The heat is always on for special TC

Clean and energy efficient electroheating is found in many industrial processes

By Morand Fachot

Electroheating, the high-power heating of material using electrical energy, is widely used in the food-processing industry. However, it is better known in other sectors for dealing with elements ranging from metals to glass, ceramics, polymers and natural fibres. More energy-efficient than other industrial processes relying on fossil fuels, it is also significantly cleaner. IEC Technical Committee (TC) 27: Industrial electroheating and electromagnetic processing, develops International Standards for the sector.

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Infrared ovens are used to colour meat products

Extremely versatile with total control…

Electroheating is widely used in a number of industrial processes for heating materials or elements without burning fossil fuels. One of its major advantages is that it allows very precise temperature control, which in turn results in more consistent, better quality finished products.

Electroheating is very precise and can bring materials to very high temperatures quickly. Alternatively it allows materials to be processed at consistently low temperatures. Electroheating covers many different technologies and can be used in heavy industrial applications, such as the melting and forging of metals, as well as in lighter processes such as the processing and sterilization of food products and the drying of textiles and of ceramic tiles.

From infrared to arc and lasers, from forging to food…

Electroheating, especially in modern continuous manufacturing, is growing in importance. Below is a non-exhaustive overview of some key technologies.

Food processing uses a variety of electroheating processes to deactivate microorganisms in food. These include radio frequency, microwave heating and conductive (or ohmic) heating, in which food material, which serves as an electrical resistor, is heated by passing electricity through it.

The use of an electric arc for melting iron dates back to the 19th century, with patents being taken out for electric arc furnaces (EAFs) in the 1880s and the first commercial EAF plant being built in the US in the early 1900s.

The advantages of EAFs in steel production are their relatively low capital cost in comparison with traditional steel mills and their capacity. They can process anything from around one tonne to hundreds of tonnes, allowing the establishment of mini-mills.

EAFs also allow steel to be made from 100% scrap metal, providing considerable energy savings when compared with primary steelmaking from ores using blast furnaces. Unlike the latter, EAFs can also be started and stopped rapidly, enabling them to cater for variation in demand.

In induction heating, an electrically conductive object (usually metal) is heated by passing an alternating current through an electromagnet. Induction furnaces are used for melting various metals including steel, copper or aluminium, or even precious metals. Their capacities range from less than one kilo to 100 tonnes. The temperature of the material to be heated can be controlled with complete precision.

Resistance heating is used extensively in electroheating. The process involves current being passed through a set of resistances that act as heating elements and is generally applied in a well-insulated enclosure so as to minimize heat losses. Resistance heating is used to heat treat, form, melt and dry metals; to cook, sterilize and roast in the food industry or to fire and dry ceramic products. Resistance heating can be indirect: heat from the resistor is transferred to the work piece via conduction (close proximity between resistances and work piece), convection (through the air) or radiation (infrared heating); it can also be direct. Direct resistance heating, also referred to as conductive heating, involves passing current directly through the work piece to be heated.

Other electroheating technologies include the use of plasma torches to cut steel plates, microwaves to treat food products, radio-frequency electric fields to dry textiles, and lasers to weld, cut and treat various materials.

Energy-efficient and flexible

Industrial applications of electroheating technologies in many sectors show them to be more energy efficient and cleaner than their "conventional" equivalents that use fossil fuels, especially at higher temperatures. The optimum efficiency of gas furnaces ranges from 40%-80%, while that of an electric furnace can reach 95%.

However, measuring the emission of CO2 and other noxious gases is complex for electroheating as it depends on the primary energy mix used to generate the electricity that the equipment needs.

Ensuring electro-heating safety and efficience

IEC TC 27, created in 1937, prepares International Standards for industrial electroheating and electromagnetic processing. The TC encompasses 13 Participating and 13 Observer countries. As of May 2015 it had issued 33 publications.

Its scope now covers all applications of industrial electroheating, including electroheat-based surface treatment technologies and their combinations as well as electromagnetic processing of materials (EPM). It also addresses specific aspects of electromagnetic compatibility (EMC) and electromagnetic fields (EMF).

As demands for energy savings, improved product quality and environmental protection grow, the range of applications is expanding. Electroheating also offers interesting prospects in new domains such as nanotechnology and optoelectronics.

TC 27 works extensively where the safety of electroheating installations is concerned, having issued 13 publications covering all electrical and non-electrical safety aspects. Its objectives for the next 3-5 years include a comprehensive revision of these publications as well as of the large series of test standards, in terms both of technological developments and market demands.

The TC will also start work on developing safety and test standards for new installations not covered by existing standards.

TC 27 intends to amend existing standards to address electrical energy efficiency, EMC and EMF issues in electroheating installations.

The increasing number of technologies being used in electroheating means that the process is constantly evolving and highly flexible, as well as becoming economically more significant and able to be implemented in countless operations.

TC 27 plans to undertake new projects aiming at the development of safety and test methods standards concerning:

  • plasma arc furnace installations
  • new casting systems
  • electromagnetic processing of materials
  • crystal growth and orientation
  • ultrasonic heating
  • spark erosion

All this points to the continuation of a very busy agenda for TC 27 in coming years.

continuous coil dryer cassosolar Heaters in continuous coil coating dryer (Photo: Casso-Solar Technologies)
Forced-convection-oven-electric-18259-2480073 Electric oven
IR for colouring of meat products Weiss Technik Infrared ovens are used to colour meat products