Retrofit of steam power plants in a petroleum refinery

• A steam system model is developed for the analysis of existing steam power plant in a refinery.
• Optimization and retrofit strategies are taken into account to improve the site performance.
• The best energy utilization is determined by the optimization.

A comprehensive mathematical model is developed for the operational optimization and retrofit of industrial steam systems. The problem of maximizing the cost reduction given by the difference in annual operating costs minus the annualized investment cost of the retrofit is formulated as a mixed integer nonlinear program (MINLP) based on a collection of unit models. The steam power plant of a traditional petroleum refinery is analyzed and retrofitted based on the proposed MINLP formulation. The operating conditions are firstly optimized to investigate whether there is room for improvement without modifying existent units or layout. Thereafter, retrofit possibilities on internal steam turbine or layout are taken into account to enhance steam utilization efficiency. Feasible method for inspiring the total site steam integration among adjacent companies is finally deliberated, where the steam ejector is adopted to upgrade the lower pressure import steam for being directed into the existent steam headers. The results of various degrees of retrofit on the steam system of a practical refinery verify the applicability of the proposed approach.