Re-condensation reclaiming system for evaporated gas of liquefied natural gas receiving station and reclaiming method thereof

Abstract

The invention discloses a re-condensation reclaiming system and a re-condensation reclaiming method for evaporated gas of a liquefied natural gas receiving station. The system comprises an evaporated gas compressor, an evaporated gas pre-cooling heat exchanger and a re-condenser, wherein the re-condenser consists of a vertical condensing tower and a high-pressure pump buffer tank; and the vertical condensing tower is positioned above the high-pressure pump buffer tank. The bottom of the high-pressure pump buffer tank is provided with a brace, and a crossed vortex breaker is arranged in the brace. The reclaiming method comprises the following steps of: (1) compressing the evaporated gas, (2) pre-cooling the evaporated gas, (3) condensing and super-cooling the evaporated gas and (4) conveying secondary pressure of LNG. The design of the buffer tank improves the running stability of a high-pressure pump; the re-condenser operates and controls the system more stably and simply; and the system and the method reduce the energy consumption, and have good adaptability to gas conveying load fluctuation.

Description

technical field [0001] The invention belongs to the field of optimization and energy-efficient utilization of boil-off gas (BOG) recondensation system at a liquefied natural gas (LNG) receiving station, and particularly relates to a method of using the cold energy carried by the LNG itself at the LNG receiving station to prevent environmental leakage during the LNG storage and transportation process. The recondensation recovery system and its recovery method of BOG produced by LNG in LNG storage tanks, equipment, pipelines, etc. caused by heat and mechanical movement of equipment. Background technique [0002] Natural gas is an important resource to diversify energy supply, ensure energy security, improve the environment and increase energy efficiency. With the rapid growth of demand for natural gas, the gap between domestic demand and supply is also growing. According to the national energy development plan, my country will build about 10 LNG receiving stations in the Yang...

AI Technical Summary

Problems solved by technology

At present, the design of the recondenser only considers the liquefaction function of BOG, and does not consider the buffer function of the suction end of the high-pressure pump. Since there is no buffer tank at the suction end of the high-pressure pump, the amount of BOG condensed in the re-condenser and the amount of LNG used to liquefy BOG are insufficient. When the high-pressure pump is supplied (or too much), the liquid level of the re-condenser will be out of control, and frequent liquid-level fluctuations will easily lead to the accident of pump trip when the high-pressure pump is turned on; at the same time, because the flow of LNG entering the re-condenser is based on quantitative The BOG flow rate and the recondenser outlet pressure set by the pressure signal source (PIC-1) at the suction end of the high-pressure pump are calculated by the ratio calculation module formula in the DCS (Distributed Control System), and the LNG flow rate is controlled according to the calculated value Control the opening of the valve (FV) to maintain the liquid level of the recondenser and keep the pressure at the suction end of the high-pressure pump constant, and the pressure signal source (PIC-1) at the suction end of the high-pressure pump needs to simultaneously adjust the LNG flow of another branch ( PV-1, PV-2) to ensure a constant pressure at the suction end of the LNG high-pressure delivery pump

Due to the complex control system and mutual interference, the operation stability of the recondenser is poor

[0007] 2. The system consumes a lot of energy, and the BOG recondensation process has poor adaptability to gas transmission load fluctuations

Generally, the gas transmission peak and valley loads of the receiving station can vary from 20% to 100%, so when the BOG volume is large, the cooling capacity required to condense BOG is also large, and the LNG consumption is also large; when the gasification load is low , the LNG output is less, and the LNG feed used to condense BOG in the re-condenser will be relatively small, and BOG cannot be completely absorbed or condensed, so it has to be liquefied by increasing the BOG outlet pressure

In order to ensure that the BOG is completely condensed, the BOG needs to be boosted to a higher pressure, resulting in a larger power consumption of the compressor

When the LNG output load is low, BOG cannot be completely liquefied, and it needs to be burned by an external flare, resulting in energy waste

[0009] To reduce the system energy consumption of the existing BOG recondensation process, reducing the outlet pressure of the BOG compressor is the key, but the reduction of the outlet pressure of the compressor means that the LNG feed volume used to condense BOG will increase accordingly, and the gas transmission load of the pipeline network is relatively high. When it is low, it will bring some difficulties to the operation

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