炉内温度分布及热辐射参数检测的实验研究
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摘要
在实际的工业应用中,炉内燃烧过程是发生在相对大的空间中,不断脉动的复杂物理化学过程。实现炉内温度分布的检测对于揭示燃烧现象的本质和发展燃烧理论,以及提高炉膛燃烧的安全性、经济性和低污染性都具有重要的意义;炉内热辐射参数,如颗粒介质辐射特性(吸收系数和散射系数)、炉膛壁面的发射率等,对于炉内辐射传热的整个过程具有举足轻重的作用,同时也是燃烧过程数值模拟计算所必须的输入参数。本文在火焰辐射成像的基础上,通过火焰图像处理与热辐射分析相结合的方法开展了炉内温度分布和热辐射参数检测的实验研究,主要工作如下:
阐述了实验研究中所采用的彩色火焰图像处理方法、辐射成像模型及相应的重建算法。在空腔辐射和等温辐射两种特殊情形下,对辐射成像模型进行了数值模拟计算,边界温度和辐射率分布的模拟计算结果与理论结果相一致,证明了辐射成像模型的准确性;开展了炉内温度分布、介质吸收系数和壁面发射率同时重建的模拟研究,结果表明,当测量误差为5%时仍然可以较好的重建出炉内温度分布和热辐射参数。
分别在煤粉炉和加热炉上开展了温度和热辐射参数检测的实验研究。在一台200MW火力发电机组的四角切圆燃煤锅炉上,用一套自主设计的便携式图像处理系统采集了炉内火焰图像,计算了火焰辐射温度和辐射率,与红外高温计的测量结果相比,平均误差小于4%;所重建的炉膛断面温度场和颗粒介质特性表明:由于四角切圆燃烧方式,炉内温度分布呈现出“中间高四周低”的单峰分布特征,火焰温度随负荷的增加而增加,煤粉燃烧颗粒介质的散射系数要大于吸收系数。在一台卧式燃油加热炉上开展了相应的检测实验研究,从炉内壁面辐射图像中计算出炉膛壁面温度,与热电偶测量结果相比,误差在2%之内;从炉内燃烧火焰图像中重建出炉内12个横截面的温度分布、介质吸收系数和壁面发射率,结果表明:炉内温度分布可以反映出燃烧火焰的分布特征,炉膛壁面所采用的材料在可见光区域具有较强的反射性。
Combustion in industrial furnaces is one of the most complex physical and chemical processes occurring in large-scale spaces. The measurement of temperature distributions is essential for the development of combustion theory and technology, as well as the increase of security, economic operation, and low-pollutant emission of boilers. Thermal radiative parameters in furnaces, such as radiative properties of particulate medium (absorption coefficient and scatter coefficient) and emissivity of wall surface, are very important to the processes of radiative heat transfer, and also the necessary input parameters for numerical simulation of combustion processes.The main research of this paper is experimental investigation on the simultaneous reconstruction of temperature distributions and thermal radiative parameters through the flame image processing and thermal radiation analysis, on the basis of the flame radiative imaging. Main work is as follows.
Color flame image processing method, radiative imaging model and the corresponding reconstruction algorithm used in the experimental investigations were described in this dissertation. Then numerical simulation based on the radiative imaging model was conducted under the two special cases, cavity radiation and isothermal radiation system. Simulation results of the boundary temperature and emissivity distributions agreed well with the theoretical results, which proved the accuracy of radiative imaging model. At the same time, simulation of the simultaneous reconstruction of temperature distributions, absorption coefficients of combustion medium and emissivity of wall surface was conducted. The results show that temperature distributions and thermal radiative parameters can still be reconstructed well when the measurement error is 5%.
The corresponding experimental investigations were carried out on a coal-fired boiler furnace and an oil-fired furnace, respectively. Firstly, in a four-cornered, tangentially firing boiler coal-fired furnace of a 200 MW power generation unit, flame images were captured by a portable imaging processing system. Flame radiative temperatures and emissivity were calculated and compared with the results measured by infrared pyrometer. Average relative error is less than 4%. The reconstruction results of cross section temperature distributions and radiative properties of granular medium show that, because of the way of four-cornered tangentially firing, temperature distributions appear to be a single-peaked shape with temperatures higher in the center and lower near the wall surfaces, and flame temperatures increase with the load. Scattering coefficients of coal combustion medium are greater than absorption coefficients. Furthermore, experimental investigations were conducted in an oil-fired tunnel furnace. Temperatures of wall surface were calculated from the radiative image of refractory wall and compared with the measured temperature of a thermocouple. Relative error between two methods was only about 2%. Then temperature distributions, absorption coefficients of combustion medium, and emissivity of refractory wall within the 12 cross sections were reconstructed from oil-fired flame images, the results show that: temperature distributions in furnace can reflect the distributions of combustion flame, and material used in furnace wall has a strong reflectivity in the visible region.
阐述了实验研究中所采用的彩色火焰图像处理方法、辐射成像模型及相应的重建算法。在空腔辐射和等温辐射两种特殊情形下,对辐射成像模型进行了数值模拟计算,边界温度和辐射率分布的模拟计算结果与理论结果相一致,证明了辐射成像模型的准确性;开展了炉内温度分布、介质吸收系数和壁面发射率同时重建的模拟研究,结果表明,当测量误差为5%时仍然可以较好的重建出炉内温度分布和热辐射参数。
分别在煤粉炉和加热炉上开展了温度和热辐射参数检测的实验研究。在一台200MW火力发电机组的四角切圆燃煤锅炉上,用一套自主设计的便携式图像处理系统采集了炉内火焰图像,计算了火焰辐射温度和辐射率,与红外高温计的测量结果相比,平均误差小于4%;所重建的炉膛断面温度场和颗粒介质特性表明:由于四角切圆燃烧方式,炉内温度分布呈现出“中间高四周低”的单峰分布特征,火焰温度随负荷的增加而增加,煤粉燃烧颗粒介质的散射系数要大于吸收系数。在一台卧式燃油加热炉上开展了相应的检测实验研究,从炉内壁面辐射图像中计算出炉膛壁面温度,与热电偶测量结果相比,误差在2%之内;从炉内燃烧火焰图像中重建出炉内12个横截面的温度分布、介质吸收系数和壁面发射率,结果表明:炉内温度分布可以反映出燃烧火焰的分布特征,炉膛壁面所采用的材料在可见光区域具有较强的反射性。
Combustion in industrial furnaces is one of the most complex physical and chemical processes occurring in large-scale spaces. The measurement of temperature distributions is essential for the development of combustion theory and technology, as well as the increase of security, economic operation, and low-pollutant emission of boilers. Thermal radiative parameters in furnaces, such as radiative properties of particulate medium (absorption coefficient and scatter coefficient) and emissivity of wall surface, are very important to the processes of radiative heat transfer, and also the necessary input parameters for numerical simulation of combustion processes.The main research of this paper is experimental investigation on the simultaneous reconstruction of temperature distributions and thermal radiative parameters through the flame image processing and thermal radiation analysis, on the basis of the flame radiative imaging. Main work is as follows.
Color flame image processing method, radiative imaging model and the corresponding reconstruction algorithm used in the experimental investigations were described in this dissertation. Then numerical simulation based on the radiative imaging model was conducted under the two special cases, cavity radiation and isothermal radiation system. Simulation results of the boundary temperature and emissivity distributions agreed well with the theoretical results, which proved the accuracy of radiative imaging model. At the same time, simulation of the simultaneous reconstruction of temperature distributions, absorption coefficients of combustion medium and emissivity of wall surface was conducted. The results show that temperature distributions and thermal radiative parameters can still be reconstructed well when the measurement error is 5%.
The corresponding experimental investigations were carried out on a coal-fired boiler furnace and an oil-fired furnace, respectively. Firstly, in a four-cornered, tangentially firing boiler coal-fired furnace of a 200 MW power generation unit, flame images were captured by a portable imaging processing system. Flame radiative temperatures and emissivity were calculated and compared with the results measured by infrared pyrometer. Average relative error is less than 4%. The reconstruction results of cross section temperature distributions and radiative properties of granular medium show that, because of the way of four-cornered tangentially firing, temperature distributions appear to be a single-peaked shape with temperatures higher in the center and lower near the wall surfaces, and flame temperatures increase with the load. Scattering coefficients of coal combustion medium are greater than absorption coefficients. Furthermore, experimental investigations were conducted in an oil-fired tunnel furnace. Temperatures of wall surface were calculated from the radiative image of refractory wall and compared with the measured temperature of a thermocouple. Relative error between two methods was only about 2%. Then temperature distributions, absorption coefficients of combustion medium, and emissivity of refractory wall within the 12 cross sections were reconstructed from oil-fired flame images, the results show that: temperature distributions in furnace can reflect the distributions of combustion flame, and material used in furnace wall has a strong reflectivity in the visible region.
引文
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[2]王淅芬.基于炉内温度场可视化的燃烧优化控制方法研究:博士学位论文.华中科技大学, 2005
[3]刘林华.炉膛传热计算方法的发展概况.动力工程, 2000, 21(1): 523-527
[4] FLUENT User’s Guide. Fluent Inc, 2003
[5]郑楚光,柳朝晖.弥散介质的光学特性及辐射传热.武汉:华中理工大学出版社, 1996
[6]刘林华,余其铮,阮立明等.煤粉燃烧产物的辐射特性.动力工程,1996,16(6):14-21
[7]余其铮,谈和平,阮立明,等.灰微粒子的光学常数和衰减系数.工程热物理学报,1993, 14(4):449-452
[8]周怀春.炉内火焰可视化检测原理与技术.北京:科学出版社, 2005
[9]戴景民,金钊.火焰温度测量技术研究.计量学报, 2003, 24(4): 297-302
[10]戴景民.辐射测温的发展现状与展望.自动化技术与应用, 2004, 23(3): 1-7
[11]黄素逸.动力工程现代测试技术.武汉:华中科技大学出版社,2001
[12] Childs P R, Greenwood J R, Long C A. Review of temperature measurement. Review of Scientific Instruments, 2000, 71(8): 2959-2978
[13]周怀春,娄新生,肖教芳等.炉膛火焰温度图象处理试验研究.中国电机工程学报, 1995, 15(5): 295-300
[14]吴占松.发光火焰的图象处理及其在燃烧检测中的应用:博士学位论文.清华大学, 1988
[15]王补宣,李天铎,吴占松.图像处理技术用于发光火焰温度分布测量的研究.工程热物理学报, 1989, 10(4): 446-448
[16]薛飞,李晓东,倪明江等.基于面阵CCD的火焰温度场测量方法研究.中国电机工程学报, 1999, 19(1): 39-41
[17]王飞,薛飞,马增益等.运用彩色CCD测量火焰温度场的试验研究及误差分析.热能动力工程, 1998, 13(2): 81-84
[18]卫成业,严建华,商敏儿等.利用面阵CCD进行火焰温度分布测量(I)—二维投影温度场的测量.热能动力工程, 2002, 17(1): 58-61
[19]卫成业,严建华,商敏儿等.利用面阵CCD进行火焰温度分布测量(II)—三维截面温度场的测量.热能动力工程, 2002, 17(2): 161-165
[20]周怀春,韩曙东,盛峰等.炉膛燃烧温度场三维可视化监测方法模拟研究.动力工程, 2003, 23(1): 2154～2159
[21]曾佳,娄春,程强等.大型电站锅炉炉内三维燃烧温度可视化试验研究.工程热物理学报, 2004, 25(3) : 523-526
[22]盛锋.基于辐射成像逆问题求解的温度场重建方法研究:博士学位论文.华中科技大学, 2000
[23]刘林华,谈和平,余其铮等.吸收散射三维矩形介质内辐射源项的反问题.工程热理学报, 2000, 21(1):71～75
[24] Zhou H C, Lou C, Cheng Q. Experimental investigations on visualization of three-dimensional temperature distributions in a large-scale pulverized coal fired boiler furnace. Proceedings of the Combustion Institute, 2005, 30: 1699～1706
[25] N Renault, S André, D Maillet, C Cunat. A two-step regularized inverse solution for 2-D heat source reconstruction. International Journal of Thermal Sciences. 2008, 47: 834–847
[26]黄群星,刘冬,王飞,严建华,池涌,岑可法.基于截断奇异值分解的三维火焰温度场重建研究.物理学报, 2007, 56(11) : 6742-6748
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