Diagnostic analysis method for backflow cavitation of nuclear power steam-driven auxiliary feed pump

Abstract

The invention relates to a diagnostic analysis method for backflow cavitation of a nuclear power steam-driven auxiliary feed pump, which comprises the following steps of: S10, judging whether a cavitation part of an impeller blade of the feed pump is positioned on a working surface of the impeller blade or not, if so, executing the step S20, and if not, executing the step S20; s20, cavitation performance parameters and operation parameters of the water feeding pump are obtained, whether the cavitation performance parameters and the operation parameters conform to the corresponding preset values or not is judged, and if yes, the step S30 is executed; s30, scanning information of the water feeding pump is obtained, an impeller simulation model is established according to the scanning information, simulation verification is conducted on the flow and cavitation performance of the water feeding pump according to the impeller simulation model, and if the verification result is true, the step S40 is executed; and S40, whether the physical performance of the water feeding pump meets the cavitation protection design requirement or not is detected, and if yes, it is judged that backflow cavitation exists. By applying the method, the occurrence of backflow cavitation can be predicted in advance, the reliability of nuclear-grade equipment is improved, and the operation of a unit is safer and more reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear power, and in particular to a diagnostic analysis method for the reflux cavitation of a nuclear power steam-driven auxiliary feed water pump. Background Art

[0002] A nuclear power plant needs to apply a nuclear power steam-driven auxiliary feed water pump. Among them, cavitation is a common phenomenon in the feed water pump. Cavitation will affect the operation reliability of the feed water pump, and the feed water pump will affect the operation reliability of the nuclear power unit. Therefore, the staff of the nuclear power plant need to study the cavitation phenomenon.

[0003] Specifically, when the medium pressure in the feed water pump is lower than the saturated steam pressure at this temperature at a certain place, vaporization will occur. A large amount of steam and dissolved gases in the water escape to form bubbles, and this process is called "cavitation". When the cavitation bubbles flow from the low-pressure area to the high-pressure area with the water flow, they quickly condense and burst under the high pressure. The high-pressure water rushes into these spaces at an extremely high speed, forming a strong impact force. Since the gas and steam in the bubbles cannot be instantaneously dissolved and condensed completely, they are decomposed into small bubbles under the action of the impact force, compressed and condensed by the high-pressure water, and repeated many times, resulting in local high-intensity and high-frequency water hammer, causing mechanical erosion damage to the flow-through components. The impact force can be as high as several hundred or even thousands of megapascals, and the impact frequency can reach tens of thousands of times per second. At the same time, active substances such as dissolved oxygen in the liquid will also cause chemical corrosion and electrochemical corrosion to the metal by means of the heat released when the bubbles condense. The cavitation phenomenon refers to the whole process of bubble formation, development, and rupture resulting in material damage.

[0004] The main reason for cavitation is the insufficient suction pressure at the inlet of the feed water pump. At present, the research on the cavitation of the feed water pump in the industry is to judge the cavitation performance of the pump by the net positive suction head (NPSH) of the feed water pump. For the reflux cavitation caused by the feed water pump operating at a small flow rate, it often occurs when the net positive suction head of the feed water pump seems to be sufficient. For such cavitation, there is no relevant research at present, resulting in technical defects in the diagnosis of the feed water pump and unable to improve the operation reliability of the feed water pump. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a diagnostic analysis method for the reflux cavitation of a nuclear power steam-driven auxiliary feed water pump.

[0006] The technical solution adopted by the present invention to solve its technical problems is: to provide a diagnostic analysis method for the reflux cavitation of a nuclear power steam-driven auxiliary feed water pump, including the following steps:

[0007] Step S10: Judge whether the part of the impeller blade of the feed water pump where cavitation occurs is located on the working surface of the impeller blade. If so, execute Step S20;

[0008] Step S20: Obtain the cavitation performance parameters and operating parameters of the feed pump, and determine whether both the cavitation performance parameters and the operating parameters meet the corresponding preset values. If so, execute Step S30;

[0009] Step S30: Obtain the scan information of the feed pump, establish an impeller simulation model based on the scan information, and perform simulation verification on the flow rate and cavitation performance of the feed pump according to the impeller simulation model. If the verification result is true, execute Step S40;

[0010] Step S40: Detect whether the physical performance of the feed pump meets the requirements of the cavitation protection design. If so, determine that there is reflux cavitation during the use of the feed pump.

[0011] Optionally, the preset values include a first preset value, a second preset value, and a third preset value. Step S20 includes:

[0012] Step S21: Obtain the operating parameters of the feed pump, compare the actual operating flow rate in the operating parameters with the first preset value, where the first preset value is obtained by referring to the operating flow rate specified in the feed pump manual. If the actual operating flow rate is less than the first preset value, execute Step S22;

[0013] Step S22: Obtain the cavitation performance parameters of the feed pump, and determine whether the cavitation performance parameters are greater than the second preset value. If so, execute Step S23;

[0014] Step S23: Calculate the total temperature rise and the minimum allowable flow rate of the feed pump according to the operating parameters, and determine whether the total temperature rise is less than the third preset value and whether the actual operating flow rate is greater than the minimum allowable flow rate; if the total temperature rise is greater than the third preset value or the actual operating flow rate is less than the minimum allowable flow rate, execute Step S30.

[0015] Optionally, the cavitation performance parameters include the ratio of the available net positive suction head to the required net positive suction head. In Step S22, the determination of whether the cavitation performance parameters are greater than the second preset value and, if so, the execution of Step S23 includes:

[0016] Determine whether the ratio of the available net positive suction head to the required net positive suction head is greater than the second preset value. If so, execute Step S23.

[0017] Optionally, the operating parameters include: the actual operating flow rate, shaft power, efficiency, and head of the feed pump; Step S23 includes:

[0018] Step S231: Calculate the total temperature rise caused by friction and recirculation of the feed pump according to the head and the efficiency. If the total temperature rise is less than the third preset value, then execute Step S232;

[0019] Step S232: Calculate the minimum allowable flow rate of the feed pump according to the shaft power, the head, and the total temperature rise. If the actual operating flow rate is greater than the minimum allowable flow rate, then end the process;

[0020] If the total temperature rise is greater than the third preset value or the actual operating flow rate is less than or equal to the minimum allowable flow rate, then execute Step S30.

[0021] Optionally, in Step S231, the calculating the total temperature rise caused by friction and recirculation of the feed pump according to the head and the efficiency includes:

[0022] Calculate the total temperature rise caused by friction and recirculation of the feed pump according to Formula 1:

[0023] ΔT = ΔT1 + ΔT2 Formula 1

[0024] where ΔT is the total temperature rise caused by friction and recirculation of the feed pump, in °C; ΔT1 is the temperature rise caused by friction of the feed pump, in °C; ΔT2 is the temperature rise caused by recirculation of the feed pump, in °C; and ΔT1 and ΔT2 are calculated according to Formula 2 and Formula 3 respectively:

[0025]

[0026] where g is the acceleration due to gravity, with a value of 9.80 m / s 2 ; H is the head, in m; η is the efficiency, expressed as a percentage; C is the specific heat capacity of water, with a value of 4.2 J / (kg·°C).

[0027] Optionally, in Step S232, the calculating the minimum allowable flow rate of the feed pump according to the shaft power, the head, and the total temperature rise includes:

[0028] Calculate the minimum allowable flow rate of the feed pump according to Formula 4:

[0029]

[0030] where Qmin is the minimum allowable flow rate of the feed pump, in m 3 / h; P is the shaft power, in KW; ρ is the density of water, in kg / m 3 ; g is the acceleration due to gravity, with a value of 9.80 m / s 2; H is the head, with the unit of m; C is the specific heat capacity of water, with a value of 4.2 J / (kg·°C); ΔT is the total temperature rise caused by the friction and recirculation of the feed pump, with the unit of °C.

[0031] Optionally, in step S30, the simulation and verification of the flow rate and cavitation performance of the feed pump according to the impeller simulation model includes:

[0032] Based on the impeller simulation model, computational fluid dynamics numerical analysis calculations are performed under multiple flow rate conditions to obtain the flow field distribution and vapor phase distribution inside the impeller in the impeller simulation model under each flow rate condition;

[0033] According to the flow field distribution and the vapor phase distribution, the gas volume fraction on the impeller surface of the impeller simulation model is obtained under each flow rate condition, and whether cavitation occurs on the surface of the impeller blades is verified according to the gas volume fraction on the impeller surface.

[0034] Optionally, the physical properties of the feed pump include: impeller material, impeller profile, impeller chemical composition, impeller hardness, and impeller roughness.

[0035] Optionally, in step S40, the detection of whether the physical properties of the feed pump meet the cavitation protection design requirements includes:

[0036] The impeller of the feed pump is inspected by CT scanning to obtain impeller material information and impeller profile information, whether there are defects in the impeller is judged according to the impeller material information, and whether the profile of the impeller is smooth is judged according to the impeller profile information;

[0037] The impeller chemical composition information is obtained by a composition detector, and whether the impeller chemical composition information meets the impeller chemical composition requirements is judged;

[0038] The impeller hardness information is obtained by a hardness detector, and whether the hardness of the impeller of the feed pump meets the impeller hardness requirements is judged according to the impeller hardness information;

[0039] The impeller roughness information is obtained by a roughness detector, and whether the roughness of the impeller of the feed pump meets the impeller roughness requirements is judged according to the impeller roughness information.

[0040] Optionally, after step S40, it further includes:

[0041] Step S50: A test return pipeline is provided between the outlet end of the feed pump and the inlet water tank of the feed pump, and the test return pipeline is provided with an isolation valve.

[0042] By implementing the present invention, the following beneficial effects are achieved: By implementing the diagnostic analysis method for the return flow cavitation of the nuclear power steam-driven auxiliary feed water pump, it is possible to quickly and accurately diagnose and analyze the return flow cavitation of the nuclear power auxiliary feed water pump, saving the overhaul duration and cost. Moreover, during the design, installation, commissioning, etc. stages of the feed water pump, the parameters of the feed water pump can be verified and diagnosed, predicting in advance the occurrence of return flow cavitation, improving the reliability of nuclear-grade equipment, and making the operation of the nuclear power unit safer and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0044] Figure 1 is a schematic flow chart of the diagnostic analysis method for the return flow cavitation of the nuclear power steam-driven auxiliary feed water pump of the present invention;

[0045] Figure 2 is a schematic diagram of the vapor phase distribution inside the feed water pump impeller of the present invention;

[0046] Figure 3 is a schematic diagram of the impeller simulation model of the present invention at an angle of 45° with the Y-axis plane;

[0047] Figure 4 is a schematic connection diagram of the test return pipeline of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the drawings.

[0049] It should be noted that the flow chart shown in the drawings is only an exemplary illustration, not necessarily including all the contents and operations / steps, nor necessarily executed in the described order. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined. Therefore, the actual execution order may change according to the actual situation.

[0050] The block diagrams shown in the drawings are only functional entities, not necessarily corresponding to physically independent entities. That is, these functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0051] As Figure 1 shown, the present invention discloses a diagnostic analysis method for the return flow cavitation of a nuclear power steam-driven auxiliary feed water pump, which can be used for the diagnostic analysis of the return flow cavitation of the nuclear power steam-driven auxiliary feed water pump. In this embodiment, the nuclear power steam-driven auxiliary feed water pump can be simply referred to as the "feed water pump".

[0052] AsFigure 1 As shown in Figure 1 , the diagnostic analysis method for the return cavitation of a nuclear power steam-driven auxiliary feed water pump includes the following steps:

[0053] Step S10: Determine whether the cavitation part of the impeller blades of the feed water pump is located on the working surface of the impeller blades. If so, execute Step S20.

[0054] In this embodiment, tools such as a reflective scope or a camera instrument can be used to check the cavitation condition on the back of the impeller blades of the nuclear feed water pump. According to the specific position of the cavitation on the impeller blades, the cavitation can be divided into overload cavitation, partial load cavitation, and return cavitation caused by low flow. Overload cavitation is generally located on the working surface of the impeller blades, that is, the non-visible surface or the back; partial load cavitation is generally located on the non-working surface of the impeller blades, that is, the front of the impeller blades visible to the naked eye; and the return cavitation caused by low flow also damages the working surface. If the cavitation occurs on the non-working surface of the impeller blades, it is judged as partial load cavitation, and the process ends. If the cavitation is located on the working surface of the impeller blades, it is necessary to further determine whether the cavitation occurring on the impeller blades is return cavitation, that is, execute Step S20. Through the method of checking with a reflective scope, the return cavitation damage condition of the impeller can be simply, quickly, and conveniently detected without damaging the impeller and without using an endoscope.

[0055] Step S20: Obtain the cavitation performance parameters and operating parameters of the feed water pump, and determine whether both the cavitation performance parameters and the operating parameters meet the corresponding preset values. If so, execute Step S30;

[0056] Step S30: Obtain the scan information of the feed water pump, establish an impeller simulation model based on the scan information, and perform simulation verification on the flow rate and cavitation performance of the feed water pump according to the impeller simulation model. If the verification result is true, execute Step S40;

[0057] Step S40: Detect whether the physical performance of the feed water pump meets the requirements of the cavitation protection design. If so, it is judged that there is return cavitation.

[0058] In some embodiments, in Step S20, the cavitation performance parameters include the required net positive suction head and the available net positive suction head; the operating parameters include the actual operating flow rate, shaft power, efficiency, and head of the feed water pump; the preset values include the first preset value, the second preset value, and the third preset value. This Step S20 includes Step S21, Step S22, and Step S23, where:

[0059] Step S21: Obtain the operating parameters of the feed water pump, compare the actual operating flow rate in the operating parameters with the first preset value, and the first preset value is obtained by referring to the operating flow rate specified in the feed water pump instruction manual. If the actual operating flow rate is less than the first preset value, execute Step S22.

[0060] In this embodiment, the actual operating flow rate of the feed pump can be directly obtained by a detection device, which includes but is not limited to a flow meter. The first preset value can be set according to the operating flow rate specified in the feed pump instruction manual. When it is determined that the actual operating flow rate of the feed pump is greater than the first preset value, it is determined that the cavitation on the feed pump is over-flow cavitation, and the process ends; otherwise, the next step is entered.

[0061] Step S22: Obtain the cavitation performance parameters of the feed pump, and determine whether the cavitation performance parameters are greater than the second preset value. If so, execute step S23.

[0062] Further, the cavitation performance parameters include the ratio of the available net positive suction head (NPSHa) to the required net positive suction head (NPSH3). The second preset value ranges from 1.1 to 1.5. In step S22, when determining whether the cavitation performance parameters are greater than the second preset value, if so, executing step S23 includes:

[0063] Determine whether the ratio of the available net positive suction head to the required net positive suction head is greater than the second preset value. If so, execute step S23.

[0064] The second preset value ranges from 1.1 to 1.5, such as 1.1, 1.2, 1.3, 1.4, or 1.5. The second preset value is preferably 1.1. Determine whether the ratio of the available net positive suction head to the required net positive suction head is greater than the second preset value. If so, execute step S23.

[0065] In this embodiment, the common parameters for judging the cavitation performance of the feed pump are the net positive suction head (NPSH) and the specific speed of cavitation (S). Whether cavitation occurs during the operation of the feed pump is related to both the layout of the suction device of the feed pump and the cavitation characteristics of the feed pump itself. The net positive suction head determined according to the actual conditions of the suction device is called the available net positive suction head (NPSHa). This parameter represents the remaining head after subtracting the vaporization head of the liquid from the head when the liquid reaches the inlet of the feed pump, also known as the net suction head of the feed pump. Head is a physical term referring to the energy level of a liquid or gas during flow. The static suction head (Static Suction Head, NPSHa) is the remaining head after subtracting the vaporization head of the liquid from the head when the liquid reaches the inlet of the feed pump, representing the cavitation resistance ability of the feed pump. The net positive suction head required for the feed pump itself not to cavitate is called the required net positive suction head (NPSH3). This parameter is independent of the operating conditions of the feed pump and is only related to the design and manufacturing factors of the feed pump itself. In engineering, the point where the head of the first-stage impeller drops by 3% is usually taken as the cavitation discrimination point. At this time, the required net positive suction head is expressed as NPSH3. NPSHa is usually taken as 1.1 to 1.5 times NPSH3 to reduce the occurrence of reflux cavitation.

[0066] It should be noted that the cavitation discrimination point is the point where the head of the first-stage impeller drops by 3%. Therefore, when judging whether there is reflux cavitation in the feed pump, it is generally to judge whether the cavitation part of the first-stage impeller blades is located on the working surface of the impeller blades, and the method provided in this application is executed to identify whether there is reflux cavitation.

[0067] In some embodiments, two parameters, namely the required net positive suction head (NPSH3) and the available net positive suction head (NPSHa), in the feed pump specification are obtained, and the ratio of the two is calculated. The value range of the second preset value is from 1.1 to 1.5, and the second preset value can be set to 1.1 as required. If the ratio of NPSHa to NPSH3 is less than 1.1, it is determined that the net positive suction head of the feed pump is insufficient, which is cavitation caused by low inlet pressure, and the process ends. Specifically, the required net positive suction head (NPSH3) is obtained from the feed pump specification, and the available net positive suction head (NPSHa) is the actual value of the feed pump. The purpose of calculating the ratio of the two is to judge whether the actual value, that is, the available net positive suction head, is 1.1 to 1.5 times the required net positive suction head. If the ratio is greater than 1.1, it indicates that the probability of reflux cavitation occurring during the operation of the feed pump is relatively high, and then the next step is entered to determine whether there is reflux cavitation.

[0068] It should be noted that in some application scenarios, the second preset value can be modified according to actual needs.

[0069] Step S23: Calculate the total temperature rise and the minimum allowable flow rate of the feed pump according to the operating parameters, and judge whether the total temperature rise is less than the third preset value and whether the actual operating flow rate is greater than the minimum allowable flow rate; if the total temperature rise is greater than the third preset value or the actual operating flow rate is less than the minimum allowable flow rate, then step S30 is executed.

[0070] In step S23, the operating parameters include: the actual operating flow rate, shaft power, efficiency, and head of the feed pump. This step S23 includes:

[0071] Step S231: Calculate the total temperature rise caused by friction and reflux of the feed pump according to the head and the efficiency. If the total temperature rise is less than the third preset value, then step S232 is executed;

[0072] Step S232: Calculate the minimum allowable flow rate of the feed pump according to the shaft power, the head, and the total temperature rise. If the actual operating flow rate is greater than the minimum allowable flow rate, then the process ends;

[0073] If the total temperature rise is greater than the third preset value or the actual operating flow rate is less than or equal to the minimum allowable flow rate, then step S30 is executed.

[0074] In step S231, the calculation of the total temperature rise caused by friction and reflux of the feed pump according to the head and the efficiency includes:

[0075] Calculate the total temperature rise caused by friction and recirculation of the feed water pump according to Formula 1:

[0076] ΔT = ΔT1 + ΔT2 Formula 1

[0077] Where, ΔT is the total temperature rise caused by friction and recirculation of the feed water pump, with the unit of °C; ΔT1 is the temperature rise caused by friction of the feed water pump, with the unit of °C; ΔT2 is the temperature rise caused by recirculation of the feed water pump, with the unit of °C; and ΔT1 and ΔT2 are calculated according to Formula 2 and Formula 3 respectively:

[0078]

[0079]

[0080] Where, g is the acceleration of gravity, with a value of 9.80 m / s 2 ; H is the head, with the unit of m; η is the efficiency, expressed as a percentage; C is the specific heat capacity of water, with a value of 4.2 J / (kg·°C).

[0081] In step S232, calculate the minimum allowable flow rate of the feed water pump according to the shaft power, the head, and the total temperature rise, including:

[0082] Calculate the minimum allowable flow rate of the feed water pump according to Formula 4:

[0083]

[0084] Where, Qmin is the minimum allowable flow rate of the feed water pump, with the unit of m 3 / h; P is the shaft power, with the unit of KW; ρ is the density of water, with the unit of kg / m 3 ; g is the acceleration of gravity, with a value of 9.80 m / s 2 ; H is the head, with the unit of m; C is the specific heat capacity of water, with a value of 4.2 J / (kg·°C); ΔT is the total temperature rise caused by friction and recirculation of the feed water pump, with the unit of °C.

[0085] When the total temperature rise is less than the third preset value and the actual operating flow rate is greater than the minimum allowable flow rate, end the process.

[0086] In one embodiment, when obtaining the operating parameters of the feed water pump, the shaft power is 400 KW, the efficiency is 0.07, the head is 1369.7 m, and the actual operating flow rate Qn is 7 m 3 / h, the preset temperature rise standard ΔT standard is 10 °C. The preset temperature rise standard ΔT standard is the third preset value, which is an empirical value. Further, according to formula 1-4, it is calculated that ΔT1 is 42.4607 °C, ΔT2 is 45.65667 °C, and ΔT is 88.11737 °C, that is, ΔT is greater than ΔT standard, and it is displayed that the temperature rise exceeds the standard; if ΔT is less than or equal to ΔT standard, it is displayed as qualified. Through the above formula calculation, the minimum allowable flow rate Qmin is 7.60667m 3 / h, that is, the minimum allowable flow rate Qmin is greater than the actual operating flow rate Qn, that is, the actual operating flow rate is less than the minimum allowable flow rate. If the actual operating flow rate is less than the minimum allowable flow rate, it is displayed that the flow rate is low; if the maximum operating flow rate is greater than or equal to the minimum allowable flow rate, it is displayed as qualified. When it is determined that the total temperature rise is greater than the third preset value or the actual operating flow rate is less than the minimum allowable flow rate, proceed to the next step.

[0087] In some embodiments, in this step S30, the flow rate and cavitation performance of the feed water pump are simulated and verified according to the impeller simulation model, including:

[0088] Based on the impeller simulation model, computational fluid dynamics numerical analysis calculations are performed under multiple flow rate conditions to obtain the flow field distribution and vapor phase distribution inside the impeller in the impeller simulation model under each flow rate condition;

[0089] According to the flow field distribution and the vapor phase distribution, the gas volume fraction on the surface of the impeller in the impeller simulation model under each flow rate condition is obtained, and whether cavitation occurs on the surface of the impeller blades is verified according to the gas volume fraction on the surface of the impeller.

[0090] In this embodiment, as Figure 2 shown, software simulation is adopted to simulate and verify the flow rate and cavitation performance of the feed water pump through the impeller simulation model. The impeller where cavitation occurs, that is, the first-stage impeller, is three-dimensionally scanned, and an impeller model of the feed water pump is established according to the three-dimensional scan. The inlet section of the feed water pump is modeled. Here, the three-dimensional scan can adopt a laser mapping scheme. Computational fluid dynamics CFD numerical analysis calculations (Computational Fluid Dynamics) are performed under multiple flow rate conditions, and the flow field distribution inside the first-stage impeller and the vapor phase distribution inside the first-stage impeller under each flow rate condition are obtained according to the calculations.

[0091] In one embodiment, as Figure 3 shown, it is a schematic diagram of the impeller simulation model at a 45° angle with the Y-axis plane. The parameters of its impeller simulation model include:

[0092] a. Mesh: To generate the mesh, a tetrahedral mesh strategy is adopted. The total number of meshes is 4.2 million, and it is optimized, and the local important areas are encrypted.

[0093] b. Boundary conditions: Pressure inlet, outlet mass flow rate, standard no-slip wall.

[0094] c. Turbulence model: Standard k-ε model is adopted.

[0095] d. Treatment of rotation: Utilize the MRF (Multiple Reference Frame) function provided by the software (CFX, a practical fluid engineering analysis tool), and adopt the single frame mode to consider the rotational effect of the blade.

[0096] e. Medium: Water at 22°C.

[0097] In one embodiment, to ensure the accuracy of numerical calculation and analyze its flow field as completely as possible, the inlet section of the feed pump is modeled, and the scanning information of the first-stage impeller where cavitation occurs is obtained by three-dimensional scanning. Under different flow rate Qn conditions: 200 m 3 / h, 180 m 3 / h, 88 m3 / h, 75 m 3 / h, 24.02 m 3 / h, 18.32 m 3 / h, 14.02 m 3 / h, CFD numerical analysis and calculation are carried out under multiple flow rate conditions, and the internal flow field distribution of the first-stage impeller and the vapor phase distribution value inside the impeller are obtained according to the calculation. Among them, the results in Table 1 are the calculation results of the vapor volume fraction on the surface of the impeller blades of the feed pump under partial flow rate conditions. Among them, the larger the vapor volume fraction value, the more serious the cavitation:

[0098] Table 1: Calculation results of the vapor volume fraction on the surface of the impeller blades of the feed pump under partial flow rate conditions

[0099]

[0100]

[0101] In some embodiments, step S40: Detect whether the physical performance of the feed pump meets the requirements of cavitation protection design; if so, it is determined that there is reflux cavitation during the use of the feed pump. That is, the feed pump meets the requirements of cavitation protection design, but there is reflux cavitation during the use of the feed pump, and the reflux cavitation is caused by the low flow rate during use.

[0102] The physical performance of the feed pump may include: impeller material, impeller profile, impeller chemical composition, impeller hardness, and impeller roughness.

[0103] In this step S40, detecting whether the physical performance of the feed pump meets the requirements of cavitation protection design includes:

[0104] Inspect the impeller of the feed water pump through CT scanning to obtain impeller material information and impeller profile information. According to the impeller material information, determine whether there are defects in the impeller, and according to the impeller profile information, determine whether the impeller profile is smooth;

[0105] Obtain the chemical composition information of the impeller through a composition detector, and determine whether the chemical composition information of the impeller meets the requirements of the impeller chemical composition;

[0106] Obtain the hardness information of the impeller through a hardness detector, and determine whether the hardness of the impeller of the feed water pump meets the requirements of the impeller hardness according to the impeller hardness information;

[0107] Obtain the roughness information of the impeller through a roughness detector, and determine whether the impeller roughness meets the requirements of the impeller roughness according to the impeller roughness information.

[0108] If the impeller material information, impeller profile information, impeller chemical composition information, impeller hardness information, and impeller roughness information all meet the requirements, then the physical performance of the feed water pump meets the requirements of the cavitation protection design. If any one of the impeller material information, impeller profile information, impeller chemical composition information, impeller hardness information, and impeller roughness information does not meet the requirements, locate the fault point that does not meet the requirements and improve the fault point. For example, if the impeller material information does not meet the impeller material requirements, improve the impeller material. If the impeller profile information does not meet the impeller profile requirements, improve the impeller profile. If the impeller chemical composition information does not meet the impeller chemical requirements, improve the impeller chemistry. If the impeller hardness information does not meet the impeller hardness requirements, improve the impeller hardness. If the impeller roughness information does not meet the impeller roughness requirements, improve the impeller roughness.

[0109] That is, if defects are found, the problems found are fed back to the design and manufacturing stages of the impeller.

[0110] The CT scanning device, composition detector, hardness detector, roughness detector, etc. can all be communicatively connected to the computer device in a wired or wireless manner.

[0111] In some embodiments, in order to reduce the risk of reflux cavitation, after step S40, step S50 may further be included: a test reflux pipeline 3 is provided between the outlet end of the feed water pump 1 and the inlet water tank 4 of the feed water pump 1, and the test reflux pipeline 3 is provided with an isolation valve 5.

[0112] In one embodiment, the auxiliary steam-driven feed water pump of the nuclear power plant is normally in a standby state. During each test, such as Figure 4As shown, the outlet valve 6 of the feed water pump is in the closed state. Only a small part of the flow rate returns to the inlet water tank 4 of the feed water pump through the balance drum leakage pipeline 2 of the feed water pump. The balance drum leakage pipeline 2 is relatively thin, and its flow rate is lower than the minimum allowable flow rate of the feed water pump. To solve the problem of insufficient flow rate during the pump test and reduce the risk of return flow cavitation, a test return pipeline 3 is added between the outlet end of the feed water pump 1 and the inlet water tank 4 of the feed water pump 1 to increase the actual flow rate of the feed water pump 1. The flow rate of the test return pipeline 3 is at least 30% of the full flow rate of the feed water pump. During the test, the isolation valve 5 on the test return pipeline 3 is opened, and after the test is completed, the isolation valve 5 is closed.

[0113] Understandably, by implementing the diagnostic analysis method for return flow cavitation of the nuclear power steam-driven auxiliary feed water pump, the return flow cavitation of the nuclear power auxiliary feed water pump can be diagnosed and analyzed quickly and accurately, saving the overhaul duration and cost. It can also verify and diagnose the parameters of the feed water pump during the design, installation, commissioning and other stages of the feed water pump, predict the occurrence of return flow cavitation in advance, improve the reliability of nuclear-grade equipment, and make the operation of the nuclear power unit safer and more reliable.

[0114] Understandably, the above embodiments only express the preferred embodiments of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can also be made, all of which belong to the protection scope of the present invention. Therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention shall fall within the scope covered by the claims of the present invention.

Claims

1. A method for diagnosing and analyzing cavitation of a nuclear power steam-assisted feedwater pump, characterized in that: The following steps are involved: Step S10: determining whether the location where cavitation occurs in the impeller blades of the water supply pump is located on the working surface of the impeller blades, if so, executing step S20; Step S20: obtaining the cavitation performance parameters and the operating parameters of the water supply pump, and determining whether the cavitation performance parameters and the operating parameters meet corresponding preset values. If so, executing step S30; Step S30: acquiring scanning information of the water supply pump, and establishing an impeller simulation model according to the scanning information, and performing simulation verification on the flow rate and cavitation performance of the water supply pump according to the impeller simulation model. If the verification result is true, executing step S40; Step S40: Detect whether the physical properties of the water supply pump meet the cavitation protection design requirements. If so, determine that backflow cavitation exists in the water supply pump during use.

2. The diagnostic analysis method for reflux cavitation of a nuclear power steam-assisted feedwater pump according to claim 1 is characterized in that: The preset value includes a first preset value, a second preset value, and a third preset value, and the step S20 includes: Step S21: acquiring the operating parameters of the water supply pump, comparing the actual operating flow in the operating parameters with the first preset value, the first preset value being obtained by referring to the operating flow specified in the manual of the water supply pump, and if the actual operating flow is less than the first preset value, executing step S22; Step S22: obtaining the cavitation performance parameter of the water supply pump, and determining whether the cavitation performance parameter is greater than the second preset value, and if so, executing step S23; Step S23: Calculate the total temperature rise and the minimum allowable flow rate of the water supply pump according to the operating parameters, determine whether the total temperature rise is less than the third preset value, and determine whether the actual operating flow rate is greater than the minimum allowable flow rate; if the total temperature rise is greater than the third preset value or the actual operating flow rate is less than the minimum allowable flow rate, execute step S30.

3. The diagnostic analysis method for reflux cavitation of a nuclear power steam-assisted feedwater pump according to claim 2 is characterized in that: The cavitation performance parameter includes a ratio of available cavitation margin to required cavitation margin. In step S22, it is determined whether the cavitation performance parameter is greater than the second preset value. If so, step S23 is executed, including: It is determined whether the ratio of the available NPSH to the required NPSH is greater than the second preset value. If so, step S23 is executed.

4. The diagnostic analysis method for reflux cavitation of a nuclear power steam-assisted feedwater pump according to claim 2, characterized in that: The operating parameters include: the actual operating flow, shaft power, efficiency and head of the water supply pump; the step S23 includes: Step S231: Calculate the total temperature rise caused by the friction and backflow of the water supply pump according to the head and the efficiency. If the total temperature rise is less than the third preset value, execute step S232; Step S232: Calculate the minimum allowable flow rate of the water supply pump according to the shaft power, the head and the total temperature rise. If the actual operating flow rate is greater than the minimum allowable flow rate, end the process; If the total temperature rise is greater than the third preset value or the actual operating flow rate is less than or equal to the minimum allowable flow rate, step S30 is executed.

5. The diagnostic and analysis method for reflux cavitation of a nuclear power steam-assisted feedwater pump according to claim 4, characterized in that: In the step S231, the total temperature rise caused by friction and backflow of the water pump is calculated according to the head and the efficiency, including: The total temperature rise caused by friction and backflow of the feedwater pump is calculated according to Formula 1: ΔT=ΔT1+ΔT2 Formula 1 Wherein, ΔT is the total temperature rise caused by the friction and backflow of the feed water pump, in °C; ΔT1 is the temperature rise caused by the friction of the feed water pump, in °C; ΔT2 is the temperature rise caused by the backflow of the feed water pump, in °C; and ΔT1 and ΔT2 are calculated according to Formula 2 and Formula 3 respectively: Among them, g is the acceleration due to gravity, which is 9.80m / s 2 ; H is the head, unit is m; η is the efficiency, expressed in percentage; C is the specific heat capacity of water, the value is 4.2J / (kg*℃).

6. The diagnostic analysis method for backflow cavitation of a nuclear power steam-assisted feedwater pump according to claim 4 is characterized in that: In the step S232, the minimum allowable flow rate of the water supply pump is calculated according to the shaft power, the head and the total temperature rise, including: The minimum allowable flow rate of the water supply pump is calculated according to Formula 4: Among them, Qmin is the minimum allowable flow rate of the water supply pump, in m 3 / h; P is shaft power, unit is KW; ρ is water density, unit is kg / m 3 ; g is the acceleration due to gravity, and its value is 9.80m / s 2 ; H is the head, unit is m; C is the specific heat capacity of water, which is 4.2J / (kg*℃); ΔT is the total temperature rise caused by friction and backflow of the water feed pump, unit is ℃.

7. The diagnostic analysis method for backflow cavitation of a nuclear power steam-assisted feedwater pump according to claim 1, characterized in that: In the step S30, the flow rate and cavitation performance of the water feed pump are simulated and verified according to the impeller simulation model, including: Based on the impeller simulation model, computational fluid dynamics numerical analysis and calculation are performed under multiple flow conditions to obtain the flow field distribution and vapor phase distribution inside the impeller in the impeller simulation model under each flow condition; According to the flow field distribution and the vapor phase distribution, the gas volume fraction on the impeller surface of the impeller simulation model under each flow condition is obtained, and according to the gas volume fraction on the impeller surface, it is verified whether cavitation occurs on the surface of the impeller blade.

8. The diagnostic analysis method for backflow cavitation of a nuclear power steam-assisted feedwater pump according to claim 1, characterized in that: The physical properties of the water supply pump include: impeller material, impeller profile, impeller chemical composition, impeller hardness and impeller roughness.

9. The method for diagnosing and analyzing backflow cavitation of a nuclear power steam-assisted feedwater pump according to claim 8, characterized in that: In step S40, the step of detecting whether the physical properties of the water supply pump meet the cavitation protection design requirements includes: Inspect the impeller of the water supply pump by CT scanning to obtain the impeller material information and the impeller profile information, determine whether the impeller has defects according to the impeller material information, and determine whether the impeller profile is smooth according to the impeller profile information; Obtaining the chemical composition information of the impeller through a composition detector, and determining whether the chemical composition information of the impeller meets the chemical composition requirements of the impeller; Obtaining the impeller hardness information through a hardness tester, and judging whether the hardness of the impeller of the water feed pump meets the impeller hardness requirement according to the impeller hardness information; The roughness information of the impeller is obtained by a roughness detector, and based on the impeller roughness information, it is determined whether the roughness of the impeller of the water feed pump meets the impeller roughness requirement.

10. The method for diagnosing and analyzing backflow cavitation of a nuclear power steam-assisted feedwater pump according to claim 1, characterized in that: After step S40, the method further includes: Step S50: a test return pipeline is arranged between the outlet end of the water supply pump and the inlet water tank of the water supply pump, and the test return pipeline is provided with an isolation valve.

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