循环流化床中磷石膏还原分解实验研究及数值模拟

【作者】 张伟；

【导师】 宁平；

【作者基本信息】 昆明理工大学 ， 环境工程， 2009， 硕士

【摘要】 磷石膏是磷酸工业生产的磷酸盐副产物。我国工业副产品磷石膏每年约3000万吨,大量堆存,利用率低。磷石膏由于有害的重金属、硫酸盐、氟硅酸盐、氢氟化物蒸发造成了水体和空气的污染。由于磷酸生产工业和磷石膏堆放对地表水污染造成了很多的环境问题。磷石膏一般的工业处理方法有很多。总结起来一般分为三个方面,即化学法、物理法和热处理法。有时在一个处理磷石膏过程中三种方法都用到。本文针对目前磷石膏分解制硫酸联产水泥技术存在的主要问题,提出以循环流化床作为反应器,用高硫煤代替焦炭还原分解磷石膏制硫酸联产水泥新技术。本文研究主要包括以下三个方面：1.磷石膏还原分解反应条件及影响因素研究在本研究中,通过利用高硫煤作为还原剂对磷石膏进行了高温热分解实验,实验、中随着反应温度的升高,磷石膏的分解率与脱硫率升高,磷石膏的分解率达到97%的反应时间逐渐减少。而且在还原性气氛增加的情况下,反应时间会减少。还原性气氛越强,磷石膏的分解率越高,反之,则磷石膏的脱硫率越低,说明磷石膏在弱还原性气氛下分解是较为有利的。2.循环流化床工艺流程及参数计算对模拟实验所用循环流化床装置及流程进行了详细研究；对磷石膏物料颗粒的临界流化速度、终端速度参数进行计算；同时对流化床实验台分布板、物料循环量进行了分析；对快速床及其特点进行了研究；对由湍流床向快速床以及快速床向密相气力输送床的流型转变进行说明并且对转变速度进行计算。3.循环流化床提升管冷态数值模拟计算运用大型流体工程计算商业软件Fluent对实验台进行了数值模拟研究,联合使用流体仿真前处理软件gambit进行了网格划分,采用气固两相流欧拉模型和标准k-ε湍流模型,克服了以往由于几何建模困难和模型选择不当问题而导致模拟结果不理想的局限。模拟采用非稳态,分离式求解器,使与实际比较接近。对气速随床高分布、磷石膏物料颗粒体积分数分布、物料颗粒迹线模拟结果分析。当分布板小孔气体进口气速增大时靠近气体分布板附近的气速也有所增大；随着流化风速的增大提升管内物料颗粒体积分数相对减小；当气速增大时,磷石膏物料颗粒在循环流化床中停留时间也相对减少；当气速为65m/s时迹线有折回和回流,也有各线条之间的交叉和混流,这就证明了流体流动的随机性、复杂性和难以预测性。对压力差分布结果、不同流化风速下湍动能、耗散率结果进行分析。当流化风速增大时,沿床高的压力差减小；当流化风速减小时,沿床高压力差增大。随着风速的增大湍动能基本呈降低趋势,而且下段湍动能减小,上段湍动能增大。同时,随着风速的增大湍动耗散率基本呈升高趋势,而且下段湍动耗散率减小,上段湍动耗散率有所增大。更多还原

【Abstract】 Phosphogypsum is a kind of gypsum that occurs as a by-product and is obtained from phosphate rock during the production of phosphoric acid in fertilizer plants. In view of the problem of phosphogypsum of 30 million tons per year in China, s industry with low utilization and high pile—up. Phosphogypsum causes water and air pollution due to the presence of noxious vapor containing heavy metals, sulphates, fluorosilicates, hydrogen fluorides. Many environmental problems arise throughout the entire chain, one of which is the production of phosphoric acid, which is particularly well-known for the discharge of waste phosphogypsum into surface water and the release of the highly polluting substances. There are various ways to treat phosphogypsums for utilisation in industry. The treatment methods can roughly be divided into three different types, namely, chemical, physical, and thermal methods of treatment. Sometimes a specific process employs a combination of these different approaches to treat the phosphogypsum and convert it into a suitable product for use in industry. This article in view of the current exist major problems in the decomposition of Phosphogypsum to product cement and sulfuric acid techniques, proposed the new technologies of that using high-sulfur coal to replace coke to restore the system decomposition of phosphogypsum to product sulfate and cement in circulating fluidized bed reactor.This dissertation is composed of three main parts:I Study on the reaction condition and influencing factors of phosphogypsum deoxidization and decomposition.In this study, Raise deoxidization and decomposition Phosphogypsum using high sulfur coal on the high temperature. In the experiment with the advance of reaction temperature, the resolution ratio and desulfurization degree of the phosphorus gypsum elevates, the resolution ratio of phosphorus gypsum achieved 97% and reaction time gradually decrease. And in the situation of increasing reducing atmosphere, the reaction time can reduce. Reducing atmosphere stronger, the resolution ratio of phosphorusgypsum higher, otherwise, the desulfurization degree of phosphorusgypsum is lower, we can conclude that the decomposition of phosphorusgypsum is more advantageous under the weak reducible atmosphere.II Circulation fluid bed technical process and parameter computationCarried out a detailed introduction flow of the simulation experiments using circulating fluidized bed plant; calculated the parameters of the Phosphogypsum material particles’ critical fluidization velocity and terminal velocity; At the same time, analyzed the gas distributor of test-bed fluidized bed plate, solid circulating rate; introduced the characteristics of fast bed; carried on the handling bed’s flow pattern transformation of turbulent bed to fast bed, as well as fast bed to the dense-phase pneumatic conveying bed and carries on the computation to the transformation speed.III Circulating fluidized bed riser cold numerical simulationUtilized large-scale fluid engineering calculation commercial software Fluent to conduct the numerical simulation research to the laboratory bench, before the union use fluid simulation, has processed software gambit to carry on the grid division, used was mad that the solid two phase current Euler model and the standard k-e rapids model, haved overcome formerly as a result of the geometry modelling difficulty and the model selection not, when the question caused the analogue result not ideal limitation. The simulation uses the unsteady state, the separation formula solution, causes with actual compared to close. Explained simulation results of the gas velocity follow bed height distribution of phosphogypsum particle, volume fraction distribution of materials, material particles trace. When the distribution of plate holes gas imports gas velocity increases near the gas distributor plate near the gas velocity has also the increase; With the flow of the wind speed increases Riser material particle volume fraction is relatively decreased; when the gas velocity increases, the phosphogypsum material particles in circulating fluidized bed in the residence time is also relatively reduced; When the gas velocity for 65m/s when the trace has to retract and return, but also between the lines cross and Francis, which is proof of the stochastic fluid flow, complexity and unpredictable nature. Analyzed the results of the stress distribution of bad results, under different flow of wind turbulence kinetic energy dissipation rate to. When the flow of the wind speed increases, the stress along the bed height decreases bad; when the flow of the wind speed decreases, the stress along the bed height increased bad. With the wind speed increases the basic turbulent kinetic energy is decreasing, but also reduced lower turbulent kinetic energy, turbulent kinetic energy increases on paragraph. At the same time, as the wind speed increased turbulent dissipation rate was increased the basic trend, but lower turbulent dissipation rate decreases, the upper turbulent dissipation rate has been increased.更多还原