US3398467A - Parallel tube gaseous jet apparatus with multisize tube bores - Google Patents

Description

E. c. BROWN 3,398,467

PARALLEL TUBE GASEOUS JET APPARATUS WITH MULTISIZE TUBE BORES Aug. 27, 1968 Filed June 14, 1967 1 1 1 1 1 1 1 I I I 1 1 1 1 1 1 1 1 1 1 1 1 m 4 l 4A 1 7 ll 1 1 6 1 1 Q A V 7 4 1 6 r |L 1 J .11 L G T I W A m A k n 15g W \IIH P\\\\A\\\\\\\\\ I 2 6 f 1 1 I 1 1 M 1 l yl l/l 1 l I I 1 1 1 1 1 1 1 1 1 1 1 1 United States Patent PARALLEL TUBE GASEOUS JET APPARATUS WITH MULTISIZE TUBE BORES Ernest C. Brown, Danvers, Mass., assignor to Wolverine Corporation, Cambridge, Mass., a corporation of Massachusetts Filed June 14, 1967, Ser. No. 646,011

5 Claims. (Cl. 34-233) ABSTRACT OF THE DISCLOSURE In tube jet dryers having a pattern of parallel tubes extending downwardly from a plenum for directing high velocity gaseous jets onto a layer of particulate material being advanced transversely beneath the tube orifices, and where the tubes are given substantial length in order to provide exhaust passageways of'large enough cross-sectional 'area to reduce the velocity of the exhausting gases sufficiently to prevent detrimental removal of particulate material to the exhaust system from the layer being treated, horsepower requirements for maintaining jet orifice exit velocities at or near the maximum as determined only by the requirement of causing no detrimental particle removal to the exhaust system, are substantially reduced by giving the tubes enlarged cross-sectional bore areas in their major upper section while retaining cylindrical bores of smaller cross-sectional area extending for a distance of approximately four times their diameter upwardly from the orifice ends so as not to change the flow characteristics of the jets beyond the orifices from those produced by tubes having the same orifice bore diameters but having bores of uniform diameter throughout their lengths.

This invention relates to gaseous jet dryers of the type described in United States Patent No. 3,060,590 and more particularly to structural improvements which permit economic increase in drying capacity for a given pattern and total cross-sectional area of jet orifices by reason of increased jet orifice exit velocity and hence increased total volume flow of drying medium in a given period of time.

In all gaseous jet treatment of particulate material in volving directing high velocity gaseous jets downwardly onto a layer of separate particles, as in the aforesaid patent, it is necessary, in withdrawing the gaseous medium, that its velocity be rapidly reduced in order to prevent particles which have been fluidized by the jets from remaining entrained in the exhausting gaseous streams for such distances as to be separated from the advancing layer of material being treated.

Such rapid decrease in velocity of the exhausting gases has been accomplished by delivering the gases through hollow tubes which are suspended downwardly and parallelly from a common plenum and terminate at a proper distance above the layer of material to be treated which advances normal to the axes of the tubes. By this expedient, sufficient space may be left between the parallel tubes to provide exhaust passages having the necessary minimum cross-sectional area so that as the gas which has issued downwardly out of the tube orifices and contacted the particles being treated reverses its direction flow and ascends upwardly between the tubes it rapidly loses velocity because of the pressure drop provided by the large cross-sectional areas between the tubes. Particles fluidized by the jets thus fall back towards the layer rather than being carried into the exhaust system with the exhausting gaseous streams.

Particle treatment machines so designed have proved so efi'icient that there has been a substantial demand for increasing their capacity without increasing their length.

3,398,467 Patented Aug. 27, 1968 Any such increase in capacity requires movement of a greater quantity of gas in a given period of time necessitating, for a given orifice pattern (number, arrangement and total cross-sectional area of orifices), increasing the exit velocity of the jets at each orifice. As the velocity is increased, however, for a given crosssectional area of exhaust passageways, there is increasing danger of entrained removal of the particles into the exhaust system putting a practical upper limit in a given design on the orifice exit velocity, governed by maintaining the exhaust velocity low enough to prevent removal of particles from the treating zone in the exhaust streams.

Accordingly, in order to permit higher orifice velocities, the exhaust passages have been made of greater and greater cross-sectional area by extending the length of the tubes to add height to the cross-sectional passageways, thus accommodating greater orifice exit velocity without detrimental entrainment of particles into the exhaust system ducts.

Such tube lengthenings have been routinely accompanied by provision for increased blower horsepower to provide the increased plenum pressure necessary to secure the increased orifice exit velocity. This has involved additional initial expense for larger motors for driving the blowers and increased operating expense caused by the greater power consumption.

These additional expenses were,'however, readily accepted as a necessary concomitant of attaining the increased capacities.

The present invention is -founded upon the heretofore unappreciated fact that much of the increased horsepower so provided has been due, not to the demand for increased orifice velocity, but to the tube lengthening. The longer the tube of a given bore diameter, the greater the pressure required in the plenum to maintain a given velocity at the orifice.

It was then realized that, so long as the tube bores retained their desired orifice cross-sectional area upwardly for a sufiicient distance to insure that the flow characteristics of the gases emanating from the orifice would remain unaffected, it was entirely unnecessary to continue the same cross-sectional bore area for the remainder of the length of the tube all the way up to the plenum. In addition it was found that a small enlargement of the bores in the upper portions of the tubes (and hence of the OD. of the tubes in the case of cylindrical tubes) did not so seriously detract from the total cross-sectional exhaust passage area as to cause entrainment of particles even at the substantially greater orifice exit velocities.

Accordingly, in apparatus of this invention, tubes are utilized which are characterized by the fact that they have bottom sections having walls defining cylindrical bores of equal diameters and of uniform lengths approximating four times their bore diameters. That geometry furnishes the same flow characteristics beyond the orifice that occurs with a bore of uniform diameter and infinite length at the same exit velocity. The bottom sections then are surmounted with walls forming bores slightly tapering outwardly and upwardly and merging into bores, of greater cross-sectional area than the orifice cross-sectional area, extending the remainder of the total length of the tubes. For example, where a tube is 21 inches in length, it is provided with a circular bottom orifice formed by the bore of a inch O.D. ZO-gauge tube extending upwardly for 3 inches from the end of the tube. The remainder of the tube is made of l-inch O.D. ZO-gauge tubing, connected by a section having a conical bore to the bottom 3-inch section. The consequences will be further described after reference is made to the accompanying drawing showing a typical embodiment of the invention and wherein FIG. 1 is a fragmentary transverse cross-sectional view p 1 .-"'3,398,46 7, g v

of a jet dryer. apparatus,-.broken away to indicate extent. similar to the dryer shown in FIG. 3 of U.S. Patent No. 3,060,590; and

FIG. 2 is an enlarged detail of one of the jet tubes.

The apparatus includes a casing 60 within which are suspended walls 61 forming a plenum 62 beneath and along the sidesof which are exhaust passageways 64 and 66leading to a fan (not shown) which may return the air to plenum 62 where it is heated by a heater 54 or by other means.

The tubes 70 extend downwardly from the plenum towards a conveyor 72 which supports particles to be treated in layer A. Suitable seals 74 embrace the lateral edges of the conveyor to restrict intake of air.

Cylindrical tubes 70 have a major upper section 76 of larger bore connected by a conical section 78 to a lower bore 80 of smaller cross-sectional area, all being identical and-formed most easily by swaging the bottom section to the configuration shown.

In order to illustrate the eifectiveness of structures embodying the invention, one may take, for example, a construction utilizing a 22 inch long tube. If the bore of this tube is of a diameter corresponding to the ID. of a inch O.D. 20-gauge tube throughout its total length, it would be necessary, in order to provide an orifice velocity of 12,000 cubic feet per minute to have a pressure at the orifice of 8.97 inches water gauge. To secure this orifice pressure, it would be necessary to have a plenum pressure of 11.38 inches water gauge. However, by enlarging the upper section of the tube so it corresponds in bore diameter to the bore diameter of a 1-inch ZO-gauge tube, the same orifice pressure of 8.97 inches water gauge can be obtained utilizing only 9.42 inches water gauge pressure in the plenum. As thus can be seen, saving in horsepower resulting from the lower operating level of plenum pressure can be substantial. Obviously the saving in horsepower cannot be accomplished by enlarging the cross-sectional diameter of the bore throughout its entire length because such enlarged area at the orifice will act to reduce the velocity in accordance with the equation Nor can the saving be effected by tapering the tubes to a minimum area orifice without loss of the desired quasi laminar flow pattern.

The objects of the invention are thus obtained by retaining so much of the small tube structure at the bottom to retain the desired flow characteristics beyond the orifices and then modifying the upper tube structure, which does not anyway aifect the flow characteristics beyond the orifice, for the purpose of reducing the pressure required in the plenum to maintain the desired pressure and velocity at the orifice. In general, the small bore section should be in length approximately four times its bore diameter and no more.

a i It is to be understood that FIG. 1 shows only one traverse row of tubes, but the apparatus will have a multiplicity of rows preferably to form a staggered diamond pattern as shown in FIG. 2 of US. Patent No. 3,060,595 with the orifice cross-sectional areas constituting usually only about 4% of the total area of the target area in the treating zone; I

What is claimed is:

1. Apparatus for treating particulate material with high velocity gaseous jets having means for supporting and advancing a layer of particulatematerial to be treated and means for directing parallel spaced jets of gas downwardly onto said layer as-itadvances, including a plenum overlying said layer and a pattern of spaced parallel hollow tubes extending from the bottom wall of said plenum downwardly towards said layer supporting means with the spaces between the tubes forming passageways for exhausting gases emanating from said tubes upwardly and away from said supporting means, said apparatus being characterized by the fact that the bottom sections of said tubes have walls defining cylindrical bores of equal diameters and of uniform lengths approximating four times their bore diameters, said bottom tube, sections being surmounted by upper tube walls defining bores slightly tapering upwardly and outwardly from said bottom sections and merging into bores of larger crosssectional area than the bores of said bottom sections, said larger bores extending upwardly throughout the remaining portions of said tubes to the points of their separate communication with said plenum.

2. Apparatus as claimed in claim 1, wherein the bores of larger cross-sectional area in the upper section of said tubes extend the major length of said tubes.

3. Apparatus as claimed in claim 1, wherein the ratio of the total length of the tubes to the length of said bottom tubesections is about 7:1.

4. Apparatus as claimed in claim 1, wherein the walls of the bottom sections of said tubes are swaged in from the upper tube walls to form the smaller bores at the bottoms of said tubes.

5. Apparatus as claimed in claim 1, wherein the bore of each tube consists of an upper cylindrical bore of larger diameter and a lowercylindrical bore of smaller diameter joined by a connecting conical bore.

References Cited UNITED STATES PATENTS 2,724,907 11/ 1955 Walter 34-160 XR 3,060,590 10/1962 Brown 34233 XR 3,060,595 10/1962 Dapses 34 3,140,157 7/1964 Fleissner et al. 34-160 3,176,412 4/1965 Gardner 34160 XR 3,199,224 8/1965 Brown 34160 XR 3,359,648 12/1967 Overly et al 34--162 XR FREDERICK MATTESON, IR., Primary Examiner. A. D. HERRMANN, Assistant Examiner.

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