Mixed salt online monitoring system and method

Abstract

The invention relates to the technical field of photo-thermal power generation and mixed salt monitoring, and discloses a mixed salt online monitoring system and method. The system comprises heat exchange equipment, a gas separation chamber, a solution preparation chamber, a first component detector and a second component detector, wherein a pressure reducing device is arranged on a connecting pipeline of the heat exchange equipment and the gas separation chamber; the liquid mixed salt enters the heat exchange equipment to exchange heat with water or water vapor, and then enters the gas separation chamber after being depressurized by the pressure reducing device, and the composition and content of gas in the gas separation chamber are detected by the first component detector; products from the gas separation chamber enter a solution preparation chamber to be prepared into a salt solution, and the concentrations of NO2 <-> and NO3 <-> in the salt solution are detected through a second component detector. The system can monitor gas component change and mixed salt composition change in real time, discover hidden heat exchange equipment leakage and mixed salt oxidation and decomposition problems in time, provide early warning for safe operation of the system, and avoid serious loss.

Description

Technical Field

[0001] The invention relates to the technical fields of photothermal power generation, flexibility transformation of thermal power units and mixed salt monitoring, and in particular to a mixed salt online monitoring system and method. Background Art

[0002] There are more and more application scenarios and cases of nitrate as heat carrier, such as potassium nitrate (KNO 3 ) and sodium nitrate (NaNO 3 ) binary salt with a ratio of 4:6, its melting point is about 220℃, and the operating temperature is 290~565℃. Its main function is to absorb solar radiation energy through binary salt to raise its own temperature to about 565℃, and then the high-temperature binary salt heats water to produce high-temperature and high-pressure steam to drive the steam turbine to generate electricity, and the binary salt itself The temperature drops to about 290℃, and the cycle repeats. KNO is also used in thermal storage frequency regulation and peak regulation of coal-fired units 3 、NaNO 3 and sodium nitrite (NaNO 2 ) The ratio of ternary salt is 53:7:40, with a melting point of about 142°C and an operating temperature of 180-450°C. Its main function is to absorb heat from steam, flue gas or electricity through ternary salts, store it after heating, and then heat water to generate steam. In these applications, binary salts or ternary salts (referred to as mixed salts) absorb and store energy, and heat water to generate steam, thereby achieving the purpose of storing and releasing energy. Although KNO 3 、NaNO 3 and NaNO 2 It is not flammable or explosive in itself, but it still has chemical reaction characteristics such as decomposition or oxidation under high temperature conditions. The change in the proportion of the components of the mixed salt after the chemical reaction will cause changes in a series of physical parameters such as the melting point, which will bring greater risks to the operation of the system.

[0003] For example, binary salts decompose under high temperature to produce NO 3 - Change to NO 2 - (As shown in Formula 1), even if the salt storage tank is connected to the outside air, this process cannot be completely suppressed. The composition of the mixed salt gradually changes to approach the ternary salt, causing the decomposition temperature of the salt to gradually decrease, and the use temperature to gradually decrease, making it impossible to produce the steam required by the design.

[0004] NO 3 - → NO 2 - + 1 / 2 O 2 (1)

[0005] The ternary salt decomposes and oxidizes to produce NO2 - The content continues to decrease (Formula 2-3), resulting in an increase in the melting point close to that of binary salt. The original heat exchange equipment will have a lower heat transfer efficiency and less stored energy due to the decrease in the temperature difference between the cold and hot media. In severe cases, the pipeline or equipment may be blocked and damaged due to poor melting of the mixed salt.

[0006] 5NO 2 - →3NO 3 - + Na 2 O+N 2 (2)

[0007] NO 2 - + 1 / 2O 2 → NO 3 - (3)

[0008] At the same time, when a tiny leak occurs in the heat exchange system, steam or water enters the high-temperature nitrate, which can accelerate the decomposition of the nitrate, not only affecting the physical parameters of the salt, but also accelerating system corrosion and causing the risk of high-temperature liquid salt leakage.

[0009] Since the high-temperature decomposition, oxidation and leakage of heat exchange equipment of mixed salt are quite hidden, it is often difficult to detect them in time once they occur, so that the system problems are not discovered until the performance of the mixed salt changes greatly or the mixed salt leaks, but at this time, irreparable and significant losses have been caused. Due to the high temperature and corrosiveness of liquid mixed salt, it is difficult for in-situ measurement instruments to monitor online for a long time.

[0010] At present, the performance and status of the mixed salt in operation are often tested offline. Usually, samples are taken from the top of the storage tank through a sampling bottle and sent to the laboratory for testing and analysis. During this process, due to the changes in ambient temperature and humidity, as well as contact with air, the test results cannot truly reflect the status and performance of the mixed salt in operation. At the same time, this sampling test method is time-consuming, and the results are usually obtained after several hours or days. It is obviously lagging for industrial operation equipment. In emergency situations such as high-temperature decomposition of mixed salt or leakage of heat exchange equipment, it often fails to play a warning role and causes huge losses.

[0011] Therefore, the industry urgently needs to establish an online monitoring method for mixed salt. Summary of the invention

[0012] The purpose of the present invention is to overcome the problem in the prior art that the results of offline detection are always lagging and often fail to serve as an early warning in emergency situations such as high-temperature decomposition of mixed salt or leakage of heat exchange equipment. An online monitoring system and method for mixed salt are provided. The system and method can monitor the changes in gas components and the changes in the composition of mixed salt in real time, and can promptly discover hidden problems such as leakage of heat exchange equipment, oxidation and decomposition of mixed salt, provide early warning for safe operation of the system, and avoid serious losses.

[0013] In order to achieve the above-mentioned object, the present invention provides an online monitoring system for mixed salts, which comprises a heat exchange device, a gas separation chamber, a solution preparation chamber, a first component detector, and a second component detector. A pressure reducing device is provided on the connecting pipe between the heat exchange device and the gas separation chamber;

[0014] The liquid mixed salt containing nitrate and / or nitrite enters the heat exchange device to exchange heat with water or water vapor, and then enters the gas separation chamber after being depressurized by the decompression device, and the composition and content of the gas in the gas separation chamber are detected by the first component detector;

[0015] The liquid product from the gas separation chamber enters the solution preparation chamber to be prepared into a salt solution, and the NO in the salt solution is detected by a second component detector. 2 - and NO 3 - concentration.

[0016] Preferably, the system further comprises a back-pressure valve, which is connected to the top of the gas separation chamber through a pipeline and is used to control the pressure and gas atmosphere of the gas separation chamber.

[0017] Preferably, a mixed salt metering pump is provided on the connecting pipeline between the gas separation chamber and the solution preparation chamber, and the mixed salt metering pump is used to control the liquid level of the gas separation chamber and meter the amount of mixed salt entering the solution preparation chamber.

[0018] Preferably, the system further comprises a three-way valve, and the mixed salt metering pump, the three-way valve and the solution preparation chamber are sequentially connected through a connecting pipeline.

[0019] Preferably, the system further comprises a check valve, and the three-way valve, the check valve and the mixed salt recovery pipeline are connected in sequence.

[0020] Preferably, the system further comprises a purge valve, wherein the purge valve is connected to a connecting pipeline between the three-way valve and the solution preparation chamber through a pipeline.

[0021] Preferably, the system further comprises a desalted water metering pump for inputting desalted water into the solution preparation chamber to prepare a salt solution and controlling the quality of the desalted water entering the solution preparation chamber.

[0022] Preferably, the gas separation chamber and the inlet and outlet pipelines are provided with a cooling device for cooling the liquid mixed salt.

[0023] A second aspect of the present invention provides a mixed salt online monitoring method, which is implemented in the system described above and comprises the following steps:

[0024] S1, passing a liquid mixed salt containing nitrate and / or nitrite and water or water vapor into the heat exchange device for heat exchange, then reducing the pressure of the liquid mixed salt by a pressure reducing device and inputting it into the gas separation chamber, and detecting the composition and content of the gas in the gas separation chamber by a first component detector;

[0025] S2, the liquid product of the gas separation chamber is input into the solution preparation chamber to be prepared into a salt solution with desalted water, and then the NO in the salt solution is detected by a second component detector. 2 - and NO 3 - concentration.

[0026] Preferably, the liquid mixed salt is a dibasic salt or a ternary salt.

[0027] Preferably, the binary salt is KNO 3 with NaNO 3 mixture.

[0028] Preferably, the ternary salt is KNO 3 、NaNO 3 and NaNO 2 mixture.

[0029] Preferably, in step S1, the product obtained by heat exchange is depressurized to a pressure of 50-500 kPag by the decompression device.

[0030] Preferably, in step S1, the product obtained by heat exchange is cooled by a cooling device while reducing the pressure;

[0031] Among them, the binary salt is cooled to 250-350℃; the ternary salt is cooled to 180-350℃.

[0032] Preferably, in step S1, the pressure of the gas separation chamber is controlled to be 50-500 kPag.

[0033] Preferably, in step S1, the liquid level of the gas separation chamber is controlled to be 40-60%.

[0034] Preferably, in step S2, the mass ratio of the liquid mixed salt input into the solution preparation chamber to the desalted water is 1:99-999.

[0035] Preferably, step S2 further comprises: according to the NO in the salt solution 2 - and NO 3 - The melting point Tm of the mixed salt is calculated based on the concentration of , where the melting point of the binary salt is calculated according to formula (1) and the melting point of the ternary salt is calculated according to formula (2).

[0036] Tm=-252.48(C NO2 - / C NO3 - )+231.58(I)

[0037] Tm=-206.09(C NO2 - / C NO3 - )+228.14(II)

[0038] Among them, C NO2 - NO in the salt solution 2 - The concentration of C is in mmol / L. NO3 - NO in the salt solution 3 - The concentration of C is in mmol / L. NO2 - / C NO3 - is the NO in the salt solution 2 - with NO 3 - molar concentration ratio.

[0039] Compared with the prior art, the present invention has at least the following advantages:

[0040] (1) By online detection of water vapor, NO and NO in the liquid mixed salt after heat exchange 2 The gas composition changes can be monitored in real time to understand the mixed salt operation status, such as NO or NO in the gas. 2 A sharp increase in the content indicates that there are hot spots in the heat exchange equipment, causing high-temperature decomposition of the mixed salt. For example, a sharp increase in the water vapor content in the gas indicates that there are leaks inside the heat exchange equipment.

[0041] (2) By online monitoring of the composition changes in the mixed salt after heat exchange, the oxidation and decomposition of the mixed salt can be understood in real time, and the melting point of the mixed salt can be calculated through the correlation equation. 2 - As the content increases, the decomposition temperature decreases, and the comprehensive performance approaches that of ternary salt, which means that the mixed salt cannot reach the design temperature. 2 - As the content decreases, the melting point of the mixed salt will increase, and the comprehensive performance will approach that of binary salt. The failure of heating may cause pipelines or equipment to be damaged due to the solidification of the mixed salt.

[0042] (3) The system of the present invention uses a set of combined online detection instruments to monitor the changes in gas components and mixed salt composition in real time, and can promptly detect hidden heat exchange equipment leakage, oxidation and decomposition of mixed salt and other problems, providing early warning for the safe operation of the system to avoid serious losses. At the same time, the system fills the technical gap in the safety of salt used for my country's solar thermal power generation and coal-fired power peak and frequency regulation flexibility transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the mixed salt online monitoring system of the present invention.

[0044] Description of Reference Numerals

[0045] 1 heat exchange equipment; 2 gas separation chamber; 3 solution preparation chamber; 4 first component detector; 5 second component detector; 6 pressure reducing device; 7 back pressure valve; 8 mixed salt metering pump; 9 three-way valve; 10 check valve; 11 purge valve; 12 desalted water metering pump. DETAILED DESCRIPTION

[0046] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0047] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0048] The mixed salt online monitoring system provided by the present invention is as follows: Figure 1 As shown, it includes a heat exchange device 1, a gas separation chamber 2, a solution preparation chamber 3, a first component detector 4, and a second component detector 5. A pressure reducing device 6 is provided on the connecting pipe between the heat exchange device 1 and the gas separation chamber 2;

[0049] The liquid mixed salt containing nitrate and / or nitrite enters the heat exchange device 1 to exchange heat with water or water vapor, and then enters the gas separation chamber 2 after being depressurized by the decompression device 6. The composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4;

[0050] The liquid product from the gas separation chamber 2 enters the solution preparation chamber 3 to be prepared into a salt solution, and the NO in the salt solution is detected by the second component detector 5. 2 - and NO 3 - concentration.

[0051] In the present invention, the liquid mixed salt can be a nitrate and / or nitrite commonly used in the art. In one embodiment, the liquid mixed salt is a binary salt or a ternary salt. In a more preferred embodiment, the binary salt is KNO 3 with NaNO 3 A mixture having a melting point of about 220°C, more preferably, KNO 3 with NaNO 3 The mass ratio of is 4:6. In another preferred embodiment, the ternary salt is KNO 3 、NaNO 3 and NaNO 2 A mixture having a melting point of about 140°C, more preferably, KNO 3 、NaNO 3 and NaNO 2 The mass ratio is 53:7:40.

[0052] In the present invention, the heat exchange device 1 can be a common device in the art. Exemplarily, the heat exchange device 1 has a shell side and a tube side. During the heat exchange process, water or water vapor flows through the tube side, and the liquid mixed salt flows through the shell side.

[0053] In the system described in the present invention, the liquid mixed salt is heat exchanged with water or water vapor in the heat exchange device 1. If the liquid mixed salt is heat exchanged with water, the liquid mixed salt can heat the water. If the liquid mixed salt is heat exchanged with water vapor, the water vapor can heat the liquid mixed salt. When the liquid mixed salt is heat exchanged with water or water vapor, abnormal operating conditions may exist. For example, if there is a leak in the heat exchange device 1, water may enter the liquid mixed salt. If there is an overheat point in the heat exchange device 1, the liquid mixed salt will decompose at high temperature, and NO or NO 2 After heat exchange, the liquid mixed salt is depressurized by a decompression device 6, so that the water vapor, NO and NO generated during the abnormal heat exchange process are 2A small amount of gas can be separated from the liquid mixed salt, and then the product containing the liquid mixed salt and a small amount of gas is introduced into the gas separation chamber 2, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If NO or NO 2 A sharp increase in the content indicates that there is an overheat point in the heat exchange equipment, causing the mixed salt to decompose at high temperature. For example, a sharp increase in the water content in the gas indicates that there is a leak in the heat exchange equipment; the product containing liquid mixed salt and a small amount of gas enters the solution preparation chamber 3 from the gas separation chamber 2, and is prepared into a salt solution with desalted water in a specific ratio, and then the NO in the salt solution is detected by the second component detector 5. 2 - and NO 3 - The concentration of NO in the mixed salt 2 - and NO 3 - The concentration changes can be used to understand the composition changes of the mixed salts, and the oxidation and decomposition of the mixed salts can be understood in real time. 2 - and NO 3 - The melting point of the mixed salt can be calculated by a correlation formula related to the concentration of the mixed salt. The comprehensive performance of the mixed salt can then be judged based on the melting point, thereby monitoring the possible hidden dangers of the operating device.

[0054] In one embodiment, Figure 1 As shown, a sampling point is set between the connecting pipeline of the heat exchange device 1 and the pressure reducing device 6 and at the high point of the mixed salt outlet pipeline of the heat exchange device 1, and the sampling point is connected to the pressure reducing device 6 through a pipeline. After the liquid mixed salt is heat exchanged in the heat exchange device 1, if it is necessary to monitor the water vapor, NO and NO in the liquid mixed salt after heat exchange online 2 If the composition of the gas and the composition of the mixed salt are changed, the liquid mixed liquid after heat exchange is passed through the decompression device 6 for subsequent detection operation. If it is not necessary to monitor the water vapor, NO and NO in the liquid mixed salt after heat exchange online, 2 The liquid mixed salt after heat exchange is discharged through the salt outlet according to the changes in gas composition and the changes in the composition of the mixed salt.

[0055] In the present invention, the decompression device 6 can be a conventional choice in the art. In one embodiment, the decompression device 6 is a pressure reducing valve. In a more preferred embodiment, in order to make the water vapor, NO and NO generated during the exchange process 2A small amount of gas can be fully separated from the liquid mixed salt, thereby improving the accuracy of the detection result of the first component detector 4, and the product obtained by heat exchange is reduced in pressure to a pressure of 50-500 kPag through the decompression device 6.

[0056] In a preferred embodiment, the gas separation chamber 2 and the inlet and outlet pipelines of the gas separation chamber 2 are equipped with a cooling device for cooling the liquid mixed salt, thereby solving the problem of diaphragm selection of the mixed salt metering pump 8. In the present invention, the cooling device can be a conventional choice in the field, as long as the purpose of cooling can be achieved. In one embodiment, the cooling medium in the cooling device can be heat transfer oil, that is, heat transfer oil is used to cool the liquid mixed salt after heat exchange. In one embodiment, the cooling device can cool the binary salt to 250-350°C and the ternary salt to 180-350°C.

[0057] In the present invention, the system further comprises a back pressure valve 7, which is connected to the top of the gas separation chamber 2 through a pipeline, and is used to control the pressure and gas atmosphere (i.e., gas composition) of the gas separation chamber 2. In the system described in the present invention, when the mixed salt is a binary salt, dried air is used as the pressure gas, and the air is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure and gas atmosphere therein; when the mixed salt is a ternary salt, nitrogen is used as the pressure gas, and nitrogen is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure and gas atmosphere therein. In a more preferred embodiment, in order to make the water vapor, NO and NO dissolved in the mixed salt 2 When the gas is completely precipitated into the upper space of the gas separation chamber 2, the accuracy and stability of the gas composition and content detection results of the first component detector 4 are improved, and the pressure of the gas separation chamber 2 is controlled to 50-500 kPag.

[0058] In one embodiment, the top outlet pipe of the gas separation chamber 2 is connected to the first component detector 4. The functions of the first component detector 4 include water vapor detection and nitrogen oxide detection. The configuration can be a dew point meter with an ultraviolet visible spectrophotometer or an infrared spectrometer to detect the water vapor content and NO, NO in the gas, respectively. 2 The content of water vapor, NO, and NO can also be measured simultaneously by gas chromatograph (with thermal conductivity detector). 2 The first component detector 4 can monitor the water vapor, NO, NO in the mixed salt in real time. 2 UV-visible spectrophotometer is an analytical instrument based on the principle of UV-visible spectrophotometry, which uses the radiation absorption of the molecules in the UV-visible spectrum to analyze the content. 2Both have absorption in the ultraviolet and visible light bands, so this instrument can be used to measure NO and NO in the gas. 2 The difference between infrared spectroscopy and ultraviolet visible light photometer is that they absorb light in different wavelengths.

[0059] In the system described in the present invention, a mixed salt metering pump 8 is provided on the connecting pipeline between the gas separation chamber 2 and the solution preparation chamber 3, and the mixed salt metering pump 8 is used to control the liquid level of the gas separation chamber 2 and to meter the amount of mixed salt entering the solution preparation chamber 3. The mixed salt metering pump 8 can be a conventional choice in the art. In order to prevent the liquid mixed salt from flowing out immediately after entering the gas separation chamber 2, causing the gas dissolved in the liquid mixed salt to be unable to be fully separated from the liquid mixed salt and fully enter the upper space of the gas separation chamber 2, resulting in the measured water vapor, NO, NO 2 In order to avoid errors in the components and contents of the liquid salt mixture, thus obtaining erroneous results, the liquid level of the gas separation chamber 2 can be controlled within a certain range so that the gas dissolved in the liquid mixed salt is fully separated from the liquid mixed salt. In a preferred embodiment, the liquid level of the gas separation chamber 2 can be controlled to be 40-60%.

[0060] In one embodiment, the system further comprises a three-way valve 9, and the mixed salt metering pump 8, the three-way valve 9 and the solution preparation chamber 3 are sequentially connected through a connecting pipeline. The mixed salt inlet of the mixed salt metering pump 8 is connected to the mixed salt outlet of the gas separation chamber 2 through a pipeline, the mixed salt outlet of the mixed salt metering pump 8 is connected to the inlet of the three-way valve 9, and one of the inlets of the three-way valve 9 is connected to the solution preparation chamber 3. The mixed salt metering pump 8 inputs the liquid mixed salt from the gas separation chamber 2 into the solution preparation chamber 3 and measures the amount entering the solution preparation chamber 3, so as to facilitate the calculation of the concentration in the prepared salt solution.

[0061] In a more specific embodiment, the system further comprises a check valve 10, and the three-way valve 9, the check valve 10 and the mixed salt recovery pipeline are connected in sequence. In this embodiment, the other inlet of the three-way valve 9 is connected to the check valve 10. When it is necessary to collect a liquid mixed salt sample, the three-way valve 9 is connected to the solution preparation chamber 3, the liquid mixed salt enters the solution preparation chamber 3 and is prepared into a salt solution, and the NO in the salt solution is detected by the second component detector 5. 2 - and NO 3 - when the sampling is completed, the three-way valve 9 is connected to the check valve 10, and the liquid mixed salt from the mixed salt metering pump 8 passes through the check valve 10 and then returns to the salt system from the mixed salt recovery pipeline for recovery.

[0062] In the system described in the present invention, the system further includes a purge valve 11, which is connected to the connecting pipeline between the three-way valve 9 and the solution preparation chamber 3 through a pipeline. When sampling is completed and the mixed salt is returned to the salt system for recycling, nitrogen is used to purge the pipeline between the three-way valve 9 and the solution preparation chamber 3 through the purge valve 11 to prevent the liquid mixed salt and gas from remaining and affecting the subsequent inspection results of the salt solution in the solution preparation chamber 3.

[0063] In one embodiment, the system further comprises a desalted water metering pump 12, which is used to input the desalted water into the solution preparation chamber 3 to prepare the salt solution and control the mass of the desalted water input into the solution preparation chamber 3, so as to ensure that the mixed salt maintains a set concentration in the solution formed with the desalted water. In a more preferred embodiment, the mass ratio of the liquid mixed salt input into the solution preparation chamber 3 to the desalted water is 1:99-999.

[0064] In the present invention, the solution preparation chamber 3 is provided with a stirrer, which is turned on and maintained for a period of time when the salt solution is prepared. After the salt solution is prepared, the second component detector 5 is used to detect NO 2 - and NO 3 - The concentration of anions is analyzed, and the melting point of the mixed salt is calculated according to the correlation formula. 2 - and NO 3 - The melting point Tm of the mixed salt is calculated based on the concentration of , where the melting point of the binary salt is calculated according to formula (1) and the melting point of the ternary salt is calculated according to formula (2):

[0065] Tm=-252.48(C NO2 - / C NO3 - )+231.58(I)

[0066] Tm=-206.09(C NO2 - / C NO3 - )+228.14(II)

[0067] Among them, C NO2 - NO in the salt solution 2 - The concentration of C is in mmol / L. NO3 - NO in the salt solution 3 - The concentration of C is in mmol / L.NO2 - / C NO3 - is the NO in the salt solution 2 - with NO 3 - molar concentration ratio.

[0068] In one embodiment, a pipeline is drawn out from the bottom of the solution preparation chamber 3 and connected to the second component detector 5. The second component detector 5 can be a liquid chromatograph equipped with an ultraviolet detector. 2 - and NO 3 - The process of anion concentration is as follows: first, the solution is passed through a high-efficiency separation column to separate NO 2 - and NO 3 - The anions are separated and the contents of the two components are measured by a UV detector. This method reduces the interference between different components and has a higher accuracy than spectral measurement.

[0069] In a more specific embodiment, Figure 1 As shown, the system includes a heat exchange device 1, a sampling point is set at the high point of the mixed salt outlet pipeline of the heat exchange device 1, the sampling point is connected to the pressure reducing device 6 through a pipeline, the pressure reducing device 6 is connected to the gas separation chamber 2 through a pipeline, the gas separation chamber 2 and the inlet and outlet pipelines are equipped with a cooling device for cooling the liquid mixed salt, the back pressure valve 7 is connected to the top of the gas separation chamber 2 through a pipeline, the top outlet pipeline of the gas separation chamber 2 is connected to the first component detector 4, the bottom outlet pipeline of the gas separation chamber 2 is connected to the mixed salt metering pump 8, and the mixed salt metering pump 8 It is connected to the three-way valve 9 through a pipeline, one of the outlets of the three-way valve 9 is connected to the solution preparation chamber 3 through a pipeline, the purge valve 11 is connected to the connecting pipeline of the three-way valve 9 and the solution preparation chamber 3 through a pipeline, one end of the check valve 10 is connected to the other outlet of the three-way valve 9, and the other end of the check valve 10 is connected to the mixed salt recovery pipeline through a pipeline, the desalted water metering pump 12 is connected to the solution preparation chamber 3 through a pipeline, an agitator is provided inside the solution preparation chamber 3, an exhaust pipeline is provided on the upper part to communicate with the atmosphere, and the lead-out pipeline at the bottom of the solution preparation chamber 3 is connected to the second component detector 5.

[0070] In the above-mentioned more specific embodiment, the operating process of the system of the present invention is: the liquid mixed salt is heat exchanged with water or water vapor in the heat exchange device 1. If the liquid mixed salt is heat exchanged with water, the liquid mixed salt can heat the water. If the liquid mixed salt is heat exchanged with water vapor, the water vapor can heat the liquid mixed salt. When the liquid mixed salt is heat exchanged with water or water vapor, there is a possibility of abnormal operating conditions. If there is a leak in the heat exchange device 1, water may enter the liquid mixed salt. If there is an overheat point in the heat exchange device 1, the liquid mixed salt will decompose at high temperature, and NO or NO 2 The content of NO or NO is increased; then the heat exchanged mixture containing hot mixed salt and a small amount of water vapor, NO or NO 2 The product is input from the sampling point into the pressure reducing device 6 for pressure reduction, so that the water vapor, NO and NO generated in the abnormal working condition exchange process are 2 A small amount of gas can be separated from the liquid mixed salt, and the cooling device cools the liquid mixed salt at the same time; then the product containing the liquid mixed salt and a small amount of gas is introduced into the gas separation chamber 2, and the gas is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure and gas atmosphere of the gas separation chamber 2, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If NO or NO 2 A substantial increase in the content indicates that there are hot spots in the heat exchange equipment, causing the mixed salt to decompose at high temperature. For example, a substantial increase in the water vapor content in the gas indicates that there is a leak in the heat exchange equipment. Then, the liquid mixed salt is introduced into the solution preparation chamber 3 through the three-way valve 9 by the mixed salt metering pump 8. At the same time, the liquid level of the gas separation chamber 2 and the amount of mixed salt entering the solution preparation chamber 3 are controlled by the mixed salt metering pump 8. Desalted water is introduced into the solution preparation chamber 3 by the desalted water metering pump 12 and the quality of the desalted water entering the solution preparation chamber 3 is controlled. The mixed salt and the desalted water are prepared into a salt solution in the solution preparation chamber 3 according to a specific ratio. The agitator is turned on when preparing the salt solution. After the salt solution is prepared, the second component detector 5 is used to detect NO in the salt solution. 2 - and NO 3 - The concentration of NO in the mixed salt 2 - and NO 3 - The concentration changes can be used to understand the composition changes of the mixed salts, and the oxidation and decomposition of the mixed salts can be understood in real time. 2 - and NO 3 - The melting point of mixed salts is calculated using a concentration-dependent correlation.

[0071] The mixed salt online monitoring method provided by the present invention is implemented in the system described above, and the method comprises the following steps:

[0072] S1, passing a liquid mixed salt containing nitrate and / or nitrite and water or water vapor into the heat exchange device 1 for heat exchange, then reducing the pressure of the liquid mixed salt by a decompression device 6 and inputting it into the gas separation chamber 2, and using a first component detector 4 to detect the composition and content of the gas in the gas separation chamber 2;

[0073] S2, the liquid product of the gas separation chamber 2 is input into the solution preparation chamber 3 to prepare a salt solution with desalted water, and then the second component detector 5 is used to detect NO in the salt solution. 2 - and NO 3 - concentration.

[0074] In the method described in the present invention, the liquid mixed salt exchanges heat with water or water vapor in the heat exchange device 1. If the liquid mixed salt exchanges heat with water, the liquid mixed salt can heat the water. If the liquid mixed salt exchanges heat with water vapor, the water vapor can heat the liquid mixed salt. When the liquid mixed salt exchanges heat with water or water vapor, abnormal operating conditions may exist. For example, if there is a leak in the heat exchange device 1, water may enter the liquid mixed salt. If there is an overheat point in the heat exchange device 1, the liquid mixed salt will decompose at high temperature, and NO or NO 2 The liquid mixed salt after heat exchange is depressurized in the decompression device 6, so that the water vapor, NO and NO generated in the exchange process under abnormal conditions are 2 A small amount of gas can be separated from the liquid mixed salt, and then the product containing the liquid mixed salt and a small amount of gas enters the gas separation chamber 2. The first component detector 4 is used to detect the composition and content of the gas in the gas separation chamber 2. If NO or NO 2 A sharp increase in the content indicates that there is an overheat point in the heat exchange equipment, causing the mixed salt to decompose at high temperature. For example, a sharp increase in the water content in the gas indicates that there is a leak in the heat exchange equipment; then the product containing the liquid mixed salt and a small amount of gas is passed from the gas separation chamber 2 to the solution preparation chamber 3 to be prepared into a salt solution with desalted water in a specific ratio, and the NO in the salt solution is detected by the second component detector 5. 2 - and NO 3 - The concentration of NO in the mixed salt 2 - and NO 3 - The concentration changes can be used to understand the composition changes of the mixed salts, and the oxidation and decomposition of the mixed salts can be understood in real time. 2- and NO 3 - The melting point of the mixed salt can be calculated by a correlation formula related to the concentration of the mixed salt. The comprehensive performance of the mixed salt can then be judged based on the melting point, thereby monitoring the possible hidden dangers of the operating device.

[0075] In the method of the present invention, the liquid mixed salt can be a nitrate and / or nitrite commonly used in the art. In one embodiment, the liquid mixed salt is a binary salt or a ternary salt. In a more preferred embodiment, the binary salt is KNO 3 with NaNO 3 A mixture having a melting point of about 220°C, more preferably, KNO 3 with NaNO 3 The mass ratio of is 4:6. In another preferred embodiment, the ternary salt is KNO 3 、NaNO 3 and NaNO 2 A mixture having a melting point of about 140°C, more preferably, KNO 3 、NaNO 3 and NaNO 2 The mass ratio is 53:7:40.

[0076] In a preferred embodiment, in order to make the water vapor, NO and NO generated during the exchange process 2 A small amount of gas can be fully separated from the liquid mixed salt, thereby improving the accuracy of the detection result of the first component detector 4. In step S1, the product obtained by heat exchange is depressurized to a pressure of 50-500 kPag through the decompression device 6.

[0077] In step S1 of the present invention, the liquid mixed salt is cooled in the gas separation chamber 2 and its inlet and outlet pipes by a cooling device. In the method described in the present invention, the cooling device can be a conventional choice in the art, as long as the purpose of cooling can be achieved. In one embodiment, the cooling medium in the cooling device can be heat transfer oil, that is, the heat transfer oil is used to cool the product after heat exchange. In one embodiment, the binary salt can be cooled to 250-350°C and the ternary salt can be cooled to 180-350°C by a cooling device.

[0078] In the present invention, the pressure and gas atmosphere of the gas separation chamber 2 can be controlled by passing gas into the gas separation chamber 2. In the method of the present invention, when the mixed salt is a binary salt, air is used as the pressure gas, and air is passed into the gas separation chamber 2 to control its pressure and gas atmosphere; when the mixed salt is a ternary salt, nitrogen is used as the pressure gas, and nitrogen is passed into the gas separation chamber 2 to control its pressure and gas atmosphere. In a more preferred embodiment, in order to make the water vapor, NO and NO dissolved in the mixed salt 2 When the gas is completely precipitated into the upper space of the gas separation chamber 2, the accuracy and stability of the gas composition and content detection results of the first component detector 4 are improved, and the pressure of the gas separation chamber 2 is controlled to 50-500 kPag.

[0079] In order to prevent the liquid mixed salt from flowing out immediately after entering the gas separation chamber 2, the gas dissolved in the liquid mixed salt cannot be fully separated from the liquid mixed salt and fully enters the upper space of the gas separation chamber 2, resulting in the measured water vapor, NO, NO 2 In order to avoid errors in the components and contents of the liquid salt mixture, thereby obtaining erroneous results, the liquid level of the gas separation chamber 2 can be controlled within a certain range so that the gas dissolved in the liquid mixed salt has enough time to be fully separated from the liquid mixed salt. In a more preferred embodiment, the liquid level of the gas separation chamber 2 can be controlled to be 40-60%.

[0080] In a more preferred embodiment, the mass ratio of the liquid mixed salt input into the solution preparation chamber 3 in step S2 to the desalted water is 1:99-999.

[0081] In the present invention, step S2 further comprises: according to the NO in the salt solution 2 - and NO 3 - The melting point Tm of the mixed salt is calculated based on the concentration of , where the melting point of the binary salt is calculated according to formula (1) and the melting point of the ternary salt is calculated according to formula (2).

[0082] Tm=-252.48(C NO2 - / C NO3 - )+231.58(I)

[0083] Tm=-206.09(C NO2 - / C NO3 - )+228.14(II)

[0084] Among them, C NO2 -is the NO in the salt solution 2 - The concentration of C is in mmol / L. NO3 - is the NO in the salt solution 3 - The concentration of C is in mmol / L. NO2 - / C NO3 - is the NO in the salt solution 2 - with NO 3 - molar concentration ratio.

[0085] The mixed salt online monitoring system and method of the present invention are further described below by way of examples. The examples are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0086] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0087] The following examples are implemented in a mixed salt online monitoring system, such as Figure 1 As shown, the mixed salt online monitoring system includes a heat exchange device 1, a sampling point is set at the high point of the mixed salt outlet pipeline of the heat exchange device 1, the sampling point is connected to the pressure reducing device 6 (pressure reducing valve) through a pipeline, the pressure reducing device 6 is connected to the gas separation chamber 2 through a pipeline, the gas separation chamber 2 and the inlet and outlet pipelines of the gas separation chamber 2 are equipped with a cooling device for cooling the liquid mixed salt, the back pressure valve 7 is connected to the top of the gas separation chamber 2 through a pipeline, the outlet pipeline at the top of the gas separation chamber 2 is connected to the first component detector 4, and the outlet pipeline at the bottom of the gas separation chamber 2 is connected to the mixed salt metering pump 8. A mixed salt metering pump 8 is connected to a three-way valve 9 through a pipeline, one of the outlets of the three-way valve 9 is connected to a solution preparation chamber 3 through a pipeline, a purge valve 11 is connected to a connecting pipeline between the three-way valve 9 and the solution preparation chamber 3 through a pipeline, one end of a check valve 10 is connected to another outlet of the three-way valve 9, the other end of the check valve 10 is connected to a mixed salt recovery pipeline through a pipeline, a desalted water metering pump 12 is connected to the solution preparation chamber 3 through a pipeline, an agitator is provided inside the solution preparation chamber 3, an exhaust pipeline is provided on the upper part to communicate with the atmosphere, and a lead-out pipeline at the bottom of the solution preparation chamber 3 is connected to a second component detector 5.

[0088] The mixed salt melting point experimental test method involved in the embodiment is carried out according to the method described in Article 5.14 of GB / T 36376-2018 Solar Molten Salt (Nitro Type) National Standard.

[0089] Example 1

[0090] In this embodiment, the liquid mixed salt is a binary salt with a composition of KNO 3 with NaNO 3 A mixture of KNO 3 with NaNO 3 The mass ratio of the liquid mixed salt is 4:6, and the liquid mixed salt exchanges heat with water in the heat exchange device 1.

[0091] Mixed salt online monitoring methods include:

[0092] (1) The liquid mixed salt is heat exchanged with water in the heat exchange device 1, and then the product after the heat exchange is input from the sampling point into the pressure reducing device 6 to reduce the pressure to 500kPag, and at the same time, the cooling device cools the liquid mixed salt to 250°C; then the product is introduced into the gas separation chamber 2, and at the same time, dry air is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure of the gas separation chamber 2 to 500kPag, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If water vapor is detected in the gas, or the water vapor content increases significantly, it indicates that there is a leak in the heat exchange equipment; if NO or NO is detected at the same time, 2 The increase in content indicates that the liquid mixed salt will decompose at high temperature and the heat exchange equipment 1 has a hot spot;

[0093] (2) Then, the liquid mixed salt is introduced into the solution preparation chamber 3 through the three-way valve 9 by the mixed salt metering pump 8, and the liquid level of the gas separation chamber 2 is controlled to be 60% by the mixed salt metering pump 8, and the amount of the mixed salt entering the solution preparation chamber 3 is metered. The desalted water metering pump 12 is used to introduce desalted water into the solution preparation chamber 3 and the mass of the desalted water entering the solution preparation chamber 3 is controlled. The mixed salt and the desalted water are prepared into a salt solution in the solution preparation chamber 3 at a mass ratio of 1:99. The stirrer is turned on when preparing the salt solution. After the salt solution is prepared, the second component detector 5 is used to detect NO in the salt solution. 2 - and NO 3 - The molar concentration ratio of NO in the mixed salt is 0.0746:1. 2 - and NO 3 - The concentration of NO 2 - and NO 3 -The melting point of the mixed salt is calculated to be 212.7°C using the concentration-related correlation formula (Formula (1)). The experimental melting point value is 213.5°C. It can be seen that the deviation between the calculated melting point value and the measured value is small.

[0094] Example 2

[0095] In this embodiment, the liquid mixed salt is a binary salt with a composition of KNO 3 with NaNO 3 A mixture of KNO 3 with NaNO 3 The mass ratio of the liquid mixed salt is 4:6, and the liquid mixed salt exchanges heat with water vapor in the heat exchange device 1.

[0096] Mixed salt online monitoring methods include:

[0097] (1) The liquid mixed salt is heat exchanged with water vapor in the heat exchange device 1, and then the product after the heat exchange is input from the sampling point into the pressure reducing device 6 to reduce the pressure to 300 kPag, and at the same time, the cooling device cools the liquid mixed salt to 350°C; then the product is introduced into the gas separation chamber 2, and at the same time, dry air is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure of the gas separation chamber 2 to 300 kPag, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If water vapor is detected in the gas, or the water vapor content increases significantly, it indicates that there is a leak in the heat exchange equipment; if NO or NO is detected at the same time, 2 The increase in content indicates that the liquid mixed salt will decompose at high temperature and the heat exchange equipment 1 has a hot spot;

[0098] (2) Then, the liquid mixed salt is introduced into the solution preparation chamber 3 through the three-way valve 9 by the mixed salt metering pump 8, and the liquid level of the gas separation chamber 2 is controlled to be 50% by the mixed salt metering pump 8, and the amount of the mixed salt entering the solution preparation chamber 3 is metered. The desalted water metering pump 12 is used to introduce desalted water into the solution preparation chamber 3 and the mass of the desalted water entering the solution preparation chamber 3 is controlled. The mixed salt and the desalted water are prepared into a salt solution in the solution preparation chamber 3 at a mass ratio of 1:500. When the salt solution is prepared, the stirrer is turned on. After the salt solution is prepared, the second component detector 5 is used to detect NO in the salt solution. 2 - and NO 3 - The molar concentration ratio of NO in the mixed salt is 0.0925. 2 - and NO 3 - The concentration of NO 2- and NO 3 - The melting point of the mixed salt is calculated to be 208.2°C using the concentration-related correlation formula (Formula (1)). The experimental melting point value is 209.4°C. It can be seen that the deviation between the calculated melting point value and the measured value is small.

[0099] Example 3

[0100] In this embodiment, the liquid mixed salt is a ternary salt, and the composition is KNO 3 、NaNO 3 and NaNO 2 A mixture of KNO 3 、NaNO 3 and NaNO 2 The mass ratio of the liquid mixed salt is 53:7:40, and the liquid mixed salt exchanges heat with water in the heat exchange device 1.

[0101] Mixed salt online monitoring methods include:

[0102] (1) The liquid mixed salt is heat exchanged with water in the heat exchange device 1, and then the product after the heat exchange is input from the sampling point into the pressure reducing device 6 to reduce the pressure to 100 kPag, and at the same time, the cooling device cools the liquid mixed salt to 180°C; then the product is introduced into the gas separation chamber 2, and at the same time, air is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure of the gas separation chamber 2 to 100 kPag, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If water vapor is detected in the gas, or the water vapor content increases significantly, it indicates that there is a leak in the heat exchange equipment; if NO or NO is detected at the same time, 2 The increase in content indicates that the liquid mixed salt will decompose at high temperature and the heat exchange equipment 1 has a hot spot;

[0103] (2) Then, the liquid mixed salt is introduced into the solution preparation chamber 3 through the three-way valve 9 by the mixed salt metering pump 8, and the liquid level of the gas separation chamber 2 is controlled to be 40% by the mixed salt metering pump 8, and the amount of the mixed salt entering the solution preparation chamber 3 is metered. The desalted water metering pump 12 is used to introduce desalted water into the solution preparation chamber 3 and the mass of the desalted water entering the solution preparation chamber 3 is controlled. The mixed salt and the desalted water are prepared into a salt solution in the solution preparation chamber 3 at a mass ratio of 1:799. The stirrer is turned on when preparing the salt solution. After the salt solution is prepared, the second component detector 5 is used to detect NO in the salt solution. 2 - and NO 3 - The molar concentration ratio of NO in the mixed salt is 0.3515:1. 2 -and NO 3 - The concentration of NO 2 - and NO 3 - The melting point of the mixed salt is calculated to be 155.7°C using the concentration-related correlation formula (Formula (2)), and the experimental melting point test value is 154.1°C. It can be seen that the deviation between the calculated melting point value and the measured value is small.

[0104] Example 4

[0105] In this embodiment, the liquid mixed salt is a ternary salt, and the composition is KNO 3 、NaNO 3 and NaNO 2 A mixture of KNO 3 、NaNO 3 and NaNO 2 The mass ratio of the liquid mixed salt is 53:7:40, and the liquid mixed salt exchanges heat with water vapor in the heat exchange device 1.

[0106] Mixed salt online monitoring methods include:

[0107] (1) The liquid mixed salt is heat exchanged with water vapor in the heat exchange device 1, and then the product after the heat exchange is input from the sampling point into the pressure reducing device 6 to reduce the pressure to 50 kPag, and at the same time, the cooling device cools the liquid mixed salt to 350°C; then the product is introduced into the gas separation chamber 2, and at the same time, air is introduced into the gas separation chamber 2 through the back pressure valve 7 to control the pressure of the gas separation chamber 2 to 50 kPag, and the composition and content of the gas in the gas separation chamber 2 are detected by the first component detector 4. If water vapor is detected in the gas, or the water vapor content increases significantly, it indicates that there is a leak in the heat exchange equipment; at the same time, NO or NO 2 The increase in content indicates that the liquid mixed salt will decompose at high temperature and the heat exchange equipment 1 has a hot spot;

[0108] (2) Then, the liquid mixed salt is introduced into the solution preparation chamber 3 through the three-way valve 9 by the mixed salt metering pump 8, and the liquid level of the gas separation chamber 2 is controlled to be 50% by the mixed salt metering pump 8, and the amount of the mixed salt entering the solution preparation chamber 3 is metered. The desalted water metering pump 12 is used to introduce desalted water into the solution preparation chamber 3 and the mass of the desalted water entering the solution preparation chamber 3 is controlled. The mixed salt and the desalted water are prepared into a salt solution in the solution preparation chamber 3 at a mass ratio of 1:999. The stirrer is turned on when preparing the salt solution. After the salt solution is prepared, the second component detector 5 is used to detect NO in the salt solution. 2 - and NO3 - The molar concentration ratio of NO in the mixed salt is 0.3248:1. 2 - and NO 3 - The concentration of NO 2 - and NO 3 - The melting point of the mixed salt is calculated to be 161.2°C using the concentration-related correlation formula (Formula (2)). The experimental melting point value is 161.8°C. It can be seen that the deviation between the calculated melting point value and the measured value is small.

[0109] Comparative Example 1

[0110] The existing method takes the liquid mixed salt out of the storage tank and naturally condenses it into a solid mixed salt. The water content of the solid mixed salt is titrated by the Karl Fischer method in the laboratory, and the melting point of the mixed salt is detected by DCS (differential scanning calorimetry). Due to the change in the state of the mixed salt and the change in the ambient atmosphere, it is impossible to accurately determine the water content and melting point information in the mixed salt, and the test results cannot truly reflect the performance and state of the mixed salt in operation. And according to the experimental equipment of different power plants (thermal power plants or solar thermal power plants), the time from sampling to obtaining results ranges from several hours to several days, which is obviously lagging for industrial operation devices. In emergency situations such as high-temperature decomposition of mixed salts or leakage of heat exchange equipment, it often fails to play a warning role and causes huge losses.

[0111] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A mixed salt online monitoring system, characterized in that: The system comprises a heat exchange device (1), a gas separation chamber (2), a solution preparation chamber (3), a first component detector (4), and a second component detector (5); a pressure reducing device (6) is provided on the connecting pipe between the heat exchange device (1) and the gas separation chamber (2); The liquid mixed salt containing nitrate and / or nitrite enters the heat exchange device (1) to exchange heat with water or water vapor, and then enters the gas separation chamber (2) after being depressurized by the decompression device (6). The composition and content of the gas in the gas separation chamber (2) are detected by the first component detector (4); The liquid product from the gas separation chamber (2) enters the solution preparation chamber (3) to be prepared into a salt solution, and the NO2 in the salt solution is detected by the second component detector (5). - and NO3 - concentration.

2. The system according to claim 1, characterized in that The system also includes a back pressure valve (7), which is connected to the top of the gas separation chamber (2) through a pipeline and is used to control the pressure and gas atmosphere of the gas separation chamber (2).

3. The system according to claim 1 or 2, characterized in that: A mixed salt metering pump (8) is provided on the connecting pipeline between the gas separation chamber (2) and the solution preparation chamber (3), and the mixed salt metering pump (8) is used to control the liquid level of the gas separation chamber (2) and to meter the amount of mixed salt entering the solution preparation chamber (3).

4. The system according to any one of claims 1 to 3, characterized in that: The system further comprises a three-way valve (9), wherein the mixed salt metering pump (8), the three-way valve (9) and the solution preparation chamber (3) are sequentially connected via a connecting pipeline; Preferably, the system further comprises a check valve (10), and the three-way valve (9), the check valve (10) and the mixed salt recovery pipeline are connected in sequence; Preferably, the system further comprises a purge valve (11), wherein the purge valve (11) is connected to a connecting pipeline between the three-way valve (9) and the solution preparation chamber (3) via a pipeline.

5. The system according to any one of claims 1 to 4, characterized in that: The system also includes a desalted water metering pump (12) for inputting desalted water into the solution preparation chamber (3) to prepare a salt solution and controlling the quality of the desalted water entering the solution preparation chamber (3).

6. The system according to any one of claims 1 to 5, characterized in that: The gas separation chamber (2) and the inlet and outlet pipelines are provided with a cooling device for cooling the liquid mixed salt.

7. A mixed salt online monitoring method, the method being implemented in the system according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1, introducing a liquid mixed salt containing nitrate and / or nitrite and water or water vapor into the heat exchange device (1) for heat exchange, then reducing the pressure of the liquid mixed salt by a pressure reducing device (6) and then introducing it into the gas separation chamber (2), and detecting the composition and content of the gas in the gas separation chamber (2) by a first component detector (4); S2, the liquid product of the gas separation chamber (2) is input into the solution preparation chamber (3) to prepare a salt solution with desalted water, and then the NO2 in the salt solution is detected by a second component detector (5). - and NO3 - concentration.

8. The method according to claim 7, characterized in that The liquid mixed salt is a binary salt or a ternary salt; Preferably, the binary salt is a mixture of KNO3 and NaNO3; Preferably, the ternary salt is a mixture of KNO3, NaNO3 and NaNO2.

9. The method according to claim 7 or 8, characterized in that: In step S1, the product obtained by heat exchange is depressurized to a pressure of 50-500 kPag through the decompression device (6).

10. The method according to claim 8 or 9, characterized in that: In step S1, the product obtained by heat exchange is cooled by a cooling device while reducing the pressure; Among them, the binary salt is cooled to 250-350℃; the ternary salt is cooled to 180-350℃.

11. The method according to any one of claims 7 to 10, characterized in that: In step S1, the pressure of the gas separation chamber (2) is controlled to be 50-500 kPag.

12. The method according to any one of claims 7 to 11, characterized in that: In step S1, the liquid level of the gas separation chamber (2) is controlled to be 40-60%.

13. The method according to any one of claims 7 to 12, characterized in that: In step S2, the mass ratio of the liquid mixed salt input into the solution preparation chamber (3) to the desalted water is 1:99-999.

14. The method according to any one of claims 7 to 13, characterized in that: Step S2 also includes: according to the NO2 in the salt solution - and NO3 - The melting point Tm of the mixed salt is calculated based on the concentration of , wherein the melting point of the binary salt is calculated according to formula (I), and the melting point of the ternary salt is calculated according to formula (II), Tm=-252.48(C NO2 - / C NO3 - )+231.58(I) Tm=-206.09(C NO2 - / C NO3 - )+228.14(II) Among them, C NO2 - is the NO2 in the salt solution - The concentration of C is in mmol / L. NO3 - NO3 in the salt solution - The concentration of C is in mmol / L. NO2 - / C NO3 - is the NO2 in the salt solution - With NO3 - molar concentration ratio.

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