PROCESS constructed detailed simulation models of a two-tower valve tray fractionation system for four different light ends separation applications. The client had purchased the system, originally designed for depropanizing and debutanizing gasoline fractions, for deethanizing pipeline propane and for producing high-purity propane, iso-butane, and n-butane from separate commercial feedstocks. The simulation models were first developed to determine the feasibility of producing the high-purity products for the four applications then later refined to determine optimum operating conditions for maximizing system processing capacity and minimizing operating costs. Sensitivity analyses were also executed for the major operating parameters (feed temperature, overhead temperature and pressure, reflux rate, product flow rates, and bottoms temperature) for the purpose of determining critical control parameters and developing a process control strategy for each application. Additional simulation runs were executed to determine system design modifications that could be implemented (e.g., feed tray location, additional trays, additional heating and cooling) to further improve system performance.