EP0526392B1 - Mixing-in device for small amounts of fluid - Google Patents

Abstract

The device for mixing in a small amount of fluid (1) into the main stream of another fluid (2) in a main duct has a nozzle injection system (3) and a static mixing element (4, 5) downstream thereof. The input cross section (F) of the mixing element is subdivided into subareas (F1, F2, F3, F4). The nozzle injection system comprises metering main pipes having a plurality of directed metering orifices (21). The flow rates through the metering orifices are proportional to the part streams through the corresponding associated subareas (F1, F2, F3, F4). This results in very uniform through-mixing over a short distance and with only a small pressure drop. The mixing-in device is particularly suitable for Denox installations. <IMAGE>

Description

The invention relates to a device for mixing a small amount of a fluid into a main stream of another fluid.

Mixing devices are known from CH-A-581493 and DE-B-2412454.

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. By using static mixers, intensive mixing can be forced over short distances, but this is associated with an increased pressure drop. Conventional mixing devices with complicated, adjustable injection systems or with simple injection systems and static mixers, however, cannot meet the high demands on the mixing qualities 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.

Very good homogeneity (with a maximum deviation of less than 5% based on the mean value) must be achieved so that the neutralization reaction takes place completely in the subsequent catalyst on the one hand, in order to be able to meet low nitrogen oxide limit values and 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 overcome these disadvantages and to provide a simple mixing device which ensures a high mixing quality over the entire channel cross section and in a wide range of load cases with a low pressure drop and over short distances. According to the invention, this object is achieved by a mixing device according to claim 1. The dependent claims relate to advantageous embodiments and further developments of the invention.

The division of the inlet cross-section of the mixing element into partial areas defined by the mixer structure on the one hand and the assignment of the directed metering openings to these partial areas on the other hand achieve a combined, particularly good homogenization effect if the flow rates through the metering openings are set proportionally to the partial flows through the corresponding partial areas. In the case of a particularly simple assignment, the total cross-sectional area of the metering openings assigned to each partial area can be directly proportional to this partial area. Very simple directional metering openings can be used as cylindrical bores the wall of the main metering tube or as outlet tubes. The metering openings can advantageously be directed towards the interior of the subchannels. Particularly simple and inexpensive arrangements for partial areas defined by layers can only have a main metering tube running perpendicular to the layer planes. In order to achieve uniform metering with all metering openings of a main metering tube, the cross section of the main metering tube can be at least twice as large as the sum of the cross-sectional areas of its metering openings. For the lowest possible pressure drops, the subchannels of the mixing element can preferably have an angle of 25 ° to 35 ° to the main flow direction. Particularly intensive turbulence mixing can also be achieved with a larger angle of 45 °, for example.

The good homogenization according to the invention can be achieved with very short mixing elements, for example with a length of the mixing element which is one to two times as large as the distance between two adjacent crossing points of the mixing element. Further mixing devices with particularly high mixing qualities with a low pressure drop can have a free post-mixing section in the main channel after the first mixing element, which is two to six times as large as the distance between adjacent crossing points of the mixing element or one to three times as large as the smallest diameter of the main channel. A second mixing element can also be arranged after the post-mixing section. And at least two mixing elements can be arranged in the main channel, which have different orientations of their subchannels. 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, c

ein Beispiel einer erfindungsgemässen Einmischvorrichtung in drei Ansichten;

Fig. 1d

von V-förmigen Mischerlagen gebildete Strömungskanäle;

Fig. 2

zwei Lagen eines statischen Mischelements mit sich kreuzenden Teilkanälen;

Fig. 3a, b, c

ein Beispiel mit drei Hauptrohren;

Fig. 4

gerichtete Dosieröffnungen als Bohrungen;

Fig. 5a, b, c

ein Beispiel mit einem Hauptrohr und auf die Mischelementlagen als Teilflächen gerichteten Dosieröffnungen;

Fig. 6a, b, c, d

ein Beispiel mit stegförmigen Mischerlagen und rechteckigen Teilkanälen;

Fig. 7a, b, c

ein Beispiel mit rundem Hauptkanalquerschnitt;

Fig. 8

eine Einmischvorrichtung mit Nachmischstrecke und nachgeordnetem zweitem Mischelement.

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

1a, b, c

an example of a mixing device according to the invention in three views;

Fig. 1d

flow channels formed by V-shaped mixer layers;

Fig. 2

two layers of a static mixing element with intersecting partial channels;

3a, b, c

an example with three main tubes;

Fig. 4

directional metering openings as bores;

5a, b, c

an example with a main pipe and metering openings directed towards the mixing element layers as partial surfaces;

6a, b, c, d

an example with bar-shaped mixer layers and rectangular sub-channels;

7a, b, c

an example with a round main duct cross-section;

Fig. 8

a mixing device with post-mixing section and downstream second mixing element.

1 shows a mixing device according to the invention in three views with a injection system 3 for an admixing fluid 1 into another fluid 2 in a main channel 7 and a static mixing element 4 connected downstream in the main flow direction Z. As can be seen in FIG. 1a, the inlet cross section F is divided into partial areas F3, F4 which are defined by the partial channels 15, 16 formed by the mixing element 4. Such a subchannel 15 of a mixing element consisting of V-shaped layers 11 (for example Sulzer SMV mixer) is shown in FIG. 1d. These form the two walls 13 of the subchannel 15 with a cross-sectional area F3, while on the open side the boundary 14 is defined by the layer plane 12. The combination of the layers 11 is shown in perspective in FIG. 2. Two layers 11 of a corrugated mixer structure here form intersecting subchannels 15 with intersection points 17. F3 is the input cross-sectional area of a subchannel 15 in a layer 11, corresponding to the edge channels in FIG. 1a. Two inner subchannels 15 of adjacent layers each add up to an inner subchannel 16 with double cross-sectional area F4 = 2 F3, which is delimited by the channel walls 13 (see FIG. 1a). The mixing element has four layers which divide the input cross-section F into ten partial channels 15 at the edge with partial areas F3 and into seven inner partial channels 16 with partial areas F4. The assigned injection system 3 consists of two main metering tubes 20 running parallel to the layer planes 12, with metering openings 21 directed towards the partial areas F3, F4 corresponding partial areas are as proportional as possible. If the flow velocity in the main channel 7 is the same over the entire input cross section F, the flow rate through the assigned metering openings is set proportionally to the partial areas, for the sake of simplicity mostly by the total cross-sectional area Q3, Q4, that of each partial area F3, F4 assigned metering openings is proportional to these partial areas. Thus, in the example of FIG. 1, an outlet pipe 22 with a cross-sectional area Q3 is assigned to each outer subchannel 15 with partial area F3 as a metering opening, while two outlet pipes 22 with a total cross-sectional area Q4 = 2 Q3 are provided for each inner subchannel 16 with double area F4. This results in a total of 24 metering openings or outlet pipes 22, each with a cross-sectional area Q3 for the input cross section F = 24 F3. 1b shows the distance P between two adjacent crossing points 17 in the main flow direction Z. The length S of the mixing element 4, which is kept as small as possible, corresponds, for example, to 1 to 2 times the distance P. In this example, S is approximately 1.3 times P and in FIG. 4 the length S is P. Thus, with minimal Pressure loss achieves a good combined homogenization effect, especially if a free post-mixing section N (FIG. 8) follows the mixing element 4, which advantageously corresponds to the distance P 2 to 6 times. In the example of FIG. 3, the same input cross section with the subchannels F3, F4 is combined with another injection device. Three main metering tubes 20 run here transversely to the layers 11 with outlet tubes 22 and 23. Either two outlet tubes 22 with cross-sectional areas 1/2 Q3 or 1 outlet tube 23 with cross-sectional area Q3 are assigned to the outer partial channels 15 with partial areas F3. Either 4 outlet pipes 22 with surface 1/2 Q3 or 2 outlet pipes 23 with surfaces Q3 are assigned to the inner partial channels 16 with partial surfaces F4. The total of 24 outlet pipes 22 and the 12 outlet pipes 23 have a summed cross-sectional area of all metering openings of 24 Q3, which corresponds to the inlet cross section F of 24 F3.

In the example of FIG. 5 with a main pipe 20 running transversely to the layer planes 12, the partial areas F1 are defined by the 10 mixer layers 11: F1 = F / 10. The uppermost and lowermost outlet pipes 24 have twice the cross-sectional area of the inner outlet pipes 23. The inner partial surfaces F1 are each assigned 3 metering tubes 23 with a cross-sectional area of 3 x 1/3 Q1 = Q1 and the top and bottom partial surfaces F1 each have an outlet tube 23 with 1/3 Q1 and an outlet tube 24 with 2/3 Q1, which again results in a total cross-sectional area Q1. The total of 28 outlet pipes 23 and 24 here have a total cross-sectional area of 10 Q1 corresponding to the total cross-sectional area F = 10 F1.

It is important that the metering openings 21 or the outlet pipes 22, 23, 24 are always directed towards the interior of partial channels 15, 16 of the mixing element 4 and not towards channel walls 13 or crossing points 17.

As illustrated in Fig. 4, the directed metering openings 21, e.g. as bores in the main pipe 20, a length L that is at least half as large as its diameter D. In the outlet pipes 22, 23, 24, L is usually larger than D.

6 shows a further example with a static mixing element which consists of crossed rectangular plates or webs which are connected to one another in the layer planes 12 at the crossing points 17. In this way, intersecting, rectangular partial channels 15 with cross-sectional areas F3 are formed, which are delimited on the closed two sides by a channel wall 13 and on the two open sides 14 by the layer planes 12. The main channel cross section F is divided into 20 partial areas F3 of the subchannels 15 of equal size, each Partial area F3 is assigned a directed outlet pipe 22 with cross-sectional area Q3.

The main channel 7 in FIG. 7 has a circular cross section F. 5 layers 11 divide this area F into approximately 5 equally sized partial areas F2. Each partial area F2 is assigned a total cross-sectional area Q2 of the outlet pipes, the three inner layers and partial areas F2 each having three outlet pipes 24 with 1/3 Q2 and the two outer layers 2 outlet pipes 23 with 1/6 Q2 and an outlet pipe 24 with 1/3 Q2 are assigned.

Fig. 8 shows a mixing device after a sheet in the main channel 7. The layer planes of the first mixing element 4 are placed in the direction of the sheet for the purpose of rapid inhomogeneity compensation. This is followed by a free post-mixing section N, which is approximately twice as long as the mixing element 4. After the post-mixing section N is followed by a second mixing element 5, the layers of which are oriented perpendicular to the layers of the mixing element 4.

The cross-section of each main metering tube should be at least twice as large as the summer of the cross-sectional areas of all metering openings of a main metering tube. A total of between 20 and 100 metering openings 21 should be provided.

Claims (16)

1. Device for mixing a small quantity of a fluid (1) into a main flow of another fluid (2) in a main channel, with an injection system (3) and at least one static mixing unit (4, 5) arranged downstream and filling the cross-section of the main channel, wherein the or each static element is built up from layers (11) with sub-channels and the sub-channels of adjacent layers cross one another and are open to one another, wherein the inlet cross section (F) of the mixing unit is divided into sub-areas (F1, F2, F3, F4), and this division is defined by layers of the mixing unit (F1, F2) or by sub-channels (F3, F4) formed by the mixing unit, wherein the injection system consists of at least one main metering pipe (20) with a plurality of metering openings (21) which are directed at the sub-areas and the length L of which is at least half as great as their diameter D, and the metering openings are associated with the sub-areas in such manner that the flow quantities through the metering openings are substantially proportional to the component flows of the main flow through the corresponding sub-areas (F1, F2, F3, F4).
2. Mixing device according to claim 1, characterised in that the total cross-sectional area (Q1 to Q4) of the metering openings associated with each sub-area is proportional to this sub-area (F1 to F4).
3. Mixing device according to claim 1 or 2, characterised in that the directed metering openings (21) consist of cylindrical bores in the wall of the main metering pipe.
4. Mixing device according to claim 1 or 2, characterised in that the directed metering openings are formed as outlet pipes (22, 23, 24).
5. Mixing device according to one of the preceding claims, characterised in that the metering openings are directed at the inside of sub-channels (15, 16).
6. Mixing device according to one of claims 1 to 5, characterised in that the sub-areas (F1, F2) are defined by layers and just one main metering pipe is provided which extends perpendicularly to the layer planes (12).
7. Mixing device according to one of claims 1 to 5, characterised in that the sub-areas (F3, F4) are defined by sub-channels, and at least two main metering pipes (20) are provided.
8. Mixing device according to one of the preceding claims, characterised in that the cross section of each main metering pipe is at least twice as great as the sum of the cross-sectional areas of all the metering openings of a main metering pipe.
9. Mixing device according to one of the preceding claims, characterised in that a total of between 20 and 100 metering openings (21) are provided.
10. Mixing device according to one of the preceding claims, characterised in that the sub-channels (15) of the mixing unit are disposed at an angle W of between 25° and 35° with respect to the main flow direction Z in the main channel.
11. Mixing device according to one of the preceding claims, characterised in that the intersecting sub-channels (15) in the main direction of flow Z define at least two adjacent intersection points (17) disposed at a spacing P and the length S of the mixing unit is between one and two times as great as the spacing P.
12. Mixing device according to one of the preceding claims, characterised in that the first mixing unit (4) is followed by a free post-mixing section N in the main channel which is between two and six times large as the spacing P of adjacent intersection points of the mixing unit.
13. Mixing device according to one of the preceding claims, characterised by a free post-mixing section N following the first mixing unit which is between one and three times as large as the smallest diameter A of the main channel.
14. Mixing device according to claim 12 or 13, characterised in that a second mixing unit (5) is arranged subsequent to the post-mixing section N.
15. Mixing device according to one of the preceding claims, characterised in that at least two mixing units (4, 5) whose sub-channels (15) point in different directions are arranged in the main channel.
16. Use of the mixing device according to one of the preceding claims in a Denox plant for mixing ammonia into to a waste-gas flow.

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