Fired heater is an essential equipment in refinery processes and the most energy consumption in oil refinery and petrochemical industries occur in fired heaters. An optimal design of fired heaters can improve the efficiency and result in decreasing cost and save more energy consumption. The type of fired heater is described by the structural configuration, radiant tube coil configuration and burner arrangement. The cabin-type fired heater is proper for large capacities and large heat duties. A fire heater consists of two main sections, radiant and convection sections. Heat transfer mostly occurs in the radiant section. Meanwhile the convection section recovers heat loss from the radiant section. In addition to those sections that are mentioned, the fired heater has stack section that the fuel gases are vented to atmosphere. There are several variables involved in the design of a fired heater including geometric variables such as dimension of fired heater, number of tubes in convection and radiant sections, number of shield tubes and numbers of rows in the convection section. These variables are modelled by using integer variables. Operating variables are used for process conditions such as temperature, flow rates, pressure drop and pressure. A Mixed Integer Nonlinear Programming (MINLP) problem is used for the optimal design of furnaces and fired heaters. This model is highly-nonlinear thus it requires good initial value for all of variables. The local solution given by this model that are closest of the initials. In this work, enumeration helps reduce the number of initial values furthermore it is easily accessible to define initial value. The model is calculated in Microsoft Excel and Visual Basic. There are two objective functions for optimal design fired heater including the total area minimization and the total annual cost minimization. The enumeration method presents the global solutions which can reduce the total area and the total annual cost from solving MINLP problem.

Enumeration of the model for optimal design of fired heaters

2019 Fall National Meeting

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