Process heat

Process heat refers to the application of heat during industrial processes. Some form of process heat is used during the manufacture of many common products, from concrete to glass to steel to paper. Where byproducts or wastes of the overall industrial process are available, those are often used to provide process heat. Examples include black liquor in papermaking or bagasse in sugarcane processing. The required temperature of the process varies widely, with about half the industrial process heat having operating temperatures above . These higher-temperature processes can generally only be supplied by dedicated supplies like natural gas or coal, although pre-heating from other sources is also common in order to reduce fuel use. Those processes operating below the median can draw on a much wider variety of sources, including waste heat from other processes in the same industrial process. Resistive heating would in theory be a possible source of process heat but even as it converts nearly 100% of the supplied electricity to heat, it is obviously less efficient to burn a fuel in a thermal power plant to produce electricity only to use that electricity for process heat than to use the fuel directly. Thus this source of heat is only used where electricity from non-thermal sources (such as hydropower) is cheap and plentiful. Heat pumps which are commonly employed for home heating, warm water and other heat applications below have too low a Carnot efficiency at high temperature differences between "hot" and "cold" end to be worthwhile. Some processes such as molten salt electrolysis provide the required process heat by the same electricity that is also needed to keep the endothermic reaction going. Heat is usually described by "grade" with higher temperatures having a higher "grade". This is because heat naturally flows from hot to cold and it is thus always possible to use a high temperature source of heat for lower temperature applications but not vice versa.