Heat is generated in a furnace using a variety of methods, including the burning of a fuel or the conversion of electricity to heat. The most common type of furnace is fuel powered due to the expense of electricity. Though various forms of fuel are the most economical, there are processes where electricity has an advantage over fuels.

How a furnace is powered makes a difference in its design. Though uncommon, there are designs that still use solid fuels. A further classification of furnaces is where the heat process takes place, with electric furnaces using resistant or induction heating.

Heating Furnace Methods

Electric Powered Furnaces

Electric furnaces use a heating element to convert electricity to heat. A variety of materials are used to produce heating elements, with iron chrome aluminum and nickel chrome alloys being the most common. In the glass industry and research and development, precious metals are used as elements but are not used for industrial purposes due to their cost.

In some electric processes, various gases are added to the heating process of the furnace to improve efficiency and the distribution of heat.

Liquid Fueled Furnaces

The aspect of liquid fuels that is combustible is the fumes. The majority of liquid fuels are made from fossil fuels with other variations being hydrogen, ethanol, and biodiesel. Oil is the most common type of liquid fuel used to heat and reheat materials for treatments. The efficient operation of a liquid fueled furnace means complete combustion of the fuel without any residue.

Electric Arc Furnaces

Electric arc furnaces are used to produce carbon steel and alloy steel by recycling ferrous scrap. Scrap is melted and converted to steel by high powered electric arcs that are formed by a cathode and one or more anodes. The scrap is loaded into a basket with limestone for slag formation then charged in the furnace. The energy required to melt the scrap and heat it is approximately 350 kWh to 370 kWh. The amount of energy necessary to power the arc varies depending on the mix of scrap and its composition.

Gas Powered Furnaces

Gas furnaces burn gas to produce heat for a variety of industrial processes. An enclosed space contains the gas until it reaches the temperature for the application. Gas furnaces have air, oxidized, inert, reducing, salt bath, or vacuum atmospheres. Natural gas is the main type of gas used for gas furnaces. For environmental protection, gas fired furnaces use oscillating combustion technology (OCT) to reduce nitrous oxide (NOx), a waste product from burning natural gas.