【作者】 王计敏；

【导师】 周孑民； 闫红杰；

【作者基本信息】 中南大学 ， 热能工程， 2012， 博士

【摘要】 铝熔炼炉是铝及铝合金熔铸厂的关键设备,其熔炼过程是铝加工过程中能耗较大的工序。近年来,随着我国铝加工材量的不断增加和优质铝合金铸件的需求,对铝熔炼炉热效率、污染物排放和产品质量提出了更高的要求。因此,本文通过数值模拟的方法,全面深入的研究铝熔炼炉熔炼过程,对促进铝熔炼炉的节能研究和优化设计具有重要的理论与实践意义。针对现有的蓄热式铝熔炼炉,结合其熔炼过程的运行特点,考虑燃料燃烧,燃烧空间和铝料间换热,铝料的升温熔化,氧化层的生长,蓄热式燃烧器的交替工作,热负荷的变化以及炉壁的热损失,在建立蓄热式铝熔炼炉熔炼过程基本模型的基础上,通过耦合用户白定义熔化模型、氧化烧损模型和燃烧器换向及燃烧量变化模型,运用FLUENT UDF和FLUENT Scheme混合编程,实现了蓄热式铝熔炼炉熔炼过程多场耦合的数值模拟。并以热平衡计算原理和UML(Unified Modeling Language)建模为基础,编写了蓄热式铝熔炼炉热平衡计算软件。结合某厂生产情况进行模拟计算,对数值模拟结果进行验证,同时,提出了提高铝熔炼炉热效率的有效措施。分析结果表明：(1)数值模拟结果和测试值的相对误差在5%左右,且它们的变化规律一致,分布类似,验证了蓄热式铝熔炼炉熔炼过程数学模型的可靠性和准确性,该模型能够较好反映铝熔炼炉的熔炼现象,可运用此模型进行铝熔炼炉熔炼过程工艺参数的优化研究。(2)铝料温度在固液区上升缓慢,而离开固液相线时铝料温度上升速度加快；炉膛温度随着熔炼时间先呈周期性增加,后又周期性阶梯降低,最后又开始周期性增加；氧化量随着熔炼时间呈抛物线增加；随着氧化层孔隙率的增加,铝料温度增加缓慢。(3)铝料温度相对标准差随着熔炼时间先增加,后减小,再增加；炉膛温度相对标准差随着熔炼时间先呈周期性减小,后周期性阶梯增加,又周期性减小；铝液面热流密度随着熔炼时间先增加,后减小。(4)熔化前期烟道温度随着液相率增加而减小,而熔化后期又开始增加；炉膛出口氧气浓度在熔化前期则随着液相率增加而增加,而在熔化后期恒定不变。结合要因分析图,依据某厂蓄热式铝熔炼炉的实际使用情况,确定燃烧器倾角(A/θ)、燃烧器高度(B/H)、辅助烟道(C)、旋流数(D/S)、燃烧器间水平夹角(E/α)、空气预热温度(F/T)、天然气流量(G/M)、空气消耗系数(H/n)为影响因子,研究其对蓄热式铝熔炼炉熔炼性能的影响。以其规律性分析为根据,选取铝料温度相对标准差(Y1)、熔炼时间(Y2)和炉膛温度相对标准差(Y3)为优化指标,建立了优化指标间的模糊比较判断矩阵,并以此构造线性规划模型,运用MATLAB编程求解权重向量,最后采用基于田口方法对蓄热式铝熔炼炉工艺参数进行多目标优化研究,找出最优的组合参数。最终获得如下结果：(1)根据模拟结果的非线性回归得到铝料温度相对标准差(Y1)、熔炼时间(Y2)和炉膛温度相对标准差(Y3)的表达式：(2)统计分析得到最优的铝熔炼炉工艺参数组合为A2B1C1D2E1F3G3H1。通过信噪比和均值的综合分析,得到重要因子D、E、F、G,稳健因子A,调节因子H,次要因子B、C。经试验验证模拟是成功的,试验设计所得的结果准确,具有再现性。采用试验设计所得最佳化参数提升了产品质量和熔炼过程的稳健性。(3)通过数值分析,获得了工艺参数对蓄热式铝熔炼炉熔炼性能的影响规律。为了减少炉衬的热损失和节约投资成本,针对铝熔铸行业广泛使用的反射式铝熔炼炉,以三层平壁炉衬结构为研究对象,计算分析了隔热方式对炉衬传热影响。以经济厚度法为依据,通过编程实现炉衬组合的计算机优化。同时以蓄热式铝熔炼炉热平衡测试为例,建立了包括炉衬的蓄热式铝熔炼炉数学模型,并运用计算流体力学软件FLUENT对炉窑工作制度为40周的优化前后的炉衬组合进行仿真,结果分析表明炉衬组合的计算机优化结果是成功的,可获得比较理想的经济效益。更多还原

【Abstract】 Aluminum melting furnaces are key equipment in melting and casting factory, and a large amount of energy may be consumed during aluminum and aluminum alloy process procedure. In recent years, along with raised aluminum processing yield and demand of high quality for aluminum alloy castings in our country, high thermal efficiency, less pollutant emission and good product are demanded. Hence, it is important for both theories and practices to comprehensively understand melting process of aluminum melting furnaces by numerical simulation, which will result in great improvement of energy-saving and optimization in aluminum melting furnaces.According to the features of melting process of regenerative aluminum melting furnaces, in the present work, this paper concerns fuel combustion, heat transfer between combustion space and aluminum bath, phase change, oxide growth, burner reversing and varying of heating load, heat loss through furnace walls. A mathematical model with user-developed melting model, oxide loss model, burner reversing and burning capacity model was established. This paper presents numerical simulation of melting process of a regenerative aluminum melting furnace using hybrid programming method of FULENT UDF and FLUENT Scheme. Based on the principle of heat balance calculation and UML (Unified Modeling Language), heat balance calculation software for regenerative aluminum melting furnaces was developed. By employing heat balance test data in a company, heat balance calculation was conducted with the program and numerical results were further verified and effective measures for increasing heat efficiency of regenerative aluminum melting furnaces were put forward. The following conclusions can be derived:(1) The numerical results are basically in good agreement with the experiment results. The trend of simulation results is in accordance with that of measured data, they have similar distribution and relative error is less than5%. Thus, the computational models were proven to be reliable and accurate. The results show that melting phenomenon of the furnace may be revealed thoroughly. It is also indicated that optimization of parameters for aluminum melting furnaces may be studied by the above model.(2) Aluminum temperature increases slowly with melting time in solid-liquid zone, but rises faster when leaving solid-liquid phase lines. Furnace temperature firstly increases periodically with melting time, then decreases stepwise, lastly increases periodically. Oxide weight parabolically increases with melting time. As oxide porosity increases, the increase of aluminum temperature becomes slow.(3) RSD (relative standard deviation) of aluminum temperature firstly increases, then decreases, finally increases. RSD of furnace temperature firstly decreases periodically with melting time, then increases stepwise, finally decreases periodically. The heat flux through aluminum surface firstly increases with melting time, then decreases slowly.(4) In early melting stage, flue gas temperature decreases with liquid fraction, then increases in later melting stage. Oxygen concentration in flue gas increases with liquid fraction in early melting stage, then remains constant in later melting stage.With cause and effect diagram of performance for aluminum melting furnaces, vertical angle of burner (A/θ), height of burner (B/H), secondary flue (C), swirl number (D/S), horizontal angle between burners (E/α), air preheated temperature (F/T), natural gas mass flow (G/M), and air-fuel ratio (H/n) were selected to investigate their effects on the performance of aluminum melting furnaces. Based on the analysis of preliminary experimental tests, RSD of aluminum temperature (Y1), melting time (Y2) and RSD of furnace temperature (Y3) were selected as evaluation criteria, and this study used fuzzy judgment matrix and created a linear programming model in order to solve the weights for the evaluation criteria by MATLAB. CFD technique, in association with the Taguchi method was employed for parameter optimization of melting process of aluminum melting furnaces. The main conclusions are drawn as follows:(1) By non-linear regression on the base of simulation results, the empirical correlations for the RSD of aluminum temperature (Y1), melting time (Y2) and RSD of furnace temperature (Y3) are obtained as follows:(2) By statistical analysis of evaluation criteria such as RSD of aluminum temperature (Y1), melting time (Y2) and RSD of furnace temperature (Y3), the optimum condition of aluminum melting furnaces is A2B1C1D2E1F3G3H1. Through ANOVA (Analysis of Variance) and ANOM (Analysis of Means) for S/N ratio (signal-to-noise ratio) and mean value, the factors are classified into four categories as follows: important factors are D, E, F and G, robust factor is A, regulatory factor is H, and secondary factors are B and C. It is indicated that numerical simulation of aluminum melting furnaces is successful through the confirmation experiment. And the results are accurate and reproducible. The product quality and robustness of process development with the optimal parameter may be improved.(3) The rules of influence factors on performance of aluminum melting furnaces are achieved by numerical analysis.To reduce heat loss and save cost, three-layer slab was simplified for furnace linings of widely-used aluminum reverb furnaces in aluminum casting industry. Heat transfer analysis of different heat-insulating mode on furnace lining was carried out. Based on economic thickness method, furnace linings were optimized by computer programming. On this basis, a three dimensional mathematical model of aluminum melting furnaces including linings was developed. Furnace linings with40-week work system of before and after optimization were simulated by CFD software FLUENT. It is indicated that the results of optimization are successful and ideal economic effect is obtained.更多还原