Combustion systems are an indispensable part of numerous industrial production processes. The exhaust gases are evacuated to atmosphere at a high temperature in many of these. This dissipates thermal energy you could convert into a higher value added energy vector, such as electricity, by using HRU technology.
The temperature of these exhaust gases sometimes needs to be reduced for subsequent treatment, through dilution processes. This involves over-dimensioning the ducts and the tail-end exhaust systems, as they have to carry a higher flow rate than at the start.
Combustion gases from melting furnaces for various materials (steel, glass, aluminium) and from heat treatment furnaces, boiler exhaust gases, gas turbines and internal combustion engines are examples of processes in which, in the majority of cases, thermal energy is lost rather than being used.