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The separation is achieved by taking advantage of the differences in the adsorption abilities of various gas components on the surface of the polymer membrane, as well as their differences in solubility and diffusion within the membrane, which results in different permeation rates. The driving force for gas permeation is the partial pressure difference across the membrane. When there is a pressure difference on both sides of the membrane, gas components with high permeation rates pass through the membrane at a very high rate, forming a permeate stream. In contrast, gas components with low permeation rates mostly remain on the feed side of the membrane, forming a residual stream. These two streams are extracted separately, thereby achieving separation. By reasonably combining membrane modules, different methane purities and recovery rates can be obtained.
Process:
The raw biogas is first pressurized to the design pressure by a biogas compressor and then enters the decarbonization unit for pre-treatment, including dehydration, oil removal, and particulate separation. When the various indicators of the incoming gas meet the design standards of the membrane separation unit, it enters the membrane separation system. The membrane separation unit can be divided into a two-stage system and a three-stage system according to the CH4 recovery rate requirements of the product gas.
In the two-stage membrane separation process: the retentate from the first-stage membrane enters the second-stage membrane for further filtration to increase methane purity. The retentate from the second-stage membrane is output as product gas, while the permeate from the first-stage membrane is discharged as tail gas. The permeate from the second-stage membrane is recycled back into the process to improve methane recovery.
In the three-stage membrane process: the retentate from the first-stage membrane enters the second-stage membrane for further filtration to increase methane purity. The retentate from the second-stage membrane is output as product gas, while the permeate from the first-stage membrane enters the third-stage membrane system. The permeate from the third-stage membrane is discharged as tail gas. The permeate from the second-stage membrane and the retentate from the third-stage membrane are recycled back into the process to improve methane recovery.
Products Quality:
Meet different natural gas standards, the main standard indicators are listed as follows:
| Item | Parameters | ||
Standard Code | GB 17820 Level 1 | GB 17820 Level 2 | GB 18047 |
Higher Calorific Value /(MJ/m3) | ≥31.4 | ≥31.4 | ≥31.4 |
| ()Total Sulfur /(mg/m3) | ≤20 | ≤100 | ≤100 |
| H2S/(mg/m3) | ≤6 | ≤20 | ≤20 |
| CO2 mol:mol /(%) | ≤3.0 | ≤4.0 | ≤4.0 |
| O2 mol:mol /(%) | / | / | ≤0.5 |
| Remark: The standard reference conditions for gas volume are 101.325kPa and 20ºC. | |||
CH4 yield: > 96% (2-stage); > 99% (3-stage)
Main equipment:
Biogas compressor, cold drying and dehydration equipment, filtering equipment, temperature control equipment, membrane components, instruments.
Characters:
- High separation efficiency, compact design
- Convenient management
- Easy to start and stop
- Easy to scale up
- Large fluctuations in biogas flowrate
- CH4(>99%,) High requirements for CH4 yield (>99%, 3 or more stage membrane system)
