While some waste heat losses from industrial processes are inevitable, facilities can reduce these losses by either improving equipment efficiency or installing waste heat recovery technologies. Waste heat recovery entails capturing and reusing the waste heat in industrial processes for heating or for generating mechanical or electrical work. Heat recovery technologies frequently reduce the operating costs for facilities by increasing their energy productivity.
Recovering industrial waste heat can be achieved via numerous methods. The heat can either be "reused" within the same process or transferred to another thermal, electrical, or mechanical process.
Ways of reusing heat locally include using combustion exhaust gases to preheat combustion air or feedwater in industrial boilers. By preheating the feedwater before it enters a boiler, the amount of energy required to heat the water to its final temperature is reduced.
Alternately, the heat can be transferred to another process; for example, a heat exchanger can be used to transfer heat from combustion exhaust gases to hot air needed for a drying oven. In this manner, the recovered heat can replace fossil energy that would have otherwise been used in the oven. Such methods for recovering waste heat can help facilities significantly reduce their fossil fuel consumption, as well as reduce associated operating costs and pollutant emissions.
In a waste heat-to-power scheme, the waste heat is converted into electricity that can be either used onsite or sold to the grid. In certain cases, an industrial plant can negotiate with the utility to sell the waste-heat-power at a premium, since a number of states count it as an eligible renewable resource in state renewable portfolio standards.
For detailed descriptions of recovery technologies including heat exchangers, recuperators, regenerators, passive air pre-heaters, regenerative/recuperative burners, finned tube heat exchangers/economizers, waste heat boilers, and load pre-heating, see:
- Waste Heat Recovery: Technologies and Opportunities in U.S. Industry (DOE, 2008, PDF 112 pgs)