WO2007003201A1

WO2007003201A1 - System and method for cleaning of a closed cavity

Info

Publication number: WO2007003201A1
Application number: PCT/DK2006/000397
Authority: WO
Inventors: Søren STOKER HAMMER
Original assignee: Cryocip A/S
Priority date: 2005-07-06
Filing date: 2006-07-05
Publication date: 2007-01-11
Also published as: WO2007003202A1

Abstract

A system for cleaning of cavities (1) is disclosed, e.g. of a food processing system, by means of blasting with solid carbon dioxide particles, so that impurities on the internal surface of the cavity are frozen and by abrasive action of the particles removed from the surface. The flow of solid carbon dioxide particles together with a carrier gas are ejected as a jet from a rotating nozzle (2) arranged stationary within the cavity, so that the jet sweeps the cavity and vortices of the particles and the carrier gas are created within the cavity. These vortices interact with the internal surfaces of the cavity and may break up into smaller vortices, before the flow of carrier gas, partly or completely vaporized particles as well as loosened debris and impurities exits from the cavity via an outlet (9) in the lower part of the cavity, such as at the bottom thereof .

Description

SYSTEM AND METHOD FOR CLEANING OF A CLOSED CAVITY

The present invention relates to cleaning of cavities, in particular of a food processing system, by means of blasting with solid carbon dioxide particles with high velocity, so that impurities on the internal surface of the cavity are frozen and by abrasive action of the particles removed from the surface.

BACKGROUND

Cleaning of the inside of cavities in food processing systems, such as of mixers or driacoaters or closed spaces filled with equipment to be cleaned are normally performed with hot water containing an aggressive detergent, followed by a treatment with hot clean water for removing the impurities as well as remaining detergent, which is normally not compatible with the use for food processing. Finally, remaining water must be removed from the cavity, e.g. by circulating heated air inside the cavity.

However, such cleaning procedure render the food processing equipment out of normal operation for an extended period of time, which is disadvantageous. Furthermore, the cleaned equipment is heated to a temperature higher than the one suitable for operation, at least for a number of food processing systems, and even more time and energy is spend on lowering the temperature to the normal operating temperature of the equipment.

The use of blasting with solid carbon dioxide particles for cleaning purposes is well- known in the art, e.g. from EP 1 054 752, where the method is applied to a kitchen ventilation duct for the removal of grease by means of a nozzle mounted on a trolley which is driven through the duct.

In US 5,932,026, in DE 195 35 557 and in DE 102 15 216, different arrangements for the cleaning of internal surfaces are disclosed, which have in common that the nozzle for the blasting with solid carbon dioxide particles is mounted on an arm that during the blasting process is moved around within the cavity so that the full surface may be reached and cleaned by the jet of particles expelled from the nozzle. However, such arrangement including a robotic arm is expensive in installation as well as maintenance because it comprises many delicate parts that all have to cooperate in operation of the cleaning device.

It is an object of the present invention to provide a device and a method for cleaning which is simpler in installation and operation than the above.

BRIEF DESCRIPTION OF THE INVENTION

The present invention solves the object by a system where the flow of solid carbon dioxide particles together with a carrier gas, such as pressurised atmospheric air, are ejected as a jet from a rotating nozzle arranged stationary within the cavity at an upper part thereof, so that the jet sweeps the cavity and vortices of the particles and the carrier gas are created within the cavity. These vortices interact with the internal surfaces of the cavity and may break up into smaller vortices, depending on the configuration of the cavity, before the flow of carrier gas, partly or completely vaporized particles as well as loosened debris and impurities exits from the cavity via an outlet in the lower part of the cavity, such as at the bottom thereof.

It has been found by the inventor that it is sufficient to apply the solid particles together with a carrier gas through one nozzle stationary arranged within the cavity provided that the nozzle is rotatable, for obtaining clean surfaces within the cavity sufficiently for use with food processing equipment, where the surfaces will come into contact with food material for human consumption. The solid carbon dioxide particles are fragile and will normally disintegrate upon collision with a solid surface, such as the internal surfaces of the cavity, and the abrasive action of the particles is thus generally limited to the first collision with a surface. By rotating the nozzle, the jet will in most positions have a sufficient distance to the internal surface it is directed to in order to allow for the generation of vortices at the edge of the jet on its way to the surface, and a part of the particles and the carrier gas together with gas entrained into the jet will be diverted into these vortices. The particles in these vortices will not collide with the surface together with the rest of the jet, but will instead interact with and clean other surfaces within the cavity at random. As a result, all surfaces within the cavity will be cleaned by the particles, either by direct interaction with the jet from the rotating nozzle or by interaction with the generated vortices of solid carbon dioxide particles.

Other advantages of the present invention will be apparent from the following description.

Thus, the present invention relates to a system for cleaning of a closed cavity, preferably of a food processing system, wherein the internal surfaces of the cavity are intended to be in contact with food products, the system comprising a rotatable nozzle having at least one opening and being arranged stationary within the cavity at an upper part thereof, such as at the top of the cavity, driving means, such as an electrical or pneumatic motor, for driving the rotation of said nozzle, means for providing a pressurised flow of solid carbon dioxide particles together with a carrier gas to the nozzle, preferably pressurised, clean atmospheric air, and an outlet provided at a lower part of the cavity, preferably at a lowermost position thereof.

The carrier gas may alternatively be carbon dioxide gas or nitrogen gas, which are both substantially inactive with respect to organic material.

The driving means may be arranged to drive the rotation of the nozzle with a speed up to 1400 rotations per minute. However, it is preferred that the driving means are arranged to drive the rotation of the nozzle with a speed of rotation in the range of 20 to 400 rotations per minute, such as within a preferred range of 40 to 250 rotations per minute. With this relatively low rotational speed, a relatively low tangential speed of the nozzle of e.g. 1-3 m/s is obtained, which has proven to be an advantage in providing a suitable ratio between particles following the direction of the jet and particles being diverted into vortices. It is most preferred that the driving means comprises one or optionally two independent drive means, such as electrical or pneumatic motors, so that the rotational speed about one or two axes may be controlled independently from the pressure of the flow of solid carbon dioxide particles together with the carrier gas.

In a particularly preferred embodiment, the nozzle is arranged to be rotated about two substantially perpendicular axes during operation of the cleaning system. Thereby, it is ensured that the jet ejected from the nozzle reaches as many surfaces as possible while a plurality of vortices with an even more widespread range of axes of rotation are generated. The speed of rotation may again be up to 1400 rotation per minute, but is preferably in the range of 20 to 400 rotations per minute, preferably in the range of 40 to 250 rotations per minute about each of said axes. The speed of rotation about the two axes may in a preferred embodiment be controlled individually, e.g. by driving the two rotational movements by separate driving means. Thereby, the operation of the nozzle may be adjusted to the particular task at hand, depending on e.g. the type and amount of debris to be removed from the internal surfaces of the cavity. However, both rotations may be driven by the same driving means with a suitable mechanism.

In a specific embodiment of the present invention, the system further comprises means to supply compressed air solely through the nozzle, alternatively or additionally means to supply compressed gaseous carbon dioxide solely through the nozzle. This flow of gas may be used to blow any remaining debris out through the outlet of the cavity, and a flow of carbon dioxide may in particular also be employed to cool down the internal surfaces within the cavity prior to cleaning with the application of solid particles of carbon dioxide. In a preferred embodiment, the system comprises a manifold having means for selectively providing a flow of particles with a carrier gas, a flow of gaseous carbon dioxide solely and a flow of atmospheric air through the nozzle.

In yet a preferred embodiment, the means for providing a flow under pressure of solid carbon dioxide particles together with a carrier gas to the nozzle comprises a source for pressurised gaseous carbon dioxide, means for preparing solid carbon dioxide particles from pressurised gaseous carbon dioxide from said source, a conduit connecting said source and said means for preparing solid carbon dioxide particles, and a conduit connecting said means for preparing solid carbon dioxide particles and said nozzle. Thus, the apparatus for producing the solid carbon dioxide particles or pellets provided to the nozzle is coupled directly to the nozzle so as to enable the provision of a large flow of particles to the nozzle. The means for preparing the solid carbon dioxide particles comprises preferably means to produce carbon dioxide snow and means to compress said snow with a pressure in the range of 160 to 650 bar, preferably in the range of 200 to 350 bar, so as to form said particles having an advantageous quality for the present use. The means for preparing the particles are preferably designed to prepare particles of a diameter in the range of 1.7 mm to 8 mm, preferably in the range of 2.5 mm to 6 mm.

Furthermore, the system has in a preferred embodiment of the present invention an exit flow cleaning circuit coupled to the outlet from the cavity, the circuit comprising a cyclone separator and a blower, wherein the outlet of the cyclone separator is coupled to the inlet of the blower, and the outlet of the blower is coupled to the inlet of the cyclone separator via a constriction, which reduces the cross-sectional flow area with a factor of at least two, and the outlet of the cavity being coupled to the arrangement between the constriction and the inlet to the cyclone separator, the circuit also comprising an outlet for the exit of a part of the flow circulated in the circuit. By providing a recirculation of at least a part of the gas from the outlet of the cyclone separator and via the blower to the inlet of the separator, an increased gas flow together with the flow of solid debris is formed, whereby the efficiency of the cyclone separator in separating the solid debris is improved.

The system comprises in yet a preferred embodiment of the present invention means for providing a carrier gas to the nozzle with a pressure of between 5 bar and 20 bar, preferably between 8 bar and 13 bar above atmospheric pressure, and in an amount of between 3 m³ and 20 m³ per minute, preferably between 6 m³ and 15 m³. The pressure at the outlet of the cavity is lower to provide a flow through the cavity, preferably between atmospheric pressure and -0.7 bar below that.

The means for providing a pressurised flow of solid carbon dioxide particles together with a carrier gas to the nozzle are likewise in a preferred embodiment suitable for providing a flow of solid carbon dioxide particles in the range of 25 to 150 kg per hour, preferably in the range of 40 to 120 kg per hour.

The present invention also relates to a method for cleaning of a closed cavity, in particular of a food processing system, by means of the steps discussed above, which e.g. could be performed with the system of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention are illustrated in the enclosed drawings, wherein

Fig. 1 is a schematic view of a system according to the present invention, and

Fig. 2 is a perspective view of a nozzle for use with the system of Fig. 1. The embodiments of the figures are discussed in details below. The figures are to be regarded as illustrations of particular embodiments of the present invention and not as limiting the scope of the invention and the protection as defined in the claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

The system shown in Fig. 1 comprises a mixer 1 for food production and having an inner cavity to be cleaned. In the top of the cavity, a rotating nozzle 2 is stationary arranged, i.e. it is during operation rotated, but is not moved around inside the cavity while the carbon dioxide pellets are ejected from the nozzle. However, in particular embodiments of the present invention, the nozzle is stored outside the cavity when the mixer 1 is in operation and is lowered into the operating position prior to ejection of the particles.

The rotation of the nozzle 2 about two perpendicular axes, a vertical and a horizontal axis is driven by two independently operating motors arranged in the motor housing 3 on top of the mixer 1. The motor housing 3 and thereby the nozzle 2 is provided with a flow of carbon dioxide pellets and compressed air from a supply section of the system comprising a pelletizer 4, which is supplied with liquid carbon dioxide via a tube 5 from a storage (not shown). The liquid carbon dioxide is turned into carbon dioxide snow by lowering the pressure thereof, and the snow is compressed into pellets with a compression pressure of about 250 bar provided by means of the liquid carbon dioxide. The pelletizer 4 is connected to a feeding arrangement 6, where the pellets are mixed with compressed air from an air compressor 7 which is used to feed a flow of the pellets and compressed air to the nozzle 2 via a pipeline 8.

A debris separation system is arranged at the outlet 9 in the bottom of the mixer 1.

The separation system comprises a cyclone separator 10, the air outlet of which is connected to a blower 11, where the pressure of the air is increased. The separated solid and liquid debris is removed from the cyclone separator through an outlet in the bottom thereof (not shown). From the blower 11, the air passes a constriction 12 in order to accelerate the air flow by reducing the cross-sectional area of the internal opening of the tube to about a third, and thereby lower the pressure to about 0.5 bar below atmospheric pressure. The outlet opening 13 of the cavity of the mixer 1 is connected to the tube 14 connecting the constriction 12 and the inlet of the cyclone separator 10, whereby vaporised and possibly solid carbon dioxide, air and debris are removed by suction from the outlet 13 into the flow of air from the constriction 12 and to the inlet 15 of the cyclone separator 10. With this arrangement, the cyclone separator 10 is operated with a higher flow of gas, i.e. atmospheric air and vaporised carbon dioxide than would be the case if the outlet opening 13 of the mixer 1 was coupled directly to the cyclone separator 10, which improves the efficiency of the separation. Also, the suction at the outlet opening 13 due to the presence of the constriction 12 and the air flow, ensures that the loosened debris is removed from the cavity of the mixer 1 as the flow will not be decelerated at the bottom of the cavity. The arrangement is equipped with a pressure-controlled outlet valve (not shown) situated right after the air outlet of the cyclone separator 10, where excess air is delivered to the environment through a bag filter.

In Fig. 2, a nozzle 2 for the system is shown, which is connected to the motor housing 3 via the vertical tube 16. The flow of pellets and pressurised air is provided through the tube 16, which is rotated about the vertical axis with a speed of about 60 to 200 rotations per minute by means of one of the motors in the motor housing 3.

The tube 16 is connected to a first part 17 of the nozzle house, on which the second part 18 of the nozzle house is arranged rotatably with respect to the first part 17 about an axis substantially perpendicular to the vertical axis of the nozzle 2 and defining a flow channel between the two parts 17, 18 from the tube 16 and to the nozzle outlet 19 arranged on the second part 18 of the nozzle house. Another motor in the motor housing 3 drives an axle (not shown) inside the tube 16 which effects a rotation of the second part 18 of the nozzle house with a speed of about 40 to 150 rotations per minute. The rotational speed in the two perpendicular directions may be adjusted individually. In an alternative embodiment, the axle is not driven by a separate motor, and the relative rotation of the axle and the first part 17 of the nozzle house is employed to drive the rotation of the second part 18 thereof.

Claims

1. A system for cleaning of a closed cavity, comprising a rotatable nozzle having at least one opening and being arranged stationary within the cavity at an upper part thereof, driving means for driving the rotation of said nozzle, means for providing a pressurised flow of solid carbon dioxide particles together with a carrier gas to the nozzle, and an outlet provided at a lower part of the cavity.

2. A system according to claim 1, wherein said driving means are arranged to drive the rotation of the nozzle with a speed of rotation in the range of 20 to 400 rotations per minute, preferably in the range of 40 to 250 rotations per minute.

3. A system according to claim 1 or 2, wherein the nozzle is arranged to be rotated about two substantially perpendicular axis during operation.

4. A system according to claim 3, wherein said driving means are arranged to drive the rotation of the nozzle with a speed of rotation in the range of 20 to 400 rotations per minute, preferably in the range of 40 to 250 rotations per minute about each of said axes.

5. A system according to claim 4, wherein the speed of rotation about each of said axes may be controlled individually.

6. A system according to any of the preceding claims, further comprising means to supply compressed air solely through the nozzle.

7. A system according to any of the preceding claims, further comprising means to supply compressed gaseous carbon dioxide solely through the nozzle.

8. A system according to any of the preceding claims, wherein said means for providing a flow under pressure of solid carbon dioxide particles together with a carrier gas to the nozzle comprises a source for pressurised gaseous carbon dioxide, means for preparing solid carbon dioxide particles from pressurised gaseous carbon dioxide from said source, a conduit connecting said source and said means for preparing solid carbon dioxide particles, and a conduit connecting said means for preparing solid carbon dioxide particles and said nozzle.

9. A system according to claim 8, wherein the means for preparing the solid carbon dioxide particles comprises means to produce carbon dioxide snow and means to compress said snow with a pressure in the range of 160 to 650 bar, preferably in the range of 200 to 350 bar, so as to form said particles.

10. A system according to any of claims 8 or 9, wherein said means for preparing particles are designed to prepare particles of a diameter in the range of 1.7 mm to 8 mm, preferably in the range of 2.5 mm to 6 mm.

11. A system according to any of the preceding claims, further comprising an exit flow cleaning circuit coupled to the outlet from the cavity, the circuit comprising a cyclone separator, and a blower, wherein the outlet of the cyclone separator is coupled to the inlet of the blower, and the outlet of the blower is coupled to the inlet of the cyclone separator via a constriction, which reduces the cross-sectional flow area with a factor of at least two, and the outlet of the cavity being coupled to the arrangement between the constriction and the inlet to the cyclone separator, the circuit also comprising an outlet for the exit of a part of the flow circulated in the circuit.

12. A system according to any of the preceding claims, comprising means for providing a carrier gas to the nozzle with a pressure of between 5 bar and 20 bar, preferably between 8 bar and 13 bar above atmospheric pressure, and in an amount of between 3 m³ and 20 m³ per minute, preferably between 6 m³ and 15 m³.

13. A system according to any of the preceding claims, wherein the means for providing a pressurised flow of solid carbon dioxide particles together with a carrier gas to the nozzle are suitable for providing a flow of solid carbon dioxide particles in the range of 25 to 150 kg per hour, preferably in the range of 40 to 120 kg per hour.

14. Method of cleaning of a closed cavity, in particular of a food processing system, comprising the steps of providing a rotatable nozzle having at least one outlet opening and being arranged stationary within the cavity at an upper part thereof, driving the rotation of said nozzle, providing a pressurised flow of solid carbon dioxide particles together with a carrier gas to the nozzle, and allowing a flow of gas and debris from the cavity of an outlet provided at a lower part of the cavity.

15. Method according to claim 14, wherein a pressure difference between the pressurised flow provided to the nozzle and the outlet of the cavity is in the range of 5 to 20 bar, preferably in the range of 8 to 13 bar.

16. Method according to claim 14 or 15, wherein the nozzle is rotated about two substantially perpendicular axis during operation.

17. Method according to claim 16, wherein the rotation of the nozzle is driven with a speed of rotation in the range of 20 to 400 rotations per minute, preferably in the range of 40 to 250 rotations per minute about each of said axes.

18. Method according to claim 17, wherein the speed of rotation about each of said axes is controlled individually.