Nitrogen Refrigeration Cycle for Small-Scale LNG Loading
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Solution Overview
Problem
Current LNG liquefaction methods for small to mid-scale plants are complex, costly, and lack integration with LNG loading operations, posing safety hazards and environmental concerns due to the use of hydrocarbon refrigerants and inefficient boil-off vapor management.
Innovation Solution
A closed refrigeration cycle using a non-hydrocarbon refrigerant like nitrogen, integrated with a cold box and heat exchanger passes, enables efficient LNG production and loading by utilizing a two-stage compressor and expander system, which is safer and more reliable, and recovers boil-off vapors to reduce emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If hydrocarbon refrigerants (propane, ethylene, propylene) are used for LNG liquefaction, then energy efficiency is improved, but safety hazards increase due to explosive and hazardous properties in case of leakage
Solution Approach 1:
The patent replaces hydrocarbon refrigerants with nitrogen gas, an inert substance that cannot explode or cause fire hazards. The nitrogen-based refrigeration cycle maintains energy efficiency for LNG liquefaction while eliminating the explosive and hazardous properties associated with hydrocarbon refrigerants, creating a safe operating environment.
2Adaptability or versatility
If small to mid-scale LNG plants are constructed close to pipelines and consumers, then delivery flexibility and cost-effectiveness are improved, but system complexity increases due to integration requirements
Solution Approach 1:
The patent combines the LNG liquefaction process with the LNG loading facility into an integrated system. The nitrogen-based refrigeration cycle is directly coupled with the LNG storage and loading operations, allowing small to mid-scale plants to produce and distribute LNG on-site without requiring separate, complex systems. This merging simplifies overall system architecture while maintaining delivery flexibility.
3Ease of operation
If conventional LNG loading operations are performed with venting of boil-off vapors, then loading simplicity is maintained, but environmental pollution and safety hazards increase
Solution Approach 1:
The patent converts the previously harmful boil-off vapors into a useful resource. Instead of venting nitrogen-containing vapors to the atmosphere, the system recycles them back into the refrigeration cycle where they provide additional cooling capacity. This eliminates emission pollution and safety hazards while maintaining loading simplicity and improving energy efficiency.
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 solution provides a simple, cost-effective, and safe method for LNG production and loading, reducing energy consumption and eliminating the need for LNG pumps, while minimizing environmental impact by using inert gases and recovering boil-off vapors, making it suitable for small to mid-scale plants.
Implementation Method 1
a first compressor unit configured to compress a refrigerant to produce a compressed refrigerant at a first pressure
Implementation Method 2
a first heat exchanger pass of the plurality of heat exchanger passes that is configured to pass the compressed refrigerant through the cold box to cool the compressed refrigerant
Implementation Method 3
a first expander configured to receive the first portion from the splitter and expand the first portion to a second pressure
Implementation Method 4
The cold box is configured to receive a natural gas feed stream and produce LNG from the feed stream using a refrigeration content from the refrigeration unit
Data Source
AI summary
An LNG plant comprises a cold box and a refrigeration unit fluidly coupled with a plurality of heat exchanger passes in the cold box. The refrigeration unit is configured to provide a first refrigerant stream to a first heat exchanger pass of the plurality of heat exchanger passes at a first pressure, a second refrigerant stream to a second heat exchanger pass at a second pressure, and a third refrigerant stream to a third heat exchanger pass at a third pressure. The second refrigerant stream comprises a first portion of the first refrigerant stream, and the third refrigerant stream comprises a second portion of the first refrigerant stream. The second pressure and the third pressure are both below the first pressure. The cold box is configured to produce LNG from a natural gas feed stream to the cold box using a refrigeration content from the refrigeration unit.