Performance evaluation of an ORC unit integrated to a waste heat recovery system in a steel mill

Waste heat revalorization creates interesting opportunities to energy intensive industries. In the present project, a large-scale ORC pilot plant along with a waste heat recovery unit (WHRU) in a steel mill has been designed, commissioned and operated. The plant is part of the European Commission funded PITAGORAS project and it has been installed at ORI MARTIN in Brescia (Italy). Waste heat is recovered from the fumes of the Electric Arc Furnace (EAF) to produce saturated steam which is then delivered to a district heating (DH) network during heating season and to the ORC for electricity generation during the rest of the year. The main challenge was the integration of these systems in a single plant since the heat source is highly unstable and steady heat load is preferable for the DH and ORC for their safe operation. A steam accumulator of 150m3 volume was implemented between the WHRU and the ORC/DH systems to maintain a steady discharge pressure, to reduce the fast transients and to extend the supply over longer periods. The ORC has a nominal power output of 1,8MW and the preliminary results of the first weeks of operation of the ORC unit resulted in a net efficiency of 21.7%. Currently the plant is undergoing monitoring campaign which will provide additional data to further evaluate and optimize the system.