Without a trace

Transferring technology is one of the key features of process engineering. Techniques developed for one application are transferred to others as a matter of routine. However, there probably hasn't been much traffic between the worlds of motor racing and process plants in the past.

Rotherham-based Inditherm, which specialises in electrical heating systems for the process and other sectors, is working to change that.

Inditherm was formed in 1993, based around an invention by Pat O'Grady, who is a director of the company. O'Grady developed an electrical system for heating Grand Prix motorbike tyres - a tricky application which requires very even heating. The original system involved a fabric woven from conductive fibres, but although this was more efficient than existing technologies, it still tended to form hot spots. The system needed refining, and that meant a collaboration with specialist polymer chemists.

The solution to the uneven heating problem, and the cornerstone of Inditherm's technology today, was a lightweight elastomeric polymer, bonded to a fabric backing. The polymer is mixed with particles of carbon black, around 30nm in diameter, to produce a very high, uniform, density of the conductive carbon.

The result is a thin, lightweight, flexible material which conducts electricity in the 6-48V range, providing uniform, consistent and controllable heating for temperatures from -40° to 120°C. 'It's very controllable, low energy, cheap temperature,' says technical director Colin Tarry. 'There are no hot or cold spots, no risk of electric shock. It even works if it's pierced.'

The company has found many applications for the material, and the process sector is an important target. 'We see two major markets we can attack with this technology - electrical trace heating, and water heating,' says Richard Hesk, commercial director of Inditherm's industrial division. In the case of trace heating, Inditherm has the advantage of uniformity and ease of use, he explains. For users of water heating, it provides a lower-cost alternative.

Trace heating - the use of electrical heating elements to provide localised warming for pipes, vessels and their fittings which handle temperature-sensitive materials - is normally achieved by wrapping an electrical element around the pipework. This, Hesk says, will always produce non-uniform heating - the areas in contact with the element will be warmer, and the heat will dissipate between windings.

Moreover, the installation of the system is difficult, involving wrapping miles of cabling around often complicated piping layouts, and the equipment can impede maintenance. There are also safety issues - for example, the water treatment industry, which needs extra heat in some locations to prevent pipes freezing in winter, is very wary of trace heating because of the potential dangers of mixing water with electricity.

Inditherm avoids these problems because it is a sheet rather than a cable. It can be cut and incorporated into heating pads and jackets of virtually any shape. Inditherm produces a range of pads which can be fastened with snaps and velcro around standard-sized pipes and tanks, but can also make custom-designed jackets to fit snugly around virtually any equipment, including pumps, valves and flanges. 'Our seamstresses are probably the most important people at our factory,' Hesk says, 'and the skills they use are the same traditional skills used in tailoring and the clothing industry.'

Trace heating, Parry says, is often seen as a 'cheap and cheerful' method of providing heat. When a more reliable, more even heat source is needed, operators would normally turn to steam or water heating, using double-walled pipes or vessels with hot water circulating between the inner and outer walls. However, this brings with it a new range of problems - boilers, pumps, valves, extra piping, all of which has to be maintained; additives to prevent scaling; and the inevitable corrosion issues. Moreover, water heating cannot be used with water-sensitive materials, as the products could be damaged or even, in some cases, explode.

The heat provided by these pads can be used for many purposes, but the main application is to maintain flow of substances which solidify or become very viscous at ambient temperatures.

One example of this is chocolate, which has to be maintained within a narrow temperature range. Too cold, and it sets; too hot, and it separates. Most of the large UK chocolate producers now use Inditherm heating, says Parry. As well as keeping product flowing through pipes, Inditherm can also be used to keep product at the correct temperature while in storage.

The company makes standard jackets for use with IBCs, drums, and various sizes of tanks and vessels. 'Heating a drum is cheaper than heating an entire storage room,' Hesk points out. For storage silos, a jacket with graduated heating can be used, with successive bands of heat at higher temperatures towards the base, where most blockages occur.

Hesk and Parry claim that Inditherm is a virtually maintenance-free solution to trace heating-type applications. However, the financial aspect is also a factor. Heating 650m of four-inch diameter pipe with hot water costs a total of £8901 per year, Parry says - £7726 for steam, and £1175 for pumping. Heating the same pipe with Inditherm would cost £4637.

Cost savings also exist if Inditherm is compared with trace heating - this generally runs off mains voltage and the temperature cannot be altered, while Inditherm runs off a much lower voltage and can be altered within its operational range. 'It works out at about a third of the running costs of trace heating,' Parry says.

Inditherm has developed a variety of different packages for the heating material. The standard option, known as the 'Stealth pad', can be provided in insulated jackets in cover materials suited to their working environments. The jackets can simply be installed over existing pipework without any need for alterations - they even work on double-walled pipes, Parry says.

For more exacting applications, such as in the food industry, a different solution is called for. Here, the company will wrap the pipes in the heating material, apply a rockwool insulation material, and cover the whole installation in a tough foil.

This ensures that the equipment can withstand cleaning-in-place, and the insulation can be removed for maintenance to the piping.

The process sector isn't the only market for Inditherm. One major application is undersoil heating for football pitches: last year, the company installed a system for Falkirk, and is to provide three undersoil systems for Chelsea's new training centre.

Medical applications include heated pads for physiotherapy and heated operating tables.

The construction industry could also benefit, with Inditherm panels encapsulated within concrete walls to provide built-in heating, and protecting bridges from frost, removing the need for corrosive deicing salts. Other applications could include clothing with battery-operated warming pads; heated steering wheels; and food delivery bags which ensure the cheese on your pizza doesn't turn rubbery.

'We always keep half an eye on R&D,' says Hesk. 'It's surprising what occurs to you.'