Pyrolysis of coal and woody biomass under N2 and CO2 atmospheres using a drop tube furnace - experimental study and kinetic modeling

Abstract

Pyrolysis is the first chemical step in the overall solid fuel thermochemical process and has a significant influence on the subsequent stages. An accurate kinetic modeling of this process is thus required for a better understanding of the solid fuel conversion and for boiler CFD. This paper presents experimental investigations on the fast pyrolysis of pulverized coal and woody biomass in a drop tube furnace recently built at the GRE research lab. Experiments are carried out at several temperatures (600°C–1400°C) and under two atmospheres (N2 and CO2). The drop tube furnace is accurately equipped to get gas and wall temperature profiles. Char may be collected at different drop distances and the fuel volatile fraction is obtained by the ash-tracer method. Slow pyrolysis experiments using thermogravimetric analysis are also considered for comparison. A thermochemical conversion model of the solid fuels in the drop tube furnace is finally proposed based on non-isothermal techniques, as the particle time–temperature history in the furnace is known. The kinetic parameters for coal pyrolysis are extracted using the Kobayashi scheme. For the woody biomass, a single first-order reaction model is successfully used. The results show that the maximum yields of volatile matter is clearly affected by the temperature set point for coal, while no significant influence is observed for woody biomass. Finally, coal gasification under CO2 atmosphere is observed only for high temperatures and long residence times, thus indicating a change of the reaction scheme.