Energetic and exergetic optimized Rankine cycle for waste heat recovery in a cement factory

The cement industry is one of the largest industries with regard to energy consumption. In the current study, the waste heat from the chimneys of Sabzevar cement factory was used to generate power with the use of the steam cycle in order to improve the energy efficiency. The results revealed that the increase in the boiler pressure decreased the total amount of the recovered energy due to the increase in the final temperature of the exhaust gases. But, the steam cycle efficiency was increased. Therefore, there would be an optimum pressure for the recovery boiler based on the energy and exergy analyses. Accordingly, the maximum exergy absorption from the waste heat of the chimneys of Sabzevar cement factory occurred at the pressure of 891.8 kPa. Considering the work consumption of air-cooled condenser fans, the maximum net power occurred at the recovery boiler pressure of 1398 kPa. The highest overall energy and exergy efficiencies also occurred at this pressure. Moreover, the effects of the important operating parameters, including the maximum cycle temperature, environmental temperature and condenser pressure on the optimum pressure were investigated. Results indicated that the boiler optimum pressure was independent from the operating parameters and remained constant, when these parameters changed.