An efficient operation method and system for a thermal cycling system

Abstract

This application relates to the technical field of energy-saving transformation of industrial furnaces, and specifically relates to an efficient operation method and system for a cold and hot circulation system. The method includes: analyzing the difference between the wall temperature data and the saturation temperature of the liquid inside the heat exchanger tube to determine the wall superheat; combining the heat flux density at the current moment, the size of the heat exchanger tube, and the heat absorbed when the liquid inside the heat exchanger tube evaporates to determine the boiling intensity index; based on the difference in heat flux density and wall superheat between the current moment and the previous adjacent acquisition moment, as well as the preset surface tension, determine the boiling stability coefficient, and combine the boiling intensity index, and the difference between the flue gas temperature and the preset flue gas acid dew point temperature to adjust the liquid flow rate inside the heat exchanger tube in the cold and hot circulation system. The purpose of this application is to optimize the efficient operation of the cold and hot circulation system, improve the energy utilization efficiency of industrial furnaces, and reduce energy waste.

Description

Technical Field

[0001] This application relates to the technical field of energy-saving transformation of industrial furnaces, and particularly relates to an efficient operation method and system for a cold and hot circulation system. Background Art

[0002] In industrial production, industrial furnaces are key equipment in many industrial processes. For example, in industries such as steel, chemical, and glass, they are used for processes such as heating, melting, and heat treatment of materials. However, industrial furnaces are large energy consumers. During the operation of industrial furnaces, the high-temperature flue gas generated by fuel combustion carries a large amount of heat. If directly discharged into the atmosphere, it will not only cause huge waste of energy but also produce thermal pollution to the environment. In order to carry out energy-saving transformation of industrial furnaces and recover the waste heat in the flue gas discharged from industrial furnaces, heat exchangers can be used to transfer the waste heat to other materials that need heat, thereby improving the energy utilization efficiency.

[0003] A heat exchanger is a device used to transfer heat between two or more fluids. Its main function is to transfer heat from a higher-temperature fluid to a lower-temperature fluid, thereby achieving the purpose of recovering waste heat and improving the energy utilization efficiency. As a part of the cold and hot circulation system, the heat transfer performance of the heat exchanger is crucial for the efficient operation of the system. Traditional cold and hot circulation systems usually set the adjustment time and range of the flow rate according to empirical values, which easily causes changes in the boiling state inside the pipe, resulting in a decrease in the heat transfer coefficient, and even causing the exhaust gas temperature not to be within the appropriate range, leading to a decrease in the recovery efficiency of the waste heat generated by the industrial furnace by the cold and hot circulation system and causing energy waste during the operation of the industrial furnace. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide an efficient operation method and system for a cold and hot circulation system, and the specific technical solutions adopted are as follows:

[0005] In the first aspect, an embodiment of this application provides an efficient operation method for a cold and hot circulation system. The efficient operation method for the cold and hot circulation system is implemented through an efficient operation system for the cold and hot circulation system. The efficient operation system for the cold and hot circulation system includes an industrial furnace and a cold and hot circulation system. The heat exchanger in the cold and hot circulation system is connected to the industrial furnace and receives the high-temperature waste gas generated by the industrial furnace. The heat of the high-temperature waste gas is transferred to the low-temperature liquid inside the heat exchanger through the wall surface of the heat exchanger, heating the low-temperature liquid, and the heated liquid is used again for industrial furnace production. The efficient operation method for the cold and hot circulation system includes the following steps:

[0006] Obtain the heat flux density between the wall surface of the heat exchanger tube and the liquid inside the tube, the temperature data of the wall surface of the heat exchanger, and the exhaust gas temperature at the outlet at each acquisition moment before and including the current moment, as well as the liquid flow rate inside the heat exchanger tube at the current moment;

[0007] Analyze the difference between the temperature data at the current moment and the saturation temperature of the liquid inside the heat exchanger tube to determine the wall superheat of the heat exchanger at the current moment;

[0008] Based on the heat flux density at the current moment, as well as the size of the heat exchanger tube and the wall superheat, determine the superheat index of the heat exchanger at the current moment, and combine with the heat absorbed when the liquid inside the heat exchanger tube evaporates to determine the boiling intensity index of the liquid inside the heat exchanger tube at the current moment;

[0009] Based on the difference in heat flux density between the current moment and the previous adjacent acquisition moment and the wall superheat, determine the heat flux difference value of the liquid inside the heat exchanger tube at the current moment, and combine with the preset surface tension to determine the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment;

[0010] Based on the boiling stability coefficient and the boiling intensity index, as well as the difference between the flue gas discharge temperature of the heat exchanger and the preset flue gas acid dew point temperature at the current moment, determine the flow adjustment factor of the liquid inside the heat exchanger tube at the current moment, and adjust the liquid flow inside the heat exchanger tube in the cold and hot circulation system at the current moment.

[0011] Preferably, the wall superheat of the heat exchanger at the current moment: ΔT sat = norm(T w - T sat ); In the formula, ΔT sat represents the wall superheat of the heat exchanger at the current moment; T w represents the temperature data of the heat exchanger tube wall at the current moment; T sat represents the saturation temperature of the liquid inside the heat exchanger tube under standard atmospheric pressure at the current moment; norm() represents the normalization function.

[0012] Preferably, the method for determining the superheat index of the heat exchanger at the current moment is:

[0013] Calculate the product of the lateral area of the heat exchanger tube and the wall superheat of the heat exchanger at the current moment, and use the ratio of the heat flux density of the heat exchanger at the current moment to the product as the superheat index of the heat exchanger at the current moment.

[0014] Preferably, the expression of the boiling intensity index of the liquid inside the heat exchanger tube at the current moment is: In the formula, B represents the boiling intensity index of the liquid inside the heat exchanger tube at the current moment; C represents the superheat index of the heat exchanger at the current moment; ρ v , h fg respectively represent the saturated vapor density and the latent heat of vaporization when the liquid inside the heat exchanger tube evaporates under standard atmospheric pressure.

[0015] Preferably, the method for determining the heat flux difference value of the liquid inside the heat exchanger tube at the current moment is:

[0016] Calculate the change rate of the heat flux density between the current moment and the immediately preceding acquisition moment, and take the product of the change rate and the superheat of the wall surface at the current moment as the heat flux difference value of the liquid in the heat exchanger tube at the current moment.

[0017] Preferably, the expression for the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment is: In the formula, W represents the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment; σ represents the preset surface tension; P represents the heat flux difference value of the liquid in the heat exchanger tube at the current moment; ε represents a preset constant greater than 0.

[0018] Preferably, the expression for the flow rate adjustment factor of the liquid in the heat exchanger tube at the current moment is: In the formula, μ represents the flow rate adjustment factor of the liquid in the heat exchanger tube at the current moment; B represents the boiling intensity index of the liquid in the heat exchanger tube at the current moment; W represents the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment; T represents the flue gas exhaust temperature at the current moment; T0 represents the preset flue gas acid dew point temperature; norm() represents the normalization function.

[0019] Preferably, the adjustment of the liquid flow rate in the heat exchanger tube in the cold and hot cycle system at the current moment includes:

[0020] According to the method for obtaining the flow rate adjustment factor of the liquid in the heat exchanger tube at the current moment, before the current moment, obtain the flow rate adjustment factors of the liquid in the heat exchanger tube at all acquisition moments within the neighborhood of the current moment;

[0021] If the flow rate adjustment factors of the liquid in the heat exchanger tube at all acquisition moments within the neighborhood are all greater than the preset value, then adjust the liquid flow rate in the heat exchanger tube in the cold and hot cycle system at the current moment; otherwise, do not adjust the liquid flow rate in the heat exchanger tube in the cold and hot cycle system at the current moment.

[0022] Preferably, the step of, if the flow rate adjustment factors of the liquid in the heat exchanger tube at all acquisition moments within the neighborhood are all greater than the preset value, then adjust the liquid flow rate in the heat exchanger tube in the cold and hot cycle system at the current moment, further includes:

[0023] Among all the acquisition moments within the neighborhood of the current moment, if the temperature data of the heat exchanger tube wall surface at the acquisition moment farthest from the current moment is greater than or equal to the temperature data of the heat exchanger tube wall surface at the current moment, then increase the liquid flow rate by a preset proportion in the heat exchanger at the current moment; otherwise, decrease the liquid flow rate by a preset proportion.

[0024] Second aspect, an efficient operation system of a cold and hot cycle system is further provided in an embodiment of the present application, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the efficient operation method of the cold and hot cycle system described in any one of the above are implemented.

[0025] The present application has at least the following beneficial effects:

[0026] By analyzing the difference between the temperature of the liquid inside the heat exchanger tube and the wall surface temperature, the wall superheat degree is constructed in the present application, which can more accurately judge whether the liquid inside the tube is in the nucleate boiling stage. By maintaining a higher wall superheat degree, the heat transfer efficiency can be improved, thereby improving the energy utilization efficiency of the industrial furnace; secondly, by analyzing the heat absorbed when the liquid inside the tube evaporates, and combining the size of the heat exchanger tube, the wall superheat degree and the heat flux density, a boiling intensity index is constructed, which can evaluate whether the boiling intensity of the liquid inside the tube is ideal, so as to determine whether it is necessary to adjust the liquid flow rate, further improving the energy utilization efficiency of the industrial furnace; further, by analyzing the difference in heat flux density between adjacent moments, and combining the wall superheat degree and the surface tension of the liquid, a boiling stability coefficient is constructed, which reflects whether the boiling state of the liquid inside the tube is stable, thus avoiding the decrease in heat transfer efficiency and equipment damage caused by the unstable boiling state, and further improving the energy-saving effect of the industrial furnace; further, by comprehensively considering the boiling stability coefficient and the boiling intensity index, as well as the difference between the flue gas temperature and the acid dew point temperature of the flue gas, a flow rate adjustment factor is constructed to determine whether it is necessary to adjust the flow rate to maintain an ideal boiling state and heat transfer efficiency, improving the energy-saving effect of the industrial furnace. By optimizing the efficient operation of the cold and hot cycle system, the present application improves the energy utilization efficiency of the industrial furnace and reduces energy waste. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a flowchart of the steps of an efficient operation method of a cold and hot cycle system provided by an embodiment of the present application;

[0029] Figure 2 It is a schematic diagram of the process of obtaining the flow rate adjustment factor provided by an embodiment of the present application. Detailed Embodiments

[0030] To further elaborate on the technical means and effects adopted by this application to achieve the intended invention purpose, the following will, in conjunction with the accompanying drawings and preferred embodiments, elaborate in detail on a method and system for the efficient operation of a hot and cold circulation system proposed according to this application, including its specific implementation manner, structure, features, and effects. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs.

[0032] The following will specifically describe the specific solutions of a method and system for the efficient operation of a hot and cold circulation system provided by this application in conjunction with the accompanying drawings.

[0033] Please refer to Figure 1 , which shows a step flowchart of a method for the efficient operation of a hot and cold circulation system provided by an embodiment of this application. The method includes the following steps:

[0034] Step S1: Obtain the heat flux density between the heat exchanger tube wall surface and the liquid inside the tube at each acquisition moment before and including the current moment, the temperature data of the heat exchanger tube wall surface, the flue gas temperature at the outlet, and the liquid flow rate inside the heat exchanger tube at the current moment.

[0035] The selected heat flux density sensor has an accuracy of ±10%, a measurement range of 500 - 5000 kW / m^2, and a response time of less than 1 s. Install the heat flux density sensor on the outer side of the heat exchanger tube wall, close to the heat exchange area between the liquid inside the tube and the tube wall surface, and ensure good thermal contact between the sensor and the tube wall. Thermal conductive glue can be used to closely attach the sensor to the tube wall. To avoid thermal interference from the surrounding environment, heat insulation materials can also be used to wrap the sensor, allowing only the sensing surface of the sensor to contact the tube wall.

[0036] The selected temperature sensor is a thermal resistance sensor with an accuracy of ±0.1 °C, a measurement range of -10 - 300 °C, and a response time of less than 1 s. Enclose the thermal resistance in a protective sleeve that can closely fit the tube wall, and the material of the protective sleeve should have good thermal conductivity to reduce measurement errors. In addition, install a temperature sensor at the outlet of the heat exchanger to measure the flue gas temperature.

[0037] The selected flow sensor has an accuracy of ±2%, a measurement range of 10 - 80 m³ / h, and a response time of less than 1 s. The flow sensor is installed on the straight pipe section of the heat exchanger inlet pipe, and there should also be straight pipe sections with a length 5 times the pipe diameter before and after the sensor installation position to ensure the stability of the fluid and improve the measurement accuracy. During installation, ensure that the flow sensor is coaxial with the pipe to avoid measurement errors caused by eccentricity.

[0038] Furthermore, a heat flux density sensor, a temperature sensor, and a flow sensor are respectively used to measure the heat flux density between the heat exchanger tube wall and the liquid inside the tube, the temperature data of the heat exchanger tube wall, and the flue gas temperature at the outlet at each acquisition moment within a preset duration before the current moment, as well as the liquid flow rate inside the heat exchanger tube at the current moment, where the data acquisition frequency is set to f.

[0039] It should be noted that the values of the preset duration and the data acquisition frequency f are both set artificially. In this embodiment, the value of the preset duration is 1 s, and the value of the acquisition frequency f is 10 Hz. Implementers can also set them according to specific situations by themselves, and this embodiment does not make special restrictions.

[0040] Furthermore, all data is subjected to data cleaning to remove outliers, and the missing data is filled in using the data interpolation algorithm for the cleaned data. Among them, data cleaning and the data interpolation method are both well-known techniques in data processing, and their specific process principles will not be elaborated here.

[0041] Step S2: Analyze the difference between the temperature data at the current moment and the saturation temperature of the liquid inside the heat exchanger tube to determine the wall superheat degree of the heat exchanger at the current moment.

[0042] Boiling heat transfer inside the heat exchanger tube is a complex heat transfer phenomenon. It occurs inside the heat exchanger tube. When the liquid is heated inside the tube to reach the saturation temperature and continues to absorb heat, boiling will occur. This boiling process is accompanied by the generation, growth, and detachment of bubbles, and it is a process where phase change and convective heat transfer coexist.

[0043] Boiling heat transfer is divided into the following processes: After the single-phase liquid enters the heat exchange tube and flows along the tube, it continuously evaporates, causing the gas-liquid content to change continuously. If the heat transfer tube is long enough, it is possible for the liquid to completely evaporate into steam in the end. Since the gas-liquid content changes continuously along the tube length, the flow characteristics of the liquid along the tube length are also different.

[0044] For different boiling states, the volume of liquid flowing through the inside of the heat exchanger pipes per unit time, i.e., the flow rate, has an important impact. The initially entering fluid in the heat exchange pipes is a single-phase liquid, and the heat transfer coefficient at this time is relatively low. When the temperature of the liquid in the pipe approaches the saturation temperature, vaporization nuclei will form at some tiny pits or impurities on the pipe wall. These vaporization nuclei are like seeds, and bubbles start to form at these locations. The initially generated bubbles are very small, and as heat is continuously absorbed, the bubbles gradually grow. Among them, the heat transfer coefficient refers to the heat transfer ability between the liquid and the solid surface, which is a well-known technology, and the specific principle explanation will not be elaborated too much.

[0045] In the nucleate boiling stage, an appropriate flow rate helps the detachment and removal of bubbles. When the flow rate increases, the liquid flow can promptly wash away the bubbles generated and growing on the heating wall surface, enabling more liquid to come into contact with the heating wall surface and maintaining a high heat transfer efficiency. If the flow rate is too small, the bubbles may accumulate on the wall surface, forming a local vapor film, which reduces the heat transfer coefficient and may even prematurely enter the transition boiling stage.

[0046] As the heat flux density further increases, the generation rate of bubbles becomes extremely fast, and bubbles begin to form an unstable vapor film on the wall surface. At this time, the direct contact between the liquid and the wall surface is partially blocked, and the heat transfer coefficient starts to decrease. This stage is the transition stage between nucleate boiling and film boiling, and its characteristic is that the heat transfer coefficient shows a complex relationship with the heat flux density. In the transition boiling stage, the wall temperature will exhibit large fluctuations because the stability of the vapor film is poor, sometimes breaking and sometimes reforming.

[0047] In this stage, a slight change in the flow rate may cause the boiling state to fluctuate between nucleate boiling and film boiling. If the flow rate increases, it is possible to return the boiling state to nucleate boiling; conversely, if the flow rate decreases, it may accelerate the transition to film boiling. Because in the transition boiling stage, bubbles form an unstable vapor film on the wall surface, and the change in the flow rate will affect the stability and thickness of the vapor film.

[0048] When the heat flux density is large enough, bubbles form a continuous and stable vapor film on the wall surface. At this time, heat is mainly transferred to the liquid through the conduction and radiation of the vapor film. Due to the large thermal resistance of the vapor film, the heat transfer coefficient in this stage is relatively low, and the wall temperature will rise sharply. When entering the film boiling stage, a larger flow rate can, to a certain extent, disperse the vapor film and improve the heat transfer situation. However, generally speaking, the heat transfer efficiency in the film boiling stage is relatively low, and this stage should be avoided as much as possible.

[0049] In summary, the heat transfer coefficient is the highest in the nucleate boiling stage. By adjusting the flow rate to keep the heat exchanger in this state, the waste heat recovery efficiency can be improved and the flue gas temperature can be effectively reduced. However, the flue gas temperature should not be lower than the acid dew point temperature of the flue gas, because low-temperature flue gas will severely corrode the metal wall and cause equipment damage.

[0050] For the boiling situation in the heat exchanger, the bubble state is an intuitive reflection of the boiling state, but it is not easy to directly observe. Therefore, the wall superheat can be calculated through the temperature of the tube wall to indirectly reflect the boiling state inside the tube. The calculation process of the wall superheat is as follows:

[0051] The wall superheat ΔT of the heat exchanger at the current moment sat has the following expression: ΔT sat = norm(T w - T sat ); In the formula, ΔT sat represents the wall superheat of the heat exchanger at the current moment; T w represents the temperature data of the heat exchanger tube wall at the current moment; T sat represents the saturation temperature of the liquid inside the heat exchanger tube under standard atmospheric pressure at the current moment; norm() represents the normalization function.

[0052] It should be noted that in this embodiment, the liquid used inside the heat exchanger tube is water, and this embodiment is for standard atmospheric pressure. The saturation temperature of water under standard atmospheric pressure is 100 °C.

[0053] Based on the wall superheat of the heat exchanger at the current moment, it can be understood that the saturation temperature is used as the reference temperature. The saturation temperature refers to the temperature at which a liquid undergoes a phase change under a specific pressure. During the boiling process inside the tube, the saturation temperature determines whether the liquid will boil and the intensity of boiling. If the wall temperature is higher than the saturation temperature, boiling will occur near the wall. The magnitude of the wall superheat will affect the generation, growth, and detachment processes of bubbles, and thus affect the efficiency and state of boiling heat transfer.

[0054] When the difference between the temperature data of the inner wall of the heat exchanger tube and the saturation temperature of the liquid inside the tube is smaller, the wall superheat is smaller, indicating that the tube may be in the initial stage of nucleate boiling, and the generation of bubbles is relatively slow, or boiling has not started yet; while when the difference between the temperature data of the inner wall of the heat exchanger tube and the saturation temperature of the liquid inside the tube is larger, and the wall superheat is larger, the nucleate boiling will be more intense, and the heat transfer coefficient is larger at this time; when the wall superheat approaches 1, it indicates that the tube may have entered the transition boiling or even film boiling stage, and the heat transfer coefficient decreases at this time.

[0055] Step S3: Based on the heat flux density at the current moment, the size of the heat exchanger tube, and the wall superheat, determine the superheat index of the heat exchanger at the current moment. Then, in combination with the heat absorbed during the evaporation of the liquid inside the heat exchanger tube, determine the boiling intensity index of the liquid inside the heat exchanger tube at the current moment.

[0056] In the nucleate boiling stage, the wall superheat generally has a certain range. However, when approaching the transition boiling, the wall superheat will start to fluctuate and may increase rapidly. Therefore, it is very difficult to accurately determine whether the boiling is in the initial stage of transition boiling or about to enter the film boiling stage only relying on the wall superheat. Due to factors such as pressure fluctuations, the wall superheat may show misleading fluctuations and cannot accurately reflect the actual changes in the boiling state.

[0057] Therefore, it is also necessary to further calculate the boiling intensity index by combining the heat flux density and the vaporization characteristics of the liquid to characterize the boiling state inside the heat exchanger tube. Specifically:

[0058] Calculate the product of the lateral area of the heat exchanger tube and the wall superheat of the heat exchanger at the current moment, and take the ratio of the heat flux density of the heat exchanger at the current moment to the product as the superheat index of the heat exchanger at the current moment;

[0059] The expression for the boiling intensity index B of the liquid inside the heat exchanger tube at the current moment is: In the formula, C represents the superheat index of the heat exchanger at the current moment; ρ v 、h fg respectively represent the saturated vapor density and the latent heat of vaporization during the evaporation of the liquid inside the heat exchanger tube under standard atmospheric pressure. It should be understood that the saturated vapor density and the latent heat of vaporization can be obtained by querying the physical property table according to the liquid temperature and pressure. In this embodiment, taking water as an example, at 100 °C and standard atmospheric pressure, the saturated vapor density is 0.5977 kg / m 3 and the latent heat of vaporization is 2229.90 kJ / kg.

[0060] It should be noted that the calculation process of the lateral area is a well-known technology, and its specific calculation steps will not be elaborated here.

[0061] Particularly, when the superheat is 0, the boiling intensity index B of the liquid inside the heat exchanger tube at the current moment takes the value of 1.

[0062] Furthermore, it can be understood from the boiling intensity index of the liquid inside the heat exchanger tube at the current moment that the heat flux density is the energy input factor affecting boiling, the wall superheat reflects the driving temperature difference of liquid boiling, and the saturated vapor density and latent heat of vaporization are related to the phase change characteristics of the liquid. In internal boiling, heat is transferred from the heating wall to the liquid, causing the liquid to reach the saturated state and generate bubbles. Therefore, the degree of boiling can be quantified from the perspectives of energy transfer and phase change. The greater the heat flux density, the more energy is provided to the liquid, and the easier it is to generate boiling; while the latent heat of vaporization determines the energy required for the liquid to transform into steam.

[0063] If the heat flux density between the heat exchanger and the liquid inside its tube is greater, the side area and wall superheat of the heat exchanger tube are smaller, and the saturated vapor density and latent heat of vaporization are smaller, then the boiling intensity index is greater, indicating that the boiling is relatively intense, and it may be in the vigorous period of nucleate boiling, with a larger heat transfer coefficient. If the flue gas temperature is appropriate at this time, it means that the flow rate setting is appropriate, and efficient waste heat recovery can be maintained. If the temperature is too low, the flow rate needs to be reduced to avoid the flue gas temperature being lower than the acid dew point temperature of the flue gas, resulting in equipment damage; on the contrary, if the heat flux density between the heat exchanger and the liquid inside its tube is smaller, the side area and wall superheat of the heat exchanger tube are larger, and the saturated vapor density and latent heat of vaporization are larger, then the boiling intensity index is smaller, indicating that the boiling state is changing to the transition boiling state, and the flow rate should be reduced to maintain nucleate boiling and avoid a decrease in the heat transfer coefficient.

[0064] Step S4: Based on the difference in heat flux density between the current moment and the previous adjacent acquisition moment and the wall superheat, determine the heat flux difference value of the liquid inside the heat exchanger tube at the current moment, and combine it with the preset surface tension to determine the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment.

[0065] Frequent adjustment of the flow rate may lead to unstable boiling states, switching between several states, and unstable boiling states may cause problems such as excessive temperature, pipeline corrosion, and equipment vibration. Therefore, it is necessary to maintain the stability of the boiling state. Thus, by analyzing the difference in heat flux density between the current moment and the previous adjacent acquisition moment, as well as the preset surface tension and the wall superheat, determine the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment, which is used to characterize the stability of the boiling state inside the heat exchanger pipeline. Specifically:

[0066] Calculate the change rate of the heat flux density between the current moment and the previous adjacent acquisition moment, and take the product of the change rate and the wall superheat at the current moment as the heat flux difference value of the liquid inside the heat exchanger tube at the current moment;

[0067] The expression of the boiling stability coefficient W of the liquid inside the heat exchanger tube at the current moment is: In the formula, σ represents the preset surface tension; P represents the heat flux difference value of the liquid inside the heat exchanger tube at the current moment; ε represents a preset constant greater than 0, which is used to prevent the denominator from being 0. The value of ε is set artificially. In this embodiment, the value of ε is 0.01. On the premise of ensuring that the denominator is not 0 and not overly affecting the calculation result, the implementer can also set it according to the specific situation by himself / herself, and this embodiment does not make special restrictions.

[0068] It should be noted that σ represents the preset surface tension, which refers to the surface tension of water in this embodiment and can be obtained by querying the physical property table according to the liquid temperature. In this embodiment, for the standard atmospheric pressure, the saturation temperature of water is 100 °C, and the surface tension of water at 100 °C is between 58 and 60 mN / m. The value of the surface tension in this embodiment is 60 mN / m. The implementer can also set it according to the specific situation by himself / herself, and this embodiment does not make special restrictions.

[0069] Among them, the heat flux density change rate between the current moment and the previous acquisition moment is the ratio of the difference in heat flux density between the current moment and the previous acquisition moment to the corresponding time interval, that is, the calculation process of the change rate is a well-known technology, and its specific calculation steps will not be elaborated here.

[0070] It should be understood that during the in-tube boiling process, the heat flux density may change due to external conditions (such as the change in the temperature of high-temperature flue gas) or internal boiling state changes (such as the transition from nucleate boiling to transition boiling). Through the heat flux density change rate, the stability of the boiling process under dynamic conditions can be reflected. At the same time, the surface tension and the wall superheat are also the key factors determining the bubble behavior and boiling state, and can more comprehensively evaluate the stability of boiling.

[0071] If the surface tension is larger, the wall superheat is smaller, and the heat flux density change rate is smaller, then the boiling stability coefficient is larger, indicating that the heat flux density change rate is relatively small, the wall superheat is stable, and the effect of the surface tension on the bubbles is also relatively regular, that is, the boiling state is relatively stable at this time. During the stable nucleate boiling stage, the flow rate can be adjusted. On the contrary, if the surface tension is smaller, the wall superheat is larger, and the heat flux density change rate is smaller, then the boiling stability coefficient is smaller, indicating that the boiling state changes more, and it is less suitable to adjust the flow rate to avoid causing changes in the boiling state.

[0072] Step S5: Based on the boiling stability coefficient, the boiling intensity index, and the difference between the flue gas exhaust temperature of the heat exchanger at the current moment and the preset flue gas acid dew point temperature, determine the flow rate adjustment factor of the liquid inside the heat exchanger tube at the current moment, and adjust the liquid flow rate inside the heat exchanger tube in the cold and hot circulation system at the current moment.

[0073] In summary, the boiling intensity index and boiling stability coefficient are calculated according to the boiling state inside the heat exchanger tubes. Further, the flow adjustment factor is calculated in combination with the flue gas temperature. The inlet water flow of the heat exchanger is adjusted according to the flow adjustment factor to maintain a relatively large heat transfer coefficient. Specifically:

[0074] The expression of the flow adjustment factor μ of the liquid inside the heat exchanger tubes at the current moment is: In the formula, B represents the boiling intensity index of the liquid inside the heat exchanger tubes at the current moment; W represents the boiling stability coefficient of the boiling stability coefficient of the liquid inside the heat exchanger tubes at the current moment; T represents the flue gas temperature at the current moment; T0 represents the preset flue gas acid dew point temperature; norm() represents the normalization function.

[0075] It should be noted that in this embodiment, the high-temperature flue gas generated by the boiler is about 210°C, and the flue gas temperature after waste heat recovery should be below 160°C, but not lower than 110°C. Therefore, the value of the preset flue gas acid dew point temperature in this embodiment is 110°C. On the premise of ensuring that the preset flue gas acid dew point temperature is not higher than the flue gas temperature, the implementer can also set it according to the specific situation, and this embodiment does not make special restrictions.

[0076] It can be understood from the flow adjustment factor of the liquid inside the heat exchanger tubes at the current moment that when the boiling state is more unstable, that is, when the boiling stability coefficient is smaller, it is less suitable for flow adjustment, that is, the flow adjustment factor is smaller. When the boiling intensity index is smaller, it means that the ideal heat transfer coefficient has not been achieved, so the flow adjustment should be carried out more, that is, the flow adjustment factor is larger. When the flue gas temperature is closer to the flue gas acid dew point temperature, the flow adjustment should be carried out more to avoid too low flue gas temperature. In actual situations, the flue gas temperature should not be lower than or equal to the flue gas acid dew point temperature. The larger the flow adjustment factor, the more the inlet water flow of the heat exchanger should be adjusted at this time, and vice versa, the less the flow should be adjusted.

[0077] Before the current moment, a neighborhood is divided with the current moment as the center. According to the method for obtaining the flow adjustment factor of the liquid inside the heat exchanger tubes at the current moment, before the current moment, the flow adjustment factors of the liquid inside the heat exchanger tubes at all the acquisition moments within the neighborhood of the current moment are obtained;

[0078] If the flow adjustment factors of the liquid inside the heat exchanger tubes at all the acquisition moments within the neighborhood are all greater than the preset value, the liquid flow inside the heat exchanger tubes in the cold and hot circulation system at the current moment is adjusted. The adjustment process is as follows: Among all the acquisition moments within the neighborhood of the current moment, if the temperature data of the heat exchanger tube wall surface at the acquisition moment farthest from the current moment is greater than or equal to the temperature data of the heat exchanger tube wall surface at the current moment, then in the heat exchanger at the current moment, the liquid flow is increased by a preset proportion, and vice versa, the liquid flow is decreased by a preset proportion.

[0079] In contrast, among all the acquisition times in the neighborhood of the current time, if the flow factor of the liquid inside the heat exchanger tube at any acquisition time is less than or equal to a preset value, the liquid flow rate inside the heat exchanger tube at the current time is not adjusted.

[0080] It should be noted that the values of the neighborhood of the current time, the preset value, and the preset ratio are all set artificially. In this embodiment, the value of the neighborhood size is 3, the value of the preset value is 0.5, and the value of the preset ratio is 5%. Implementers can also set them according to specific situations by themselves, and this embodiment does not make special restrictions.

[0081] Precise flow adjustment can ensure that the boiling inside the inner tube of the heat exchanger is always in an ideal state. When the boiling intensity is insufficient, the inlet water flow rate is appropriately reduced to allow the liquid to have more sufficient time to absorb heat inside the tube, promoting the continuous progress of nucleate boiling, thereby improving the heat transfer efficiency. When the boiling stability is threatened, the flow rate is adjusted in a timely and reasonable manner to restore stable nucleate boiling, avoiding a reduction in heat transfer efficiency caused by the deterioration of the boiling state. At the same time, it ensures that the flue gas temperature is reduced and not lower than the flue gas acid dew point temperature, ensuring the efficient operation of the cold and hot cycle system and improving the energy-saving transformation efficiency of the industrial furnace.

[0082] Preferably, the schematic diagram of the process for obtaining the flow adjustment factor provided in this embodiment is as Figure 2 shown.

[0083] Based on the same inventive concept as the above method, the embodiment of the present application also provides an efficient operation system for a cold and hot cycle system, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above methods for the efficient operation of a cold and hot cycle system.

[0084] It should be noted that the above sequence of the embodiments of the present application is only for description and does not represent the superiority or inferiority of the embodiments. And the above description of specific embodiments of this specification is made. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0085] Each embodiment in this specification is described in a progressive manner. The same or similar parts between each embodiment can be referred to each other, and the key points of each embodiment are the differences from other embodiments.

[0086] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. An efficient operation method for a thermal cycling system, characterized in that The efficient operation method of the cold and heat cycle system is realized through the efficient operation system of the cold and heat cycle system. The efficient operation system of the cold and heat cycle system includes an industrial furnace and a cold and heat cycle system. The heat exchanger in the cold and heat cycle system is connected to the industrial furnace and receives the high-temperature waste gas generated by the industrial furnace. The heat of the high-temperature waste gas is transferred to the low-temperature liquid in the heat exchanger through the wall surface of the heat exchanger, heating the low-temperature liquid, and the heated liquid is used again for industrial furnace production. The efficient operation method of the cold and heat cycle system includes the following steps: Obtain the heat flux density between the tube wall surface and the liquid inside the tube at each acquisition moment before and including the current moment, the temperature data of the tube wall surface of the heat exchanger, the smoke exhaust temperature at the outlet, and the liquid flow rate inside the heat exchanger tube at the current moment; Analyze the difference between the temperature data of the tube wall surface of the heat exchanger at the current moment and the saturation temperature of the liquid inside the heat exchanger tube to determine the wall superheat degree of the heat exchanger at the current moment; Based on the heat flux density at the current moment, the size of the heat exchanger tube, and the wall superheat degree, determine the superheat index of the heat exchanger at the current moment, and combine with the heat absorbed when the liquid inside the heat exchanger tube evaporates to determine the boiling intensity index of the liquid inside the heat exchanger tube at the current moment; Based on the difference in heat flux density between the current moment and the previous adjacent acquisition moment and the wall superheat degree, determine the heat flux difference value of the liquid inside the heat exchanger tube at the current moment, and combine with the preset surface tension to determine the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment; Based on the boiling stability coefficient and the boiling intensity index, and the difference between the smoke exhaust temperature of the heat exchanger at the current moment and the preset flue gas acid dew point temperature, determine the flow adjustment factor of the liquid inside the heat exchanger tube in the cold and heat cycle system at the current moment, and adjust the liquid flow rate inside the heat exchanger tube in the cold and heat cycle system at the current moment.

2. The efficient operation method of a hot and cold cycle system according to claim 1, characterized in that, The wall superheat of the heat exchanger at the current moment: ; In the formula, represents the wall superheat of the heat exchanger at the current moment; represents the temperature data of the heat exchanger tube wall at the current moment; represents the saturation temperature of the liquid in the heat exchanger tube under standard atmospheric pressure at the current moment; norm( ) represents the normalization function.

3. The efficient operation method of a hot and cold cycle system as described in claim 1, characterized in that, The method for determining the superheat index of the heat exchanger at the current moment is as follows: Calculate the product of the lateral area of the heat exchanger tube and the wall superheat degree of the heat exchanger at the current moment, and take the ratio of the heat flux density of the heat exchanger at the current moment to the product as the superheat index of the heat exchanger at the current moment.

4. The efficient operation method of a cold and hot cycle system as described in claim 1, characterized in that, The expression for the boiling intensity index of the liquid inside the heat exchanger tube at the current moment is as follows: ; where B represents the boiling intensity index of the liquid inside the heat exchanger tube at the current moment; represents the superheat index of the heat exchanger at the current moment; , respectively represent the saturated vapor density and the latent heat of vaporization when the liquid inside the heat exchanger tube evaporates under standard atmospheric pressure.

5. The efficient operation method of a cold and hot cycle system as claimed in claim 1, wherein, The method for determining the heat flux difference value of the liquid inside the heat exchanger tube at the current moment is as follows: Calculate the change rate of the heat flux density between the current moment and the previous adjacent acquisition moment, and take the product of the change rate and the wall superheat degree at the current moment as the heat flux difference value of the liquid inside the heat exchanger tube at the current moment.

6. The efficient operation method of a hot and cold cycle system according to claim 1, characterized in that The expression for the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment is as follows: ; In the formula, represents the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment; represents the preset surface tension; P represents the heat flux difference value of the liquid inside the heat exchanger tube at the current moment; represents a preset constant greater than 0.

7. The efficient operation method of a cold and hot cycle system as claimed in claim 1, characterized in that, The expression for the flow rate adjustment factor of the liquid inside the heat exchanger tube at the current moment is as follows: ; In the formula, represents the flow rate adjustment factor of the liquid inside the heat exchanger tube at the current moment; B represents the boiling intensity index of the liquid inside the heat exchanger tube at the current moment; represents the boiling stability coefficient of the liquid inside the heat exchanger tube at the current moment; represents the flue gas temperature at the current moment; represents the preset flue gas acid dew point temperature; norm( ) represents the normalization function.

8. The efficient operation method of a cooling and heating cycle system according to claim 1, characterized in that The adjustment of the liquid flow rate inside the heat exchanger tube in the cold and heat cycle system at the current moment includes: According to the acquisition method of the flow adjustment factor of the liquid inside the heat exchanger tube at the current moment, before the current moment, obtain the flow adjustment factors of the liquid inside the heat exchanger tube at all acquisition moments within the neighborhood of the current moment; If the flow adjustment factors of the liquid inside the heat exchanger tube at all acquisition moments within the neighborhood are all greater than the preset value, then adjust the liquid flow rate inside the heat exchanger tube in the cold and heat cycle system at the current moment, otherwise, do not adjust the liquid flow rate inside the heat exchanger tube in the cold and heat cycle system at the current moment.

9. The efficient operation method of a hot and cold cycle system according to claim 8, characterized in that, If the flow adjustment factors of the liquid in the heat exchanger tubes at all acquisition times within the neighborhood are greater than the preset value, the liquid flow in the heat exchanger tubes of the hot and cold circulation system at the current time is adjusted, including: Among all the acquisition times within the neighborhood of the current time, if the temperature data of the heat exchanger tube wall surface at the acquisition time farthest from the current time is greater than or equal to the temperature data of the heat exchanger tube wall surface at the current time, then in the heat exchanger at the current time, a preset proportion of the liquid flow is increased; otherwise, a preset proportion of the liquid flow is decreased.

10. An efficient operation system for a cooling and heating cycle system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements an efficient operation method for a hot and cold circulation system according to any one of claims 1-9.

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