Optimization design based on the thermal resistance analyses of heat recovery systems for rotary kilns

Abstract

Heat loss from the rotary kiln accounts for a certain amount of the total energy input in cement production. In order to reduce the heat loss, a heat recovery system with nine heat recovery exchangers is proposed in this paper. Experimental measurements are carried out to investigate the heat transfer characteristics of each heat recovery exchanger. Then, integration of thermal resistance and fluid flow performance analyses yields the mathematic relations connecting the heat transfer areas and the mass flow rates of heat recovery exchangers to the system requirements. Based on the relations, two optimization problems are formed to deduce the optimization equation groups by the conditional extremum principles. Solving the equation groups gives the optimal arrangement of the structural and operating parameters of the heat recovery exchangers. Finally, the optimization cases of a series-parallel system with practical heat recovery exchangers are studied. The results illustrate that the optimization method based on thermal resistance analyses can obtain the optimal area allocation and mass flow rate distribution of each heat recovery exchanger compared with the traditional method such as the control variate method. The total heat transfer area and power consumption are reduced by 10.8% and 12.1%, respectively.