Feasibility study for recovering waste heat in reduction system of Kroll process: Energy analysis and economic valuation

The feasibility of developing a waste heat recovery system from waste hot air generated by the reduction system in Kroll process to pre-heat water is studied in this paper, in order to reduce energy loss. In the proposed system, the hot air from reduction reactor was first collected by pipelines with insulating material, and then supplies to a shell-and-tube heat exchanger to heat up water. And the energy, exergy analysis of the whole waste heat recovery system have been carried out firstly on the basis of material, energy and exergy balance. Then, the thermo-economic analysis and economic analysis of the waste heat recovery system are also discussed. The results show that the waste heat recovery system presented in this paper could be applied not only for restricted category of reduction system in Kroll process, although the energy efficiency and exergy efficiency of the waste heat recovery system are as low as 26.84% and 11.09%, respectively. And more than two times equivalent energy could be obtained from the waste heat recovery system. The payback period of a waste heat recovery system is about 4.39 years.