Thermal decomposition mechanism analysis of circulating solids sampled from Ende pulverized‐coal gasifier

Abstract

Ende pulverized‐coal gasifier (EPCG) is a type of circulating fluidized bed gasifier, in which the circulating solids are resent into the furnace through a return conduit for regasification. Since the solid circulation in the return conduit mainly relies on gravity self‐balancing, it is easy to cause low and unstable solid circulation rate and increase unburned combustible of fly ash. To solve these problems, a circulation enhancement technique using an ejector to provide a stable pressure barrier to promote solid circulation was proposed. To verify its feasibility, considering that the circulating solid‐CO2 reaction is a rate‐controlling step in the gasification process, it is of great significance to explore the reactivity characteristics of the circulating solids under CO2 atmosphere. In this work, thermal decomposition characteristics of Hailar circulating solids (HLE‐CS), Hailar char (HLE‐C), and Shenhua circulating solids (SH‐CS) were investigated by non‐isothermal thermogravimetric analysis to compare the gasification reaction characteristics of circulating solids and char. The HLE‐CS and SH‐CS used in the experiments were taken from the return conduit of 45,000 and 20,000 Nm3/h EPCGs, respectively, while HLE‐C was made from the raw coal of 45,000 Nm3/h EPCG. The effects of different samples under the same thermal decomposition temperature range were investigated. The kinetic parameters were determined by the distributed activation energy model. The results indicated that remarkable peaks were found in the relationship between temperature (T) and activation energy (E) for HLE‐CS and SH‐CS, but there was no significant peak for HLE‐C, and kinetic compensation effects also existed between ln(k0) and E for different samples. The circulating solids of HLE‐CS and SH‐CS were more easily gasified than that of HLE‐C in the lower temperature ambience. Moreover, HLE‐CS and SH‐CS have obvious pyrolysis and gasification stages, which can be completely introduced into EPCG for regasification, and increasing the circulating solid rate and temperature within a certain range is beneficial to enhance the gasification rate.