DE102011077877A1 - Stirrer of standing stirred tank for suspending substrates, has lower stirring plane stirring blade with external end that is rotated in clockwise direction at right angle - Google Patents

Abstract

The stirrer (2) has flat elongated stirring blades (3-6) that are attached perpendicular to rotational axis (7). The angle of incidence of the flat elongated stirring blades with respect to a stirring plane is 30-60[deg] . The stirring blade (6) of lower agitation plane with external end (8) is rotated in clockwise direction at an angle of 90[deg] . The length and width of the stirring blades of different stirring plane is different.

Description

The invention relates to a stirrer for mixing and homogenizing solids, such as corn silage or clover grass, and for dispersing gases in medium to high viscosity media.

In such stirrers complete homogenization of the solids and a high dispersion of gases in a highly viscous medium in the shortest possible time to be achieved.

In practical operation, the addition of solids or substrates usually takes place at the edge or in the outer third of the cross section of the container containing the medium. This uneven use of solid additionally complicates the homogenization of the solids in a high-viscosity medium.

The font AT 352 690 describes a stirrer in which each stirring blade carried by a stirring arm arranged on the stirring shaft consists of two or more individual blades which are spaced apart on a plane perpendicular to the central axis of the stirring arm. The individual sheets influence each other in such a way that fluidically interference effects between them occur. The disadvantage of this stirrer is that it has been designed for an axial downward direction and thus impedes the mixing in of solids or the dispersion of gases.

The DD 283 338 A5 relates to a stirrer, which are arranged at equal intervals on the stirring axis in odd total number of Rührblattebenen two circular stirring blades. This stirrer is intended to produce a homogenization in a high-viscosity medium in that an agitating plane generates an opposite axial flow than the agitating plane above / below this agitating plane. This stirrer has the disadvantage that the stirring blades do not cover the edge region of the container and the energy input through the opposing large-surface stirring blades is very high.

In DE 42 19 733 A1 is described a multi-stage agitator, which has only an employed, radially tapered stirring blade per Rührebene. The stirrer produces an axial downward movement and thus a funnel shape of the medium, in which the solids collect and can only be homogenized poorly.

The font DE 60 2005 000 650 T2 describes a stirrer with stirring blades arranged radially to the axis of rotation, which are attached to the stirrer shaft via a stirring arm, with an angle of incidence in the direction of rotation and additional angled segments at the top and bottom of the stirrer blades. This stirrer has relatively narrow and very high stirring blades, which only partially produce the desired flow and additionally have a high energy input.

The font JP 56-152732 discloses a helical blade stirrer with four stirring blades per stirring plane and with counter-rotating spiral stirrers to improve the downward movement at the edge of the container. This stirrer requires a high energy input.

In US 5,791,780 For example, a stirrer with asymmetrical, concavely curved stirring blades for dispersing gases in a liquid is described. However, this stirrer is only partially suitable for mixing in solids.

In most known stirrers, the generated downflow in the center of the container creates a funnel into which the solids added to the rim do not enter. The added solids or substrates float on the liquid surface and can not be homogenized to the desired extent. The dispersion of gases can only be achieved incompletely with the known stirrers, since a gas-generated upward movement at the edge of the container discharges the introduced gas quite quickly.

At present, compulsory mixers are sometimes used in biogas technology, in which the solids of the freshly supplied substrate are to be mixed with the highly viscous medium in a locally highly turbulent flow predetermined by a flow channel. The energy requirement for this is very high. The essentially consisting of a fixed to a console and aligned transversely to the container agitator with surrounding flow channel existing compulsory mixer generated in the container a flow through which the introduced air to be distributed. However, the container flow is often not sufficient for highly viscous media to mix the entire container contents, since the energy of the turbulent flow is completely dissipated in this case after a short run length. Therefore, it is regularly necessary for larger containers to install on the opposite side of the container a so-called drive stirrer, which ensures complete mixing of the container. The compulsory mixer and the drive stirrer are usually driven at intervals due to the large power consumption, so that this is only active when entering air and / or the entry of solids. The disadvantage of this technique is further that the compulsory mixer generates only a limited throughput and thus takes the stirring of solids much time; this is especially true for corn silage and clover grass. Another disadvantage is the limited feed radius, so that the solids are always introduced in the vicinity of the compulsory mixer have to. The generated flow of the compulsory mixer in the container is irregular, uneven and weak.

Other stirrers often used for gas introduction are disc stirrers. A disk stirrer generates a flow radially to the stirring axis. As a result, vortices are created above and below the stirrer, through which the gas is dispersed. In highly viscous liquids, these stirrers can not be used due to the high energy absorption and their short range.

Most of the stirring arrangements described in the prior art have the disadvantage that they are suitable either only for the dispersion of gases or for suspending solids in liquid media or for homogenizing viscous media in other viscosity media. Furthermore, these stirrers do not have the desired flows to stir the "light" solids into the high viscosity medium.

However, it is essential and therefore the object underlying the invention that both solids are stirred into a highly viscous medium and homogenized and gas bubbles are evenly distributed in the medium. In addition, the stirrer should work with a low energy input.

The object is achieved by a stirrer having the features specified in claim 1. The other claims give expedient embodiments of the inventive solution again.

According to the stirrer for standing stirred tank for suspending substrates and their homogenization and, if necessary, for dispersing gases in medium to highly viscous media, which has at least two Rührebenen and at least two attached to a rotation axis stirring blades per Rührebene, characterized in that the flat elongated blades are arranged perpendicular to the axis of rotation of the stirrer, have an angle between 30 ° and 60 ° to the stirring plane and against the direction of rotation and that the stirring blades of the lowest stirring plane at its outer ends, seen in its longitudinal extent, are rotated clockwise.

In order to allow an under stirring of the solids and a dispersion of gases with high efficiency, a flow is generated by the employment of the stirring blades, which generates a downward movement at the edge of the container. For this purpose, the flow in a plane which is located in the middle between the container wall and the stirring axis of the container, contrary to known central stirrer, directed upward. On the surface, the medium is thereby pushed upwards and finally forcibly outwards.

At the stirrer shaft are at least two Rührebenen. An agitating plane contains at least two stirring blades, which have an angle of attack between 30 ° and 60 °. The stirring blades are evenly distributed on the agitator shaft in the circumference. The stirring shaft is a rigid, rod-shaped drive shaft of any length and any diameter, which may have different cross sections, but preferably has a round cross section.

When using more than one scrub layer, the scrub layer spacing should not be less than 0.06 × container diameter and not over 0.13 × container diameter. If there are too few scrubbing layers, the active principle no longer works; if you have too many scrubbing levels, the desired saving effect is no longer available or the energy input is too high.

The diameter of the stirrer should be chosen so that the active principle is maintained, but the energy input is not too high. Priority is to choose a stirrer diameter between 0.5 and 0.8 × container diameter.

The Rührebenen are, depending on the number of stirring blades per Rührebene seen in the direction of the drive shaft, rotated by 30 ° to 90 ° against each other.

Advantageously, the stirring blades of the lowermost stirring plane are at their outer ends, seen in their longitudinal extent, rotated in a clockwise direction relative to the plane of the other stirring blade by 90 °.

The lengths and / or widths of the stirring blades of a stirring plane may be different from those of another stirring plane.

The invention will be explained below using an exemplary embodiment with reference to the figures in the drawings.

In the drawings show:

1 : a stirrer with four stirrer levels in a container in side view,

2 : the stirring blades in a plan view,

3 : the shape of the stirring blades,

3a) : the top three levels,

3b) : the lowest level,

4 : the flow pattern of the stirrer.

As in 1 To see, are in the container 1 used stirrer 2 in the upper three levels the stirring blades 3 . 4 . 5 and in the bottom fourth level, the stirring blades 6 at the axis of rotation 7 arranged.

The plan view of the stirrer according to 2 shows the spatial distribution of the stirring blades 3 to 6 The four levels, it can be seen that the stirring blades are offset by 45 ° over the circumference of the stirrer against each other.

In 3a is a stirring blade 3 the top three levels and in 3b a stirring blade 6 the lower level shown. Out 3b is the twist 8th at the end of the stirring blade 6 to detect 90 °.

4 gives the flow pattern in the medium when using the stirrer according to the invention again. As can be seen, the flow runs in the central region on the axis of rotation 7 and on the container inner wall vertically downwards. In the middle area of the stirring blades, the flow reverses into a flow upwards. The fact that no solid deposits form at the bottom of the inner wall of the container, is the twist 8th at the end of the lower stirring blades 6 responsible. As practical experiments have shown, the upwardly flowing medium forms a curvature on the surface of the medium, which can be regarded as proof of the intensity of the flows and as a prerequisite for intensive homogenization of the solids in the medium.

By continuous stirring in the laminar flow field, a uniform and constant flow is produced with the stirrer according to the invention with very little expenditure of energy. This eliminates the very high torque when starting a stirrer and thus also a peak load. Energy losses due to the turbulent energy dissipation are avoided. Overall, the stirrer, compared to the prior art stirrers, leads to a reduction of the energy input with much more reliable and homogeneous mixing of solids.

LIST OF REFERENCE NUMBERS

1

 container

2

 stirrer

3

 Stirring blade of the upper three levels

4

 Stirring blade of the upper three levels

5

 Stirring blade of the upper three levels

6

 Stirring blade of the lower fourth level

7

 axis of rotation

8th

 twisting

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• AT 352690 [0004]
• DD 283338 A5 [0005]
• DE 4219733 A1 [0006]
• DE 602005000650 T2 [0007]
• JP 56-152732 [0008]
• US 5791780 [0009]

Claims (6)

Stirrer for standing stirred containers for suspending substrates and homogenizing them and for dispersing gases in medium to high-viscosity media, which has at least two stirring planes and at least two at one axis of rotation ( 7 ) attached stirring blades ( 3 to 6 ) each Rührebene, characterized in that the flat elongated stirring blades ( 3 to 6 ) perpendicular to the axis of rotation ( 7 ) of the stirrer ( 2 ), have an angle of attack between 30 ° and 60 ° to the stirring plane and counter to the direction of rotation and that the stirring blades ( 6 ) of the lowest stirring plane at its outer ends ( 8th ), seen in their longitudinal extent, are twisted in a clockwise direction. Stirrer according to claim 1, characterized in that the distance of the Rührebenen each other is 0.06 to 0.13 × container diameter. Stirrer according to claim 1 or 2, characterized in that the stirrer diameter is 0.5 to 0.8 × container diameter. Stirrer according to one of the preceding claims, characterized in that the stirring blades ( 3 to 6 ) of the stirring planes, in the direction of the axis of rotation ( 7 ) are rotated between 30 ° and 90 ° relative to the stirring blades of the previous or subsequent stirring plane. Stirrer according to one of the preceding claims, characterized in that the stirring blades ( 6 ) of the lowest stirring plane at its outer ends ( 8th ), seen in their longitudinal extent, are rotated clockwise by 90 °. Stirrer according to one of the preceding claims, characterized in that the lengths and / or widths of the stirring blades ( 3 to 6 ) of a Rührebene different from those of another Rührebene are different.

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