GIS 22-201

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Guidance on Industry Standard for

API 537 Flare Details

GIS 22-201

BP GROUP

ENGINEERING TECHNICAL PRACTICES

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Foreword

This is the first issue of Engineering Technical Practice (ETP) BP GIS 22-201. It is based on API Std 537 “Flare Details for General Refinery and Petrochemical Service” and available documents of three merged companies: BP, Amoco, and Arco.

In addition, reference is made to other standards and reports that provide guidance in use of heritage documents or similar documents.

Normative references are mandatory to extent that they are referenced and not superseded by this guide.

British Petroleum

RP 44-3 Design Guidelines for Relief Disposal System.

Amoco

A FE-FLR-00-E Fabricated Equipment—Flares—Engineering Specification.

A FE-FLR-00-G Fabricated Equipment—Flares—Guide.

A FE-STK-00-E Fabricated Equipment—Stacks—Engineering Specification.

A FE-STK-00-G Fabricated Equipment—Stacks—Guide.

A PC-PRD-00-E Process Control-Pressure-Relief Devices-Device Selection and System

Design Specification.

A PC-PRD-00-G Process Control-Pressure-Relief Devices Guide.

PSS#6 Flare, Blowdown, Pressure Relief, Vent, and Drain Systems for Process

Units.

GOMDW

1400-20-PR-RP-2002-13 Flare System Design Guideline. 1400-20-ME-SP-2510 Flare Stack, Tip, and Igniter.

PTA

PTA FE-FLR-00-P Fabricated Equipment Vertical Elevated Flares Procurement Specification.

Copyright  2005, BP Group. All rights reserved. The information contained in this document is subject to the terms and conditions of the agreement or contract under which Copyright  2006, BP Group. All rights reserved. The information contained in this document is subject to the terms and conditions of the agreement or contract under which

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Introduction

a. Guidance for flare details is based on API Std 537, 2003.

b. Guidance statements of this GIS are modifications to API Std 537.

c. Modifications to API Std 537 are identified as Add, Modify to Read, or Delete. d. Paragraph numbers in this GIS correspond to API Std 537.

e. Paragraphs of API Std 537 that are not revised remain applicable.

f. In this GIS, term “approve”, as applied to BP, is used if BP does not wish design to proceed unless certain features have been agreed upon in writing with Vendor. This does not imply that all details of a document have been considered by BP and does not affect design

responsibilities of Vendor.

g. Throughout this document, words “will”, “may”, “should”, and “shall”, if used in context of actions by BP or others, have specific meanings. For the purposes of this GIS, the following terms and definitions apply:

1. Will: used normally in connection with action by BP, rather than by Vendor. 2. May: used if alternatives are equally acceptable.

3. Should: used if a provision is preferred. 4. Shall: used if a provision is mandatory.

h. In application of this GIS, BP may select options or waive requirements, depending on nature of project concerned. This may involve any requirement stated in this GIS.

By necessity, API Std 537 provides more flexibility than required by BP. API Std 537 does not include specific BP experience. This GIS adds the requirements that BP has found are necessary for safe and cost effective operation.

This GIS may refer to certain local, national, or international regulations, but responsibility to ensure compliance with legislation and any other statutory requirements lies with user. User should adapt or supplement this GIS to ensure compliance for specific applications.

1. Scope

Add to First Paragraph

a. This GIS provides general requirements for procurement of equipment and materials for flare systems to be used in general refinery, petrochemical, and offshore marine environments. b. This GIS defines minimum requirements for procurement of flare systems for design,

materials, fabrication, inspection, testing, documentation, and preparation for shipment as proposed in data sheets and specifications.

c. Guidelines added in this GIS are based on BP operating experience, preferences, and project execution requirements.

d. Flares for the following facilities are within the scope of this GIS: 1. Refineries.

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2. Chemical plants.

3. Terminals.

4. Offshore installations (shallow and deepwater).

5 Crude oil and natural gas gathering and processing centres. 6 Pipelines: buried, aboveground, or subsea.

7. Storage installations.

8. Floating production systems. 9. Well testing.

10. Liquefied natural gas (LNG) facilities (plants and terminals). Add to Third Paragraph

The following types of flares are within the scope of this GIS: d. Pit flares.

e. Marine or sea flares.

f. Oil production platform boom flares. g. Portable/temporary flares.

Add to Fourth Paragraph

a. API Std 537 provides equipment data sheets in Appendix A. Equipment data sheets are not included in this GIS. Equipment data sheets and instructions for use of data sheets are in DS 22-201. Equipment data sheets can be selected with SI units or U.S. customary units. b. Vendor shall be fully acquainted with bid specifications and clarify all questions before bid

submittal. BP or its representative will issue clarifications or responses to questions in form of addendum to these documents. Clarifications will be provided to Vendors.

Add

a. API Std 537 and this GIS do not include issues associated with design of system for relieving gases by venting into atmosphere.

b. API Std 537 does not include issues associated with procurement and warranty. These requirements are in Annex D of this GIS.

2. Referenced publications

API

Add

Std 673 Centrifugal Fans for Petroleum, Chemical and Gas Industry Services.

ASME

Add

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ASTM

Add

ASTM C155 Standard Classification of Insulating Firebrick.

ASTM C401 Standard Classification of Alumina and Alumina-Silicate Castable Refractories.

Add

BP

GN 22-XXX BP Safety Critical Equipment Definition for PI.

DS 22-201 Data Sheet for Flares.

BS

6651 Code of Practice for Protection of Structures against Lightning.

CONCAWE

Report No. 2/79

ISO

13705 Fired Heaters For General Refinery Service.

23251 Petroleum, Petrochemical and Natural Gas Industries - Pressure Relieving and

Depressuring Systems.

3. Definition of terms

Modify to Read

Terms used in this Standard as they relate to flares are defined in 3.1 through 3.89.

3.9 Coanda flare

Modify to Read

Flare tip that uses Coanda effect.

Coanda effect is aerodynamic skin adhesion effect in which gas follows the profile of a curved surface, entraining air up to 20 times its own volume.

Flares of this type generally use pressure of gas to achieve smokeless performance.

3.30 Flare

Modify to Read

Term used to designate device or system to safely dispose of relief gases in an environmentally compliant manner through combustion. System may be flare stack, flare boom, ground flare, or enclosed flare.

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3.31 Flare burner or flare tip

Add

Flare burner includes all auxiliaries as attached to supporting stack or boom.

3.54 Pin actuated device

Add

a. These devices can be reset in place without breaking flange and may be considered as alternates for rupture disc devices.

b. Pin actuated valves are more costly and some offered valves might have questionable operating characteristics.

3.60 Smokeless capacity

Add

Requirements are defined by local regulations, such as UK Clean Air Act 1956, Section 34(2), and U.S. EPA CFR 60.18.

Add

3.69 Combustion support

Addition of fuel gas to effluent to be flared for any of the following reasons:

a. To increase fuel concentration to make effluent flammable and achieve required combustion destruction efficiency.

b. To increase volume of effluent in order to increase flare tip velocity to avoid: 1. Burn back in flare tip.

2. Flame lick outside flare tip.

3. Lazy flame situation that could damage adjacent flare tip. c. To maintain adequate slot velocity in flare tip using Coanda effect.

d. To increase flame stability during high wind conditions (only as temporary solution until flare flame instability is resolved).

3.70 Flare boom

Horizontally displaced or inclined boom, together with other items listed for flare stack.

3.71 Flare stack

Elevated stack (either self supported, guyed, or structure supported), flare tip, pilot burners, igniters, smoke suppressing devices, flame heat radiation suppressing devices, service pipes, and

miscellaneous auxiliaries.

3.72 Flare system

Whole closed disposal system for fluids discharged from pressure relief valves, other pressure relieving devices, control valves, or manually operated valves, terminating in one or more flares.

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3.73 Flare vendor

Contractor who undertakes design, supply, and erection of flare.

3.74 Purge gas rate

Rate of flow of inert or combustible gas required to prevent oxygen concentration exceeding specified level at specified location in flare stack or supply ducting if oxygen egress is undesirable.

3.75 Maximum flaring rate

Maximum rate of flow to flare calculated in accordance with specified blowdown and relief philosophy for plant.

3.76 Maximum smokeless rate

Maximum rate of flow to flare that is required to be burned smokeless.

3.77 Operating range

Range of gas flows and conditions for which flare is required to operate.

3.78 Marine or sea flare

Flare remotely located from drilling or production platform. Typically used in shallow water platforms.

3.79 Low pressure tip

Flare tip that operates at low differential pressure across flare tip.

3.80 High pressure tip

Flare tip that operates at medium and high differential pressure across flare tip.

3.81 Variable orifice

Flare tip that continuously changes size of exit orifice to maintain higher exit velocities contributing to better mixing between air and gas achieving higher nonsmoking rates.

3.82 Water injection

System that provides water injection into flare combustion zone, achieves flame temperature reduction, and also lowers heat radiation rates emitted by flare flames.

3.83 Water curtain

Systems consisting of numerous spray nozzles that provide water curtain protection from intensive heat radiation emitted by flare flames.

3.84 Radiation shield

Structure, typically steel plate or other heat resistant materials, that provides personnel or critical equipment protection from intensive heat radiation emitted by flare flames.

3.85 Operational flaring load

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3.86 Emergency flaring loads

Load results from emergency flare pressure relief devices (relief from upset and/or emergency blowdown system is activated).

3.87 FPSO

FPSO: floating production storage and offloading. Ship used to store and offload hydrocarbon oil and gas production.

3.88 FSO

FSO: Floating storage and offloading. Ship without hydrocarbon processing facilities used to store and offload hydrocarbon liquids.

3.89 Jin pole

Jin poles and lifting cables are provided with derrick supported flare stack to facilitate removal of flare burner.

4. Flare equipment overview

4.1 System purposes

Add

The following are general requirements for flare Vendor related to supply of flare system: a. Vendor design shall be based on process information provided in data sheets.

b. Required equipment and accessories necessary for proper system operation shall be provided by Vendor.

c. Calculations that demonstrate sufficiency of proposed design shall be submitted and shall be subject to BP approval. Calculations shall be presented in logical manner and demonstrate consideration given for different operating scenarios.

d. Sufficient information shall be provided to clarify computerised calculation based on inhouse computer programs or list titles of commercial programs used to perform design calculations. e. Flare riser and support structure design assembly and flare burner and accessories for flare

system may be furnished by separate Vendors.

f. Vendor shall confirm adequacy of all BP presized process equipment in its detail design and provide all process warranties as stipulated in data sheets and specifications.

g. Recommendation in regard to any special problem or alternate design shall be included in proposal.

h. Requirements for inspection and maintenance for flare system and specific impact on plant operations shall comply with BP specifications.

4.2 Types of flares

Add

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Modify Title to Read 4.2.1 Vertical and inclined flare

Modify to Read

The following are general requirements for flare Vendor related to supply of vertical and inclined flare system:

a. Vendor providing flare burner and accessories shall confirm adequacy of height of flare stack. b. Vendor supplying riser and flare support structure shall perform structural design calculation

as outlined in specifications.

c. Flare structures shall be designed to withstand loads imposed by known environmental conditions, such as wind, ice, and temperature, that will be specified by BP.

d. In addition to environmental loadings, structure shall be designed to withstand thrusts from liquid slugs (if there is risk that these can occur), gas discharging from flare tips, and imposed structural and equipment loads.

e. Structural plans indicating complete arrangement, including flare foundation requirements, manner of reinforcements, ladders, and platforms, shall be provided.

f. Structure shall be analysed for rhythmical oscillations and ensure adequate structural design. g. Structure shall be designed for maintenance loads, such as supporting spare flare tip during tip

replacement, additional scaffolding, lifting beams, tools, and personnel.

h. Guidelines or recommendations for transportation to site and for installation of stack shall be provided.

i. Minimum flare height shall be 7,6 m (25 ft). Shorter flare stacks are allowed, provided that flaring does not impose excessive thermal radiation or other safety hazards in vicinity. j. Due to lower overall installation cost, elevated flares should be guy supported or self

supported, if practical, unless special requirements call for another type.

k. If two or more services with dedicated tips are installed on single stack, the following issues shall be addressed:

1. Flame impingement from tip to tip. 2. Combined heat radiation rates and noise. 3. Difficulty to schedule maintenance work. 4.2.1.1 Self-supported (see Figure 1)

Modify to Read

a. Flare riser pipe shall provide structural support for all flare components.

b. This type of flare should be used for short and medium height flares, typically from 9 m to 30 m (30 ft to 100 ft), but can be designed for up to 76 m (250 ft) if minimum ground area is available.

c. In same cases, base of stack can incorporate water seal drum.

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4.2.1.2 Guyed (see Figure 2) Modify to Read

a. Guided stack should be used for heights up to 107 m (350 ft).

b. Since guyed supported structure requires large plot area, minimum allowance for deadman radius and anchor points for support of vertical flare stack shall be proposed.

c. Guy wires are typically positioned in triangular plan and shall be anchored by buried concrete block foundations.

d. Proposal for detail design of guyed structure shall outline all design scenarios to be considered and shall include load types, load directions, and stack conditions for design.

e. If more than four levels of guys are required to support stack, derrick supported structure should be proposed as alternate.

f. Vendor shall list and recommend maintenance procedures, recommended frequency for non destructive testing (NDT), inspection, special tools required, such as hydraulic tensioners, and lubricants required for guy ropes. This will allow maintaining guyed wire ropes and prevent corrosion that could extend facility life.

4.2.1.3 Derrick supported Add to First Paragraph

a. Documentation to verify structural design and other general requirements for transportation of structure to final site shall be provided.

b. Fixed derrick structure on offshore facilities shall have davit provision for tip removal or maintenance.

Generally fixed derrick supported structure for flare riser is typically used for FPSO and FSO facilities.

c. Design alternate may be quoted, subject to BP approval. Add

4.2.1.4 Boom and tower mounted flares

Except for structural details, sizing of this type of flare is similar to elevated flare commonly used for onshore installations. Heat radiation limits imposed by platform design criteria have important influence on flare boom length and on overall cost of platform. Use of heat radiation reduction options, such as inclined tip orientation, water injection, water curtains, and radiation shields, may be cost effective solutions resulting in boom length reduction and significant savings in overall platform cost.

a. BP will specify or flare Vendor may propose flare as tower or boom type, either on offshore platform or FPSO/FSO.

b. High pressure (HP) flare, low pressure (LP) flare, and atmospheric vent shall, if possible, be located on common flare stack on typical offshore production platform.

c. HP flare should be low radiation sonic tip. Other types of HP flare tips may be proposed. HP system collects pressure safety valve (PSV) discharges from vessels designed for 700 kPag (100 psig) maximum allowable working pressure (MAWP) or greater.

d. LP flare may be standard pipe tip flare and collect PSV discharges from equipment with low design pressures less than 700 kPag (100 psig) but not less than 14 kPag (2 psig).

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e. Atmospheric vent

1. Atmospheric vent is unlit open end pipe and services tanks or other equipment designed for operating pressure less than 14 kPag (2 psig).

2. Atmospheric vent may terminate midway up flare boom or at end of flare boom and point away from boom structure.

3. Atmospheric vents shall have flame snuffing system to prevent vents from burning (if vents are accidentally ignited) that may result in flare boom structural damage.

f. In addition to radiation heat concerns, design of flare structure shall take into consideration, possibility and effect of liquid carryover and dispersion and location of hot gas plume. g. If several flare tips have to be sited in close proximity (i.e., high pressure and low pressure

service), attention shall be given to possibility of interactive thermal damage to flare tips.

h. Maintenance and inspection

1. Access to flare tips may be required for maintenance and inspection.

2. Maintenance platform, if used, shall be capable of withstanding heat produced by flare flame and anticipated loads.

3. If platform is not needed, alternative method for access to flare tips should be provided. 4. Mechanical system may be provided to allow removal and replacement of flare tip. 5. As alternate to mechanical system, helicopter or barge based crane is effective but costly

to provide mechanical system for tip installation or replacement.

i. Flare structure, riser, and flare tip shall be constructed of materials suitable for both operating temperatures and marine environment.

j. Materials for structure will be specified by BP or shall be subject to BP approval if specified by others.

k. Except for instruments required to be located at flare tip, instruments shall be accessible for testing, repair, and replacement without shutdown.

4.2.1.5 Marine flares/remote flares

a. Flare systems shall preferably be on platform.

b. The following are general requirements for flare Vendor related to supply of marine flare system:

1. If amount of gas to be flared is so high that flare on platform is not practical or if local statutory regulations require, remote flare facilities shall be provided.

2. Specific attention shall be given in design of system to include: a) Subsea equipment (lines and risers, knockout drum).

b) Condensate removal methods.

c) Maintenance and repair (no hoists or cranes permanently available).

d) Provision to avoid liquid accumulation from carryover, vapour condensation, or seaspray into flare line.

3. Location of bridge linked flare shall be chosen to prevent wind from carrying hot flared gas and any unburned gas to affect personnel and equipment on main platform.

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4. Fully remote flares typically are HP flare only.

5. LP flare pressure may be sufficient to allow mounting on bridge linked structure. Otherwise, facilities for LP flaring should be provided on main platform.

Modify Title to Read 4.2.2 Horizontal or pit flares

Add

a. Although this type of flare has been used in BP and other company facilities, due to potential for negative environmental impact, such as flue gas dispersion and ground water

contamination, future use shall be limited or completely eliminated.

b. Horizontal flares may be required to allow operation of temporary installations in remote locations and are subject to BP approval.

c. If horizontal flare is considered, the following general requirements for flare selection and design shall be addressed:

1. Local regulations.

2. Spacing requirements.

3. Smoke formation.

4. Dispersion of combustion produced gases. 5. Flare tip life expectancy.

6. Pilot ignition system life expectancy. 7. Need for use of assisting media.

d. Flare lines leading to flare header shall not be buried.

e. The following design enhancement options could be considered in existing or new pit flare design:

1. Tip location: Consider installation of tip on upwind side of prevailing wind direction.

Wind will then carry flame away from flare tip. Because these flares are typically operated at low tip pressure, gas exit velocities are low, allowing wind at lower release rates to blow air inside tip causing internal combustion and premature tip mechanical failure.

2. Tip heat protection: Consider use of additional tip protection from heat or burning flash fires caused by presence of liquids. Options may include selection of higher metallurgy for tip, refractory protection of tip, and use of heat shields.

3. Use of retractable pilots: Retractable pilots can significantly increase flare safety and availability by allowing onstream pilot repair and replacement.

4.2.3 Enclosed flame flares Add

a. BP or its representative will propose use of enclosed ground flares. Vendor may, however, propose alternate for BP approval.

b. If enclosed flame flare is considered, the following general requirements for flare selection and design shall be addressed:

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1. Performance guaranteed to meet all operating conditions specified in data sheets shall be provided.

2. If facilities are located close to populated areas, Vendor shall provide explanation on how flare design and operation will ensure that waste stream is continuously ignited and shall provide guarantee for maximum emissions limits.

3. Wall or fence to cut off direct route for light and noise to surroundings shall screen air inlet at bottom of box.

4. Plenum height shall be specified and provided by Vendor and shall be subject to BP approval.

Adequate plenum height is required to avoid wind causing downdrafts that force flames outside bottom of flare.

5. If vent stream to be burned is low BTU gas, it is important to have stable and complete combustion especially if toxic gases are present.

6. Flare gases or hazard shall have adequate dispersion if combustion products are toxic or in event of flameout.

7. Exhaust gas temperature shall be optimised to suit site and operating conditions. 8. Auxiliary elevated flare shall be used for emergency flaring to provide supplemental

capacity to enclosed flame flare.

9. Noise levels shall comply with general requirements specified in data sheets and, in addition, shall be sufficiently low so as not to cause nuisance to local residents.

10. Potential maintenance problems with enclosed flame flares should be identified at early stage in project.

4.2.4 Single point and multi burner 4.2.4.1 Single point flares

Add

The tip used for single point flares can be a low pressure type, such as utility or open pipe type, or tips that operate at medium or high differential pressure across the tips. The majority of the tips that are currently being offered by flare Vendors are either a “generic” type design for relatively simple service applications or proprietary designs for more demanding operating characteristics/performances.

4.2.4.2 Multi burner staged flares Add

Multi burner staged flares may have tips located near grade or on elevated structures/stack.

If use of multi burner staged flare is considered, the following general requirements for flare selection and design shall be addressed:

a. Performance guaranteed to meet all operating conditions specified in data sheets shall be provided.

b. Vendor may quote multi burner staged flare installation that uses staged operation to provide smokeless operation as specified in data sheets.

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c. Purge gas shall be carefully considered for these types of flares that use flow staging, such as: 1. Proper purge gas rates are maintained at all times to avoid internal combustion in raisers

and header.

2. At low flow rates, only first stage of multi tip array should be open to atmosphere, and this stage is only one that needs to be included in purge rate calculations.

d. Provisions for adding purge gas in all stages shall be provided to avoid internal combustion if control valve in one or more stages develops a leak.

e. Purge gas requirements and estimate of service life of burners at normal and at minimum purge rates shall be provided.

f. Potential noise problem should always be considered. The following are additional flare noise requirements:

1. Flare Vendors, in their quotations, shall provide information on noise emission from flare at maximum emergency flow and at maximum smokeless flaring rate.

2. Noise emission data shall be provided as test report containing sound power levels in octave bands from 31 Hz to 8 kHz.

3. Flare shall be sited such that noise at positions normally accessible to personnel, at maximum emergency flow should not exceed 115 dB(A), except with BP approval. BP may specify lower noise limit to be applied in a particular case, e.g., offshore platform ground flare.

4. To reduce noise in specific areas, siting of flare, if possible, should be such that flare is not in direct line of sight from area.

The high kinetic energy and velocity needed to produce smokeless combustion also creates a higher level of noise than might be expected from a tip not using forced air or steam for assistance.

The main contributor to the noise in a smokeless flare is the steam jet noise. Therefore, in general, the lower the ratio of steam to flared gas, the quieter the flare.

This noise may not be a problem in isolated areas, in shielded ground installations, or on elevated stacks of sufficient height.

g. Gas flow control

1. Gas flow to flare stages shall be controlled by main control logic housed in control panel enclosure that is usually located near staging manifold.

2. Control logic shall be integrated into plant control system. 3. Control valves shall be located at end of main flare header.

4. As header protection from overpressure, in case of control valve(s) or control system malfunctions, rupture disk or pin valve bypass lines shall be installed for each stage. h. Vendor shall outline maintenance procedures, provide estimates for annual cost, and list all

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Add

4.2.4.3 Multi burner ground flares

In addition to general requirements outlined for multi burner staged flares, the following are additional requirements that are specific to multi burner ground flares:

a. Proper number of pilot burners shall be provided on flare to maintain stable source of ignition for discharged gases.

b. Radiation protection

1. Multi burner ground flares provide visible flames at grade level. Therefore, installations located in areas adjacent plants and close to public facilities shall be surrounded by radiation fence.

2. Radiation shielding may be limited to stage manifold area or may be required around entire area.

3. If radiation shields are used, care shall be taken in design to ensure sufficient airflow to burners.

4. Radiation fence shall normally be approximately 3,7 m (12 ft) high. Height of fence shall be determined by specific shielding requirements for each particular installation.

5. If radiation protection is not required, some normal fencing of area should be undertaken to restrict unauthorised access to flare area.

c. Burners shall be designed with stainless steel casting instead of lower cost fabricated designs, which will reduce maintenance and extend life of burners.

4.2.5 Smokeless and non smokeless flares 4.2.5.1 Smokeless flares

Modify to Read

Smokeless flares shall be designed and operated in accordance with GP 44-80, Section 8.6. However, some of the mechanical aspects and flare components of smokeless flares are addressed in various sections of this GP.

The following are additional requirements that are specific to smokeless flares: a. Smokeless flares eliminate noticeable smoke over specified range of flows.

b. Smokeless combustion shall be achieved by using gas, air, steam, pressure energy, or other means to create turbulence and entrain air within flared gas stream.

c. Smoking shall be defined by Ringelmann numbering scale (#1 Ringelmann is 20% opacity, Ringelmann 0 is clear).

d. Smokeless flaring requirement may be achieved by any of the following methods: 1. Inspirating additional air into combustion zone with fuel gas.

2. Inspirating additional air into combustion zone by tip design/Coanda effect. The following are options that should be considered for this application:

a) Slots may be fixed or variable.

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c) With variable slots, mechanism should be robust and well protected against ambient conditions.

d) Additional protection from system overpressure, such as use of bypass with rupture disk or pin type valve, should be considered.

e) Steam may be used in Coanda effect to draw in air for mixing with gas in single large units.

3. Providing highly turbulent condition within flame by using energy of incoming gas or turbulence caused by steam or air injection.

e. Flow rates for both smokeless and non smokeless flaring will typically be specified by BP. f. Vendor may propose flow rates, which will be subject to BP approval.

4.2.6 Endothermic (fuel gas assisted) flares Add

a. If other means, such as steam, air assisting, or high differential pressure across flare tip, are not available or are not economical solutions, fuel gas assisted flare design can be used for flare smoke suppression.

b. If flare gas LHV is less than 150 to 200 BTU/ (scf), this may be the only viable option to achieve complete combustion of flare gas. This option will generally be proposed by BP and confirmed by Vendor. Fuel assist gas supply requirement for design shall be listed Vendor.

4.3 Selection considerations

4.3.1 Add

a. BP or its representative will select type of flare to be used for application. b. This requirement will be specified in data sheets and specifications. c. Design alternates may be quoted by Vendor.

4.3.1.1 Add

To select and implement the most cost effective solution and to minimise the effect on the environment, the environmental considerations for all releases should be discussed thoroughly with regulatory authorities at an early stage of process design.

The following issues shall be addressed by Vendor during flare design:

a. Safety and well being of all personnel in vicinity (both onsite and offsite) under all conditions of flare operation. This shall include startup, purging, operational and emergency flaring, shutdown, inspection, and maintenance of all or parts of system.

b. Protection of plant and equipment in vicinity of flare system under all conditions. c. Protection of flare system from damage by external events, e.g., fires.

d. Inherent safety of flare system itself, especially with respect to the following: 1. Flammable or explosive mixtures.

2. Blockages or flow restrictions.

3. Toxic components.

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5. Mechanical damage.

6. Corrosion, erosion, and hydrogen embrittlement. 7. Flare flame stability.

8. Security of ignition. 9. Security of pilots.

10. Change over to another flare

e. Flare as disposal device shall be evaluated to determine if it can be classified as “Safety Critical Equipment”.

f. Evaluation can be performed in accordance with “BP Safety Critical Equipment Definition For PI” document.

This document will be added as a reference document in ETP Library.

g. Guidance in assessing consequences and impact of secondary hazards shall be obtained from BP.

4.3.1.2 Add

To determine overall cost of flare installation, Vendor shall review and address the following major requirements that heavily influence system design and performance:

a. Safety and environmental requirements (dispersion, smoking limits, radiation limits, noise, etc.).

b. Type and quantities of released gases and nature of flaring event (toxic or non toxic fluids, emergency and routine flaring, etc.).

c. Type of enclosed disposal system selected (single or multi service system, etc.).

d. Disposal device selection (elevated flare, ground flare, enclosed flare, marine and platform flare, etc.).

e. Site and plant requirements (distance from unit to flare, additive effect of radiation from multiple flare installation, possibility of burning liquid droplets, etc.).

f. Construction materials requirements (seawater environment, corrosive products of

combustion, high heat flame intensity, intermittent operation, multiple tips in close vicinity, etc.).

g. Utilities availability and cost (steam, air, high pressure gas, electricity, etc.).

h. Accessibility (marine flare, boom flare, site with multiple flares, multiple tips on common stack, remote site location, etc.).

i. Climate conditions (artic, desert, offshore, etc.).

j. Alternates to this GIS that may result in improved safety or economy for design may be quoted.

4.3.1.3 Add

BP will typically provide design and requirements data for flare design. Data will be specified in flare data sheets and include the following information:

a. Flare gas flowrate. b. Flare gas composition.

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c. Molecular weight. d. Flare gas temperature.

e. Frequency and duration of process streams discharging into flare system at any one time. f. Inherent restrictions imposed, e.g., allowable backpressure, solids deposition.

g. Depressuring flow rates especially if depressuring is activated because of fire or if due to utilities failure that might cause all depressuring valves to open simultaneously (all fail open depressuring valves).

4.3.2 Interrelationships Add

Issues that are related to interrelationship are not discussed in one particular section of this GIS. They are instead imbedded into numerous sections covering flare system design requirements.

4.4 Major components

Add

a. BP will select major flare components for each installation. b. Vendor shall provide only components as outlined in this GIS.

c. Vendor may, however, recommend optional component in its proposal and itemise associated cost for each option.

4.4.1 Modify to Read

Major and optional components for elevated flare are:

a. Flare burner with or without smoke suppression capability. b. Pilot(s).

c. Retractable pilot(s) (optional). d. Pilot igniter(s).

e. Pilot flame detector(s).

f. Retractable thermocouple(s) (optional). g. Buoyancy or velocity seal (optional). h. Support structure.

i. Knockout drum (optional).

j. Flame/detonation arrestor (optional). k. Liquid seal (optional).

l. Piping.

m. Smoke suppression control system (optional). n. Blower(s) (optional).

o. Ladders (caged or with safety climbing system) and platforms (optional). p. Davit for tip removal (optional).

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r. Radiation heat shields (optional). s. Rain shields (optional).

t. Flashback prevention (optional).

u. Purge system.

v. Isolation system (optional). w. Gas sampling system (optional). x. Oxygen analyser (optional).

y. Flow, temperature, and level measurements and alarms (optional). z. Pumpout facilities for drum (optional).

aa. Fire protection (optional).

bb. Flame snuffing system (optional). cc. Insulation (optional).

dd. Heating and heat tracing (optional).

ee. Cold liquid/vapour vaporisation and heating system (optional). ff. Flare gas recovery system (optional).

4.5 Mechanical design basis

Add

a. Protection of flare system from damage by external events, e.g., fires.

b. Material selection suitable for operational temperatures, corrosion, erosion, hydrogen embrittlement, temperature cycling embrittlement, etc.

c. Material selection should take into consideration special issue associated with potential autorefrigeration from depressuring.

d. Typical operating conditions (e.g., flare that is exposed to low flow operating condition for a long period of time might result in flames sitting well down in tip causing damage; therefore, range of operating conditions needs to be fully considered in deriving mechanical design). e. Vendor shall be responsible for mechanical design of flare system.

f. Mechanical design bases are provided in data sheet and specifications.

g. Presized equipment information provided in data sheet shall be confirmed by Vendor.

4.6 System design criteria

4.6.1 Modify to Read

Note that issues that are related to system design are imbedded into numerous sections of this GIS.

BP or its representatives will perform general system design criteria development for the flare system. Vendor shall typically verify if BP proposed system would meet all requirements. Vendor may quote alternate system design that would provide overall improvement to the flare system design resulting in improved safety, operability, and reliability.

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The following are major system design criteria that are outlined, in greater detail, in GP 44-80:

• Choice of disposal system (GP 44-80, Section 5).

• Closed systems (GP 44-80, Section 7).

• Flare system design (GP 44-80, Sections 8.1, 8.3, 8.6, 8.7, 8.12, and 8.16).

• Liquid removal (GP 44-80, Section 9).

a. The following additional points shall be given specific attention in overall design of flare system:

1. Required life of flare system components.

2. Philosophy to be adopted on inspection and maintenance of flare system and impact of these requirements on plant operation (flare system sparing requirements).

3. Meteorological and any other relevant environmental conditions pertaining to site.

4. National and local regulations, particularly concerning smokeless burning, flare visibility, pollution and noise restrictions.

5. Need for winterisation, especially of liquid seals.

6. Need for segregation of relief headers for reasons of temperature, toxicity, corrosive materials, etc.

BP Safety Critical Equipment Definition For PI Segregation is particularly required to prevent freezing of water wet streams, solidification of viscous materials, or reactions that could lead to plugging of lines.

7. Handling systems for safe disposal of condensed hydrocarbons and sour water from both knockout and seal drums.

8. Secure supply of seal fluid to seal drum with provision to prevent overfill to flare, header, and knockout drum(s).

9. Plot space/layout considerations.

10. Requirement for cold liquid/vapour vaporisation and heating system in situations where cold flare cannot be justified.

b. The following is a checklist of possible hazards that should be considered in the design of flare systems.

1. Flammable/explosive mixtures in flare system. These may result from air entering the system by any of the following mechanisms:

a) Down draft due to buoyancy effects, loss of purge gas flow, failure of purge reduction (molecular) seal.

b) Condensation of vapours in flare system can cause air to be sucked in at flare tip or through open vents or drains. This can be a very serious problem, since capacity of flare pipework to absorb heat can lead to very large and rapid contraction in volume.

c) Cooling of hot vapours discharged into cold flare system can also lead to air being sucked into system.

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d) Buoyancy of light gases can create subatmospheric pressure in low level flare pipework. Resultant pressure differential may induce air to enter system through any openings, vents, drains, etc.

e) Vacuum systems connected to flare can cause air to be sucked in. Especially high integrity segregation mechanisms are required to prevent this.

f) Process air may enter flare due to loss of control in oxidation plants or uncontrolled air purging.

g) Blockages/flow restrictions.

h) Freezing of liquid seals or condensate in flare lines or molecular seals or steam condensing, freezing in flare tip during low steam flow in winter condition, due to low ambient temperatures, low temperature discharges, or autorefrigeration. i) Polymerisation products, hydrates, waxes, corrosion products.

j) Solids carried forward from plants, catalyst, polymers etc.

k) Liquids trapped through faulty drains, bad design, and level control failure. l) Valves incorrectly closed or failing closed.

2. Toxic components

a) Streams containing more than 10% H2S or other highly toxic material should be run

in separate line to flare (as required by and preferably coupled to main flare gas stream near flare tip to minimise exposure of main flare pipework to corrosive effects of H2S).

b) Careful consideration should be given to disposal of foul liquid effluents from flare seals, drains, etc.

3. Chemical reactions within flare system, scales, acetylenes, peroxides, etc.

4. Mechanical damages, hydraulic surge of liquid slugs, propulsion of solid ice slugs, hydrates, impact, low temperature embrittlement through autorefrigeration, external fire damage, burn back at flare tip, flame lick, venting of high temperature gases into flare system.

4.6.1.1 Reliable effective burning Modify to Read

a. Reliable effective burning shall be achieved by proper system design. b. Design criteria and specifications will be provided by BP.

c. Alternate design and quote as options may be proposed.

d. BP may request testing of flare burners to performed by Vendor for simulated tested operated conditions at designated test facility.

e. Minimum heat content of flare gas shall be maintained as required by U.S. Environmental Protection Agency (EPA) document AP 42, Volume 1 and Chapter 13.5. Minimum heat content of flare gas should be 11,250 kJ/m3 _{(300 Btu/ft}3_{) to ensure high combustion efficiency}

for flare. Concentrations below 9300 kJ/m3 _{(250 Btu/ft}3_{) shall require addition of fuel gas for}

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4.6.1.2 System hydraulics Modify to Read

BP or its designated representative will typically perform hydraulic design for the flare system. Flare Vendor may, however, be requested to review and confirm the proposed design. The basis and methods to be used for determining system pressure losses shall be subject to BP approval.

The following are general considerations required if providing hydraulic design for flare system: a. Total allowable pressure loss through flare system, including stack, flare tip, liquid seal (if

any), knockout drums, and piping is normally dictated by back pressure limitation on critical relief valves, and shall be subject to BP approval. Evaluations shall take account of:

1. Potential relief, depressurising, and process venting conditions as specified in data sheets. 2. Pipe roughness consistent with pipe material and operating conditions.

3. Final piping configuration details, including fittings and entrance losses.

Pressure drop limitations may dictate the flare stack diameter and flare tip size.

b. Flare Vendor shall refer calculated flare tip exit velocity to BP, which shall be subject to approval. Velocity shall be chosen to satisfy requirements for flame stability, noise, and dispersion.

The latest designs of pipe flare tips permit smokeless flaring at velocities above 0.2 Mach No., but if this velocity is exceeded, experience of satisfactory operation of the design should be examined. For emergency flaring, 0.5 Mach No. is generally accepted as a maximum. Above that figure, the flame could become unstable and lifts off,

resulting in the risk of flame extinction. A Sonic flare tip, 1.0 Mach No., can, however, be specified for offshore flare applications.

c. Relief header shall be sized using pipe roughness of 0,46 mm (0.018 in) instead of normally adopted value for clean steel pipe of 0,046 mm (0.0018 in). This reflects BP experience of increased roughness in relief headers.

d. If back pressure is not significant and governing factor is fluid velocity, flare line shall be sized to limit maximum velocity to 0.5 Mach No., as long as relief valve pipes supports is assured adequate. Allowable Mach No. may be increased to 1.0 for offshore application. e. Relief header shall be self draining towards knockout drum. Header upstream of flare tip shall

similarly drain back to drum. 4.6.1.3 Liquid removal

Modify to Read

The flare knock drums are used for removal of the bulk of the liquid carryover. A drum shall be provided in all cases where significant quantities of liquid can be relieved from within the battery limit.

An onsite knockout drum should normally be provided within the battery limit of each plant or group of plants served by the flare system. The offsite knockout drum is typically located in the flare area.

The offsite and onsite knockout drums have similar design requirements.

The choice between a horizontal and a vertical drum should be made on economic considerations, taking into account the vapour flow rate, the liquid storage required,

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and the necessary slope of the flare header. BP will, however, typically select the type of drum for each service.

a. BP or its representatives will size flare knockout drum, which will typically be supplied by others.

b. Flare Vendor may be requested to confirm size of knockout drum, even if it is not included in Vendor scope of supply.

c. The following are specific considerations/requirements for design and sizing of knockout drums:

1. Offsite knockout drum (onshore)

a) Each flare system shall have offsite knockout drums.

b) Drums shall be located as close as practical to flare, taking account of access requirements and potential use of liquid seals that shall be located downstream of drum.

c) Calculation method shall comply with API RP 521.

d) Onsite knockout drums shall be designed for full vacuum and maximum allowable working pressure of at least 3,5 barg (50 psig).

e) Liquid storage capacity of drum shall allow for minimum of 20 min holdup at maximum liquid inflow to drum. Capacity shall be provided between maximum normal liquid level (i.e., pump trip in level) and maximum level allowable in drum. f) Offsite knockout drum, typically referred to as flare drum, shall be sized to remove liquid droplets above 600 µm at maximum emergency gas flow to flare and above 150 µm from gas flow equivalent to maximum smokeless capacity of flare. In exceptional cases, for flares that are capable of burning larger sized droplets, waiver of these requirements may be accepted, subject to BP approval. g) Any flashing of relieved liquid at knockout drum pressure.

h) Because of potential for blockage from scale or waxy deposits, use of demister pad to limit size of drum should be avoided. Applications shall be restricted to clean systems if there is no practical alternative.

i) Unless specified otherwise, knockout drum shall have automatic hydrocarbon liquid removal.

Since the liquid in the KO drum may be toxic or flammable or have toxic or flammable material dissolved in it, particular care should be taken in the design and operation of any drain points. If there is any risk of toxic materials being released, the drain should be routed to a closed system. If there is any risk of the materials freezing, a second valve in series is required as a minimum.

j) If appropriate, separate facilities for water or heavy hydrocarbon removal shall also be provided - these may be automatic or manual. Disposal route and facilities for these liquids shall be subject to BP approval. Particular attention should be paid to prevent creation of hazard due to release to atmosphere of flammable or toxic materials from drain points.

k) Instrumentation and control systems for the drum shall comply with data sheets provided by BP.

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l) Piping systems entering and leaving drum shall comply with BP piping specifications.

m) If specified on BP data sheet, winterisation shall be provided.

n) Personnel protection shall be provided in accordance with BP data sheet requirements.

o) Facilities shall be provided, if specified on BP data sheet, for isolation, venting and purging, inspection, maintenance, and cleaning of drum.

p) Specific attention shall be given to requirements of inspection, maintenance, and cleaning if associated plants cannot be shutdown. Proposals shall be subject to BP approval..

q) Specific attention shall be given to liquid removal facilities in flare systems that are required to dispose of both “cold” and “wet” streams.

In this context, a “cold” stream is defined as a stream at a temperature below 0°C (32°F) that could cause freezing of water in a knockout drum or on mixing with a stream containing free or dissolved water. The situation is most likely to occur in plants handling liquefied gases or gas streams at high pressure.

If practical, cold streams shall have separate systems, with segregation maintained until the streams become compatible. Flare Vendor proposals shall be subject to BP approval.

r) Cold liquid collection drums may require vaporisation facilities. Cold vessel material of construction shall be appropriate for minimum design temperature. s) Attention shall also be given to presence of other materials that freeze or are highly

viscous at temperatures above 0°C (32°F).

t) Attention is drawn to special sealing provisions for cold service. Seal provision in u) is generally followed.

u) Water seals shall only be used if temperature of vapour cannot fall below 0°C (32°F). To guard against freezing in cold weather, seals shall be fitted with automatic heating, either electrical or steam coil, as specified by BP.

Some chemicals can raise the freezing point of water above 0°C (32°F). If such

chemicals could be relieved, suitable adjustments should be made to water seal or seal liquid.

v) For cold service, glycol or other suitable material shall be used, either pure or with water, depending on anticipated temperature of vapours.

2. Knockout drum (offshore facility)

The liquid removal facilities should be designed to remove entrained droplets (which may carryover as burning hydrocarbons) from the gas flow and provide sufficient liquid holdup capacity to collect any surges of liquid.

a) Holdup capacity should be based on longest estimated time required to isolate incoming flow. Typically, for most offshore platforms, isolation time may be 1.5 min.

b) Maximum use should be made of surge capacity within process area to accommodate liquid relief.

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c) Devices that provide warning (and if necessary execute shutdown action) shall be fitted to all relief valves which can discharge liquids to flare.

4.6.1.4 Air infiltration Modify to Read 4.6.1.4.1 Flashback prevention

a. Reliable method of flashback prevention shall be incorporated into flare system design. The following methods may be used, either singly or in combination (choice of method shall be subject to BP approval):

1. Gas purge

2. Liquid seals

3. Efflux velocity accelerators

The above methods are primarily intended to prevent diffusion of air into the flare stack. Note that gas seals, i.e., molecular seals are not sufficient by themselves to prevent flashback. If flare gas recovery is used, both gas purge and liquid seals should be installed.

b. Use of flame arrester shall be considered only if none of methods in a. are suitable and shall be subject to restrictions in a.

c. The following conditions conducive to formation of flammable mixtures within flare system shall be evaluated and addressed if:

1. Vacuum systems are linked to flare.

2. Lighter than air gases, particularly hydrogen, are being flared. 3. Condensation or rapid cooling can occur within flare system.

It may be possible to reduce or even prevent condensation by heating and insulating the flare line. However, such measures may be expensive to install and difficult to maintain in a reliable condition.

4. Flashback velocity may be reduced by addition of inert gases to flammable mixture. Best location for addition of inert gas is as close to flare tip as possible, compatible with good mixing of gases before burning at tip.

5. Care shall be taken to ensure flare gas heat value is above minimum allowed at all phases of operation. Otherwise, pilot and main flames can be extinguished.

6. BP will specify if it is necessary to keep flare lit.

7. Velocity accelerators and inert gas addition may be used in combination. d. Method of calculating flashback velocity

1. Method of calculating flashback velocities for some gases commonly occurring in flare systems when mixed with nitrogen, carbon dioxide, or both has been developed by Van Krevelin and Chermin and reported in transactions of Seventh International Symposium on Combustion, 1959, pages 358-368.

2. This method may be used to calculate inert gas flow corresponding to peak flashback velocity of gas mixture. Excess inert gas flow of 25% above calculated value should provide ample margin of safety to compensate for measuring errors and minor flow disturbances.

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4.6.1.4.2 Gas purge

a. Inert gas (e.g., nitrogen), fuel gas, or natural gas from reliable source shall be continuously introduced as purge into vapour disposal systems. Choice should primarily be evaluated on cost. If economically viable, inert gas shall be used.

b. Purge gas supply shall be from high reliability source approved by BP.

c. If necessary to achieve overall acceptable reliability, automatic backup supplies should be used.

d. Purge system shall be designed such that loss of single purge gas source or injection point does not allow hazardous conditions to occur.

e. Maximum calculated purge rate shall be established to required purge rate to balance flashback and efflux velocities for variety of relief flow rates.

f. Minimum purge gas velocity or flow rate shall be maintained at flare tip to: 1. Minimise air ingress due to wind effects.

2. Prevent burn back inside flare tip. g. Larger of the two flow rates shall be used.

h. Minimum purge rate to minimise air ingress due to wind effects shall be calculated using H.W. Husa’s correlation formulae given in Annex C. Purge rate shall be such that oxygen content in flare gases 8 m (25 feet) down from top of flare shall be less than 6%.

Note that the Husa correlation applies if typical wind speeds do not exceed

approximately 13,4 m/s (30 mph). Locations where prevailing winds can often exceed this wind speed may need somewhat higher purge rates.

i. If either purge gas or flare gas is low molecular weight (e.g., containing high concentrations of hydrogen), maximum oxygen content shall not exceed:

1. Maximum oxygen of 5 volume percent for flare gases with MW greater than 6 but not

exceeding 8.

2. Maximum oxygen of 4 volume percent for flare gases with MW greater than 4 but not

exceeding 6.

3. Maximum oxygen of 3 volume percent for flare gases with MW less than or equal to 4.

j. Minimum purge required to prevent burn back inside non refractory lined flare tips shall be specified by Flare Vendor. Flow velocity shall be verified, based on selected proprietary flare tip or molecular seal design. If tip is refractory lined, purge rate only needs to be based on that required to prevent air ingress due to wind effects.

k. Required purge rate using gas mixture heavier than air shall be calculated using nitrogen parameters in Husa equation in Annex C.

For flammable purge gases heavier than air, the minimum purge rate could

theoretically be achieved with very low flow rates. This may result in burning inside the tip, resulting in higher tip temperatures and shorter tip life or flame extinguishment.

l. Minimum flow rate required shall be adequate to maintain flare alight, while problem of internal burning shall be economically evaluated against the following alternatives:

1. To increase purge gas velocity at tip to typical velocities of between 0,15 m/s and 0,3 m/s (0.5 f/s and 1.0 f/s).

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2. To upgrade material specification for flare tip.

3. Provided there is alternative relief route during flare shutdown, to replace tip more often. 4. To provide additional cooling for flare tip.

m. Unless specified otherwise, flares shall have oxygen monitoring. n. Oxygen monitoring system shall comply with the following:

1. Oxygen monitoring equipment shall ensure that, if minimum purge rate is used, explosive atmosphere does not result. Monitoring equipment should also highlight spurious ingress of oxygen due to operating deviations, e.g., suck back.

2. If inert gas is being used for flashback prevention and system is of high integrity, oxygen monitoring may not be required.

3. Oxygen sampling probe shall be located 8 m (25 ft) or 15 diameters, whichever is smaller, below tip exit.

4. Oxygen analysing installation should be located at base of stack or at boundary of restricted access zone. If located in area where radiation level may exceed 4,73 kW/m2

(1500 Btu/ft2_{h), oxygen analysing installation shall have suitable shielding.}

5. Sample gas shall be withdrawn by diaphragm type vacuum pump, fitted upstream with liquid knockout pot and returned to stack above sample point. This is required to avoid a fluctuating pressure in sampling line, due to changes in pressure drop through stack induced by changes in flow rates.

6. Portion of sample gas shall be taken through regulating needle valve to oxygen analyser of type specified by BP and exhausted to atmosphere. Local and control room indications and alarms shall be provided as specified by BP.

4.6.1.4.3 Liquid seals

Liquid seals may be employed for prevention of air ingress into the flare header network due to most thermal contraction events and for diversion of vapour flows (e.g., for flare gas recovery systems). (See ISO 23251 or API RP 521).

Liquid seals may not prevent flashback in cases where a large volume of gas is relieved. Incidents have shown the flame can propagate back through a continuous flow of bubbles. Hence, a continuous purge or other method should be used to ensure the flare header is air free.

a. If used, liquid seals should be incorporated in relief disposal systems as close as practical to all elevated flares.

b. Liquid seals should normally be used in conjunction with continuous gas purging.

c. If more than one flare is connected to relief header and automatic pressure actuated valves are used, full capacity backup route to flare shall be provided via liquid seal or another BP approved alternative that ensures “open” relief route.

d. If liquid seals are impractical, another system shall be required that provides both guaranteed emergency relief route and guaranteed protection against air ingress to flare and header systems.

e. Water seals normally should be used if either ambient temperature or temperature of relief streams cannot fall below 0°C (32°F). To guard against freezing in cold weather, seals shall be

GIS 22-201

Guidance on Industry Standard for

API 537 Flare Details

GIS 22-201

BP GROUP

ENGINEERING TECHNICAL PRACTICES

Foreword

British Petroleum

Amoco

GOMDW

PTA

Table of Contents

Introduction

1.

Scope

2.

Referenced publications

API

ASME

ASTM

BP

BS

CONCAWE

ISO

3.

Definition of terms

4.

Flare equipment overview