【作者】 李勇刚；

【导师】 胡仰栋；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2011， 博士

【摘要】 随着新材料工业的发展,工业电加热设备应用越来越广泛。严格控制产品质量、降低生产能耗、保障生产安全是工业电加热设备技术进步的不懈追求。本文以过程系统工程理论为指导,采用有限元方法对高温电阻炉加热过程进行了较系统的数学模拟和工艺优化研究,以期为高温电加热过程的发展有所裨益。论文评述了过程系统工程、有限元法以及艾奇逊式电阻炉的特点及发展。介绍了开源有限元模拟分析软件FEPG;讨论了高温电阻炉的进展,重点分析了碳化硅合成炉和石墨化炉在炉型改进、工艺提高和模拟优化方面的国内外研究动态。在分析电阻炉加热过程中所存在问题的基础上,提出了本文的研究方向。通过对艾奇逊式电阻炉的炉型分析,应用虚功原理,建立了高温电阻炉在二维动态非线性传热有限元模型;同时,对反应过程产生气体的情况进行了分析,建立了二维传热-渗流耦合的有限元模型;结合炉体和部件的应力和形变情况,又建立了三维的传热-形变-应力耦合的有限元模型。因为炉料由多种颗粒组成,采用混合模型将其简化为分层拟均相模型,并采用修正的热逾渗理论模型进行描述。通过对直通电石墨化炉的有限元计算,并与现有文献比较,结果表明:本文所建立的传热有限元模型和多种颗粒组成炉料的有效导热系数的计算方法是有效的。采用建立的传热有限元模型,对一有效宽高为2.1m×1.9m、炉芯宽高为0.35m×0.6m、单位体积炉芯负荷8.5×10~5W/m~3的艾奇逊炉碳化硅生产过程进行了模拟和分析:(1)具体分析了炉内动态的温度场分布、不同时刻炉料水平线上温度梯度变化、热流密度变化情况,系统的考察了炉内产品产量和单位产品能耗随生产进行的变化趋势。结果表明产品产量随时间线性增长,单位产品能耗呈现从高到低,然后平稳,最后上升的变化趋势。考察炉芯表面温度可知其与产品能耗密切相关。能耗较低的平稳阶段对应于从炉芯表面温度上出现了2600℃温度点,到全部表面温度均超过2600℃。这意味着该阶段是炉芯热效率最高的阶段。炉芯表面完全达到碳化硅分解温度的时刻,正是能耗较低产量较高的时刻,因此也是生产停炉的最佳时刻。对温度梯度和热流密度进行分析,发现温度梯度最大的阶段出现在合成碳化硅的温度区域内,而且随着时间增长炉表面散热的热流密度也增长。(2)喷炉问题是碳化硅炉生产中迄今仍没有完全解决的问题。本文应用传热-渗流耦合的有限元模型,分别系统地考察了正常生产条件、增大炉芯功率和增加密度导致渗流系数变小三种条件下,炉底气体压力和炉表气体流量变化。发现了喷炉的具体原因:1)炉料配置不合理,导致气体渗流系数变小。2)功率过高,导致化学反应过快造成炉产生的气体不能及时渗透出去。(3)石墨电极在碳化硅或石墨化炉生产过程中,部分在炉体外部,部分与炉内高温物料接触,并且自身也会通电发热。为考察电极在这种情况下是否发生损坏,应用传热-形变-应力耦合的有限元模型进行过程分析。具体考察了电极内部和外部的温度分布、电极的整体形变和电极的主应力分布的情况。结果显示:凸出炉体外部电极表面温度不超过90℃,不会发生氧化反应导致的损耗;电极整体温差小于20℃,不会因为热应力和体积力作用导致电极发生形变。因此电极在正常生产条件下不会发生损坏现象。为进一步加强电极保护,根据计算结果提出了电极保护涂层的厚度的工艺方案。为解决现有艾奇逊碳化硅炉生产能耗高、有喷炉安全隐患的问题。本文以系统过程工程理论为指导,应用传热-渗流耦合有限元模型,对有效宽高2.3m×2.1m、炉芯宽高0.4m×0.6m、单位体积炉芯负荷8.8×10~5W/m~3的碳化硅炉型生产过程进行模拟。作者将生产过程分为三个阶段:1)生产前期,热能主要用于炉体预热、碳化硅合成尚未开始或反应微弱,该过程应尽快完成以减少散热损失。2)生产中期,炉料开始反应到炉芯表面局部达到2600℃,该阶段应尽快完成,但要注意避免发生喷炉。3)生产后期,从炉芯表面局部达到到全部超过2600℃的阶段,该阶段应在保证碳化硅继续生产的同时控制碳化硅的分解和炉表的散热。在对三个阶段分析基础上,以喷炉压力为主要限制条件,建立以能耗最小化为目标函数的优化模型和简化的优化策略,获得了优化的功率曲线。计算结果表明应用优化的功率曲线可避免喷炉发生;选择不同的停炉时间,可分别获得能耗降低约8%且产量增加3%和增产约12%且能耗降低约5%的两种较优的结果。现有文献表明,石墨化炉和碳化硅炉由于炉料预热和炉表散热,单炉热效率仅为50%左右,热损失巨大。在对两炉有限元分析的基础上,提出了直通电石墨化炉联产碳化的新工艺,以上述单位体积炉芯负荷为8.5×10~5W/m~3的炉型为例。研究表明:扣除石墨生产耗能后,生产碳化硅的能耗为原碳化硅炉的50%,产量为54-68%;此外联产炉还减少了总的废气排放;为解决现有炉型保温效果不佳、通气性差容易发生喷炉、产品品质不高、能耗高和粉尘污染等问题,本文提出了一种增强保温的并联式、全透气的生产碳化硅的新炉型。对该炉型不仅增强了保温效果,而且还彻底解决了喷炉问题,使生产中产生的气体不仅及时的排放出去而且还为炉体的保温做了贡献,新炉型还可配合气体收集装置将气体汇总处理减少了环境污染,该炉型可以由现有炉型经简单改造而成,改造后能耗降低达15-17%,节能效果显著。更多还原

【Abstract】 With the development of new material industry, the industrial electric heating equipment is widely applied. Controlling product quality, decreasing energy consumption, keeping production safety are the goals for the development of industrial electric heating equipment. This paper treated the Process System Engineering (PSE) Theory as guide, applied the Finite Element Method (FEM) to analyze the heating process of high-temperature resistance furnace for benefiting the high-temperature electric heating process research.This thesis reviewed the feature and development of PSE, FEM and Acheson resistance furnace. The open source FEM software-FEPG was introduced; this work discussed the development of high-temperature resistance furnace, analyzed the research trends of furnace type improvement, process improvement and simulation optimization of silicon carbide (SiC) furnace and graphitizing furnace at domestic and overseas. Based on the analysis of question of resistance furnace heating process, this work presented the research directions.Through the analysis of Acheson resistance furnace, the 2D nonlinear dynamic heat transfer FEM model was built by principle of virtual work. Through the analysis of process of reaction release the gas, the 2D thermal-seepage coupled FEM model was built. Considering the deformation and stress of furnace and equipment component, the 3D thermal-deformation-stress coupled FEM model was built. Because the charge material is built by a variety of particle, the mixed model was simplified to stratified homogeneous model and was described by modified heat percolation model. Based on the FEM calculation and comparison with existing literature, the results showed that the FEM model built by this work and the calculation method of effective heat conductivity of charge material are effective. By the FEM model, the production process was analyzed for Acheson SiC furnace (effective width and highness is 2.1m×1.9m, furnace core profile width and highness is 0.35m×0.6m, the unit volume load of furnace core is 8.5×10~5W/m~3):(1)The dynamic temperature field distributions, temperature gradient on one horizontal line at different moment, the heat flux change were analyzed. The yield and unit product energy consumption were investigated with the process of production trend. The results showed the yield linear increase dependence the time, and the unit product energy consumption have the trend from high to low, then steady, at last rising. The temperature of furnace core surface has the closely relation with energy consumption. the steady low energy consumption phase corresponds to the process of form some point of core surface reaching 2600℃to total over 2600℃.it is means the phase is the highest stage of thermal efficiency. it is the best moment for production shutdown when the temperature of core total over 2600℃. Through analysis the temperature gradient and heat flux, the maximum temperature gradient occur the zone synthesis SiC, and the heat flux of furnace surface is increasing dependence time.(2) The spouting of Acheson SiC furnace still is the problem not resolved. This thesis applied thermal-seepage coupled FEM, investigated the pressure and gas flux with normal production condition, increasing load of core, increasing charge material density with seepage coefficient become smaller. The spouting reasons were discovered: 1) Unsuitable charging mixture ratio lead to gas seepage coefficient become smaller. 2) The higher load causes the reaction too fast to release the gas.(3) The graphite electrode part in furnace and part out of furnace, and connect with high temperature charging and itself product heat with the production process. For investigating if the electrode will be damage, the thermal-deformation-stress coupled FEM was applied. The temperature distribution, deformation and main stress of electrode were acquired. The results showed that the outer electrode temperature blow 90℃and no oxidation reaction damage, the total temperature difference less than 20 and no deformation. So the electrode will be safe in normal production condition. For enforcing the electrode safety, the programs of thickness of electrode protective coating was put forward basing the calculation results. For solving the problem of high energy consumption and spouting of Acheson SiC furnace, this work applied thermal-seepage coupled FEM with PSE theory to simulate production process of SiC furnace(effective width and highness is 2.3m×2.1m, furnace core profile width and highness is 0.35m×0.6m, the unit volume load of furnace core is 8.8×10~5W/m~3). Author divided the production process into three phases: 1) The Pre-production, the heat is used to heat the charge material and the SiC synthesis reaction not yet start, this phase should be finished as soon as possible for saving energy. 2) The mid-production, it is the phase that form reaction start to temperature of core surface over 2600℃, this phase should be finished as soon as possible but spouting must be controlled. 3) The latter-production, the phase is form some points reach 2600℃to all the surface reach 2600℃of furnace core, the reaction should be controlled to keep product increasing and decrease SiC decomposition and heat loss of furnace surface. Based on analysis of three phases, this work built minimum energy consumption as objective function and simplified optimization strategy with spouting as main limiting condition, acquired optimized power curve. The calculation results showed that applying optimal power curve will avoid spouting, the optimal results can be got that are energy consumption decreasing 8% and output increasing 3%, output increasing 12% and energy consumption decreasing 5% by choosing different shutdown time.According to the references, the thermal efficiency of SiC furnace and graphitizing furnace is about 50% because of great heat loss. based on FEM analysis of two type furnace, the LWG graphitizing furnace vice-product SiC process was put forward and the example (above mentioned unit volume load of furnace core is 8.8×10~5W/m~3 ) was simulated. The results showed that the SiC energy consumption is half of Acheson SiC furnace and output is 54-68% of Acheson SiC furnace after deduction the graphite manufacture energy, and the new process reduce the total waste gas emission; For solving the Acheson furnace’s problem of poor insulation, spouting, low product quality, high energy consumption and dust pollution, this paper put forward a new type SiC furnace with enforcing insulation, parallel, good ventilation. The new type furnace not only enforces the insulation but also avoid spouting, and the gas released as the insulation layer. The new type furnace also easy transports the gas to waste gas gathering unit. The new type furnace can be got by reform exiting Acheson SiC furnace and have 15-17% energy consumption saving after reform.更多还原