Parallel compression in LNG plants using a positive displacement compressor
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Solution Overview
Problem
Liquefied natural gas (LNG) production in existing systems is often limited by the capacity and efficiency of refrigerant compression systems, particularly when operating near surge or stonewall conditions, and the addition of parallel dynamic compressors leads to inflexible and costly designs that struggle to balance flow and pressure.
Innovation Solution
Incorporating a positive displacement compressor in parallel with dynamic compressors in the refrigerant compression system, allowing for efficient splitting and compression of the refrigerant stream, with the positive displacement compressor handling a significant portion of the flow to enhance overall system capacity and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dynamic compressors are used for refrigerant compression in LNG plants, then high capacity and variable speed capability are achieved, but the system becomes inflexible when operating near surge or stonewall conditions
Solution Approach 1:
The refrigerant compression system is segmented into multiple compression trains, with at least one dynamic compressor and one positive displacement compressor operating in parallel. This segmentation allows independent operation and load distribution among different compressor types, enabling the system to maintain flexibility while achieving high compression capacity. The positive displacement compressor handles variable flow requirements without surge or stonewall constraints, while dynamic compressors provide base-load capacity.
2Productivity
If additional dynamic compressors are added in parallel to increase capacity, then refrigerant compression capability is enhanced, but system complexity and cost increase due to matching requirements
Solution Approach 1:
The positive displacement compressor serves multiple functions: it operates in parallel with dynamic compressors to increase total capacity, provides operational flexibility without surge or stonewall limitations, and eliminates the need for precise compressor matching. Its ability to handle variable flow rates makes it a universal solution that complements dynamic compressors across different operating conditions, simplifying overall system design.
3Stress or pressure
If the compressor operates near the anti-surge line to maximize head capability, then pressure ratio is improved, but the refrigerant flow rate is limited
Solution Approach 1:
The system merges the output streams from multiple compressors (dynamic and positive displacement) into a common discharge line. The positive displacement compressor compensates for the flow limitation of dynamic compressors operating near surge, combining their capabilities to achieve both high pressure ratio and adequate total flow rate. This merging allows the system to operate dynamically optimized compressors at peak efficiency while maintaining sufficient overall refrigerant circulation.
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 configuration effectively debottlenecks the compression system, increasing LNG production capacity by up to 3.9% while maintaining operational efficiency and flexibility, even under varying ambient conditions, without the need for costly matching of compressor sizes.
Implementation Method 1
positive displacement compressors function by reducing the volume of the fluid being compressed
Implementation Method 2
Dynamic compressors function by increasing the momentum of the fluid being compressed
Implementation Method 3
Natural gas is cooled, liquefied, and/or sub-cooled by indirect heat exchange against the refrigerants in the heat exchangers
Data Source
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AI summary
A system and method for increasing the capacity and efficiency of natural gas liquefaction processes by debottlenecking the refrigerant compression system. A secondary compression circuit comprising at least one positive displacement compressor is provided in parallel fluid flow communication with at least a portion of a primary compression circuit comprising at least one dynamic compressor.