JPS5915006B2 - fluid mixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid mixing device used to mix ammonia into exhaust gas, for example, in order to denitrate the exhaust gas.

Conventionally, a fluid mixing device is known in which a jet nozzle for spouting another fluid is disposed in a fluid pipe line through which one fluid flows, but this device is designed to prevent the spouted other fluid from flowing into a turbulent flow. Because it uses only so-called jet diffusion, the time required for mixing is longer.
There is a disadvantage that the fluid pipe line becomes long and the device becomes large.

Furthermore, in order to utilize jet diffusion, the ejection speed of the other fluid must be made larger than the speed of the first fluid, which also has the disadvantage of increasing the size of the ejection mechanism including the pump. The present invention has been made to solve the above-mentioned conventional drawbacks, and consists of an ejection pipe corresponding to the above-mentioned conventional ejection nozzle consisting of a main pipe and a nozzle, so that the ejection opening of the nozzle is connected to the downstream area of the main pipe. By setting the temperature within
The purpose is to downsize the device.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 11 denotes a fluid pipe, and this fluid pipe 11
A fluid, such as boiler exhaust gas, is flowing through the arrow 1.
It flows in the direction shown by 2.

An ejector 13 for ejecting another fluid, such as ammonia gas, is disposed in the fluid pipe line 11, and the ejector 13 is directed in a direction 14 perpendicular to the flow direction 12 of the first fluid. A main pipe 15 arranged along the main pipe 15
It consists of a nozzle IT having a spout 16 in a trailing region (to be described later) of a main pipe 15 attached to the rear surface. The other fluids mentioned above are supplied to the main pipe 15 in the direction shown by arrow 18 and are ejected from the nozzle 17 in the direction shown by arrow 19. At the rear end of the fluid pipe 11, a processing device 20 such as a reactor for denitrification is installed. The fluid pipe line 11
As shown in FIG. 2, its cross-sectional shape is a square with a side length B, and within this conduit 11, a plurality of main pipes 15 are erected at equal intervals 1, and each main pipe 15, a plurality of nozzles 17 are also attached at equal intervals e.

In this example, [=e. The main pipe 15 is the third
As shown in the figure, a nozzle 17 made of a circular tube is welded to the main tube 15.

The spout 16 of the nozzle 17 is connected to the wake area 2 of the main pipe 15.
1, but this wake area 2
1 is defined here as follows. Although the flow in the wake is unsteady, the temporal average velocity distribution is as shown in Figure 3.

Here, u is the velocity inside the wake, U(X) is the velocity of the surrounding steady flow, and Δu is the difference U between the above two velocities. The velocity deficit is equal to O-u, ΔUmax is the maximum velocity deficit occurring on the center line 22 of the wake, and y is the distance from said center line 22, respectively. The speed deficit Δu is 1 of the maximum speed deficit ΔUmax
The width b, which is /2, is called the half-width of the wake, and is usually taken as a representative value representing the width of the wake. Here, the wake width is defined as twice the half width b. That is, -b
The region yb is defined as the wake region 21. next,
The fact that by setting the ejection port 16 of the nozzle 17 within the wake region 21 of the main pipe 15, the other fluid ejected from the ejection port 16 and the above-mentioned one fluid are rapidly mixed. This will be explained using the measurement results shown in FIGS. 5 and 6.

First, as shown in FIG. 4, the inner diameter of the nozzle 17 is d, the temperature of the other ejected fluid is C1, the maximum concentration occurring on the center line 22 of this jet is Cmaxl, and the concentration at the jet nozzle 16 is Cmax.
O, the distance from the jet port 16 along the center line 22 is X1, and the distance from the center line 22 is y. moreover,
Width f where the density C is 1/2 of the maximum density Cmax
is defined as the half-width of the concentration distribution, and FIG. 5 shows a downstream change in the half-width f, and FIG. 6 shows a downstream change in the maximum concentration Cmax. In both figures, G indicates the measurement result of this example, and H indicates a calculated value calculated from a theoretical calculation formula for turbulent diffusion of a jet flow, which corresponds to the conventional example described above. FIG. 5 shows that the half-width f increases more rapidly toward the downstream than before, and FIG. 6 shows that the maximum concentration Cmax decreases more rapidly toward the downstream than before. This represents the fact that the other ejected fluid is rapidly mixed with one fluid flowing around it. q Furthermore, the wake region 21 shown in FIG. 3 exists only in a limited portion downstream of the main pipe 15, and furthermore, the mixing promotion effect due to the turbulent wake becomes more and more downstream. Therefore, in order for the fluid mixing device of the present invention to function effectively, it is considered that the shape and arrangement of the main pipe 15 and the nozzle 17 must satisfy a certain relationship.

Therefore, the inventors conducted an experiment and found that the main pipe 15
It has been found that it is desirable that the outer diameter D of the main tube 15, the set interval of the main pipe 15, and the length l of the nozzle 17 be set so as to satisfy the following relational expression. First, in the above equation (1), D/t≧0.
I will explain the reason why I chose 2.

Since the wake region 21 shown in FIG. 3 exists only in a limited downstream part of the main pipe 15, the outer diameter D of the main pipe 15
Compared to this, if the set interval t of the main tube 15 in FIG. 2 is too large, the wake will not spread throughout the fluid conduit 11, and as a result, the mixing effect of this wake will not reach the entire area.

FIG. 7 shows the results of measuring the half width f of the concentration of other ejected fluids. This measurement was carried out with three different lengths l of the nozzle 17, G1 was l/D=0, G2 was l
/D-1.17 and G3 respectively show the case of l/D=3.28. In addition, the dashed line J is the half width b of the wake of the main pipe 15.
shows. As shown by the curves G1 to G3 in FIG. 7 above, immediately after the jet of other fluid is ejected from the nozzle 17, the width of the jet gradually expands due to the force of the jet, but after that, for a while. It shows a rapid expansion for a period of time, and then changes to a gradual expansion again.

This is because the jet expands rapidly until it fully expands into the wake, but after it fully expands, it only expands as the width 2b of the wake increases. Therefore, in order to achieve rapid mixing, it is necessary for adjacent jets to overlap or for the jet to reach the inner wall of the fluid conduit 11 (see Figure 2) before the rapid expansion of the jet is completed. You must do so. It has been found from various experiments that the width of the jet when it is fully expanded into the wake is approximately 5D. From now on, if the set interval t of the main pipe 15 in FIG. 2 is set to t≦5D, that is, rapid mixing is guaranteed.

Next, using the above equation (1), D/ZO. The reason why it was set as 6 is S.
State t=3.

When D/t is large, the fluid pipe line 1 by the main pipe 15 in FIG.
The blockage of fluid pipe 1 increases, pressure loss in fluid pipe line 11 increases, and the power required for a blower or a pump to flow fluid in fluid pipe line 11 increases.

This situation is shown in FIG. In the figure, the pressure loss coefficient on the vertical axis is the pressure difference between the upstream side and the downstream side of the main pipe 15, that is, the pressure loss ΔP, divided by the dynamic pressure σUZ/2 of the one fluid. As is clear from this Figure 8, D/
When 1 becomes 0.6 or more, the pressure loss coefficient increases rapidly. Therefore, it is desirable to

Next, the reason why the above formula (2) holds true will be described.

The strength of the mixing action of the wake is proportional to the maximum velocity deficit ΔUmax shown in FIG. On the other hand, this maximum speed deficit △Um
Ax is generally 1? It decreases in proportion to the downstream direction. The state of this decrease is shown in FIG. Here, the above-mentioned X is the distance from the center 23 of the main pipe 15 toward the downstream. The figure shows a theoretical example where the main tube 15 is a circular tube and the Reynolds number Re=UOOD/v is in the range of 103 to 4×105, which is the normal range for this type of fluid mixing device. Calculated values are shown. Note that ν represents the kinematic viscosity coefficient of one fluid. According to this Figure 9, △
Umax/UOO is approximately 0.5 at x/D=5, x/D-
It can be seen that it decreases from about 0.3 at x/D-20 to about 0.2 at x/D-20. Therefore, with this decrease, the strength of the mixing effect of the wake also decreases. This means that nozzle 1
If the length l of 7 is made too long, this means that the mixing effect will be extremely reduced. In order to avoid this extreme drop in mixing effect, /U
;::v It turned out that it was necessary.

As described above, according to the present invention, the fluids are mixed rapidly, so that the fluid pipe line 11 necessary for mixing shown in FIG.
The required expression L becomes smaller.

When an experiment was actually conducted to investigate this length L, the following results were obtained. That is, as shown in FIG. 10, the distance downstream from the jet nozzle 16 of the nozzle 17 along the center line 22 of the jet is X1, the concentration of the jet is C1, and the average concentration on the cross section perpendicular to the jet is C. Assuming that the maximum width of the concentration distribution is 2ΔC, the measurement results shown in FIG. 11 were obtained.

In this measurement, the set interval t of the main pipe 15, the nozzle 17
The relationship between the installation interval e, the outer diameter D of the main pipe 15, and the length l of the groove 17 is t=ElD/t=0.46, l/
It was designated as D-3. The horizontal axis of FIG. 11 represents the distance X1 made dimensionless by the set interval t, and the vertical axis represents the ratio of ΔC, which is half of the maximum width, to the average density C.
ΔC/c on the vertical axis becomes smaller as mixing is promoted, and eventually reaches zero, resulting in a uniform mixed flow.
Practically speaking, if ΔC/σ -0.05 to 0.01, it can be considered to be uniformly mixed, so from Figure 11 it can be seen that the distance required for mixing is X1/t = 5 to 7. . Therefore, the required length L of the fluid conduit 11 is as follows.

The above required length L is, when there is one nozzle 17,
Replace the set interval t(-e) with the second winning pipe width B,
becomes.

If a large number of nozzles 17 are arranged and the set interval t is made small,
The above required length L becomes smaller.

Note that when the cross section of the fluid pipe line 11 is not rectangular, the above (4)
) formula, the pipe width B is virtually calculated by assuming that the pipe cross-sectional area is A.
] ▲ Represented in Kg. In addition, since this invention uses the turbulence of the wake of the main pipe 15 to mix, the ejection speed of other fluids ejected from the nozzle 17 is much higher than when using jet diffusion as in the past. Since it can be small, there is also the effect that the blowing mechanism including the blower and pump can be made smaller.

In the embodiments shown in FIGS. 1 to 11 above, a circular pipe was used as the main pipe 15, but in order to enlarge the wake region 21 or strengthen the turbulence in the wake region 21, , a rectangular tube as shown in FIG. 12, or a fin 25 as shown in FIG.
A circular tube with a main tube 15 may be used.
The width in the direction perpendicular to the flow corresponds to the outer diameter D of the circular tube in the above embodiment.

As explained above, according to the present invention, the required length of the fluid pipe line required for mixing is shortened, so the fluid pipe line is shortened, and the fluid ejection mechanism is also downsized, so the fluid mixing The entire device is made very small.

[Brief explanation of the drawing]

1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line 2-2 in FIG. 1, and FIG. 3 is a sectional view taken along line 2-2 in FIG.
Figure 4 is a schematic diagram showing the concentration distribution of the jet, Figure 5 is a characteristic diagram showing the change in the half-width of the jet toward the downstream, and Figure 6 is the maximum of the jet. A characteristic diagram showing the change in concentration toward the downstream. Figure 7 is a characteristic diagram showing the change in the half width of the jet concentration toward the downstream using the length of the nozzle as a parameter. Figure 8 is the setting of the main pipe. FIG. 9 is a characteristic diagram showing the pressure loss of the fluid pipe line with respect to the spacing. FIG. 9 is a characteristic diagram showing the change in the maximum velocity deficit toward the downstream. FIG. Fig. 11 is a characteristic diagram showing the change in the maximum width of the concentration distribution in Fig. 10 toward the downstream, Fig. 12 is a sectional view showing a modification of the main pipe, and Fig. 13 is a diagram showing another modification of the main pipe. FIG. 11...Fluid pipe line, 12...Flow direction, 13...Ejector, 14...Orthogonal direction, 15...Mother Pipe, 16... spout, 17... nozzle.

Claims (1)

[Claims] 1. An ejector that ejects another fluid is disposed in a fluid pipeline through which one fluid flows, and this ejector is connected to a main pipe arranged along a direction perpendicular to the flow direction of the first fluid. , a nozzle attached to the rear surface of the main pipe and having a spout in the wake region of the main pipe.