System and method for liquefaction of natural gas
Find Innovative SolutionsGenerate Solutions
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 high power requirements and increased costs, as well as the need for large cooling units and gas-liquid separators due to limited power generation from the expander and significant temperature differences.
Innovation Solution
A method and system that involve reducing the pressure of natural gas using a first expander to generate power, cooling and separating the gas to produce a top fraction, compressing the gas phase component using the expander power, and liquefying it through heat exchange with a refrigerant, while minimizing the cooling capacity by optimizing heat exchanger usage and recirculating liquid phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the feedstock gas is cooled before being expanded in the expander, then the cooling unit requires a relatively large capacity, but this increases the initial costs and the running costs of the cooling unit
Solution Approach 1:
The system performs preliminary cooling of the natural gas feed using a cooling unit before the gas enters the expander. This preliminary cooling condenses heavier components (C5+ hydrocarbons) out of the gas phase, allowing them to be removed in a separator. By performing this cooling action beforehand, the expander receives gas with fewer condensable components, which improves expansion efficiency and reduces the cooling capacity required during subsequent stages.
Solution Approach 2:
The system discards (removes) the heavier components (C5+ hydrocarbons) that condense during preliminary cooling of the feedstock gas. By removing these heavier components before expansion, the system recovers the cooling effort invested and prevents these components from interfering with the expansion process and subsequent liquefaction stages.
2Temperature
If cooling of the feedstock gas will cause condensates to be produced, then it is necessary to provide a gas-liquid separator to separate condensates from the feedstock gas, but this increases device complexity
Solution Approach 1:
The system extracts (removes) the heavier components (C5+ hydrocarbons) from the natural gas feed by cooling the feedstock gas to condense these components and then separating them in a gas-liquid separator. By removing these heavier components beforehand, the system simplifies subsequent processing stages as the remaining gas has a more uniform composition that is easier to liquefy.
Solution Approach 2:
The gas-liquid separator is positioned to receive cooled feedstock gas before it enters the expander. By performing the separation action at this preliminary stage, the system removes condensates that would otherwise interfere with the expansion process and subsequent liquefaction stages, simplifying the overall process flow.
3Power
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, but this requires a correspondingly high capacity for the cooling unit
Solution Approach 1:
The cooling process is segmented into multiple stages: preliminary cooling of the feedstock gas before expansion, cooling of the compressed gas after the first compressor, and final cooling in the liquefaction unit. By segmenting the cooling process, the system can manage temperature differences more effectively at each stage rather than attempting to handle the entire temperature range in a single high-capacity cooling unit.
Solution Approach 2:
The cooling unit serves multiple functions: it cools the natural gas feed before expansion, cools the compressed gas after the first compressor, and provides refrigerant for the liquefaction unit. By making the cooling unit multi-functional, the system optimizes its capacity utilization across different process stages rather than requiring separate dedicated cooling systems for each function.
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 allows for increased compressor outlet pressure and reduced cooling capacity, enhancing the efficiency and cost-effectiveness of the liquefaction process by utilizing expander-generated power and optimizing heat exchange processes.
Implementation Method 1
reducing the pressure of the natural gas feed in a first expander (3) generating power to produce a reduced pressure material gas
Implementation Method 2
cooling the reduced pressure material gas
Implementation Method 3
removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction
Implementation Method 4
exchanging heat between the gas phase component and the compressed material gas to produce at least a cooled compressed material gas
Implementation Method 5
at least partially liquefying the cooled compressed material gas by exchanging heat with a refrigerant
Implementation Method 6
at least partially liquefying the cooled compressed material gas
Data Source
Figure 1
Figure 2
Figure 3
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 expanding 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 the power generated in the first expander; a second heat exchanger for exchanging heat between the material gas introduced into the first compressor and the material gas compressed by the first compressor; and a liquefaction unit (21) for liquefying the material gas compressed by the first compressor by exchanging heat with a refrigerant.