Monitoring and control of continuous multi-compartment fluidized bed spray granulation: Real-time predictions and flow-topology based process actuation

尽管流态化喷雾造粒已有60多年的历史，但对产品粒度的控制仍然是一个挑战。我们项目的目标是开发一种实时监测和预测框架，该框架能够控制连续多室流态化造粒过程中的产品粒度分布。这一目标将通过三个创新支柱来实现：用于流态化操作的新颖开关拓扑、允许在线过程控制的实时模拟以及在线粒度测量设置。实验研究的中心部分将是配备底流堰的两级实验室规模的沸腾床。我们建议利用分离现象来影响哪些颗粒进入喷雾区，从而增大颗粒尺寸。通过从均匀曝气到非均匀曝气的转换，颗粒循环格局的拓扑结构将发生变化。在均匀曝气模式下，底流堰只将较大的颗粒交给连续级，而较小的颗粒留在顶部喷雾区。喷吹速度较快的气流(非均质曝气)会引起床层内的循环，从而使颗粒尺寸分布均匀。大粒子会和小粒子一样长得更远。作为一种新的测量概念，我们打算评估颗粒通过各个级之间的底流闸门时的颗粒尺寸分布。为此，底流堰门配备了反射镜和成像系统。通过定期拍摄快照，我们将收到一组粒子通过星门飞行的图像。在线数字图像分析将提供瞬时PSD。喷雾造粒过程的控制将通过递推CFD(RCFD)方法对床层动力学进行实时模拟。RCFD使用短时间CFD-DEM模拟的递归图(递归数据库)，基于相似状态将具有类似的近时间演化的假设来时间外推快速动力学。使用这种方法，可以比实时更快地模拟系统的内部状态，这是纯CFD-DEM模拟所不可能的。在这个项目中，这一全新的方法学将进一步发展用于多分散体系。为此，我们必须跟踪和修改局部的颗粒尺寸分布。沸腾床控制系统将与rCFD解算器集成，以使系统状态与数据库的选择同步。这包括出口空气温度和湿度的通信，以及从浇口测量设置和用于控制开关机构的接口确定的颗粒尺寸分布。因此，rCFD解算器的预测将用于选择正确的流动拓扑，以产生所需的产品粒度分布。

Even though the fluidized bed spray granulation has been applied for more than 60 years, it is still a challenge to control the product particle size. The aim of our project is the development of a real-time monitoring and prediction framework, which enables the control of the product particle size distribution in continuous multi-compartment fluidized bed granulation processes. This objective will be achieved by three innovative pillars: novel switching-topology for fluidized bed operation, real-time simulations allowing for online process control and on online particle size measurement setup. Central part of the experimental investigations will be a two-stage lab-scale fluidized bed equipped with an underflow weir. We propose to use the phenomenon of segregation to influence which particles enter the spray zone and thus increase in particle size. By switching from homogeneous aeration to heterogeneous aeration, the topology of the particle circulation pattern will be changed. In homogeneous aeration mode, only larger particles are handed over to the consecutive stage by an underflow weir while smaller particles remain in the top-spray zone. The injection of a higher velocity gas stream (heterogeneous aeration) will cause circulation within the fluidized bed and thus homogenize the particle size distribution. Large particles will grow further just the same as smaller particles. As a novel measurement concept, we intend to assess the particle-size-distribution while particles pass the underflow gate between individual stages. To this end, the underflow weir gate is equipped with a mirror and an imaging system. By taking periodic snap-shots we will receive images of a set of particles on their flight through the gate. Online digital image analysis will provide instantaneous PSDs. The control of the spray granulation process will be performed by real-time simulations of fluidized bed dynamics by the recurrence CFD (rCFD) approach. rCFD uses recurrence plots of short-time CFD-DEM simulations (recurrence database) to time-extrapolate the fast dynamics based on the assumption that similar states will have a similar near-time evolution. Using this method, the internal state of the system can be simulated faster than real-time, which is not possible with pure CFD-DEM simulations. In this project, this radically new methodology will be further developed for poly-disperse systems. For this purpose we have to track and modify local particle size distributions. The fluidized bed control system will be integrated with the rCFD solver to synchronize the system state with choice of the database. This includes communication of outlet air temperature and humidity, as well as particle size distribution determined from the gate measurement setup and an interface for the control of the switching mechanism. Thus, the predictions from the rCFD solver will be used to choose the correct flow topology to yield the desired product particle size distribution.