Modeling Water-Induced Base Particle Migration in Loaded Granular Filters Using Discrete Element Method

Results are reported from a series of filtration tests simulated using coupled computational fluid dynamics and the discrete element method (CCFD-DEM) to investigate the factors controlling the mechanism of base particle erosion and their subsequent capture in loaded granular filters. Apart from geometrical factors such as particle and void sizes, the filter effectiveness was found to be controlled by the magnitudes of the hydraulic gradients and the effective stresses. The results of numerical simulations revealed that the base soils exhibit significant stress reduction that reduces further due to seepage, and the base particles migrate into the filter, bearing very low effective stresses (i.e., localized piping in base soil). Based on the limit equilibrium of hydraulic and mechanical constraints, a linear hydromechanical model has been proposed that governs the migration and capture of base particles in the filter (i.e., filter effectiveness avoiding piping) for cases simulated in this study. Nevertheless, the proposed model agrees closely with the simulation results of this study and those adopted from other published works, thereby showing a reasonable possibility of using the proposed model as a measure of retention capacity of loaded protective filters.

Determination of hydraulic conductivity for granular filters based on constriction size and shape parameters

This experimental study is an attempt to apply the constriction size concept for determination of hydraulic conductivity of filter material. Five shapes of granular filter material having varying gradations were used for the experimental investigations. The controlling constriction size of selected shapes having varying gradations were worked out and related to the experimental results of hydraulic conductivity. The empirical model for hydraulic conductivity determination based on controlling constriction size for each selected shape of granular filter material was developed. Finally, a combined empirical model for the determination of hydraulic conductivity of granular filters was developed based on shape parameters and the controlling constriction size.

Numerical Simulation of the Aerosol Particle Motion in Granular Filters with Solid and Porous Granules

In this work, a study was carried out to compare the filtering and hydrodynamic properties of granular filters with solid spherical granules and spherical granules with modifications in the form of micropores. We used the discrete element method (DEM) to construct the geometry of the filters. Models of granular filters with spherical granules with diameters of 3, 4, and 5 mm, and with porosity values of 0.439, 0.466, and 0.477, respectively, were created. The results of the numerical simulation are in good agreement with the experimental data of other authors. We created models of granular filters containing micropores with different porosity values (0.158–0.366) in order to study the micropores’ effect on the aerosol motion. The study showed that micropores contribute to a decrease in hydrodynamic resistance and an increase in particle deposition efficiency. There is also a maximum limiting value of the granule microporosity for a given aerosol particle diameter when a further increase in microporosity leads to a decrease in the deposition efficiency.

Chemical Clogging and Evolution of Head Losses in Steel Slag Filters Used for Phosphorus Removal

The objective of this study was to propose a conceptual model of clogging in alkaline granular filters. Two slag columns were operated for 600 days and monitored using piezometers and tracer tested at regular intervals. The type of influent (organic or inorganic) affected the loss of effective porosity in the filters. Well organized and loose crystal structures were observed by scanning electron microscopy in columns with inorganic and organic influents, respectively. It was postulated that the formation of crystals in unorganized structures results in confined voids that are not accessible for water flow, thus accelerating porosity loss. The effect of the combination of chemical clogging and biofilm on the porosity loss is higher than the effect of these two factors separately. The Kozeny-Carman equation for hydraulic conductivity could not efficiently predict the evolution of head losses in the column fed with an inorganic influent. The crystal structure and connectivity in the presence of homogeneous or heterogeneous precipitation are concepts that could improve predictions of hydraulic conductivity. The results of this study highlighted the importance of the inlet zone on the development of pressure head in alkaline granular filters. Future research on clogging should focus on precipitation mechanisms in the inlet zone and on the design of the feeding system.

Особенности возникновения и предупреждение взрывоопасных режимов в системах аспирации с фильтрами-пылеуловителями

Обоснованы преимущества использования зернистых фильтров в системах аспирации производственных помещений, в которых образуется и обращается горючая пыль. Рассмотрены некоторые известные конструкции, имеющие достаточно узкое применение, однако перспективные для обработки взрывоопасных пылегазовых потоков. Дано описание лабораторного стенда и приведены результаты экспериментальных исследований процесса фильтрования зернистыми фильтрами, подтверждающие необходимость контроля взрывоопасных ситуаций в работе пылеуловителя. Предложен автоматизированный способ контроля аспирации для предупреждения взрывоопасных состояний фильтра.There is a large number of technological operations associated with the treatment of combustible dusts at production facilities. Such industries include food, pharmaceutical, woodworking, metalworking, textile and other industries, the main technological equipment of which is supplemented with aspiration systems. According to the requirements of ecology, labour protection and fire safety, this system must include a dust collector. When choosing a dust collector for such systems granular filters are found particularly effective. They allow to precipitate combustible dust. The article presents the known constructions of granular filters, the narrow application of which is associated with insufficient study of their operation with explosive flows. Therefore, the authors developed an experimental stand and analyzed the operation of different filters: with metal balls, screws, peas and pea mash, grain, which can be used as filter material. During the experiment it was found a state in which the filter operation is explosive. According to the results of the analysis, the criteria for the descriptions of normal and explosive operation are introduced - the criteria of geometric form, characterizes the filter and dust - K, and the rate of filtration - T. Numerical values of criteria are given for automated control of the filter operation. The automated control method of the filter allows to make the operation of the aspiration system more efficient and prevents explosive situations by timely regeneration and replacement of the layer, taking into account the calculated value of criteria K and T. In the scheme there are shown fire extinguishing modules, which are triggered by sensors when the temperature rises above normal.