Abstract: High fidelity three-dimensional (3-D) numerical simulations of commercial-scale coal gasifiers are very time consuming and expensive. This article proposes a reduced-order modeling approach that uses quasi one-dimensional (1-D) CFD-DEM simulation results to serve as an accurate initial condition for the 3-D simulation, which significantly shortens the physical time from several hours to minutes to achieve steady states. The 3-D simulation employs a previously validated coarse-grained CFD-DEM approach, which further accelerates the simulation. Both 1-D and 3-D simulations adopt a particle shrinkage scheme to correctly account for the particle volume change due to chemical reaction and thus provides an accurate bed height. Comparison with available experimental measurements of the bed temperature and synthesis gas composition is used to validate the simulation. The final syngas composition and flowrates are strongly affected by the fuel or gasification agent rate and process operating conditions as expected. This approach is then used to optimize two important operating conditions (air and steam flows) to achieve specific gasifier performance goals for the production of Fischer-Tropsch synthesis gas and production of fuel gas for gas turbines.