Kinetic study on CO2 gasification of brown coal and biomass chars: reaction order

• Higher CO2 partial pressure leads to higher gasification reaction rate.
• Reaction orders for coal and biomass chars pyrolyzed at high temperature are high.
• At low gasification temperature, reaction order for biomass is higher than coal.
• At high gasification temperature, reaction orders for biomass and coal are similar.
• Reasons for above behaviors are related to catalytic effect and pore distribution.

The clean utilization of low-quality coal and biomass has been focused by researchers. Many researchers investigated the kinetics of coal and biomass gasification. Most of them focused on activation energy E and frequency factor A, and assumed the reaction order n as 1 without further study on it. In the present study, the gasification behavior of German Rhenish brown coal and wheat straw chars under different CO2 partial pressure was studied in a small fixed bed reactor and the reaction order was determined. In addition, the effects of different feeds (biomass and coal), pyrolysis temperatures of chars and gasification temperatures on reaction order were investigated. The results showed that the reaction orders in this study ranged from 0.3 to 0.7. For all cases, higher CO2 partial pressure leaded to higher reaction rate. For both Rhenish brown coal and wheat straw chars, the reaction orders increased with higher pyrolysis temperature. For wheat straw chars, the gasification temperature just had little effect on reaction order. However, for brown coal chars, reaction order increased at high gasification temperature. The possible mechanism was also provided as the effects of catalytic compounds and pore distribution, which were rarely found in literature.