Waste heat recovery utilized for an Organic Rankine Cycle in a steel hot-forging industry

Waste heat recovery in industrial activities is virtually an “energy saving method” which can be introduced into a productive system with successful results as far as technical, economic and environmental aspects are concerned. It is now in fact evident that a careful heat waste management leads not only to primary energy savings, but also to a reduction in greenhouse gas emissions, often with economic sustainability. The case presented here refers to a steel hot-forging industry situated in the Nord-west of Italy that is equipped with steel hot processing devices, and, in particular, with methane ovens for the hot cutting machines. Therefore, the objective of the present work was to carry out a project aimed at the recovery of the hot flows exiting from the ovens in order to produce electric and thermal power that could be used in the same industrial activity or in tertiary activities near the factory itself. After an in-depth analysis in this technological activity inside the factory concerning the electricity and natural gas consumption and hot gas flow-rate availability, different power plant solutions were considered and evaluated. At the end of the analysis process, the choice fell upon an Organic Rankine Cycle with a power of 50 [kWel]. The technical and economic analysis of this powerplant furnished a pay-back period between the 17th and the 18th year, as far as electrical energy is concerned, which was considered excessively long. An acceptable payback period, that is, of less than ten years, was instead found for the recovery of the thermal power of the ORC plant, which could be utilized, through a remote heating system, for public buildings, such as elementary/primary schools and the City Hall, which are located very close to the factory. In short, with this plant solution, it will be possible to produce more than 150 MWh/year of electric energy and about 600 MWh/year of thermal energy, with a reduction in CO2 emission of around 174 tons per year and also the energy saving, in terms of “Tons of Oil Equivalent” , has been calculated around a mean value of 24 tons/year.