Natural gas expansion

Expansion turbines are related in many design features to the centrifugal compressor. The key exception being that the turbine receives a high pressure gas for expansion and power recovery to a lower pressure and is usually accompanied by the recovery of the energy from the expansion. For example, applications can be (1) air separation plants (2) natural gas expansion and liquefaction (for gas let-down in pipeline transmission to replace throttle valves where no... 

Figure 6.35 Pressurized synchronous generator powered by a four-cylinder reciprocating natural gas expansion engine.

Schematic diagram of a natural gas expansion station. preheater for pressure relief valve...

Figure 9.9 shows a natural gas expansion unit with an integrated turbine-generator set. 

Figure 9.8 Gas expansion turbine (left side) in a natural gas expansion station, coupled with an explosion protected 300kWasynchronous generator. The classic pressure relief valve is shown at the right side (according to [17] and [22]).

Operation experience with the natural gas expansion plant of EWV Stolberg... 

Condensable hydrocarbon components are usually removed from gas to avoid liquid drop out in pipelines, or to recover valuable natural gas liquids where there is no facility for gas export. Cooling to ambient conditions can be achieved by air or water heat exchange, or to sub zero temperatures by gas expansion or refrigeration. Many other processes such as compression and absorption also work more efficiently at low temperatures. 

The pressure used in producing gas wells often ranges from 690— 10,300 kPa (100—1500 psi). The temperature of the inlet gas is reduced by heat-exchange cooling with the gas after the expansion. As a result of the cooling, a liquid phase of natural gas liquids that contains some of the LPG components is formed. The liquid is passed to a set of simple distillation columns in which the most volatile components are removed overhead and the residue is natural gasoline. The gas phase from the condensate flash tank is compressed and recycled to the gas producing formation. 

Condensable Hquids also are recovered from high pressure gas reservoirs by retrograde condensation. In this process, the high pressure fluid from the reservoir produces a Hquid phase on isothermal expansion. As the pressure decreases isotherm ally the quantity of the Hquid phase increases to a maximum and then decreases to disappearance. In the production of natural gas Hquids from these high pressure wells, the well fluids are expanded to produce the optimum amount of Hquid. The Hquid phase then is separated from the gas for further processing. The gas phase is used as a raw material for one of the other recovery processes, as fuel, or is recompressed and returned to the formation. 

Pressures Turboexpanders ean be designed to operate at up to 3,000 psi and higher inlet pressures as required by eonditions. Expansion pressure ratios ean also be adjusted for eaeh proeess over a wide range. A majority of effieient expansion ratios are below 5 1, although pressure ratios up to 10 1 ean be aeeommodated with reasonable effieieney. Smaller, lower pressure units are popular for air separation and helium liquefaetion. Intermediate pressure (100-1,000 psi) and high pressure expanders (1,000-3,000 psi) are widely used in natural gas proeessing and industrial gas liquefaetion. 

As stated earlier, turboexpanders are normally used in cryogenic processes to produce isentropic expansion to cool down the process gas. Two common applications are natural gas processing plants and chemical plants. In natural gas processing plants, turboexpanders are installed to liquify heavier hydrocarbon components and produce lean natural gas with specified dew point limits to meet required standards. 

Expansion turbines—three in Phase 1 and two in Phase 2—cool the gas to -90°C, at which point more liquid drops out in another separator. In this system, the cold methane gas emerges from the expansion turbines at a reduced pressure of 325 psi and is recirculated to the original heat exchanger to reduce the temperature of the natural gas entering the plant. 

The methane warms to 10°C. It then passes through the booster compressors on the expansion turbine shaft, increasing in pressure from 325 psi to 375 psi before being introduced into other gas compressors tliat boost the pressure back up to 600 psi. This is the pressure needed for reintroduction of the natural gas back into the TransCanada pipeline. This 50 psi boost, which makes use of available energy from the expansion turbines, provides a significant savings in electrical power. 

Today, a network of more than 300,000 miles of interstate natural gas pipelines sei"vcs markets across the U.S, Construction of this network began in the 1920s, but large-scale expansion was limited by the technology of the day, the Great Depression and, finally. World War II. 

Process refrigeration is used at many different temperature levels to condense or cool gases, vapors, or liquids. Refrigeration is necessary when the process requires cooling to a temperature not reliably available from the usual water service or other coolant source, includingjoule-Thompson, or polytropic expansion of natural gas or process system vapors. 

Doane, R. C., Recovering Tow Eevel Heat via Expansion of Natural Gas, Chem. Eng, McGraw-Hill, Inc., p. 89, April 2, (1984). All rights reserved. 

Adamantane and diamantane are usually the dominant diamondoids found in petroleum and natural gas pipeline deposits [74, 75]. This is because diamondoids are soluble in light hydrocarbons at high pressures and temperatures. Upon expansion of the petroleum fluid coming out of the underground reservoir and a drop in its temperature and pressure, diamondoids could deposit. 

NITECH A cryogenic process for removing nitrogen from natural gas, mainly methane. The high-pressure gas is liquified by expansion and then fractionated. The essential feature is the use of an internal reflux condenser within the fractionating column. Developed by BCCK Engineering and demonstrated on a full-scale plant in Oregon in 1994. 

Once the well is drilled, the oil is either released under natural pressure or pumped out. Normally crude oil is under pressure (were it not trapped by impermeable rock it would have continued to migrate upward), because of the pressure differential caused by its buoyancy. When a well bore is drilled into a pressured accumulation of oil, the oil expands into the low-pressure sink created by the well bore in communication with the earth s surface. As the well fills up with fluid, a back pressure is exerted on the reservoir, and the flow of additional fluid into the well bore would soon stop, were no other conditions involved. Most crude oils, however, contain a significant amount of natural gas in solution, and this gas is kept in solution by the high pressure in the reservoir. The gas comes out of solution when the low pressure in the well bore is encountered and the gas, once liberated, immediately begins to expand. This expansion, together with the dilution of the column of oil by the less dense gas, results in the propulsion of oil up to the earth s surface As fluid withdrawal continues from the reservoir, the pressure within the reservoir gradually decreases, and the amount of gas in solution decreases. As a result, the flow rate of fluid into the well bore decreases, and less gas is liberated. The fluid may not reach the surface, so that a pump (artificial lift) must... 

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