Recovery of BOG gas The BOG of LNG plant actually comes from the feed gas. The venting of BOG caused by improper treatment is the direct loss of the owner and will also lead to environmental protection problems. In general, BOG recovery will be used entirely for the installation of fuel gas, so that BOG can be recycled. The BOG of LNG plant mainly comes from liquefied cold box, LNG storage tank and LNG loading . Cold box BOG recovery The BOG flow of the cold box depends on the temperature of LNG out of the cold box, nitrogen content in LNG and flash pressure. In order to control the flow of BOG in the cold box, the temperature of LNG out of the cold box shall be stable at - 163 ℃ in design and operation; After the nitrogen content in the feed gas is higher than a certain value, a denitrification tower shall be configured. The BOG flashed out in the LNG separator returns to the liquefaction heat exchanger and enters the fuel gas system after recovering the cooling capacity. LNG storage tank bog recovery The BOG flow of LNG storage tank also depends on LNG temperature, nitrogen content in LNG and storage tank pressure. The low-temperature storage tank BOG is reheated by the bog heater, pressurized by the BOG compressor and recovered. LNG loading  bog recovery The BOG on the loading  is also low temperature. After being reheated by the BOG heater, it is pressurized by the BOG compressor and then recovered. The flow of cold box BOG and storage tank bog is relatively stable, while the flow of BOG on the loading  changes greatly with the loading volume, so the BOG compressor system needs to be able to respond to this large fluctuation in time. We use the air intake regulation of the compressor (slide valve regulation of screw machine or air intake valve regulation of reciprocating machine). When the air intake regulation reaches the maximum, we use the return valve to assist the regulation, so that the BOG pressurization can fully adapt to the large-scale flow change and achieve the complete recovery of BOG. Cold box leakage When the cold box of LNG plant operates at a low temperature of about - 163 ℃, its heat exchanger, valve and pipeline need to experience the impact of temperature stress during startup, normal operation and shutdown, which may lead to the leakage of combustible gas in the system due to design or manufacturing reasons, resulting in combustion or explosion accidents. We have taken multiple measures to eliminate such problems: The cold box design includes pipeline stress analysis to control the pipeline stress within the allowable range from the source. There is no flange connection between the pipes and vessels in the cold box, and all are welded connections. All valves are set outside the cold box, which not only eliminates the leakage point, but also facilitates the valve maintenance. The cold box is equipped with combustible gas probe and temperature probe to monitor the gas concentration and temperature in the cold box in real time. Perform helium mass spectrometry leak detection as required.