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Analysis of Energy Savings by Painting a Rotary Kiln Surface
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Rotary Kilns has been widely used for processing minerals, producing cement, calcining petroleum cokes, or drying biomass and wastes. Most of rotary kilns consume energy intensively. Therefore it is desired to assess the thermal losses from the kiln surface and find a way to reduce the energy losses. This paper investigates the feasibility and potential of energy savings by painting the kiln outer surface with a low-emissivity paint. However, it must be careful to evaluate the insulation effect of the paint because good insulation will increase the metal shell temperature. Too much temperature increase could result in structural problems induced by differential thermal expansion between the shell metal and the refractory bricks. A detailed heat transfer analysis is conducted to help make a decision concerning paint selection and the potential consequence of painting the kiln surface. The results show that the thermal losses depend largely on the surface temperature. Every 25°C increase in the surface temperature will increase the thermal loss by approximately 17% with the same surface emissivity at 0.9. The paint emissivity has a significant effect on the kiln surface heat transfer. Lower emissivity paint decreases thermal losses but increases the kiln surface temperature. A commercial available paint with the emissivity of 0.65 is selected to achieve the optimum result of an energy saving of 133 kW (0.46 MMBtu/hr) without imposing detrimental destruction to the refractory brick's integrity inside the kiln.
Li, X.; Wang, T.; Tonti, R. T.; Edwards, L. (2007). Analysis of Energy Savings by Painting a Rotary Kiln Surface. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from