Airlift Blending Apparatus

Abstract

A blending apparatus for mixing dry powdered materials consisting of an upright silo with a gas-permeable divider and a gas supply providing fluidizing gas up through the divider. A hollow blending column, open at its top and bottom, is vertically mounted in the silo with its bottom end spaced from the gas-permeable divider and gas is directed upwardly through the blending column at a velocity higher than the fluidizing gas velocity in the silo to circulate material from the silo upwardly through the blending column.

Description

BACKGROUND OF THE INVENTION

This invention relates to bulk blending apparatus for the mixing and blending of dry pulverulent materials. Materials to be blended are usually introduced into a suitable bin or vessel. It is essential that the various materials be completely intermingled and mixed prior to being discharged from the vessel. This invention is concerned more specifically with the blending of dry powdered materials that are not free-flowing and which require fluidization, such as cement raw materials.

Various means have been employed to achieve the aforementioned blending of materials. The blending of mixtures of dry powdered fluidizable materials is frequently accomplished by introducing a diffused flow of gas through the material to produce a fluidized condition of the air-material mixture. Blending can thus be accomplished in a vessel with a porous bottom through which the fluidizing gas is diffused and introduced into the powdered material. By adjusting the velocity of gas through the material it is possible to introduce various degrees of turbulence and as a consequence, various rates and completeness of blending within the vessel.

A further improvement of the aforementioned type of apparatus is disclosed in U.S. Pat. No. 3,003,752 and U.S. Pat. No. 2,844,361 and includes a vessel provided with a gas-permeable floor. The gas-permeable floor is separated into quadrants with means provided for individually varying the amount of airflow through a selected quadrant. In this way, increased airflow through a given quadrant will decrease the density of the air-material mixture above the more active quadrant thereby reducing the pressure of the material over this quadrant. The material over the more active quadrant rises upwardly and flows over the top of the fluidized material in the less active adjacent quadrants. Furthermore, the more dense material in the less active quadrants flows inwardly to replace the less dense material in the active quadrant thereby promoting the blending action. As the diameter and height of the blending receptacle are increased, the delineation of the active zone becomes less distinct. This, of course, reduces the blending efficiency of the apparatus.

It is, therefore, an object of this invention to create a well-defined and controlled column of a reduced density of gas-material mixture in a fluidized mass of material which will increase circulation of material and thereby increase blending efficiency.

SUMMARY OF THE INVENTION

This invention relates to a blending system for dry pulverulent material comprising an upright vessel with a material inlet port and a material outlet port, a gas-permeable divider positioned in the vessel and dividing the vessel into an upper material chamber and a plenum chamber, at least one blending column vertically mounted inside said vessel, said blending column being hollow and open at its top and bottom with the bottom being spaced from the divider to provide a material intake opening into the blending column, fluidizing gas means in fluid flow communication with the plenum chamber for supplying fluidizing gas to the material chamber through the divider, and blending gas supply means adapted to supply gas into the bottom of the blending column at a velocity higher than that of the fluidizing gas supplied to the material chamber. A plurality of blending columns can be used and the columns can be varied in height and/or can have openings positioned along their length to create intermixing at various levels of the material.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a sectional view of a blending apparatus of the present invention;

FIG. 2 is a sectional view of an alternate embodiment of the invention;

FIG. 3 is a sectional view of a modified form of blending chamber of the apparatus of FIGS. 1 or 2 having openings in the walls thereof; and

FIG. 4 is a modification of the apparatus of FIG. 1 having a material discharge port located in the upper portion of the material chamber.

DETAILED DESCRIPTION

Referring to the drawings, the blending system comprises an upright vessel or bin 10 such as a large outdoor storage silo for cement raw materials having a circular side wall 14 with a material inlet port 12 at its upper end and a material outlet port 13 at its lower end. The material discharge port 13 is connected to a discharge conduit 15 having a cutoff valve 16 therein to control material discharge from the bin. Spaced from the bottom 17 of the bin 10 is a gas-permeable divider 18 which divides the bin into an upper material chamber 27 and a lower plenum chamber 19. The divider 18 slopes from all points on the upper surface thereof toward the material outlet port 13. Thus the divider of FIG. 1 is an inverted truncated cone and that of FIG. 2 is a sloping trough. The divider 18 may be comprised of any suitable gas-permeable medium such as porous stones, fabric or perforated metal and overlies the plenum chamber 19. A gas conduit 20 delivers gas under pressure, suitably air for inert materials, to the plenum chamber 19 to provide fluidizing air for the material chamber 27. An advantage of the truncated cone-shaped divider 18 is that it assists the flow of material along the upper surface of the divider toward the blending column thus eliminating segregation of the material. This is particularly important in the modification of FIG. 4 in which the cutoff valve 16 is closed and the blender operates continuously with the material discharging through a material discharge conduit 15' located in the upper portion of the material chamber 27. In this arrangement of FIG. 4, the material conduit 15' acts like a material overflow to discharge material in a continuous operation. The cutoff valve 16 is then used as a cleanout valve for removing oversized particles from the material chamber. Like parts of the apparatus of FIG. 4 have the same numerals as FIG. 1 and operate in the same manner as described with reference to FIG. 1.

A hollow blending column 21 in the form of a cylindrical tube or casing and open at its top and bottom and having a funnel-shaped bottom 23 is mounted vertically in the vessel 10. The blending chamber 21 is connected to the vessel by connecting means, such as metal rods 22, and the lower end of the chamber is spaced from the divider 18 to provide a material intake opening 28. Nozzles 24 receive gas from the gas conduit 20 and direct a higher velocity gas into the blending column 21. This higher velocity gas has a greater lifting action than the fluidizing air passing through the gas-permeable divider 18, thereby creating a less dense column of material in the column 21. The less dense column is displaced upwardly through the column 21 by the more dense material flowing into the chamber through intake opening 28.

In FIG. 2 is shown a form of the invention in which a plurality of blending columns 21' of varying heights are mounted in the material vessel by supports (not shown) in a manner similar to the chamber 21 in FIG. 1. The varying heights permit discharge of material at different levels, thus creating intermixing of different levels of material. The columns may, of course, be of the same height. In this form of the invention a separate gas conduit 26 is utilized for supplying the blending gas to the nozzles 24. This permits better control of the velocities of the fluidizing gas supplied by gas conduit 20 and blending gas supplied by conduit 26. One velocity can be modified without directly affecting the other, thus permitting rapid adjustments that may be necessary due to the condition of or type or material to be blended.

In FIG. 3 is shown a modified form of blending column of the type shown in FIGS. 1 and 2, but containing a plurality of openings 25 through its wall at various elevations. These openings permit partial flow of material into and out of the blending column at various levels, thereby intermingling the material in the column with materials at various levels in the material chamber 27. It will be understood that the openings may be only at the top, or bottom, or any combination of positions of the column dependent upon the blending conditions desired.

The operation of the assembly is largely evident from the foregoing description. A low volume of air is supplied into the plenum chamber 19 of the vessel 10 to provide fluidizing air to pass up through the divider 18 and into the vessel 10. Fluidizing air at a substantially higher volume is directed into the blending column 21 or 21' for expanding material in the chamber. The expanded material column in the column is less dense, and therefore, has less-pressure head than the surrounding material in the material chamber 27. A material flow pattern is thereby established with the high-pressure material surrounding the vertical blending column flowing toward and into the bottom of the blending column and being displaced upwardly through the chamber and out through the top of the column and across the top of the material in the vessel, as shown by the arrows. This creates a continuous and rapid circulation of material upwardly through the column despite the fluidized mass of material in the chamber 27, and produces a rapid blending action which accomplishes the blending operation in a shorter period of time and with a reduced total air requirement. The degree of mixing, as noted, can be varied by the provision of additional vertical columns disposed within the vessel, by making the columns of different heights, thus providing discharge zones at different levels in the vessel thereby creating mixing of different levels within the vessel, and by providing the column or columns with openings at various points along their length which permits partial flow of material into and out of the column at various elevations.

It will be understood that is is intended to cover all changes and modifications of the disclosure of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

Claims

I claim:

1. A blending system for dry pulverulent material comprising an upright vessel with a material inlet port and a material outlet port, a gas-permeable divider positioned in the vessel dividing the vessel into a material chamber and a lower plenum chamber, said gas permeable divider being in the general form of an inverted truncated cone, at least one blending column vertically mounted inside said vessel and extending upwardly from said divider, said blending column being hollow and open at its top and bottom with the bottom being spaced from the divider to provide a material-intake opening into the blending column, fluidizing gas means in fluid flow communication with the vessel for supplying fluidizing gas to the material chamber through the divider, and blending gas supply means adapted to supply gas into the bottom of the blending column at a velocity higher than that of the fluidizing gas supplied to the material chamber.

2. The apparatus of claim 1 in which a plurality of blending columns are mounted in said vessel.

3. The apparatus of claim 2 in which said blending columns terminate at different heights above the gas-permeable divider.

4. The apparatus of claim 2 wherein the blending columns contain openings positioned along their length.

5. The apparatus of claim 3 wherein the blending columns contain openings positioned along their length.

6. The apparatus of claim 1 wherein the material outlet port is located in the upper portion of the upright vessel.