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Filtration
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
The operations are divided into two broad categories: “cake” and “depth” filtration. In cake filtration, particles in a slurry form a deposit as a filter cake on the surface of the supporting porous medium while the fluid passes through it. After an initial period of deposition, the filter cake itself starts to act as the filter medium whilst further particles are deposited. From the viewpoint of a driving force, cake filtration is further divided into pressure, vacuum, gravity, and centrifugal operations. In depth filtration (sometimes called filter medium filtration or clarifying filtration), particles are captured within the complex pore structures of the filter medium, and the cake is not formed on the surface of the medium. In many processes, a stage of depth filtration precedes the cake formation. The first particles can enter the medium, and with very dilute slurries, there can be a time lag before a cake begins to form. Smaller particles enter the medium, whereas larger particles bridge the openings and start the buildup of a surface layer. Depth filtration is generally used to remove small quantities of contaminants. Cake filtration is primarily employed for more concentrated slurries. In practice, cake filtration is employed in industry more often than depth filtration. The following discussion will be concerned with cake filtration.
Removal of Particulate Matter by Filtration and Sedimentation
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
The disadvantages of precoat filtration are as follows: There is continued cost of filter medium, usually discarded at the end of each filter cycle.It is less cost-effective for water that requires pretreatment for algae, color, or taste and odor problems. Water containing only larger plankton such as diatoms can sometimes be treated economically by microstraining prior to the precoat filtration.Proper design, construction, and operation are absolutely essential to prevent the dropping or cracking of the filter cake during operation, which might result in failure to remove the target particulates.Mechanical devices require maintenance and can fail.”
Filtrative Particle Removal
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
To the extent that particle removal is dependent upon sieve retention, the filter efficiency, in terms of the percentage of the total particles that are removed, should not be affected by the differential pressure. This is because sieving is essentially independent of the challenge level, or of the flow rates as dictated by the differential pressure. There are some negative effects, however. Compactions caused by higher differential pressures may render filter cakes less penetrable by the fluid. Foreshortened throughputs may result. Slower rates of flow may also result from the densification of the diffused polarized particle layer suspended in front of the filter (Figure 5.10). Where particles smaller than the pores are present, filter cake densification, as also cake buildup, should progressively increase the filter efficiency by retaining smaller particles. Differential pressure can have a profound effect upon filter efficiency where particles are subject to adsorptive removals. Increased liquid flow rates, the product of higher ∆Ps, reduce the residence time of the particle in the pore passageway. This diminishes the prospects for its adsorptive sequestration to take place. The longer the mutual exposure of particles and pore wall surfaces, the greater the chances of their adsorptive connection. Lower delta pressures increase retentions where the adsorption mechanism is involved because longer residence times increase the probabilities of pore wall encounter, and of resulting particle captures. This accords with the experience that employing lower ∆Ps tends to increase filter efficiencies.
Study on the solid-liquid separation mechanism of the inverting filter centrifuge’s dewatering process
Published in Drying Technology, 2023
Da Li, Bao Rong, Xiaoting Rui, Yixin Liu, Guoping Wang
Figure 1 depicts the shape and basic structure of inverting filter centrifuge and Figure 2 shows the discharging stage’s principle. As shown in the left figure of Figure 2, The drum is closed during the production stages, which include the feeding, pre-dewatering, washing, and dewatering stages. And it is driven by motor 1 to reach the preset rotational speed. Slurry enters the drum through the feed pipe, is broken up by the rotating columns in the drum and moves toward the drum wall. The filter medium traps particles and particles accumulate to create a filter cake. The filtrate housing will receive liquid once it has passed through the filter cake and filter medium. The load cell system records and outputs the total weight of the materials in the drum during the production stages. It enters the discharging stage when the production stages are finished. During discharging stage, the drum’s rotational speed reduces, and it is subsequently propelled by the motor 2 to achieve the open state, as shown in the right figure of Figure 2. The filter medium is turned over to unload solid material from the golden arrow shown in Figure 1. Except for the discharging stage, particles fed into the centrifuge are contained inside the drum. Figure 3 shows the size of inverting filter centrifuge’s drum. The drum’s height is h = 400 mm and its width is R = 1000 mm. The dashed line in this figure represents the axisymmetric coordinate system.
Study on the working mechanism of fluid loss additive for chlorination titanium blast furnace slag
Published in Journal of Dispersion Science and Technology, 2023
Ping Zhou, Yuanpeng Wu, Huiting Liu, Ming Li, Weiyuan Xiao, Meng Liu, Jianzhang Hao, Yanming Li, Chengxin Li
In order to reduce the filtration rate of cement slurry, fluid loss additive is usually used in cement slurry system.[1–4] Fluid loss additive is a kind of material which can control the liquid phase filtration of cement slurry to permeable formation, so as to maintain the proper water cement ratio of cement slurry. It can effectively ensure cementing quality and reservoir safety.[5] The working mechanism of fluid loss additive is mainly physical filling plugging effect, adsorption and aggregation effect, and improving liquid viscosity.[6–10] Constantin Tiemeyer[11] synthesized a kind of five component polymer by water-based free radical. It was found that the fluid loss reduction mechanism of AHPS based copolymer is that the permeability of filter cake decreased due to the co-precipitation of FLA and tartaric acid retarder mediated by Ca2+. Zhang Xianmin[12] synthesized a high-temperature bridging-type anti-collapse agent QFT. After experimental tests, the anti-collapse agent can prevent the solid particles in the base slurry from agglomerating at high temperature by bridging with the clay to ensure a certain amount of fine particles in the base slurry. It is beneficial to form filter cake with low porosity and control water loss.
Ultrafine coal flotation and dewatering: Selecting the surfactants of proper hydrophilic–lipophilic balance (HLB)
Published in International Journal of Coal Preparation and Utilization, 2020
Zeynep Yeşilyurt, Behzad Vaziri Hassas, Fırat Karakaş, Feridun Boylu
As the concentrate of the flotation is approximately 10% wt. solid content, further dewatering is generally essential for final products. The efficiency of the filtration process is strongly related to the properties of the filter cake structure. It is a very common practice to consider a filter cake as a bundle of capillary tubes through which the filtrate flows and leaves the cake. Capillaries within any structure are capable of withholding some water owing to very high capillary pressure. In order to remove this water, according to Laplace equation, an external pressure of higher than capillary pressure should be applied to the system. This pressure is a function of the surface tension and contact angle of liquid and the radius of capillaries (Equation 1).