EP0526393B1 - mixing-in device - Google Patents

Abstract

The static mixing element in a flow channel (7) has at least two baffles (30) on mounts (20) at a distance from the wall of the channel. The baffles form an angle W from 10 DEG to 45 DEG with the main flow direction Z. They have different orientations, and the projection FZ of the baffles in the main flow direction is from 5% to 50% of the channel cross section F. As a result, very efficiently cross-mixing cross flows are generated in a simple manner. If dosing tubes (20, 21) are used as mounts, a very effective mixing-in device is produced. <IMAGE>

Description

The invention relates to a mixing device for mixing a small amount of a fluid into a main stream of another fluid. Simple static mixing elements with baffles are known, but they still have a very limited mixing and homogenizing effect and still cause a relatively high pressure drop. More complex static mixers, for example consisting of intersecting subchannels of fins (Sulzer SMV mixers) probably have very good mixing properties, but are often still relatively expensive to manufacture. A good mixing action is also particularly necessary when mixing a small amount of one fluid into a main stream of another fluid in a flow channel with a nozzle system. When relatively small amounts, for example less than 10%, of a gas or a liquid are added to the flow of another gas or another liquid, very long mixing sections are required in the empty tube in order to achieve homogeneous mixing. Conventional mixing devices with complicated adjustable injection systems are not able to meet high demands on the mixing quality in a wide load range and, above all, even with very low volume flow ratios. In Denox plants, for example, denitrification is carried out by adding gaseous ammonia to the flue gas stream in a very low ratio of 1: 1000 to 1: 10000. A very good homogeneity (with a maximum deviation of less than 5% based on the mean value) must be achieved so that the reaction of NH3 with NOX takes place as completely as possible everywhere in the subsequent catalyst, in order to be able to comply with low nitrogen oxide limit values and also on the other hand no excess ammonia breaks through. The stoichiometric mixing ratios must therefore be met uniformly and continuously over the entire channel cross section. This mixing quality must also be achieved over short distances and with a low pressure drop, for which known mixing devices are not yet sufficient.

It is therefore an object of the present invention to achieve a very good mixing effect with a relatively low pressure drop using the simplest possible means and to achieve advantages over the known mixer types in the sum of all properties, and it is another object to create a simple mixing device with the static mixing element, which ensures a high mixing quality across the entire duct cross-section and in a wide range of load cases with a low pressure drop and short distances.

According to the invention, these objects are achieved by a mixing device According to claim 1. By attaching baffles to brackets at a distance from the channel wall, the baffles are completely flowed around on the front and rear side as loss-free as possible, thus creating an efficient deflection and swirling in the direction of the angle W. By arranging a few guide surfaces with different orientations, intersecting partial flows are generated in the radial direction in the simplest possible manner and with little pressure loss. A relatively large turbulence cone is generated in the main stream by the guide surfaces and deflected in the direction of W1. At the same time, the metering tube feeds the admixing fluid in the direction of its axis at the same location into this deflected turbulence cone. This forces an immediate intensive mixing of the two fluids and, due to the local deflection in the directions W, the at least two oppositely oriented guide surfaces, a cross flow is generated, which causes intensive mixing over the entire cross section of the flow channel. Overall, the device according to the invention thus achieves both intensive mixing of the two fluids in the region of the injection and good homogenization over the entire channel cross section with simple means and a low pressure drop. The dependent claims relate to advantageous developments of the invention. The projection FZ of the guide surfaces in the main flow direction can only be 5% to 25% of the channel cross section and thus achieve an optimal mixing with very little effort and pressure drop. The guide surfaces can be rectangular, triangular, trapezoidal, round, kinked, curved, cylindrical and also perforated, they can be against each other be staggered and also cover the entire channel cross-section in a substantially uniform manner. At least two consecutive mixing elements of this type can form a mixer arrangement, the elements being able to have guide surfaces which are offset or rotated relative to one another. A post-mixing section can be provided after a mixing element, which further increases the mixing effect.

In particularly effective designs, the guide surfaces can be at least ten times as large as the outlet cross section of a metering tube, and the angle W2 to the tube axis can be between 0 ° and 15 °. The devices according to the invention are also particularly well suited for mixing ammonia into the flue gas stream of a denitrification plant.

Fig. 1a, b

ein Mischelement mit zwei Leitflächen an einer Halterung in zwei Ansichten;

Fig. 2

ein Beispiel mit mehreren Leitflächen, welche den Kanalquerschnitt F regelmässig überdecken;

Fig. 3a bis d

Beispiele von Leitflächenformen;

Fig. 4a, b

Beispiele mit unterschiedlichen Leitflächen in runden Strömungskanälen;

Fig. 5

eine Mischeranordnung mit Leitflächen in zwei Querschnittsebenen des Strömungskanals;

Fig. 6a, b

Beispiele von aus Blechstreifen gestanzten Leitflächen mit Halterungen;

Fig. 7

eine Mischeranordnung mit zwei Mischelementen und einer Nachmischstrecke;

Fig. 8a, b

eine erfindungsgemässe Einmischvorrichtung mit zwei Dosierrohren als Halterungen und zwei Leitflächen in zwei Ansichten;

Fig. 9a, b

ein weiteres Beispiel mit einem Dosierrohr und zwei Leitflächen;

Fig. 10

ein Beispiel mit mehreren Dosierrohren und Leitflächen;

Fig. 11a, b, c, d

verschiedene Beispiele von Leitflächen an Dossierrohren;

Fig. 12

eine Einmischvorrichtung mit Dosierrohren und Leitflächen in zwei Ebenen.

The invention is explained in more detail below with reference to figures and exemplary embodiments. It shows:

Fig. 1a, b

a mixing element with two guide surfaces on a holder in two views;

Fig. 2

an example with several baffles that regularly cover the channel cross-section F;

3a to d

Examples of control surface shapes;

4a, b

Examples with different baffles in round flow channels;

Fig. 5

a mixer arrangement with baffles in two cross-sectional planes of the flow channel;

6a, b

Examples of guiding surfaces stamped from sheet metal strips with holders;

Fig. 7

a mixer arrangement with two mixing elements and a post-mixing section;

8a, b

a mixing device according to the invention with two metering tubes as holders and two guide surfaces in two views;

9a, b

another example with a metering tube and two guide surfaces;

Fig. 10

an example with several dosing tubes and guide surfaces;

11a, b, c, d

various examples of guide surfaces on dossier tubes;

Fig. 12

a mixing device with metering tubes and guide surfaces in two levels.

1 shows a mixing element 4 with two guide surfaces 30 fixed to a holder 20 in a flow channel 7 in two views. The rectangular guiding surfaces are offset from one another and each by an angle W of, for example, 30 ° to the main flow direction Z of the fluid 2 inclined with opposite orientations. The guide surfaces 30 produce corresponding, in the directions 16, 17 deflected, turbulent flow cones 26, 27, which intersect offset. The projection FZ of both guide surfaces in the flow direction Z is less than 50% of the cross-sectional area F of the flow channel (FIG. 1b). Even with a proportion FZ of, for example, 10% to 20% of F, turbulent, intensely mixing cross flows can be generated according to the invention.

2 shows an analogous example with a plurality of guide surfaces 30 on two brackets 20 which regularly cover an entire channel cross section F with (in the figure) alternating upward and downward partial streams 16, 17 of the cross currents generated. The guide surfaces 30 can have different shapes according to FIGS. 3a to d and, for example, have a trapezoidal shape 31 or around 32 or can be perforated 24. The holder is formed here from tubes which have a relatively high inherent rigidity. Bracket and guide surface can also be formed from one piece, for example according to FIG. 3c as a bent stamped part 33 welded to the channel wall, in which the narrow extension 23 of the wide guide surface 30 serves as a holder. A similar, curved version 34 is shown in Fig. 3d. 4a with two smaller guide surfaces 35 pointing to the left and an approximately twice as large central guide surface 36 facing to the right, FIG. 4b shows a version with two different guide surfaces 37, 38.

The bracket can also have reinforcements and stiffeners, particularly for high flow velocities and heavy loads on the guide surfaces. Together with the guide surfaces, these can form lattice-like or truss-like structures, as shown, for example, with the struts 22 in FIGS. 4b and 5. The bracket can also consist of ropes on which the guide surfaces are set like sails in the desired optimal direction W.

FIG. 5 shows a mixer arrangement with guide surfaces in two cross-sectional planes 41, 42. The guide surfaces of plane 42 are offset from those of the first plane 41. They can also be twisted against one another, for example by 90 °. The arrangement of the guide surfaces 30, 39 in one plane corresponds to the illustration in FIG. 2, but here larger rectangular guide surfaces are used with a total surface FZ (one plane) projected in the Z direction, which amounts to 50% of the cross-sectional area F. . 5 can be punched and folded from sheet metal strips according to FIG. 6a very easily, inexpensively and without cutting losses. The guide surfaces 30 and 39 are alternately bent to one or the other side, while the remaining strip 21 serves as a holder 20. Analogously to this, the guide surface arrangement of FIG. 2 can also be produced from a sheet metal strip by trapezoidal toothed punching. This creates two rows of guide surfaces 30, 31 with brackets 20 from a sheet metal strip.

7 shows a mixer arrangement with two mixing elements 3, 4, with at least the first mixing element 3 being followed by a post-mixing section N which enables further cross-mixing by the turbulent, intersecting partial flows generated in the mixing element. The mixing elements 3, 4 are here rotated 90 ° relative to each other.

The arrangement of FIGS. 8a, b shows a mixing device according to the invention with two metering tubes 21 on a main tube 20 as holders at the outlet openings 28 of which a guide surface 30 is attached at an acute angle W to the main flow direction Z. The length L of the metering tubes 21 is at least as large as their diameter D. The guide surfaces 30 form an angle W2 of 0 ° to 45 ° to the tube axis 25 and are oriented in opposite directions with respect to Z. The guide surfaces produce deflected turbulent flow cones 26, 27 of the main flow fluid 2, which intersect with the injection cones 8 of the admixing fluid 1 and thereby mix intensively. The two guide surfaces 30 and the metering tubes 21 are oriented in opposite directions with respect to Z and are arranged offset with respect to one another along the main tube 20. This creates intersecting partial flows 16, 17, which cause intensive mixing and homogenization of the two fluids 1 and 2 and across the main channel cross section.

9a, b show an example with only one metering tube 21 running parallel to the main flow direction Z, to the outlet opening 28 of which two guide surfaces 30 are attached. These guiding surfaces are again opposite oriented and offset from one another to produce intersecting partial streams 16, 17.

10 shows a further injection device with a plurality of metering tubes 21 and guide surfaces 30 on two main tubes 20 as holders, which are evenly distributed over the entire channel cross section F. As a result, the main stream is evenly divided into intersecting partial streams by the offset and oppositely directed guide surfaces. The partial flow directions 16, 17 run alternately upwards and downwards. In order to generate the largest possible intersecting partial flows, the guide surfaces 30 can be dimensioned relatively large, their total surface FZ projected in the Z direction preferably being between 5% and 50% of the cross-sectional surface F. Particularly good mixing effects with minimal pressure drop are often achieved with an area ratio of 10% to 15%.

11a to d show various examples of suitable shapes of guide surfaces on the metering tubes: rectangular 43, triangular 44, round 45 or bent as a tube piece 46.

12 shows an arrangement with metering tubes 21 as holders and guide surfaces 30 in two levels 41 and 42, the metering tubes with guide surfaces of the second level being arranged offset from those of the first level. The direction of the metering tubes with guide surfaces W in the second level can also be rotated relative to that in the first level, preferably by 90 °. In an experimental example, using mixing elements according to the invention In the form of the guide surfaces on the metering tubes, the mixing quality can be improved from 4% to just 2% concentration fluctuation.

Claims (12)

1. A device for mixing a small quantity of a fluid (1) into a main flow of another fluid (2) in a flow channel (7), the device having an injection system (3) comprising dispensing tubes (20, 21) and constructed as a static mixing element with the dispensing tubes as mounting for at least two deflectors (30), wherein at least one deflector is disposed at the outlet aperture (28) of each dispensing tube (21) at a distance from the channel wall, each deflector forms an angle W of from 10° to 45° to the main flow direction Z, adjacent deflectors are disposed with different orientations in a substantially crossing arrangement, the surface FZ of the deflectors projected in the main flow direction amounts to from 5% to 50% of the channel cross-section surface F, the length L of each dispensing tube (21) carrying a deflector is at least equal to its internal diameter D, and each deflector forms an angle W2 of from 0° to 45° with the axis 25 of the associated dispensing tube.
2. A device according to claim 1, characterised in that the projection FZ of the deflectors in the main flow direction amounts to from 5% to 25% of the channel cross-section F.
3. A device according to claim 1 or 2, characterised in that adjacent deflectors are offset from one another.
4. A device according to any of claims 1 to 3, characterised in that the deflectors are rectangular or triangular or trapezoidal.
5. A device according to any of claims 1 to 3, characterised in that the deflectors are round or bent or curved or cylindrical.
6. A device according to any of the previous claims, characterised in that the deflectors are perforate.
7. A device according to any of the previous claims, characterised in that the deflectors are disposed substantially in a cross-sectional area F of the channel.
8. A device according to claim 7, characterised by a number of deflectors distributed uniformly over the channel cross-section.
9. A device according to any of the previous claims, characterised in that the deflectors are at least ten times as large as the outlet cross-section of the dispensing tube (20).
10. A device according to any of the previous claims, characterised in that the angle W2 to the tube axis is between 0̸° and 15°.
11. Use of a device according to any of the previous claims for mixing ammonia into the flue gas flow.
12. Use according to claim 11 in a denoxing installation.

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