Ethane-Nitrogen Cascade Liquefaction for Arctic Natural Gas Processing
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Solution Overview
Problem
Existing natural gas liquefaction technologies face inefficiencies in the Arctic climate, including incomplete use of environmental cold, complex control schemes, high energy consumption, and excessive equipment requirements, which complicate operation and increase capital expenditures.
Innovation Solution
The Arctic Cascade technology employs pure ethane as a refrigerant for pre-cooling and sub-cooling, using ethane vaporizers and nitrogen-nitrogen heat exchangers, simplifying the process and reducing equipment complexity, while leveraging ambient air or water for cooling and utilizing a single gas turbine drive for compressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If C3MR technology is used with propane-based vapor compression cycle, then natural gas can be cooled, but in Arctic climate the environmental cold is not fully utilized and main compressor power is excessively spent on compressing mixed refrigerant
Solution Approach 1:
The patent changes the refrigerant composition parameter from mixed refrigerant (C3MR) to pure ethane, and operates at elevated pressures (30-70 bar) to enable complete liquefaction. This parameter change allows the system to achieve both cooling and full liquefaction while reducing compressor power consumption by 15-20% compared to conventional C3MR technology.
Solution Approach 2:
The patent implements preliminary cooling of natural gas using cold ambient air or water from Arctic environments before entering the main liquefaction process. This preliminary action reduces the thermal load on the ethane refrigeration system and maximizes utilization of free environmental cooling, thereby reducing overall energy consumption.
2Temperature
If Philips Cascade technology is used with sequential cooling by propane, ethylene and methane, then natural gas can be liquefied, but the equipment complexity increases with three three-stage compressors and nine anti-surge circuits
Solution Approach 1:
The patent extracts and eliminates the complex multi-refrigerant cascade system (propane, ethylene, methane) and replaces it with a single ethane-based refrigeration cycle operating at elevated pressures. This extraction of unnecessary complexity reduces the system from three three-stage compressors with nine anti-surge circuits to a single-stage compressor, while achieving complete liquefaction.
Solution Approach 2:
The patent makes ethane serve multiple functions that were previously distributed across three different refrigerants (propane, ethylene, methane). A single ethane-based cycle performs pre-cooling, main cooling, and sub-cooling functions, eliminating the need for multiple specialized refrigerant circuits and their associated control systems.
3Use of energy by moving object
If low pressure of 41 bar is used in Philips Cascade technology, then equipment requirements are reduced, but specific energy consumption of the liquefaction process increases
Solution Approach 1:
The patent changes the operating pressure parameter from conventional low pressure (41 bar) to elevated pressure (30-70 bar). This pressure increase enables complete liquefaction of natural gas in a single stage, reducing specific energy consumption by 15-20% while maintaining equipment requirements at manageable levels through optimized heat exchanger design.
4Productivity
If Shell DMR technology is used with two mixed refrigerants, then gas can be liquefied in two circuits, but the control scheme complexity increases
Solution Approach 1:
The patent extracts and removes the complex two-circuit mixed refrigerant system and replaces it with a single ethane-based circuit operating at elevated pressures. This simplification reduces the control scheme from managing two separate refrigerant circuits to controlling a single refrigeration cycle, while maintaining or enhancing liquefaction capacity.
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 costs, and achieves stable operation with lower energy consumption, specifically around 220 kW per ton of LNG produced, compared to previous methods.
Implementation Method 1
pre-cooling by means of ethane evaporation
Implementation Method 2
cooling sequence: first, in three heat exchangers using an independent propane-based vapor compression cycle
Implementation Method 3
liquefied gas sub-cooling using cooled nitrogen as a refrigerant
Implementation Method 4
heat removal from gas and mixed refrigerant (MR) in the propane circuit
Implementation Method 5
main compressor power is spent on compressing the mixed refrigerant of the second circuit
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.