The recovery of heat from the waste gases of industrial processes is not new. However, until recently this has essentially been in a closed loop with the process itself; termed primary heat recovery.

Usually, waste gases still present an air pollution control problem after primary heat recovery. Since they are still typically too hot, particularly for fabric filters, cooling devices are used before the gases are cleaned.

Many problems arise when attempts are made to use gas cooling devices as secondary heat recovery sources. How these problems were addressed in providing secondary heat recovery systems with cupola gas cleaning systems is described. The economics of doing so are also ex-amined.

The conclusions are that secondary heat recovery can be viable but a general case cannot be made and each installation must be examined for its merits.