Avaliação exergética e otimização de uma unidade industrial utilizada para a produção de clínquer

Abstract

The cement production is an energy intensive process. It is characterized by a high production associated to a high energy demand. In this process, about 90% of the total thermal energy required is consumed in the clinker production step, which is carried out in the pyro processing unit. Consequently, fuel demand for this step is considerable. This causes some issues, as high process emissions and high cost associated to the fuel supplyment. Due to this, some strategies are adopted in clinker production in order to minimize the energy spent. Two of them are the adition of a precalciner in the pre-heating stage and the use of co-processing. In order to evaluate the clinker production process performance, exergetic analysis is frequently used, since it allows calculate process heat losses and irreversibilities losses. Thus, based on the exergy analysis, the aim of the present work is to perform an optimization in order to determine an optimum operational condition for the clinker production. Co-processing and pre-calcination were taken into consideration in the analysis. For this, an algorithm to predict the inlet streams mass flows and compositions for a given clinker goal of production was developed. In addition, considering that the exergy analysis does not have a standard methodology defined in the literature, different methodologies were tried in the study. The obtained results indicated that the best methodology for the exergy analysis consists in to consider all the chemical exergy contribution and in to define the exergy efficiency as the ratio between the desired product exergy and the exergy given to the process. Considering this methodology, exergy efficiency for the standard operational condition of the pyro processing unit was 29.4%. The optimization pointed to that the ideal process runs with exclusive use of coke in the conventional fuel and exclusive use of tires in the alternative fuel, with 25% of thermal substitution and with 28% of the total thermal energy directed towards the rotary kiln and the last thermal energy directed towards the calciner. For the ideal condition, the unit exergy efficiency was 30.8%. It was also simulated a scenario with tire restriction. In this case, two possible optimum operational conditions were defined.