旋风分离器最大效率入口气速的试验与数值模拟研究

The performances of cyclone separator have vital impacts on fluidization processes productions. The inlet gas velocity affects cyclone performances significantly. The cyclone efficiency will not be best, unless operated near the maximum efficiency inlet gas velocity (MEIGV). Because of the unclear reason for MEIGV phenomenon, the design of inlet gas velocity depends on experiences significantly. However, old experiences are not always suitable for new conditions. Therefore, the cyclone can not reach its full efficiency. By Computational Fluid Dynamics simulation and experiment, the proposed research will explore two relationships at various combinations of gas inlet and outlet dimensions, cylinder diameters and particle characters. One is between inlet gas velocity and processing vortex core (PVC) phenomenon characters, such as amplitude and frequency. The other is between PVC phenomenon characters and the quantity of particle re-entrainment. As a result, the physical mechanisms injuring separation efficiency is clarified, which is aggravated the PVC phenomenon caused by increasing inlet gas velocity makes more particle captured by cyclone wall escape. According to the principles of compromise in competition, the research simulates the compromise of two dominant mechanisms. One is improved centrifugal force caused by increasing inlet gas velocity enhance particle capture. The other is aggravated the PVC phenomenon caused by increasing inlet gas velocity makes the particle captured by cyclone wall escape more significantly. The research is aimed at establishing calculation methods for maximum efficiency inlet gas velocity, and thereby significant enhancing the cyclone performances in industry.

旋风分离器性能的优劣对流态化工业装置的安全生产，经济和环境效益的保护意义重大。入口气速显著影响旋风分离器的性能，只有在最大效率入口气速附近操作分离效率才会最佳。由于对该现象的形成机理认识不足，目前预测最大效率入口气速离不开经验，设计时会因为经验的局限而未能充分考虑实际工况条件，影响旋风分离器性能的充分发挥。本申请用数值模拟和实验方法，重点研究在不同进、排气口尺寸，分离器直径，颗粒自身特性条件下，入口气速、涡核旋转频率和摆动幅值、颗粒返混情况之间的关系，揭示涡核动态行为对颗粒返混情况的影响规律，阐明入口气速增加强化内流场的非稳态性加剧颗粒逃逸这一损害分离效率的物理机制。根据“主导机制在竞争中协调”这一物理原理，分析入口气速提升增强离心作用促进颗粒捕集与入口气速增加强化内流场的非稳态性加剧颗粒逃逸两项主导机制在竞争中的协调关系，构建最大效率入口气速的预测模型，为优化设计旋风分离器提供科学依据。

旋风分离器性能的优劣对流态化工业装置的安全生产，经济和环境效益的保护意义重大。入口气速显著影响旋风分离器的性能，只有在最大效率入口气速附近操作分离效率才会最佳。由于对该现象的形成机理认识不足，目前预测最大效率入口气速离不开经验，设计时会因为经验的局限而未能充分考虑实际条件，影响旋风分离器性能的充分发挥。.了解最大效率入口气速现象的机理，关键在于理解为何过高的入口气速会损害效率。研究表明，旋进涡核是造成颗粒返混从而损害效率的重要因素之一。因此，重点探索入口气速——涡核旋转特性——颗粒返混量三者之间的关系。涡核旋转特性由旋转频率与涡核偏离分离器几何中心的距离两个参数衡量，二者随入口气速的变化规律是本课题的主要研究内容。由于最大效率入口气速受分离器的入口结构影响，进一步研究了进口尺寸、排气管尺寸、分离器直径对涡核旋转特性的影响。归纳总结上述研究发现，分离器内径向汇流的能量对涡核旋转特性有重要影响，当径向汇流的能量超过入口总能量的14%时，涡核摆动明显，无论径向汇流的能量是因结构参数而变化还是因操作条件而变化。.上述研究发现，在排尘口安装圆锥可以有效限制旋进涡核。分析带有稳涡结构的旋风分离器内的颗粒跑损情况，再与无稳涡结构的旋风分离器对比，归纳涡核旋转频率和偏心距对颗粒返混量的影响。综合上述研究结果，归纳入口气速与因旋进涡核造成的颗粒跑损量之间的数学关系。除旋进涡核，随短路流逃逸是颗粒跑损的另一重要因素。通过追踪颗粒，构建入口气速与因短路流跑损的颗粒量之间的数学关系。二者加合后即可构建入口气速与分离效率之间的数学关系式。据此，将效率对入口气速求导，取其极大值，即得到最大效率入口气速的表达式。.本项目的研究成果有助于理解最大效率入口气速的形成机理，在旋进涡核形成原因方面提出了新见解。归纳出的最大效率入口气速计算方法对旋风分离器的优化设计有应用价值。相关拓展研究为旋风分离技术发展提供新思路。