GS EP SAF 227 - SAFETY RULES FOR FIRED HEATERSpogc.ir/portals/10/imeni/doc/GS_EP_SAF_227_EN.pdf ·...

Exploration & Production

This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.

GENERAL SPECIFICATION

SAFETY

GS EP SAF 227

Safety rules for fired heaters

03 01/2011 General Review

02 10/2005 Addition of EP root to document identification

01 10/2003 Change of Group name and logo

00 04/2001 Old TotalFina SP SEC 227

Rev. Date Notes

Owner: EP/HSE Managing entity: EP/SCR/ED/ECP


General Specification Date: 01/2011

GS EP SAF 227 Rev: 03


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Contents

1. Scope ....................................................................................................................... 4 1.1 Purpose of the specification ............................................................................................... 4

1.2 Applicability ........................................................................................................................ 4

2. Reference documents ............................................................................................. 4

3. Terminology and definitions .................................................................................. 7

4. Layout .................................................................................................................... 10 4.1 Location and minimum distances .................................................................................... 10

4.2 Hazardous areas ............................................................................................................. 12

4.3 Ventilation ........................................................................................................................ 13

4.4 Drainage of liquid spills .................................................................................................... 13

4.5 Floors and clearances ..................................................................................................... 13

5. Design .................................................................................................................... 15 5.1 General ............................................................................................................................ 15

5.2 Heaters structural design ................................................................................................. 15

5.3 Igniters ............................................................................................................................. 16

5.4 Air flow ............................................................................................................................. 16

5.5 Dampers and flame arresters .......................................................................................... 17

5.6 Safety shutdown devices ................................................................................................. 17

5.7 Stack ................................................................................................................................ 19

5.8 Specifics to liquid-fuels .................................................................................................... 19

5.9 Design validation ............................................................................................................. 20

6. Controls and Safety instruments ......................................................................... 20 6.1 General ............................................................................................................................ 20

6.2 Process fluids .................................................................................................................. 21

6.3 Combustion ...................................................................................................................... 21

6.4 Gas detection ................................................................................................................... 22

6.5 Shutdowns ....................................................................................................................... 22

6.6 Alarms .............................................................................................................................. 26

6.7 Installation of analysers ................................................................................................... 27

7. Operating requirements ........................................................................................ 28





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7.1 Start-up ............................................................................................................................ 28

7.2 Dual-fuel operation .......................................................................................................... 29

7.3 Shutdowns ....................................................................................................................... 30

8. Fire protection ....................................................................................................... 30 8.1 Fire detection ................................................................................................................... 30

8.2 Fire-proofing .................................................................................................................... 31

8.3 Fire-fighting systems ........................................................................................................ 31

Bibliography ................................................................................................................. 34 Appendix 1 Typical schematics – Fuel gas ........................................................................... 36

Appendix 2 Typical schematics - Liquid fuel ......................................................................... 37

Appendix 3 Ignition Logic diagram ........................................................................................ 38

Appendix 4 Recommendation for safety valves arrangement .............................................. 39





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1. Scope

1.1 Purpose of the specification The purpose of this general specification is to define the safety requirements for the design and installation of fired heaters and associated equipment. There are different types of heaters, and the aim of this specification is to define some basic safe practices applicable in every case unless otherwise stated.

1.2 Applicability This specification applies to all types of fuel-fired heaters with a total heat release greater than 100 Kw, including liquid bath indirect heaters, reboilers and waste incinerators. This specification is not retroactive. It shall apply to new installations and to major modifications or extensions of existing installations, both onshore and offshore.

This specification is applicable to typical fired heaters used in the E&P industry such as:

• Glycol reboilers,

• Crude Oil or Process Gas heaters,

• Hot oil or pressurised hot water heaters,

• Steam boilers,

• Molecular sieve dryer regeneration gas heater,

• Incinerators.

This specification does not cover:

• Electrical heaters,

• Fired heaters used where chemical reactions take place in the tubular coils,

• Manually operated fired heaters (not applicable for new designs, upgrading requirements for existing units as per NFPA 85 if needed),

• Pulverised coal firing, which is at present not used in Company’s upstream facilities,

• Specific safety requirement for fired heaters using premix burners,

• Oxy-combustion equipment using enriched air or pure oxygen,

• Domestic use fired heaters.

2. Reference documents The reference documents listed below form an integral part of this General Specification. Unless otherwise stipulated, the applicable version of these documents, including relevant appendices and supplements, is the latest revision published at the EFFECTIVE DATE of the CONTRACT.

The applicability of the referenced documents is as follows:

• ISO 13705 / API STD 560 covers the minimum requirements for the design, materials, fabrication, inspection, testing, preparation for shipment, and erection of fired heaters for general refinery service. ISO 13705 / API STD 560 is mainly dealing with combustion process and mechanical technical matters, and with fabrication, inspection, testing,





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preparation for shipment, and erection on site. It is not devoted to safety or operational matters.

• NFPA 86 This standard applies to Class A, Class B, Class C, and Class D ovens (refer to chapter 3), dryers, and furnaces, thermal oxidizers, and any other heated enclosure used for processing of materials and related equipment.

Class A, Class B, or Class C oven is any heated enclosure operating at approximately atmospheric pressure and used for commercial and industrial processing of materials.

This standard does not cover to the following:

(1) Coal or other solid fuel-firing systems,

(2) Listed equipment with a heating system(s) that supplies a total input not exceeding 44 kW (150,000 Btu/h).

This standard provides the requirements for furnaces to minimize the fire and explosion hazards that can endanger the furnace, the building, or personnel.

• NFPA 85 code shall apply to single burner boilers, multiple burner boilers, stokers, and atmospheric fluidized-bed boilers with a fuel input rating of 3.7 MW (12.5 million Btu/hr) or greater, to pulverized fuel systems, to fired or unfired steam generators used to recover heat from combustion turbines [heat recovery steam generators (HRSGs)], and to other combustion turbine exhaust systems.

The purpose of this code shall be to contribute to operating safety and to prevent uncontrolled fires, explosions, and implosions in equipment described here above. This code establishes minimum requirements for the design, installation, operation, training, and maintenance of pulverized fuel systems, boilers, HRSGs, combustion turbine exhaust systems, and their systems for fuel burning, air supply, and combustion products removal.

Standards

Reference Title

ISO 13705 / API STD 560 Petroleum, petrochemical and natural gas industries - Fired heaters for general refinery service

Professional Documents

Reference Title

NFPA 12 Standard on Carbon Dioxide Extinguishing Systems

NFPA 17 Standard for Dry Chemical Extinguishing Systems

NFPA 85 Boiler and Combustion Systems Hazards Code

NFPA 86 Standard for Ovens and Furnaces





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Regulations

Reference Title

Not applicable

Codes

Reference Title

Not applicable

Other documents

Reference Title

Operating Philosophy

Total General Specifications

Reference Title

GS EP INS 110 Instrumentation for package units

GS EP SAF 021 Layout

GS EP SAF 216 Area classification

GS EP SAF 228 Liquid drainage

GS EP SAF 253 Impacted area, restricted area and fire zones

GS EP SAF 261 Emergency Shut-Down and Emergency De-Pressurisation (ESD & EDP)

GS EP SAF 311 Rules for the selection of fire-fighting systems

GS EP SAF 312 Fire and gas detection systems

GS EP SAF 322 Fixed fire water systems

GS EP SAF 331 Carbon dioxide fixed fire extinguishing system

GS EP SAF 334 Foam fire extinguishing systems

GS EP SAF 337 Passive fire protection: Basis of design





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3. Terminology and definitions There are five types of statements in this specification, the “shall”, “should”, “may”, “can” and “must” statements. They are to be understood as follows:

Shall Is to be understood as mandatory. Deviating from a “shall” statement requires derogation approved by Company.

Should Is to be understood as strongly recommended to comply with the requirements of the specification. Alternatives shall provide a similar level of protection and this shall be documented.

May Is to be understood as permission.

Can Is to be understood as a physical possibility.

Must Expresses a regulatory obligation

Note that “will” is not to be understood as a statement. Its use is to be avoided, unless it is necessary to describe a sequence of events.

For the purpose of this specification, the following definitions shall apply:

Alarm Audible or visible signal indicating an off-standard or abnormal condition.

Burner Device or group of devices for the introduction of fuel and air into a heater at the velocities, turbulence, and concentration necessary to maintain ignition and combustion of the fuel within the heater.

Burner, atomising Burner in which oil is divided into a fine spray by an atomising agent, such as steam or air.

Burner, combination fuel-gas and oil

Burner that can burn either fuel-gas or oil, or both simultaneously.

Burner, dual-fuel Burner designed to burn either fuel-gas or oil, but not both simultaneously.

Burner, pressure atomising

Burner in which oil under high pressure is forced through small orifices to emit liquid fuel in a finely divided state.

Casing Metal plate used to enclose a fired heater.

Convection section Portion of the heater in which the heat is transferred by convection.

Damper A device for introducing a variable resistance for regulating volumetric flow of flue gas or air (ISO 13705 / API STD 560).

Duct Conduit for air or flue gas flow.

Flame detector Device that senses the presence or absence of flame and provides a usable signal.

Flue gas Gaseous product of combustion including the excess air.

Furnace Portion of a fired heater enclosure within which the combustion process takes place and wherein the heat transfer occurs predominantly by radiation.





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Fired heaters A vessel in which the temperature of a fluid is increased by the addition of heat supplied by a flame within the vessel (Company from API). Fired heaters is a generic terms that covers all type of heaters including steam boilers, reboilers (flame tube or flue gas tube), indirect heaters (hot oil or hot water), incinerators, etc. Fired heaters are sorted into the following classes: • Class A: A heater that has heat utilisation equipment operating

at approximately atmospheric pressure wherein there is a potential explosion or fire hazard that could be created by the presence of flammable volatile or combustible materials processed or heated in the heater.

• Class B: A heater that has heat utilisation equipment operating at approximately atmospheric pressure wherein there are no flammable volatile or combustible materials being heated.

• Class C: A heater that has a potential hazard due to a flammable or other special atmosphere being used for treatment of material in process. Not used in oil and gas production business and not developed further in present specification.

• Class D: A heater that operates below atmospheric pressure. Not used in oil and gas production business and not developed further in present specification.

Igniter Permanent device that provides proven ignition energy to light the main burner immediately. Igniters are further sorted into the following classes: • Class 1: Device applied to ignite fuel input through the burner

and to support ignition under any lighting or operating conditions; its energy generally exceeds 10% of the main burner. Igniters, Class 1 can be considered as permanent pilots.

• Class 2: Device applied to ignite fuel input through the burner and under prescribed lighting conditions; its energy is generally in the 4% - 10% range of the main burner.

• Class 3: Device applied to ignite gas and oil burners under prescribed lighting conditions; its energy generally does not exceed 4% of the main burner.

• Special: A Class 3 high energy electrical igniter capable of directly igniting the main burner.

Ignition time Period of time between the fuel first entering the combustion chamber and the first indication of the flame by the flame detection.

Inerting Dilution of the oxygen content of an air/fuel mixture through the addition of an inert gas or vapour to a point where it is no longer explosive.

Pass Flow circuit consisting of one or more tubes in series connected by return fittings or manifolds.





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Pilot A flame that is used to light the main burner (NFPA 86). According American vocabulary pilot is equivalent to Igniters, Class 1 (see above). The wording pilot is often used in an erroneous import to cover any type of igniter. Therefore the use of the word pilot (when referring to fired heaters) shall be avoided and the term igniter shall be used instead.

Purge Flow of air or inert gas through the furnace, gas passages, and associated flues and ducts that effectively removes any gaseous or suspended combustibles and replaces them with air or inert gas.

Register Control device in the air duct to set the air flow rate to a burner. Registers, having a control function, are different from dampers used as safety devices an operating on/off.

Restricted area Area within the boundaries of the installation and hence under the control of Company, which is affected permanently by normal operation of the installation or exceptionally by the consequences of an emergency situation caused by a major failure (Company).

Safety time Tolerance time during which the effectiveness of a safety device may be impaired without a hazardous condition occurring. For a system comprising burners, this means the following:

Safety time, ignition: when starting-up the burner, the period of time between the fuel first entering the combustion chamber and the de-energising of the quick-acting fuel shut-off valve if the flame monitor does not detect a flame.

• Safety time, main burner: when there is an ignition safety time applicable to an igniter burner only, the period of time between the fuel of the main burner entering the combustion chamber and the de-energising of the quick-acting shut-off valve of the main burner if the flame monitor does not indicate a flame.

• Safety time, extinction: during operation of the burner, the period of time between the extinction of the flame and the de-energising of the quick-acting shut-off valve.

Soot-blower Mechanical device for discharging steam or air to clean up heat absorbing surfaces from soot.

Stack Vertical conduit used to discharge flue gas to the atmosphere.

Unit purge Air purge rate that is flowed through the unit from the Forced Draught fan through the stack for a period of 2 minutes or 4 changes in volume of the heater enclosure, whichever is longer.

Valve, Safety main fuel trip

Automatically actuated remote valve that shall be accessible even in case of fire and explosion and that closes the main fuel source. Company's practice is to assimilate this valve to an ESDV on P&IDs.





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Valve, Safety shut-off Fast-closing valve that automatically and completely shuts-off the fuel supply to main burners or igniters in response to a trip. NFPA uses also the wording "fuel trip valve". Company's practice is to assimilate this valve to a SDV on P&IDs.

Valve, Safety shut-off, quick acting

Safety shut-off valve closing in less than 1 second.

4. Layout

4.1 Location and minimum distances

4.1.1 Onshore A heater or a group of heaters shall be located immediately adjacent to an access road and adequate access for fire-fighting from all sides shall be provided. Wherever several heaters are contiguous, they shall be separated from each other by roads of restricted access.

The area under a heater shall be paved and free from hazards so as to allow personnel to move freely. Clearance between ground and heater bottom shall be sufficient to allow access for inspection and maintenance and shall not be less than 0.76 m in all cases. An area extending 2 metres around the heater external wall in all directions shall be free from obstruction by pipe-work, supporting structure, etc.

Fired heaters shall be located outside hazardous areas, at the limit of the process plant. Where possible, heaters shall be up the prevailing winds from process equipment to minimise likelihood of a vapour cloud ignition.

Company's practice is to segregate their installation into fire zones. Process and utilities, liquid hydrocarbon storage, liquefied hydrocarbon storage, wellheads and buildings (LQ, workshops, offices, etc. but not including technical room or control room) shall always be in separate fire zones (refer to GS EP SAF 253). In this context, fired heaters shall always be located in the process and utility fire zone and distance between fired heater and other equipment located in other fire zones shall be as per GS EP SAF 021 and GS EP SAF 253. Within the process and utility fire zone, distances between fire heaters and other equipment shall be as per table below, unless applicable local regulations impose otherwise:





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Equipment Minimum distance (m)

Other fired process heater 7.5

Main pipe-ways main/secondary 30/7.5

Oily water basins 45

Heater ESD valve 15

Electrical/Power station 15/30

Other utilities (air, water, water inj., etc.) 15

Overhead power lines 45

Process equipment 30*

Compression P > 70 barg / P ≤ 70 barg 60 / 30*

Diesel storage 30

Fuel gas skid 30

Main flare header 45

Control room 30

Vents 30**

Note *: Distance increased to 45 metres for heaters larger than 10 MW.

Note **: Indication only; depends upon dispersion and radiation calculation.

4.1.2 Offshore The general principles exposed above (fire zone segregation and location outside hazardous areas created by other equipment, refer to section 4.1.1) are also applicable offshore.

In addition, fired heaters shall be located on the upper deck.

The presence of any equipment above a fired heater in a radius of 5 metres extending around its external wall shall be prohibited.

Fired heaters should be preferably grouped with other machinery (gas turbine driven compressors, generator sets, etc.), as far as feasible from process area and upwind (with respect to prevailing wind) from process equipment.

In case of a complex of different platforms, linked together by bridges heaters should also be upwind wellheads platforms and (if any) other process platforms.

If, for reasons of available space, it proves impossible to install the fired heater outside the hazardous areas generated by other equipment, the fired heater can be shielded from said hazardous area by a fire wall. The fire wall shall be rated H 120 (Refer to GS EP SAF 337) for fire resistance and shall offer blast resistance characteristics compatible with the worst heater explosion scenario (blast resistance for an explosion occurring outside the area delineated by the fire wall is not required).

The concept of minimum distance is not applicable offshore, however a minimum path 3 metres wide shall be left between fired heaters, from skid edge to skid edge. In addition fired heaters shall be located outside the crane(s) normal swing zones. In the case of a fired heater fitted





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with a flame tube, sufficient room reservation shall be made to allow for maintenance (flame tube dismantling and lay-down).

4.2 Hazardous areas

4.2.1 Areas classification GS EP SAF 216 shall be adhered to. In essence:

• Applicable to all type of fired heaters (Class A or Class B) it shall be considered that the fuel gas line(s) and appurtenances (flanges, filters, valves, instrument tappings, etc.) generate a 3-metre wide Zone 2 classified area around themselves.

Figure 1 - Hazardous areas around fired heaters

• Burners do not generate classified area and shall therefore be located at least 3 metres off the closest joint pertaining to the fuel gas system (1), however all electrical material located within 1.5 m of the burner shall, be nevertheless suitable for operation in Zone 2 hazardous area.

• As a consequence of what precedes, air intakes for natural draught fired heaters can be located in the immediate vicinity of the burner, as long as they are outside the Zone 2 hazardous area generated by the fuel lines.

• Fired heaters themselves do not generate hazardous area.

• Class A heaters (i.e. flammable substances on the process side) generate a 3-metre wide Zone 2 classified area around the incoming/outgoing process streams flanges. Burners shall be at least 3 metres away from process flanges.

3 m

1.5 m

Fuel gas line

Zone 2 hazardous area.

Non hazardous area but material suitable for zone 2 required.

Processfluid

3 m





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4.2.2 Fuel leakage avoidance

4.2.2.1 Fuel network All pipe-work connections within 15 m of the heater shall be welded or flanged, screwed joints are forbidden, and the number of flanged connections shall be kept minimum and be easily accessible for testing. Within at least 3 metres around the burner(s) fuel lines shall have welded connections.

4.2.2.2 Process fluid Applicable to Class A heaters only, all tubes and pipes in the radiant or convection sections shall be seamless. If tubes cannot be furnished in a single continuous length, only one intermediate circumferential weld is permissible.

4.3 Ventilation Fired heaters shall be located to make maximum use of natural ventilation, to minimise restrictions to adequate explosion relief, and to provide sufficient air supply for personnel. In case a fired heater is isolated from hazardous area by a fire proof wall (refer to section 4.1.2 ) it shall be verified that the presence of the fire wall does not impair necessary natural ventilation.

Where fired heaters are located in basements or enclosed areas, sufficient forced ventilation shall be supplied to provide required combustion air and to prevent the hazardous accumulation of vapours.

Fired heaters designed for use with fuel-gas heavier than air shall be located at, or above, grade and shall be located to prevent the leakage of fuel-gas from accumulating in basements, pits, or other areas below the heater.

4.4 Drainage of liquid spills Heaters processing liquids combustible or harmful to the environment shall be equipped with an open drain system installed under and around the heater and the purpose of which is to direct accidental liquid spills away from the heater and from the nearby equipment which might be exposed. The recommended solution is to provide a paved area with curbing around the heater and to direct by gravity accidental liquid spills collected therein to a safe location.

For details refer to GS EP SAF 228.

4.5 Floors and clearances

4.5.1 General Heaters shall be located with adequate space above and on all sides to allow inspection and maintenance.

External parts of heaters that operate at temperatures in excess of 70°C shall be guarded by location, guard rails, shields or insulation to prevent accidental contact with personnel.

4.5.2 Radiant chamber doors and sight doors For proper operation and lighting and maintenance the following access doors, observation doors and ports shall be provided.

Vertical cylindrical heaters less than 6.0 m in outside diameter shall have one 600 x 600 mm access door in the floor. Larger diameter heaters shall have two such doors.





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Cabin type heaters shall have one 600 x 1200 mm access door at each end.

The number and design of sight-doors shall allow observation of:

• each burner from the burner valves location. Tube spacing may be increased to provide a direct view of the burners.

• the tubes, including shield tubes,

• the flames, including pilot burner ones,

• absence of coke formation on the fuel tips, pilots, swirlers and burner tiles,

• the skin thermocouples.

Heaters shall have in the roof of each cell at least one sight-door, or a 75 mm diameter connection to install a movie camera to watch flames and burner tiles.

For radiant sections taller than 9.0 m, intermediate level sight doors shall be installed on side walls between floor and arch levels. These sight doors shall allow observation of shield tubes and top U-bends.

Cylindrical vertical heaters shall be equipped with two opposite intermediate sight doors.

Cabin type heaters shall be equipped with two intermediate sight doors on each end wall.

Vertical heaters prone to coking shall be equipped with additional sight-doors in the heater floor to observe possible flame impingement on tubes.

Heaters shall be equipped with ports in the walls to allow vertical heat flux profile measurements by means of radiometers. These ports shall be evenly spaced. The arrangement shall be submitted to Company for approval.

The vertical tube heaters shall have one or more tube-pulling door.

Door recommended size shall be as per ISO 13705 / API STD 560.

4.5.3 Convection sections doors and sight doors Convection section breeching shall be equipped with one access door every 9.0 m. These doors shall be accessible by platform.

Doors shall be installed on both sides of the convection section in sufficient number, to enable inspection and cleaning of the tubes. These doors shall be located horizontally about every two meters, and vertically every six rows of tubes. These doors shall be accessible by platforms.

Convection sections with a refractory floor shall be equipped with one side door at each end, in order to allow observation of the shield tubes. One door allowing access during turn around shall be supplied on the side opposite the tube inlets/outlets. These doors shall be accessible by platforms.

4.5.4 Access platforms Platforms shall be provided as follows:

• At burner and burner controls that are not accessible from grade,

• At all observation doors and ports,

• At auxiliary equipment, such as fans, drivers, and air pre-heaters,

• At both ends of the convection section for maintenance purposes,





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• At damper and soot-blower locations for maintenance purposes,

• At analysers and instruments tapping points for maintenance purposes.

4.5.4.1 Platforms Dead ends longer than 5 metres are forbidden. The minimum clear width of platforms shall be:

• Operating platforms: 0.90 m (1.20 m recommended for maintenance),

• Walkways: 0.80 m.

4.5.4.2 Stairs Stairs shall comply with the following characteristics:

• Minimum width: 0.80 m,

• Min. tread width/max. tread riser: 0.24 m,

• Maximum slope/flight: 75%/4.5 m,

Intermediate landings shall be provided where necessary.

4.5.4.3 Ladders Ladders exceeding 2.5 m above grade shall be caged. Ladder maximum flight shall be 7.5 m. Intermediate landings shall be provided where necessary.

4.5.4.4 Headroom and handrails The minimum headroom over platforms, walkways, stairways shall be 2.2 m. Handrails shall be provided on all platforms, walkways, stairways.

4.5.4.5 Vertical cylindrical heaters Vertical cylindrical heaters with shell diameter exceeding 3 m shall have a full circular platform. Individual ladders and platforms at each observation door may be used if shell diameter is less than 3 m. Accesses should be located near the ends of the platforms and supplementary access shall be provided so that dead ends never exceed 6 m.

5. Design

5.1 General It is strongly recommended that a heater contain a single process fluid. With the exception of waste heat recovery units, the number of tube passes should be minimised in order to avoid over-complexity. The heater design shall permit safe operation at the design duty and at turndown specified by Process requirements. The turndown shall be 60% if no specific process requirements exist.

Low NOx burners technology shall be provided.

5.2 Heaters structural design The furnace part of a fired heater shall be capable of withstanding a transient gauge pressure of +8700 Pa (positive) or -8700 Pa (negative) without permanent deformation due to yield or buckling of any support member. Refer to NFPA 85 for further details.





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Fired heaters shall be constructed and located to keep outside skin temperatures at combustible floors, ceilings, and walls below 70°C. Combustible materials shall be maintained at a fire-safe distance, of not less than 0.75 m, from a heater and its associated ductwork.

Fired heaters flue gas stacks that are inside the restricted area shall have a maximum skin temperature of 200°C (refer to GS EP SAF 216).

Bursting discs or panels, or other parts of a fired heater from which flame or hot gases could be discharged shall be located or guarded to prevent injury to personnel.

5.3 Igniters Each burner shall be provided with its own igniter. Igniters shall be small (NFPA Class 2 or Class 3) and shall not fire permanently. The use of igniters firing permanently (NFPA Class 1), sometimes referenced to as "permanent pilots", shall be avoided. If an igniter of less than 4% of the main burner capacity is not found practical a derogation process shall be required for the use of a smaller igniter. The use of electrical devices directly igniting the main burner (NFPA Class 3, Special) should be avoided with the exception of small (less than 117 kW) heat input burners.

The installation of igniters Class 1 and Class 3, Special would require a justification dossier which shall be submitted to Company's approval, and in any case igniters Class 1 can be installed only on natural draught burners.

The ability of the igniter to ignite the burner shall be verified during the burner supplier shop test for the maximum and minimum heat release, and for the range of gas composition specified.

5.4 Air flow Forced draught is the preferred solution because it fulfils three fundamentally important functions:

• Achieve a reliable and fully comprehensive purge sequence before lighting up,

• Allow suitable location (out of any hazardous area plus at least 2 m safety margin) for combustion air intake,

• Permit positive gas detection into the burner combustion air duct. If forced draught is selected, fans shall be sufficient to supply the burners with a combustion air flow 20% greater than that required for operation at 110% of the heater design load, with the specified excess air.

Air-flow monitoring shall ensure that there is always sufficient air flow to support combustion at minimum flow rate. Admissible deviations from the pre-determined values of the fuel/air ratio shall be stated in the operating manual. Inadmissible deviations shall automatically cut-off the fuel supply and the air supply.

Fans and associated air flow control systems shall be governed by the heater control system provided by the package Vendor.





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5.5 Dampers and flame arresters

5.5.1 Forced draught Gas-tight dampers shall be installed on the air inlet of forced draught fired heaters. Air inlet dampers shall be controlled by the heater own control system (Logic Solver or other), provided by the package Vendor.

Dampers shall be regarded as safety devices and fitted with mechanical stops and limit switches.

Dampers position in emergency situation must be assessed specifically by a risk analysis as soon as the type of heater is decided. In all cases the recommended position when no tube break situation is observed shall be OPEN. In case of snuffing steam, the air damper shall be closed and the flue damper shall be open and, the snuffing steam shall be kept open until the system has cooled down (this may be in excess of 30 minutes). When CO2 is used closure of all dampers is recommended before release of CO2.

Spurious closure of dampers shall automatically close the fuel safety shut-off valves and electric motors driving forced draught fans shall be fitted with a failure sensor that shall automatically close the damper installed on the air suction duct. For further details refer to chapter 7, of the present specification.

Forced draught combustion air ducts shall not be fitted with flame arresters. Exhaust stacks shall not have a spark arrester.

5.5.2 Natural draught Natural draught fired heaters shall be equipped with flue gas and combustion air duct dampers.

Flue gas damper shall be located at the base of the stack. Automatic dampers may be preferred over manually operated types.

The combustion air duct shall not be equipped with a flame arrester.

No spark arrestor is required in the exhaust stack unless a particular risk has been identified.

5.6 Safety shutdown devices

5.6.1 Safety main fuel trip valve Applicable to all types of fired heaters, Class A or Class B, liquid or gas fired, a common and remote safety main fuel-trip valve shall be installed on the main fuel supply line, upstream of branched feeding each burner or igniters.

Although this valve does not entirely match the functional criteria applicable to ESDVs (battery limit or fire zone interconnections), it is Company's practice to assimilate the safety main fuel trip valve to an ESDV, to specify it as such (fire resistance, reset mode, etc.), to mark it accordingly on P&IDs and to locate it so that fire or explosion, occurring at the heater or its fuel lines, does not prevent access and operation of this valve and does not put its integrity at risk. In practice a distance of 15 metres from the heater shell is recommended or, if not feasible, protection so that it shall not undergo a radiation flux greater than 15.9 kW/m2 (5000 BTU/Sqft/hr) and shall not be submitted to an explosion overpressure greater than 300 mbar.

The safety main fuel trip valve shall close upon signal from the heater Burner Management System and the installation general ESD system. Both signals from the installation ESD system





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and BMS shall be independent and directly hard-wired to the main fuel shut-down valve, being hard-wired. The installation ESD system and the BMS shall trip the fuel shut-down valve by means of their own dedicated solenoid valves.

5.6.2 Safety shut off valves In addition to the safety main fuel trip valve mentioned above in section 5.6.1, the fired heater Fuel supply lines to main burners and igniters shall have the following configurations:

• Fired heater with a maximum of four main burners, see solution 1 (Appendix 1),

• Fired heater with a number of main burners greater than four, solution 2 (Appendix 4).

Any deviation from above rules (sections 5.6.1 & 5.6.2) shall be supported by an auditable reliability/availability study.

5.6.2.1 General functional requirements Safety shut-off valves shall be fail-close and shall automatically close the fuel sources in case of a shutdown.

Open/closed position indication shall be provided for all safety shut-off valves to main burners or igniters.

Positive means to prevent leakage of gas or liquid into an idle furnace shall be provided in the form of a spectacle blind installed downstream of the safety main fuel trip valve. Any line to an igniter or a main burner shall also include facilities to vent the piping upstream the last valve.

At least one of the two safety shut-off valves arranged in series shall be of quick-acting design, closing within 1 second, the second safety shut-off valves closing within 5 seconds.

5.6.2.2 Fuel gas network specifics Each main burner fuel line shall be fitted with a double-block and bleed assembly of automatic safety shut-off valves; the opening of the bleed valve shall be automatic upon closure of the safety shut-off valves. The bleed if installed shall be connected to atmosphere at safe location.

Each fuel line to igniter Class 1 and other igniters (Class 2 or Class 3) whose heat input exceeds 117 kW shall be fitted with a double-block and bleed assembly of automatic safety shut off valves; the opening of the bleed valve shall be automatic upon closure of the safety shut-off valves. Fuel lines to igniters Class 2 or Class 3 whose heat input is less than 117 kW shall be equipped with two automatic safety shut-off valves but the bleed valve can be omitted.

All main burner safety shut-off valves shall be located as close to the burner as practicable, although the 3-metre distance imposed by hazardous area shall be respected.

5.6.2.3 Liquid fuel network specifics Each igniter or main burner shall be fitted with two automatic safety shut-off valves without any bleed valve.

Atomising lines if any shall be equipped with a shutdown safety valve.

All main burner safety shut-off valves shall be located as close to the burner as practicable to minimise the volume of fuel left downstream of the burner valves in the burner lines.





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5.6.3 Process back-flow Fired heater handling flammable fluids shall be protected against back-flow (to avoid fueling an internal fire consecutive to a tube leak) by a check valve installed in the tube outlet piping. If a check valve cannot be used (due to process problems), automatic block valves (SDVs) shall be installed on the heater discharge. These valves shall be designed to fail close.

For multiple pass arrangement, an assessment shall be made as to whether each pass is protected from back-flow individually or if one single check valve is fitted at the common outlet; the use of SDV's is not recommended.

The process mitigation measures undertaken after a tube failure shall be defined case by case with the Company’s process department.

5.7 Stack In order to avoid explosion of unburned gases sent by gas purging in a hot stack, it is not recommended to have common flue gas duct and heaters equipped with individual stacks are given preference. If common flue gas duct is however installed, then gas purging should be achieved with damper closure and dedicated vent opening.

The design of the stack shall be such that the following requirements are fulfilled:

• Draught: Gauge pressure shall be negative, and not less negative than -25 Pa (gauge pressure of -200 Pa are acceptable) at any point in the heater under all operating conditions, including a 30% overload with design excess air.

• Personnel protection

- It shall be 6 m above the top platform of the unit or other nearby units,

- It shall be 3 m above the highest operating platform within a 30 m radius of the stack.

• Separation of sources of fuel and ignition

- It shall be at least 2 m above the upper limit of the hazardous area, if any,

- Skin temperature shall be less than 250°C by default or less than 80% of the auto-ignition temperature (°C) of the flammable gas or vapours that may enter into contact with the stack.

• Environment - A minimum flue gas exit velocity of 9 m/s to optimise dilution in atmosphere,

- A maximum velocity of 30 m/s to avoid noise.

• Corrosion: A minimum temperature of 150°C to avoid condensation

Electro-filters involved in some new designs are a potential source of ignition. Their use requires a justification dossier which shall be issued for approval by Company.

Aircraft warning lights shall be fitted if required by national or local regulations. Adequate protection against lightning shall also be provided.

5.8 Specifics to liquid-fuels The use of liquid fuels present particular hazards and may therefore impose specific safety related requirements applicable on top of other demands relevant only to fuel gas. When firing a heater with liquid fuel, it shall be ascertained that the following issues are addressed:





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• Provisions for alternate fuel to igniter (light oil, fuel gas, propane, LPG, etc.) when the normal liquid-fuel viscosity is too high to feed the igniters during the lighting sequence,

• Removal of harmful contaminants, where applicable and necessary, by installation of adequate strainers, filters, traps, sumps, etc.,

• In case normal liquid fuel requires pre-heating to achieve the viscosity required for proper atomisation, the pre-heating system shall be such that the liquid fuel temperature:

- under un-pressurised conditions does not reach 90°C (to avoid boiling and two phase flow) or its flash point at atmospheric pressure, whichever is lower,

- under pressurised conditions, does not reach the corresponding water boiling temperature 5°C at operating pressure,.

• The pre-heating system shall comprise at least the following:

- An automatic temperature control loop (with controller and control valve),

- High and low temperature alarms,

- Very high temperature switch cutting-off the heat source.

• Provisions for the supply and control of the atomising medium where the liquid-fuel is atomised with the assistance of another medium (air, steam, etc.).

• Installation of an automatic scavenging system to get rid of liquid-fuel left after a shutdown in the passages of an atomiser.

5.9 Design validation Each fired heater package shall be HAZOP'ed during detailed engineering.

6. Controls and Safety instruments

6.1 General Control and safety instruments shall be as per GS EP SAF 261, and more particularly with its chapter Shutdown devices. Refer to Appendices 1 and 2 for typical P&IDs.

A Burner Management System (BMS) shall be used for ignition and extinguishment automation functions of fired heaters. It shall also ensure the fired heating in safe situation by shutting down equipment in case of anomalies.

As a minimum, there shall be one dedicated BMS for each fired heater. All start-up operations shall be under local operator control (from a safe location e.g. behind fire wall or minimum 15 meters distance) and be sequenced by BMS. Burners Shutdown sequences shall also be managed by BMS. BMS shall act on safety shut-off valves that automatically and completely shuts-off the fuel supply to main burners or igniters in response to a trip. All critical safety sensors shall be triplicated and voted 2oo3.

BMS shall be treated as a P3 package (refer to GS EP INS 110).

BMS Logic Solver shall be certified for SIL3 if a prescriptive approach is used otherwise an auditable SIL assessment shall be produced.





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6.2 Process fluids

6.2.1 Balanced flows Coil layout and manifolds shall be such that passes shall have similar equivalent length in order to achieve flow rate differences between passes below 2%.

In absence of control valves on each phase of a two-phase flow feed, the distribution at heater inlet shall be designed to prevent unequal distribution: liquid and vapour shall flow in equal proportion to each pass in normal operation and reduced load.

• The number of passes in the shock tubes and radiant section shall be minimised for services with a two phases flow in the furnace (partial or complete evaporation of a liquid feed.

Flow control to each pass shall be required (without prejudging the limit of supply) for the following applications:

• Feedstock degradation susceptible to cause tube fouling,

• Liquid feedstock susceptible of salt deposit in case of liquid boiling.

A temperature indicator shall be installed on the coil inlet manifold and on each pass outlet.

6.2.2 Safety trips Process trips shall be defined case by case by Company's Process Department, however they shall include at least the following:

• FSLL: Very low flow switch(es) on the inlet lines of each heater pass. They shall be located near the heater.

• TSHH: Very high outlet temperature switch(es) on outlet lines of each heater pass. They shall be located as close as possible to the heater.

• LSLL: Very low liquid level in the shell of flame tube heaters and indirect bath heaters.

6.2.3 Relief valves To avoid large internal tube pressures, generally because both the inlet and outlet lines are blocked in, a pressure relief system shall be connected to heater at a point on the piping which will allow for the most complete evacuation of the tubes content, and which is not isolatable for the tubes.

It is not the purpose of this general specification to define the process mitigation measures undertaken after a tube blockage. These shall be defined case by case by Company's Process Department.

6.3 Combustion

6.3.1 Very low fuel pressure Very low pressure switch(es) shall be installed on the fuel supply line.

6.3.2 Flame failure Each main burner and each igniter Class 2 and Class 3 shall have their own dedicated and independent flame failure detector.





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This rule is not applicable to other type of igniters:

• Class 1 (pilots). In case of flame failure, the pilot and the burner shall be shutdown, since generally there is only one flame detector, monitoring the pilot flame,

• Class 3, Special. These igniters are electrical and there is no fuel fired.

However it is reminded that Class 1 and Class 3, Special igniters shall not be installed unless specifically approved. See section 5.3 above.

The main flame detectors shall be self-checking.

The safety devices shall observe the safety times summarised below for all types of burners when starting-up the burner or when the flame extinguishes during operation.

Type of fuel and burner Maximum safety time during start-up

Maximum safety time during normal operation

Liquid main burner 5 s* 3 s

Gas main burner 5 s 3 s

Gas igniter burner 10 s NA

Note*: This safety time may be made longer for heaters burning viscous fuel-oils and shall be assessed on a case by case basis.

6.3.3 Draught fan failure Controls shall be installed on forced and induced draught heaters to detect a low draught condition. Monitoring shall be accomplished through the use of pressure sensitive devices as opposed to the practice of monitoring draught fan driver operation. This practice is a guard against possible fan-driver coupling failure.

6.3.4 Very high stack temperature A very high stack temperature sensor shall be installed. It shall protect the heater against: fire-box excessive temperature and tube leakage in heaters class A.

6.4 Gas detection For fired heaters located in a flammable gas restricted area or having external hot points which might be ignition sources, gas detectors shall be installed to prevent gas concentration in the air intake and ignition of gas cloud coming from nearby equipment.

The gas detectors shall be installed in the vicinity of the air intake, and around the heaters just at the limit of the unit and near the potential ignition sources.

6.5 Shutdowns The following summarises the logic of automatic shutdowns, total or partial.





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6.5.1 Process (not limited to, but including)

6.5.1.1 Causes

• Very low product flow (FSLL),

• Very high product outlet temperature (TSHH),

• Possibly LSLL.

6.5.1.2 Actions Heater shutdown, i.e.:

• All individual main burner safety shut-off valves close and bleed valve open,

• Individual igniter safety shut-off valves close, bleed valve (if any) open and associated spark latched de-energised,

• Igniters header safety shut-off valves close,

• Safety main fuel trip valve (ESDV) close,

• Draught fan(s) stop (s).

6.5.2 Fire and Gas

6.5.2.1 Causes

• 50% LFL in air inlet,

• 50% LFL around the heater,

• Very high stack temperature TSHH.

6.5.2.2 Actions

• Same as in section 6.5.1,

• Close the dampers,

• Release the inert gas (CO2).

6.5.3 External causes

6.5.3.1 Causes

• Remote push-button,

• SD-2 or higher (ESD-1, ESD-0).

6.5.3.2 Actions

• Same as in section 6.5.1.





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6.5.4 Combustion (fuel gas firing)

6.5.4.1 Causes Loss of individual main burner flame with one or more additional stable main burner flames present.

• Actions

- Individual main burner safety shut-off valves close,

- Its individual igniter safety shut-off valves close,

- Its associated ignition devices are de-energised.

6.5.4.2 Causes Loss of igniter flame.

• Actions

- Individual igniter safety shut-off valves close and bleed valve open.

6.5.4.3 Causes Igniter fuel-gas pressure out of stable range.

• Actions

- Individual igniter safety shut-off valves close and bleed valve open,

- Igniters header safety shut-off valves close.

6.5.4.4 Causes - Major or total loss of induced draught fans (XS),

- Major or total loss of forced draught fans (XS),

- Very low air combustion flow rate (FSLL),

- Very high heater pressure (PSHH),

- Very high pressure of main burners fuel header (PSHH),

- Very low pressure of main burners fuel header (PSLL),

- Very high fuel flow to the burners FSHH,

- Power failure for the safety devices,

- Flue gas re-circulation fan (if any) failure XS,

- Very high ratio: flue gas re-circulation flow/burner firing rate XSHH,

- Very low ratio: flue gas re-circulation flow/burner firing rate XSLL,

- Loss of all flames (XS),

- Partial loss of flame introducing hazard (XS).

• Actions

- Individual igniter safety shut-off valves close and bleed valve open,

- Igniters header safety shut-off valves close,





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- All individual main burner safety shut-off valves close,

- Safety main fuel trip valve (ESDV) close.

6.5.4.5 Causes A local manual pushbutton located in a safe position (at least 15 m away from the heater) shall activate the same actions as in section 6.5.4.4 and, in addition, shall be provided with a hard-wired redundancy to close ESDV. The manual pushbutton can be replaced by a manual block valve, close to the ESDV, to shut-off the fuel supply.

6.5.4.6 Causes Minor and partial loss of Induced Draught fans (XS),

Minor and partial loss of Forced Draught fans (XS).

• Actions

- The main fuel-gas supply shall be reduced in order to maintain the proper air/fuel-gas ratio.

6.5.4.7 Causes Unless it can be demonstrated that a safe tube skin temperature limit cannot be exceeded, an excess temperature limit controller shall be provided. This device shall be as per recommendation of NFPA 86, chapter 5-16.

6.5.5 Combustion (liquid fuel firing) Basically the same as for fuel-gas (see sections 6.5.1 through 6.5.4), with the following differences:

6.5.5.1 Causes Very low igniter atomising medium pressure (PSLL).

• Actions


- Its individual igniter safety shut-off valves close,

- Its associated ignition devices are de-energised.

6.5.5.2 Causes In case of very low atomising medium pressure (PSLL).

• Actions

- Individual igniter safety shut-off valves close,

- Igniters header safety shut-off valves close,


- Safety main fuel trip valve (ESDV) close.

6.5.5.3 Causes There is no trip in case of very high main burner pressure.





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6.5.6 Combustion (dual fuel firing) Each fuel source shall be submitted to the applicable specific shutdown logic as exposed here-above (see sections 6.5.1 through 6.5.5). In addition, the following principles shall apply:

6.5.6.1 Causes (fuel gas trip) Any failure affecting fuel-gas only.

• Actions

- Main burner fuel-gas safety shut-off valves close and bleed valve open,

- Igniter fuel-gas safety shut-off valves close and bleed valve open,

- Safety main fuel trip valve (ESDV) closes.

6.5.6.2 Causes (liquid fuel trip) Any failure affecting liquid fuel only.

• Actions

- Main burner liquid fuel safety shut-off valves close,

- Its individual igniter liquid fuel safety shut-off valves close,

- Safety main fuel trip valve (ESDV) closes.

6.5.6.3 Causes (complete safety shutdown) Any failure affecting both fuels

Either fuel gas or liquid fuel trip when only that fuel is fired.

• Actions

- Same as in sections 6.5.6.2 and 6.5.6.3, above.

6.6 Alarms In addition to the trips listed in here-above sections 6.5.1 though 6.5.6, separately annunciated alarms shall compulsorily be provided locally. In addition a minimum of a grouped remote alarm or, alternately, the duplication of alarms in a remote control room shall be provided, depending on OPERATING PHILOSOPHY.

• Process (not limited to, but including)

- Low product flow (FAL),

- High product outlet temperature (TAH).

• Fire and Gas - 20% LFL in air intake,

- 20% LFL around the heater,

- High stack temperature TAH.

• Combustion (fuel gas firing) - Low fuel supply pressure (PAL),





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- High fuel supply pressure (PAH),

- Low igniter header fuel pressure (PAL),

- High igniter header fuel pressure (PAH),

- High heater pressure (PAH),

- High heater draught (DPAH),

- Loss of operating induced draught fan (XS) (note 1),

- Loss of operating forced draught fan (XS) (note 1),

- Low heater air flow rate (FAL),

- Partial loss of flames (XA),

- Main burners safety shut-off valves not closed (ZC) (note 2).

Note 1: If there are spare ID or FD fans.

Note 2: After a shutdown and for burners exceeding 44 kW heat input.

• Combustion (liquid fuel firing) Basically the same as for fuel-gas (see above), with the following differences:

- Low temperature (high viscosity) of main liquid-fuel (TAL),

- Low atomising medium pressure (PAL),

- Low igniter atomising medium pressure (PAL).

Additionally the following alarms are recommended:

• High skin temperature (TAH),

• High CO content (GAH),

• Low O2 content (GAL),

• Low air/fuel ratio (XAL),

• High air/fuel ratio (XAH),

• Low flue gas temperature,

• Excess tube skin temperature.

6.7 Installation of analysers Analysers shall be installed for both monitoring of the heater/furnace combustion efficiency and to protect the environment (O2, NOx, CO, VOC, SOx, soot, ash ….).

These analysers should be listed in the Safety Concept and/or Operating Philosophy. As a minimum the following analysers shall be provided (portable or fixed equipment):

• Flue gas oxygen (O2) content analyser,

• Flue gas carbon mono-oxide (CO) content.

The O2 and CO analyzers should have their sampling location at the top of the radiation section, below the shock tubes.





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The whole analyser(s) installation, including tapping and valves, shall be easily accessible (without scaffolding) for maintenance service.

7. Operating requirements Types of heaters, requirements of various processes, differences in fuels, and variations in control systems will all affect lighting and shutdown techniques as used on fired heaters. However, some basic safe practices are applicable in almost every case. Refer to Appendix 3.

7.1 Start-up

7.1.1 Heater purging procedure Prior to each start-up, precautions shall be taken to ensure the removal of all flammable vapours that might have entered the heating chambers during the shutdown period. The fired heater shall be therefore equipped with an automatic purge sequence, initiated by a local push-button, and complying with the following logic:

• Check that the following safety shut-off valves are closed:

- Safety main fuel trip valve, - All individual igniters safety shut-off valves,

- All individual main burners safety shut-off valves.

• Check that the dampers (if any) are open,

• Start the draught fan (if forced draught heater) or the ventilation fan if natural draught heater and check that the required fans are running,

• Check that the air flow rate is at purge rate (25% mini. of full-load mass air flow rate, 40% is recommended),

• Maintain the purge flow so that each component which may contain a source of ignition is purged for either a period of at least 2 minutes minimum or 4 volumes changes of that component, whichever is longer.

The purge sequence is complete and the ignition system shall remain active for a period of 3 minutes.

7.1.2 Igniting sequence The logic described below is applicable to any main burner and it is assumed that main burners are being lit up, one by one in sequence. For large heaters with many main burners, human intervention to lit up individually each burner is not required and it is accepted that the heater control system may manage automatically the ignition of all burners in sequence.

Each main burner shall be equipped with an automatic ignition sequence, initiated by a local pushbutton. This pushbutton is active only after the purging sequence has been completed and shall remain active for 3 minutes.

The igniting sequence (igniter + main burner) shall not exceed 15 seconds but can be repeated while the ignit pushbutton remains activate. If ignition of at least one main burner has not been achieved within less than 3 minutes after completion of the purge sequence, the system shall be automatically deactivated and a new purge sequence shall be accomplished prior to resuming attempt to ignite.





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Caution: this approach, designed for easy operation, is regarded safe for a forced draft heater, but cannot be implemented on a natural draft burner where a purge shall be achieved between each ignition attempt.

For fired heaters equipped with igniters Class 2 or Class 3, the logic shall be as follows:

• Upon activation of the Ignit pushbutton the heater control system shall:

- Check that ignition device is ready for ignition,

- Check that the flame detection is operational,

- Check that minimum pre-heating temperature for oil has been reached,

- Set and check that fuel control valve and dampers are in start position,

- Open the safety main fuel trip valve.

If any one of these conditions is not met, then the start up sequence shall be de-activated.

• Light up individual igniter: - Open the igniter fuel shut-off valves and energise the ignition spark for 10 seconds,

- If after 10 seconds the igniter flame detector confirms ignition, then next step; if not, the igniter fuel safety shut-off valves shall close, the safety main fuel trip valve shall close, the dampers and the fuel control valve shall close and the sequence is latched, but the start pushbutton remains active until the 3-minute delay has elapsed.

• Light main burner from its igniter: - Open the burner fuel shut off valves for 5 seconds,

- If after 5 seconds the main burner flame detector confirms ignition, then next step, if not the main burner fuel safety shut off valves shall close the igniter fuel safety shut off valves shall close, the safety main fuel trip valve shall close, the dampers and the fuel control valve shall close and the sequence is latched, but the start pushbutton remains active until the 3-minute delay has elapsed.

• Shut-off fuel supply to igniter,

• Restore FCV and damper automatic operation.

7.2 Dual-fuel operation

7.2.1 Fuel selection Where gas and liquids can be fired alternately, a manual fuel selector shall be provided to permit operation and activate safety devices for the selected fuel and maintain the spare fuel system in a closed safe status. The fuel change-over while a heater is operating shall be initiated by a manual action only.

7.2.2 Fuel change-over Where it is necessary or desirable to change-over fuel source without stopping the heater, provisions shall be taken to prevent a fuel-rich condition, and to avoid a hazardous heater condition.

If a combustion transfer control system is designed for simultaneous firing of gas and liquid fuels on a continuous basis, common rules shall apply.





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If a combustion control system is designed for firing only one fuel at a time, provisions for automatic adjustment of the air-flow shall be provided, and the change-over sequence shall be fully automatic upon manual activation.

7.3 Shutdowns

7.3.1 Normal shutdown Normal heater shutdown shall be achieved through a sequence of step reduction of flow and firing rates until total shutdown can be achieved. Points to remember are:

• Burners and, more generally, heater internal arrangement shall be such that, as individual burners are shutdown to reduce the heat rate, adequate heat distribution can be maintained by employing a staggered pattern.

• When the main fuel valve for gas burners begins to close, and in order to prevent all burners from going out as well as flash-backs in premix burners, adequate valving shall be provided so that some burners can be shut-off entirely while the heater continues operating with adequate fuel pressure delivered to other burners.

• If applicable, specific heater cool-down procedures (opening the stack damper, air dampers, access doors, etc.) shall be provided by the Vendor.

7.3.2 Safety shutdown The necessity (or not) to control the cool-down sequence shall be carefully considered when defining safety shutdown steps and requirements. In all cases, the product and the fuel lines shall be isolated. This will entail shutting down the charge pumps, closing automatic isolation valves (if any) and de-pressurisation (if necessary).

• If the shutdown is due to a technical problem, the dampers could remain open and the fan (if any) operating. In this case, it is better to cool-down the heater after the isolation of fuel-gas and product. If necessary, the draught fan(s) shall be supplied by essential power.

• If the shutdown is due to a Fire and Gas detection, the dampers, if any (stack and air intake) shall close, and the fans shall stop to avoid possible ignition of an external gas cloud. Automatic injection of inert gas inside the fire-box shall be activated. See section 8.3 below.

8. Fire protection

8.1 Fire detection

8.1.1 Common rule Fired heaters shall be equipped with fire detectors of a suitable type (fusible plugs, combination of UV/IR detectors, etc.) installed near the heater to detect external fire where necessary. The fire detection characteristics shall be in compliance with the installation general requirements and shall adhere to the requirements conveyed in GS EP SAF 312.





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8.1.2 In addition

• An excessive heat input in the heater due to the rupture of a tube flowing a flammable process fluid shall be detected with a TSHH in the stack,

• Heaters firing liquid-fuel and/or heating flammable process fluids shall be equipped with fire detectors located near the grade to detect pool-fire in case of tube failure/liquid spill,

The fire detection shall trigger the heater automatic emergency shutdown. For further details, refer to GS EP SAF 312.

8.2 Fire-proofing As per common rule, fired heaters and their structural elements shall be fire-proofed where necessary. Fire-proofing specification shall be in compliance with the general requirements in the installation. For further details, refer to GS EP SAF 311 and GS EP SAF 337.

8.3 Fire-fighting systems

8.3.1 General The common rule is that fire heaters shall not be equipped with a deluge system, either with automatic sprinklers or water spray unless imposed by local regulation for heaters class A containing or processing sufficient combustible materials to sustain a fire. This general rule is not applicable to flame tube heaters (e.g. glycol reboilers) where the installation of a foam solution spray system is required. For further details, refer to GS EP SAF 311.

The fixed fire-fighting systems can consist in:

• Monitors (common rule),

• Inert gas extinguishing system (mandatory), either CO2 or N2 extinguishing system (base case) or steam extinguishing system (Company preferred option where available); the functional requirement is to reduce the oxygen content so that no sustained combustion is possible.

• Foam extinguishing system (where pool fires are possible),

• Dry chemical system as an additional protection for heaters containing materials that produce surface burning fires.

In addition, portable protection equipment (portable extinguishers, inside hose connections) shall be provided. Doors or other effective means of access shall be provided in furnaces and ductwork so that portable extinguishers and hose streams can be used effectively.

8.3.2 Monitors As per common rule, monitors shall be provided in adequate locations around fired heaters. The drainage system shall be designed to cope with the fire-water flow and preclude any risk to promote pool fire in surrounding areas.

Particular attention shall be paid to avoid mechanical damage of the structural shell of the heater which could result in an excessive cooling rate, and to the prevention of the stack from falling. For further details, refer to GS EP SAF 322.





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8.3.3 Deluge and water curtains As already stated a deluge system is not required to protect heaters, unless imposed by local applicable regulation. The only exception being flame tube heaters where the installation of a foam solution deluge is advisable to control a fire that would involve thermal insulation soaked with flammable product.

If necessary, i.e. if the heater(s) cannot be located far enough from other equipment water curtains can be considered as a suitable alternative to absorb fire radiation energy without any risk of mechanical damage to the heater. For further details, refer to GS EP SAF 322.

8.3.4 Foam For heaters firing liquid-fuel and/or heating flammable process fluids, fire-fighting foam is required to control and mitigate pool fires which may develop on the ground beneath or around the heater involved. The recommended solution consists in installing water/foam monitors, with sufficient storage of foaming agent (minimum 1000 litres for each monitor).

The compatibility between foam and combustible liquids from the heater shall be checked before use. In particular, glycol re-boilers require specific foams. For further details, refer to GS EP SAF 334.

8.3.5 Inert gas Inert gas (CO2) shall be installed to provide an inert atmosphere (and to avoid possible ignition) in the fire-box. This system shall be automatic (stack TSHH) and manual (pushbutton). The forced draught and the stack dampers (if any) shall close before the inert gas discharges.

The CO2 fire extinguishing system design and sizing shall be as per NFPA 12, chapter 2.

In brief:

C = F x A x B x k

with:

C: Calculated quantity of CO2 kg

A: Isolatable volume between dampers m3

B: Volume factor (see table below) kgCO2/ m3

F: Conversion factor (see table below)

k: Temperature correction factor k = 1 + (Tf - 93)/280

Tf: Flue gas firebox outlet temperature °C (default value consider 900°C)

This formula is valid for CO2 snuffing only (not continuous flow).





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Product CO2 conc. % F A

(m3) B

(kg/m3)

Natural gas 37% 1.1 0 to 4 1.15

Gasoline 34% 1 4 to 14 1.07

Dowtherm* 46% 1.5 14 to 45 1.01

Crude oil 36% 1.1 45 to 130 0.9

Glycol 46% 1.5 130 to 1400 0.8

Over 1400 0.77

* Note: Or other fluids used as heating medium.

For all fired heaters and unlike other equipment (refer to GS EP SAF 331) a spare capacity of 100% shall be provided.

Where steam is available, it shall be given preference over CO2 because it avoids thermal shock. Steam fire extinguishing systems shall be as per Appendix E of NFPA 86.

Where Nitrogen is used, response time and survivability of the N2 snuffing process shall be defined case by case in an auditable document.

8.3.6 Dry chemical Dry chemical fire extinguishing systems, if any, shall be as per NFPA 17.





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Bibliography

Reference Title

EN 746-2 Industrial thermoprocessing equipment - Part 2: Safety requirements for combustion and fuel handling systems

EN 12952 Water-tube boilers and auxiliary installations

EN 12953-7 Shell boilers - Part 7: Requirements for firing systems for liquid and gaseous fuels for the boilers

Reference Title

API RP 14C Recommended Practice for Analysis, Design, Installation, and Testing of Basic Surface Safety Systems for Offshore Production Platforms

API RP 14J Recommended Practice for Design and Hazards Analysis for Offshore Production Facilities

API publ 535 Burners for Fired Heaters in General Refinery Services

API RP 556 Instrumentation and Control Systems for Fired Heaters and Steam Generators

Reference Title

IP Code, Part 15 Area classification code for petroleum for installations, part 15 of the Institute of Petroleum Model Code of Safe practice (March 1990)





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Appendix: Typical schematics & drawings

The drawings and figures (Appendix 1, 2, 3 & 4) contained in this specification are illustrative only and should not be regarded as detailed engineering documents. They illustrate some of the points made in the specification and should be used as a basis for the preparation of detailed engineering drawings.




Appendix 1


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Appendix 1 Typical schematics – Fuel gas

Figure 2 - Heater with four burners maximum

FSLL

ZSOZSC

FSLL

TT

TSHH

FC

FCFC

BURNER No.1 BURNER No.2

STA

CK

FO

Fuel Gas

Air

BE BSL

BE BSL

ZSC ZSO ZSC ZSO

PSHH

PSHH

PSHH

PSLL

PSLL

FIC PSLL

FIC

PCV

PCV

BE BSL

BE BSL

SDV

SDV SDV

TSHH

AT

SDVSDV

BDV

PG PG

PG

PG

ESDV FT

ZSC

ZSO

SDV SDV

ZSC ZSO

Note 1

Note 1

ESD

Vent

ESD

ESD

ESD

ESD

ESD

ESD

ESD

ESD

SDV

FC

ZSC ZSO FO

BDV

VentZSC ZSO

FCZSC ZSO

ESD

ESD

ESD

ZSC

ZSO

FC FCFC

FC

Note 1

FC

ZSC

ZSO

FC

ZSC

ZSO

FC

FC

Note 1

O2

Pro

cess

flui

d

ESD

ESD

Note 1 : Heater control loop not shownNote 2 : Trips (PSLL, PSHH, FSLL...) are generated in the BMS derived

from analog transmitters.




Appendix 2


Page 37/39

Appendix 2 Typical schematics - Liquid fuel

FSLL

ZSOZSC

FSLL

TT

TSHH

FC

FCFC

BURNER No.1 BURNER No.2

STA

CK

Liquid Fuel

Air

BE BSL

BE BSL

ZSC ZSO ZSC ZSO

PSHH

PSHH

PSHH

PSLL

PSLL

FIC

PSLL

FIC

PCV

BE BSL

BE BSL

SDV

SDV SDV TSHH

AT

SDV

PG

PG PG

ESDVFT

ZSC

ZSO

SDV

ZSC ZSO

Note 1

Note 1

ESD

ESD

ESD

ESD

ESD

ESD

ESD

ESD

ESD

SDV

FC

FCZSC ZSO

ESD

ESD

ESD

ZSC

ZSO

FC FC

FC

FC

FC

FC

Note 1

O2

Proc

ess

fluid

TG

TSLL

ESD

ESD

ESD

FC

SDV

ZSC

ZSO

SDV

FC

ZSC

ZSO

SDV

FOZSC ZSO

SDV

SDV

ZSO

ZSC

PG

PCVPG

PSLL

ESD

Air

C3 or gas

Recycle

PG

ZSC

ZSO

SDV

SDV

ZSO

ZSC

ZSC

ZSO

Note 1

Note 2Note 2

PGPGFC FC

ESD

Note 2 : Minimun spacing between SDVs (avoid TSV)Note 3 : Trips (PSLL, PSHH, FSLL...) are generated in the BMS derived

from analog transmitters.

Note 1 : Heater control loop not shown




Appendix 3


Page 38/39

Appendix 3 Ignition Logic diagram

&

PB

&

PB

or

&

PURGEPB

FAULT RESET

Shut off valves closed(igniter + burner + main trip)

OPENDAMPERS

& Damper position OK

SET AIR DAMPER&

START FAN(S)

&Draught fan running(or purge fan)

& Air flow rate OKNSTOP

Y

T2'

PURGECOMPLETE

T3'

&

PB

&

PB

or

IGNIT.PB

FAULT RESET

&Liq. fuel temp. OK(if applicable)

DAMPER SETON STARTPOSITION

& Damper position OK

FCV SETON STARTPOSITION

OPEN SAFETYMAIN FUEL TRIP

VALVE

&Safety shut off valveleak test OKN

Y

T10"

OPEN IGNITERSAFETY SHUT OFF

VALVES

ENERGISEIGNITER

SPARK PLUG

&N

Y

Igniter flame detection

OPEN BURNERSAFETY SHUT OFF

VALVES

T5"

&Burner flamedetectionN

Y

CLOSE IGNITERSAFETY SHUT OFF

VALVES

RESTORE FCVAUTOMATICOPERATION

RESTORE REGISTERAUTOMATICOPERATION

RESTORE DAMPERAUTOMATICOPERATION

CLOSE IGNITERSAFETY SHUT OFF

VALVES

CLOSE BURNERSAFETY SHUT OFF

VALVES

CLOSE SAFETY MAINFUEL TRIP

VALVE

CLOSEDAMPERS

CLOSEFCV

STOP XA

RUNNING

STOP

Note : Diagrams shows lighting sequence for first main burner.




Appendix 4


Page 39/39

Appendix 4 Recommendation for safety valves arrangement

Figure 3 - Fuel Gas Heater with five burners minimum

Fuel Gas

PCVESDVPSLL

FIC

FCV SDV SDV

BDV

PSHH

At safelocation

PCVPSLL

SDV SDVPSHH

Burner 2

Burner 3

Burner 4

Burner 5

Igniter 2

Igniter 3

Igniter 4

Igniter 5

Burner 1

Burner 6

Igniter 1

Igniter 6

Date post:	20-Mar-2018
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