Gasification is a process in which a solid fuel is transformed into a gas, which acts as a useful energy source. Coal gasification provides a wide range of products such as chemical, power, liquid, and gaseous fuels. A simulation study was undertaken to calculate the composition, mass flow rate, temperature, pressure of syngas, ash slag layer thickness, heat dissipation from the reactor, and carbon conversion of the coal under steady state conditions. The effect of changes in the input parameters such as the changes in the O2 and H2O to coal ratios, operating temperature, and most importantly the change in the fuel, was considered. Besides steady state simulations, dynamic simulations were also conducted to predict the starting and shutdown conditions of the gasifier. The g-proms process modeling software was utilized to conduct the simulations based on mathematical equations, which are capable of calculating time dependent derivatives. In order to obtain the actual physical and chemical properties of coal and its ash, as well as the reaction kinetics of coal, some experiments were performed. Proximate analysis, elemental analysis, and coal pyrolysis, combustion and gasification kinetics were conducted using thermogravimetry (TGA), elemental analysis method (EA), and a pressurized wire mesh heating reactor (PWMR), respectively. Ash viscosity and ash mineral composition were determined using rheometer and X-ray fluorescence (XRF), respectively. The results of these experiments were fitted into the model and served as input for the calculations. Berau and Kideco are low rank Indonesian coals with different characteristics. The results showed major problems associated with slag tapping in the case of Kideco coal. On the other hand, Berau coal performed without any issues.