DIXON RINGS – A REVOLUTIONARY RANDOM COLUMN PACKING
Robert Alford, Mark Burns and Neil Burns (pages 218-223)
Dixon rings were developed in 1946 by Dr Olaf George Dixon while working for ICI and are currently used where high performance is essential. There are a number of published papers on the characterisation of Dixon rings as used in distillation applications; however, there is little published work on the countercurrent (scrubbing) performance of Dixon rings. Croft Engineering Services have developed a revolutionary manufacturing method for Dixon rings that can be used in both countercurrent absorption (scrubbing columns) including scrubbing of CO2 from air, as well as hard distillation separations such as tritium from water. This cylindrical mesh item of small size in comparison to the market leaders (Pall rings, Intalox saddles) offers superior performance in a range of applications. The current paper contains a detailed analysis of Dixon rings in a random column packing operating within countercurrent absorption applications.
WET PARTICLE CLASSIFICATION BELOW 1 µm – CHALLENGE FOR BASIC RESEARCH AND TECHNICAL DEVELOPMENT
Harald Anlauf (pages 223-229)
The conventional processes of wet and dry classification in the particle range of more than 1 µm are sieving and the different variants of stream classification. Approaching particle sizes of 1 µm and below the conventional methods reach their present physical and technical limits. The economic relevance of particle systems below 1 µm, and especially between 1 µm and 0.1 µm, is constantly growing and thus a high demand for improved and new classification processes exists. The grade efficiency, selectivity and cost effectiveness of the methods used for such applications are unsatisfactory or don’t exist. In this paper the physical background of classification processes and the problems of fine particle classification are described and discussed. The different physical principles and phenomena are analysed with regard to their potential for technical classification systems in the sub-micron range. Examples are given for promising techniques together with ideas for new approaches.
EFFECT OF ACOUSTIC WAVES ON THE PERFORMANCE OF A MULTI-CYCLONE – FILTER SYSTEM
Leonid Moldavsky, Chaim Gutfinger and Mati Fichman (pages 229-232)
Many air filtration systems include cyclones for pre-cleaning. The performance of the system changes with time because of filter clogging. The cyclones reduce the concentration of aerosol particles, but their sizes are reduced as well, which leads to deeper particle penetration into the filter. Acoustic waves enhance filtration efficiency and cause sedimentation of the very small particles on the filter surface. They also cause the filter layer to be more porous, which leads to a reduction in pressure drop across the filter. In the present study a cyclone-filter system, similar to that in heavy vehicles, was used to assess the effect of acoustic waves on the pressure drop across the filter. It was shown that a low frequency acoustic field reduces the pressure drop across the filter and increases the flow rate through the system, which leads to a reduction of the time between filter replacements or regeneration, ensuring improved performance.
A POROMETER ROUND ROBIN PROGRAM USING FILTER MEDIA OVER A RANGE OF PORE SIZES
Uwe Beuscher, Jeffrey Brake, Michael Doby and Ernest Mayer (pages 233-242)
A round robin program was undertaken to evaluate the techniques and methods used during the operation of various porometers. Two companies participated in the round robin testing of a total of ten Porous Materials, Inc. (PMI) porometers at various locations throughout the world. A variety of filtration media with a wide pore size range were run on the porometer units for comparison. As fragility of some conventional filter media continues to increase primarily due to decreasing fibre diameter and media thickness, porometer testing can sometimes be quite tedious for certain samples. At high compressive load during porometry, damage can occur to the samples producing misleading results. Measures to safely handle samples and operate porometers when working with fragile media were addressed.
The aforementioned samples were processed on each porometer using identical wetting liquid, support plates and parameter files throughout the program. The experimental data are discussed with possible explanations for the deviations presented. The results indicate that the industry should focus on standardising equipment design and developing a procedure for testing to ensure an accurate comparison among porometers.
EXPLORING THE INFLUENCE OF FEED MATERIAL PROPERTIES ON FULL CYCLE OPTIMISATION OF FILL, SQUEEZE AND BLOW PLATE AND FRAME PRESSURE FILTERS
Ross G. de Kretser and Peter J. Scales (pages 243-248)
Investigation of the response of plate and frame filter performance to changes in design and operating variables is complicated by the large matrix of potential variables and the inter-dependent kinetics of the fill, press and air blow stages. However, through some key simplifying constraints an integrated optimisation framework has been recently developed. Initial demonstration of the utility of the framework for minerals filtration was completed on an incompressible iron ore fines material which illustrated a strong dependency of the optimum filling duration on filter specifications such as the ratio of pressing to filling pressure and cavity thickness employed.
The current paper extends this work by exploring how these trends change with varying material properties, specifically treating the cases where the compressibility and permeability are varied. Comparison of optimisation examples for a lower permeability lead-zinc tailings material and the higher permeability iron ore fines revealed a common feature of an optimum fill duration, generally at early times, beyond which throughput deteriorated. A significant difference was observed in the optimum split of cycle stage durations due to the strong effect of desaturation kinetics on the finer tailings dewatering. However, a generic trend was implied whereby an optimum cavity thickness existed, but that this was for a cavity thickness whose optimum fill duration was zero, i.e. the press stage was initiated as soon as the filter cavities were filled.
THE EFFECT OF FACE VELOCITY, PLEAT DENSITY AND PLEAT ORIENTATION ON THE MOST PENETRATING PARTICLE SIZE, PRESSURE DROP AND FRACTIONAL EFFICIENCY OF HEPA FILTERS
Iyad Al-Attar, Richard Wakeman, Steve Tarleton and Adel Husain (pages 248-256)
The increasing need for clean air in critical industrial applications has highlighted the importance of the role of air filters in providing improved air quality. Actual performance of air filters installed in air handling units and in the intake of gas turbines tends to deviate from the performance predicted by laboratory results. Therefore, accurate filter performance prediction is important to estimate filter lifetime, and to reduce energy and maintenance operating costs. To ensure that the desired efficiency of a HEPA filter is attained, the effects of face velocity, pleat density and pleat orientation on the Most Penetrating Particle Size (MPPS) of pleated HEPA filters must be examined. This paper compares the effects of varying these parameters on the MPPS. The paper also presents the initial pressure drop response and fractional efficiency curves using DEHS testing according to DIN 1822 for vertical and horizontal pleat orientations. It analyses the underlying reasons causing surface area losses for different flow rates, pleat density and orientation as well as the effects on filter permeability. The tests conducted in this study used full scale HEPA pleated V-shaped filters from Heating Ventilation and Air Conditioning (HVAC) and gas turbine applications.