US3460811A - Mixing device - Google Patents

Description

,1969 v G. HUGLI 3,460,811

MIXING DEVICE Filed Nov. 30, 1967 2 Sheets-Sheet 1 Aug. 12, 1969 M GJHU'GLII 3,460,811

MIXING DEVICE Filed Nov. 30. 1967 2 Sheets-Sheet 2 d d e United States Patent US. Cl. 259-97 6 Claims ABSTRACT OF. THE DISCLOSURE Apparatus for mixing materials including a cylindrical 3,460,231 1 Patented Aug. 12, 1969 sleeve will coincide with the axis of the device. However, it is also possible to arrange said axis at an angle and/or to shift it with respect to the impeller axis.

For certain applications, the two communicating com- 5 partments of the device can be arranged side by side or housing with a coaxial cylindrical jacket disposed therein to form an inner chamber and an outer chamber, an impeller disposed in the inner chamber, and a plurality of baffles disposed in the outer chamber to define a plurality of flow paths having varying cross sectional areas throughout the outer chamber.

This invention relates to an improved mixing apparatus particularly suitable for the mixing of viscous liquids.

Conventional mixers using agitators and stirrers are frequently not able to produce a satisfactory mixing action in highly viscous liquids.

It is known to use built-in annular arrangements such as encased propellers to improve the performance of such stirrers. Even then, the mixing effect remains unsatisfactory because either the flow speed is too low or there is to little forced rotary motion of the contents.

It is, therefore, a principal object of the invention to provide a mixing device which improves the mixing effect, particularly in viscous liquids.

Other objects and advantages will be apparent from a consideration of the specification and claims.

The mixer according to the invention contains a cylindrical jacket which divides the inner space into two communicating compartments whereby said jacket is on its inner face provided with longitudinal bafiles and surrounds an impeller producing vertical flow. In the space between said jacket and the outer wall of the tank, there are provided either at least one vertical baffle and at least one inclined batfle, or at least two inclined baflles in order to produce a large speed gradient and high speeds.

The portions of the fluid flowing around the edge of the propeller jacket where said portions are not subjected to the action of the dividing baffles and flow at high but widely differing speeds, are subjected to high shearing stresses and pressure drops which produce a very intensive blending of said portions.

Due to the built-in guiding means, the forced flow, which provides for a mixing effect independent of the impeller, can be maintained in all sections of the device even for liquids of very high viscosity; this is not possible in conventional mixing devices.

The cross-sectional ratio of propeller compartment to jacket compartment is preferably in the range of 1.5:1 to 5:1.

The number of deflecting baffles disposed in the interspace between the outer wall and the jacket is chosen with advantage so as to provide at least one inclined baffle in addition to two vertical baflies or only at least two inclined bafiies. Preferably, two to nine bafiles will be provided. An excessive number of baffles increases the frictional losses.

The slope of the inclined baffles is preferably in the range of 15 to 45 to the vertical.

Normally, the axis of the cylindrical inner jacket or one behind the other.

The device of the invention is particularly suitable for viscous liquids such as solutions of high molecular polymers, fertilizers, and the like.

An illustrative embodiment of the device of the invention is shown, by way of example, in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a mixing device according to the invention showing the arrangement of the impeller, inner jacket, and baflies;

FIG. 2 shows the arrangement of the various bafiles with respect to the inner jacket in top view, side view, and as development of the jacket; and

FIG. 3 is a perspective view of the mixer.

Referring to the drawings, an inner cylindrical sleeve 11 divides the cross-sectional area of the mixer in the proportion of 3 (inside):1 (outside). An impeller b produces between vertical deflecting bames c a strong current of preferably 0.5-6 m./sec. in vertical direction inside said sleeve. The outer ring space is divided by three deflecting bafiies into three zones or flow paths through which the materials to be mixed moves in parallelly divided flows; two of the bafllles d are vertical while one baflie c is inclined to the vertical by an angle of 15 to 45 In this way, the liquid is divided into flow paths of three diflierent speeds.

The different speeds or flow rates in the flow paths cause intensive mixing at the top and bottom of the jacket where the flow paths communicate due to high speed gradients and shearing stresses, and intensive mixing occurs in the outer ring space or chamber due to the varying cross sectional areas of the flow paths defined by one longitudinal baflle d and inclined bafiie e which are skewed with respect to each other.

EXAMPLE A mixing tank of 450 liter capacity and an outer diameter of 940 mm. contained an inner cylinder of 700 mm. diameter which was provided with two outwardly projecting vertical baffles of about mm. width and a third outwardly projecting baffle which is inclined at an angle of 30 to the vertical. Said baffles extended over the entire length of the jacket. The three-bladed propeller had a diameter of 550 mm.

The mixer was used for the decomposition of a raw phosphate with nitric acid at a temperature of 50-56 C. 1500 kg./hour of raw phosphate and 41.00 kg. of 58% nitric acid were continuously passed through the mixer whereby the products were introduced near the bottom of the mixer by means of a dip tube and the acidulated mixture was drawn off through a lateral outlet provided below the upper edge of the stirrer. The speed of the propeller was 220 r.p.m. The viscosity of the produced mesh was 10-60 poise (non-Newtonian liquid). The mixer was operated for more than 3 months without interruptions.

To obtain the same effect with a conventional mixer, such mixer must have a capacity of about 5000' liter, and material strongly adheres to the walls, requiring frequent stoppages for cleaning.

I claim:

1. Apparatus for mixing materials comprising a cylindrical housing, a cylindrical jacket having an inner surface and an outer surface and disposed ,within said housing to form an inner chamber defined by the inner surface of said jacket, and an outer chamber communicating with said inner chamber and defined by said housing and the outer surface of said jacket;

an impeller disposed in said inner chamber for causing materials to be mixed to flow through said inner chamber and said outer chamber; and

a plurality of baffles disposed in said outer chamber to define a plurality of flow paths through said outer chamber, said plurality of baflies including a pair of adjacent baflies skewed with respect to each other such that the cross sectional area of a first flow path defined between said adjacent baflies varies throughout said outer chamber whereby intensive mixing of materials occurs in said outer chamber.

2. The invention as recited in claim 1 wherein said pair of adjacent bafiies includes a first bafile disposed in longitudinal alignment with said jacket and a second bafiie disposed at an incline to said first baffie.

3. The invention as recited in claim 2 wherein said plurality of baffles includes a third bafile arranged in parallel with said first baffie to define a second flow path through said outer chamber between said first bafiie and said third baflie and a third flow path through said outer chamber between said second baflie and said third bafiie, said third flow path having a cross sectional area varying throughout said outer chamber, whereby intensive mixing of materials occurs where said first flow path, said second flow path and said third flow path communicate due to diflFerent flow rates in the flow paths.

4. The invention as recited in claim 3 wherein said jacket and said housing are coaxial.

5. The invention as recited in claim 3 wherein said second baffle has an incline of from 15 to 45 with respect to said first baflie.

6. The invention as recited in claim 3 wherein the ratio between the cross sectional area of said inner chamber and the cross sectional area of said outer chamber is in the range of 1.5:1 to 5:1.

References Cited UNITED STATES PATENTS 1,255,944 2/1918 Stevens 25997 1,701,164 2/1929 Shafor 25997 2,390,460 12/1945 Presser 25997 2,530,814 11/1950 Becze 25997 X ROBERT W. JENKINS, Primary Examiner

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