NO141501B - PROCEDURE AND DEVICE FOR DISPERGING A GAS IN A LIQUID - Google Patents

Description

The present invention relates to a method and a device

ning for dispersing a gas, e.g. air, in a liquid el-

laughing mud that is in motion. As an example of the invention's field of application, particular mention should be made of flotation

cells.

Within the mineral enrichment technique, flotation is used for

separation of valuable minerals from waste rock. Generally speaking, by using a flotation method, the in-

different grains are separated from each other at the interface between two flowing phases that touch each other, of which at least one must be a liquid. The interface can be formed by liquid

liquid or liquid-gas. The separation takes place by bringing part of the grains, e.g. using suitable chemicals, to attach at said interface, as the other grains do not attach to this.

For the practical implementation of a flotation process, devices called flotation machines or cells are used. The tasks of the flotation machine are: 1. to provide the aforementioned interface, e.g. between the liquid and gas phases. 2. to bring the grains to be separated as well as the aforementioned boundary surface into contact with each other, and 3. to line the grains to be taken care of and those to be discarded to different states.

For effective separation during flotation, it is advantageous that the largest possible interface between the phases occurs, and that the grains collide with this interface as abundantly as possible. Modified, the same applies when it comes to the dissolution of a solid substance or a dissolution in another solution.

The present invention aims to solve the two first-mentioned tasks and a device to carry them out.

The method developed by Ds is also suitable for implementation

of flotation, for any process where a gas is to be caused to mix as small bubbles in a liquid or slurry.

With regard to the flotation phenomenon in particular, it should be noted that a high energy consumption by the flotation device alone does not guarantee a good and economical end result, but the decisive factor in the adaptation of the principles given above is that the dispersion of the gas is effective, the mineral grains are kept in motion and that the formation of gas bubble mineral grain aggregates is effective.

The number of different flotation device models in the race

of the 60 years that the flotation technique has been used to a significant extent has been enormous. However, most models have appeared only to immediately disappear again. The main types currently marketed are the following:

1. Pneumatic flotation machines, in which the ore slurry is held as a suspension by blowing low-pressure air towards the bottom of the machine via a rudder, nozzle, or the like. However, the proportion of these ma-skin types is currently relatively small. 2. Mechanical flotation machines, where a rotor belonging to the machine's drive mechanism sucks in air from outside the machine and disperses the air in the sludge and keeps the sludge as a suspension. 3. Mechanically pneumatic flotation machines, where the rotor's task is to keep the sludge in the form of suspension, but where the necessary air with excess pressure is fed in from the outside of the machine. The dispersion of the air usually occurs by the action of the rotor.

In mechanical and mechanically pneumatic flotation machines, the drive mechanism is formed by a rotor-stator combination. The currently most typical machine types found on the market are: 1. The so-called Denver mechanism, the basic type of which was first patented by A W Fahrenwald in 1934 (US patent no. 1 934 366). This comprises a rotating horizontal disc-like propeller with low wings, both on the upper and lower surfaces. The propeller is surrounded by a stationary limiting device with radial blades below. The propeller sucks in air through a protective rudder that surrounds the machine's shaft. The opposite edges of both the propeller and the limiting device's wings are vertical. 2. The so-called Fagergren mechanism (US patent no. 1 963 122/1934), in the older type of which both the rotor and the stator consist of mutually similar "cages" composed of two end pieces and coils that bind them together.

The rotor rotating inside the stationary stator sucks up sludge with the lower gable piece and air through a protective

rudder that surrounds the axle with the upper gable piece.

In the newer Fagergren type, they previously had approx. 300-400 mm

hbye coils have been changed to direct from the center of the rotor emanating and outward folded vertical wings at the same time that the stator consists of a cylinder with a perforated mantle that surrounds the rotor.

3. In the Agitair flotation machine (US patent no. 3,327,851) the rotor consists of a rotating, on its upper flat plane disk, whose edges have downwards, and at regular intervals arranged vertical fingers. The stator consists of radial rectangular discs, with the rotor rotating in their open centre. 4. The drive mechanism of the VX-3 flotation machine (Finnish patent no. 45,416) comprises a horizontal disc-like rotor with wings on both sides. On the upper side of the rotor there is a closed counter disc, whereby between this and the upper surface of the rotor, when the rotor is rotated, a suction is formed which feeds the sludge into the machine. The rotor's lower wings disperse the overpressure air forced through the hollow shaft into the sludge and feed the sludge between the disks on the stator composed of radial rectangular vertical disks that surround the rotor.

Ds flotation machines that appear on the market beyond those previously oe;3required are more or less modifications of these. A flawed feature seems to be that the machine's construction is based more on practical experience and random ideas than on a mathematical consideration.

The following presentation of the method according to the invention

is limited to consideration of a situation where air or another gas is dispersed in a liquid. consider-

the nings are also limited to touching on a situation that almost occurs in flotation machines or in another air-

mixing in a liquid or dispersing another gas, as a targeted implementation of a general consideration would be extremely extensive. The considerations put forward are, however,

dende also in more general cases.

Method according to the invention starts from the obvious fact

that the ability of the surface unit of the dispersion surface to dissolve air in a liquid as small bubbles/is limited, and that if this limit is exceeded the quality of the result decreases, in this

trap grows closest to the size of the bubbles, and whose surface unit

ten's load is further increased, the air begins to penetrate directly through the sludge to the surface of the cell without being dispersed at all. When the size of the cell grows, it is okono-

misc and technically advantageous to still use an air splitting mechanism per cell pool or in any

trap as few mechanisms as possible depending on the type,

and with this, the amount of air to be split through a mechanism becomes large. The method according to the invention charac-

is seen by what is stated in the following main requirements.

and the characteristics of the device according to the invention appear in patent claim 2.

In the following, the situation for mechanical cells is considered for

Synth with rotor and stator. However, mechanical cells can also lack an actual stator in the general sense.

When cell size increases and if the cell's shape remains unchanged,

secondly, the cell's volume grows proportionally to the third power of its measure, the cell's free liquid surface and likewise the

large amount of air grows proportionally to the second power of the dimensions and in the case of mechanical cells the circumference of the rotor, at which the air is split, grows proportionally to the dimensional

nene's first potency. If then the size of the cell grows, the depth of the zone of the rotor which acts as the effective dispersing part should also grow in proportion to the dimensions,

and the dispersing surface should also grow proportionally

with the second power of the dimensions, such as the amount of air to be dispersed. Obviously, this is not the case, but the effective height of the dispersion zone is almost a fixed amount of hydrostatic pressure difference, regardless of the size of the rotor. If the rotor construction is such that a yoked 1outfeed can

press the liquid surface in the rotor and within the dispersion zone downwards, i.a. Agitair and Fagergren, and thus almost by itself the dispersion surface, the air in the rotor has a corresponding pressure against the lower surface of the liquid and the air is not emitted evenly through the free surface present against the liquid, but primarily in the area that exhibits the smallest external pressure , i.e. generally from the upper part of the mechanism and hardly at all from the area of higher pressure, i.e. from the lower part. If the free interface between the air and the liquid in the dispersion zone is determined by the construction, i.a. at Denver, the situation is the same provided that the air release strongly favors areas with the least external pressure in the boundary in question, in which, therefore, when the air input increases, overload first occurs. A proof that the height of the dispersion zone in known cell types does not automatically increase with cell

lens and the size of the mechanism, is that when the size increases,

often up to to a considerable extent have been forced to change the mechanism's construction.

In the method according to the invention, one creates under utilization

calculation of the dynamic pressure caused by the liquid in motion, a situation where said dynamic pressure compensates for the differences in the hydrostatic pressure which affects the dispersion surface at different depths so that the entire dispersion surface regardless of depth is exposed to the same external pressure. This results in the situation that the supplied air does not particularly favor certain parts of the zone, but is distributed evenly over the entire surface. According to this principle, a reali-

With regard to its area, the effective dispersion surface is also considerably larger than with known devices, which is why the large amount of air required for large cells can easily be dispersed with good results, i.e. as finely divided bubbles.

With an air splitting mechanism according to this principle, the dispersion surface, in contrast to what is the case with known mechanisms, grows proportionally to the square of the mechanism's linear dimensions, which is why an air splitting is also successful with particularly large cells, and the construction and shape of the splitting mechanism can be independent of the size of the mechanism .

An advantage of the method is also that, as the air splitting takes place under the same conditions essentially over the entire surface, these conditions can be chosen optimally with regard to the splitting and efficient consumption, and thus significant power savings can also be achieved in comparison with known constructions, and these power savings can also be achieved with relatively small cells. Examples of dynamic pressure include of the centrifugal force caused pressure, of the velocity caused negative pressure e.g. in a venturi, the pressure affecting a body in a flow, e.g. a damming pressure or, generally speaking, the pressure distribution along the body's surface, etc.

In the following, a simplified mathematical consideration will be carried out for the case when the pressure is caused by the centrifugal force. The figure below shows a rotating, ring-shaped element of a liquid.

The angular velocity of the fluid is CJ. The differential pressure change in the ring is

2

dp<j = Pw r^ r

and the pressure change when transitioning from the surface of the rotor to

the stator surface or r^—> rs is

Assume that p is constant and UJ a function of the depth and the radius according to the formula: . is achieved

The dimension of the integral is [ L j - 2. It is obtained in dimensionless form by division, e.g. with rcs, where rc is a constant, a radius whose magnitude is essentially the same as r^ and r , and s is the dispersion gap. How to get:

X(^) is in most cases almost constant and in value ^l and the value for rc can be chosen so that ..e.g. at the upper part of the mechanism X(O) = 1..

It is expedient to transfer W( z) to the form ui{ z) = UQ-ri(^), whereby the angular velocity change in the space is reproduced in the expression

(jj is the angular velocity at the points r = rc, z = zQ = the upper edge of the dispersion zone. For p^, the expression is obtained: and for the total pressure affecting the dispersion surface, the expression is obtained: In the upper part of the dispersion space is = o and

By dividing the difference of the equations by the last expression of the last equation, we get:

Before, it was established that usually in normal mechanism constructions n>l. From the derived equation it can be established that the space grows with & zy and that the shape of the space is strongly dependent on the way in which the angular velocity changes as a function of the depth or of -TL(£) . In this way, the expression for X(^) is considered in a special case.

The value for rc can be defined so that at the upper edge of the mechanism X(0) = 1. This also applies to a general case. X is a function of £ = A z/r , because either r or r. or both are functions of £. In most cases, however, X(£) is .^1 as a first approximation.

If the angular velocity change as a function of the radius

r is different than in the example shown, the expression for X (£) is also different. If ri and rg do not change particularly much

in the dispersion zone, X(£) is -^1 throughout the range.

Equation (9) expresses the core of the invention by an adaptation to a mechanical cell: the mechanism's dispersion space is shaped as a function of the depth, i.e. the opposing surfaces of the stator and the rotor are designed so that the centrifugal force^ acting in the suspension which is in rotating motion in the space at essentially all levels of the dispersing zone^ compensates the change in the hydrostatic pressure occurring at different depths so that a constant pressure prevails in it smallest on the main part of the dispersing surface. A change in angular velocity as a function of depth, the parts that cause /!(£), e.g. The internal structure of the rotor and the direction of circulation of the seeding (which happens from above and/or below) can also form targets for the orihandled design, e.g. when striving for a space that changes in the desired way. Due to the general nature of the method, equation (9) can be realized in an infinite number of ways.

In addition to the aforementioned constant pressure condition, an advantageous function requires that in addition to air, slurry also flows into the dispersion zone, the flow of which is evenly distributed over the surface in question, and the size of which is in a suitable relationship to the air flow in order for an air sludge suspension to be produced under advantageous conditions.

The flow within the stator area and elsewhere in the cell space must be sufficiently turbulent for conditions to exist for collisions between the bubbles and the mineral particles and the formation of agglomerates. Moreover, this flow of sludge produced by the mechanism must be sufficiently strong for the solid material to be kept mixed in the liquid, so that agglomerators can be formed.

The invention shall be described in more detail below, for example with reference to the attached drawings, where

Figures 1-7 show different embodiments of a device according to the invention, which comprises a rotor-stator combination,

figures 8-11 show some advantageous cross-sections of the rotor,

figures 12-14 show, with reference to previous figures, alternative ways of admitting air into the rotor,

With reference to the above-mentioned theory taken as an example

as a starting point for the following consideration a device shown in Figure 1, which e.g. can constitute a flotation cell. Its most important parts are a rotating rotor 1 as well as a stationary sta-

tor 2. The rotor rotates in the slurry around a vertical ac-

seal and via the rotor, air is fed into the space 3 between the rotor and the stator.

In this case, the construction of the rotor is in accordance

with the cross-sectional view 15 and it thus includes alternating air passages 5 and mud openings 8 extending out to the dispersing surface. Thanks to the mud openings, the rotor also works

as a pump that feeds the slurry to the dispersing surface.

The air flows out over the air passages to the said surface. The

during the flotation, finely divided bubbles appear at the dispersing surface in the space 3. In the section of the rotor in the figure, on the right-hand side, the liquid flow between the rotor's

wings and on the left side an air inflow room which

is in connection with a hollow shaft.

In this case, the rotor's mantle surface consists of a cylinder

and the constant pressure condition for the dispersing surface has been realized by i.a. the design of the stator. The air is brought to the dispersing surface along the entire height of the rotor via separate air passages (figure 15), which divide up the rotor's mantle surface

ter in alternating air passages and sludge openings. Those in cross-

section V-shaped mud openings are in this case open at their upper end, so that the mud can flow into these and leave

to the dispersing surface by the rotor's centrifugal action and further air mixed via the stator to the cell. The stator dem-

per not quite the circulation impulse that the rotor gives the sludge3

but the cell's entire amount of sludge is in a rotational motion

gels. When the sludge flows from the upper side of the mechanism towards the

the rotor, the angular velocity of its rotational motion increases with the expression of the impulse, which is why it is in rotational motion when it arrives at the rotor. The rotor provides external

more speed to the rotational movement in a way that depends on the arrangement of the rotor's mud collection, on the shape and construction of the mud openings and dispersing surface and, among other things, of the residence time of the sludge inside the rotor. The sludge flowing from inside the rotor to the dispersing surface thus has an angular velocity which, among other things, a. in a way depending on the above factors is a function of the depth coordinate. The rotary walking mud

current is surrounded by an entrained rectified current, which passes

past the rotor directly into the dispersing space, where the turbulence and mixing is effective, as well as to the stator,

where its smaller rotational impulse reduces the force of the vortices between

lom the stator discs. Blue. this additional flow changes the sludge's angular velocity in the dispersion gap from that given by the rotor, resulting in a kind of angular velocity change

dleiing uj = uj(z,r), which is a function of the depth and the radius.

By considering the front of the dynamic pressure, lignin is obtained

gene (9), which includes the condition that a constant pressure situation

tion must appear. Accordingly, X(£) lives

changes in a way that depends on_o?(f) and on Az. % = & z/ rc' A(^) is in most constructions almost

constant /=*1, why in most cases s/sq must change in the aforementioned way. The change of the space s as a func-

tion of the depth Az is essentially dependent on the angular

the change in slope as a function of depth iy = Az/rc.

It must also be noted that -0.(£) depends on the outside of the rotor

shape and internal construction and of the method of inflow of the sludge and that the space s(£) or more specifically f— on its

so

side depends on Sl{ %) and on Az, which is why the gap is in many ways a function of the mechanism's other construction.

Figure 1 thus showed a case where a cylindrical rotor was surrounded by a stator, which was designed in such a way that constant pressure

the award is carried out. The mud openings of the rotor are open at the top

end, why a so-called upper sludge circulation occurs in the mechanism, where the angular velocity of the sludge during dispersion flac-

ten grows downwards. With such a construction, it is the dispersing space that makes the constant pressure condition a reality in most cases mainly downwardly growing, while the space in the upper part can be constant or upwardly growing.

Figure 2 also shows a similar construction to Figure 1,

but the mud openings are open downwards. In the mechanism thus arises

a lower circulation, where the angular velocity of the sludge at the dispersion surface grows upwards. In the upper parts, angular velocity can

the heat be independent of the height. To achieve constant pressure-

at will, the space grows strongly downwards, and at its top

part possibly be constant or nearly constant.

Figure 3 also shows a similar construction to Figures 1 and 2, but the sludge openings are open both upwards and downwards, whereby both an upper and a lower circulation occurs. The angular velocity of the sludge in the space is lowest at both the upper and lower parts of the dispersion zone. The gap required to achieve the constant pressure condition is mainly downward growing, possibly constant or upward growing at its upper part. Figure 4 shows a case where the inner tangential surface of the stator is cylindrical and the constant pressure condition is achieved by the design of the rotor. Sludge inflow to the rotor from above is prevented and the sludge reaches the dispersing surface so that the rotor via its lower section with a smaller cross-section sucks up sludge from the cell, which is ejected by the rotor from its upper section with a larger cross-section under the influence of the centrifugal force. A pure downward circulation thus occurs in the cell, and the angular velocity of the sludge increases strongly upwards. The gap required to achieve the constant pressure condition is strongly downward growing, possibly constant or nearly constant at its upper part. The change in the space is realized by the design of the rotor.

Figure 5 shows an otherwise similar construction to Figure 4,

but the sludge openings are also open at their upper end, whereby in addition to the lower circulation, an upper circulation also occurs. This affects the angular speed of the sludge in the space. The space required to achieve the constant pressure condition is mainly strongly growing downwards, at its upper part possibly constant or almost constant or growing upwards.

Figure 6 shows a construction where the rotor expands downwards. Sludge inflow to the rotor from below is prevented and the sludge reaches the dispersing surface so that the rotor via its upper part with a smaller diameter sucks up sludge from the cell, which is ejected from the rotor from its lower part with a larger diameter under the influence of centrifugal force. A pure upper circulation thus occurs in the cell and the angular velocity of the sludge increases strongly downwards. The gap required to achieve the constant pressure condition

is growing downwards or almost constantly. The space's pre-

change is realized either at the output of the rotor or the stator

shaping.

Figure 7 also shows a similar construction to Figure 6,

but the sludge openings are also open at their lower end, whereby in addition to the upper circulation, a lower circulation also occurs.

This affects the angular velocity of the sludge in the space. The

space required to achieve the constant pressure condition is downwardly increasing or almost constant, at its upper part possibly strongly increasing downwards.

Figures 8-11 show a number of suitable cross-sections for the rotor for transporting the air required for dispersion to the dispersion surface.

In the embodiment according to Figure 8, air is mixed into the sludge

already for the rotor, e.g. with a construction according to Figure 12 where the air is fed in via a protective rudder above the roto-

clean sludge openings, from which the mixed in the sludge transport

tered out to the dispersing surface.

In the constructions according to figures 9-11, the air is introduced

to a special air space in the inside of the rotor, e.g. in the manner shown in figure 13 via a hollow shaft or according to figure 14

via a protective rudder 4. In the cases shown in fig.

clean 13-14, the air is emitted from the rotor's air space to the sludge which flows in the sludge openings and is transported with this to the dispersing surface. In the construction according to Figure 15, the air is transported via special air passages directly to the dispersion

surface, and only then is it mixed up with the sludge.

In all cases, the air should be mixed up in the sludge so that the air content in the sludge that reaches the dispersing surface is essential

equal in all respects. This, in turn, assumes that a situation corresponding to the constant pressure condition prevails also at the air discharge points, i.e. air discharge

openings should be placed so that the pressure with which the mud affects them is the same everywhere. In the case shown in Figure 17, only the constant pressure condition needs to be

fulfilled at the dispersing surface. If the air is mixed up with the sludge already at an early stage, the constant pressure condition must also prevail in the air outlet openings.

Naturally, in the cases according to figures 1-11, constructions that follow the same contours can be used, but regarding the air intake method and the construction of the rotor, they differ from those shown in the figures.

Figures 19 and 20 show examples of pneumatic cells which, with their construction and operation, resemble those considered above, but where the circulation movement of the sludge in the dispersing space is produced instead of by a rotor with a special sludge pump, from which the sludge is fed tangentially directly into the dispersing device or in a cylindrical chamber situated in front of it, from which it enters the dispersing device. The rotor corresponding to part .7, over which the air is fed, can either rotate freely with the flow or usually be stationary. In the arrangement according to Figure 19, the air-mixed suspension departs mainly radially,

and according to figure 20 mainly axially.

Claims (5)

1. Procedure for dispersing a gas, e.g. air in a liquid, e.g. a slurry where the dispersion takes place by means of a rotor which is immersed in the liquid and rotates about a vertical axis of rotation, in which gas is introduced through a vertical axis and blown out from a zone on the surface of the rotor's side which thereby functions as the rotor's gas dispersion surface. and whereby the change in the hydrostatic pressure that increases with increasing depth calculated from the top of the rotor is compensated by a dynamic pressure that varies correspondingly with the depth so that the total liquid pressure on the dispersion surface will be substantially the same over the largest part of the dispersion surface , characterized in that a ring of the liquid around and up to the rotor's gas dispersion surface, which is produced by limiting the free rotation space around the rotor in such a way that said space increases with increasing depth, is brought into rotation by means of the rotor so that thereby the centrifugal force which acts on the downwardly increasing in thickness liquid ring causes the aforementioned dynamic compensatory ion pressure, as the gas dispersion surface extends along essentially the entire height of the side part of the rotor. 2. Device for carrying out the method according to claim 1 which partially comprises a rotor (1) rotatable around a vertical axis of rotation, where the side surface of the rotor (1) is designed as a gas dispersion surface along essentially its entire height and is immersed in a liquid and is provided with with a vertical, hollow gas supply axis and a dispersion surface on the side of this, which is arranged to dissipate gas supplied from the gas supply axis in the liquid, partly a stator (2) arranged around the rotor at a distance from it which, together with the rotor, defines an annular room (3), characterized in that the outside of the rotor (1) and the inside of the stator (2), which together delimit the ring shaped space (3), is designed with downwards mutually increasing distance so that the space (3) expands downwards and thereby produces a liquid ring that increases in thickness along the rotor side and can be rotated by the rotor. 3. Device according to claim 3 or 4, characterized in that the stator (2) on the inside has an essentially constant cross-section along the height, while the rotor (1) on the outside has a downwardly tapering cross-section. 4. Device according to claim 3 or 4, characterized in that the stator (2) on the inside has a downwardly increasing cross-section while the rotor (2) on the outside has an essentially constant or similar to the stator, but more slowly downwardly increasing cross-section along the height. 5. Device according to each of claims 3 to 6, characterized in that the rotor (1) has outflow openings (5) for gas and outflow openings (8) for liquid arranged alternately in the peripheral direction of the rotor and are separated by means of partitions so that the gas and the liquid has its own, separate channels where-under the channel the liquids are open upwards and or downwards.