Membrane Facility for Methane-Carbon Dioxide Separation
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Solution Overview
Problem
Current membrane processes for separating methane and carbon dioxide from biogas struggle to meet stringent methane emission regulations with low energy consumption and minimal equipment, often requiring high recycle rates or additional methane removal steps, which increase costs and decrease efficiency.
Innovation Solution
A membrane separation facility with four membrane units, where the permeate outlet of the fourth unit is connected to a methane oxidation unit, and the third permeate is directly discharged to the atmosphere, using membranes with a carbon dioxide to methane selectivity of at least 30, configured to achieve a carbon dioxide concentration of 90-99% in the first permeate stream and a methane content of 0.3% or less in the third permeate stream without oxidative post-treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high recycle rates are used in membrane processes to meet methane emission regulations, then methane content in discharged streams is reduced, but energy consumption and equipment complexity increase
Solution Approach 1:
The membrane separation process is divided into multiple stages (first, second, third membrane units) with different functions. The first unit performs initial separation, the second unit further purifies the retentate, and the third unit treats the permeate. This segmentation allows each unit to operate at optimized conditions, reducing the need for high recycle rates while meeting emission standards.
Solution Approach 2:
A condensation unit is introduced as an intermediary between the membrane units and the atmosphere. The condensation unit cools the third permeate stream, condensing water and potentially other components, which reduces the volume and methane content of the gas stream before discharge. This intermediary step enables compliance with emission regulations without requiring high recycle rates through the membrane units.
2Object-affected harmful factors
If additional methane removal steps are added to carbon dioxide enriched streams, then methane emission is reduced, but equipment complexity and investment costs increase
Solution Approach 1:
The system segments the gas streams into different pathways: the retentate stream is purified through the second membrane unit to achieve low methane content for direct discharge, while the permeate stream is treated through condensation. This segmentation eliminates the need for additional methane removal steps on the carbon dioxide enriched stream, as each stream is treated appropriately for its intended use or discharge.
Solution Approach 2:
The third permeate stream, which contains carbon dioxide and some methane, is directed to a condensation unit rather than requiring further membrane separation. The condensation process removes water and reduces the gas volume, and the resulting gas stream has sufficiently low methane content for atmospheric discharge. This converts a potentially harmful stream into a safely dischargeable stream without complex additional equipment.
3Use of energy by moving object
If membrane processes are designed for low energy consumption, then operating costs are reduced, but the ability to meet stringent methane emission regulations is compromised
Solution Approach 1:
The condensation unit serves as a low-energy intermediary that reduces the methane content of the third permeate stream without requiring high-energy processes. By cooling the gas stream and condensing liquids, the system reduces the volume and methane concentration of the discharged gas, enabling compliance with emission regulations while avoiding the high energy consumption associated with additional membrane units or thermal oxidation.
4Device complexity
If the third permeate stream is directly discharged without oxidative treatment, then equipment and operating costs are reduced, but methane emission regulations may not be met
Solution Approach 1:
The condensation unit is positioned as an intermediary treatment step for the third permeate stream before atmospheric discharge. This unit reduces the gas stream volume and methane content through condensation, enabling direct discharge that complies with methane emission regulations. This approach avoids the need for complex oxidative treatment equipment while still meeting emission standards.
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 investment and operating costs, minimizes the volume flow of the fourth permeate stream, and allows for continuous compliance with methane emission regulations, achieving high methane yields and low methane emissions while avoiding the need for additional methane removal steps.
Implementation Method 1
each membrane separation unit comprising a gas separation membrane having higher permeance for carbon dioxide than for methane
Implementation Method 2
the fourth permeate stream is passed to a methane oxidation unit and oxidized in this unit to provide an off-gas stream containing less than 0.3% by volume methane
Data Source
AI summary
A facility and a process with four membrane separation units, where the second separation unit separates the retentate of the first unit, the third separation unit separates the permeate of the first unit, the fourth separation unit separates the retentate of the third unit, the permeate of the second unit and the retentate of the fourth unit are recycled to the feed to the first unit, the permeate of the fourth unit is passed to a methane oxidation unit and the permeate of the third unit is discharged to the atmosphere allows separating methane and carbon dioxide from a gas stream, providing a methane rich stream with the retentate of the second unit at a high methane yield and adhering to low limits for methane discharge to the atmosphere with a small size methane oxidation unit.