Reliquefaction system and process for liquefying bog by self-compression and expansion of bog

Abstract

The invention relates to a reliquefaction system and technique for compressing expanded liquified BOG through the BOG. The number of equipment is decreased, the cost is reduced, energy consumption is low, the starting and stopping response speed is high, the operating flexibility is high, the load varying capacity is high, and the application range is wide. The BOG generated through a liquefied natural gas (LNG) storage tank is subjected to cold quantity recycling through a heat exchanger and then enters a BOG buffer tank to be converged with BOG serving as a cooling agent. Then the BOG enters a BOG compressor. The compressed BOG is divided into two parts through a first cooler. The first part of BOG enters the heat exchanger to be further cooled and liquified and then enters a gas-liquid separator through a throttling valve to be subjected to gas-liquid separation. The second part of BOG serves as the cooling agent of the first part of the BOG. The second part of BOG is pressurized through a turbine expansion machine, then enters a second cooler for water cooling and enters the heat exchanger to be cooled, and enters the turbine expansion machine to be expanded. The expanded BOG returns to the heat exchanger to supply cold quantity while being reheated for entering the BOG buffer tank to be converged with the first part of BOG. Circulation is conducted in this way.

Description

technical field [0001] The invention relates to a reliquefaction system and process for liquefying BOG by using BOG self-compression and expansion. Background technique [0002] As a high-quality and clean energy, natural gas has a high calorific value and less environmental pollution, and is considered to be the preferred energy source in the future. Atmospheric pressure liquefied natural gas (LNG), as a form of natural gas, its volume is only equivalent to 1 / 625 of the standard volume, which is very convenient for transportation and storage. With the development of the world and our country's economy, the demand for natural gas is increasing day by day. LNG is favored by countries all over the world for its high economy and flexibility. Due to the special storage conditions of LNG, a large amount of BOG gas is generated in LNG liquefaction plants, LNG transfer stations and LNG receiving stations. The main source is natural evaporation in LNG storage tanks and a large amou...

AI Technical Summary

Problems solved by technology

Currently, there are roughly two types of BOG reliquefaction processes: one is the nitrogen compression expansion refrigeration process, which uses nitrogen as the refrigerant, and the compression expansion provides cooling capacity for BOG; this process requires an independent nitrogen refrigeration cycle, and there are many process equipments And complex, relatively high energy consumption

The second is to use BOG direct condensation method. BOG is compressed by BOG compressor and mixed with LNG from the pump, and then condensed again, using the cold energy of LNG output from the LNG storage tank; this process has low energy consumption, but it is only suitable for The case of continuous LNG export

However, the technological process of this technical solution and the energy consumption per unit volume of BOG processed by the system are very high (3.45~7.655KW.h / Nm as pointed out in the patent 3 ), there is still a lot of room for optimization

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