WO2005033601A2

WO2005033601A2 - Method and apparatus for treating a product with conditioned air

Info

Publication number: WO2005033601A2
Application number: PCT/NL2004/000702
Authority: WO
Inventors: Pieter Jellema; Jelle Luutzen Nijdam
Original assignee: Solutherm B.V.
Priority date: 2003-10-06
Filing date: 2004-10-06
Publication date: 2005-04-14
Also published as: WO2005033601A3; NL1024469C2

Abstract

A method and apparatus for treating a product with conditioned air, wherein this product is conveyed from a first passage (3) in and through an enclosed space (2) to a second passage (4) and is treated zone-wise by conditioned air in longitudinal direction of the enclosed space (2), while the air is conditioned in a conditioning unit (14) arranged outside the enclosed space (2), is contacted with the product in the enclosed space (2) and is recirculated to the conditioning unit (14). The conditioned air is then supplied to the enclosed space (2) adjacent one of the passages (3, 4) and returned to the conditioning unit (14) adjacent the other passage, while from a thus created air flow between both passages (3, 4) air is zone-wise extracted at least on two locations, which extracted air is blown at increased velocity in the direction of the product whereupon this air will rejoin the air flow.

Description

Title: Method and apparatus for treating a product with conditioned air.

The invention relates to a method for treating a product with conditioned air, wherein the product to be treated is conveyed from a passage in and through an enclosed space to a further passage located at a distance from said passage and is treated in the enclosed space by the conditioned air coming from a conditioning unit which is arranged outside the enclosed space, extracts air from the enclosed space and, after conditioning, returns it to the enclosed space while, for treatment of the product in the enclosed space, air is zone-wise separated from an air flow created therein, which separated air is blown at increased velocity in the direction of the product to be treated, whereupon this air will rejoin the air flow. The invention also relates to an apparatus for carrying out such a method and to a treatment unit to be used with such an apparatus. Such a method is known from GB- 2 329 698-A and intended for drying products such as textile articles of clothing before these are packaged at a reduced pressure in an airtight manner, and restoring the desired moisture content of the products after transport thereof. This is effected by supplying conditioned air in the enclosed space at each location where the products are treated by a separated air flow. However, for cooling or freezing products, wherein in particular products with geometrical shapes with a relatively great surface/volume ratio are considered, such as IQF (Individually Quickly Frozen) products and liquid or jelly-shaped masses, which are spread on the conveyor belt in the form of a layer, this known manner of operation is less suitable. When conditioned air is supplied locally, the heating of the air is no more than, typically, 1°C. This limited heating entails that the recirculation flow rate is great with an accordingly great volume of the conditioning unit and a high electric capacity for transporting the recirculation flow. The limited heating of the air, when used as freezer, further means that the air becomes oversaturated rapidly, leading to snow formation, in particular at the product supply, and hence to reduction of the maximum production time of the apparatus, i.e. the time during which the apparatus can remain continuously operational without maintenance. The object of the invention is to improve an apparatus of the sort described in the opening paragraph such that the above-described drawbacks are avoided as much as possible, while the apparatus as a whole can be realized lighter and simpler. This is achieved according to the invention when air, extracted from the enclosed space at an outlet position, after having been conditioned, is reintroduced into the enclosed space at an inlet position, which is separated from the outlet position by at least two zones in which product treatment takes place through separation of air from the air flow. Due to these features, by each time extracting the conditioned air from and adding it to the air flow created between both passages, it is repeatedly contacted with the product to be treated in the zones which are, as it were, serially connected. This manner of operation has a series of advantages. For instance, by using the air more than once, the total amount of air to be circulated for the treatment is smaller than the total amount of air to be contacted with the product to be treated. Compared to the described the state of the art, this means a considerably smaller fan capacity and electric power. When used repeatedly over the treatment path, the air will undergo a greater change in temperature than the 1°C typical in the state of the art. A temperature change of, for instance, 10°C can then be involved, which means that when used for freezing, the air can take up and discharge considerably more moisture to the conditioning apparatus, so that snow formation is minimized and the production time of the apparatus is increased. The temperature change that is ten times higher than that in the state of the art entails a decrease of the conditioning flow rate by the same factor, resulting in a considerably lighter, simpler and less bulky apparatus. Treating the product zone-wise by urging a part of the circulating, conditioned air zone -wise in the direction of the product can be realized in several manners. However, according to a further embodiment of the invention, it is preferred that zone-wise extraction of air is carried out by extracting air symmetrically from the air flow, sucking it into a treatment unit and blowing it from the treatment unit, in a symmetrically distributed manner over a treatment zone to the product to be treated. Hence, treating the product with a minimum of pressure differences over the product can be accurately regulated and controlled and an intensive contact with the product to be treated can be effected, which can be further optimized when according to a further embodiment of the invention, it is provided that blowing off from the treatment unit is performed by blowing the air extracted from the air flow in a manner distributed over a great number of relatively fine air jets substantially perpendicularly, from the treatment unit to the product. In order to promote that the entire partial or zone surface of the product is uniformly blown on, according to a further embodiment of the invention, it is ensured that air blown from the treatment unit, after contact with the product to be treated, is urged away symmetrically to the left and the right, viewed in longitudinal direction of the enclosed space. By discharging the air in two directions, it is further realized, relative to the state of the art, that the velocity of the air discharged sideways is halved. This means that the pattern of the air jets ejected from the treatment unit is disturbed considerably less than with air discharged to one side. Also, in this manner, a symmetrical flow pattern is obtained, so that at the passages, minimum mixture with ambient air takes place resulting in a further minimization of the formation of snow. Depending on the product to be treated and the design of the conveyor belt it is possible that in a treatment zone, air is blown in the direction of the product to be treated only from above, or, conversely, that in a treatment zone air is blown in the direction of the product to be treated both from above and from below. It is further possible that then, the air flow proceeds in opposite direction to, or in the same direction as the product to be treated, while the method can be used both for cooling, also including deep freezing, and for drying the product to be treated. The invention further relates to an apparatus for treating a product with conditioned air, which apparatus is provided with a tunnel-shaped enclosed space with a passage forming a supply and a passage forming a discharge for the product to be treated, a conveyor belt having at least one part that can bear the product to be treated and which extends from the supply to the discharge, drivable in longitudinal direction through the tunnel-shaped enclosed space, a conditioning unit arranged outside the tunnel-shaped enclosed space and which is connected via a duct to both an inlet into, and an outlet from the tunnel-shaped enclosed space. With such an apparatus, according to the invention, it is proposed that in the tunnel-shaped enclosed space, between the inlet and the outlet at least two treatment units are arranged, each of which is provided with air suction means facing substantially away from the conveyor belt and with air blow out means facing the conveyor belt. Due to these features, an apparatus with a simple modular and universal structure is obtained in which a circulating air flow in longitudinal direction of the tunnel-shaped enclosed space can be created, from and to which air flow partial air flows can be extracted and can be added at the desired positions and to the desired extent, the apparatus being relatively light in weight and compact in structure and relatively insensitive to snow formation and hence continuously employable for a relatively long period. With a further preferred embodiment of the invention, the treatment unit is provided with a hollow housing with a wall facing substantially away from the conveyor belt part and bearing a fan for sucking air into the hollow housing, and with a wall which, while covering a partial surface of the conveyor belt part, faces it and is provided with air blow out openings distributed over the partial surface. In this manner, a relatively high contact intensity of air and product can be obtained, in that the air jets can be directed, at high velocity, perpendicularly to the product, for instance in the order of 20 m/s. Thus, relatively high convective heat transfer coefficients can be achieved in the order of 150 to 250 W/m².°C with a limited blow rate in the order of 1500 to 2500 m³/h per m² of blow surface. High air velocities can be Obtained when the air blow out openings consist of holes with a relatively small passage with which the resistance can be kept low when each hole has a circumferential area which is bent outwards and deflected in the direction of the conveyor belt part. It is noted here that it can be preferred to provide air blow openings in the shape of slits adjacent a passage, so that more air can be supplied to the product to be treated per m² of surface, which can reduce the formation of snow. Such a feature has, for that matter, no influence on the conditioning unit because of the independence of the recirculation rate obtained according to the invention. As already stated, it is particularly advantageous when after contact with the product, the air is discharged sideways, symmetrically to the left and to the right. In order to promote this advantageous air flow, according to a further embodiment of the invention, it is proposed that the wall facing the conveyor belt part is provided with at least one groove formed from wall . material not provided with air blow out openings and which extends substantially at right angles to the longitudinal direction of the conveyor belt part reaching into the hollow housing. Depending on the treatment and the product to be treated and the design of the conveyor belt it can be selected that the conveyor belt part runs centrally between two treatment units or, conversely, that the treatment units are located on one side of the conveyor belt part only. Partly in view of the desired compactness of the entire apparatus, the formation of an air flow in longitudinal direction of the tunnel-shaped enclosed space and the relatively small recirculation rate, it is further possible according to the invention that the conditioning unit is placed in a channel surrounded by a similar encasing as the tunnel-shaped enclosed space, for instance in a separated space above the tunnel-shaped enclosed space. The invention further relates to a treatment unit for use with a method or apparatus according to the invention, as discussed hereinabove. A treatment unit according to the invention is provided with a hollow housing with a first wall bearing a fan for sucking air into the hollow housing, and a second wall comprising at least one surface which is provided with air blow out openings distributed over this surface. With such a treatment unit, a build-up of the apparatus is made possible which is simple, modular and optimally adjusted to the intended object. It is then preferred that with a second wall containing more than one surface with air blow out openings distributed over the surface such as punched out holes and/or slits with circumferential areas which are pushed through outwards and deflected relative to the interior of the hollow housing, these several surfaces are in one common plane and further surfaces forming this wall are recessed in the hollow housing, relative to the several surfaces, it further being preferred that these further surfaces form parallel grooves and are not provided with air blow out openings. With reference to the accompanying drawing, presently, a possible embodiment of the invention will be discussed albeit only by way of non- limitative example. In the drawing: Fig. 1 schematically shows, in side view, a longitudinal cross section through an apparatus according to the invention; Fig. 2 shows a cross section along the line A-A in Fig. 1; Fig. 3 shows, in enlarged scale, a side view of a treatment unit; Fig. 4 shows a bottom view of the treatment unit of Fig. 3; Fig. 5 shows, in enlarged scale, a detail of Fig. 4; and Fig. 6 shows a cross section of a detail of Fig. 5. In Fig. 1, an encasing 1 is represented, defining an enclosed tunnel- shaped space 2 with a supply 3 and a discharge 4. Through the tunnel-shaped enclosed space 2, a conveyor belt 5 extends, which has a part 5a that is moveable from the supply 3 to the discharge 4 for conveying a product to be treated (not shown) through the tunnel-shaped, enclosed space 2. Above the part 5a, a number of treatment units 6 have been arranged in succession, each consisting of a hollow housing 7 with an upper wall bearing a fan 8 and a lower wall provided with air blow out openings to be discussed further. Opposite each treatment unit 6, on the lower side of the part 5a, arranged in mirrored relation, there is a similar unit 9. Above the tunnel-shaped enclosed space 2, separated by a ceiling 10, there is a channel 11 connected to the tunnel-shaped enclosed space 2 via an inlet 12 and an outlet 13. In the channel 11, a conditioning device 14 and a fan 15 are arranged. As appears from Fig. 2, the treatment units 6 and 9 and the conveyor belt 5 are designed and dimensioned such that there is a clear space on the left and on the right adjacent these apparatus elements. Fig. 3 shows in enlarged scale a treatment unit 6 (or 9) with the hollow housing 7, whose upper wall 7a bears the fan 8, via which air is sucked into the hollow housing 7. The hollow housing 7 has a lower wall 7b, provided with a number of grooves 16 recessed into the hollow housing 7 and extending transversely to the conveyor belt 5 over the full width of the lower wall 7b. As shown in Fig. 5, the partial surfaces of the lower wall 7b contiguous to the recessed grooves 16 are provided with a pattern of air blow out openings 17, formed by holes punched into the lower wall, which holes, as shown in Fig. 6, have been somewhat pushed through in the direction of the conveyor belt 5 for reducing the outflow resistance of the hollow housing 7. For treating a product with the apparatus described hereinabove, the following operation is followed. With the aid of the fan 15, a circulating air flow is created through the conditioning device 14, the channel 11, the inlet 12, the channel-shaped enclosed space 2, the outlet 13 and, again, the channel 11. With the conditioning device 14, the circulating air is brought into the condition suitable for the desired treatment, whereupon the product to be treated is introduced via the supply 3 into the tunnel-shaped enclosed space on the part 5a. The fans 8 of the treatments units 6 and 9 are activated such that each time a predetermined amount of air is extracted from the circulating air flow by sucking it into a hollow housing 7. From the hollow housing 7, the air is ejected at high velocity through the holes 17 as fine air jets in the direction of the product lying on the part 5a, which product is thus treated with the conditioned air. After contact with the product to be treated, the air is urged away sideways to the left and the right, which is facilitated by grooves 16 extending in that direction. Via the clear spaces at the sides of the conveyor belt 5 and the treatment units 6 and 9, the urged away air rejoins and mixes with the air flow circulating from the inlet 12 to the outlet 13, so that this air can, once again, rejoin a partial flow which, at a subsequent treatment unit, is extracted from this circulating air flow and is sucked into the hollow housing. The air moving thus through the tunnel-shaped enclosed space 2 is exhausted at the outlet 13 and led to the conditioning unit 14. It is self-evident that within the framework of the invention as laid down in the accompanying claims, many further modifications and variants are possible with respect to the embodiment represented expressly by way of non-limitative example. By way of example, in the following, a number of possible variant embodiments are noted. For instance, with the embodiment represented, a circulating air flow is indicated proceeding in opposite direction to the product flow; air flow and product flow can also have the same direction of movement. Also, two treatment units arranged opposite each other is only a possible embodiment. Depending on the use and design, also, treatment units can be provided on only one side of the conveyor belt part 5a or treatment units can be arranged alternately below and above the conveyor belt part 5a. The channel 11 is situated entirely above the tunnel-shaped enclosed space 2. This channel can also be present below or as well as below the conveyor belt 5. It is further also possible to supply partial flows to the air flow through the tunnel-shaped enclosed space 2 on one or several locations between the inlet 12 and the outlet 13. The upper part 5a of the conveyor belt 5 is to proceed through the tunnel- shaped enclosed space 2. This does not hold for the lower part. This could also proceed from the discharge 4 to the supply 3 outside of the encasing 1, in which case the encasing 1 can be of smaller design and, in case the treatment units 9 were to be absent, even terminate directly below the part 5a. In case a greater volume of ejected air is desired, for instance for reducing snow formation at the supply 3 or the discharge 4, this can be realized by designing the holes 17 at that location to be greater by giving them the shape of, for instance, slotted holes. In Figs. 3 and 4, the slits 16 are represented having a passage which remains the same over the width. The passage could also be designed to increase from the middle towards the sides, becoming, for instance, deeper. Although blowing on the product to be treated is preferably carried out with fine air jets, this can also be performed in a different manner, for instance by omitting at least parts of the lower wall 7b of the hollow housing 7.

Claims

1. A method for treating a product with conditioned air, wherein the product to be treated is conveyed from a passage in and through an enclosed space to a further passage located at a distance from said passage and is treated in the enclosed space by the conditioned air coming from a conditioning unit which is arranged outside the enclosed space, extracts air from the enclosed space and, after conditioning, returns it to the enclosed space while, for treatment of the product in the enclosed space, air is zone-wise separated from an air flow created therein, which separated air is blown at increased velocity in the direction of the product to be treated, whereupon this air will once again rejoin the air flow, characterized in that air, extracted from the enclosed space at an outlet position, after having been conditioned, is reintroduced into the enclosed space at an inlet position which is separated from the outlet position by at least two successive zones in which product treatment takes place through separation of air from the air flow.

2. A method according to claim 1, characterized in that zone-wise extraction of air is carried out by extracting the air symmetrically from the air flow, sucking it into a treatment unit and blowing it off, symmetrically distributed over a treatment zone, from the treatment unit to the product to be treated.

3. A method according to claim 2, characterized in that blowing off from the treatment unit is carried out by blowing the air extracted from the air flow distributed over a great number of relatively fine air jets substantially perpendicularly from the treatment unit on the product.

4. A method according to claim 3, characterized in that air blown off from the treatment unit, after contact with the product to be treated, is urged away symmetrically to the left and the right, viewed in longitudinal direction of the enclosed space.

5. A method according to any one of the preceding claims, characterized in that in a treatment zone air is blown in the direction of the product to be treated only from above.

6. A method according to any one of claims 1 — 4, characterized in that in a treatment zone air is blown in the direction of the product to be treated both from above and from below.

7. An apparatus for treating a product with conditioned air, which apparatus is provided with a tunnel-shaped enclosed space with a passage forming a supply and a passage forming a discharge for the product to be treated, a conveyor belt having at least one part which can bear the product to be treated and extends from the supply to the discharge, drivable in longitudinal direction through the tunnel-shaped enclosed space, a conditioning unit arranged outside the tunnel-shaped enclosed space and which is connected via a duct to both an inlet to, and an outlet from the tunnel- shaped enclosed space, charactejized in that in the tunnel-shaped enclosed space between the inlet and the outlet at least two treatment units are arranged which are each provided with air suction means facing substantially away from the conveyor belt and with air blow out means facing the conveyor belt.

8. An apparatus according to claim 7, characterized in that the treatment unit is provided with a hollow housing with one wall facing substantially away from the conveyor belt part and bearing a fan for sucking air into the hollow housing, and with a wall which, while covering a partial surface of the conveyor belt part, faces it and is provided with air blow out openings distributed over the partial surface.

9. An apparatus according to claim 8, characterized in that the air blow out openings consist of holes with a relative small passage.

10. An apparatus according to claim 11, characterized in that each hole has a circumferential area which is bent outwards and deflected in the direction of said conveyor belt part.

11. An apparatus according to any one of the claims 8 - 10, characterized in that the wall facing said conveyor belt part is provided with at least one groove formed from wall material not provided with air blow out openings and which extends substantially at right angles to the longitudinal direction of said conveyor belt part, into the hollow housing.

12. An apparatus according to claim 11, characterized in that the conveyor belt part runs between two treatment units.

13. An apparatus according to claim 11, characterized in that the treatment units are located on one side of the conveyor belt part.

14. An apparatus according to any one of claims 7 — 13, characterized in that the conditioning unit is placed in a channel surrounded by a similar encasing as the tunnel-shaped enclosed space.

15. A treatment unit for use with an apparatus according to any one of claims 7 - 14, provided with a hollow housing with a first wall bearing a fan for sucking air into the hollow housing, and a second wall comprising at least a surface which is provided with air blow out openings distributed over this surface.

16. A treatment unit according to claim 15, characterized in that with a second wall containing more than one surface with air blow out openings distributed over the surface, those several surfaces are in one common plane, and further surfaces forming this wall are recessed in the hollow housing relative to said several surfaces.

17. A treatment unit according to claim 16, characterized in that said further surfaces form parallel grooves and are not provided with air blow out , openings.

18. A treatment unit according to claim 17, characterized in that the air blow out openings are punched holes and/or slits with a circumferential area pushed through outwards and deflected relative to the interior of the hollow housing.