Calculation method for closing emptying valve of centrifugal fan according to slope

Abstract

The invention discloses a calculation method for closing an emptying valve of a centrifugal fan according to a slope, and the calculation method comprises the following specific steps: recording pressure Y1 and flow X1 when the fan is started and runs to a certain rotating speed; according to the current pressure Y2 and flow X2, calculating the slope K of pressure and flow change: K = (Y2-Y1) / (X2-X1); whether the emptying valve can be closed or not is judged, and if any one of the following three conditions is established, the emptying valve can be closed; y2lt; p1 and Klt; a; p2gt, P2gt; y2 and K2gt; a; p1lt; y2 and K1lt; a; wherein P1 and P2 are limited pressure values, K1 and K2 are slope limit values at high pressure and low pressure respectively, A is a maximum allowable slope constant, whether the emptying valve can be safely closed or not is judged by calculating the slope of pressure and flow change according to the running track data of the centrifugal fan, and overpressure and surge of the fan are avoided.

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 to avoid overpressure, surging 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 determine whether the vent valve can be closed, avoiding the risks of overpressure, surging 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, which uses the operating trajectory data of the centrifugal fan to calculate the slopes of pressure and flow rate changes to determine whether the vent valve can be safely closed, avoiding overpressure and surging 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 any of the following three situations is satisfied, then the vent valve can be closed:

[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 tests.

[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: The present invention can effectively determine whether the vent valve can be closed by accurately calculating the slope of pressure and flow rate changes, thereby avoiding the risk of fan overpressure, surge or damage caused by premature or improper closure 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 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 small;

[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. Detailed implementation manners

[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 to judge whether the vent valve can be safely closed by calculating the slope of the pressure and flow rate changes, so as to avoid overpressure and surge of the fan.

[0032] Furthermore, 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 cases 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 pressure and low pressure respectively, and A is the maximum allowable slope constant.

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

[0041] Furthermore, the time interval 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 cases 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 timely response to abnormal fluctuations in pressure and flow 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 per 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. The ordinate in this figure is the pressure (mmaq), and the abscissa is the flow rate (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 by increasing the speed 3 / min, the pressure rise trend is not obvious, because the centrifugal fan cannot directly discharge the compressed air to overcome the pressure at the rear end when it starts. At this time, 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 remains almost unchanged or increases slightly during this process, it means that the exhausted gas can be completely discharged from the rear end and there is no additional resistance. At this time, close the vent valve 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 the 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 lead to pressure exceeding the limit, surge, etc. How to let the system analyze whether the vent valve can be closed? The following lists several situations that may be encountered during startup and analyzes them in detail.

[0054] We first analyze the turtle pressure formed when the pressure at the rear end 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 up 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 horizontal right, Figure 3 The running trajectory is more inclined to the upper right. Based on this, it is judged that different pressures are increased after closing the vent valve due to different slopes of the running path. When the slope is too large, the running state after closing the vent valve belongs to the surge or overpressure state.

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

[0057] Such as Figure 5 shown, the initial operating pressure rises from 3000 mmaq / -20 m 3 / min by increasing the rotational speed, and the pressure rises to 5000 mmaq - 30 m 3 / min. After that, when the rotational speed is continuously 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 has been rising without reaching the inflection point, and the running trajectory continues to move to the right with a large slope, resulting in damage to the fan due to the surge state after closing the vent valve.

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

[0059] Such as Figure 6 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 shown, the initial operating pressure rises from 3000 mmaq / -20 m 3 / min by increasing the rotational speed, and the pressure rises to 9500 mmaq - 31 m 3 / min. After that, when the rotational speed is continuously increased, it rises from 9500 mmaq - 31 m 3 / min to 9500 mmaq - 46 m 3 / min. After closing the vent valve, the operating condition changes to 9800 mmaq - 44 m 3 / min. At this time, the fan pressure is already on the high side and about to exceed the limit, resulting in a fault, but it can still operate at present.

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

[0062] like Figure 8 As shown, 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-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A calculation method for closing a vent valve of a centrifugal fan according to a slope, characterized in that: Using the operating trajectory data of a centrifugal fan, by calculating the slope of the pressure and flow rate changes, it is determined whether the vent valve can be safely closed to avoid overpressure and surge of the fan.

2. A calculation method for closing a vent valve of a centrifugal fan according to a slope according to claim 1, characterized in that: 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 whether the vent valve can be closed. 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; Among them, 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.

3. A calculation method for closing a vent valve of a centrifugal fan according to a slope according to claim 2, characterized in that: The values of K1, K2, P1, P2, and A are obtained through actual tests.

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

5. The calculation method for closing the vent valve of a centrifugal fan according to the slope according to claim 2 is characterized in that: A (the maximum allowable slope constant) 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; DN100A: A = 157; DN110A: A = 182; DN120A: A = 172.

6. The calculation method for closing the vent valve of a centrifugal fan according to the slope according to claim 2 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.

7. A calculation method for closing a vent valve of a centrifugal fan according to a slope according to claim 2, 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 that abnormal fluctuations in pressure and flow rate can be promptly responded to at any time.

8. A calculation method for closing a vent valve of a centrifugal fan according to a slope according to claim 7, 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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