Feed gas pretreatment system The process method selected for the process flow of feed gas pretreatment system has the following characteristics: (1) Compared with MEA method, MDEA method has the characteristics of less foaming, less corrosion and less amine loss. (2) The unit adopts MDEA wet decarburization, and there is no consumption of regeneration gas. (3) MDEA circulating pump adopts high-speed single-stage centrifugal pump, which has high reliability, low power consumption and less maintenance. (4) Molecular sieve adsorption can be used for deep dehydration, and it still has high adsorption characteristics even under low water vapor partial pressure. (5) Using activated carbon to remove heavy hydrocarbons can basically remove aromatic hydrocarbons and C6 + heavy hydrocarbons, completely solve the problem of low-temperature freezing and blocking, and ensure long-term operation. (6) Mercury reacts with sulfur on sulfur impregnated activated carbon to produce mercury sulfide, which is adsorbed on activated carbon to achieve the purpose of mercury removal. Using sulfur impregnated activated carbon to remove mercury has low price. (7) The precision filter element can filter the molecular sieve and activated carbon dust to 5 μm below. Liquefaction and refrigeration system The selected process method of liquefaction and refrigeration system is MRC (mixed refrigerant) cycle refrigeration, which is characterized by: (1) Low energy consumption. This method has the lowest energy consumption among the commonly used refrigeration methods, making the product price competitive in the market. (2) The refrigerant proportioning system is relatively independent of the circulating compression system. During operation, the proportioning system replenishes refrigerant to the circulating compression system to maintain the stable working condition of the circulating compression system; After the unit is shut down, the proportioning system can store the refrigerant from the high-pressure part of the compression system without discharging the refrigerant. The purpose of doing this: first, save refrigerant, and second, shorten the time of next startup. The start-up time of liquefaction unit is less than 5 hours. (3) The volume and pressure of the refrigerant system shall be reasonably designed. After the unit is shut down, considering that all refrigerants are reheated to normal temperature and pressure is balanced, the system can still contain all refrigerants, ensure that all parts of the system are not overpressured and vented, and allow the refrigerant to remain in the system for a long time. (4) All valves of the low-temperature liquefaction unit are set outside the cold box and are welded to reduce leakage points and facilitate valve maintenance. There is no flange connection in the cold box to minimize possible leakage points in the cold box. Multi point thermometer and gas probe are arranged to monitor the possible leakage in the cold box in real time. (5) Advanced technology is widely used in cold box design. Complete frame, pipeline and local stress analysis will be carried out to ensure the reliability of cold box from the design quality. Firstly, the professional 3D Design Software Solidworks is used to establish the 3D model of cold box frame and pipeline equipment; Then, cosmos is used to analyze the stress of the frame; In order to meet the flexible design of low-temperature pipeline, professional pipeline stress analysis software CAESAR II is used for pipeline stress analysis; When encountering the problem of opening on the pipeline or even large opening, in order to ensure that the stress at the opening is within the allowable range specified in the national standard, ANSYS software will be used for local stress analysis. See Chapter 14 for details.