Small-Scale LNG Liquefaction Using Elevated-Pressure Nitrogen Cooling
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Solution Overview
Problem
Small-scale LNG production faces challenges in achieving high efficiency, low costs, and enhanced safety while maintaining environmental protection, particularly in remote locations without the economies of scale and experienced personnel of larger plants.
Innovation Solution
A method and plant design for liquefying pre-processed natural gas that involves pre-cooling, liquefaction, and sub-cooling at elevated pressures, followed by expansion to near atmospheric pressure, using a serially connected pre-cooling and liquefaction process with nitrogen as a cooling medium, which reduces equipment complexity and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional LNG liquefaction processes are used for small-scale production, then production capacity is sufficient for local needs, but specific energy consumption increases and efficiency decreases
Solution Approach 1:
The patent changes the operating pressure parameter from conventional atmospheric pressure to elevated pressure (40-100 bara) throughout the liquefaction process. This parameter change enables smaller plant sizes with reduced specific energy consumption while maintaining efficient liquefaction, resolving the contradiction between small-scale productivity and energy efficiency
Solution Approach 2:
The patent introduces nitrogen as an intermediary cooling medium in a closed circuit system. The nitrogen circulates through heat exchangers to provide cooling without direct contact with the natural gas, enabling efficient heat transfer at elevated pressures and reducing specific energy consumption in small-scale applications
2Object-affected harmful factors
If small-scale LNG plants are built in remote locations, then local energy needs are met and environmental impact is reduced, but equipment complexity and safety requirements increase
Solution Approach 1:
The patent segments the liquefaction process into distinct functional units operating at elevated pressure: pre-cooling section, liquefaction section, and sub-cooling section. Each section is equipped with specific heat exchangers and control systems, allowing modular deployment in remote locations while managing complexity through functional separation
Solution Approach 2:
The patent maintains an inert nitrogen atmosphere throughout the elevated pressure system. Nitrogen serves as both the cooling medium and an inert environment that prevents combustion hazards, reducing safety concerns in remote locations while managing equipment complexity through standardized inert gas handling
3Use of energy by stationary object
If elevated pressure is used throughout the liquefaction process, then specific energy consumption is reduced and plant size is minimized, but equipment requirements and operational safety standards increase
Solution Approach 1:
The patent maintains elevated pressure (40-100 bara) throughout the liquefaction process using nitrogen as an inert atmosphere. This eliminates combustion hazards associated with high-pressure hydrocarbon systems, allowing energy-efficient compressed liquefaction while meeting safety standards through the inherent safety of nitrogen as the process medium
Solution Approach 2:
The patent uses nitrogen as an intermediary substance that enables elevated pressure operation. The nitrogen circulates in a closed circuit through heat exchangers, transferring cooling energy without requiring direct compression or expansion of the natural gas, thereby reducing safety risks while maintaining the energy efficiency benefits of high-pressure operation
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 the construction of energy-efficient small-scale LNG plants at lower costs, maintaining high safety standards and reducing specific energy requirements, thus addressing the limitations of existing small-scale LNG production methods.
Implementation Method 1
cooling of the gas is performed in a pre-cooling part and a thereto serially connected liquefaction part
Implementation Method 2
one or more part gas streams is (are) withdrawn from the gas stream introduced into the liquefaction part, heated in liquefaction part, returned in conduit(s) to the pre-cooling part
Implementation Method 3
expanding the compressed and cooled gas to a pressure of 1 to 1.3 bara to further cool the gas to produce a liquid and a gaseous phase
Implementation Method 4
separating the phases, withdrawing the gaseous phase from the plant, withdrawing and exporting the liquid phase from the plant as LNG
Implementation Method 5
expanded in expander(s) and used as cooling medium to cool the incoming gas stream in the pre-cooling part
Data Source
AI summary
A method for liquefaction of a pre-processed natural gas, comprising pre-cooling, liquefaction and sub-cooling of the gas at an elevated pressure, expanding the compressed and cooled gas to a pressure of 1 to 1.3 bara to further cool the gas to produce a liquid and a gaseous phase, separating the phases, withdrawing the gaseous phase from the plant, withdrawing and exporting the liquid phase from the plant as LNG, where the cooling of the gas is performed in a pre-cooling part (1) and a thereto serially connected liquefaction part (2), wherein the pressure in the pre- cooling part (1) is substantially equal to the pressure in the liquefaction part (2), and wherein one or more part gas streams is (are) withdrawn from the gas stream introduced into the liquefaction part (2), heated in liquefaction part (2), returned to the pre-cooling part (1), expanded and used as cooling medium to cool the incoming gas stream in the pre-cooling part (1), and a plant for performing the method, are described.