US2817907A - Drying apparatus - Google Patents

Description

De cf31, 1957 R. D. M MILLAN ETAL 2,817,907

DRYING APPARATUS I Filed March 18, 1954 I 2 sheets-sheet 1 Dec. 31, 1957 R. D. M MlLLAN ETAL v2,817,907

DRYING APPARATUS 2 Sheets-Sheet 2 Filed March 18, 1954 United rates PatentO F DRYING APPARATUS Robert Davidson MacMillan, Birmingham, Charles George McKeown, Dudley, and Paul Otto Rosin, London, England; said MacMillan and said McKeown assignors to Controlled Heat & Air Limited, Smethwick, England, a British company Application March 18, 1954, Serial No. 417,148

Claims priority, application Great Britain March 25, 1953 3 Claims. (Cl. 34-57) This invention relates to an improved drying apparatus for materials which can be conveyed in suspension in a flow of heated gas and is particularly suitable for use where the material to be dried, such as wood fibres, is of a kind which would be damaged by subjection to relatively high temperatures, or where the application of high temperatures involves a risk of fire.

The object of the present invention is to provide an apparatus for the aforesaid purpose which without subjecting the material to relatively high temperatures will thoroughly dry the material, this desideratum. being effected by passing the material in suspension through a first system in which the major portion of the moisture content of the material is driven off into the conveying gases, extracting the partially dried material from the moisture laden gases in this system and introducing said material into a second system which initially contains no more than atmospheric moisture plus that produced by combustion of the fuel for heating the drying and conveying gases.

The invention consists of drying apparatus for the purpose set forth comprising a first and second system of piping in each of which an independent heated gas stream is adapted to be positively circulated from a gas inlet end to an outlet end with sufiicient rate of flow to maintain the material to be dried in suspension, said first system being provided with means for feeding the material to be dried into the system adjacent the gas inlet end and a separator adjacent the gas outlet end for separating the partially dried material from the conveying gases and feeding such material from said first system into the second system adjacent the gas inlet end thereof, a separator adjacent the gas outlet end of the second system being provided to separate the material from the conveying gases, the two systems working in parallel as far as the gas streams are concerned and in series as far as the material flow is concerned.

A convenient embodiment of the present invention will now be described with particular reference to the accompanying diagrammatic drawings in which Fig. 1 is a diagrammatic plan of the apparatus.

Fig. 2 is a diagrammatic section on the line 22 of Fig. 1.

Fig. 3 is a diagrammatic side elevation of the apparatus seen in Fig. 1 with the system shown in Fig. 2 omitted for the sake of clarity.

Fig. 4 is a diagrammatic section on the line 44 of Fig. 1, and

Fig. 5 is a diagrammatic section on the line 5-5 of Fig. 1.

There are provided two systems X and Y, the pipings whereof extend generally parallel to one another either in a vertical or horizontal plane or in runs of any formation best suited to site conditions. In order to conserve space and at the same time give the length of travel necessary for eflicient drying, the piping of both systems is 2,817,907 Patented Dec. 31, 1957 of known kind, for feeding into the air stream the material to be dried. This material gives up moisture while it is carried in suspension in the heated air stream through the piping to cyclone separators 9, arranged either singly or in plurality. These cyclone separators 9, two of which are incorporated in the construction shown, are of the kind each incorporating a tangentially disposed inlet 9a at its upper end through which the air with material in suspension is introduced into an annular space between the interior wall of the outer casing 9b of the cyclone separator and a concentrically disposed tube 9c which extends downwardly into the separator and at its upper end has a tangentially disposed outlet 9d which is connected to piping 10 leading to the fan 7 for drawing the material through the system. In the cyclone separators 9 due to the centrifugal separating action the material in suspension is deposited in an inverted truncated conical lower portion of the separator while the air is drawn out through the tube in known manner. It will be appreciated that the material deposited in the bottom of the cyclone separators 9 has been partially dried and that a large proportion of its moisture content has been given up to the conveying air which is drawn from the outlet tube of the separators. If desired in order to minimise heat losses in the first system, a proportion of the heated air drawn from the cyclone separators 9 can be reintroduced into this first system through the port 11 adjacent the inlet end of the system While the remainder is exhausted to atmosphere through the piping 12.

The partially dried material deposited at the bottom of the cyclone separators 9 which has given off the majority of its moisture content is introduced by rotary feeding devices 13 of known kind, disposed at the bottom of the cyclone separators into the piping of a second system Y adjacent the inlet end.

The second system Y incorporates a separate direct fired furnace 14 at or adjacent the inlet end for heating the incoming air and a fan 15 at the outlet end for drawing the air through the system. The material fed into this second system is carried in suspension while being further dried through the piping to a sifter or separator 16 of known type, such as that disclosed in British Letters Patent No. 452,382 or 499,428 which is of such a kind that material which is sufficiently dried and therefore of lower density is drawn ofi in suspension through an outlet 16a connected to piping 17, While that which is not fully dried and heavier is deposited. The dry material is drawn oil through the piping 17 to cyclone type separators 18 which are exactly similar to the separators 9 the outlet tubes of these separators 13 being connected through piping 19 to the fan 15 which causes the flow of heated air through this second system and exhausts through piping 20 to atmosphere. Material which is deposited at the bottom of the sifter or separator 16, due to its not being sufficiently dried, is reintroduced by a rotary feeding device 21 of known kind, into the second system, so as to partake of a partial recirculation in this system to effect its final drying.

The sifter or separator 16 is of the kind which incorporates an adjustable baflle 1612 which can be set to proportion the flow entering the sifter or separator between the inlet pipes 16c and 16d and also incorporates angularly adjustable baflles 16a and 16 which can be set to accord with the characteristics of the material, the baflie 162 also having an adjustable extremity 16g whereby the efiective length of this battle can be varied.

Withapparatusin accordancei with thepresent invention, since the material to be dried, after its initial drying in the first system X, is separated from the moisture laden air to which it has given the majority of its moisture content, is introduced into the second system Y which containslittle morethan atmospheric moisture, ,it is unnecessarytoemploy relatively high' temperatures such as would damage material, such'as wood' fibres, or-involve a risk: offire, and as anexample of the temperatures required, (it is envisaged that in the first system X the temperature can be in the region 'of 300 C., Whilein the second system the temperature can be in .the region of 150 C.

At 22 is shown aihopper whichsis adapted to feed the moisture laden material ontoan endless belt constood that the secondsystem Y can thus be used independent of the first system X.

We claim:

1. In a drying apparatus of the class described, in combinatioma first elongated system of piping having an inlet and an outlet, first exhausting means for exhausting gas from the outlet to produce a gas stream through the piping between inlet and outlet, means for heating gas admitted at the inlet, means for introducing, material to be dried into the gas stream adjacent the gas inlet, a first:separator in thesystem adjacent the outlet of the first system for separating the material from the gas stream, means for introducing a portion of the heated output gas of the first exhausting means into thefirst system near the inlet end thereof, a second elongated system of piping having an inlet and an outlet, second exhausting means for exhausting gas from the outlet to produce a gas stream through the second system, means for heating gas admitted at the inlet end, means for feeding the output material of the first separator into the second system adjacent the inlet end thereof, a classifying separator in the second system, means for introducing incompletely dried output material of the classifying separator into the gas stream of the second system between the inlet and the classifying separator, and means for separating the dried material from the gas stream as the gas approaches the outlet of the second system.

2. Drying apparatus according to claim 1 wherein feeding means are. provided for the second system adjacent the inlet end thereof for feeding material into the second system from a source outside of the first system and a reversible conveyor is provided to selectively feed material to said feeding means and to the means for introducing material into the gas stream adjacent the gas inlet of the first system, whereby the second system can be used independently of the first system should the ma-- terial to be dried be so dry that it is unnecessary to pass it through both of the systems.

3. Drying apparatus according to claim 1 wherein the incompletely driedoutput material of the classifying separator is introduced into the gas stream of the second system between the inlet of the second system and the classifying separator at a point which is closer to the classifying separator than it is to the inlet.

References Cited in the file of this patent UNITED STATES PATENTS 1,528,995 Singer Mar. 10, 1925 1,759,702 Koon May 20, 1930 1,951,879 Newton Mar. 20, 1934 1,994,343 Graves Mar. 12, 1935 2,156,924 Schneider May 2, 1939 2,236,006 Mulvaney Mar. 25, 1941 2,513,370 Shaw July 4, 1950

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