Nitrogen Expander Loops for Lower-Energy LNG Refrigeration
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Solution Overview
Problem
Current LNG production technologies face high energy demand, complexity, and safety concerns due to combustible refrigerants, particularly in offshore installations, which limits their efficiency and profitability.
Innovation Solution
A method and apparatus utilizing a single component, inert gas refrigerant with multiple expanders in a single-phase refrigeration cycle, allowing for separate control of mass flows, temperatures, and pressure levels to minimize heat exchanger losses and optimize efficiency, adapted for varying gas compositions and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If multi component refrigerant technology is used in cascades arrangements, then energy efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the complex multi-component refrigerant system, replacing it with a single-component nitrogen refrigerant. This removes the need for complex cascade arrangements, gas make-up assemblies, and sophisticated control systems while maintaining energy efficiency through the use of expanders for refrigeration.
Solution Approach 2:
The invention changes the fundamental parameter of refrigerant composition from multi-component to single-component (nitrogen). This parameter change simplifies the entire system architecture, eliminates the need for complex gas composition control, and reduces equipment requirements while achieving comparable or better energy efficiency.
2Loss of energy
If multi component refrigerant technology is used, then energy efficiency is improved, but control speed and robustness decrease
Solution Approach 1:
The invention removes the complex control systems required for multi-component refrigerant cascades, replacing them with simple control of a single-component nitrogen system. The control only needs to manage nitrogen flow and expander operations, which are inherently more robust and faster responding.
3Loss of energy
If combustible refrigerant is used, then energy efficiency is improved, but safety concerns increase especially in offshore installations
Solution Approach 1:
The invention replaces combustible refrigerants with nitrogen, an inert gas that cannot support combustion. This creates a safe operating environment particularly for offshore installations, eliminating fire and explosion hazards associated with traditional refrigerants while maintaining the required refrigeration performance through expander-based cooling.
4Productivity
If refrigerant is divided into separate flows expanded to lowest pressure, then refrigeration is achieved, but energy consumption increases
Solution Approach 1:
The invention changes the pressure management strategy by using a single-phase nitrogen refrigerant system where nitrogen is compressed to high pressure and then expanded through expanders to produce refrigeration. This approach avoids the energy-wasting practice of expanding all flows to the lowest pressure and allows for more efficient heat exchanger operation.
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 reduces specific energy consumption, simplifies control, and enhances safety by using non-flammable nitrogen as the refrigerant, resulting in a more compact, cost-effective, and environmentally friendly LNG production process.
Implementation Method 1
heat absorption includes phase change of refrigerant
Implementation Method 2
heat exchanger assembly for heat absorption from natural gas
Implementation Method 3
the refrigerant is divided into at least two separate flows which are cooled and expanded in at least two separate expanders
Data Source
AI summary
A method and system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising: at least two expanders (1-3); a compressor assembly (5-7); a heat exchanger assembly (8) for heat absorption from natural gas; and a heat rejection assembly (10-12). The novel features according to the present invention are arranging the expanders (1-3) in expander loops; using only one and the same refrigerant in all loops; passing an expanded refrigerant flow from the respective expander into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and serving the refrigerant to the respective expander in a compressed flow by means of the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.