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

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

Evaluation of particle degradation due to high-speed impacts in a pneumatic handling system

Particle degradation can be a significant issue in particulate solids handling and processing, particularly in pneumatic conveying systems, in which high-speed impact is usually the main contributory factor leading to changes in particle size distribution (comparing the material to its virgin state). However, other factors may strongly influence particles breakage as well, such as particle concentrations, bend geometry,and hardness of pipe material. Because of such complex influences, it is often very difficult to predict particle degradation accurately and rapidly for industrial processes. In this article, a general method for evaluating particle degradation due to high-speed impacts is described, in which the breakage properties of particles are quantified using what are known as "breakage matrices". Rather than a pilot-size test facility, a bench-scale degradation tester has been used. Some advantages of using the bench-scale tester are briefly explored. Experimental determination of adipic acid has been carried out for a range of impact velocities in four particle size categories. Subsequently, particle breakage matrices of adipic acid have been established for these impact velocities. The experimental results show that the "breakage matrices" of particles is an effective and easy method for evaluation of particle degradation due to high-speed impacts. The possibility of the "breakage matrices" approach being applied to a pneumatic conveying system is also explored by a simulation example

Resolving lateral segregation effects of static blenders

To date static blenders have mainly been used for mixing fluids, but recent research has shown the potential of static blenders for blending powders and granular materials as well. A problem when using a static blender in conjunction with powders and granular materials is trajectory induced segregation at the output of the blender. In order to evaluate the blending process two granular materials exhibiting extreme particle densities and sizes have been discharged into a static blender. The blend is collected in a radially compartmentalised receiving container and the blend composition of each compartment is then analysed. This paper presents a simple counter measure to reduce the effect of trajectory induced segregation. In addition this research has shown that, contrary to expectations, an increased number of blending stages does not necessarily bring improvements in homogeneity of the output stream. The results presented in this paper are of special interest to anyone blending powders and granular materials in an industrial environment

Segregation of bulk particulates through multiple process handling steps

Segregation or de-blending of bulk particulates is a problem that is encountered in many industrial sectors. The magnitude of segregation can often determine whether a complete production batch can be transferred for onward processing within the plant or released to market. It is a phenomenon that impacts directly upon the profitability of a process. Segregation can occur through a coincidence of a range of variables that relate to the process and bulk particulate properties, common mechanisms for this include; percolation, surface effect (rolling) and elutriation. The importance to industry of predicting the sensitivity of bulk particulates to segregation cannot be under-estimated, and to this end various test procedures have been developed. Within many industries striving to improve product quality and reduce wastage, the determination of variability in blend consistency caused by segregation is an increasing priority. This paper considers recent work undertaken to evaluate the effects of multiple handling operations on the degree of segregation that results. The bulk properties of segregability (and resulting flowability) can not only influence the product consistency, but can have great influence over the process (production) control and performance

Modelling dosator filling and discharge of powder

Dosators and other dosing mechanisms operating on generally similar principles are very widely used in the pharmaceutical industry for capsule filling, and for dosing products that are delivered to the customer in powder form such as inhalers. This is a trend that is set to increase. However a significant problem for this technology is being able to predict how accurately and reliably, new drug formulations will be dosed from these machines prior to manufacture. This paper presents a review of the literature relating to powder dosators which considers mathematical models for predicting dosator performance, the effects of the dosator geometry and machine settings on the accuracy of the dose weight. An overview of a model based on classical powder mechanics theory that has been developed at The University of Greenwich is presented. The model uses inputs from a range of powder characterisation tests including, wall friction, bulk density, stress ratio and permeability. To validate the model it is anticipated that it will be trialled for a range of powders alongside a single shot dosator test rig

Direct measurement of powder flavour adhesion on to a food surface using a novel adhesion tester

The firm adhesion of flavouring particles onto crisp surfaces during coating processes is a major concern in the snack production industry. Detachment of flavouring powders from products during handling and production stages can lead to substantial financial losses for the industry, in terms of variable flavour performance and extended cleaning down time of fugitive particle build-up on process equipment. Understanding the adhesion strength of applied bulk particulates used for flavouring formulations will help analysts to evaluate the efficiency of coating processes and potentially enable them to assess the adhesion strength of newly formulated flavouring powder prior to commitment to full scale plant trials. A rapid prototype of a novel adhesion tester has been designed and constructed. The apparatus operates according to the principle of impact force acting on particles attached to the surface of the food substrate. The main component is a circular plate to which four sample holders are attached and which is subjected to vertical travel down a guide shaft. Several flavouring powders have been tested extensively. By plotting the detachment versus impact force, the difference obtained between adhesion strength of different flavouring powders (which is a strong function of particle size) has been discussed

Effect of machine dependence on wall failure property measurements, Jenike versus an annular shear tester

Annular, ring or torsional shear testers are commonly used in bulk solids handling research for the purpose of powder characterisation or equipment design. This paper reports from a DEFRA sponsored project which aims to develop an industrial powder flow-ability tester, (based on the annular shear tester) that is economic to buy and quick and easy to use in trained but unskilled hands. This paper compares the wall failure loci measured with an annular shear cell with measurements obtained using the accepted standard wall friction tester, the Jenike shear cell. These wall failure loci have been measured for several bulk solids which range from fine cohesive powders to free-flowing granular materials, on a stainless steel 304 2B wall surface

Evaluation of air induced segregation tendencies in pharmaceutical blends using a bench scale tester

Summary Segregation is a complex mechanism that leads to separation of various particulate fractions in bulk solids. The nucleation and acceleration of segregation can potentially happen at various stages in the process or handling of a given bulk particulate. Any bulk solid composed of particulates under 50μm size range and exhibiting variations in particle characteristics can be susceptible to air induced segregation. The pharmaceutical sector uses many types of dry powders exhibiting these characteristics in various manufacturing processes and products. The presented work was undertaken to evaluate the susceptibility of an exemplar pharmaceutical blend to segregate under the influence of counter current air-flow using a bench size tester. The results of the segregation tests have then been used to predict the variation in the fine particles (often active content) of the bulk particulate. The techniques for minimising segregation are largely dependent on establishing the most dominant mode governing the segregation mechanism (in particular process and handling conditions). The air induced segregation tester has been shown to be a useful and reliable tool for predicting the propensity of fine powder blends to be susceptible to counter air current segregation, while the QPM segregation tester has been proven to indicate the propensity for surface segregatio