Experimental and kinetics analyses of a typical Zhundong coal reaction in O2/CO2/H2O atmosphere

Oxy-fuel combustion is one of the most potential carbon capture technologies. The abundant high alkali Zhundong coal will serve as the backbone of energy supply for a long time in China. Oxy-fuel combustion may reduce the evaporation of alkali metals by adjusting combustion temperature, so as to alleviate the slagging and fouling of heating surface for Zhundong coal-fired boilers. The gasification of coal by high contents of CO2 and H2O in the flue gas interacts with the oxidation reaction by O-2, which affects the combustion reactivity and the final combustion efficiency. However, the existing kinetic models usually ignore the gasification by CO2 and H2O, which results in insufficient prediction ability. In this study, the interaction between gasification and oxidation was obtained on a fixed bed experimental platform, and the co-gasification reaction model of CO2 and H2O was established based on the Langmuir-Hinshelwood model. The results show that there was no competition between char-O-2 and char-CO2 (or H2O), while CO2 and H2O competed at some active sites when reacting with char. Then, based on the in-situ optical measurement system a novel method considering the chemical cooling effect for calculating char-O-2 reaction rate under high temperature and complex atmosphere (O-2/CO2/H2O) was proposed, and finally a comprehensive high temperature gasification reaction model was established. The reaction rate increased with the increasing flue gas temperature and O-2 concentration. As CO2 concentration increased, the reaction rate first increased slightly and then decreased. The reaction rate reached the minimum value at 26% H2O concentration.

Automated summary

Oxy-fuel combustion is a promising carbon capture technology that can alleviate the slagging and fouling issues in high alkali Zhundong coal-fired boilers. However, the existing kinetic models often neglect the gasification reactions by CO2 and H2O, leading to insufficient prediction accuracy. This study established a co-gasification reaction model and proposed a novel method considering the chemical cooling effect to calculate the char-O-2 reaction rate under high temperature and complex atmosphere. A comprehensive high temperature gasification reaction model was successfully developed.