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

0001The invention relates to a device for mixing a fluid with a large gas volume flow (basic flow) flowing in a gas channel, in particular for introducing a reducing agent into a flue gas containing nitrogen oxides, with at least one nozzle lance with at least one nozzle for the supply of the fluid whose axis forms an angle with the direction of flow of the gas flow, and at least one flat mixing element which is assigned to the nozzle at a distance and forms an angle with the direction of flow of the gas flow Mixing element, and at least some of the fluid passes into these flow vortexes.

0002Such a device is known from the <patcit id="pcit0001" dnum="DE3723618C1"><text>DE 37 23 618 C1</text></patcit> , the reducing agent being introduced into the large gas flow (flue gas) in the form of a gas. The static mixing element is used to shorten the generally very long mixing paths.

0003In the case of SCR plants for the denitrification (selective catalytic reduction) of smoke gases, eg of power plant firings by means of reducing agent and catalyst, it is customary that in the case of NH 3 as a reducing agent this is stored in the form of pressure-liquefied NH 3 or ammonia water (NH 4 OH) and pre-evaporated NH 3 with a carrier gas stream is injected into the flue gas stream and mixed therewith. In the case of urea as a reducing agent, an aqueous urea solution is first produced, which is then also gassed into the flue gas stream after suitable workup.

0004In the known device, the mixer element is a rectangular sheet extending across the width of the flue gas duct. The nozzle lance with the nozzle is located essentially laterally and parallel to the edge of the mixer plate which is upstream of the flow direction of the flue gas stream and the nozzle jet of the gaseous reducing agent in the form of the NH 3 gas mixture is laterally sprayed on the rear side of the mixer element. The distribution takes place in the flow vortexes directly on and behind the mixing plate and through the increased turbulence in the flue gas flow downstream of the mixing plate. In the case of a large channel cross-section, nozzle lances, as well as a plurality of flow plates associated with the nozzle lances, are provided next to one another.

0005It is also an injection of ammonia water (liquid NH40H) or urea solution has been proposed without pre-evaporation directly in the flue gas stream on the back of a mixer element, wherein the nozzle on the back side (lee side) is arranged of the mixing member, that the injection direction parallel to the gas stream of the flue gas. The nozzle jet consists of a mixture of gas and liquid droplets, which evaporate in the approx. 300 ° C warm environment after a certain time. There is the risk that reducing agent droplets, together with dust particles contained in the flue gases, can lead to concrete-like lining formation on the mixing device (s), support elements for the mixing element and possibly on the flue gas duct walls. The nozzle must therefore be arranged so far away from the mixer element that non-vaporized droplets can not hit the mixer disk even under the influence of backflows (vortex heads). This leads to an extension of the installation-free flue gas channel length required for the mixing. Additional static mixing elements in the flue gas stream after injection can not be used because of the risk of the formation of deposits.

0006It is the object of the invention to improve the apparatus of the invention in such a way that, in the case of direct injection of a liquid as a fluid, in particular a liquid reducing agent, in the case of a short mixing path, formation of the coating is substantially avoided.

0007This object is achieved in a device according to the invention in that the nozzle lance is connected to a supply of liquid and is equipped with at least two atomizer nozzles which are inclined towards the flow direction of the gas flow and mutually inclined to one another is guided in such a way that the vaporized gaseous components contained in the jet stream emerging from the atomizer nozzles respectively enter into the flow vortexes while the non-evaporated droplet-shaped components do not enter into the flow vortexes near the mixer disk due to their inertia and the atomizer angle.

0008The atomizer nozzles are arranged downstream of the gas flow or upstream of the mixer disk.

0009In both embodiments it is ensured that large, non-vaporized drops largely follow the original beam axis due to their inertia and can not strike the mixer disk and lead to the formation of deposits is entrained in the swirling troughs which roll behind the mixer disc. In this way, a predistribution is also achieved in the direct injection of NH.sub.4H.

0010Preferably, the mixer disc is circular, elliptical, oval, parabola, rhombic or triangular in shape as shown in FIG <patcit id="pcit0002" dnum="DE3723618C1"><text>DE 37 23 618 C1</text></patcit>, Sp.2, lines 40-45.

0011It is expedient if the angle between the two atomizing nozzles is in the range between 60 ° and 120 °, preferably 90 °.

0012The mixing disk is preferably inclined at an angle in the range between 30 ° and 90 ° to the flow direction of the gas flow.

0013It is expedient if the atomizer nozzles are 2-substance nozzles with an atomizing auxiliary medium, preferably with compressed air or water vapor as atomizing auxiliary. A fine droplet spectrum can be generated with 2-substance nozzles.

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

0015To a. The spraying nozzles can be equipped with blocking or fogging air.

0016In order to optimize the droplet trajectories still in their alignment, the plane which is spanned by the nozzle jets of the atomizer nozzles is inclined at an angle in the range of 0 ° to 30 ° against the flow direction of the gas flow.

0017The invention is explained in more detail below by way of example with reference to the figures. It shows:<dl id="dl0001"><dt>Fig.1</dt><dd>a three-dimensional representation of a horseshoe vertebra, which is directed at a flow of a gas flow and inclined against the current at an angle α,</dd><dt>Fig.2</dt><dd>a side view transverse to the line A - A according to FIG <figref idrefs="f0001">FIG</figref>.</dd><dt>Figure 3</dt><dd>FIG. 12 is a front view looking at the lee side of the disk transverse to the line B - B in the illustration according to FIG <figref idrefs="f0001">FIG</figref>.</dd><dt>Figure 4</dt><dd>a side view comparable <figref idrefs="f0001">Fig.2</figref> in a first embodiment of the device according to the invention in which the atomizer nozzles are arranged downstream of the mixer disk in relation to the gas flow, the cross-section of the gas channel carrying the gas flow being also shown</dd><dt>Figure 5</dt><dd>FIG. 9 is a rear view looking towards the windward side of the disk transverse to the line B - B in the illustration according to FIG <figref idrefs="f0001">FIG</figref>.</dd><dt>Figure 6</dt><dd>a side view comparable <figref idrefs="f0002">Figure 4</figref> in a second embodiment of the device according to the invention, in which the atomizer nozzles are arranged upstream of the mixer disk in relation to the gas flow, and FIG</dd><dt>Figure 7</dt><dd>FIG. 12 is a front view looking at the lee side of the disk transverse to the line B - B in the illustration according to FIG <figref idrefs="f0001">FIG</figref>,</dd></dl>

0018The formation of vertebral tracts is a natural phenomenon in three-dimensional flows on a body. (<nplcit id="ncit0001" npl-type="s"><text>Cf. Prandtl, Oswatitsch, Wieghardt: Guide to the Theory of the Flow, 9th edition, 1990; ISBN 3-528-28209-6, p. 229, figure 4.41 and associated description</text></nplcit>s).

0019The formation, the shape and position of such vortexes in the effluent of mixing discs are first shown in the <figref idrefs="f0001">Figs. 1-3. Fig</figref> schematically illustrated and described thereon.

0020A circular disk 1 is inclined at an angle .alpha <figref idrefs="f0001">Fig.1</figref> flowing gas stream 2 coming from below. On the windward side 1a of the disk, the gas flow is deflected out of its main flow direction and an overpressure region is formed. The partial flow 2 a of the gas flow 2 flows along the disk at a predetermined angle. On the lee side 1b of the disk, a vacuum region is formed, which is filled by the partial flow 2b of the gas flow through the edge of the disk. By means of the flow deflection at the edge of the disc, a horseshoe vertebra 3 is formed with the vortex axis 3a shown by dashed lines, which continues in the form of a vortex slider with two symmetrically rotating vertebrae downstream of the disc. The lateral vertebrae of the horseshoe vertebrae continue as a vertebra, superimpose with the gas flow (basic flow) and spread with ground flow. The flow condition within the vortex vane is highly turbulent. The schematically represented boundary 3b of the horseshoe vertebra and vertebral tract may not be understood as a sharp delineation. The position and the structure of the opposite directions of rotation of the two vortexes can be determined experimentally by means of a suitable measuring technique.

0021In other disk shapes, such as ellipse shape, oval shape, parabolic shape, diamond shape or triangular shape, comparable vertebrae with vertebrae are formed.

0022The turbulent mixing of vortex trawls and gas flow is used to distribute a nearly punctiform gas flow evenly over a very large cross-section.

0023In the embodiment of the device according to the invention according to FIG <figref idrefs="f0002">FIGS. 4 and 5</figref> two atomizing nozzles 4a and 4b are arranged on the head 4c of a nozzle lance 5 extending into a flue gas channel R. (More than two atomizing nozzles can be used, and the use of pressure nozzles is also possible). The atomizing nozzles are arranged on the lee side 1 b of the preferably circularly shaped mixer disk 1 at a predetermined distance from it. The nozzle jet emerging from one of the nozzles 4a and 4b respectively contains gaseous constituents 6a and non-vaporized droplets 6b. The two atomizing nozzles 4a and 4b enclose an angle β of 120 ° and are inclined against the basic flow. Other angles are possible. The range is preferably between 60 ° and 120 °.

0024The plane stretched by the nozzles 4a and 4b is not inclined against the ground flow.

0025In the <figref idrefs="f0002">FIGS. 4 and 5</figref> the liquid reactant 5a is atomized by means of a sputtering auxiliary medium 5c and the nozzle jet 6 is surrounded by fogging air 5c.

0026In the <figref idrefs="f0002 f0003">Figs. 4-7. Fig</figref> the currents 6a (gaseous component of the nozzle jet 6) and 6b (non-vaporized droplets) of the injection flow 6 are shown schematically in addition to the partial flows 2a and 2b. The vaporized part 6a of the injection stream, as shown in the figures, follows the curvatures of the basic flow and is fed into the vortex flow 3. The non-vaporized droplets 6b follow their inertia below the selected injection angle β and thus penetrate the leeward side 1b of the disk 1 the vortexes leading back to the lee side, so that formation of deposits from droplets and fine dust from the flue gas is essentially avoided.

0027The droplets of the partial stream 6b later evaporate in the exhaust stream and are sufficiently intermixed by the turbulences present there.

0028The partial stream 6a can also contain fine droplets, which, however, evaporate rapidly and therefore contribute little to the formation of the coating, if at all. Based on the amount of reducing agent, the partial stream 6a contains substantially more reducing agent than the partial stream 6b. However, if the vortex braids were not penetrated according to the invention, the lower partial flow 6b would lead to considerable deposit formation.

0029In the embodiment according to FIGS <figref idrefs="f0003">FIGS. 6 and 7</figref> the nozzle head with the atomizing nozzles 4a and 4b is arranged upstream of the mixer disk 1. The atomizing nozzles 4 a and 4 b are arranged in such a way that the axes of the nozzle jets 6 extend on both sides at a sufficient distance next to the mixer disk 1. The distance to the pane can preferably be approximately 0.5 m. In this embodiment too, the trajectories of trajectories 6b penetrate the mixing disk to form directed swirls.

0030In the embodiment according to FIGS <figref idrefs="f0003">6 and 7</figref> the plane stretched by the nozzles 4a and 4b is inclined against the basic flow by the angle γ = 20 °.

0031In this embodiment and in the embodiment according to FIG <figref idrefs="f0002">Figs. 4-5</figref> an inclination angle γ is possible in the range of 0 ° to 30 °.

0032In the embodiment according to FIG <figref idrefs="f0003">FIGS. 6 and 7</figref> it is of advantage that the space, which is often unused for technical reasons, can be used for the arrangement of the nozzle lance 5 upstream of the jet disk 1. In addition, in this embodiment, the freedom from the nozzle lance 5 can be guided from the wall of the channel K to the injection point, irrespective of the inclination of the mixer disk 1, against the basic flow without the very complicated penetration of the mixer disk 1 having to be performed.

0033It is self-evident that in the case of large channel cross-sections, a plurality of mixing discs with associated atomizing nozzles can be provided distributed over the channel cross-section. More than two nozzles, eg in the hedgehog arrangement, can also be assigned to a mixer disc. They must be arranged in such a way that the droplet trajectories penetrate the vertebrae.

LIST OF REFERENCE NUMBERS

0034<dl id="dl0002" compact="compact"><dt>1</dt><dd>Disc (mixing disc)</dd><dt>1a</dt><dd>Luv - side of the disc</dd><dt>1b</dt><dd>Lee - side of the disc</dd><dt>2</dt><dd>Gas flow rate</dd><dt>2a</dt><dd>Gas flow, partial flow on the windward side 1a of the disk</dd><dt>2 B</dt><dd>Gas flow, partial flow to the lee side of the disk</dd><dt>3</dt><dd>Horseshoe vertebra and vertebra</dd><dt>3a</dt><dd>vortex axis</dd><dt>3b</dt><dd>External boundary of the vertebra</dd><dt>4</dt><dd>nozzle lance</dd><dt>4a</dt><dd>atomizer</dd><dt>4b</dt><dd>atomizer</dd><dt>4c</dt><dd>nozzle head</dd><dt>5a</dt><dd>Delivery of liquid reducing agent</dd><dt>5b</dt><dd>Supply of gaseous atomizer auxiliary medium</dd><dt>5c</dt><dd>Supply of blocked air or fogging air</dd><dt>6</dt><dd>jet</dd><dt>6a</dt><dd>gaseous fraction</dd><dt>6b</dt><dd>non-vaporized droplets</dd><dt>R</dt><dd>Flue</dd></dl>