微波冶金炉加热效率的若干问题基础研究

发布时间：2018-05-12 09:54

本文选题：微波冶金炉 + 加热效率　；参考：《昆明理工大学》2015年博士论文

【摘要】：微波冶金炉是微波冶金的关键设备之一。但长期以来,微波冶金炉的加热效率问题一直困扰着学术界和工业界,从而影响该项技术的应用和推广。许多研究者从调整冶金工艺参数的角度对此进行了大量的改进。但是研究表明,微波冶金炉的加热效率与被加热物料的吸波性能、炉子内衬耐火材料的透波性能以及电磁波的入射角和极化方式密切相关,这些因素以复杂的方式交互影响着微波加热的效率。因此,要提高微波冶金炉的加热效率,必须将炉子的内衬、物料和电磁波等作为一个耦合整体来加以考虑。影响微波冶金炉加热效率的直接因素就是微波能转化成内热源的效率问题。而影响微波能转化成内热源的本质因素主要包括三个方面：一是被加热物料的吸波特性；二是电磁波的极化方式和入射角；三是内置炉衬及承载体的透波性能。本研究致力于提高微波冶金炉的加热效率,提升微波冶金炉的设计水平,针对影响微波加热效率的上述本质因素,具体研究了典型冶金物料和微波冶金常用耐火材料的物性参数、几何尺寸和入射电磁波频率、极化方式和入射角等因素对被加热物料吸波效率和耐火材料透波效率的影响问题。具体研究内容如下：(1)为了研究内置炉衬及物料的微波冶金炉电磁热耦合场的分布情况,根据多物理场耦合理论,研究了内置炉衬(耐火层、保温层)和物料的微波谐振腔内电磁场、温度场的分布,分析了物料以及耐火保温层在微波加热过程中温度热点以及电磁场的动态变化情况。研究结果表明：炉衬和物料电磁参数的变化对电磁场、温度场的分布有较大影响；微波加热前期,微波能大都耗散于物料内,炉衬吸收的微波能较少；微波加热中后期,炉腔温度较高时,炉衬吸收的微波能多于物料吸收的微波能；高温时,物料主要靠表层部分吸收微波能,加热不均匀现象变得明显；波导馈口处温度高,微波能损耗大,使得该处的微波穿透深度最小,8000s之后,微波穿透深度小于10 cm。在一般情况下,温度场的分布与电磁场分布基本一致,即高场强与温度热点对应；但是随着温度的升高,当材料的复介电常数变化较大时,电磁场的谐振模式就会发生跳变。而此时温度场不能马上跟随作相应变化,只能在新的电磁场模式下慢慢地跟随电磁场的变化,即温度场的变化滞后于电磁场的变化。(2)针对微波加热效率严重依赖于物料的介电特性的问题,根据垂直入射电磁波的反射损耗理论,分别针对微波垂直入射三种典型冶金物料(氯化钠、石英砂、石油焦),分析了含水率、温度、料层厚度对物料吸波性能的影响规律。研究结果表明：氯化钠料层的最佳加热工艺参数为温度60℃,料层厚度0.04m,该结论与文献中的实验结果基本一致。不同含水率、温度下的料层的反射损耗均与料层厚度有关；随着厚度的增加,反射损耗曲线会出现若干吸波峰,并且吸波峰的位置会随着温度和含水率的变化而偏移；在整个微波干燥过程中都取得最大的加热效率只能存在于偏移值小于八分之一波长时；并给出了典型冶金物料获得最大吸波性能的厚度范围。(3)为了探讨电磁波入射角及极化方式对微波加热效率的影响,根据斜入射电磁波的反射损耗理论,研究了微波斜入射氯化钠、石英砂和石油焦三种典型冶金物料的反射损耗,分析了微波入射角以及微波极化方式对吸波性能的影响规律。研究结果表明：微波入射角和极化方式对物料吸收微波的能力有很大影响,在整个微波加热过程中取得最大的微波吸收效率可以通过改变入射角及极化方式来达到；在水平极化电磁波(TE)下,温度为20℃,厚度为0.143m的石英砂物料在入射角为8。时取得最大的吸波效率；入射角和极化方式对不同物料吸波性能的影响并无统一的规律可循,需要根据物料的具体电磁特性进行计算分析；最后给出了三种冶金物料获得最大吸波效率的入射角范围。(4)为提高微波能在耐火材料中的传输效率,根据电磁波的功率透过系数理论,针对几种微波冶金常用耐火材料(莫来石陶瓷、氧化铝陶瓷、二氧化硅陶瓷等),研究了微波频率、温度、耐火层厚度对耐火材料透波性能的影响规律。结果表明：在2.45 GHz频率下,[0,0.1m]厚度区间内,20℃～1000℃范围内二氧化硅陶瓷的透波效率均在70%以上；耐火材料的功率透过系数曲线随着耐火层厚度的增加呈波动状分布,其中存在若干个透波峰；随着温度的升高,透波峰位置出现了向较小厚度方向偏移的现象,且随着材料厚度增加,透波峰偏移值增大；功率透过系数曲线中透波峰幅值随着温度的升高和厚度的增加而减小；最后给出了耐火材料选用原则及厚度优选范围。
[Abstract]:Microwave metallurgical furnace is one of the key equipment of microwave metallurgy. But for a long time, the heating efficiency of the microwave metallurgical furnace has been puzzling the academic and industrial circles, which affects the application and popularization of this technology. Many researchers have made a great deal of improvement on the angle of adjusting metallurgical parameters. However, the research shows that microwave metallurgy is used. The heating efficiency of the furnace is closely related to the wave performance of the heated material, the wave performance of the refractory material and the incidence angle and polarization mode of the electromagnetic wave. These factors interact with the microwave heating efficiency in a complex way. Therefore, to improve the heating efficiency of the microwave metallurgical furnace, the lining, material and electricity of the furnace must be improved. The direct factor affecting the heating efficiency of the microwave metallurgical furnace is the efficiency of the conversion of microwave to the internal heat source. The essential factors affecting the conversion of microwave to internal heat source include three aspects: the first is the absorption characteristic of the heated material; the two is the polarization mode and the entry of the electromagnetic wave. This study is devoted to improving the heating efficiency of the microwave metallurgical furnace and improving the design level of the microwave metallurgical furnace. In view of the essential factors affecting the microwave heating efficiency, the physical parameters, geometry size and entry of the typical metallurgical materials and the microwave metallurgy Refractory materials are studied in this study. Three The influence of electromagnetic wave frequency, polarization mode and incident angle on the absorption efficiency of heated materials and the permeability of refractories is studied. (1) in order to study the distribution of the electromagnetic thermal coupling field of the microwave metallurgical furnace with built-in furnace lining and material, the internal lining (fire resistance) is studied based on the theory of multi physical field coupling. The distribution of the electromagnetic field and temperature field in the microwave resonant cavity of the material, the distribution of the temperature field in the microwave resonant cavity of the material, and the dynamic change of the hot spot and the electromagnetic field in the material and the fire-resistant insulating layer during the microwave heating process. In the pre heating period, the microwave energy is mostly dissipated in the material, and the microwave energy absorbed by the lining is less. In the middle and late stages of the microwave heating, the microwave energy absorbed by the furnace lining is more than the microwave energy absorbed by the material. When the temperature is high, the material mainly absorbs the microwave energy on the surface part, and the heating unevenness becomes obvious; the temperature of the waveguide feed outlet is high and microwave is high. After 8000s, the depth of the microwave penetration is less than 10 cm., and the distribution of the temperature field is basically the same as the distribution of the electromagnetic field, that is, the high field intensity corresponds to the hot spot. The temperature field can only follow the change of the electromagnetic field slowly in the new electromagnetic field mode, that is, the change of the temperature field lags behind the change of the electromagnetic field. (2) the microwave heating efficiency depends heavily on the dielectric properties of the material, and the reflection loss of the vertical incident electromagnetic wave is based on the problem of the dielectric properties of the material. Three typical metallurgical materials (sodium chloride, quartz sand, petroleum coke) are analyzed in theory. The influence of water content, temperature and thickness of material layer on the absorbing properties of materials is analyzed. The results show that the optimum heating parameters of the NaCl layer are temperature 60 C and the thickness of the material 0.04m. The conclusion is with the experimental knot in the literature. The reflection loss of the material layer at different water content is related to the thickness of the material layer. With the increase of the thickness, the reflection loss curve will appear a number of absorption peaks, and the position of the absorption peak will shift with the change of temperature and water content, and the maximum heating efficiency can only be saved during the whole microwave drying process. In order to investigate the influence of the incident angle and polarization of the electromagnetic wave on the microwave heating efficiency, the influence of the incident angle and polarization of the electromagnetic wave on the microwave heating efficiency is given. (3) the microwave oblique incidence of sodium chloride, quartz sand and petroleum coke three are studied in order to investigate the influence of the incidence angle and polarization mode of the electromagnetic wave on the microwave heating efficiency. The influence of microwave incidence angle and microwave polarization mode on the absorption properties of typical metallurgical materials is analyzed. The results show that microwave incidence angle and polarization mode have great influence on the ability of microwave absorption, and the maximum microwave absorption efficiency can be changed into the microwave heating process. In the horizontal polarization electromagnetic wave (TE), the quartz sand materials with the temperature of 20 and the thickness of 0.143m obtain the maximum absorption efficiency when the incident angle is 8.. The influence of the incident angle and polarization mode on the absorbing properties of different materials is not uniform, and the specific electromagnetic properties of the material should be calculated. In the end, the incidence angle range of the maximum absorption efficiency of three metallurgical materials is given. (4) in order to improve the transmission efficiency of microwave energy in the refractory material, according to the theory of the power transmission coefficient of the electromagnetic wave, some microwave metallurgy Refractory materials (mullite ceramics, alumina ceramics, silica ceramics, etc.) are studied. The effect of frequency, temperature and thickness of refractory layer on the permeability of refractories has been studied. The results show that in the 2.45 GHz frequency and within the thickness range of [0,0.1m], the transmittance efficiency of silica ceramics within the range of 20 to 1000 C is above 70%, and the power transmission coefficient curve of the refractories fluctuates with the increase of the thickness of the refractory layer. With the increase of temperature, the displacement of the wave peak is shifted to a smaller thickness. With the increase of the thickness of the material, the displacement of the wave peak is increased, and the peak amplitude of the power transmission coefficient decreases with the increase of temperature and thickness. Finally, the refractory material is selected as the original. And the optimum range of thickness.

【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TF061

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