LNG Feed Stream Splitting for Better Work and Cold Recovery
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Solution Overview
Problem
Current LNG plants have high energy requirements due to inefficient use of work energy from the feed natural gas and limited cold recovery from flashed vapour, leading to increased costs.
Innovation Solution
A method involving dividing the feed stream into two parts, liquefying the majority at high pressure, cooling the smaller stream, combining them before pressure reduction in a flash vessel, and utilizing the gaseous stream for direct cooling, thereby increasing work energy and cold recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the feed natural gas stream is reintroduced into the liquefied natural gas stream after pressure reduction through a valve, then the plant can operate continuously, but the available work energy from the feed natural gas is not fully utilized
Solution Approach 1:
The feed natural gas stream is divided into two separate streams: a first feed stream (at least 90 mass % of total feed) that is liquefied at high pressure (20-100 bar), and a second feed stream that is cooled through a heat exchanger. This segmentation allows each stream to be processed differently to maximize energy utilization.
Solution Approach 2:
The pressure parameter is changed for the combined LNG stream by reducing it after combination, creating conditions for flash evaporation in the flash vessel. This parameter change enables the gaseous stream to be recovered and used for cooling purposes, thereby fully utilizing the available work energy.
2Loss of energy
If the flashed vapour from expansion stages is used as plant fuel gas, then energy is recovered, but the cold energy recovery is limited and energy requirements remain high
Solution Approach 1:
The flashed vapour, which was previously only used as fuel gas, is now converted into a useful cooling resource. The gaseous stream from the flash vessel is used to cool the second feed stream in the heat exchanger, transforming what was considered waste into a beneficial cooling source that reduces overall plant energy requirements.
Solution Approach 2:
The first liquefied natural gas stream and the cooled second feed stream are merged into a combined LNG stream before pressure reduction. This merging allows the cold energy from the flashed vapour to be effectively utilized in cooling the second feed stream, maximizing cold energy recovery.
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 energy requirements by maximizing work energy utilization and cold recovery, leading to cost savings and improved efficiency in LNG plant operations.
Implementation Method 1
cooling the second feed stream through a heat exchanger to provide a cooled feed stream
Implementation Method 2
passing the combined LNG stream through a flash vessel to provide a product LNG stream and a gaseous stream
Data Source
AI summary
A method of liquefying a hydrocarbon stream such as natural gas from a feed stream, the method at least comprising the steps of: (a) providing a feed stream (10); (b) dividing the feed stream (10) of step (a) to provide at least a first feed stream (20) comprising at least 90 mass % of the initial feed stream (10), and a second feed stream (30); (c) liquefying the first feed stream (20) of step (b) at a pressure between 20-100 bar to provide a first liquefied natural gas (LNG) stream (40); (d) cooling the second feed stream (30) of step (b) to provide a cooled feed stream (50); (e) combining the first LNG stream (40) of step (c) with the cooled feed stream (50) of step (d) to provide a combined LNG stream (60); (f) reducing the pressure of the combined LNG stream (60) of step (e); and (g) passing the combined LNG stream (60) of step (f) through a flash vessel (12) to provide a product LNG stream (70) and a gaseous stream (80).