Experimental study on thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion represents an advanced coal-fired power generation technology advantageous for CO2 capture and system efficiency enhancement. This study employed a pressurized tube furnace experimental system to investigate the thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere. The carbon conversion under varying pressures (0.1-1.3 MPa), atmospheres, and residence times were analyzed. The physical and chemical structural evolutions of char, which are directly related to its reactivity, were elucidated using nitrogen adsorption, XPS, Raman, and FTIR analysis. The findings indicate that both pressurization and increasing O2/CO2 enhanced char conversion. Transitioning from kinetic to diffusion control in the O2/CO2/H2O atmosphere necessitated high pressure. The influence of CO2 on the physical and chemical structure of char under pressurized conditions was found to be less significant compared to that of O2 and H2O. Furthermore, pressurization and elevated O2 ratios were observed to reduce the microporous structure's contribution to the specific surface area of the char. Pressurization also increased the degree of graphitization of the char. Elevated O2/CO2 concentrations facilitated the breakdown of C-C structures, the melting of large aromatic rings, and the reduction in the degree of graphitization, particularly under higher pressures. In the O2/ CO2/H2O pressurized atmosphere, more oxygen-containing functional groups were formed within the char structure, with the C-OH structure forming initially, followed by the O-C--O structure.