Energetic and Exergetic Evaluation of 4 Systems for a Rotary Kiln Improvement

Abstract

The energy balance of a rotary kiln used for calcination of 4400 kg/h of dolomite in a magnesium production company identified the kiln shell (26.35% of the input energy) and exhaust gases (18.95%) as the major sources of heat losses. To increase the efficiency of the kiln, the following systems are analyzed by the use of energy and exergy analysis: (i) system for preheating of the combustion air by heat exchange with the exhaust gas; (ii) system for space and DHW heating in the company by water heating with the exhaust gas sensible heat; (iii) system that consists of a recuperator that use sheat loss from the kiln shell to preheat the combustion air (designatedas iii-a) and the system given in (ii); and (iv) system that consists of (iii-a) and an cogeneration system that uses organic Rankine cycles upplied with heat by heat exchange with the exhaust gas. The system (ii) is the optimal solution by economic criteria because the company uses relatively expensive heavy fuel oil for space heating, where as exergetically, the most efficientis the the system (iv), which enables the kiln to have the exergetic efficiency of 36.02%.