Richard Caulkin

An investigation of packed columns using a digital packing algorithm

This paper presents results concerning the validation of a recently developed packing algorithm. The basic ethos of this algorithm is to digitise particle shapes, and to use the digitised shapes to generate digital packing structures. A variety of simulations of packed columns, comprising mono, binary and ternary mixtures of spherical particles, have been undertaken and the results compared to existing experimental data with good agreement. The ultimate aim of this work is to develop the packing algorithm as a design tool for use in optimising the performance of packed bed systems and, as a first step, to enable the characterisation of any particle population and prediction of particle behaviour in packing, segregation and mixing.

The role of geometric constraints in random packing of non-spherical particles

A generic and digitally implemented geometrical packing algorithm is compared with a discrete element method based dynamic packing model, through ten case studies encompassing oblate-to-prolate spheroids, in terms of bulk volume packing fraction, bed height, orientation distribution and mean coordination number. The broad agreement in simulation results points to the conclusion that geometrical constraints play a dominant role over physical contact forces in determining the structure of a random packing and physical contact forces are a means to enforce geometrical constraints.

An investigation of sphere packed shell-side columns using a digital packing algorithm

This paper on the fundamental structural properties of shell-side packed columns presents an investigative study using a novel packing algorithm with the aim of validation against experimental results. The novel contribution in the predictive approach employed is the digitalisation of particles, container and packing space to generate complex life-like stochastic packing structures of particulate systems at relatively high speed (when compared to traditional vector-based approaches) which are comparable with experimentally packed beds without need for further conversion of numerical data. A variety of packed column simulations, comprising more complex beds than often seen in the literature, namely shell-side beds with increasing complexity of internal structure and packed with spherical particles, have been undertaken and the resulting averaged numerical data compared like-for-like with experimental results with key trends reproduced. The overall aim of this work is to demonstrate the usefulness of the technique and associated computer code as an engineering aide for research, design and optimisation of the performance of packed bed systems of any geometric complexity in terms of packing structure, as well as to highlight possible areas for further development of the code.

A Numerical Case Study of Packed Columns

This paper presents results concerning the validation of a recently developed packing algorithm. The basic ethos of this algorithm, known as DigiPac, is to use three- dimensional methods to digitise particle shapes, and to use this digital information directly in computations of how particles pack together without further conversion or the need for modelling. A variety of simulations of packed columns, comprising mono, binary and ternary mixtures of spherical particles, together with shell-side containers, have been undertaken and the results compared to existing experimental data with good agreement being found. The ultimate aim of this work is to develop the packing algorithm as a design tool for use in optimising the performance of packed bed systems, and to enable the characterisation of any particle population and prediction of particle behaviour in packing, segregation and mixing. Particulate beds are commonly encountered in chemical and allied engineering fields, with the application of packed bed systems covering a wide range of areas including heterogeneous catalysis, solids handling, heat recovery, absorption, filtration and distillation. The design and performance prediction of such systems depends greatly on mathematical models that describe the behaviour of fluid flow, heat and mass transfer, and the pressure drop of the fluid through the bed. The models themselves are to a great extent dependant on accurate experimental data describing transport parameters such as effective thermal conductivity coefficients, wall heat transfer coefficients and dispersion coefficients. In turn, these parameters are sensitive to the structural properties of packed beds, namely the global and local voidages. The significance and magnitude of bed voidage is influenced by a number of factors, including the geometry of the particles and container, the method of particle loading and the treatment of the packing matrix during and after deposition. To design effective models of fixed-bed systems a variety of problems must therefore be addressed. Amongst those that merit investigation, the present study assesses the ability of DigiPac to predict the global and local voidage of beds containing mixed-sized particles. These systems occur by design, and in situations when particle breakage occurs, for example, during catalyst dumping.

Prediction of the Permeability of Packed Beds of Non-Spherical Particles

Abstract This paper details the ongoing development of a virtual permeameter which will have value in the design and performance assessment of filters used in a variety of chemical and process engineering applications. Having previously established the basic simulation requirements for such a permeameter with spherical glass beads, further experimental investigation and associated simulations are reported for non-spherical particles, namely mono-disperse sand and arbitrary poly-disperse, polymorphous minerals. To test the validity and applicability of the previously established guidelines with regard to sample size, resolution and accuracy, the micro-structural details of representative porous media samples are acquired using x-ray micro-tomography. Small sample arrays of such media are then used as input into lattice Boltzmann method (LBM) simulations for predicting their bulk permeability and related properties under laminar flow conditions. It is established that LBM is able to predict the flow rates through the beds at varying fluid pressures, with average error margins between experimental data and simulation predictions of 28% for glass beads, 27% for silica sand and 31% for polymorphous particles.

Application of a digital packing algorithm to cylindrical pellet-packed beds

Abstract A digital packing algorithm is used in an investigation to predict the structures of cylinder packed columns. Simulation results of the computational approach are compared with packing data from experimentally measured beds as a means of model validation. The algorithm has been modified from that reported previously (Caulkin et al., 2005) to include particle collisions that guide pellet movement in such a way that it does not sacrifice the advantage of simulation speed, yet is able to better recreate the packing of non-spherical particles. The results of both the original and modified models are presented, with predicted bulk and local voidage values compared directly with data determined by optical analysis of corresponding experimental columns. The results demonstrate that while the original version of the algorithm qualitatively predicts the trend in voidage for cylindrical pellets, the modified version is capable of providing more quantitative results. Therefore, the influence of physical interactions upon the packing cannot be disregarded if realistic packing structures are to be obtained.

Validation of a digital packing algorithm for the packing and subsequent fluid flow through packed columns

Abstract A new packing algorithm, called DigiPac, was validated for packed columns in a paper presented at ESCAPE 15. The columns considered contained mono, binary and ternary mixtures of particles in conventional beds, as well as spherical particles in shell-side beds which contained fixed arrays of tubes in order to represent the more realistic geometries found in industry. Predicted voidages were compared with experimental data, with good agreement observed. The present paper extends this work to simulate both bed structures and, using lattice Boltzmann modelling, the fluid flow and pressure drop through a number of beds for which experimental data are available in the literature. The results demonstrate the usefulness of these combined techniques for the design of unit operations based on packed beds.