Exergy, CO2 and economical analyses of the hydrogen production using waste heat from molten slag in the steel industry

A feasibility study of the hydrogen production from high temperature waste heat in the steel industry is carried out from the viewpoints of thermodynamics and economics. The waste heat of molten slag is chemically recovered by endothermic methane-steam reforming. To recover the sensible/latent heat of molten slag directly, it is granulated by a spinning disk atomizer and is cooled by a mixture of steam and methane. In this study, exergy analysis of the proposed system was conducted on the basis of the total unrecovered waste heat. A simple heat and material balance model was employed to evaluate the possibility of Japanese steelworks as a hydrogen station by calculating exergy loss and cost benefit. The results show that the proposed heat recovery system for the production of hydrogen has a less exergy loss of only 12% as compared to the unrecovered system. It also gives a cost benefit totaled US$ 277 million based on the annual steel production of 102 million tons. The results also offer a possibility for hydrogen production with high cost performance by utilizing waste heat from high temperature industries.