Furnaces, Kilns, Ovens, Lehrs
and Thermal Oxidizers
Download PDF of this page Print this page

Electric Heating Elements for Industrial Furnaces, Kilns and Ovens

  • Stainless Steel Open Coil
Click to enlarge

Depending on application and economics, furnaces and kilns can be electric heated with metallic or non-metallic heating elements.

Our specialists at Keith Company design electric furnaces and kilns with a wide range of heating element choices. The fundamental operational limitation of any electric heating element is the maximum element surface temperature (MET). The maximum surface temperature is reached either when the basic element material begins to decompose (or change phase) or when the reaction of the element material with the furnace atmosphere proceeds so rapidly that it makes the element life unacceptably short.

In general, limitations of elements are given in terms of the MET in a specific atmosphere. Since an electric heating element transfers heat by convection and radiation to the interior of the furnace and to the load, the element surface temperature is always higher than the furnace/process temperature during the heat-up and soaks portions of the firing curve.

The element surface temperature may even be higher than the furnace/process temperature during portions of the cool-down curve in order to compensate for heat losses to other areas of the furnace. A secondary, but nevertheless important, limitation is the maximum specific power loading of the element, which is generally specified in watts/cm2 or watts/in2 of element radiating surface area. This parameter is often simply referred to as the watt loading. In general, the higher the MET, the higher the maximum allowable watt loading. However, each type of element has an absolute maximum watt loading regardless of the element temperature. This limit is based on experience and relates to the deterioration of the basic element material on a microscopic level.

Most of our Keith high-temperature thermal processing systems are heated by one (or a combination thereof) of the following heating elements: