LMG Fractional Distillation for Variable-Nitrogen Feed Gas
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Solution Overview
Problem
Existing methods for producing Liquefied Methane Gas (LMG) from biogas face challenges such as high capital and operational costs, energy inefficiency, and difficulty in adapting to varying methane gas flow rates and nitrogen concentrations, making it hard to establish small-scale, efficient, and cost-effective production facilities, especially in remote areas.
Innovation Solution
A method involving a fractional distillation column and cryogenic refrigerant circuits that operate at lower pressures, allowing for continuous production of LMG from mixed methane gas streams with variable nitrogen concentrations, including those with little to no nitrogen, using a combination of heat exchangers and a nitrogen phase separator to separate and recycle nitrogen, thereby reducing energy consumption and capital costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional LNG production plants are used, then large amounts of LNG can be produced, but the capital investment cost is substantial and the plants are not suitable for small-scale production
Solution Approach 1:
The patent divides the LNG production system into modular components including compression units, cooling units, storage tanks, and nitrogen removal systems that can be configured in different scales. This modular approach allows the system to be scaled down for small production facilities while maintaining functional integrity, thereby reducing capital investment costs for small-scale production.
Solution Approach 2:
The patent employs variable speed compressors and adjustable cooling capacities that can operate at different throughput levels. By changing operational parameters rather than requiring complete reconfiguration, the system can adapt to small-scale production needs without proportionally reducing capital investment, thus improving ease of manufacture for smaller capacities.
2Ease of manufacture
If mini LNG plants are used for small-scale production, then capital investment costs are reduced, but energy efficiency deteriorates with 20-35% methane loss
Solution Approach 1:
The patent incorporates a nitrogen removal system with sensors and control mechanisms that continuously monitor gas composition and adjust operating parameters to optimize methane recovery. This feedback control prevents excessive methane venting by dynamically adjusting the nitrogen removal process, thereby reducing energy loss while maintaining small-scale production economics.
Solution Approach 2:
Instead of discarding methane-rich gas during nitrogen removal or startup/shutdown operations, the patent implements recovery systems that capture and recycle this gas back into the production process. This approach significantly reduces methane loss while maintaining the cost-effectiveness of mini LNG plants.
3Productivity
If existing LMG production methods are used, then LMG can be produced from biogas, but the process cannot adapt to varying nitrogen concentrations and flow rates
Solution Approach 1:
The patent implements variable speed compressors and adjustable cooling capacities that can dynamically respond to changing feed gas conditions. The nitrogen removal system is also designed with adjustable parameters that can adapt to varying nitrogen concentrations in the biogas feed, enabling continuous operation across different operating conditions without compromising LMG production capability.
4Productivity
If base load production plants are used, then large LNG production capacity is achieved, but the plants require substantial upfront investment and are not suitable for remote areas
Solution Approach 1:
The patent divides the LNG production system into modular, containerizable units that can be transported and assembled at remote locations. This segmentation allows the system to maintain adequate production capacity while reducing the complexity and footprint of the overall plant, making it suitable for remote area deployment without requiring extensive infrastructure.
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 production of LMG at lower costs and with greater energy efficiency, allowing for the establishment of small-scale, flexible, and cost-effective production facilities that can operate continuously regardless of nitrogen levels, enhancing the feasibility of LMG production in remote areas.
Implementation Method 1
passing the mixed methane gas feed stream through a first heat exchanger and then through a second heat exchanger to condense at least a portion of the mixed methane gas feed stream, the first heat exchanger using a first cryogenic refrigerant and the second heat exchanger using a second cryogenic refrigerant
Implementation Method 2
to condense at least a portion of the mixed methane gas feed stream
Implementation Method 3
sending the mixed methane gas feed stream coming out of the second heat exchanger though a mid-level inlet of a fractional distillation column; separating the mixed methane gas feed stream inside the fractional distillation column into a methane-rich liquid fraction and a nitrogen-rich gas fraction
Implementation Method 4
withdrawing the gas phase from inside the nitrogen phase separator vessel and passing the withdrawn gas phase directly into an expansion valve; using the expanded gas coming out of the expansion valve as the first cryogenic refrigerant
Implementation Method 5
introducing the nitrogen-rich gas fraction coming out of the fifth heat exchanger into a nitrogen phase separator vessel where a liquid phase is separated from a gas phase
Data Source
AI summary
The method is carried out for continuously producing a liquefied methane gas (LMG) from a pressurized mixed methane gas feed stream. It is particularly well adapted for use in relatively small LMG distributed production plant, for instance those ranging from 400 to 15,000 MT per year, and/or when the mixed methane gas feed stream has a wide range of nitrogen-content proportions, including nitrogen being substantially absent. The proposed concept can also be very useful in the design of medium-scale and/or large-size plants, including ones where the nitrogen content always remains above a certain threshold. The methods and arrangements proposed herein can mitigate losses of methane gas when venting nitrogen, for instance in the atmosphere.