Complete two dimensional population balance modelling of wet granulation in twin screw.

In this study, a complete two dimensional (internal coordinates) population balance model (2D-PBM) is developed, calibrated and validated as a predictive tool for predicting the particle size and the liquid content distribution of the granules produced from twin screw granulation (TSG). The model is calibrated and validated using experimental distributions for the two internal coordinates that are captured using image processing. Granulation runs are conducted at multiple liquid to solid (L/S) ratios and liquid binder viscosities, and then used to calibrate and validate the 2D-PBM. The mathematical model accounts for aggregation and breakage of the particles occurring in three zones of the TSG with inhomogeneous screw configurations (2 conveying zones and 1 kneading zone). A Madec aggregation kernel, and a linear breakage selection function are used in the 2D-PBM and finite volume numerical approximation is used for solving the model. The calibrated model shows that the aggregation rate in the conveying elements is higher than in the kneading elements while the breakage rate in the kneading elements is much higher than in the conveying elements. Also, the increase in L/S ratio and liquid viscosity leads to higher aggregation rates and lower breakage rates.

Kinetics of steel slag dissolution: from experiments to modelling.

Carbon dioxide sequestration via carbonation of steel slags is a promising way of combining two waste products to create value. Understanding the dissolution kinetics of steel slags, which are alkaline and rich in calcium, in acidic media is essential to configure such a process. In this study, we seek to analyse the dissolution mechanism from experimental studies and develop a mathematical model considering the heterogeneous characteristics of slag. We found that the reduction in calcium extraction efficiency with an increase in particle size, which is normally associated with surface passivation or non-uniformity of samples, can be explained by considering the morphological features associated with the distribution of MgO-FeO (RO) phase in the calcium silicate matrix. We present a population balance model and show that the reduction in calcium extraction efficiency in coarse particle fractions is due to increased sporulation of the RO phase. The findings in the study suggest that the leaching of metal ions from slag is controlled by proton-promoted surface dissolution reaction, where the dependence of acid concentration follows the Langmuir-Hinshelwood adsorption isotherm. The model shows good agreement with a large set of parametric studies and demonstrates the importance of considering morphological features, as we progress towards development of a priori dissolution models for multi-mineral oxides and silicates.

Disintegration of Nannochloropsis sp. cells in an improved turbine bead mill.

The Nannochloropsis sp. cells in aqueous solution were disintegrated in an improved bead mill with turbine agitator. The disintegration rates of cell samples disrupted under various operating parameters (i.e., circumferential speed, bead size, disintegration time, and cell concentration) were analyzed. An experimental strategy to optimize the parameters affecting the cell disintegration process was proposed. The results show that Nannochloropsis sp. cells can be effectively disintegrated in the turbine stirred bead mill under the optimum condition (i.e., circumferential speed of 2.3m/s, concentration of 15vol.%, disintegration time of 40min and bead size of 0.3-0.4mm). The disintegration mechanism was discussed via the selection and breakage functions from population balance modelling. It is revealed that the impact and compression effects of stirring beads are more effective for the disruption of coarser fraction of cells, and the shear effect dominates the production of finer fractions of disintegrated cells.

Separation of nanoparticles: Filtration and scavenging from waste incineration plants.

Increased amounts of nanoparticles are applied in products of everyday life and despite material recycling efforts, at the end of their life cycle they are fed into waste incineration plants. This raises the question on the fate of nanoparticles during incineration. In terms of environmental impact the key question is how well airborne nanoparticles are removed by separation processes on their way to the bag house filters and by the existing filtration process based on pulse-jet cleanable fibrous filter media. Therefore, we investigate the scavenging and the filtration of metal nanoparticles under typical conditions in waste incineration plants. The scavenging process is investigated by a population balance model while the nanoparticle filtration experiments are realized in a filter test rig. The results show that depending on the particle sizes, in some cases nearly 80% of the nanoparticles are scavenged by fly ash particles before they reach the bag house filter. For the filtration step dust cakes with a pressure drop of 500Pa or higher are found to be very effective in preventing nanoparticles from penetrating through the filter. Thus, regeneration of the filter must be undertaken with care in order to guarantee highly efficient collection of particles even in the lower nanometre size regime.