(67a) Lehigh University: Crude Lights End

A Light Ends Separation unit was required to process 607.08 kmol/h of light hydrocarbon material from the Pipestill column in a large refinery. Ethane, propane, isobutane, n-butane, mixed pentanes, and heavy naphtha components were separated by a series of distillation columns to meet given product purities. Conventional distillation columns, absorption columns, and divided wall columns were considered as potential separation methods of these components. An optimum scheme was chosen that included one absorption column, two conventional distillation columns, and a divided wall column, meeting all product purity specifications. Dynamic simulations of step changes in crude stock flow rate and composition, in Aspen Dynamics, were performed on separation schemes optimized in Aspen Plus on a Total Annualized Cost (TAC) basis. The plant was able to appropriately handle the given step changes, converging to a new steady state in a maximum of 11 hours and 12 hours for changes in feed flow rate and feed composition steps, respectively.