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Flare system commonly consists of collection networks, liquid Knock-Out drum (with liquid retention capability), knock-out pump and flare stack with tip. Some flare system may includes liquid seal drum, air ingress & purge reduction seal, flare recovery system, liquid heater and/or vaporiser, etc. Sometime, two or more flare knock-out drums (KOD) are installed in parallel to reduce KOD size on large flare design flow. However, in some design, two or more flare KODs are installed in series within the flare collection system. What are the common reasons behind providing KODs in series ?

(i) Vapor & Liquid Recover to Source
In a plant, there may consist several production trains with common flare system. This is one of the strategy to minimize capital investment cost. Typical plant with multiple trains and common flare is Liquefied Natural Gas (LNG) and gas processing plant. Example Qatar gas LNG plant has at least 7 trains, Australia North West Shelf has at least 5 trains, etc. Although all trains are located in same place sharing common flare system, however the owner of these train may be different. Probably Train 1, 2 & 3 are owned by company ABC, train 4 & 5 own by company MMM and train 6 & 7 own by company XYZ. Vapor and liquid hydrocarbon leaks or relief from a train, this valuable hydrocarbon may be recovered back to its train process system by same owner. Thus, providing a dedicated KOD for trains belonging to dedicated owner may serve above purpose.

(ii) Design limitation of Main Flare On Operational Non-Smoking Requirement
Common main flare shall be designed for largest load from all trains in any relieving scenario. Common relieve scenario contributes to large relief load are cooling water failure, total power failure, total plant blowdown, etc. This possibly lead to common main flare with large capacity. However, it is also common requirement to have non-smoking flaring during normal operation with low flow. As common main flare with large capacity may have limited turndown and exceeded the minimum normal operational flow, thus a dedicated operational flare may be provided for train(s) with same owner. Providing a dedicated KOD and operational flare for trains belonging to dedicated owner may serve above purpose.

iii) Mixing of Product may not be recoverable in any plant
Some plants with common flare system but relieve different of product. There is potential the mixture of the products may not be recoverable by any of the plant. Thus, a dedicated KOD for dedicated plants are provided so that the product relief from dedicated plant is recoverable in the plant which relieved the fluid.

(iv) Mixing of Fluid Cause Slugging
Common main flare system for plant with hot fluid and cold fluid may lead to condensation and results slugging flow in the flare header. Slugging in flare header potentially results severe erosion, noise and vibration. Providing a dedicated KOD will remove liquid from the relieve fluids and minimise the potential of slugging in the common header. This may only minimise, but not totally avoid as hot vapor may still mix with cold vapor in the common header and condensation/slugging flow may still possibly present. However, providing of dedicated KOD will reduce the slugging flow potential. In the event, severe slugging still possibly present and results problem to flare support, it is always advisable to provide separate flare system.

(v) Reduce Common Header Size
Providing dedicated KOD would possibly reduce relief flow (liquid) to the common header during common relief scenario. Reduction in relief flow will reduce the main flare header size.

Related Topic

• Elevated Flare (SI Unit) Datasheet
• ANSI/API Std 537 / ISO 25457 2nd edition, Dec 2008 is Released
• Flare Tip Quick Selection Chart
• Flare Smokeless Ringlemann Chart
• Guideline on Quick Determination of Flare Stack Support Type
  
• Must Read Flare Handbook
• Why not bury flare pipe header ?

Labels: Combustion, Flare, FLARENET

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Pressure relief to protect system from overpressure and emergency depressuring to evacuate system inventory to safe location are common plant safety system. Fluid is discharge in the proper designed collection system will then be send to flare for proper combustion. Different fluid characteristics, pressure available in the collection header, carbon-hydrogen ratio, concentration of toxic component, local requirement, etc will require different type of flare tip for proper flaring.

There are several typical flare type :

• Pipe flare (subsonic)
• Sonic flare (single tip & multiple tips)
• Coanda tip (single & multiple)
• Steam assisted flare tip
• Air assisted flare tip
• Enclosed flare
• Endothermic flare
• Liquid burner
• Other proprietary tip

A process / package engineer will prepare flare tip datasheet and flare tip vendor will base on the provided information and requirement to select a proper tip. It is sometime interesting to know what type of flare tip will typically be selected by vendor. This is to ease preliminary design and plant layout consideration.

A simple flare selection chart has been provided to ease process engineer in flare tip type selection.

Related Topic

• Flare Smokeless Ringlemann Chart
• Guideline on Quick Determination of Flare Stack Support Type
  
• Must Read Flare Handbook
  
• ANSI/API Std 537 / ISO 25457 2nd edition, Dec 2008 is Released
• Why not bury flare pipe header ?
• Use Ultra-Sonic Flowmeter in FLARE Gas Header for emission monitoring
• FLARE combustion efficiency
• Factors and Criteria for Vent Stack Design

Labels: Combustion, Flare

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American Petroleum Petroleum (API) released the ANSI / API Std 537 / ISO 25457:2008 "Flare Details For General Refinery and Petrochemical Service" Second Edition, Dec. 2008 in December 2008. First important change is it has been upgraded as ISO compliance. User shall remember although it is a standard, it is solely users responsibility to make sound, scientific, engineering, safe, environment friendly judgment. Neither API nor its employee, etc make warranty for the use of this standard. Detail refer to "Special Note" in relevant Standard.

API Std 537 / ISO 25457 is primarily to provide mechanical related information related to flare. For flare system design and related criteria and limitation, user may refer to API Std 521 / ISO 23251 "Pressure Relieving and Depressuring System".

• A simple flowchart for Flare Type Selection has been included in this new standard. This flowchart will provide a quick way to understand the potential flare tip type may be selected by the flare vendor. Read more in "Flare Tip Quick Selection Chart"
  

• Larger the flare tip diameter, more number of pilots is required. The following table provide minimum requirement of pilots for flare burner diameter. This table presented a minimum pilots per burner, one shall remember there is possibility of pilot, mixer, ignition, etc fail. Thus, redundancy / spare shall be provided.

• Minimum pilot fuel gas consumption is 13.2 kW (45000 btu/h). Knowing the Lower/Net heating value of fuel gas, the minimum pilot gas consumption per pilot can be determined. Together with above information, a process engineer may estimate continuous fuel gas consumption for all pilot

• This standard recommends a minimum corrosion allowance of 1.6 mm (1/16") to be provided for carbon steel riser contact with relief fluid.

• Smokeless flaring is normally achieved by utilizing air, steam, water, pressure energy, etc. The requirement of smokeless flaring is determine by local authority or company requirements. Ringlemann number is used for the definition of smokeless level. Read more related to Ringlemann chart in "Flare Smokeless Ringlemann Chart".
  

• Minimum LHV of 7450 kJ/Nm3 (200 Btu/scf) for unassisted flare whilst 11175 kJ/Nm3 (300 Btu/scf) for assisted flare (Ref.: 40 CFR PT 60.18). This may be applicable to normal pipe flare. For sonic flare tip, a higher LHV value i.e 800 BTU/scf (subject to vendor) may be required.

• As highlighted, a steam assisted flare, noise level is the combination of combustion noise and steam jet noise, typically high. Additional attention is required for steam and water assisted flare.

• For low ambient (subzero during winter), there is potential partial/total blockage of steam/water header due to ice formation. Additional attention is required for steam and water assisted flare.

• There are typical Flare Tip datasheet available in this standard which assist purchaser, contractor and manufacturer in proper communication of information.
  

• Flare Smokeless Ringlemann Chart
• Guideline on Quick Determination of Flare Stack Support Type
  
• Must Read Flare Handbook
  
• Steam in FIRE...
• Why not bury flare pipe header ?
• Use Ultra-Sonic Flowmeter in FLARE Gas Header for emission monitoring
• FLARE combustion efficiency
• Factors and Criteria for Vent Stack Design

Labels: Combustion, Flare

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Smokeless flaring is one of the common requirement for open flare to ensure proper combustion of relief gases and minimize greenhouse effect and pollution. Smokeless flaring may be achieved by direct air blowing, steam injection, water injection, pressure energy to create turbulence, etc. Minimum requirement of smokeless flaring is determined by local authority or company policy. One of the way to quantify smokeless is using Ringlemann number.

The Ringelmann system is virtually a scheme whereby graduated shades of gray, varying by five equal steps between white and black, may be accurately reproduced by means of a rectangular grill of black lines of definite width and spacing on a white background. The rule given by Professor Ringelmann by which the charts may be reproduced is as follows:

Card 0—All white.
Card 1—Black lines 1 mm thick, 10 mm apart, leaving white spaces 9 mm square.
Card 2—Lines 2.3 mm thick, spaces 7.7 mm square.
Card 3—Lines 3.7 mm thick, spaces 6.3 mm square.
Card 4—Lines 5.5 mm thick, spaces 4.5 mm square.
Card 5—All black.

The chart provides the shades of cards 1, 2, 3, and 4 on a single sheet, which are known as Ringelmann No. 1, 2, 3, and 4, respectively. Refer following samples.

Labels: Combustion, Flare

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Gas turbine generator or gas turbine driven compressor is common used in refinery, LNG and gas plant. These turbine basically will burn gas fuel from the plant itself and hot flue gas is passed through the gas turbine. Gas turbine is then rotate and drive motor or compressor to generate power and head.

Flow and Heating Value Changes in Gas burner
Gas fuel burnt in gas burner which typically has fixed orifice nozzles. Heat output from the fixed orifice burner is proportional to flow (Q) and heating value (HV) of the gas fuel. As fuel composition change, flow and heating value will have to be changed to maintain a correct heat output. However, the magnitud of flow and heating value changes may not change linearly or there is not fix relation between flow and heating value. How to relate these two parameters ?

• End Flash Gas which contains very high inerts (as high as 50%-55% Nitrogen level) and low heating value
• Flash gas from Amine regeneration unit which contains high level of CO2 and H2S, Hydrocarbon component varies from ethane to Decane including BTEX
• Demethaniser overhead which contain high Methane level
• Boil-off gas (BOD) which contains very high level of methane and low level of nitrogen
• Flash gas from Ethane, Propone, and LPG storage
  
• Make-up which composition varies from Methane to Decane

Labels: Combustion, Design

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Flare system is a common safe and environment friendly gas disposing facilities in Oil & Gas development, Refinery and Petrochemical plants.

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If you are looking for a Flare Handbook, i would recommend you The John Zink Combustion Handbook, a publication of John Zink, "grand daddy" in Flare. Chapter 20 "FLARES" describes in details of

• Flare Systems - description of flare application, types & components
  
• Factors Influencing Flare Design - How flow rate, composition, temperature, etc affecting flare design
  
• Flare Design Consideration - Aspect to be considered in flare design
  
• Flare Equipments - Details description of flare burner, pilots system, KO drum, seal drum, etc
  
• Flare Combustion Products - Overview of combustion efficiency, emission and dispersion
  

This is a great handbook for a young engineer to get the basic understanding and fundamentals of flare system. You may preview (Click HERE) or get copy for yourself (Click HERE).

• Use Ultra-Sonic Flowmeter in FLARE Gas Header for emission monitoring
• FLARE combustion efficiency
• Why not bury flare pipe header ?
• Several Concerns in High CO2 Field Development
• Factors and Criteria for Vent Stack Design

Labels: Combustion, Flare

The goals of the IFC are:

• Provide emission factors for production and refinery flares, including the effect of steam rate, composition and flow rate of fuel, and wind speed.
• Establish optimal operating conditions, maximizing combustion efficiency and minimizing pollutant emissions.
• Set operating envelope outside of which flares should not be operated.
  

"This paper compares and contrasts reaction efficiency findings on properly designed and operated industrial flares with those of rudimentary field flares and shows that the results on the latter hardly apply to the former. We review the most significant of the contributions to flare emissions research of the last three decades and provide the background perspective of researchers who were directly involved in leading and executing the 1980's flare efficiency studies that formed the foundation for future studies. These landmark studies demonstrated that properly designed and operated industrial flares are highly efficient and led to the codification in the United States Environmental Protection Agency's 40CFR60.18 General Requirements for Flares of the conditions that ensure the proper operation of industrial flares."

One of the interesting parameter that i have always been looking for is the Flare combustion efficiency...from this article...98% combustion efficiency and it is supported by a well known organization.

For those would like to made to reference...here is the place.

Labels: Combustion, Flare