Energy Efficiency - Technology advances make for energy saving04 April 2005

There are many ways in which plant and factory operators can improve energy efficiency. Some are simple, but many rely on taking advantage of the latest advances in technology.

Space does not permit us to describe more than a fraction of everything that can be done. Therefore we have decided in this issue to select three areas where particularly dramatic savings can be achieved using new, commercially available technologies: pneumatics; switching to LEDs for ultraviolet light curing and localised lighting; and refrigeration.

Airing opportunities for economy

It is generally agreed that compressed air represents about 10% of all UK industrial electricity consumption, rising to 30% in some sectors. Despite considerable efforts to economise and constant government efforts to promote economy, it is generally agreed that much of this energy is still wasted.

Whenever one visits a factory that runs equipment from a compressed air ring main, too often one can hear, during quiet periods, the gentle hiss of air escaping from leaks. If the air was not transparent and odourless, but made up of the banknotes used to paid for it, the leaks would be stopped at once. Furthermore, old-fashioned compressors can often be heard cycling on and off, consuming energy whenever they run. It is not uncommon for such machines to run on long after they have restored the reservoir to full pressure, in order to minimise the number of hard starts that the motor has to endure in any given hour. A soft starter in a modern system should allow a motor to be started any number of times; variable speed drives, available from a multitude of sources, are widely considered to offer energy savings in the range 25-35%.

At February's Machine Building exhibition in Birmingham, we choose to ask some of the vendors of pneumatic products for their opinions as to how users could best invest a few of their hard-earned pennies to reduce unnecessary waste in compressed air systems.

David Harris, managing director of Devon-based Aylward Engineering and Pneumatics (AEP Ltd), part of the West Group, suggests buying new compressors with more efficient Class 1Eff motors. He also suggests replacing old desiccant dryers that use 20% of the air to dry the desiccant with modern ones that only use 7%.

He further points out that his company supplies aluminium as opposed to steel ring mains that do not corrode - a major source of leaks in many existing systems. He additionally recommends the use of modern two-stage quick-release couplings. These do not release air when uncoupled, and are much less likely to leak when they are coupled.

Ken King of Pneumatic Solutions International in Waterlooville recommends the use of more efficient valves. He extols the virtues of some new Mac valves that work particularly quickly because they only have an approximately 1mm stroke before they open fully, reducing the time during which air is being used without achieving anything useful. They also present a minimal pressure drop. More information can be found at www.macvalves.com.

Raymond Murray, a market specialist manager with Asco Joucomatic tells us that many companies are looking at reducing their system operating pressure from 8 bar to 6 bar, because 8 bar is not really necessary. This reduces energy costs by 25% at a stroke. He further explains that energy economy is one of the main driving forces behind placing valve islands on machines or applications as opposed to placing valves in cabinets. Reducing pipe runs saves costs in terms of both piping (because of the energy required to pressurise air in a long pipe) and wasted operating time (because air movement is far from instant).

Air leaks are still a major problem. A graph on the US web site www.ecompressedair.com claims that, looking at the five-year life cycle costs of a compressed air system: 9% is capital, 3% is maintenance, 8% is water and 80% is energy. While these figures are open to debate, it is generally agreed that energy costs are definitely more than half of the total. Even if energy only represents 55% of the whole, the lowest figure we have encountered, it might be still be worth considering total replacement if a new system was likely to be as little as 10 or 20% more efficient.

LEDs cure a range of problems

The recent availability of high-efficiency 395nm ultraviolet light-emitting diodes (LEDs) has allowed a Hampshire company to develop solid-state adhesive curing systems with indefinite lamp life, reduced costs and far lower energy consumption than competing conventional systems. The company expects to extend the technology to allow its use in photodynamic therapy in the health sector, in machine vision and in bioscience sensors. It also foresees the use of LEDs becoming the technology of choice for a very wide range of lighting applications.

"This is just the start," Nick Edwards, managing director of Coolled, says of his company's first handheld UV curing system. Coolled is a spinoff from long-established top-end electronic manufacturer, Custom Interconnect Ltd (CIL) based in Whitchurch. One of its particular skills is in the manufacture of multichip modules with wire-bonded bare silicon dies. The breakthrough in Coolled is in using this ability to bond 120 UV LED dies on each square centimetre of surface, and combining these with copper micro-reflectors for each LED. Additional copper plating on the rear surface of the ceramic wafer on which the LEDs are mounted improves thermal contact with a heat sink.

The result is a device which is 15% efficient, about three times as good as an incandescent lamp, with an estimated 10,000 hour lifetime and a high degree of ruggedness. The use of bare dies allows the achievement of a much higher light intensity than would be possible using packaged LEDs, where it is only possible to group about nine on each square centimetre of surface. Efficiency is further assisted by using the copper reflectors, which redirect the 45% of the light that would normally be lost out of the sides.

The competing technology is mercury vapour lamps, which have limited lifetimes, are easily broken, produce additional short UV wavelengths and ozone - both hazardous to health - contain mercury, and require hefty amounts of electric power to drive them.

The Coolled 2600 curing pen, by contrast, can not only be used hand held, but also battery powered if necessary. Its electronic controller imposes a maximum work cycle of 5s on and 15s off, further improving energy usage and raising its effective lamp life to 40,000h, more than the likely working lifetime of the rest of the device. Unlike most UV-lamped systems, it has been tested to IEC/EEN60825-1(2001) and comes out as class 1 (safe as long as you don't look at it through a magnifying glass). It is primarily designed for curing adhesive bonds. Target markets are those needing to undertake on-site repairs, and makers of jewellery and models. For more productionoriented work, the company has also developed a system with a water-cooled head. Both products will be sold through Jenton International.

Nick Edwards insists that "we are just peeling the corner off the technology." UV curing is used in many industries. It can be used in inkjet printers to cure the ink so printed products can immediately be handled without smudging. It is used in stereolithography-based rapid prototyping machines. It is used for paint curing, and has the potential to be used in many applications where the hazards and costs of conventional UV lamps have until now rendered it unacceptable or unattractive.

Furthermore, as efficiencies of LEDs generally continue to be improved and costs continue to come down, it is likely that LEDs will supplant incandescent lamps within the next few years.

One company firmly committed to this view is Forge-Europa, based in Ulverston in Cumbria. The company develops custom designs as well as distributing products such as splined LEDs, or SPLEDs, which are LED bulb replacements that can be used without a printed circuit board. Its latest offering is XLamp LEDs, made by Cree Lighting based in North Carolina. The company's 7090 series products are up to 50% brighter than other commercially available solutions and produce up to 100 lumens in white and 40-60 lumens in blue and green.

But looking further ahead, LEDs are far from the last word in solid-state lighting. Technologies such as light-emitting polymers and the organic electroluminescent diodes being developed by companies such as Elam-T are potentially even more energy efficient.

Concentrate the cold

Working fluids made from suspensions of submillimetre sized ice crystals in brine have five to seven times the cold energy densities of water. Developed in Germany, these fluids allow cooling plants to be made 70% smaller, with considerable consequent energy savings.

CryoSol is the brainchild of a research group at the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) in Oberhausen. Dr Christian Dötsch, head of the energy systems department says: "Our ice slurry reminds one of the slush drinks we had as kids." The secret, he confides, is to keep the ice crystals very small. The suspensions can be pumped at up to 35% ice content, but research is still under way to establish the optimum.

The ice crystals are put into the suspension by using a rotating scraper to abrade those that form on the inner walls of an externally cooled hollow cylinder. The suspension of ice in brine can then transferred to a storage container, to be used as required. Brine and ice mixtures are stable because water ice forms a separate phase from salt solution from 0°C down to the eutectic temperature at -21.2°C.

The high cold energy storage capability arises because of the latent heat of fusion of ice, 93 kWh/t, which gives CryoSol with 40% ice an enthalpy of 37 kWh/t, compared with 7 kWh/t for water at 6°C. The suspension thus offers a particularly good way of providing a reservoir of cold that can be quickly delivered to meet peak demands. These can be as much as 300 to 900% or more of maximum refrigerating capacity.

An experimental demonstration plant is already in service in the laboratory. The researchers report that this 10 kW plant can handle cold demand peaks of up to 120 kW.

Applications are seen in the retrofitting of cooling networks and the equipping of supermarkets, cold storage houses, breweries, dairies, the pork and beef industries, canteen kitchens, chemical industries (process and emergency cooling), in portable units for offices and in refrigerated trucks. The institute says that for those who wish to install CryoSol systems, it can offer consulting, planning, installation and implementation and optimisation for real-world loading cases.

In the next edition of Plant Engineer, we intend to look at ways of extracting energy from rubbish.

SOE

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