Characteristics comparison of tar from lignite pyrolysis with inherent and simulated moisture for adopting a two-stage gasification process

To utilize low rank coal cleanly and high efficiently, a new fluidized bed two-stage gasification (FBTSG) process, mainly consisting of a FB pyrolyzer and a transport bed gasifier, has been proposed to treat pressurized coal (below 10 mm) with relatively high moisture for the production of clean fuel gas. In this study, a laboratory FB pyrolysis apparatus was adopted to examine the influence of moisture mode on pyrolysis behavior from 600 °C to 900 °C, especially in the yield and property of pyrolysis tar. Two common experimental methods in literatures, namely wet coal with inherent moisture and dried coal with the simulated moisture by introducing steam, were systematically analyzed. Compared to the simulated moisture, inherent moisture in coal can facilitate effectively the generation of tar at 700 °C and 800 °C, and had strong reforming effect on tar conversion to light fraction, leading to more production of light fractions and micro-molecule compounds. All of these differences were much related to the difference in interaction pathway between volatile matter and moisture.