Natural gas liquefying system and liquefying method
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Solution Overview
Problem
Conventional natural gas liquefaction systems face challenges in increasing the outlet pressure of the compressor and reducing the cooling capacity, leading to inefficiencies and higher costs due to limited power generation from expanders and excessive cooling requirements.
Innovation Solution
The system incorporates a first expander to generate power for the compressor, a second cooling unit to adjust the material gas temperature, and additional compressors and heat exchangers to optimize pressure and temperature conditions for efficient liquefaction, including a spool-wound heat exchanger and electric motors for stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the outlet pressure of the compressor is increased to reduce the load on the liquefaction unit and maximize efficiency, then a correspondingly large power is required which exceeds the limited power generated by the expander
Solution Approach 1:
The compression process is divided into two stages: a first compressor performs initial compression, and a second compressor performs final compression to achieve the desired high outlet pressure. This segmentation allows the system to reach high pressure levels without requiring a single compressor to consume excessive power, as each stage can be optimized independently and the expander power can be effectively utilized in the first stage.
Solution Approach 2:
The first cooling unit acts as an intermediary between the expander and the distillation unit. It cools the material gas after expansion, enabling the distillation process to proceed efficiently. This intermediate cooling step facilitates the overall process by preparing the gas for separation, allowing the system to achieve its goals with the available expander power.
2Temperature
If the feedstock gas is cooled before expansion in the expander, then a relatively large capacity is required for the cooling unit, increasing initial costs and running costs
Solution Approach 1:
The first cooling unit performs preliminary cooling of the material gas after expansion but before the distillation process. This preliminary action prepares the gas at an appropriate temperature for efficient distillation, removing the need for excessive cooling capacity elsewhere in the system and reducing overall cooling requirements and costs.
3Temperature
If cooling of the feedstock gas causes condensates to be produced, then a gas-liquid separator is required to separate condensates from the feedstock gas
Solution Approach 1:
The gas-liquid separator extracts and removes condensates from the material gas stream after cooling. By taking out the harmful condensate phase separately, the system prevents interference with subsequent distillation and compression processes, maintaining efficiency without requiring complex integrated separation systems.
4Stress or pressure
If the temperature of the feedstock gas at the outlet end of the compressor is high, then a significant temperature difference arises between the intermediate inlet point of the liquefying unit and the refrigerant, requiring a correspondingly high capacity for the cooling unit
Solution Approach 1:
The cooling process is segmented into multiple stages with intermediate cooling units. The first cooling unit cools the material gas after expansion, and additional cooling units are positioned at strategic points in the compression and liquefaction process. This segmentation allows temperature differences to be managed in smaller increments, reducing the required capacity of individual cooling units while maintaining overall process efficiency.
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 increases the compressor outlet pressure, reduces cooling capacity needs, and enhances the efficiency of the liquefaction process by optimizing pressure and temperature conditions, resulting in a more efficient and cost-effective natural gas liquefaction system.
Implementation Method 1
a first expander (3) for generating power by expanding natural gas under pressure as material gas
Implementation Method 2
a first cooling unit (11, 12) for cooling, using a propane refrigerant, the material gas depressurized by expansion in the first expander
Implementation Method 3
a distillation unit (15) for reducing or eliminating a heavy component in the material gas by distilling the material gas cooled by the first cooling unit
Implementation Method 4
a first compressor (4) for compressing the material gas from which the heavy component was reduced or eliminated by the distillation unit
Implementation Method 5
a liquefaction unit (21) for liquefying the material gas compressed by the first compressor by exchanging heat with a refrigerant
Data Source
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AI summary
By using the power generated by an expander by an expansion of material gas, the outlet pressure of a compressor is increased, and a requirement on the cooling capacity of a cooler is reduced. The liquefaction system (1) for natural gas comprises a first expander (3) for generating power by using natural gas under pressure as material gas; a first cooling unit (11, 12) for cooling the material gas depressurized by expansion in the first expander; a distillation unit (15) for reducing or eliminating a heavy component in the material gas by distilling the material gas cooled by the first cooling unit; a first compressor (4) for compressing the material gas from which the heavy component was reduced or eliminated by the distillation unit by using power generated in the first expander; and a liquefaction unit (21) for liquefying the material gas compressed by the first compressor by exchanging heat with a refrigerant.