Granulation Systems: Collision and Growth of Wet Particles

The development of new medicines is a major factor in improving patients` health. The tablet is one of the most popular medicines used and is therefore the subject of the research project. Tablets consist of compressed granules containing small powders. To make such particles easy to handle, they are transformed into large agglomerates (as collections of particles) in a process called granulation. In this process, several steps are taken: i) sticky solutions (as binders) are sprayed over the particles to make them wet; ii) the wet powders are brought into contact by the air flow or mechanical agitation; iii) collision with neighbouring particles causes the wet particles to form binary granules through the liquid bridges; iv) on collision with other granules/particles, these granules grow in size. However, these collisions can lead to the breakage of the bridge and thus the granules. At this step, the granules are ready for further processing for tablet production. The design and optimisation of the granulation process is a major challenge, which requires fundamental research to be carried out in order to understand the mechanism of granulation. Therefore, in this project we focus on the collision of wet particles, as the most fundamental phenomenon in the granulation process. Our main objective is to understand which parameters influence the strength of the granules against fracture. This can be done by evaluating the forces acting on the primary particles through the fluid bridges. Using numerical approaches, we discretise our particles and the fluid bridges (known as the computational domain) into very small cells with uniform properties in terms of velocity, pressure, fluid fraction, etc. Then we solve the equations describing the force balance for all cells in the computational domain. This calculation has the potential to provide us with an understanding of how the fluid is distributed across the particles as they collide, adhere to each other and rebound. Furthermore, this approach can give us a deep insight into how the fluid is redistributed when another particle collides with this binary system to form larger granules. Following this, we will evaluate the contribution of the forces to the granule thickness. We will perform this analysis for a very small to very large amount of fluid bridging the particles. In this study, we will be able to quantify the conditions under which agglomeration or fracture of the particles can occur. This study can help us quantify the rate of particle agglomeration. This can be a basis to improve the design and optimisation of granulation processes in the pharmaceutical industry.

This project aimed to develop a practical regime map, obtained from detailed computer simulations, that shows when wet particles stick together, bounce apart, or break during granulation. Granules are small clusters of particles used in many products, including medicines, food powders, fertilizers, detergents, and chemical materials. Although granulation is widely used in industry, predicting the final granule size, strength, and quality remains difficult. The main reason is that the small-scale collision between wet particles remains poorly understood. When particles collide, a small amount of liquid between them can act like a binder. Depending on the collision speed, liquid amount, and liquid properties, the particles may form a stable granule, separate again, or cause an existing granule to break. Today, many industrial granulation processes still rely heavily on trial and error. In this project, advanced simulations were used to study these collisions in detail. They showed how the liquid binder moved, deformed, and created forces between particles during impact. We also developed a regime map for fluidization to see under which conditions particle agglomeration can happen. The simulation-based regime map was the project's central outcome. It provided researchers and engineers with clearer guidance for designing and optimizing granulation processes. Instead of relying mainly on costly experiments, industry could use such knowledge to better control product quality, reduce material waste, and improve process efficiency. In the long term, the project may support more reliable and efficient production in the pharmaceutical, chemical, food, and agricultural industries, where powder processing is essential.