Abstract This contribution is concerned with the stability problems occurring during the operation of continuous fluidized bed spray granulation processes with external sieve mill cycle. These processes are in general operated by a mass controller, which guarantees that the overall mass of particles in the granulation chamber stays in well-defined bounds. It is well-known that, depending on the milling diameter, instabilities may occur, which result in a nonlinear limit cycle of the particle size distribution. To overcome this problem two approaches have been proposed in the literature, constrain the admissible parameter space to exclude regions of instability and design additional stabilizing control loops. In the present contribution, the cause of this instability phenomenon will be studied. It will be shown that the instability is not inherent to the process, which turns out to be open-loop stable over the studied parameter range, but due to the mass controller. More specifically, it will be demonstrated that the zero dynamics of the granulation process become unstable for certain parameter ranges resulting in closed-loop unstable process behavior. To point out, that this behavior does not depend on the specific mass controller design procedure, three prototypical mass controllers of practical relevance are designed and analyzed.

中文翻译：

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控制流化床喷雾造粒中引起的不稳定性

摘要 该贡献涉及在具有外部筛磨循环的连续流化床喷雾造粒工艺的操作过程中出现的稳定性问题。这些过程通常由质量控制器操作，从而保证造粒室中颗粒的总质量保持在明确定义的范围内。众所周知，根据研磨直径，可能会出现不稳定性，从而导致粒度分布的非线性极限循环。为了克服这个问题，文献中提出了两种方法，约束可容许参数空间以排除不稳定区域并设计额外的稳定控制回路。在目前的贡献中，将研究这种不稳定现象的原因。将证明不稳定性不是过程固有的，结果证明在研究的参数范围内是开环稳定的，而是由于质量控制器。更具体地说，将证明造粒过程的零动力学对于某些参数范围变得不稳定，从而导致闭环不稳定的过程行为。需要指出的是，这种行为不依赖于特定的质量控制器设计程序，设计和分析了三个具有实际相关性的原型质量控制器。