Innovative system for electricity generation from waste heat recovery

摘要

Energy intensive industries face strong international competition, growing energy prices and environmental limitations. In sectors like glass, cement and metals a number of industrial plants are at present dissipating in the environment huge amounts of heat. These flue gases have to be cooled before the gas treatment unit, via heat exchanger or adding fresh air. Both solutions introduce additional energy consumption. Only in few cases this heat is recovered for internal needs, to satisfy heat demand or through an absorption chiller to cover cooling needs. Even less frequently it is exploited for external uses as feeding heat/cold to other industrial plants nearby or to a district heating/cooling system. Another possibility to be evaluated is to convert the waste heat into electricity, usually self-consumed. This electricity, generated without additional emission and fuel consumption, substitutes electricity withdrawn from the grid. One of the solutions to generate electricity recovering heat, otherwise dispersed into the environment, is the Organic Rank-ine Cycle (ORC), with plants available in sizes from tents of kW to various MW. The ORC plants are characterized by fully automatic operation, generation efficiency modestly reduced at partial load and low maintenance costs. Those characteristics are relevant differences in comparison to traditional steam cycles. There are already a number of successful installations of ORC in cement and glass sectors worldwide, while in the metal sector the first known experiences started very recently. An innovative installation of heat recovery for electricity generation through an ORC in the steel sector is described. The paper illustrates the characteristics of the steel shop, the system layout and the solutions for the heat exchange.