NZ244418A - Mesh conveyor for freezing apparatus cleared by pressurised gas directed through mesh apertures to clear refrigerant build-up - Google Patents

Description

244418 Patents Form 5 N.Z. No. 244418 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION DRY ICE REMOVAL FROM A WOVEN MESH BELT We, NEW ZEALAND INDUSTRIAL GASES LIMITED, a New Zealand company of NZIG House, 133-137 The Terrace, Wellington, New Zealand do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 1 2444 This invention relates to a method of, and device for, removing a build up of dry ice from a woven mesh belt. One application of the invention relates to removal of dry ice build up on the woven mesh conveyer belt of a typical continuous cryogenic freezing apparatus.

A continuous cryogenic freezing apparatus typically comprises a conveyer belt of woven mesh material disposed within a freezing tunnel or spiral. Carbon dioxide is utilised as a cryogenic refrigerant gas. After a period of time a build up of dry ice particles occurs within the weave of the mesh. This is often affected by the distribution of food or other products on the belt and the distribution of dry ice already present. The build up of dry ice can accumulate to such an extent that it completely blocks the mesh belt and prevents good heat transfer through it. The hinderance of effective heat transfer leads to less effective freezing rates, inhomogeneous freezing and greater consumption of carbon dioxide to effect such freezing. The layer of dry ice also acts as an insulant to heat transfer to the underside of the product. Furthermore, the accumulation of dry ice can cause lumps to collect until they are large enough to fall off the belt. This can happen at the exit end of the tunnel or spiral. The deposition of lumps of carbon dioxide into the working environment can lead to elevated levels of carbon dioxide gas in the vicinity of the workers, thus causing a hazard to health.

To date, manual removal is generally required to clear the belt of dry ice build up.

This may be necessary at an unsociable hour as often such apparatuses are worked on a 24 hour basis. Typically the clearing operation may take up to three hours. Alternatively, more regular shutdowns to tap the belt free of dry ice result in at least 244418 two operators being unproductive during portions of the working day while this operation is being performed.

A further advantage arises from the invention in that when the woven mesh belt becomes impregnated with a build up of dry ice particles, the exhaust system's efficacy decreases with a resultant clouding of C02 and water vapour near the inlet end of the freezer. This clouding can be hazardous to personnel working in the area, typically loading food items onto the belt.

The aim of the invention is to provide a method of and device to automatically remove the build up of dry ice from the belt thus obviating the need to shutdown the freezer apparatus and overcoming the abovementioned disadvantages.

According to one aspect of the invention there is provided Freezing Apparatus comprising means for causing refrigeration, a mesh conveyor, and mesh clearing means, said mesh clearing means being suitable for creating a pressurized flow of cleaning gas and directing said cleaning gas through said mesh conveyor such that an undesired build up of refrigerant in the mesh conveyor is cleared away.

According to another aspect of the invention there is provided a method of cleaning freezing apparatus which is in accordance with the immediately preceding paragraph, said method comprising the steps of: a. operating said mesh conveyor, b. operating said means for causing refrigeration such that an atmosphere of refrigeration is achieved, and 3 244418 c. causing said mesh clearing means to create a flow of cleaning gas such that said cleaning gas passes through gaps in said conveyor with the result that an undesired build up of refrigerant is cleared from said gaps.

In further describing the invention according to a preferred embodiment, reference will be made to the accompanying drawings in which Figure 1 is a partial schematic view of the device fitted adjacent a woven mesh conveyer belt, and Figure 2 is an end elevation of Figure 1.

Referring to the drawings, the device 10 is intended to be used in conjunction with the woven mesh conveyer belt of a cryogenic freezing apparatus, which apparatus is not shown in the accompanying drawings. The device 10 consists of a tube 11 which may expediently be made of stainless steel approximately 25mm in diameter. Other cross sections of tube, for example square, and materials could satisfactorily be utilised. The tube 11 is provided with at least one row of apertures 12 along its length, the apertures preferably of a size in the range of, for example, .5 to 2mm. The apertures 12 are spaced at intervals to coincide with the gaps in the woven mesh of the belt.

The tube 11 is supported at each of its ends by brackets 13. The brackets 13 are located either side of the woven mesh belt 14 with the tube 11 oriented substantially 90" transverse to the direction of motion of the belt, and mounted very close to the upper surface of the belt. A suitable spacing above the surface of the belt would be in the range of 1 to 10mm. The tube is preferably positioned over the return portion 4 2444 of the belt as shown in Figure 1 of the drawings. One convenient location along the belt is such that the gas discharge from the device (and through the belt) and dislodged dry ice is directed towards the exhaust collection duct of the freezer apparatus.

Gas flow to the tube is controlled in one embodiment of the invention by a manually operated ball valve 15 located outside the freezing apparatus. The consumption of gas will depend upon the length and width of the belt and the belt speed. A typical application may use 50kg of carbon dioxide in one 15 minute blowing per 8 hour shift. The consumption may rise to 250kg for large tunnel and spiral freezers. However, compared with the gas consumption for freezing food the method offers a saving overall. The high velocity and force of gas discharge dislodges and blows the accumulated dry ice from the belt.

Other advantages of the invention may be summarised as follows. The use of dry carbon dioxide gas as opposed to air ensures that no moisture is introduced to the tunnel leading to water ice formation. The carbon dioxide also has bacteriostatic properties and therefore introduces no live organisms.

While some preferred aspects of the invention have been described by way of example, it should be appreciated that modifications and improvements can occur without departing from the scope of the appended claims.

Claims (15)

WHAT WE CLAIM IS: / 24441 8

1. Freezing apparatus comprising means for causing refrigeration, a mesh conveyor, and mesh clearing means, said mesh clearing means being suitable for creating a pressurized flow of cleaning gas and directing said cleaning gas through said mesh conveyor such that an undesired build up of refrigerant in the mesh conveyor is cleared away.

2. Freezing apparatus according to claim 1, wherein the mesh clearing means incorporates a valve for controlling said flow of cleaning gas.

3. Freezing apparatus according to claim 1 or 2, wherein the mesh clearing means incorporates a plurality of apertures which are positioned across the mesh conveyor.

4. Freezing apparatus according to claim 2 or 3, wherein said apertures are spaced at intervals which coincide with gaps in the mesh conveyor.

5. Freezing apparatus according to claim 2, 3 or 4, wherein said apertures are spaced along the length of a hollow elongate member.

6. Freezing apparatus according to any one of claims 2-5, wherein said apertures are positioned across the mesh conveyor such that they are over a return portion of said conveyor. 6 244418

7. Freezing apparatus according to any one of claims 2-6, wherein said apertures have a diameter of from substantially 0.5mm to substantially 2.0mm.

8. Freezing apparatus according to any one of claims 2-7, wherein said apertures are spaced from substantially 1mm to substantially 10mm from the mesh conveyor.

9. Freezing apparatus according to claim 5, wherein said elongate member is a length of stainless steel pipe.

10. Freezing apparatus according to any one of the preceding claims, wherein said mesh conveyor comprises a woven conveyor belt.

11. Freezing apparatus substantially as herein described with reference to the accompanying drawings.

12. A method of cleaning freezing apparatus which is in accordance with any one of the preceding claims, said method comprising the steps of: a. operating said mesh conveyor, b. operating said means for causing refrigeration such that an atmosphere of refrigeration is achieved, and c. causing said mesh clearing means to create a flow of cleaning gas such that said cleaning gas passes through gaps in said conveyor with the result that an undesired build up of refrigerant is cleared from said gaps. 7 ^4 4 4

13. A method according to claim 12, wherein said cleaning gas is C02.

14. A method according to claim 12 or 13, wherein said build up of refrigerant comprises a build up of dry ice.

15. A method of cleaning freezing apparatus substantially as herein described with reference to the accompanying drawings. NEW ZEALAND INDUSTRIAL GASES LIMITED By their attorneys HENRY HUGHES LTD Per; miji 8 t