Downer reactors have been the choice for catalytic reactions necessi-tating control on intermediates, short residence time and high solid loading. The noncatalytic gas-solid reactions exhibit different hydro-dynamics due to continuous variation of particle morphology during the reaction. This study addresses the challenges with numerical experimentation of reactive gas-solid system possessing shrinking particle characteristics and verification with the results from pilot scale test facility. Petcoke with ash content about 0.322% by weight is selected to justify the shrinking particle characteristics during com-bustion. The particle size ranges from       2 µm to 130 µm with an average size of 60 µm. The powder is cohesive with Hausner ratio of 1.43 and occupies cohesive regime in the Geldart’s classification. Ansys Fluent v19.0R1 is employed in simulating the reaction with a shrinking particle model and the kinetic parameters deduced with the help of TGA has been incorporated in the numerical model as well. The optimum multiphase interaction parameters using numerical experiments established with coupled CFD-RSM method also been included. The simulation tests are conducted for the same experimen-tal conditions with the pilot plant test facility. The temperature profile and concentration profile are obtained for different solid/gas loading ratios and compared with the experimental data obtained with the pilot plant test facility. The study establishes the significance of appro-priate drag models along with the interacting parameters for reliable and robust simulation. The simulation model presented here can be used for design and analysis of the performance of a downer reactor for reactive systems with shrinking particle characteristics.