CN118031881A - Dust deposit thickness layering on-line monitoring method of rotary air preheater - Google Patents
Dust deposit thickness layering on-line monitoring method of rotary air preheater Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 40
- 238000012544 monitoring process Methods 0.000 title claims abstract description 25
- 239000000428 dust Substances 0.000 title claims description 21
- 239000012530 fluid Substances 0.000 claims abstract description 55
- 239000002184 metal Substances 0.000 claims abstract description 44
- 229910052751 metal Inorganic materials 0.000 claims abstract description 44
- 230000008021 deposition Effects 0.000 claims description 29
- 238000012546 transfer Methods 0.000 claims description 17
- 239000004071 soot Substances 0.000 claims description 16
- 238000009825 accumulation Methods 0.000 claims description 10
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000011144 upstream manufacturing Methods 0.000 claims description 5
- 230000000694 effects Effects 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 3
- 239000000779 smoke Substances 0.000 claims description 3
- 239000007787 solid Substances 0.000 claims description 3
- 239000002956 ash Substances 0.000 abstract description 50
- 238000004364 calculation method Methods 0.000 abstract description 14
- 230000009466 transformation Effects 0.000 abstract 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 9
- 239000003546 flue gas Substances 0.000 description 9
- 238000004140 cleaning Methods 0.000 description 5
- 238000007664 blowing Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 238000005338 heat storage Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 210000003298 dental enamel Anatomy 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- TXKMVPPZCYKFAC-UHFFFAOYSA-N disulfur monoxide Inorganic materials O=S=S TXKMVPPZCYKFAC-UHFFFAOYSA-N 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000010881 fly ash Substances 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000011895 specific detection Methods 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910001868 water Inorganic materials 0.000 description 1
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L15/00—Heating of air supplied for combustion
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
- G01B21/085—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness using thermal means
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Air Supply (AREA)
Abstract
The invention discloses a layering on-line monitoring method for the thickness of deposited ash of a rotary air preheater, which is characterized in that a calculation model is built for a conventionally arranged air preheater rotor, reasonable assumption is made, the model is simplified, grids are divided, and the temperature of deposited ash, metal and fluid is synchronously calculated by using a finite difference method. And comparing the average temperature of the air side outlet obtained by each cycle iteration calculation with the measured fluid outlet temperature value, and carrying out layering correction on the assumed deposited ash thickness, thereby obtaining relatively accurate average deposited ash thickness of each layer. According to the method, no transformation is needed to be carried out on the preheater body, calculation of the accumulated ash thickness can be completed only through the conventional access point measuring point data, the accumulated ash thickness is displayed more intuitively, the number of layering and sorting is not limited, and the adaptability and the expansibility are strong.
Description
Technical Field
The invention belongs to the technical field of boiler dust deposit monitoring, and particularly relates to a dust deposit thickness layering on-line monitoring method of a rotary air preheater.
Background
In coal-fired boilers, the rotary air preheater is a heating surface device widely used for tail flue gas waste heat utilization. However, ammonia, sulfur oxide, water, fly ash and the like exist in the upstream flue gas, so that dust deposition is easy to generate on the surface of the corrugated plate in the upstream flue gas, the heat transfer efficiency of the preheater is reduced, and when the heat transfer efficiency of the preheater is severe, the channel is blocked, the fan is overloaded, and the shutdown and the maintenance are forced. When the heating surface generates accumulated ash, if the thickness distribution of the accumulated ash in the rotary air preheater can be monitored, soot blowing can be performed pertinently, and the shutdown maintenance times can be effectively reduced.
It is particularly important to accurately monitor the thickness of the deposited ash in the air preheater, and existing patents propose deposited ash monitoring solutions to the problem, but all the problems are insufficient.
In the patent ' a rotary air preheater surface area ash on-line monitoring device ', a detection rod ' is used for carrying out sectional soot blowing on the rotary air preheater from a flue gas inlet to a flue gas outlet, but a specific detection instrument used by the rotary air preheater is not described, and the arrangement method cannot obtain specific soot deposit distribution under the existing detection means, so that the accuracy is poor. The device has a complex structure, the air preheater is transversely arranged, and the heated and accumulated ash cloth is more uneven.
The patent 'method for monitoring the ash accumulation layer of the rotary air preheater based on the finite difference method' calculates the temperature of each layer in the rotor of the rotary air preheater through known temperature measuring points and assumed heat transfer coefficients, and corrects the heat transfer coefficients of each layer by comparing the measured values, thereby obtaining the heat transfer coefficients. Although the method can obtain the reduction degree of the heat transfer coefficient, the thickness condition of each laminated ash cannot be intuitively embodied, and the method is not obvious for practical application guidance.
Disclosure of Invention
Aiming at the problems, the invention provides a layering online monitoring method for the thickness of deposited ash of a rotary air preheater, which simplifies a rotor on the premise of keeping the rotor arranged vertically, establishes a calculation model, divides grids and synchronously calculates the temperature of deposited ash, metal and fluid by using a finite difference method. The thickness of the accumulated ash is assumed and corrected by comparing with the measured fluid outlet temperature value, and the method is suitable for the multi-layer multi-bin rotary air preheater.
The invention is realized by adopting the following technical scheme:
the method for monitoring the thickness of deposited ash of the rotary air preheater in a layered and on-line manner comprises the following steps:
Step one: modeling a rotor of the rotary air preheater, establishing a cylindrical coordinate system, and taking small enough sector cylinder microelements to obtain a heat transfer control volume;
Step two: in the control volume infinitesimal, three areas are divided according to the types of fluid and solid, namely a heat accumulator metal area, an ash deposition area and a fluid area;
Step three: respectively establishing a heat balance equation for the microcell inner fluid region, the heat accumulator metal region and the dust accumulation region;
Step four: dispersing and simplifying the three heat balance equations established in the third step;
Step five: inputting the rotating speed of a rotor of the three-compartment air preheater, the layered structure parameter and the compartment working condition parameter, and inputting the dust accumulation parameter;
Step six: inputting the assumed thickness distribution of each layer of ash, and substituting the thickness distribution into a corresponding equation set of each layer;
Step seven: initializing the inlet temperature of each sub-bin fluid, assigning a temperature initial value to the first layer of smoke bin heat accumulator metal and the first row of accumulated ash nodes, substituting the temperature initial value into a given boundary temperature condition, and calculating the node temperature distribution of the bin lattice by solving a metal, fluid and accumulated ash discrete equation set simultaneously;
Step eight: transmitting the node values of the bin dust and the metal temperature to the next bin in the rotation direction, sequentially calculating all bin temperature fields of the layer by combining the hypothesized inlet temperature of the next bin, and carrying out checking iteration on the temperature according to the rotation continuity until the precision requirement is met;
Step nine: transmitting the laminar flow temperature node to the next layering, calculating according to the method until the whole rotor is calculated, comparing all air side outlet temperature node calculated values with the assumed temperature, and iterating according to the deviation until the whole temperature field deviation meets the accuracy requirement;
Step ten: comparing the calculated value of the air side outlet temperature with the actually measured node, if the deviation of the calculated value and the actually measured node does not meet the accuracy requirement, returning to the seventh step to again assume the accumulated ash thickness and calculate until the calculated value meets the accuracy requirement, and outputting the temperature and the accumulated ash thickness distribution.
The invention further improves that in the second step, the method further comprises the following steps: (1) The radial temperature of the rotor is uniformly distributed, and radial heat conduction is ignored.
The invention further improves that in the second step, the method further comprises the following steps: (2) ignoring radiative heat transfer.
The invention further improves that in the second step, the method further comprises the following steps: (3) neglecting the effect of carrying out air leakage.
The invention further improves that in the second step, the method further comprises the following steps: (4) rotor inlet fluid temperature and composition are evenly distributed.
The invention is further improved in that in the third step, a heat balance equation established for the fluid region in the microcell is as follows:
Wherein: ρ g represents the fluid density, kg/m 3;ug represents the apparent velocity of the fluid, m/s; c p represents the constant pressure specific heat capacity of the fluid, J/kg.K -1;Tg represents the average temperature of the fluid, K; h represents the convection heat transfer coefficient between the fluid and the deposited ash, and W/m 2·K-1; sigma represents heat exchange area density, m 2/m3;Ta represents accumulated ash average temperature, K; z denotes the rotor axis direction.
The invention is further improved in that in the third step, a heat balance equation established for the metal region of the heat accumulator in the infinitesimal is as follows:
Wherein ρ m represents a metal conversion density, kg/m 3; omega represents the revolution speed of the heat accumulator and rad/s; c m represents the constant pressure specific heat capacity of the metal, J/kg.K -1;Tm represents the average temperature of the metal, K; lambda m represents the metal heat conductivity W/m.K -1; ; Representing porosity without regard to the volume of soot; lambda a represents the ash deposition heat conductivity coefficient W/m.K -1;δa represents the average ash deposition thickness; θ represents the rotor circumferential direction.
The invention is further improved in that in the third step, a heat balance equation established for the dust accumulation area in the infinitesimal is as follows:
Wherein ρ m represents the deposition conversion density, kg/m 3;Ca represents the deposition constant pressure specific heat capacity, and J/kg.K -1;Ta represents the metal average temperature, K; the left side of the equation represents the energy increase of the accumulated ash, the first term on the right side represents the heat exchange with the fluid, and the second term represents the heat exchange with the heat accumulator metal.
The invention further improves that in the fourth step, three heat balance equations established in the third step are discretized and simplified into:
AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (4)
wherein i=1, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (5)
Where i=2, 3, …, k, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BmTm,i,j-1/2＝0 (6)
wherein i=k, j=1, 2, …, l;
Ta,i,j+1/2+Ta,i,j-1/2＝Ca,nTg,i-1/2,j+Ca,sTg,i+1/2,j (7)
Where i=1, 2, …, k, j=1, 2, …, l; wherein An,As,Ann,Ass,Ban,Ba,Bas,Bm,Ca,n,Ca,s are equation coefficients; taking the grid of the ith row and the jth column as a central grid, in the subscript of the post-discretization T g, i+1/2 represents a central grid fluid outlet node, i-1/2 represents a central grid fluid inlet node, i+3/2 represents a downstream adjacent grid fluid outlet node, i-3/2 represents an upstream adjacent grid fluid inlet node, and the ordinate j represents the central grid ordinate; in the subscripts of the discrete T a and T m, i represents the abscissa of the central grid, j+1/2 represents the central grid rotation outlet deposition node and the metal node, and j-1/2 represents the central grid rotation inlet deposition node and the metal node.
The invention has at least the following beneficial technical effects:
1. The model and the algorithm adopted by the invention are suitable for soft measurement and monitoring of the dust accumulation thickness of the multi-layer multi-bin rotary air preheater; the method takes different layers and different bin numbers as variable input parameters, and is applicable and high in expansibility if the number is increased or decreased; the partial air preheater aims at reducing air leakage or dust deposit, the air preheater is modified, a quarter-bin or five-bin rotary air preheater is formed, namely the number of the sub-bins is more than 3, the partial air preheater is used for reducing cold end corrosion, a plurality of layers of heat storage elements are arranged, and most of the cold end elements are corrosion-resistant enamel plating elements, namely the number of layers is more than 1; for two cases, the calculation method ensures that the number of layers and the number of bins do not influence calculation convergence by means of independent assignment of the transmission temperature and each bin, and has wide adaptability;
2. The model and algorithm adopted by the invention can directly obtain the thickness of the deposited ash, and are more visual than indirect variables such as cleaning factors adopted in other documents and patents; in the disclosed dust accumulation monitoring method, the dust accumulation degree is indirectly reflected by adopting a cleaning factor, and the definition of the cleaning factor is mainly based on the dimensionless number of the inlet and outlet temperature, pressure or heat transfer coefficient of the air preheater; although the cleaning factor can reflect the ash deposition degree, the direct connection between the data such as the inlet temperature and the ash deposition related parameters is not described; for example, the corresponding relation between the heat transfer coefficient and the deposited ash thickness cannot be quantified, and the method can directly obtain the specific deposited ash thickness, so that guidance on operators is more visual, and the soot blowing efficiency is improved.
3. The model and the algorithm adopted by the invention are suitable for online monitoring of the dust deposit of any conventionally arranged rotary air preheater, and no special detecting device is needed to be added; the method disclosed in some published patents and documents needs to carry out complex reconstruction work such as adding a detection rod, measuring points at special positions and the like when the method is realized, but the method does not need to carry out any reconstruction, only needs to acquire measuring point data such as inlet and outlet temperature, pressure, flow measuring points and the like which are all arranged on a conventional air preheater, and completes calculation and monitoring of the dust deposit thickness on a computing platform, so that the operation of the air preheater is not influenced and the method is economical.
Drawings
Fig. 1 is a control volume diagram of a rotor according to the present invention.
FIG. 2 is a flow chart of the calculation according to the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
As shown in fig. 2, the method for monitoring the deposition thickness of the rotary air preheater in a layering manner comprises the following steps:
Step one: modeling a rotary air preheater rotor, establishing a cylindrical coordinate system, and taking small enough sector cylinder microelements to obtain a heat transfer control volume, as shown in figure 1.
Step two: in the control volume infinitesimal, three areas are divided according to the types of fluid and solid, namely a heat accumulator metal area, an ash deposition area and a fluid area. The following assumptions are made to facilitate the solution: (1) The radial temperature of the rotor is uniformly distributed, and radial heat conduction is ignored; (2) ignoring radiative heat transfer; (3) neglecting carry over wind leakage effects; (4) rotor inlet fluid temperature and composition are evenly distributed. The heat balance equation is established for the fluid region within the microcell as follows:
Wherein: ρ g represents the fluid density, kg/m 3;ug represents the apparent velocity of the fluid, m/s; c p represents the constant pressure specific heat capacity of the fluid, J/kg.K -1;Tg represents the average temperature of the fluid, K; h represents the convection heat transfer coefficient between the fluid and the deposited ash, and W/m 2·K-1; sigma represents heat exchange area density, m 2/m3;Ta represents accumulated ash average temperature, K; z denotes the rotor axis direction. The heat balance equation is established for the heat accumulator metal area in the infinitesimal as follows:
Wherein ρ m represents a metal conversion density, kg/m 3; omega represents the revolution speed of the heat accumulator and rad/s; c m represents the constant pressure specific heat capacity of the metal, J/kg.K -1;Tm represents the average temperature of the metal, K; lambda m represents the metal heat conductivity W/m.K -1; Representing porosity without regard to the volume of soot; lambda a represents the ash deposition heat conductivity coefficient W/m.K -1;δa represents the average ash deposition thickness; θ represents that the rotor circumferential direction establishes a heat balance equation for the infinitesimal gray deposition area as follows:
Wherein ρ m represents the deposition conversion density, kg/m 3;Ca represents the deposition constant pressure specific heat capacity, and J/kg.K -1;Ta represents the metal average temperature, K. The left side of the equation represents the energy increase of the accumulated ash, the first term on the right side represents the heat exchange with the fluid, and the second term represents the heat exchange with the heat accumulator metal.
Step three: the equation is discretized and reduced to:
AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (4)
wherein i=1, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (5)
Where i=2, 3, …, k, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BmTm,i,j-1/2＝0 (6)
wherein i=k, j=1, 2, …, l;
Ta,i,j+1/2+Ta,i,j-1/2＝Ca,nTg,i-1/2,j+Ca,sTg,i+1/2,j (7)
Where i=1, 2, …, k, j=1, 2, …, l; wherein An,As,Ann,Ass,Ban,Ba,Bas,Bm,Ca,n,Ca,s are equation coefficients. Taking the grid of the ith row and the jth column as a central grid, in the subscript of the post-discretization T g, i+1/2 represents a central grid fluid outlet node, i-1/2 represents a central grid fluid inlet node, i+3/2 represents a downstream adjacent grid fluid outlet node, i-3/2 represents an upstream adjacent grid fluid inlet node, and the ordinate j represents the central grid ordinate; in the subscripts of the discrete T a and T m, i represents the abscissa of the central grid, j+1/2 represents the central grid rotation outlet deposition node and the metal node, and j-1/2 represents the central grid rotation inlet deposition node and the metal node.
Step four: inputting the rotating speed of a rotor of the three-compartment air preheater, the layered structure parameter and the compartment working condition parameter, and inputting the dust accumulation parameter;
Step five: the assumed thickness distribution of each layer of the layer ash is input and substituted into the corresponding layer equation set.
Step six: initializing the inlet temperature of each sub-bin fluid, assigning a temperature initial value to the first layer of smoke bin heat accumulator metal and the first row of accumulated ash nodes, substituting the temperature initial value into a given boundary temperature condition, and calculating the node temperature distribution of the bin lattice by solving a metal, fluid and accumulated ash discrete equation set simultaneously;
Step seven: transmitting the node values of the bin dust and the metal temperature to the next bin in the rotation direction, sequentially calculating all bin temperature fields of the layer by combining the hypothesized inlet temperature of the next bin, and carrying out checking iteration on the temperature according to the rotation continuity until the precision requirement is met;
Step eight: and transmitting the laminar flow temperature node to the next layering, calculating according to the method until the whole rotor is calculated, comparing all air side outlet temperature node calculated values with the assumed temperature, and iterating according to the deviation until the deviation of the whole temperature field meets the accuracy requirement.
Step nine: comparing the calculated value of the air side outlet temperature with the actually measured node, if the deviation of the calculated value and the actually measured node does not meet the accuracy requirement, returning to the seventh step to again assume the accumulated ash thickness and calculate until the calculated value meets the accuracy requirement, and outputting the temperature and the accumulated ash thickness distribution.
Examples
Taking an example of an air preheater in operation of a coal-fired power plant, the model and algorithm of the invention are used for carrying out soft measurement on the dust deposit thickness.
The diameter of the rotor of the preheater is 10900mm, the heat storage elements are divided into cold and hot sections and different heat storage element plate types are adopted, wherein the height of a hot section is 1140mm, the plate thickness is 0.5mm, the height of a cold section is 950mm, and the plate thickness is 1.05mm. The altitude of the area where the power plant is located is 1520m, and the reference rotating speed of the rotor is 1r/min. The air preheater is of a three-compartment structure and comprises a flue gas compartment, a primary air compartment and a secondary air compartment. The nominal bin division angle of the flue gas bin is 180 degrees, the nominal bin division angle of the primary air bin is 27.18 degrees, the nominal bin division angle of the secondary air bin is 131.25 degrees, and the sealing angles of the three bins are all 15 degrees.
According to the calculation flow, the structural parameters of the air preheater are input into an algorithm, and then the working condition parameters are set. In the embodiment, the temperature of the flue gas at the inlet of the flue gas bin is 355 ℃, and the flow rate is 702000kg/h; the temperature of the air at the inlet of the primary air bin is 27.18 ℃, and the flow rate of the air is 291509kg/h; the temperature of the air at the inlet of the secondary air bin is 15.7 ℃, and the flow rate of the air is 402408kg/h. And inputting the working condition parameters into an algorithm, and performing iterative calculation. Before calculation, the ash density, the heat conductivity coefficient and the heat capacity are respectively set to 1200kg/m 3,0.117W/m·K-1 and 250J/kg.K -1 according to the running conditions and the coal quality parameters.
Firstly, assuming that the thickness of deposited ash is 0, namely the rotor of the air preheater is in a clean state, inputting the boundary temperature of an inlet, and solving a discrete equation set of fluid, metal and deposited ash for each bin to obtain a converged overall temperature field. The air side outlet average temperature was calculated at this time to be 305.2 ℃. Meanwhile, the measured average temperature of the air side of the air preheater at the moment is 300.9 ℃, which is smaller than the calculated temperature, namely the air temperature increasing amount is smaller than the cleaning state, which shows that the actual heat exchange amount is lower, the heat exchange performance is poorer, namely the actual accumulated ash thickness is not 0. At this time, the soot thickness is increased according to the set step length, which is set here by way of example to 0.05mm. After multiple times of circulation, the average calculated temperature of the air side outlet is 310.2 ℃, and the iteration deviation meets the precision requirement under the assumption that the iteration maximum error is 0.5 ℃, and the thickness of the accumulated ash is 0.25mm. Therefore, according to the working condition and the actual measurement parameters, the average deposition thickness of the hot section and the cold section is monitored to be 0.25mm. According to the method, iterative calculation is completed every 3 seconds, so that implementation monitoring of the thickness of the air preheater can be realized, the calculation period is limited to the equipment working capacity, and complete real-time monitoring can be realized theoretically without considering the calculation platform capacity.
While the invention has been described in detail in the foregoing general description and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (9)
1. The method for monitoring the thickness of deposited ash of the rotary air preheater in a layered and on-line manner is characterized by comprising the following steps of:
Step one: modeling a rotor of the rotary air preheater, establishing a cylindrical coordinate system, and taking small enough sector cylinder microelements to obtain a heat transfer control volume;
Step two: in the control volume infinitesimal, three areas are divided according to the types of fluid and solid, namely a heat accumulator metal area, an ash deposition area and a fluid area;
Step three: respectively establishing a heat balance equation for the microcell inner fluid region, the heat accumulator metal region and the dust accumulation region;
Step four: dispersing and simplifying the three heat balance equations established in the third step;
Step five: inputting the rotating speed of a rotor of the three-compartment air preheater, the layered structure parameter and the compartment working condition parameter, and inputting the dust accumulation parameter;
Step six: inputting the assumed thickness distribution of each layer of ash, and substituting the thickness distribution into a corresponding equation set of each layer;
Step seven: initializing the inlet temperature of each sub-bin fluid, assigning a temperature initial value to the first layer of smoke bin heat accumulator metal and the first row of accumulated ash nodes, substituting the temperature initial value into a given boundary temperature condition, and calculating the node temperature distribution of the bin lattice by solving a metal, fluid and accumulated ash discrete equation set simultaneously;
Step eight: transmitting the node values of the bin dust and the metal temperature to the next bin in the rotation direction, sequentially calculating all bin temperature fields of the layer by combining the hypothesized inlet temperature of the next bin, and carrying out checking iteration on the temperature according to the rotation continuity until the precision requirement is met;
Step nine: transmitting the laminar flow temperature node to the next layering, calculating according to the method until the whole rotor is calculated, comparing all air side outlet temperature node calculated values with the assumed temperature, and iterating according to the deviation until the whole temperature field deviation meets the accuracy requirement;
Step ten: comparing the calculated value of the air side outlet temperature with the actually measured node, if the deviation of the calculated value and the actually measured node does not meet the accuracy requirement, returning to the seventh step to again assume the accumulated ash thickness and calculate until the calculated value meets the accuracy requirement, and outputting the temperature and the accumulated ash thickness distribution.
2. The method for online monitoring of soot thickness of a rotary air preheater according to claim 1, wherein in step two, further comprising the following steps: (1) The radial temperature of the rotor is uniformly distributed, and radial heat conduction is ignored.
3. The method for online monitoring of soot thickness of a rotary air preheater according to claim 2, wherein in step two, further comprising the following steps: (2) ignoring radiative heat transfer.
4. The method for online monitoring of soot thickness of a rotary air preheater according to claim 3, wherein in step two, further comprising the following steps: (3) neglecting the effect of carrying out air leakage.
5. The method for online monitoring of soot thickness of a rotary air preheater according to claim 4, wherein in step two, further comprising the following steps: (4) rotor inlet fluid temperature and composition are evenly distributed.
6. The method for online monitoring of soot deposition thickness of rotary air preheater according to claim 1, wherein in step three, a heat balance equation established for the fluid region in the microcell is as follows:
Wherein: ρ g represents the fluid density, kg/m 3;ug represents the apparent velocity of the fluid, m/s; c p represents the constant pressure specific heat capacity of the fluid, J/kg.K -1;Tg represents the average temperature of the fluid, K; h represents the convection heat transfer coefficient between the fluid and the deposited ash, and W/m 2·K-1; sigma represents heat exchange area density, m 2/m3;Ta represents accumulated ash average temperature, K; z denotes the rotor axis direction.
7. The method for on-line monitoring of soot thickness of rotary air preheater as defined in claim 6, wherein in step three, the heat balance equation established for the metal region of the thermal accumulator in the microcell is as follows:
Wherein ρ m represents a metal conversion density, kg/m 3; omega represents the revolution speed of the heat accumulator and rad/s; c m represents the constant pressure specific heat capacity of the metal, J/kg.K -1;Tm represents the average temperature of the metal, K; lambda m represents the metal heat conductivity W/m.K -1; Representing porosity without regard to the volume of soot; lambda a represents the ash deposition heat conductivity coefficient W/m.K -1;δa represents the average ash deposition thickness; θ represents the rotor circumferential direction.
8. The method for online monitoring of soot thickness of rotary air preheater according to claim 7, wherein in step three, a heat balance equation is established for the soot region in the infinitesimal as follows:
Wherein ρ m represents the deposition conversion density, kg/m 3;Ca represents the deposition constant pressure specific heat capacity, and J/kg.K -1;Ta represents the metal average temperature, K; the left side of the equation represents the energy increase of the accumulated ash, the first term on the right side represents the heat exchange with the fluid, and the second term represents the heat exchange with the heat accumulator metal.
9. The method for online monitoring of the deposition thickness of the rotary air preheater according to claim 8, wherein in the fourth step, three heat balance equations established in the third step are discrete and simplified into:
AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (4)
wherein i=1, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+AssTg,i+3/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BasTa,i+1,j-1/2+BmTm,i,j-1/2＝0 (5)
Where i=2, 3, …, k, j=1, 2, …, l;
AnnTg,i-3/2,j+AnTg,i-1/2,j+AsTg,i+1/2,j+BanTa,i-1,j-1/2+BaTa,i,j-1/2+BmTm,i,j-1/2＝0 (6)
wherein i=k, j=1, 2, …, l;
Ta,i,j+1/2+Ta,i,j-1/2＝Ca,nTg,i-1/2,j+Ca,sTg,i+1/2,j (7)
Where i=1, 2, …, k, j=1, 2, …, l; wherein An,As,Ann,Ass,Ban,Ba,Bas,Bm,Ca,n,Ca,s are equation coefficients; taking the grid of the ith row and the jth column as a central grid, in the subscript of the post-discretization T g, i+1/2 represents a central grid fluid outlet node, i-1/2 represents a central grid fluid inlet node, i+3/2 represents a downstream adjacent grid fluid outlet node, i-3/2 represents an upstream adjacent grid fluid inlet node, and the ordinate j represents the central grid ordinate; in the subscripts of the discrete T a and T m, i represents the abscissa of the central grid, j+1/2 represents the central grid rotation outlet deposition node and the metal node, and j-1/2 represents the central grid rotation inlet deposition node and the metal node.
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