Bioreactor Methanation With CO2 Feedback for Gas Quality
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Solution Overview
Problem
Existing biological methanation processes struggle to produce a methane-enriched gas with high methane content and low hydrogen and carbon dioxide levels efficiently and economically, particularly for integration into public gas distribution systems, due to the high cost of hydrogen production and the need for precise control of reaction conditions.
Innovation Solution
A bioreactor-based process that regulates the supply of carbon dioxide and hydrogen gases based on the carbon dioxide content in the product gas, maintaining a target CO2 concentration between 0 and 5 vol %, using a controller to adjust the educt gas ratios and pH stabilization through CO2 content management, without direct pH adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If biological methanation is carried out with a ratio of H2 to CO2 of 4:1 to achieve complete reaction according to the methanation equation, then the methane content in the product gas is maximized, but the hydrogen content in the product gas may exceed the supply limits for integration into public gas distribution systems
Solution Approach 1:
The system continuously measures the composition of the product gas and uses this information to dynamically adjust the ratio of H2 to CO2 supplied to the bioreactor. This feedback control ensures that the hydrogen content in the product gas remains below the 5 vol% supply limit for public gas distribution systems while maintaining high methane content through optimized reaction conditions.
2Object-generated harmful factors
If the hydrogen supply to the bioreactor is restricted to reduce hydrogen content in product gas, then the methane content may decrease, but the hydrogen produced by electrolysis must be temporarily stored
Solution Approach 1:
CO2 acts as an intermediary substance that mediates between hydrogen supply and methane production. By independently controlling CO2 supply in addition to H2 supply, the system can adjust the reaction balance to keep product gas hydrogen content below 5 vol% while maintaining high methane production rates, avoiding the need to temporarily store excess hydrogen.
3Manufacturing precision
If CO2 content in the product gas is regulated to a value of zero to maximize methane purity, then the hydrogen supply must be continuously adjusted, increasing system complexity
Solution Approach 1:
Instead of regulating CO2 content to exactly zero, the system applies partial action by maintaining CO2 content within an optimized range (0-5 vol%) in the product gas. This approach achieves sufficiently high methane purity for practical applications while significantly reducing control system complexity and improving process stability compared to strict zero-CO2 regulation.
4Productivity
If the ratio of H2 to CO2 is strictly maintained at 4:1 to optimize methanation reaction efficiency, then the system lacks flexibility to respond to variations in feed gas composition and demand fluctuations
Solution Approach 1:
The system transitions from a static fixed 4:1 H2 to CO2 ratio to a dynamic adjustable ratio that responds to real-time variations in feed gas composition and product demand. The controller dynamically optimizes the H2 and CO2 supply rates based on measured product gas composition, maintaining high methanation efficiency while adapting to changing operating conditions.
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
Achieves a stable, high-quality methane-enriched gas with low CO2 content, suitable for public gas distribution, while optimizing economic efficiency and reducing the need for additional pH adjustments, utilizing existing infrastructure and technology.
Implementation Method 1
processes for biological methanation, in which the biomethane is formed by methanogenic microorganisms
Implementation Method 2
the biomethane is formed by methanogenic microorganisms
Implementation Method 3
the hydrogen is provided by the electrolysis of water with the aid of an electrolyser
Data Source
AI summary
A process for the production of a methane-enriched gas including the steps of providing a bioreactor having at least one device for supplying a gas, and at least one outlet for removing the methane-enriched gas generated in the bioreactor; providing a device for determining the proportion of carbon dioxide in the methane-enriched gas removed from the bioreactor; specifying a target value S for the proportion of carbon dioxide in the methane-enriched gas removed from the bioreactor; supplying carbon dioxide-containing gas to the bioreactor; supplying hydrogen-containing gas to the bioreactor; forming methane-enriched gas in the bioreactor; removing the methane-enriched gas formed in the bioreactor from the bioreactor; determining an actual value for the proportion of carbon dioxide in the methane-enriched gas removed from the bioreactor; comparing the target value S with the determined actual value; regulating the quantity of supplied carbon dioxide-containing gas and/or regulating the quantity of supplied hydrogen-containing gas in a manner such that the determined actual value corresponds to the specified target value S, wherein the target value S specified for the proportion of carbon dioxide in the methane-enriched gas removed from the bioreactor satisfies the condition 0 vol %<S≤5 vol %.