Food Engineering

Supersonic processing

August 1, 2005
Marine propulsion technology has been adapted to handle pumpable foods, and the developers are rolling it out to processors on both sides of the Atlantic Ocean.

Kester Scrope, commercial director, Pursuit Dynamics plc, Hertfordshire, UK
It sounds like the Swiss army knife of food and beverage processing equipment: a single unit that can cook, mix, pump, homogenize and emulsify a wide range of products. Even better, processing time is accelerated by a factor of 10 or more, and low-cost steam is the energy source. The technology was developed by Alan R. Burns, an Australian inventor who conceived it as a marine propulsion system for watercraft. The temperature difference between the steam and the working fluid-seawater in Burns' original concept; beverages, soups and a wide range of other human consumables in food processing-produces rapid pressure reduction in the mixing zone. The pressure drop draws in working fluid and propels it toward the outlet; condensation of the steam unleashes significant energy, creating an implosion effect. A mist of air and water droplets can be added to increase mass flow rate and enhance momentum transfer.

The genius of Burns' system was not lost on John Heathcote, a British venture capitalist who acquired the rights to the technology and formed Pursuit Dynamics plc in 2000. Years of modification and refinement preceded commercialization early this year of a system that already has been licensed to Coca-Cola Enterprises, Campbell Soup and Greene King plc, a $1 billion British brewer and pub operator. Pursuit Dynamics has invested $14.5 million so far to make the technology appropriate for a range of industries, beginning with food and beverage. Steam jacketed kettles, scraped-surface heat exchangers and high-shear pumps are among the conventional processing systems the units can augment or replace. The absence of impellers and other moving parts and elimination of product burn-on mean minimal system maintenance.

Helping to bring Pursuit Dynamics' technology to market is commercial director Kester Scrope. Scrope joined the firm early last year, after serving as innovation director at Mondi Packaging Europe, a division of Anglo-American plc. Scrope is a graduate of the University of Newcastle Upon Tyne and received his MBA from Cranfield School of Management, one of the top business schools in the UK. Food Engineering recently spoke with him about the technology's development and its potential in food and beverage processing.

FE: What are the principles of the technology?

Scrope: The system uses steam in a completely novel way. Steam enters through an annular expansion chamber and achieves velocities three times greater than the speed of sound. The direction of the steam is managed as it condenses and contracts in the chamber, resulting in the transfer of heat and mixing and pumping energy to the process flow in a supersonic vapor phase, followed by a controllable condensation shockwave.

Total control of the supersonic region is critical. By extending the point of condensation, we can increase mixing action to create emulsions with ingredients at the sub-micron level. Alternatively, condensation can occur very early, resulting in low-shear activity that permits processing of soft fruits such as strawberries without any damage. Control is achieved without constrictions or moving parts, resulting in minimal maintenance.

A schematic of Pursuit Dynamics’ shock wave technology illustrates the essence of the system. After steam moving at two to three times the speed of sound hits a fluid flow, a near-vacuum is created and condensation occurs, resulting in rapid heating and/or mixing of ingredients. Source: Pursuit Dynamics plc.
FE: What changes were necessary to adapt marine propulsion to food processing?

Scrope: Development of the marine drive focused on creating a wide power band, which led to a system having a wide turndown range in flow rate, mixing capability and heat-transfer rate. We experimented to ensure the system would not block or be damaged by foreign objects, and it was then that we realized we had the ability to pass materials through undamaged or, alternatively, homogenized by the supersonic condensation shockwave.

In fine tuning our technology for food processing, we were able to reduce energy consumption by up to 50 percent. Top-end speed is up to 15 times faster than conventional methods, and reduction of thermal shock and burn-on improves product quality.

FE: Why is the phenomenon dubbed a "supersonic shockwave?"

Scrope: It's called that because the reaction ends in a wave, and it is our ability to move that region and control it that is totally novel. For example, we did some work with starches that demonstrated we could get very good activation at 72

FE: The system is variously described as PDX or Sonic. What's the distinction?

Scrope: Sonic is the skid-mounted system we designed for food and beverage. It's followed by a number that refers to the dimension of the mixing zone. The Sonic 25, for example, is 25 mm, or about 1 in. in diameter. It has PLC controls and can be programmed to run specific recipes. There's not a lot to go wrong: there are no moving parts, and there are few opportunities for operator error. The goal was to optimize the process and make it very easy to use.

The technology is totally scalable, and as you move into higher volumes of throughput and retrofits of existing systems, the PDX design comes into play. The PDX 47, for example, has throughput of 60,000 litres (almost 16,000 gallons) an hour. It's being used for clean-in-place in a brewery application. We go up to a pipe dimension of 63 mm, almost 3 in. Multiple units can be combined for even higher volumes.

FE: Are there any regulatory hurdles to clear before this technology can be applied in the US?

Scrope: Everything is food grade, basically constructed out of 316 stainless. We're talking to a number of systems integrators in North America to do the fabrication. We haven't looked at the 3A sanitary standards, but the design is intrinsically hygienic. We are most of the way through approval from EHEDG (the European equivalent of 3A). We believe EHEDG is one of the most onerous standards in the world and should meet the requirements of North American processors.

FE: Major breweries are focusing on continuous processes in lieu of batch. Does this technology support that effort?

Scrope: Research conducted by Brewing Research International demonstrated that PDX is suitable for both continuous and batch processing in mashing. Conventional technologies have tied people to a batch process. PDX can be retrofitted to a batch process, or it can be part of a new continuous process.

Brewing is quite energy intensive; this is faster, cheaper and more space efficient. It's not just a little faster, either: it processes up to 15 times as quickly. That's the sort of step change in performance that doesn't happen every day. There's a wonderful robustness because it's not based on a lot of clever valves that need maintaining. When you factor in reduced maintenance costs, reduction in the number of operators, the smaller footprint and the sheer increase in output, we're talking about paybacks in less than 12 months.

FE: Does it have applications in aseptic processing?

Scrope: We've done some preliminary work to demonstrate we can kill E. coli surrogates at a lower temperature than existing technology. That's something we'll pursue later. For now, we're focused on quick wins, and we have a lot of traction with pumpable foods because the system is versatile, energy efficient and represents a quantum improvement in processing time.