Method and system for calculating wall temperature of heating surface of boiler

Abstract

The invention discloses a boiler heating surface wall temperature calculation method and system, and the method comprises the steps: segmenting a boiler heating surface according to the structural characteristics, obtaining the equipment parameters and operation parameters of each pipe section, and calculating the heating surface wall temperature of each pipe section through a specific formula. According to the formula, factors such as working medium average temperature, average temperature difference, pipe section wall thickness, pipe diameter ratio, flow equalizing coefficient, steel heat conductivity coefficient, unit heat absorption average value and steam side convection heat release coefficient are comprehensively considered, so that the calculation accuracy and reliability are ensured, a reliable basis is provided for safe operation of the boiler, and the phenomenon of overheating of the pipe wall is effectively prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal power plant boilers and relates to a method and system for calculating the wall temperature of a boiler heating surface. Background Art

[0002] With the rapid development of the national economy and the acceleration of the industrialization process, thermal power units, as an important pillar of energy supply, have experienced a leap from low pressure to supercritical and even ultra-supercritical technology, significantly improving power generation efficiency and environmental performance. This process not only promotes the stable supply of electricity, but also promotes the green transformation of the power industry. However, with the continuous improvement of thermal power unit parameters and unit capacity, the energy utilization efficiency and environmental protection issues in its operation process have become increasingly prominent, especially the safe and stable operation of the boiler heating surface has become a key factor restricting the efficient, economical and environmentally friendly operation of thermal power units.

[0003] In thermal power units, water-cooled walls, superheaters, reheaters and economizers are the main heating surfaces, directly bearing the dual effects of high-temperature and high-pressure steam and high-temperature flue gas. Their operating status is directly related to the safety and economy of the entire unit. In particular, the "four-tube burst" (i.e., the burst of water-cooled walls, superheaters, reheaters and economizers) problem has become one of the most common and most influential problems in boiler accidents. According to statistics, more than 65% of boiler accidents are caused by the failure of these four major heating surfaces.

[0004] The causes of "four-tube explosion" are complex and diverse, including but not limited to material degradation, tube wall overheating, coking and ash accumulation, medium corrosion, uneven thermal stress, etc. Among them, the superheater and reheater have extremely high operating temperatures, and with the increase of boiler unit capacity and steam parameters, their layout area continues to expand, making the convective heat transfer and radiation heat transfer effects more significant, but at the same time it also aggravates the imbalance of tube wall overheating and thermal stress, becoming the main risk point for overheating and tube explosion.

[0005] In order to meet this challenge, thermal power units currently generally adopt a series of monitoring and prevention measures, such as strengthening the temperature monitoring of superheaters and reheaters, optimizing combustion adjustments to reduce coking and ash accumulation, and improving the high temperature resistance of pipes. However, these measures often sacrifice the economic efficiency of the unit and are difficult to fundamentally solve the problem of overheating and tube bursting. In particular, even if the equipment temperature is reduced by 5-15℃, it is still impossible to completely avoid the occurrence of tube wall overheating. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problem in the prior art that power plant boiler explosion (BTF) threatens the stable operation of power generation equipment, and to provide a method and system for calculating the wall temperature of a boiler heating surface.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a method for calculating the wall temperature of a boiler heating surface, comprising the following steps: The boiler heating surface is segmented according to the structural characteristics of the heating surface to obtain multiple pipe sections; Obtaining parameters of each pipe section, wherein the parameters of each pipe section include equipment parameters and operation parameters; Based on the parameters of each pipe section, the wall temperature of the heating surface of each pipe section is calculated; the wall temperature of the heating surface of each pipe section is:

[0008] in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

[0009] Further, the ratio of the outer diameter to the inner diameter of the pipe section is described as:

[0010] in, is the outer diameter of the pipe section.

[0011] Furthermore, the flow-averaging coefficient is the ratio of the actual average heat flux density on the longitudinal cross section of the pipe section to the heat flux density without the counterflow effect.

[0012] Further, the Described as:

[0013] in, is the dust pollution coefficient of the heating surface, is the flue gas temperature, is the heat release coefficient of flue gas side convection.

[0014] Further, the flue gas temperature is described as:

[0015] in, is the average flue gas temperature at the pipe section, is the smoke temperature deviation value.

[0016] Further, the average temperature of the flue gas at the pipe section is described as:

[0017] in, Indicates the smoke temperature at the pipe inlet. Indicates the smoke temperature at the pipe section outlet. Indicates the heating surface area of ​​the pipe section. H Indicates the height between the upper and lower sections of the pipe segment.

[0018] Further, the flue gas side convection heat release coefficient is described as:

[0019] in, is the heating area of ​​the pipe section, is the average convective heat transfer coefficient, is the radiation heat release coefficient.

[0020] Further, the calculation method of the radiation heat release coefficient is: For the first row of pipes in the pipe section and the last row of pipes behind the boiler, when the air chamber depth is not less than When , the radiation heat release coefficient is:

[0021] in, is the radiant heat load of the boiler, is the temperature of the dirt layer on the heated tube wall, is the working fluid flow rate; is the longitudinal pitch; When the calibration tube and the air chamber and screen arranged in front of it are separated only by condenser tubes or pipes with no more than four rows, the screen should also be considered for the radiation of the tube, and the radiation heat release coefficient is:

[0022] in, is the radiation heat release coefficient of the air chamber in front of the pipe section, is the angle coefficient of the pipe section between the furnace and the gas chamber, is the air chamber blackness; If there is only one air chamber between the calibration tube and the front screen, the radiation heat release coefficient is:

[0023] For the second row of the tube bundle, the second to third rows of staggered tubes, and all rows after the first row of screens, the radiation heat release should take into account the exposure factor, the air chamber in front of the furnace or tube, and the radiation heat release coefficient is:

[0024] in, is the exposure factor, .

[0025] Further, the current sharing coefficient is described as:

[0026] in, is the diameter of the tube, is the actual heat load at radius r, is the maximum value of heat absorption, is the bending radius.

[0027] A second aspect of the present invention provides a boiler heating surface wall temperature calculation system, comprising: Segmentation module, used to segment the boiler heating surface according to the structural characteristics of the heating surface to obtain multiple pipe sections; A data acquisition module is used to obtain parameters of each pipe section; The calculation module is used to calculate the wall temperature of the heating surface of each pipe section; the wall temperature of the heating surface of each pipe section is:

[0028] in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for calculating the wall temperature of a boiler heating surface. By finely segmenting the boiler heating surface according to structural characteristics and comprehensively considering the equipment parameters and operating parameters of each pipe section, the method can more accurately reflect the actual working conditions of each pipe section. This refined processing method effectively reduces the error caused by the overall estimation, so that the calculated wall temperature of the heating surface is closer to the true value, providing a reliable basis for the safe operation of the boiler; by introducing detailed physical models and parameters, such as average temperature difference, wall thickness, pipe diameter ratio, flow coefficient, etc., it is possible to comprehensively evaluate the thermal stress status of each pipe section, timely discover potential thermal overload risks, and provide a time window for taking preventive maintenance measures, thereby significantly improving the safety of boiler operation; in the calculation process, considering the maximum heat load that different pipe sections may bear and the average value of their unit heat absorption, the method helps to accurately design the cooling system and avoid energy waste caused by overcooling. At the same time, by accurately evaluating the wall temperature of each pipe section, it is possible to reduce dependence on high-grade alloy steel materials, reduce material costs, and improve the overall economy of the boiler unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 The block diagram of the method for calculating the wall temperature of the boiler heating surface of the present invention; Figure 2 This is the structural diagram of the platen superheater; Figure 3 The block diagram of the calculation system of the wall temperature of the heating surface of the boiler of the present invention; Figure 4 This is the flow change diagram of the header press.

[0032] Among them: 301-segmentation module; 302-data acquisition module; 303-calculation module. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention described and marked in the drawings here can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0036] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0037] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0038] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings: The present invention is a method for calculating the wall temperature of the heating surface of a boiler based on a platen superheater; see Figure 2 , is the structural diagram of the screen superheater, and its working principle is: As a key component in the boiler, the platen superheater is usually divided into four levels for design and optimization according to the characteristics of heat absorption and structural layout. First, the first stage includes the clad wall superheater, which is widely distributed in the front furnace top, rear furnace top, both sides of the horizontal flue, the rear flue wall, and the hanging pipe of the low-temperature reheater. The starting point of this stage is the saturated steam at the drum outlet, which first enters the inlet header of the ceiling superheater and then is divided.

[0040] The main steam flow (accounting for about 83.5% of the total flow under MCR conditions) travels along the front furnace top pipe and then enters the ceiling superheater. During this process, the steam flow rate is controlled at a low level (no more than 1300kg / (m²·s)) to reduce flow resistance. After completing the ceiling superheating, the steam is further distributed to three different paths: the front wall pipe of the front flue, the front and rear wall pipes of the rear flue, and the part that serves as the low-temperature reheater hanging pipe. These steam paths eventually converge at different positions in the rear flue and enter the horizontal flue and the pipes on both sides of the rear flue, and finally gather at the header at the split screen outlet.

[0041] Subsequently, the steam flows down to the inlet header of the low-temperature superheater through two rows of low-temperature superheater hanging tubes. In the low-temperature superheater, the steam flows from top to bottom, in the opposite direction of the flue gas, and is effectively heated and sent to the outlet header. After that, the steam is mixed three times and treated with primary water spraying to reduce the temperature, and is evenly divided into two paths, entering the two inlet headers of the partition screen respectively. Inside the partition screen, the steam is heated in multiple large superheater tube bundles, and then collected in the outlet header of the partition screen, and then introduced into the inlet header of the rear screen superheater through the connecting pipe.

[0042] In the rear screen superheater, the steam is further heated by 18 screens, collected in the rear screen outlet header, and undergoes the second stage of water mist cooling treatment to achieve full mixing and temperature balance of the steam. Finally, the treated steam enters the high-temperature superheater inlet header, where it is heated to the standard temperature and then transported to the high-pressure cylinder of the steam turbine through the main steam pipeline to complete its mission of heat energy conversion.

[0043] In the design of the entire heating surface system, the working fluid undergoes two important mixing processes to reduce the deviation of the steam temperature on both sides. At the same time, the configured two-stage water spray cooling device not only improves the accuracy of steam temperature regulation, but also enhances the flexibility of operation, ensuring the efficient and stable operation of the boiler system.

[0044] See also Figure 1 The present invention discloses a method for calculating the wall temperature of a boiler heating surface, comprising the following steps: S1, dividing the boiler heating surface into sections according to the structural characteristics of the heating surface to obtain multiple pipe sections; S2, obtaining parameters of each pipe section; S3, calculate the wall temperature of the heating surface of each pipe section; the wall temperature of the heating surface of each pipe section is:

[0045] in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

[0046] The present invention discloses a method for calculating the wall temperature of a boiler heating surface, comprising the following steps: The boiler heating surface is segmented according to the structural characteristics of the heating surface to obtain multiple pipe sections; the boiler heating surface is segmented according to the structural characteristics of the heating surface, usually multiple pipe sections are obtained, and these pipe sections are classified according to their positions, functions and heating characteristics. The present invention divides the pipes of the heating surface into six types: intermediate pipes, end pipes, hanging pipes, pipes close to the side of the pipe fitting (close to the pipeline), pipes with different adjacent pipes on both sides, and the first row of pipes.

[0047] The middle tube is located in the middle of the heating surface and usually bears a relatively uniform heat load and fluid flow. The terminal tube is located at the end or edge of the heating surface and may be affected by a relatively uneven heat load or fluid flow. The suspended tube (or suspended tube) is a tube fixed by a suspension device (such as a hanger or bracket). It is not in direct contact with other tubes and mainly plays a supporting and fixing role. The tube close to the side of the pipe fitting (close to the pipeline) is a tube arranged close to the side of the pipe fitting (such as a header or a manifold), and usually has a direct heat transfer and fluid flow relationship with the pipe fitting. The different adjacent tubes on both sides (special-shaped tube group) are tube combinations in which the adjacent tubes on both sides are different in material, diameter, arrangement, etc. The first row of tubes usually refers to the row of tubes located at the front end of the heating surface or closest to the heat source (such as flame or high-temperature flue gas).

[0048] S2, obtaining parameters of each pipe section; S3, calculating the wall temperature of the heating surface of each pipe section based on the parameters of each pipe section; the wall temperature of the heating surface of each pipe section is:

[0049] in, It is the average temperature of the working fluid at the cross section of the pipe section, which is obtained by fluid thermodynamic calculation or measurement; is the mean temperature difference; is the wall thickness of the pipe section, obtained through design specifications or measurement; is the ratio of the outer diameter to the inner diameter of the pipe section, , is the outer diameter of the pipe section; is the steam side convection heat release coefficient, which is related to the steam flow rate, temperature and tube wall surface characteristics and is obtained by thermal calculation; is the current sharing coefficient, , where is the diameter of the tube, is the actual heat load at radius r, is the maximum value of heat absorption; is the bending radius; is the thermal conductivity of the steel used for the pipe wall at the pipe section, which is determined by the material properties and obtained from the material data sheet; is the average unit heat absorption of the tube with the highest heat load, ; is the dust pollution coefficient of the heating surface, obtained by thermal calculation; is the flue gas temperature, , is the average flue gas temperature at the pipe section, is the smoke temperature deviation value; , Indicates the smoke temperature at the pipe inlet. Indicates the smoke temperature at the pipe section outlet. Indicates the heating surface area of ​​the pipe section. H Indicates the height between the upper and lower sections of the pipe segment.

[0050] is the heat release coefficient of flue gas side convection; ; is the heating area of ​​the pipe section, is the average convective heat transfer coefficient, is the radiation heat release coefficient. The calculation method of the radiation heat release coefficient is: For the first row of tubes and the last row of tubes behind the furnace or gas chamber, the depth of the gas chamber is not less than When , the radiation heat release coefficient is:

[0051] in, is the radiant heat load of the boiler, is the temperature of the dirt layer on the heated tube wall, is the working fluid flow rate; is the longitudinal pitch; When the calibration tube and the air chamber and screen arranged in front of it are separated only by condenser tubes or pipes with no more than four rows, the screen should also be considered for the radiation of the tube, and the radiation heat release coefficient is:

[0052] in, is the radiation heat release coefficient of the air chamber in front of the pipe section, is the angle coefficient of the pipe section between the furnace and the gas chamber, is the air chamber blackness; If there is only one air chamber between the calibration tube and the front screen, the radiation heat release coefficient is:

[0053] When the radiation heat release factor is taken into account for the exposure factor, the air chamber in front of the furnace or the tube for the second row of the tube bundle, the second to third rows of staggered tubes, and all rows after the first row of screens, the radiation heat release factor is:

[0054] in, ; φ is the exposure factor of the boiler tube that constitutes the maximum heat load selected according to the thermal calculation standard.

[0055] The present invention adopts the above method to screen type See also Figure 3 The present invention discloses a boiler heating surface wall temperature calculation system, comprising: Segmentation module 301, used to segment the boiler heating surface according to the structural characteristics of the heating surface to obtain multiple pipe segments; The data acquisition module 302 is used to obtain the parameters of each pipe section; The calculation module 303 is used to calculate the wall temperature of the heating surface of each pipe section; the wall temperature of the heating surface of each pipe section is:

[0056] in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

[0057] The present invention is based on the above method, the coal type received basic analysis table, pipeline metal property parameters, standard flue gas property parameters and thermal calculation parameters, etc.; the pipe section wall temperature of the boiler unit is calculated, and the calculation results are as follows: Calculation results of the outermost tube section of the high-temperature superheater:

[0058] Calculation results of the outermost tube section of the rear screen superheater:

[0059] The coal quality received basis analysis table is:

[0060] The metal physical parameters of the pipeline are:

[0061] Standard flue gas physical parameters are:

[0062] The thermal calculation parameters are:

[0063] The working process / working principle of the present invention is as follows: In boiler units, with the increasing use of high-capacity, high-parameter boilers, the widespread use of screen heating surfaces and radiation heating surfaces, and the emergence of direct-current boilers and natural circulation boilers, the wall temperature of boiler heating surfaces will increase, especially superheaters and reheaters. The wall temperature of the tube is very close to its limit temperature. At present, there are two main problems with the heating surface of the boiler unit. These problems are mainly concentrated in two aspects: one is that the heating surface frequently bursts due to overheating, endangering the safe operation of the unit; the other is that the high-quality flow design and high-cost alloy materials used to prevent bursting reduce the operating economy and increase the manufacturing cost. Therefore, the present invention is designed by taking into account the thermal non-uniformity and flow distribution unevenness during the operation of the boiler; its principle is as follows: Uneven traffic distribution: In the heating surface system of high-temperature boilers, superheated steam is used as the flow medium in the pipeline, and its flow distribution often varies significantly due to a variety of factors. These differences are mainly due to the combined effects of complex factors such as the resistance coefficient of the header, static pressure changes, heavy pressure head, and uneven heat absorption between pipelines.

[0064] like Figure 4 As shown, since the inlet and outlet of the heated surface pipeline are connected to the header, in the length direction of the header end, due to the unevenness of the header mass flow, header resistance coefficient, and header weight pressure head, the pipe ring pressure is different, and affects the pressure difference between the inlet and outlet of the connected pipeline, resulting in different working fluid flow rates in each pipe section, and is related to the layout of the inlet and outlet headers, that is, the lead-out, introduction method, size and material performance factors of the fluid.

[0065] When the fluid is introduced from the manifold, the dynamic pressure is very large due to the large flow introduced from the manifold side, and the static pressure is very small, causing the fluid in the manifold to be diverted to the parallel pipeline side, making the flow very small, the dynamic pressure decreases, and then the static pressure gradually increases until it reaches the highest peak at the end of the manifold; for the converging manifold, when the fluid is led out from the manifold, the fluid from the manifold merges, resulting in an increase in flow, a large dynamic pressure, and a small static pressure, until it reaches the minimum value when it is led out.

[0066] Therefore, when other conditions are the same, the pressure difference between the inlet and outlet of the pipe connected to the end of the header is the largest, and the maximum flow rate will be obtained for the layout type (Z-type layout). Since the pressure difference between the inlet and outlet of the connecting pipe is the smallest, the flow rate is the smallest, and the pipe may cause a pipe burst.

[0067] In boiler units, due to the increase in working fluid flow and the change in pipe diameter, the axial flow velocity of the working fluid in the header increases, so the static pressure difference on both sides of the header increases, resulting in increased flow unevenness. Damage to local heating surfaces, especially the reheater system, is caused because the working fluid pressure decreases, the specific volume increases, and the axial flow velocity of the fluid in the header increases, causing the header effect. The uneven flow distribution will lead to more serious damage. Uneven flow distribution not only affects the thermal efficiency of the boiler, but may also cause local heating surfaces to overheat and increase the risk of tube burst, especially in the reheater system.

[0068] Therefore, in the design process, reasonable box diameter parameters should be selected, and the Z-shaped arrangement of the inlet and outlet should be avoided. Multiple pipes should be arranged along the length of the header, and introduced or extracted evenly to reduce the static pressure changes in the header and greatly reduce the resulting uneven flow distribution.

[0069] However, uneven flow distribution may still occur, for example, flow deviation caused by fluid impact or suction phenomenon at the working fluid inlet, and in the same pipe section, the flow distribution is uneven.

[0070] The magnitude of the flow distribution unevenness depends on the difference in static pressure changes between the inlet and outlet of each pipe, and also on the resistance coefficient and heat absorption of each pipe.

[0071] It can be seen from the fluid mechanics formula that when the fluid flows through the pipe, the pressure difference between the outlet and the inlet (i.e. resistance) is proportional to the flow velocity of the fluid and the resistance coefficient of the pipe; when the pressure difference is constant, the greater the resistance coefficient of the pipe, the lower the flow rate. The resistance coefficient of the pipe is related to the radius and metal material.

[0072] High temperature heated surfaces usually use U-shaped pipe structure, so the bending angle, length and bending radius of the pipe section must be different on the same pipe. In recent years, the heating surface pipeline has increased the pipe diameter and the structure of connecting the same pipe with different pipe diameters or pipes along the length. Therefore, due to the arrangement of the pipes from the upper part of the header, the inner diameter of the pipe and the material of the flat pipe can also cause the difference in the resistance coefficient, resulting in different flow rates in the pipe.

[0073] When the pipe resistance coefficient and the pressure difference on both sides are constant, the flow rate G of the pipe is inversely proportional to the average specific volume of the fluid. The specific volume of the fluid is related to the amount of heat absorbed by the pipe. The more heat is absorbed, the larger the specific volume of the fluid is, the smaller the flow rate is, the smaller the heat absorption is, the smaller the specific volume of the fluid is, and the larger the flow rate is. The phenomenon that the flow rate of each pipe is different due to the difference in heat absorption of the pipe is called thermal effect flow deviation. In practice, due to the difference in width and heat absorption of the same heating surface, the heat flow of each pipe is different, and the flow deviation will also cause uneven flow distribution in each pipe.

[0074] Thermal Inhomogeneity: The equipment is designed and operated differently during actual operation, and the heat load of different pipes on the heating surface is very different. Therefore, the heat absorption of each pipe is very large and the heat flow is different. This phenomenon is called thermal non-uniformity. It mainly includes three aspects: thermal non-uniformity of flue width; thermal non-uniformity between heating surfaces; thermal non-uniformity along the height (or depth) of the flue.

[0075] For boiler units, U-shaped tubes are connected by heated surface tubes. The structure of this pipe section determines the difference in heat absorption between different tubes in the pipeline, and the difference is mainly reflected in the following aspects: The radiant heat in the flue space before or after the pipe is received by the heating surface is related to the position of the flue gas flow in the heating surface. The heat radiated from the furnace flue gas or the furnace to the superheater accounts for about 20-40% of the total heat absorption of the heating surface, and the convection heating surface is about 5-25%.

[0076] When the surface is heated by radiation from the furnace or the flue gas from the front screen, the angle coefficient of the tube receiving the radiation and the degree of radiation reduction are different, so the amount of heat exchange received by the heating surface of each tube section is also different.

[0077] The heating surface is usually arranged in the first row, and the longitudinal pitch S2 is smaller than the transverse pitch S1. The tubes of the heating surface of the present invention are divided into six types: intermediate tubes; end tubes; hanging tubes, with no adjacent tubes on four sides; tubes close to the side of the pipe (close to the pipeline); adjacent tubes on both sides are different and the first row of tubes.

[0078] In the heat absorption process of the heating surface, the radiant heat of the flue gas in the flue between the heating surfaces accounts for about half. The heating surface of the flue gas radiation in the screen heating surface is different. The accumulation of ash on the surface of the pipe is reduced because of the existence of the longitudinal gap. Therefore, the middle pipe can only be radiated by the flue gas between the two sides. The longitudinal spacing between the front and the back is different, resulting in the pipe being subjected to three-sided flue gas radiation. The first and last rows of pipes are exposed to the front and back flue gas space. This factor leads to an increase in the heat absorption of the outer ring pipe, the inner ring pipe and the hanging pipe, and the pipe part absorbs more flue gas radiation heat. The convective heat transfer coefficient is related to the physical properties of the flue gas and fluid, the working fluid flow rate and working fluid temperature, and is also related to the geometric shape of the pipe section (pipe section arrangement, pipe spacing and other factors), which are affected by the following three aspects: 1. The pipes can be arranged in staggered or sequential order. The flow properties of smoke when it flushes the sequential pipe section are mainly related to the relative pitch ratio. About, when When it is small, the scour of the last row of pipe sections is in the tail vortex of the front row of pipe sections; When it is large, the wake of the front pipe section has no effect on the rear pipe section.

[0079] 2. Fluid movement mode: When the fluid is in a turbulent state, convective heat transfer is stronger than laminar flow. As boilers develop to high capacity and high parameters, the flue gas flow rate on the convective heating surface of the boiler unit gradually increases, and the Reynolds number can reach 30,000-40,000. Therefore, the Reynolds number has a significant effect on convective heat transfer.

[0080] 3. The physical properties of the working fluid that affect convective heat transfer are mainly related to the density of the working fluid, the viscosity of the working fluid, the thermal conductivity of the working fluid and the specific heat capacity of the working fluid.

[0081] Most generator sets use a four-corner tangential combustion method. The main characteristics of this combustion method are: a single burner itself will not produce strong disturbances, but the inertial force of the adjacent pulverized coal gas causes the combustion torch to have a certain rotation angle and mix with the unevenly distributed flame, so that the entire furnace is used as a large burner and can burn more coal more stably. However, due to the spiral airflow in the furnace, there is still residual smoke rotation intensity at the furnace outlet, which has an adverse effect on the heat load distribution in the convection flue. Four-corner tangential combustion is to arrange the burners at the four corners of the furnace. The center line of the burner outlet is deflected at a certain angle to the diagonal line of the furnace. After the pulverized coal gas flows through the burner and enters the furnace, it produces strong rotation combustion in the imaginary tangential circle.

[0082] When the burner outlet flow is tangential to both sides of the furnace at the same time, due to the spatial asymmetry on both sides of the ejector, the pressure difference is caused by different gas supply conditions, impact extrusion and centrifugal force. The adjacent airflow causes the airflow to enter the water-cooled wall. A deflection is generated, which in turn is deflected to the center of the furnace through the jet outlet of the burner. The mutual push of the ejector thus produces a deflected jet trace, forming a "dynamic rotating tangent". The tangential circle is formed during the disturbance of the airflow, disappears as the disturbance of the airflow stops, and changes with the change of the parameters of the inlet jet, which is called "dynamic tangent". The size, shape and position of the dynamic tangential circle are determined by the balance of momentum between the jet volume, incident direction and diffusion characteristics. Under normal circumstances, the dynamic tangential circle formed by the actual airflow in the furnace is larger than the designed tangential circle.

[0083] In a four-corner tangential burner, when the injection intensity of any one or more strands is different or the swing amplitude of the burner is different, the normal airflow conditions in the furnace will be affected, especially in single corner, double corner and other operating modes. When the airflow in the furnace is normal, the uneven distribution of fuel at the burner corner will cause the combustion to be tilted. In severe cases, the wall will be coked, and the smoke temperature and smoke velocity distribution will be affected.

[0084] In addition to the combustion deflection, the rotation direction of the flue gas in the flue of the boiler has an impact on the flue gas flow. The airflow is generated in tangential combustion because the heating surface on the upper part of the boiler cannot eliminate the residual rotation of the flue gas, and the airflow speed in the flue is deviated, and due to the centrifugal force of the rotating airflow in the flue gas, when the airflow is deflected to the right, the solid particles (ash particles and unburned coal powder) are concentrated to one end of the flue, increasing the amount of flue gas at the end of the flue, and the tangential counterclockwise combustion mode, when the heating surfaces on both sides are arranged symmetrically, the deviation of the flue gas flow rate and the deviation of the heat capacity make the steam flow rate evenly distributed, and after heat exchange, there is a difference between the flue gas temperature and the steam temperature. In order to prevent the heating surface from overheating, it is necessary to design different steam flow rates on both sides, and adjust the different water spraying amounts on both sides or adjust the combustion conditions in the furnace after debugging.

[0085] In short, the existence of flue gas velocity and flue gas temperature deviations in the flue gas flow at the furnace outlet is an inherent problem of four-corner tangential combustion, but many operating factors, such as: tertiary air and operating mode, four-corner air volume and fuel volume deviations, burner four-corner operating mode and deviations in feed water and steam flow on both sides will also have an adverse effect on it.

[0086] In summary, in order to ensure the safe and efficient operation of the boiler unit, the present invention comprehensively considers the problems of thermal non-uniformity and flow distribution unevenness, and optimizes the calculation method of the heating surface wall temperature by considering parameters such as header parameters, pipeline layout and combustion conditions, so as to achieve uniform heating and flow distribution of the heating surface, reduce the risk of pipe burst, and improve the economy and reliability of the unit operation.

[0087] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the wall temperature of a boiler heating surface, characterized in that: The following steps are involved: The boiler heating surface is segmented according to the structural characteristics of the heating surface to obtain multiple pipe sections; Obtaining parameters of each pipe section, wherein the parameters of each pipe section include equipment parameters and operation parameters; Based on the parameters of each pipe section, the wall temperature of the heating surface of each pipe section is calculated; the wall temperature of the heating surface of each pipe section is: in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

2. The method for calculating the wall temperature of the boiler heating surface according to claim 1, characterized in that: The ratio of the outer diameter to the inner diameter of the pipe section is described as: in, is the outer diameter of the pipe section.

3. The method for calculating the wall temperature of the boiler heating surface according to claim 1, characterized in that: The flow-averaging coefficient is the ratio of the actual average heat flux density on the longitudinal cross section of the pipe section to the heat flux density without the counterflow effect.

4. The method for calculating the wall temperature of the boiler heating surface according to claim 1, characterized in that: Said Described as: in, is the dust pollution coefficient of the heating surface, is the flue gas temperature, is the convective heat release coefficient on the flue gas side.

5. The method for calculating the wall temperature of the boiler heating surface according to claim 4, characterized in that: The flue gas temperature is described as: in, is the average flue gas temperature at the pipe section, is the smoke temperature deviation value.

6. The method for calculating the wall temperature of the boiler heating surface according to claim 5, characterized in that: The average flue gas temperature at the pipe section is described as: in, Indicates the smoke temperature at the pipe inlet. Indicates the smoke temperature at the pipe section outlet. Indicates the heating surface area of ​​the pipe section. H Indicates the height between the upper and lower sections of the pipe segment.

7. The method for calculating the wall temperature of the boiler heating surface according to claim 4, characterized in that: The flue gas side convection heat release coefficient is described as: in, is the heating area of ​​the pipe section, is the average convective heat transfer coefficient, is the radiation heat release coefficient.

8. The method for calculating the wall temperature of the boiler heating surface according to claim 7, characterized in that: The calculation method of the radiation heat release coefficient is: For the first row of pipes in the pipe section and the last row of pipes behind the boiler, when the air chamber depth is not less than When , the radiation heat release coefficient is: in, is the radiant heat load of the boiler, is the temperature of the dust layer on the heated tube wall, is the working fluid flow rate; is the longitudinal pitch; When the calibration tube and the air chamber and screen arranged in front of it are separated only by condenser tubes or pipes with no more than four rows, the screen should also be considered for the radiation of the tube, and the radiation heat release coefficient is: in, is the radiation heat release coefficient of the air chamber in front of the pipe section, is the angle coefficient of the pipe section between the furnace and the gas chamber, is the air chamber blackness; If there is only one air chamber between the calibration tube and the front screen, the radiation heat release coefficient is: For the second row of the tube bundle, the second to third rows of staggered tubes, and all rows after the first row of screens, the radiation heat release should take into account the exposure factor, the air chamber in front of the furnace or tube, and the radiation heat release coefficient is: in, is the exposure factor, .

9. The method for calculating the wall temperature of the boiler heating surface according to claim 1, characterized in that: The current sharing coefficient is described as: in, is the diameter of the tube, is the actual heat load at radius r, is the maximum value of heat absorption, is the bending radius.

10. A boiler heating surface wall temperature calculation system, based on the boiler heating surface wall temperature calculation method according to claim 1, characterized in that: include: A segmentation module is used to segment the boiler heating surface according to the structural characteristics of the heating surface to obtain multiple pipe sections; A data acquisition module is used to obtain parameters of each pipe section; The calculation module is used to calculate the wall temperature of the heating surface of each pipe section; the wall temperature of the heating surface of each pipe section is: in, is the average temperature of the working fluid at the pipe section, is the mean temperature difference, is the wall thickness of the pipe segment, is the ratio of the outer diameter to the inner diameter of the pipe section, is the current sharing coefficient, is the thermal conductivity of the steel used for the pipe wall at the pipe section, is the average unit heat absorption of the tube with the highest heat load, is the convection heat transfer coefficient on the steam side.

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