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

Abstract

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 CO 2 gasification of char produced from PBs. The reaction rate patterns generated during the CO 2 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 CO 2 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 °C.