JPH0416221A - Fluid mixing device - Google Patents

Abstract

PURPOSE:To permit different kinds of fluids to be homogeneously intermixed effectively by providing in a duct adapted to allow a first fluid to flow therethrough an orifice smaller in diameter than this duct, on the downstream side of the injection openings provided in the duct to supply a second fluid. CONSTITUTION:An injection nozzle 20 (injection pipe) having six injection openings 21 formed therein to supply a second fluid is inserted into a duct 2 adapted to allow a first fluid (e.g. exhaust gas) to flow to the direction of the arrow A, and an orifice plate 22 provided with an orifice 23 smaller in diameter than the duct 2 is fixed into a duct flange 31, on the downstream side of the injection nozzle 20. Since the orifice 23 is smaller in diameter than the duct, the fluid velocity is sharply increased, when the fluid is passing through the orifice 23. In this way, the fluid becomes turbulent violently, resulting in a complete intermixing of the two kinds of the fluids.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a fluid mixing device for effectively and uniformly mixing different types of fluids. Such a fluid mixing device is used, for example, in an exhaust gas denitrification device that uses a reducing agent and a selective catalytic reduction catalyst to remove nitrogen oxides contained in the exhaust gas of an internal combustion engine. It can be preferably used to

[Conventional technology]

Exhaust gas from internal combustion engines such as diesel engines contains nitrogen oxides (NO) that cause environmental pollution, so it is necessary to perform denitrification treatment to decompose NO in the exhaust gas before releasing it into the atmosphere. There is. A typical exhaust gas denitrification apparatus that has been conventionally used for such denitrification processing will be explained with reference to FIG. 6. Exhaust gas discharged from the exhaust gas outlet of an internal combustion engine, for example, a diesel engine 1, is passed through a duct 2 to an exhaust gas muffler 3.
It is further guided to the denitrification reactor 4 and finally released into the atmosphere from the chimney 5. A bypass 6 is provided in the duct 2, and the exhaust gas discharged from the muffler 3 can be led directly to the chimney 5 through the bypass 6 by operating a valve 7.8 as required. A reducing agent inlet 10 of a reducing agent injection bag W17 is provided in the duct 2 between the muffler 3 and the denitrification reactor 4 and in the vicinity of the denitrification reactor 4. The reducing agent injection device 17 is
Consisting of a flow rate measuring device 11, a flow rate control valve 12, and a piping system thereof, the reducing agent from the reducing agent inlet W9 is transferred to the reducing agent inlet 1 via the flow rate measuring device 11 and the flow rate control valve 12.
0 into the exhaust gas flowing through the duct 2. The amount of exhaust gas in the duct and the concentration of NO in the exhaust gas are measured by the exhaust gas flow rate meter 14 and the NO concentration meter 13, each of which has a detection end upstream of the reducing agent inlet 10, and based on these measured values. A control signal is sent from the control device 15 to the reducing agent flow rate control valve 12, and the amount of reducing agent injected from the reducing agent inlet 10 is controlled. As a reducing agent, a gaseous reducing agent such as ammonia gas,
A liquid reducing agent such as ammonia water or urea water is used, and the exhaust gas injected with such a reducing agent comes into contact with a catalyst in the denitrification reactor 4, and NO in the exhaust gas is converted into harmless N2 by a reduction reaction. After being converted into N20, it is released into the atmosphere from the chimney 5 along with the exhaust gas.

[Problems to be solved by the invention]

In the denitrification device as described above, various measures are required to uniformly and effectively mix the reducing agent injected from the reducing agent inlet 10 and the exhaust gas. For example, providing a gas mixer in which a plurality of tubes are arranged in at least two rows on a plane perpendicular to the gas flow direction in the duct, and the directions of these tube rows are arranged to cross each other; It has also been proposed to make each tube in this tube row triangular in cross section (Japanese Utility Model Publication No. 36331/1983). Furthermore, the structure of the injection part of the reducing agent injection device includes a main pipe arranged along the direction perpendicular to the flow direction of gas in the flue, and a downstream region of the main pipe attached to the rear surface of the main pipe. A mixer W (Japanese Patent Publication No. 59-15006) has also been proposed, which includes a nozzle having an injection port (inlet) therein. Furthermore, when using a gaseous reducing agent, as shown in Figure 6, the reducing agent injection device is often devised to premix the gaseous reducing agent with a blower 16 to ensure complete mixing with the exhaust gas. . However, installing a gas mixer with a special structure as described above or manufacturing a specially shaped jet nozzle will increase the cost of the denitrification equipment, so it is difficult to reduce the amount of nitrogen without increasing the equipment cost. There is a need for a device that can effectively and uniformly mix the agent and the exhaust gas. SUMMARY OF THE INVENTION An object of the present invention is to provide a fluid mixing device with an extremely simple structure that can effectively and uniformly mix different types of fluids such as a reducing agent and exhaust gas.

[Means for solving the problem 1] That is, the present invention includes an inlet for injecting the second fluid provided in a duct through which the first fluid flows, and an inlet disposed in the duct downstream of the inlet. and an orifice plate having an orifice smaller than the diameter of the duct. The second fluid inlet used in this invention may be formed in any manner as long as it is for injecting a different type of fluid into the duct through which the fluid is flowing. It may be an injection port formed in various injection means or discharge means arranged in a duct having a structure conventionally used in the past, or simply by inserting an injection pipe into the duct and opening the tip of the injection pipe. The injection port may be simply provided on the side wall of the duct, or the injection port may be simply provided on the side wall of the duct, with the tip end of the injection tube connected and communicating with the side wall of the duct. Further, the orifice plate can be easily installed in the duct by, for example, sandwiching and fixing the orifice plate to the flange portion of the duct. The fluid mixing device of the present invention is incorporated into an exhaust gas denitrification device for an internal combustion engine as shown in FIG. It can be particularly preferably used when [Function] When the second fluid is injected from the injection port into the first fluid flowing in the duct, the two fluids flow downstream in the duct without being uniformly mixed, and reach the orifice plate. . Since the orifice provided in this orifice plate is smaller than the duct diameter, the flow rate of the fluid is rapidly increased as the fluid passes through the orifice. As a result, the fluid becomes highly turbulent and the two fluids are completely mixed. In addition, when the exhaust gas and reducing agent are mixed in the duct in the exhaust gas denitrification system for an internal combustion engine as shown in Figure 6, pulsations occur in the exhaust gas from the internal combustion engine, so turbulence due to the orifice and exhaust gas Mixing is promoted synergistically by the pulsation of

【Example】

The invention will be described below with reference to embodiments shown in the drawings. 1 to 3 show one embodiment of the fluid mixing device of the present invention, which is composed of an injection port 21 provided in an injection nozzle 20 inserted into a duct 2 and an orifice plate 22. ing. That is, in the duct 2 through which the first fluid (e.g. exhaust gas) is flowing in the direction of arrow A, the second fluid (e.g. reducing agent) is introduced.
An injection nozzle (injection pipe) 20 in which six injection ports 21 are arranged.
is inserted into the duct flange 31 on the downstream side of the injection nozzle 20, and an orifice plate 22 provided with an orifice 23 smaller than the diameter of the duct 2 is inserted and fixed. In the illustrated example, a fluid mixing device consisting of a duct portion 2a having an inlet forming portion and an orifice plate fixing portion is detachably attached to the duct body portion 2 via flanges 32, 33. The distance between the inlet 21 and the orifice plate 22 and the inner diameter of the orifice 23 vary depending on the dimensions of the duct 2 to which the fluid mixing device of the present invention is actually applied, the type of fluid, the flow rate, etc., so complete mixing can be achieved by simple experiments. What is necessary is to determine a suitable optimum value. If the inner diameter of the orifice 23 becomes smaller, the pressure drop of the fluid flowing in the duct 2 when it passes through the orifice 23 becomes larger, and the fluid mixing effect becomes worse. However, when a reducing agent is injected and mixed into the exhaust gas of an internal combustion engine, if the pressure drop at the orifice 23 becomes excessive, this is undesirable as it puts a load on the exhaust gas outlet of the internal combustion engine and even on the internal combustion engine itself. Therefore, the upper limit of the pressure drop at the orifice 23 is determined by the limit of the exhaust gas outlet pressure of each internal combustion engine. Generally, it has been found that effective mixing can be achieved by providing an orifice inner diameter such that the fluid pressure drop across orifice 23 is approximately 30.times.1^q or greater. Note that when a gaseous reducing agent such as ammonia gas is mixed into the exhaust gas as a reducing agent in the exhaust gas denitrification device, in addition to using the fluid mixing device of the present invention, the premixing blower shown in FIG. 16 may be installed, and various mixing promoting means may also be installed. The effects of the fluid mixing device of the present invention will be specifically explained below with reference to experimental examples. Experimental Example 1 Using the fluid mixing device shown in FIG. 1, carbon dioxide gas was injected and mixed into the air flowing in the duct 2, and a fluid mixing test was conducted. The device dimensions, experimental conditions, etc. are as follows. Duct inner diameter: 450 wm Orifice inner diameter Orifice plate (1) 400 sm Orifice plate 1) 300■■ Carbon dioxide gas inlet: Diameter 6V++X6 pieces Distance between inlet and orifice plate: 350am Air flow rate:
89 Na3/win Carbon dioxide gas addition amount: Approximately 1000 pp. The mixing effect is determined by measuring the carbon dioxide concentration in the air flow in the duct 2 at a location 1 to 5 meters downstream from the orifice plate 22 installation location, and determining that the carbon dioxide concentration is complete at a location where the measured value of the carbon dioxide concentration is approximately constant. Mixing was assumed to have been achieved. The results are shown in Figures 4A-C. In the figure, the horizontal axis indicates the location where the carbon dioxide concentration in the airflow in the duct was measured, and is expressed as a distance (mixing distance) from the orifice plate installation location. The vertical axis indicates the carbon dioxide concentration in the air flow at the measurement point. Figure 4A shows the case without an orifice plate, and complete mixing is achieved 4m after passing through the orifice, but 3m
Significant fluctuations were observed in the measured values of carbon dioxide concentration at locations indicated by , indicating that uniform mixing was not achieved. Figure 4B shows the results using the orifice plate (1), and the pressure loss at the orifice was 5-cm. At a point 3 m after passing through the orifice, the fluctuation of the measured value of carbon dioxide concentration is considerably smaller than that in FIG. 4A, indicating that the mixing effect is improved by the installation of the orifice plate. Figure 4C shows the results using the orifice plate (n), and the pressure loss at the orifice was 30I-^q. It can be seen that complete mixing is achieved 2 m after passing through the orifice. In addition, the orifice inner diameter of the orifice plate is 3001■
When made smaller, the distance for complete mixing did not change. Therefore, in this experiment, it was found that sufficient complete mixing could be achieved with an orifice inner diameter of 300 as and a pressure loss of 30 v++^q. Experimental example 2 500KW diesel engine (made by Niigata Iron Works, BL
The exhaust gas denitrification device shown in Figure 6 was installed on the 1QCX type), and the mixing state of the reducing agent and exhaust gas was measured with and without the fluid mixing device equipped with the orifice plate (II) used in Experimental Example 1 above. , was investigated by measuring the denitrification rate. The exhaust gas properties are shown in the table below. Diesel fuel A heavy oil Exhaust gas amount 3.500
Na3 /H exhaust gas temperature 350℃ No concentration 1.000
PPH reducing agent Ammonia gas duct diameter 350cm Denitrification catalyst amount 1-Denitrification reactor SV value 3,5001/11 (exhaust gas superficial velocity) Experiments were conducted with the target denitrification rate changed to 50% and 80%. The results are shown in Figure 5. As shown in Figure 5, the target denitrification rate is 5096.80%.
In both cases, when the orifice plate is not installed, the denitrification rate is low and does not reach the target value, whereas when the orifice plate is installed, the target denitrification rate is achieved, and the reducing agent and exhaust gas have no effect. It can be seen that they are mixed.

【Effect of the invention】

As explained above, the fluid mixing device of the present invention has an extremely simple configuration in which an orifice plate having an orifice smaller than the diameter of the duct is disposed in the duct on the downstream side of the injection port, so that the fluid flowing in the duct can be injected. Complete mixing with the mixed fluid can be efficiently achieved. Therefore, when the fluid mixing device of the present invention is used to inject a reducing agent into the exhaust gas of an internal combustion engine, complete mixing of the reducing agent and the exhaust gas can be achieved within a relatively short distance downstream after the reducing agent is injected. As a result, the distance between the reducing agent inlet and the denitrification reactor can be shortened, and the entire denitrification device can be made more compact.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the fluid mixing device of the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. 4A is a graph showing the mixing effect when carbon dioxide gas is injected into the air flow without installing the fluid mixing device of this invention, and FIG. 4B is a graph showing the mixing effect of the fluid mixing device of this invention (orifice inner diameter 45 UC is a graph showing the mixing effect when the fluid mixing device of this invention (orifice inner diameter 300 as) is installed. Figure 5 is a graph showing the mixing effect when the fluid mixing device of the present invention (orifice inner diameter 300 as) is installed. FIG. 6 is a graph showing changes in the denitrification rate when the fluid mixing device of the present invention is installed in the device and when it is not installed, and FIG. 6 is an explanatory diagram showing a typical example of the conventional exhaust gas denitrification device. 2... Duct, 21... Inlet, 22... Orifice plate, 23... Orifice. Agent tail 4-male distance (m > Mixed distance (m) Zeni mouth distance (m > Figure 2 Figure 2

Claims (1)

[Claims] 1. An injection port for injecting a second fluid provided in a duct through which the first fluid flows, and an orifice smaller than the diameter of the duct provided in the duct downstream of the injection port. 1. A fluid mixing device comprising: an orifice plate having an orifice plate; 2. Claim 1, wherein the first fluid is exhaust gas from an internal combustion engine, and the second fluid is a reducing agent.
The fluid mixing device described.