Fuel Based Furnace Types and Applications

Large furnace in production (Hotfoil-EHS)

With fuel-based systems, heat is generated by the combustion of solid, liquid, or gaseous fuel, and transferred either directly or indirectly to the material. The combustion gases can be either in contact with the material (direct heating), or be con ned and thus be separated from the material (indirect heating, e.g., radiant burner tube, retort, muffle). Examples of fuel-based process heating equipment include furnaces, ovens, kilns, lehrs, and melters.

Fuel-based process heating systems are common in nearly every industry segment, and include furnaces like ovens, heaters, kilns, and melters, but also the surface treatment in ambient air. Typical fuel-based furnaces include the following:

• Atmosphere generators. Used to prepare and/or condition protective atmospheres. Processes include the manufacture of endothermic gas used primarily to protect steel and iron during processing, and exothermic gas used to protect metals, but also to purge oxygen or volatile gases from con ned areas.
• Blast furnaces. Furnaces that burn solid fuel with a blast of air, often used to smelt ore.
• Crucible furnaces. A furnace in which the heated materials are held in a refractory vessel for processes such as melting or calcining.
• Dryer. A device that removes free water, or other volatile components, from materials through direct or indirect heating. Dryers can be grouped into several categories based on factors such as continuous versus batch operation, type of material handling system, or source of heat generation.
• Indirect process heaters. Used to indirectly heat a variety of materials by remotely heating and circulating a heat transfer uid.
• Kilns. A furnace used to bake, dry, and re ceramic ware or wood. Kilns are also used for

  

  Heat treating furnace (Hotfoil-EHS)

  calcining ores.
• Lehrs. An enclosed oven or furnace used for annealing, or other forms of heat treatment, particularly in glass manufacturing. Lehrs may be the open type (in which the flame comes in contact with the ware), or the muffle type.
• Muffle furnaces. A furnace in which heat is applied to the outside of a refractory chamber or another enclosure containing the heated material that is enveloped by the hot gases. The heat must reach the charge by flowing through the walls of the container.
• Ovens. A furnace-like chamber in which substances are heated for purposes, such as baking, annealing, curing, and drying. Heated systems can use forced convection or infrared.
• Radiant-tube heat-treating furnaces. Used for processing iron, steel, and aluminum under a controlled atmosphere. The flame is contained within tubes that radiate heat to the work. Processes include carburizing, hardening, carbo-nitriding, and austempering. The atmosphere may be inert, reducing, or oxidizing.
• Reverberatory furnaces. Furnaces in which open flames heat the upper portion of a chamber (crown). Heat is transferred to the material mainly by radiation ( flame, reflection of the flame by the crown) and convection (combustion gases).
• Salt bath furnaces. Metal pot furnaces filled with molten salt where heat is applied to the outside of the pot or inside of the pot by radiant tube. Salt bath furnaces are used for processes such as heat treating metals and curing plastics and rubber.
• Solid waste incinerators. Used to dispose of solid waste material through burning.
• Thermal oxidizers. Used to oxidize volatile organic compounds (VOC) in various industrial waste streams. Processes include paint and polymer curing and/or drying.