A spiral fin tube economizer and configuration parameter optimization method

Abstract

The present invention discloses a spiral finned tube economizer and a configuration parameter optimization method. The spiral finned tube comprises: a mother tube and fins spirally wound on the mother tube wall; the fin comprises a plurality of fin units connected end to end; the mother tube wall between two adjacent fin units is a groove structure; the axial section of the spiral finned tube is a double elliptical configuration; the axial section comprises a plurality of fin sections and a plurality of groove sections; the fin section is a fin semi-ellipse; the groove section is a mother tube semi-ellipse; the vertex of the fin semi-ellipse is the intersection of the mother tube and the fin, the long semi-axis of the fin semi-ellipse is the height of the fin, and the short semi-axis of the fin semi-ellipse is the root thickness of the fin; the vertex of the mother tube semi-ellipse is the intersection of the mother tube and the fin, the long axis of the mother tube semi-ellipse is the spacing between two adjacent fin units, and the short semi-axis of the mother tube semi-ellipse is the depth of the groove structure. The present invention can improve the anti-ashing performance, heat exchange efficiency and service life of the spiral finned tube.

Description

Technical Field

[0001] The invention relates to the technical field of economizers, and in particular to a spiral fin tube economizer and a configuration parameter optimization method. Background Art

[0002] Economizer is a device that uses the heat of the flue gas at the tail end of the boiler to heat the boiler feed water. It has significant advantages such as saving fuel, improving the working conditions of the steam drum, and reducing the cost of the boiler. It is an indispensable heat exchange device in modern boilers. At present, many types of economizers have been developed. According to the structural form, they can be divided into: smooth tube type, diaphragm tube type, H fin type, spiral fin type, etc.; according to the manufacturing method, they can be divided into: welded (high-frequency welding or brazing) fin tube type and integral fin tube (hot rolling forming) type, etc.

[0003] Economizers in power plant boilers generally have problems such as dust accumulation, low heat exchange efficiency and wear. The welding defects between the main tube and the fins of the welded economizer make the above problems particularly serious. The integral spiral fin economizer is an advantageous technology that overcomes the above problems and represents the main technical development direction in the future, and has received widespread attention. Yu Shaofang invented an integral spiral fin tube to improve the industrial heat exchange efficiency and service life; Zhu Yanmin invented an integral extruded rectangular spiral fin tube, with a rounded transition between the fin and the base tube; Huang Yuren invented a trapezoidal cross-section integral spiral fin tube, with a rounded transition between the fin and the base tube to improve self-cleaning. Xu Jie et al. conducted a detailed review of zero thermal resistance integral trapezoidal fin tubes, pointing out that the heat transfer coefficient of zero thermal resistance integral trapezoidal fin tubes is twice that of H-type fin tubes, and has better anti-dust characteristics; Guo Yi et al. conducted a comprehensive analysis and introduction of the performance of integral spiral fin tubes; Ouyang Xiaorui et al. reported the innovative application of integral spiral fin tubes in economizer renovation projects. At present, the integral spiral finned tube economizer still faces a series of technical challenges and key difficulties in engineering practice. For example, the integral spiral finned tube is the core unit of the economizer. The specific configuration of the spiral finned tube is a key factor affecting dust accumulation, service life, and heat exchange efficiency. This is also the premise of optimal design evaluation. However, the existing configuration structure is not enough to meet the application requirements, which limits the wide application of integral spiral finned tubes in the field of economizers. The anti-dust performance, heat exchange efficiency and service life of the existing configuration structure still need to be improved. Summary of the invention

[0004] Based on this, it is necessary to provide a spiral fin tube economizer with excellent comprehensive performance and a fin tube configuration parameter optimization method to improve the anti-ash deposition performance, heat exchange efficiency and service life of the spiral fin tube.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A spiral fin tube comprises: a mother tube and fins spirally wound on the mother tube wall; the fins comprise a plurality of fin units connected end to end; the mother tube wall between two adjacent fin units is a groove structure.

[0007] The axial cross-section of the spiral fin tube is a double elliptical configuration; the axial cross-section includes multiple fin cross-sections and multiple groove cross-sections; the fin cross-section is a fin semi-ellipse; the groove cross-section is a mother tube semi-ellipse; the vertex of the fin semi-ellipse is the intersection of the mother tube and the fin, the long semi-axis of the fin semi-ellipse is the height of the fin, and the short semi-axis of the fin semi-ellipse is the root thickness of the fin; the vertex of the mother tube semi-ellipse is the intersection of the mother tube and the fin, the long axis of the mother tube semi-ellipse is the spacing between two adjacent fin units, and the short semi-axis of the mother tube semi-ellipse is the depth of the groove structure.

[0008] Optionally, the spiral fin tube is integrally formed.

[0009] Optionally, the spiral fin tube is formed by spiral hot rolling.

[0010] Optionally, the vertices of the fin semi-ellipse and the mother tube semi-ellipse coincide with each other, and the slopes of the fin semi-ellipse and the mother tube semi-ellipse are the same.

[0011] The present invention also provides an economizer, comprising: a plurality of the spiral finned tubes described above; the plurality of spiral finned tubes are connected end to end in sequence through a U-shaped connecting tube to form a serpentine tube unit; one end of the serpentine tube unit is a water inlet, and the other end of the serpentine tube unit is a water outlet.

[0012] Optionally, the economizer further comprises a box body; the box body comprises an upper top plate, a lower bottom plate, a side plate and a grid plate;

[0013] The spiral fin tubes in the serpentine tube unit are arranged inside the box; the U-shaped connecting tubes in the serpentine tube unit penetrate the side plate and extend to the outside of the box; the water inlet and the water outlet of the serpentine tube unit both penetrate the side plate and extend to the outside of the box; the grille plate is arranged at the front of the box; the smoke enters the box through the grille plate, and the water inside the spiral fin tube flows from the water inlet of the serpentine tube unit to the water outlet.

[0014] Optionally, the box body also includes a double-plate guide device; the double-plate guide device includes an upper guide plate and a lower guide plate; the upper guide plate is set at the connection between the grille plate and the upper top plate through a rotating shaft; the lower guide plate is set at the connection between the grille plate and the lower bottom plate through a rotating shaft; the upper guide plate and the lower guide plate both realize circular rotation with the corresponding rotating shaft as the center of the circle to adjust the size and direction of the main airflow; under normal operating conditions, when the smoke passes through the grille plate into the box body, the upper guide plate and the lower guide plate are both perpendicular to the grille plate; under cleaning conditions, when the smoke passes through the grille plate into the box body, the upper guide plate and the lower guide plate both form a set acute angle with the grille plate.

[0015] The present invention also provides a method for optimizing the configuration parameters of a fin tube, which is used for the spiral fin tube described above; the method comprises:

[0016] A multi-index coupling evaluation criterion is constructed based on fin efficiency, flow resistance and dust accumulation characteristics;

[0017] Based on the multi-index coupling evaluation criteria, a configuration parameter optimization equation group is established according to the multivariate function extreme value;

[0018] The Newton method is used to iteratively solve the configuration parameter optimization equation group to obtain the configuration parameters of the spiral fin tube in the economizer.

[0019] Optionally, the multi-index coupling evaluation criterion is

[0020]

[0021] Among them, η is the fin efficiency, f is the flow resistance, β t is the dust accumulation coefficient, R t is the total thermal resistance at time t, α 1 is the weight factor, α 1 ∈(0.5,2),η 0 is the reference value of fin efficiency, f 0 is the reference value of flow resistance, R 0 It is the reference value of total thermal resistance.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention proposes a spiral fin tube, an economizer and a method for optimizing the configuration parameters of a fin tube. The spiral fin tube comprises: a mother tube and fins spirally wound on the mother tube wall; the fin comprises a plurality of fin units connected end to end; the mother tube wall between two adjacent fin units is a groove structure; the axial section of the spiral fin tube is a double elliptical configuration; the axial section comprises a plurality of fin sections and a plurality of groove sections; the fin section is a fin semi-elliptical; the groove section is a mother tube semi-elliptical. The spiral fin tube of the double elliptical configuration provided by the present invention has a good inhibitory effect on the deposition of dust in the horizontal flue gas on the fins, and has good anti-ashing performance; the top of the semi-elliptical fin is like a mushroom-shaped anti-wear cap, covering the upper part of the fin body, has good wear resistance, and can increase the service life; the fin body can approach the fin configuration of the optimal configuration (parabolic, triangular and trapezoidal ribs, etc.) and has good heat exchange performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 A schematic diagram of the structure of a spiral fin tube provided in an embodiment of the present invention;

[0026] Figure 2 An axial cross-sectional view of a spiral fin tube provided in an embodiment of the present invention;

[0027] Figure 3 A comparison diagram of an elliptical fin structure and a trapezoidal fin structure provided in an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the structure of an economizer provided in an embodiment of the present invention;

[0029] Figure 5 A schematic diagram of the structure of a serpentine pipe unit provided in an embodiment of the present invention;

[0030] Figure 6 A schematic diagram of the structure of a double-plate flow guide device provided in an embodiment of the present invention;

[0031] Figure 7 The coordinate system of the elliptical cross-section fin and the spiral microelement surface diagram provided by the embodiment of the present invention;

[0032] Figure 8 A dimensional diagram of an axial cross section of a spiral fin tube provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Based on the traditional evaluation indicators of heat transfer and resistance performance of spiral finned tubes, the present invention proposes a method for obtaining and describing the anti-ash deposition performance of spiral finned tubes with different configurations, develops a multi-index coupling optimization design criterion that comprehensively considers the heat transfer, resistance and ash deposition performance of spiral finned tubes with different configurations, and based on this criterion, invents a double-elliptical configuration spiral finned tube and economizer with excellent comprehensive performance.

[0036] Figure 1 A schematic diagram of the structure of a spiral fin tube provided in an embodiment of the present invention; Figure 2 An axial cross-sectional view of a spiral fin tube provided in an embodiment of the present invention.

[0037] See also Figure 1-Figure 2 The spiral fin tube provided in this embodiment includes: a mother tube 1 and fins 2 spirally wound on the mother tube wall; the fins 2 include a plurality of fin units connected end to end; the mother tube wall between two adjacent fin units is a groove structure.

[0038] The axial cross section of the spiral fin tube is a double elliptical configuration; the axial cross section includes multiple fin cross sections and multiple groove cross sections; the fin cross section is a fin semi-ellipse; the groove cross section is a mother tube semi-ellipse; the vertex of the fin semi-ellipse is the intersection of the mother tube 1 and the fin 2, the long semi-axis of the fin semi-ellipse is the height of the fin, and the short semi-axis of the fin semi-ellipse is the root thickness of the fin; the vertex of the mother tube semi-ellipse is the intersection of the mother tube 1 and the fin 2, the long axis of the mother tube semi-ellipse is the spacing between two adjacent fin units, and the short semi-axis of the mother tube semi-ellipse is the depth of the groove structure. The vertices of the fin semi-ellipse and the mother tube semi-ellipse coincide, and the slopes of the fin semi-ellipse and the mother tube semi-ellipse are the same.

[0039] The spiral fin tube is integrally formed. Specifically, the entire thick-walled steel tube can be formed into a spiral fin tube with a double elliptical configuration by spiral hot rolling. Under the condition of integral forming, welding defects and large thermal resistance are avoided, and smooth tangency between the mother tube wall and the fin connection point is achieved, which not only greatly improves the heat exchange efficiency and service life of the fin, but also has good anti-dust self-cleaning performance. The semi-elliptical smooth transition design of the mother tube wall surface between two adjacent fin units, and the short axis b1 of the semi-elliptical mother tube can achieve smooth tangency between the fin and the mother tube under the condition of taking a smaller length, which reduces the mother tube wall groove depth and mother tube wall thickness compared to direct arc transition, which is beneficial to improve heat exchange efficiency.

[0040] Under the condition of a large major axis and minor axis ratio (major axis: minor axis is about 4), the semi-elliptical fin top is like a mushroom-shaped anti-wear cap, covering the upper part of the fin body, with good wear resistance, and the fin body can approach the fins of the optimal configuration (parabolic, triangular and trapezoidal ribs, etc.) The configuration not only has good heat exchange performance, but also has better wear resistance, which can further improve the service life. In practical applications, the inner diameter of the mother tube can be 3.6cm-7.6cm, the height of the fin can be 7mm-17mm, and the spacing between two adjacent fin units can be 5mm-12mm.

[0041] The following is a comparison between the elliptical fin structure in this embodiment and the existing trapezoidal fin structure. Figure 3 As shown. The height of the elliptical fin in this embodiment is 12mm, and the short axis is 3mm. It can be connected to a trapezoid with a height of 11.31mm, an upper base of 1mm, and a lower base of 3mm. The cross-sectional size of this trapezoid is the commonly used size of the trapezoidal spiral fin tube in current engineering. The top of the fin of the elliptical fin structure in this embodiment is like a mushroom-shaped anti-wear cap, which covers the upper part of the fin body and has good wear resistance. The fin body can approach the fin configuration of the optimal configuration, which not only has good heat exchange performance, but also has better wear resistance, which can further improve the service life.

[0042] The present invention also provides a coal economizer, Figure 4 A schematic structural diagram of an economizer provided in an embodiment of the present invention.

[0043] See also Figure 4 The economizer provided in this embodiment includes: a plurality of spiral finned tubes as described above; the plurality of spiral finned tubes are connected end to end through a U-shaped connecting tube 3 to form a serpentine tube unit 15; one end of the serpentine tube unit 15 is a water inlet 4, and the other end of the serpentine tube unit 15 is a water outlet 5. The structural diagram of the serpentine tube unit is shown in FIG. Figure 5 shown.

[0044] The economizer of this embodiment also includes a box body; the box body includes an upper top plate 6, a lower bottom plate 7, a side plate 8 and a grid plate 9; the spiral finned tubes in the serpentine tube unit 15 are arranged inside the box body; the U-shaped connecting pipe 3 in the serpentine tube unit 15 penetrates the side plate 8 and extends to the outside of the box body; the water inlet 4 of the serpentine tube unit 15 penetrates the side plate 8 and extends to the outside of the box body and is connected to the inlet header 13, and the water outlet 5 penetrates the side plate 8 and extends to the outside of the box body and is connected to the outlet header 14; the grid plate 9 is arranged at the front of the box body, located at the flue gas inlet; the flue gas enters the box body through the grid plate 9, and the water inside the spiral finned tube flows from the water inlet 4 of the serpentine tube unit 15 to the water outlet 5. The side plate 8 is provided with a circular hole equal to the outer diameter of the base tube of the spiral finned tube to pass the spiral finned tube.

[0045] The box body also includes a double-plate flow guide device, the structure of which is as follows Figure 6 As shown. The double-plate guide device includes an upper guide plate 10 and a lower guide plate 11; the upper guide plate 10 is provided at the connection between the grid plate 9 and the upper top plate 6 through a rotating shaft 12; the lower guide plate 11 is provided at the connection between the grid plate 9 and the lower bottom plate 7 through a rotating shaft 12; the upper guide plate 10 and the lower guide plate 11 both realize circular rotation with the corresponding rotating shaft 12 as the center of the circle to adjust the size and direction of the main airflow; when the smoke is allowed to enter the box through the grid plate 9 for normal operation, the upper guide plate 10 and the lower guide plate 11 are both perpendicular to the grid plate 9, and when the smoke is allowed to enter the box through the grid plate 9 for cleaning operation, the upper guide plate 10 and the lower guide plate 11 are both set at an acute angle with the grid plate 9 to control the direction of the main smoke. The side length of the grid in the grid plate 9 can be 0.1-0.2 times of the flue width, and the length of the upper guide plate 10 and the lower guide plate 11 can be 0.3-0.5 times of the flue height.

[0046] See also Figure 6 During operation, the guide plate is placed horizontally, and the grid plate 9 can evenly arrange the flue gas, improve the heat exchange efficiency, and at the same time, the grid plate 9 has a certain interception and deceleration effect on dust particles, which can reduce the wear of the spiral fin tube by the airflow; and when the surface of the spiral fin tube is more dusty, the guide plate can rotate in a circle with the rotating shaft 12 as the center. When the surface of the heat exchange tube is more dusty, the relative position of the A end and the B end of the guide plate can be changed to change the direction and speed of the flue gas, so as to facilitate the upper, middle and lower dust cleaning operations. During normal operation, the grid plate 9 is used to evenly arrange the flue gas, improve the heat exchange efficiency, and at the same time, the grid plate 9 has a certain interception and deceleration effect on dust particles, which can reduce the wear of the airflow fin heat pipe.

[0047] After the flue gas passes through the grid plate 9 horizontally, it impacts the spiral fin tube horizontally, and the water inside the fin flows from top to bottom. When the flue gas enters the economizer, the flue gas temperature is approximately the same on the flue cross section, and the water flows from top to bottom, making the flue gas temperature lower in the upper part and higher in the lower part, so that the flue gas can undergo local natural convection, improving the heat exchange and anti-ashing effects.

[0048] The spiral fin tube with optimized double elliptical configuration will still have dust deposits on the fin surface under long-term operation conditions. According to the particle deposition principle, the airflow characteristics (size and direction) have an important influence on the particle deposition and removal characteristics. Therefore, when designing the economizer based on the spiral fin tube in this embodiment, a grid plate 9 is provided to achieve air distribution, and a double-plate guide device is also designed for air guidance to adjust the direction and size of the main airflow. The upper guide plate 10 and the lower guide plate 11 in the double-plate guide device are respectively fixed to the upper top plate 6 and the lower bottom plate 7 of the box body through the rotating shaft 12 near the end of the grid plate 9. The upper guide plate 10 and the lower guide plate 11 rotate in a circle with the rotating shaft 12 as the center to form inlets of different directions and sizes, so as to realize soot blowing operations such as upward blowing, middle blowing and downward blowing. When blowing upward, the opening of the lower guide plate 11 is upward (for example, the lower guide plate 11 is at an angle of 30 degrees to the grid plate 9, and the upper guide plate 10 is perpendicular to the grid plate 9 or at an angle greater than 30 degrees), and the smoke blows upward; when blowing in the middle, the openings of the upper guide plate 10 and the lower guide plate 11 are toward the middle (for example, the lower guide plate 11 is at an angle of 30 degrees to the grid plate 9, and the upper guide plate 10 is at an angle of 30 degrees to the grid plate 9), and the upper and lower airflows are small; when blowing downward, the opening of the upper guide plate 10 is downward (for example, the upper guide plate 10 is at an angle of 30 degrees to the grid plate 9, and the lower guide plate 11 is perpendicular to the grid plate 9 or at an angle greater than 30 degrees), and the middle and upper airflows are small. When operating normally, the double-plate guide device is horizontal and will not affect the grid air distribution; when dust cleaning is required, it can be achieved through the double-plate guide device.

[0049] The grid plate 9 and the double-plate flow guide device constitute an air distribution and flow guide device based on the control of the main air flow field. The mainstream flue gas evenly passes through the fin tube bundle, which can improve the heat exchange efficiency and avoid dust deposition caused by local dead zones and excessive wear of the tube bundle caused by excessive local smoke velocity. Therefore, a grid plate 9 is set at the flue gas inlet of the economizer. The grid of the grid plate 9 is relatively large, with a depth of 0.1-0.5 meters, which basically does not increase the pipeline resistance.

[0050] Based on the influence of local and main airflow control on the comprehensive performance of fin tubes, the double elliptical configuration integral spiral fin tube anti-ash deposition economizer designed in this embodiment can be used in a high-efficiency recovery device for waste heat from flue gas at the tail end of a boiler.

[0051] The above-mentioned integral spiral finned tubes with double elliptical configuration in this embodiment have excellent comprehensive performance in terms of wear resistance, dust resistance and heat exchange efficiency, but the influence of the spiral finned tube structural parameters on the comprehensive performance is obviously competitive, and there is an optimal value. For example, reducing the fin spacing can improve the fin heat exchange efficiency, but it will increase the dust accumulation. The dust accumulation will in turn increase the heat transfer resistance and reduce the heat exchange efficiency. The two compete with each other and there is an optimal value. Therefore, developing a new multi-index comprehensive evaluation criterion and optimization design method for the configuration parameters of the integral spiral finned tube is a necessary condition for optimizing the spiral finned tube and developing a new spiral finned tube economizer. At present, there is a lack of relevant design standards for integral spiral finned tube economizers. Technical indicators such as dust accumulation, slagging, wear, and heat exchange efficiency are usually coupled and related. The traditional design method based on a single technical indicator has limitations, and there is a lack of design methods and evaluation methods based on multi-index coupling. Therefore, this embodiment also establishes evaluation indicators for the integral spiral fin tube economizer based on multi-index coupling, and develops an optimization design method for the integral spiral fin tube economizer based on multi-index coupling to guide the optimization design of the specific configuration of the spiral fin tube, which has important engineering application value.

[0052] The configuration optimization design of the spiral finned tube in this example is to achieve the optimization design of the comprehensive performance of the finned tube from the perspective of local airflow control, and the main airflow characteristics also have an important influence on the comprehensive performance of the economizer. The mainstream flue gas passes through the finned tube bundle evenly, which can improve the heat exchange efficiency and avoid dust deposition caused by local dead zones and excessive wear of the tube bundle caused by excessive local smoke velocity. It is of great significance to set up a low-resistance air distribution device. The spiral finned tube with an optimized double elliptical configuration will still have dust deposits on the fin surface under long-term operation conditions. According to the particle deposition principle, the airflow characteristics (size and direction) have an important influence on the particle deposition and removal characteristics. The air guide device is set to control the size and direction of the main airflow to achieve the cleaning function and restore the heat exchange capacity of the economizer.

[0053] The parameter optimization method for the economizer provided by the present invention respectively establishes theoretical models of heat exchange efficiency, resistance, and dust accumulation of the integral spiral finned tube, and establishes a multi-index coupling evaluation criterion based on the actual competitive relationship between the three, so as to perform a multi-index comprehensive evaluation of the configuration parameters of the new integral spiral finned tube and an optimal design of the structural parameters. The parameter optimization method for the economizer specifically includes:

[0054] Step 101: construct a multi-index coupling evaluation criterion based on fin efficiency, flow resistance and dust accumulation characteristics.

[0055] Step 102: Based on the multi-index coupling evaluation criteria, a configuration parameter optimization equation group is established according to the multivariate function extreme values.

[0056] Step 103: adopting Newton's method to iteratively solve the configuration parameter optimization equation group to obtain the configuration parameters of the spiral fin tube in the economizer.

[0057] Wherein, step 101 specifically includes:

[0058] (1) Description of fin efficiency and flow resistance characteristics of spiral finned tubes

[0059] Take the double elliptical spiral fin tube as an example. Figure 7 As shown in the figure, assuming that the heat transfer coefficient of the fin tube surface is the same, the center of the fin ellipse is taken as the coordinate origin, and a one-dimensional coordinate system along the major axis is established. According to the heat transfer theory, the one-dimensional heat conduction equation in the spiral fin at one pitch can be derived:

[0060]

[0061] Where h is the surface heat transfer coefficient, k is the fin thermal conductivity, T ∞ is the fluid temperature, T is the temperature at different heights y of the spiral fin, D 1 is the outer diameter of the fin tube, a is the short semi-axis of the fin semi-ellipse, and b is the long semi-axis of the fin semi-ellipse (such as Figure 8 shown),

[0062]

[0063]

[0064] f in the heat transfer equation of other configurations of spiral finned tubes 1 and f 2 The factor can be derived based on actual conditions, where P is the distance between two adjacent fin units. The boundary conditions are:

[0065]

[0066] According to equations (1) and (4), the finite volume integration method can be used to obtain the temperature distribution inside the fin, and then the spiral fin efficiency can be obtained as:

[0067]

[0068] Among them, A c is the contact area between the fin and the mother tube on a pitch, T 0 is the root temperature, A is the area of ​​the small elliptical groove between the fins within a pitch, and the influence of the small ellipse can be ignored and calculated based on the cylindrical surface. From equation (5), it can be seen that the efficiency of the spiral fin is determined by factors such as the thermal conductivity of the material, the surface heat transfer coefficient, the tube diameter, the characteristic dimensions of the fin (major axis and minor axis), and the pitch.

[0069] The surface heat transfer coefficient h in formula (6) can be determined by an empirical formula, usually written as:

[0070] h=h(f 0 ,Pr,Re) (6)

[0071] Where Re is the Reynolds number, Pr is the Planck number, and f 0 is the resistance factor, which can be described as:

[0072] f 0 =f 0 (G,ΔP,ρ in ,ρ out ) (7)

[0073] Where G is the mass flow rate on the minimum free cross section, ΔP is the pressure drop, and ρ in and ρ out Indicates the inlet and outlet fluid density.

[0074] The heat transfer efficiency and resistance are coupled to each other and can be described in the form of functions (5), (6) and (7). A semi-empirical formula can be obtained by combining experimental and simulation verification methods.

[0075] (2) Dust accumulation feature model

[0076] The ash deposition characteristics are closely related to the fin configuration and flue gas flow characteristics. The ash deposition characteristics can be simulated by using a particle deposition model. In the normal direction of the incident surface, an energy model that considers the drag work of the particle deformation process is used as the particle deposition criterion:

[0077]

[0078] Among them, Q k is the initial incident normal kinetic energy, Q df Q is the work done by the drag force on the incident particle during its elastic-plastic collision deformation. A,a is the surface adhesion energy generated by the attraction between the incident particle and the collision surface, Q el is the elastic energy stored in the elastic deformation of the particle, Q pe is the elastic energy stored by the plastic deformation of the particle, Q p is the energy loss caused by the plastic deformation of the particles, Q A,r is the adhesion energy of the particle during the recovery phase. If the elastic energy Q stored in the first phase el +Q pe Less than the adhesion energy Q required to overcome during the recovery phase A,r , the particles will be deposited on the collision surface.

[0079] The critical incident angle model in the tangential direction of the surface is:

[0080]

[0081] θ cr is the critical angle of incidence, μ * is the friction coefficient between the particle and the surface, v is the Poisson coefficient, β is the equivalent coefficient of the contact radius of the incident particle, β=(0.143μ * ) 2 / 3 .

[0082] When the incident angle is greater than the critical collision angle, no adhesion occurs. The particle deposition characteristics can be calculated by coupling the flow field with equation (8) and (9), and the ash deposition thermal resistance can be calculated based on the particle thermal conductivity, and then the total thermal resistance can be calculated.

[0083] The total thermal resistance increases with time. Based on the thermal resistance without dust accumulation, an empirical formula for the total thermal resistance can be established.

[0084]

[0085] in, is the structural characteristic parameter vector of the fin tube (fin height, thickness, spacing, etc.), d 1 is the particle concentration in the flue gas.

[0086] Formula (10) can be used in the following specific form:

[0087]

[0088] Among them, β t is the dust accumulation coefficient, which is a function of the dust concentration in the flue gas, the Reynolds number, the fin spacing, and the fin parameters such as the ellipse length and short axis. Its expression can be fitted by combining the numerical simulation method mentioned above with the experimental numerical value. When the dust concentration and Reynolds number are the same, R t It is only affected by the fin shape and can be used for fin shape optimization. At this time, the dust accumulation growth coefficient can be expressed as:

[0089]

[0090] Among them, β 0 is the dust accumulation coefficient under reference dust concentration, Reynolds number and fin parameters, l 0 is the reference fin spacing, t is the time, t total is the total time, and the exponents m, n, q can be fitted by the numerical simulation method mentioned above combined with the experimental values.

[0091] (3) Multi-index coupling comprehensive evaluation criterion Z

[0092] The structure of the finned tube directly affects the heat transfer efficiency, resistance and dust accumulation characteristics. When the fin structure changes and promotes the heat transfer efficiency of the finned tube, the resistance will inevitably increase. When the increase in resistance is lower than the increase in heat transfer efficiency, it is effective. Reducing the fin spacing can improve the heat transfer efficiency and increase the resistance, but it will also increase the amount of dust accumulation, which will reduce the heat transfer efficiency. When the dust accumulation increases to a certain extent, it may cause the total heat transfer coefficient to decrease, and the resistance will increase instead. Therefore, it is necessary to comprehensively consider the coupled competitive relationship between heat transfer, resistance and dust accumulation, and establish a comprehensive evaluation criterion for multi-index coupling, namely:

[0093]

[0094] Among them, η is the fin efficiency, f is the flow resistance, β t is the dust accumulation coefficient, R t is the total thermal resistance at time t, α 1 is the weight factor, α 1 ∈(0.5,2),η 0 is the reference value of fin efficiency, f 0 is the reference value of flow resistance, R 0 It is the reference value of total thermal resistance.

[0095] Among them, step 102 and step 103 are specifically as follows:

[0096] After determining the coefficients in the evaluation criterion Z for a spiral fin tube of a specific configuration by combining numerical and experimental methods, the configuration parameters and flow parameters can be input to calculate the Z value for configuration evaluation.

[0097] When the flow characteristics are the same, after determining the cleaning time interval t, the partial derivatives of the optimization parameters can be used to establish the configuration parameter optimization equation group according to the evaluation criterion formula:

[0098]

[0099] Among them, g i , i=1,…,n are the configuration parameters to be optimized, n is the number of parameters to be optimized, and the nonlinear equation (14) of the unknown parameters to be optimized can be established. Equation (14) can be solved iteratively using the Newton method. Among them, the configuration parameters to be optimized include fin height, width, spacing, etc.

[0100] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0101] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A spiral fin tube, characterized in that: include: A mother tube and fins spirally wound on the mother tube wall; the fins include a plurality of fin units connected end to end; the mother tube wall between two adjacent fin units is a groove structure; The axial cross section of the spiral fin tube is a double elliptical configuration; the axial cross section includes a plurality of fin cross sections and a plurality of groove cross sections; the fin cross section is a fin semi-ellipse; the groove cross section is a mother tube semi-ellipse; the vertex of the fin semi-ellipse is the intersection of the mother tube and the fin, the long semi-axis of the fin semi-ellipse is the height of the fin, and the short semi-axis of the fin semi-ellipse is the root thickness of the fin; the vertex of the mother tube semi-ellipse is the intersection of the mother tube and the fin, the long axis of the mother tube semi-ellipse is the spacing between two adjacent fin units, and the short semi-axis of the mother tube semi-ellipse is the depth of the groove structure; the vertices of the fin semi-ellipse and the mother tube semi-ellipse coincide, and the slopes of the fin semi-ellipse and the mother tube semi-ellipse are the same; The spiral fin tube is integrally formed.

2. The spiral fin tube according to claim 1, characterized in that: The spiral fin tube is formed by spiral hot rolling.

3. A coal economizer, characterized in that: include: A plurality of spiral finned tubes as described in any one of claims 1 to 2; the plurality of spiral finned tubes are connected end to end in sequence through a U-shaped connecting tube to form a serpentine tube unit; one end of the serpentine tube unit is a water inlet, and the other end of the serpentine tube unit is a water outlet.

4. The economizer according to claim 3, characterized in that: It also includes a box body; the box body includes an upper top plate, a lower bottom plate, side plates and a grille plate; The spiral fin tubes in the serpentine tube unit are arranged inside the box; the U-shaped connecting tube in the serpentine tube unit penetrates the side plate and extends to the outside of the box; the water inlet and the water outlet of the serpentine tube unit both penetrate the side plate and extend to the outside of the box; the grille plate is arranged at the front of the box; The smoke enters the box through the grid plate, and the water inside the spiral fin tube flows from the water inlet of the serpentine tube unit to the water outlet.

5. The economizer according to claim 4, characterized in that: The box body also includes a double-plate guide device; the double-plate guide device includes an upper guide plate and a lower guide plate; the upper guide plate is set at the connection between the grille plate and the upper top plate through a rotating shaft; the lower guide plate is set at the connection between the grille plate and the lower bottom plate through a rotating shaft; the upper guide plate and the lower guide plate both realize circular rotation with the corresponding rotating shaft as the center of the circle to adjust the size and direction of the main airflow; under normal operating conditions, when the smoke passes through the grille plate into the box body, the upper guide plate and the lower guide plate are both perpendicular to the grille plate; under cleaning conditions, when the smoke passes through the grille plate into the box body, the upper guide plate and the lower guide plate are both at a set acute angle with the grille plate.

6. A method for optimizing fin tube configuration parameters, characterized in that: The method is used for the economizer according to any one of claims 3 to 5; the method comprises: A multi-index coupling evaluation criterion is constructed based on fin efficiency, flow resistance and dust accumulation characteristics; Based on the multi-index coupling evaluation criteria, a configuration parameter optimization equation group is established according to the multivariate function extreme value; The Newton method is used to iteratively solve the configuration parameter optimization equation group to obtain the configuration parameters of the spiral fin tube in the economizer.

7. A fin tube configuration parameter optimization method according to claim 6, characterized in that: The multi-index coupling evaluation criteria are: Among them, η is the fin efficiency, f is the flow resistance, β t is the dust accumulation coefficient, R t is the total thermal resistance at time t, α1 is the weight factor, α1∈(0.5,2), η0 is the reference value of fin efficiency, f0 is the reference value of flow resistance, and R0 is the reference value of total thermal resistance.

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