Optimal operation of an ethylene plant utility system

The algorithm developed allows the selection of the pressure and temperature conditions of the high, medium and low pressure vapor headers and the deaerator pressure of an ethylene plant utility system. The utility system optimization can be done simultaneously with the ethylene plant optimization including four decision variables: Conversion and dilution ratio of the pyrolysis reactor, cracked-gas compressor inlet pressure and demethanizer column pressure. Their values are calculated, solving a Nonlinear Programming subproblem where the modeling equations of the utility system and the ethylene plant are considered. A rigorous simulation of the utility system is carried out using a water property prediction package. There is a strong integration between the ethylene plant and the utility system due to the generation of high steam pressure in the pyrolysis reactor or the use of residual gas as fuel gas in the boilers. The sensitivity of the profit function with respect to the ethylene and utility plant optimization variables is shown for different ethylene prices optimal solutions.