norma pdvsa k-337

PDVSA N° TITLE

REV. DATE DESCRIPTION PAG. REV. APPD. APPD.

APPD.BY DATEDATE

VOLUME 9–II

� PDVSA, 1983

K–337 FURNACE AND BOILER INSTRUMENTATION

FOR APPROVAL

Alexis Arévalo Jesús E. RojasDIC.99 DIC.99

ENGINEERING SPECIFICATION

AUG.94

AUG.96

DIC.99 Y.K.

L.T.

L.T.

2

1

0

APPROVED

GENERAL REVISION 26

27

21

A.A.

E.J.

E.J.

J.E.R.

A.N

A.N.

ENGINEERING DESIGN MANUAL

ESPECIALISTAS

APPD.BY

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FURNACE AND BOILER INSTRUMENTATIONPage 1

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Menú Principal Indice manual Indice volumen Indice norma

Index1 SCOPE 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

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

4 FIRED HEATERS 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 General 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Fuel systems 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Measurement 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Burner Management System 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Controls 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Alarms and Shut–down 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 BOILERS 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 General 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Fuel System 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Measurement 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Burner Management System 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Controls 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Alarms and Shut–down 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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

http://www.intevep.pdv.com/santp

http://www.intevep.pdv.com/santp/mid/indice_mid.htm

http://www.intevep.pdv.com/santp/mid/vol09-2/indice_vol09-2.htm

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1 SCOPEThis document covers minimum PDVSA instrumentation requirements for thedesign, specification, installation and commissioning of fired heaters and boilerslocated at petroleum refineries and production facilities.

This standard applies to all fired heaters and boilers and is based on NFPA 8502,ASME CSD–1 and API 556.

The user of this standard must recognize the complexity of firing fuel with regardto the type of equipment and the characteristics of the fuel. It is intended that thedesigner shall be capable of applying a rigorous analysis to special or unusualproblems. The validity of the design shall be approved by PDVSA.

This specification does not cover the following:

� Steam control systems used for purging natural draft process fired heaters priorto burner light off.

� Pilot gas system supplies (filters and LPG vaporizers).� Instrumentation systems for inert gas generators, incinerators, pulverized fuel

and sulfur furnaces.

2 CODES, STANDARDS AND PRACTICESNFPA 8502 Standard for the Prevention of Furnace

Explosions/Implosions in Multiple Burner–Boilers.NFPA 8501 Standard for Single Burner Boiler Operation.API RP–551, 552 Process Measurement InstrumentationAPI 555 Process AnalyzersAPI Std 560 Fired Heaters for General Refinery ServicesAPI RP–556 Instrumentation and Control System for Fired Heaters

and Steam Generators.ASME CSD–1 Controls and Safety Devices for Automatically Fired

Boilers.ANSI Z83.3 Gas Fired BoilersPDVSA B–201–PR Calentadores de Fuego DirectoPDVSA K–300 IntroductionPDVSA K–303 Level InstrumentationPDVSA K–334 Instrumentation and Thermocouple Extension CablesPDVSA K–335 Packaged Unit InstrumentationPDVSA K–336 Safety Instrumented SystemsPDVSA– K–369 Instrumentation QA/QCPDVSA IR–E–01 Clasificación de Areas




http://www.intevep.pdv.com/~citonline/espanol/cat_norm_inter_frame.htm

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PDVSA IR–M–01 Separación entre Equipos e InstalacionesPDVSA IR–P–01 Sistemas de Parada de Emergencia, Bloqueo,

Despresurización y Venteo de Equipos y PlantasPDVSA IR–S–01 Filosofía de Diseño SeguroPDVSA N–201 Obras EléctricasEven though the NFPA 8502 standard scope does not cover process heaters, thisstandard (PDVSA K–337) considers that, from the security point of view, theprincipal purpose of both standards “contribute to operating safety and to preventfurnace explosions and implosions” is the same and the premises of the NFPA8502 shall be followed for the design, installation, operation, and maintenance offired heaters and boilers and their fuel burning systems.

NOTE: This document originated as a compilation of the PDVSA K–337 “FurnaceInstrumentation” Rev–1, Aug.1996 and PDVSA K–338 “Boiler andInstrumentation” Rev–1, Aug. 1996 standards.

3 DEFINITIONSThe following definitions are included to understand this standard.

Continuous pilot

An igniter applied to the fuel input through the burner and to support ignition underany burner light–off or operating conditions. This pilot burns throughout the entireperiod the unit is in service whether or not the main burner is firing. This type of pilotrequires a reliable gas source. This term is equivalent to igniter, class 1 accordingto NFPA 8502.

Intermittent pilot

An Igniter applied to the fuel input through the burner under prescribed light – offcondition. This pilot is automatically lighted each time there is a call for heat. Itburns during the entire period the main burner is firing. This term is equivalent toigniter, class 2 according to NFPA 8502.

Interrupted pilot

The pilot is automatically lighted each time there is a call for heat. The pilot fuel iscut off automatically at the end of the main burner flame–establishing period. Thisterm is equivalent to igniter, class 3 according to NFPA 8502.

Reliable gas source

A pilot gas source that meets all of the following conditions:

� Separate from the main fuel gas supply such that both supplies will not besimultaneously interrupted by a single contingency such as power or instrumentair failure or inadverted valve closing.




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� 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 properstart–up, operation and normal shut–down of a heater or boiler with interlocks toensure that the operation follows established procedures. See Section 6–8 andfigures A.6.8.1.1 (a) and (b) on NFPA 8502.

Furnace

The portion of the heater or boiler enclosure within which the combustion processtakes place and wherein heat transfer occurs predominantly by radiation.

Blowdown Control

The primary purpose of blowdown is to maintain the dissolved solids concentrationand silica content of the water in the steam generator within acceptable limits.Proper blowdown control will limit scale formation on heat transfer surfaces, limitthe solids content of the steam drum, and assure maximum benefit from watertreatment chemicals.

Note: For further definitions on Heater And Boiler instrumentation refer to NFPA8502, Chapter 3, Definitions.

4 FIRED HEATERS

4.1 General

4.1.1 All fired heaters have the following functional requirements:

� Process control.

� Burner Management System.

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

4.1.2 The instrumentation system shall ensure the safe operation of the heater andinclude a control system to ensure optimum heat transfer at maximum, normal, andminimum loads.

4.1.3 Electrical equipment or instruments shall be specified and installed according tothe intended service (fuel, gas, etc.) and the area classification. Special care shallbe taken to position the local control panel and push button station in a safe areato be operated under emergency and harsh environment conditions according toPDVSA IR–P–01 and HAZOP study results.

4.1.4 The main fuel heater safety shut–off valves shall be located at a safe distance fromthe furnace, according to PDVSA IR–P–01 and HAZOP study results.




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4.1.5 For cable routing, see specification PDVSA K–334. and PDVSA N–201.

4.2 Fuel systems

4.2.1 The fuel for pilot burners (igniters) shall be natural gas.

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

4.2.3 Safety shut–off valves (for igniters and main burners) shall be fail safe and notreadily bypassed or blocked open and shall not be used as modulating controlvalves.

Modifications to this requirement shall be supported by cost–benefit and riskanalysis, considering equipment dimensions, operation site, operating conditions,etc.

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

4.2.5 Main fuel control valve shall fail–closed and shall have a closed position switch tobe monitored by the BMS. This control valve shall be sized and arranged to ensurea fuel flow adequate for all operating requirements of the units.

4.2.6 The fuel gas system arrangement for pilots and burner shall be in accordance toNFPA 8502, Part 6.3 “System Requirements” and 7.3 for fuel oil system.

4.2.7 Any modification in existing heaters (i.e. revamping) shall consider as first optionto design the fuel gas system arrangement for pilots and burner recommended byNFPA 8502, Part 6.3. As a second option for existing heaters with few burners, aSupervised 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 bycost–benefit and risk analysis, considering equipment dimensions, operation site,operating conditions, etc.

4.2.8 All individual burner safety shut–off valves shall be located as close to the burneras practical, to minimize the volume of fuel left downstream of the burner valvesin the burner lines.

4.2.9 The double block and vent arrangement shall consist of two (2) shut–off valves andone (1) vent valve, each one independent from the others. An integral type valvemight be considered and shall be approved by PDVSA.




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4.2.10 Provision should be made to leak–test the individual shut–off valves. On dual fuelunits with combination burners, leak tests may be done on one fuel system whileunit is operated with the other.

4.2.11 On forced draft heater automatic shut–off for the combustion air, isolating dampersshall be provided. This damper shall close when the main flame is not alight.Provision shall be made to open these dampers during furnace purging, burnerlight–off, and post–purging if required.

4.2.12 Furnaces with a large number of small burners, making pilots impractical, and aconstant firing rate, shall have a Main Fuel Low Pressure Indicator with a MainFuel Low Pressure Alarm for shut–off of fuel to all burners on main fuel lowpressure.

4.3 MeasurementTypical measurements used to maintain automatic control or to actuate alarmdevices are discussed below. Sensors and instruments shall be accessible forreading and maintenance. Certain local check measurements at the source arenecessary. Refer to API RP 551 and PDVSA MID, Volume 9, for installation details.

Modifications to this requirement shall be supported by cost–benefit and riskanalysis, 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:

d. Radiant section.

e. Convection Section.

f. Flue gas stack, before the damper, at approximately 2 diameters from stackentrance, and preferably near the sampling point for flue gas analysis.

g. At inlet and outlet manifolds of process fluid.

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

i. On furnaces with high risk of coking, tube skin temperature measurement onradiant coil tubes shall be considered. Measurement points shall be within two orthree tube diameters of the outlet, but may be best selected by considering theexpected temperature profile. It is important that the temperature be determinedat or near the highest section of the temperature profile. Multiple skinthermocouples distributed along the potential coking area should also beconsidered.




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j. Radiant coil tube skin metal thermocouples shall be installed according to Figures2 and 3 on API RP 556. The thermocouples must be in direct contact with the tube.All scale and oxide must be cleaned from the tubes before attaching thethermocouple sheath or block. Consult the fired heater manufacturer forrecommended location for tube skin temperature measurement points

k. Where steam–air decoking is specified, to prevent damage from spalling, thethermowells shall be located downstream of swing bends. To measure decokingeffluent temperature, additional thermowells with thermocouples shall be locatedin decoking outlet lines.

Where reverse steam–air decoking is specified, additional skin thermocouplesshall be installed in each pass, on one of the shock tubes.

l. Where provision is made for future reverse steam – air decoking, a thermowell withthermocouple shall be installed at the normal inlet end of each individual passwhich will become an outlet during decoking. This thermowell shall be located inthe decoking piping, not the process piping, on the side of the swing bend awayfrom the heater.

m. In the liquid fuel manifold, as close to the burners as possible.

4.3.2 PressureThe 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.




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– Pressure tapings only shall be provided in each crossover on all vaporizing dutyfurnaces.

e. Draft:

– Pressure measurements should be made at the outlet of the forced–draft fan,across the air pre–heater, in the preheated air duct before the burners, in thefirebox (near the burners and at the top of the radiant section), and across thedampers.

– At firebox in natural draft burners.

– On induced draft fired heater fitted with natural draft burners, if natural draftbackup is not inherent in the fired heater design, the heater shall be shut–downon 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 furnacefirebox at different positions.

– At outlet of the convection section.

4.3.3 FlowThe flow shall be measured at, but not limited to, the following points:

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

b. Fuel gas and oil flow in the main line located upstream of the fuel control valves.

c. An additional flow element for pilot fuel gas if it is piped independently of the maingas supply.

d. Flow meter located upstream of the heater coil; if the process fluid is divided intotwo or more streams through the heater the flow in each pass shall be measured,if practical.

4.3.4 Level

a. In pyrotubular type heaters a level indicator shall be installed. A low level signalshall be required for interlock purpose.

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

4.3.5 Analysis

a. Sample point facilities shall be provided for taking samples of the flue gas at theexit of each combustion chamber, just above the radiant section, and in the exit ofthe convection section so the composition of flue gas may be determined byanalysis.




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b. If required both oxygen and unburned combustibles shall be measured on the fluegas and indicated on the local firing panel and in the control room to obtain a goodmeasurement of the quality of combustion.

c. Samples shall be taken as near as possible to the point where combustion iscompleted, normally at the exit of the radiant section.

d. The sample points shall be provided with screwed closures.

e. When toxic gases or liquids are burnt in the furnace, analyzers shall be installedin the stack to monitor exhaust gas quality.

f. Sample points shall also be provided near the damper and near the stacktemperature thermocouple.

All analyzer sample points must include facilities for manual sample take–offs.

4.4 Burner Management SystemFor Burner Management System see section 6.

4.5 Controls

4.5.1 Load Control

a. Continuos control functions shall be executed on independent devices (sensors,controllers, final control elements) different from sequential control devices.

b. A fuel gas pressure controller (for natural draft heaters) or flow controller (forforced draft heaters) shall be installed in the heater fuel supply header.

c. The furnace load controller (outlet temperature) shall be actuated on the fuel andcombustion airflow controller set points. The basic principle is that both fuel andcombustion airflow are controlled in parallel, with limit (maximum for fuel, minimumfor air) to avoid sub–stoichiometric combustion. See API RP–556 FIG. 5 for forcedDraft Heater and FIG. 6. For Natural Draft Heater.

d. In case that load variation is expected a heater feed process flow controller withP.I. actions should be implemented. It should guarantee process flow stability. Theprocess flow control valve shall be fail–open.

e. For single and multiple burner heaters minimum combustion air flow shall beensured by an adjustable mechanical minimum stop on the combustion airdamper, while the maximum combustion air flow is limited by the capacity of theblower and air register resistance.

f. Minimum fuel flow condition (during start up or minimum burner load operation)shall be ensured by an active minimum stop, implemented by a pressure controlleror a self regulated valve, on the fuel gas or fuel oil control valve.




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g. The combustion control system shall maintain heater fuel and air ratio inaccordance with demand. The air/fuel ratio shall be set to provide a small amountof excess air for efficient and safe combustion.

h. Atomizing steam for the fuel oil burner is controlled at a constant pressuredifferential to the burner fuel oil pressure.

i. Depending on the variation in the MW of the fuel gas, flow measurement shall becorrected for changes in gas density.

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

k. In forced and induced draft heaters, control systems for regulation of fuel or air, orboth, shall maintain air/fuel ratio at the optimum design excess air rate (for naturalgas normally 5%, for oil 6%, and for coal 10%).

l. All fired heater stack dampers shall be positioned manually or automatically witha manual loading station located at grade adjacent to the fired heaters or with asignal from the combustion control system, if it is required that the loop be closed.Damper position shall be indicated.

m. Fuel oil firing system shall ensure a constant differential between steam and oilpressures. The recommended value of differential pressure shall be specified bythe burner supplier.

n. With any change of the rate of furnace input, the airflow and fuel flow shall bechanged simultaneously to maintain proper air/fuel ratio during and after thechanges. This shall not eliminate the requirements for air lead and lag duringchanges in the fuel firing rate.

o. A control strategy shall be implemented such that setting fuel flow control onautomatic without the airflow control on automatic shall not be permitted.

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

4.5.2 Sequential Control

Start–up and shut–down sequence recommendations shall be submitted toPDVSA by heater manufacturer. However manufacturer shall guarantee that thestart–up and shut–down systems execute, at least, the following functions:

4.5.3 Start–Up Sequence

a. Automatic verification of , but not limited to, the following interlocks:

– High burner fuel pressure.– Low igniter fuel pressure.




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

b. Purging

– For forced draft heaters the system shall be equipped with an automatic purgesequence. Upon activation of the “purge start” the combustion air damper is fullyopened during the period set on the purge timer. After the purge time haselapsed and all permissive conditions are cleared, the burner can be started. Anew purge cycle is only required in case of a combustion air failure. After anyother sequence failure, a waiting time of 1 minute to restart is sufficient.

– For natural draft heater purging shall be performed based on an operationalprocedure.

– Igniters light–off.– Burners light–off.

4.5.4 Shut–down Sequence

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




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a. Partial Shut–down

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

b. Total Shut–down

A master trip is activated after a predetermined period of time in a partialshut–down condition, or at least, when any signal listed in section 4.6, Alarms andShut–down, is activated:

Prior to start–up, the fuel safety shut–off valves shall be closed, and the fuel flowcontrollers are automatically set to “manual” with zero output. This will drive the fuelcontrol valves to the minimum stop setting.

4.6 Alarms and Shut–down

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

4.6.2 The following typical alarms and shut–down signals shall be provided. Applicationdepends on the process conditions and furnace design. A risk analysis andHAZOP study should support the final design.

4.6.3 For instrument taps locations refer to Figure A–6.5.1.2(b) of NFPA 8502.




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Description Alarms PartialShut–off

TotalShut–off

Local ControlCenter

Low flow in passes XLow flow process XLow–low flow process x x xPass outlet high temperature XHigh–high process outlet temperature x X xLow–low and high–high gas pressure at igniterheader

x x X

Low–low and High–high pressure at fuel supply(gas and liquid)

x x

High–high pressure at burner header x x xLow–low pressure at burner header x x xLow atomizing steam pressure at burner xLow percentage oxygen in the flue gas xHigh percentage combustibles in the flue gas xLow combustion air flow on forced draft burners x xHigh wind box pressure x Note 3Low wind box pressure x Note 3Flame failure (one burner) in a single burnerheater

x x x

Flame failure in multi–burner heaters x x Note 1High stack temperature xHigh–high stack temperature x xHigh smoke density (on fire) x Note 4High–high tube skin x Note 4Fan failure x Note 2Stack damper closed x xCombustible gas on air duct intake x xLoss of air pre–heater driver xManual ESD station x Note 5Low energy supply (Instrument air or electricalsupply)

x

Loss of energy supply (Instrument air orelectrical supply)

x Note 6

High level in fuel gas K.O. drum xHigh–high level in fuel gas K.O. drum x x

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




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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 all burners and igniter valves, even whencontinuous igniter type is used.

Note 6: Not necessarily automatically initiated. A risk cost–benefit analysis shouldsupport the final decision.

5 BOILERS

5.1 General

5.1.1 This chapter applies to boilers in which steam or vapor is generated at a pressureexceeding 15 psig. For lower pressure boilers refer to ASME CSD–1.

5.1.2 All boilers have three basic functional requirements:

� Maintain steam production automatically at the required pressure andtemperature under varying operating conditions (e.g. a sudden increase ordecrease in demand of steam).

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

condition.

5.1.3 The instrumentation system shall ensure the safe operation of the boiler andinclude a control system to ensure optimum heat transfer under varying loadconditions.

5.1.4 Boiler designs vary depending upon the specific process design – power plant,waste heat, etc.

5.1.5 Electrical equipment or instruments shall be specified and installed according tothe intended service (fuel, gas, etc.) and the area classification. Special care shallbe taken to position the local control panel and push button station, so that theyare located in a safe area to be operated under emergency and harsh environmentconditions according to PDVSA IR–P–01 and HAZOP study results.

5.1.6 The main fuel safety shut–off valves shall be located at a safe distance from theboiler. Refer to PDVSA IR–P–01 and HAZOP study results.

5.1.7 For cable routing, see specification PDVSA K–334. and PDVSA N–201.

5.2 Fuel SystemFor fuel system see section 4.2.




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5.3 MeasurementTypical measurements employed to maintain automatic control or to actuate alarmdevices are discussed below. Sensors should be accessible for reading andmaintenance. Certain local check measurement at the source are necessary.Refer to API RP 551 and PDVSA MID volume 9 for installation details.

5.3.1 Temperature

a. Temperature measuring elements complete with thermowells shall be provided, atleast, 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 of thermowell and its immersion length shall be carefully selected.Special tapered well shall be considered for high pressure and high velocityservice. Tapered wells shall be designed for particular installations to preventcracking due to metal fatigue caused by velocity–induced vibration. Typically,wells in super–heated steam service are flanged (RF).

c. Radiant coil tube skin metal thermocouples shall be installed according to figures2 and 3 on API RP 556, appendix 2.0. The thermocouple must be in direct contactwith the tube. All scale and oxide must be cleaned from the tubes before attachingthe thermocouple sheath or block. Consult the boiler manufacturer forrecommended location for tube skin temperature measurement points

5.3.2 Pressure

a. Pressure shall be measured at, but not limited to, the following locations:

Boiler feed water

– Battery limit inlet

Steam

– Steam drum vapor phase– Steam header– Upstream of superheated steam supplies flow meter




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5.3.3 Flow

a. Flow shall be measured at, but not limited to, the following locations:

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 Level

a. Level shall be measured at, but not limited to, the following locations:

– Continuous steam drum water level in accordance with details inspecification K–303. One d/p cell for control and a second d/p cell for highand low alarms

– Level gauge in accordance with ASME “Boiler and Pressure Vessel Code– Condensate (Purge) separators

5.3.5 Analysis

a. Some of the recommended quality measurements are:

Feed–Water:

– PH– Conductivity– Hardness– Turbidity

Combustion quality measurement:

– Oxygen contents in flue stack– CO




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Required by regulatory agencies:

– SOx– NOx

Additional information on installation can be obtained in API Technical Paper 555.

5.4 Burner Management SystemFor Burner Management System see section 6

5.5 Controls

5.5.1 General

The control system must be adequate to cover all operation conditions of the boilerduring startup, normal operation, shut–down, and any emergency situation.

Provision shall be included for indication at the local control panel and convenientoperator adjustment of all necessary set points at the main control location.

The control system shall guarantee steam demand, evaporated water make upand efficient use of the fuel; in order to achieve these three functions the followingautomatic controllers have to be implemented: steam pressure, drum level, fuelflow, air flow and furnace draft pressure.

5.5.2 Steam pressure control

Each fired steam boiler or system of commonly connected steam boilers shallhave, at least, one steam pressure control device that will shut–off the fuel supplyto each boiler when the steam pressure reaches a preset maximum operatingpressure.

In addition to the steam pressure control, each fired steam boiler shall have a highsteam pressure limit control that will prevent generation of steam pressure inexcess of the maximum allowable working pressure.

In multiple boiler installation one master steam pressure controller shall serve asthe primary control for a group of boilers.

If the fuel pressure is subject to significant fluctuation, the steam pressurecontroller might be cascaded to a fuel flow or pressure controller. The masterpressure controller compares the pressure in the main steam heater with its setpressure and automatically adjusts its output to each boiler’s combustion controlsto request more or less steam.

If steam demand is subject to significant fluctuation, consideration should be givento use feed forward control strategy on the master pressure controller.

When two or more boilers operate in parallel, they must share the total load invarious proportions. In order to divide the total load, the output signal of the master




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pressure controller is fed into a loading station (Boiler master) provided for eachboiler.

5.5.3 Feed–water control

There are three basic types of water makeup control. These are:

� Single element� Two element� Three elementThe single element water makeup control is used on small capacity boilers below75,000 pph. This control consists of adding water to the boiler by means of a levelcontroller on the boiler drum. See Figure 1 on Appendix.

Two element water makeup control operates in accordance with the variation insteam flow and drum level, is used on medium capacity boilers (75,000 to 200,000pph), where load changes are not too severe, and where the water pressure isrelatively constant. See Figure 1 on Appendix .

Three element water makeup control (recommended for new installations)operates in accordance with the variation in feed–water flow, steam flow and drumlevel, is used on higher capacity boilers (200,000 pph and up), or on mediumcapacity boilers where load changes are severe and for boilers with steamingeconomizers. See Figure 1 on Appendix .

Three element water makeup control shall be used when drum level is unsteadydue to: small drum size, ”swell and shrink effect”, poor heat input regulation, or highsolids concentration; or when boilers are not equipped with modern steamseparating devices.

5.5.4 Combustion controls

The combustion controls shall act to increase airflow before increasing fuel flowand to decrease fuel flow before decreasing airflow in order to maintain safe air/fuelratio.

Oxygen controllers may be used to adjust air/fuel ratio to obtain efficientcombustion.

The air/fuel ratio shall be set to give a small amount of excess air for efficient andsafe 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–up and shut–down.

5.5.5 Furnace Draft Control

Furnace pressure is controlled to about – 0.2 in.w.g on balanced draft boilers andto 10 in.w.g on pressure fired boilers by sensing the furnace pressure and adjustingeither the stack damper or the induced draft fan speed to maintain the desiredfurnace draft.




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5.5.6 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 orautomatic control valve.

5.6 Alarms and Shut–downMain shut–down valves shall remain in the shut–down position until manuallyreset.

The following table is referential, Its application depends on process conditionsand furnace design. A risk analysis and HAZOP study should support the finaldesign.

The following are typical alarms provided on the local panel and the main controlcenter:




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Description Alarm Shut–downLocal Control

Center1 Boiler feed water to drum Low flow x

Low–low flow X x NOTE 12 Boiler drum Low level x

Low–low level X x xHigh level xHigh–high level X x xLow pressure xHigh pressure xHigh–high pressure X x x

3 Boiler drum (steam phase) Low temperature xHigh temperature x

4 Steam Low flow xHigh temperature x NOTE 1High flow x

5 Boiler drum blowdown High conductivity x6 Chemical additive tank Low level x7 Chemical to boiler drum Low level x8 Superheater outlet Low temperature x

High temperature x9 Main fuel gas supply Low pressure x

High pressure x10 Main fuel oil supply Low pressure x11 Main atomizing steam Low pressure x12 Pilot gas Low pressure x

Low–low pressure X x NOTE 2High pressure xHigh–high pressure X x NOTE 2Flame failure X x NOTE 3

13 Main burner (gas) Low pressure xLow–low pressure X x XHigh pressure xHigh–high pressure X x xFlame failure X x NOTE 4

14 Main burner (fuel oil) Low pressure xLow–low pressure X x xHigh pressure x




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High–high pressure X x xFlame failure x X

15 Main burner (atomizing steam) Low pressure xLow–low pressure X x x

16 Main burner (air) Low flow xLow–low flow X x x

17 Wind box (forced draught) Low pressure xHigh pressure x

18 Flue gas outlet High oxygen xHigh temperature xHigh % combustibles xHigh CO / SOx/ NOx x

19 Boiler tube skin High temperature x

NOTE 1: For boiler without steam drums this shall be considered as a shut–downcondition.

NOTE 2: Only for continuous and intermittent igniter types.NOTE 3 : Depending in the numbers of burners and their physical arrangement,

individual igniter valves shall be closed or the whole burner is shut–down. Thisapplies to continuous and intermittent igniter types.

NOTE 4: Depending in the numbers of burners and their physical arrangement.

6 FLAME DETECTION / BURNER MANAGEMENT SYSTEM

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

6.2 Main and pilot burner flame failure equipment is required, in accordance with NFPA8502. The type and manufacturer shall be approved by PDVSA. Any deviationfrom NFPA 8502 shall be (mandatory) supported by a cost–benefit and a risk studyand 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–down, trial timing forignition, and flame monitoring.

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




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

6.5 The flame detectors shall be ultra violet type, dedicated, stand alone, fail–safe withcontinuous and dynamic self–checking. Ultra violet detectors shall operate on24Vdc, 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 generatedby 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, analternate 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 theigniter system power supply. If this is not possible, provisions shall be made toinstall isolating transformers in the igniter system power supply in order to avoidelectrical interference with the rest of the equipment.

6.9 The flame detection logic shall be determined by the type of pilot burner (i.e. Class1, 2 or 3).

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

6.11 A common alarm in the control room shall be provided to indicate when flamefailure 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 flameverification using redundant detectors should be provided. Redundant flamesensors 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 insuch a way that it can sense pilot flame during start–up sequence and main burnerflame during normal furnace operation.

6.14 Data hi–way communications between the burner management system and othersystems is permitted, but signals that initiate mandatory master fuel trip shall behardwired.




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

6.16 The heater start–up and light–off shall always be performed locally and supervisedby the operators, even when automatic start–up and automatic combustion controlsystems are provided.

6.17 The system design shall ensure that the maximum flame establishment period is5 seconds for gas and 10 seconds for fuel oil.

7 PROTECTION SYSTEMS

7.1 Protection Systems (Automatic shut–down system) shall conform to PDVSAK–336, PDVSA IR–P–01 and NFPA 8502.

7.2 The protection system function is to protect against improper operation by limitingactions to a prescribed operating sequence or by initiating trip devices whenapproaching an undesirable or unstable operating condition.

7.3 The protection system shall be fail–safe i.e. in normal operating conditionsinitiating contacts shall be closed, relays and solenoid valves energized by DCvoltage.

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

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

7.6 A hardwired Emergency Shut–down switch or pushbutton shall be provided in thecontrol room, at the fired heater local or remote control panel, and where the riskanalysis 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 ashut–down initiator.

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




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

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

7.12 The protection system for boiler feed water pumps shall be in accordance withspecification PDVSA K–339.

8 INSTALLATION AND COMMISSIONING

8.1 All field mounted electric / electronic equipment shall be protected adequatelyagainst environmental damages.

8.2 Connections

Instrumentation coupling connections shall be:

Furnace and Stack Connection Size, NPS (inch)Draft Gauge 1–1/2Pressure 1–1/2Thermowell 1–1/2O2 and other Analyzers Connection per Analyzer

Manufacturer’s requirementFlue Gas Sampling 1–1/2

8.3 Connections shall be self–draining into the heater. Flexible connections shall beused when exposed to vibration. Instruments shall be preferably installed in aplace without vibration.

8.4 Separate nozzles shall be installed for flue gas sampling, smoke and temperaturemeasurements.

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

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

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




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

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

8.10 UV design and installation must consider the following:

� 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’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. Flamerod electrode shall have a good ground connection.

8.12 For horizontal or slightly tilted pilots, flame rods must be placed sideways or underthe pilot.

8.13 Fire resistant isolated wire shall be used for ignition sparking devices and flamerod electrodes.

9 QUALITY ASSURANCE / QUALITY CONTROLAll items shall conform to the procedures detailed in specification PDVSA K–369.




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10 APPENDIXFigure 1. Feed–water Control Schemes




norma pdvsa k-337

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