Jet propelled

There aren't many similarities between building speedboats and designing process plants, but one technology seems set to make the leap.

Originally designed as a speedboat engine, Pursuit Dynamics' PDX pump combines a set of properties which seem to run completely counter to common sense - a pump which can handle liquids, solid suspensions and slurries, with no moving parts, which can also act as a mixer, macerator, and heater, which is virtually impossible to clog, self-cleaning, and is intrinsically safe.

Based in Hertfordshire, Pursuit Dynamics has been developing the system for almost four years. At heart, it's a simple idea. The pump transfers energy from steam to accelerate a stream of process fluid. It consists of a shaped open-bore tube, through which the process fluid runs. Steam is injected into this stream via a series of nozzles set around the tube's diameter. As it enters the stream, it breaks up the process fluid into droplets moving at supersonic speeds in the vapour. The steam condenses almost immediately, with the near-instantaneous pressure drop setting up a supersonic shockwave. The pressure drop - down to about 70 per cent vacuum - also draws fluid into the tube's inlet. At the same time, the force of the shockwave can tear apart any soft solids passing through the system.

Pursuit Dynamics' chief executive John Heathcote first came across the technology in Australia in 2000. 'It was at an embryonic stage and being developed purely as a marine propulsion system, but it was obvious that there was something very interesting here,' he says. 'What was striking was that it created a standing supersonic shockwave which was controllable, and which improved the flow through the system.' Refining the systems to control the shockwave took some work, but it wasn't until this was complete that the technology's potential in the process sector became clear.

'We were carrying out ingestion tolerance testing last year, basically trying to disrupt the system, to stop it functioning' Heathcote says. 'We dangled straps through it, tried blocking it with cabbages and mop-heads, and eventually resorted to hammering rubber bungs into the inlet. But everything we put in one end, just came out the other - and even the rubber bungs were ripped apart.' It became clear that the engine could also function highly effectively as a pump, while the power of the shockwave could be harnessed as a mixing mechanism. 'It's an extraordinary mixing system,' says Heathcote. 'With an oil-in-water emulsion, we can get oil droplet sizes below 1µm at flow-rates of 10 000litre/hr.'

The key to this is the control of the shockwave. PD's engineers used high-speed videos and CFD modelling to discover how the shockwave forms, and how its shape and power depended on the configuration of the pump and the pressure of steam used to power the system. Heathcote explains that the shockwave type is determined by the initial design of the pump, particularly the angle of the nozzles that inject the steam into the main fluid stream. 'The client tells us what they want the unit to do — an emulsifier, for example, and we set up the nozzle geometries for the pump to perform that function. The geometries of the steam treatment chambers, upstream of the nozzles, are also crucial,' he says. Once these have been determined, the intensity of the shockwave can be controlled simply by adjusting the steam flow valve.

The variations that can be achieved range from an ultra-high shear, for disrupting and macerating soft food components such as fruit or fats, down to a low-shear, non-mixing mechanism usable as a pump. 'It's ideally suited for the process sector,' Heathcote says. 'It runs off closed-circuit steam, typically at 2.5-7bar, which covers 98 per cent of available steam in the process industries. It's in-pipe, so there's no need for any major piping circuit redesign - it can be retrofitted extremely easily. And it's intrinsically safe.'

The PDX is particularly suited to applications in the food industry, where it can be used to mix components, macerate fruit and vegetables. The heat from the condensing steam can even be used to cook, for example in soup or sauce production. The same maceration effect could also be useful in the pulp and paper industries - paper and board going in one end of the pump would emerge as a wet slurry.

The capacity of the pump is limited only by the diameter of the main tube - flow-rates of 100tonne/hr are achievable, Heathcote says.

PD have also managed to operate the pump at elevated temperatures. 'The pump depends on steam condensation, and people thought we might have problems getting the steam to condense at high temperatures, but we can get around that by injecting cold water droplets into the zone,' Heathcote says. However, it is unsuitable for processes which are sensitive to water - chocolate processing is a typical example of these - although PD is working on techniques to replace the steam with another condensible gas to avoid these problems.

One attractive feature of the unit is its toughness, which allows it to pump mixtures of solids and liquids. 'Basically, anything that's going in one end will come out of the other,' Heathcote says. High solids content is not a problem, with the pump capable of handling a mixture with 30 per cent solids by volume, compared with around 6 per cent for a sand pump. Corrosion resistance can be imparted by the choice of materials and liners, and as there are no nooks and crannies where debris can collect, it is easy to clean through CIP systems - indeed, the nozzles are constantly blasting out steam, which makes them self-cleaning.

Combining process steps is, of course, the definition of process intensification, and Heathcote believes the PDX could have major cost-saving implications. Depending on the process, he claims, a PDX could reduce capital costs by up to £180 000, as it would replace pumps, homogenisers, in-line mixers, heaters and other equipment. It also has potential for converting batch processes, such as hydration, to continuous processing.

PD is looking for partners to help commercialise the technology, which is already attracting interest. 'We've had enquiries from food manufacturers, soft drinks, brewing, waste water, healthcare, confectionary, even the nuclear industry,' Heathcote says.

Despite its versatility, however, Heathcote doesn't believe the PDX will compete directly with existing of-the-shelf pumping solutions. 'This is a custom product. Its design will vary depending on exactly what the customer wants to do with it, and we'll optimise the design around their existing steam circuit and applications. Every one we sell is likely to be different.' It will be priced accordingly, he adds, but this is unlikely to be a barrier to its acceptance. 'If you think in terms of the amount of money we can save people, we still think it'll be attractive.'

BHR conference focuses on drivers

Despite its undeniable advantages in terms of increased efficiency in a smaller space than conventional techniques, uptake of PI has remained slow. Process intensification specialist BHR Group is putting the spotlight on the advantages of PI at its fifth major conference, to be held in Maastricht on 13-15 October. The conference will address the reasons for and the barriers against adopting PI, and will seek to find ways of overcoming these barriers.

One of the most daunting factors of adopting process intensification is that it almost always switches the process from batch to continuous operation - an unfamiliar world to many operators outside the high-volume bulk chemicals world. It's not just a matter of replacing a stirred pot with a new type of reactor. 'It may require redesign of other operations such as heat transfer, separation, crystallisation,' says BHR.

'It may open up new opportunities for improvements to the chemistry through changes in operating conditions and/or catalysis.' Issues of fouling and reliability need consideration, and HR and management issues can be significant.

The conference, which is co-sponsored by the UK Engineering and Physical Sciences Research Council and DSM and Novem of the Netherlands, aims to tackle these issues. The keynote speech, from Earl Hutchinson of GlaxoSmithKline, and a discussion forum led by a panel of suppliers, contractors, technologists and end-users all look at how PI can improve performance.

The papers to be presented at the conference cover the full range of process intensification, from the heavy end, with designs for cheaper, more efficient ethylene, crackers and for the use of membranes in natural gas sweetening, dehydration and CO2 removal; to the bulk chemicals field, with the design of an integrated urea-melamine process; through to the ultra-microscopic field, with a study of the interface between process integration, nanotechnology and biotechnology.

Other papers single out particular process equipment, such as dynamic spargers and electrodynamic pumps, sprays and mixers.