【作者】 孙振邦；

【导师】 阎富生；

【作者基本信息】 东北大学 ， 动力工程及工程热物理， 2017， 硕士

【摘要】 石灰是一种非常重要的工业原料,被广泛的应用于建筑、冶金、化工以及水处理等多个领域。生产石灰的主要设备是石灰窑,它具有高能耗、高二氧化碳单比排放量等特点,传统石灰窑由于结构的限制,使得石灰窑内物料的受热均匀性无法保证,导致了能源利用率低下并且生产的生石灰质量越来越无法满足工业生产的需求。在这种情况下套筒式对烧石灰窑应运而生,其主要特点是燃烧室在环形窑的相同高度内外套筒上成环形交错分布,并且每个燃烧室的出口位置设有挡火墙,意在避免火焰与物料直接接触造成局部高温。套筒式对烧石灰窑是新型环形窑的一种,国内外鲜有研究。本文研究的主要目的是深刻理解石灰石的分解机理以及相应的操作参数对套筒式对烧石灰窑温度场分布的影响,最后从节能环保的角度提出建设性意见。研究套筒式对烧窑主要是为了提高生石灰的活性度以及降低燃料消耗。这就需要认真研究石灰石的分解机理以及相应的操作参数对石灰窑内气、固温度分布的影响。为此,本文一方面建立了收缩核模型来研究石灰石的分解行为以及粒径、温度、二氧化碳浓度对石灰石分解过程的影响;另一方面建立了石灰窑内预热带、煅烧带、冷却带的温度场控制模型,研究了燃料的燃烧位置、燃料种类以及产量对套筒式对烧石灰窑内气、固温度的分布的影响。本文主要采用的研究方法是C语言编程计算,即在Visual C++6.0平台下采用改进欧拉法通过C语言编程来分析了相关参数对石灰石分解过程的影响,并且在建立预热带、煅烧带、冷却带数学模型的基础上,运用四阶-龙格库塔法编写程序解决各带复杂的微分方程组并获得石灰窑内连续的温度场分布。最后通过能量分析法以及(火用)分析法对套筒式对烧窑的节能潜力进行了研究。主要研究结论为:(1)石灰石在空气的气氛中分解的起始温度为750℃,分解过程中将会经历三个阶段,初始阶段石灰石反应区前沿温度和颗粒表面的温度都会迅速增加,但颗粒表面的温度会升高的更快些;之后进入稳定阶段,颗粒吸收的热量绝大部分用于石灰石分解所需要的反应热,颗粒表面的温度与石灰石反应界面前沿的温度基本上保持相应的稳定值;进入终了阶段后石灰石分解基本停滞,反应区前沿温度与颗粒表面温度快速升高到环境温度值。(2)当石灰石所处的外界气氛以及温度相同时,随石灰石颗粒直径的增加,石灰石分解所需要的时间增大幅度越来越大,即直径越大,内部越难分解;当石灰石所处的外界气氛以及粒径相同时,随温度的增加,石灰石分解所需要的时间越来越短;当石灰石所处的外界环境温度以及粒径相同时,环境中二氧化碳的浓度越高,石灰石分解越慢,石灰石分解所需要的时间随二氧化碳浓度的增加呈指数型增长。(3)当燃料在套筒式对烧窑的燃烧室内完全燃烧时,由于燃料的化学能在燃烧室内瞬间完全释放出来,致使燃烧室出口段烟气持续高温,最高温度为1718℃,增大了石灰石烧结的概率,不利于氧化钙活性度的提高;若50%的燃料在燃烧室内燃烧,窑膛内的最高温度为1455℃,比燃料完全在燃烧室燃烧降低了 263℃,这样不仅可以避免持续高温区,而且可以减轻火焰与物料直接接触所造成的影响。(4)在套筒式对烧窑内当所采用的燃料种类变化时,燃料的热值与空燃比共同决定了窑内煅烧带气体与固体温度分布的高低,若燃料的热值越大,空燃比越小,窑内煅烧带气体与固体的温度越高。(5)在套筒式对烧石灰窑内当日产量降低时,预热带的初始阶段气、固温度变化率会变大,煅烧带相同位置处气、固的温度有所升高,冷却带的冷却速度会变大,产品的出口温度会减小。(6)(火用)分析法要比能量分析法更加全面,它能够识别和量化热力学过程的不可逆性;在套筒式对烧石灰窑相同的操作参数下,(火用)效率(34.69%)要明显低于其热效率(77.07%);(火用)分析法为提高石灰窑的节能潜力提供了新的研究方向,即为了降低石灰窑内燃料的消耗不仅要减少石灰窑烟气所带出的(火用)损失,而且要重点关注燃料燃烧过程和热量与动量传递过程所造成的(火用)破坏。更多还原

【Abstract】 Lime is a very important industrial raw material,which is widely used in construction,metallurgy,chemical,water treatment and so on.The apparatus for producing lime is lime kiln,the characters of which are high energy consumption and high single carbon dioxide emission.The traditional lime kiln can’t ensure the uniformity of heating in the lime kiln due to their structures,which lead to the low energy efficiency and the quality of quicklime more and more unable to meet the needs of industrial production.In this case the double-sleeved twin burn limekiln came into being,the characters of which are the annular staggered distributed combustion chambers on the inner and outer sleeves at the same height of the shaft kiln and the fire walls arranged at the exit position of each combustion chamber intended to avoid particles directly contact with the flame causing local high temperature.The double-sleeved twin burn limekiln is a kind of new type annular shaft kiln,which is rarely researched at home and abroad.The main purpose of this study is to deeply understand the decomposition mechanism of limestone and the impact of corresponding operating parameters on the temperature field of the double-sleeved twin burn limekiln,and finally put forward constructive suggestions from the perspective of energy saving and environmental protection.Researching the double-sleeved twin burn limekiln is mainly to increase the activity of lime and reduce the fuel consumption.It is necessary to careful study of the decomposition mechanism of limestone and the impact of corresponding operating parameters on the temperature distribution of gas and solid in the lime kiln.On the one hand,the shrinking core model is established to study the decomposition behavior of limestone and the effects of particle size,temperature and C02-concentration on the decomposition process of limestone.On the other hand,the temperature field controlling model is established,which including preheating zone,calcination zone and cooling zone,meanwhile,the effects of fuel combustion location,fuel type and yield on the temperature distribution of gas and solid in the double-sleeved twin burn limekiln are studied.In this treatise,the calculation process is carried on by the C language programming,which is to use the Improved-Euler method to analyze the effect of relevant parameters on the limestone decomposition process under the Visual C++6.0 platform.With the mathematical model including preheat zone,calcination zone and cooling zone developed,the complex differential equations are solved by fourth-order Runge-Kutter method based on programming to get continuous temperature distribution in the lime kiln.At last,the energy saving potential of the double-sleeved twin burn limekiln is studied by energy analysis and exergy analysis.The main conclusions are as follows:(1)The decomposition starts in the air when temperature of limestone is 750℃,and the decomposition process will go through three stages.In the initial stage,the front temperature of reaction zone and the particle surface temperature will increase rapidly,but the former will increased faster;after that coming into steady stage,the heat absorbed by the particles is mainly used to the decomposition of limestone,and the front temperature of reaction zone and the particle surface temperature will basically maintain the corresponding stable value;in the final stage,the decomposition of limestone will be basically stagnant,and the front temperature of reaction zone and particle surface temperature will quickly increase to ambient temperature values.(2)When the gas composition and calcination temperature are the same,the increasing amplitude of limestone decomposition time becomes greater with the diameter of limestone particle increasing,that is to say,the larger the diameter of limestone is,the harder for the decomposition to proceed;when the gas composition and particle diameter are the same,the higher the temperature is,the shorter decomposition time is required;when the ambient temperature and particle size of the limestone are the same,the higher concentration of carbon dioxide is,the slower the decomposition process is,meanwhile,the calcination time of limestone rises exponentially with increasing CO2 partial pressure.(3)When the fuel combusts completely in the chamber of the double-sleeved twin burn limekiln,the temperature of gas on the exit section keeps rather high due to the chemical energy releasing completely in a short time in chambers,the maximum of which is up to 1718℃,leading to the probability of sintering increased and the activity of lime hardly to improve;while the maximum temperature is 1455℃ in the kiln chamber,and the temperature of gas reduces to 263℃,when only fifty percent of the fuel burns,in this case,the continuous high temperature zone can be avoided,and the impact of flame directly contacting with of materials can be reduced.(4)When the fuel is changed,both the calorific value of the fuel and the air-fuel ratio determine the temperature distribution of the gas and solid in the calcined zone.If the calorific value of the fuel is larger and the air-fuel ratio is smaller,the gas and solid temperature is higher in the burning zone.(5)When the daily output of the double-sleeved twin burn limekiln reduces,the gas and solid temperature changing rate will increase at the initial stage of the preheating zone,the temperature of gas and solid at the same location of the calcination zone will increase,the cooling rate will increase in the cooling zone and the temperature of production will be lower.(6)Exergy analysis method is more comprehensive than the energy analysis,which can identify and quantify the irreversibility of thermodynamic process;the exergy efficiency(34.69%)is significantly lower than the thermal efficiency(77.07%)for the same operating parameters of the double-sleeved twin burn limekiln.The exergy analysis provided a new research direction for improving the energy saving potential of the double-sleeved twin burn limekiln.In order to reduce the consumption of lime kiln fuel,it is necessary not only to reduce the exergy lost with the exhaust gases,but also to focus on the exergy destruction due to combustion and the exergy destruction due to heat and momentum transfer.更多还原