Gas Flare Stack Process
Download as PPTX, PDF10 likes7,057 views
The document provides an in-depth explanation of gas flaring, including its purpose as a safe emergency release system in the oil and gas industry to combust waste gases. It details various flare stack classifications, the process involved in flaring, and specific components that ensure efficient and safe operation, such as knockout drums, liquid seals, and burner tips. Additionally, it covers the environmental considerations and compliance aspects tied to flaring practices.
Gas Flare Stack Process
- 1. GAS FLARE STACK PROCESS Shad B. Ibrahim MohammedA. Abdulkadir Rabar M. Mahmood 1
- 2. Introduction What is Flaring? Purpose of Flaring Flare Stack Classification: Height of the Flare Method to Enhance Mixing Flare Stack Process (P&ID Drawing) Process Description: Knock out Drum Liquid Seal Gas Seal BurnerTip Pilot Burner Steam Jets Controls References CONTENT 2
- 3. INTRODUCTION The flame at the top of an oil production site is an iconic image for the oil and gas industry. Yet few people know why the flare is there and its purpose. The flare is a last line of defense in the safe emergency release system in a refinery or chemical plant. It provides a means of safe disposal of the vapor streams from its facilities, by burning them under controlled conditions such that adjacent equipment or personnel are not exposed to hazards, and at the same time obeying the environmental regulation (EPA) of pollution control and public relations requirements. 3
- 4. WHAT IS FLARING ? Flaring is a high-temperature oxidation process used to burn combustible components (mostly hydrocarbons) of waste gases from industrial operations. Natural gas, propane, ethylene, propylene, butadiene and butane constitute over 95 percent of the waste gases flared. In combustion, gaseous hydrocarbons react with atmospheric oxygen to form carbon dioxide (CO2) and water (H2O). Presented below, as an example, is the combustion reaction of propane. C3H8 +5O2 → 3 CO2 +4H2O 4
- 5. PURPOSE OF FLARING Flares are used extensively to dispose: 1) Purged and wasted products from refineries. 2) Unrecoverable gases emerging with oil from oil wells. 3) Vented gases from blast furnaces. 4) Unused gases from coke ovens. 5) Gaseous wastes from chemical industries. 5
- 6. Flares Height of the flare Elevated Self Supported Stack GuyWired Supported Stack Derrick Supported Stacks Demountable Derrick Supported Stacks Ground Open Enclosed Method to enhance mixing at flare Steam-Assisted Air-Assisted Non-Assisted PressureAssisted FLARE STACK CLASSIFICATION 6
- 7. HEIGHT OFTHE FLARE Elevated Flare 1-Self supported stacks This is the simplest and most economical design for applications requiring short-stack heights. Their installation space required is relatively less . Simple to erect reducing capital costs. Under 50 meters overall height. 2-Guy wired supported stacks Sets of 3 wires are anchored 120º apart at various elevations (1 to 6). It’s Investment is generally lower than the other types. Their installation require large amounts of land to accommodate the wires. 50 – 150 meters height range. 7
- 8. HEIGHT OFTHE FLARE Elevated Flare 8 3-Derrick supported stacks Can be the optimum solution for flare systems installed inside plants. When higher elevation is required to limit ground radiation, thermal expansion A single-diameter riser supported by a bolted framework of supports which offer greater support than guyed stacks. Cost 50 to 100% more to build. Stack heights above 200 meters. 4-Demountable derrick Multiple flares can be installed in a single derrick structure. Require three or four additional foundations for the derrick legs. Allows one flare to be worked on or replaced while the other flare(s) remain in service. Flare tip can be lowered to grade level for maintenance, inspection, or repair activities.
- 9. Open Ground Flare Have a series of headers spaced across open ground with multiple burner tips to distribute the flame. A radiation fence typically surrounding the area. Open ground flares are able to burn larger quantities at a time. Handling large gas flow rate with smokeless operations. Requires large clearances. It’s units contain a limited amount of space for the burners. This means that the units must be kept at a distance for safety reasons. Bright light, noise and heat emissions require that the unit be used in a more secluded area. Enclosed Ground Flare More common than an open ground flare. It’s burner heads are inside a shell that is internally insulated. This shell reduces noise, luminosity, and heat radiation and provides wind protection. Equipped with a vertical combustion chamber and the height must be adequate for creating enough draft to supply sufficient air for smokeless combustion and for dispersion of the thermal plume. Suitable for managing low and medium gas flow rates. Reliable and high combustion efficiency can be attained under any atmospheric conditions. HEIGHT OFTHE FLARE 9
- 10. SteamAssisted AirAssisted NonAssisted PressureAssisted Predominant flare type found in refineries and chemical plants. For disposal of heavier waste gases which have a greater tendency to smoke . Used where high efficiency combustion of heavy hydrocarbons is required. Steam causes turbulence which improves mixing and combustion efficiency. Can be used where steam is not available. Dispose of heavier waste gases which have a greater tendency to smoke. Combustion air is provided by a fan in the bottom of the cylinder. The amount of combustion air can be varied by varying the fan speed. Flare tip without any auxiliary provision to enhance the mixing. Limited to gas streams that have a low heat content and C/H2 ratio, that burn readily without producing smoke. Where smokeless combustion of heavy hydrocarbons is not required. Gases with lower combustion temperatures. Lower capital cost for safe disposal of waste gases. Use the actual pressure of the waste gas to create turbulence. Pressure-assisted flares generally have the burner arrangement at ground level. They have multiple burner heads that are staged to operate based on the quantity of gas being released. METHODTO ENHANCE MIXING 10
- 11. FLARE STACK PROCESS (P&ID DRAWING) 11
- 12. Knock Out Drum Remove liquids that may be in the vent gas stream or that have condensed out in the collection header and transfer lines. This drum must be sized for worst case conditions. Horizontal drum is more economical when large liquid storage and, high vapor flow and lowest pressure drop is desired. Vertical knockout drums used if the liquid load is low or limited space is available. They are usually quite large. Zone 1: Inlet distribution zone. Zone 2: Fine separation zone. Zone 3: Liquid collection and drain zone. PROCESS DESCRIPTION 12
- 13. PROCESS DESCRIPTION Liquid Seal Process vent streams are passed through a liquid seal before going to the flare stack. Can be downstream of the knockout drum or incorporated into the same vessel. Preventing air infiltration in the flare stack and header system. Stop flame propagation and prevent possible flame flashback. Quenching possible flame with a barrier of water. Acts as a large check valve so that gas cannot travel upstream for any reason. Dis-entrain liquid droplets. Maintains a positive pressure on the upstream system. 13
- 14. Molecular Seal Installed just below the flare tip flange. Force the gas travelling up the stack to make a 180° turn down then it must turn again to go up to the flare tip. Light gases collected at the top of the seal creating a barrier to any oxygen. Considerably larger and more expensive than velocity seals. Also collects liquids which can freeze in cold environments. Velocity Seal A cone or chevron, located inside the flare tip just above the flare tip flange. Breaks the flow of air into the system by disrupting the flow passage of the air to the wall and creates a velocity differential barrier in the purge gas. Doesn’t collect liquids or require draining, making it suitable for cold weather environments. They are less expensive than a molecular seal. Reduces the operating purge gas requirements. Gas Seals PROCESS DESCRIPTION 14
- 15. PROCESS DESCRIPTION BurnerTip Give environmentally acceptable combustion of the vent gas. Keep an optimum burn and control over all flow rates. The tip does not come into contact with the flame making the tips reliable and long lasting. The maximum and minimum capacity of a flare to burn a flared gas with a stable flame is a function of tip design. With modern flame holder designs, a stable flame can be achieved over gas exit velocity. 15
- 16. PROCESS DESCRIPTION 16 Pilot Burners Flame and pilot gas supply should be stable and continuous (also required by EPA regulations). Positioned around the outer perimeter of the flare tip . The number and duty of the pilot burners should be determined by the size of the flare and its application. Maintenance or replacement is not possible while the flare is in operation. Features three main components (mixer, orifice and burner nozzle). Reliable operation of the pilot burner is governed by achieving the right air fuel ratio. Withstand extreme weather conditions (along with direct flame from the flare tip). Ignited by an ignition source system.
- 17. High velocity steam injection nozzles. Positioned 1-15 around the outer perimeter of the flare tip. Increase gas turbulence in the flame boundary zones, drawing in more combustion air and improving combustion efficiency. Reducing the temperature in the core of the flame and suppress thermal cracking. To optimize steam usage infrared sensors are available that sense flare flame characteristics and adjust the steam flow rate automatically to maintain smokeless operation. Automatic control, based on flare gas flow and flame radiation, gives a faster response to the need for steam and a better adjustment of the quantity required. Disadvantages of steam usage are the increased noise and cost. Steam Jets PROCESS DESCRIPTION 17
- 18. PROCESS DESCRIPTION Controls Flame Front Generator Electronic Spark Ignition Ballistic Pellet Ignition Originally developed for offshore use. Instead of a fireball, it comprises a launching cabinet containing the ignition pellets. The fuse is released and the pellet explodes producing a shower of sparks over the flare tip thereby lighting the gas. Found in production facilities but not very often in process plants. Mixes plant or air with pilot ignition gas at grade and fills a line running up to the pilot burner. At grade an electrically generated spark ignites the mixture and the resulting fireball travels up to the pilot and ignites the gas. Disadvantage is that moisture or solids can block the fireball from making it up to the pilot. Gas/air mixture could get too lean or too rich and the spark doesn’t ignite. Advantage is that all items need maintenance are at grade and can be serviced while the flare is in operation. 18 Becoming the preferred system. Two basic forms of these systems; high energy (HE) and high tension (HT). The most common and primary method of pilot ignition for newer systems. HEI systems use an electric probe inserted near the pilot burner to create a spark and ignite the pilot fuel gas/air mixture. A capacitor is used to discharge the spark across a low tension spark plug in a short time and with a high current. Full automatic systems.
- 19. REFERENCES A L Ling, July 2007. FLARE SELECTION AND SIZING (ENGINEERING DESIGN GUIDELINE), Johor Bahru: KLMTechnology Group. Leslie B. Evans, William M. Vatavuk, Diana K. Stone, Susan K. Lynch, Richard F. Pandullo, September 2000. VOC Destruction Controls, North Carolina, Durham: Office of Air Quality Planning and Standards, U.S Environmental ProtectionAgency. Ludwig, Ernest E., 1999. APPLIED PROCESS DESIGN FORCHEMICAL AND PETROCHEMICAL PLANTS, Volume 1,Third Edition, United States of America: Gulf Publishing Company. Charles E. Baukal, JR., 2014. The John Zink Hamworthy Combustion Handbook, Second Edition:Volume 3 – Applications, Boca Raton, Fort Lauderdale, USA:Taylor & Fransic Group LLC. Nicholas P. Cheremisinoff, Apr 1, 2013. INDUSTRIALGAS FLARING PRACTICES, New Jersey USA: John Wiley & Sons Cooperation. 19
- 20. THANKYOU 20