Variable-Speed LNG Expanders for Subcooled Liquefaction
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Solution Overview
Problem
The depletion of natural gas wells is difficult to predict, and existing methods for extending their lifetime are costly and inefficient, particularly due to high energy consumption and contamination of natural gas with nitrogen during extraction.
Innovation Solution
A method involving a variable speed liquid LNG expander in series with a variable speed two-phase LNG expander, optimizing their rotational speeds to maximize liquid LNG production and minimize vapor and boil-off, thereby reducing the need for nitrogen injection and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nitrogen gas is injected into the gas well to maintain pressure, then the well production can be sustained, but the natural gas becomes contaminated with nitrogen and overall liquefaction costs increase
Solution Approach 1:
The patent changes the temperature parameter of the LNG from saturation temperature to subcooled temperature. By subcooling the LNG to below its bubble point temperature, the system prevents nitrogen from evaporating and contaminating the natural gas, while maintaining well production pressure
Solution Approach 2:
The patent utilizes phase transition control by maintaining LNG in a subcooled liquid phase rather than allowing it to reach saturation. This prevents the phase change that would cause nitrogen evaporation and contamination, solving the contradiction between maintaining production and preventing contamination
2Stress or pressure
If conventional LNG expansion methods are used, then pressure reduction is achieved, but significant vapor and boil-off are produced reducing liquid LNG output
Solution Approach 1:
The patent changes the temperature parameter by subcooling the LNG below its saturation temperature before expansion. This parameter change allows the LNG to undergo pressure reduction while minimizing vapor formation, thereby maximizing liquid LNG output
Solution Approach 2:
The patent applies preliminary subcooling action before the expansion process. By pre-cooling the LNG to a subcooled state, the system prepares the fluid to withstand pressure reduction without significant vaporization, thus maximizing liquid output
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 extends the lifetime of gas wells by reducing feed gas requirements and boil-off losses, achieving energy savings and increased production with a short payback time for investment, making it an economical solution for both existing and new liquefaction plants.
Implementation Method 1
Evaporation cooling occurs at the liquid-vapor interface. A liquid-to-vapor phase change process requires vaporization heat, which is extracted from the remaining liquid part. Consequently any partial vaporization of a liquid cools the remaining part of the liquid.
Implementation Method 2
A liquid-to-vapor phase change process requires vaporization heat, which is extracted from the remaining liquid part. Consequently any partial vaporization of a liquid cools the remaining part of the liquid.
Implementation Method 3
Dr William Cullen, Professor in Chemistry at the Universities of Glasgow and Edinburgh formulated in 1765 his theory of heat and combustion. In 1775 he developed a simple method for producing ice by simply evaporating the air and water vapor from a tank filled with liquid water.
Data Source
AI summary
A variable speed liquid LNG expander (X1) and a variable speed two-phase LNG expander (X2) in line, downstream from X1. The rotational speed of both expanders can be controlled and changed independent from each other. The speed of expander X1 and expander X2 is determined in such way that the amount of liquid LNG downstream from the PHS compared to the feed gas supply is maximized and the amount of vapor and boil-off downstream of X2 is minimized.