US3041737A - Pneumatically acting driers - Google Patents

Description

July 3, 1962 A. MARK 3,041,737

v PNEUMATICALLY ACTING DRIERS Filed Feb. 20, 1959 2 Sheets-Sheet 1 LLHM S MHQ;

July 3, 1962 Filed Feb. 20, 1959 A. MARK 3,041,737

PNEUMATICALLY ACTING DRIERS I I f 2 Sheets-Sheet 2 INVENTOR.

3,641,737 Fatentecl July 3, 1962 3,041,737 PNEUMATIQALLY ACTING DRIERS Andi- Mark, 54 Gears Lafayette (Rhone), Lyon, France Filed Feb. 20, 1959, Ser. No. 794,565 Claims priority, application France Feb. 25, 1958 12 Claims. (Cl. 3457) This invention refers to driers for divided products wherein the product to be treated is carried along in the suspended state by a drying gas. It is known in such apparatus to re-cycle selectively the heaviest particles, which are generally those with the highest moisture content, from the outlet of the drying conduit into the inlet thereof together with a portion of the drying gas. These apparatus are cumbersome owing to the length of the drying conduit. The heat-insulation of the latter is expensive and nevertheless the residual heat losses are still important. In the case of sticky substances the conduit has to be fre quently cleaned and this is often quite a difficult problem.

It is an object of the present invention to provide a recycling pneumatic drier of reduced overall dimensions, wherein heat losses will be quite low and which may be readily cleaned whenever desired.

In accordance with the present invention the drying conduit is formed by a system of transverse partitions disposed between two parallel vertical walls, one at least of which is easily removable to permit free access to the inside of the conduit. It will be appreciated that such an arrangement reduces to a minimum the space required for the drying conduit, as well as the outer surfaces from which heat losses are liable to take place. The partitions which determine the drying conduit may conveniently consist of a band of sheet-iron or the like, of regular width, so coiled on itself as to form a spiral passage for the drying gas and the material in suspension therein, the said passage leading to an outlet opening provided in the central portion of one at least of the vertical walls. Each turn or convolution of the said spiral passage preferably comprises an ascending vertical portion of relatively small cross-sectional area, a curved portion of progressively increasing cross-sectional area, a descending portion of relatively large cross-sectional area, and a second curved portion which leads into the ascending portion of the next turn or convolution.

In accordance with another feature of the present invention, the drier comprises re-cycling means for the drying gas and the material under treatment, such means being disposed between the successive turns or convolutions of the above-mentioned spiral passage. In a preferred embodiment of such re-cycling means, the sheet-iron band is out between two successive turns or convolutions of the passage, in the lowermost zone of the said turns and the cut ends are vertically displaced in such a manner as to form a convergent nozzle in the outer passage and a recycling aperture connecting the inner turn with the outer turn immediately in front of the said nozzle. The spiral gas passage may extend below the aforesaid outlet opening in the form of a central chamber having its lower end in communication with a re-cycling aperture in such a manner that the heaviest particles, which have not been carried along by the drying gas which exhausts through the outlet opening, may be re-cycled once more before returning towards the said outlet opening.

In the annexed drawings:

FIG. 1 is a general side View of a pneumatic drier according to the present invention.

FIG. 2 is a front view thereof, with the front wall removed.

The drier illustrated comp1ises a fixed rear vertical wall 1, as for instance of sheet-iron, which carries a system of transverse partitions formed of a sheet-iron band 2, of regular width, appropriately coiled on itself, as more fully described below, the said band being secured to the vertical wall 1 by one of its edges, as for instance by welding or otherwise. A second vertical wall 3 is removably disposed against the other edge of the said band 2 and thus forms a detachable cover which permits free access to the spaces formed by the band.

The sheet-iron band 2 is coiled on itself in the form of an irregular spiral comprising rectilinear vertical portions, the successive turns or convolutions being more widely spaced in the left portion in KG. 2 than in the right portion. Considering the spiral passage thus formed by the said band and starting from the outer or inlet end thereof, the said passage comprises an ascending rectilinear portion a of relatively reduced cross-section, then a curved upper portion b of progressively increasing cross-section which is substantially semi-circular in shape, then a descending rectilinear portion c of relatively large cross-section. The passage is thereafter curved as indicated at d and becomes horizontal, its cross-section decreasing progressively. At the lowermost point the sheet-iron band 2 is cut on the inner or upper side of the passage, the ends 201, 2b thus formed being displaced vertically with the downstream end 2b raised with respect to the upstream end 2a. The curved portion of the passage extends as at d with a substantially wider cross-section and it is followed by another rectilinear ascending portion e, then by a second curved upper portion 1 of progressively increasing cross-section. Then comes a second relatively wide rectilinear descending portion g which is followed by a lower curved portion h which returns towards the point Where the sheet-iron band 2 is cut, the cut ends 2a and 2b now being disposed on the outer or lower side of the passage. The curved portion extends as indicated at h with a substantially reduced cross-section owing to the vertical displacement of the cut ends 2a, 2b. The passage thereafter rises vertically at 1', comprises a third curved upper portion 1' of progressively increasing cross-section and a relatively wide descending rectilinear portion k again followed by a lower curved portion l of decreasing cross-section, the inner turn of the sheet-iron band ending at the lowermost point of the passage, as indicated at 2c. The curved portion thereafter extends at l with a much wider cross-sectional area and it is again followed by a fourth ascending portion m, which is itself followed by a fourth curved upper portion which ends in front of an outlet opening 0 provided in the rear wall 1. As indicated in FIG. 1 the said opening 0 is connected by a conduit 4 with a centrifugal separator 5 having an exhaust pipe 6 connected with the inlet of an exhaust blower 7. The dried material collected in the separator is discharged through a conventional airlock 8.

The air passage formed by the sheet-iron band 2 extends below the outlet opening 0 in the form of a vertically elongated chamber p having a lower end of progressively decreasing cross-section which is curved as indicated at q and opens into the above described portion 1' of the air passage above the cut end 20.

It will be noted that the sheet-iron band 2 finally forms in the central portion of the apparatus a dead space r.

The drier further comprises a main blower 9 the outlet of which is connected by a conduit 10 with the inlet of the above described air passage, i.e. with the lower end of the first ascending portion a. The inlet of the main blower 9 is connected by a conduit 11 with a hot air generator 12. A branch pipe 13 extends vertically from the said conduit 11, this pipe 13 supporting an inlet air lock 14 on which is mounted a feed hopper 15.

The operation is as follows:

The hot air forced at high speed by the main blower carries in the form of suspended particles the material introduced through the inlet air lock 14. In the ascending portion a of the spiral air passage the air velocity is relatively high owing to the reduced cross-section and therefore all the particles are carried along by the air flow, the heaviest particles (i.e. those for which the drying operation may be ditficult) however rising more slowly and being submitted to the action of hot air for a longer time than the lightest ones (which are easily dried). The air velocity decreases in portion b of the passage, and in the descending portion it is hardly greater than the mean free falling velocity of the particles which therefore move downwardly at a substantially uniform speed. In the portion d the air velocity increases and the air issues from the nozzle A formed by the cut end 2a in the form of an air jet which acts as an injector and therefore draws air from the next inner turn of the spiral air passage through the space or aperture B provided between the ends 2a and 2b, thus ensuring a first re-cycling of drying air and of particles, as more fully explained below.

The air and particles issuing from nozzle A, together with the air and particles re-cycled through aperture B, pass through the curved portion d and thus reach the second turn of the spiral air passage. They rise at e, the air velocity being sufiicient for carrying along all the particles, they pass through the curved portion 1 and are returned downwardly at g, all the particles falling substantially at the same speed. The air velocity increases in the lower portion h and the heaviest particles (i.e. those with the highest moisture content) are preferentially directed through the re-cycling aperture B, while the lightest ones pass through portion h and enter the third turn of the air passage at i. This third turn comprises portions 1', j, k Where the particles rise at different speeds and return downwardly substantially at the same speed, as already explained for the first and second turn. In the lower portion 1 the air velocity increases owing to the progressively decreasing cross-section and the air with the particles in suspension therein issues in the form of a jet from the nozzle C formed by the end 2c of the sheet-iron band 2. Here again an injector action takes place, air being drawn through the outlet D of the curved lower end q of the elongated chamber p. It is however to be remarked that the recycling action thus obtained is not selective, the whole of the air and of the particles which flow through the said end 4 being recycled into the next portion 1 of the air passage.

The air stream rises through the ascending portion In and is deviated by portion n towards the outlet opening 0. Some of this air stream exhausts through opening 0 with a portion of the suspended particles, while the remainder of the drying air and of the particles flows downwardly through chamber p and is recycled at the lower end q thereof. It is to be noted that the air which exhausts through the outlet opening 0 is submitted to a deviation at right angles in such a manner that the heaviest particles, ie those which are not yet dry, pass downwardly into the lower chamber p to be re-cycled at D, the separator therefore only collecting the lightest particles.

The drier described is not cumbersome and its outer surface is reduced. Its inner space is readily accessible by removing the front wall 3 which may be secured in position by easily disengageable devices, such as swingable bolts 16 (FIG. 1) or the like.

Various modifications may be effected on the drier as described. The material to be dried may be fed into the outlet of the blower, or between the latter and the inlet of the spiral passage. The conduit which connects the blower with the drier may be directed downwardly, if desired. The exhaust blower may be suppressed in some cases.

I claim:

1. A pneumatic drier comprising two substantially parallel vertical walls, one of said walls having a central opening; a substantially spiral-shaped Wall forming a gas passage extending over a plurality of nested successive convolutions separated from each other by the successive convolutions; means to define an inlet for said gas passage on the outermost convolution thereof; means to define an outlet for said gas passage through said central opening, with said central opening directly communicating with the innermost convolution of said spiralshaped gas passage; means to supply a drying gas stream into the inlet of said passage; means to introduce a material to be dried into said gas stream in the form of discrete particles to cause said material to be pneumatically conveyed by said gas stream through said passage; and means to separate the material from the gas issuing from said passage.

2. In a pneumatic drier as claimed in claim 1, each convolution of said spiral-shaped passage comprising ascending substantially rectilinear wall portions; upper substantially semi-circular wall portions of increasing crosssectional area; descending substantially rectilinear wall portions of larger cross-sectional area than said ascending wall portions; and lower substantially semi-circular wall portions connecting said descending wall portions with the ascending wall portions of the next convolution of said passage.

3. In a pneumatic drier as claimed in claim 1, gas and material re-cycling means between two successive convolutions of said passage.

4. In a pneumatic drier as claimed in claim 1, said passage being cut between two successive convolutions of said passage substantially in the lowermost zone of said convolutions, to form an upstream end and a downstream end, said upstream end being lowered to provide a nozzle portion on the outer one of said two successive convolutions, and said downstream end being raised to provide a gas and material re-cycling aperture between the inner one and the outer one of said two successive convolutions.

5. In a pneumatic drier as claimed in claim 1, said spiral-shaped passage extending downwardly beyond said outlet opening in the form of a chamber connected with the next inner convolution said passage substantially in the lowermost zone thereof.

6. A pneumatic drier comprising two substantially parallel vertical walls, one of said walls having a substantially centrally located opening; a band having a width equal to the distance apart of said walls, transversely disposed between same and coiled on itself in a substantially spiral shape to form successive convolutions spaced from each other to leave between them a substantially spiral-shaped gas passage having an inlet, and having an outlet through said opening and having a number of successive convolutions separated from each other by the successive con volutions of said band, the inner convolution of the gas passage communicating directly with the central opening; means to supply a drying gas stream into the inlet of said gas passage; means to introduce a material to be dried into said gas stream in the form of substantially discrete particles to cause said material to be pneumatically conveyed by said gas stream between said inlet and said outlet; and means to separate the material from the gas issuing from said outlet.

7. In a pneumatic drier as claimed in claim 6, each convolution of said gas passage being formed of four successive portions the first portion being upwardly directed and substantially rectilinear, the second portion being substantially semi-circular and of increasing cross-sectional area, the third portion being downwardly directed, substantially rectilinear and of larger cross-sectional area than said first portion, and the fourth portion being substantially semi-circular and of decreasing cross-sectional area.

8. In a pneumatic drier as claimed in claim 6, gas and material re-cycling means between two successive convolutions of said gas passage.

9. In a pneumatic drier as claimed in claim 6, each convolution of said gas passage having a lowermost zone; and gas and material re-cycling means disposed between the lowermost zones of two successive convolutions of said gas passage.

10. In a pneumatic drier as claimed in claim 6, said band forming an elongated chamber extending downwardly from said outlet to the inner turn of said gas passage.

11. A pneumatic drier comprising two substantially parallel vertical walls one of said walls having a substantially centrally located opening; a discontinuous band having a width equal to the distance apart of said walls, transversely disposed between same and coiled on itself in a substantially spiral shape to form successive convolutions spaced from each other to leave between them a sub stantially spiral-shaped gas passage having an outer inlet, and having an inner outlet through said opening and a number of successive convolutions separated from each other by the successive convolutions of said band, each convolution of said band having a lowermost zone and said band being cut in the lowermost zone of one of the convolutions of said band between two successive convolutions of said gas passage, so as to form with respect to each of said last-named convolutions an upstream end and a downstream end, said upstream end being lowered to provide a convergent nozzle portion on the outer one of said two successive convolutions of said gas passage, and said downstream end being raised with respect to said upstream end to provide a gas and material re-cycling aperture between the inner one and the outer one of said two successive convolutions of said gas passage; means to supply a drying gas stream into the inlet of said gas passage; means to introduce a material to be dried into said gas stream in the form of substantially discrete particles to cause said material to be pneumatically conveyed by said gas stream between said inlet and said outlet; and means to separate the material from the gas issuing from said outlet.

12. A pneumatic drier comprising a gas conduit coiled on itself in a substantially vertical plane to form in said plane successive convolutions each extending through 360, each having an uppermost and a lowermost zone, said gas conduit having an inlet and having an outlet; means to supply drying gas stream into the inlet of said conduit; means to introduce a material to be dried into said gas stream in the form of substantially discrete particles to cause said material to be pneumatically conveyed by said gas stream between said inlet and said outlet; means to separate the material from the gas issuing from said outlet; and gas and material recycling means between the lowermost zones of two successive convolutions of said gas conduit.

References Cited in the file of this patent UNITED STATES PATENTS 2,351,091 Bar June 13, 1944 2,361,758 De Fligue Oct. 31, 1944 2,819,890 Rosa et a1 Jan. 14, 1958

Images