CLEAN AIR COMPRESSORS
costs involved with this, clean air compressors have always been large, needing their own plant room
and expensive, inefficient connections. Now, Vert Rotors, a specialist inmicro-
compressor technology founded in 2013, has launched the Vert.80, the second product in a pioneering range ofmicro-compressors. Vert.80 is a powerful but very portable compressor for on- demand clean air. Themachine is a water-injected portable compressor, half the size and said to be 34 per centmore energy efficient than comparable machines. It produces 42 per centmore oil free air for 13 per centmore electric power. “Our ultimate goal was to create a clean air
compressor, able to produce clean air at its point of use,” says Olly Dmitriev, CEO at Vert Rotors. “This was not possible with existing technology, so we had to come up with a totally new design and mathematicalmodel to create the first compressor of its kind.” Vert’s proprietary technology is a rotary conical
screw design whichminimises noise and vibration while deliveringmassive energy and cost savings. It is the result of five years of intense research and development. Being small andmobile, it solves the problemof getting oil-free air where and when it is needed. “Formany businesses, environmental impact is a
big issue,” Dmitriev continues. “We believe that our technology can play a big role in cutting energy spending, tackling climate change.” The conical rotary compressor is a new type of
screw compressor. Screw compressors are known to produce high pressure without vibration, and at very high efficiency.However, up to now, only large screw compressors have been available (2kWand bigger). Vert’s new conical technology has changed that and opened a newmarket of small – evenminiature – screw compressors that produce high pressure without vibration. In the Vert’s conical compressor, the inner conical
screw revolves inside the outer conical screw. It defines a fundamental difference fromtraditional screw compressors, which include two screws sitting side-by-side in a housing. In the traditional twin- screw system(developed 80 years ago) the clearance between the two screws and the housing allows the high-pressure gas to leak back, and efficiency is reduced. In the conical rotary compressor, there is no housing, whichmakes it very difficult for high- pressure gas to escape. The compression chamber is formed by the volume trapped in between the inner and the outer rotors. In operation, a compressible gas is drawn into the assembly at the large end of the cone. The absence of the blowhole is perhaps the single
most important difference between the conical screw and themore common twin-screw types. Leakage flow through the blowhole is themain cause of reduced efficiency in twin-screw compressors. Vert’smachine performs “progressive
compression: first, a portion of gas is captured inside the compression chamber, and as both screws
20 /// Environmental Engineering /// April 2017 FEATURES & BENEFITS
Features FAD 220 L/min at 8 bar g pressure Pressure 6-10 bar g 2kWshaft power
Benefits 50%size reduction 34%better energy efficiency 42%more air, 13%more electric power
revolve, it travels fromthe suction (large) end of the cone to the discharge (small) end of the cone; the compression chamber reduces in volume and pressure increases.High-pressure gas discharges fromthe assembly at the small end of the cone. On the other hand, the rotors in the conical screw
‘ We believe
that our technology can play a big role in cutting energy spending
Olly Dmitriev CEO at Vert Rotors
’
compressor are in continuous rolling and sliding contact, and friction can present a challenge. In the Vert.80, to improve endurance,materials are chosen that forma low-friction pair. The female rotor is manufactured froma composite polymermaterial with PTFE (low-friction) characterised by very low absorption of water. Themale rotor is produced fromCZ121 brass, which has good corrosion resistance. The conical rotors and bearings are enclosed in an aluminiumhousing. The price of stainless or composite bearings is
quite high, and this increases the cost of the compressor. It should be noted, however, that in batch production quantities, the additional cost of the bearings would only account for a few percent of the total bill ofmaterials. The primary separator needs to be produced fromstainless steel, which is also expensive, or cast fromaluminium. The long-termimpact of sliding and rolling
friction between the conical rotors in the water- injected compressor needs to be studiedmore, since water is amuch weaker lubricant compared with machine oil. During trials, a number of composite materials were analysed for their friction properties andmachinability. Some very promisingmaterials, such as graphite-filled composites and nylons, were discarded because they either have poor machinability or deformdue to high absorption of water. It was demonstrated that, with low-friction composite polymersmodified with PTFE, as selected, the energy requirement of themachine could be reduced by asmuch as 30 per cent. To achieve the exceptional tolerances demanded,
Vert Rotors kept the full design and production cycle in-house at the company’smanufacturing plant in Edinburgh. Frominitial simulation and design, through CAD and CAMto production, testing, verification and improvement, Vert controls design and production on site. All parts are bespoke and manufactured using simultaneousmachinemilling on five axes and five planes with precision probe measurements taken at 400 touch points on a 40mmscrew. Ultra precisemilling of very complex shapes to
super fine tolerances of 5microns or less, preferably 2-3microns, is an extremely advanced technology. Vert Rotors performs five-axismilling to tolerances as high as 3-5microns for very complex shapes, such as theminiature conical screw. This capability is achieved with high-speed five-axis CNCmills and advanced offline CAD-CAMsoftware. EE
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