Induction or microwave heating…These words may sound familiar but whereas for most of us they refer to ways of cooking dinner they can also describe different forms of industrial electroheating processes. While these may be less often alluded to, they are widespread – in industries such as food processing, steel, ceramics, medical and textiles. These use different electroheating techniques which are more efficient, precise, cleaner and safer than their counterparts which operate on fossil fuels.
Electroheating can be employed to kill microorganisms in the food processing industry, for instance, using a variety of techniques which include microwave or conductive heating. In the steel industry, the use of electric arc furnaces (EAF) offers considerable advantages compared to traditional furnaces. EAFs can make steel from 100% scrap metal and glass can be melted wasting much less energy than fuel-fired furnaces, for example.
Over the last several decades, IEC TC 27 has prepared International Standards in the field of industrial equipment and installations intended for electroheating. They cover equipment for induction, microwave, plasma, laser, dieletric, electron beam and infrared radiation heating, to name but a few.
New Standards and Technical Specifications continue to be produced and maintained by the different working groups which are part of the TC. Older Standards are constantly being revised, updated and withdrawn when required.
Safety is key
Safety standards are crucial in the field of electroheating as there are a number of potential hazards associated with the various heating techniques which could have an impact on the health of workers in the industries that use them. For example, operating EAFs can expose workers to explosion hazards, if safety standards and safe working practices are not put in place and adhered to.
IEC TC 27 has been at the forefront of the effort to standardize safety in electroheating. Recently it has been examining the issue of exposure to electromagnetic nearfields provoked by induction heating processes. Sweden’s Per Olov Risman together with Norway’s Ketil Hornaes are the co-convenors of Working Group (WG) 32 (now Maintenance Group 33) which has been focusing on the issue of hazards caused by electromagnetic nearfields. “We met in 2012 and immediately realised that we had similar interests. Ketil was a total expert in electromagnetic engineering and was working for a large Norwegian producer of induction heating devices. We were aware that there was a requirement for Technical Specifications on touch current and voltages as well as a need to neutrally assess the hazards of electromagnetic nearfields,” explains Risman.
Both men led a group of six members from China, the US, Poland and Germany. It has recently published IEC TS 62997 which evaluates the hazards caused by electromagnetic nearfields from 1 Hz to 6 MHz and IEC TS 62996 which specifies the limits for contact and touch currents and voltages and electric fields from 1 kHz to 6 MHz. Of the process, he says: “It was a big project and there was more work than we initially expected. We established a new concept of coupling value to bodyparts, for instance. We proposed several methods of assessing safety depending on the availability of qualifications and instrumentation.”
The group looked at the interaction between external influences such as magnetic fields and currents in the body using computer simulation and other methods. “We found that in certain positions workers exposed to the levels we looked at could probably feel a slight tingle in their hands but nothing more. There is certainly no risk of electric shock. According to our findings, working in magnetic nearfields is in fact less hazardous than earlier anticipated, notably by the 2013 EU directive on electromagnetic fields (EMF),” says Risman.
Follow the sun
Even though electroheating is a mature field, there are a number of areas which could require further standardization. New applications include the use of induction directional solidification system furnaces for the production of multi crystal silicon used in the photovoltaic (PV) industry. The furnaces have been tested in an industrial environment, on the manufacturing premises of one of the biggest Chinese producers. The next step is to use them in a mass production process.
“There are some interesting areas which could require Standards, including electrolysis for instance,” notes Risman. “The requirement for safety Standards is growing. The fear of liability, which is high in countries like the US where defective product lawsuits can be filed for millions of dollars, is boosting demand. Another driver is that safety Standards help companies export products to various markets,” he adds.
Milestones along the way
Before his stint at the helm of WG 32, Risman was involved in many other working groups inside the TC which he joined in 2002. Previously, he was Chair of IEC SC 61B: Safety of microwave appliances for household and commercial use. “I joined the IEC in the 1970s which was a great time to work on microwave technology. Applications were in industry which is where the work of TC 27 is focused but also in household appliances, under the remit of TC 61,” he remembers.
IEC TC 27 was founded in 1937 but its first Standards were published in the 1960s, most notably IEC 60239, which dealt with dimensions of graphite electrodes for arc furnaces. The committee currently comprises 10 participating and 15 observer countries. A number of crucial milestones were reached in the 1970s with the publication of the first of the IEC 60519 series on safety in electroheating installations. These have been updated extensively since then. Of the 90 or so publications the TC has issued since its creation, 33 are still valid. As it is vital to keep Standards in the area of industrial electroheating up to date, many of the original publications have been withdrawn, to ensure compliance with technology and safety requirements is maintained.