PROCESS simulated a continuous reaction system designed to produce sodium hydrosulfide (NaHS) from H2SH2S gas and NaOH solution. Multiple cases were run quickly to optimize the reaction system (maximizing NaHS product concentration, minimizing Na2SNA2S formation in the product, and maximizing yield) by manipulating reactor volume, NaOH concentration, and reactor recycle rate and recycle stream temperature. In addition, designs were completed for system ancillary towers (vent gas scrubber, inlet gas stream HCl absorber, and reactor offgas H2SH2S scrubber). For each tower, the software was used to determine the number of required theoretical stages, the HETP, and the optimum tower diameter. A process flow diagram of the entire reaction system was generated by the software once the process design was completed.