Experts in filtration and separation

We advance and disseminate knowledge in the design and use of filtration and separation techniques in industry, commerce and other walks of life.

Volume 7, Issue 3 Abstracts from the FILTRATION journal

CHARACTERISATION OF PARTICLE PENETRATION AND DUST HOLDING CAPACITY OF SURFACE TREATED NEEDLEFELTS
W. Hoeflinger, H. Rud and G. Mauschitz (pages 196-200)

For surface treated filter media porosity properties at and just below the filter surface are essential to particle penetration and particle clogging behaviour. In order to compare different surface treated filter media it is necessary to develop suitable parameters and measuring devices regarding these porosity properties. In this work a transmission microscope together with image analysis software was used to determine a so called hydraulic diameter and a pore volume equivalent, which can be measures for comparing the particle penetration and the particle holding capacity of different surface treated filter media. The experimental verification was performed with a gas/particle system filtered using different surface treated filter media. Generally, the parameters for comparing different surface treated filter media should be also applicable to liquid/particle systems, but for correctness this needs further experimental verification.

DESIGN CONSIDERATIONS FOR CRANKCASE VENTILATION SYSTEMS TO MEET FUTURE DIESEL ENGINE EMISSION REGULATIONS
P. Banerjee, B. Verdegan, B. Schwandt, C. Holm and S. Heckel (pages 201-205)

Successful application of crankcase ventilation (CV) systems to diesel engines is critical for engine manufacturers to meet future emission requirements. This paper discusses the challenges associated with filtering crankcase blow-by and explains the technical considerations for designing a CV system for specific engine platforms. The paper also compares the performance of CV systems from various filter manufacturers using common performance metrics and presents our approach for optimizing CV system design to support diesel engine manufacturers’ efforts to meet emission requirements of 2007 and beyond.

STREAMING CURRENT MONITORING (SCM) OF INDUSTRIAL FLOCCULATION PROCESSES
E. Mayer (pages 206-214)

Conventional wastewater (WW) treatment usually involves coagulation or polymer flocculation prior to clarification by sedimentation or dewatering by filter presses, belt filter presses, or centrifuges. Polymer dosage control is critical for optimum performance as well as reducing costs. Many devices have been developed over the years to measure both floc size as well as the excess charge in solution. The Water Environment Federation (WEF) has recently conducted a research program on three such devices that concluded the Streaming Current Monitor (SCM) has the most merit. This paper will discuss this relatively new technology and how it was applied in a rigorous fashion to industrial flocculation processes. Case histories will be presented that highlight its usefulness.

MEMBRANE FILTRATION CONCEPT AND CATALYTIC FILTRATION
G.G. Pranghofer (pages 214-219)

Various technologies have been developed for the control of Poly-Chlorinated-Di-benzo- Dioxins and -Furans (PCDD/F). In flue gas cleaning systems of municipal waste incineration plants the most commonly used methods are (i) adsorption technology by utilizing pulverized activated carbon (PAC) or lignite coke (Herdofenkoks, HOK) in fabric filters, and (ii) catalytic destruction by means of a selective catalytic reactor system (SCR). The adsorption technology is well proven but does not destroy the PCDD/F; they are collected on the surface of the carbon particles and disposed of with the fly ash. SCR systems destroy PCDD/F but cannot control particulate matter. About 10 years ago a new system was developed which is an evolution of two proven technologies: catalysis and surface filtration.

The new system developed for the control of Poly-Chlorinated-Di-benzo- Dioxins and -Furans (PCDD/F) consists of an ePTFE (Poly-Tetra-Flouro-Ethylene) membrane and a catalytic felt substrate. In this paper the catalysis and surface filtration principles are detailed. Performance results in different incineration plants are provided. PCDD/F concentrations up to 10 ng ITEQ/m³ in the raw gas have been reduced well below the limit of < 0.1 ng ITEQ/m³.

NANOFILTRATION – A METHOD FOR SOLUTE REMOVAL FROM LIQUID HYDROCARBONS
E.S. Tarleton and J.P. Robinson (pages 220-225)

In relation to potential applications in hydrocarbon processing, the separation characteristics of a dense polydimethylsiloxane (PDMS) membrane were studied using alkyl and aromatic solvents and low-polarity, sulphur bearing, organometallic (OM) and poly-nuclear aromatic (PNA) solute compounds. Solute rejection was found to be dependent on trans-membrane pressure, crossflow rate (hydrodynamic conditions), solute size and the degree of swelling induced by the solvent. Rejection increased progressively with pressure whilst a threshold condition was observed above which further increases in crossflow had a negligible influence on rejection. Measurements over the molecular weight range 84-612 g/mol showed the membrane to have a cut-off in the region 350-400 g/mol to all but one of the tested PNA compounds (rubrene). An additional correlation using molecular dimensions instead of molecular weight showed the cut-off size to be in the region of 1-2 nm, with all data falling on a well defined rejection/size curve.

Solvent type influenced membrane swelling to an extent dependent on the relative magnitude of the solubility parameters for the solvent and PDMS; similar values led to more swelling, higher fluxes and lower rejections. Results support the concept of viscous solvent flow whilst solute transport could be either predominantly viscous or a combination of viscous and diffusive. With larger molecules a size exclusion mechanism was dominant.

MEASUREMENT OF THE EFFICIENCY OF DEPTH FILTERS FOR WATER TREATMENT
M. Zielina and L. Hejduk (pages 225-228)

Conventional granular filters have been widely used in drinking water treatment technology since the first half of the previous century. Numerous laboratory experiments and theoretical analysis of depth filtration have been done by many researchers, but there are still no satisfactory complete mathematical models to calculate the hydraulic head loss and the effluent quality during the whole process. While transport of suspended particles in the filter medium is quite well recognized, the ability to predict the adhesion efficiency is poor. For this reason, and because of variable conditions in filter plants, continuous observation of the filtrate quality and head loss are practically the only possibility for predicting accurate results. In most filter plants “on-line” information about the efficiency of the suspended solid removal is estimated using turbidity sensors. The interpretation of the turbidity (especially nephelometric) is quite complex and difficult without detailed information about the suspension. Laser particle size analyzers give interpretative information about the suspension and removal efficiency through the filter, but its application in drinking water treatment plants remains limited.

A laboratory set-up has been designed and built, which includes filtration by a 3 m deep column together with the inflow system for preparing the suspension in raw water. Several experiments were performed in the laboratory set-up and in the full scale water treatment plant for various flow rates, medium heights, grain stratifications and suspensions. The filter efficiency change versus time was analyzed with the laser particle size instrument and the turbidimeter. The significant differences between results depending on the measuring method were observed and compared to the theory. An interpretation of the predicted filter efficiency on the basis of both methods is proposed.

CLEAN PRODUCTION AND SIGNIFICANT ENERGY SAVINGS WITH A HYBRID SEPARATION PROCESS – HI-BAR STEAM PRESSURE FILTRATION
T. Langeloh and R. Bott (pages 228-233)

Hi-Bar steam pressure filtration is an innovative hybrid separation process which combines mechanical and thermal dewatering. This advanced variant of continuous pressure filtration enables a simplified separation process design with lower emissions and significant energy savings. The process is currently establishing itself in the chemical, pharmaceutical, food and life science industry particularly for the demanding applications of filtration, washing and dewatering of high value products.

INFLUENCE OF LEAKS IN SURFACE FILTERS ON PARTICULATE EMISSIONS
B. Bach and E. Schmidt (pages 235-239)

Compliance with severe limit values of dust emissions is a main characteristic of surface filters that is due to the high particle collection efficiency of surface filters. Besides regular operation it is necessary to consider phenomena such as a “pinhole” bypass in surface filters to ensure the above mentioned compliance with the limit values at all times. “Pinhole” bypass is suspected to be the main mechanism concerning particle penetration through leaks in installed filters.

Experimental research has been carried out to observe and understand “pinhole” bypass and the behaviour of pinholes with filtration time. To work out the influence of different filtration conditions, the parameters pinhole diameter, filter face velocity and dust cake thickness were varied.

The results can be explained using formulae that are usually used to the calculate volumetric flow rates of orifice gauges. The experiments and calculations lead to the conclusions that bigger pinholes decrease the collection efficiency and higher filter face velocities increase the collection efficiency of pinholed filter media. Worst case clean gas concentrations can be calculated by the theoretical model provided.

Keywords: Solid/gas separation; surface filtration; filter efficiency.

PERFORMANCE OF BAGHOUSE DUST COLLECTORS IN THE WOODWORKING INDUSTRY
D. Bémer, X. Simon, R. Régnier, I. Subra and B. Honnert (pages 240-247)

Baghouse dust collectors are frequently used in the woodworking industry for the removal of dust that causes several diseases, including a number of serious ones. Common practice involves resorting to air recycling after filtration, which enables the costs associated with air heating to be curtailed. However, performance of dust collectors must be ascertained, given the dangerous nature of the dust and the low concentration limit value in recycled air (≤ 0.2 mg m-3). Measurements were carried out on installations that exhibit different characteristics (e.g. age, design, airflow, filtration process, etc.). Filtration efficiency was measured using two methods, namely tracing with a fluorescent aerosol and optical counting. Downstream concentration was determined by isokinetic sampling and gravimetry.

Tests allowed the authors to validate and improve the tracing method. Measurements generally revealed low wood dust concentrations that were usually below the established limit (0.2 mg m-3). An exception was during cleaning phases although the concentration remained low (< 1 mg m-3). On the other hand, air recycling reintroduces sub-micronic wood dust particles into the workshop for which the effects on health remain unknown. Keywords: Aerosol; filtration; fluorescein; baghouse filter; wood dust.

CONTINUOUS METAL RECOVERY PROCESS USING POLYMER ENHANCED ULTRAFILTRATION
J. Sabaté, M. Pujolà, J. Llorens and P. Marco (pages 248-250)

The separation of metals from aqueous streams by continuous polymer enhanced ultrafiltration (PEUF) was modelled in order to understand, evaluate and optimise the feasibility of the process. The mathematical model developed has three sections: mass balances, equilibrium of metal-polymer complexation and rules for UF membrane separation. On the one hand, the model allows an examination of the influence of physico-chemical variables (affinity between the metal ion and the complexing polymer groups) and engineering parameters (mainly expended acid and base reagents, amount of polymer used and recycling stream flow) on the quality and productivity of the treated water stream. On the other hand, a suitable representation of the simulation results has been shown to be helpful in choosing operation parameter values that lead to the stable output of treated water with the desired quality and productivity.

Keywords: Metal; recovery; ultrafiltration; continuous; simulation.

STATISTICAL MODELLING OF THE PORE STRUCTURE OF STOCHASTIC FIBRE NETWORKS
W.W. Sampson (pages 251-254)

A model is presented that accounts for the influence of grammage and porosity on the pore radius distribution in stochastic fibre networks. The influence of fibre width on the mean pore radius of two-dimensional random networks is derived. The model shows that increasing grammage and decreasing porosity decreases the mean pore radius in random and non-random networks. The standard deviation of pore radii is shown to be proportional to the mean in agreement with experimental observation; the proportionality is shown to be sensitive to the uniformity of the constituent layers of multiplanar structures.

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