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烟气直接加热结晶硫酸氨的研究
Experimental Research on Crystallization of Ammonium Sulfate by Flue Gas Direct Heating
【作者】 张廷发；
【导师】 王助良；
【作者基本信息】 江苏大学 ， 热能工程， 2009， 硕士
【摘要】 分析了氨法脱硫中硫酸铵结晶典型的工艺与设备,对传统的氨法烟气脱硫技术进行了改进和创新,研制出了新型气-液直接换热结晶系统。该系统利用烟气热能直接加热结晶硫酸铵,取消了传统工艺上的蒸汽加热系统,节能环保;结晶器通过气-液直接接触换热,换热效率高,阻力小,不易结垢。对结晶器结晶过程和气-液直接换热蒸发过程进行了数学分析,导出了结晶动力学和气-液换热蒸发传热传质相关公式,分析了气-液换热蒸发结晶硫酸铵的影响因素;设计了实验装置和关键参数的测量方法。进行了结晶器加热蒸发过程流动特性实验研究,分析了烟气流量、气体分布器型式、结晶器流动型式和溶液粘度对气泡粒度与分布和床层含气率的影响。结果表明:溶液粘度对气泡粒度及分布产生决定性影响,空气-硫酸铵体系中气泡平均直径只有0.5mm左右,粒度均匀分布。工作流量区含气率随流量呈线性变化;结晶器的流动型式对含气率的影响较大;溶液粘度对含气率的影响主要与结晶器流动型式相关,直接鼓泡床中粘度增加可以提高床层含气率,环流鼓泡床中可忽略粘度影响。实验条件下单孔环流鼓泡结晶器使用空气-硫酸铵体系,全床平均含气率变化范围为0.12～0.25,主气床平均含气率变化范围为0.40～0.70。进行了结晶器换热结晶特性的实验研究,分析了烟气流量、气体分布器型式、结晶器流动型式和热空气初始温度对硫酸铵晶体粒度大小和分布的影响。结果表明:热空气流量是控制硫酸铵结晶产量的关键控制手段;热空气初始温度是控制硫酸铵晶体粒度和产量的重要参数;使用环流鼓泡床可以提高硫酸铵晶体的粒度和产量。实验条件下,单孔环流鼓泡床结晶器硫酸铵晶体粒度大、分布均匀且产量高,晶体主粒度范围一般在180μm～420μm,通过调节热空气初始温度,硫酸铵晶体主粒度范围可以增加到200μm～2000μm;通过实验结果计算表明单孔环流鼓泡床结晶器是一种理想的高效节能型结晶系统,换热效率为88.6%。
【Abstract】 Typical technology and equipment of ammonium sulfate crystallization in Ammonia desulfurization process are analyzed and a new type of gas-liquid direct heat crystallization system has been designed by improvement and innovation on the traditional ammonia flue gas desulfurization technology. The system provides the advantages of energy-saving, environmental protection, high heat transfer efficiency and easy scaling because Steam Heating system has been abolished by gas-liquid direct heat evaporating to crystallize ammonium sulfate using of flue gas thermal energy.The mathematical analysis of crystallization and gas-liquid direct heat evaporation process is conducted. The relevant formulas of crystallization kinetics and heat and mass transfer of gas-liquid heat evaporation are derived. The experimental setup and measurement methods of key parameters are designed by analyzing of Influencing factors of crystallization and heat transfer process.The experimental study on flow characteristics of heating evaporation process of crystallizer were carried out and the effect of flue gas flow, gas distributor type, crystallizer flow patterns and solution viscosity on bubble size and distribution and on the bed void fraction were analyzed. The main results are described as follows. Solution viscosity has a decisive impact on bubble size and distribution. In air-ammonium sulfate system, the average diameter of the bubble is only about 0.5 mm and particle size distribution is even. The effect of solution viscosity on bed gas holdup is associated with crystallizer flow patterns. Increase of the viscosity in straight bubble column can enhance the bed gas holdup, but the effect of viscosity on the bed gas holdup can be neglected in circulating bubble column. Under the experimental conditions, the range of average gas holdup in crystallizer using single jet gas distributor is from 0.12 to 0.17 and the average gas holdup in the main bed is from 0.40 to 0.70.The experimental study on crystallization characteristics of crystallizer were carried out and the effect of flue gas flow, gas distributor type, crystallizer flow patterns and the initial temperature of hot-air on the ammonium sulfate crystal size distribution and yield were analyzed. The main results are described as follows. Hot air flow is a key means to control ammonium sulfate crystal yield and the initial temperature of hot air is important parameter to control ammonium sulfate crystal size and yield. The size and yield can improve by using circulating bubble column. Under the experimental conditions, there are larger size, more even distribution and higher yield of ammonium sulfate crystal in circulating bubble column crystallizer using single jet gas distributor, in which the range of ammonium sulfate crystals main particle size is from 180μm to 420μm. By adjusting the initial temperature of hot air, the range of ammonium sulfate crystals main particle size can be increased from 200μm to 2000μm in circulating bubble column crystallizer using single jet gas distributor. The circulating bubble column crystallizer using single jet gas distributor is an ideal efficient energy-saving crystallization system because its heat exchanger efficiency is 88.6% by calculating experimental date.