Abstract:

The highly chaotic entropy dissipation across solids bed will trigger non-uniform fluidization, although distributor plays an important role in obtaining homogenous gas stream. For dense gas solids flow, total solids pressure loading (Φ _T), the pressure drop ratio between solids bed and distributor, were introduced here to present the gas solids interaction. The boundary between uniform and non-uniform fluidization can be detected by stability analysis based on Prigogine’s minimum of extra entropy production principle since the dense solids bed is far from equilibrium state and contains inelastic dissipation. Based on the framework of stability analysis of uniform distribution for dense gas solids flow, a phase diagram, illustrating the effects from operational parameter (Φ _T), geometrical characteristics of distributor (C _d) and property of solids (Ga) on instability of uniformity, were attained to draw some useful conclusions of robust uniform fluidization. Besides, the gas tracer method and pressure analysis have been provided to verify the effect of total solids pressure loading on the stability of uniform distribution in cold flow fluidized bed (ID 300mm). The framework has been also applied to calculate the critical point and provides guideline to find better operational conditions and design principle for various industrial fluidized bed reactors.

Key words: fluidization, stability analysis, uniform distribution, distributor

摘要：

流化床因其均匀且剧烈的气固相互作用保证了其优异的流动和传递性能，因而广泛应用于化学工业中。因此，构建定量计算气固均匀分布的失稳临界点既是重要的学术问题又具有工程意义。本文分别使用气相和固体颗粒相的质量分数表示气固分布状态；引入颗粒床层压力载荷（Φ _T）描述分布器输入的规则负熵和固体颗粒床层自身混沌熵产生之间相互作用；由于密相颗粒床层远离平衡态且具有强非线性耗散项，因此需基于普利高津最小超量熵增原理给出气固密相流在并联系统均布状态的失稳临界点（Φ _Tc）：分布器和固体颗粒床层总熵增在气固均布和气固非均布情况下相等；由于并联系统的对称性，可将N单元路径并联系统气固均布稳定性分析简化为判断单元路径压降二阶导数正负；在此基础上讨论了操作参数、固体颗粒性质和分布器结构参数对气固密相床层均布稳定性的影响。此外，通过气体示踪和压力脉动频谱分析在直径为300mm冷模实验验证了颗粒床层压力载荷（Φ _T）对密相气固均布稳定性的影响；同时应用该方法论计算了工业流化床反应器临界床层高度、临界表观气速以及分布器临界阻力系数，指导了操作工况的调整和分布器结构设计，对比分析了改造前后的反应情况。

关键词: 气固流态化, 稳定性分析, 均匀分布, 分布器