compressed air systems
Heat recovery, but not as we know it The waste heat generated by compressors can be recovered and put to good use, saving energy and reducing carbon emissions. However, using waste heat for space or water heating is not always practical, which has led rotary vane compressor manufacturer Mattei to develop a heat recovery prototype that generates more useful electrical energy. Andy Jones, managing director at Mattei, explains more.
E
nergy efficiency is high on everyone’s agenda, and businesses are increasingly searching for ways to reduce their energy costs and carbon emissions. Many have already put processes in place to reduce their energy use, carbon emissions and costs, but the Government’s Energy Savings Opportunity Scheme (Esos) aims to ensure that efficiency is front of mind for every major consumer of energy. Esos requires eligible companies* to carry out an audit of the energy used by their buildings, industrial processes and transport to identify cost-effective energy saving measures. And, with compressed air often considered to be industry’s fourth utility, and compressors accounting for around 10 per cent of the total electricity consumed in the sector, they can be a good place to start making savings. One way to reduce the amount of energy a compressed air system uses is through heat recovery. Compressors generate a lot of heat (around 90 per cent of the electrical input used to power a compressor’s motor is turned into heat), and around 80 per cent of this waste heat can be recovered and put to good use. It is possible to use the recovered heat for local space heating, but in many cases this is not practical (if the heat is required on the opposite side of the factory to the compressor, for example, it will be costly, and won’t actually be that efficient), or alternatively the waste heat is used to generate hot water. The water can actually reach temperatures of up to 90ºC, and can be used for a number of different purposes, such as to pre-heat boiler-feed water or for sanitary use. However, although this type of system can deliver energy savings, the benefits can only be realised if a factory or plant has a constant need for space heating or hot water (a compressor generally runs all year, so it is more efficient to have a continuous demand) – which isn’t always the case. In response to this issue, Mattei’s R&D team has developed a unique prototype called the Xpander that uses waste heat to generate electrical energy. We see the product as an important breakthrough, as where there isn’t always a need for heating and hot water in a factory, there will always be a need for electricity. The prototype is based on the Organic Rankine Cycle (ORC) – a ‘steam’ cycle employing organic fluids instead of water that can generate electricity from waste heat. So far, ORC has been used in medium-sized applications where high temperature waste heat (i.e.
150 to 500°C) is available. But Mattei’s Xpander is a high efficiency ORC based system that allows the recovery of energy from very low temperature waste heat (i.e. 80 to 150°C) – meaning it can be used in a greater number of applications. Designed to work with air compressors of 50-100kW, the Xpander recovers heat from hot compressor oil, which is ordinarily cooled by a fan, and converts it into electrical power. It can produce 3kWe, which can be fed back into the compressor. When the Xpander is cooling the oil, the compressor’s normal fan cooling system can be turned off, saving a further 2kW. The overall reduction in the specific energy efficiency of the compressor is around six per cent. With spiralling energy costs, carbon emission reduction commitments and Esos to consider, heat recovery must be a key consideration for any business running a compressed air system. Conventional heat recovery can only deliver savings if there’s a need for space or water heating, but by generating more useful electrical energy from waste heat, Mattei’s Xpander will ensure that a greater number of businesses can reduce their energy costs and carbon emissions. To learn more about the Xpander go to: https://youtu.be/ Sb9mfnVbvRw. *Esos applies to large UK undertakings and their corporate groups. It mainly affects businesses but can also apply to not-for-profit bodies and any other non public sector undertakings that are large enough to meet the qualification criteria. A large undertaking is any UK company that either: • employs 250 or more people • has an annual turnover in excess of 50 million euro and an annual balance sheet total in excess of 43 million euro • an overseas company with a UK registered establishment which has 250 or more UK employees (paying income tax in the UK)
Mattei Compressors Ltd 01789 450577 www.mattei.co.uk info@mattei.co.uk twitter.com/matteiuk linkedin.com/company/mattei-compressors-ltd Energy Efficient Solutions | 2015/16 | 33
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