A calculation method for closing the vent valve of a centrifugal fan based on the slope

Abstract

The present invention discloses a calculation method for closing a vent valve according to the slope of a centrifugal fan. The specific steps of the calculation method include: when the fan starts and runs to a certain speed, record the pressure Y1 and the flow rate X1; according to the current pressure Y2 and the flow rate X2, calculate the slope K of the pressure and flow rate change: K = (Y2 - Y1) / (X2 - X1); judge the condition for closing the vent valve. If any of the following three situations is established, the vent valve can be closed: P2 < Y2 < P1 and K < A; P2 > Y2 and K2 > A; P1

Description

Technical Field

[0001] The present invention relates to the technical field of fans, and particularly to a calculation method for a centrifugal fan to close a vent valve according to a slope. Background Art

[0002] When a centrifugal fan starts, the vent valve needs to be kept open until the fan reaches a stable state. At this time, the timing of closing the vent valve is crucial because it cannot be accurately judged solely by the values of pressure or flow rate. During the operation of the fan, the changes in pressure and flow rate are affected by factors such as pipeline resistance and back-end pressure.

[0003] In view of the above problems, an algorithm is needed to analyze the change slopes of pressure and flow rate to determine whether the vent valve can be safely closed, so as to avoid situations such as overpressure, surge or damage of the fan. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a calculation method for a centrifugal fan to close a vent valve according to a slope. By accurately calculating the slopes of pressure and flow rate changes, it can effectively judge whether the vent valve can be closed, avoiding the risks of overpressure, surge or damage of the fan caused by premature or improper closing of the vent valve. Through real-time monitoring and algorithm judgment, the failure rate of the fan can be greatly reduced, and the reliability and service life of the fan can be improved.

[0005] Technical Solution:

[0006] A calculation method for a centrifugal fan to close a vent valve according to a slope uses the operating trajectory data of the centrifugal fan. By calculating the slopes of pressure and flow rate changes, it judges whether the vent valve can be safely closed, avoiding overpressure and surge of the fan.

[0007] Further, the specific steps of the calculation method include:

[0008] When the fan starts and runs to a certain speed, record the pressure Y1 and the flow rate X1;

[0009] According to the current pressure Y2 and flow rate X2, calculate the slope K of the pressure and flow rate changes: K = (Y2 - Y1) / (X2 - X1);

[0010] The conditions for judging whether the vent valve can be closed are that the vent valve can be closed if any of the following three situations is satisfied:

[0011] ]P2 < Y2 < P1 and K < A;

[0012] P2 > Y2 and K2 > A;

[0013] P1 < Y2 and K1 < A;

[0014] Among them, P1 and P2 are limited pressure values, K1 and K2 are slope limit values ​​at high pressure and low pressure respectively, and A is the maximum allowable slope constant.

[0015] Furthermore, the values ​​of K1, K2, P1, P2, and A are obtained through actual testing.

[0016] Furthermore, the interval between the time differences Y1 and Y2 is 3 to 10 seconds.

[0017] Furthermore, A (maximum allowable slope constant) is related to the inner diameter of the outlet of the vent valve, and the specific values ​​are as follows: DN30A: A=1366; DN35A: A=906; DN40A: A=721; DN45A: A=566; DN50A: A=461; DN55A: A=383; DN60A: A=328; DN65A: A=290; DN70A: A=263; DN75A: A=239; DN80A: A=220; DN90A: A=201; DN100A: A=157; DN110A: A=182; DN120A: A=172.

[0018] Furthermore, if none of the three conditions are met, the vent valve will not be closed, and the fan will be stopped when an overload alarm occurs subsequently.

[0019] Furthermore, the step of determining whether the vent valve can be closed further includes real-time monitoring of the operating status of the fan to ensure that abnormal fluctuations in pressure and flow can be responded to in a timely manner at any time.

[0020] Furthermore, the real-time monitoring includes obtaining real-time pressure and flow data using sensors of the fan, and calculating a real-time slope through a data processing system to determine whether the conditions for closing the vent valve are met.

[0021] Beneficial Effects: This invention effectively determines whether the vent valve can be closed by accurately calculating the slope of pressure and flow rate changes, thus avoiding the risk of fan overpressure, surge, or damage caused by premature or improper closure of the vent valve. Through real-time monitoring and algorithmic judgment, the fan failure rate can be greatly reduced, and the reliability and service life of the fan can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a calculation flow chart of the present invention;

[0023] Figure 2 is a performance diagram of a centrifugal fan according to an embodiment of the present invention;

[0024] Figure 3 This is a running trajectory diagram of the centrifugal fan when the pressure is relatively low;

[0025] Figure 4It is the operation trajectory diagram of the centrifugal fan when the backpressure of the present invention is relatively large;

[0026] Figure 5 It is the operation trajectory diagram of the centrifugal fan when the backpressure of the present invention is extremely large;

[0027] Figure 6 It is the operation trajectory of the centrifugal fan when the pressure before the vent valve of the present invention is relatively high Figure 1 ;

[0028] Figure 7 It is the operation trajectory of the centrifugal fan when the pressure before the vent valve of the present invention is relatively high Figure 2 ;

[0029] Figure 8 It is the operation trajectory diagram of the centrifugal fan when the operating pressure before the vent valve of the present invention is relatively low and the slope of the operating path is relatively small. Specific embodiments

[0030] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0031] As Figure 1 shown, a calculation method for closing the vent valve according to the slope of a centrifugal fan uses the operation trajectory data of the centrifugal fan. By calculating the slope of the pressure and flow rate changes, it is judged whether the vent valve can be safely closed to avoid overpressure and surge of the fan.

[0032] Further, the specific steps of the calculation method include:

[0033] When the fan starts and runs to a certain speed, record the pressure Y1 and the flow rate X1;

[0034] According to the current pressure Y2 and flow rate X2, calculate the slope K of the pressure and flow rate changes: K = (Y2 - Y1) / (X2 - X1);

[0035] Judge the conditions for closing the vent valve. The vent valve can be closed if any of the following three situations is satisfied:

[0036] P2 < Y2 < P1 and K < A;

[0037] P2 > Y2 and K2 > A;

[0038] P1 < Y2 and K1 < A;

[0039] Among them, P1 and P2 are the defined pressure values, K1 and K2 are the slope limit values at high and low pressures respectively, and A is the maximum allowable slope constant.

[0040] Further, the values of K1, K2, P1, P2, and A are obtained through actual tests.

[0041] Furthermore, the interval time between the time differences Y1 and Y2 is 3 to 10 seconds.

[0042] Furthermore, A (the maximum allowable slope constant) is related to the inner diameter of the air outlet of the vent valve, and the specific values are as follows:

[0043]

[0044]

[0045] Furthermore, if none of the three situations holds, the vent valve is not closed, and the fan stops when an overload alarm occurs subsequently.

[0046] Furthermore, in the step of determining whether the vent valve can be closed, it further includes real-time monitoring of the operating state of the fan to ensure that abnormal fluctuations in pressure and flow can be promptly responded to at any time.

[0047] Furthermore, the real-time monitoring includes using the sensors of the fan to obtain real-time pressure and flow data, and calculating the real-time slope through a data processing system to determine whether the conditions for closing the vent valve are met.

[0048] Example 1: P2 < Y2 < P1 and K < A

[0049] When the centrifugal fan is running, the vent valve needs to be opened first and run to a certain speed and maintain a certain pressure before the vent valve can be closed. However, whether the pressure at the time of closing the vent valve is appropriate cannot be effectively judged from a single value. We can judge by analyzing several groups of data composed of pressure and flow within a unit time.

[0050] As Figure 2 shown, it is the performance diagram of the centrifugal fan used in this example. This example has a rated pressure of 100 KPA and a rated power of 85 KW. In this figure, the vertical axis is pressure (mmaq), the horizontal axis is flow (m 3 / min), the left-side numerical values and the long solid curve are the speed values and speed lines, the right-side numerical values and the downward-sloping dotted line are the power values and power lines, and the fan model is ATB100HP - 1.0.

[0051] As Figure 3 shown, it shows the operating trajectory diagram of the centrifugal fan assuming that the current back-end pressure is 8000 mmaq and adding a little pipeline resistance appropriately.

[0052] The initial operating pressure rises from 3000 mmaq / -20 m 3 / min to 8000 mmaq - 29 m 3 / min after the operation pressure rise trend is not obvious, because the centrifugal fan can not directly overcome the pressure at the rear end to discharge the compressed air when it starts, and most of the discharged gas is discharged from the vent valve. Since the outlet size of the vent valve is fixed, the speed increases and the pressure increases, and the flow rate increases slightly. Continue to increase the speed when 8000mmaq-29m 3 / min increased to 8000mmaq-50m 3 / min, when the pressure in this process remains almost unchanged or increases slightly, it indicates that the exhausted gas can be completely discharged from the rear end and there is no additional resistance. At this time, the vent valve is closed and the operating point data is from 8000mmaq-50m 3 / min changed to 8400mmaq-48m 3 / min, stable operation. Generally, the startup and operation process of a centrifugal fan under ideal conditions is as above.

[0053] However, when there is additional resistance in the pipeline or the rear-end pressure exceeds the expected pressure, it is unknown whether closing the vent valve will cause pressure exceeding the limit, surge, etc. How to let the system analyze whether the vent valve can be closed? The following lists several situations encountered during startup and analyzes them in detail.

[0054] We first analyze the turtle pressure formed when the rear-end pressure is constant due to the resistance in the pipeline or at the outlet, which causes the speed to increase and the pressure to increase accordingly. When the turtle pressure is small, it will not cause too much adverse effect. When the turtle pressure is large, it will cause the total pressure to exceed expectations, resulting in pressure over-limit and surge failure.

[0055] like Figure 4 As shown, the initial operating pressure is 3000mmaq / -20m 3 / min increase the speed and pressure to 7000mmaq-27m 3 / min, continue to increase the speed from 7000mmaq-27m 3 / min rise to 8000mmaq-50m 3 / min, after closing the vent valve, the operating condition changes to 9000mmaq-35m 3 / min. Compare Figure 2 and Figure 3 From the data, we can conclude that when the pressure rises to the inflection point, the flow rate begins to increase. Figure 2 The pressure rise is lower than Figure 3 , so when the vent valve is closed, Figure 2 The rising pressure is lower than Figure 3 At the same time we intercept Figure 2 and Figure 3 From the data between the inflection point and the closing of the vent valve, it can be seen that Figure 2The running trajectory is more inclined to the right horizontally, Figure 3 The running trajectory is more inclined to the upper right. Based on this, it is judged that the increased pressure after closing the vent valve is different due to the different slopes of the running paths. When the slope is too large, the running state after closing the vent valve belongs to the surge or overpressure state.

[0056] When the normal gas outlet cannot be achieved, the pipeline valve opening is insufficient or the internal pressure of the pipeline is severely blocked, the actual pressure will far exceed the expectation, resulting in damage to the fan.

[0057] Such as Figure 5 As shown, the initial operating pressure rises from 3000 mmaq / -20 m 3 / min. When the rotational speed is increased, the pressure rises to 5000 mmaq - 30 m 3 / min. After that, when the rotational speed is further increased, it rises from 5000 mmaq - 30 m 3 / min to 8000 mmaq - 50 m 3 / min. After closing the vent valve, the operating condition changes to 10000 mmaq - 10 m 3 / min. At this time, the fan is already in the surge state and the fan is about to be damaged. By comparing Figure 2 and Figure 4 data, we can conclude that the pressure keeps rising without reaching the inflection point and the running trajectory continues to move to the right with a large slope, resulting in the fan being in the surge state and being damaged after closing the vent valve.

[0058] Example 2: P2 > Y2 and K2 > A

[0059] Such as Figure 6 As shown, when the pressure before closing the vent valve is high, it is necessary to judge whether the vent valve can be closed according to the running path before closing, and confirm that the pressure is within the limit after closing the vent valve. Otherwise, it will cause the pressure to exceed the limit and damage the fan.

[0060] Such as Figure 7 As shown, the initial operating pressure rises from 3000 mmaq / -20 m 3 / min. When the rotational speed is increased, the pressure rises to 9500 mmaq - 31 m 3 / min. After that, when the rotational speed is further increased, it rises from 9500 mmaq - 31 m 3 [[ID=4३]] / min to 9500 mmaq - 46 m 3 / min. After closing the vent valve, the operating condition changes to 9800 mmaq - forty-four m 3 / min. At this time, the fan pressure is already on the high side and about to exceed the limit, resulting in a failure, but it can still operate at present.

[0061] Example 3: P1 < Y2 and K1 < A

[0062] like Figure 8 As shown in the figure, when the operating pressure is low and the slope of the operating path is small, the vent valve can be closed normally without affecting the fan.

[0063] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A calculation method for closing the vent valve of a centrifugal fan according to the slope, characterized in that: Using the operating trajectory data of a centrifugal fan, by calculating the slope of the pressure and flow rate changes, determine whether the vent valve can be safely closed to avoid overpressure and surge of the fan; The specific steps of the calculation method include: 1) When the fan starts and runs to a certain speed, record the pressure Y1 and the flow rate X1; 2) According to the current pressure Y2 and flow rate X2, calculate the slope K of the pressure and flow rate changes: K = (Y2 - Y1) / (X2 - X1); 3) Determine the conditions for closing the vent valve. The vent valve can be closed if any of the following three situations holds: P2 < Y2 < P1 and K < A; P2 > Y2 and K2 > A; P1 < Y2 and K1 < A; Where, P1 and P2 are the specified pressure values, K1 and K2 are the slope limit values at high and low pressures respectively, and A is the maximum allowable slope constant; The values of K1, K2, P1, P2, and A are obtained through actual tests.

2. The calculation method for closing the vent valve of a centrifugal fan according to claim 1 is characterized in that: The time interval between the time differences Y1 and Y2 is 3 to 10 seconds.

3. The calculation method for closing the vent valve of a centrifugal fan according to claim 1 is characterized in that: The maximum allowable slope constant A is related to the inner diameter of the outlet of the vent valve. The specific values are as follows: DN30A: A = 1366; DN35A: A = 906; DN40A: A = 721; DN45A: A = 566; DN50A: A = 461; DN55A: A = 383; DN60A: A = 328; DN65A: A = 290; DN70A: A = 263; DN75A: A = 239; DN80A: A = 220; DN90A: A = 201; DN\(100\)A: A = 157; DN\(110\)A: A = 182; DN\(120\)A: A = 172.

4. The calculation method for closing the vent valve of a centrifugal fan according to claim 1 is characterized in that: If none of the three situations holds, the vent valve is not closed, and the fan is stopped when an overload alarm occurs subsequently.

5. The calculation method for closing the vent valve of a centrifugal fan according to claim 1 is characterized in that: In the step of determining whether the vent valve can be closed, it further includes real-time monitoring of the operating state of the fan to ensure timely response to abnormal fluctuations in pressure and flow rate at any time.

6. The calculation method for closing the vent valve of a centrifugal fan according to claim 5 is characterized in that: The real-time monitoring includes using the sensors of the fan to obtain real-time pressure and flow rate data, and calculating the real-time slope through a data processing system to determine whether the conditions for closing the vent valve are met.

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