Two-Stage Membrane Biogas Purification for Methane Liquefaction
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Solution Overview
Problem
Existing biogas purification methods for producing high-purity methane are energy-inefficient, use harmful chemicals, require high operating costs, and do not integrate well with liquefaction processes, while traditional CO2 management is inefficient and discontinuous.
Innovation Solution
A two-stage purification process using membrane separation units to achieve methane purity of less than 5% CO2 in the first stage and less than 400 ppm CO2 in the second stage, combined with efficient heat exchange systems and optional distillation, to produce high-purity methane suitable for liquefaction, with CO2 valorization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional purification methods (amine scrubbing, adsorption) are used to achieve high methane purity, then CO2 removal efficiency is improved, but energy consumption increases and harmful chemicals are used
Solution Approach 1:
The purification process is divided into two distinct stages: a first purification stage using membrane separation to remove the bulk of CO2, and a second polishing stage using adsorption to achieve high purity. This segmentation allows each stage to be optimized for its specific function, reducing overall energy consumption compared to using a single high-performance method throughout.
Solution Approach 2:
A membrane separation unit is introduced as an intermediary component between the raw biogas and the final polishing stage. The membrane unit performs preliminary CO2 removal, reducing the burden on the subsequent adsorption system and thereby lowering total energy consumption while avoiding the need for high-energy amine scrubbing processes.
2Manufacturing precision
If amine scrubbing is used for CO2 removal, then purification efficiency is improved, but harmful chemicals are introduced and operating costs increase
Solution Approach 1:
The harmful amine chemicals are completely extracted from the purification process and replaced with a membrane separation unit that uses physical selective permeation. This extraction of the harmful substance eliminates the associated environmental and safety issues while maintaining effective CO2 removal capability.
Solution Approach 2:
The chemical absorption mechanism of amine scrubbing is replaced with a physical membrane separation process. The membrane unit uses selective permeability based on gas properties rather than chemical reactions, eliminating harmful chemicals from the system while achieving comparable or superior CO2 removal efficiency.
3Manufacturing precision
If adsorption units (PTSA, PSA, TSA) are used for fine polishing, then methane purity is improved, but process complexity and operating costs increase
Solution Approach 1:
Instead of using complex multi-component adsorption systems (PTSA, PSA, TSA) for the entire purification process, the invention applies adsorption only partially in the second polishing stage after preliminary CO2 removal by membrane separation. This partial application reduces process complexity while achieving the required high purity level.
4Manufacturing precision
If traditional purification stages are implemented, then CO2 content is reduced, but energy efficiency deteriorates and CO2 management is discontinuous
Solution Approach 1:
The membrane separation unit operates continuously to remove CO2 from the biogas stream, providing continuous CO2 management rather than discontinuous batch processing. This continuous operation improves energy efficiency by eliminating idle times and maintaining steady-state conditions throughout the purification process.
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 energy-efficient, continuous production of high-purity methane for liquefaction, reduces operating costs, and effectively manages CO2, optimizing methane recovery and utilization.
Implementation Method 1
a second purification unit (7) comprising a membrane separation unit configured to produce the second gas stream enriched in methane with less than 400 ppm of carbon dioxide
Implementation Method 2
the first heat exchange system being configured to exchange heat between the cold source and the first methane-enriched gas stream in order to cool the first methane-enriched gas stream
Data Source
Figure 1~2
Figure 3
AI summary
Installation (1) for the treatment of a gas stream (10), in particular biogas, comprising methane and carbon dioxide, the installation (1) comprising a first cold source (6) and a gas circuit for the gas stream (10), the gas circuit comprising, arranged in series and fluidly connected by a set of pipes, a first compressor (2), a first purification unit (3) configured to produce a first gas stream enriched in methane (11) with less than 5% carbon dioxide, and a gas stream enriched in carbon dioxide (12), a first heat exchange system (4, 5), and a second purification unit (7) configured to produce a second gas stream enriched in methane (13) with less than 400 ppm of carbon dioxide, and a gas stream depleted in methane (14).