Cryogenic purification of biogas with withdrawal at an intermediate stage and external solidification of carbon dioxide
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current biogas purification processes are inefficient in separating and liquefying methane and carbon dioxide with minimal methane loss and require multiple operations, especially when recovering cold used in CO2 solidification is not possible.
Innovation Solution
A combined plant and process for cryogenic separation and liquefaction of methane and carbon dioxide from biogas, involving a distillation column with a cold section at the top and a hot section at the bottom, external containers for trapping solid CO2, and a refrigeration circuit using methane as a refrigerant to recover and reuse cold, allowing for simultaneous separation and liquefaction in a single operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cryotrapping based on reversible exchangers is used to separate and liquefy methane and CO2, then separation and liquefaction can be achieved in two separate steps, but the cold used in CO2 solidification cannot be recovered and multiple exchangers are required
Solution Approach 1:
The patent combines the CO2 sublimation/liquefaction exchanger with the methane liquefaction exchanger into a single integrated exchanger unit. The CO2-enriched liquid from the bottom of the distillation column is fed to this combined exchanger where CO2 sublimates providing cold that is used for methane liquefaction, eliminating the need for separate exchangers and enabling cold recovery.
Solution Approach 2:
The patent converts the previously wasted cold from CO2 solidification into a useful resource by using the CO2-enriched liquid to sublime CO2 and generate cold that is then applied to liquefy methane. This transforms the harmful waste cold into a beneficial cooling source, reducing energy consumption.
2Manufacturing precision
If conventional purification processes are used, then CO2 can be removed from biogas, but additional supplementary modules are required to obtain liquid biomethane and CO2 content remains too high for efficient liquefaction
Solution Approach 1:
The patent merges the purification function with the liquefaction function into a single integrated distillation and liquefaction system. The distillation column separates CO2 from methane with high precision, and the integrated exchanger immediately liquefies both components in one unit, eliminating the need for separate purification and liquefaction modules.
3Productivity
If multiple operations are used for separation and liquefaction, then complete processing can be achieved, but the number of operations increases and energy efficiency decreases
Solution Approach 1:
The patent establishes a continuous process where CO2-enriched liquid from the distillation column bottom continuously sublimates in the exchanger, generating cold that continuously liquefies methane. This continuous action eliminates intermediate steps and energy losses associated with batch operations, maintaining complete processing while improving energy efficiency.
Solution Approach 2:
The patent implements a feedback loop where the cold generated by CO2 sublimation is immediately fed back to liquefy methane, and the liquefied methane is separated and returned to the distillation column as reflux. This internal feedback mechanism optimizes energy utilization and maintains process efficiency.
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 method enables efficient separation and liquefaction of methane and carbon dioxide with minimal methane loss and energy recovery, reducing the number of operations and optimizing energy use by integrating thermal processes for cold recovery.
Implementation Method 1
a distillation column K01 supplied with the cooled mixture and making it possible to produce methane at the top of the column and a CO2-enriched liquid at the bottom of the column
Implementation Method 2
an exchanger E02 for liquefying the methane produced at the top of the column
Implementation Method 3
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
Implementation Method 4
This system is based on the solidification of the CO2 present in the biogas on a cold surface (trapping), followed by a step of sublimation or liquefaction of the CO2 using a hot source
Data Source
AI summary
A combined plant for cryogenic separation and liquefaction of methane and carbon dioxide in a biogas stream, including a mixing means, a compressor, a first exchanger, a distillation column, a second exchanger, a separating means, an expanding means, and a separator vessel. Wherein, the mixing means is configured such that the recycle gas is the overhead vapour stream, and the first exchanger and the expanding means are combined.