Robust recovery of natural gas letdown energy for small scale liquefied natural gas production
a technology of letdown energy and natural gas, applied in the field of apparatus and method for liquefaction of natural gas, can solve the problems of limited lng production capacity, low thermodynamic efficiency, and yield significant fluctuations, and achieve the effect of reducing costs, maximizing utilization of letdown energy, and maintaining production
Inactive Publication Date: 2018-02-08
LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
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Benefits of technology
The present invention presents flexible solutions for small scale LNG (liveried natural gas) schemes. By combining natural gas turbo-expansion for pre-cooling and a refrigeration cycle, the invention can maintain production while reducing costs, even when the letdown capacity varies. The refrigeration cycle can use either a nitrogen refrigeration cycle or a mixed refrigerant refrigeration cycle. One specific feature is a refrigerant by-pass that removes a portion of refrigerant coolant from the heat exchanger to reduce the amount of cooling provided to the boosted pressurized natural gas stream.
Problems solved by technology
In the latter case, the plant does not require an external source of energy, but its major drawback is that the ratio of expanded natural gas flow over the LNG production is very high (usually 6 to 10) leading to a limited LNG production capacity due to low thermodynamic efficiency.
Fluctuations in the feed pressure, return pressure, or flowrate yields significant fluctuations in the operation of the liquefier.
Method used
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[0036]While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.
[0037]FIG. 1 is an example of a typical small LNG scheme that utilizes a nitrogen cycle (N2 compressor and two turbine boosters) in a closed loop 10. Natural gas NG is cooled and condensed into LNG in passages separate and adjacent to the N2 in the heat exchanger 40. In most small scale LNG plants, heavy hydrocarbons (HHC), which freeze at LNG temperatures, condense and are removed from the natural gas via a knock out drum 50. The specific power of such plant is highly dependent on the natural gas feed pressure and usually varies between 450 and 550 kWh / ton of LNG produced.
[0038]In one embodiment of the present invention, the ...
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A method for liquefaction of natural gas using refrigeration from a combination of sources including a refrigeration cycle and letdown energy of natural gas is provided. The natural gas to be liquefied (LNG) is boosted in pressure using a booster that is powered by expansion of a portion of the natural gas flow from the booster through a first natural gas turbine. A second flow of natural gas is expanded in a second natural gas turbine, and the resulting expanded stream, along with the natural gas expanded in the first natural gas turbine, are warmed against the natural gas to be liquefied. The flow rate of the natural gas in the second natural gas turbine is decoupled from the booster, thereby allowing for variation in flow rates and pressures while maintaining a constant production of LNG.
Description
CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a non-provisional application of U.S. Provisional Applicant No. 62 / 371,497, filed Aug. 5, 2016, which is herein incorporated by reference in its entirety.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to an apparatus and method for liquefaction of natural gas using available letdown energy of a high pressure natural gas pipeline. More specifically, embodiments of the present invention are related to liquefying a natural gas stream utilizing a combination of natural gas letdown and a nitrogen refrigeration cycle that provide for increased flexibility and efficiencies.BACKGROUND OF THE INVENTION[0003]Many locations utilize a high pressure (transmission) network and a lower pressure (distribution) network to supply natural gas through an area. The transmission network acts as a freeway to send the gas to the general area, while the distribution network acts as the roads to send the gas to the individu...
Claims
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Login to View More IPC IPC(8): F25J1/00F25J1/02
CPCF25J1/005F25J1/0022F25J2220/40F25J1/0254F25J1/0203F25J1/0037F25J1/0072F25J1/0204F25J1/0232F25J1/0288F25J1/0292F25J1/0294F25J2210/06F25J2220/64F25J2230/20F25J2230/30F25J2230/32F25J2245/42F25J2270/06F25J2270/16C01B3/56C01B2203/042C01B2203/061
Inventor FARGES, ORIANETURNEY, MICHAEL A.DE BESOMBES, LOUIS
Owner LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE