Biogas, generated through the anaerobic digestion of organic waste, such as animal manures and straw offcuts, holds immense potential as a renewable energy source. With an annual output of approximately 15 billion m3 in China alone, biogas production has emerged as a promising solution to the energy crisis. However, the presence of impurities, such as CO2 and H2S, hinders its efficiency and poses environmental risks. Biogas upgrading, a process that aims to remove these impurities, not only enhances economic income for biogas plants but also reduces greenhouse gas emissions. In this context, the advent of biogas upgrading technologies has paved the way for innovative solutions, with researchers focusing on chemical absorption methods to address key challenges.
While pressurized water scrubbing and pressure-swing adsorption are widely used for CO2 and H2S removal, they suffer from a significant disadvantage – high CH4 loss. The greenhouse effect of CH4 is about 21 times that of CO2, making the loss of CH4 detrimental to the environmental impact of biogas production. Chemical absorption methods, on the other hand, offer negligible CH4 loss and exhibit high reaction rates. By forming stable salts through the chemical reaction between the absorbent and acid gas, these methods address the drawbacks of energy consumption and CO2 absorbent loss. Prof. Shuiping Yan and his team have taken this approach one step further by proposing a revolutionary solution that combines renewable ammonia aqueous absorbent from biogas slurry and the principles of green energy engineering.
The study conducted by Prof. Yan and his team, published in the journal Frontiers of Agricultural Science and Engineering, presents a game-changing approach to simultaneously removing CO2 and H2S from biogas using renewable ammonia aqueous solvent in a gas-liquid membrane contactor. Unlike traditional chemical absorbents, the CO2-rich renewable ammonia aqueous absorbent can be directly applied as an ammonium nitrogen fertilizer in farmland, eliminating the issues associated with disposal. By utilizing renewable ammonia, the team achieved an impressive 97% removal of H2S from biogas, with minimal impact from impurities. Further adjustments to the renewable ammonia aqueous solution allowed for the production of purified biogas suitable for pipeline distribution as biomethane.
To ensure the efficiency of the simultaneous removal of CO2 and H2S, the team explored various operating parameters in the hollow fiber membrane contactor. Factors such as temperature and gas-liquid flow rate were investigated to determine the optimum conditions for membrane absorption. This comprehensive analysis provided the team with a specific theoretical basis and technical support for the green development of the biogas upgrading process.
The study conducted by Prof. Yan and his team marks a significant milestone in the field of biogas upgrading. By harnessing the power of renewable ammonia, this innovative approach offers a sustainable solution to the challenges posed by CO2 and H2S impurities in biogas. With its potential application as an ammonium nitrogen fertilizer, the utilization of renewable ammonia aqueous absorbent presents a groundbreaking opportunity for more environmentally friendly biogas production. As the world strives towards a greener future, the integration of renewable ammonia into biogas upgrading processes holds the key to unlocking the full potential of this renewable energy source.
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