Energetic and exergetic assessments of a cement rotary kiln system

Abstract

The cement production is one of the most energy consuming processes, typically accounting for 50 to 60% of the production costs. However, there are several ways of heat recovery opportunities to achieve better energetic and exergetic efficiencies for the whole system. In this paper, energetic and exergetic analyses of an existing rotary kiln system are presented, and first and second law efficiencies are calculated. Two distinct cogeneration systems which use the waste heat from both pre-heater and clinker cooler exhaust gases to produce either electricity and/or to preheat the raw material before entering the kiln system. The effect of these two heat recovery systems on the overall efficiency of the system is also discussed. The results showed that the energy and exergy efficiencies of the existing system are 54.9 and 28.1%, respectively. With the cogeneration, these exergy efficiencies have been obtained to be 70.6% for the use of waste heat recovery steam generator (WHRSG) and 81.5% for the use of heat to pre-heat the raw material, respectively, which dictates a remarkable improvement over the existing system. Key words: Cement process, rotary kiln system, energy and exergy audit, cogeneration.