CN111174569A - Method and system for online prediction of flue gas temperature in calcination section in rotary kiln - Google Patents
Method and system for online prediction of flue gas temperature in calcination section in rotary kiln Download PDFInfo
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- CN111174569A CN111174569A CN202010046835.6A CN202010046835A CN111174569A CN 111174569 A CN111174569 A CN 111174569A CN 202010046835 A CN202010046835 A CN 202010046835A CN 111174569 A CN111174569 A CN 111174569A
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- 239000003546 flue gas Substances 0.000 title claims abstract description 176
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title claims abstract description 136
- 238000001354 calcination Methods 0.000 title claims abstract description 80
- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000000463 material Substances 0.000 claims abstract description 54
- 238000002485 combustion reaction Methods 0.000 claims abstract description 32
- 239000007789 gas Substances 0.000 claims abstract description 12
- 239000008188 pellet Substances 0.000 claims description 51
- 239000000446 fuel Substances 0.000 claims description 22
- 238000004364 calculation method Methods 0.000 claims description 15
- 238000012795 verification Methods 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 7
- 230000017525 heat dissipation Effects 0.000 claims description 7
- 238000004088 simulation Methods 0.000 claims description 5
- 238000012546 transfer Methods 0.000 claims description 4
- 230000009286 beneficial effect Effects 0.000 abstract description 11
- 238000004519 manufacturing process Methods 0.000 abstract description 10
- 239000000779 smoke Substances 0.000 abstract description 2
- 230000008859 change Effects 0.000 description 7
- 238000005259 measurement Methods 0.000 description 6
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000009795 derivation Methods 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 239000004568 cement Substances 0.000 description 2
- 238000011960 computer-aided design Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 238000007363 ring formation reaction Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 239000007983 Tris buffer Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 238000012886 linear function Methods 0.000 description 1
- 239000003949 liquefied natural gas Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
- F27B7/20—Details, accessories or equipment specially adapted for rotary-drum furnaces
- F27B7/42—Arrangement of controlling, monitoring, alarm or like devices
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
Abstract
本发明涉及一种在线预测回转窑内煅烧段烟气温度的方法及系统，具体包括以下步骤：构建回转窑内关于Q二次风、Q燃、Q烟气、Q壁和Q物料的热量平衡模型；通过回转窑稳定工作时的参数计算出所述热平衡模型中的Q壁、Q物料和Q二次风的数值；将获得的Q壁、Q物料和Q二次风的数值代入所述步骤S1中的回转窑热量平衡模型中，获得Q燃和Q烟气之间的关系式，进而获得煅烧段烟气温度tr与窑尾烟气温度ty的关系式；测量窑尾烟气温度ty，并通过煅烧段烟气温度tr与窑尾烟气温度ty的关系式获得煅烧段烟气温度tr；所述热量平衡模型具体为：Q二次风+Q燃＝Q烟气+Q壁+Q物料。本发明的有益效果是有效预测回转窑燃烧段的温度，为回转窑的生产提供理论支撑。
The invention relates to a method and a system for online prediction of flue gas temperature in a calcination section in a rotary kiln, which specifically includes the following steps: constructing the heat balance of Q secondary air , Q combustion , Q flue gas , Q wall and Q material in the rotary kiln Model; calculate the values of Q wall , Q material and Q secondary air in the heat balance model through the parameters of the rotary kiln during stable operation; substitute the obtained values of Q wall , Q material and Q secondary air into the steps In the heat balance model of the rotary kiln in S1, the relationship between Q combustion and Q flue gas is obtained, and then the relationship between the flue gas temperature tr in the calcination section and the kiln tail flue gas temperature ty is obtained; measure the kiln tail flue gas temperature ty , and obtain the flue gas temperature tr in the calcining section through the relational expression between the flue gas temperature tr in the calcining section and the kiln tail flue gas temperature ty ; the heat balance model is specifically: Q secondary air + Q combustion = Q smoke Gas + Q wall + Q material . The beneficial effect of the invention is to effectively predict the temperature of the combustion section of the rotary kiln, and provide theoretical support for the production of the rotary kiln.
Description
Technical Field
The invention relates to the technical field of rotary kilns, in particular to a method and a system for predicting flue gas temperature of a calcining section in a rotary kiln on line.
Background
The rotary kiln is a key device widely applied to production links of cement, metallurgy and the like, and the control of the internal temperature of the rotary kiln is directly related to the stable operation, the product quality and the production cost of the whole production line. The heat released by the fuel combustion can generate a high temperature zone, generally about 1350 ℃ for the pellet rotary kiln under stable work, the temperature is a very key process parameter in production, and is directly related to the fuel consumption, the pellet quality, the emission of nitrogen oxides and barrel ring formation. However, the high-temperature flue gas temperature at the calcining section of the rotary kiln cannot be directly measured for three reasons:
1) the rotary kiln is high-temperature equipment, and the temperature of a calcining section of the lime kiln is about 1350 ℃; the temperature of the calcining section of the cement kiln is even higher than 1500 ℃; the temperature of the calcining section of the pellet rotary kiln is generally higher than 1200 ℃ and does not exceed 1400 ℃;
2) the rotary kiln is in a rotating state when working, the calcining section is positioned in the kiln, and a measuring tool is difficult to extend into the kiln;
3) the fluid in the rotary kiln is in a fast flowing state, generally about 20m/s, and even more than 50m/s at the nozzle, so that the measurement difficulty is high.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method and a system for on-line prediction of flue gas temperature of a calcining section in a rotary kiln, and aims to solve the technical problem.
The technical scheme for solving the technical problems is as follows:
a method for on-line prediction of flue gas temperature of a calcining section in a rotary kiln specifically comprises the following steps:
s1, constructing the Q in the rotary kiln according to the heat balance principle when the rotary kiln stably worksSecondary air、QBurning device、QFlue gas、QWall(s)And QMaterial(s)The heat balance model of (1);
s2, calculating Q in the heat balance model according to the parameters of the rotary kiln in stable operationWall(s)、QMaterial(s)And QSecondary airThe value of (d);
s3, mixing the Q obtained in S2Wall(s)、QMaterial(s)And QSecondary airSubstituting the value of (A) into the rotary kiln heat balance model in the step S1 to obtain QBurning deviceAnd QFlue gasThe relation between the two, and then the flue gas temperature t of the calcining section is obtainedrTemperature t of kiln tail flue gasyThe relational expression of (1);
s4, measuring the temperature t of the kiln tail flue gasyAnd passing through the flue gas temperature t of the calcination sectionrTemperature t of kiln tail flue gasyObtaining the flue gas temperature t of the calcining section by the relational expressionr；
The heat balance model specifically comprises: qSecondary air+QBurning device＝QFlue gas+QWall(s)+QMaterial(s)；
QSecondary airThe energy of the high-temperature combustion-supporting air which directly enters the rotary kiln from the ring cooling section in unit time is expressed;
Qburning deviceRepresents all heat released after the fuel sprayed by the nozzle is completely combusted in unit time;
Qflue gasThe energy of the kiln tail outlet flue gas increased relative to the normal temperature flue gas temperature in unit time is represented;
Qwall(s)The heat quantity dissipated by the wall surface of the kiln in unit time is represented;
Qmaterial(s)Means the increased energy per unit time of pellets exiting the rotary kiln after the completion of the calcination section relative to the energy entering the kiln.
The invention has the beneficial effects that: the invention provides an on-line prediction method for the flue gas temperature of a calcination section of a rotary kiln, which solves the problem that the flue gas temperature of the calcination section cannot be directly measured when the rotary kiln stably works.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the specific step of S2 includes:
s21: uniformly dividing the kiln wall of the combustion section of the rotary kiln into n sections;
s22: measuring the temperature t of each sectioniAnd surface area SiAnd the ambient temperature t corresponding to the kiln wall of the combustion section of the rotary kiln∞；
S23: measuring the temperature t of each section according to the step S22iAnd surface area SiAnd the ambient temperature t corresponding to the kiln wall of the combustion section of the rotary kiln∞Obtaining the heat dissipation Q of the kiln wall facing the external environment in unit time when the rotary kiln stably worksWall(s)。
The beneficial effect of adopting the above further scheme is that the kiln wall of the rotary kiln is equally divided into a plurality of sections, the temperature and the surface area of each section are measured, the temperature is usually measured by an infrared thermometer, so that the heat dissipation capacity of each section is calculated, the whole rotary kiln is further calculated, and the accuracy is high.
Further, in the S23, QWall(s)The calculation formula of (a) is as follows:
in the formula, h represents the convective heat transfer coefficient between the wall surface of the kiln and the external environment.
The beneficial effect of adopting above-mentioned further scheme is that through the summation of integrals calculate the heat dissipation capacity of whole rotary kiln wall when the rotary kiln steady operation, the accuracy is high.
Further, the specific step of S3 includes:
s31: measuring the mass m of finished pellets flowing out of a kiln head in unit time and the temperature t of finished pellets discharged from the kiln when the rotary kiln stably worksoutInitial temperature t of green pellets put into the kiln in unit timein；
S32: according to the mass m of finished pellets flowing out of the kiln head in unit time and the temperature t of finished pellets discharged from the kiln in the step S31outAnd the initial temperature t of green pellets entering the kiln per unit timeinObtaining the energy Q increased by the pellets before and after entering the kilnMaterial(s)。
The beneficial effect of adopting the above further scheme is that the quality of finished pellet ore flowing out of the kiln head in unit time is measured in a manner imaginable to those skilled in the art when the rotary kiln works stably, and the temperature of finished pellets discharged from the kiln and the initial temperature of green pellets entering the kiln in unit time are measured by the infrared thermometer, so that the measurement is convenient and fast.
Further, in the S32, QMaterial(s)The calculation formula of (a) is as follows:
Qmaterial(s)＝m×cm×(tout-tin)，
In the formula, cmRepresents the specific heat capacity of the pellets.
The beneficial effect of adopting the above further scheme is that the heat of the material is calculated according to each measured parameter and the heat formula.
Further, the specific steps of the steps include:
s41: measuring primary air temperature t sprayed from kiln head in unit time when rotary kiln stably works1Volume of secondary air V2And secondary air temperature t2；
S42: according to the measured primary air temperature t sprayed from the kiln head in the unit time measured in the step S421Volume of secondary air V2And secondary air temperature t2Obtaining the heat Q brought by the secondary air in unit timeSecondary air。
The beneficial effect of adopting the above further scheme is that the volume of the secondary air is calculated by the way that can be thought by the technical personnel in the field, and the primary air temperature and the secondary air temperature are measured by the infrared thermometer, so that the measurement is convenient and fast.
Further, in the S42, QSecondary airThe calculation formula of (a) is as follows:
Qsecondary air＝V2×ρ2×c2×(t2-t1)，
In the formula, ρ2Representing secondary air gas density, c2Represents the specific heat capacity of the secondary air.
The beneficial effect of adopting the further scheme is that the heat of the secondary air is calculated according to the measured parameters and the heat formula.
Further, QBurning deviceAnd QFlue gasThe relation between is (V)y-V2)×ρr×cr×(tr-t1)＝Vy×ρy×cy×(ty-t1)-Q，
In the formula, VyIs the volume (m) of the outlet flue gas of the rotary kiln in unit time3)；ρyIs the density of the outlet flue gas; c. CyIs the specific heat capacity of the outlet flue gas; t is tyIs the outlet flue gas temperature; rhorThe density of the high-temperature flue gas at the calcining section; c. CrThe specific heat capacity of the high-temperature flue gas at the calcining section; t is trIs the high temperature flue gas temperature of the calcining section.
The beneficial effect of adopting the further scheme is that Q is constant, then the heat of the fuel and the flue gas is expressed by a heat formula, a new formula is obtained, and the derivation is convenient and fast.
Further, the step of simulating the calcination section flue gas temperature t obtained in the step S3 by using a simulation is further included between the step S3 and the step S4rTemperature t of kiln tail flue gasyThe relational expression (2) is verified, and if the verification is passed, the step S4 is executed, and if the verification is not passed, the step S2 is returned to be executed.
The method has the beneficial effect that the obtained calcining section flue gas temperature t is subjected to simulationrTemperature t of kiln tail flue gasyIf the verification is passed, the step S4 is executed, and if the verification is not passed, the step S2 is executed again, so that the accuracy is greatly improved.
A system for on-line prediction of flue gas temperature of a calcining section in a rotary kiln comprises the following modules,
a heat balance model building module for building Q-value in the rotary kiln according to the heat balance principle when the rotary kiln stably worksSecondary air、QBurning device、QFlue gas、QWall(s)And QMaterial(s)The heat balance model of (1);
a model parameter calculation module for calculating Q in the heat balance model according to the parameters of the rotary kiln in stable operationWall(s)、QMaterial(s)And QSecondary airThe value of (d);
a relational expression obtaining module for obtaining QWall(s)、QMaterial(s)And QSecondary airSubstituting the numerical value into a rotary kiln heat balance model to obtain QBurning deviceAnd QFlue gasThe relation between the two, and then the flue gas temperature t of the calcining section is obtainedrTemperature t of kiln tail flue gasyThe relational expression of (1);
a calculation module for measuring the kiln tail flue gas temperature tyAnd passing through the flue gas temperature t of the calcination sectionrTemperature t of kiln tail flue gasyObtaining the flue gas temperature t of the calcining section by the relational expressionr；
The heat balance model specifically comprises: qSecondary air+QBurning device＝QFlue gas+QWall(s)+QMaterial(s)；QSecondary airThe energy of the high-temperature combustion-supporting air which directly enters the rotary kiln from the ring cooling section in unit time is expressed;
Qburning deviceRepresents all heat released after the fuel sprayed by the nozzle is completely combusted in unit time;
Qflue gasThe energy of the kiln tail outlet flue gas increased relative to the normal temperature flue gas temperature in unit time is represented;
Qwall(s)The heat quantity dissipated by the wall surface of the kiln in unit time is represented;
Qmaterial(s)Means the increased energy per unit time of pellets exiting the rotary kiln after the completion of the calcination section relative to the energy entering the kiln.
The beneficial effect of adopting above-mentioned further scheme is that the system of calcining section flue gas temperature in rotary kiln is provided to the prediction on line, can be according to the rotary kiln burning section heat balance formula fast prediction rotary kiln burning section flue gas temperature, convenient and fast.
Drawings
FIG. 1 is a flow chart of the method for on-line prediction of flue gas temperature at the calcining section in a rotary kiln according to the present invention;
FIG. 2 is a schematic view of the construction of a rotary kiln according to the present invention;
FIG. 3 shows the kiln tail flue gas temperature t in the present inventionyAnd the temperature t of the flue gas in the calcination sectionrThe relationship toggles a trend line.
Detailed Description
The principles and features of this invention are described in connection with the drawings and the detailed description of the invention, which are set forth below as examples to illustrate the invention and not to limit the scope of the invention.
As shown in fig. 1 to 3, the invention provides a method for online predicting flue gas temperature of a calcining section in a rotary kiln, which specifically comprises the following steps: s1, constructing the Q in the rotary kiln according to the heat balance principle when the rotary kiln stably worksSecondary air、QBurning device、QFlue gas、QWall(s)And QMaterial(s)The heat balance model of (1);
s2, calculating Q in the heat balance model according to the parameters of the rotary kiln in stable operationWall(s)、QMaterial(s)And QSecondary airThe value of (d);
s3, mixing the Q obtained in S2Wall(s)、QMaterial(s)And QSecondary airSubstituting the value of (A) into the rotary kiln heat balance model in the step S1 to obtain QBurning deviceAnd QFlue gasThe relation between the two, and then the flue gas temperature t of the calcining section is obtainedrTemperature t of kiln tail flue gasyThe relational expression of (1);
s4, measuring the temperature t of the kiln tail flue gasyAnd passing through the flue gas temperature t of the calcination sectionrTemperature t of kiln tail flue gasyObtaining the flue gas temperature t of the calcining section by the relational expressionr；
The heat balance model specifically comprises: qSecondary air+QBurning device＝QFlue gas+QWall(s)+QMaterial(s)；QSecondary airThe energy of the high-temperature combustion-supporting air which directly enters the rotary kiln from the ring cooling section in unit time is expressed;
Qburning deviceRepresents all heat released after the fuel sprayed by the nozzle is completely combusted in unit time;
Qflue gasThe energy of the kiln tail outlet flue gas increased relative to the normal temperature flue gas temperature in unit time is represented;
Qwall(s)The heat quantity dissipated by the wall surface of the kiln in unit time is represented;
Qmaterial(s)Means the increased energy per unit time of pellets exiting the rotary kiln after the completion of the calcination section relative to the energy entering the kiln.
The invention provides an on-line prediction method for the flue gas temperature of a calcination section of a rotary kiln, which solves the problem that the flue gas temperature of the calcination section cannot be directly measured when the rotary kiln stably works.
In addition, the temperature of the rotary kiln is 50-200 ℃ when the rotary kiln works stably.
In the present invention, the specific step of S2 includes:
s21: uniformly dividing the kiln wall of the combustion section of the rotary kiln into n sections;
s22: measuring the temperature t of each sectioni(° c) and surface area Si(m2) And the ambient temperature t corresponding to the kiln wall of the combustion section of the rotary kiln∞(℃)；
S23: measuring the temperature t of each section according to the step S22i(° c) and surface area Si(m2) And the ambient temperature t corresponding to the kiln wall of the combustion section of the rotary kiln∞The temperature is measured to obtain the heat dissipation Q of the kiln wall facing the external environment in unit time when the rotary kiln stably worksWall(s)。
In S23, QWall(s)The calculation formula of (a) is as follows:
in the formula, h represents the convective heat transfer coefficient between the wall surface of the kiln and the external environment.
The kiln wall of the rotary kiln is divided into a plurality of sections equally, the temperature and the surface area of each section are measured, the temperature is usually measured by an infrared thermometer, and therefore the heat dissipation capacity of each section is calculated, the whole rotary kiln is further calculated, and the accuracy is high; the heat dissipation capacity of the kiln wall of the whole rotary kiln is calculated through integral summation when the rotary kiln stably works, and the accuracy is high.
In the present invention, the specific step of S3 includes:
s31: measuring the mass m (kg) of finished pellets flowing out of a kiln head in unit time and the temperature t of finished pellets discharged from the kiln when the rotary kiln stably worksout(DEG C) and the initial temperature t of green pellets entering the kiln in unit timein(℃)；
S32: according to the mass m (kg) of the finished pellets flowing out of the kiln head in unit time and the temperature t of the finished pellets discharged from the kiln measured in the step S31out(DEG C) and the initial temperature t of green pellets entering the kiln in unit timein(DEG C) to obtain the energy Q increased by the pellets before and after entering the kilnMaterial(s)。
In said S32, QMaterial(s)The calculation formula of (a) is as follows:
Qmaterial(s)＝m×cm×(tout-tin)，
In the formula, cmRepresents the specific heat capacity of the pellet [ J/(kg. K)]。
The quality of finished pellets flowing out of a kiln head in unit time when the rotary kiln stably works is measured in a mode which can be thought by a person skilled in the art, and meanwhile, the temperature of finished pellets discharged from the kiln and the initial temperature of green pellets entering the kiln in unit time are measured by an infrared thermometer, so that the measurement is convenient and quick; and calculating the heat of the material according to the measured parameters and a heat formula.
In the present invention, the specific step of S4 includes:
s41: measuring primary air temperature t sprayed from kiln head in unit time when rotary kiln stably works1(° c), secondary air volume V2(m3) And secondary air temperature t2(℃)；
S42: according to the measured primary air temperature t sprayed from the kiln head in the unit time measured in the step S421(° c), secondary air volume V2(m3) And secondary air temperature t2The temperature is higher than the temperature of the secondary air in unit time to obtain the heat Q brought by the secondary air in unit timeSecondary air。
In said S42, QSecondary airThe calculation formula of (a) is as follows:
Qsecondary air＝V2×ρ2×c2×(t2-t1)，
In the formula, ρ2Represents the secondary air gas density (kg/m)3)，c2Represents the specific heat capacity of secondary air gas [ J/(kg. K)]。
The volume of the secondary air is calculated in a manner which can be thought by a person skilled in the art, and the primary air temperature and the secondary air temperature are measured by an infrared thermometer, so that the measurement is convenient and quick; and calculating the heat of the secondary air according to the measured parameters and a heat formula.
In the invention, the heat balance formula of the rotary kiln in S1 can be obtained, wherein Q is QWall(s)+QMaterial(s)-QSecondary air，QBurning device-Q＝QFlue gas。
By converting the formula in step S1, it can be known that the heat dissipated from the kiln wall of the rotary kiln, the heat of the material and the heat of the secondary air can be measured, and therefore the difference between the heat of the fuel and the heat of the flue gas is the theorem Q.
Derivation of Q from the above equationBurning deviceAnd QFlue gasThe relation between is
(Vy-V2)×ρr×cr×(tr-t1)＝Vy×ρy×cy×(ty-t1)-Q，
In the formula, VyIs the volume (m) of the outlet flue gas of the rotary kiln in unit time3)；ρyThe density of the outlet flue gas (kg/m 3); c. CySpecific heat capacity of outlet flue gas [ J/(kg. K)]；tyThe temperature (DEG C) of the outlet flue gas is shown; rhorIs the density (kg/m) of high-temperature flue gas in a calcining section3)；crIs the specific heat capacity of high-temperature flue gas at the calcining stage [ J/(kg. K)]；trThe air temperature (DEG C) of the high-temperature flue gas at the calcining section is shown.
And Q is a constant, and then the heat of the fuel and the smoke is expressed by a heat formula to obtain a new formula, so that the derivation is convenient and quick.
In the invention, the flue gas temperature t of the calcination sectionrTemperature t of kiln tail flue gasyHas the relation of
The flue gas temperature t of the calcining section is obtained through the change of a formularTemperature t of kiln tail flue gasyThe derivation is convenient and fast.
In the invention, the step of simulating the calcination section flue gas temperature t obtained in the step S3 by using a simulation is further included between the step S3 and the step S4rTemperature t of kiln tail flue gasyThe relational expression (2) is verified, and if the verification is passed, the step S4 is executed, and if the verification is not passed, the step S2 is returned to be executed.
The simulation usually adopts Ansys software, which is large-scale general Finite Element Analysis (FEA) software developed by Ansys corporation in the united states, is Computer Aided Engineering (CAE) software growing fastest worldwide, and can interface with most Computer Aided Design (CAD) software to realize data sharing and exchange.
In the present invention, the heat balance analysis of the rotary kiln is as follows:
for the pellet rotary kiln, the heat balance in the steady operation state can be expressed by the simplified relation in step S1, which is simplified by two points:
1) for gas, the energy brought by normal temperature air (i.e. primary air) entering the rotary kiln is taken as a standard, namely the energy is considered to be 0 relatively;
2) for the material, the temperature of the pellet from the grate (feeding the pellet into the rotary kiln) is taken as a standard, that is, the energy brought by the pellet entering the rotary kiln is relatively 0;
Qsecondary air+QBurning device＝QFlue gas+QWall(s)+QMaterial(s)
In the formula, QSecondary airIndicating that high-temperature combustion-supporting air directly entering the rotary kiln from a ring cooling section is carried by the high-temperature combustion-supporting air in unit timeThe energy of (a);
Qburning deviceRepresents all heat released after the fuel sprayed by the nozzle is completely combusted in unit time;
Qflue gasThe energy of the kiln tail outlet flue gas increased relative to the normal temperature flue gas temperature in unit time is represented;
Qwall(s)The heat quantity dissipated from the wall surface of the kiln to the outside in unit time is represented;
Qmaterial(s)Means the increased energy per unit time of pellets exiting the rotary kiln after completion of the calcination section relative to their entry into the kiln.
For a rotary kiln operating steadily, QSecondary air、QBurning device、QFlue gas、QWall(s)、QMaterial(s)All the components are constant, however, according to actual production conditions, in the stable working process of the rotary kiln, the internal temperature field is not absolutely stable, certain fluctuation exists, manual regulation is sometimes needed, the temperature of the flue gas at the calcining section is transient, in this case, the heat balance is broken, and Q is obtainedBurning deviceAt a small instantaneous change, the temperature t of the calcination sectionrAlso can change to a certain extent, because the flue gas flow velocity in the kiln is larger, the kiln tail flue gas tyAn immediate corresponding change is immediately followed. At this time, QBurning device、QFlue gasIs independent variable and dependent variable; qSecondary airIs still constant; because the temperature of the outer wall surface of the kiln is influenced by the temperature of the inner wall surface of the kiln through heat conduction, the heat conductivity coefficient is very low due to the obstruction of refractory materials, and the reaction of the outer wall of the kiln to the temperature in the kiln needs a period of time, therefore QWall(s)Is also a constant; the pellet at the outlet is completely calcined, so that the temperature can not obviously change due to internal chemical reaction, and the temperature change caused by heat conduction due to the temperature change of the wall surface of the kiln can not be immediately receivedMaterial(s)Is also a constant. Therefore, the temperature of the molten metal is controlled,the above relationship can be converted to the following relationship:
Qburning device＝QFlue gas+Q
In the formula: q ═ QWall(s)+QMaterial(s)-QSecondary airAre constant and can be further calculated by measurable data,
in the formula, h represents the convective heat transfer coefficient between the wall surface of the kiln and the external environment; si represents the wall surface area (m) of the i-th stage2)；ti、t∞Respectively representing the temperature of the kiln wall surface of the i-th section and the ambient temperature (DEG C); because the wall temperature of the kiln is not uniform, the temperatures of different sections are different, the temperatures of different areas need to be measured for many times and are obtained by utilizing formula integration,
Qmaterial(s)＝m×cm×(tout-tin)
Wherein m represents the mass (kg) of the outlet pellet per unit time; c. CmRepresents the specific heat capacity of the pellet [ J/(kg. K)]；tout、tinRespectively showing the temperature (DEG C) of the pellets at the outlet and the pellets at the inlet of the rotary kiln;
Qsecondary air＝V2×ρ2×c2×(t2-t1)
In the formula (I); v2Represents the volume (m) of secondary air entering the rotary kiln in unit time3)；ρ2Represents the secondary air gas density (kg/m)3)；c2Represents the specific heat capacity of secondary air gas [ J/(kg. K)]；t2、t1Respectively representing the temperature (DEG C) of secondary air and primary air;
the heat released by the fuel combustion can generate a high temperature zone, generally about 1350 ℃ for the pellet rotary kiln under stable work, the temperature is a very key process parameter in production, and is directly related to the fuel consumption, the pellet quality, the emission of nitrogen oxides and barrel ring formation. The temperature of the area is very high and is positioned in the kiln cylinder, the specific position is difficult to determine, and the velocity of the flow field in the kiln is also high, so that the measurement is difficult. Therefore, the study on the temperature field problem in the kiln is very important! The above contents also show that the kiln tail flue gas temperature and the temperature of the high-temperature area in the kiln have a definite relation, and the kiln tail flue gas temperature is relatively convenient to measure in production, so that the finding of the relation between the kiln tail flue gas temperature and the temperature of the high-temperature area in the kiln is significant.
In addition, QBurning deviceThe rotary kiln has several types of fuels for fuel combustion, the common types of the fuels comprise coal powder, natural gas or liquefied natural gas and the like, and the main combustion component of the rotary kiln is solid C or gaseous CH4The general combustion equation is as follows:
C(s)+O2(g)→CO2(g)
CH4(g)+2O2(g)→CO2(g)+2H2O(g)
the two relationships are the complete overall reaction of fuel combustion, and it can be seen that either solid C combustion or gaseous CH4And (3) combustion, wherein the molecular weight of the gas state before and after the reaction is unchanged, so that the volume of the gas before and after the combustion is not increased. The CO formation is not considered because the oxygen in the rotary kiln is in excess, and even if there is a trace amount of CO at the exit, it is generally not more than 600ppm and can be ignored. NO consideration is given to NO production because the content is also very low, generally not more than 800ppm, which is negligible, and NO production is mainly of fuel type and thermodynamic type, the mechanism for producing NO of fuel type is too complicated, which is not yet clear, and the molecular weight of NO of thermodynamic type is not changed before and after the reaction. Based on this, there are:
Qflue gas＝Vy×ρy×cy×(ty-t1)
In the formula, VyThe volume (m) of the outlet flue gas of the rotary kiln in unit time3)；ρyDenotes the density (kg/m) of the outlet flue gas3)；cyRepresents the specific heat capacity of the outlet flue gas [ J/(kg. K)]；ty、t1Respectively showing the temperature of outlet flue gas and the temperature of primary air (DEG C);
Qburning device＝(Vy-V2)×ρr×cr×(tr-t1)
In the formula, ρrShows the density (kg/m) of high-temperature flue gas immediately after the completion of heat release by combustion of fuel3) Namely the density of high-temperature flue gas in the calcining section; c. CrRepresents the specific heat capacity of the high-temperature flue gas in the calcining section [ J/(kg. K)]；tr、t1Respectively showing the high-temperature flue gas air temperature and the primary air temperature (DEG C) of the calcining section;
in summary, the following relationships are further derived:
(Vy-V2)×ρr×cr×(tr-t1)＝Vy×ρy×cy×(ty-t1)-Q
because the secondary air entering the rotary kiln, the flue gas after the fuel is completely combusted and the flue gas at the tail of the rotary kiln are high-temperature gases (the temperature is higher than 1100K), and N is mainly contained2、CO2、O2And a trace amount of NOxCO and the like, the main components are basically the same, and the density rho and the specific heat capacity c can be considered to be the same, so that the relational expression can be finally simplified to obtain tyAnd trThe relation of (1):
in the formula, Vy、V2、Q、t1Constant, rho, which can be measured when the rotary kiln works stablyy、cyThe density and specific heat capacity of high-temperature flue gas at the outlet of the rotary kiln are the properties of the substance and are constant. The above relation expresses an important meaning: when the rotary kiln works stably, the kiln tail flue gas temperature and the high-temperature flue gas temperature fluctuation of the calcining section have a linear relation, and the linear relation is a linear function relation, and the slope of the linear relation is only related to the kiln tail flue gas flow and the secondary air inlet flow.
The invention also provides a system for on-line prediction of the flue gas temperature of the calcining section in the rotary kiln, which is characterized by comprising the following modules,
a heat balance model building module for building Q-value in the rotary kiln according to the heat balance principle when the rotary kiln stably worksSecondary air、QBurning device、QFlue gas、QWall(s)And QMaterial(s)The heat balance model of (1);
a model parameter calculation module for calculating Q in the heat balance model according to the parameters of the rotary kiln in stable operationWall(s)、QMaterial(s)And QSecondary airThe value of (d);
a relational expression obtaining module for obtaining QWall(s)、QMaterial(s)And QSecondary airSubstituting the numerical value into a rotary kiln heat balance model to obtain QBurning deviceAnd QFlue gasThe relation between the two, and then the flue gas temperature t of the calcining section is obtainedrTemperature t of kiln tail flue gasyThe relational expression of (1);
a calculation module for measuring the kiln tail flue gas temperature tyAnd passing through the flue gas temperature t of the calcination sectionrTemperature t of kiln tail flue gasyObtaining the flue gas temperature t of the calcining section by the relational expressionr；
The heat balance model specifically comprises: qSecondary air+QBurning device＝QFlue gas+QWall(s)+QMaterial(s)；QSecondary airThe energy of the high-temperature combustion-supporting air which directly enters the rotary kiln from the ring cooling section in unit time is expressed;
Qburning deviceRepresents all heat released after the fuel sprayed by the nozzle is completely combusted in unit time;
Qflue gasThe energy of the kiln tail outlet flue gas increased relative to the normal temperature flue gas temperature in unit time is represented;
Qwall(s)The heat quantity dissipated by the wall surface of the kiln in unit time is represented;
Qmaterial(s)Means the increased energy per unit time of pellets exiting the rotary kiln after the completion of the calcination section relative to the energy entering the kiln.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
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