Biogas Upgrading Chain Using Low-Pressure Membrane Purification
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Solution Overview
Problem
Current methods for converting biogas to a compressed natural gas (CNG) equivalent are costly and complex, making it difficult to economically process smaller sources of biogas, as they fail to meet CNG vehicle fuel standards due to low methane content, high carbon dioxide, nitrogen, and sulfur levels, and require removal of volatile organic compounds like siloxane, which are harmful to engines.
Innovation Solution
A simpler process chain using refrigeration for moisture removal, non-regenerative media for VOC and sulfur compound removal, and a single-stage membrane for carbon dioxide and hydrogen sulfide removal, operating at lower pressures to reduce power consumption and maintenance, with optional second-stage membranes and gas recycle for higher methane recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional multi-stage processing systems are used to meet CNG standards, then gas purification is improved, but device complexity and operational cost increase
Solution Approach 1:
The patent combines multiple purification functions (moisture removal, VOC removal, sulfur removal, CO2 removal) into a single integrated membrane separation unit. This single-stage membrane system simultaneously performs what traditionally required multiple separate processing stages, thereby reducing device complexity while maintaining gas purification effectiveness and meeting CNG standards.
Solution Approach 2:
The membrane separation unit is designed as a universal device that performs multiple purification functions simultaneously - removing moisture, VOCs, sulfur compounds, and CO2 in one operation. This multi-functional approach eliminates the need for separate dedicated units for each contaminant removal, simplifying the overall process chain while achieving comprehensive gas purification.
2Manufacturing precision
If high-pressure compression systems are used to achieve CNG standards, then gas compression is improved, but power consumption increases
Solution Approach 1:
The membrane separation unit performs preliminary purification of the biogas stream before compression, removing contaminants that would require excessive compression energy to eliminate. By pre-treating the gas to remove moisture, VOCs, sulfur compounds, and CO2, the subsequent compression stage operates more efficiently at lower pressures, reducing overall power consumption while still achieving CNG standards.
3Manufacturing precision
If complex regenerative media systems are used for VOC and sulfur removal, then gas purification is improved, but maintenance requirements and operational cost increase
Solution Approach 1:
The patent employs disposable or easily replaceable membrane modules that can be discarded or regenerated when fouled, eliminating the need for complex regenerative systems requiring careful maintenance. The membrane units are designed to be replaced rather than regenerated, simplifying operations and reducing maintenance requirements while maintaining effective removal of VOCs and sulfur compounds throughout their service life.
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 solution achieves 65-85% methane recovery, producing a CNG equivalent that meets standards, with cost savings from reduced power consumption and maintenance, enabling the use of waste gas for power generation or blending with existing biogas systems, and producing a premium renewable fuel.
Implementation Method 1
a single-stage membrane for carbon dioxide removal and further moisture and hydrogen sulfide removal
Implementation Method 2
refrigeration for bulk moisture removal
Implementation Method 3
non-regenerative media for VOC removal and sulfur compounds removal
Data Source
AI summary
Biogas is converted to a vehicle fuel equivalent to compressed natural gas high in methane in a simple, low cost process involving steps of refrigeration, non-regenerative activated carbon purification and carbon dioxide removal using low-pressure membrane technology.