Gas heat carrier pyrolysis of low rank coal and associated heat transfer characteristics

Abstract

A small scale gas heat carrier pyrolysis fixed-reactor (6-9 kg h-1) was established. The pyrolysis temperature and residence time effect the dehydration process, pyrolysis products, caking property, and temperature profile characteristic. The dehydration process is completed below 300 °C. High temperature and short transfer distance shorten the pyrolysis time. With an increase in the final pyrolysis temperature, the yield of the volatiles and tar increases; however, that of the char decreases. The residence time significantly influences the char yield at 460 °C. The coal begins to agglomerate after 25 min at 460 °C for the first time. Agglomeration of the coal particles increases with an increase in the pyrolysis temperature and residence time. Based on the temperature profile, the temperature curve in the coking chamber can be divided into three stages: the rapid temperature-decline, coal temperature-increase stage, and coal temperature constant stage. The temperature of coal and gas achieves a short relative balance, which causes the temperature turning point between the first two stages. The exothermic heat makes the final temperature of coal higher than that of the inlet gas, thus the exothermic reaction cannot be ignored.