Pyrolysis Characteristics and Evolution of Char Structure during Pulverized Coal Pyrolysis in Drop Tube Furnace: Influence of Temperature

The aim of the presented work was to investigate the pyrolysis behavior of pulverized coal in a drop tube furnace (DTF), two typical Chinese coals Shenhua bituminous and Pingzhuang lignite were used to conduct the pyrolysis experiment in DTF under the temperature of 600–1000 °C (100 °C increments). Fourier transform infrared analysis technique was used to analyze the functional groups in pyrolysis coal char, and pyrolysis gas was measured online by an online flue gas analyzer. The results showed that pyrolysis in DTF was also a dehydration upgrading process, increasing temperature caused more volatiles released from coal. There were more H2 and CO, but less CO2 and CH4 in pyrolysis gas when the temperature was rising. Compared to bituminous, lignite was more sensitive to the changes of coal pyrolysis temperature, and more valuable combustible gases could be obtained from lignite in DTF with less thermal power cost. From infrared analysis results, after the pyrolysis process in DTF, the aromatic structure in coal char increased, apparent aromaticity and coal rank improved, unsaturated bonds in coal decreased, and coal char structure became more stable and mature. Because of the hydrophilic oxygen-containing groups lost after pyrolysis in DTF, the dried coal char had a good ability for reducing moisture reabsorption.