FLNG Pretreatment Membrane Cooling for Lower LNG Train Load
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Solution Overview
Problem
Offshore FLNG facilities face challenges in energy efficiency and space constraints due to the need for large pretreatment systems that require significant energy to cool natural gas to -160°C for liquefaction, with conventional systems delivering gas at temperatures that are too high for efficient refrigeration.
Innovation Solution
A pretreatment system incorporating a membrane system for CO2 removal, a heat exchanger for cross-exchanging heat, and additional components for mercury removal, gas sweetening, and dehydration, which reduces the temperature of the gas stream entering the LNG train, thereby minimizing energy consumption and equipment size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pretreatment systems are used to deliver natural gas to the LNG train, then the gas stream is purified to about 99 percent purity, but the gas temperature remains high (37°C to 49°C) requiring significant energy for refrigeration
Solution Approach 1:
The membrane system performs preliminary cooling of the natural gas stream before it enters the LNG train. By removing CO2 and cooling the gas in advance, the system reduces the refrigeration load on the LNG train, achieving energy savings of 5-15% while maintaining gas purity requirements
Solution Approach 2:
The membrane system extracts CO2 from the natural gas stream, separating it into a CO2-rich permeate stream and a CO2-depleted non-permeate stream. This extraction process simultaneously purifies the gas and cools it, addressing both purity and temperature requirements
2Use of energy by moving object
If a membrane system is added to cool the gas stream before the LNG train, then energy consumption is reduced by 5-15%, but the footprint of the pretreatment system increases
Solution Approach 1:
The membrane system combines CO2 removal and gas cooling functions into a single integrated process. By merging these two functions, the system achieves cooling without adding separate equipment, thereby reducing the overall footprint compared to conventional approaches that would require separate cooling and purification equipment
Solution Approach 2:
The membrane system performs multiple functions simultaneously: CO2 removal, gas cooling, and preliminary purification. This multi-functionality allows the system to achieve energy savings while maintaining a compact footprint suitable for FLNG facilities with limited space
3Use of energy by stationary object
If the gas stream temperature is reduced before entering the LNG train, then the refrigeration process requires less energy, but additional cooling equipment is needed
Solution Approach 1:
The membrane system uses the natural cooling effect that occurs during CO2 removal to cool the gas stream. The process is self-cooling, meaning the separation process itself provides the cooling without requiring external refrigeration equipment, thereby reducing both energy consumption and system complexity
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
The system delivers the natural gas stream at a lower temperature, reducing the energy required for refrigeration by 5-15% and minimizing the footprint of the pretreatment system, leading to significant energy and cost savings while optimizing energy efficiency.
Implementation Method 1
a membrane system that removes carbon dioxide from an inlet natural gas stream, producing a cooled CO2-rich permeate stream and a cooled CO2-depleted non-permeate stream
Implementation Method 2
a heat exchanger that cross-exchanges heat from the cooled non-permeate and permeate streams with the substantially water-free natural gas outlet stream
Data Source
AI summary
A pretreatment system and method for a floating liquid natural gas (“FLNG”) facility are presented. The inlet natural gas stream flows through a membrane system to remove carbon dioxide and a heat exchanger, producing first and second cooled CO2-depleted non-permeate streams. The first cooled CO2-depleted non-permeate stream is routed to additional pretreatment equipment, while the second cooled CO2-depleted non-permeate stream is routed directly to a LNG train. Alternatively, the inlet natural gas stream may flow through a membrane system to produce a single cooled CO2-depleted non-permeate stream that is routed to the LNG train after sweetening and dehydration. Because the pretreatment system delivers the incoming gas stream to the LNG train at a lower temperature than conventional systems, less energy is needed to convert the gas stream to LNG. In addition, the pretreatment system has a smaller footprint than conventional pretreatment systems.