Flue gas mixing apparatus

FIG. 1( a ) shows a perspective configuration view of a gas mixer 1 of Example 1 of the present invention. The gas mixer 1 of the present Example 1 is provided on a flow channel cross-section of a flue gas duct into which combustion flue gas to which a reducing agent which reduces nitrogen oxide in the combustion flue gas is added is introduced and which is on an upstream side of a denitration apparatus provided with a denitration catalyst. In general, a flow channel cross-section of a denitration apparatus provided with a denitration catalyst used for a large-scale power generation facility is rectangular, and the flow channel cross-section of a flue gas duct which introduces flue gas into the denitration apparatus is also often rectangular. Therefore, description will be made, supposing that the gas mixer 1 of the present example is applied to a flue gas mixing apparatus configured by segmenting the flow channel cross-section of the flue gas duct into a plurality of rectangular regions and stacking and arranging gas mixers whose sizes correspond to the rectangular regions into stages and into a plurality of columns.

As shown in FIG. 1( a ) , the gas mixer 1 of the present Example 1 is formed to have a gas flow channel of a cuboid space 3 through which combustion flue gas G flowing in from a direction indicated by an arrow 2 shown in the figure is caused to flow. The gas flow channel of the present example is formed of a cross-sectionally rectangular flow channel wall 4 formed by disposing flat plates 4 ( a to d ) on faces of the cuboid space 3 which are parallel in the gas flow-in direction 2 . In the figure, an opening face which is proximal relative to the cross-sectionally rectangular flow channel wall 4 is set to be a gas flow-in face, and an opening face which is distal relative to the same is set to be a gas flow-out face. Inside the cross-sectionally rectangular flow channel wall 4 , a gas flow channel partition plate 6 composed of four partition plate elements 6 a to 6 d which are formed into the same shapes is disposed. All the partition plate elements 6 a to 6 d are formed into the same shapes.

Each of the gas flow-in face and the gas flow-out face of the gas flow channel of the present Example 1 is segmented into four rectangular regions which have the same symmetric areas by two perpendicular straight lines ( 9 a and 9 b ), ( 10 a and 10 b ) which are parallel to sides of the gas flow-in face or the gas flow-out face and pass through a center 7 , 8 of the gas flow-in face or the gas flow-out face. The gas flow channel partition plate 6 is formed so as to introduce the combustion flue gas G caused to flow in each of the regions of the gas flow-in face into each of the regions of the gas flow-out face at positions at which the regions are shifted one-by-one around a line segment L 3 connecting the centers 7 and 8 of the gas flow-in face and the gas flow-out face clockwise in the present example. In other words, the partition plate elements 6 a to 6 d are installed by being rotated around a common side, where the line segment L 3 is the common side, at a pitch of 90° clockwise in the present example.

The partition plate elements 6 a to 6 d are formed of bent plates each of which shuts a gas flow between the rectangular regions of the gas flow-in face and the gas flow-out face at symmetric positions. Referring to FIG. 1( b ) , a configuration of the partition plate element 6 a is described in detail. As shown in the figure, the partition plate element 6 a is constituted of four triangular plates A to D. Now, three-dimensional coordinates [xyz] of respective vertices of the rectangular region of the gas flow-in face are respectively set to be [000], [100], [110] and [010] clockwise from the intersection 7 of the two perpendicular straight lines 9 a and 9 b . Moreover, three-dimensional coordinates [xyz] of respective vertices of the rectangular region of the gas flow-out face at symmetric positions of those vertices are respectively set to be [001], [101], [111] and [011] clockwise from the intersection 8 of the two perpendicular straight lines 10 a and 10 b.

The triangular plate A is a triangular flat plate which has a line segment L 1 connecting the vertex [100] and the vertex [011] as a base and has a point P 1 on a line segment L 2 connecting the vertex [110] and the vertex [111] as a vertex. The triangular plate B is a triangular flat plate which has the common side L 3 as a base and has a point P 2 on the line segment L 1 as a vertex. The triangular plate C is a triangular flat plate which has a line segment L 4 connecting the vertex [000] and the vertex [100] as a base and has the point P 2 as a vertex. The triangular plate D is a triangular flat plate which has a line segment L 5 connecting the vertex [011] and the vertex [001] as a base and has the point P 2 as a vertex. The position of the point P 1 of the triangular plate A on the line segment L 5 may be displaced from the center of the line segment L 2 within ⅓ of the length of the line segment L 2 . Moreover, the position of the point P 2 of the triangular plates B to D may be displaced from the center of the line segment L 1 within ⅓ of the length of the line segment L 1 .

Moreover, omitted from the figure, the partition plate elements 6 b to 6 d are formed of the triangular plates A to B into the same shapes similarly to the partition plate element 6 a , and are installed by being rotated around the common side, where the line segment L 3 is the common side, at the pitch of 90° clockwise in the present example. Edge parts of the partition plate elements 6 a to 6 d in contact with the flat plates 4 ( a to d ) are respectively fixed to the flat plates 4 ( a to d ) by welding or the like. As shown in FIG. 1( b ) , edge parts of the partition plate elements 6 a to 6 d which are not in contact with the flat plates 4 ( a to d ) are fixed to rod-like support members 11 such as pipes installed along the two perpendicular straight lines ( 9 a and 9 b ) and ( 10 a and 10 b ) and the line segment L 3 by welding or the like.

FIG. 2 shows an example of the flue gas mixing apparatus constituted of the gas mixer 1 of the present Example 1 as lattice elements. As shown in the figure, it is an example in which the gas mixers 1 are disposed on the whole cross-section in the flue gas duct 25 on the upstream side of the denitration apparatus so as to be adjacent to one another. While in Example 1, the cross-sectionally rectangular flow channel wall 4 composed by disposing the flat plates 4 ( a to d ) encloses a structure body of the gas flow channel partition plates 6 a to 6 d , a case of not providing the cross-sectionally rectangular flow channel wall 4 is as in the figure. Notably, FIG. 2 is an example, and the flue gas mixing apparatus of the present invention is configured by disposing a plurality of gas mixers 1 on at least part of the flow channel cross-section of the flue gas duct 25 on the upstream side of the denitration apparatus into a plurality of stages and into a plurality of columns. Namely, when the gas mixers 1 are disposed into two stages and into a plurality of columns, a horizontal partition plate 14 and vertical partition plates 15 are provided, and an outer circumferential wall of the flue gas duct 25 is used for an outer circumferential wall of the entirety of the gas mixers 1 .

The flow channel cross-section of a denitration apparatus including a denitration catalyst used for a large-scale power generation facility is rectangular, and the cross-section of a flue gas duct on its upstream is also often rectangular. Accordingly, it is desirable that sectional dimensions of the gas flow channel of the gas mixer 1 be determined to meet the shorter dimension of vertical and horizontal dimensions of the cross-section of the flue gas duct. For example, in the present Example 1, the size of the flue gas duct was supposed to be 18.4 m×4.6 m. The sectional size of the gas mixer 1 took, as a reference, 2.3 m which was ½ of the shorter dimension 4.6 m with ability in production and ability in maintenance taken into consideration. Notably, the size of the gas mixer 1 is properly set depending on ways of distributions of a gas flow rate and a molar ratio, and the size of a regulation region for reducing agent injection nozzles. For example, since the gas mixer 1 of the present invention is of a type in which a rotational flow is generated, it desirably has a square cross-section as seen in the gas flow direction. Nevertheless, it does not cause a problem to change a vertical/horizontal aspect ratio more or less depending on the size of the flue gas duct. In the present Example 1, to set it to be a square of 2.3×2.3 m enables it to appropriately fit to the horizontal width dimension of the flue gas duct.

According to the gas mixer 1 of Example 1 described above, the combustion flue gas G caused to flow in the four rectangular regions of the flue gas flow-in face is caused to flow out from the gas flow-out face by its gas flow direction being drifted one region-by-one region (for example, clockwise) around the line segment L 3 connecting the centers of the gas flow-in face and the gas flow-out face by the gas flow channel partition plate 6 ( a to d ). As a result, a main flow of the combustion flue gas G flowing through the gas mixer 1 of the present example receives rotational force into a rotational flow, which is discharged from the gas flow-out face. This rotational flow promotes mixing of the combustion flue gas G and a reducing agent such, for example, as ammonia. As a result, a small amount of reducing agent or the like fed into the flue gas duct (flue) on the upstream of the denitration apparatus can be uniformly dispersed in a short distance. Furthermore, since a rotation angle of the flowing-in combustion flue gas G is 90°, a pressure loss due to the rotational flow of the combustion flue gas G can be suppressed from increasing. Notably, when the numbers of segments of the gas flow-in face and the gas flow-out face are set to be more than four regions, the pressure loss can be further suppressed from increasing though the rotational force becomes weaker.

For example, by configuring the flue gas mixing apparatus using the gas mixers 1 of the present example, a change rate CV (standard deviation/average value) of the molar ratio of NH 3 /NOx can be set to be 7% or less, and a change rate CV (standard deviation/average value) of the gas flow rate can be set to be 15% or less. Furthermore, a pressure loss of the gas mixer 1 can be suppressed from increasing.

FIG. 3 shows a perspective configuration view of a gas mixer 30 of Example 2 of the present invention. In the present Example 2, the difference from the gas mixer 1 of Example 1 is that flat plates 4 a and 4 c are disposed only on upper and lower two faces which are parallel to the gas flow-in direction 2 in the rectangular solid space 3 , and the other partition plates on the two faces in the vertical direction are omitted to form the gas flow channel. In other words, one pair of two faces facing each other out of the four faces which are parallel to the gas flow which flows in the cuboid space are formed of the flat plates, and the other pair of two faces are opened. The others are identical to those in Example 1, and are given the same signs to omit their description.

FIG. 4 shows a perspective configuration view of a gas mixer 40 of Example 3 of the present invention. Its difference in the present Example 3 from the gas mixer 1 of Example 1 or the gas mixer 30 of Example 2 is in that all the flat plates 4 a to 4 d on the four faces which are parallel to the gas flow-in direction 2 in the cuboid space 3 are omitted. In other words, the four faces which are parallel to the gas flow which flows in the cuboid space 3 are opened. Moreover, not shown in the figure, edge parts of the partition plate elements 6 a to 6 d of the gas flow channel partition plate 6 are fixed to rod-like support members such as pipes by welding or the like to secure their strength.

Next, Table 1 presents numerical analysis results of the change rates CV [%] of the molar ratio of NH 3 /NOx, the change rates CV [%] of the gas flow rate, and the pressure losses [Pa] in Examples 1 to 3 of the present invention, these being compared with numerical analysis results in Comparative Examples 1 to 3. Comparative Example 1 is an example of a flue gas duct in which any of the gas mixers of the respective Examples 1 to 3 are not installed. Comparative Example 2 is an example in which a flue gas mixing apparatus is configured by installing gas mixers in Patent Literature 2. Comparative Example 3 is an example in which a flue gas mixing apparatus is configured by installing gas mixers in Patent Literature 3 shown in FIG. 5( a ) in the flue gas duct 25 as shown in FIG. 5( b ) .

Notably, the numerical analysis presented in Table 1 was performed using numerical analysis software FLUENT Ver. 6, to which initial values with which the change rate of the gas flow rate on the inlet face was CV=20% were given, for flue gas mixing apparatuses in an actual scale. Moreover, also for ammonia nozzles, structures which reflected an actual size were used, and an ammonia injection amount was changed in accordance with the inlet gas flow rate.

As presented in Table 1, it is found that although for all of Examples 1 to 3, the pressure loss is higher than that in Comparative Example 1 in which gas mixers are not included by approximately 40 Pa, the molar ratio CV of NH 3 /NOx is lower and mixing ability is excellent. In other words, since Comparative Example 1 did not include gas mixers, the molar ratio CV of NH 3 /NOx was highest to be 9.2%, which did not satisfy 7% which was typically required, although there was no problem for the gas flow rate CV.

Moreover, it is found that both mixing ability and rectification performance are excellent for all of Examples 1 to 3 since the pressure loss is lower than that in Comparative Example 2 and both the NH 3 /NOx molar ratio CV and the gas flow rate CV are lower. In other words, it can be considered that Comparative Example 2 does not almost change the molar ratio CV of NH 3 /NOx as compared with Comparative Example 1, and an effect is smaller than those in the present Examples 1 to 3.

Examples 1 to 3 are excellent in mixing ability since both the pressure loss and the NH 3 /NOx molar ratio CV are lower than those in Comparative Example 3. Now, the gas mixer of Comparative Example 3 has a structure in which sets of two triangular plates 17 and 18 are alternately opposite to each other relative to their vertex part, having the structure in which after a gas flow entering from the inlet is once dispersed by the upstream-side two triangular plates 17 in two directions, it merges to go out from the outlet face since the following two triangular plates 18 exist at alternate positions. In other words, it mainly has an effect of collecting a gas flow, and is not a structure for giving the gas flow a large rotational flow. Based on these, it has been found that the gas mixers of Examples 1 to 3 of the present invention are higher in effect than those of Comparative Examples 1 to 3.

As above, while the present invention has been described based on the examples, it is apparent for the skilled in the art that the present invention is not limited to these but can foe implemented in modes modified or changed within the scope and spirit of the present invention, and that such modified or changed modes are within the technical scope of the present invention.

For example, while in the aforementioned Examples 1 to 3, the partition plate elements 6 a to 6 d of the gas flow channel partition plate 6 are formed by combining the triangular plates A to D together, they are not limited to these. In short, they may be formed using flat plates which are processed into gently curved surfaces so as to introduce the combustion flue gas G caused to flow in each of the regions of the gas flow-in face into each of the regions of the gas flow-out face at positions at which the regions are shifted one-by-one around the line segment L 3 connecting the centers of the gas flow-in face and the gas flow-out face.

Moreover, the gas flow channel partition plates 6 of the aforementioned Examples 1 to 3 are formed so as to introduce the combustion flue gas G caused to flow in each of the regions of the gas flow-in face into each of the regions of the gas flow-out face at positions the regions at which are shifted one-by-one around the line segment connecting the centers of the gas flow-in face and the gas flow-out face clockwise. Nevertheless, in the present invention, even when they are formed so as to introduce the combustion flue gas G caused to flow in each of the regions of the gas flow-in face into each of the regions of the gas flow-out face at positions at which the regions are shifted one-by-one around the line segment connecting the centers of the gas flow-in face and the gas flow-out face counterclockwise, the same technical effect is achieved.

Furthermore, the gas flow channel of the present invention may be composed to be formed by joining sides of a plurality of isosceles triangle plate materials together, and by bringing joint parts of the plate materials, the joint parts being concave or convex, to be adjacent to each other or to be set such that their recess parts and projection parts are sequentially alternate with respect to the gas flow direction.