Answer the questions:

1. What liquid is suitable for food application processes?

2. What qualities should the pressure medium possess?

3. What is the system pressurized in the case of internal compression?

4. What is advantage of internal compression?

5. What does the operating presser in the case of internal compression equal?

6. How does pressurization by means of external compression take place?

7. What is the main advantage of this technique?

8. What is recommended for operational efficiency in case of pressurization by means of external compression?

9. What is the main bottleneck for all high pressure processing equipment?

New Developments in Batch Systems.

The Agrotechnological Research Institute (ATO), Unilever Research Vlaardingen, Stork Food Processing Group, and The Netherlands Department of Economic Affairs have jointly developed the cost-efficient Barawing system for high pressure treatment of food products. The system is based on the conclusion of recent microbiological research that efficient, high-quality sterilization of food products can only be achieved at pressures of 700 MPa or higher. The Barawing system has three main features: an internal intensifier, a composite vessel, and an axial cylinder.

Internal intensifier. A cost-competitive operation requires short cycle times, and therefore fast pressurizing. The viscosity of pressure fluids that can be used in food applications increases at high pressures. At high pressures and relatively low fluid speed, a substantial pressure drop has been recorded over a high pressure line (length 5 meters, diameter 1.6 mm, come-up time 150 seconds), as shown in Figure 18. For this reason, the Barawing system uses an internal intensifier design, which allows short pressurizing time, low external pressure, and high energy efficiency. In addition, it offers the option of using an accumulator for even faster pressurizing.

Composite vessel. The Barawing system adopts a vessel that is reinforced with high-strength synthetic fibers. In order to optimize the advantages of this construction, a prestressing technique has been developed. The advantages of this system over conventional high pressure processing systems are:

higher working pressure;

high number of cycles due to better fatigue resistance;

lower weight (density of composites is about 20% of the density of steel);

faster handling;

low heat transfer (no cold spots under adiabatic temperature rise).

Figure 19 shows a composite test vessel designed for operation at 1100 MPa. Because of the properties of these composites, in the future they may also be used for yokes. This would yield a significant reduction in mass for the complete unit.

Axial cylinder. The Barawing system uses an axial cylinder for fast closing and opening of the vessel, thus reducing total cycle time. The design of the axial cylinder has several advantages. It reduces shear stresses in the composite material; it reduces tensile stress on the inner fiber caused by transverse Poisson effects; and it allows an easier liner and seal design because extrusion of the liner is prevented.

I n the first phase of the project, small-scale high pressure vessels constructed of various composite materials have been built and extensively tested. Recently, participants in the joint project started a second three-year phase of the project with the goal of further commercialization of the concept. In May 2000, a pilot unit became operational. Commercialization of this new high pressure system is planned by Stork in association with Fokker Special Products.

Fig.18. Pressure drop over a high pressure line

(length 5 meters, diameter 1.6 mm, come-up time 150 seconds).

F ig.19. Composite pressure vessel ready to be tested.

Pressure is supplied by means of an external intensifier.

During pressurizing, the vessel is compressed axially by means of a hydraulic press, positioned at the bottom of the vessel.