喷动床反应干燥制备超细碳酸钙过程研究

【作者】 朱涛；

【导师】 林诚；

【作者基本信息】 福州大学 ， 化学工程， 2002， 硕士

【摘要】 目前，国内外生产超细碳酸钙主要采用碳化法。前人的研究虽然取得了一定的进展，还存在着如下的共同问题：整个过程要经过反应、结晶、过虑、干燥、粉碎等几个单一的步骤才能获得最终产品；此外，尽管通过提高气体的传质速率强化了碳化反应过程，但在浆液体系中，由于产物结晶有可能包裹反应物颗粒表面，阻滞反应的进行，这极可能是造成在理论上极快的离子型反应过程而在浆液中反应却需多次循环持续时间达一个小时左右甚至几个小时的原因。 喷动床技术，由于具有良好的气固接触特性和对该技术研究的逐渐深入，其应用领域不断拓展，已发展成为一项新型干燥技术。 鉴于碳化法制备超细碳酸钙反应特征和气固喷动床特点，我们提出用气固喷动床制备超细碳酸钙的反应—干燥集成化技术新概念。即在喷动床内以惰性粒子为辅助介质，通入热混合气体（空气和二氧化碳）的情况下喷动或流化，同时加入氢氧化钙溶液，浆液在喷嘴出口处被雾化并均匀地分布在流化的固体颗粒上，同时在颗粒的碰撞作用下完成反应与干燥过程。所以，本实验研究工作分为以下两部分： （1）在内径为42mm的喷动床中，实验考察了C0₂分压，Ca（OH）₂初始浓度和进气温度等操作参数对碳化反应转化率和产品形貌的影响；研究了各影响因素与反应转化率的关系，建立了碳化反应宏观动力学方程。 （2）在200×30×480mm的二维锥形喷动床进床进行了喷动床流体力学实验研究。测定了不同物料、静床高和喷动气速对床层压降、最小喷动速度和床层空隙率的影响。实验研究获得了以下主要结果： 　（1）经透射电镜、XRD射线衍射和水份分析仪分析检测，在惰性粒子喷动床（PPSB）中，以氢氧化钙和二氧化碳为原料，工艺条件为混合气体进气温度60℃（此时，床内温度为311K），C0₂分压为0.312atm，Ca（OH）₂浓度为1.1mol／L，制得了粒径为80nm，含水量低于0.15％的方解石型超细碳酸钙。 （2）对在喷动床中的碳化反应进行了物料衡算，得到转化率与操作条件的关系式 福州大学硕士学位论文 摘要 并且利用实验数据进行了回归拟合，得到了模型参数 ho、E、n和 m的值和宏观动 力学方程为： ．＿＿＿n．、。－。。一7if09／ t＿1．Ic o， no二2＿一0598‘““”W， I、r。l＝IN X 4 M”—“t”“、“’”o／R T／ 飞一厂J／一二J·O J I7。几J。e”“‘（’ A岁——”—一‘c口二 一／口 一 人JJ 模型计算值与实际测量值能较好地吻合。 和 （3）在二维锥形喷动床中，随着入口喷动气体的表观速度增加，根据表观流体 和总压降的关系以及床内颗粒的运动状态，锥形床中依次出现固定床、起始喷动床、 喷动床和射流喷动床；反向减小喷动气速时，依次出现射流喷动床、喷动床、起始 流化床和固定床，两条压降曲线不重合。 （4）对不同静床高、不同颗粒下的最小喷动速度数据进行多元非线性处理，回 归拟合得出了二维锥形喷动床最小喷动速度的经验式： 一。二，t4、，只。凡2奸（P尸一A）。口．s；。。 比、＝ 0石 X卜子）（二）’’【－］”旧’“’。 ”八””八 尸9更多还原

【Abstract】 The conventional process to manufacture the ultra-fine CaCO3 powder is to introduce carbon dioxide (CO2) gas into calcium hydroxide (Ca(OH)2) slurry to produce CaCO3 by reactive precipitation. The precipitated CaCO3 is then dried, pulverized and classified to produce as final dry powders. Apparently, this process is composed of several operation steps, and the complexity of the process causes difficulty in controlling the operating conditions to be suitable for the powder product. Although carbonation reaction is a fast ion reaction, in fact, the precipitation operation takes a very long time because the reactants were coated by reaction product. Therefore, to develop a new process with less operation steps is very important to the production of the ultra-fine powders.Spouted bed owing to its excellent properties in heat and mass transfer between particles and gas play an important part in the drying and chemical process.In accordance with the characteristics of the carbonation reaction and the spouted bed, a new process to produce the ultra-fine CaCO3 powders was developed by using a powder-particles spouted bed (PPSB). In this process, the powder-particle spouted bed (PPSB) was used as a reactor in which gas involving CO2 was reacted to Ca(OH)2 slurry, and the producted CaCO3 powders were simultaneously dried by the hot gas. This process supplies a method to produce dry fine particles simultaneously. Experiments were carried out in a spouted bed with a 42mm diameter to study the effects of theoperating conditions on conversion of Ca(OH)2 and properties of the powder product. In a two-dimensional spouted bed, using glass bead and millet as experimental materials, we had surveyed the effect operation parameter ( static bed height, spouting velocity ) and the properties of experiment materials on hydrodynamics of two-dimensional spouted bed, which include bed pressure drop, minimum spouting velocity and voidage distribution. The following resulting were obtained:(1) Under the present experiment condition, powder product with average diameter 80 nm, calcium hydroxide conversion over 90% and moisture content below 0.15% had been achieved.(2) Based on the experimental results, a model considering various operating condition was developed for calcium hydroxide conversion in spouted bed.The conversion of Ca(OH)2 calculated from this model agrees well withexperiment data. The equation for carbonation reaction kinetics was obtained:(3) With increases in spouting gas velocity, there are four successive regimes found in the two-dimensional spouted bed, namely: fixed bed regime, beginning spouted bed regime, spouted bed regime and jetting spouted bed regime.(4) By regressing the experimental data, the correlation used to calculate the minimum spouting gas velocity was obtained:更多还原