Fused salt heat exchanger leakage detection device and method

Abstract

The invention discloses a molten salt heat exchanger leakage detection device and method.The molten salt heat exchanger leakage detection device comprises a sampling module, a gas monitoring module and a control system, and the sampling module communicates with a flue at the downstream of a molten salt heat exchanger to extract flue gas; the gas monitoring module can measure the concentration of the molten salt decomposition product in the flue gas extracted by the sampling module and form a concentration signal; the control system comprises a data transmission module, a data processing module and an alarm module, the gas monitoring module is connected with the data processing module through the data transmission module, the data transmission module transmits a concentration signal to the data processing module, the data processing module judges whether the fused salt leaks or not according to the concentration signal, and if leakage occurs, the alarm module gives an alarm. Calculating the molten salt leakage rate and the leakage area; the alarm module is connected with the data processing module, and when the data processing module judges that the fused salt leaks, the alarm module sends out an alarm signal. According to the invention, the accuracy and reliability of fused salt leakage detection can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchanger equipment monitoring, and more specifically, to a molten salt heat exchanger leakage detection device and method. Background Art

[0002] Molten salt heat exchangers are widely used in solar thermal power generation, nuclear energy and other fields, and have been used in the flexibility transformation of coal-fired units. The leakage problem of molten salt heat exchangers is one of the main hidden dangers that plague their safe operation.

[0003] At present, the common methods for detecting leakage of molten salt heat exchangers mainly include electrical signal monitoring, pressure monitoring, temperature monitoring and acoustic monitoring. Although these methods can detect molten salt leakage to a certain extent, they have some limitations: 1. Electrical signal monitoring is suitable for scenes with relatively stable external environment, such as the outer wall and bottom of the salt storage tank, and the outer wall of the pipeline in the ordinary environment. It is not suitable for environments that are easy to damage the circuit, such as high temperature, high corrosion or high humidity. In addition, the heat transfer medium contains fly ash, which will quickly wash away and damage the detection circuit, which limits the arrangement of the detection circuit inside the heat exchanger. 2. The pressure monitoring method detects by detecting the pressure changes at the inlet and outlet of the heat exchanger molten salt, but the early leakage signal is easily submerged in the pressure changes caused by changes in working conditions and system fluctuations. It is difficult to capture the small leakage changes inside the system and cannot monitor the early leakage. 3. The temperature monitoring method is easily affected by the ambient temperature and operating conditions, and the detection accuracy is limited. 4. The acoustic monitoring method is easily affected by the noise interference of the environment and the fluid inside the heat exchanger, and the detection accuracy is limited. In addition, some existing methods, such as tracer gas, need to be carried out when the equipment is out of production (such as maintenance, fault diagnosis), and cannot be applied to online continuous monitoring of heat exchangers.

[0004] Existing leakage detection methods have major deficiencies in terms of usability, sensitivity, and environmental adaptability, and cannot meet the needs of online leakage monitoring of molten salt heat exchangers in complex working environments.

[0005] Therefore, how to improve the accuracy and reliability of molten salt leakage monitoring to ensure the safe and stable operation of the molten salt heat exchanger has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0006] In view of this, an object of the present invention is to provide a molten salt heat exchanger leakage detection device to improve the accuracy and reliability of molten salt leakage monitoring and ensure the safe and stable operation of the molten salt heat exchanger.

[0007] Another core of the present invention is to disclose a molten salt heat exchanger leakage detection method.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] Molten salt heat exchanger leakage detection device, comprising:

[0010] A sampling module, the sampling module is connected to the flue downstream of the molten salt heat exchanger to extract flue gas;

[0011] The gas monitoring module can measure the concentration of the decomposition products of the molten salt in the flue gas extracted by the sampling module and form a concentration signal;

[0012] The control system includes a data transmission module, a data processing module and an alarm module. The gas monitoring module is connected to the data processing module through the data transmission module. The data transmission module transmits the concentration signal to the data processing module. The data processing module determines whether the molten salt leaks according to the concentration signal. If a leak occurs, the leakage amount and leakage area of ​​the molten salt are calculated. The alarm module is connected to the data processing module. When the data processing module determines that the molten salt leaks, the alarm module sends an alarm signal.

[0013] Optionally, in the above-mentioned molten salt heat exchanger leakage detection device, the sampling module includes a sampling tube and an exhaust fan connected to the sampling tube, the sampling tube is connected to the flue downstream of the molten salt heat exchanger, and a valve is arranged between the exhaust fan and the flue downstream of the molten salt heat exchanger.

[0014] A molten salt heat exchanger leakage detection method, using the above-mentioned molten salt heat exchanger leakage detection device, comprises the steps of:

[0015] Extracting flue gas from the flue downstream of the molten salt heat exchanger;

[0016] Detect the composition and concentration of molten salt decomposition products in the extracted flue gas;

[0017] Determine whether the molten salt leaks. If leakage occurs, perform the following steps:

[0018] Calculate the mass flow rate of leaked molten salt;

[0019] Calculate the leakage area of ​​the leaked molten salt.

[0020] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, the step of determining whether the molten salt has leaked specifically includes:

[0021] Obtaining a baseline concentration of molten salt decomposition products in a flue downstream of the molten salt heat exchanger;

[0022] The change rate of the concentration of the molten salt decomposition products detected by the gas monitoring module compared to the reference concentration is calculated, and it is determined whether it exceeds the threshold; if it exceeds the threshold, the molten salt leaks.

[0023] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, the step of calculating the mass flow rate of the leaking molten salt specifically includes:

[0024] Calculate the maximum volume of the flow field of the decomposition products of molten salt leakage;

[0025] Calculate the mass relationship between the decomposition products of molten salt and the leaked molten salt;

[0026] Calculate the relationship between the concentration change rate of molten salt decomposition products and the mass flow rate of leaked molten salt;

[0027] The mass flow rate of the leaked molten salt is calculated based on the detected concentration change rate of the molten salt decomposition products.

[0028] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, when leakage occurs at the molten salt outlet of the heat exchange pipe of the molten salt heat exchanger, the flow field volume between the molten salt outlet of the heat exchange pipe to the gas monitoring module is the maximum volume of the molten salt decomposition product flow field.

[0029] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, in the step of calculating the maximum volume of the molten salt leakage decomposition product flow field, the maximum volume of the molten salt decomposition product flow field is calculated according to the geometric dimensions of the molten salt heat exchanger, the position of the heat exchange pipe inside the molten salt heat exchanger, the geometric dimensions of the heat exchange pipe, the size of the flue downstream of the molten salt heat exchanger and the size of the sampling tube.

[0030] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, the step of calculating the relationship between the concentration change rate of the molten salt decomposition product and the mass flow rate of the leaked molten salt specifically includes:

[0031] Calculating the volume of the flue gas, and calculating the volume of the flue gas according to the maximum volume of the flow field of the molten salt decomposition products, the path length of the molten salt decomposition products and the flow rate of the flue gas;

[0032] Calculate the mass flow rate of the molten salt decomposition products according to the volume of the flue gas and the concentration change of the molten salt decomposition products;

[0033] Calculate the mass flow rate of leaked molten salt;

[0034] Determine the relationship between the concentration change rate of the molten salt decomposition products and the mass flow rate of the leaked molten salt.

[0035] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, in the step of calculating the leakage area of ​​the leaking molten salt, the relationship between the molten salt mass flow rate and the leakage area is determined by finite element simulation.

[0036] Optionally, in the above-mentioned molten salt heat exchanger leakage detection method, the finite element simulation specifically includes the following steps:

[0037] Establish a finite element model of the molten salt heat exchanger;

[0038] Set a leak port and establish a model of a molten salt heat exchanger with a leak port;

[0039] Through simulation, the relationship between the leakage area and the mass flow rate of the leaked molten salt is obtained;

[0040] The leakage area is enlarged to obtain the relationship between different leakage areas and the mass of leaked molten salt.

[0041] It can be seen from the above scheme that the molten salt heat exchanger leakage detection device disclosed in the present invention can determine whether the molten salt has leaked by measuring the concentration of the molten salt decomposition products contained in the flue gas in the downstream flue of the molten salt heat exchanger, can realize online monitoring, can monitor small leakage, has high detection accuracy, has high reliability and accuracy, and can ensure the stable operation of the molten salt heat exchanger. The molten salt heat exchanger leakage detection method and the heat exchanger leakage detection device have the same technical effects, which will not be repeated. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a structural schematic diagram of a molten salt heat exchanger leakage detection device disclosed in an embodiment of the present invention;

[0044] Figure 2 A flow chart of a molten salt heat exchanger leakage detection method disclosed in an embodiment of the present invention;

[0045] Figure 3 A flowchart of the step of calculating the mass flow rate of leaking molten salt in the molten salt heat exchanger leakage detection method disclosed in an embodiment of the present invention;

[0046] Figure 4 The present invention is a flow chart for calculating the relationship between the concentration change rate of molten salt decomposition products and the mass flow rate of leaked molten salt in the molten salt heat exchanger leakage detection method disclosed in an embodiment of the present invention.

[0047] Among them, 1. flue gas inlet, 2. flue gas molten salt heat exchanger, 3. flue, 4. molten salt outlet, 5. molten salt inlet, 6. heat pipe duct, 7. sampling tube, 8. valve, 9. exhaust fan, 10. gas monitoring module, 11. data transmission module, 12. data processing module, 13. alarm module. DETAILED DESCRIPTION

[0048] The core of the present invention is to disclose a molten salt heat exchanger leakage detection device to improve the accuracy and reliability of molten salt leakage monitoring and ensure the safe and stable operation of the molten salt heat exchanger.

[0049] Another core of the present invention is to disclose a molten salt heat exchanger leakage detection method.

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0051] In order to facilitate the understanding of the following text, the molten salt heat exchange system is first introduced. Figure 1 As shown, the molten salt heat exchange system includes a molten salt heat exchanger 2. In the molten salt heat exchanger 2, there are a molten salt circuit and a flue gas circuit. High-temperature flue gas (temperature is generally 450°C) enters the molten salt heat exchanger 2 from the flue gas inlet 1, and cold molten salt enters the heat exchange pipe 6 from the molten salt inlet 5. The high-temperature flue gas and the cold molten salt exchange heat in the molten salt heat exchanger 2. After the high-temperature flue gas temperature decreases (temperature is generally 230°C), it enters the flue 3 downstream of the molten salt heat exchanger 2. The molten salt temperature increases and becomes hot molten salt, which is discharged from the molten salt outlet 4 of the heat exchange pipe 6 and can be stored in the molten salt tank. The molten salt and flue gas exchange heat in a countercurrent manner.

[0052] The main components of molten salt include 53% potassium nitrate (KNO3), 40% sodium nitrite (NaNO2) and 7% sodium nitrate (NaNO3), with a melting point of 142°C and a vaporization point of 500°C. When the temperature reaches 334°C, potassium nitrate (KNO3) begins to decompose and decomposes into potassium nitrite and oxygen. When the temperature reaches 380°C, sodium nitrate (NaNO3) begins to decompose and decomposes into sodium nitrite and oxygen. When the temperature reaches above 450°C, sodium nitrite (NaNO2) will decompose slowly, but due to the influence of impurities, the decomposition temperature will further decrease. For example, it will decompose slowly at 300°C and decompose rapidly at higher temperatures. The decomposition products of NaNO2 include nitric oxide (NO) and nitrogen dioxide (NO2). The decomposition products of the leaked molten salt enter the flue gas and enter the downstream flue 3 with the flue gas. Therefore, it is possible to determine whether the molten salt has leaked by measuring the concentration of O2, NO or NO2 in the downstream flue 3. The present invention determines whether the molten salt has leaked by measuring the concentration of the molten salt decomposition products in the flue gas in the flue 3 downstream of the molten salt heat exchanger 2 .

[0053] like Figure 1 As shown, the molten salt heat exchanger leakage detection device disclosed in the embodiment of the present invention includes a sampling module, a gas monitoring module 10 and a control system.

[0054] Among them, the control system includes a data transmission module 11, a data processing module 12 and an alarm module 13. The sampling module is connected to the flue 3 downstream of the molten salt heat exchanger 2 to sample the flue gas in the flue 3. The gas monitoring module 10 measures the concentration of the molten salt decomposition products in the flue gas extracted by the sampling module and generates a concentration signal, and transmits the concentration signal to the data processing module 12 through the data transmission module 11. The data processing module 12 receives the concentration signal and analyzes it to determine whether the molten salt has leaked. If a leak occurs, the leakage amount and leakage area of ​​the molten salt are further calculated. The alarm module 13 is connected to the data processing module 12. When the data processing module 12 determines that the molten salt has leaked, the alarm module 13 sends an alarm signal.

[0055] The sampling module can be connected to the control system, and the sampling can be controlled by the control system. The sampling can be performed in a periodic sampling manner, such as at preset time intervals, the sampling module extracts flue gas from the downstream flue 3; or sampling can be performed according to sampling requirements.

[0056] The sampling module can be set in multiple groups, which can be set specifically according to the actual situation.

[0057] The molten salt heat exchanger leakage detection device disclosed in the embodiment of the present invention determines whether the molten salt has leaked by measuring the concentration of molten salt decomposition products contained in the flue gas in the downstream flue 3 of the molten salt heat exchanger 2. It can realize online monitoring and monitor small leakage situations. It has high detection accuracy, high reliability and accuracy, and can ensure the stable operation of the molten salt heat exchanger.

[0058] It should be noted that the gas monitoring module 10 includes a concentration measuring element and a data collector. The concentration measuring element is used to measure the concentration of NO2 in the extracted flue gas. The data collector converts the concentration value of NO2 measured by the concentration measuring element into a digital signal.

[0059] The data transmission module 11 can be connected to the gas monitoring module 1 through hard wiring, field bus, industrial Ethernet, zigbee, 5G, wifi, etc.

[0060] The alarm signal sent by the alarm module 13 may include a sound signal, a light signal, or both a sound signal and a light signal. At the same time, the alarm module 13 can send out alarm signals of different levels according to the severity of the leakage. For example, when the leakage is serious, a rapid alarm sound can be issued without an interval; when the leakage is slight, the alarm sound can be issued for three seconds, with an interval of one second, and then the cycle continues. Of course, this is only an example, and it can be specifically set according to the actual situation. This setting method makes it easy for the staff to distinguish the severity of the leakage and take corresponding measures in time. The alarm module 13 and the data processing module 12 can choose an integrated design.

[0061] In some specific implementations, the control system includes a display screen, which can display in real time the concentration data of the molten salt decomposition products detected by the gas monitoring module, the amount of leaked molten salt when a leak occurs, the leakage area, and the alarm information issued by the alarm module 13.

[0062] In some specific embodiments, Figure 1 As shown, the sampling module includes a sampling tube 7 and an exhaust fan 9 connected to the sampling tube 7, the sampling tube 7 is connected to the flue 3 downstream of the molten salt heat exchanger 2, and the exhaust fan 9 provides exhaust power. In order to improve the reliability of the system and the flexibility of operation, a valve 8 is arranged between the exhaust fan 9 and the flue 3 downstream of the molten salt heat exchanger 2.

[0063] The valve 8 can be a shut-off valve, which is convenient for the inspection and maintenance of the exhaust fan 9 and the gas monitoring module 10, or the sampling tube 7 can be cut off in time when the molten salt heat exchanger 2 fails, so as to reduce the damage to the exhaust fan 9 and the gas monitoring module. The valve 8 can also be a regulating valve with a shut-off function, so as to adjust the flow rate of the extracted flue gas. The valve 8 can be a manually controlled valve or an electrically controlled valve, preferably an electrically controlled valve, and the valve 8 is connected to the control system, and the exhaust fan 9 is connected to the control system. This setting method can realize automatic sampling of the sampling module.

[0064] The present invention also discloses a molten salt heat exchanger leakage detection method, comprising the following steps:

[0065] S1, extracting flue gas in the flue 3 downstream of the molten salt heat exchanger;

[0066] The gas monitoring module is started to extract flue gas from the downstream flue 3. Specifically, the valve 8 is opened, and the exhaust fan 9 is turned on to extract the flue gas.

[0067] S2. Detect the composition and concentration of molten salt decomposition products in the extracted flue gas;

[0068] The gas monitoring module 10 monitors the composition and concentration of the gas in the extracted flue gas and converts the measured NO2 concentration into a concentration signal;

[0069] S3, determine whether the molten salt leaks, if leakage occurs, perform the following steps;

[0070] The data transmission module 11 transmits the concentration signal measured by the gas monitoring module to the data processing module 12. The data processing module 12 receives the concentration signal and analyzes it to determine whether the molten salt leaks. If a leak occurs, step S4 and step S5 are executed; if no leak occurs, wait for the next sampling to continue detection.

[0071] S4. Calculate the mass flow rate of the leaked molten salt.

[0072] S5. Calculate the leakage area of ​​the leaked molten salt.

[0073] It should be noted that the alarm setting index of the alarm module can be set according to the concentration change rate threshold of the molten salt decomposition product, the leakage alarm threshold, the leakage change threshold, the leakage area threshold and other indicators.

[0074] It is generally believed that nitrogen oxides in flue gas contain about 5% NO2 and about 95% NO. It is preferred to determine whether the molten salt has leaked by measuring the concentration of NO2 in the flue gas in the downstream flue 3 and comparing it with the concentration of NO2 in the flue gas when no molten salt leakage occurs. This is used as an example for explanation below. Usually, the molten salt heat exchanger 2 is coupled with a coal-fired unit. The high-temperature flue gas generally comes from the coal-fired unit. The concentration of NO2 in the flue gas emitted by the coal-fired unit before entering the desulfurization and denitrification stage is the concentration of NO2 in the flue gas when no molten salt leakage occurs.

[0075] In some specific embodiments, step S3 specifically includes the following steps:

[0076] S31, obtaining a reference concentration of molten salt decomposition products in the flue 3 downstream of the molten salt heat exchanger;

[0077] Specifically, the control system is connected to the DCS system (distributed control system) of the coal-fired unit. When the molten salt heat exchanger 2 is running, the DCS system of the coal-fired unit obtains the NO2 concentration of the high-temperature flue gas before entering the desulfurization and denitrification link, and uses the average concentration within the preset time as the NO2 reference concentration under the current working condition. The preset time can be selected according to actual needs, such as 10 minutes, 20 minutes, etc. According to the actual operating conditions, the NO2 reference concentration can be 10mg / m 3 .

[0078] S32, calculating the change rate of the concentration of the molten salt decomposition product detected by the gas monitoring module compared with the reference concentration, and judging whether it exceeds the threshold value, if it exceeds the threshold value, the molten salt leaks.

[0079] Specifically, the rate of change = (concentration detected by the gas monitoring module - reference concentration) / reference concentration. For example, if the threshold is 5%, and the concentration of NO2 detected by the gas monitoring module is 11 mg / m 3 , then the rate of change = (11-10) / 10 = 10%>5%, then molten salt leakage occurs; if the concentration of NO2 detected by the gas monitoring module is 10.2mg / m 3 , then the rate of change = (10.2-10) / 10 = 2%<5%, so no leakage occurs at this time.

[0080] The molten salt heat exchanger leakage detection method disclosed in the embodiment of the present invention, step S4 specifically includes the following steps:

[0081] S41, calculating the maximum volume of the flow field of the molten salt decomposition product;

[0082] The volume of the decomposition product flow field under the most extreme scenario of molten salt leakage is calculated. When leakage occurs at the molten salt outlet 4 of the heat exchange pipe 6 of the molten salt heat exchanger 2, the molten salt decomposition product flow field is the largest, and the maximum volume of the molten salt decomposition product flow field is the flow field volume between the molten salt outlet 4 of the heat exchange pipe 6 and the gas monitoring module 10.

[0083] First, determine the geometric dimensions of the area through which the molten salt decomposition products flow, which can be calculated based on the geometric dimensions of the molten salt heat exchanger 2, the position of the heat exchange pipe 6 inside the molten salt heat exchanger 2, the geometric dimensions of the heat exchange pipe 6, the dimensions of the downstream flue 3, the dimensions of the sampling tube 7 and the physical properties of the flue gas.

[0084] S42, calculating the mass relationship between the decomposition products of the molten salt and the leaked molten salt;

[0085] According to the type of molten salt and the inlet and outlet temperatures of flue gas, the decomposition ratio of molten salt, the composition of decomposition products and the ratio of each component are determined, and the mass relationship between the decomposition products of molten salt and the leaked molten salt at each temperature is calculated. Specifically, the chemical equations for the decomposition of molten salt can be determined according to the type of molten salt, so as to obtain the molar mass and mass of each decomposition product, and then the relationship between the mass of the decomposition products of molten salt and the mass of the leaked molten salt can be obtained. By changing the temperature, the corresponding relationship between the mass of the decomposition products of molten salt and the mass of the leaked molten salt in different temperature ranges can be obtained.

[0086] S43, calculating the relationship between the concentration change rate of the molten salt decomposition products and the mass flow rate of the leaked molten salt;

[0087] The relationship between the concentration change rate of the molten salt decomposition product and the mass flow rate of the leaked molten salt is calculated according to the maximum volume of the molten salt decomposition product flow field calculated in step S41, the characteristics of the molten salt decomposition product in step S42, the flue gas flow rate and the characteristic parameters of the gas monitoring module. Specifically, the characteristic parameters of the gas monitoring module include the range, resolution, measurement accuracy, response time and recovery time of the NO2 concentration detection element.

[0088] S44. Calculate the mass flow rate of the leaked molten salt according to the detected concentration change rate of the molten salt decomposition products.

[0089] The molten salt heat exchanger leakage detection method disclosed in the embodiment of the present invention, step S43 specifically includes the following steps:

[0090] S431. Calculate the volume of smoke;

[0091] Specifically, it can be calculated based on the maximum volume of the molten salt decomposition product flow field, the path length of the molten salt decomposition product and the flow rate of the flue gas. The volume of the flue gas = the flow rate of the flue gas × the average cross-sectional area of ​​the flue gas flowing through the molten salt heat exchanger 2, and the average cross-sectional area of ​​the molten salt heat exchanger 2 = the maximum volume of the molten salt decomposition product flow field / the flow path length of the molten salt decomposition product.

[0092] S432, calculating the mass flow rate of molten salt decomposition products;

[0093] Specifically, the mass flow rate of the molten salt decomposition product = the volume of the flue gas × the concentration change. The concentration change here is the preset concentration change, which is the concentration of the newly added NO2 within the preset time. For example, it can be assumed that the concentration change in one minute (the sum of the response time and the recovery time of the NO2 concentration monitoring element) is 0.1 mg / m 3 .

[0094] S433, calculating the mass flow rate of the leaked molten salt;

[0095] Specifically, the mass flow rate of the leaked molten salt = the mass flow rate of the decomposition products of the molten salt per unit time calculated in step S431 / the mass flow rate of the decomposition products generated by the molten salt under a unit mass flow rate.

[0096] S434, determining the relationship between the concentration change rate of the molten salt decomposition product and the mass flow rate of the leaked molten salt;

[0097] According to the concentration fluctuation range of NO2 in the flue gas, the relationship between the preset concentration change and the concentration change rate in step S431 is determined, and the relationship between the concentration change rate of the molten salt decomposition product and the mass flow rate of the leaked molten salt can be obtained according to the mass flow rate of the leaked molten salt obtained in step S432.

[0098] In some specific embodiments, in step S5, the leakage area of ​​the leaking molten salt is calculated, and the relationship between the mass flow rate of the molten salt and the leakage area is determined by finite element simulation. Specifically, the following steps are included:

[0099] S51. Establish a model of a molten salt heat exchanger;

[0100] According to the geometric parameters of the molten salt heat exchanger 2 and the heat exchange pipe 6, the physical parameters of the molten salt (including the density, specific heat, thermal conductivity, viscosity and other parameters of the molten salt), the physical parameters of the flue gas (including the flow rate, pressure, inlet and outlet temperature, density, viscosity, specific heat, thermal conductivity and other parameters of the flue gas), and the physical parameters of the heat exchange pipe 6 (including the specific heat and thermal conductivity of the heat exchange pipe 6), a coupled heat absorption and release model of the molten salt heat exchanger 2 is established. The physical parameters of the heat exchange pipe 6 are determined according to the material of the heat exchange pipe 6.

[0101] In the finite element simulation software, the solver configuration is as follows:

[0102] Three-dimensional, double-precision, pressure-based, steady-state solver to ensure convergence stability; SIMPLE algorithm is used for pressure and velocity decoupling;

[0103] The momentum, turbulent kinetic energy, turbulent dissipation rate and energy are measured using the second-order upwind scheme;

[0104] The shell of the molten salt heat exchanger 2 adopts an impermeable, no-slip adiabatic boundary;

[0105] The flue gas inlet 1 of the molten salt heat exchanger 2 adopts a velocity inlet, and the fluid velocity, temperature and corresponding turbulence conditions are given; the inlet fluid temperature is interpolated according to the position; the shell outlet adopts the pressure outlet boundary condition; the convergence criterion of the continuity equation is that the residual is less than 10 -4 The convergence criterion of the energy equation is that the residual is less than 10 -6 .

[0106] S52, setting a leakage port, and establishing a model of a molten salt heat exchanger (2) with a leakage port;

[0107] In order to ensure the accuracy of the simulation, the leakage port is established based on the smallest leakage port or common form when leakage occurs in actual maintenance situations.

[0108] According to the actual maintenance situation, the leakage holes mainly include two types: cracks and corrosion holes. The size of the cracks is 8mm×0.5mm at most. According to the literature records, the corrosion holes have a porous structure, and there is no specific size introduction. The square holes of 0.1mm×2mm are used to replace the corrosion holes.

[0109] S53, simulating and obtaining the relationship between the leakage area and the mass flow rate of the leaked molten salt;

[0110] For step S52, a model of a molten salt heat exchanger (2) with a leakage port is established to perform simulation calculations to obtain the relationship between the leakage area and the mass flow rate of the leaking molten salt under a steady state.

[0111] S54. Expand the leakage area to obtain the relationship between different leakage areas and the mass of leaked molten salt.

[0112] The area of ​​the leakage port in step S52 is enlarged to obtain a series of models of the molten salt heat exchanger 2 coupled with the heat absorbing and releasing working medium under different leakage areas. Each model is simulated separately to obtain the relationship between different leakage areas and the mass of the leaked molten salt.

[0113] For ease of understanding, the above steps are described in detail with a specific example. For example, the molten salt heat exchanger 2 is a prism with a square cross section, the prism height is 15m, and the side length of the square cross section is 3m;

[0114] The heat exchange pipe 6 is an S-shaped elbow located in the middle of the molten salt heat exchanger 2. The S-shaped elbow includes a horizontal straight pipe and bent pipes located at both ends of the horizontal straight pipe. Figure 1 As shown in . The length of the horizontal straight pipe is 2m, the outer diameter of the pipe is 18mm, and the inner diameter is 12mm; the corresponding angles of the inlet and outlet of the bent pipe in the S-shaped bend pipe are 180°, the turning radius is 0.125m (the diameter is 0.25m), the outer diameter of the pipe is 18mm, and the inner diameter is 12mm. A single S-shaped heat exchange pipe 6 contains 50 horizontal straight pipes and 49 bent pipes, a total of 60 heat exchange pipes 6, and the interval between two adjacent heat exchange pipes 6 is 0.05m.

[0115] The downstream flue duct 3 is a circular tube with a diameter of 2 m, and the length of the downstream flue duct 3 from the flue gas outlet of the molten salt heat exchanger 2 to the sampling tube 7 is 3 m.

[0116] The sampling tube 7 is a circular tube with a diameter of 0.1 m and a length of 1 m.

[0117] In the above specific embodiment, the maximum volume of the molten salt decomposition product flow field is calculated as follows:

[0118] The maximum volume of the flow field is the volume between the molten salt outlet 4 and the tail of the molten salt heat exchanger 2 - the volume of the heat exchange pipe 4 + the volume of the downstream flue 3 + the volume of the sampling tube 7, that is, V max (maximum volume of molten salt decomposition product flow field) = V 熔盐换热器 -V 换热管道 +V 下游烟道 +V 取样管 .

[0119] Volume V between the molten salt outlet 4 and the tail of the molten salt heat exchanger 2 换热器 = heat exchanger cross section × (height of molten salt heat exchanger 2 - height from flue gas inlet 1 to outlet of heat exchange pipe 6) = heat exchanger cross section × (height of molten salt heat exchanger 2 - 0.5 × (height of molten salt heat exchanger 2 - height of heat exchange pipe 6), where the height of heat exchange pipe 6 = number of bends × bend diameter = 49 × 0.25m; V 换热器＝ 3m×3m×(15m–0.5×(15m–49×0.25m))=122.625m 3 .

[0120] The total volume of the heat exchange pipe 6 is the sum of the volumes of 60 heat exchange pipes 6, and each heat exchange pipe 6 includes 50 straight pipes and 49 curved pipes. According to the calculation formula of the torus, the volume of the torus = 2π 2 R 2 , where R represents the radius of the outer circle of the torus, r represents the radius of the cross-section circle of the torus, and the bent pipe can be regarded as half a torus, so the volume of the bent pipe = π 2 R 2, where R is the turning radius 0.125m, r is the radius of the corresponding cross-section circle of the outer wall of the curved pipe 0.009m, then the volume of a single straight pipe V 直 =2m×π×(0.018m / 2) 2 =0.0005m 3 ; The volume of a single elbow is V 弯 =π 2 ×0.125m×(0.009m) 2 =0.0001m 3 The total volume of the heat exchange pipe 6 is V 换热管道 =60×(50×0.0005m 3 +49×0.0001m 3 )=1.794m 3 .

[0121] Volume V of downstream flue 3 烟道 =π×(2m / 2) 2 ×3m=9.425m 3 .

[0122] The volume V of the sampling tube 7 取样管 =π×(0.1m / 2) 2 ×1m=0.00785m 3 .

[0123] Then the maximum volume of the flow field is Vmax=V 换热器 -V 换热管 +V 下游烟道 +V 取样管 =122.625m 3 -1.794m 3 +9.425m 3 +0.00785m 3 =130.26m 3 .

[0124] The specific calculation of step S42 is as follows:

[0125] In flue gas, the decomposition ratio of molten salt is 5%-10%. In the entire working temperature range, the following decomposition reactions mainly occur:

[0126]

[0127] From the above chemical equation, we can know that 2molNaNO2 completely decomposes to produce 1molNO and 1molNO2, that is, 138gNaNO2 reacts to produce 30gNO and 46gNO2. The mass proportion of NaNO2 in molten salt is 40%, so the mass of NO2 that can be produced by completely decomposing 1kg molten salt is calculated as follows:

[0128] 1000×0.4×46 / 133=133g,

[0129] The amount of substance converted is 133 / 46=2.89 mol.

[0130] In flue gas, the decomposition ratio of molten salt is 5%-10%. Taking the minimum decomposition situation, that is, the decomposition ratio of molten salt is 5%, when 1kg of molten salt leaks and decomposes, the mass of NaNO2 that can be produced is 133g×5%=6.65g, about 6.65 / 46=0.1445mol.

[0131] The specific calculation process of step S43 is as follows:

[0132] S431. Calculate the volume of smoke;

[0133] Specifically, the volume of flue gas = flue gas flow rate × average cross-sectional area of ​​flue gas flowing through molten salt heat exchanger 2, the average cross-sectional area of ​​molten salt heat exchanger 2 = maximum volume of molten salt decomposition product flow field / length of molten salt decomposition product flow path, wherein the length of molten salt decomposition product flow path = (15m-0.5×(15m-49×0.25m))+1m+3m=17.625m, then the average cross-sectional area of ​​flue gas flowing through molten salt heat exchanger 2 = 130.26m 3 / 17.625m=7.39m 2 , the volume of flue gas = 9m / s (flue gas velocity) × 60s × 7.39m 2 =3990.6m 3 .

[0134] S432, calculating the mass flow rate of molten salt decomposition products;

[0135] The preset concentration change is 0.1mg / m 3 , the preset time is 1 minute, then when the preset concentration change is reached, the mass of NO2 = preset concentration change × flue gas volume = 0.1 mg / m 3 ×3990.6m 3 =399mg=0.399g.

[0136] S433, calculating the mass flow rate of the leaked molten salt;

[0137] The concentration of nitrogen oxides NOx (usually considered to be a mixture of 5% NO2 + 95% NO) in flue gas is usually between 200 and 300 mg / m 3 The fluctuation range of NO2 is 200×40%-300×40%=10-15mg / m 3 , the concentration change rate is 1%, corresponding to a concentration change of 0.1 mg / m 3 Up to 0.15 mg / m 3, take the lower limit of 0.1mg / m 3 Calculate. The mass of the leaked molten salt = 0.399g / 6.65g×1kg=0.06kg, where 6.65g means that when 1kg of molten salt leaks and decomposes, the mass of NO2 that can be produced is 133g×5%=6.65g;

[0138] S434. Determine the relationship between the concentration change rate of the molten salt decomposition products and the mass flow rate of the leaked molten salt.

[0139] According to step S433, when the leakage of molten salt is 0.06 kg / min (1 g / s), the concentration fluctuates by 1%. For every 1% increase in NO2 concentration, the corresponding increase in the leakage of molten salt is 1 g / s.

[0140] Specifically, in step S51, the physical properties of the molten salt vary with temperature as follows: density ρ (kg / m 3 ) changes with temperature t(℃): ρ = 2278.799-0.7484×t; specific heat Cp (J / (kg·K)) changes with temperature t(℃): Cp = 1507-0.1×t; thermal conductivity changes with temperature t(℃): λ = 0.8099+0.0007827×t+1.043e-07×t 2 ; The viscosity η (kg / (m·s)) changes with temperature t (℃): η=0.06248+0.0002253×t+2.7903e-07×t 2 +1.1738e-10×t 3 .

[0141] The main components of flue gas are water vapor, sulfur dioxide, nitrogen, oxygen, carbon monoxide, carbon dioxide, hydrocarbons, NO and NO2 (the ratio of NO to NO2 is about 95%:5%). The flow rate is 9m / s, the flue gas inlet temperature is 450℃, the outlet temperature is 230℃, the pressure is -30Pa, and the density, kinematic viscosity and thermal conductivity are shown in the table below.

[0142]

[0143]

[0144] The material of the heat exchange pipe 6 is TP347H (high carbon niobium-containing Cr-Ni austenitic stainless steel), with a specific heat Cp of 440 J / (kg·K) and a thermal conductivity λ of 21 W / (m·K).

[0145] In some specific embodiments, in step S52, a square hole with a size of 0.1mm×2mm is set near the outlet of the heat exchange pipe 6 to construct a model of the molten salt heat exchanger 2 with a leakage port. In step S53, after simulation, a square hole with a size of 0.1mm×2mm is obtained, resulting in a molten salt leakage of 0.645g / s, and the NO2 concentration increases by 0.645%. In step S54, when the number of square holes is increased to 2-8, the molten salt leakage increases approximately linearly. From the above simulation, it can be seen that for every 1% increase in NO2 concentration, the leakage port area increases by approximately 1% / 0.645%×0.1mm×2mm=0.31mm 2 , thus the relationship between the change rate of molten salt concentration and the molten salt leakage area is obtained.

[0146] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0147] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A molten salt heat exchanger leakage detection device, characterized in that: include: A sampling module, the sampling module being connected to a flue (3) downstream of the molten salt heat exchanger (2) to extract flue gas; A gas monitoring module (10), wherein the gas monitoring module (10) is capable of measuring the concentration of molten salt decomposition products in the flue gas extracted by the sampling module and forming a concentration signal; A control system, the control system comprising a data transmission module (11), a data processing module (12) and an alarm module (13); the gas monitoring module (10) is connected to the data processing module (12) via the data transmission module (11); the data transmission module (11) transmits a concentration signal to the data processing module (12); the data processing module (12) determines whether molten salt is leaking according to the concentration signal; if leakage occurs, the leakage amount and leakage area of ​​the molten salt are calculated; the alarm module (13) is connected to the data processing module (12); when the data processing module (12) determines that molten salt is leaking, the alarm module (13) sends an alarm signal.

2. The molten salt heat exchanger leakage detection device according to claim 1, characterized in that: The sampling module comprises a sampling tube (7) and an exhaust fan (9) connected to the sampling tube (7); the sampling tube (7) is connected to a flue (3) downstream of the molten salt heat exchanger (2); and a valve (8) is provided between the exhaust fan (9) and the flue (3) downstream of the molten salt heat exchanger (2).

3. A molten salt heat exchanger leakage detection method, using the molten salt heat exchanger leakage detection device as claimed in claim 2, characterized in that: Includes steps: extracting flue gas from a flue (3) downstream of the molten salt heat exchanger; Detect the composition and concentration of molten salt decomposition products in the extracted flue gas; Determine whether the molten salt leaks. If leakage occurs, perform the following steps: Calculate the mass flow rate of leaked molten salt; Calculate the leakage area of ​​the leaked molten salt.

4. The molten salt heat exchanger leakage detection method according to claim 3, characterized in that: The step of determining whether the molten salt has leaked specifically includes: Obtaining a baseline concentration of molten salt decomposition products in a flue (3) downstream of the molten salt heat exchanger; The change rate of the concentration of the molten salt decomposition products detected by the gas monitoring module compared to the reference concentration is calculated, and it is determined whether it exceeds the threshold; if it exceeds the threshold, the molten salt leaks.

5. The molten salt heat exchanger leakage detection method according to claim 3, characterized in that: The step of calculating the mass flow rate of the leaked molten salt specifically includes: Calculate the maximum volume of the flow field of the decomposition products of molten salt leakage; Calculate the mass relationship between the decomposition products of molten salt and the leaked molten salt; Calculate the relationship between the concentration change rate of molten salt decomposition products and the mass flow rate of leaked molten salt; The mass flow rate of the leaked molten salt is calculated based on the detected concentration change rate of the molten salt decomposition products.

6. The molten salt heat exchanger leakage detection method according to claim 5, characterized in that: When leakage occurs at the molten salt outlet (4) of the heat exchange pipe (6) of the molten salt heat exchanger (2), the flow field volume between the molten salt outlet (4) of the heat exchange pipe (6) and the gas monitoring module (10) is the maximum volume of the molten salt decomposition product flow field.

7. The molten salt heat exchanger leakage detection method according to claim 6, characterized in that: In the step of calculating the maximum volume of the flow field of the decomposition products of the molten salt leakage, the maximum volume of the flow field of the decomposition products of the molten salt is calculated based on the geometric dimensions of the molten salt heat exchanger (2), the position of the heat exchange pipe (6) inside the molten salt heat exchanger (2), the geometric dimensions of the heat exchange pipe (6), the dimensions of the flue (3) downstream of the molten salt heat exchanger (2) and the dimensions of the sampling tube (7).

8. The method for detecting leakage of a molten salt heat exchanger according to claim 5, characterized in that: The step of calculating the relationship between the concentration change rate of the molten salt decomposition products and the mass flow rate of the leaked molten salt specifically includes: Calculating the volume of the flue gas, and calculating the volume of the flue gas according to the maximum volume of the flow field of the molten salt decomposition products, the path length of the molten salt decomposition products and the flow rate of the flue gas; Calculate the mass flow rate of the molten salt decomposition products according to the volume of the flue gas and the concentration change of the molten salt decomposition products; Calculate the mass flow rate of leaked molten salt; Determine the relationship between the concentration change rate of the molten salt decomposition products and the mass flow rate of the leaked molten salt.

9. The molten salt heat exchanger leakage detection method according to claim 4, characterized in that: In the step of calculating the leakage area of ​​the leaking molten salt, the relationship between the mass flow rate of the molten salt and the leakage area is determined by finite element simulation.

10. The method for detecting leakage of a molten salt heat exchanger according to claim 9, characterized in that: Finite element simulation specifically includes the following steps: Establishing a finite element model of a molten salt heat exchanger (2); Setting a leakage port and establishing a model of a molten salt heat exchanger (2) with the leakage port; Through simulation, the relationship between the leakage area and the mass flow rate of the leaked molten salt is obtained; The leakage area is enlarged to obtain the relationship between different leakage areas and the mass of leaked molten salt.

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