Reaction Characteristics of Shenmu Coal Pyrolysis Volatiles with an Iron-Based Oxygen Carrier in a Two-Stage Fixed-Bed Reactor

Abstract

Volatiles reaction with oxygen carrier is a common issue in the chemical looping combustion of coal or in the chemical looping hydrogen making from pyrolysis gas. A two-stage fixed-bed reactor was used to explore the reaction characteristics of the pyrolysis volatiles of Shenmu coal with an Fe-based oxygen carrier. The effect of oxygen/carbon (O/C) ratios (0-1.31) and temperature (750-900 °C) on the three-phase products (carbon deposition, tar and gas) was systematically studied. The results show that with the increase in O/C ratios (φ), the carbon in tar decreases, while in gas and carbon deposition increases. Moreover, reducing gases decrease slowly but CO2 increases greatly, indicating that the increment of CO2 is mostly resulted from the carbon in tar. Besides, phenols drop fast and bicyclic (except naphthalene) and polycyclic aromatic hydrocarbons decrease slowly, and that of naphthalene decreases sharply only at φ>0.63. With the increase in temperature, the carbon deposition decreases, but CO increases and the effect of temperature to the increase ratio of CO2 is less than the O/C ratio. At 750 °C, tar substances (except naphthalene) have dropped to a lower value, but naphthalene decrease sharply only when the temperature exceeds 800°C.

Keywords: Reaction characteristics, Coal volatile matter, oxygen carrier, Tar catalytic cracking, CO2 selectivity, Chemical looping process