循环流化床半干法脱硫装置烟道流场模拟优化

Flue flow field simulation and optimization in CFB semi-dry desulfurization plant

在循环流化床半干法脱硫系统中,流场特性对于系统安全稳定运行、提高脱硫效率至关重要,其中,流场均匀性和稳定是整个系统的关键点。只有流化床设计和输送设备合理才可能保证脱硫系统的稳定高效运行。采用CFD数值模拟方法,结合某300 MW燃煤机组炉外半干法脱硫工程实例,针对脱硫塔区域烟道以及除尘器后烟道的流场进行建模计算,研究半干法脱硫系统普遍存在的烟气流场不均匀性问题及有效的改善措施。试验建立了2个模型,模型A范围自预除尘器出口4个喇叭口的联箱至布袋除尘器入口,此区域为主要脱硫反应的发生区;模型B范围自布袋除尘器出口至引风机入口联箱,该区域优化主要目的为降低系统阻力。计算过程中分析了不同导流叶片的布置位置、数量对烟气速度场、速度矢量及压力场特性的影响。优化结果表明,在模型A预除尘器出口采用典型的扩容联箱方案可以提升流场均匀性。但需考虑在扩容流速降低带来的积灰现象,调整烟道、钢结构积灰荷载的设计,提高安全裕度。在脱硫塔底部设置一块导流叶片,可以有效改善偏流现场,保证进入文丘里的烟气速度均匀性,同时系统阻力也得到较好控制,总阻力在2 200 Pa左右。布袋除尘器出口烟道(模型B)的核心优化要素为降低系统阻力。在弯头1处设置导流叶片,可有效改善速度分布,降低烟道阻力。导流叶片的数量为1~2片时效果较差,导流叶片的数量超过3片时,阻力基本达到最优值,气流分布也较好。弯头2处的导流叶片对降低阻力、提高烟气流场均匀性的影响不大。

Flow field characters have influential impacts on the improvement of desulfurization efficiency and system stability in the circulating fluidized bed semi dry desulfurization system,among whichthe uniformity and stability of the flow field are two key points of the whole system.Only when the design of fluidized bed and conveying equipment are reasonable,the stable and efficient operation of the desulfurization system can be guaranteed.Using CFD method and taking a semi-dry desulfurization plant of 300 MW coal-fired unit as the research objectives,and based on the calculation of the flue gas field in the desulfurization tower area and flue behind the dust collector,the non-uniformity of the flue gas flow field in the semi dry desulfurization system and improvement methods were investigated.Two models were established in the experiment.Model A is from the header of the 4 trumpet outlets of the pre-dust collector to the entrance of the bag dust collector,which is the main desulfurization reaction area.Model B is from the outlet of the bag filter to the inlet header of the induced draft fan and the main purpose of this area optimization is to reduce system resistance.Computational fluid dynamics simulation has been taken for analyzing placement and the number of guide vane as factors affecting flue flow field,velocity vector and pressure field.The result of optimization showed that the uniformity of the flow field can be improved by the application of the expansion header at the outlet of the pre-dust collector in model A.However,it is necessary to consider the ash accumulation caused by the reduction of the expansion flow rate,adjust the design of the ash accumulation load of the flue and steel structure and improve safety margin.A deflector blade is installed at the bottom of the desulfurization tower,which can effectively solve the bias problem and ensure the uniformity of the flue gas velocity entering the venturi,and the system resistance is also well controlled.The total resistance is around 2200 Pa.The main optimization element of the bag flue outlet flue(model B)is to reduce the system resistance.The guide vane at the elbow 1 can effectively improve the speed distribution and reduce the resistance of the flue.When the number of guide vanes is 1-2,the effect is poor.When the number of guide vanes exceeds 3,the resistance basically reaches the optimal value and the air flow distribution is apparently improved.The guide vanes at the elbow 2 have little effect on reducing the resistance and improving the uniformity of flue gas flow field.