Biogas, a green renewable energy source, is primarily produced through the anaerobic digestion of organic waste. It is considered an efficient fuel for power generation and heat production. China has been a pioneer in large-scale biogas production, with an annual output of approximately 15 billion m3. As biogas contains impurities such as CO2 and H2S, it is crucial to remove these impurities to increase the share of methane in the fuel, a process known as biogas upgrading. The emergence of biogas upgrading technology not only enhances the economic benefits of biogas plants but also reduces greenhouse gas emissions. One such technology is the use of renewable ammonia aqueous absorbent, which offers advantages over other methods.
Biogas typically consists of approximately 60% CH4, 40% CO2, and trace impurities such as H2S and H2O. The presence of CO2 in biogas significantly reduces its combustion performance, while H2S contributes to corrosion of pipelines and equipment. Therefore, removing these impurities is essential to improve the quality and usability of biogas. Various biogas upgrading technologies have been developed, including pressurized water scrubbing, pressure-swing adsorption, chemical absorption, membrane separation, and cryogenic technology. However, methods like water scrubbing and pressure-swing adsorption result in high CH4 loss, reducing the overall efficiency of the process.
To overcome the limitations of other biogas upgrading methods, Prof. Shuiping Yan and his team proposed the use of a renewable ammonia aqueous absorbent derived from biogas slurry, a byproduct of anaerobic digestion. This approach combines the principles of green energy engineering and offers several advantages. The team achieved the simultaneous removal of CO2 and H2S from biogas using a gas-liquid membrane contactor and renewable ammonia aqueous solvent. The results demonstrated that a 0.1 mol·L-1 NH3 renewable ammonia aqueous solvent effectively removes 97% of H2S from biogas. The removal efficiency of H2S is less affected by impurities in this absorbent compared to physical absorption methods. By adjusting the renewable ammonia aqueous solution to 0.5 mol·L-1 NH3, the biogas can be purified to pipeline-quality biomethane.
The use of renewable ammonia aqueous absorbent offers several advantages over traditional methods of biogas upgrading. Firstly, the absorbent is derived from biogas slurry, making it a renewable and sustainable solution. Additionally, it can be used as an ammonium nitrogen fertilizer, providing direct application to farmland. This utilization of renewable ammonia aqueous absorbent not only solves the problem of waste disposal but also offers a practical and eco-friendly solution for the agricultural sector. Furthermore, the chemical absorption method with this absorbent reduces system energy consumption and CO2 absorbent loss, addressing the challenges faced by other biogas upgrading technologies.
The research team also determined the optimum operating conditions for the simultaneous removal of CO2 and H2S using a hollow fiber membrane contactor. Various operating parameters, including temperature and gas-liquid flow rate, were explored to achieve maximum efficiency during the membrane absorption process. These findings provide a theoretical basis and technical support for the green development of the biogas upgrading process. The use of renewable ammonia aqueous absorbent has the potential to revolutionize biogas upgrading, making it more economically viable and environmentally friendly.
The development of renewable ammonia aqueous absorbent offers a promising solution for biogas upgrading. By efficiently removing CO2 and H2S from biogas, this method improves the quality and usability of biogas as a green renewable fuel. Moreover, the utilization of renewable ammonia aqueous absorbent provides additional benefits such as waste disposal and agricultural application. With further research and implementation, this technology has the potential to play a significant role in the transition towards a sustainable and carbon-neutral energy future.