High-pressure press

Abstract: High-pressure press, preferably for treatment of foodstuffs by high-pressure, comprising a cylinder element (20), provided in a vessel volume (4) of a pressure vessel (1) and accommodating a movable piston (24). The cylinder element (20) is arranged with a gap (21) in relation to the surrounding pressure vessel wall (8) such that the same pressure prevails inside and outside of said cylinder element (20).

Description: The invention relates to a high-pressure press according to the precharacterising part of claim 1. In recent years, high-pressure treatment has started to be utilized as a method for, among other things, inactivating microorganisms (e.g. bacteria) in foodstuffs, especially fruit juices and the like, which have a particularly high quality. The advantage of high-pressure treatment as compared with the more frequently used heat-treatment is that the microorganisms in the freshly pressed juice are inactivated without destroying vitamins and flavour, which occurs during heat treatment and which requires additives in the heat-treated juice to restore, as far as possible, the nutritive value and taste of the freshly pressed juice. During high-pressure treatment of foodstuffs, it is desirable that the surfaces in the pressure chamber with which the foodstuff may come into contact, be made of a material which is inert in relation to the foodstuff. An example of such a material is stainless steel. The problem with stainless steel, however, is that its strength is considerably lower than the strength of the high-strength, non-stainless steels from which pressure vessels for high pressures are normally manufactured. This means, among other things, that the upper limit to the pressure, to which food-stuffs have hitherto been capable of being subjected for the above-mentioned purpose, has been at around 4,000 bar. Pressures of this order of magnitude are sufficient to inactivate microorganisms, but not to inactivate enzymes, which, for example, as far as fruit juices are concerned, contribute to separate the juice. Nor are these pressures sufficient to inactivate spores. The GB-A-1 038 907 describes a press which is able to withstand high pressures without using a precompressed cylinder wall for the pressure chamber as used in conventional presses of that kind. In order to achieve this end there is arranged a thick-walled cylinder element within the pressure chamber which forms a gap between its outer cylindrical wall and the inner cylindrical wall of the pressure chamber. The pressure chamber is provided with an opening in which slides a first piston which is provided on its inner side with a firmly attached second piston of smaller diameter. This second piston protrudes into the bore of the cylinder element and seals against the inner cylindrical wall of the cylinder element, thus defining the proper pressure chamber for the treatment of goods. The gap between the outer pressure chamber and the cylinder element communicates with the opening in the outer pressure chamber and is filled with a liquid pressure medium. Under operation this liquid is pressurized, thus generating a compressive force on the outer wall of the cylinder element. This pressure is selected such that there is a limited relief of the stresses built up in the cylinder element by the pressure on its inside under operation. The invention aims at developing a high-pressure press of the above-mentioned kind, which is particularly but not exclusively intended for treatment of foodstuffs up to pressures of the order of magnitude of 14,000 bar in order to make it possible, among other things, also to inactivate enzymes and spores during high-pressure treatment. To achieve this aim the invention suggests a high-pressure press according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention, a cylinder element is achieved which, under operation of the press, is completely relieved of pressure differences, since the pressure of the substance on the inside of the piston, serving as a movable wall of the pressure chamber, during movement of the piston to a balanced position becomes equal to the pressure of the pressure medium on the outside of the piston, which pressure also prevails in the gap between the outside of the cylinder element and the inner cylinder wall of the pressure vessel and balances the pressure of the substance against the inner wall of the cylinder element. Thus, the embodiment makes it possible to use a pressure vessel of high-strength, non-stainless steel which withstands the stresses which arise at pressures up to 14,000 bar and thereabove, and a cylinder element of a low-strength material, for example stainless steel, which is inert in relation to the substances which are to be treated by pressure, so that substances in the cylinder element cannot be precipitated in the foodstuff which has been treated by pressure and give flavour thereto. By way of example, the invention will now be described in greater detail with reference to the accompanying drawings showing in Figure 1 a longitudinal section through a schematically represented high-pressure press according to the invention, Figure 2 a slightly modified embodiment of the press in Figure 1. In Figure 1, 1 designates a pressure vessel, comprising a thick-walled cylinder 1a of high-strenght steel which may be prestressed by means of a prestressed steel wire (not shown) wound in conventional manner around the cylinder. Together with an upper end member 2 and a lower end member 3, the pressure vessel 1 defines a vessel volume 4. The lower end member 3 comprises a plate 5 with a cylindrical opening 6 for a plunger 7 which is connected to a hydraulic piston-cylinder arrangement (not shown in detail). Between the plunger 7 and the cylindrical wall 8 of the pressure vessel 1, a high-pressure seal 9, known per se, is fixed. A corresponding high-pressure seal 10 is fixed to the upper end of the pressure vessel 1, between the wall 8 and a portion 11 of the upper end member 2, said portion 11 projecting down into the vessel volume 4. What has been described so far with respect to Figure 1 constitutes the prior art within the field of high-pressure presses. According to the invention, a cylinder element 20, which may consist of a material different from the material in the cylinder 1a of the pressure vessel 1, is fixed in the vessel volume 4 so as to form a gap 21 between the pressure vessel wall 8 and the outer envelope surface 22 of the cylinder element 20. In the embodiment shown, the cylinder element 20, which preferably consists of stainless steel, is suspended from the upper high-pressure seal 10 so as to form a gap 23 between the lower seal 9 and the lower edge of the cylinder element 20. In the cylinder element 20, a free moving piston 24 is displaceably housed. The piston 24 is provided with a seal 25, which seals against the inner envelope surface 26 of the cylinder element. Together with the cylinder element 20 and the end member 2 the piston 24 defines a pressure chamber 27 for substances to be treated by pressure. The press shown in Figure 1 is intended for pumpable substances as, for example, juices or sauces and exhibits an inlet valve 28 and an outlet valve 29 in the upper end member 2. These valves are hydraulically operated valves with a non-return valve function, as shown in Figure 1. A further hydraulic valve 30 with a non-return valve function is arranged in the upper end member 2. Via the valve 30, an annular gap 31 above a seal 32 and a channel 33 in the cylinder element, fluid can be drained from the gap 21. Via a channel 34 in the lower end member 3, pressure fluid from a low-pressure pump (not shown) can be supplied when the plunger 7 is returned to its position indicated by the broken line 12. Lines 35 and 36, respectively, for cleaning liquid, for example water, open out into the respective inlet and outlet valves 28, 29 and communicate with pumps 37 and 38, respectively. In an alternative embodiment (not shown), the plunger 7 comprises pressure medium channels which connect the vessel volume 4 with an outside pump, also when the plunger 7 is inserted into the vessel volume 4. The mode of operation of the press is as follows: Upon start-up of a working cycle, the plunger 7 is in the lower position shown by the broken line 12. A predetermined volume of the product which is to be treated by pressure is now supplied to the pressure chamber 27 via the inlet valve 28. Thereafter, the vessel volume 4 is supplied with pressure medium with a pressure of the order of magnitude of up to 200 bar via the channel 34, the product in the pressure chamber thus being precompressed when the piston 24 moves upwards, such that the volume of air contained in the system is practically eliminated. Increase of pressure up to the previously mentioned pressures in the order of magnitude of 14,000 bar is then obtained by pressing the plunger 7 a predetermined distance into the vessel volume 4 with the aid of a piston-cylinder arrangement (not shown). The pressure in the vessel volume 4, that is, in the gap 21 and in the space 39 on the outside of the piston 24, will thereby be equal to the pressure in the pressure chamber 27, the cylinder element thus being completely relieved of pressure differences. According to an alternative embodiment (not shown) the plunger 7 is during the whole operation in its upper position, projecting into the vessel volume. In fact, the plunger 7 may in this embodiment be non-movable. This plunger comprises pressure medium channels, which connect the vessel volume 4 with an outside pump through the plunger 7. With this embodiment it is possible to obtain high pressures in the vessel volume without moving the plunger 7. Instead, the high pressure is obtained by utilizing a high pressure pump, which supplies pressure medium at pressures up to about 6,000 bar into the vessel volume through the pressure medium channels comprised in the plunger 7. When the product has been treated by pressure for a predetermined period of time, the plunger 7 is restored to its original position, whereupon the outlet valve 29 is opened. The product can now be pressed out by the piston 24 by supplying additional pressure medium to the vessel volume 4 via the channel 34. Any leakage of product substance from the pressure chamber 27 can be drained by opening the valve 30 for a short period, thus ensuring that the vessel volume 4 in its entirety is filled with the current pressure medium only, which preferably is an "eatable" oil, for example olive oil or castor oil, which has good lubrication qualities, but the pressure medium can also be pure water if seals with self-lubricating properties are used. The piston 24 is restored to its original position during the subsequent filling of the next volume of the product while draining pressure medium from the vessel volume 4 via the channel 34. If the product contains solid substances, which may adhere to the valves 28, 29 these may be cleaned prior to the next work cycle by spraying water into the valves via the channels 35 and 36, respectively. In an alternative embodiment (not shown) of the press, intended for pressure treatment of batches of non-pumpable products, for example prepacked solid foodstuffs, the valve arrangement in the upper end member 2 is replaced by an opening provided with a lid, through which opening the products are supplied and removed. Instead of fixing the cylinder element 20 suspended from the upper high-pressure seal 10 with a gap 23 between the lower edge of the cylinder element 20 and the lower high-pressure seal 9, the cylinder element 20 can rest against the lower seal and be provided with channels, which connect the space 39 with the gap 21. The width of the gap 21 is to be so adapted to the viscosity of the pressurized pressure medium and the deformation of the pressure vessel 1, caused by the compressive stresses in the pressure vessel, that the contraction-of the pressure vessel during pressure relief does not cause throttling of the flow in the gap with an ensuing too great non-uniformity in the distribution of pressure. Figure 2 shows an embodiment of a high-pressure press according to the invention which differs from the one described in Figure 1 in that the piston 24 is shorter in the axial direction to increase the available volume in the chamber 27. To eliminate the risk of the piston becoming wedged, the piston is connected to a guide pin 40 which is guided in a bore 41 in the plunger 7. An alternative for increasing the volume of the pressure chamber 27 without risking locking of the piston 24 is also shown in Figure 1, where the dash-dotted line 42 indicates a cup-shaped design of the piston. In both of the alternative embodiments of the piston 24, emptying of the chamber is required in some other way than what has been described above, for example by supplying a gas, such as CO 2 , to the chamber through an inlet disposed at a suitable location.

Claims: High-pressure press for pressurizing substances, for example foodstuffs, pharmaceuticals or cosmetics, with a thick-walled cylinder (1a) and a pair of end members (2,3) which together form a pressure vessel (1) with a vessel volume (4), with at least one piston (24) which is axially displaceable in the pressure vessel (1) and seals against an outer wall, with a cylinder element (20) arranged in said vessel volume (4) in such a way that a gap (21) is formed between the outer envelope surface (22) of the cylinder element (20) and the inner wall (8) of the pressure vessel (1), and with said axially displaceable piston (24) being arranged in said cylinder element (20) and sealing against the wall (26) thereof, characterized in that said piston (24) is freely moveable in said cylinder element (20), and that the space (39) between the outside of said piston (24) and the respective end member (3) communicates with the gap (21) to create the same pressure medium pressure on the outside of the cylinder element (20) as on the outside of the piston (24). High-pressure press according to claim 1, characterized in that the cylinder element (20) consists of a material which is inert in relation to the substance which is to be pressurized, whereas the surrounding wall (8) of the pressure vessel (1) consists of high-strength steel. High-pressure press according to claim 2, characterized in that the cylinder element (20) consists of stainless steel. High-pressure press according to any of the preceding claims, characterized in that the other end member (2) comprises means (28, 29) for respectively supplying and removing the substance which is to be pressurized. High-pressure press according to claim 4, characterized in that said means are formed of hydraulically operated valves (28, 29) with non-return function. High-pressure press according to any of the preceding claims, characterized in that first means (34) are arranged to supply pressure medium to the vessel volume (4) to bring about a displacement of said piston (24) a first distance against the action of the pressure in the pressure chamber (27) to a first predetermined pressure level and that second means (7) are arranged adapted to bring about a further pressure increase in the vessel volume above said level. High-pressure press according to claim 6, characterized in that said second means comprises a piston element (7) which is insertable into the vessel volume (4) by means of an external force. High-pressure press according to claim 7, characterized in that said piston element (7) comprises pressure medium channels which connects the vessel volume (4) with an outside pump also when said piston element is inserted into the vessel volume (4). High-pressure press according to claim 6, characterized in that said second means (7) are arranged stationary extending into the vessel volume (4) and comprising pressure medium channels which connect the vessel volume (4) with an outside pump.

Inventors: BERGMAN CARL, TRAEFF ANDERS, BERGMAN, CARL, TRAEFF, ANDERS, Träff, Anders
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1993
Main classification: B01J3
IPC codes: B30B11, B01J3, C22C38, A23L3, B30B1, B30B9