WO1998007334A1

WO1998007334A1 - Method, apparatus and processing plant for sterilizing and/or heat treating particulate products

Info

Publication number: WO1998007334A1
Application number: PCT/DK1997/000332
Authority: WO
Inventors: Per Martinsen; Verner Christiansen
Original assignee: Atlas-Stord Denmark A/S
Priority date: 1996-08-23
Filing date: 1997-08-19
Publication date: 1998-02-26
Also published as: ES2175444T3; DK173834B1; DK0923318T3; NO985135L; ATE216194T1; US6071474A; EP0923318A1; NO317036B1; AU3847297A; EP0923318B1; DE69712074D1; NO985135D0; DE69712074T2; DK88996A; CA2254842A1

Abstract

A method, an apparatus and a plant for sterilization and/or heat treatment of products in particle form, for example bone meal, said product being introduced in batches into a pressure vessel which lies substantially horizontal, in that said pressure vessel is arranged to rotate and is provided on the inside with a built-in helical vane arrangement along the inner wall/jacket of the pressure vessel. The pressure vessel (5) is closed and evacuated of air and heated, said heating being effected by supplying steam to the vessel's jacket (4) and also possibly by the supply of steam under pressure to the inside of the vessel. The heating and pressure treatment is effected for a given period of time, in that the process parameters are a function of the product to be treated. The pressure vessel is made to rotate, said rotation giving rise to a mixing/movement of the particle-formed product and, as a consequence of the inner vane arrangement, the movement of the product from the one end of the vessel to the other. The process vessel is then relieved of pressure, after which the heat treated/sterilized product is emptied from the process vessel and the batch process starts from the beginning. There is hereby achieved an apparatus and a method with a continuous and uniform mixing and sterilization of the product with optimum utilization of the vessel's capacity, while at the same time there is little risk of defects arising in the apparatus and during the process itself.

Description

METHOD, APPARATUS AND PROCESSING PLANT FOR STERILIZING AND/OR HEAT TREATING PARTICULATE PRODUCTS

The invention concerns a method, an apparatus and a processing plant for the sterilization and/or heat treatment of products in particle form, e.g. bone meal, fish meal and other feedstuffs, in a horizontally-lying, rotatable pressure vessel.

It is known to sterilize bone meal and similar products in batches by heating the meal during stirring in a pressure vessel. The known pressure vessels for this purpose can be horizontally-lying vessels with a through-going horizonal axle which comprises mechanical stirring elements in the form of vanes which are secured to the vessel's through- going axle. Such a sterilization plant is characterized by high power consumption and risk of great wear and corrosion, in that the moving parts, i.e. the axle with the vanes, are constantly in contact with the product which is to be stirred/mixed. The risk of these parts suffering defects is thus very high, and the stirring is not as efficient as desirable.

The known types of apparatus with through-going, rotatable axle often have problems with the bearings and associated stuffing-boxes, namely where the axle passes the vessel walls. Here it is possible for the product to gain ingress to the stuffing-box and cause wear, one of the results being that the stuffing-boxes become leaky. There also hereby arises the possibility of the product being contaminated, possibly by non-sterile product remains, so that a batch which can be expected to be sterile nevertheless proves to be contaminated.

It is the object of the present invention to provide a method and apparatus which is not encumbered with the disadvantages of the known technique, and whereby a continuous mixing and uniform sterilization of the product is achieved with an optimum utilization of the vessel's capacity, while at the same time the risk of any defects arising is very small.

This is achieved by a method of the kind disclosed in the preamble to claim 1, and also where the pressure vessel is arranged to rotate and is provided with a built-in, inner helical-vane arrangement along the inner wall/jacket of the pressure vessel, said pressure vessel being closed and evacuated of air and heated, said heating being effected by a supply of steam to the jacket of the pressure vessel, and also possibly by a supply of steam under pressure to the inside of the vessel, said heating and pressure treatment taking place for a given period of time, in that the process parameters are a function of the product to be treated, and said pressure vessel being made to rotate, said rotation giving rise to a mixing/movement of the particle-formed product, and a movement of the product from the one end of the pressure vessel to the other as a result of the inner helical-vane arrangement, said process vessel then being relieved of pressure, after which the process vessel is emptied of heat-treated/sterilized product and the batch process starts from the beginning.

By carrying out a mixing as disclosed, a continuous and constant mixing of the product takes place, so that the product is in constant movement and is heated uniformly, partly by the surfaces of the pressure vessel which, of course, are heated via the steam supply, and also by the supply of steam which possibly takes place inside the pressure vessel. There is hereby achieved a uniform processing of the product.

The apparatus according to the invention can be configured wholly or partly of stainless steel, so that corrosion by the meal, which in certain cases can be aggressive, is avoided.

By using a method according to the invention as disclosed in claim 2, there is achieved a continuous and efficient sterilization in relation to the chosen process parameters.

By using a method according to the invention as disclosed in claim 3, an optimum mixing and an optimum and uniform sterilization of the product is achieved.

By using a method according to the invention as disclosed in claim 4, an optimum utilization of the thermal characteristics of the steam is achieved.

By using a method according to the invention as disclosed in claim 5, a desired automation of the process is achieved.

By using a method according to the invention as disclosed in claim 6, it is achieved that the sterilized product is not contaminated during its removal.

The invention also concerns an apparatus for the sterilization and/or heat treatment of products in particle form, e.g. feedstuffs such as bone meal and fish meal, comprising a substantially horizontal and rotatable pressure-tight vessel. The apparatus also comprises a mixing arrangement provided in the vessel, said arrangement comprising a helical vane lying along the vessel ' s inner wall, called the outer vane, and a second helical vane called the inner vane fastened to said outer vane and at a distance from the inner wall, which vanes extend from the one end of the vessel towards the other. There is hereby achieved a continuous mixing and uniform sterilization of the product with an optimum utilization of the vessel's capacity, while at the same time the risk that defects may arise is very small.

By using an apparatus according to the invention as disclosed in claim 8, it is achieved that the product is conveyed forwards and backwards over the heating surfaces, i.e. the jacket, and at the same time does not clump together with the risk of a subsequent heterogeneous mixing of the product.

By using an apparatus according to the invention as disclosed in claim 9, it is achieved that the sterilized product is not contaminated during removal.

By configuring an apparatus according to the invention as disclosed in claim 10, an expedient construction of the apparatus is achieved, so that the possibilty is provided of being able to use and control all functions during operation, i.e. without having to stop the rotation of the vessel .

By using an apparatus according to the invention as disclosed in claim 11, it is achieved that the risk of leakage is minimized.

Claims 12 and 13 disclose preferred embodiments of the invention.

The invention also concerns a processing plant for the production of sterile bone meal while using the method and the apparatus as disclosed, and where the processing apparatus forms the boundary between the non-sterile and the sterile areas of the plant. It is hereby achieved that a contamination of the sterilized product does not occur during the full handling of the product from the momemt that it is brought into the hall for processing until it again leaves the hall after the processing has taken place.

The invention will now be described in more detail with reference to the drawing, where

fig. 1 shows the pressure vessel from the side,

fig- 2 shows the pressure vessel seen from above,

fig. 3 shows the pressure vessel seen from the side and with partial cross-section included,

fig. 4 shows the inside of the pressure vessel with helical vanes,

fig. 5 shows the helical vanes in detail, and

fig. 6 shows a preferred embodiment of a self-locking valve mechanism according to the invention.

Figs. 1, 2 and 3 show a horizontally-lying and rotatable processing apparatus according to the invention, comprising a pressure-tight vessel 5 with a steam-heated jacket 4 to which steam is supplied via components etc. 1, and from which condensate can be removed via a tapping-off arrangement 27 for this purpose. The vessel 5 rotates around an axle journal 7 at each side. In the end opposite to that at which the steam is supplied 1, compressed air is introduced via an element 6. A valve 8 is placed in the same end for the connection of vacuum via the pipe 9 and the bearing construction in the right-hand side, where the supply of compressed air which is explained later also takes place. The valve 8 is also used for the de-flashing of the product vessel after the heat treatment. The actual introduction of the product takes place through a filling valve 2 which sits on the jacket of the pressure vessel 5, and from which the emptying valves 3 are placed at an axial distance. Extending around the valves 2, 3 there are stationary product channels 2a and 3a secured to a frame 25, and annular channel parts 2b, 3b which are secured to the jacket 4 and thus rotate herewith. During filling via the valve 2, the rotation is stopped, preferably with the valve facing vertically upwards as shown. The channels 2a, 2b serve as protective covering for the valve 2 and collect possibly spilled raw material. During emptying via the valves 3 during rotation, the channels 3a, 3b serve as a further collection element from which the sterile product is removed at the bottom 26 for further transport. The valves 2, 3 and the channels 2a, 3a are disposed at a distance from one another and are completely separate. With this construction it is ensured that no contamination of the valves takes place during the emptying of the treated/sterilized product.

The product can be emptied out without changing the direction of rotation. The product valves 2, 3 can be opened and closed by remote control and during rotation. Filling takes place with stationary process vessel. The product valves are preferably self-locking and are completely sealed by means of an 0-ring in each valve.

A pipe 9 leads from the inside of the pressure vessel 5 to the valve 8 for the exhaust of a possible over-pressure.

All valves are preferably manoeuvred pnue atically and electrically controlled. All valves can be manoeuvred during rotation of the vessel, in that compressed air for this purpose is supplied via the pipe 19 through the one bearing, and electric current for valve control is supplied via a multi-conductor cable 20 in the same bearing construction. This end of the vessel is called the discharge end.

At the other side, the drive end (left-hand side in the drawing), the bearing construction is such that steam under pressure can be introduced via a pipe 1.

The process vessel is suspended in bearings 24 via axle journals 7, but can also be supported by support rollers or similar elements.

Both bearing constructions are completely screened by shields 21, so that stuffing-boxes etc. cannot come in contact with the product. This is possible because no use is made of any through-going axles.

In the shown embodiment, the process vessel is supported by bearing brackets 22 and is driven by an adjustable electric motor via belt or chain drives.

Fig. 4 shows the inside of the vessel, and where it will be seen that helical vanes are provided for the stirring of the product. These helical vanes comprise outer vanes 12 and inner vanes 11. The outer vanes 12 lie longitudinal to the pressure vessel's jacket, to which they are secured, while the inner vanes are disposed at a distance to the outer jacket and are secured to the outer vanes 12 via a joint 13, for example by welding. The helices of the outer and the inner vanes run in opposite directions, so that upon rotation of the pressure vessel 5 the material which is lying outermost will be conveyed from the one end of the pressure vessel 5 to the other, whereas the material which is lying at a greater distance and corresponding to where the inner vanes 11 are disposed will be conveyed in the opposite ditrection. The outer vanes 12 are fastened to the inner surface of the jacket 4 along the edge 15 of the vane 12, for example by welding.

In this way, a good mixing of the material is ensured, which results in a uniform heating, partly through the heating which takes place inside the pressure vessel itself by the injection of steam, and partly as a consequence of the transfer of heat which takes place from the heat surfaces of the jacket 4.

The steam for heating is supplied to the jacket's 4 cavity 14, through which the steam migrates from the one end 17 to the other end 18 of the pressure vessel 5. In the other end of the pressure vessel, the steam can possibly be led into the inside of the vessel depending on the position of the valve 16, and hereby effect a further heating of the product. The steam pressure can be in the range of approx. 100% vacuum to approx. 5 baro, but is preferably around 2 baro ( bar overpressure ) .

The typical dimensions for a pressure vessel as disclosed will be a length of approx. 3-7 and a diameter of approx. 1.5-3 m. The capacity for sterilization will be in the order of 1-10 tons/hour.

The speed at which the pressure vessel is rotated can be varied continuously from approx. 0.2 to 25 rpm.

In fig. 5 is seen the construction of the helical vanes in detail, and where it appears clearly how the helix of the inner vane 11 extends the opposite way in relation to the outer vane 12, hereby ensuring that the products are conveyed in opposite directions. In fig. 3, the valves 2, 3 are shown in the form of ordinary clack valves, so-called butterfly valves, which are manoeuvred by a pneumatic mechanism. However, it is preferred to use a self-locking valve mechanism as shown in fig. 6, e.g. in connection with a clack valve or the like, similarly shown in fig. 6, but other forms of valves can also be used, in that it is important that the valve can be closed in a pressure-tight manner against the vessel pressure, and that the closing mechanism is self-locking so that it cannot be opened even though the pressure supply fails. This provides increased security against malfunction, accidents with escaping steam etc.

In fig. 6 is seen a valve flap 32 which can be turned around a pivot point or an axle 33 by means of a self- locking mechanism 31. The mechanism 31 and the valve 30 are shown in both the open and the closed position. A working cylinder 37, preferably pneumatically activated, can tilt around a point 39 and has a piston rod 38 in engagement with a V-shaped arm 36 with a pivot point 35 and an arm 41 which is in engagement with a valve arm 34 which, as shown in the drawing, is in engagement with the valve flap 32. The arms 34, 36 constitute a self-locking toggle mechanism, so that the axes 40, 41 do not lie completely in extension of each other when the valve flap 32 is closed, but "snap" slightly downwards so that the valve flap cannot be opened. In order to be able to open the valve flap 32, it is necessary for pressure to be applied to the working cylinder 37 for the retraction of the piston rod 38, so that the toggle mechanism 34, 36 is drawn out of engagemen .

During the processing, the product is introduced through the supply valve 2. The product will normally be supplied direct from other production equipment, and will normally be heated, e.g. to about 100°C. The pressure vessel 5 is made to rotate during the whole of the process, whereby the product is made to move from the one end of the pressure vessel 17 to the other end 18 during heat treatment/ sterilization with heat and pressure.

It is expedient for the vessel to be at least 1/3 full in order to ensure that both the inner helical vane as well as the outer helical vane are taken into use. Otherwise, a sufficient mixing of the product will not always occur, and the handling of the product will thus not be uniform and will not ensure an end product which is sufficiently contamination-free.

The selected process parameters are a function of the product, e.g. in that heating to 133 "C should be effected for 20 minutes when the size of the largest clumps in the material to be treated is 50 mm. The steam heating is carried out at a process pressure of approx. 2 baro, the result being that a complete sterilization is obtained. In the event of the size of the relevant clumps/particles being in excess of 50 mm, the selected process parameters must naturally be changed.

Upon conclusion of the product processing, the steam is de- flashed via the pipe/valve 8 and atmospheric pressure is established. The sterile product is now led out through the discharge valves 3 and the channel 3a, 3b, and can now be transported away, e.g. for packaging.

The process vessel is rotated during the whole of the processing, i.e. both during the sterilization process and during the emptying, in that the vanes ensure that the product is conveyed towards the discharge valves for emptying. The rotation thus contributes both during the processing and during the emptying of the vessel. In order to ensure that the vessel is adequately filled, during the filling it can be necessary to add the product several times with intermediate rotation of the vessel.

The rotating vessel itself can form the boundary between the non-sterile part of a plant and its sterile part, in that the boundary between the parts extends between the filling valve 2 and the discharge valves 3, e.g. as indicated by the line 23 in fig. 3.

The method, the apparatus and the plant will be able to be used in connection with any form of heat treatment and sterilization of products in particle form, whether this be feedstuffs, bone meal, fish meal or other kinds of granulate materials, and where it is desirable to reduce or totally eliminate any possible bacterial flora in these products .

Since all of the valves can be operated during the rotation of the vessel, one or more of the following functions can take place and can be controlled externally, e.g. from a PLC, a PC screen or operator's control panel:

- Steam is led constantly to the heat jacket.

- Steam is led constantly to the process vessel.

- Condensate is constantly drained from the jackets.

- Constant supply of compressed air for valve operation.

- Constant supply of electrical signals for valve operation.

- Pressure relief/vacuum suction can be opened and closed.

- Product discharge valves can be opened and closed. There are no rotating stuffing-boxes in connection with the product under pressure.

The vessel is filled with product in one or more definite positions.

Claims

C L A I M S

1. Method for the sterilization and/or heat treatment of products in particle form, for example bone meal, said product being introduced in batches into a pressure vessel which lies substantially horizontal, c h a r a c t e r i z e d in that

a) the pressure vessel is arranged to rotate and is provided on the inside with a built-in helical vane arrangement along the inner wall/jacket of the pressure vessel ,

b) said pressure vessel is closed, evacuated of air and heated, said heating taking place by supplying steam to the jacket of the pressure vessel and also possibly by the supply of steam under pressure to the inside of the vessel, said heating and pressure treatment taking place for a given period of time, in that the process parameters are a function of the product to be treated,

c) and said pressure vessel is made to rotate, said rotation giving rise to a mixing/movement of the particle-formed product, and that the product is conveyed from the one end of the pressure vessel to the other as a consequence of the inner helical vane arrangement ,

d) said process vessel is relieved of pressure,

e) hereafter, the heat treated/sterilized product is emptied from the process vessel and the batch process starts from the beginning.

2. Method according to claim 1, c h a r a c t e r i z e d in that the process conditions are a minimum temperature of 133 °C for 20 minutes under a continuous and constant steam pressure of a minimum of 2.0 baro, and that during the actual sterilization/heat treatment, a constant supply of steam at a minimum pressure of 2.0 baro is also fed to the pressure vessel .

3. Method according to any of the foregoing claims, c h a r a c t e r i z e d in that during the rotation of the vessel, the product lying closest to the vessel's jacket moves from the one end of the vessel towards the other, and that the product lying at at a greater distance from the jacket moves in the opposite direction, this oppositely-directed product movement resulting in a mixing of the product.

4. Method according to any of the foregoing claims, c h a r a c t e r i z e d in that the supply of steam is effected at the one end of the vessel to the vessel's jacket cavity, which steam migrates along the surfaces of the jacket cavity to the opposite end of the vessel, after which it is led into the vessel or led away.

5. Method according to any of the foregoing claims, c h a r a c t e r i z e d in that the rotating process vessel is further supplied with compressed air and electric current for the manoeuvring and control of the valves which control the heat treatment/sterilization of the product.

6. Method according to any of the foregoing claims, c h a r a c t e r i z e d in that the heat treated/ sterilized product is introduced into the vessel through an opening/valve which is different and at an axial distance from the opening/valve through which the product is discharged.

Apparatus for sterilization and/or heat treatment of products in particle form, for example feedstuffs such as bone meal and fish meal, comprising a pressure-tight vessel which is rotatable and lies substantially horizontal, c h a r a c t e r i z e d in that the apparatus also comprises a mixing arrangement which is provided inside the vessel, this arrangement comprising a first helical vane lying along the inner wall of the vessel and called the outer vane, and a second helical vane called the inner vane fastened to said first outer vane and at a distance from the inner wall, said helical vanes extending from the one end of the vessel towards the other.

8. Apparatus according to claim 7, c h a r a c t e r i z e d in that the helix of the inner vane extends in the opposite direction in relation to the helix of the outer vane, which helices upon rotation of the vessel convey the product towards each their ends .

9. Apparatus according to claim 7 or 8, c h a r a c t e r - i z e d in that the vessel has a product inlet and a product outlet which are disposed at an axial distance from each other.

10. Apparatus according to any of the claims 7-9, c h a r - a c t e r i z e d in that the process vessel comprises further coupling connections for pipes for the steam- heating of the vessel's jacket, for steam for the heating of the product to sterilization temperature, for steam de- flashing and for a vacuum pipe, said connections comprising valves which can be manoeuvred during the rotation of the vessel.

11. Apparatus according to any of the claims 7-10, c h a r a c t e r i z e d in that both the inlet valve and the outlet valve are sealed with gaskets which are arranged so that they do not come into contact with the product.

12. Apparatus according to any of the claims 7-11, c h a r a c t e r i z e d in that the vessel is suspended in bearings in brackets in such a manner that the bearings are disposed outside the vessel.

13. Apparatus according to any of the claims 7-12, c h a r a c t e r i z e d in that the manoeuvring of each inlet valve and each outlet valve is effected by a mechanism (31) which is self-locking in the closed condition, preferably with the use of a toggle-joint mechanism (34, 36) comprising a V-shaped arm (36) coupled between a working cylinder (37) and the valve (30).

14. Process plant for the production of sterile bone meal while executing the method according to any of the claims 1-6 and/or using an apparatus according to any of the claims 7-13, c h a r a c t e r i z e d in that the process apparatus form(s) the boundary between the non-sterile and the sterile areas of the plant, said boundary lying between the product inlet and the product discharge arrangement.