Numerical Simulation of Airflow Temperature Field in Rotary Kiln

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Sensors & Transducers, Vol. 6, Issue, December 03, pp. 7-76 Sensors & Transducers 03 by IFSA http://www.sensorsportal.

1 Sensors & Transducers, Vol. 6, Issue, December 03, pp Sensors & Transducers 03 by IFSA Numerical Simulation o Airlow Temperature Field in Rotary Kiln, Gonga Li, Jia Liu, Hegen Xiong, Jianyi Kong, Zhen Gao, Wentao Xiao, Yikun Zhang, Fuwei Cheng Hubei Key Laboratory or Eicient Utilization and Agglomeration o Metallurgic Mineral Resources College o Machinery and Automation, Wuhan University o Science and Technology, Wuhan China Tel.: , ax: ligonga@wust.edu.cn Received: 30 September 03 /Accepted: November 03 /Published: 30 December 03 Abstract: With the continuous development o the metallurgical industry, kiln calcinations increasingly sophisticated technology, the kiln equipment technology more emphasis on perormance. The rotary kiln is one o the most representatives o the urnace equipment, also put orward higher requirements in response to the call o the national energy saving rotary kiln, and want to be able to design the optimal energy consumption and stable perormance equipment. To analyze the energy consumption o the rotary kiln and it is necessary to study the heat transer process o the rotary kiln. The stability o the thermal system is directly related to the sintering material quality, and kiln gas temperature is an important actor inluencing thermal system, thereore, it has the very vital signiicance to research air temperature distribution inside the rotary kiln. Firstly, to determine the lame temperature o the kiln and throughout the heat transer coeicient, then analyzed air temperature ield distribution inside the rotary kiln which using dierent uels and dierent wind speed, ound that change trend o rotary kiln internal air temperature ield along the long direction o the kiln was basically the same when gas and methane as uel, and the temperature o each part in the length o rotary kiln was also very close. The internal air temperature in rotary kiln is higher than o 000 Pa when the induced drat an discharge pressure is 8000Pa, and to extend the length o high temperature calcination zone. We actualized the lame and the heat low simulation or rotary kiln according to the working condition o the rotary kiln to simulate the combustion, which was indicate the method o the simulation o combustion lame was easibility and accuracy. Copyright 03 IFSA. Keywords: Airlow, Rotary kiln, Temperature ield, Numerical simulation, Simulation.. Introduction Rotary kiln is one o the most commonly used thermal technology equipment in metallurgical industry, its thermal stability is directly related to burn into the quality o the material, the gas temperature o inside the kiln is important inluence actors o thermal system []. So research the airlow temperature distribution inside the kiln, it s very vital signiicance to understand the status o the rotary kiln in the heated, and real-time control the calcination condition o the materiel in rotary kiln. Martins M A, et al. [] has done some research on the internal heat transer process o the rotary kiln, he Article number P_75 7

2 Sensors & Transducers, Vol. 6, Issue, December 03, pp analyzed the dynamic characteristics and low characteristics o the materiel phase and gas phase transer process, and their eect on the inluence o internal heat transer process o rotary kiln. With in the process o rotary kiln calcination material within the physical and chemical reaction process is also considered, and the semi-empirical ormula is used to describe the high temperature lue gas, rotary kiln lining and material bed between the process o heat conduction, convection and radiation. On this basis, establish one-dimensional heat transer mathematical model o a rotary kiln calcination process. At the same time by using numerical simulation method, within the rotary kiln on the material phase and gas phase and the axial temperature distribution o rotary kiln wall and rotary kiln in exhaust lue gas composition and its percentage is orecasted, the results o the predicted results with the actual industrial production measured are in good agreement. Industrial production process, the internal o the physical and chemical reaction is bound to have impact on heat transer when the rotary kiln is running, the reaction process itsel can not only accompanied by exothermic and endothermic but also makes phenomena o phase transer in dierent interphase, so it is necessary to considerate the mass transer process and its inluence o incidental reaction the in analysis o the internal heat transer process o rotary kiln. The model ully considered the inluence on heat transer or the mass transer process, so that the model has a certain practical value, but also or uture generations o research provides a new basis. Ma Aichun etc. [3] make alumina materials calcination rotary kiln as the research object, have the internal heat transer paths o rotary kiln or more in-depth analysis and research, and comprehensive considerate the heat conduction, convection and radiation heat transer o the high temperature lue gas, rotary kiln wall and material bed, established the one-dimensional heat transer model o alumina material calcination o rotary kiln in this base. The Runge Kutta method is adopted to the calculate the one dimensional heat transer model, it is concluded that the temperature data on any cross section o high temperature airlow and materials, research the heat transer law o relative movement or the sealing o high temperature gas and low temperature material inside the kiln. It can be used or the temperature prediction and parameter optimization o the sealed section o the internal rotary kiln gas and material with this one-dimensional model, in the case o lack o experimental conditions is very eective. Obtained the lame temperature and airlow velocity o induced drat an in the end o rotary kiln, then urther simulated the temperature distribution o inner low rotary kiln with Fluent [4] heat transer model. In the course o the study, we transorm the temperature inluence degree o material or airlow into the heat convection coeicient [9, 0]; the induced drat an was set in the end o rotary kiln, which has great inluence on the airlow temperature inner rotary kiln. So we can transorm the eects o induced drat an into speed and applied to the boundary condition, and the heat convection o inner kiln belongs to the orced convection which applying the boundary condition o kiln end low velocity.. Rotary Kiln Temperature Simulation o the Internal Flow It is necessary to considerate the kiln end induced drat an and lame radiation and the high temperature airlow by it which simulate the inner airlow temperature distribution o the rotary kiln. It is need to determine the boundary condition o lame temperature and the heat transer coeicient which simulate the inner airlow temperature... Determined the Initial Flame Temperature The lame temperature o dierent size under the condition that dierent uels and dierent import and export conditions, the simulated lame temperature ranging rom 00 K to 330 K, we can choose a value, 800 K, as the initial lame temperature conditions to simulate... Determine the Heat Transer Coeicient The heat convection o inner kiln belongs to the orced convection, and equation o orced convection heat transer was: u Re Pr N () R e where R - Reynolds number; e d v () knu, (3) d Pr - Prandtl number; v - Flow kinematic viscosity, m /s ; - Thermal conductivity, - Airlow velocity, m/s; d - Kiln diameter, m; k - Correction coeicient; w/ mk ; - Convective heat transer coeicient, w/ m k. From the reerence []: P r =0.75, =0.086 w/ mk, because d =3 m, so k =.06. And 7

3 Sensors & Transducers, Vol. 6, Issue, December 03, pp rom the air temperature plot in reerence [] we know that the average air temperature is 000 o C in the kiln, and under this condition calculated low kinematic viscosity v =0.35e0-6 m /s. The air velocity initial value =5 m/s, and calculated the convective heat transer coeicient was =3.37 w/ m k. Due to the lame radiation was diicult to as a boundary condition or apply directly, in the project will be converted radiation heat convection into convective heat transer coeicient, which the equivalent heat transer coeicient was determined by the ormula [3]: where: - blackness; b ( b T ) T hr T T - Stean-Boltzmann's Constant; T, T - the two radiation point temperature. (4) The temperature o dierent calcination zone in kiln wall has great dierence, should be calculated separately. Generally speaking, along the length direction o the rotary kiln that can be divided into dry section, preheating, decomposing section, exothermic reaction section, iring section, cooling section [4]. In the premise o the results is not been aected, the calculation o radiation heat transer can be divided into three typical temperature section (preheating section, the iring section and the cooling section). For the rotary kiln calcination section o each dierent, the length was not the same, this study assumes three typical temperature segment o the same length, were 0 m, air temperature curve kiln in reerence [], take average temperature or three section were T y =000 o C, T s =400 o C and T l =00 o C, respectively. According to the reerence [], the gas combustion lame blackness was 0.3, and Stean Boltzmann constant is 5.67e-8. Equivalent convection heat transer coeicients o the three sections were calculated as ollows. The preheating section: Comprehensive convection heat transer coeicient o the iring section: rs h rs =3.33 w / m k The cooling section: h rl b( T Tl ) =69.56 w / m k T T l Comprehensive convection heat transer coeicient o the cooling section: rl h rl =00.93 w / m k Ater determine the boundary conditions and parameters, obtained the internal airlow temperature distribution o rotary kiln which was shown Fig.. Further extracted the distribution curve o temperature along the length o the kiln which was located the internal air low and the kiln wall contact side, as shown in Fig.. It can be seen rom the igure that the change trend o internal temperature directly. Fig.. The cloud picture o internal airlow temperature in rotary kiln. h ry b( T Ty ) =43.38 w / m k T T y Comprehensive convection heat transer coeicient o the preheating section: ry h ry =87.75 w / m k The iring section: h rs b( T Ts ) =00.96 w / m k T T s Fig.. The distribution curve o airlow temperature along the length o the kiln. 73

Sensors & Transducers, Vol. 6, Issue, December 03, pp. 7-76 3.

4 Sensors & Transducers, Vol. 6, Issue, December 03, pp Comparative Analysis o Internal Airlow in Rotary Kiln with Dierent Fuels Dierent uels will result in dierent lame temperature, which generate dierent airlow temperature [8]. Comparatively analyze the two kinds o uel that gas and methane [6]. With the same energy consumption, the high temperature airlow was generated by gas that was 700 K and by methane was 800 K, which as the initial condition or analysis. The airlow temperature distribution which simulated gas combustion as shown in Fig. 3, urther extracted the distribution curve o temperature along the length o the kiln which was located the internal air low and the kiln wall contact side, as shown in Fig. 4, we can see rom the graph that was three sections o smooth curves apparently, and the temperature mutated in transition. This was because the research process o rotary kiln was divided into three typical temperature (the preheating section T y, the iring section T s and the cooling sectiont l ), in actually it without the three temperature mutations. So can be ignored when analysis the results, instead o smooth curves. Obtain the airlow temperature distribution as shown in Fig. 5 which simulation methane combustion in the same condition, urther extracted the distribution curve o temperature along the length o the kiln which was located the internal air low and the kiln wall contact side, and as shown in Fig. 6. Fig. 5. The airlow temperature distribution o methane combustion. Fig. 6. The distribution curve o airlow temperature along the length o the kiln. Fig. 3. The airlow temperature distribution o gas combustion. Comparative the Fig. 4 and Fig. 6 can be seen, the airlow temperature change trend along the length direction o the kiln is basically the same which was produced by gas and methane, and the each section temperature o the kiln was also very close. So the gas and methane can be used as alternative uels are used interchangeably, and two uels mixture combustion has little eect on the calcination. 4. The Analysis o Internal Airlow in Rotary Kiln with Dierent Induced Wind Velocity Fig. 4. The distribution curve o airlow temperature along the length o the kiln. Dierent velocity o induced wind will inluence on the inner airlow velocity o rotary kiln, which have a certain inluence on the heat transer o kiln inner wall with air low and the material. It can obtain the degree o eect on velocity o induced wind or inner airlow through simulate temperature ield distribution o inner airlow under dierent induced wind speed [5]. 74

5 Sensors & Transducers, Vol. 6, Issue, December 03, pp The velocity o induced wind depends on the exhaust capacity o induced drat an o rotary kiln, and dierent speed an generated dierent gas low velocity. The an was connected with the end o rotary kiln through pipelines, so the simulated airlow velocity should urther transorm into the outlet airlow velocity o rotary kiln ends. At the same time, the exhaust gas low o rotary kiln and induced drat an output was the same, so it can be through ormula (5) to convert. v nr v r (5) where: r - The inner radius o the rotary kiln; v - The airlow speed o rotary kiln end; r - The inner radius o induced drat an pipeline; v - The inner airlow speed o induced drat an pipeline; n - The number o induced drat an. Take the simulated airlow velocity which the exhaust pressure o 000 Pa and 8000 Pa as initial condition to carry out contrast analysis [7]. I use o 4 induced drat an, though the ormula (5) convert, the airlow velocity in rotary kiln end is.44 m/s and 5.3 m/s respectively. The simulated temperature distribution as shown in Fig. 7 which the an exhaust pressure o 000 Pa, urther extracted the distribution curve o temperature along the length o the kiln which was located the internal air low and the kiln wall contact side [8], and as shown in Fig. 7. was about 700 K, kiln end temperature is about 480 K, and the highest temperature o kiln located in the place where ar apart rom the kiln head o 0 m which the an exhaust pressure o 8000 Pa and the temperature was about 750 K, kiln end temperature is about 580 K. Further analysis showed that, an exhaust pressure increases, the an speed was accelerated, and the internal low o rotary kiln temperature went up, and the maximum temperature o the kiln moved to tail or some distance, extending the length o high temperature calcination zone. Fig. 8. The distribution curve o airlow temperature along the length o the kiln. Fig. 9. The inner airlow temperature distribution o kiln an with exhaust pressure o 8000 Pa. Fig. 7. The inner airlow temperature distribution o kiln an with exhaust pressure o 000 Pa. The simulated temperature distribution as shown in Fig. 9 which the an exhaust pressure o 8000 Pa urther extracted the distribution curve o temperature along the length o the kiln which was located the internal air low and the kiln wall contact side, and as shown in Fig. 0. Comparing Fig. 8 and Fig. 0, can be seen that the highest temperature o kiln located in the place where ar apart rom the kiln head o 8 m which the an exhaust pressure o 000 Pa and the temperature Fig. 0. The distribution curve o airlow temperature along the length o the kiln. 75

Sensors & Transducers, Vol. 6, Issue, December 03, pp. 7-76 So or the dierent calcination requirements, should adjust the velocity o an end to improving calcination eect. 5.

6 Sensors & Transducers, Vol. 6, Issue, December 03, pp So or the dierent calcination requirements, should adjust the velocity o an end to improving calcination eect. 5. Conclusions Through the analysis the inner airlow temperature distribution o the rotary kiln which using dierent uels and dierent induced wind speed, ounded that temperature eect on the internal airlow o rotary kiln was basically the same when gas and methane as uel, so the gas and methane as uel reserve are used interchangeably,and the an velocity was greater and the internal airlow temperature o rotary kiln was higher, and extend the length o high temperature calcination zone. So or dierent calcination requirements, should adjust the end o an speed, provided the theory reerence or the optimization o energy consumption in production o rotary kiln. Acknowledgments This research reported in the paper is supported by Hubei Key Laboratory or Eicient Utilization and Agglomeration o Metallurgic Mineral Resources and the "Twelth Five-Year National Science and technology support program (0BAB05B0). This support is greatly acknowledged. Reerences []. Zhang Yiming, The second resource utilization, Central South University Press, Chang Sha, 00. []. Martins M. A., Oliveira L. S., Modeling and Simulation o Petroleum Coke Calcination in Rotary kilns, Fuel, 80,, 00, pp [3]. Ma Aichun, Zhou Jiemin, A one-dimensional thermal model or the alumina clinker kiln, Energy or Metallurgical Industry, 3,, 004, pp [4]. Lu Shu-Sheng, Shen Run-Jie, Simulation o pressure ield under centriugal acceleration based on FLUENT, Journal o Mechanical & Electrical Engineering, 8, 5, 0, pp [5]. Hai Ying, Chen Jing-Yu, Simulation on characteristics o louvered-in type heat exchanger in airlow maldistribution, Journal o Mechanical & Electrical Engineering, 8, 9, 0, pp [6]. Wang Meng-Wen, Calculation and analysis o eddycurrent ield and temperature ield or insulation shell o permanent magnet shat coupling, Journal o Mechanical & Electrical Engineering, 0, 8, 00, pp [7]. Hou Jun, Zhang Ji-Jun, The pressure compensation project design o air combustion-supporting brothelurnace during commutation period, Journal o Mechanical & Electrical Engineering, 4,, 007, pp [8]. Shen Jin-Yong, Yao Xiu-Li, Steady-state Thermal Analysis and optimization o 3300 tpd Rotary Kiln, Cement Technology,, 0, pp [9]. Mei Zhi, Simulation and optimization o non-errous metallurgical urnace, Metallurgical Industry Press, Beijing, 00. [0]. Yang Shi-Ming, Tao Wen-Quan, Heat transer, High Education Press, Beijing, Copyright, International Frequency Sensor Association (IFSA). All rights reserved. ( 76

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