GB2079917A - Tunnel freezers - Google Patents

Abstract

A freezer (1) comprising a tunnel (6) having an inlet (2) and an outlet (12), a passage (11) surrounding said tunnel, a perforate conveyor (3) extending along said tunnel (6) for carrying shredded material from the inlet to the outlet of said tunnel (6), a spray (5) adjacent said outlet for introducing a cryogenic fluid into said tunnel, and at least one fan (7) between said inlet and said outlet for withdrawing gas from said tunnel into said passage and blowing said gas around said passage and through said perforate conveyor back into said tunnel (Fig. 2, not shown), is characterized in that a baffle (20) is provided in said passage (11) between said spray (5) and said fan (7) to inhibit said fan blowing gas into that part of said passage which surrounds said spray and further characterized in that at least one flexible multifingered curtain (25, 26) is provided at the outlet of said tunnel to inhibit the passage of gas through the outlet (12). <IMAGE>

Description

SPECIFICATION Freezer This invention relates to freezers and, more particularly but not exclusively, is concerned with freezers for tyres.

During the last two years industry has started to accept the use of cryogenics in the reclamation of rubber from tyres. Figure 1 shows a schematic longitudinal section of the first commercial tyre freezer which we designed and installed. Referring to this figure, shredded automobile and truck tyres are introduced through the inlet 2 of freezer 1 onto a perforate conveyor 3 which carried the shredded material through tunnel 6. As the shredded material moves through the tunnel 6 it is progressively cooled and finally enters an airlock 4 in a fully embrittled state at about --600C.

Cooling is effected by introducing liquid nitrogen through spray header 5 into the tunnel 6 and allowing the cold nitrogen vapour to flow towards the inlet 2 of the freezer 1 in countercurrent flow to the shredded material.

In order to maintain good heat transfer between the shredded material and the cold gas, fans 7, 8, 9 and 10 are provided which each withdraw gas from the top of the tunnel 6 and force it downwardly through passage 11 which is defined between the tunnel 6 and outer casing 24.

The gas then re-enters the tunnel 6 through the perforate conveyor 3. This can be better seen in Figure 2 which is a section taken on line Il-Il of Figure 1.

As the gas circulates through the tunnel 6 and the passage 11 it is gradually forced towards the inlet 2 of the freezer 1 by the nitrogen entering through spray bar 5. In this connection airlock 4 was regarded as absolutely essential to inhibit the loss of cold nitrogen through the outlet 12 of the tunnel 6.

The inventor was present at the trials of the freezer described and realised that considerable capital savings could be made if the airlock 4 and its associated control equipment could be dispensed with. He was aware of modifications to food freezers to reduce this type of problem but there the top of the freezer outlet was only a few centimetres above the top of the conveyor compared with a distance of about 45 centimetres in the present case. None of the food freezing modifications appeared satisfactory.

The inventor then conceived the idea of making two modifications to the tyre freezer described with reference to Figures 1 and 2 which he felt would enable him to dispense with the airlock 4.

These modifications were: 1. to place a flexible multifingered curtain across the outlet 12 of the tunnel 6; and 2. provide a baffle across the passage 11 between the spray header 5 and the fan 7.

He later proposed to refine these essential modifications with the following optional features, viz: 3. the top run of the perforate conveyor 3 was to be sloped upwardly in the section adjacent the outlet 12; and 4. two flexible multifinger curtains were to be used across the outlet of the tunnel 6 which were to be arranged in a special way.

It was felt by the design team of the first freezer that such modifications would not be sufficient to obviate the need for airlock 4 and would not be adopted.

Ironically our next enquiry came from a customer in England having a factory with a very low roof which could not accommodate the airlock 4 and it was decided to try the inventor's idea before excavating a pit for the mill.

Our trials have now shown that the inventor's modifications obviate the need for the airlock 4 and indeed the flexible multifingered curtain appears to be stopping air entering the outlet as much as inhibiting nitrogen escaping from within the freezer.

Viewed in its broadest aspect the present invention provides a freezer comprising a tunnel having an inlet and an outlet, a passage surrounding said tunnel, a perforate conveyor extending along said tunnel for carrying shredded material from the inlet to the outlet of said tunnel, a spray adjacent said outlet for introducing a cryogenic fluid into said tunnel, and at least one fan between said inlet and said outlet spray for withdrawing gas from said tunnel into said passage and blowing said gas through said passage and said perforate conveyor back into said tunnel, characterized in that a baffle is provided in said passage between said spray and said fan to inhibit said fan blowing gas into that part of said passage which surrounds said spray and further characterized in that at least one flexible multifingered curtain is provided at the outlet of said tunnel to inhibit the passage of gas through said outlet.

Preferably, the top run of the perforate conveyor is inclined upwardly towards the outlet of the tunnel.

Advantageously, two multifingered curtains are provided at the outlet of the tunnel and are so shaped and arranged that the fingers of one curtain lie directly over the joints between the fingers of the other curtain.

For a better understanding of the invention reference will now be made, by way of example, to Figures 3 to 5 of the accompanying drawings in which: Figure 3 is a schematic longitudinal section through a freezer in accordance with the present invention; Figure 4 is a section taken along line lV-lV of Figure 3; and Figure 5 is a view taken on line V-V of Figure 3.

Many of the parts of the freezer shown in Figures 3 to 5 are identical to those in Figures 1 to 2 and such parts have been identified by the same reference numerals as used previously. However, the freezer shown in Figures 3 to 5 differs from that shown in Figures 1 and 2 in that it is provided with a baffle 20 which extends across the passage 11 between the top 21 and vertical sides 22, 23 of the tunnel 6 and the outer casing 24 of the freezer. A portion of the baffle 20 also extends from just below the perforate conveyors to the outer casing 24. In addition the outlet 12 of the freezer is provided with two flexible multifinger curtains 25 and 26 which are made of MYLAR (RTM) which are arranged so that the fingers of one curtain overlap the joints between the fingers of the other curtains as can be seen in Figure 5.

Various modifications to the freezer described are envisaged, for example, whilst the baffle is preferably the solid structure shown in Figure 4 it could conceivably contain a few holes. All that is essential is that the baffle prevents the majority of nitrogen from the fan 7 being blown into the passage surrounding the spray bar 5 from whence it could find its way to the outlet 12 in substantial quantities. Furthermore, spray bar 5 could be replaced with a single nozzle spray or a spray ring.

If desired, a baffle similar to baffle 20 could be positioned between the fan 7 and the fan 8.

It will, of course, be appreciated that the baffle(s) inhibit the ingress of any air which passes flexible multifinger curtains 25 and 26 further into the freezer in addition to inhibiting the egress of nitrogen.

Claims (4)

1. A freezer comprising a tunnel having an inlet and an outlet, a passage surrounding said tunnel, a perforate conveyor extending along said tunnel for carrying shredded material from the inlet to the outlet of said tunnel, a spray adjacent said outlet for introducing a cryogenic fluid into said tunnel, and at least one fan between said inlet and said outlet for withdrawing gas from said tunnel into said passage and blowing said gas through said passage and said perforate conveyor back into said tunnel, characterized in that a baffle is provided in said passage between said spray and said fan to inhibit said fan blowing gas into that part of said passage which surrounds said spray and further characterized in that at least one flexible multifingered curtain is provided at the outlet of said tunnel to inhibit the passage of gas through said outlet.

2. A freezer as claimed in Claim 1, characterized in that the top run of the perforate conveyor is inclined upwardly towards the outlet of the tunnel.

3. A freezer as claimed in Claim 1 or 2, characterized in that two multifingered curtains are provided at the outlet of the tunnel and are so shaped and arranged that the fingers of one curtain lie directly over the joints between the fingers of the other curtain.

4. A freezer substantially as hereinbefore described with reference to and as shown in Figures 3 to 6 of the accompanying drawings.