A void zone, the so-called raceway, may be formed when gas is laterally injected into a particle packed bed and the char particles may combust when the gas enters at a high temperature for example coke combustion in the raceway of ironmaking blast furnaces. Experimental and numerical studies of multiphase flow in the raceway have been conducted widely in recent years, however, the study of reacting flows in the raceway is still limited at a particle scale. This work is to study the gas-solid reacting flows in the raceway using a particle scale CFD-DEM approach, featuring heat and mass transfers and chemical reactions between the gas and solid phases. The simulation results are comparable with the measurements in the physical experiments and previously calculated results. The key phenomena of flow and thermochemical behaviour related to the raceway formation at the particle scale are obtained. Then the model is used to study the dependency of raceway formation and thermochemical behaviour on several key raceway variables including gas inlet velocity, particle size, bed height and particle discharge rate. The simulation results indicate that before generating a stable raceway, a larger blast inlet velocity or a larger discharge rate can form a larger raceway cavity, while the effect of packed bed level shows an opposite trend. The model provides fundamental insights into the complex reacting flows in the raceway zone for a better understanding and optimization in operations. (C) 2019 Elsevier B.V. All rights reserved.