Simulation method of pilot-operated safety valve in two-phase heat and mass transfer process

Abstract

This invention belongs to the field of reactor safety valve technology, specifically to a method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process. The method includes the following steps: Step 1: Determining the virtual throat diameter (L) of the pilot-operated safety valve; Step 2: Functional simulation of the pilot-operated safety valve opening process; and Step 3: Two thermal-hydraulic design verifications. This method can simulate the behavior and function of a pilot-operated safety valve throughout a fluid system, providing technical support for mechanical analysis, transient simulation, and safety assessment in the industrial fluid field.

Description

Technical Field

[0001] The invention belongs to the technical field of reactor safety valves, and in particular relates to a pilot safety valve simulation method for a two-phase heat and mass transfer process. Background Art

[0002] As we all know, pilot-operated safety valves are advanced and complex valves with a wide range of applications in the industrial field. For a long time, the design technology and manufacturing processes of this type of valve have been monopolized by foreign countries. In recent years, under the environment of independent and controllable development in the industrial field, China has also begun to develop pilot-operated safety valves and has achieved certain results. While designing the hardware of the pilot-operated safety valve body, it is necessary to conduct multiple functional tests to ensure that it can perform the corresponding safety overpressure protection and release functions. Among these, the simulation of the valve function involving two-phase heat and mass transfer processes is one of the technical difficulties. Because when the pilot-operated safety valve performs functions such as automatic overpressure protection and release, due to the large upstream and downstream pressure difference, the water seal will vaporize during the process of passing through the valve. Therefore, the fluid passing through the valve throat and downstream pipeline is actually a two-phase flow.

[0003] Therefore, there is an urgent need to provide a pilot-operated safety valve simulation method for the two-phase heat and mass transfer process to provide reliable technical support for the development of domestic pilot-operated safety valves. Summary of the Invention

[0004] The technical problem solved by the present invention is to establish and provide a pilot-operated safety valve simulation method for a two-phase heat and mass transfer process, which can simulate the behavior and function of the pilot-operated safety valve in the entire fluid system, and provide technical support for mechanical analysis, transient simulation, and safety evaluation in the field of industrial fluids.

[0005] The technical solution adopted in the present invention is:

[0006] A method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process includes the following steps:

[0007] Step 1: Determine the virtual throat diameter L of the pilot-operated safety valve; Step 2: Functionally simulate the opening process of the pilot-operated safety valve; Step 3: Perform two thermal-hydraulic design checks.

[0008] The process of determining the virtual throat diameter L is as follows:

[0009] Step 1.1. Obtain the displacement information of the pilot-operated safety valve: record the upstream pressure of the manufacturer's vapor phase displacement test as P1, and the upstream pressure of the liquid phase displacement test as P2;

[0010] Step 1.2, determine the virtual diameter L1: adjust the upstream pressure of the pilot safety valve to P1, the upstream fluid is saturated steam at P1 pressure, the downstream of the pilot safety valve is 1 standard atmosphere, and the pilot safety valve is set to the fully open state; calculate the steam flow through the valve using the Henry-Fauske critical flow model, adjust the valve fully open area, and perform multiple calculations until the steam flow is equal to Q g , at this time, the throat diameter corresponding to the valve is obtained as the virtual diameter L1;

[0011] Step 1.3, determine the virtual diameter L2: adjust the upstream pressure of the pilot safety valve to P2, the upstream fluid is a subcooled liquid, the downstream of the valve is 1 standard atmosphere, and set the pilot safety valve to the fully open state; calculate the liquid phase flow through the valve using the Henry-Fauske critical flow model, adjust the valve fully open area, and perform multiple calculations until the liquid flow equals Q l ; At this time, the throat diameter corresponding to the valve is the virtual diameter L2;

[0012] Step 1.4. Determine the virtual throat diameter of the pilot-operated safety valve: When the system is in a water-sealed discharge state, select the larger value of L1 and L2 as the virtual throat diameter L; if the system is in a low-pressure water-tight state, select the smaller value of L1 and L2 as the virtual throat diameter L.

[0013] The functional simulation of the pilot-operated safety valve opening process includes valve action simulation technology and two-phase heat and mass transfer simulation.

[0014] The valve action simulation:

[0015] Assuming that the dead time of the pilot-operated safety valve is t1, the fully open time is t2, and the valve throat area is S, the valve position changes continuously during the opening process until the safety valve reaches the fully open state. For different transient processes, there are certain differences in the selection of system analysis programs to simulate the valve opening process:

[0016] When conducting overpressure accident analysis

[0017] The opening process takes into account both the dead time and the fully open time. The valve state during the opening process is described by the change in the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the valve opening area at any time during the modeling process is as follows:

[0018] ① Starting from time T, the valve remains closed until the dead time ends (i.e. t≤T+t1);

[0019] ② After the dead time, the valve slowly opens and the flow area s gradually increases. The change in flow area during the opening process is obtained based on the change in valve position during the opening process;

[0020] ③ When the full opening time is reached (i.e. t = T + t1 + t2), the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter. After that, the valve flow area no longer changes;

[0021] When performing a discharge load analysis

[0022] The opening process only considers the full opening time t2. The opening process is described by the change of the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the opening area of the valve at any time during the modeling process is as follows:

[0023] ① Starting from time T, before the end of the fully open time (i.e. t≤T+t2), the valve slowly opens and the flow area s gradually increases. The change in flow area during the opening process is obtained based on the change in valve position during the opening process;

[0024] ② When the full opening time is reached (i.e. t = T + t2), the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter. After that, the valve flow area no longer changes.

[0025] The two-phase heat and mass transfer simulation:

[0026] During the valve opening process, the flow area will continue to increase, establishing an upstream and downstream connection. Due to the potentially huge upstream and downstream pressure difference, the fluid passing through the valve throat is very likely to be a vapor-liquid two-phase flow. The entire process involves critical flow, phase change, and heat and mass transfer between the vapor and liquid phases. Therefore, it is necessary to reasonably reproduce these complex phenomena:

[0027] ① Since the opening time of the pilot-operated safety valve is generally less than 1.0 second, it is necessary to open the valve at least every 1.0×10 -3 Calculate and record the changes of all thermal hydraulic parameters once every second, including: valve upstream pressure, valve downstream pressure, valve throat vapor flow, valve throat liquid flow, valve upstream liquid temperature, valve upstream vapor temperature, valve downstream liquid temperature, valve downstream vapor temperature, valve downstream cavitation fraction;

[0028] ② Use the MOODY critical flow model or the modified Henry-Fauske critical flow model to simulate the flow of two-phase fluid through the valve;

[0029] ③ Use the flow pattern conversion model and interphase heat and mass transfer model in RELAP, ARSAC (or WCOBRA-TRAC program to simulate the two-phase heat and mass transfer downstream of the valve.

[0030] The first thermal hydraulic analysis and verification:

[0031] After determining the virtual throat diameter and reasonably simulating the valve action and the thermal-hydraulic phenomena of the valve opening process, use the system analysis program RELAP or ARSAC to simulate the vapor phase discharge process and the liquid phase discharge process for the pilot-operated safety valve respectively, and calibrate and compare the vapor phase flow rate with the rated vapor phase displacement when the valve is fully open; when the pilot-operated safety valve performs the overpressure function, the calculated vapor phase flow rate should be less than or equal to the rated vapor phase displacement, and the calculated liquid phase flow rate should be less than or equal to the rated liquid phase displacement; when simulating the discharge process, the calculated vapor phase flow rate should be greater than or equal to the rated vapor phase displacement, and the calculated liquid phase flow rate should be greater than or equal to the rated liquid phase displacement.

[0032] Second thermal analysis verification: When simulating the discharge load, the lower limit of the opening time and the upper limit of the displacement should be selected for verification, and a certain degree of conservatism should be considered according to the engineering design requirements.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention provides a two-phase heat and mass transfer process simulation method for a pilot-operated safety valve, which can be applied to various types of overpressure transient analysis, pressurizer discharge load analysis, and RDP discharge load analysis of nuclear power plant units. It demonstrates whether the pilot-operated safety valve can meet safety requirements in terms of automatic overpressure protection and release functions in independently designed reactor systems, and provides a corresponding means for simulating the function of the pilot-operated safety valve in reactor design transient analysis and accident analysis.

[0035] (2) The pilot-operated safety valve simulation method for a two-phase heat and mass transfer process provided by the present invention can be applied to the functional simulation of all other pilot-operated safety valves involving two-phase flow heat and mass transfer processes in the industrial field, and can also provide technical support for hardware function demonstration in the design of domestically produced independent pilot-operated safety valves. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process provided by the present invention. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0040] like Figure 1 As shown, the present invention provides a pilot-operated safety valve simulation method for a two-phase heat and mass transfer process, comprising the following steps:

[0041] Step 1: Determine the virtual throat diameter L of the pilot-operated safety valve

[0042] Pilot-operated safety valves typically consist of a main valve, a pilot valve, and a relief valve, resulting in a complex structure. When conducting thermal-hydraulic analysis, especially when two-phase heat and mass transfer processes are involved, it can be difficult to accurately simulate the valve's internal structure. Therefore, it's necessary to determine the virtual throat diameter L (corresponding to the throat area S) of the pilot-operated safety valve. Specifically, the process for determining the virtual throat diameter L is as follows:

[0043] Step 1.1: Get the displacement information of the pilot-operated safety valve

[0044] First, determine the vapor and liquid displacements of the pilot-operated safety valve based on the valve specifications provided by the pilot-operated safety valve manufacturer. The upstream pressure used by the manufacturer for the vapor displacement test is recorded as P1, and the upstream pressure used for the liquid displacement test is recorded as P2.

[0045] Step 1.2: Determine the virtual diameter L1

[0046] Adjust the upstream pressure of the pilot safety valve to P1, the upstream fluid is saturated steam at P1 pressure, the downstream of the pilot safety valve is 1 standard atmospheric pressure, and the pilot safety valve is set to the fully open state; calculate the steam flow through the valve using the Henry-Fauske critical flow model, adjust the valve fully open area, and perform multiple calculations until the steam flow equals Qg At this time, the throat diameter corresponding to the valve is obtained as the virtual diameter L1.

[0047] Step 1.3: Determine the virtual diameter L2

[0048] Adjust the upstream pressure of the pilot safety valve to P2, the upstream fluid is a subcooled liquid (the temperature of the subcooled liquid is consistent with the upstream liquid temperature when the manufacturer conducts the liquid displacement experiment), the downstream of the valve is 1 standard atmospheric pressure, and the pilot safety valve is set to the fully open state; calculate the liquid flow through the valve using the Henry-Fauske critical flow model, adjust the valve fully open area, and perform multiple calculations until the liquid flow equals Q l ; At this time, the throat diameter corresponding to the valve is the virtual diameter L2.

[0049] Step 1.4: Determine the virtual throat diameter of the pilot-operated safety valve

[0050] When the system is in a water-seal discharge state, the larger value of L1 and L2 is selected as the virtual throat diameter L; if the system is in a low-pressure water-tight state, the smaller value of L1 and L2 is selected as the virtual throat diameter L.

[0051] Step 2: Functional simulation of the pilot-operated safety valve opening process

[0052] Functional simulation of the pilot-operated safety valve opening process includes valve action simulation technology and two-phase heat and mass transfer simulation.

[0053] Step 2.1: Valve action simulation

[0054] Assume that the dead time of the pilot-operated safety valve is t1, the fully open time is t2, and the valve throat area is S. During the opening process, the valve position changes continuously until the safety valve reaches the fully open state. For different transient processes, the system analysis program selected to simulate the valve opening process has certain differences:

[0055] When conducting overpressure accident analysis

[0056] The opening process takes into account both dead time and full opening time. The valve state during the opening process is described by the change in the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the valve opening area at any time during the modeling process is as follows:

[0057] ① Starting from time T, the valve remains closed until the dead time ends (i.e. t≤T+t1);

[0058] ② After the dead time, the valve slowly opens and the flow area s gradually increases. The change in flow area during the opening process is obtained based on the change in valve position during the opening process;

[0059] ③ When the full opening time is reached (i.e. t = T + t1 + t2), the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter, and the valve flow area no longer changes.

[0060] When performing a discharge load analysis

[0061] The opening process only considers the full opening time t2, and the opening process is described by the change in the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the valve opening area at any time during the modeling process is as follows:

[0062] ① Starting from time T, before the end of the fully open time (i.e. t≤T+t2), the valve slowly opens and the flow area s gradually increases. The change in flow area during the opening process is obtained based on the change in valve position during the opening process;

[0063] ② When the full opening time is reached (i.e. t = T + t2), the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter. After that, the valve flow area no longer changes.

[0064] Step 2.2: Two-phase heat and mass transfer simulation

[0065] During the valve opening process, the flow area will continue to increase, establishing a connection between the upstream and downstream. Since the upstream and downstream pressure difference may be huge (for example: upstream greater than 10MPa, downstream 0.1MPa), the fluid passing through the valve throat is very likely to be a vapor-liquid two-phase flow. The entire process involves critical flow, phase change, and heat and mass transfer between the vapor and liquid phases. Therefore, it is necessary to reasonably reproduce these complex phenomena:

[0066] ① Since the opening time of the pilot-operated safety valve is generally less than 1.0 second, it is necessary to open the valve at least every 1.0×10 -3 Calculate and record the changes of all thermal hydraulic parameters once every second, including: valve upstream pressure, valve downstream pressure, valve throat vapor flow, valve throat liquid flow, valve upstream liquid temperature, valve upstream vapor temperature, valve downstream liquid temperature, valve downstream vapor temperature, valve downstream cavitation fraction;

[0067] ② Use the MOODY critical flow model or the modified Henry-Fauske critical flow model to simulate the flow of two-phase fluid through the valve;

[0068] ③ Use the flow pattern conversion model and interphase heat and mass transfer model in RELAP, ARSAC (or WCOBRA-TRAC program to simulate the two-phase heat and mass transfer downstream of the valve.

[0069] Step 3: Two thermal hydraulic design checks

[0070] Step 3.1: First thermal-hydraulic analysis and verification

[0071] After determining the virtual throat diameter and properly simulating the valve action and the thermal-hydraulic phenomena during the valve opening process, use the system analysis program RELAP or ARSAC to simulate the vapor and liquid phase discharge processes for the pilot-operated safety valve, respectively. Verify and compare the vapor flow rate when the valve is fully open with the rated vapor displacement. Verify and compare the vapor flow rate when the valve is fully open with the rated vapor displacement. When the pilot-operated safety valve is performing the overpressure function, the calculated vapor flow rate should be less than or equal to the rated vapor displacement, and the calculated liquid flow rate should be less than or equal to the rated liquid displacement. When simulating the discharge process, the calculated vapor flow rate should be greater than or equal to the rated vapor displacement, and the calculated liquid flow rate should be greater than or equal to the rated liquid displacement.

[0072] Step 3.2: Second thermal analysis verification

[0073] Because the full valve opening time and displacement may deviate slightly from the design values, the valve opening process simulation and "throat diameter" should be appropriately adjusted to ensure that the simulation method can encompass design deviations from a conservative perspective. For example, when simulating discharge loads, the lower limit of the opening time and the upper limit of the displacement should be selected for verification, and a certain degree of conservatism should be considered based on engineering design requirements.

[0074] After two complete thermal-hydraulic analysis and verifications, if the requirements are met, it proves that the determination of the virtual throat diameter of the pilot-operated safety valve and the simulation of the valve opening process are reasonable. Otherwise, the virtual throat diameter and the simulated valve opening process should be re-determined.

[0075] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0076] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process, characterized in that: The steps include: Step 1: Determine the virtual throat diameter L of the pilot-operated safety valve; Step 2: Functionally simulate the opening process of the pilot-operated safety valve; Step 3: Perform two thermal-hydraulic design checks; The functional simulation of the pilot-operated safety valve opening process includes valve action simulation technology and two-phase heat and mass transfer simulation; The valve action simulation: Assuming that the dead time of the pilot safety valve is t1, the fully open time is t2, and the valve throat area is S, during the opening process, the valve position changes continuously until the safety valve reaches the fully open state. For different transient processes, there are certain differences in the selection of system analysis programs to simulate the valve opening process: When conducting overpressure accident analysis The opening process takes into account both the dead time and the fully open time. The valve state during the opening process is described by the change in the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the valve opening area at any time during the modeling process is as follows: ①Start timing from time T, and the valve will remain closed until the dead time ends; ② After the dead time, the valve slowly opens and the flow area s gradually increases. The change in flow area during the opening process is obtained based on the change in valve position during the opening process. ③ When the full opening time is reached, the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter. After that, the valve flow area no longer changes; When performing a discharge load analysis The opening process only considers the full opening time t2. The opening process is described by the change of the flow area of the safety valve over time. Assuming that at time T, the system pressure reaches the set value of the pilot-operated safety valve, the opening area of the valve at any time during the modeling process is as follows: ① Starting from the time T, before the end of the fully open time, the valve slowly opens and the flow area s gradually increases. The change in the flow area during the opening process is obtained based on the change in the valve position during the opening process; ② When the full opening time is reached, the flow area is the largest, which is the throat area S corresponding to the virtual throat diameter. After that, the valve flow area no longer changes; The two-phase heat and mass transfer simulation: During the valve opening process, the flow area will continue to increase, establishing a connection between the upstream and downstream. The entire process involves critical flow, phase change, and heat and mass transfer between the vapor and liquid phases. These phenomena need to be reasonably reproduced: ① Since the opening time of the pilot-operated safety valve is less than 1.0 second, the changes of all thermal hydraulic parameters should be calculated and recorded at least every 1.0×10-3 seconds, including: valve upstream pressure, valve downstream pressure, valve throat vapor flow, valve throat liquid flow, valve upstream liquid temperature, valve upstream vapor temperature, valve downstream liquid temperature, valve downstream vapor temperature and valve downstream cavitation fraction; ② Use the MOODY critical flow model or the modified Henry-Fauske critical flow model to simulate the flow of two-phase fluid through the valve; ③ Use the flow pattern conversion model and interphase heat and mass transfer model in the RELAP, ARSAC or WCOBRA-TRAC program to simulate the two-phase heat and mass transfer downstream of the valve.

2. The method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process according to claim 1, characterized in that: The process of determining the virtual throat diameter L is as follows: Step 1.

1. Obtain the displacement information of the pilot-operated safety valve: record the upstream pressure of the manufacturer's vapor phase displacement test as P1, and the upstream pressure of the liquid phase displacement test as P2; Step 1.

2. Determine the virtual diameter L1: Adjust the upstream pressure of the pilot-operated safety valve to P1, the upstream fluid to saturated steam at P1 pressure, and the downstream pressure of the pilot-operated safety valve to 1 standard atmosphere. Set the pilot-operated safety valve to the fully open state. Calculate the steam flow through the valve using the Henry-Fauske critical flow model, adjust the valve fully open area, and perform multiple calculations until the steam flow equals Qg. At this point, the corresponding throat diameter of the valve is the virtual diameter L1. Step 1.

3. Determine the virtual diameter L2: Adjust the upstream pressure of the pilot-operated safety valve to P2, the upstream fluid to a subcooled liquid, and the downstream pressure of the valve to 1 standard atmosphere. Set the pilot-operated safety valve to the fully open state. Calculate the liquid flow through the valve using the Henry-Fauske critical flow model. Adjust the fully open area of the valve and perform multiple calculations until the liquid flow equals Q1. At this point, the corresponding throat diameter of the valve is the virtual diameter L2. Step 1.

4. Determine the virtual throat diameter of the pilot-operated safety valve: When the system is in a water-sealed discharge state, select the larger value of L1 and L2 as the virtual throat diameter L; if the system is in a low-pressure water-tight state, select the smaller value of L1 and L2 as the virtual throat diameter L.

3. The method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process according to claim 2, characterized in that: The first thermal hydraulic analysis and verification: After determining the virtual throat diameter and properly simulating the valve action and the thermal-hydraulic phenomena during the valve opening process, use the system analysis program RELAP or ARSAC to simulate the vapor and liquid phase discharge processes for the pilot-operated safety valve, respectively. Verify and compare the vapor phase flow rate when the valve is fully open with the rated vapor phase displacement. Verify and compare the vapor phase flow rate when the valve is fully open with the rated vapor phase displacement. When the pilot-operated safety valve performs the overpressure function, the calculated vapor phase flow rate should be less than or equal to the rated vapor phase displacement, and the calculated liquid phase flow rate should be less than or equal to the rated liquid phase displacement. When simulating the emission process, the calculated vapor phase flow rate should be greater than or equal to the rated vapor phase displacement, and the calculated liquid phase flow rate should be greater than or equal to the rated liquid phase displacement.

4. The method for simulating a pilot-operated safety valve in a two-phase heat and mass transfer process according to claim 3, characterized in that: Second thermal analysis verification: When simulating the discharge load, the lower limit of the opening time and the upper limit of the displacement should be selected for verification, and a certain degree of conservatism should be considered according to the engineering design requirements.

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