Leve Level l

a.

In pyrotu pyrotubula bularr type type hea heaters ters a level level indic indicator ator shall shall be be install installed. ed. A low low level level signal signal shall be required for interlock purpose.

b.

A high level switch switch shall shall be installed installed in in the fuel gas gas K.O. K.O. drum for interloc interlock k purpose. purpose.

4.3.5 a.

Analysis Sample Sample point point facili facilities ties shall shall be be provided provided for for taking taking sample samples s of the flue flue gas gas at the exit of each combustion chamber, chamber, just above the radiant section, and in the exit of the convection section so the composition of flue gas may be determined by analysis.


PDVSA



DATE

2

DIC.99


Indice manual

Indice volumen

9

Indice norma

b.

If required required both both oxyge oxygen n and unburned unburned combu combustib stibles les shall shall be be measured measured on the flue gas and indicated on the local firing panel and in the control room to obtain a good measurement of the quality of combustion.

c.

Samples Samples shall shall be taken taken as as near near as poss possible ible to the the point point where where combu combustio stion n is completed, normally at the exit of the radiant section.

d.

The sample sample point points s shall shall be provi provided ded with screwed screwed closures closures..

e.

When When toxic toxic gases gases or liquid liquids s are burnt burnt in the the furnace furnace,, analyzer analyzers s shall shall be install installed ed in the stack to monitor exhaust gas quality.

f.

Sample Sample point points s shall shall also also be be provide provided d near near the damper damper and and ne near ar the the stack stack temperature thermocouple. All analyzer sample points must include facilities for manual sample take – take – offs. offs.

4.4

Burne Burnerr Ma Mana nagem gement ent System System For Burner Management System see section 6.

4.5 4.5

Contro trols

4.5.1

Load Control

a.

Continuos Continu os control control funct functions ions shall shall be be execute executed d on indepen independent dent devic devices es (senso (sensors, rs, controllers, final control elements) different from sequential control devices.

b.

A fuel fuel gas gas press pressure ure control controller ler (for natu natural ral draft draft heat heaters) ers) or flow flow control controller ler (for forced draft heaters) shall be installed in the heater fuel supply header.

c.

The furna furnace ce load load controll controller er (outle (outlett temp tempera eratur ture) e) shall shall be actua actuated ted on the the fuel and and combustion airflow controller set points. The basic principle is that both fuel and combustion airflow are controlled in parallel, with limit (maximum for fuel, minimum for air) to avoid sub – stoichiometric stoichiometric combustion. See API RP – RP – 556 556 FIG. 5 for forced Draft Heater and FIG. 6. For Natural Draft Heater.

d.

In case case that that load load variatio variation n is expec expected ted a heate heaterr feed process process flow flow contr controlle ollerr with P.I. actions should be implemented. implem ented. It should guarantee process flow stability. The process flow control valve shall be fail – fail – open. open.

e.

For singl single e and multi multiple ple burner burner heat heaters ers minimu minimum m combusti combustion on air flow shall shall be ensured by an adjustable mechanical minimum stop on the combustion air damper, while the maximum combustion air flow is limited by the capacity of the blower and air register resistance.

f.

Minimum Minimum fuel fuel flow flow conditi condition on (durin (during g start start up or or minimum minimum burne burnerr load operatio operation) n) shall be ensured by an active minimum stop, implemented by a pressure controller or a self regulated valve, on the fuel gas or fuel oil control valve.


PDVSA


Menú Men ú Principal

Indice manual

Indice volumen


DATE

2

DIC.99

Page

10

Indice norma

g.

The combu combustio stion n control control system system shall shall maint maintain ain heate heaterr fuel fuel and air ratio ratio in accordance with demand. The air/fuel ratio shall be set to provide a small amount of excess air for efficient and safe combustion.

h.

Atomizi Atomizing ng steam steam for for the fuel fuel oil burn burner er is contr controlle olled d at a consta constant nt pressu pressure re differential to the burner fuel oil pressure.

i.

Depending Depend ing on the the varia variation tion in in the MW MW of the fuel fuel gas, gas, flow flow measu measureme rement nt shall shall be be corrected for changes in gas density.

j.

For multi – – burner burner heaters, a master flow controller shall be located in a common header, cascading via individual bias and ratio relays to individual pass flow controllers.

k.

In forced forced an and d ind induced uced draft heat heaters, ers, contro controll systems systems for for regulati regulation on of fuel or or air, air, or both, shall maintain air/fuel ratio at the optimum design excess air rate (for natural gas normally 5%, for oil 6%, and for coal 10%).

l.

All fired fired heater heater stack stack dampe dampers rs shall shall be positi positioned oned manua manually lly or autom automatic atically ally with with a manual loading station located at grade adjacent to the fired heaters or with with a signal from the combustion control system, if it is required that the loop be closed. Damper position shall be indicated.

m.

Fuel Fuel oil firing firing system system shall shall ensur ensure e a constant constant diff differen erential tial betw between een steam steam and and oil pressures. The recommended value of differential pressure shall be specified by the burner supplier.

n.

With any any chang change e of the the rate of furnac furnace e input, input, the airflow airflow and and fu fuel el flow flow sha shallll be changed simultaneously to maintain proper air/fuel ratio during and after the changes. This shall not eliminate the requirements for air lead and lag during changes in the fuel firing rate.

o.

A control control strat strategy egy shall shall be be implemen implemented ted such such that that setting setting fuel fuel flow flow control control on on automatic without the airflow control on automatic shall not be permitted.

p.

Control action Control action to increase increase ffuel uel and and decrease decrease air shall shall be blocked blocked when when the air/fuel air/fuel ratio falls below a preset value.

4.5.2

Sequential Control Start – – up up and shut – – down down sequence recommendations shall be submitted to PDVSA by heater manufacturer. However manufacturer shall guarantee that the start – – up up and shut – – down down systems execute, at least, the following functions:

4.5.3 a.

Start –Up Sequence Automatic verification of , but not limited to, the following interlocks: – High burner fuel pressure. – Low igniter fuel pressure.


PDVSA



Indice manual

Indice volumen


DATE

2

DIC.99

Page

11

Indice norma

– Low process flow in passes. – High and low combustion air – Automatic start – – up up push button activation check. b.

Purging – For forced draft heaters the system shall be equipped with an automatic purge sequence. Upon activation of the “purge start” start” the combustion air damper is fully opened during the period set on the purge timer. After the purge time has elapsed and all permissive conditions are cleared, the burner can be started. A new purge cycle is only required in case of a combustion air failure. After any other sequence failure, a waiting time of 1 minute to restart is sufficient. – For natural draft heater purging shall be performed based on an operational procedure. – Igniters light – – off. off. – Burners light – – off. off.

4.5.4

Shut –down Sequence A master fuel trip that results from any of the emergency conditions tabulated on the table below shall stop all fuel flow to the furnace for all burners by tripping the main and individual burner safety shut – shut – off off valves. All vent valves shall be opened. The main igniter safety shut – – off off valve and individual igniter safety shut – shut – off off valves shall be tripped, except for continuous igniter types which only can be tripped by a Manual ESD Station. The igniter sparks shall be de – de – energized. energized. If a furnace inerting system is installed, the inerting system shall be operated simultaneously with the master fuel trip. Master fuel trips shall operate to stop all fuel flow into the furnace within a period that does not allow a dangerous accumulation of fuel in the furnace. A master fuel trip shall not initiate a forced draft fan or induced draft fan trip. Electrostatic precipitators, fired reheaters, or other ignition sources shall be tripped.


PDVSA



a.

Indice manual

Indice volumen


DATE

2

DIC.99

Page

12

Indice norma

Partial Shut –down The main control valve shall be closed to minimum flame condition. If after a predetermined period of time normal condition is not reestablished (through an operator local reset action), shut – shut – off off valve shall be closed automatically. For partial shut – – down down signals, refer to section 4.6, Alarms and Shut – Shut – down. down.

b.

Total Shut –down A master trip is activated after a predetermined period of time in a partial shut – – down down condition, or at least, when any signal listed in section 4.6, Alarms and Shut – – down, down, is activated: Prior to start – – up, up, the fuel safety shut – – off off valves shall be closed, and the fuel flow controllers are automatically set to “manual” manual” with zero output. This will drive the fuel control valves to the minimum stop setting.

4.6

Alarms Alarms and Shut– Shut–do down wn

4.6.1

All shut – – down down valves shall remain in the shut – shut – down down position until manually reset.

4.6. 4.6.2 2

The The follo followi wing ng typ typic ical al ala alarm rms s and and shut shut – – down down signals shall be provided. Application depends on the process conditions and furnace design. A risk analysis and HAZOP study should support the final design.

4.6.3 4.6.3

For For instr instrum ument ent taps taps locati location ons s refer refer to to Figur Figure e A – A – 6.5.1.2(b) 6.5.1.2(b) of NFPA 8502.


PDVSA

PDVSA K –337



Indice manual

Indice volumen

Description

Alarms Local

Low flow in passes Low flow process Low – low flow process Pass outlet high temperature High – high process outlet temperature Low – low low and high – high high gas pressure at igniter header Low – low low and High – high high pressure at fuel supply (gas and liquid) High – high pressure at burner header Low – low pressure at burner header Low atomizing steam pressure at burner Low percentage oxygen in the flue gas High percentage combustibles in the flue gas Low combustion air flow on forced draft burners High wind box pressure Low wind box pressure Flame failure (one burner) in a single burner heater Flame failure in multi – – burner heaters High stack temperature High – high stack temperature High smoke density (on fire) High – high tube skin Fan failure Stack damper closed Combustible gas on air duct intake Loss of air pre – heater driver Manual ESD station Low energy supply (Instrument air or electrical supply) Loss of energy supply (Instrument air or electrical supply) High level in fuel gas K.O. drum High – high level in fuel gas K.O. drum

x x x

x x

DATE

2

DIC.99

Page

13

Indice norma

Partial Total Shut –off Shut –off

Control Center X X x X X x

x x X

x x x

REVISION

x x x x x x x x x x x x x x x x x x

x x

x Note 3 Note 3 x Note 1 x Note 4 Note 4 Note 2 x x x

x x

Note 5

x

Note 6

x x

x

Note 1: Depending on the numbers of burners and their physical arrangement.


PDVSA



Indice manual

Indice volumen


DATE

2

DIC.99

Page

14

Indice norma

Note 2: See Part 4.3.2 item “e”. Note 3: Applies only for forced draft heaters. Note 4: Only in unattended facilities. Note 5: This command shall shut – – off off all burners and igniter valves, even when continuous igniter type is used. Note 6: Not necessarily automatically initiated. A risk cost – cost – benefit benefit analysis should support the final decision.

5

BOILERS

5.1

General

5.1.1

This chapte chapterr applies applies to to boilers boilers in which steam or vapor vapor is gener generated ated a att a pressur pressure e exceeding 15 psig. For lower pressure boilers refer to ASME CSD – CSD – 1. 1.

5.1.2 5.1 .2

All boilers boilers have three three basic basic function functional al requirem requirements ents:: S

Maintain steam production automatically at the required pressure and temperature under varying operating conditions (e.g. a sudden increase or decrease in demand of steam).

S

Burner start – – up up management system Automatic shut – – down down system in the event any of the variables reach an unsafe condition.

S

5.1.3 5.1. 3

The instru instrument mentatio ation n system system shall shall ensure ensure the the safe safe operatio operation n of th the e boiler boiler and and include a control system to ensure optimum heat transfer under varying load conditions.

5.1.4 5.1. 4

Boiler Boiler desig designs ns vary vary depend depending ing upon upon the the s speci pecific fic proce process ss design design – – power power plant, waste heat, etc.

5.1.5 5.1. 5

Electric Electrical al equipm equipment ent or or instrum instruments ents shall shall be spec specifie ified d and installe installed d accordi according ng to the intended service (fuel, gas, etc.) and the area classification. Special care shall be taken to position the local control panel and push button station, so that they are located in a safe area to be operated under emergency and harsh environment conditions according to PDVSA IR – IR – P – 01 01 and HAZOP study results.

5.1. 5.1.6 6

The The mai main n fue fuell saf safet ety y shu shutt – – off off valves shall be located at a safe distance from the boiler. Refer to PDVSA IR – P – 01 01 and HAZOP study results.

5.1.7 5.1 .7

For For cable cable routi routing ng,, see see spec specifi ificat cation ion PD PDVS VSA A K – K – 334. 334. and PDVSA N – 201. 201.

5.2 5.2

Fuel Fuel Sy Syst stem em For fuel system see section 4.2.


PDVSA



5.3 5.3

Indice manual

Indice volumen


DATE

2

DIC.99

Page

15

Indice norma

Meas Me asur urem emen ent t Typical measurements employed to maintain automatic control or to actuate alarm devices are discussed below. below. Sensors should be accessible for reading and maintenance. Certain local check measurement at the source are necessary. Refer to API RP 551 and an d PDVSA MID volume 9 for for installation details.

5.3.1 a.

Temperature Temperature emperature measuring measuring elements elements complete complete with with thermo thermowell wells s shall shall be provi provided ded,, at least, at the following locations: Boiler feed water – Battery limit inlet – Entrance to the steam drum Steam – – – –

Steam drum liquid phase Steam drum vapor phase Saturated steam supply line Superheated outlet

b.

The type type of of thermowe thermowellll and its immers immersion ion lengt length h shall shall be caref carefully ully selec selected. ted. Special tapered well shall be considered for high pressure and high velocity service. Tapered wells shall be designed for particular installations to prevent cracking due to metal fatigue caused by velocity – velocity – induced induced vibration. Typically, Typically, wells in super – – heated heated steam service are flanged (RF).

c.

Radiant Radiant coil tube skin metal thermocouple thermocouples s shall shall be iinstalle nstalled d accordin according g to figures figures 2 and 3 on API RP 556, appendix appendix 2.0. The thermocouple must be in direct contact with the tube. All scale and oxide must be cleaned from the tubes before attaching the thermocouple sheath or block. Consult the boiler manufacturer for recommended location for tube skin temperature measurement points

5.3.2 a.

Pressure Pressur Pressure e shall shall be measur measured ed at, at, but not not limited limited to, to, the the followi following ng locatio locations: ns: Boiler feed water – Battery limit inlet Steam – Steam drum vapor phase – Steam header – Upstream of superheated steam supplies flow meter


PDVSA



5.3.3 a.

Indice manual

Indice volumen


DATE

2

DIC.99

Page

16

Indice norma

Flow Flow Flow shall shall be measure measured d at, but n not ot limited limited to, tthe he fo follow llowing ing locat locations ions:: Boiler feed water – Battery inlet limit – Economizers, desuperheaters, etc., one in each line, for large and complex boilers Steam – – – –

Steam drum outflow Steam header Condensates (Purge) Purge flow

Chemicals – One for each of the chemicals added to the boiler, if applicable 5.3.4 a.

Level Level Level shall shall be be measur measured ed at, at, but not limite limited d to, the ffollo ollowing wing location locations: s: – Continuous steam drum water level in accordance with details in specification K – 303. 303. One d/p cell for control and a second d/p cell for high and low alarms – Level gauge in accordance with ASME “Boiler and Pressure Vessel Code – Condensate (Purge) separators

5.3.5 a.

Analysis Some So me of the the reco recomm mmen ende ded d quality measurements are: Feed –Water: – – – –

PH Conductivity Hardness Turbidity

Combustion quality measurement: – Oxygen contents in flue stack – CO


PDVSA


FURNACE AND BOILER INSTRUMENTATION Indice manual

Indice volumen


DATE

2

DIC.99

Page

17

Indice norma

Required by regulatory agencies: – SOx – NOx Additional information on installation can be obtained in API Technical Paper 555.

5.4

Burne Burnerr Ma Mana nagem gement ent System System For Burner Management System see section 6

5.5 5.5 5.5.1

Contro trols General The control system must be adequate to cover all operation conditions of the boiler during startup, normal operation, shut – shut – down, down, and any emergency situation. Provision shall be included for indication at the local control panel and convenient operator adjustment of all necessary set points at the main control location. The control system shall guarantee steam demand, evaporated water make up and efficient use of the fuel; in order to achieve these three functions the following automatic controllers have to be implemented: steam pressure, drum level, fuel flow, air flow and furnace draft pressure.

5.5.2

Steam pressure control Each fired steam boiler or system of commonly connected steam boilers shall have, at least, one steam pressure control device that will shut – shut – off off the fuel supply to each boiler when the steam pressure reaches a preset maximum operating pressure. In addition to the steam pressure control, each fired steam boiler shall have a high steam pressure limit control that will prevent generation of steam pressure in excess of the maximum allowable working pressure. In multiple boiler installation one master steam pressure controller shall serve as the primary control for a group of boilers. If the fuel pressure is subject to significant fluctuation, the steam pressure controller might be cascaded to a fuel flow or pressure controller. The master pressure controller compares the pressure in the main steam heater with its set pressure and automatically adjusts its output to each boiler ’s combustion controls to request more or less steam. If steam demand is subject to significant fluctuation, consideration should be given to use feed forward control strategy on the master pressure controller. When two or more boilers operate in parallel, they must share the total load in various proportions. In order to divide the total load, the output signal of the master


PDVSA



Indice manual

Indice volumen


DATE

2

DIC.99

Page

18

Indice norma

pressure controller is fed into a loading station (Boiler master) provided for each boiler. 5.5.3

Feed –water control There are three basic types of water makeup control. These are: Single element S Two element S Three element The single element water makeup control is used on small capacity boilers below 75,000 pph. This control consists of adding water to the boiler by means of a level controller on the boiler drum. See Figure 1 on Appendix. S

Two element water makeup control operates in accordance with the variation in steam flow and drum level, is used on medium capacity boilers (75,000 to 200,000 pph), where load changes are not too severe, and where the water pressure is relatively constant. See Figure 1 on Appendix . Three element water makeup control (recommended for new installations) operates in accordance with the variation in feed – feed – water water flow, steam flow and drum level, is used on higher capacity boilers (200,000 pph and up), or on medium capacity boilers where load changes are severe and for boilers with steaming economizers. See Figure 1 on Appendix . Three element water makeup control shall be used when drum level is unsteady due to: small drum size, ”swell and shrink effect” effect ”, poor heat input regulation, or high solids concentration; or when boilers are not equipped with modern steam separating devices. 5.5.4

Combustion controls The combustion controls shall act to increase airflow before increasing fuel flow and to decrease fuel flow before decreasing airflow in order to maintain safe air/fuel ratio. Oxygen controllers may be used to adjust air/fuel ratio to obtain efficient combustion. The air/fuel ratio shall be set to give a small amount of excess air for efficient and safe combustion. The excess air in the flue gas shall not exceed 15% (corresponding to 5% oxygen) at any boiler operating condition other than during start – start – up up and shut – – down. down.

5.5.5

Furnace Draft Control Furnace pressure is controlled to about – – 0.2 0.2 in.w.g on balanced draft boilers and to 10 in.w.g in.w.g on pressure fired fi red boilers by sensing the furnace pressure and adjusting either the stack damper or the induced draft fan speed to maintain the desired furnace draft.


PDVSA



5.5.6

Indice manual

Indice volumen


DATE

2

DIC.99

Page

19

Indice norma

Blowdown control Blowdown analysis shall be made periodically, by means of conductivity tests. Blowdown shall be controlled by chemical injection by means of a manual or automatic control valve.

5.6 5.6

Alar Alarms ms and and Shut Shut – –down d own Main shut – – down down valves shall remain in the shut – shut – down down position until manually reset. The following table is referential, Its application depends on process conditions and furnace design. A risk analysis and HAZOP study should support the final design. The following are typical alarms provided on the local panel and the main control center:


PDVSA



Indice manual

Description

1 2

Boiler feed water to drum Boiler drum

3

Boiler drum (steam phase)

4

S te a m

5 6 7 8

Boiler drum blowdown Chemical additive tank Chemical to boiler drum Superheater outlet

9

Main fuel gas supply

10 11 12

Main fuel oil supply Main atomizing steam P i l o t ga s

13

14

Main burner (gas)

Main burner (fuel oil)

Low flow Low – low flow Low level Low – low level High level High – high level Low pressure High pressure High – high pressure Low temperature High temperature Low flow High temperature High flow High conductivity Low level Low level Low temperature High temperature Low pressure High pressure Low pressure Low pressure Low pressure Low – low pressure High pressure High – high pressure Flame failure Low pressure Low – low pressure High pressure High – high pressure Flame failure Low pressure Low – low pressure High pressure

Indice volumen

Alarm Local Control Center x X x x X x x X x x x X x x x x x x x x x x x x x x x x X x x X x X x x X x x X x X x x X x x


DATE

2

DIC.99

Page

20

Indice norma

Shut –down

NOTE 1 x x

x

NOTE 1

NOTE 2 NOTE 2 NOTE 3 X x NOTE 4 x


PDVSA



15

Main burner (atomizing steam)

16

Main burner (air)

17

Wind box (forced draught)

18

Flue gas outlet

19

Boiler tube skin

NOTE 1: NOTE 2: NOTE 3 :

NOTE 4:

6

PDVSA K –337

Indice manual

High – high pressure Flame failure Low pressure Low – low pressure Low flow Low – low flow Low pressure High pressure High oxygen High temperature High % combustibles High CO / SOx/ NOx High temperature

Indice volumen

X

X X

x x x x x x x x x x x x x

REVISION

DATE

2

DIC.99

Page

21

Indice norma

x X x x

For boiler without steam drums this shall be considered as a shut – shut – down down condition. Only for continuous and intermittent igniter types. Depending in the numbers of burners and their physical arrangement, individual igniter valves shall be closed or the whole burner is shut – shut – down. down. This applies to continuous and intermittent igniter types. Depending in the numbers of burners and their physical arrangement.

FLAM FLAME E DET DETEC ECTI TION ON / BURN BURNER ER MAN MANAG AGEM EMEN ENT T SYS SYSTE TEM M

6.1

The system shall be designed with a local panel containing a Burner Management System with Emergency Master Fuel Trip pushbuttons, Interlock System (Automatic shut – – down down system) to limit improper sequence of events and to shut – – down down the related equipment, Alarm System and Combustion Control System measurement indications and controls necessary for heaters and boilers operation.

6.2

Main and pilot burner flame failure equipment is required, in accordance with NFPA 8502. The type and manufacturer shall be approved by PDVSA. Any deviation from NFPA 8502 shall be (mandatory) supported by a cost – cost – benefit benefit and a risk study and approved by PDVSA.

6.3

The burner management safety functions shall include, but shall not be limited to, proper purge interlocks and timing, mandatory safety shut – shut – down, down, trial timing for ignition, and flame monitoring. monitoring .

6.4

The burner management system shall be a dedicated stand alone fail – fail – safe safe and fail – – checking checking system, in accordance with NFPA 8502. An option of a high integrity


PDVSA



Indice volumen


DATE

2

DIC.99

Page

22

Indice norma

PLC may be used for BMS and Sequence and Control functions. This option shall be PDVSA approved.

6.5

The flame detectors shall be ultra violet type, dedicated, stand alone, fail – fail – safe safe with continuous and dynamic self – – checking. checking. Ultra violet detectors shall operate on 24Vdc, or 120Vac (only in existing systems) depending on the power available .

6.6

The UV Flame controller unit shall have an indication of the signal level generated by the UV detector.

6.7

Flame sensor design shall minimize all possible causes of spurious trips (x rays, ground faults, etc). If adverse conditions are unavoidable for continuous pilot, an alternate design approach must be considered, such as the use of flame rods.

6.8

Power supply for control and protection panels shall be independent from the igniter system power supply. supply. If this is not possible, provisions shall be made to install isolating transformers in the igniter system power supply in order to avoid electrical interference with the rest of the equipment.

6.9

The flame detection logic shall be determined by the type of pilot burner (i.e. Class 1, 2 or 3).

6.10

For Fired heaters with more than one burner and continuous pilots, each pilot shall be equipped with a detector. These detectors shall be connected to an interlock system which prevents any fuel gas protective system valve from opening during startup.

6.11

A common alarm in the control room shall be provided to indicate when flame failure is detected on one or more pilots when continuous pilot type is used.

6.12

In fired heaters with one burner and continuous pilot type, continuous main flame verification using redundant detectors should be provided. Redundant flame sensors shall be justified by a risk analysis, and shall also be approved by PDVSA.

6.13

For intermittent and interrupted type pilots the flame detector shall be located in such a way that it can sense pilot flame during start – start – up up sequence and main burner flame during normal furnace operation.

6.14

Data hi – – way way communications between the burner management system and other systems is permitted, but signals that initiate mandatory master fuel trip shall be hardwired.


PDVSA



Indice volumen


DATE

2

DIC.99

Page

23

Indice norma

6.15

All measurements / process control functions shall be available in the local panel or the control room. For facilities with control room panel, the local field control panel shall be provided with the minimum required control and indication functions to allow heater start – – up up and light – – off. off.

6.16

The heater start – – up up and light – – off off shall always be performed locally and supervised by the operators, even when automatic start – start – up up and automatic combustion control systems are provided.

6.17

The system design shall ensure that the maximum flame establishment period is 5 seconds for gas and 10 seconds for fuel oil.

7

PROTECTION SYSTEMS

7.1

Protection Protecti on Systems (Automatic (Aut omatic shut – – down down system) shall conform to PDVSA K – 336, 336, PDVSA IR – P – 01 01 and NFPA 8502.

7.2

The protection system function is to protect against improper operation by limiting actions to a prescribed operating sequence or by initiating trip devices when approaching an undesirable or unstable operating condition.

7.3

The protection system shall be fail – – safe safe i.e. in normal operating conditions initiating contacts shall be closed, relays and solenoid valves energized by DC voltage.

7.4

Both main shut – – off off valve and main vent valve shall be provided with limit switches in the open and closed position.

7.5

Automatic shut – – off off and lockout of main fuel control valve on low fuel flow shall be provided, with manual reset.

7.6

A hardwired Emergency Shut – – down down switch or pushbutton shall be provided in the control room, at the fired heater local or remote control panel, and where the risk analysis so recommends, to close all fuel and pilot gas protective system valves.

7.7

Forced and induced draft fans shall be continually supervised.

7.8

Gas detector(s) shall be installed at the inlet of the fan. Gas detection shall be a shut – – down down initiator.

7.9

Minimum fuel flow and pressure limiting devices are required to assure that each burner has sufficient fuel for safe operation.


PDVSA



Indice manual

Indice volumen


DATE

2

DIC.99

Page

24

Indice norma

7.10

Lockup devices shall be installed to lock fuel and feedwater valves and dampers in position on instrument air failure.

7.11

The boiler shall be shut – – down down on low – low low level and also on high – high high pressure in the steam drum.

7.12

The protection system for boiler boi ler feed water pumps shall be in accordance with specification PDVSA K – 339. 339.

8

INST IN STAL ALLA LATI TION ON AN AND D COMM COMMIS ISSI SION ONIN ING G

8.1

All field mounted electric / electronic equipment shall be protected adequately against environmental damages.

8.2

Connections Instrumentation coupling connections shall be: Furnace and Stack Draft Gauge Pressure Thermowell O2 and other Analyzers Flue Gas Sampling

Connection Size, NPS (inch) 1 – 1/2 1/2 1 – 1/2 1/2 1 – 1/2 1/2 Connection per Analyzer Manufacturer ’s requirement 1 – 1/2 1/2

8.3

Connections shall be self – – draining draining into the heater. Flexible connections shall be used when exposed to vibration. Instruments shall be preferably installed in a place without vibration.

8.4

Separate nozzles shall be installed for flue gas sampling, smoke and temperature measurements.

8.5

On applications where there may be coking or solidification, orifice flanges shall have a double set of tappings, one for flow control and the other for alarm/shut – – down. down.

8.6

Ignition transformers shall be installed close to the burner in order to minimize the length of the high voltage lead wire to the sparking device electrodes.

8.7

The view path tube must be installed downwards to minimize accumulation of falling soot on the sensor glass.


PDVSA



Indice volumen


DATE

2

DIC.99

Page

25

Indice norma

8.8

For flame sensors that might get soot on their cover glass, a forced air purge/cleansing system should be considered.

8.9

Shut – – down down signals are to originate from their own process taps and are to be completely separated from transmitters used for control and pre – pre – alarms. alarms.

8.10

UV design and installation must consider the following: S S S

A clear view path of the flame being monitored is required at all times. Sensors shall not be affected by sparks during start up. Detector’ Detector ’s view path must focus on the first third of the flame.

8.11

If flame rods are used, they shall be in contact with the center of the flame. Flame rod electrode shall have a good ground connection.

8.12

For horizontal or slightly tilted pilots, flame rods must be placed sideways or under the pilot.

8.13

Fire resistant isolated wire shall be used for ignition sparking devices and flame rod electrodes.

9

QUAL QUALIT ITY Y AS ASSU SURA RANC NCE E / QUAL QUALIT ITY Y CONT CONTRO ROL L All items shall conform to the procedures detailed in specifica tion PDVSA K – 369. 369.


PDVSA



10 APPENDIX Figure 1. Feed – water water Control Schemes

Indice volumen


DATE

2

DIC.99

Page

26

Indice norma

Norma Pdvsa K-337

Recommend Documents