Performance prediction of riser termination devices using barracuda

In fluidized bed reactors, one of the locations where attrition is significant is cyclones. One way to reduce the attrition in cyclones is to reduce the amount of catalyst going into the cyclones. This is achieved by separating the catalyst particles from the combined gas solid flow before the stream enters the cyclones. Using a riser flow along with a riser terminator, some of the catalyst particles can be separated from gas stream. In this work, we will discuss how Barracuda has been used at The Dow Chemical Company to investigate two riser termination devices for separating catalyst particles from gas phase. The two types of riser terminators simulated are (1) flat disk and (2) slots-elbow, as shown below in Figure 1. The results indicate that the slots-elbow type terminator has an overall separation efficiency of more than 95% whereas the disk terminator has approximately 80% efficiency. Please click Additional Files below to see the full abstract

Comparisons of intra-tablet coating variability using DEM simulations, asymptotic limit models, and experiments

This is the final version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0009250915001852.Discrete element method (DEM) computer simulations are used to investigate intra-tablet coating thickness variability. Two new post-processing algorithms are presented. The first algorithm uses an image-based method to track the exposure to a simulated spray of small area panels on each tablet׳s surface so that the distribution of spray exposure times over the tablet׳s surface can be determined directly from DEM data. The second algorithm predicts the asymptotic limit of intra-tablet coating uniformity. This second algorithm includes the influence of tablet orientation and shadowing when considering exposure to the spray, averaged over many tablets. The DEM simulations produce the first direct evidence that non-spherical tablets approach asymptotic intra-tablet coating variability values. The asymptotic limits are predicted well using the new asymptotic prediction model. In general, tablet caps have thicker coatings than tablet bands. Moreover, tablets that have a more elongated shape tend to have less coating on the smaller radius of curvature portions of the bands. Of particular importance in this new asymptotic modeling approach is the inclusion of shadowing effects. When shadowing is not included and only tablet orientation is considered, the predictions over-predict the asymptotic intra-tablet coating variability values and also change the observed rank order of the asymptotic values for different tablet shapes. The asymptotic intra-tablet coating variability values using the new algorithm correlate reasonably well with tablet sphericity, with increasing sphericity improving coating uniformity. This paper also presents the first attempt to directly compare experimental and simulated coating thickness distributions. The asymptotic coating thickness predictions compare well qualitatively with terahertz thickness measurements made on tablets from coating experiments. Unfortunately, only qualitative comparisons could be made due to the limited number of tablets sampled experimentally and differences in spray zone areas and flux distributions. The tablets in the experiments, however, displayed similar features as those found in the simulations.The authors would like to thank Bob Green from Pfizer for manufacturing the tablets used in this study. R. Kumar and C. Wassgren are grateful to the National Science Foundation Engineering Research Center for Structured Organic Particulate Systems (NSF ERC-SOPS, 0951845-EEC) for financial support. K. Su and J.A. Zeitler would like to acknowledge the UK Engineering and Physical Science Research Council (EP/L019922/1 and EP/K503721/1)

A compartmental approach to studying particle motion in mixer/coaters using discrete element modeling

Systems of particles can be modeled in a number of ways. The discrete element method (DEM) is among the most detailed of all possible approaches. When using DEM, the trajectory of each and every particle is computed. Naturally, this comes at a high computational cost. At a more abstract, vessel scale level, population balance (PB) modeling is also used. In this approach a system of partial differential equations is written (similar to the conservation equations of mass, momentum, and energy) which describes the evolution of the distribution of particle properties (e.g., size, composition, and age). Unfortunately PB cannot directly account for the motion of material in a vessel in a computationally efficient manner. In this work, a novel multi-scale modeling approach is presented in which DEM and PB models are combined via a compartment model (CM) to account for flow heterogeneity in a particle mixer-coater. Using this approach, the mixer is decomposed into bed and spray regions, and particle trajectories taken from the DEM model are used to generate an intermediate sub-CM that matches the residence time distributions of particles in these regions. A system of PB models is then generated from the CM. The CM presents a simplified, but still accurate description of the particle residence times in the regions of the mixer. A case study of a simple top spray coating system shows the method is 80% faster than using DEM alone with 13% of the error of using PB alone. Approaches to estimating the minimum DEM simulation time are also presented. Parametric studies are performed which demonstrate that as operating parameters of the mixer are varied, the CM structure remains and only the CM parameters change. This fact allows generation of a single CM structure for a given system. The method is applied to three mixer geometries: a dual-axis paddle mixer, a horizontal axis rotating drum, and a vertical axis mixer. The approach is limited to systems in which the residence time in a region is statistically independent of the residence time in any other region. Also, a region’s residence time distribution must be able to be modeled in terms of a network of ideal compartments. The mixer flow must also have reached a steady state so that each region’s residence time distributions does not vary with time. Within these constraints, the multi-scale modeling approach developed in this thesis is capable of drastically reducing computational time and increasing total process understand via the reduction of a full DEM simulation to a simple CM