Optimization pays an important role in the growing world of competition in the industrial countries. It is the aim of this research to optimize the topping unit of a Gas Refinery in Iran (i.e., Khangiran Gas Refinery) using Hysys software. To obtain this objective, a nonlinear SQP (Sequential Quadratic Program) model has been adopted in this study for the optimization purposes. The objective function was chosen in a way that it would maximize the annual income by considering the utility and maintenance cost. To impose some limits on the primary and secondary variables for the optimization purposes, the operating variables must not exceed an allowable limit and the unit have got to operate in the steady state condition. The primary variables that are adopted in this study for the optimization are the two feed streams to the unit. Given that the composition of the two feed differs and the product must be kept constant, we could obtain the optimal values. The result demonstrates that we have got to impose a constraint function on the secondary parameters so as to minimize the reboiler and condenser heating loads. In this research we maximized the rate of naphtha production with regard to the solvent and diesel fuel and minimized it with respect to kerosene, while maintaining the same overall capacity. The findings of this study revealed that through the sale of the unit products we would be able to make a net profit in the margin of about $ 7863626 annually, and raise the annual income by as much as 1.4 percent through the optimization scheme.

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