Process Heating System Types
Infuel-based process heating, heat is generated by the combustion of solid, liquid or gaseous fuels and transferred either directly or indirectly to the materials. The combustion gases are either in contact with the material (direct heating) or are confined and separated from the materials (indirect heating such as radiant burner tube, radiant panel or muffle). Examples of fuel-based process heating equipment include furnaces, ovens, heaters, kilns and melters.
Electric-based systems (electrotechnologies)use electric currents or electromagnetic fields to heat materials. Direct heating methods generate heat within the material by either passing an electrical current through the material, inducing an electrical current into the material, or by exciting atoms/molecules within the material with electromagnetic radiation. Indirect heating methods use one of these three methods to heat a heating element or susceptor, which transfers the heat either by conduction, convection, radiation or a combination of these to the material. Examples of electric-based heating system include induction heating and melting, electric arc furnaces, infrared ovens and vacuum furnaces.
Steam-based systemsuse steam to supply heat to the materials directly or indirectly. Direct steam heating systems inject steam into liquids or gases. Indirect systems use a heat exchanger in which steam is cooled and condensed in tubes; the heated tubes supply heat to the liquids and gases. Steam offers several advantages in process heating operations such as high heat capacity, ease of transport, low toxicity and cost, and it can be generated by a variety of byproduct fuels. Examples of steam-heated systems include distillation columns, water or air heating, paper drying and humidification.
Hybrid systemsuse a combination of process heat systems employing different energy sources. An example is a paper drying process that combines an electric-based infrared technology with a fuel-based dryer.