Arctic LNG Cascade Cycle Using Ethane Pre-Cooling and Nitrogen Sub-Cooling
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Solution Overview
Problem
Existing natural gas liquefaction technologies face inefficiencies in the Arctic climate, including incomplete use of environmental cold, high energy consumption, complex control schemes, and increased equipment needs, which affect operational stability and capital expenditures.
Innovation Solution
The method employs ethane evaporation for pre-cooling and uses cooled nitrogen as a refrigerant, simplifying the process by eliminating the need for mixed refrigerants and reducing equipment complexity, with a single drive system and energy-efficient design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If mixed refrigerant cycles are used for natural gas liquefaction in Arctic climate, then cooling capability is improved, but device complexity and capital expenditures increase
Solution Approach 1:
The patent extracts and eliminates the complex mixed refrigerant system from the liquefaction process, replacing it with a simplified cascade cycle using only propane and ethane as refrigerants. This removes the need for complex MR composition control while maintaining effective cooling capability through sequential cooling stages.
Solution Approach 2:
The patent changes the refrigerant parameters by switching from mixed refrigerants with variable composition to pure components (propane and ethane) with fixed properties. This simplifies the thermodynamic parameters and eliminates the need for dynamic composition adjustment, reducing control system complexity.
2Use of energy by moving object
If main compressor capacity is increased to shift power consumption balance towards mixed refrigerant compression, then energy efficiency is improved, but equipment size and weight increase
Solution Approach 1:
The patent segments the compression work into two separate compressors of appropriate sizes - a propane compressor and an ethane compressor - rather than using one oversized main compressor. This distributes the compression load efficiently and avoids the need for excessive compressor capacity in a single unit.
Solution Approach 2:
The refrigerant compression is integrated into the liquefaction process itself, where the propane and ethane compressors serve dual purposes: compressing the refrigerants for cooling while also contributing to the overall liquefaction workflow. This eliminates the need for separate, oversized drive systems.
3Productivity
If sequential cooling with multiple refrigerants is implemented, then liquefaction efficiency is improved, but quantity of equipment increases
Solution Approach 1:
The patent merges the cooling functions into two integrated cascade cycles (propane and ethane) that work sequentially rather than as separate parallel systems. The heat exchangers and compressors are combined into cohesive cycles, reducing the total number of independent equipment units while maintaining efficient sequential cooling.
Solution Approach 2:
The propane and ethane refrigerants serve multiple functions: they provide sequential cooling at different temperature levels, act as refrigerants in their respective cycles, and enable efficient heat transfer throughout the system. This multi-functionality reduces the need for specialized equipment for each cooling stage.
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 simplifies the liquefaction process, reduces capital expenditures, and achieves stable operation under changing parameters with lower energy consumption, specifically around 220 kW per ton of LNG produced.
Implementation Method 1
prior to pre-cooling the natural gas is compressed, ethane is evaporated during the multi-stage pre-cooling of liquefied gas with simultaneous evaporation of ethane using cooled ethane as a refrigerant
Implementation Method 2
nitrogen being compressed, cooled, expanded and fed to the natural gas sub-cooling stage
Implementation Method 3
Gas is liquefied in two circuits, in each of which gas is cooled by mixed refrigerants of different composition. Each circuit uses a multithread coil heat exchanger.
Data Source
AI summary
A technology liquefies natural gas. The natural gas liquefaction method pre-cools treated natural gas by ethane evaporation, sub-cools liquefied gas using cooled nitrogen as a refrigerant, reduces liquefied gas pressure, separates non-liquefied gas and diverts liquefied natural gas. Before pre-cooling the natural gas is compressed, ethane is evaporated during the multi-stage pre-cooling of liquefied gas with simultaneous evaporation of ethane using cooled ethane as a refrigerant. Ethane generated by evaporation is compressed, condensed and used as a refrigerant during the cooling of liquefied gas and nitrogen, with nitrogen being compressed, cooled, expanded and fed to the natural gas sub-cooling stage. The natural gas liquefaction unit contains a natural gas liquefaction circuit, an ethane circuit and a nitrogen circuit. The natural gas liquefaction circuit includes a natural gas compressor, a cooler unit, ethane vaporizers, a closed-end subcooling heat exchanger, and a separator, connected in series.