【作者】 霍旺；

【导师】 高翔； 程乐鸣； 倪明江；

【作者基本信息】 浙江大学 ， 能源环境工程， 2009， 博士

【摘要】 近年来随着国家对二氧化硫排放标准的日趋严格,我国引进了当前世界范围内使用较多的石灰石-石膏湿法烟气脱硫技术,应用在大型燃煤电厂上进行排放二氧化硫控制。我国发电机组普遍存在煤种不稳定、机组参与调峰等本国国情,因此在国外机组上应用情况良好的湿法脱硫工艺在国内应用过程中出现了投运率不足及脱硫性能不达标等问题。由于石灰石-石膏湿法脱硫工艺涉及到的传质及化学反应机理十分复杂,尤其是吸收段碱性液滴与二氧化硫间的气液传质机理、塔内二氧化硫浓度场的分布、脱硫过程中亚硫酸盐的氧化及硫酸盐结晶等直接关系到系统运行的稳定性和脱硫性能,有必要对此加以深入研究。本文通过深入分析石灰石浆液吸收二氧化硫过程中的物理及化学反应过程,建立了石灰石-石膏湿法吸收二氧化硫模型,通过对模型求解得出了化学反应对二氧化硫吸收的增强影响。结果表明,二氧化硫吸收化学反应增强因子随着石灰石浆液pH值的升高而增大,随着二氧化硫传质驱动力的增大呈对数关系衰减。基于模型计算结果进行了石灰石-石膏湿法二氧化硫吸收过程的数值模拟,并结合实验对数值模拟结果进行了验证,得出了进口二氧化硫浓度、烟速和喷淋量对塔内二氧化硫浓度场分布和脱硫效率的影响,研究结果可为实际喷淋塔优化设计提供指导。采用数值模拟和粒子成像技术(PIV)研究了氧气在液相中的动态传质过程。结果表明,在相同搅拌速度下,圆盘涡轮式搅拌器产生的湍流动能分布范围要大于桨式搅拌器产生的湍流动能,而且湍流动能分布更均匀,湍流强度更大,圆盘涡轮式搅拌器更有助于氧气的传质。研究了亚硫酸盐的氧化反应涉及到气液界面的动力学性质,给出了亚硫酸盐氧化反应动力学特性和传质机理。分析了亚硫酸钙由固相到液相的溶解、氧从气相到液相的扩散、液相中的化学反应对亚硫酸根氧化速率的影响,并对亚硫酸根氧化速率控制步骤进行了推断。采用铁锰金属离子作为添加剂,通过改变pH值、浆液浓度、空气流量、温度等参数,研究了石灰石-石膏湿法脱硫工艺条件对亚硫酸盐氧化速率的影响,得出了氧化速率与工艺条件的关系。结果表明在一定的pH值和亚硫酸根的浓度条件下,铁锰金属离子的存在可提高亚硫酸根氧化速率达到10-30倍。研究了石灰石-石膏湿法脱硫结晶过程对二水硫酸钙晶体的诱导时间、结晶速率、晶体尺寸分布以及形态的影响,为进一步量化金属离子对石膏晶体脱水性能的影响,开发了对SEM电镜照片的边缘检测程序。在结合离子活度的基础上,给出了湿法脱硫条件下金属离子对固相石膏晶体表面能及结晶速率的影响,实验结果表明金属离子的存在提高了结晶的诱导时间,抑制了晶体在特定方向的增长。同时金属离子对不同结晶面的生长速率影响各不相同,从而使固相石膏晶体由板状结构变为针状结构。更多还原

【Abstract】 In recent years, the emission standards of sulfur dioxide have been increasingly stricted.In carrying out to control the emissions of sulfur dioxide, limestone-gypsum wet FGD has been introduced and applied to the large-scale coal-fired power plant.Due to the prevalence of coal instability and the shaving peak for the national power plant, the local problem has occurred in application of wet FGD technology, such as the decreased operation hours and the removal efficiency.As a result of limestone-gypsum wet FGD technology involved in mass transfer and chemical reaction mechanism is very complex, especially the mass transfer mechanism in the absorption of sulfur dioxide by the falling alkaline droplets and the distribution of sulfur dioxide gas concentration field in the tower, the process of the oxidation of sulfite and the crystallization of sulfate were directly bearing on the operation of the system stability and desulfurization performance. These factors are very important for designing the reaction devices, reducing initial investment and operation cost, operating stably and maintaining easily and it is worth of research in depth.Both the physical performance of the spray liquid in the scrubber and the involved chemical reactions are analyzed, and a model describing the absorption process of SO2 into limestone slurry with a spray scrubber is presented, in the model. The calculations show that the enhancement factor exponentially grows with an increasing value of pH and logarithmically decays with an increasing value of the resistance force. To verify the accuracy of the model, experiments were also carried out, and the results suggest that the model, after combining the physical performance of the spray and the enhancement factor, can more precisely describe SO2 absorption in a spray scrubber. Furthermore, including the effects of the concentration of inlet SO2, flue gas velocity and spry on the fileld distribution and desulfurization performance, several simulations were launched which describe and clarify the effects of variables on SO2 absorption. The results of numerical simulation can provide a basis for further design and optimization of the scrubber.The process of oxygen transfer in a vessel was presented by CFD simulations and PIV (Particle Image Velocity). The logarithmical expression has been found which successfully describe the relation between the concentration of oxygen and the dissolution time. The disc impeller which can bring the larger turbulent kinetic energy dissipation than the narrow impeller and the dissolution concentration of oxygen grows faster with an increasing value of impeller speed.To further look through the oxidation mechanism of sulfite, mathematical models of the general oxidation of calcium sulfite were presented,which included the dissolution of calcium sulfite from solid to liquid,diffusion of oxygen from gas to liquid,and chemical reaction in liquid.Based on the experimental results of characterized kinetics,the rate control step of macroscopical kinetics was inferred. The effects of manganese and ferric ions on the rate of the sulfite oxidation was studied which is similar to the conditions of WFGD. It is shown that the combined effect of both manganese and ferric ions has 10-30 times acceleration.The influence of the presence of magnesium and ferric ions at different ratios on the rate of gypsum crystallization was explored which is similar to the conditions of WFGD. The results show that addition of both Mg2+ and Fe3+ increased induction time and decreased the growth efficiency compared with the baseline(without impurity) depending on the concentration and type of impurity. The effects of the presence of Mg2+ and Fe3+ on the surface energy and the rate of nucleation are estimated by employing the classical nucleation theory. Furthermore, an edge detection program was developed to quantify the effects of impurity on the filtration rate of gypsum product. The presence of Mg2+ and Fe3+, have a much greater reduction on the growth rate of the special faces of gypsum crystal, which leads to the formation of needle crystals compared to the baseline which favors the formation of plate or flakes.更多还原