In a significant stride towards enhancing the efficiency and durability of biomass chemical looping combustion (CLC) systems, researchers have developed a novel composite oxygen carrier that shows promise in mitigating chlorine-induced corrosion. This innovation, spearheaded by Dezhe Wang from the State Key Laboratory of Coal Combustion and Low Carbon Utilization at Huazhong University of Science and Technology, addresses a critical challenge in the energy sector: the corrosive effects of chlorine present in biomass and coal.
Chemical looping combustion is a cutting-edge technology that offers a cleaner alternative to traditional combustion methods by capturing carbon dioxide more efficiently. However, the presence of chlorine in biomass can corrode oxygen carriers and boiler equipment, posing a substantial hurdle to the widespread adoption of CLC. “The lack of research on hydrochloric acid (HCl) in CLC processes motivated us to explore solutions that could enhance chlorine fixation and corrosion resistance,” Wang explained.
The study, published in the journal *Energy and Environmental Protection*, focuses on the development of composite oxygen carriers using Ca-based and Ba-based adsorbents. These carriers were synthesized using the sol-gel method and tested in a batch fluidized bed setup. The results were promising: the addition of alkaline earth metals like calcium and barium significantly improved the performance of Cu-based oxygen carriers. “We found that Ca and Ba doping preferentially form stable chlorides with HCl, which enhances the lattice oxygen activity and promotes gas-solid reactions for chlorine capture,” Wang noted.
The enhanced oxygen carriers demonstrated superior combustion characteristics, with peak CO2 production and peak height significantly higher than those of standard Cu oxygen carriers. Additionally, the doping improved the gasification of biomass coke, leading to more complete conversion of gases like H2 and CH4. The peak CO concentrations were measured at 0.08%, 0.07%, and 0.06% for Ca-Cu, Ba-Cu, and Cu carriers, respectively, indicating enhanced CO conversion efficiency.
The study also investigated the impact of temperature and oxygen-fuel ratio on combustion and dechlorination performance. Increasing the temperature from 800 ℃ to 900 ℃ resulted in a notable improvement in combustion efficiency for the Cu oxygen carrier, rising from 87.0% to 94.7%. The Ba oxygen carrier showed a significant improvement as well, increasing from 88.0% to 94.7%. In contrast, the Ca oxygen carrier maintained stable performance, with only a slight decrease in efficiency.
When the oxygen-fuel ratio was raised from 1.5 to 2.0, the chlorine fixation efficiency for Cu carriers increased from 84.3% to 96.3%. Both Ca- and Ba-based oxygen carriers maintained 100% chlorine fixation efficiency, suggesting that lower oxygen-fuel ratios could be utilized in biomass dechlorination processes, thereby reducing operating costs.
The research highlights the potential of alkaline earth metals in enhancing the performance of oxygen carriers, promoting the development and application of chlorine-resistant carriers. “This study helps us understand the chlorine fixation characteristics of alkaline earth metals, which is crucial for advancing the field of chemical looping combustion,” Wang concluded.
The findings of this research could have significant implications for the energy sector, particularly in the development of more efficient and durable CLC systems. By addressing the challenge of chlorine-induced corrosion, this innovation paves the way for cleaner and more sustainable energy solutions. As the energy industry continues to seek ways to reduce emissions and improve efficiency, the work of Wang and his team offers a promising avenue for future developments in the field.