1 Introduction China's LNG industry has formed a relatively complete industrial chain from liquefaction, transportation, terminal gasification to terminal utilization, and its development speed and maturity are becoming more and more perfect, laying a good development foundation for the downstream utilization of natural gas in China. At present, 14 coastal LNG terminals have been built and are under construction in China, and the total receiving capacity will exceed 50million tons / year after all are completed. There are still a number of projects under preliminary work ⑴. Liquefaction plants, satellite stations and vehicle and vessel refueling are also developing rapidly. As of may2013, more than 50 liquefaction plants have been built and put into operation nationwide, with a total liquefaction capacity of 23million m3 / day. LNG storage characteristics at -162 ℃ and normal pressure, special transportation conditions, pressure change of LNG storage tank during unloading and filling, heat leakage of storage tank and pipeline, etc., will produce a large amount of vaporized gas, namely bog. In order to protect the normal operation and safety of transport ships, storage tanks and pipelines, it is necessary to consider the treatment of a large number of bogs and maintain the dynamic balance of pressure to keep the pressure within the safe control range. Therefore, for the purpose of operation safety and energy saving, the treatment process of bog under different conditions is studied to improve the recovery rate of bog and reduce the waste of natural gas.   2 method design For a 4 x 160000m3 receiving station, the daily evaporation rate is 0 According to the calculation of 05%, the daily LNG evaporation is about 320 cubic meters, and the generated bog is about 192000 cubic meters, about 144 tons / day; Under the unloading condition, the amount of bog produced by temperature exchange and pressure change will be several times or even ten times that under the conventional condition. Treating bog with reasonable process can not only reduce the potential damage to equipment and personnel, but also save energy, reduce consumption and reduce cost. In order to study the treatment process of bog under different conditions, taking a receiving station and a satellite station as an example, the process selection is considered from the quantity of bog. Take a receiving station in Fujian (4 x 160000m3 storage tanks) and a satellite station in Shandong (10 100m3 storage tanks). Basis for analogy: different tank types have different evaporation rates, and different treatment methods will affect the subsequent processing of bog. Appropriate treatment process shall be selected for different tank types and LNG treatment scales.   3 conventional treatment of bog There are generally four treatment methods for the generated bog, one is re condensation; Second, direct compression; 3. Combustion or venting; Fourth, return to LNG carrier. (1)  Re-condensation treatment process. After passing through the gas-liquid separation tank, the bog enters the bog compressor. The pressurized bog enters the Recondenser and is mixed with the exported LNG that is pressurized to the same pressure. The bog is condensed by the cooling capacity carried by the supercooled LNG and mixed with the LNG by-pass into the high-pressure pump, and then is vaporized by the vaporizer and transmitted to the high-pressure pipe network (2). The recondensation process flow chart of the terminal is shown in Figure 1. (2) Direct compression process. Bog is directly output to the pipe network after being compressed by the compressor. (3) Flare burning or venting. When the pressure in the tank and cabin reaches a certain value, vent or flare combustion is often adopted to reduce the pressure to a safe and controllable range. Venting or flare burning will be a great waste of natural gas. Therefore, this method is a safety treatment measure in case of emergency. (4) Bog is transported to LNG ship through return arm to balance pressure and fill vacuum generated by unloading of LNG storage tank on board. This method is convenient and fast, but it is only suitable for unloading of LNG ship.   Contact us:   Sichuan Rongteng Automation Equipment Co., Ltd. www. rtgastreat.com E-mail: sales01@rtgastreat.com Phone/whatsapp: +86 138 8076 0589