Industrial Electrical Heating: Applications
Overview
This article provides an overview of the most appropriate applications of industrial electrical heating (electro-heating). Main application areas of electro-heating =
Each electro-heat technology has specific advantages and specific application domains where these advantages can be fully exploited:
Resistance heating
- Indirect resistance heating – Its energy efficiency is often rather poor, but indirect resistance heating can still be cost-effective by making use of special electricity tariffs at periods of low demand (e.g. at night), and by optimizing the geometrical position and by heat recuperation.
Advantages include a consistent product quality (essential in the food and drinks industry) and uniform energy supply over the volume (essential in metallurgy). It leads to an exact production capacity (essential for some drying processes) and a high degree of modularity (essential in many chemical processes). The fact that it avoids the production of flue gasses is essential in many metallurgical processes to avoid surface oxidation.
- Direct resistance heating – This is much less common, but is used frequently in the glass industry. Energy efficiency is much better than with indirect resistance heating. A reduced initial investment cost, compact furnaces, and relatively simple operation are the reasons why the glass industry prefers direct resistance heating over natural gas furnaces.
Infrared heating
This is a widely employed heating technique for surface treatments (heating or drying) and pre-heating purposes. It is frequently used in the food industry for baking and in the metallurgy and textile industries for fixing coatings and drying paint. Its major advantages are the low investment cost of the installation and its high power density, resulting in very compact installations with a high heating rate.
Induction heating
This is mainly used as a melting technique for non-ferrous alloys. It is intrinsically more efficient than a gas oven, since it generates heat directly inside the material. It is also intrinsically more efficient than infrared for heating metal strips, since there is no reflection loss involved. In reality, this high efficiency is only achieved if certain measures are taken: a reduction of the stray fields, sufficient cooling, a good coupling between the inductor and the work-piece, and operation at optimal frequency.
It also offers a high power density: it can reach high temperatures at high speed, homogeneously distributed over the work-piece. It’s suitable for automation, and leads to very precise control of heat localization.
Dielectric heating
This is used for materials with proper dielectric characteristics, namely good electrical insulators. Despite its relatively low energy efficiency, it will often be the most energy efficient option for materials with low thermal conductivity, such as rubber and certain plastics. The technology is particularly common in the food and drink industry, where the vacuum environment guarantees a clean workspace, and volumetric heating avoids agglomeration and the overheating of the contact surface. The highly controlled heating is ideal for tempering, thawing, and viscosity control. For the pasteurization and sterilization of food, dielectric heating can ensure that all the volume has passed through the imposed temperature-time curve.
Electric arc and plasma heating
These methods are ideal for creating very high temperatures. Electric arc furnaces are common for melting steel. Approximately one third of all melting furnaces for crude steel in Europe use the electric arc technology. The technology is also common for melting cast steel, thanks to its low melting times. Electric arc furnaces are also used in stone wool manufacturing, the production of inorganic chemicals, the reduction and pre-reduction of non-ferrous metals, and the production of high-carbon ferro-alloys. Plasma heating is an established technique for reaching very high temperatures in waste incineration plants.
Electron beam heating
Electron beam heating is the least well-known of the electro-heat technologies. Nevertheless, it is a common technique for melting refractory metals with a high melting point. It is also used in the textile industry for starting polymerization reactions, having the advantage that solvent free formulations can be used. Further information =
Application note: Introduction to industrial electrical heating: http://www.leonardo-energy.org/good-practice-guide/introduction-industrial-electrical-heating
Application note: Dielectric heating: http://www.leonardo-energy.org/good-practice-guide/dielectric-heating
Application note: Induction heating: http://www.leonardo-energy.org/good-practice-guide/induction-heating
Application note: Infrared heating: http://www.leonardo-energy.org/good-practice-guide/infrared-heating
