Water pump anti-cavitation device and control system

Abstract

The invention discloses a water pump anti-cavitation device and a control system, the water pump anti-cavitation device comprises N first flow passages and N second flow passages which are connected in parallel, each first flow passage comprises a first water pump and a first regulating valve which are connected in series, and each second flow passage comprises a second water pump and a second regulating valve which are connected in series; the first water pump and the second water pump are both provided with flow limiting values, the first adjusting valve automatically adjusts the opening degree of the valve according to the flow value output by the first water pump so that the output flow value can be smaller than or equal to the flow limiting values, and the second water pump adjusts the power supply frequency so that the output flow value can be smaller than or equal to the flow limiting values. The limited flow value is smaller than the critical cavitation flow value, the limited flow value is a positive root of a rooting result obtained through calculation of the effective net positive suction head, the necessary net positive suction head and the safety margin, and the critical cavitation flow value is a flow value obtained when the effective net positive suction head is the same as the necessary net positive suction head. According to the invention, the operation cost can be reduced while cavitation can be effectively prevented.

Description

Technical Field

[0001] The invention relates to the technical field of energy conservation in circulating water systems, and in particular to a water pump anti-cavitation device and a control system. Background Art

[0002] The water pump is the core equipment in the industrial circulating water system. At the same time, as an important link in the public process system, its safe and stable operation can ensure the smooth operation of the production process. With the continuous development of water pump technology, water pumps are constantly breaking through in the direction of high efficiency, energy saving and intelligence. Through BIM (Building Information Modeling) design and integrated sensor analysis, it has multiple functions such as automatic adjustment and fault warning.

[0003] At present, medium and large pumping stations in industrial circulating water systems often use different types of water pumps (variable frequency pumps, industrial frequency pumps) from different manufacturers and at different production periods. In order to ensure the normal operation of the pumping station, on the one hand, management personnel usually use manual operations to reduce the use of automation and reduce the impact of abnormal flow disturbances on the pumping station process. However, the pumping station in the above scenario is prone to cavitation, which leads to water pump failure and thus affects its service life. Therefore, how to achieve anti-cavitation and safe operation of a circulating water pumping station is a technical problem to be solved by the present invention. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a water pump anti-cavitation device and control system, which can not only effectively avoid the occurrence of cavitation in the device and ensure the long-term stable operation of the water pump, but also effectively reduce the operating costs of the device.

[0005] According to a first aspect of an embodiment of the present application, a water pump anti-cavitation device is provided, the device comprising N first flow paths and N second flow paths connected in parallel, the first flow path comprising a first water pump and a first regulating valve connected in series, the second flow path comprising a second water pump and a second regulating valve connected in series, and N is a positive integer;

[0006] The first water pump and the second water pump are both provided with a limiting flow value, the first regulating valve automatically adjusts the valve opening according to the flow value output by the first water pump so that the output flow value is less than or equal to the limiting flow value, and the second water pump adjusts the power supply frequency so that the output flow value is less than or equal to the limiting flow value; wherein, the limiting flow value is less than the critical cavitation flow value, the limiting flow value is the positive root of the root-finding result obtained by calculating the effective cavitation margin, the required cavitation margin and the safety margin, and the critical cavitation flow value is the flow value when the effective cavitation margin is the same as the required cavitation margin.

[0007] In one embodiment, the effective NPSH is related to the operating flow of the water pump, the inner diameter of the outlet pipe of the water pump, the suction pressure of the water pump, the vaporization pressure of the circulating water at the current temperature, and the density of the circulating water.

[0008] In one embodiment, the required NPSH is related to the circulating water flow rate.

[0009] In one embodiment, the calculation formula of the limiting flow value is:

[0010]

[0011] Among them, Q S is the flow rate limit, a, b, c are fitting parameters, d is the inner diameter of the outlet pipe of the water pump, P1 is the suction pressure of the water pump, P v is the vapor pressure of circulating water at the current temperature, ρ g is the circulating water density and 0.5 is the safety margin.

[0012] In one embodiment, the device further comprises a third flow passage and a fourth flow passage, the third flow passage is connected in series with the flow inlet ends of the first flow passage and the second flow passage, and the fourth flow passage is connected in series with the flow outlet ends of the first flow passage and the second flow passage;

[0013] The third flow passage is provided with a first pressure sensor, the fourth flow passage is provided with a second pressure sensor and a temperature sensor, and the second pressure sensor and the temperature sensor are connected in series;

[0014] The flow inlet end of the first water pump is provided with a third pressure sensor, the flow inlet end of the second water pump is provided with a fourth pressure sensor, the flow outlet end of the second water pump is provided with a fifth pressure sensor, and the flow outlet end of the second regulating valve is provided with a sixth pressure sensor.

[0015] In one implementation, the lift of the second water pump is the difference between the pressure value at the flow outlet end of the second water pump and the pressure value at the flow inlet end of the second water pump.

[0016] In one embodiment, the operating flow rate of the second water pump at different speeds is related to the speed ratio of the water pump, the water pump head, the head when the water pump flow rate is 0, and the resistance coefficient of the water pump.

[0017] In one embodiment, the calculation formula for the operating flow rate of the second water pump at different speeds is: Among them, Q1 is the operating flow rate at different speeds, K1 is the speed ratio of the second water pump, P1 is the head of the second water pump when the flow rate is 0, P4 is the flow pressure value at the outlet of the second water pump, P3 is the flow pressure value at the inlet of the second water pump, and S1 is the resistance coefficient of the second water pump.

[0018] In one embodiment, the first water pump and the second water pump allocate flow in real time by using an equal operating cost change rate method.

[0019] In one embodiment, the calculation formula of the equal operating cost change rate is:

[0020]

[0021] in, Q i is the operating flow of the i-th water pump, M is the total operating cost, M i is the operating cost of the ith pump, minM is the minimum value of the total operating cost, Q e is the total demand flow of the water pump, λ is the rate of change of equal operating cost, Q imax is the upper limit of the flow rate of the water pump, Q imin is the lower limit of the flow rate of the water pump. When the water pump is the first water pump, Q imin For the Q imax 60% of the total water pump, when the water pump is the second water pump, the Q imin For the Q imax The product of the minimum value of K1.

[0022] According to a second aspect of an embodiment of the present application, a water pump anti-cavitation control system is provided, the system comprising a control system and the above-mentioned device, the control system being connected to the device, the control system being used to set a limiting flow value and distribute flow in real time.

[0023] The beneficial effects of the present invention are as follows: (1) the present invention sets limiting flow values ​​for the first water pump and the second water pump; the first regulating valve automatically adjusts the valve opening according to the flow value output by the first water pump so that the output flow value is less than or equal to the limiting flow value; the second water pump adjusts the power supply frequency so that the output flow value is less than or equal to the limiting flow value; thereby avoiding the occurrence of cavitation and ensuring long-term stable operation of the water pump.

[0024] (2) The present invention adopts the equal operating cost change rate method to distribute the flow of the first water pump and the second water pump in real time, thereby effectively reducing the operating cost of the device and improving the intelligent control effect of the circulating water system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1is a schematic structural diagram of a water pump anti-cavitation device according to an exemplary embodiment;

[0026] Figure 2 is a graph showing a relationship between effective NPSH and required NPSH with respect to flow rate according to an exemplary embodiment;

[0027] Figure 3 is a flow chart showing real-time traffic allocation using equal operating cost change rate method according to an exemplary embodiment;

[0028] Figure 4 It is a schematic structural diagram of a water pump anti-cavitation control system according to an exemplary embodiment. DETAILED DESCRIPTION

[0029] Unless otherwise defined, the technical terms or scientific terms used in this specification and claims shall have the usual meanings understood by persons with ordinary skills in the technical field to which the invention belongs. The specific embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be noted that in the specific description of these embodiments, in order to provide a concise description, it is impossible for this specification to provide a detailed description of all the features of the actual embodiments. Without departing from the spirit and scope of the present invention, those skilled in the art may modify and replace the embodiments of the present invention, and the resulting embodiments are also within the scope of protection of the present invention.

[0030] In the related art, according to the cavitation mechanism of the pump, the anti-cavitation performance of the water pump is improved mainly by reducing the required cavitation margin NPSHR and increasing the effective cavitation margin NPSHA. Among them, the methods of reducing the required cavitation margin NPSHR mainly include adopting a water pump impeller with good cavitation resistance, increasing the impeller inlet diameter, increasing the blade inlet edge width to reduce the flow velocity of the impeller inlet part, or adopting a double-suction impeller, etc. The methods to improve the effective cavitation margin NPSHA mainly include reducing the flow loss of the suction pipeline and reasonably determining the geometric installation height or backflow height of the pump. Other effective anti-cavitation measures include installing a deoxygenation device on the suction pipeline of the water pump to reduce the gas content in the liquid or installing a pressure stabilizing device to increase the inlet pressure of the pump. However, the above measures are mainly used in the project design and construction stages, and it is difficult to achieve the above operations in the actual operation stage.

[0031] In addition to the cavitation problem, there is another technical problem that needs to be solved in the related technology. Since the industrial frequency water pumps in the circulating water pump station can be driven by motors or steam, the conventional pump station minimum power and maximum operating efficiency method cannot guarantee the lowest operating cost of the pump station. In order to achieve the optimized operation of the circulating water system pump station in the related technology, it is generally necessary to determine the optimal state combination of the operating water pumps under the premise of meeting the water supply pressure, thereby minimizing the power consumption of the pump station. The following two methods are conventionally used:

[0032] (1) By setting the minimum flow difference (i.e., the difference between the optimal water supply and the required water supply of the pumping station), the minimum energy consumption of the pumping station, and the maximum operating efficiency of the pumping station as the control target, the other two are set as constraints for solution.

[0033] (2) Relying on big data, the pump station model is established and solved using intelligent algorithms such as genetic algorithm, frog leaping algorithm, and improved particle swarm algorithm.

[0034] Therefore, how to realize a circulating water pump station to operate safely while preventing cavitation and achieving the lowest operating cost is a technical problem that can be solved by the present invention.

[0035] In order to solve the above technical problems, the present application proposes a water pump anti-cavitation device and control system, which can not only effectively avoid the occurrence of cavitation and ensure the long-term stable operation of the water pump, but also effectively reduce the operating costs of the device.

[0036] An embodiment of the present application provides a water pump anti-cavitation device, such as Figure 1 As shown, it includes two first flow passages 1 and two second flow passages 2 connected in parallel. The first flow passage 1 includes an industrial frequency water pump 11 and a dynamic balance electric regulating valve 12 connected in series, and the second flow passage 2 includes a variable frequency water pump 21 and a manual regulating valve 22 connected in series.

[0037] In this embodiment, Figure 1 As shown, both the industrial frequency water pump 11 and the variable frequency water pump 21 are provided with limited flow values, the dynamic balancing electric regulating valve 12 automatically adjusts the valve opening according to the flow value output by the industrial frequency water pump 11 so that the output flow value is less than or equal to the limited flow value, and the variable frequency water pump 21 adjusts the power supply frequency so that the output flow value is less than or equal to the limited flow value; wherein, the limited flow value is less than the critical cavitation flow value, the limited flow value is the positive root of the root-finding result obtained by calculating the effective cavitation margin, the required cavitation margin and the safety margin, and the critical cavitation flow value is the flow value when the effective cavitation margin is the same as the required cavitation margin.

[0038] In one embodiment, the dynamic balancing electric regulating valve 12 is set to have a 100% valve opening corresponding to a limited flow value of the industrial frequency water pump 11 .

[0039] In this embodiment, Figure 2 FIG. 1 is a graph showing a relationship between effective NPSH and required NPSH with respect to flow rate according to an exemplary embodiment; Figure 2 As shown, the ordinate H represents the head, the abscissa Q represents the flow rate, and 0.5 represents the safety margin. When the effective cavitation margin is equal to the required cavitation margin, the two curves related to the flow rate intersect, and the flow rate corresponding to the intersection is the critical cavitation flow rate value, where the critical cavitation flow rate value is the critical value for judging the occurrence of cavitation in the power frequency water pump and the variable frequency water pump. If the limit flow value is set to be less than the critical cavitation flow rate value, the power frequency water pump and the variable frequency water pump are within the cavitation safety zone, ensuring the long-term stable operation of the power frequency water pump and the variable frequency water pump.

[0040] In this embodiment, the effective NPSH is related to the running flow of the water pump, the inner diameter of the outlet pipe of the water pump, the suction pressure of the water pump, the vaporization pressure of the circulating water at the current temperature, and the density of the circulating water.

[0041] The specific calculation formula for effective NPSH is: Among them, NPSHA is the effective cavitation margin, Q is the operating flow rate of the pump, d is the inner diameter of the outlet pipe of the pump, P1 is the suction pressure of the pump, P v is the vapor pressure of circulating water at the current temperature, p g is the circulating water density.

[0042] In this embodiment, the NPSH must be related to the circulating water flow rate.

[0043] The specific calculation formula for the required NPSH is: NPSHR = a + bQ + cQ 2 ; Among them, NPSHR is the required cavitation margin, a, b, c are fitting parameters, and Q is the operating flow rate of the pump.

[0044] In this embodiment, the limiting flow value is the positive root of the root-finding result obtained by calculating the effective cavitation margin, the required cavitation margin and the safety margin. Set NPSHR = NPSHR + 0.5, where 0.5 is the safety margin. This formula is a quadratic equation for the flow rate, that is, NPSHR = NPSHA-0.5. At this time, NPSHR is the minimum cavitation margin allowed for the industrial frequency water pump and the variable frequency water pump. Any flow rate higher than this value may cause cavitation in the pump. Therefore, the flow rate corresponding to the NPSHR value calculated by the above formula is the limiting flow value, where the limiting flow value is less than the critical cavitation flow value.

[0045] The specific calculation formula is: NPSHA = NPSHR + 0.5, that is By transposing the terms, we can obtain a quadratic equation related to the flow rate, as shown below: According to the quadratic equation, the limiting flow value is: Among them, Q S is the flow rate limit, a, b, c are fitting parameters, d is the inner diameter of the outlet pipe of the water pump, P1 is the suction pressure of the water pump, P v is the vapor pressure of circulating water at the current temperature, ρ g is the circulating water density and 0.5 is the safety margin.

[0046] Another exemplary embodiment of the present application is as follows Figure 1 As shown, the device also includes a third flow passage 3 and a fourth flow passage 4, the third flow passage 3 is connected in series with the flow inlet ends (not shown) of the first flow passage 1 and the second flow passage 2, and the fourth flow passage 4 is connected in series with the flow outlet ends (not shown) of the first flow passage 1 and the second flow passage 2.

[0047] In this embodiment, Figure 1 As shown, the third flow passage 3 is provided with a first pressure sensor 31, and the fourth flow passage 4 is provided with a second pressure sensor 41 and a temperature sensor 42, and the second pressure sensor 41 and the temperature sensor 42 are connected in series.

[0048] In this embodiment, Figure 1 As shown, the flow inlet end (not shown) of the industrial frequency water pump 11 is provided with a third pressure sensor 13, the flow inlet end (not shown) of the variable frequency water pump 21 is provided with a fourth pressure sensor 23, the flow outlet end (not shown) of the variable frequency water pump 21 is provided with a fifth pressure sensor 24, and the flow outlet end (not shown) of the manual regulating valve 22 is provided with a sixth pressure sensor 25. Setting a temperature sensor and multiple pressure sensors can effectively observe the flow condition and take effective measures in real time to prevent damage caused by excessive flow or excessive temperature.

[0049] In this embodiment, the head of the variable frequency water pump 21 is the difference between the pressure value at the flow outlet end of the variable frequency water pump 21 and the pressure value at the flow inlet end of the variable frequency water pump 21 .

[0050] In this embodiment, the operating flow rate of the variable frequency water pump 21 at different speeds is related to the speed ratio of the water pump, the water pump head, the head when the water pump flow rate is 0, and the resistance coefficient of the water pump.

[0051] In this embodiment, the calculation formula for the running flow of the variable frequency water pump 21 at different speeds is: Among them, Q1 is the operating flow rate at different speeds, K1 is the speed ratio of the variable frequency water pump, H1 is the head of the variable frequency water pump when the flow rate is 0, P4 is the flow pressure value at the outlet end of the variable frequency water pump, P3 is the flow pressure value at the inlet end of the variable frequency water pump, S1 is the resistance coefficient of the variable frequency water pump, and H1 and S1 can be obtained by fitting the rated QH curve (Q: flow rate, H: head of the pump) in the selection report of the corresponding water pump.

[0052] In an exemplary embodiment, the industrial frequency water pump 11 and the variable frequency water pump 21 allocate the pump station flow in real time by using the equal operating cost change rate method.

[0053] In one embodiment, the calculation formula for the equal operating cost change rate is:

[0054] in, Q i is the operating flow of the i-th water pump, M is the total operating cost, M i is the operating cost of the ith pump, minM is the minimum value of the total operating cost, Q e is the total demand flow of the water pump, λ is the rate of change of equal operating cost, Q imax is the upper limit of the flow rate of the water pump, Q imin is the lower limit of the flow rate of the water pump. When the water pump is a power frequency water pump, Q imin Q imax When the water pump is a variable frequency water pump, Q imin Q imax The equal operating cost change rate method searches for the flow point with the same change rate of operating cost for each pump, and takes this point as the optimal real-time flow distribution plan between pumps in the pumping station.

[0055] Another exemplary embodiment of the present application is as follows Figure 3 As shown, a flow chart of real-time flow distribution for operating water pumps in a water pump anti-cavitation device using the equal operating cost change rate method is shown.

[0056] Step 101: Set the flow lower limit value Q of all industrial frequency water pumps and variable frequency water pumps imin , flow rate upper limit Q imax And the characteristic curves of operating cost and flow rate of industrial frequency water pump and variable frequency water pump are initialized;

[0057] Step 102: Input the total required flow rate Q of all industrial frequency water pumps and variable frequency water pumps e ;

[0058] Step 103: Calculate the total rated flow of all power frequency pumps and variable frequency pumps The rated total flow Subtract the total demand flow Qe Get excess flow;

[0059] Step 104: Determine whether the excess flow is greater than the flow upper limit value Q of any power frequency water pump or variable frequency water pump imax ;

[0060] Step 105: If the excess flow is greater than the flow upper limit Q of any power frequency water pump or variable frequency water pump imax , according to the startup sequence, x water pumps are turned off, x is a positive integer not less than 1, and step 108 is continued;

[0061] Step 106: If the excess flow is less than the flow upper limit Q of any water pump in the device imax , then determine the rated total flow Is it less than the total demand flow Q e ;

[0062] Step 107: If the rated total flow Less than the total demand flow Q e , then according to the startup sequence, add or start y water pumps, y is a positive integer not less than 1, and continue to execute step 108;

[0063] Step 108: If the rated total flow Greater than the total demand flow Q e , then find out the equal operating cost change rate, and use the equal operating cost change rate method to find out the flow value with the same operating cost change rate for all running water pumps in the device;

[0064] Step 109: Determine the flow value Q of the i-th water pump i Is it greater than the flow limit Q of the i-th water pump? imax ;

[0065] Step 110: If the flow value Q of the i-th water pump i Greater than the flow limit Q of the i-th water pump imax , then the i-th water pump is set to the upper limit value of flow Q imax Operation, and the total demand flow Q e Subtract the flow limit Q of the i-th pump from imax , and then distribute the remaining flow rate between the remaining industrial frequency water pumps and the variable frequency water pumps, and continue to execute step 108;

[0066] Step 111: If the flow value Q of the i-th water pump i Less than the upper limit Q of the flow rate of the i-th water pump imax , then continue to determine the flow value Q of the i-th water pump i Less than the lower limit Q of the flow rate of the i-th water pump imin ;

[0067] Step 112: If the flow value Q of the i-th water pump i Less than the lower limit Q of the flow rate of the i-th water pump imin , then the i-th water pump is set to the lower flow limit value Q imin Operation, and the total demand flow Q e Subtract the lower limit value Q of the flow rate of the i-th water pump from imin , and then distribute the remaining flow rate between the remaining industrial frequency water pumps and variable frequency water pumps in the device, and continue to execute step 108;

[0068] Step 113: If the flow value Q of the i-th water pump i Greater than the lower limit Q of the flow rate of the i-th water pump imin , then input the flow distribution results of all industrial frequency water pumps and variable frequency water pumps.

[0069] After the commonly used water pump combination of the pump station is confirmed, the flow of the pump station is allocated in real time by adopting the equal operating cost change rate method, reducing the flow of the pumps with a large operating cost change rate, and increasing the flow of the pumps with a small operating cost change rate. While ensuring that each water pump operates under cavitation-free conditions, the operating costs of the pump station are effectively reduced and the intelligent control effect of the circulating water system is improved.

[0070] In an exemplary embodiment, the devices and data used in the above embodiments are assigned specific values, and the detailed data are referred to as follows:

[0071] Assume that there are 7 running water pumps in a water pump anti-cavitation device, and currently there are 3 running water pumps, including 1 power frequency water pump and 2 variable frequency water pumps. The rated parameters of the water pump are flow rate 950m 3 / h, head 47m, motor power 185kW, pump outlet diameter DN350. Since the rated parameters of the three pumps are the same, according to the selection report, NPSHR = 1.366-(4.08*10 -4 )Q+(5.58*10 -6 )Q 2 The pump inlet pressure P1 is 99640Pa, the circulating water temperature is 31.4℃, and the density is 995.22kg / m 3 , the vapor pressure Pv is 4600.123Pa, and the calculated Qs is 1286.6m 3 / h. A DN400 dynamic balancing electric regulating valve is installed at the outlet of the power frequency pump. When the valve is 100% open, the corresponding flow limit is 1286.6m 3 / h. At the same time, according to the equal operating cost change rate method, the operating flow of the industrial frequency water pump is 794m 3 / h, the outlet dynamic balance electric regulating valve automatically adjusts the opening according to the flow rate. The operating flow rate of the two variable frequency water pumps is 792m 3 / h, 42Hz operation. The total operating cost is 281.58 yuan / h, of which the operating power of the water pumps is 113.668kW, 83.956kW, and 83.956kW respectively. At this time, the operating cost is the lowest.

[0072] In the related technology, in the same time, the actual head of the running water pump is about 36m, one power frequency water pump runs at power frequency, and two variable frequency water pumps run at 38-40Hz. At this time, the power frequency water pump is prone to cavitation. In order to avoid this situation, the outlet pressure of the power frequency water pump is increased to 549640Pa (gauge pressure 4.5bar), and the opening of the power frequency water pump outlet regulating valve is set to 50%. At this time, the real-time operating flow rate Qe of the three power frequency water pumps and the variable frequency water pump is 2370m 3 / h, of which one power frequency water pump has a running flow of 1062.76m 3 / h, the running flow of the two variable frequency water pumps is 658.12m 3 The total operating cost is 287.7 yuan / h, of which the operating power of the water pumps is 166.6kW, 60.8kW, and 60.3kW respectively, and the electricity price is 1 yuan / kWh.

[0073] Figure 4 FIG. 1 is a block diagram of a water pump anti-cavitation control system according to an exemplary embodiment. Figure 4 As shown, the water pump anti-cavitation control system includes a control system 5 and an anti-cavitation device shown in the above embodiment, the control system 5 is connected to the anti-cavitation device, and the control system 5 is used to set the limit flow value and distribute the flow in real time. The control system 5 can be used to collect the pressure value measured by the first pressure sensor 31, the pressure value measured by the second pressure sensor 41, the temperature value measured by the temperature sensor 42, the pressure value measured by the third pressure sensor 13, the pressure value measured by the fourth pressure sensor 23, the pressure value measured by the fifth pressure sensor 24, and the pressure value measured by the sixth pressure sensor 25. And the water pump start and stop state, the variable frequency water pump operating frequency parameters, etc. The control system 5 realizes the frequency adjustment of the industrial frequency water pump and the variable frequency water pump according to the built-in real-time flow distribution algorithm.

[0074] In addition, one or more of the first pressure sensor, the second pressure sensor, the third pressure sensor, the fourth pressure sensor, the fifth pressure sensor and the sixth pressure sensor can be set according to the use requirements. The first water pump and the first regulating valve in the first flow path, and the second water pump and the second regulating valve in the second flow path can be appropriately increased or decreased according to the needs. In addition, the user can also arbitrarily set one or more pressure sensors or temperature sensors in the device according to the use requirements.

[0075] In the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. The term "plurality" refers to two or more than two, unless otherwise clearly defined.

[0076] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A water pump anti-cavitation device, characterized in that: The device comprises N first flow passages and N second flow passages connected in parallel, the first flow passage comprises a first water pump and a first regulating valve connected in series, the second flow passage comprises a second water pump and a second regulating valve connected in series, and N is a positive integer; The first water pump and the second water pump are both provided with a limiting flow value, the first regulating valve automatically adjusts the valve opening according to the flow value output by the first water pump so that the output flow value is less than or equal to the limiting flow value, and the second water pump adjusts the power supply frequency so that the output flow value is less than or equal to the limiting flow value; wherein, the limiting flow value is less than the critical cavitation flow value, the limiting flow value is the positive root of the root-finding result obtained by calculating the effective cavitation margin, the required cavitation margin and the safety margin, and the critical cavitation flow value is the flow value when the effective cavitation margin is the same as the required cavitation margin.

2. The device according to claim 1, characterized in that The effective NPSH is related to the running flow of the water pump, the inner diameter of the outlet pipe of the water pump, the suction pressure of the water pump, the vaporization pressure of the circulating water at the current temperature and the density of the circulating water; the required NPSH is related to the circulating water flow.

3. The device according to claim 2, characterized in that The calculation formula of the limiting flow value is: Among them, Q s is the flow rate limit, a, b, c are fitting parameters, d is the inner diameter of the outlet pipe of the water pump, p1 is the suction pressure of the water pump, P v is the vapor pressure of circulating water at the current temperature, ρ g is the circulating water density and 0.5 is the safety margin.

4. The device according to claim 1, characterized in that The device further comprises a third flow passage and a fourth flow passage, the third flow passage being connected in series with the flow inlet ends of the first flow passage and the second flow passage, and the fourth flow passage being connected in series with the flow outlet ends of the first flow passage and the second flow passage; The third flow passage is provided with a first pressure sensor, the fourth flow passage is provided with a second pressure sensor and a temperature sensor, and the second pressure sensor and the temperature sensor are connected in series; The flow inlet end of the first water pump is provided with a third pressure sensor, the flow inlet end of the second water pump is provided with a fourth pressure sensor, the flow outlet end of the second water pump is provided with a fifth pressure sensor, and the flow outlet end of the second regulating valve is provided with a sixth pressure sensor.

5. The device according to claim 4, characterized in that The head of the second water pump is the difference between the pressure value at the flow outlet end of the second water pump and the pressure value at the flow inlet end of the second water pump.

6. The device according to claim 5, characterized in that The operating flow rate of the second water pump at different speeds is related to the speed ratio of the water pump, the water pump head, the head when the water pump flow rate is 0, and the resistance coefficient of the water pump.

7. The device according to claim 6, characterized in that The calculation formula for the operating flow rate of the second water pump at different speeds is: Among them, Q1 is the operating flow rate at different speeds, K1 is the speed ratio of the second water pump, H1 is the head of the second water pump when the flow rate is 0, P4 is the flow pressure value at the outlet of the second water pump, P3 is the flow pressure value at the inlet of the second water pump, and S1 is the resistance coefficient of the second water pump.

8. The device according to claim 1, characterized in that The first water pump and the second water pump distribute flow in real time by using the equal operating cost change rate method.

9. The device according to claim 8, characterized in that The calculation formula for the change rate of operating expenses is: in, Q i is the operating flow of the i-th water pump, M is the total operating cost, M i is the operating cost of the ith pump, minM is the minimum value of the total operating cost, Q e is the total demand flow of the water pump, λ is the rate of change of equal operating cost, Q imax is the upper limit of the flow rate of the water pump, Q imin is the lower limit of the flow rate of the water pump. When the water pump is the first water pump, Q imin For the Q imax 60% of the total water pump, when the water pump is the second water pump, the Q imin For the Q imax The product of the minimum value of K1.

10. A water pump anti-cavitation control system, characterized in that: The system comprises a control system and the device according to any one of claims 1 to 9, wherein the control system is connected to the device, and the control system is used to set a flow limit value and allocate flow in real time.

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