Experimental study on the effect of temperature and oxygen on pyrolysis-gasification decoupling characteristics of Yili coal

Abstract

Pyrolysis, as the initial process of coal clean utilization, is essential to ensure the operation of pyrolysis-gasification decoupling technology. This paper aims to investigate the effects of temperature and oxygen content on coal pyrolysis product distribution and the char structure and reactive properties. Results demonstrate that in the range of 800–1100 °C, the increase in temperature is conducive to the release of volatiles and tar cracking, to enhance the gas phase yield and syngas concentration. However, as Raman spectroscopy analysis shows, higher temperature (>900 ℃) will intensify the graphitization of char, which is not conducive to the next gasification step. In addition, oxygen introduction at 900 ℃ can accelerate the release of volatiles and intensify the occurrence of depolymerization reaction, which increased the gas yields of CO and CO2 in the gaseous product. Besides, the presence of trace oxygen in the pyrolysis process reduces the degree of coal char graphitization and improves the gasification reactivity. However, at high oxygen content (8 %) conditions, combustion occurs on the surface of the char as SEM results show, which destroys the structure and reduces the gasification activity of the char. Hence, the pyrolysis product distribution and post-pyrolysis char gasification activity can be adjusted by introducing trace oxygen in pyrolysis-gasification decoupling technology.