The use of producer gases from gasification and combustion of fossil fuels and biofuels in steel reheating furnaces represents a promising future application. Prior to the direct implementation of such gases as an alternative fuel for high quality steel products, a comprehensive thermochemical study of possible impurities inside the furnace is crucial. This is especially important for heating of high quality steel products. Ash is one of these impurities, which contains particular compounds like Sodium (Na), Potassium (K), Chloride (Cl), and other minerals. The depositions of these compounds, which cause a formation of sticky layer of solutions on the steel slabs surface, are responsible for low quality products. Furthermore, it is a challenge and energy consuming process to remove these elements from the slabs. In this paper, the combustion of a producer gas mixture including ash particles inside a batch type steel reheating furnace has been investigated. In the first step, a computational fluid dynamics (CFD) approach is utilized to investigate the feasible locations of ash particles at the interface layer of the flaring gas media and the steel slab surface. After that, result from thermodynamic calculations considering the slab temperature, particle concentrations, ash compositions, and its reactions with the steel slab are presented. The results show that the concentration of particles is highly dependent on the flow field, slab temperature, as well as their size distribution. Also, the most probable places of particles at the interface layer of flaring gas media and the steel slab surface is primarily found near the steel slab cross sectional sides in the heating zone. It is believed that the present results could be helpful for a further optimization of furnace and combustion system design.