DE19818738A1 - Controlled reduction of solids in the outflow from a continuous feed dispersion mixer - Google Patents

Abstract

A continuous mixing unit has a vessel (1) of diameter dB, with an agitator (5,6), liquid inlet (3) and solids feed system (4,8,10), and an extended bottom outlet (12,15) of diameter dR . To maximize the downflow velocity of the liquid, dR is significantly less than dB. To reduce the concentration of dispersed solids in the outflow stream, the charging rate of solids to the mixer from the rotary lock (9) is reduced, and the liquid downflow velocity in the mixing vessel is adjusted so that it exceeds the settling velocity of the disperse phase. The effect of this is to ensure that all liquid discharging from the vessel entrains the maximum solids, and so reduces the time taken to lower the solids content within the vessel.

Description

The invention relates to a method for reducing the solids concentration in a disperser device, in particular a stirred tank, continuously from the bottom of a mixture a liquid and in this floating solid particles is withdrawn, and one for Device suitable for carrying out the method.

In numerous technical processes, it is necessary to be intimately involved with liquids and solids to mix and continuously offer this mixture for further processing. The Dispersion of the solids in the liquid is caused by the input of mechanical energy set for example by stirring in the desired manner.

Such methods can be used in the hydraulic conveying of bulk materials, for example Find plastic granules.

State of the art

From the publication "DIN standards in process engineering", page 201 f., Fig. 3.169 and A device for dispersing solid particles in a liquid is known from 3.171. she consists of a cylindrical container into which the nozzles arranged in the lid are continuous Solid particles and liquid can be entered in the required ratio. On the The prepared dispersion can also flow continuously from the bottom of the container dissipated and fed into a conveyor line. The container assigns one in comparison the dimensions of the large diameter outlet.

The substances filled into the container are stirred using a rotating anchor tool, via a shaft penetrating the lid and projecting vertically into the container is driven, mixed.  

The known device is suitable for passing a certain mass flow of solid particles the introduction of mechanical energy sufficiently evenly to a certain extent to distribute electricity to liquid.

If the solids concentration of the mixture in the container is to be reduced, it is usually the case the mass flow of the added solid is reduced and the mass flow of liquid so increases that the level in the container does not change substantially and continues continuously Mixture can be withdrawn from the container.

This method is particularly useful when mixing solids in the liquid drive, the disadvantage that the desired reduced solids concentration in the mixture in in practice only after a very long mixing time (which is theoretically infinitely long). The buoyancy of the solid particles can arise either from the fact that the solid is a ge has a lower density than the liquid or due to adhering gas bubbles in the liquid rises.

Alternatively, the container and a subsequent delivery line can be emptied completely and then then refilled by adding solid and liquid in a changed mass ratio become. However, this procedure can lead to problems if the mixture by means of a Pump is withdrawn from the container that is not suitable for dry running or a Subsequent process no interruption of the mixture supply allowed.

task

The invention has for its object to reduce the amount of time required to Solids concentration in the dispersion continuously taken from the container from a pre decrease given value to another predetermined value.  

solution

The object is achieved in that the addition of solid in the dis pergiervorrichtung reduced and the downward flow rate of the Liquid in the dispersing device is adjusted so that it increases the rate of buoyancy of the Solid in the liquid exceeds.

This measure ensures that each particle from the contained in the container Mixture of high solids concentration is withdrawn safely because of the liquid flow is pulled down faster than it can rise due to buoyancy. Of the The transition from high to low solids concentration is not gradual, but within a relatively short, predeterminable period of time. Possibly the entry of mechanical energy into the filling of the container during this time broken in order not to produce any undesirable upward flows in the filling.

The containers used to disperse solids in liquids usually have a largest diameter, which ent a multiple of the diameter of the delivery line speaks. To set a sufficiently large, downward flow in the container, must in this case, a considerable volume flow can be taken from it via the delivery line. It can therefore make sense to use a tapered container and to check the fill level in the Lower the container by changing the addition of liquid to the taper, causing the required flow velocity in the delivery line is kept at a low value can be.

In this case, it is possible to extract the volume flow of mixture drawn from the container Keep liquid and solid constant while maintaining the downward flow speed in the dispersing device to the required level. The down directional flow should be turbulent, which changes the velocity profile equalized and particles close to the wall can be reliably detected.

A dispersing device is particularly suitable for carrying out the method provided with an outlet on the bottom side, which can be emptied into a delivery line, with a through breaks for the addition of liquid and solid, wherein the outlet of the container in the delivery line opening, essentially vertical pipe section is arranged downstream and Suitable means are provided for measuring the fill level in the pipe section.  

The interior of the container usually has a largest horizontal cross-sectional area that a multiple of the largest horizontal cross-sectional area of the downstream pipe section corresponds.

The level in the pipe section can be measured, for example, using the hydrostatic one Pressure or by means of an optical level indicator. Use is also conceivable of sensors with rotating or vibrating sensors, the movements of which when immersed in the mixture will be hindered.

Usually such a device becomes a means of mixing the liquid and the solid Have particles of material to segregate processes due to the density differences to prevent. The means can consist of an agitator, but for example also in one suitable supply of liquid swirling the contents of the container.

The pipe section preferably has a cylindrical shape, so that light, control engineering nical fluctuations in the level of the level in the pipe section does not change the lead downward flow. However, it is basically possible to use the pipe section also geometrically in another way, for example conical.

Usually the largest cross-sectional area of the pipe section will be larger than the cross sectional area of the subsequent delivery line to the flow velocity in the pipe did not cut beyond what was necessary and the effort required to regulate the Level increase. When using delivery lines with unusually large cross sections, it is however conceivable that the largest cross-sectional area of the pipe section does not exceed this. In In special cases, the pipe section can pass continuously into the delivery line.  

characters

The figures exemplify one for carrying out the method according to the invention suitable device.

Show it:

Fig. 1 shows an inventive device in the initial state

Fig. 2 shows the same device after lowering the level

Fig. 3 shows the speed relationships in the pipe section of the device according to the invention after lowering the level

Fig. 4 shows the change in solids concentration over time at the beginning of the delivery line.

The device shown in Fig. 1 consists of an essentially cylindrical container 1 , in which a mixture of liquid and solid particles is prepared. The lid 2 of the loading container 1 is provided with openings through which a feed line 3 for the liquid, a feed line 4 for the solid particles and a shaft 5 for driving a stirring tool 6 protrude into the container 1 . The supply of liquid can be influenced by adjusting a valve 7 , while the supply of solids is dependent on the adjustable speed of a metering element designed as a rotary valve 8 . The cellular wheel sluice is optionally fed with one of two types of solids via the feed lines 10 , 10 'which can be shut off by slides 9 , 9 '.

The solids have a lower density than the liquid and are prevented by the rotating stirring tool 6 from collecting on the surface of the filling in the container 1 .

The bottom 11 of the container 1 has an outlet 12 from which the prepared mixture emerges. It is discharged via a delivery line 13 by means of a pump 14 .

Downstream of the outlet 12 is a cylindrical tube section 15 , which opens into the delivery line 13 and through which the prepared mixture flows. The diameter d _{R of} the pipe section 15 is larger than the diameter d _{F of} the subsequent delivery line 13 , but significantly smaller than the diameter d _{B of} the container 1 . In the middle of the pipe section 15 , a schematically illustrated level indicator 16 is arranged.

In normal operation, the filling level of the mixture in the container 1 is regulated to a height h ₁ , for example by changing the supply of liquid with a constant supply of solids and a constant withdrawal of the prepared mixture. Since the changes in the supply of liquid are small and increases and decreases in the supply compensate for themselves over time, an essentially uniform solid concentration of the mixture will result in the container.

The following is the procedure for reducing the concentration of the solid in the mixture described a solids content of zero. Such a reduction may be necessary if the device described is part of a system for the hydraulic conveying of bulk material goods and without moving the delivery lines to another, for example of a different color Product should be avoided.

The bypassing process is initiated in that the supply of solids is interrupted by shutting off the supply line 10 and emptying the cellular wheel sluice 8 . Then the level in the container 1 is quickly lowered by closing the valve 7 for the supply of liquid with continued removal of the mixture by the pump 14 . Reports the level detector 16 that the level h ₂ in the container downstream pipe section 15 he has reached, the valve 7 is opened again and the level in the pipe section 15 is regulated by changing the supply of liquid to the height h ₂ , as in Fig. 2 shown. The diameter d _{R of} the pipe section 15, which is larger than the diameter d _{F of} the delivery line 13 , facilitates the regulation of the fill level h ₂ .

At this point, the stirring tool 6 is no longer immersed in the mixture and can be shut down.

The horizontal cross-sectional area of the pipe section 15 is dimensioned such that a downward, turbulent flow is set in the pipe section 15 at the constant delivery rate of the pump 14 , the speed of which V _{S is} greater than the rate of ascent v _{A of} the solid particles. The turbulent flow has an essentially block-shaped speed profile, thereby avoiding that individual solid particles rise in the channel region near the wall.

The distribution of the flow velocity v _S in the pipe section 15 and the lower ascent velocity v _{A of} a solid particle compared to V _S are shown schematically in FIG. 3.

After the solids concentration in the pipe section 15 has been reduced to zero, the fill level in the container can be raised again. This can be achieved by an increased addition of liquid if further solid-free conveying is to be carried out temporarily, or by the simultaneous addition of liquid and differently colored solid to transport it to the destination.

Fig. 4 shows by the solid line by way of example, the decrease of the solid content in the dispersing device over time when using the method according to the invention. Area I shows the normal operating state, that is to say the preparation of a solid / liquid mixture with a certain solid concentration, which is continuously withdrawn from the device. In area II the supply of bulk goods has ended. In addition, since the supply of liquid is temporarily interrupted in order to lower the level in the dispersing device from the height h ₁ to the height h ₂ , the solids concentration of the mixture entering the delivery line does not change yet. In area III the fill level in the dispersing device has dropped so far that the stirring tool is no longer immersed in the mixture. As the solid particles begin to rise, the concentration of the mixture removed temporarily drops slightly before the ascending solid particles also enter the delivery line. The solids concentration then drops to zero in a very short time.

The dash-dotted line shows for comparison the decrease in the solids concentration when using the method previously described in the prior art, in which the fill level in the container is kept at the height h ₁ during the bypass. After the solids supply is switched off, the relative solids content exponentially decreases and approaches the value zero asymptotically.

Reference list

1

container

2nd

cover

3rd

Supply line for liquid

4th

Feed line for solid particles

5

wave

6

Agitator

7

Valve

8th

Cell wheel lock

9

Slider

10th

Supply line

11

ground

12th

Outlet

13

Conveyor line

14

pump

15

Pipe section

16

Level indicator

Claims (8)

1. A method for reducing the solids concentration in a dispersing device, in particular a stirred tank, from which a mixture of a liquid and solids particles floating in this is continuously drawn off at the bottom, characterized in that the addition of solids in the dispersing device is reduced and the downward directed Flow rate of the liquid in the dispersing device is adjusted so that it exceeds the rate of buoyancy of the solid in the liquid. 2. The method according to claim 1, characterized in that the fill level in the disperser device lowered by changing the addition of liquid to a predetermined level becomes. 3. The method according to claim 2, characterized in that the per unit time from the Dispersed device withdrawn volume flow of mixture of liquid and solid is kept constant. 4. The method according to any one of claims 1 to 3, characterized by a turbulent flow in the disperser. 5. Device for carrying out the method according to one of the preceding claims, comprising a bottom side with an outlet ( 12 ), in a delivery line ( 13 ) emptied container ( 1 ) with openings for the addition of liquid and solid, the outlet ( 12 ) of the container ( 1 ) is followed by an essentially vertical pipe section ( 15 ) opening into the delivery line ( 13 ) and suitable means ( 16 ) are provided for measuring the fill level in the pipe section ( 15 ). 6. The device according to claim 5, characterized in that means ( 6 ) for mixing the liquid and the solid particles are arranged in the container ( 1 ). 7. The device according to claim 5 or 6, characterized in that the tube section ( 15 ) has a cylindrical shape. 8. Device according to one of claims 5 to 7, characterized in that the largest horizontal cross-sectional area of the pipe section ( 15 ) is larger than the cross-sectional area of the subsequent conveyor line ( 13 ).