Efficient operation method and system of cold and heat circulation system

Abstract

The invention relates to the technical field of industrial furnace energy-saving transformation, in particular to an efficient operation method and system for a cold and hot circulation system, and the method comprises the steps that the difference between wall surface temperature data and the saturation temperature of liquid in a heat exchanger tube is analyzed, and the wall surface superheat degree is determined; determining a boiling intensity index by combining the heat flow density at the current moment, the size of the heat exchanger tube and the heat absorbed when the liquid in the heat exchanger tube evaporates; and determining a boiling stability coefficient based on the difference of the heat flow density between the current moment and the adjacent previous collection moment, the wall surface superheat degree and the preset surface tension, and adjusting the liquid flow in a heat exchanger pipe in the cold and hot circulation system in combination with the boiling strength index and the difference between the smoke exhaust temperature and the preset smoke acid dew point temperature. The industrial furnace aims at optimizing efficient operation of the cold and heat circulation system, improving the energy utilization efficiency of the industrial furnace and reducing energy waste.

Description

Technical Field

[0001] The present application relates to the technical field of energy-saving transformation of industrial furnaces, and in particular to a method and system for efficiently operating a cold and hot circulation system. Background Art

[0002] In industrial production, industrial furnaces are key equipment in many industrial processes. For example, in the steel, chemical, glass and other industries, they are used for material heating, smelting, heat treatment and other processes. 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 it is directly discharged into the atmosphere, it will not only cause a huge waste of energy, but also cause 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 by industrial furnaces, heat exchangers can be used to transfer the waste heat to other materials that require heat, thereby improving 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 fluid to a lower fluid, thereby recovering waste heat and improving energy efficiency. As part of a hot and cold circulation system, the heat exchange performance of the heat exchanger is crucial to the efficient operation of the system. Traditional hot and cold circulation systems usually set the flow adjustment time and range based on empirical values, which can easily cause changes in the boiling state in the tube, resulting in a decrease in the heat transfer coefficient, and even causing the exhaust gas temperature to be out of the appropriate range, resulting in a decrease in the recovery efficiency of the hot and cold circulation system for the waste heat generated by the industrial furnace, resulting in 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. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides an efficient operation method of a cold and hot circulation system, which is implemented by an efficient operation system of the cold and hot circulation system, wherein the efficient operation system of the cold and hot circulation system comprises an industrial furnace and a cold and hot circulation system, wherein a heat exchanger in the cold and hot circulation system is connected to the industrial furnace and receives high-temperature exhaust gas generated by the industrial furnace, and the heat of the high-temperature exhaust gas is transferred to a low-temperature liquid in the heat exchanger through the wall of the heat exchanger, and the low-temperature liquid is heated, and the heated liquid is used again for industrial furnace production, and the efficient operation method of the cold and hot circulation system comprises the following steps:

[0006] Obtain the heat flux density between the heat exchanger tube wall and the liquid in the tube at the current moment and at each previous acquisition moment, the temperature data of the heat exchanger tube wall and the exhaust gas temperature at the outlet, and the liquid flow rate in 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 in the heat exchanger tube to determine the wall superheat of the heat exchanger at the current moment;

[0008] The superheat index of the heat exchanger at the current moment is determined by comprehensively considering the heat flux density at the current moment, the size of the heat exchanger tube and the wall superheat, and the boiling intensity index of the liquid in the heat exchanger tube at the current moment is determined by combining the heat absorbed by the liquid in the heat exchanger tube when evaporating;

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

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

[0011] Preferably, the wall superheat of the heat exchanger at the current moment is: ΔT sat =norm(T w -T sat );where ΔT sat Indicates the wall superheat of the heat exchanger at the current moment; T w Indicates the temperature data of the heat exchanger tube wall at the current moment; T sat It represents the saturation temperature of the liquid in the heat exchanger tube at the 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] The product of the lateral area of ​​the heat exchanger tube and the wall superheat of the heat exchanger at the current moment is calculated, and the ratio of the heat flux density of the heat exchanger at the current moment to the product is used as the superheat index of the heat exchanger at the current moment.

[0014] Preferably, the expression of the boiling intensity index of the liquid in the heat exchanger tube at the current moment is: In the formula, B represents the boiling intensity index of the liquid in 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 They respectively represent the saturated steam density and latent heat of vaporization when the liquid evaporates in the heat exchanger tube under standard atmospheric pressure.

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

[0016] The change rate of the heat flux density between the current moment and the previous acquisition moment is calculated, and the product of the change rate and the wall superheat at the current moment is taken as the heat flux difference value of the liquid in the heat exchanger tube at the current moment.

[0017] Preferably, the expression of the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment is: Wherein, 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 flow 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 of the flow adjustment factor of the liquid in the heat exchanger tube at the current moment is: Wherein, μ represents the flow 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 exhaust gas temperature at the current moment; T0 represents the preset flue gas acid dew point temperature; norm() represents the normalization function.

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

[0020] According to the method for obtaining the flow adjustment factor of the liquid in the heat exchanger tube at the current moment, before the current moment, the flow adjustment factor of the liquid in the heat exchanger tube at all the collection moments in the neighborhood of the current moment is obtained;

[0021] If the flow adjustment factors of the liquid in the heat exchanger tube at all collection moments in the neighborhood are greater than the preset value, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is adjusted; otherwise, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is not adjusted.

[0022] Preferably, if the flow adjustment factor of the liquid in the heat exchanger tube at all the collection moments in the neighborhood is greater than a preset value, then adjusting the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment further includes:

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

[0024] In a second aspect, an embodiment of the present application further provides an efficient operation system for a cold and hot circulation system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of an efficient operation method for a cold and hot circulation system described in any one of the above items are implemented.

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

[0026] The present application constructs the wall superheat by analyzing the difference between the temperature of the liquid in the heat exchanger tube and the tube wall, which can more accurately determine whether the liquid in the tube is in the nucleate boiling stage. By maintaining a high wall superheat, the heat exchange efficiency can be improved, thereby improving the energy efficiency of the industrial furnace; secondly, by analyzing the heat absorbed by the liquid in the tube when evaporating, and combining the size of the heat exchanger tube, the wall superheat and the heat flux density, a boiling intensity index is constructed, which can evaluate whether the intensity of the boiling of the liquid in the tube is ideal, thereby determining whether the liquid flow needs to be adjusted, further improving the energy efficiency of the industrial furnace; Furthermore, by analyzing the difference in heat flux density between adjacent moments, and combining the wall superheat and the surface tension of the liquid, a boiling stability coefficient is constructed, which reflects whether the boiling state of the liquid in the tube is stable, thereby avoiding the decrease in heat exchange 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 boiling intensity index, as well as the difference between the exhaust temperature and the flue gas acid dew point temperature, a flow adjustment factor is constructed to determine whether the flow needs to be adjusted to maintain the ideal boiling state and heat exchange efficiency, thereby improving the energy-saving effect of the industrial furnace. This application improves the energy utilization efficiency of the industrial furnace and reduces energy waste by optimizing the efficient operation of the cold and hot circulation system. BRIEF 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 drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A flowchart of a method for efficiently operating a cold and hot circulation system provided in one embodiment of the present application;

[0029] Figure 2 A schematic diagram of a process for obtaining a flow adjustment factor provided in one embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following is a detailed description of the efficient operation method and system of a cold and hot circulation system proposed in the present application, its specific implementation method, structure, features and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0032] The following is a detailed description of an efficient operation method of a cold and hot circulation system and a specific scheme of the system provided by the present application in conjunction with the accompanying drawings.

[0033] See also Figure 1 , which shows a flowchart of a method for efficiently operating a cold and hot cycle system provided by an embodiment of the present application, the method comprising the following steps:

[0034] Step S1: Obtain the heat flux density between the heat exchanger tube wall and the liquid in the tube at the current moment and at each previous acquisition moment, the temperature data of the heat exchanger tube wall and the exhaust gas temperature at the outlet, and the liquid flow rate in the heat exchanger tube at the current moment.

[0035] The selected heat flux density sensor has an accuracy of ±10%, a measurement range of 500-5000kW / m^2, and a response time of less than 1s. The heat flux density sensor is installed on the outside of the heat exchanger tube wall, close to the heat exchange area between the liquid in the tube and the tube wall. It is necessary to ensure good thermal contact between the sensor and the tube wall. The sensor can be tightly attached to the tube wall with thermal conductive glue. In order to avoid thermal interference from the surrounding environment, the sensor can also be wrapped with thermal insulation materials to allow only the sensing surface of the sensor to contact the tube wall.

[0036] The temperature sensor selected is a thermal resistor sensor with an accuracy of ±0.1°C, a measurement range of -10 to 300°C, and a response time of less than 1s. The thermal resistor is encapsulated in a protective cover that fits tightly against the pipe wall, and the material of the protective cover must have good thermal conductivity to reduce measurement errors. In addition, a temperature sensor is installed at the outlet of the heat exchanger to measure the exhaust temperature.

[0037] The selected flow sensor has an accuracy of ±2%, a measurement range of 10-80m^3 / h, and a response time of less than 1s. The flow sensor is installed on the straight pipe section of the heat exchanger water inlet pipe, and there should be a straight pipe section 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 in the tube at each collection time within a preset time period before the current moment, the temperature data of the heat exchanger tube wall and the exhaust gas temperature at the outlet, and the liquid flow rate in the heat exchanger tube at the current moment, wherein the data collection frequency is set to f.

[0039] It should be noted that the values ​​of the preset time length and the data collection frequency f are both manually set. In this embodiment, the preset time length is 1s, and the collection frequency f is 10Hz. The implementer can also set them according to the specific situation. This embodiment does not impose any special restrictions.

[0040] Furthermore, all data are cleaned to remove outliers, and the missing data are supplemented using a data interpolation algorithm for the cleaned data. Data cleaning and data interpolation are both well-known technologies in data processing, and their specific process principles will not be repeated here.

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

[0042] Boiling heat transfer in the heat exchanger tube is a complex heat transfer phenomenon that occurs in the tube of the heat exchanger. When the liquid is heated to the saturation temperature in the tube and continues to absorb heat, boiling will occur. This boiling process is accompanied by the generation, growth and separation of bubbles. It is a process in which phase change and convection heat transfer exist simultaneously.

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

[0044] For different boiling states, the volume of liquid flowing through the inside of the heat exchanger pipe per unit time, that is, the flow rate, has an important influence. The first liquid to enter the heat exchange pipe is a single-phase liquid, and the heat transfer coefficient is low at this time. When the temperature of the liquid in the pipe is close to the saturation temperature, vaporization cores will form at some tiny pits or impurities on the wall of the pipe. These vaporization cores are like seeds, and bubbles begin to form in these places. The bubbles generated at first are very small, and as heat is continuously absorbed, the bubbles will gradually grow. Among them, the heat transfer coefficient refers to the heat exchange capacity between the liquid and the solid surface. It is a well-known technology, and the specific principle explanation will not be repeated in detail.

[0045] In the nucleate boiling stage, the appropriate flow rate helps to detach and carry away the bubbles. When the flow rate increases, the flow of liquid can promptly wash away the bubbles generated and grown on the heated wall surface, so that more liquid can contact the heated wall surface and maintain a high heat transfer efficiency. If the flow rate is too small, the bubbles may gather on the wall surface to form a local vapor film, which will reduce the heat transfer coefficient and may even enter the transition boiling stage prematurely.

[0046] As the heat flux increases further, the rate of bubble generation becomes very fast, and the bubbles begin to form an unstable vapor film on the wall. At this time, the direct contact between the liquid and the wall is partially blocked, and the heat transfer coefficient begins 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 change of heat flux. In the transition boiling stage, the wall temperature will fluctuate greatly because the vapor film is less stable, sometimes breaking and sometimes re-forming.

[0047] At this stage, a slight change in 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, the bubbles form an unstable vapor film on the wall, and changes in flow rate will affect the stability and thickness of the vapor film.

[0048] When the heat flux is large enough, the bubbles form a continuous and stable vapor film on the wall. At this time, the 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 at this stage is low, and the wall temperature will rise sharply. After entering the film boiling, a larger flow rate can disperse the vapor film to a certain extent and improve the heat transfer. But in general, the heat transfer efficiency of the film boiling stage is relatively low, and you should try to avoid entering this stage.

[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 exhaust temperature can be effectively reduced. However, the exhaust temperature cannot be lower than the flue gas acid dew point temperature, because the low-temperature flue gas will seriously corrode the metal wall and cause equipment damage.

[0050] For the boiling condition in the heat exchanger, the bubble state is an intuitive reflection of the boiling state, but it is not easy to observe directly. Therefore, the wall superheat can be calculated by the temperature of the tube wall, which reflects the boiling state in the tube from the side. The calculation process of the wall superheat is:

[0051] The wall superheat of the heat exchanger at the current moment ΔT sat The expression is: ΔT sat =norm(T w -T sat );where ΔT sat Indicates the wall superheat of the heat exchanger at the current moment; T w Indicates the temperature data of the heat exchanger tube wall at the current moment; T sat It represents the saturation temperature of the liquid in the heat exchanger tube at the standard atmospheric pressure at the current moment; norm() represents the normalization function.

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

[0053] According to 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 the liquid undergoes a phase change under a specific pressure. During the boiling process in the tube, the saturation temperature determines whether the liquid will boil and the intensity of the boiling. If the wall temperature is higher than the saturation temperature, boiling will occur near the wall. The size of the wall superheat will affect the generation, growth and detachment of bubbles, and thus affect the efficiency and state of boiling heat exchange.

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

[0055] Step S3: The superheat index of the heat exchanger at the current moment is determined by comprehensively considering the heat flux density at the current moment, the size of the heat exchanger tube and the wall superheat, and the boiling intensity index of the liquid in the heat exchanger tube at the current moment is determined in combination with the heat absorbed when the liquid in the heat exchanger tube evaporates.

[0056] In the nucleate boiling stage, the wall superheat usually has a certain range, but when approaching transition boiling, the wall superheat will begin to fluctuate and may rise rapidly. Therefore, it is difficult to accurately judge whether the boiling is in the early stage of transition boiling or about to enter film boiling by relying solely on the wall superheat. Due to factors such as pressure fluctuations, the wall superheat may fluctuate misleadingly and cannot accurately reflect the actual changes in the boiling state.

[0057] Therefore, it is necessary to further calculate the boiling intensity index in combination with the heat flux density and the vaporization characteristics of the liquid to characterize the boiling state in 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 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;

[0059] The expression of the boiling intensity index B of the liquid in the heat exchanger tube at the current moment is: Where C represents the superheat index of the heat exchanger at the current moment; ρ v 、h fg They represent the saturated steam density and latent heat of vaporization when the liquid evaporates in the heat exchanger tube under standard atmospheric pressure. It should be understood that the saturated steam density and 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 steam density is 0.5977 kg / m 3 , 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 repeated here.

[0061] In particular, when the superheat degree is avoided to be 0, the boiling intensity index B of the liquid in the heat exchanger tube at the current moment is 1.

[0062] Furthermore, according to the boiling intensity index of the liquid in the heat exchanger tube at the current moment, it can be understood that the heat flux is the energy input factor that affects boiling, the wall superheat reflects the driving temperature difference of liquid boiling, and the saturated steam density and latent heat of vaporization are related to the phase change characteristics of the liquid. In the boiling in the tube, heat is transferred to the liquid by heating the wall, so that the liquid reaches a saturated state and produces bubbles. Therefore, the degree of boiling can be quantified from the perspective of energy transfer and phase change. The greater the heat flux, the more energy is provided to the liquid, and the easier it is to produce 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 in its tube is larger, the side area and wall superheat of the heat exchanger tube are smaller, and the saturated steam density and latent heat of vaporization are smaller, then the boiling intensity index is larger, indicating that the boiling is more intense and may be in the vigorous period of nucleate boiling, with a larger heat transfer coefficient. If the exhaust temperature is appropriate at this time, it means that the flow 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 exhaust temperature being lower than the flue gas acid dew point temperature, which will damage the equipment. On the contrary, if the heat flux density between the heat exchanger and the liquid in its tube is smaller, the side area and wall superheat of the heat exchanger tube are larger, and the saturated steam density and latent heat of vaporization are larger, then the boiling intensity index is smaller, indicating that the boiling state is changing to the overboiling state, and the flow rate should be reduced to maintain nucleate boiling to 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 acquisition moment and the wall superheat, determine the heat flux difference value of the liquid in the heat exchanger tube at the current moment, and determine the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment in combination with the preset surface tension.

[0065] Frequent adjustment of the flow rate may lead to an unstable boiling state and switching between several states. The unstable boiling state may lead to problems such as overtemperature, pipeline corrosion and equipment vibration, so it is necessary to maintain the stability of the boiling state. Therefore, by analyzing the difference in heat flux density between the current moment and the previous acquisition moment, as well as the preset surface tension and the wall superheat, the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment is determined to characterize the stability of the boiling state in the heat exchanger tube, specifically:

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

[0067] The expression of the boiling stability coefficient W of the liquid in the heat exchanger tube at the current moment is: In the formula, σ represents the preset surface tension; P represents the heat flow difference value of the liquid in 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 artificially set. In this embodiment, the value of ε is 0.01. Under the premise of ensuring that the denominator is not 0 and does not excessively affect the calculation results, the implementer can also set it by himself according to the specific situation. This embodiment does not impose any special restrictions.

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

[0069] Among them, the heat flux change rate between the current moment and the previous acquisition moment is the ratio of the difference in heat flux 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 are not repeated here.

[0070] It should be understood that during the boiling process in the tube, the heat flux density may change due to external conditions (such as changes in the temperature of high-temperature flue gas) or changes in the internal boiling state (such as the transition from nucleate boiling to transition boiling). The heat flux density change rate can reflect the stability of the boiling process under dynamic conditions. At the same time, surface tension and wall superheat are also key factors that determine bubble behavior and boiling state, which 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 surface tension has a more regular effect on the bubbles, that is, the boiling state is relatively stable at this time, and the flow rate can be adjusted in the stable nucleate boiling stage. 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 and the boiling intensity index, as well as the difference between the 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 in the heat exchanger tube at the current moment, and adjust the liquid flow in 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 in the heat exchanger tube, and the flow adjustment factor is further calculated in combination with the exhaust gas temperature. The water inlet flow of the heat exchanger is adjusted according to the flow adjustment factor to maintain a larger heat transfer coefficient. Specifically:

[0074] The expression of the flow adjustment factor μ of the liquid in the heat exchanger tube at the current moment is: Wherein, 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 exhaust 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 exhaust temperature after waste heat recovery should be below 160°C, but not lower than 110°C. Therefore, in this embodiment, the preset flue gas acid dew point temperature is 110°C. On the premise of ensuring that the preset flue gas acid dew point temperature is not higher than the exhaust temperature, the implementer can also set it according to the specific situation, and this embodiment does not impose any special restrictions.

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

[0077] Before the current moment, a neighborhood is divided with the current moment as the center, and according to the method for obtaining the flow adjustment factor of the liquid in the heat exchanger tube at the current moment, the flow adjustment factor of the liquid in the heat exchanger tube at all the acquisition moments in the neighborhood of the current moment is obtained before the current moment;

[0078] If the flow adjustment factor of the liquid in the heat exchanger tube at all sampling moments in the neighborhood is greater than the preset value, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is adjusted. The adjustment process is: among all sampling moments in the neighborhood of the current moment, if the temperature data of the heat exchanger tube wall at the sampling moment farthest from the current moment is greater than or equal to the temperature data of the heat exchanger tube wall at the current moment, then in the heat exchanger at the current moment, the preset proportion of liquid flow is increased, otherwise, the preset proportion of liquid flow is reduced.

[0079] On the contrary, among all the neighboring collection moments of the current moment, if the flow factor of the liquid in the heat exchanger tube at any collection moment is less than or equal to the preset value, the liquid flow in the heat exchanger tube at the current moment is not adjusted.

[0080] It should be noted that the neighborhood, preset value and preset ratio at the current moment are all set manually. In this embodiment, the neighborhood size is 3, the preset value is 0.5, and the preset ratio is 5%. The implementer can also set them according to the specific situation. This embodiment does not impose any special restrictions.

[0081] Accurate flow adjustment can ensure that the boiling in the heat exchanger tube is always in an ideal state. When the boiling intensity is insufficient, the water flow rate is appropriately reduced to allow the liquid to have more time to absorb heat in the tube, promote the continuous nucleate boiling, and thus improve the heat exchange efficiency. When the boiling stability is threatened, the flow rate is adjusted in a timely and reasonable manner to restore stable nucleate boiling to avoid the reduction of heat exchange efficiency due to the deterioration of the boiling state. At the same time, the exhaust gas temperature is reduced and not lower than the flue gas acid dew point temperature, which ensures the efficient operation of the cold and hot circulation system and improves the efficiency of energy-saving transformation of industrial furnaces.

[0082] Preferably, the flow adjustment factor acquisition process diagram provided in this embodiment is as follows: Figure 2 shown.

[0083] Based on the same inventive concept as the above method, an embodiment of the present application also provides an efficient operation system for a cold and hot circulation system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor implements the steps of any one of the above-mentioned methods for efficient operation of a cold and hot circulation system when executing the computer program.

[0084] It should be noted that the above sequence of the embodiments of the present application is for description only and does not represent the advantages and disadvantages of the embodiments. The above is a description of a specific embodiment of this specification. In addition, the processes depicted in the accompanying 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] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0086] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for efficiently operating a cold and hot circulation system, characterized in that: The efficient operation method of the cold and hot circulation system is realized by the efficient operation system of the cold and hot circulation system, and the efficient operation system of the cold and hot circulation system includes an industrial furnace and a cold and hot circulation system, a heat exchanger in the cold and hot circulation system is connected with the industrial furnace and receives the high-temperature exhaust gas generated by the industrial furnace, and the heat of the high-temperature exhaust gas is transferred to the low-temperature liquid in the heat exchanger through the wall surface of the heat exchanger, and the low-temperature liquid is heated, and the heated liquid is used again for industrial furnace production, and the efficient operation method of the cold and hot circulation system includes the following steps: Obtain the heat flux density between the heat exchanger tube wall and the liquid in the tube at the current moment and at each previous acquisition moment, the temperature data of the heat exchanger tube wall and the exhaust gas temperature at the outlet, and the liquid flow rate in the heat exchanger tube at the current moment; Analyze the difference between the temperature data at the current moment and the saturation temperature of the liquid in the heat exchanger tube to determine the wall superheat of the heat exchanger at the current moment; The superheat index of the heat exchanger at the current moment is determined by comprehensively considering the heat flux density at the current moment, the size of the heat exchanger tube and the wall superheat, and the boiling intensity index of the liquid in the heat exchanger tube at the current moment is determined by combining the heat absorbed by the liquid in the heat exchanger tube when evaporating; Based on the difference in heat flux density between the current moment and the previous acquisition moment and the wall superheat, the heat flux difference value of the liquid in the heat exchanger tube at the current moment is determined, and combined with the preset surface tension, the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment is determined; Based on the boiling stability coefficient and boiling intensity index, as well as the difference between the exhaust temperature of the heat exchanger at the current moment and the preset flue gas acid dew point temperature, the flow adjustment factor of the liquid in the heat exchanger tube at the current moment is determined, and the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is adjusted.

2. A high-efficiency operation method of a cold and hot circulation system as claimed in claim 1, characterized in that: The wall superheat of the heat exchanger at the current moment: ΔT sat =norm(T w -T sat );where ΔT sat Indicates the wall superheat of the heat exchanger at the current moment; T w Indicates the temperature data of the heat exchanger tube wall at the current moment; T sat It represents the saturation temperature of the liquid in the heat exchanger tube at the standard atmospheric pressure at the current moment; norm() represents the normalization function.

3. The high-efficiency operation method of a cold and hot circulation system according to claim 1, characterized in that: The method for determining the superheat index of the heat exchanger at the current moment is: The product of the lateral area of ​​the heat exchanger tube and the wall superheat of the heat exchanger at the current moment is calculated, and the ratio of the heat flux density of the heat exchanger at the current moment to the product is used as the superheat index of the heat exchanger at the current moment.

4. The high-efficiency operation method of a cold and hot circulation system according to claim 1, characterized in that: The expression of the boiling intensity index of the liquid in the heat exchanger tube at the current moment is: In the formula, B represents the boiling intensity index of the liquid in 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 They respectively represent the saturated steam density and latent heat of vaporization when the liquid evaporates in the heat exchanger tube under standard atmospheric pressure.

5. The high-efficiency operation method of a cold and hot circulation system according to claim 1, characterized in that: The method for determining the heat flow difference value of the liquid in the heat exchanger tube at the current moment is: The change rate of the heat flux density between the current moment and the previous acquisition moment is calculated, and the product of the change rate and the wall superheat at the current moment is taken as the heat flux difference value of the liquid in the heat exchanger tube at the current moment.

6. A high-efficiency operation method for a cold and hot cycle system as claimed in claim 1, characterized in that: The expression of the boiling stability coefficient of the liquid in the heat exchanger tube at the current moment is: Wherein, 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 flow difference value of the liquid in the heat exchanger tube at the current moment; ε represents a preset constant greater than 0.

7. A high-efficiency operation method for a cold and hot circulation system as claimed in claim 1, characterized in that: The expression of the flow adjustment factor of the liquid in the heat exchanger tube at the current moment is: In the formula, μ represents the flow 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 exhaust gas temperature at the current moment; T0 represents the preset flue gas acid dew point temperature; norm() represents the normalization function.

8. A high-efficiency operation method for a cold and hot circulation system as claimed in claim 1, characterized in that: The adjusting of the liquid flow in the heat exchanger tube of the cold and hot circulation system at the current moment includes: According to the method for obtaining the flow adjustment factor of the liquid in the heat exchanger tube at the current moment, before the current moment, the flow adjustment factor of the liquid in the heat exchanger tube at all the collection moments in the neighborhood of the current moment is obtained; If the flow adjustment factors of the liquid in the heat exchanger tube at all collection moments in the neighborhood are greater than the preset value, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is adjusted; otherwise, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is not adjusted.

9. A high-efficiency operation method for a cold and hot circulation system as claimed in claim 8, characterized in that: If the flow adjustment factor of the liquid in the heat exchanger tube at all the collection moments in the neighborhood is greater than the preset value, the liquid flow in the heat exchanger tube in the cold and hot circulation system at the current moment is adjusted, further comprising: Among all the collection moments in the neighborhood of the current moment, if the temperature data of the heat exchanger tube wall at the collection moment farthest from the current moment is greater than or equal to the temperature data of the heat exchanger tube wall at the current moment, then in the heat exchanger at the current moment, the liquid flow rate is increased by a preset proportion, otherwise, the liquid flow rate is reduced by a preset proportion.

10. An efficient operation system of a cold and hot circulation 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, the steps of the efficient operation method of the cold and hot circulation system as described in any one of claims 1-9 are implemented.

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