Method for producing liquefied natural gas

Abstract

The invention provides a process for producing liquefied natural gas, which comprises the following steps of: introducing purified feed gas into a first heat exchanger for precooling; introducing the precooled feed gas into a heavy hydrocarbon separator for gas-liquid separation; introducing the separated gaseous fluid into a second heat exchanger, and liquefying to obtain liquid-state fluid; and depressurizing and throttling to obtain the liquefied natural gas, wherein a refrigeration cycle consists of two independent mixed working medium refrigeration cycles in a high temperature area and a low temperature area; the feed gas can pass through a reversing heat exchanger to enter the first heat exchanger; and the separated heavy hydrocarbons and BOG return to the heat exchanger for reheating. In the process, the energy consumption is low; each mixed working medium refrigeration cycle is controlled by only one throttle valve in a cold box, and the operation is simpler; due to the reversing heat exchanger, the production process is more stable and safe; and the cold quantity of the separated heavy hydrocarbons and BOG is fully recycled and discharged out of the cold box, and the energy consumption is reduced.

Description

technical field [0001] The invention relates to a method for producing liquefied natural gas, in particular to a method for producing liquefied natural gas by using natural gas, coal bed methane or other methane-rich gas as raw materials. Background technique [0002] Liquefied natural gas (LNG) refers to a low-temperature liquid mixture formed by liquefying raw material gas (natural gas, coalbed methane or other methane-rich gas) through pretreatment, purification and removal of impurities, and is liquefied by low-temperature cryogenic methods. It is a clean and efficient energy source. After the combustion of natural gas, the emission of sulfur dioxide and dust is reduced by nearly 100%, the carbon dioxide and nitrogen oxides produced are only 50% and 20% of coal, and the pollution is 1 / 4 of liquefied petroleum gas and 1 / 800 of coal. After natural gas is liquefied, its volume is reduced by about 600 times, which can greatly save storage and transportation space and cost, a...

AI Technical Summary

Problems solved by technology

The mixed working medium refrigeration cycle mainly has the following types: First, the propane precooling plus mixed working medium refrigeration cycle of APCI Company, that is, the PPMR cycle. The precooling process is based on the cooling capacity provided by propane under different evaporation pressures. There are many application examples in the construction of plants and stations, which occupy a very important position. However, due to the fact that propane evaporates and exchanges heat under different pressures to provide cooling capacity, the entire system is relatively cumbersome, and the structure of the propane compressor is also complicated. Compressors have very high requirements; one is the PRICO process invented by BV Company, which is a single-stage mixed refrigeration process. The refrigerant only needs to be compressed by a single compressor, and a single throttle valve is used to throttle the refrigeration. It has less equipment and is easy to operate. Currently The production capacity has reached 1.3 million tons per year. However, the biggest disadvantage of this technology is that the production capacity is limited by the processing capacity of a single compressor. Especially for domestic compressors, if this process is adopted, the processing capacity is small; there is also a It is a double-mixed refrigerant liquefaction process, that is, the DMR process, such as Axens and Shell. The DMR process is similar to the PPMR process, but the propane refrigerant is replaced by a mixed refrigerant, and cooling capacity is provided under different evaporation pressures. The pre-cooling section mixes The refrigerant components are generally ethane, propane, butane

However, this process is similar to the PPMR process, the heat exchange process is cumbersome, the structure of the compressor in the pre-cooling section is complex, and the requirements are high, and domestic equipment is not easy to implement

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