Answer the questions:

What is the Barawing system based on?

What are three main features of it?

What advantages does an internal intensifier provide?

What are advantages of a composite vessel?

What are advantages of the axial cylinder design?

Continuous Processing: New Developments.

A semicontinuous high pressure processing system for processing of liquids has been developed by Flow, ACB Pressure System-Alstom, and Kobe Steel. Figure 20 presents an overview of the process. A low-pressure transport pump pumps liquids into the pressure vessel. After closing the valves, the vessel is pressurized by means of the high pressure pump. A floating piston separates the pressure transfer medium and the product. After treatment, the product is transferred to a surge vessel. By coupling a number of pressure vessels, the energy stored in a pressurized vessel can be used to pressurize a second vessel at ambient pressure, thus saving energy and process time.

U nilever patent WO97/43914 describes a continuous high pressure processing system. In this system (Figure 21), the product is conducted in a steady flow through an open-end tube while the pressure difference between the entrance and the exit of the tube is maintained at 100 MPa or more using a high pressure pump. The pressure difference is the result of the viscous friction in the system, especially because of the exponential pressure-dependent viscosity behavior. Viscosity may increase by a factor of 10³ to 10⁴ at increased pressure. The pressure buildup in an open tube is possible with a long tube (50 to 100 m); the ratio of length to average diameter of this tube should be at least 1000 and preferably 10,000. The residence time can easily be adjusted by inserting a chamber at the upstream of the tube. Unilever suggests that an effective preservation technique might be obtained if this system is combined with pulsating electrical fields.

Fig.20. The semicontinuous high pressure processing system for processing of liquids.

Fig.21. Continuous high pressure processing system for processing of liquids.

At Unilever Vlaardingen and at ATO, continuous high pressure processing laboratory-scale systems combined with pulsating electrical fields have been developed. The effects of several combinations of pressure and electrical field strength on spores and microorganisms are being currently evaluated.

Answer the questions:

1. Who has developed a semicontinuous high pressure processing system?

2. How does it work?

3. What are peculiarities of Unilever’s system perfomance?

4. What does Unilever’s system suggest?

Codes and Rules for Construction.

For a company to use high pressure equipment, an inspection and certification by a local (national) inspection institute is required. For inspection and certification, a code describing requirements and criteria is to be used. Portions of several codes could be used for the certification of high pressure equipment, but the code that is most specifically adapted for this application is the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section VIII, Division 3 (Alternative rules for high pressure vessels, 1997). The rules of Division 3 include requirements for the design, construction, inspection, and overpressure protection of metallic pressure vessels with design pressures generally above 10,000 psi (approximately 69 MPa). It consists of several parts.

General requirements. Scope, jurisdiction, responsibilities, duties, and general rules for inspection.

Material requirements (for metals). Test requirements, requirements for bolting, and material design data.

Design requirements:

• the basic design;

• fatigue evaluation, including design fatigue curves;

• fracture mechanics;

• design rules for autofrettage;

• design for openings, closures, heads, boltings, seals, and supports;

• special design requirements for layered vessels;

• special design requirements for wire-wound vessels and frames;

• special design requirements for strip-wound vessels;

• design requirements for welded vessels;

• experimental design verification.

  • Fabrication requirements. Welding requirements; protective linings; heat treatment of weldments; and several additional fabrication requirements for autofrettaged vessels, quenched and tempered steels, layered vessels, wire-wound vessels, and strip-wound vessels.

  • Pressure-relief devices. Requirements for rupture disk device, pressure-relief valves, and flow capacity of relief valves.

  • Examination requirements. Examination procedures (radiographic, ultrasonic, etc.), examination of material and welds, and acceptance criteria.

  • Testing requirements. Impact test, hydrostatic test, gages, and transducers.

  • Marking, stamping, reports, and records.