Natural Gas Industry AECH 1103 PDF

Topic 3 Natural Gas Industry AECH 1103 Industrial Process Overview  Introduction There are primarily three sources for “raw” natural gas. These are recognized as: Crude oil wells Gas wells Condensate wells Natural gas that comes along...

Topic 3 Natural Gas Industry AECH 1103 Industrial Process Overview  Introduction There are primarily three sources for “raw” natural gas. These are recognized as: Crude oil wells Gas wells Condensate wells Natural gas that comes along with crude oil is normally known as associated gas. It can exist separately from crude oil, forming what is known as a gas cap or dissolved in the crude oil. Natural gas from gas wells and from condensate wells-in which there is little or no oil- is termed, on the other hand non-associated or free gas. Gas wells differ from condensate wells, since the former type produces raw natural gas only, while the latter one produces natural gas along with very light liquid hydrocarbon known as natural gasoline because it has a high octane number. 2  Natural Gas Composition Raw natural gas consists primarily of methane. It also contains varying amounts of: Heavier gaseous hydrocarbon: ethane (C2H6), propane (C3H8), normal butane (n-C4H10), isobutane (i-C4H10), pentanes and even higher molecular weight hydrocarbons. Acid gases: carbon dioxide (CO2), hydrogen sulfide (H2S) and mercaptans such as methanethiol (CH3SH) and ethanethiol (C2H5SH). Other gases: nitrogen (N2) and helium (He). Water: water vapor and liquid water. Liquid hydrocarbons: perhaps some natural gas condensate (also referred to natural gasoline) and/or crude oil. Mercury: very small amounts of mercury primarily in elemental form, but chlorides and other species are possibly present. 3  Natural Gas Composition Constituent Typical % of Chemical Heating Value gas Structure (BTU/lb) Methane 70-95 CH4 23,571 Ethane 2.5-12 C2H6 21,876 Propane 1-6 C3H8 21,646 Butanes* 0.2-2.5 C4H10 21,293 Pentane 0.2-1 C5H12 20,877 *Butane includes iso and N varieties Don’t forget H2O, CO2, H2S, N2, O2 in small amounts 4 Natural Gas Composition LNG — Liquefied Natural Gas, is gas that has been Liquified at very low temp. and is transported as a liquid. NGL — Natural Gas Liquids,are heavier gaseous hydrocarbons that are included in the raw natural gas stream LPG — Liquefied Petroleum Gas gas that is liquid near room temperature and at some extent of pressure. 5  Advantages of Natural Gas Gas is the cleanest-burning hydrocarbon, producing around half the carbon dioxide (CO2) and just one tenth of the air pollutants of coal when burnt to generate electricity (less pollution). Does not produce ashes after energy release. Has high heating value of 24,000 Btu per pound. A gas-fired power station takes much less time to start and stop than a coal-fired plant. This flexibility makes it a good partner to renewable sources of energy such as solar and wind, which are only available when the sun shines and the wind blows. It is cheaper to produce gas than coal. The most efficient gas-fired plant has investment costs of $1,100 per kilowatt, according to the IEA, compared with $3,700 for the most efficient coal-fired plant. 6  Gas Usage Electricity Generation: Modern gas-fired power plants are: cleaner efficient Larger and cheaper to build Less noise Less pollution Petrochemical, Steel and Fertilizer Ethylene and propylene → Polyethylene, PVC plastics, antifreeze, paints Ammonia → Fertilizer Transport Fuel Residential Gas Markets 7  Natural Gas Processing The raw natural gas must be purified to meet the quality standards specified by the major pipeline transmission and distribution companies. In general, the standards specify that the natural gas: 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. 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 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 Contain no more than trace amounts of components such as hydrogen sulfide, carbon dioxide, mercaptans, nitrogen, and water vapor. Maintain mercury at less than detectable limits (approximately 0.001 ppb by volume) primarily to avoid damaging equipment in the gas processing plant 8  Natural Gas Processing Natural gas processing and the removal of various components from it tend to involve the most complex and expensive processes. All of the H2S and most of the water vapor, CO2, and N2 must be removed first. The separation of the hydrocarbons, known as NGL (C2 plus) is carried out next producing methane as the sole product commercially marketed as natural gas. A system for natural gas processing my basically involve two main stages, apart from the oil and gas condensate removal step. Stage I and is known as gas treatment or gas conditioning Stage II and is known as gas processing 9 Natural Gas Processing 10  Natural Gas Processing Gas sweetening Gas dehydration Recovery and extraction of NGL (C2 plus) Fractionation of NGL into individual products, which may include: ethane, propane, butane, isobutene, and natural gasoline. 11  Natural Gas Processing Natural gas that contains more than 5.7 milligrams of H2S per one cubic meter of natural gas is “sour”. However, if it contains only CO2 and no other sulfur compounds, it is called “sweet” gas. It is usually desirable to remove both H2S and CO2 to prevent corrosion problems in the first place and to increase the heating value of the natural gas by eliminating CO2. The methods used for natural gas sweetening can be classified under three categories: Reactive chemical solvents Physical methods Other methods 12 Classification of Gas Sweetening Processes 13  Natural Gas Processing Amine treating unit is the most widely used process. Based on the use of polymeric membranes to dehydrate and separate the carbon dioxide and hydrogen sulfide Sulfur recovery unit which converts the hydrogen sulfide in the acid gas into elemental sulfur Claus process Tail gas treating unit (TGTU) to recover and recycle residual sulfur-containing compounds back into the Claus unit. 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 14  Natural Gas Processing Water vapor removal using either: Glycol dehydration → Triethylene glycol (TEG) Pressure Swing adsorption (PSA) Mercury removal using adsorption processes. Nitrogen removal: Cryogenic process: using low temperature distillation. This process can be modified to also recover helium, if desired. Absorption process: using lean oil or a special solvent as the absorbent. Adsorption process using activated carbon or molecular sieves as the adsorbent. This process may have limited applicability (loss of butanes and heaver hydrocarbons). 15  Natural Gas Processing NGL recovery by using cryogenic low temperature distillation process involving expansion of the gas through a turbo-expander purified sales gas which is pipelined to the end-user markets NGL fractionation consist of three distillation towers in series: dethanizer → ethane depropanizer → propane debutanizer → normal and isobutane and C5+ mixture The recovered streams of propane, butanes and C5+ are each "sweetened” to convert undesirable mercaptans into disulfides and, along with the recovered ethane, are the final NGL by-products from the gas processing plant. 16  What is LNG? Natural Gas LNG is natural gas that has been cooled that it LNG condenses to a liquid Temperature -256oF (-161oC) Atmospheric pressure. Volume is reduced 600 times Thus, economical to transport locally and between continents in specially designed ocean vessels Liquefaction technology makes natural gas available throughout the world 17  LNG Properties Non-toxic and non-corrosive Colorless and odorless Can not ignite Contact is hazardous due to extremely cold temperature. 18  Major LNG Exporters in 2021 https://www.statista.com/chart/27839/biggest-liquefied-natural-gas-exporters/ 19  Qatar’s North Fields Proven reserves of more than 900 trillion cubic feet of natural gas Approximately 15% of the world’s total proven gas reserves The largest non-associated natural gas field in the world 20 LNG Process 1) Exploration and Production 2) Gas treatment and purification 3) Liquefaction process 4) LNG transportation 5) LNG storage 6) Re-gasification and Quality adjustment 21  Gas to liquid (GTL) Gas-to-liquids (GTL) technology converts natural gas – the cleanest-burning fossil fuel – into high-quality liquid products that would otherwise be made from crude oil. These products include transportation fuels, motor oils and the ingredients for everyday necessities like plastics, detergents and cosmetics. GTL products are colorless and odorless. They contain almost none of the impurities – Sulphur, aromatics and nitrogen – that are found in crude oil. 22  GTL Production The GTL process consists of three stages: In the first stage synthesis gas, a mixture of hydrogen and carbon monoxide, is manufactured from natural gas by partial oxidation. Impurities are removed from the syngas. A second stage (Fischer–Tropsch process) converts the synthesis gas into liquid hydrocarbons using a catalyst. In this stage, a liquid is formed which looks and feels like wax at room temperature. The final stage is cracking and isomerization, which “tailors” the molecule chains into products with desired properties. This yields high-quality liquids such as diesel, kerosene and lubricant oil. https://www.youtube.com/watch?v=rKbLg3FAk4I 23