Stepped down gas device

ES 2 525 154 T3

DESCRIPTION

Apparatus and method for mixing two gas streams

Field and background

The present invention relates, in general, to the field of furnaces and boilers, and, in particular, to an apparatus and a method for efficiently mixing two gas streams with different temperatures and / or compositions in which at least one of the Streams contains particles.

The use of air foils for the distribution and mixing of air streams in secondary air supply ducts and in Selective Catalytic Reduction (SCR) system throws is known. The usual arrangement comprises a plurality of entire sheets in the center of the shaft, and half sheets in the walls of the shaft. Another prior art air blade example uses an air blade configuration for bypass economizer draft gas distribution and mixing used at Kansas City Power & Light, Hawthorn Station, in its draft SCR system. This system uses a basic air foil system, but has added gas flow management plates. The contour lines in an air flow diagram of such a device show how the air sheets and plates act in the air stream to improve the mixing of the gases in the duct, see document US 2006/0266267 A1 of Albrecht and others.

Furthermore, air foils have been widely used for flow measurement and control. The use of diamond-shaped flow devices for low pressure drop flow control is also known. For example, many commercially available dampers contain diamond-shaped blades. Such devices achieve good flow control with minimal pressure drop.

The disadvantages of the above-described prior art arrangements add pressure loss, potential degradation of the ammonia mixture, when added, and the requirement for a larger draft to accommodate the system components. Zone controlled ammonia injection (AIG) grids are known and have been installed to deliver a prescribed rate of ammonia for NOx reduction SCR systems. Static mixers are commercially available in various forms and have been proposed to reduce thermal species and / or draft gas gradients by adding turbulent mixing in draft SCR systems. Koch and Chemineer are the manufacturers that produce some such commercially available static mixers. Design requirements for secondary drafts and SCR systems include specification of flow distribution and thermal gradients downstream of mixing devices. The goals are to achieve a uniform flow and to minimize thermal gradients. For example, in an SCR mixer and flow system, flow uniformity across the ammonia injection screen should be sufficient to maintain catalyst performance and life. Devices such as those of the prior art have been used to achieve these ends. Although it is also desirable to minimize unrecoverable pressure loss for the system, space constraints limit the installation of an air foil for gas mixing and a separate AIG for ammonia distribution in an SCR system. Thus, a uniform distribution system was needed for such applications that also minimized pressure loss therein.

US 2006/0266267 A1 to Albrecht et al., Mentioned above, describes a flow improvement arrangement for ducts such as rectangular flue ducts, in which a series of teardrop-shaped sheets are spaced apart and mounted in the duct extending from the top to the bottom thereof, and where a series of diamond-shaped vanes, extending from the top to the bottom of the duct as well, are spaced and mounted between the teardrop-shaped blades to provide a more uniform flow distribution and thereby lower pressure. A series of baffles can also be used that extend both from both the teardrop blades and from the diamond blades.

US Patent 6,887,435 B1 to Albrecht et al. Discloses an integrated air blade and ammonia injection grid and provides a plurality of air blades through a draft gas carrying draft. Each air blade has a leading curved edge and a rear tapered and pointed end. At least one injection tube is positioned within each air blade, and has at least one nozzle for injecting ammonia into the draft gas flowing through the air blades. Preferably, a plurality of injection tubes are provided which are positioned one after the other in each sheet of air, and each injection tube in a given sheet of air has a length different from the length of the other injection tubes of the same sheet. of air. The longest injection tube of a given sheet of air is located furthest downstream and closest to the tapered and pointed edge, and the shortest injection tube of the same sheet of air is placed the most upstream, being, between the injection tubes of the same air sheet, the tubes that are placed further upstream are progressively shorter. Apertures may be provided on opposite side sides of the air blades to introduce a flow of gas into the draft gas passing through the air blades. The ammonia flow to each injection tube can be individually controlled.

US 4980099 A1 to Myers et al. Describes an apparatus for spraying an atomized mixture

ES 2 525 154 T3 in a gas stream and comprises an airfoil line stream member having a large radius leading edge and a small radius trailing edge. A nozzle assembly pierces the leading edge of the air blade member and is concentrically surrounded by a pod which directs shielding gas from within the air blade member around the nozzle assembly. A fluid medium to atomize and atomization gas to atomize the medium are supplied in passages concentric to the nozzle. In a plurality of nozzles, each surrounded by a pod, the nozzles are spaced along the leading edge of the air blade member.

Air foils have been used to distribute and mix gas streams in secondary air supply lines and in Selective Catalytic Reduction (SCR) system throws. The arrangement consists of a plurality of entire sheets in the center of the shaft and / or half sheets in the shaft wall, as used for the Eastman Kodak installation identified above.

Another example of an airfoil configuration for the distribution and mixing of draft gases with a bypass economizer was used at the Kansas City Power & Light, on the Hawthorn Station SCR draft system. Furthermore, air foils have been widely used for flow measurement and control. Zone controlled ammonia injection grids (AIG) have been installed to deliver a prescribed percentage of ammonia for NOx reduction SCR systems. Static mixers are commercially available in various forms and have been proposed to reduce flue gas and / or thermal species gradients by adding turbulent mixing to SCR flue systems. Koch and Chemineer produce some examples of commercially available static mixers.

Diamond-shaped flow devices have been used for low pressure drop flow control. For example, many commercially available dampers contain diamond-shaped blades. Such devices achieve good flow control with minimal pressure drop.

Design requirements for secondary conduits and SCR systems include specification of flow distribution and thermal gradients downstream of mixing devices. The objectives are to achieve flow uniformity and minimize thermal gradients. Additionally, space constraints limit the installation of an air foil for gas mixing and a separate AIG for ammonia distribution in an SCR system.

Alternatives are to use air blades to distribute the draft gas within the draft and to include plates or baffles to promote mixing of flow in the duct / draft. The downside to such an arrangement adds pressure loss, potential mix degradation, and a larger draft to accommodate the system components.

There remains a need for a simple and efficient apparatus for mixing gas streams, in particular streams of different temperatures and / or compositions, and containing particles such as ash.

The particular aspects and embodiments of the invention are set forth in the attached independent and dependent claims.

Viewed from one aspect, the present invention is generally drawn to devices for the distribution and mixing of particles or gas-laden injected air in conduits and, more particularly, to devices such as those used in the conduits of power generation stations that may contain ammonia for NOx reduction devices.

Some aspects can provide flow uniformity and minimize thermal gradients. For example, it may be appropriate in an SCR system to provide mixing and flow uniformity in the injection grid with enough ammonia to maintain catalyst performance and life. Some aspects can minimize irrecoverable pressure loss to the system. The described arrangements can accomplish the above by using an integrated device that satisfies the SCR system design requirements.

The mixing characteristics described produce a device and method that promotes uniform flow distribution with low pressure drop. The device and method also eliminate any limitations on the amount of recirculation flow through the invention, by allowing variations in the cross-sectional flow area of ​​the recirculation portion of the device. In addition, through the use of special discharge outlets, its use in vertically or horizontally oriented pipes or ducts is facilitated.

The various features of novelty which characterize the invention are pointed out with particularity in the claims appended to and forming a part of this description. For a better understanding of the present description, its operational advantages and specific objects achieved by its uses, reference is made to the accompanying drawings and descriptive matter in which detailed embodiments are illustrated.

Brief description of the drawings

In the drawings:

Figure 1 is a top plan view of an illustrative example of an apparatus for mixing two gas streams of different temperature or composition or both, one with the other, where at least one of the streams contains particles;

FIG. 2 is an illustrative example showing a side elevational view of one of the secondary plural gas stream conduit assemblies;

Figure 3 is an end elevational view of the conduit assembly of Figure 2;

Figure 4 is a top plan view of a plurality of secondary gas stream conduit assemblies in accordance with the illustration;

Figure 5 is a side sectional view of the secondary gas stream conduit assembly of Figure 4, taken along line 5-5 of Figure 4;

Figure 6 is a side sectional view of the secondary gas stream conduit assembly taken along line 6-6 of Figure 5;

Figure 7 is a side sectional view of the secondary gas stream conduit assembly taken along line 7-7 of Figure 5;

Figure 8 is a side sectional view of the secondary gas stream conduit assembly taken along line 8-8 of Figure 5;

Figure 9 is a cross-sectional view of an alternative shape for a gas flow baffle replacing the diamond-shaped baffle of the embodiment of Figures 4-8; and Figure 10 is a cross-sectional view of a further alternative shape for a gas flow baffle replacing the diamond-shaped baffle of Figures 4-8.

Although the invention is susceptible to various modifications and alternative forms, specific exemplary embodiments are shown in the drawings and described in detail herein. It should be understood, however, that the drawings and the detailed description thereof are not intended to limit the invention to the particular form described, but rather the invention is to cover all modifications, equivalents and alternatives that fall within within the scope of the present invention as defined by the appended claims.

Referring now to the drawings, in which similar reference numerals are used to refer to the same or similar elements, Figure 1 shows an apparatus for mixing two gas streams 14 and 20 of different temperatures or of different compositions or of both. differences, one with the other, where at least one of the streams contains particles. The apparatus comprises a main conduit 12 for conveying a first gas stream in a first direction 14, for example upward, and thus off the page in Figure 1.

A plurality of conduit assemblies 16 extend into the main conduit 12, the conduits being generally transverse to the first direction 14, each conduit assembly 16 having a plurality of inlets 18 for each receiving portion of the second stream 20 of Gas moving inward from the right in Figure 1, that is, in a second direction that is generally transverse to the first direction 14. Directions 14 and 20 can be approximately 90 degrees from each other, but need not be exactly 90 degrees, as any general amount of transverse orientation (eg, approximately 40 to 140 degrees) is effective.

Referring now to Figures 2 and 3, each conduit assembly 16 has a plurality of outlets 22 for discharging the portions of the second gas stream that entered the various inlets 18, in a direction that is generally parallel to the first direction. 14, each conduit assembly 16 comprising a plurality of secondary conduits 24, 26, and 28 having mutually different lengths from their inlet 18 to their outlet 22, for each respective secondary conduit 24, 26, or 28. Outlets 22 of secondary conduits 24, 26, and 28 are separated from each other through primary conduit 12 to distribute the parts of the second gas stream into the first gas stream 14 of the main duct 12. Plural assemblies 16 are provided to further distribute the multiple portions of the second total gas stream across the entire breadth and width of main conduit 12, as illustrated in FIG. 1.

In the illustrative example of Figures 1-3, a gas flow deflector 30 is connected to an upstream end of each conduit assembly 16 facing the first main gas flow direction 14 in the opposite direction to temporarily divert the first stream. gas from first address 14 before

ES 2 525 154 T3 is combined with each part of the second gas stream 20 downstream of each outlet 22, to mix the first and second gas streams with each other as the first gas stream passes through the plurality of conduit assemblies 16 main duct 12. The deflector 30 of this illustrative example has a curved sheet shape and is on a front side of its respective conduit assembly 16, facing toward the first direction 14 and opposite the outlet 22 of each conduit assembly 16. In an alternative illustrative example, which is also illustrated in Figure 3, the deflector 30 'is wedge-shaped with flat sidewalls (shown) or concave sidewalls (not shown) and is located on the front side of its respective mount 16 of conduit facing the first direction 14 and again opposite the outlet 22 of each conduit assembly 16.

For a sense of scale, the outlets 22 in Figure 2 are each approximately 0.81 meters wide in dimension A for a total width of about 2.44 meters for the main duct 12, and the same maximum length Approximate for center duct mounting 16 on main duct 12 as shown in figure

1. The assemblies 16, which have an elbow 40 near their respective inlets 18 of Figure 1, and which extend outward from the center assembly 16, have a greater maximum length to help expand the outlets 22 of the various assemblies 16, which they look up, thus, off the page of Figure 1, evenly across the area of ​​main conduit 12 to better mix the streams with each other. Referring now to Figures 2 and 3, a typical height B of the shorter secondary conduits 24 and 26 is approximately 0.28 m and a height C is approximately 0.35 m of the longest conduit 28. Dimension F, which are the perpendicular heights B and C, is typically about 0.6 m. Although three secondary conduits are shown for each conduit assembly, at least two, and at most five can be used, and the various dimensions can be selected depending on the gas streams that are services.

As illustrated in Figure 1, the conduit assemblies 16, other than the central one, each have the second direction elbow 40 20 at a location downstream of the inlets 18 of the secondary conduits 24, 26, and 28, to assist to expand the outlets and their respective secondary gas stream parts, around the main conduit 12. An example of the length D of the main conduit 12 is approximately 13m, with a width E of approximately 3.4m to accommodate foot 8 or the greatest length of each conduit assembly 16. To avoid ash traps, a filler such as plates 42 is extended from the ends of the mounts 16 to the adjacent walls of the main duct 12.

A second common gas stream conduit 44 for supplying the entire second gas stream in direction 20 is also provided with vent slats 50 which are shown in a closed position in Figure 1, but which can be rotated on their respective axis. actuator to a respective open position, and which are parallel to each other for the free passage of the second gas stream.

In Figures 4 to 8, each deflector 30 is downstream of the outlet 22 of each secondary conduit 24, 26 and 28, of each conduit assembly 16, so that the portions of the second gas stream at the outlets 22, which now face the first gas stream in the opposite direction and direction 14, are mixed with the first gas stream of the main conduit 12.

The baffles 30 of Figures 5 through 8 are each diamond-shaped and are each downstream of the outlet 22 of each conduit assembly 16, so that the portions of the second gas stream at the outlets 22 face the first direction 14 and therefore the main gas stream in the opposite direction, so that it mixes with the first gas stream in the main conduit 12. The side walls of the upstream and downstream sides of the diamond-shaped baffles 30 can be flat, as shown, or they can be convex or concave. As shown in Figure 6, a typical upstream angle M can form about 45 degrees with a typical downstream angle N of about 35 degrees (Figure 6). A typical inlet width H 18, in FIG. 5, is about 0.9m, with a typical outlet width G of about 0.9m. A typical maximum length K of conduit mount 16 is 2.7 m, in Figure 5, and a typical width J width of mount 16 is 1.8 m.

Figures 6 to 8 better show the secondary gas streams upstream from the outlets 22 and the primary gas streams 14 downstream of the main conduit 12, as they are partially deflected by the baffle surfaces of the diamond baffle 30 to meet. , thereafter, and are mixed on the sides of the baffles 30 and then carried upwards, in Figures 6 to 8, in the direction 14 of the first main or primary gas streams, where induced current can cause certain particles, such as ash, to collect on top of mounts. These particles are rapidly dispersed by the continuous main flow of gas stream, upward in the illustrations of Figures 6 to 8.

As illustrated in Figures 9 and 10, other baffle shapes are possible, such as a wedge shape with flat side walls on the upstream side (Figures 9 and 10) with a transverse flat surface downstream of outlet 22 ( Figure 10) or with concave surfaces downstream of the outlet 22 (Figure 9), so that the parts of the second gas stream at the outlets 22 face the first direction 14 to be mixed with the first gas stream of the main conduit .

Design requirements for secondary drafts and SCR systems include specification of flow distribution

ES 2 525 154 T3 and the thermal gradients downstream of the mixing devices. Objectives may include achieving flow uniformity and minimizing thermal gradients. For example, it may be appropriate in an SCR system that mixing and flow uniformity in the ammonia injection grid is sufficient such that catalyst performance and life are maintained. To accomplish these goals, devices such as those listed in the prior art have been used.

It is also desirable to minimize irrecoverable pressure loss to the system. Additionally, space constraints limit the installation of an air foil for gas mixing and a separate AIG for ammonia distribution in an SCR system.

Some of the arrangements described herein use some prior art mixing characteristics to produce an integrated device that satisfies system design requirements, but with better pressure drop and other flow and mixing characteristics that could not be achieved. simply using a prior art apparatus. The techniques described are unique in that they combine the mixing characteristics of air blades and / or diamond blades to produce a device that promotes uniform flow distribution with low pressure drop. The device also eliminates limitations on the amount of recirculation flow through the invention by allowing variations in the cross-sectional flow area of ​​the recirculation portion of the device. In addition, through the use of special discharge outlets, the use in vertically or horizontally oriented pipes or ducts is enabled.

By integrating an air blade deflector or diamond-shaped or with another shape on the front, flow uniformity downstream of the mixing device is achieved, through the calibration of each outlet section that exits with the recirculated gas flow. The flow, through each section, is distributed in such a way that it does not mix with the main gas flow stream. Turbulence caused by the main gas flow moving around the air sheet or diamond shaped front section of the mixing device provides the means for mixing the main and recirculating gas streams downstream of the mixing device.

A characteristic of the present teachings is their flexibility to distribute the mixing gases within a non-uniform or complex shaft or duct such as that of Figure 1. One of the problems addressed by the present teachings is that in an upward vertical draft, such as shown in Figures 2 and 3, the ash in the flue gas can be deposited within the mixing device if installed with the mixing device outlets positioned for the downstream side of the flue. A further problem of the prior art is the issue of insufficient gas mixing on the downstream side due to insufficient turbulence and stratification of gas after the mixing device. To address this issue, the mixing device is installed with the discharge facing the upstream gas side of the mixing device, and special baffle joints are used to minimize ash drift within the device's mixing throws.

In the figures. 4-8, the discharge of the devices in accordance with the present teachings incorporates a flow outlet deflector that is used to discharge the flow within the device into the stream of the mass of gas. By incorporating this feature to discharge the gas into the gas mass vapor, the orientation of this mixing device is not influenced by the ash in the draft gas, and the accumulation of particles within the mixing device will be minimized. This feature is a special concept of the present teachings that allows the device to be used in both horizontally and vertically oriented shots. This feature is also new for vertically upward gas shots, where particles could easily be collected in the mixing device. When the system is not in use, the normal flow of leaks around the bypass dampers would clear any ash build-up within the mixing device. Optional types of discharge outlet designs are shown in Figures 9 and 10.

The mixing of the two draft gas streams minimizes thermal gradients in a manner similar to the previously described sheets of air. Through good mixing of the draft gas streams, small variations in temperature over the cross section of the draft are achieved.

Certain alternatives within the scope of the invention use sheets of air to distribute the draft gas within the draft and to include plates or path modifiers to promote mixing of flow in the draft / duct. However, such approaches can lead to added pressure loss, potential degradation of the mix, and a larger draft to accommodate system components.

Although specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be carried out in other ways without departing from the scope of the present invention as defined by the appended claims. .