You might be able to name a few sources of waste heat, but do you know what distributes the largest content?
Waste heat losses arise both from equipment inefficiencies and from thermodynamic limitations on equipment and processes.
Some typical sources of waste heat include combustion exhausts like glass melting furnaces, cement kilns, fume incinerators, aluminum reverberatory furnaces and boilers to cooling water from furnaces and air compressors. The list can go on.
But, the maximum waste heat content actually comes out of steam boilers.
But it’s important to note that while steam boilers have higher waste heat loss, this is due to the large number of industrial boilers rather than due to boiler inefficiency. Typical boiler efficiencies (80 to 85%) are much higher than other fired units such as glass furnaces. Heat losses from boilers are in the low temperature range, as evidenced by the low heat content from a 300°F (150°C) reference.
We should also note that the values reported above do not reflect total waste heat losses by industry, but rather the waste heat losses from selected processes. Iron/steel includes coke ovens, blast furnaces, basic oxygen furnaces, and electric arc furnaces. Aluminum includes primary refining cells and secondary melting furnaces. Metal casting melting includes aluminum reverberatory furnaces, stack melters, and iron cupolas in metal casting facilities. Aluminum includes primary and secondary refining furnaces.
Several studies and investigations have been carried out for the estimation of the waste heat recovery. Based on such estimations of waste heat losses in selected applications, several trends are identified regarding opportunity areas and Research & Development needs for waste heat recovery.