【作者】 伍成波；

【导师】 张丙怀；

【作者基本信息】 重庆大学 ， 冶金工程， 2004， 博士

【摘要】 我国的铝电解工业正处在空前的繁荣昌盛时期，然而，国内的铝电解槽的槽寿命较国外普遍偏低。焙烧技术对铝电解槽的寿命有至关重要的影响，因此，焙烧技术的开发与研究对铝电解生产尤为重要。 本论文针对目前国际上火焰直接加热的燃料焙烧技术的不足，首次提出了一种新的燃料焙烧技术——铝电解槽的高温烟气焙烧技术，即用燃料燃烧产生的高温烟气来加热铝电解槽，并根据高温烟气焙烧技术的要求，开发了铝电解槽高温烟气焙烧装置，并对该技术所涉及的一些理论问题进行了深入、系统的研究。 针对电解槽炭极及扎固糊表面是否会被严重氧化等问题，首次用实验方法研究了炭极以及扎固糊在烟气中的氧化特性。实验测得，温度低于700℃时，炭极在烟气中的氧化速率在0.5mg／min·cm~2以下，仅为在空气中的3-5％；在温度高于700℃以后，电极的氧化速率开始升高，但也仅为在空气中的9％左右。另外，还用热力学和动力学理论研究了炭极的氧化机理，研究认为炭极的氧化速率取决于界面化学反应，并且在焙烧温度范围内，炭极在烟气中的氧化反应属于一级反应，反应速率常数与温度的关系在不同的温度区间相差较大。在700℃以前为：lnk=-13617／T+7.1823；在700℃以后为：lnk=-4452.5／T-2.5997。 对铝电解槽高温烟气焙烧的传热理论计算与模拟槽上进行的高温烟气焙烧的实验研究表明：高温烟气焙烧的升温速度可调的范围很大，因此，高温烟气焙烧技术能满足铝电解槽启动前的焙烧要求。由于调节灵活，升温速度和温度分布控制方便，可用此方法克服铝液焙烧和焦粒焙烧之缺点。与其它焙烧方法(焦粒焙烧、铝液焙烧、石墨焙烧)相比，该技术使电解槽升温和焙烧均匀，并且可以使阴极表面温度按优化的升温曲线自动升温，从而可以有效避免因热应力而导致的阴极裂缝现象，同时对扎缝和边部扎固糊的焙烧充分，能达到其它焙烧方法无法达到的效果。 针对高温烟气焙烧的特点，对阴极碳块导热系数对阴极温度分布的影响进行了研究，研究表明：在阴极碳块导热系数为6～10w／m.K时，阴极下表面的温度达753-817℃，阴极碳块上下表面温度差在103-163℃之间。使用导热系数小于6w／m.K的阴极碳块时，导致更大的温差，不能较好的满足电解槽的焙烧要求。因此，在阴极碳块的导热系数小于6w／m.K时，不宜用高温烟气焙烧技术来加热电解槽。 高温烟气焙烧技术装置的关键是燃烧器和分配室。针对该技术对燃烧器的特殊要求，用燃烧数学模型研究了燃烧器的性能。研究认为，燃烧器预燃室的存在重庆大学博士学位论文对提高燃烧器的燃烧效率有利，无预燃室，燃烧效率较低，最大为60%，加装预燃室后，燃烧效率能达到80%以上，但燃烧室的温度由1850K提高到了2O00K，这对燃烧室的使用寿命不利。因此，降低壁温是加装预燃室后的燃烧器设计中所要考虑的问题。由于三次风的存在，燃烧室壁温降低13OK，这对燃烧器的寿命有利。另外，通过建立分配室流动与传热的数学模型研究了分配室的流场与温度场。研究认为矩形断面分配室优于圆形断面分配室，分配室各喷口的流量与能量分配的均匀性主要受分配室入口位置、形状和入口方向、分配室断面尺寸以及喷射管结构的影响，与入口速度关系较小。并对分配室的结构参数进行了优化，得到了较合理的分配室结构尺寸。 针对铝电解槽槽内腔形状复杂同时存在多块阳极的计算对象，首次应用整体建模及祸合求解的思想，建立了铝电解槽烟气焙烧过程的数学模型，避免了计算对象中复杂的几何边界条件的处理以及大量的导热与对流的祸合边界问题，使温度场的求解简单方便，较好地解决了高温烟气焙烧时电解槽内的温度场计算。应用所建立的数学模型，计算了160KA系列和75KA系列电解槽高温烟气焙烧时的温度分布，结果表明，采用高温烟气焙烧该技术不但能方便地按升温要求焙烧好槽底阴极，而且能使边部扎固糊取得很好的焙烧效果，弥补了其它焙烧方法不能很好地焙烧边部扎固糊的缺陷。在加热末期，阴极上表面最大温差被控制在100℃左右，下表面温度可达到750℃左右，能较好地满足铝电解槽焙烧的工艺要求。同时，该方法也为复杂结构下的流动与传热的研究提供了新的途径，丰富和充实了冶金热能工程的理论研究。 研究成果应用于中国铝业广西分公司的16OKA系列和山西关铝股份公司的75KA系列电解槽上，可以做到使阴极内衬表面温度缓慢均匀上升，阴极表面温度均匀;同时，避免了燃料焙烧时扎固糊及阴极碳块燃烧损坏的可能性。 综上所述，本论文开发的高温烟气焙烧技术既具有燃料焙烧的优点，还弥补了目前国外燃料焙烧易使炭极及扎固糊表面燃烧氧化的不足，是一种较理想的铝电解槽焙烧技术，该技术的开发成功，不但填补了我国在燃料焙烧新技术的研究和开发中的空白，而且也充实和完善了铝电解槽燃料焙烧理论。关键词:铝电解槽，焙烧，高温烟气，数值计算，模型更多还原

【Abstract】 Though the reduction aluminum industry of China is in an unprecedented booming age, the life of aluminum reduction cells is totally shorter than that abroad. The baking-out of aluminum reduction cell highly affects the life of reduction cells, therefore, the research and development of bake-out technology is of great importance for the production of aluminum.Aiming at the deficiency of direct flame heating bake-out technology used internationally, this paper innovatively put forward a kind of novel fuel bake-outtechnique-high temperature fume bake-out for aluminum reduction cells. In thistechnique, the high temperature fume created from fuel burning is used to heat the aluminum cell. Also in the paper research work, the high temperature fume bake-out device has been developed according with the requirements of high temperature fume baking parameters. Furthermore, some of the theoretical problems relating to this technique were studied profoundly and systematically in this paper.Against the heavily oxidizing problem on surface of the carbon electrode and ramming paste in the fume, the oxidizing properties were firstly experimented. The results showed that when temperature is below 700, the oxidation rate of carbon in the fume is below 0.5 mg/min.cm2, which is only 3-5% of that in air. When temperature is above 700, the oxidation rate is increased very fast, but it is still 9% of that in air. In addition, the oxidation mechanism of carbon is also studied by thermodynamic and kinetic theory. From that, the oxidation rate of carbon depends on the interface chemical reaction. Within the temperature range of bake-out, the oxidation reaction of carbon in the fume belongs to the first-order reaction. The relationship between the reaction rate constant and temperature differs greatly in various temperature zones: Ink=-13617/T +7.1823 (below 700 ), Ink= -4452.5/T- 2.5997 (above 700).The theoretical calculation of heat transfer and the experimenting, on the simulating cell baked in high temperature fume, revealed that the high temperature fume bake-out technique possesses a wide range of heating speed adjusting. So that, this technique can perfectly meet the preheating requirements for the start-up of aluminum reduction cells. Owing to its flexible adjustment and convenient control on heating-up speed and temperature distribution, this technique can overcome the shortcomings ofthe bake-out by liquid aluminum and coke granule. Comparing with other bake-out methods such as coke granule bake-out, liquid aluminum bake-out and graphite bake-out, this technique makes the cell heating-up and bake-out become uniformly, and also makes temperature of the surface of cathode heat-up automatically according to a given optimized heating-up curve. As a result, the cathode crack caused by thermal stress can be avoided and the joint and ramming paste of the edge can be baked thoroughly, which can not be realized by other bake-out methods.Against the characteristics of high temperature fume bake-out, a study was also given in the coefficient of heat conductivity of cathode block effecting on the cathode temperature distribution. When the coefficient of heat conductivity of cathode block is 6~10w/m.K, temperature of the cathode lower surface is 753-817, the temperature difference of the upper and lower surface is 103-163. When using the cathode block whose coefficient of heat conductivity below 6w/m.K, more temperature differences appear so that it could not satisfy the needs of the cell bake-out. Accordingly, when the coefficient of heat conductivity is below 6w/m.K, it does not recommend to use high temperature fume bake-out to heat the cell.The key equipments in high temperature fume bake-out are the burner and dispensing house. According to the special requirements for it, the burner was mathematically modeled. The results showed that the existence of prechamber in the burner is beneficial to improve the combustion efficiency. The maximum combustion efficiency is 60% without perchamber, which is very low. When a prechamber added, the combust更多还原