The steam power system (SPS) should be operated under the optimal scheme to meet the varying demand for steam and power and to reduce cost and save energy for petrochemical industry.A mixed integer linear program (MILP) model was presented for multi-period operational optimization of utility system.The objective function of the model was to find the minimum annual operational cost of utility systems during the multiple periods

by considering fuel cost

feed-water cost

maintenance cost and startup/shutdown charge.An improved particle swarm optimization(PSO) was employed to obtain the optimum solution of the MILP model.This improved PSO utilized two linearly changing inertia weights to make particles have the tendency to reach global optimum.The application of the proposed optimization approach was illustrated through one case study.