Análise de exergia química e física de um forno rotativo de produção de cimento com composição mássica pela minimização da energia de Gibbs

Abstract

The development of the cement industry has increased energy demand, exerting strong influence on the use of energy resources. The utilization energetic is extremely important because it enables the cement industry greatly reduce their costs. In this work, an exergetic and energetic analysis model of a rotary kiln of cement production is proposed. The proposed model of exergetic analysis contemplates the effects of the chemical and physical exergy of the system. In the literature, the composition of the system used in the exergetic analysis is an input data, previously provided for the model. In this study, the model will also predict the equilibrium concentration of the chemical species present in the rotary kiln. The technique employed is to minimize the Gibbs energy of the reaction medium present in the rotary kiln. The optimization problem was proposed, by defining thus the objective function and restrictions to be resolved employing the commercial software Matlab®. To assess the performance of thermodynamic data, a validation was performed with data from the literature, as the energy and exergy balance directly depends on this data set. Based on the results obtained, the thermodynamic database was validated. The solution of the optimization problem resultant provides the description of composition output of the clinker. The applied methodology is able to reproduce satisfactorily the information provided by industry and obtained in the literature that describe the combustion of the clinker. Industrial data were provided by two cement industries (industry B and C) operating in the state of Minas Gerais, Brazil. The results obtained indicated an exergetic efficiency of 62.56% for Industry B and 86.08% for Industry C, considering the influence of chemical and physical exergy. However, considering only the effects of physical exergy in the input flow, exergetic efficiency of 55.21% was obtained for Industry B and 47.82% for Industry C. The results obtained indicated that the most suitable methodology for exergy analysis consists of in considering the full contribution of chemical exergy.