Waste Heat Recovery

Waste Heat generated in an industrial process by way of fuel combustion or chemical reaction and not brought to use in a meaningful way is termed as waste heat.  Sources of waste heat could be hot combustion gases discharged to the atmosphere, heated products exiting industrial processes, and heat transfer from hot equipment surfaces. Boilers, kilns, ovens, Diesel generators and furnaces generate large volumes of hot gasses on combustion of fuel that goes put to the environment through stack. Heat is also radiated out from the hot surfaces of these devices. 

Though some waste heat losses from industrial processes are unavoidable, facilities can reduce these losses by improving equipment efficiency or installing waste heat recovery technologies. Waste heat recovery involves capturing and reusing the waste heat in industrial processes for heating or for generating mechanical or electrical work. Example uses for waste heat include generating electricity, preheating combustion air, preheating furnace loads, absorption cooling, and space heating.

For energy saving tips

https://www.eec-fncci.org/page/energy-efficiency-in-furnace-and-whr