Methods for design of hoppers. Silos, bins and bunkers for reliable gravity flow, for pharmaceutical, food, mineral and other applications

It is now four and a half decades since Andrew Jenike introduced the first integrated method for characterising powders for flow, and using this information to design a hopper that would discharge without hang-up. Sadly, many users and designers of hoppers still do not benefit from this, so a lot of process vessels in industry still suffer from rat-holing, arching and bridging. Objections of cost, time and questionable accuracy were levelled at the original hopper design method, in spite of the breakthrough it represented. However, over the last 40 years these problems have been overcome with the introduction of faster, easier to use and more sensitive powder flowability measurement techniques, and a lot of experience of what measurements matter with which materials and in what operational scenarios. This paper will pull together various lessons learned from many years of hopper and silo design projects, and show a practical approach to deciding (i) what flow pattern is required (mass flow or core flow), (ii) what measurements need to be made of the powder properties, and (iii) what design models should be used, based on the material being handled and the operational requirements of any given case

Simulating and modelling the impact of secure communication latency for closed loop control

Closed loop control systems have been implemented to conduct a variety of tasks (e.g. manufacturing and automation). Industrial Control System (ICS) have been used to regulate a closed loop process; however, ICS are exposed to the same security vulnerabilities associated with enterprise networks. Cryptography has been deployed to overcome the associated data communication weaknesses between each ICS node through the use of block ciphers; however, the drawback of applying cryptographic algorithms to ICS is the additional communication latency. This paper investigates the relationship between security constructs and latency for closed loop control system with test conducted in a simulated environment. A case scenario is illustrated to demonstrate the impact of the results obtained to a real world context

Breakage characteristics of granulated food products for prediction of attrition during lean-phase pneumatic conveying

Pneumatic conveying is utilised in a variety of industries to convey food products exhibiting diverse handling characteristics. Attrition of particles caused by this conveying process can result in a number of undesirable outcomes such as loss in product quality or issues in subsequent handling processes. The ability to predict the breakage behaviour of particulate materials is desirable in both new system design and resolving issues in existing plants. This work considers two different particulate materials (Salt and Golden Breadcrumbs) across a range of particle sizes, and quantifies their breakage behaviour under varying impact conditions. Narrow size fractions of each material was degraded; material retained on 250 µm and 355 µm sieves for salt, and 500µm, 710µm and 1000 µm sieves for Golden Breadcrumbs. Velocity was found to be the most influential factor with respect to particle attrition. The results from the narrow size fraction tests were superimposed to form a simulated full size distribution breakage behaviour, which was then compared to the experimentally determined behaviour. A good agreement was found, however the proportion of material predicted for size fractions smaller than 355 µm for Golden Breadcrumbs and 180 µm for Salt was under-predicted. Recommendations for increasing accuracy of the prediction method are given

The effects of reverse jet pulse over-pressurisation on dust filter performance

Industrial use of air filtration systems is widespread and the range of approaches to achieve particle capture reflects the fact that such systems need to be tailored to specific applications if good performance is to be achieved. Commonly the budget for air filtration systems is one the early victims to ‘value engineering’ in plant projects – with obvious implications for the specification of particle capture equipment. The method of cleaning filter systems can range from agitated frame supported bags to reverse jet cleaning systems (the latter becoming increasingly the norm in industry). The quality of engineering in reverse jet cleaning systems can vary considerably – with the end user usually being oblivious of the implications for life cycle for different styles of system. This paper considers the operational aspects of parallel and tapered form pleated cartridges based on pulse pressure propagation and particle dislodgement (and more critically particle retention at different pulse conditions)

Development and application of a novel cake strength tester

Caking can cause many problems in industries during processing or storage of particulate materials. Caking magnitude depends on several factors, for instance temperature, consolidation stress and storage time. In this research paper, a novel force displacement and easy-to-use caking tester for measuring quantitatively cake strength as a result of elevated temperature, consolidation stress and storage time is introduced. The developed tester outweighed the conventional uniaxial unconfined failure caking tester due to the defined location of the failure plane to maximise repeatability, the necessity for a lower quantity of powder, maximised exposed surface and lower wall friction as well as production costs. The experimental design has been conducted by changing the temperature, consolidation stress and storage duration. The results showed that the tester could distinguish cake strength between different experimental conditions. A statistical model has been successfully developed to study the effect of each variable on the cake strength

Investigation into the effects of cyclic particle loading onto filter media

Virtually all industrial sectors employ air filtration as part of their processes. Unlike liquid based processes where the separation of solids from liquids forms a value adding step, in dry processes the capture of particulate material is usually not a value adding element of plant – but rather a requirement for air quality or process stability. The different roles of particle capture for wet and dry systems leads to a situation whereby models and information predicting wet filtration performance and capability are easily accessible, whilst comparable information for dry filtration (outside of the automotive and pharmaceutical sectors) is relatively poorly provisioned. This paper reviews the ongoing investigative work undertaken on air filter media at The Wolfson Centre for Bulk Solids Handling Technology, UK. Aspects for filter life cycle are considered and loading phenomena are discussed

A new uniaxial compression tester: development and application

Powder flow characterization with some of the conventional shear testers can be costly, time consuming and requires a trained operator, therefore the application of a cheaper, simpler, and sometimes faster uniaxial compaction tester (UCT) have often been suggested as an alternative. However, it has been known for many years that the results derived from the two methods are not necessarily the same, due to the lower state of compaction attained in the traditional design of UCT. Additionally, the traditional design of UCT tends to give a wide scatter in the results. To overcome these limitations of the UCT, this work developed an easy-to-use uniaxial tester in order to reduce the difference between flow properties reported by the two techniques. In this regard, flow functions of four powders in the cohesive and very cohesive range were measured with shear testers, conventional uniaxial compaction tester (UCT) and the new uniaxial tester at the University of Greenwich (“Greenwich Uniaxial Tester” or GUT). A method in the style of Janssen approach for correcting wall friction effect on the compaction stress of UCT was applied. Results showed the unconfined yield strength attained from GUT is in line with the results obtained from shear testers while the results from UCT are well below the shear tester results suggesting the advantage of the new GUT

Evaluation of the Restricted Air Entry on the Discharge Rate from Silos

Storage and distribution of solid materials, as well as control under powder discharge, has been fundamental to ore transportation and lately, Additive Manufacturing (AM). AM demands fine powders materials to be fed with high accuracy, by hoppers. It is not only the reliability of flow that becomes important but also to have a trace of repeatability of material discharges and flow characteristics. In this perspective, two types of hopper feeders have been utilized the most: screw feeder and scraper feeder. In the present work, the characteristics of a steady granular flow through an orifice in scraper feeders with a flat and conical bottom have been experimentally investigated under the influence of top ventilation. The discharge rate of granular particles of magnesium, alumina, glass beads and crushed glass have been studied as a function of the outlet diameter and the ventilation configuration. Tests were performed three times under the same configuration, which consisted for both apparatuses, a measurement of discharge time and the mass through outlet orifices of 15, 30 and 50 mm, with different vent area percentage. The results have shown that the discharge rate increases with the increasing outlet diameter and top ventilation in the majority of the materials studied. In both hopper geometries, a rise in mass flow rate was generally observed when ventilation was added to the system, even though the difference when doubled the vent area was not significant

CFD Approach to the Influence of Particle Size on Erosive Wear in Coal Riser Pipes

Pneumatic conveying of finely pulverised coal particles is an important process in the steelmaking industry, used to transport coal to the blast furnace. Erosive wear caused by high velocity particles impacting on the inner wall surfaces of pneumatic conveying riser pipes causes a severe problem in the steel-making industry. Continuous erosion left unmaintained eventually leads to pipe punctures. This paper aims to help minimise the erosive wear in industrial risers by investigating the effects of different particle sizes on the wear rates in industrial coal conveying ducts to control the grind size in industrial gas-solid flow processes and optimise reduced wear. Computational fluid dynamics (CFD) simulations and 4 semi empirical erosion models were used to analyse these effects, with an Eulerian-Lagrangian technique to model the multiphase gas-solid flow in the riser. The continuous phase (air) was modelled by solving Eulerian Reynolds-averaged Navier Stokes equations and the discrete phase (coal) was modelled using the Lagrangian discrete phase model (DPM) approach. The particle sizes investigated ranged from 1 to 1000 µm. The results showed the curves for each erosion model representing the changes in erosive wear with an increase in particle size for each erosion model. Every model showed similar curve shapes but varied in degree of wear rates. The curves of each model showed a steady increase in wear between particle diameters of 1 and 150 µm, followed by a sharp increase in wear at 200 µm, with the maximum erosion rates recorded between 300 and 350 µm. Subsequently, the wear rates began to drop, with a steady decrease in wear with particle diameters between 600 and 1000 µm. The behaviour of the curves was characterised by analysing the Stokes’ number and kinetic energy at each particle size. It was concluded that the sharp increase at 200 µm occurred, due to the number of particles (which possess sufficient kinetic energy) and the number density escaping the continuous phase and impacting the riser walls. Larger particles may have possessed greater individual kinetic energies; however, the fewer particles tend to impact the riser walls at higher particles sizes due to significantly lower number densities, resulting in a decrease in wear rates

3D printing of personalised Carvedilol tablets using selective laser sintering

Selective laser sintering (SLS) has drawn attention for the fabrication of three-dimensional oral dosage forms due to the plurality of drug formulations that can be processed. The aim of this work was to employ SLS with a CO2 laser for the manufacturing of carvedilol personalised dosage forms of various strengths. Carvedilol (CVD) and vinylpyrrolidone-vinyl acetate copolymer (Kollidon VA64) blends of various ratios were sintered to produce CVD tablets of 3.125, 6.25, and 12.5 mg. The tuning of the SLS processing laser intensity parameter improved printability and impacted the tablet hardness, friability, CVD dissolution rate, and the total amount of drug released. Physicochemical characterization showed the presence of CVD in the amorphous state. X-ray micro-CT analysis demonstrated that the applied CO2 intensity affected the total tablet porosity, which was reduced with increased laser intensity. The study demonstrated that SLS is a suitable technology for the development of personalised medicines that meet the required specifications and patient needs