WO2001030487A1

WO2001030487A1 - Method for reducing the solids content of a dispersion consisting of solid matter and liquid and a device for carrying out said method

Info

Publication number: WO2001030487A1
Application number: PCT/EP1999/008123
Authority: WO
Inventors: Bernhard Stark
Original assignee: Coperion Waeschle Gmbh & Co. Kg
Priority date: 1998-04-27
Filing date: 1999-10-27
Publication date: 2001-05-03
Also published as: DE19818738C2; DE19818738A1

Abstract

The invention relates to a method for reducing the solids content in a dispersion device, especially an agitated tank. The aim of the invention is to continually draw off a mixture from the bottom side of said device. The mixture consists of a liquid and solid particles raising therein. The solid matters added into the dispersion device are reduced and the flow rate of the liquid in the dispersion device is adjusted in such a way that said flow rate being directed towards the bottom exceeds the buoyancy speed of the solid matter in the liquid. A device comprising a container (1) that is provided with an outlet (12) on the bottom side thereof and can be emptied into a transport line (13) and openings for adding liquid (3) and solid matters (4) is especially useful for carrying out the inventive method. An essentially vertical pipe section (15) is arranged downstream in relation to the outlet (12) of the container (1) and leads into the transport line (13). Appropriate means (16) are provided for measuring the level in the pipe section.

Description

Method for reducing the solid concentration of a dispersion of solid and liquid and device for carrying out the method

description

The invention relates to a method for reducing the solids concentration of a dispersion of liquid and solid particles, in which the liquid and the solid particles are fed and mixed in a container, the solid particles having a lower density than the liquid and therefore tending to rise in the liquid , in which the addition of solid particles into the container and in which the addition of liquid is maintained, and a device suitable for carrying out the method.

In numerous technical processes it is necessary to mix liquids and solids intimately and to offer this mixture continuously for further processing. The dispersion of the solids in the liquid is adjusted in the desired manner by the introduction of mechanical energy, for example by stirring.

Such methods can be used in the hydraulic conveying of bulk goods, for example plastic granules. State of the art

A device for dispersing solid particles in a liquid is known from the publication "DIN standards in process engineering", page 201f., Figures 3.169 and 3.171. It consists of a cylindrical container into which solid particles and liquid are continuously fed into the nozzles arranged in the cover The prepared dispersion can also be continuously discharged from the container and fed into a conveying line via the bottom outlet. The container has a large diameter compared to the dimensions of the outlet.

The substances filled into the container are mixed with the aid of a rotating, anchor-like stirring tool, which is driven by a shaft penetrating the cover and projecting vertically into the container.

The known device is suitable for distributing a certain mass flow of solid particles sufficiently uniformly in a certain mass flow of liquid by introducing mechanical energy.

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

This method has the disadvantage, in particular when mixing in solids that float in the liquid, that the desired reduced solids concentration in the mixture does not set in practice until after a very long mixing time (which is theoretically even infinitely long). The buoyancy of the Solid particles can either arise from the fact that the solid has a lower density than the liquid or it rises due to adhering gas bubbles in the liquid.

Alternatively, the container and a subsequent delivery line can be completely emptied and then refilled by adding solid and liquid in a changed mass ratio. However, this procedure can lead to problems if the mixture is withdrawn from the container by means of a pump which is not suitable for dry running or a subsequent process does not allow the mixture supply to be interrupted.

task

The invention has for its object to reduce the time required to reduce the solids concentration in the dispersion continuously removed from the container from a predetermined value to another predetermined value.

solution

The object is achieved in that the mixing of the dispersion is interrupted, that subsequently the downward

The flow rate of the dispersion in the container is adjusted so that it exceeds the rate of buoyancy of the solid particles in the liquid and is subsequently mixed again. Alternatively, the dispersion flows through a vertical pipe section after it has been removed from the container, the addition of the liquid into the container being less than the removal of the liquid from the container, so that the fill level drops into the region of the vertical pipe section. The downward flow rate of the dispersion in the vertical pipe section is adjusted so that it exceeds the rate of buoyancy of the solid particles in the liquid. Thereafter, the addition of the liquid in the container becomes greater than its removal from the container, so that the fill level in the container rises again to the original level. Mixing then starts again.

This measure ensures that each particle is safely withdrawn from the mixture of high solids concentration contained in the container, because it is drawn downward by the liquid flow faster than it can rise as a result of buoyancy. The transition from high to low solids concentration is not gradual, but within a relatively short, predeterminable period of time. The introduction of mechanical energy into the filling of the container is interrupted during this time in order not to produce any undesirable upward flows in the filling.

The containers used to disperse solids in liquids generally have a largest diameter which corresponds to a multiple of the diameter of the delivery line. In order to set a sufficiently large, downward flow in the container, a considerable volume flow must be removed from it via the delivery line in this case.

It can therefore make sense to use a tapered container and to change the level in the container by changing the amount of liquid added Lower the taper, whereby the required flow velocity in the delivery line can be kept at a low value.

In this case, it is possible to keep the volume flow of mixture of liquid and solid withdrawn from the container constant and still increase the downward flow rate in the dispersing device to the required level. The downward flow should be turbulent, which makes the velocity profile more even and particles near the wall can be reliably detected.

To carry out the alternative method, a device is particularly suitable which has a container with means for mixing the dispersion in the container, inlets into the container for the addition of the liquid and the solid particles, a bottom outlet from the container and a delivery line downstream of the container includes.

According to the invention, a pipe section arranged essentially vertically between the outlet and delivery line is provided, the diameter d _{R of which is} significantly smaller than the diameter d _{B of} the container, means for measuring the fill level of the dispersion being provided in the pipe section.

The interior of the container generally has a largest horizontal cross-sectional area, which corresponds to a multiple of the largest horizontal cross-sectional area of the downstream pipe section.

The level in the pipe section can be measured, for example, via the hydrostatic pressure or by means of an optical level indicator. It is also conceivable to use sensors with rotating or vibrating sensors, the movements of which are impeded when immersed in the mixture. Such a device will usually have means for mixing the liquid and the solid particles in order to prevent segregation processes due to the density differences. The means can consist of an agitator, but also, for example, in a suitable supply of liquid swirling the contents of the container.

The pipe section preferably has a cylindrical shape, so that slight fluctuations in the level of the fill level in the pipe section do not lead to a change in the downward flow. However, it is fundamentally possible to also geometrically design the pipe section in a different manner, for example conically.

Usually, the largest cross-sectional area of the pipe section will be larger than the cross-sectional area of the subsequent delivery line by which

Do not increase the flow speed in the pipe section beyond the required amount and increase the effort for regulating the fill level. When using delivery lines with unusually large cross sections, however, it is conceivable that the largest cross-sectional area of the pipe section does not exceed this. In special cases, the pipe section can pass continuously into the delivery line.

characters

The figures represent an example of a device suitable for carrying out the method according to the invention. Show it:

1 shows a device according to the invention in the initial state; FIG. 2 shows the same device after lowering the fill level; FIG. 3 shows the speed ratios in the pipe section of the device according to the invention after lowering the fill level; FIG. 4 shows the change in the solids concentration over time at the beginning of the delivery line

The device shown in Figure 1 consists of an essentially cylindrical container 1, in which a mixture of liquid and solid particles is prepared. The lid 2 of the 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 solid is dependent on the adjustable speed of a metering element designed as a rotary valve 8. The Zelienradschleuse is optionally supplied 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 dR 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 _{ß of} the container 1. In 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 hi, for example by changing the supply of liquid with a constant supply of solid matter 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 procedure for reducing the concentration of the solid in the mixture to a solids content of zero is described below. Such a reduction may be necessary if the device described is part of a system for the hydraulic conveyance of bulk materials and is to be switched over to another product, for example of a different color, without emptying the delivery lines.

The bypassing process is initiated in that the supply of solids is interrupted by shutting off the supply line 10 and emptying the Zelienradschleuse 8. Then the level in the container 1 is continued by closing the valve 7 for the supply of liquid Removal of the mixture quickly lowered by the pump 14. If the fill level indicator 16 reports that the fill level has reached the height h ₂ in the pipe section 15 downstream of the container, the valve 7 is opened again and the fill level in the pipe section 15 is regulated to the height h ₂ by changing the supply of liquid, as in FIG. 2 shown. The diameter ÖR 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 occurs in the pipe section 15 at the constant delivery rate of the pump 14, the speed of which vs is greater than the rate of ascent v _{A of} the solid particles. The turbulent flow has an essentially block-shaped velocity profile, which prevents individual solid particles from rising in the channel region near the wall.

The distribution of the flow velocity vs in the pipe section 15 and the ascent velocity vs _{A of} a solid particle, which is lower, 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 increasing the amount of liquid, if further solid-free conveying is to take place temporarily, or by simultaneously adding liquid and a different colored solid to transport it to the destination. 4 shows the solid line as an example of the decrease in the solids content in the dispersing device over time when using the method according to the invention.

The normal operating state is represented in area I, 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 fill level in the dispersing device from the height hi to the height h ₂ , the solids concentration of the mixture entering the delivery line does not change yet. In the IM area, 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 the decrease in the comparison

Solids concentration when using the method previously described in the prior art, in which the fill level in the container during the bypass at the height h. is held. After the solids supply is switched off, the relative solids content decreases exponentially and approaches the value zero asymptotically. Bezugszeicheniiste

1 container

cover

Supply line for liquid

Feed line for solid particles

wave

agitator

Valve

Zelienradschleuse

Slider 0 supply line 1 bottom 2 outlet 3 delivery line 4 pump 5 pipe section 6 level indicator

Claims

claims

1. A method for reducing the solids concentration of a dispersion of liquid and solid particles, in which the liquid and the solid particles are fed to a container (1) and mixed there, the solid particles having a lower density than the liquid and therefore the tendency to rise in the liquid in which the dispersion is continuously withdrawn from the bottom region of the container, in which the addition of the solid particles into the container and in which the addition of the liquid in the container is maintained, characterized in that the mixing of the dispersion is interrupted, that subsequently the downward flow rate of the dispersion in the container is adjusted so that it exceeds the rate of buoyancy of the solid particles in the liquid and that the mixture is subsequently mixed again.

2. A method for reducing the solids concentration of a dispersion of liquid and solid particles, in which the liquid and the solid particles are fed to a container (1) and mixed there, the solid particles having a lower density than the liquid and therefore the tendency to rise in of the liquid in which the dispersion is continuously withdrawn from the bottom region of the container, in which the addition of the solid particles into the container and in which the addition of the liquid in the container is maintained, characterized in that the dispersion after its removal a vertical one from the container

Flows through pipe section (15) that the addition of the liquid into the container is less than the removal of the liquid from the container, that the fill level drops to the region of the vertical pipe section, that the downward flow rate of the dispersion in the vertical pipe section is so is set to be the lift speed of the Solid particles in the liquid exceed that afterwards the addition of the liquid into the container is again greater than the removal of the liquid from the container and that the mixture is subsequently mixed again.

3. The method according to claim 1 or 2, characterized in that the volume flow of the dispersion of liquid and solid particles discharged per unit of time is kept constant.

4. Device for reducing the solids concentration of a dispersion of liquid and solid particles for performing the method according to claim 2 with a container (1), with means (6) for mixing the dispersion in the container, with inlets (3), (4) in the container for the addition of the liquid and the solid particles, with a bottom outlet (12) from the container and with a delivery line (13), which is arranged downstream of the container, characterized in that a pipe section (15) is provided, the diameter of which d _{R is} significantly smaller than the diameter de of the container, which is arranged essentially vertically between the outlet and the delivery line and that means (16) are provided for measuring the fill level of the dispersion in the pipe section.

5. The device according to claim 4, 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).