THE TEST MODEL A recent study was conducted by Mattei to verify the effectiveness of intracooling processes. A prototype of a sliding-vane air compressor was set up equipped with the instruments required to measure the temperature and pressure of air and lube-oil in all key points of the circuit, as well as the injected oil flow rate and the electrical power. Thirteen different configurations of the pressure swirl nozzles which inject the oil in the intracooling duct were tested, all with the same pressure and temperature injection conditions. The results were compared with a conventional single-stage and an intercooled compressor. The overall pressure ratio as well as the air and liquid inlet temperatures are the same for all cases.

by Andy Jones, managing director, Mattei A

s developed nations come under increasing pressure to lower their

carbon footprint, industry is looking for ways to improve energy efficiency through technological innovation. The compressed air sector, which is a heavy user of electricity, is no stranger to the ever-evolving technological landscape. Andy Jones, managing director at Mattei, explores how an innovative intracooling system is being developed to reduce the energy consumption of industrial compressed air systems. Many industries use compressed air

systems as power sources for tools and equipment used for pressurising, atomising, agitating, and mixing applications. Even though Sliding Vane Rotary Compressors (SVRC) are already highly efficient, there is still plenty of room for raising their energy performance. Working with the Politecnico di Milano (Polytechnic University of Milan) we are currently carrying out research into designing a two-stage sliding vane compressor coupled with a novel intracooling system to push the mechanical and electrical efficiency of compressors to the next level.

INTER VS INTRA COOLING Historically, intercooling is a common practice in compressor technology for reducing the power required for


operation. This method works by first separating the air from oil, then reducing the temperature of the compressed gas between the low and high pressure stages of compression using a heat exchanger. Typically, water or air acts as the coolant. With intercooling, the thermal power is transferred from the gas to the environment. The latest research by Mattei, however,

shows that the similar, but not identical concept of ‘intracooling’ achieves even better results in two-stage compressors. This technology promises to save up to 10 per cent of the energy required compared with a conventional single- stage compressor for typical air compression applications. So, what exactly is intracooling?

Essentially, it is the process of cooling the compressed gas between two compression stages by spraying cooled lubricant oil as small droplets into the gas flow within an intracooling/ connection duct. As explained previously, air and oil is separated in an intercooled system before the air enters the next stage of the process and compressed further. In intracooling however, the oil is not separated from the gas after the first stage. It is left in the flow to lubricate the next compression stage and cool the compressed air, before it is separated from the compressed gas at the end.

Above: Intracooling test rig

Below: Andy Jones, managing director, Mattei

POSITIVE RESULTS Ultimately, the investigation demonstrates that a conceptual two stage compressor which utilises intracooling can reach energy savings of up to 10 per cent, when compared with a single stage system. The intracooled system also required 2.3 per cent less input power compared to an intercooled system due to a better compression process. This is because the oil droplets used during the low-pressure stage of the intercooled compressor are larger, improving the heat transfer from the air to the oil. The air pressure is also lower between the two stages of compression in an intercooled system. If the air pressure is lower as it enters the high pressure stage of compression, the higher the amount of power needed to compress it. What’s more, at the height of its performance, the intracooling setup reduced temperatures by up to 10 °C across the duct between the two stages. With such positive findings, the two-


stage intracooled compressor, which exploits part of the oil needed for the high pressure compression stage to enhance the air cooling between different stages, appears to offer a viable solution to improve the efficiency of sliding-vane rotary compressors. It also opens up the possibility of extending their operating range of pressure, and requires fewer pieces of equipment. Oil injection is also better in the first stage of compression process.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46