Conventional BOG processing methods in LNG plant

There are generally four treatment methods for the generated BOG in LNG plant, one is to re-condensate; the other is to directly compress; the third is to burn or vent; the fourth is to return to the LNG carrier.

(1) Re-condensation treatment process. After BOG passes through the gas-liquid separation tank, it enters the BOG compressor. The pressurized BOG enters the re-condenser and is mixed with the external LNG that has been pressurized to the same pressure. The BOG from processing and sweetening natural gas is condensed by the coldness carried by the subcooled LNG and then bypassed. The LNG is mixed into the high-pressure pump, and then vaporized by the vaporizer before being transported to the high-pressure pipeline network

(2) Direct compression process. After BOG is compressed by the compressor, it is directly output to the pipe network.

(3) Flare burning or venting. When the pressure in the tank and cabin reaches a certain value, venting or torching is often used to reduce the pressure to a safe and controllable range. Venting or flaring would be a huge waste of natural gas and should therefore be considered a safe approach in emergency situations.

(4) BOG is transported to the LNG ship through the return arm to balance the pressure and fill the vacuum generated by the unloading of the LNG storage tank on the ship. This method is convenient and fast, but it is only suitable for use when unloading the LNG ship .

Energy consumption analysis of BOG treatment process in the LNG liquid process

(l) In the BOG re-condensation and direct compression energy consumption analysis table of the LNG receiving station, a comparison of energy savings under different working conditions is achieved by fixing a certain parameter.Using the actual operating equipment parameters of the BOG processing system of the LNG receiving station and the process data records during operation, the re-condensation and direct compression processes were compared, and the BOG generated under different conditions was analyzed based on the data simulation results, in order to achieve the optimal goal The purpose is to save energy, reduce consumption, improve efficiency and reduce costs.

⑵ Analysis of BOG re-condensation and direct compression energy consumption of satellite stations.

Comparative analysis

(1) In LNG receiving stations, when the amount of BOG generated is larger, the re-condensation process consumes less energy than direct compression. However, recondensation of BOG requires additional cooling capacity.

(2) The energy consumption under the re-condensation condition is related to the BOG amount, inlet and outlet pressure, and external transmission pressure. When the inlet pressure is different and the inlet and outlet pressures are the same, the compressor energy consumption decreases significantly as the inlet pressure increases.

(3) Under the same inlet pressure, as the outlet pressure increases, the energy consumption of the compressor increases significantly more than that of the high-pressure pump. That is to say, when the pressure of the external pipeline network is high, the energy consumption of the re-condensation process is lower.

(4) From the relationship between compressor outlet pressure and equipment power consumption in Table 2, it can be seen that the power consumption of the in-tank pump increases as the outlet pressure increases. The total power consumption of the equipment is positively related to the outlet pressure, but the in-tank pump and high-pressure pump The change in power consumption is not large, indicating that the increase in total power consumption is caused by the increase in compressor power consumption.

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