yes. the max biomass particle size might be larger than the min mesh.

yes. semi-resolved approach. the analytical solution of infinite cylinder could be obtained from textbook. the convective heat transfer coefficient could be obtained from Fluent. the radiation heat transfer coefficient might also be obtained from FLuent. the instantaneous temperature profile of the particle could be calculated. If I could get these values, then I could get the instantaneous mean temperature. then use this mean temperature in chemical kinetics model and DPM surface combustion and CPD model. then the large particle combustion could be modeled in FLUENT. 

Fluent provide Macroscopic particle model to consider the flow motion, but not combustion.

I didn't know whether this idea works. Could you give me some suggestion? 

Thank you.