Not much has happened of note in the world of air compressors for some considerable time. For the best part of a century the screw compressor has been king, with no new technologies emerging to take its crown.
This is important. According to the Carbon Trust, 10% of electricity supplied to industry is consumed by compressed air systems, so a new technology that offered a step change in efficiency levels could have a major impact.
"Everywhere where there is a piston cylinder, from compressors to engines to expanders, we essentially have a need for a more efficient mechanism," observed Steve Lindsey, who is CEO of Lontra. He is also the inventor of the blade compressor technology which he believes offers such a step change in efficiency.
"What you have essentially got here is a replacement for a piston cylinder," said Lindsey. "That can be everything from a bicycle pump to an air compressor to a cathedral diesel engine."
It is an idea that came to Lindsey over a decade ago and he has spent the intervening years building up Lontra and the design team. Lindsey commented: "I think they are inspired by the machine because looking at it is there isn't actually a great deal to it.It is one of those ideas that once you show people how it works they say, 'That must have been done before', or 'That's so simple'."
The premise is that a good compressor needs to do four things: take in air efficiently, let it out efficiently, not leak too much and compress the air. "What was interesting was that if you look at most of the compressors that came before they are not very good at least one, if not two of those," claimed Lindsey.Screw compressors have issues with leakage, for example, and the Roots blower, the device of choice for aerating in the water treatment industry, doesn't actually compress the air.
Lontra's Blade Compressor, which is its core technology, is a departure from the traditional piston-based systems. Instead of having a linear piston that draws air in on the outward stroke and compresses it on the inward, the Blade Compressor effectively wraps a cylinder in a circle, with a constantly rotating 'piston head'. A constantly open inlet means that air is drawn in for the first 180 degrees of the devices rotation. The chamber is bisected by a perpendicular blade, which means the trapped air that was behind the piston is now in front of it, and it is compressed for the remaining 180 degrees of the rotation and released through a series of holes in the end of the chamber.
The unique thing about this is that while the piston is compressing the air in front of it, it is drawing in the next volume of air behind it, so it is a continuous cycle. While the operation may be difficult to describe in words, its simplicity is evident when seen - there is a short video on vimeo (https://vimeo.com/90876721).
For initial design Lindsey called in the services of a draftsperson friend, but when Lontra came into being he started using PTC's Creo. "It is an expensive package but it is very, very good for the things that we do," said Lindsey. "A lot of our customers use the same grade of CAD package and so we can transfer documents very easily to them."
Design transfer and joint development with customers, is important as Lontra are not making products themselves but are selling the technology under licence. For this reason, and with different implementations of the designs being worked on simultaneously, the company has equipped all of its designers with Windchill, PTC's product Lifecycle management package, to ensure there is control of the design.
The key here to efficient operation is in the fluid dynamics, but the design team has not used an off–the-shelf CFD package for this. Lindsey said: "They built their own analysis package to model the compressor from scratch, which takes in everything from gas dynamics to heat transfer to wave motion. It has been fantastically powerful - whereas you hear some people who have built 1000 prototypes before they had a product that worked, it means that we can virtually prototype and speed up the development process massively."
This modelling environment is based on a lot of theoretical work that has been done over the years, for example, by Gordon Professor Blair at Queen's University Belfast and also some work from the old Gas Research Council. "There was some fantastic work on the core of gas dynamics done many years ago," continued Lindsey. "What we have done is taken all of those and built them into a mathematical model specific to our compressor, so this allows us to put in specific geometry, specific shapes and it will spit out what size ports we should really need, what the leakage will be, what the efficiency will be and then we can optimise from there. So the IP that we are selling is not just patents, it is more of the background IP and modelling, which I think is pretty unique and it is an approach that hasn't necessarily been taken in this depth in a lot of industries before."
An early demonstration of this came with the model – the first prototype of its size - that was sent for testing to Severn Trent Water. Waste water treatment is a massive user of compressed air – according to Lindsey 1% of all the electricity used in the UK powers air compressors for sewage treatment. It is natural bacteria that actually breaks down the sewage in a process called 'activated sludge', but they need an enormous amount of air and, as that typically needs to be pumped to the bottom of a 5 – 8m tank, it needs to be compressed.
Severn Trent Water did a six month trial with a Lontra air compressor rated at 1800m3 per hour – relatively modest by water industry standards – at a site in Worcester. The company measured the essential performance of the unit (efficiency based on power in to air out) and compared it to an existing Roots blower unit that was twice as big.The trial was conducted over the course of six months and showed an efficiency gain of 21.2%. "Industries normally chase improvements in efficiency of 1 or 2%!" added Lindsey. "And that was our first prototype of that size that showed those gains, while other compressors have been developed and gradually improved over 80 or 100 years. The next devices we have got on test are already well in excess of that original efficiency gain."
As 10% of industry's electricity is used compressing air, some basic arithmetic indicates that if such efficiency gains could be made across all industrial sectors, this technology could trim 2% off the UK's total electricity bill. And while the waste water industry has been the first target, other immediate applications are likely to include car superchargers and factories.
