Electrical consumpon in the industrial sector is esmated to constute over 50 per cent of global usage

(6673TWh), and up to 20 per cent (1335 TWh) of this can be aributed to air compression and delivery to final uses. With this in mind, it is clear that saving energy through industrial compressed air systems can make a significant contribuon to reducing greenhouse gas emissions. Andy Jones, managing director at Maei, explores how the latest innovaon in compressor technology is opening up opportunies to achieve further energy eciency

any industries use compressed air systems as power sources for tools and equipment used for

pressurising, atomising, agitating, and mixing applications. As 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. Even though Sliding Vane Rotary Compressors (SVRC) are already highly efficient, there is still plenty of room for raising their energy performance. Here, we look at how a two-stage sliding vane compressor coupled with a novel intracooling system has been developed to push the mechanical and electrical efficiency of compressors to the next level.

What is ‘intracooling’?

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 ten per cent of the energy required by a conventional single-stage compressor for typical air compression applications. So, what exactly is intracooling? Essentially, it is the process of cooling of 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 for lubricating the next compression stage, and separated from the compressed gas at the end.

Trialled and tested

A recent study was conducted by Mattei to verify the effectiveness of the 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.

Efficiency gains

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

uDiagram 2: Intracooling process

compression process. This is because the oil droplets used during the low- pressure stage of the intercooled compressor are larger, affecting 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.

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 amount of 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.

So what’s next? The aim is for Mattei to continue the development activity focusing on the design of the high pressure stage. Furthermore, a smart system for the nozzles activation control will be also developed in order to guarantee the fine-tuning of the temperature at the inlet of the second stage.

uDiagram 1: Intercooling process 16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MAY 2019

uMain image: A prototype of a slidingvane air compressor was set up and equipped with the instruments required to measure the temperature and pressure of air and lubeoil

ENERGY OPTIMISATION Stepping up efficiency for air compressors

Mattei air

compressors and services

of Italy-based Ing. Enea Mattei SpA – a global pioneer in rotary vane air-compressor design and manufacture, and related products and services. The company’s insight into customers’ needs drives continuous product development, which results in creative, innovative technologies and practices that meet and exceed expectations.

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