Method for separating all or some of the compounds from a biogas in the liquid state or in the two-phase state
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional biogas purification methods fail to achieve high purity levels of methane and carbon dioxide recovery, are unsuitable for liquefied biogas containing hydrocarbons, and produce solid carbon dioxide particles that cause blockages.
Innovation Solution
A two-stage cryogenic distillation process involving a first distillation column with a liquefaction agent injection to prevent dry ice formation and a second column for further separation, using hydrocarbons from the C3 to C7 family to achieve high purity recovery of methane and carbon dioxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If biogas is cleaned and conditioned before upgrading by removing water, CO2, and other impurities, then the quality of biogas for upgrading is improved, but the complexity of the process increases due to multiple treatment steps required
Solution Approach 1:
The patent combines multiple biogas treatment operations (washing, drying, CO2 removal, and upgrading) into a single integrated reactor system. The biogas flows through one continuous process where water is removed by a hydrophobic membrane, CO2 is absorbed by alkaline liquid, and methane is upgraded, eliminating the need for separate sequential treatment units and reducing overall process complexity.
Solution Approach 2:
The reactor system performs multiple functions simultaneously: it acts as a washing unit to remove water, a drying unit to eliminate moisture, a CO2 removal unit using alkaline absorption, and a methane upgrading unit. This multi-functional approach replaces multiple specialized devices with a single versatile system that handles all purification and upgrading tasks in one pass.
2Loss of substance
If biogas is dried by condensation or adsorption methods, then water content is reduced, but the energy consumption increases due to heating or cooling requirements
Solution Approach 1:
The patent replaces thermal-based drying methods (condensation requiring heating/cooling) with a mechanical/physical separation approach using a hydrophobic membrane. The membrane selectively passes water molecules from the biogas stream through its pores while blocking larger hydrocarbon molecules, achieving water removal without any heating or cooling energy input.
Solution Approach 2:
The invention employs a hydrophobic porous membrane as the core drying mechanism. The membrane's pore structure and hydrophobic properties enable it to selectively adsorb and remove water vapor from biogas at ambient conditions, eliminating the need for energy-intensive thermal drying processes while effectively reducing water content.
3Quantity of substance
If CO2 is removed from biogas using traditional methods, then methane concentration is increased, but additional treatment steps and equipment are required
Solution Approach 1:
The patent integrates CO2 removal functionality directly into the upgrading reactor by introducing alkaline liquid (such as potassium hydroxide solution) that flows counter-current to the biogas stream. This allows CO2 absorption to occur simultaneously with water removal and methane upgrading in a single integrated unit, rather than requiring separate CO2 removal equipment.
Solution Approach 2:
The invention changes the chemical parameter of the treatment liquid to alkaline conditions (using KOH or NaOH solutions), which fundamentally alters the removal mechanism from physical adsorption to chemical absorption. This parameter change enables efficient CO2 removal through neutralization reactions, achieving high methane concentration without complex separation equipment.
4Reliability
If multiple separate treatment units are used for biogas purification, then each function is performed effectively, but the overall process requires more space and time
Solution Approach 1:
The patent implements a continuous single-pass treatment process where biogas flows through the integrated reactor and undergoes water removal, CO2 absorption, and methane upgrading simultaneously in one continuous operation. This eliminates the need for sequential batch processing through multiple units, reducing both processing time and the risk of contamination between stages while maintaining purification effectiveness.
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
The process achieves purity levels of 99.9% for both methane and carbon dioxide, prevents dry ice formation, and recovers hydrocarbons for reuse, addressing the limitations of existing methods.
Implementation Method 1
drying the biogas by means of a hydrophobic membrane
Implementation Method 2
removal of carbon dioxide by means of an alkaline liquid
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for separating all or some of the compounds from a biogas in the liquid state or in the two-phase liquid/vapour state containing methane, CO2 and optionally a hydrocarbon or a mixture of hydrocarbons from the C3 to C7 family, wherein the methane is separated from the other compounds by cryogenic distillation by injecting, into a distillation column, the liquefied biogas at an equilibrium temperature which makes it possible to obtain a two-phase mixture, ensuring the separation of the different compounds, and a liquefying agent, in the liquid state, composed of a hydrocarbon or a mixture of hydrocarbon(s) from the C3 to C7 family, the liquefying agent being injected at the top of the column, above the biogas inlet, at a temperature lower than or equal to the CO2 desublimation temperature at a given pressure of the column and in an amount proportional to the vapour flow rate of the CO2 ascending at the top of the column.