Membrane-based biogas purification and utilization technology

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1. Regarding biogas, China has over 3,000 large-scale biogas projects, as well as hundreds of landfills, which generate large amounts of biogas and landfill gas each year. Generally, the crude biogas accumulated in biogas digesters/tanks contains 40–60% methane, and it also includes impurities such as sulfur and ammonia; therefore it cannot be used directly. It needs to be purified through certain methods to produce clean, dry biogas with a high methane content (i.e., biomethane), so that it can be utilized more effectively. 2. Data from the natural gas market indicate that by 2015, China’s natural gas supply structure is expected to consist of 170 billion cubic meters of domestically produced gas and 90 billion cubic meters of net imports. Natural gas consumption is projected to reach 260 billion cubic meters, with its share of total primary energy consumption rising from the current 4% to around 8%. Domestic natural gas production is expected to reach 185 billion m3, resulting in a supply-demand gap of 75 billion m3. This relies on imported natural gas to meet domestic demand. At the same time, natural gas vehicles in our country are mainly concentrated in the commercial vehicle and taxi sectors, and have reached a certain scale. Due to rising oil prices and **policy incentives, buses and taxis in various cities have increasingly switched to natural gas, which has created a huge market for biomethane. 3. Our technology uses advanced gas membrane separation techniques to purify crude biogas into biomethane. Compared with traditional PSA adsorption methods and chemical absorption methods, this technology offers numerous advantages such as reduced space requirements, lower investment costs, and diminished energy consumption. It has become the development trend in biogas purification and refinement processes. The purification principle of gas membrane technology is as follows: when the various components in a mixed gas pass through a polymer (polyimide) membrane, their solubility and diffusion rates within the membrane fibers differ, thereby achieving separation. Based on this property, various gases can be divided into “fast gases” and “slow gases”. When membrane separation is used for biogas purification, the pre-treated compressed biogas flows through the inner cavity of the hollow fiber membranes. Driven by the pressure difference, gases with high solubility and diffusion coefficients (such as CO2 and H2S, known as \"fast gases\") pass through the membrane walls preferentially, while other gases (such as CH4, known as \"slow gases\") are more hindered in passing through, resulting in a lower rate of transmission. This mechanism achieves the separation of CH4 from CO2, thereby completing the process of purifying and refining biogas. 4. Technical advantages: ü Extremely low energy consumption ； ü Modular structure, saving space ； ü Reliable and durable, with good safety features ； ü Wide adjustable range, extremely high flexibility ； ü Can be miniaturized, reduced in size, and made mobile ； ü Short production process, simple equipment maintenance ； ü It is possible to extract two types of concentrated gases, CO2 and CH4, simultaneously. 5. Application of the technology: This technology can be widely applied in areas such as biogas production from industrial organic wastewater, biogas generated from kitchen waste, biogas from wastewater from livestock and poultry farming, and biogas from urban sludge wastewater. Through the latest international gas membrane separation technology, biogas and landfill gas can be purified to the quality level of vehicle fuel and conventional natural gas, thereby significantly improving their quality, expanding their range of applications, and enhancing their utility value. This technology changes the current situation in which biogas and landfill gas can mainly be used for cooking and power generation, resulting in limited utility value, and provides a new approach for the efficient and high-value utilization of biogas. This technology purifies biogas to produce natural gas, particularly compressed natural gas (CNG), for use as vehicle fuel, industrial gas, or urban gas. The purification process requires only electricity; the methane purity is ≥95%, and the methane recovery rate is ≥97%. The total purification cost of CNG is 1.2–1.6 yuan per m3 of methane; in certain areas along the eastern coast, the price of industrial gas can reach as high as 3–5 yuan per m3, resulting in significant economic benefits ； Compared to other utilization methods, biogas refined into natural gas products offers a high added value, large profit potential, minimal energy loss, and the greatest amount of transportable energy.