A steady-state Aspen Plus model of municipal solid waste (MSW) combustion has been developed to simulate the influence of operating conditions and hydrodynamic parameters on the concentrations of air pollutants and performance indicators. To simulate the hydrodynamic characteristics, a FORTRAN subroutine was coupled to Aspen Plus software. Model validated against the experimental data is available in the literature and found to be in good agreement. Results showed that the operating pressure has a negligible influence on gas composition and performance indicators, but it plays a major role in the commercialization of thermal conversion of carbon-based fuels due to a significant reduction in the capital costs. It was also concluded that as the U-mf increases from 1.2 to 2.5, the concentrations of pollutants released increase, probably due to a considerable decrease in the rate of reactions involved, especially at the end of combustor.