Mechanism Analysis of Coal with CuO in the In Situ Gasification Chemical-Looping Combustion and In Situ Gasification Chemical-Looping with Oxygen Uncoupling Process

Temperature showed obvious effect on the reaction rate and conversion when CuO was used as an oxygen carrier (OC), in which in situ gasification chemical-looping combustion (iG-CLC) occurred at low temperature and in situ gasification chemical-looping with oxygen uncoupling (iG-CLOU) took place at high temperature. This study focused on the reaction mechanism investigation of the coal iG-CLC and iG-CLOU process. The reaction mechanism and definite temperature limits between iG-CLC and iG-CLOU could provide useful information for the development of mixed CuO-based OCs. In this study, the experiments of coal with CuO were tested in N-2 and CO2 atmospheres. Results showed that char was mainly oxidized by CuO in the temperature range of 620-810 degrees C in a N-2 atmosphere. Chemical-looping combustion changed into chemical-looping with oxygen uncoupling, in which the reaction of char with gaseous oxygen was dominated when temperature was above 810 degrees C. Under a CO2 atmosphere, the initial temperature of char combustion was still 620 degrees C, but the reaction path of char combustion changed. From about 746 degrees C, char could be gasified by CO2 first, and then the gasification product was oxidized by CuO. With the temperature increased to 775 degrees C, the oxygen released from CuO led to the reaction rate increasing. Char could be gasified by CO2, and then the gasification product preferentially reacted with gaseous oxygen. Moreover, char gasification was also the rate-limiting step in the iG-CLOU process. Considering the reactivity and stability of CuO, alkali metals and alkaline earth metals with low content and inert support that could improve the high temperature resistance should be used as modifications of CuO in the iG-CLOU process.

Automated summary

Temperature significantly affects the reaction mechanism of coal with CuO as an oxygen carrier, leading to different processes at low and high temperatures. Understanding the definite temperature limits and reaction mechanisms could inform the development of mixed CuO-based oxygen carriers.