Fertilizers, detergents, pharmaceuticals, animal feed or food ingredients – many products of our daily life are solids produced by fluidized bed spray granulation. The particles are fluidized by a heated gas stream while a solid-containing liquid is sprayed onto them via installed nozzles. When the liquid evaporates, the solid material forms a layer around the core particles resulting in an onion-like growth.

The properties of the outgoing particles depend on the one hand on the properties of the used materials and on the other hand on the process parameters including gas velocity, temperature, spray rate and pressure. Thermal conditions influence, for instance, the dynamics of the evaporation process and thereby the dynamics of layer formation and with that the final layer thickness and porosity. These in turn influence the flowability and the dissolution kinetics of the particles. By the adjustment of process parameters, tailor-made particles with desired product properties, like particle size, density and porosity, can be produced in order to meet the requirements (e.g. flowability, strength, dissolution behavior) for the above-mentioned applications. For the correct adjustment of process parameters, both at the start of an operation and during its execution, a deep understanding of the micro-processes and their dependence on process parameters and material properties is necessary, e.g. the actual process state needs to be tracked in order to avoid batch faults that could result in a waste of material and energy.

To ensure a high and consistent product quality, reliable monitoring and control of the process are crucial. Especially the in-line control of the outgoing product properties during fluidized bed spray granulation is still very challenging. Typical problems occurring during spray granulation are instabilities, dead zones. or nozzle blockages, which result in excess undersized or oversized particles, wall adhesions, lump formation or bed defluidization. These phenomena are often detected too late, as conventional approaches rely on a limited number of stationary sensors and off-line measurements of small samples, which often fail to capture localized or transient phenomena inside the bed. As a result, the entire batch needs to be discarded.

The ultimate goal of the project is to get a detailed understanding of the micro-processes of the particle formation and to detect the particle state in the process chamber. This will be addressed at first by stationary Eulerian sensors and product sampling and later on also by agile and smart particles that are traveling as Lagrangian sensors on the same trajectories as the bed particles recording a representative “life-line”. The sensors will be equipped with mechanical, electrical and software functionality, which will allow the measurement of several process conditions, e.g. temperature and humidity. With the knowledge gained by the detailed measurements of the Lagrangian sensors, in addition to other stationary Eulerian sensor probes and off-line analysis methods, it will then be possible to map the entire process states for the material system of interest with high spatial and temporal resolution and to create a regime map indicating the process parameter-particle property relation. This allows the adjustment of process conditions for the production of tailor-made particles optimized for a certain application. In addition, the in-line sensor data will help the plant operator to identify occurring problems, e.g. a blockage of the nozzle, and to intervene as necessary.