Apparatus for mixing a fluid with a large gas stream, especially for introducing a reducing agent into a flue gas comprising nitrogen oxides

[0001] The invention relates to a device for mixing a fluid with a large gas stream (primary stream), flowing in the gas channel, in particular for introducing a reducing agent into the flue gas, containing nitrogen oxides, with at least one nozzle lance with at least one nozzle for supplying fluid, whose axis forms an angle with the direction of gas flow and at least one flat mixer element, assigned with a distance to the nozzle, which creates an angle with the direction of gas flow, wherein flow vortices are formed on the mixer element and at least part of the liquid enters these flow vortices.

[0002] Such a device is known from DE 37 23 618 C1, wherein the reducing agent is introduced in gaseous form into a large gas stream (flue gas). A static mixing element is used to shorten substantially very long mixing paths.

[0003] In the case of SCR installations for the denitrification of flue gases (Selektive Catalytische Reduktion) from, for example, power plant furnaces with a reducing agent and catalyst, it is assumed that in the case of NH3 as reducing agent it is stored as liquefied NH3 under pressure or ammonia water (NH4OH) and pre-evaporated NH3 are injected with the stream of carrier gas into the flue gas stream and mixed with it. In the case of urea as a reducing agent, an aqueous urea solution is first produced, which, after appropriate preparation, is also injected in gaseous form into the flue gas stream.

[0004] With the known device, the mixing element is a rectangular plate extending across the width of the flue gas channel. The nozzle lance with the nozzle lies essentially to the side and parallel to the edge of the mixer plate lying against the current in relation to the direction of flow of the flue gas stream, and the nozzle stream of the reducing agent gas mixture in the form of a mixture of NH3 and carrier gas is injected laterally on the back side of the mixer element. The distribution takes place in stream vortices directly on and behind the mixing plate and through increased turbulence in the flue gas stream with mixing plate current. In the case of a large cross-section of the channel, they are provided side by side, filling the cross-section of the nozzle lances and the numerous flow sheets assigned to the nozzle lanterns.

[0005] It has also been proposed to inject ammonia water (liquid NH4OH) or urea solution without pre-evaporation directly into the exhaust gas stream on the rear side of the mixing element, the nozzle being so arranged on the rear side (windscreen side) of the mixing element that the injection direction runs parallel to the gas stream, flue gas. The nozzle stream consists of a mixture of gas and liquid droplets which are evaporated after a certain time in an environment with a temperature of about 300 ° C. There is the risk that the droplets of reducing agent together with the dust particles contained in the flue gas will lead to the formation of a concrete coating on the used or used mixer elements, load-bearing elements for the mixer element and possibly on the walls of the flue gas channel.

ΕΡ 1 962 995 Β2

The nozzle must therefore be positioned far enough away from the mixing element that the non-evaporated droplets also under the influence of backflow (vortex braids) cannot reach the mixing disk. This leads to an increase in the flue gas duct length, without built-in components, required for mixing. Additional static mixer components in the flue gas stream after injection cannot be used due to the risk of tarnish formation.

[0006] The object of the invention is to improve this type of device such that when direct injection of a liquid as a liquid, especially a liquid reducing agent, a short sludge formation is avoided with a short mixing path.

[0007] This task is solved with this type of device by that the nozzle lance is connected to the liquid supply and is equipped with at least two atomizing nozzles, inclined to the direction of gas flow and opposite to each other, and the spray nozzles are assigned to the mixing element, made in the form of a shield, and the spraying is done so that evaporated gas shares, contained in the nozzle stream, each time coming out of the spray nozzles, they enter the flow vortices, whereas the unvaporized droplet fractions due to their inertia and spraying angle do not enter the flow vortices near the mixer disk.

[0008] Spray nozzles are arranged with respect to the gas flow with or against the agitator disk.

[0009] In both embodiments, it is ensured that large, non-evaporated droplets due to their inertia largely adapt to the original axis of the stream and will not hit the mixer disk and lead to the formation of a precipitate there, while NH3 evaporated in hot the flue gas originates from the supplied liquid reducing agent stream of the flue gas and is incorporated as gas into a series of vortices developing directly behind the mixing disk. In this way, preliminary distribution is also obtained by direct injection of NH4OH.

[0010] Preferably, the mixer disk is made in a circular, elliptical, oval, in the form of a parabola, rhombus or triangle, as is known from DE 37 23 618 C1, column 2, lines 40-45.

[0011] It is expedient if the angle between the two spray nozzles is between 60 "and 120", preferably 90 ".

[0012] The mixer disk is preferably inclined at an angle in the range between 30 "to 90" to the direction of flow of the gas stream.

[0013] It is expedient if the spray nozzles are pneumatic spray nozzles with a spraying aid, preferably with compressed air or steam as the spraying aid. The fine droplet spectrum can be produced with the help of pneumatic spray nozzles.

[0014] However, pressure nozzles without an auxiliary medium can also be used as atomizing nozzles.

[0015] In order to avoid droplets falling at the exit of the nozzle, the spray nozzles can be provided with barrier or shielding air.

[0016] To optimize the droplet paths yet in terms of their positioning, the plane formed by the nozzles of the spray nozzles is inclined at an angle in the range of 0 'to 30' with respect to the flow direction of the gas stream.

[0017] The invention will then be further explained, for example, by way of figures. They present on them:

FIG. 1 three-dimensional view of a horseshoe vortex with a series of vortices, settling on a circular disk, inclined with respect to the stream at an angle ai on which the gas stream flows, Fig. 2, side view transversely to the line A-A according to Fig. 1, fig. 3, front view with view of the windshield of the disc transversely to line B-B in the view according to fig. 1, FIG. 4, a side view comparable to FIG. 2 for the first embodiment of the device according to the invention, in which the spray nozzles are arranged in relation to the gas stream with the current of the mixing disk, the cross section of the gas channel leading the stream gas fig. 5 rear view with a view to the windward side of the dial transversely to the line B - B in the view according to fig. 1, FIG. 6, a side view comparable to FIG. 4 in the case of the second embodiment of the device according to the invention, in which the spray nozzles are arranged with respect to the gas flow against the current of the agitator disk, and FIG. 7, front view with a view to the windshield disk transversely to the line B - B in the view according to Fig. 1.

[0018] The formation of vortex trains is a natural phenomenon in three-dimensional streams on the body (compare Prandtl, Oswatitsch, Wieghardt: FOhrer durch die Strómungslehre, 9th edition 1990; ISBN 3-528-28208-6, p. 229, image 4.41 and associated description).

[0019] The formation, shape and position of such vortex trains in the outlet of the mixer disks is to be first schematically shown and described on the basis of Figs. 1-3.

[0020] The circular disk 1 is inclined at an angle a relative to the flowing gas stream 2 originating in figure 1 from below. On the windward side 1a of the disc, the gas stream deflects from its main flow direction and an area of ​​overpressure is created. The partial stream 2a of the gas stream 2 flows longitudinally with a given angle under the disc. On the windscreen side 1b of the disk a vacuum area is created, which is filled by the partial stream 2b of the gas stream 2 through the edge of the disk. By changing the direction of flow at the edge of the disk, a horseshoe vortex 3 is formed with the axis 3a of the vortex, represented intermittently, spreading with the current of the disk in the form of a series of vortices with two symmetrically rotating vortices. The lateral vortices of the horseshoe vortex spread as a vortex draft, overlap with the gas stream (basic stream) and expand with the basic stream. The state of the flow inside the vortex is highly turbulent. The schematically illustrated boundary 3b of a horseshoe vortex and a series of vortices should not be understood as sharp demarcations. The position and structure as well as the opposite directions of rotation of both vortices can be determined experimentally using an appropriate measuring technique.

[0021] Other shield shapes, such as the shape of an ellipse, the shape of an oval, the shape of a parabola, the shape of a rhombus or the shape of a triangle create comparable vortices with vortex trains.

ΕΡ 1 962 995 Β2 [0022] Turbulent mixing of vortex trains and the gas stream is used to separate an almost injected gas stream evenly over a very large cross-section.

[0023] In the embodiment of the device according to the invention according to Figs. 4 and 5, two spray nozzles 4a and 4b are arranged on the head 4c of the nozzle lance 5 running into the flue gas channel R. (More than two spray nozzles can be used; pressure nozzles can also be used). The spraying nozzles are arranged on the windscreen side 1b of the preferably circular mixer disk 1 at a given distance from it. The nozzle stream, coming out of one of the nozzles 4a or 4b in each case, contains gaseous components 6a and non-evaporated droplets 6b. Both spray nozzles 4a and 4b form an angle β of 120 ° and are inclined relative to the base stream. Other angles are possible. A range between 60 'and 120 ° is preferred.

[0024] The plane covered by the nozzles 4a and 4b is not inclined relative to the base stream.

[0025] In Figures 4 and 5, the liquid reaction medium 5a is atomized by means of the atomizing aid 5c, and the nozzle jet 6 is surrounded by barrier or shielding air.

10026] In fig. 4-7 are schematically represented in addition to partial streams 2a and 2b, streams 6a (gas component of stream 6 of the nozzle) and 6b (non-evaporated droplets) of injected stream 6. The evaporated portion 6a of the injected stream adapts - as shown in the figures - to the curvatures of the base stream and is coiled to the vortex flow 3. The unvaporized droplets 6b adjust with their inertia at the selected injection angle β and thus penetrate on the windscreen side 1b of the disk 1 vortices leading to the windscreen, so that the formation of droplets from fine droplets and fine dust from flue gas is avoided.

[0027] The droplets of the partial stream 6b later evaporate in the flue gas stream and are sufficiently mixed in by the turbulence occurring there.

[0028] Partial stream 6a may also contain even the smallest droplets, which, however, evaporate quickly and therefore only slightly - if at all - contribute to the formation of a tarnish. With respect to the amount of reducing agent, partial stream 6a contains significantly more reducing agent than partial stream 6b. However, if the vortex braid does not penetrate according to the invention, the smaller partial stream 6b would, however, lead to a significant formation of coating.

[0029] In the embodiment according to Figures 6 and 7, the nozzle head is arranged with the spray nozzles 4a and 4b against the current of the mixer disk 1. The spray nozzles 4a and 4b are arranged such that the axes of the jet nozzles 6 run on both sides at a sufficient distance next to the mixer disk 1. The distance from the disk may preferably be about 0.5 m. Also in this embodiment, the droplet paths 6b penetrate the mixer disk creating directed vortices.

[0030] In the embodiment according to figures 6 and 7, the plane formed by the nozzles 4a and 4b is inclined relative to the base stream by an angle y = 20 °.

[0031] With this embodiment and with the embodiment according to Figs. 4-5, an angle of inclination y in the range of 0 ° to 30 ° is possible.

[0032] In the embodiment according to Figs. 6 and 7, it is advantageous that the upstream space of the mixer disk 1, often unused for technical reasons, can be used to position the nozzle lance 5. In addition, in this embodiment there is freedom of guiding the lance nozzle 5 irrespective of the inclination of the mixer disk 1 relative to the jet

EP 1 962 995 B2 from any direction from the wall of the K channel to the injection site, without having to carry out, as is known, a very high-throughput penetration of the mixer disk 1.

[0033] It is obvious that with large cross-sections of the channel, a plurality of mixer disks with associated spray nozzles on the cross-section of the channel can be arranged. They can also be assigned to more than two nozzles, e.g. They must be placed so that the droplet paths penetrate the vortices.

List of markers [0034] disk (mixing disk)

1a windward side of the disc b vent side of the disc gas flow

2a gas stream, partial stream on windward side 1 a of the target

2b gas stream, partial stream to the windward side 1b of the disc, horseshoe vortex and vortex train

3a vortex axis

3b outer boundary of the vortex nozzle lance

4a spray nozzle

4b spray nozzle

4c nozzle head

5a. Supplying a liquid reducing agent

5b supplying a gas spraying aid

5c Supply of barrier air or shield air. Nozzle jet

6a gas share

6b not evaporated droplets

R flue