Natural Gas Liquefaction Using Split Streams and Nitrogen Cold Recovery
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Solution Overview
Problem
Existing methods for liquefying natural gas on sea-going vessels face challenges in energy-matching and equipment complexity, particularly with the use of liquid nitrogen, where the energy balance and equipment count are not optimally managed.
Innovation Solution
A method and apparatus that divide the gaseous hydrocarbon stream into two streams, with one stream expanded or compressed, and both streams liquefied using heat exchange with liquid nitrogen, allowing for efficient cold energy utilization without significant pressure changes, thereby reducing equipment needs and operational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If liquid nitrogen is used to liquefy natural gas on sea-going vessels, then the cold energy can be utilized for liquefaction, but the energy-matching between liquefaction and evaporation becomes difficult to balance
Solution Approach 1:
The natural gas feed stream is divided into two separate streams (first stream and second stream) that are processed differently. The first stream is expanded in a turbine while the second stream is compressed, allowing independent optimization of each path's energy balance and cold energy utilization.
Solution Approach 2:
The patent applies different pressure changes to the two streams: the first stream undergoes pressure reduction through turbine expansion, while the second stream undergoes pressure increase through compression. This parameter differentiation enables flexible energy-matching and resolves the contradiction by allowing each stream to be optimized for its specific energy requirements.
2Productivity
If multiple cooling stages and equipment are used to liquefy natural gas, then the liquefaction efficiency can be improved, but the equipment count and operational complexity increase
Solution Approach 1:
The feed stream is segmented into two paths with different processing routes. One path uses turbine expansion for cooling while the other uses compression, allowing the system to achieve efficient liquefaction through parallel processing rather than sequential multi-stage cooling, thereby reducing overall equipment complexity.
Solution Approach 2:
The liquid nitrogen serves multiple functions: it cools the expanded first stream in the first heat exchanger and also cools the compressed second stream in the second heat exchanger. This multi-functional use of the same refrigerant stream improves liquefaction efficiency without requiring additional cooling equipment for each stream.
3Use of energy by moving object
If the nitrogen stream pressure is significantly changed during heat exchanging, then the heat exchange efficiency can be improved, but the operational complexity and equipment needs increase
Solution Approach 1:
The patent maintains the nitrogen stream at substantially constant pressure throughout both heat exchange processes. By keeping the nitrogen at a steady pressure state, the system achieves efficient heat exchange without the operational complexity of pressure regulation equipment and control systems that would be needed if significant pressure changes were implemented.
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 enables efficient liquefaction of natural gas with reduced equipment complexity and energy requirements, achieving sufficient cold recovery to produce liquefied hydrocarbon streams at different pressures, optimizing the use of liquid nitrogen's cold energy.
Implementation Method 1
liquefying the first stream downstream of step (c) using heat exchanging against a liquid nitrogen stream
Implementation Method 2
heat exchanging against the at least partly evaporated nitrogen stream of step (d)
Implementation Method 3
an at least partly evaporated nitrogen stream
Implementation Method 4
liquid nitrogen, whose cold energy can then be used in the liquefaction of natural gas
Implementation Method 5
expanding the first stream or compressing the second stream, or both
Data Source
AI summary
A method and apparatus for liquefying a gaseous hydrocarbon stream such as natural gas. The method comprises at least the steps of providing a feed stream (10) and dividing the feed stream (10) to provide at least a first stream (20) and a second stream (30). The first stream (20) is liquefied using heat exchange against a liquid nitrogen stream (40) to provide a first liquefied hydrocarbon stream (60) and an at least partly evaporated nitrogen stream (70). The second stream (20) is cooled and liquefied by heat exchanging against the at least partly evaporated nitrogen stream (70) to provide a second cooled hydrocarbon stream (80).