Characteristics of coal slime pyrolysis with integrated CO₂ capture

Faced with increasingly severe energy and environmental issues, the clean and efficient utilization of coal slime is an urgent problem to be solved. Due to the concerns about carbon reduction and the intention to produce high quality gaseous products, pyrolysis experiments of coal slime coupled with in-situ and ex-situ CO₂ capture were carried out in a fixed-bed reactor. The effect of pyrolysis temperatures, mixing ratios of coal slime and CaO, and the CO₂ capture ways were investigated. The gaseous products from coal slime pyrolysis mainly included H₂, CO, CO₂, CH₄, etc. It was revealed that after adding CaO, the hydrogen content in the pyrolysis gas increased significantly, while the CO₂ content decreased. When the temperature increased from 600 to 800 °C, the generation of gas products was enhanced. Due to the different interactions between the coal slime and CaO, the CO₂ capture efficiency of in-situ capture was higher than that of ex-situ capture, but ex-situ capture presented a relatively higher hydrogen production. When the coal slime/CaO mixing ratio is 1:1 and the pyrolysis temperature is 600 °C, the in-situ CO₂ capture ratio could reach 92.1%, and H₂ content at this situation is 56.5%. For ex-situ CO₂ capture, the capture efficiency of CO₂ increased with the increasing proportion of CaO. When the coal slime/CaO mixing ratio was 1:1, the ex-situ capture efficiency of CaO for CO₂ is 74% at 600 °C while the H₂ content is 59.3%. After CO₂ was captured by CaO, the diffraction peaks of CaCO₃ appeared in XRD patterns, and the microscopic morphology of CaCO₃ particles was clustered. Peaks corresponding to CaCO₃ also appeared in the C 1s, Ca 2p, and O 1s regions of the XPS peak spectrum, and showed a trend of first increasing and then decreasing as the temperature gradually increased. This study will provide a theoretical guidance on the efficient and clean utilization of coal slime.