JPH07133799A - Rotor blade control type axial flow fan - Google Patents

Abstract

PURPOSE:To detect stable index differential pressure corresponding to a flow without being influenced from the condition of flow. CONSTITUTION:In a rotor blade control type axial flow fan in which multiple rotor blades 4 rotating in the direction perpendicular to a flow passage are arranged in the flow passage of gas formed out of an outer casing 2 and an inner casing 3, a suction port pressure detecting port 6 is provided at the suction port 1a of gas of the flow passage and a pressure before rotor blade detecting port 10 is provided before the rotor blade 4, the differential pressure of gas in the flow passage between both pressure detecting ports is detected by means of both pressure detecting ports, and gas is forcedly fed through the rotor blades 4, the pressure detecting port 10 before rotor blade is provided on the position on the upper stream side close to and directly before rotor blades 4 of the inner casing 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable blade axial flow fan used in a thermal power plant or the like, and in particular, it is stable in proportion to the flow rate even on the small flow side of the total flow rate (air volume). The present invention relates to a blade variable axial flow fan suitable for detecting index differential pressure.

[0002]

2. Description of the Related Art A moving blade variable axial flow fan is used for blowing air in a thermal power plant, a Tonrune, etc., and transferring burned gas. The configuration is such that the angle of each moving blade can be changed by hydraulic pressure or the like, and the flow rate and wind pressure can be efficiently controlled over a wide operating range. But,
As the inevitable and fatal characteristics of axial fans, the flow rate,
The air pressure fluctuates drastically, and therefore, there is a wind pressure region where the axial flow fan itself is not allowed to operate with mechanical damage, that is, a surging region.

In particular, when the variable blade axial fan is used by incorporating it into important equipment of a thermal power plant, a system for issuing an alarm when approaching the surging area is installed and data necessary for plant control is installed. Therefore, it is necessary to always know the flow rate and the wind pressure at all operating points of the variable blade axial fan so that the air flow can be supplied.

As shown in FIG. 3, the flow rate is grasped by the suction port pressure detecting port 6 provided at the suction port 1a of the variable blade axial flow fan and the outer casing 2 immediately in front of the moving blade 4. A pressure difference called an index differential pressure measured by the pressure detecting port 7 before the moving blade is obtained, and the gas flow rate flowing in the direction of the arrow shown in the figure obtained in correlation with this index differential pressure is detected. This is because the correlation between index differential pressure and flow rate is
Since it has been obtained in advance from the in-plant test of the variable blade axial fan, the flow rate can be easily measured by measuring the index differential pressure when the variable blade axial fan is actually installed in a local thermal power plant. Because you can ask. In FIG. 3, 3 is an inner casing, 4a is a tip side of the moving blade 4, 4b is a root side of the moving blade 4, and 8 is an upstream side of the moving blade 4 connecting the outer casing 2 and the inner casing 3. A plurality of stays, 9 are differential pressure transducers.

As a measure to reduce the surging area and expand the operating area, the outer casing 2 facing the tip side 4a of the moving blade 4 may be subjected to a treatment such as a casing treatment and an air separator (not shown). .

[0006]

However, when the pressure detecting port 7 before the moving blade is provided in the outer casing 2 immediately in front of the moving blade 4, there is a structural advantage that the pressure detecting port 7 before the moving blade is easily provided. However, there were the following problems.

That is, as shown in the diagram for explaining the stagger angle in FIG. 4 which is a view taken along the line IV-IV in FIG. 3, the rotor blade 4 has a velocity triangle corresponding to the peripheral velocity at each radius in the radial direction with respect to the rotation axis. To form the moving blade 4 tip.
The stagger angle is different between the side 4a and the root side 4b. Fig. 4 shows an example of the stagger angle when the angle of the blade 4 is controlled to the small flow rate side. As shown in the figure, the stagger angle (+ θroot) on the root side 4b is positive, and the flow is opposite to the tip side 4a. However, the stagger angle (-θtip) on the tip side 4a becomes negative and a backflow occurs.

When the angle of the moving blade 4 is controlled to the small flow rate side in this way, the flow partially becomes unsteady on the tip side 4a of the moving blade 4 and backflow occurs, and the pressure immediately before the moving blade 4 is correctly detected. As a result, as shown by a dotted line in FIG. 5 showing an example of index differential pressure characteristics, an apparent index differential pressure different from the actual flow rate is generated, and an unstable flow rate range is formed. There is.

In order to prevent the above phenomenon, it is effective to separate the pressure detecting port 7 before the moving blade from the moving blade 4 to the upstream side (suction port side) as much as possible, and at the same time, the flow upstream of the moving blade 4 is sufficiently rectified. Although it is essentially necessary to detect the pressure later, in both cases, the size of the entire apparatus becomes large and it is difficult to take sufficient measures.

The present invention has been made in view of the above problems of the prior art.
An object of the present invention is to provide a variable blade axial flow fan capable of detecting a stable index differential pressure corresponding to a flow rate without being affected by a flow state in the entire flow rate range including a small flow rate side.

[0011]

In order to achieve the above object, the present invention provides a large number of blades rotating in a direction perpendicular to the flow passage of gas formed by an outer casing and an inner casing. And a suction port pressure detection port is provided at the gas suction port of the flow channel, and a front blade detection pressure detection port is provided in front of the moving blade. In the variable blade axial flow fan that detects the pressure difference of the gas of the above, and sends the gas under pressure through the moving blade, the position of the upstream side immediately before the moving blade front pressure detection port is close to the moving blade of the inner casing. It is configured to be installed in.

[0012]

With the above-described structure, the pressure in the flow path is measured from the tip side of the moving blade, which becomes unstable when the gas flow is on the small flow rate side, and the stagger angle of the moving blade shown in FIG. Positive (+
θroot) is performed at the position where the gas flow is moved to the stable base side, and even when the blade angle is controlled to the small flow rate side, the pressure immediately before the blade is not affected by the flow condition. Can be correctly detected.

For this reason, it is possible to perform stable pressure measurement over the entire area including the small flow rate side, which is impossible in the conventional state in which the position of the pressure detecting port before the moving blade is provided in the outer casing immediately in front of the moving blade. By obtaining a stable index differential pressure, it is possible to measure the flow rate with much higher accuracy than in the past.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a side sectional view showing an example of a moving blade variable axial flow fan, and FIG. 2 is a detailed view of a pressure detection unit in FIG. FIG. 5 is a diagram showing a characteristic example of the index differential pressure generated with respect to the actual flow rate. In the figure, FIG.
Those having the same reference numerals as those in FIG.

In FIG. 1, reference numeral 1 is a suction casing, 5 is a discharge casing, and 10 is a pressure detecting port before moving blades provided in the inner casing 3. The mounting position thereof is as shown in FIGS. However, the distance from the moving blade 4 may be substantially the same as the position shown in FIG. In addition, the mounting quantity of the pressure detection port 10 before the moving blade is
Although only one is provided in the figure, it is also possible to arrange a plurality of them on the circumference of the inner casing 3 at an appropriate pitch and average the measured pressures. 11 is a pressure detecting port 1 in front of the moving blade
The pressure measured at the front pressure detecting port 10 of the moving blade is guided to the outside of the outer casing 2 through the inside of the stay 8 by a conduit connecting 0 and the differential pressure converter 9. Front pressure detection port 1
The diameter of 0 is usually about 10 mm, but a large diameter of about 50 mm may be adopted for applications such as an induced draft fan containing dust. The conduit 11 may be attached to the outside without using the stay 8, and may be guided to the outside by using a pipe separately provided between the inner casing 3 and the outer casing 2. The conduit 11 is usually made of stainless steel in consideration of corrosion. The differential pressure converter 9 is attached to the outer casing 2
It may be installed inside the inner casing 3 instead of outside.

In the above structure, the gas sucked from the suction port 1a of the suction casing 1 is rectified through the flow passage formed by the outer casing 2 and the inner casing 3,
The pressure is boosted by the moving blades 4 and discharged from the discharge casing 5.
The pressure before the moving blade of the gas sucked from the suction port 1a is not the tip side 4a of the moving blade 4 which becomes unstable when the gas flow is on the small flow rate side, but the stagger angle of the moving blade 4 is as shown in FIG. As shown in, the measurement is always performed at the position on the root side where the gas flow is stable and stable. Therefore, even when the angle of the moving blade 4 is controlled to the small flow rate side, the conventional unstable characteristic portion shown by the dotted line in FIG. 5 is eliminated, and the moving state is not affected by the flow state as shown by the solid line. It is possible to correctly detect the pressure immediately before the blade 4.

Therefore, stable pressure measurement, which has been impossible in the past, can be performed over the entire area including the small flow rate side, and by obtaining a stable index differential pressure, the flow rate can be measured with much higher accuracy than the conventional one. It will be possible.

Further, even if the casing treatment and the air separator are treated, they do not interfere with the treatment at all.

[0019]

As described above, in the variable blade axial flow fan of the present invention, the pressure detecting port before the moving blade is provided at the upstream side position immediately before the moving blade of the inner casing. In the entire flow rate range including the side, a stable index differential pressure that matches the flow rate can be detected without being affected by the flow state.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a moving blade variable axial flow fan according to an embodiment of the present invention.

FIG. 2 is a detailed view of a pressure detection unit in FIG.

FIG. 3 is a detailed view of a conventional pressure detector.

FIG. 4 is an IV-IV arrow view of FIG. 3 and is a diagram for explaining a stagger angle.

FIG. 5 is a diagram showing a characteristic example of index differential pressure.

[Explanation of symbols]

1a ... suction port, 2 ... outer casing, 3 ... inner casing,
4 ... moving blade, 4a ... moving blade tip side, 4b ... moving blade root side, 6 ...
Suction port pressure detection port, 7, 10 ... Pressure detection port before moving blade, 8 ...
Stay, 9 ... Differential pressure detector, 11 ... Conduit.

Claims (1)

[Claims] 1. A large number of blades rotating in a direction perpendicular to the flow passage are arranged in a gas flow passage formed by an outer casing and an inner casing, and a suction port is provided at a gas suction port of the flow passage. A pressure detecting port is provided and a pressure detecting port before the moving blade is provided in front of the moving blade, and the pressure difference of the gas in the flow path between the pressure detecting ports is detected by the both pressure detecting ports, and the gas is moved to the moving blade. A variable-blade variable axial flow fan that is pressure-fed via a rotor, wherein the front-blade pressure detection port is provided at a position on the upstream side immediately before being close to the moving blade of the inner casing.