Natural gas liquefying system by vurtue of double-stage mixed-refrigerant circulation

Abstract

The invention discloses a natural gas liquefying system by virtue of double-stage mixed-refrigerant circulation. The liquefying system comprises a precooling cold box, a deep-cooling cold box, a precooling mixed-refrigerant refrigeration circulating mechanism and a deep-cooling mixed-refrigerant refrigeration circulating mechanism. The natural gas liquefying system has the advantages that deep-cooling circulation adopts two-stage refrigeration, so that the refrigerating efficiency is increased; the double-stage mixed-refrigerant circulation is adopted, so that the adjusting range of components of a precooling refrigerant and a deep-cooling refrigerant is wide, and the refrigerant proportioning is convenient; the refrigerating temperature of the precooling refrigerant circulation can be correspondingly adjusted according to the natural gas components and the ambient temperature, the adaptability is strong; in double-stage mixed-refrigerant circulation, the refrigerating loads in two circulations can be reasonably distributed, and the manufacturing of a precooling heat exchanger and a deep-cooling plate-fin heat exchanger is convenient.

Description

technical field [0001] The invention relates to a two-stage mixed refrigerant cycle natural gas liquefaction system, which belongs to the technical field of natural gas liquefaction. Background technique [0002] At present, large-scale natural gas liquefaction devices mainly adopt propane precooled mixed refrigerant liquefaction process, cascade liquefaction process and DMR liquefaction process developed by Shell. The propane pre-cooling mixed refrigerant liquefaction process uses pure propane as the pre-cooling refrigerant, the pre-cooling temperature is fixed, the adaptability to the ambient temperature and natural gas is poor, and the propane pre-cooling system has a large number of heat exchangers and the system is complicated; The three sets of refrigeration systems in the cascade liquefaction process use propane, ethylene and methane as refrigerants respectively, which have high requirements on the purity of the refrigerants, the process of the liquefaction process is...

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Problems solved by technology

The propane pre-cooling mixed refrigerant liquefaction process uses pure propane as the pre-cooling refrigerant, the pre-cooling temperature is fixed, the adaptability to the ambient temperature and natural gas is poor, and the propane pre-cooling system has a large number of heat exchangers and the system is complicated; The three sets of refrigeration systems in the cascade liquefaction process use propane, ethylene and methane as refrigerants respectively, which have high requirements on the purity of the refrigerants, the process of the liquefaction process is complex, the number of equipment is large, and the investment is large; the DMR process developed by Shell Company Both the pre-cooling cycle and the deep-cooling cycle use coiled tube heat exchangers, and the pre-cooling cycle uses two coiled tube heat exchangers in series. The heat exchanger has few manufacturers, high cost, and long delivery cycle. Shell company The pre-cooling is only throttling under two pressures, the temperature difference of the heat exchanger is large, and the overall energy consumption is high

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