Utilization of low-temperature waste heat for internal purposes

Abstract

The power generation from waste heat was investigated for two cement plants, Rohrdorf cement, located in Germany, and Gmundner Zement, located in Austria. The investigations for the cement plant in Rohrdorf show that due to the already installed waste heat recovery (WHR) power plant- based on the steam water cycle - the cement plant has no WHR potential left, except for the heat loss of the rotary kiln. Due to systems complexity of the rotary kiln this heat source is not further investigated in this work. In the case study for the cement plant in Gmunden, different types of WHR-power plants (SRC, ORC & Kalina) were considered and compared by means of different one-dimensional, steady state numerical simulations. Heat from the rotary kiln exhaust gas and from the mid air tap of the clinker cooler were taken into account for the simulations. This case study includes two different types of clinker cooler mid-air routing (conventional off-gas and recirculating). The calculations show that the Kalina cycle has the highest power output followed by the ORC with an internal heat exchanger and Cyclopentane as the working fluid. The commonly used SRC power plant, however, has the lowest power output. Furthermore, the recirculating clinker cooler has a higher power output than the conventional one. Since this concept follows the principle of no additional emission source (no stack required) this is the method of best choice. All simulations are performed with the IPSEpro simulation program and do not include economical aspects.