Since boilers and industrial furnaces are one of the largest consumers of fossil fuels, optimization and retrofitting these facilities are of the most essential tasks which can be done to reduce fuel consumption and pollutant emission into the environment. The objective of this paper is to investigate the effects of excess air and inlet air preheating on temperature, flow, and efficiency of the furnace of a fired heater used in an oil refinery. For this purpose, a three-dimensional modeling was performed, using CFD, to simulate the furnace and one of the swirling bluff-body burners. Examining the result of several turbulence and radiation models, it was found that Reynolds stress model (RSM) can simulate turbulence caused by swirling and bluff-body burners more precisely than k–ε models. Moreover, discrete ordinate (DO) model offers better performance than P1, for radiation. Comparisons between the numerical results, and field measurements showed the simulation can predict the flow and temperature fields in the heater with acceptable accuracy. The results show that internal and external recirculation zones (IRZ & ERZ) are caused by swirling and bluff-body flows, respectively. In addition, the flow is asymmetric and two recirculation zones form near the vertical walls. Variation of excess air has more impact on IRZ, and high percentage of excess air leads to narrower IRZ, while preheating totally affects ERZ. The optimal value of excess air is 18% and increasing excess air beyond 18% reduces the flame temperature and the furnace efficiency. Furthermore, it is found that preheating increases the furnace temperature as well as the efficiency, and the effect of preheating is reduced at high inlet temperatures.

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