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Encyclopedia > Natural gas processing
A natural gas processing plant
A natural gas processing plant

Natural gas processing plants are used to purify the raw natural gas extracted from underground gas fields and brought up to the surface by gas wells. The processed natural gas, used as fuel by residential, commercial and industial consumers, is almost pure methane and is very much different from the raw natural gas. Image File history File links NaturalGasProcessingPlant. ... Image File history File links NaturalGasProcessingPlant. ... Natural gas is a gaseous fossil fuel consisting primarily of methane. ... Natural gas rig Oil and natural gas are produced by the same geological process: anaerobic decay of organic matter deep under the Earths surface. ... An oil well is a term for any perforation through the Earths surface designed to find and release both petroleum oil and gas hydrocarbons. ... Fuel is any material that is capable of releasing energy when its chemical or physical structure is changed or converted. ...


Raw natural gas typically consists primarily of methane (CH4), the shortest and lightest hydrocarbon molecule. It also contains varying amounts of: Methane is a significant and plentiful fuel which is the principal component of natural gas. ... Hydrocarbons are refined at oil refineries and processed at chemical plants A hydrocarbon is a chemical compound that consists only of the elements carbon (C) and hydrogen (H). ...

The raw natural gas must be purified to meet the quality standards specified by the major pipeline transmission and distribution companies. Those quality standards vary from pipeline to pipeline and are usually a function of a pipeline system’s design and the markets that it serves. In general, the standards specify that the natural gas: Ethane is a chemical compound with chemical formula C2H6. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3. ... Butane is an alkane hydrocarbon with the molecular formula C4H10. ... Pentane (also known as amyl hydride or skellysolve) is an alkane hydrocarbon with the chemical formula CH3(CH2)3CH3. ... The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... Acid gas or Sour gas, also sour acid gas or acid sour gas, is natural gas which contains up to 20% hydrogen sulfide contaminant by weight and the aromatic hydrocarbons benzene, toluene, mixed xylenes and ethylbenzene. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs and flatulence. ... In chemistry, thiols (formerly known as mercaptans) are those compounds which contain the thiol group -SH attached to a carbon atom. ... Methanethiol (also known as methyl mercaptan) is a colorless gas with a smell like rotten cabbage. ... Ethanethiol, also known as ethyl mercaptan, is an organic compound used as an odorant in propane. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... Impact of a drop of water. ... Water vapor, also aqueous vapor, is the gas phase of water. ... Natural Gas Condensate is a natural gas by-product. ... Pumpjack pumping an oil well near Sarnia, Ontario Petroleum (from Greek petra – rock and elaion – oil or Latin oleum – oil ) or crude oil is a thick, dark brown or greenish liquid. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Atomic mass 200. ...

  • Be within a specific range of heating value (caloric value). For example, in the United States, it should be about 1,035 ± 5% Btu per cubic foot of gas at 1 atmosphere and 60 °F (41 MJ ± 5% per cubic metre of gas at 1 atmosphere and 0 °C).
  • Be delivered at or above a specified hydrocarbon dew point temperature (below which some of the hydrocarbons in the gas might condense at pipeline pressure forming liquid slugs which could damage the pipeline).
  • Be free of particulate solids and liquid water to prevent erosion, corrosion or other damage to the pipeline.
  • Be dehydrated of water vapor sufficiently to prevent the formation of methane hydrates within the gas processing plant or subsequently within the sales gas transmission pipeline.[2][3]
  • Contain no more than trace amounts of components such as hydrogen sulfide, carbon dioxide, mercaptans, nitrogen, and water vapor.
  • Maintain mercury at less than detectible limits (approximately 0.001 ppb by volume) primarily to avoid damaging equipment in the gas processing plant or the pipeline transmission system from mercury amalgamation and embrittlement of aluminum and other metals.[1][4][5]

Contents

The British thermal unit (BTU) is a non-metric unit of energy, used in the United States and, to a certain extent, the UK. The SI unit is the joule (J), which is used by most other countries. ... It has been suggested that Thousand Cubic Feet be merged into this article or section. ... A megajoule (abbreviation: MJ) is a unit of energy equal to 1000000 joules. ... The cubic meter (symbol m³) is the SI derived unit of volume. ... The hydrocarbon dew point is the temperature (at a given pressure) at which the hydrocarbon components of any hydrocarbon-rich gas mixture, such as natural gas, will start to condense out of the gaseous phase. ... Parts per billion (ppb) is a measure of concentration that is used where low levels of concentration are significant. ...

Types of raw natural gas wells

Raw natural gas comes primarily from any one of three types of gas wells: crude oil wells, gas wells, and condensate wells. An oil well is a term for any perforation through the Earths surface designed to find and release both petroleum oil and gas hydrocarbons. ...


Natural gas that comes from crude oil wells is typically termed associated gas. This gas can exist separate from the crude oil in the underground formation, or dissolved in the crude oil.


Natural gas from gas wells and from condensate wells, in which there is little or no crude oil, is termed non-associated gas. Gas wells typically produce only raw natural gas, while condensate wells produce raw natural gas along with a very low density liquid hydrocarbon called natural gas condensate (sometimes also called natural gasoline or simply condensate.


Raw natural gas can also come methane deposits in the pores of coal seams. Such gas is referred to as coalbed gas and it is also called sweet gas because it is relatively free of hydrogen sulfide.


Description of a natural gas processing plant

There are a great many ways in which to configure the various unit processes used in the processing of raw natural gas. The block flow diagram below is a generalized, typical configuration for the processing of raw natural gas from non-associated gas wells. It shows how raw natural gas is processed into sales gas pipelined to the end user markets.[6][7][8][9][10] It also shows how processing of the raw natural gas yields these byproducts: In manufacturing, a unit process is single component part of the end-to-end manufacturing process that transforms raw materials into finished goods. ... We dont have an article called Process flow diagram Start this article Search for Process flow diagram in. ...

  • Natural gas condensate
  • Sulfur
  • Ethane
  • Natural gas liquids (NGL): propane, butanes and C5+ (which is the commonly used term for pentanes plus higher molecular weight hydrocarbons)

Raw natural gas is commonly collected from a group of adjacent wells and is first processed at that collection point for removal of free liquid water and natural gas condensate. The condensate is usually then transported to an oil refinery and the water is disposed of as wastewater. General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ...


The raw gas is then pipelined to a gas processing plant where the initial purification is usually the removal of acid gases (hydrogen sulfide and carbon dioxide). There a many processes that are available for that purpose as shown in the flow diagram, but amine treating is the most widely used process. Amine gas treating is a means to remove organosulfur and other undesirable compounds from acid gas by contacting the gas with amine. ...


The acid gases removed by amine treating are then routed into a sulfur recovery unit which converts the hydrogen sulfide in the acid gas into elemental sulfur. There are a number of processes available for that conversion, but the Claus process is by far the one usually selected. The residual gas from the Claus process is commonly called tail gas and that gas is then processed in a tail gas treating unit (TGTU) to recover and recycle residual sulfur-containing compounds back into the Claus unit. Again, as shown in the flow diagram, there are a number of processes available for treating the Claus unit tail gas. The final residual gas from the TGTU is incinerated. Thus, the carbon dioxide in the raw natural gas ends up in the incinerator flue gas stack. This article needs to be cleaned up to conform to a higher standard of quality. ... Flue gas stack at GRES-2 Power Plant in Ekibastus, Kazakhstan is 420 meters tall[1] A Flue gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. ...


The next step in the gas processing plant is to remove water vapor from the gas using the either regenerable absorption in liquid triethylene glycol (TEG)[3] or a pressure swing adsorption (PSA) unit which is regenerable adsorption using a solid adsorbent.[11] Another newer process using membranes may also be considered. Look up absorption in Wiktionary, the free dictionary. ... Diethylene glycol (DEG, 3-oxa-1,5-pentanediol, diglycol, ethylene diglycol, or dihydroxy diethyl ether) is a diol, an alcohol with two -OH groups, a dimer of ethylene glycol. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... Membrane operation or membrane process is considered like an unit operation in chemical engineering. ...


Mercury is then removed by using adsorption processes (as shown in the flow diagram) such as activated carbon or regenerable molecular sieves.[1] Activated carbon from a water filter used for carbon filtering in powder and block form Activated carbon, also called activated charcoal or activated coal, is a general term which covers carbon material mostly derived from charcoal. ... A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. ...


Nitrogen is next removed and rejected using one of the three processes indicated on the flow diagram:

  • Cryogenic process[12] using low temperature distillation. This process can be modified to also recover helium, if desired.
  • Absorption process[13] using lean oil or a special solvent[14] as the absorbent.
  • Adsorption process using activated carbon or molecular sieves as the adsorbent. This process may have limited applicability because it is said to incur the loss of butanes and heaver hydrocarbons.

The next step is to recover of the natural gas liquids (NGL) for which most large, modern gas processing plants use another cryogenic low temperature distillation process involving expansion of the gas through a turbo-expander followed by distillation in a demethanizing fractionating column.[15][16] Some gas processing plants use lean oil absorption process[13] rather than the cryogenic turbo-expander process. Continuous distillation is a distillation process, which does not require interruption for adding raw material. ... A turboexpander (also referred to as turbo expander, expansion turbine or simply expander) is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is typically used to drive a compressor. ... A fractionating column is an essential item used in the distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in their volatilities. ...


The residue gas from the NGL recovery section is the final, purified sales gas which is pipelined to the end-user markets.


The recovered NGL stream is processes through a fractionation train consisting of three distillation towers in series: a dethanizer, a depropanizer and and a debutanizer. The overhead product from the deethanizer is ethane and the bottoms are fed to the depropanizer. The overhead product from the depropanizer is propane and the bottoms are fed to the debutanizer. The overhead product from the debutanizer is a mixture of normal and iso-butane, and the bottoms product is a C5+ mixture. The recovered streams of propane, butanes and C5+ are each "sweetened" in a Merox process unit to convert undesirable mercaptans into disulfides and, along with the recovered ethane, are the final NGL by-products from the gas processing plant. Merox is short for Mercaptan oxidation. ... In chemistry, a disulfide is an ion formed by sulfur atoms. ...

Image File history File links NatGasProcessing. ...

External links

The University of Calgary is a public university located in the north-western quadrant of Calgary, Alberta, Canada. ... The AP 42 Compilation of Air Pollutant Emission Factors, was first published by the U.S. Public Health Service in 1968. ... The United States Department of Transportation (DOT) is a Cabinet department of the United States government concerned with transport. ...

References

  1. ^ a b c Mercury Removal from Natural Gas and Liquids UOP website page
  2. ^ Dehydration of Natural Gas by Prof.Jon Steiner Gudmundsson, Norwegian University of Science and Technology
  3. ^ a b Glycol Dehydration (includes a flow diagram}
  4. ^ Desulfurization of and Mercury Removal From Natural Gas by Bourke, M.J. and Mazzoni, A.F., Laurance Reid Gas Conditioning Conference, Norman, Oklahoma, March 1989.
  5. ^ Using Gas Geochemistry to Assess Mercury Risk, OilTracers, 2006
  6. ^ Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation to Market
  7. ^ Example Gas Plant
  8. ^ From Purification to Liquefaction Gas Processing
  9. ^ Feed-Gas Treatment Design for the Pearl GTL Project
  10. ^ Benefits of integrating NGL extraction and LNG liquefaction
  11. ^ Molecular Sieves (includes a flow diagram of a PSA unit)
  12. ^ Gas Processes 2002, Hydrocarbon Processing, pages 84-86, May 2002 (schematic flow diagrams and descriptions of the Nitrogen Rejection and Nitrogen Removal processes)
  13. ^ a b Market-Driven Evolution of Gas Processing Technologies for NGLs Advanced Extraction Technology Inc. website page
  14. ^ AET Process Nitrogen Rejection Unit Advanced Extraction Technology Inc. website page
  15. ^ Cryogenic Turbo-Expander Process Advanced Extraction Technology Inc. website page
  16. ^ Gas Processes 2002, Hydrocarbon Processing, pages 83-84, May 2002 (schematic flow diagrams and descriptions of the NGL-Pro and NGL Recovery processes)

 
 

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