- The Filtration Society - http://www.filtsoc.org -

Volume 7, Issue 4

PERFORMANCE OF PRESSURISED AGRICULTURAL VEHICLE CABS AGAINST PESTICIDES – AEROSOL TESTING METHOD
D. Bémer, I. Subra, M.T. Lecler, J.P. Larrat and D. Schaeffner (pages 282-285)

A method for determining the efficiency of a vehicle cab for agricultural tractors with respect to an aerosol has been developed. The method has been used to evaluate the efficiency of two cabs differing in their filtration system (medium and high efficiency filters) and ventilation designs. For the cab fitted with the high-efficiency filter, the measured efficiency was corrected according to the aerosol internal source. Results obtained for the cab fitted with a medium performance filter revealed an efficiency higher than that of the filter itself. This increase in efficiency is achieved by partially recycling the air through the filter. Results obtained for the cab fitted with a very high performance filter were contrary, inasmuch as the measured efficiency was lower than that of the filter itself. Measurements of the aerosol were taken near a tractor cab during pesticide application in an orchard. A tracing method was applied to determine cab efficiency, as well as concentration and particle size distribution of the pesticide aerosol.

WHO ARE THE CULPRITS? – POTENTIAL CONTAMINANTS OF FOODS AND BEVERAGES
G. Shama (pages 286-290)

The ‘culprits’ of the title are actually extremely diverse, and include both living organisms and what might be referred to as ‘complex biochemical agents’. This last, somewhat contrived, term is intended to cover viruses, viroids and prions. These latter may be thought of as occupying the evolutionary gap between molecules and living organisms.

All of these agents have the ability to contaminate foods and beverages, and the potential to cause food poisoning in different ways and with various degrees of severity ranging from mild enteric discomfort to death. Whilst methods of detection for known pathogens continue to improve, it is also the unknown that we need to be constantly vigilant over. The nature of the unknown is literally unknowable, but some guidance as to what new types of foodborne agents might emerge in the future may be gained by considerations of recent discoveries in microbiology that are helping to (re)define the boundaries of the possible. Consequently, whilst primarily focussing on well-characterised foodborne pathogens, some speculation about the ‘next generation’ has also been included where strictly relevant.

MINIMISING THE PRESSURE DROP ACROSS FILTERS WITH MULTI-CYLINDRICAL FILTER TUBES
M. Buzanowski and D. Fadda (pages 290-292)

Effective, efficient and economical removal of dust, dirt, scale, rust, and other solid foreign particles from different types of gas streams is a process requirement often encountered in the design of chemical plants, pipeline stations, gasoline plants, refineries, town border stations for distribution systems and various other industrial plants. Gas filters are used where a high degree of solids removal is required. Pressure drop, the negative factor associated with filtration, can be decreased by optimizing filter media geometry. Computational fluid dynamics (CFD) analysis is used to optimize cylindrical filters currently used as gas filters and filter separators. The computational method used in this analysis is described and its results are presented.

TESTING ANTI-MICROBIAL EFFECTIVENESS IN POOL FILTER MEDIA
P.J. Angelini (pages 293-297)

Anti-microbial containing filter media designed for pool and spa applications have been in commercial use for five years. Currently there are two commercial suppliers of these media. The purpose of treating the filter media with an anti-microbial material is to provide a means of inhibiting bacterial growth on the surface of the filter. By doing this the service interval between cleanings will be extended.

LARGE SCALE BAG FILTRATION ENHANCED BY ELECTROSTATICS
C.-V. Rasmussen, M. Koch, H.V. Pedersen and G. Krammer (pages 297-299)

This work comprises the evaluation of industrial measurements carried out on FLSmidth Airtech (FLS A) fabric filters (FFs) positioned downstream of two different cement mills. One mill in Aalborg, Denmark features an upgraded electrostatic precipitator (ESP) into a hybrid filter where part of the electrodes were removed and filter bags were fitted in place in 2001. Here tests were carried out with and without ESP in operation. The second mill in Kunda, Estonia is exclusively equipped with a FF from start up of the plant in 2005. The filtration behaviour of the filters in different operational states is assessed using the permeability distribution (PD) method to characterize the different filtration behaviour of the cloth/dust combinations observed.

EXPERIMENTAL COMPARISON OF FRACTIONAL EFFICIENCY MEASUREMENTS ACCORDING TO ISO TS 11155-1, ISO 5011, EN 779 AND ISO CD 20564
M. Schmidt and S. Schütz (pages 300-303)

International standards – ISO TS 11155-1 for cabin air filters, EN 779 for general air ventilation filters, ISO 5011 for engine air filters or filter media, and ISO CD 20564 for crankshaft ventilation filters – are developed for the producer and user of these filters to compare their special characteristics under defined and comparable conditions.

International round robin tests according to ISO TS 11155-1/DIN 71460-1 and EN 779 accomplished by different laboratories using these test systems have previously shown large differences, especially in fractional efficiency measurements. For example, the international round robin tests according to ISO 11155-1 accomplished in 1999 and 2004 showed differences in initial fractional efficiency at 0.3 micron of up to 70%. Nonetheless, the measurement of fractional efficiency is an important tool to characterise the efficiency of filters and filter media unambiguously.

We will show that good comparisons of different test rigs according to ISO 11155-1/DIN 71460 can be achieved even when using different particle measuring systems. Additionally, we will present the comparison of two HMT-1000 Palas test rigs for blow-by filters and two Palas® test rigs for filter media testing of cabin air filters or motor air engine intake filters.

ROLE OF FLOCCULANT INJECTION AND MIXING CONDITIONS IN SLUDGE FLOCCULATION
P. Ginisty, C. Peuchot and A. Premel (pages 304-308)

This work deals with the effects of dispersion/mixing parameters on sludge flocculation efficiency before thickening on a drainage table and dewatering on a belt filter. The first part of the paper concerns sludge flocculation in an agitated tank at the laboratory scale. Camp numbers were determined. The kinetics of floc growth were followed by a Turbiscan apparatus and the efficiency of flocculation was determined by gravity drainage and CST tests. The main parameters influencing the process are the energy dispersed and the time of polymer dispersion and floc growth. Additional factors are the impeller design and polymer characteristics. Results enabled a new laboratory protocol to be defined and the optimisation of sludge flocculation. The second part of the paper concerns sludge flocculation in pipes in wastewater treatment plant.

A specific apparatus was designed to measure Camp numbers and to test different kinds of injectors, addition points and in-line mixers. The impact of the hydrodynamic conditions used during flocculation on drainage table and belt filter performances was evaluated. Results showed that Camp numbers are not sufficient to qualify hydrodynamic conditions and compromises should be found between floc growth and breakage. Even though the mechanisms of sludge flocculation were difficult to fully understand, practical and specific recommendations are made to enable optimised hydrodynamic conditions to be chosen according to site configuration.

AN IMPROVED METHOD FOR WASHING LIGNIN PRECIPITATED FROM KRAFT BLACK LIQUOR – The key to a new biofuel
F. Öhman, H. Wallmo and H. Theliander (pages 309-315)

In a previous study on the washing of lignin precipitated from kraft black liquor, problems with complete or partial plugging of the filter cake and/or filter media were encountered that resulted in uneven washing and high sodium contents in the final lignin product. This effect was ascribed to large gradients in pH and ionic strength during the washing process. Based on this understanding of the phenomenon involved, an improved method for lignin washing was developed, which gave very successful results in laboratory scale trials.

In the continuing studies on lignin separation from black liquor within the FRAM (Future Resource Adapted pulp Mill) research programme, this method was evaluated in bench scale and small pilot scale trials. These trials were equally successful and it was shown that kraft lignin with low sodium content (<0.5% by weight), high dry solids content (62.5% on average) and high calorific value (LHV 25.4 MJ/kg) could be produced. There were no particular problems encountered in scaling up the new method from laboratory scale (filter area 20 cm2) to the small pilot scale (filter area 1.7 m2). The investigated separation properties concerning filtration and washing were found to be similar for bench scale and pilot scale experiments.

EXAMPLES OF AIR FLOW PATTERNS IN FOOD PRODUCTION AREAS
D. Burfoot (pages 315-322)

Air movements can transport particles, including those containing microorganisms, around food production areas. The sources of particles may be within or outside the production area. Sources of such contamination must be restricted and the air guided such that the risk of particles landing on the food is low. Examples are given of the movements of airborne particles in chilled food factories, bakeries, and slaughterhouses. Although the level of sophistication of the air handling systems are different in each case, and the composition of the aerosols are also dissimilar, the need to maintain a good direction of air flow remains important. In general, air should flow out of the production area, and from clean areas near to the food towards lower-care areas. It will be demonstrated that providing sufficient clean air to produce a positive pressure in the production area, based on average flow rates, is not always sufficient to prevent contamination entering the production area.

THE PRODUCTION AND CERTIFICATION OF PRECISION SLOTTED SIEVE STANDARDS
G. Rideal (pages 322-324)

Calibration of slotted sieves using vernier micrometers has given rise to measurement uncertainties in the past. Calibration microspheres have been shown in a recent report to give promising results but their accuracy depends on two important factors. Firstly, the ability to accurately measure the widths of melt produced glass microspheres, which are not 100% spherical and, secondly, the need for narrow particle size distributions that give the highest resolution in the calibration process. This paper discusses the production of narrow particle size distribution glass microspheres and the development of a high precision slot device for calibrating the standards. The certified reference standards were then used to calibrate a 2.5 mm slotted sieve.

PARTICLE-PRESSURE INDUCED TRANSIENT CHANGES IN OSCILLATED PARTICLE-FLUID SYSTEMs
M. Davis and M.A. Koenders (pages 326-336)

From the general flow equations for a particle-fluid mixture both the oscillatory behaviour and the secular (that is, quasi-static) process can be derived. The two are coupled via a mean net stress component, called the particle pressure, in a rapidly agitated medium. In a septum-vibrated dead-end filter the particle pressure is generated near the septum. The secular changes that take place as the vibration is increased can be gathered in a set of coupled equations. The effects that are observed in permeation experiments are then reproduced from the theory. These include a critical point at which the flow rate rapidly increases. The rheology of a packed bed that is agitated by a cyclic strain is then investigated and its non-linear character is elucidated. The non-linear clogged septum rheology is also investigated, so as to obtain an impression of the stress dependence of the clogged septum permeability. Combining rheology and incremental secular equations of motion enable an understanding of the features of the flow rate vs. oscillation amplitude. Rough estimates of the various parameters show that the effects the theory describes are corroborated by experiments. Of special interest is the critical point, at which the flow rate through the filter increases rapidly with incremental oscillation amplitude.

ARTIFICIAL NEURAL NETWORK MODEL TO PREDICT COMPRESSION-PERMEABILITY CHARACTERISTICS OF SOLID/LIQUID SYSTEMS
M. Iwata, M.S. Jami and S. Shiojiri (pages 337-344)

A statistical modelling tool called artificial neural network (ANN) is used in this work to predict the compression-permeability (C-P) characteristics of a solid/liquid system. An extensive cake properties database containing experimental data that spans various material types, particle size distribution, flocculated and unflocculated particles has been developed and used to train two ANNs. The input parameters for the first ANN were the applied pressure and the particle size distribution whereas the output parameter was the porosity of the compressed cake. In the case of the second ANN, the input parameters were the porosity and the particle size distribution. The logarithm of the specific cake resistance multiplied by the particle true density of the cake (log (αρs)) was chosen as the output parameter of this network.

The use of porosity obtained from gravitational and centrifugal sedimentation experiments as one of the input parameters to the ANNs gave excellent results in predicting both the cake porosity and the specific cake resistance. With the help of this method, after the ANN is thoroughly trained with various slurries, the C-P characteristics of another slurry can be predicted with much less of the target slurry compared with that used in a conventional C-P test.