Method for separating all or some of the compounds from a biogas in the liquid state or in the two-phase state
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Solution Overview
Problem
Conventional methods for separating methane and carbon dioxide from biogas in the liquid or two-phase state, such as membrane separation, PSA, and cryogenic distillation, fail to achieve high purity levels, are unsuitable for treating liquefied biogas, and can result in clogging due to dry ice formation.
Innovation Solution
A method involving cryogenic distillation in a first column with a liquefying agent injected above the biogas inlet to prevent dry ice formation, followed by a second distillation column for further separation, achieving high purity levels of methane and carbon dioxide by controlling temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cryogenic distillation is used to separate methane from carbon dioxide, then separation efficiency is improved, but dry ice formation causes blockages in heat exchangers and packing material
Solution Approach 1:
The patent applies preliminary anti-action by injecting a liquefying agent (such as nitrogen or carbon monoxide) into the distillation column before carbon dioxide can desublimate and form dry ice. This preventive injection counteracts the harmful effect of dry ice formation by maintaining the carbon dioxide in a liquid or supercritical state throughout the distillation process, thereby preventing blockages in heat exchangers and packing material while preserving separation efficiency
Solution Approach 2:
The patent uses a liquefying agent as an intermediary substance injected into the distillation column. This intermediary prevents the direct phase transition of carbon dioxide from gas to solid by providing a liquid phase medium, thereby eliminating dry ice formation and its associated blockage problems while maintaining effective separation of methane and carbon dioxide
2Device complexity
If membrane separation is used to separate methane from carbon dioxide, then equipment complexity is reduced, but the method is unsuitable for treating liquefied biogas containing hydrocarbons
Solution Approach 1:
The patent applies parameter changes by operating the distillation column at cryogenic temperatures and controlled pressures where hydrocarbons remain in liquid phase. This parameter regime allows the system to handle liquefied biogas containing hydrocarbons effectively, as the hydrocarbons do not interfere with the separation process under these conditions, unlike in membrane separation where they cause degradation
3Device complexity
If PSA is used to separate methane from carbon dioxide, then equipment simplicity is improved, but desired purity levels of 99.9% cannot be achieved
Solution Approach 1:
The patent utilizes phase transitions by operating the distillation column in a cryogenic regime where methane and carbon dioxide exhibit distinct volatility differences. Through controlled condensation and vaporization cycles, the system achieves high-purity separation of 99.9% methane, overcoming the purity limitations of PSA while maintaining operational simplicity through the natural phase behavior of the gases
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 method achieves high purity levels of 99.9% for methane and carbon dioxide, prevents dry ice formation, and allows for efficient recovery of both gases without clogging issues.
Implementation Method 1
a first separation for separating the methane from the other compounds is carried out by cryogenic distillation in a first distillation column comprising a column top brought to the condensation temperature of the methane at a given pressure
Implementation Method 2
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 T1 lower than or equal to the carbon dioxide desublimation temperature
Implementation Method 3
the biogas liquefied at an equilibrium temperature making it possible to obtain a two-phase mixture ensuring the separation of the various compounds
Data Source
AI summary
A method is used for separating all or some of the compounds from a biogas in the liquid or the two-phase liquid/vapor state containing methane, CO2 and optionally hydrocarbon(s) from the C3 to C7 family. The methane is separated from the other compounds by cryogenic distillation by injecting, into a distillation column, the liquefied biogas at an equilibrium temperature that 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 is 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 vapor flow rate of the CO2 ascending at the top of the column.