Optimation of the acetylene selective hydrogenation unit of an ethylene production plant

A methodology for the optimization of the operation of the selective hydrogenation of acetylene reactors of a commercial ethylene plant (Olefins Plant II of El Tablazo Complex, Zulia State, Venezuela) is presented. The methodology consists of two stages:, first, the determination of the actual kinetic constants of the hydrogenation reactions taking place in the process, and second, the use of these values to optimize the operation of the unit. The actual data required are taken directly from the plant by means of the data acquisition system (PI). These data are reconciled to assure their consistency, then the reconciled data are used in the determination of the kinetic parameters. To facilitate and automate this procedure, a computer program was prepared to collect and handle all the pieces of information required. The data reconciliation, the determination of the kinetic parameters, and the optimization are performed by the commercial process simulation package Aspen Plus. The kinetic parameters can be periodically determined and stored to monitor the catalyst activity decay; with this, estimates of the catalyst life can be made. The model presented here was validated, and has been used to monitor the acetylene selective hydrogenation unit to evaluate and to optimize the operating conditions of the unit. For three weeks, the reactors were operated at the conditions nearest to the ones calculated by the model as the optimum conditions, and a reduction of ethylene losses by overhydrogenation in this unit of 5 MTD was achieved (about 1600 MTA of additional ethylene production).