Method for analyzing transient response of mixed deaerator during steam stopping

Abstract

The invention discloses a method for analyzing transient response of a mixed deaerator during steam stopping, which comprises the following steps of: recording spray water entering the deaerator as a phase I, recording a steam phase in the deaerator as a phase II, and recording a liquid phase as a phase III; and establishing a calculation formula of parameters such as enthalpy of spray water flowing into the system, enthalpy of drain water flowing out of the system and heat absorption of the system in the deaerator, which are divided into two parts, namely total heat transfer power of a contact part of a phase II and a metal wall surface and total heat transfer power of a contact part of a phase III and the metal wall surface, at the moment t, so as to obtain a time-varying curve of the working medium in the deaerator. By adopting the calculation model provided by the invention, accurate transient analysis can be carried out on the water temperature response of the outlet of the deaerator under the condition that the steam turbine of the nuclear power plant stops steam. In the design stage, effective countermeasures can be made according to the result provided by the analysis, namely, the temperature reduction rate of the water temperature at the outlet of the deaerator, so that the condition that the working condition of the nuclear island evaporator is greatly fluctuated and the safe operation of a nuclear power plant is influenced is avoided.

Description

Technical Field

[0001] The present invention relates to an analysis method for a hybrid deaerator in a nuclear power plant. The analysis method is applicable to the case where the secondary circuit of the nuclear power plant stops supplying steam, and is used to analyze the outlet temperature response of the working medium in the hybrid deaerator under the steam stop condition, and belongs to the technical field of power station heat exchanger equipment design. Background Art

[0002] A hybrid deaerator is usually installed in a nuclear power plant to remove the oxygen content of the working fluid in the water supply circuit. Its working principle is: the high-temperature extraction steam from the steam turbine enters the deaerator, directly mixes with the low-temperature water entering the deaerator from the water supply pipeline, and heats the latter. When the pressure in the deaerator remains unchanged, the dissolved oxygen capacity in the water supply decreases as the temperature increases, thereby achieving the purpose of deoxygenation. After the condensed steam is fully mixed with the heated water supply, it flows out from the deaerator outlet pipeline and enters the lower-level equipment.

[0003] In steady-state operation, the operating pressure in the deaerator always maintains self-balance, and the internal water level and the temperature of the working fluid at the outlet are relatively stable. However, there are some occasional abnormalities in actual operation. Once these abnormalities occur, the secondary circuit stops supplying steam to the turbine, and the deaerator loses the heating steam source and enters an unsteady-state condition.

[0004] The unsteady-state working condition of the deaerator will affect the outlet water temperature, and then affect the cooling water temperature entering the evaporator, resulting in nuclear island load fluctuations, posing a threat to the stability and safety of the nuclear island. The present invention establishes an analysis method for verifying the outlet temperature response of the hybrid deaerator in the steam shutdown state, providing a reference for the formulation of safe operation strategies for nuclear power plants.

[0005] Among the research literature in this field, there are several studies with high similarity:

[0006] (1) Zhu Bao, Zhejiang University, 2014.

[0007] The biggest differences between the model established by this research and the model established by the present invention are: a. This model is used for thermal power units, while the present invention is used for nuclear power units, and the two units have significant differences in unit structure; b. In terms of premise assumptions, this research believes that "the water storage capacity of the deaerator water tank changes significantly, and the calculation process uses the minimum possible water storage capacity", while the present invention believes that after the steam is shut down, the water level in the deaerator will not change much. Therefore, the premise assumptions of the two models are quite different.

[0008] (2) “Transient Analysis of Deaerator in Nuclear Power Turbine Load Rejection Condition” [J], Author: Tong Baoyu, Zhang Fujun, Zhang Mingbao, Unit: Harbin Boiler Plant Co., Ltd., Year: 2018.

[0009] The model established by the research institute is not a transient model in the strict sense. The time differential term dt is not introduced in the model, but the time is simply divided into finite segments, such as 1s. In essence, the research still establishes a steady-state analysis model within a finite time period, rather than a transient analysis model. At the same time, the research does not specify the assumptions of the model, especially the question of "whether to consider the heat capacity of metal", while the present invention explicitly includes the heat storage of metal into the calculation item.

[0010] (3) “Transient Analysis of Head-type Sprinkler Deaerator after Turbine Load Rejection” [J], Author: Zhu Yanfang, Qin Shuli, Li Changsheng, Unit: Dongfang Boiler Co., Ltd. of Dongfang Electric Corporation, Year: 2019.

[0011] This study is similar to (2). The time differential term dt is not introduced into the model. Instead, 0.2 s is used as a time step. In essence, a steady-state calculation model is established, rather than the transient analysis model established in the present invention. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a transient analysis model for a hybrid deaerator, which is used to analyze the outlet temperature response of the working medium in the hybrid deaerator when the secondary circuit of the nuclear power plant stops supplying steam.

[0013] In order to solve the above problems, the present invention provides a method for analyzing the transient response of a hybrid deaerator during steam shutdown:

[0014] The spray water entering the deaerator is recorded as phase I, the vapor phase in the deaerator is recorded as phase II, and the liquid phase is recorded as phase III; at time t, the enthalpy of the spray water flowing into the system is recorded as Hi(t), and the enthalpy of the water out of the system is recorded as Ho(t). The heat absorption of the system in the deaerator is divided into two parts: the total heat transfer power W1(t) of the contact part between phase II and the metal wall surface, and the total heat transfer power W2(t) of the contact part between phase III and the metal wall surface.

[0015] At the initial moment of main steam valve shutoff:

[0016] No new steam enters the system. Phases II and III are both in saturation state. The saturation parameter is ①.

[0017] The thermal parameters of the phase I spray water entering the system remain unchanged temporarily;

[0018] After phase I enters the deaerator, it contacts phase II, partially cooling phase II, and the temperature of phase I rises accordingly, but does not reach the saturation temperature;

[0019] Phase II is partially condensed by cooling, the space of phase II remains unchanged, and the pressure decreases;

[0020] A pressure difference appears at the interface between phase III and phase II, part of the liquid at the interface flashes, absorbing heat from the ambient liquid, and the temperature of the remaining liquid in phase III drops;

[0021] After absorbing heat, phase I turns into liquid and enters phase II, where it mixes with phase II, assuming that the mixing is fully carried out;

[0022] Phase II and phase III reach a new saturated equilibrium state, and the temperature and pressure are lower than the previous moment. This is the saturated equilibrium state, and the saturation parameter is ②;

[0023] There is a temperature difference between the metal wall and phase II and phase III, and heat is released to phase II and phase III;

[0024] Phase II and phase III absorb heat, the temperature rises, and the saturation pressure rises. At this time, it is a saturated equilibrium state, and the saturation parameter is ③;

[0025] For saturation parameters, ①>③>②;

[0026] The analysis method is specifically as follows:

[0027] H o (t) = G o (t)h o (T o (t))

[0028] T o (t) is the function of the deaerator drain outlet temperature with respect to time; G o (t) is the drainage flow rate at time t, H o (t) is the total outlet enthalpy at time t;

[0029] H i (t) = G i (t)h i (T i (t))

[0030] G i (t) is the water supply flow at time t, T i (t) is the water supply temperature at time t, which is a known quantity. According to the specific input conditions, T i The relationship between t and

[0031] The heat transferred from the metal container to each phase during the time dt is equal to the heat storage reduced by the metal during the time dt, that is:

[0032] W(t)dt=-C p (T o (t))d(T o (t))=-C p (T o (t))T o '(t)dt

[0033] During the time dt, all processes occurring in the system should satisfy the energy balance, that is:

[0034] H o (t)dt-H i (t)dt+dE f =W(t)dt

[0035] The above formula can be written as follows:

[0036] G o (t)h o (T o (t))dt-G i (t)h i (T i (t))dt+M f d(h o (T o (t)))=-M m C p (T o (t))T o '(t) (1)

[0037] M f is the total mass of the working fluid in the deaerator, which is the sum of phase II and phase III; M m The mass of the heat storage metal shell of the deaerator;

[0038] M f d(h o (T o (t))) should be expanded to the following form:

[0039] M f d(h0(T0(t)))=M g d(h og (T0(t)))+M l d(h ol (T0(t))) (2)

[0040] h ol (T o (t)) is the saturated liquid enthalpy at the corresponding temperature; h og (T o (t)) is the saturated vapor enthalpy at the corresponding temperature; h i (T i The pressure of (t)) is always the inlet pressure of phase I flow. i (T i (t)) have different coefficients;

[0041] The simultaneous equations (1) and (2) can be solved by numerical method to obtain the curve of the working fluid in the deaerator changing with time.

[0042] Preferably, the key boundary conditions of the analysis method of the transient response of the hybrid deaerator during steam shutdown are as follows:

[0043] An abnormal situation occurred in the nuclear power plant, causing the turbine to shut down urgently and the main steam valve to be cut off instantly;

[0044] The deaerator loses its heating steam source and there is no new steam source of any other nature input;

[0045] There is no upstream drain input in the deaerator;

[0046] Cooling water still enters from the deaerator water supply inlet.

[0047] Preferably, the analysis method of the transient response of the hybrid deaerator during steam shutdown assumes the following conditions:

[0048] Each equilibrium state is always located on the saturation curve;

[0049] Ignore the pressure fluctuations and the resulting water level changes during the non-equilibrium process;

[0050] The volume of the vapor phase space remains unchanged;

[0051] The metal wall temperature is uniformly distributed overall and is consistent with the temperature of each phase in equilibrium.

[0052] The calculation model provided in this application can accurately analyze the transient response of the deaerator outlet water temperature when the nuclear power plant steam turbine is shut down. In the design stage, effective countermeasures can be formulated based on the results provided by the analysis, that is, the cooling rate of the deaerator outlet water temperature, to avoid huge fluctuations in the operating conditions of the nuclear island evaporator and affect the safe operation of the nuclear power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic model of the internal system of the hybrid deaerator;

[0054] Figure 2 The curve showing the relationship between the outlet temperature of the working medium and time in the deaerator obtained in the embodiment. DETAILED DESCRIPTION

[0055] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0056] The present invention provides an analysis method for the transient response of a hybrid deaerator when the steam source is shut down. For a hybrid deaerator, when the heating steam source disappears, the internal system can be abstracted as follows: Figure 1In the model shown, the spray water entering the deaerator is recorded as phase I, the vapor phase in the deaerator is recorded as phase II, and the liquid phase is recorded as phase III; at time t, the enthalpy of the spray water flowing into the system is recorded as Hi(t), and the enthalpy of the hydrophobic water flowing out of the system is recorded as Ho(t). The heat absorption of the system in the deaerator is divided into two parts: the total heat transfer power W1(t) of the contact part between phase II and the metal wall surface, and the total heat transfer power W2(t) of the contact part between phase III and the metal wall surface.

[0057] The key boundary conditions for the above model are as follows:

[0058] (1) An abnormal situation occurs in a nuclear power plant, causing the turbine to shut down urgently and the main steam valve to be instantly cut off;

[0059] (2) The deaerator loses its heating steam source and no new steam source of any other nature is input;

[0060] (3) There is no upstream drain input in the deaerator;

[0061] (4) Cooling water still enters from the deaerator water supply inlet.

[0062] At the initial moment of main steam valve shutoff:

[0063] (1) No new steam enters the system. Phases II and III are both saturated. The saturation parameter is ①.

[0064] (2) The thermal parameters of the phase I spray water entering the system remain unchanged temporarily;

[0065] (3) After phase I enters the deaerator, it comes into contact with phase II, partially cooling phase II. The temperature of phase I rises accordingly, but does not reach the saturation temperature.

[0066] (4) Phase II is partially condensed by cooling, the space of phase II remains unchanged, and the pressure decreases;

[0067] (5) A pressure difference appears at the interface between phase III and phase II. Part of the liquid at the interface flashes and absorbs heat from the ambient liquid. The temperature of the remaining liquid in phase III decreases.

[0068] (6) After absorbing heat, phase I turns into liquid and enters phase II, where it mixes with phase II, assuming that the mixing is complete;

[0069] (7) Phase II and phase III reach a new saturated equilibrium state, and the temperature and pressure are lower than the previous moment. This is the saturated equilibrium state, and the saturation parameter is ②;

[0070] (8) There is a temperature difference between the metal wall and phase II and phase III, and heat is released to phase II and phase III;

[0071] (9) Phase II and phase III absorb heat, the temperature rises, and the saturation pressure rises. At this time, it is a saturated equilibrium state, and the saturation parameter is ③;

[0072] (10) For saturation parameters, ①>③>②.

[0073] Based on the above analysis, the following assumptions are made:

[0074] (1) Each equilibrium state is always on the saturation curve;

[0075] (2) Ignore the pressure fluctuations during the non-equilibrium process and the resulting water level changes;

[0076] (3) The volume of the vapor phase space remains unchanged;

[0077] (4) The metal wall temperature is uniformly distributed overall and is consistent with the temperature of each phase in the equilibrium state.

[0078] The analysis method is specifically as follows:

[0079] H o (t) = G o (t)h o (T o (t))

[0080] T o (t) is the function of the deaerator drain outlet temperature with respect to time; G o (t) is the drainage flow rate at time t, H o (t) is the total outlet enthalpy at time t;

[0081] H i (t) = G i (t)h i (T i (t))

[0082] G i (t) is the water supply flow at time t, T i (t) is the water supply temperature at time t, which is a known quantity. According to the specific input conditions, T i The relationship between t and

[0083] The heat transferred from the metal container to each phase during the time dt is equal to the heat storage reduced by the metal during the time dt, that is:

[0084] W(t)dt=-C p (T o (t))d(T o (t))=-C p (T o (t))T o '(t)dt

[0085] During the time dt, all processes occurring in the system should satisfy the energy balance, that is:

[0086] H o(t)dt-H i (t)dt+dE f =W(t)dt

[0087] The above formula can be written as follows:

[0088] G o (t)h o (T o (t))dt-G i (t)h i (T i (t))dt+M f d(h o (T o (t)))=-M m C p (T o (t))T o '(t) (1)

[0089] M f is the total mass of the working fluid in the deaerator, which is the sum of phase II and phase III; M m The mass of the heat storage metal shell of the deaerator;

[0090] M f d(h o (T o (t))) should be expanded to the following form:

[0091] M f d(h0(T0(t)))=M g d(h og (T0(t)))+M l d(h ol (T0(t))) (2)

[0092] h ol (T o (t)) is the saturated liquid enthalpy at the corresponding temperature; h og (T o (t)) is the saturated vapor enthalpy at the corresponding temperature; h i (T i The pressure of (t)) is always the inlet pressure of phase I flow. i (T i (t)) have different coefficients; among them, h ol (T o (t))、h og (T o(t)) is fitted according to the Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam published by IAPWS. i (T i (t)) Fitting is performed based on specific input conditions and the IAPWS document Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam.

[0093] After fitting the relationship to be fitted, equations (1) and (2) are combined and the numerical solution is used to solve the combined equations to obtain the curve of the working fluid in the deaerator changing with time.

[0094] Example

[0095] Assume that a hybrid deaerator is in the following boundary conditions just before the steam source stops:

[0096] <![CDATA[G0(t) / (kg·s -1 )]]> <![CDATA[T i0 / ℃]]> <![CDATA[P i0 / MPa]]> <![CDATA[T sat0 / ℃]]> 297.5 132.2 2.37 162.1

[0097] The subscript 0 is the parameter value at t = 0. The subscript sat represents the saturation temperature at the corresponding pressure.

[0098] The parameters of each phase in the cavity at t = 0 are as follows:

[0099]

[0100] The relevant parameters of metal containers are as follows:

[0101] equipment <![CDATA[M m / kg]]> <![CDATA[Cp(T o (t)) / (kJ·kg -1 ·K -1 )]]> Deaerator 54613.77 Average 0.46

[0102] According to the existing literature (IAPWS, Revised Release on the IAPWS IndustrialFormulation1997 for the Thermodynamic Properties of Water and Steam [EB / OL], https: / / iapws.org / relguide / IF97-Rev.html, 1997.), in P i When (t) = 2.37Mpa, the following fitting formula can be obtained:

[0103] h i (Ti (t))=4.23T i (t)-2.8

[0104] At the same time, the T i (t) The following conditions are met:

[0105]

[0106] The model established by the present invention is used to calculate the time period from t = 0 (s) to t = 510 (s) to obtain the outlet temperature T of the working fluid in the deaerator. o The relationship curve between (t) and time t is as follows Figure 2 shown.

Claims

1. A method for analyzing the transient response of a hybrid deaerator during steam shutdown, characterized in that: The spray water entering the deaerator is recorded as phase I, the vapor phase in the deaerator is recorded as phase II, and the liquid phase is recorded as phase III; at time t, the enthalpy of the spray water flowing into the system is recorded as Hi(t), and the enthalpy of the water out of the system is recorded as Ho(t). The heat absorption of the system in the deaerator is divided into two parts: the total heat transfer power W1(t) of the contact part between phase II and the metal wall surface, and the total heat transfer power W2(t) of the contact part between phase III and the metal wall surface. At the initial moment of main steam valve shutoff: No new steam enters the system. Phases II and III are both in saturation state. The saturation parameter is ①. The thermal parameters of the phase I spray water entering the system remain unchanged temporarily; After phase I enters the deaerator, it contacts phase II, partially cooling phase II, and the temperature of phase I rises accordingly, but does not reach the saturation temperature; Phase II is partially condensed by cooling, the space of phase II remains unchanged, and the pressure decreases; A pressure difference appears at the interface between phase III and phase II, part of the liquid at the interface flashes, absorbing heat from the ambient liquid, and the temperature of the remaining liquid in phase III drops; After absorbing heat, phase I turns into liquid and enters phase II, where it mixes with phase II, assuming that the mixing is fully carried out; Phase II and phase III reach a new saturated equilibrium state, and the temperature and pressure are lower than the previous moment. This is the saturated equilibrium state, and the saturation parameter is ②; There is a temperature difference between the metal wall and phase II and phase III, and heat is released to phase II and phase III; Phase II and phase III absorb heat, the temperature rises, and the saturation pressure rises. At this time, it is a saturated equilibrium state, and the saturation parameter is ③; For saturation parameters, ①>③>②; The analysis method is specifically as follows: H o (t)=G o (t)h o (T o (t)) T o (t) is the function of the deaerator drain outlet temperature with respect to time; G o (t) is the drainage flow rate at time t, H o (t) is the total outlet enthalpy at time t; H i (t)=G i (t)h i (T i (t)) G i (t) is the water supply flow at time t, T i (t) is the water supply temperature at time t, which is a known quantity. According to the specific input conditions, T i The relationship between t and The heat transferred from the metal container to each phase during the time dt is equal to the heat storage reduced by the metal during the time dt, that is: W(t)dt=-C p (T o (t))d(T o (t))=-C p (T o (t))T o '(t)dt During the time dt, all processes occurring in the system should satisfy the energy balance, that is: H o (t)dt-H i (t)dt+dE f =W(t)dt The above formula can be written as follows: G o (t)h o (T o (t))dt-G i (t)h i (T i (t))dt+M f d(h o (T o (t)))=-M m C p (T o (t))T o '(t) (1) M f is the total mass of the working fluid in the deaerator, which is the sum of phase II and phase III; M m The mass of the heat storage metal shell of the deaerator; M f d(h o (T o (t))) should have the following form after expansion: M f d(h0(T0(t)))=M g d(h og (T0(t)))+M l d(h ol (T0(t))) (2) h ol (T o (t)) is the saturated liquid enthalpy at the corresponding temperature; h og (T o (t)) is the saturated vapor enthalpy at the corresponding temperature; h i (T i The pressure of (t)) is always the inlet pressure of phase I flow. i (T i (t)) have different coefficients; The simultaneous equations (1) and (2) can be solved by numerical method to obtain the curve of the working fluid in the deaerator changing with time.

2. The method for analyzing the transient response of a hybrid deaerator during steam shutdown according to claim 1, characterized in that: The key boundary conditions are as follows: An abnormal situation occurred in the nuclear power plant, causing the turbine to shut down urgently and the main steam valve to be cut off instantly; The deaerator loses its heating steam source and there is no new steam source of any other nature input; There is no upstream drain input in the deaerator; Cooling water still enters from the deaerator water supply inlet.

3. The method for analyzing the transient response of a hybrid deaerator during steam shutdown according to claim 1, characterized in that: Assumptions are as follows: Each equilibrium state is always located on the saturation curve; Ignore the pressure fluctuations and the resulting water level changes during the non-equilibrium process; The volume of the vapor phase space remains unchanged; The metal wall temperature is uniformly distributed overall and is consistent with the temperature of each phase in equilibrium.

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