System overview The feed natural gas enters the natural gas pretreatment system after filtration, separation, pressure regulation and metering. After CO2, Hg and H2O are removed, it enters the liquefaction cold box, which is cooled, liquefied and nitrogen removed in the plate fin heat exchanger, and then returns to the cold box to continue cooling, undercooling, throttling and flashing to the flash tank. The separated liquid phase enters the LNG storage tank as LNG products. The main process and technical methods of the unit are: Use MDEA to remove carbon dioxide; Molecular sieve is used to remove trace water; Removal of mercury by sulfur impregnated activated carbon; Use precision filter elements to filter molecular sieve and activated carbon dust Nitrogen removal by low temperature distillation; MRC (mixed refrigerant) cycle refrigeration process is adopted to liquefy all purified natural gas   The process system includes: Metering and separation of raw gas; Pretreatment system (including decarburization, mercury removal, dehydration and dust removal); MR proportioning system and MR compression circulation system; LNG liquefaction system; LNG storage and loading system. Bog recovery system Feed gas filtration separation and pressure regulating unit The feed natural gas from the upstream flows through the pipeline at a pressure of 5.0 ~ 6.0MpaG enters the feed gas inlet filter separator after pressure regulating, and enters the downstream system after separation and metering. The main process equipment is feed gas filter separator, flowmeter, pressure regulator, etc. 2）Design parameters Processing capacity: 20×104Nm3/day Adjustment range: 50% ~ 110% Pretreatment system Feed gas deacidification unit 1）Process description The feed gas from the upstream enters the deacidification gas unit, which uses MDEA solution to remove acid gases such as CO2 and H2S in the feed gas. Natural gas enters from the lower part of the absorber （absorbing tower） and passes through the absorber from bottom to top; The fully regenerated MDEA solution (lean solution) enters from the upper part of the absorber and passes through the absorber from top to bottom. The reverse flow MDEA solution and natural gas are fully contacted in the absorber, the CO2 in the gas is absorbed and enters the liquid phase, and the unabsorbed components are led out from the top of the absorber and enter the decarbonization gas cooler and separator. The gas from the decarbonization gas separator enters the feed gas mercury removal unit, and the condensate goes to the flash tank. The content of CO2 in the treated natural gas is less than 50ppmv. The MDEA solution absorbing CO2 is called rich solution, which is sent to the flash tower, and the natural gas flashed by depressurization is sent to the fuel system. After heat exchange between the flash rich liquid and the solution (lean liquid) flowing out from the bottom of the regeneration tower, raise the temperature to ~ 98 ℃ to the upper part of the regeneration tower, and carry out stripping regeneration in the regeneration tower until the lean degree of the lean liquid reaches the index. The lean liquid out of the regeneration tower passes through the rich and poor liquid heat exchanger and lean liquid cooler. The lean liquid is cooled to ~ 40 ℃, pressurized by the lean liquid pump and enters from the upper part of the absorption tower. The outlet gas at the top of the regeneration tower enters the acid gas separator through the acid gas cooler, the gas from the acid gas separator is sent to the acid gas discharge system, and the condensate is sent to the flash separator after being pressurized by the recovery pump. The heat source of reboiler of regeneration tower is heated by heat transfer oil. The main process equipment of this unit are absorption tower and regeneration tower.