An ASPEN model has been developed of the Stretford Sulfur Recovery, Section 4000, of the Great Plains Gasification Plant. The bases for this model are the process description given in Section 3.4.13 of the Great Plains Project Management Plan, and Lummus flowsheet E-7102-250-3. In the Stretford process, H2S is dissolved in an aqueous solution containing a reducing agent that reduces the H2S to sulfur. The solution is buffered with sodium carbonate. The vapor-liquid equilibrium involves ionic species. Because ionic equilibrium calculations are unavailable in ASPEN, except in the FLASH block, the model treats the two absorbers as two SEP blocks. A second model also was prepared with ten flash stages using ionic equilibrium. This model can be used to predict the H2S recovery in the absorbers, and the recovery factor then can be used in the overall model. The ASPEN model that has been developed calculates the material and energy balances of the entire flowsheet, and the equipment duties for a given set of process conditions. The entire set of gasifier raw gas components is used. The K-values for all of the flash blocks are calculated using the Peng-Robinson equation of state, modified for water. Values of the parameters for the gases in water were subjected to regression analysis, and included in the insert file PRKIJ. Because of the lack of data, no consideration was given to the effect on solubility of the ionic species. Table 10 summarizes the design basis used in the simulation. The overall model, in its present form, is unable to predict changes in process conditions that would result from load changes on equipment of fixed sizes. The model can be used to simulate the steady-state operation of the plant, at or near design conditions, or to design other Stretford sulfur removal plants. 24 references, 12 tables.