Cryogenic purification for biogas with drawing to an intermediate stage and external solidification of carbon dioxide
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Solution Overview
Problem
Current biogas purification processes are inefficient in separating and liquefying methane and carbon dioxide with minimal methane loss and operational complexity, particularly due to high CO2 content and the need for multiple cryo-trapping systems that do not recover cold energy.
Innovation Solution
A combined installation and process incorporating a cryogenic separation and liquefaction system with a distillation column, recycle gas, and refrigeration circuit that recovers cold energy by using methane as a refrigerant, allowing for simultaneous separation and liquefaction of methane and carbon dioxide with thermal integration and external container regeneration to manage CO2 solidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple cryo-trapping systems are used in parallel to achieve continuous biomethane production, then separation efficiency is improved, but device complexity and operational costs increase
Solution Approach 1:
The patent combines the cryogenic separation and CO2 trapping functions into a single integrated distillation column system. The column simultaneously performs methane separation and CO2 solidification in different sections, eliminating the need for multiple parallel exchangers while maintaining continuous production capability.
Solution Approach 2:
The distillation column is designed to perform multiple functions: separating methane in the upper section and trapping CO2 in the lower section. This multi-functional design replaces several specialized devices with one versatile unit, reducing overall system complexity.
2Manufacturing precision
If CO2 is solidified on a cold surface for separation, then purification efficiency is improved, but cold energy is lost without recovery
Solution Approach 1:
The patent recovers the cold energy used for CO2 solidification by using it to pre-cool the incoming biogas feed stream. This heat exchange arrangement captures the cold energy that would otherwise be wasted and reuses it in the separation process, significantly improving energy efficiency.
Solution Approach 2:
The system implements a feedback loop where the cold energy generated during CO2 trapping is fed back into the process to cool the incoming gas. This internal energy recycling creates a self-sustaining thermal balance that reduces external cooling requirements.
3Manufacturing precision
If absorption or permeation techniques are used for biogas purification, then CO2 removal is improved, but additional modules are required for liquefaction and operational complexity increases
Solution Approach 1:
The patent merges the CO2 removal and methane liquefaction operations into a single cryogenic distillation column. The column simultaneously achieves CO2 separation through solidification and methane purification through distillation, eliminating the need for separate absorption/permeation modules and downstream liquefaction equipment.
Solution Approach 2:
The system exploits phase transitions of CO2 (gas to solid) and methane (gas to liquid) within the distillation column to achieve both separation and liquefaction in one operation. The controlled temperature gradient enables CO2 to solidify in the lower section while methane is condensed and collected as liquid in the upper section.
4Productivity
If biogas is compressed to distillation pressure for cryogenic separation, then separation efficiency is improved, but energy consumption increases
Solution Approach 1:
The patent recovers compression energy by implementing a recycle stream where the overhead vapor from the distillation column is compressed and fed back into the column. This internal recycling reduces the need for continuous external compression and minimizes overall energy consumption.
Solution Approach 2:
The system maintains continuous operation with the distillation column running at steady state, where the recycle stream ensures continuous separation without requiring intermittent compression cycles. This continuous operation optimizes energy efficiency by avoiding repeated start-stop compression.
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 enables efficient separation and liquefaction of biogas components in a single operation, minimizing methane loss and recovering energy used in the liquefaction process, thus reducing operational costs and environmental impact.
Implementation Method 1
A distillation column K01 fed by the cooled mixture and for producing methane at the top of the column and a liquid enriched in CO2 at the bottom of the column
Implementation Method 2
An exchanger E01 for cooling the compressed mixture
Implementation Method 3
An exchanger E02 for liquefying the methane produced at the top of the column
Implementation Method 4
A means M3 for expanding and heating the liquid enriched in CO2 recovered at the bottom of the column and for recovering the cold from the liquid enriched in CO2
Implementation Method 5
A separator pot V01 for receiving the flow enriched in CO2 from the means M3 and for recovering a top vapor and liquid CO2 7
Implementation Method 6
At least two containers V04 A/B external to the distillation column for bringing the liquid of the cold section and the rising vapor of the hot section into contact and trapping all the solid CO2
Implementation Method 7
a means for introducing this fluid into the external container(s) being regenerated so as to cause the solid CO2 to melt
Data Source
Figure 1
Figure 2~3
AI summary
Combined cryogenic separation and liquefaction installation for methane and carbon dioxide contained in a biogas stream, comprising: - A means M1 for mixing biogas 1 with a recycled gas R, - A compressor for compressing the mixture to distillation pressure, - A heat exchanger E01 for cooling the compressed mixture, - A distillation column K01 fed by the cooled mixture and producing methane at the top of the column and a CO2-enriched liquid at the bottom of the column, - A heat exchanger E02 for liquefying the methane produced at the top of the column, - A means M2 for separating the liquefied methane into two parts: a "reflux" part 6 and a "product" part 5, - A means M3 for expanding and heating the CO2-enriched liquid recovered at the bottom of the column and for recovering the cold from the CO2-enriched liquid.and - A separator pot V01 for receiving the CO2-enriched stream from the medium M3 and recovering overhead vapor and liquid CO2 7, - A means for drawing off vapor V1 from an intermediate stage of the distillation column K01, - A means for partially condensing the vapor V1 and producing a two-phase stream D1, - A means for reinjecting the two-phase stream D1 into the distillation column K01 at the stage corresponding to the equilibrium temperature, With - The medium M1 such that the recycle gas R corresponds to the overhead vapor recovered at the outlet of the separator pot V01, - the exchanger E01 and the medium M3 being identical, and - the cryogenic separation unit comprising an external carbon dioxide solidification device.