GB2043860A - Multistage Continuous Drying Apparatus, Especially for Tanned Hides - Google Patents

Abstract

In a drying assembly having a succession of drying chambers A, B, C through which a conveyor belt 1 travels for conveying the material to be dried, such as tanned hides, from a chamber to the next, throttling dampers (11, 12) are provided between a chamber and its adjoining chambers to allow a longitudinal airstream to be provided along the entire chamber row, said airstream flowing in countercurrent with the individual airstream within each chamber. No dampers are provided in the first and the last chamber of the row, which communicate with the intake and outlet conduits 16, 14, respectively. Heating tubes 6 are provided and dampers 11, 12 may be automatically controlled, in response to humidity or temperature sensors in the chamber(s). <IMAGE>

Description

SPECIFICATION Multistage Continuous Drying Apparatus, Especially for Tanned Hides This invention relates to a multistage continuous drying apparatus, with a counterflow air stream and control and adjustment of the working temperature in each stage and control of the humidity of the emerging air and continuous regulation of the exchange and recovery of heat.

The assembly is particularly recommendable for drying tanned hides, more particularly for drying the hides after varnishing or padding, but the basic ideas can be adopted with advantage in any drying procedure, that is, both by evaporation from the surface and by diffusion from the inner layers.

The principal object of the invention is to obtain in a combined manner, an optimum thermal efficiency of the drying procedure while concurrently achieving the subjection of the product to be dried to optimum environmental conditions, both as regards the temperature and the moisture contents.

Another object of the invention is to provide an installation in which the automatic control to which the product to be dried is subjected during processing is simplified to the utmost.

In order that these objects, along with others which will appear as the disclosure proceeds, may be obtained according to this invention, a drying assembly comprises a conveyor for the materials to be dried, said conveyor travelling in sequential order through a plurality of stages: these are chambers in each of which means for heating and causing to circulate air are provided, said drying assembly being characterized by comprising conduits equipped with throttling valves which establish a communication between each of said chambers and the adjoining ones so as to convey the air discharged from a chamber to the next preceding chamber (in the machine direction of the conveyor), the first and the last chamber being connected with air suction conduits, and with air outlet conduits, respectively.

The invention will now be described more detailedly with the aid of the accompanying drawings which show a particular embodiment of the invention given by way of example only without limitation.

In the drawings: Figure 1 is a diagrammatical side elevational view of the drying assembly according to the invention: in a particular embodiment comprising three sequentially arranged stages with a total air recycling within each stage.

Figure 2 is a view like Figure 1 but in which air is allowed to flow totally from each stage to its next.

Figure 3 shows the cross-sectional view taken along the line Ill-Ill of Figure 1, of the same drying assembly.

In the embodiment shown in the accompanying drawings, the assembly comprises a conveyor belt 1 (Figs. 1 and 2), composed, for example, by an array of parallel nylon strands carried by driving drums and supporting drums, which cause the material to be dried, such as tanned hides, to be forwarded along the direction shown by the arrows.

The apparatus proper is composed by a sequential array of drying stages and the assembly shown herein comprises three stages, which are indicated generally at A, B and C.

Each stage comprises two sections, viz.: a channelling ring 2, best seen in Figure 3, to feed the intake of an exhauster 3 driven by an electric motor 4. The second section of the stage comprises a hood 5, a heating set 6 composed for example by an array of gilled tubes arranged in coils and through which a heating fluid, such as steam, hot water, diathermic oil or otherwise, is caused to flow, a set of filter boxes 7, a set of grids 8 through which the air is distributed on the entire surface of the materials to be dried, a set of screens 9 and a distributor box 10, the latter being in practice the suction conduit of the exhauster 3.

The same equivalent parts of each stage are indicated by the same reference numerals, and each manifold 2 communicates through two throttling dampers 11 and 12, with the box 10 of the next preceding stage, and of the stage to which the exhauster 3 is associated, respectively.

Apparently, the manifold 2 of the first stage A, inasmuch as there is no next previous stage, has no damper 1 2 and communicates, instead, with a conduit 1 6 which draws air from the atmosphere, as will be better explained hereinafter.

The last stage C, has, in its downstream portion, an additional exhausting unit generally indicated at D, which is entirely correspondent to the unit composed by the exhauster 3 4 and its intake manifold 2 such as provided in each of the stages A, B and C aforesaid.

The outlet of the unit D (Figure 2) can be connected, with advantage, by the piping 14, to a conventional heat exchanger, 15, and the inlet piping 1 6 to the channelling ring 2 of the initial stage A of the assembly, so as to achieve at least a partial recovery of the heat required for the operation of the assembly.

The operation of the assembly will become apparent from what has been described hereinbefore and from the accompanying drawings as well.

Having now reference, at the outset, to Figure 1 wherein the assembly is shown with the dampers 12 closed and the dampers 11 open, in each stage A, B and C, an internal circulation of air takes place, this air being impelled against the material carried by the belt 1 and then drawn out by the exhauster 3 again, heated and filtered at 6 and 7 and then sent to the respective box 10 and manifold 2 to be recirculated. The unit D is now inoperative.

Figure 2 shows the assembly with the dampers 11 closed and the dampers 12 open. In this case each pumping unit 3 of a stage is fed with air drawn from the box 10 of the next preceding stage, with the obvious exception of stage A which draws air from the atmosphere.

The unit D draws air from the stage C.

In this case, a circulation of air is established, which originates a stream flowing through the entire assembly from end to end in countercurrent relationship relative to the material being conveyed on the conveyor belt 1.

Once these two limiting conditions of operations have been understood, it is easy to imagine the intermediate conditions of the actual operation: by partially opening the dampers 11 and the dampers 12 as well, two streams are circulated concurrently, viz.: one is an internal circulation within each stage, and the other is a longitudinal end-to-end circulation through the whole assembly, from each stage to its following next.

The recirculation within a stage originates a sharp increase of the humidity of the air which sweeps the material to be dried and a simultaneous heating.

It becomes thus convenient to act upon the rate of flow of the longitudinal stream as originates by opening the dampers 12, to limit the increase of humidity by introducing less moist air from the outside.

The relative degree of aperture of the dampers 11 and 12 can be rendered automatic with facility by servoing the manipulations to sensors of humidity and/or temperature in one or more stages.

By virtue of the structure of the assembly according to this invention it has been ascertained, for example, that it is merely sufficient to adopt a sensor of humidity in the stage C, to drive the opening of the dampers 12, and the throttling of the dampers 11 so as to maintain the humidity to a preselected magnitude. Other simple types of adjustment can be used, which are based on the temperature readout only and also combined adjustment of both temperature and humidity in every stage.

According to the invention, the material is reliably and constantly subjected, when being dried, to the action of air the contents of moisture and the temperature of which are gradually decreased, the advantages both from the point of view of the quality of the goods and efficiency of the assembly being obvious. As a matter of fact, the very moist material in the stage C is capable of undergoing high temperatures for a quick removal of the impregnating liquor, whereas the less moist material of the stage A is subjected to the action of colder air which has, however, a low contents of humidity so that a quick, but still gentle, drying action can be achieved.

The discharge into the atmosphere, which takes place in the last stage C, only, is air having a high contents of water and has a temperature which is a maximum and near to saturation in general. This limits the volumes of discharged air and the advantage is apparent as to savings of heat and a substantial reduction of the shortcomings due to the ejection of large volumes of air, as it would occur when ejecting air from each stage discretely, with the attendant smaller average waterload in the air per unit of volume.

A reduced expelled volume of air makes it possible to adopt, if necessary, a cheaper purification treatment of the exhausted air and facilitates the installation of a heat exchanger as indicated at 1 5.

As outlined above, the embodiment described hereinabove in detail is but an example as many modifications can be introduced both as regards the number of the stages and the particular configuration of each of them. It is essential, for this invention, to have a type of circulation of air from one stage to the next irrespective of the shape and arrangement of the component parts.

Claims (4)

Claims

1. A drying assembly comprising a conveyor for the material to be dried which travels in succession along a plurality of stages composed by chambers, in each of which are provided means of heating and circulation of air, characterized in that conduits equipped with throttling dampers establish a communication between each chamber and the next adjoining chambers to convey air discharged from a chamber into the next preceding chamber in the direction of travel of the conveyor, the first and the last chamber being connected with the outside and with intake and exhaust conduits for the air, respectively.

2. An assembly according to Claim 1, characterized in that the means for circulating air comprises an exhauster which introduces air above the conveyor by taking air beneath said conveyor from a manifold, the intake side of the exhauster being connected in the first stage through throttling dampers both with the atmosphere and with the manifold of such first stage, and in the subsequent stages both with the manifold of the previous stage and with the manifold of the stage concerned.

3. An installation according to Claim 2, characterized in that each stage comprises a chamber through which a conveyor runs and above which are mounted said heating means through which flows the air sent to the conveyor and drawn therebeneath from the manifold, the manifold communicating with the suction side of the exhauster by a duct adjacent to the chamber, aligned therewith and having a passageway for said conveyor.

4. An assembly according to Claim 1, characterized in that said suction and exhaust ducts are interconnected by a heat exchanger to exchange heat between the fluids flowing through said ducts.