Process for removing CO2 from a methane-containing gas
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Solution Overview
Problem
Existing processes for removing CO2 from methane-containing gases are inefficient, requiring complex and costly purification steps, and often result in significant methane slip, making it difficult to achieve low CO2 concentrations necessary for efficient liquefaction and energy use.
Innovation Solution
A process involving freezing-out of CO2 followed by a pressure-temperature swing adsorption (PTSA) step, where the product gas is used as treatment gas to regenerate the PTSA, reducing energy consumption and methane slip, and allowing for efficient recycling of CO2-laden gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional purification processes (amine scrubs, PSA, PTSA, membranes) are used to remove CO2 from biogas, then CO2 concentration is reduced, but the processes require complex reconditioning/regeneration or replacement of separating apparatuses and often need multi-stage processes which increase costs and cause methane slip
Solution Approach 1:
The invention utilizes the phase transition of CO2 from gas to solid (deposition) at temperatures below -78.5°C to remove CO2 from biogas. By cooling the biogas to this temperature range, CO2 directly transitions from gaseous to solid state and can be separated, while methane remains gaseous. This phase transition-based separation eliminates the need for complex regeneration processes required by adsorption-based methods.
Solution Approach 2:
The invention replaces complex mechanical separation systems (PSA, PTSA, membrane modules) with a simpler thermal processing system. Instead of using mechanical adsorption devices that require regeneration cycles and complex control systems, the method uses temperature control to induce CO2 deposition, followed by simple filtration or settling to separate the solid CO2 from the gaseous methane.
2Quantity of substance
If multi-stage purification processes are used to achieve low CO2 concentrations, then CO2 removal efficiency is improved, but additional costs and methane slip increase
Solution Approach 1:
By utilizing the phase transition of CO2 at -78.5°C, the invention achieves highly effective CO2 removal in a single stage. The phase transition creates a distinct physical state difference between CO2 (solid) and methane (gas), enabling complete separation without the need for multiple purification stages that would otherwise be required to achieve the same low CO2 concentrations.
Solution Approach 2:
The invention changes the temperature parameter to below -78.5°C to induce CO2 deposition. This parameter change fundamentally alters the separation mechanism, allowing for highly efficient CO2 removal in a single pass through the cooling and separation system, thereby minimizing methane slip that would occur in multi-stage processes.
3Quantity of substance
If conventional purification processes are used to achieve CO2 concentrations below 215 ppm for liquefaction, then CO2 removal is achieved, but the processes are time- and cost-intensive
Solution Approach 1:
The phase transition of CO2 to solid state at -78.5°C provides a rapid and complete separation mechanism. This physical transformation occurs quickly and allows for fast removal of CO2 to concentrations below 215 ppm, eliminating the time-consuming sequential stages required by conventional methods such as amine scrubbing, PSA, and membrane separation.
Solution Approach 2:
The invention replaces time-intensive mechanical separation processes with a rapid thermal processing approach. The phase transition-based separation can be achieved in a single continuous pass through the cooling and separation system, dramatically reducing the purification time compared to multi-stage conventional processes that require sequential treatment and regeneration cycles.
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 effectively reduces CO2 concentrations in methane-containing gases to below 215 ppm, minimizing methane slip and energy consumption, while also simplifying the purification process and enhancing the efficiency and cost-effectiveness of CO2 removal.
Implementation Method 1
CO2 is separated from the gas by freezing-out (step b). To this end the methane-containing gas is cooled, preferably to or below −78.5° C., at atmospheric pressure.
Implementation Method 2
the CO2 concentration of the methane-containing gas is then further reduced in a pressure temperature swing adsorption (PTSA) apparatus
Data Source
AI summary
A process for removing CO2 from a methane-containing gas, having the steps of providing a methane-containing gas containing at least CO2 as an impurity, cooling the gas to remove CO2 from the methane-containing gas by freezing out same, and additionally reducing the CO2 concentration of the gas using a pressure temperature swing adsorption apparatus (PTSA), whereby a methane-enriched product gas is obtained. At least a part of the product gas is then used as treatment gas and is passed through the PTSA for treatment of the PTSA, whereby CO2 is absorbed by the treatment gas and is removed from the PTSA as a CO2-enriched treatment gas. The treatment gas is then recycled and admixed with the methane containing gas.