Nonlinear optimization of a hydrocracker fractionation plant

Chemical process optimization is studied using an equation based flowsheeting strategy and MINOS 5.1 to solve large nonlinear programming problems. Case studies are based on Sunoco's Sarnia hydrocracker fractionation plant. The case studies highlight some difficulties that must be addressed for a successful practical optimization implementation. The profit function includes utility consumption, chemicals pricing, gasoline quality and the heating value of streams destined for fuel. The complete plant model, embedded as constraints within a nonlinear programming problem, contains 2891 variables with 10 degrees of freedom. Each degree of freedom corresponds to a setpoint for the control system in the plant. There were significant differences between the solutions found by optimizing single units as compared to solving the complete plant model. A case with a fouled heat exchanger showed that most of the setpoints must be changed to optimally compensate for the equipment performance deterioration.