Two ASPEN models were developed for the Steam Generation and Distribution, Area 5000/5100, of the Great Plains Gasification Plant: a complete flowsheet simulation model, and a rigorous model for the simulation of the steam boilers and steam superheaters. The complete flowsheet model can be run by specifying either the heat and power requirements or the steam flowrates for all the steam consumers in the plant. The flowsheet model will give the material and energy balances for a given set of process conditions, and is used best for simulating the steam system at or near design conditions. This model cannot be used for rating because it is lacking fired heater, heat exchanger, and turbine rating models. The results of several case study runs that were made using each model were as expected. The flowsheet model showed a decrease in steam production as the plant load was decreased. The rigorous steam boiler and superheater model showed higher NO/sub x/ concentrations as the excess air was increased and lower NO/sub x/ concentrations as the equilibrium combustion temperature was decreased. It is not practical to integrate the steam generation and distribution flowsheet model with the individual plant section flowsheet models because of the large amount of computer storage and long running time that would be required. 1 reference, 4 figures, 16 tables.