BOG Multistage Compressor Load Ratio Control
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Solution Overview
Problem
Conventional BOG multistage compressors face increased gas load due to differential pressure between suction and discharge gases, leading to excessive temperature and potential operational limitations, without effective countermeasures for managing this increased load.
Innovation Solution
The operation control method for a BOG multistage displacement compressor adjusts the load ratio between low-pressure and high-pressure stage compression units, using capacity adjusting devices to increase the low-pressure stage compression ratio and decrease the high-pressure stage compression ratio, thereby reducing the gas load on the high-pressure stage side, even when the low-pressure stage suction gas temperature is higher than in steady operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the compression ratio of the high-pressure stage is increased to achieve higher discharge pressure, then the discharge pressure is improved, but the gas load and temperature rise excessively
Solution Approach 1:
The compression process is divided into multiple stages (low-pressure stage and high-pressure stage) with intercooling between stages. This segmentation allows the total compression ratio to be distributed across stages, reducing the temperature rise in each individual stage and preventing excessive discharge gas temperature while achieving the required discharge pressure.
Solution Approach 2:
A cooler is introduced as an intermediary component between the low-pressure and high-pressure compression stages. This cooler removes heat from the compressed gas between stages, acting as a mediator that reduces the temperature before the gas enters the high-pressure stage, thereby preventing excessive temperature rise in the final discharge.
2Quantity of substance
If the compression ratio of the low-pressure stage is increased to reduce the differential pressure in the high-pressure stage, then the gas load on the high-pressure stage is reduced, but the compression ratio distribution becomes unbalanced
Solution Approach 1:
The compression system employs dynamic capacity adjusting devices that can independently adjust the compression capacity of each stage based on operating conditions. This dynamic adjustment capability allows the system to optimize the compression ratio distribution between stages in real-time, maintaining balanced operation and efficient gas load management across varying demand conditions.
3Quantity of substance
If the load ratio of the high-pressure stage is reduced to prevent excessive gas load, then the gas load is controlled, but the overall compression capacity is reduced
Solution Approach 1:
The compression system is segmented into multiple independent stages, each capable of operating at optimized load ratios. The low-pressure stage can operate at higher load to pre-compress the gas, reducing the burden on the high-pressure stage. This segmentation allows each stage to operate within its optimal capacity range, preventing excessive gas load on the high-pressure stage while maintaining overall compression capacity through the combined output of both stages.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses the increase in gas load due to differential pressure, preventing it from exceeding allowable limits and maintaining operational temperatures within safe ranges, thus ensuring continuous compressor operation.
Implementation Method 1
since the BOG is adiabatically compressed, higher compression ratio raises the temperature of BOG
Implementation Method 2
discharge gas of a low-pressure stage side compression unit is cooled by the cooler to reduce the temperature
Implementation Method 3
the discharge gas is supplied to a high-pressure stage side compression unit
Data Source
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AI summary
Provided is an operation control method for a BOG multistage displacement compressor including connected multiple displacement compression units (9,10) for compressing boil off gas (BOG) generated from liquefied natural gas, including: under a predetermined state, performing operation control so that the ratio (load ratio) of a load of a low-pressure stage compression unit (9) to a load of a high-pressure stage compression unit (10) in the BOG multistage displacement compressor is larger than load ratios under states other than the predetermined state. Namely, the BOG multistage displacement compressor is configured so that suction temperature in the low-pressure stage compression unit (9) can be detected, and the predetermined state is set to a state where the detected temperature of the suction temperature is equal to or higher than a set temperature that is preset. According to such a method, even if the low-pressure stage side suction gas has a temperature higher than that in steady operation, the load (gas load) due to a differential pressure between suction gas and discharge gas on the high-pressure stage side can be prevented from exceeding an allowable gas load.