C1 Production of functional granules and agglomerates with high energy dissipation densities

Figure 1: Double hull with filling material.

Processing of the project:

Maike Orth, M.Sc., Institute of Solids Process Engineering and Particle Technology

Supervision:

Prof. Dr.-Ing. habil. Dr. h.c. Stefan Heinrich, Prof. Dr.-Ing. habil. Alexander Düster

Objectives

Damage reduction in ship collisions by inserting granular filling material into ship double hulls:

Force on outer walls in transferred to the indside
Energy dissipation due to breakage of filling materials

Requirements for filling materials:

Non-toxic (Environmental protection)
Compliance with fire, explosion and health protection regulations
Pumpability and conveyability (easy removal for maintenance)
Hydrophobicity (no weight gain due to moisture)
mass and density (additional buoyancy)

Production of granules/agglomerates via fluidized bed spray granulation

Figure 2: Fluidized bed spray granulation scheme.

Figure 3: Texture Analyser (Stable Micro Systems) for single particle compression test.

Figure 4: CFD/DEM simulation of a spouted bed.

Methodology and work programme

Characterization of granules/agglomerates and evaluation with regard to energy dissipation density:

Nanoindentation
Single particle compression test (Young's modulus, breaking strength)
Impact test with pneumatic air gun (with or without looping)

Imaging techniques for characterization of the micro structure:

Scanning electron microscopy (SEM)
Confocal laser-scanning microscopy

Modelling und simulation of the granulation process and the resulting granules/agglomerates using multi scale approaches:

Coupled Computational Fluid Dynamics (CFD) Discrete Element Method (DEM) simulations

Results

Within the framework of project C1, coating experiments were performed using different materials. Porous glass particles (Poraver®, Germany) with a diameter between 2 and 4 mm were used as core particles. Due to their high porosity of 77 % (closed pores) in addition to their mechanical stability, these particles have promising properties for the application as granular filling material. However, the dust that is formed due to abrasion when particles move against each other or the wall, poses a challenge. On the one hand, this affects the mechanical properties of the particles, on the other hand, the dust impairs the maintenance. To optimize the particle properties regarding their applicability as filling material, the particles were coated via fluidized bed spray granulation. As coating materials, Candelilla wax (Novero GmbH, Germany) and a two component silicone (Silikonfabrik.de, Germany) were used.

Figure 5: Scanning electron microscope image of the cross-section of a porous glass particle coated with Candelilla wax.

The coating influences the mechanical properties of the particles that can for example be characterized by the breakage force that represents the maximum force in the stress-strain curve. Another important property is the resistance to abrasion under dynamic loads. While the breakage force in a single particle compression test was not significantly influenced by applying a coating layer on the glass particles, compression tests involving multiple particles showed pormising results. In the multi particle experiments, wax coated particles showed an improved amount of absorbed energy and the silicone coated particles had a higher breakage force compared to untreated glass particles. Considering the applicationas filling material, this corresponds to a higher energy that needs to be introduced into the system in order to break the granules and thus to a higher energy dissipation once the particles break.

Furthermore, both coatings lead to a reduced dust fraction after one hour of mechanical stress in a solids mixer when compared to uncoated particles. For untreated glass particles, 14.6 % of the initial particle mass turned into dust, whereas wax coated particles only showed a material degradation of 0.3 %. In case of silicone coated particles, no significant mass loss was detected.

As expected, not only the mechanical stability but also the bulk density of the particles is increased as a consequence of the coating. According to the initially formulated requirements, this is not wanted. However, a low weight gain of the particles is inevitable when applying an additional dense layer on the particle surface. For wax and silicone particles, a density increase of 15.6 % and 6.8 % due to the coating was measured which is within an acceptable range for both materials.

Overall, the mechanical properties of glass particles were improved by applying a wax and a silicone coating, while still fulfilling the requirements for granular filling materials in a ship double hull.

Literature

[1] Fries, L. (2012): Discrete particle modeling of a fluidized bed granulator, Dissertation, Technische Universität Hamburg-Harburg.

[2] Dosta, M., Dale, S., Antonyuk, S., Wassgren, C., Heinrich, S., Litster, J.D. (2016): Numerical and experimental analysis of influence of granule microstructure on its compress ion breakage, Powder Technology, 299, pp. 87–97.

[3] Eckhard, S., Fries, M., Antonyuk, S., Heinrich, S. (2017): Dependencies between internal structure and mechanical properties of spray dried granules – Experimental study and DEM simulation, Advanced Powder Technology, 28, 1, pp. 185-196.

[4] Orth, M., Rotter, S., Safdar, W., Tasdemir, S., Pietsch-Braune, S., Heinrich, S., Düster A. (2023): Fluidized Bed Spray Coating for Improved Mechanical Properties of Particles, Processes, 11.