Hardwood Branch Char Gasification with CO2: Characterization of Reactivity and Proposal of a Semiempirical Kinetic Model

Pruned branches (PBs) from fruit trees are the only woody biomass produced in agriculture in Japan and are thus considered a local resource. Yet, the use of fruit-tree PBs to produce energy on a small scale has not been investigated. Here, fuel characteristics of PB char were studied considering its use in gasification for heat and power generation, and a gas-solid reaction model was proposed to describe the CO2 gasification of char produced from PBs. The reaction rate patterns generated during the CO2 gasification of the studied char can be broadly classified into those associated with cultivated fruit-tree PBs, park tree PBs, and timber waste. The porous structure of the char indicated that the CO2 molecules diffused into the pores via Knudsen diffusion, and fruit-tree PBs had a smaller average pore diameter but a higher Brunauer-Emmett-Teller (BET) surface area. In addition, the extended modified random pore model (eMRPM) was proposed as a new gas-solid reaction model. This model describes the peak of gasification rate at the end of gasification more accurately than conventional models. Furthermore, higher K and Ca contents in char resulted in a higher degree of correlation between the eMRPM and experimental data at 800 degrees C.