Modeling of coal char gasification in coexistence of CO_2 and H_2O considering sharing of active sites

摘要

In a coal gasifier, CO_2 gasification and H_2O gasification occur at the same time. Many researchers have constructed CO_2 gasification model and H_2O gasification model separately. Only a few models explain the competition between CO_2 gasification and H_2O gasification. These models are divided into two types according to the properties of the active sites. Some models assume that CO_2 gasification and H_2O gasification occur at separate active sites, whereas others assume that all of the active sites are shared and are common to both CO_2 and H_2O gasification. There are some coals whose gasification reaction rates, with CO_2 and H_2O in coexistence, cannot be described by the conventional models. In this study, a Langmuir-Hinshelwood type gasification model was modified to explain the char gasification by CO_2 and H_2O. In the proposed model, CO_2 gasification and H_2O gasification partially share active sites. Coal chars, which were prepared through pyrolysis using a drop tube furnace at ambient pressure and 1673 K, were gasified with CO_2 and H_2O using a pressurized drop tube furnace (PDTF) and a thermogravimetric analyzer (TGA) at various temperatures. The proposed model was found to describe the gasification reaction rates of the experiments more accurately than the conventional models.