Techno-Economic Analysis of Waste Heat Recovery with ORC from Fluctuating Industrial Sources

A significant portion of the consumed energy by the industrial sector is rejected as waste heat in the medium temperature range. Organic Rankine Cycles (ORC) are a valuable technology to recover the available waste heat at medium temperatures, and produce electricity or combined heat and power (CHP). A trade-off has to be found between the reduced environmental impact of an industrial site and investment costs for waste heat recovery (WHR). Very challenging for the WHR are the large fluctuations in temperature and/or mass flow rate. In the present work, the economic feasibility of industrial WHR with ORC is analyzed for different applications, with and without heat storage: hot air from clinker cooling (fluctuating heat source temperature), exhaust gas from rolling mill reheating furnace (fluctuating heat source mass flow rate) and a case of exhaust gas from electric arc furnace (both fluctuating heat source temperature and mass flow rate). The different configurations are developed and simulated by combining MATLAB® and EBSILON®Professional. A latent heat buffer with LiNO3 appeared to be the best option for WHR from cement clinker cooling. In case of rolling mill reheating furnace, a design for the minimum mass flow rate and bypass of any exceeding fluctuation appeared the most economical solution, whereas the best environmental performance was achieved for lower bypass of the heat source. In case of electric arc furnace, the best economic solution appeared to be without storage, even though the latent buffer could guarantee the highest CO2-savings. The described design and analysis method should help investors, designers and decision makers take better choices to increase the efficiency and improve the economy of industrial sites with ORC technology.