US2979363A - Shot mixing device - Google Patents

Description

April 11, 1961 J. BRZESKI snow MIXING DEVICE 2 Sheets-Sheet 1 Filed July 2, 1957 FIG. 4

INVENTOR. Jerzy Brzeski ATTORNEY 2 Sheets-Sheet 2 Filed July 2, 1957 INVENTOR.

Jerzy Brzeski ATTORNEY Unite States Patent.

r 2,979,363 Patented Apr 1 SHOT NHXING DEVICE Jerzy Brzeski, Glasgow, Scotland, assignor to The 'Babcock &' Wilcox Company, New York, N .Y., a corporation of New Jersey Filed July 2, 1957, Ser. No. 669,684 Claims priority, application Great Britain July 4, 1956 4 Claims. (Cl. 302-53) This invention relates to mixing devices for use in fluid carrier systems for solid particles of the kind including a convergent nozzle and particle inlet means for the pas sage of particles into a fluid carrier stream flowing from the nozzle. While of wider application, the invention is of utility in connection with apparatus, such as that described in British Patent No. 745,556, for cleaning the surfaces of heat exchange means. In the cleaning system described in the said specification, solid cleaning particles are showered upon heat exchange surfaces disposed in an upright heating gas pass, are collected at the bottom of the pass and are elevated by a gaseous particle conveying medium to a separator in which the particles are separated from the carrier medium for re-use. Suitably, the particles are in the form of steel pellets or shot and cleaning systems of the nature indicated are frequently termed shot cleaning systems.

In the operation of a shot cleaning system, considerable expense and inconvenience are liable to arise due to wear of parts of the particle conveying system. Thus, rapid wear is particularly liable to take place at the mixing device and at bends in the pipe line between the mixing device and the separator. Reduction of wear and facility of replacement of worn parts are, therefore, matters of considerable importance. Another matter of importance affecting the power used in conveying the particles, is the efiiciency of the mixing device.

The present invention includes a mixing device for supplying particles to a fluid carrier medium in a conveying system for solid particles, the device including a convergent nozzle and particle inlet means for the passage of particles into a fluid carrier stream flowing from the nozzle, wherein the nozzle is adapted to discharge with its axis upright, through an aperture in the bottom of a particle feed chamber and into a tubular member coaxial with the nozzle and extending downwardly from the top of the chamber and the particle inlet means are so arranged at the bottom of the tubular member as to permit the convergence of particles passing through the inlet means in an approximately symmetrical manner towards theaxis of the tubular member.

The invention, as illustrated by a preferred embodiment, includes a mixing device for supplying particles to a fluid carrier medium in a conveying system for solid particles, the device including a convergent nozzle and particle inlet means for the passage of particles into a fluid carrier stream flowing from the nozzle, wherein the nozzle is adapted to discharge, with its axis upright, through an aperture in the bottom of a particle feed chamber and into' a tubular member, co-axial with the nozzle and extending downwardly from the top of the chamber to define between the bottom of the tubular member and an opposing surface an annular gap constituting the particle inlet means.

The invention will now be described, by way of example, with reference to the accompanying, partly diagrammatic drawings, in which:

Figure 1 is aline diagram illustrating the layout of a system utilizing a mixing device according to the present invention;

' Figure 2 is a sectional'side elevation of a mixing device;

Figure 3 is a sectional plan view on the stepped line 3-3 of Figure 2; and

Figure 4 is a sectional side elevation of an alternative embodiment of the mixing device.

Referring to Figure 1 of the drawings, heat exchange means 1 include, for example, a low temperature superheater, and an econornizer, each comprising a bank or banks of horizontal tubes, the banks being disposed one above the other in a vertical gas pass 2 arranged for the downward flow therethrough of hot furnace gases and provided at its lower end with a hopper 3. Below the hopper and attached to the outlet therefrom is a particle collecting duct 4, the construction of which is suitably that disclosed in said British Patent No. 745,556.

Mounted externally of duct 4 is a chute 5 connected at its lower end to a collecting bin 6. The collecting bin 6 has a bottom outlet provided with a cut-oil? valve 7 such as that disclosed in British Patent No. 745,620. A short pipe 8 connects the valve 7 with a mixing device 9. The mixing device is set in an upright, straight, pipeline 10 which connects it with the inlet to a particle separating means 11 such as that disclosed in said British Patent No. 745,556. At least one pipe 12 attached to an outlet from the particle separating means 11 passes through a gastight seal in the roof of the gas pass 2 and terminates in a particle distributor 13 situated above the heat exchange means 1.

The particle distributor may suitably be of the form disclosed in a co-pending application, Serial No. 652,158, filed April 11, 1957, now abandoned.

Referring to Figures 2 and 3 the mixing device includes a cylindrical, circular chamber 21 formed with an upper flange 22, an upper cover plate 23 secured to the upper flange 22 by bolts 24 passing through a flange 25 on the pipe 10 and a bottom 26 of frusto-conical form, the generator of the curved surface of which is inclined to the'horizontal by an angle slightly less than the angle of repose of the particles.

A part or diffuser 28 of tubular form including a short lower convergent part 27 and a main upper divergent part 33 is arranged within the cylindrical chamber 21 with its axis co-axial with that of the chamber, and its end of greater diameter 29 in register with, and welded to, the periphery 30 of a central aperture in the upper cover plate 23. At its lower end 31, the part of tubular form 28 terminates at a short distance above the bottom 26 so that an annular particle inlet means 32 is formed between the lower end 31 of the part of the tubular form and the bottom 26.

The cylindrical wall of the chamber 21 is provided with a door 34 permitting inspection of the part of tubular form 28 and the clearing of accidental blockages. The cyiindrical wall is further provided with a particle entry chute 35 formed with particle retarder means 36. Suitably, the chute 35 changes in cross-section from a circular form at its upper flanged end to a rectangular form adjacent its juncture with the cylindrical wall of the .chamber 21, the sides of greater dimension extending at the underside of the chute 35, is an enlargement or box constituting the retarder means 36. A convergent nozzle 40 co-axial with the tubular part 3 28 is welded to the bottom 26 with its upper end 41, of lesser diameter, in register with an aperture 40 of smaller diameter than the internal diameter of the part 28 at the lower end thereof, in the bottom 26 of the chamber 21. The lower end 43 of the nozzle 40 is provided with a circular flange 44 for connection by means of bolts 45 with a similar flange 46 on an air supply pipe 47.

In operation, the convergent nozzle 40 is supplied with a stream of air from a suitable source (not shown) of air under pressure, the velocity of the air stream being increased within the convergent nozzle 40 to such an extent that particles falling into the stream at the annular gap 32 are accelerated and carried upwardly within the stream through the part 28 of tubular form and connecting pipe to the particle separating means 11. Within the particle separating means 11 the entrained particles are separated from the stream of air and fall under the influence of gravity within pipe 12 to the distributing means 13 whence they are scattered over substantially the whole of the horizontal cross-section of the gas pass 2, so that they fall through the heat exchange means 1 and clean the surfaces thereof.

The particles, after passage through the heat exchange means 1 fall into the hopper 3, and collecting duct 4, being cleaned and graded before passing to the storage bin 6. From the bin the particles pass through the shutoff valve 7 to the delivery pipe 8 and the retarder means 36 which slows down the particles before they enter the chamber 21, still at an appreciable velocity. The particles leaving the chute 35 strike the particles resting on the bottom 26 of the chamber 21 and scatter them around the nozzle 40 so that an approximation to even distribution of the particles passing through the particle inlet means 32 is obtained.

Replacement of the part 28 of tubular form, the only part of the mixing device liable to appreciable wear, is afiected by removing the bolts 24 from the upper cover plate 23, the bolts 45 from the air supply pipe flange 45 and the bolts 38 from the chute flange 37, thereby releasing the mixing device from the other parts of the apparatus.

The mixing device may then be withdrawn sidewardly and, after the part 28 has been replaced, re-inserted and bolted in position.

In the modification shown in Figure 4 a simplified but slightly less eflicient form of the part 28 is utilized. In the embodiment shown a part 28' in the form of a circular cylinder is welded in register with the periphery 30, and a bottom 26 is constituted by a flat plate attached to a flange 49, formed on the lower edge of the cylindrical wall of the chamber 21, by bolts 50.

Replacement of the part 28 may be effected by removing the bolts 24 from the upper cover plate 23, the bolts 38 from the chute flange 37 and the bolts 50 from the lower flange 49 so that the chamber 21 is withdrawable laterally with respect to the convergent nozzle 40. Alternatively, instead of removing the bolts 50 from the lower flange 49, the bolts 45 may be removed from the air supply pipe flange 46 so that the chamber 21 together with the convergent nozzle 40 may be withdrawn sidewardly, as previously described in connection with Figures 2 and 3.

It will be appreciated that the mixing device described above is particularly suited for use in conjunction with a particle conveying apparatus in which the pipe line conducting the gaseous fluid carrier stream and entrained particles is without bends and, therefore, subject to rela- ,4 described above has the additional advantage that it is capable of more efficient operation, leading to a saving in power consumption by the apparatus, than mixing devices of orthodox form.

The mixing device having a particle inlet means in the form of an annular gap results in a conveyance of particles in substantially symmetrical manner towards the axis of the tubular member, with the consequence that a substantially zero resultant transverse velocity of particles is obtained in the region encircling by the inlet means. Wear of the part of tubular form or the pipe beyond the part of tubular form which would be caused by a transverse component of velocity of the particles is, therefore, avoided.

It will be apparent that instead of employing an annular gap, the inlet means may comprise two or more equiangularly spaced inlet openings adapted to eflect the desired substantially symmetrical conveyance of particles towards the axis of the part of tubular form.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A mixing device for supplying particles to a fluid carrier medium in a conveying system comprising walls defining an upright chamber of circular cross-section having a top and bottom closure, a nozzle having an upright axis positioned with its discharge end flush with the bottom closure of said chamber and arranged to discharge fluid carrier medium into the lower portion of said chamber, a tubular member coaxial with said nozzle and extending downwardly through said chamber to a position spaced upwardly from the fluid discharge end of said nozzle, said tubular member having its lower end opening of greater diameter than said nozzle, and particle inlet means located in a side wall of said chamber intermediate the height thereof for the delivery of particles to said chamber, the particle inlet means being located so that the angle of repose of the particles delivered by said inlet means to said chamber is spaced below the lower end of said tubular member whereby particles passing through said inlet means scatter in approximately symmetrical manner around the axis of the tubular memher.

2. A mixing device according to claim 1 wherein the bottom closure of said chamber is formed as a flat plate normal to the axis of the chamber.

3. A mixing device according to claim 1 wherein the bottom closure of said chamber is formed as an inverted frusto-conical plate coaxial with the chamber and with an inclination less than the angle of repose of said particles thereon.

4. A mixing device for supplying particles to a fluid carrier medium in a conveying system comprising walls defining an upright chamber of circular cross-section having a top and bottom closure, a nozzle having an upright axis positioned with its discharge end flush with the bottom wall of and coaxial with said chamber and arranged to discharge fluid carrier medium into the lower portion of said chamber, a tubular member coaxial with said nozzle and extending downwardly through the top of said chamber to a position spaced upwardly from the fluid discharge end of said nozzle, said tubular member having its lower end opening of greater diameter than said nozzle, a particle inlet chute opening through a side wall of said chamber intermediate the height thereof for the delivery of particles to said chamber, the particle inlet chute being located so that the angle of repose of the particles delivered therethrough to said chamber is spaced below the lower end of said tubular member 5 whereby particles passing through said inlet means scatter in approximately symmetrical manner around the axis of the tubular member, and an open top box formed in the lower surface thereof to define a particle retarder to thereby reduce the velocity of the particles entering said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 6 Jacomini Apr. 27, 1948 Goodson et a1. Aug. 5, 1952 Bergstrom et al. Oct. 20, 1953 Smith Feb. 15, 1955 Bergstrom July 24, 1956 Bourquet Oct. 2, 1956 Guala Oct. 16, 1956 Bourquet Nov. 13, 1956 Hall et al. Sept. 17, 1957 FOREIGN PATENTS Germany July 4, 1930 Great Britain Oct. 17, 1930 Great Britain Feb. 29, 1956

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