Flow rate, filter media

Generally, any septum having an opening of less than 0.005 in. should be satisfactory for the medium flow rate filter aids. In metal cloths the most commonly used weave is 24 X 110 single dutch with 0.016 in. x 0.011 in. wire. A 60 x 60 twill with 0.011 in. wire and a 70 X 80 twill with 0.007 in. wire are also satisfactory. Keep in mind that mesh does not necessarily indicate the size opening it also depends upon the wire diameter. 

Thickening Pressure Filters. The most important disadvantage of conventional cake filtration is the declining rate due to the increased pressure drop caused by the growth of the cake on the filter medium. A high flow rate of Hquid through the medium can be maintained if Httle or no cake is allowed to form on the medium. This leads to thickening of the slurry on the upstream part of the medium filters based on this principle are sometimes called filter thickeners. 

The two steps in the removal of a particle from the Hquid phase by the filter medium are the transport of the suspended particle to the surface of the medium and interaction with the surface to form a bond strong enough to withstand the hydraulic stresses imposed on it by the passage of water over the surface. The transport step is influenced by such physical factors as concentration of the suspension, medium particle size, medium particle-size distribution, temperature, flow rate, and flow time. These parameters have been considered in various empirical relationships that help predict filter performance based on physical factors only (8,9). Attention has also been placed on the interaction between the particles and the filter surface. The mechanisms postulated are based on adsorption (qv) or specific chemical interactions (10). 

In a filtering centrifuge, separating sohds from liquid does not require a density difference between the two phases. Should a density difference exist between the two phases, sedimentation is usually at a much more rapid rate compared to filtration. In both cases, the solid and liquid phases move toward the bowl under centrifugal force. The sohds are retained by the filter medium, while the liqmd flows through the cake solids and the filter. This is illustrated in Fig. 18-138/ . 

When solid particles undergo separation from the mother suspension, they are captured both on the surface of the filter medium and within the inner pore passages. The penetration of solid particles into the filter medium increases the flow resistance until the filtration cycle can no longer continue at economical throughput rates, at which time the medium itself must either be replaced or thoroughly cleaned. 

When the space above the suspension is subjected to compressed gas or the space under the filter plate is under a vacuum, filtration proceeds under a constant pressure differential (the pressure in the receivers is constant). The rate of filtration decreases due to an increase in the cake thickness and, consequently, flow resistance. A similar filtration process results from a pressure difference due to the hydrostatic pressure of a suspension layer of constant thickness located over the filter medium. 

Because pore sizes in the cake and filter medium are small, and the liquid velocity through the pores is low, the filtrate flow may be considered laminar hence, Poiseuille s law is applicable. Filtration rate is directly proportional to the difference in pressure and inversely proportional to the fluid viscosity and to the... 

In the case of multiparticle blockage, as the suspension flows through the medium, the capillary walls of the pores are gradually covered by a uniform layer of particles. This particle layer continues to build up due to mechanical impaction, particle interception and physical adsorption of particles. As the process continues, the available flow area of the pores decreases. Denoting as the ratio of accumulated cake on the inside pore walls to the volume of filtrate recovered, and applying the Hagen-Poiseuille equation, the rate of filtration (per unit area of filter medium) at the start of the process is ... 

Filter medium face velocity The volume flow rate divided by the effective area of the filter element. 

After seeding the nutrient medium with the preformed inoculum previously described, the mixture was subjected to agitation and aeration under aseptic conditions for 72 hours at 27°C to 28°C for the first 24 hours, then at 25°C to 26°C for the next 48 hours during this period, the pH was in the range of 6.4 to 6.8. Aeration was accomplished by cultivation under submerged conditions at an air flow rate of one volume of air per volume of medium per minute. After termination of the process, the mycelium was removed by filtration and the filtered broth found to contain 450 7of oleandomycin per ml of solution. 

They must be readily accessible for cleaning, which should be carried out as frequently as necessary to ensure that pressure drop across the filter does not affect normal oil flow rates. The filtering medium should be of corrosion-resistant material such as Monel metal, phosphor-bronze or stainless steel. All first-stage filters should be provided with isolating valves. 

Upon what variables would you expect the rate of filtration of a suspension of fine solid particles to depend Consider the flow through unit area of filter medium and express the variables in the form of dimensionless groups. 

Filtration time. The filtration rate depends on the pressure difference, the solids content in the slurry, the particle shape and size distribution, the resistance of the filter medium to flow, and properties of the liquor. Observations show that the volume of the permeated liquor increases parabolically with time (see Fig. 5.3-26). 

Filter paper, 9.5-cm diameter, medium flow rate... 

A schematic of the flow through the cake and filter medium is shown in Fig. 13-6. The slurry flow rate is Q, and the total volume of filtrate that passes through the filter is V. The flow through the cake and filter medium is inevitably laminar, so the resistance can be described by Darcy s law and the permeability of the medium (K) ... 

A packed bed that consists of the same medium as that in Problem 3 is to be used to filter solids from an aqueous slurry. To determine the filter properties, you test a small section of the bed, which is 6 in. in diameter and 6 in. deep, in the lab. When the slurry is pumped through this test model at a constant flow rate of 30 gpm, the pressure drop across the bed rises to 2 psia in 10 min. How long will it take to filter 100,000 gal of water from the slurry in a full-sized bed... 

A plate-and-frame filter press contains 16 frames and operates at a constant flow rate of 30 gpm. Each frame has an active filtering area of 4 ft2, and it takes 15 min to disassemble, clean, and reassemble the press. The press must be shut down for disassembly when the pressure difference builds up to 10 psi. What is the total net filtration rate in gpm for a slurry having properties determined by the following lab test. A sample of the slurry is pumped at a constant pressure differential of 5 psi through 0.25 ft2 of the filter medium. After 3 min, 1 gal of filtrate has been collected. The resistance of the filter medium may be neglected. 

A slurry is to be filtered with a rotary drum filter that is 5 ft in diameter and 8 ft long, rotates once every 10 s, and has 20% of its surface immersed in the slurry. The drum operates with a vacuum of 20 in.Hg. A lab test was run on a sample of the slurry using 1/4 ft2 of the filter medium at a constant flow rate of 40 cm3/s. After 20 s the pressure drop was 30 psi across the lab filter, and after 40 s it was 35 psi. How many gallons of filtrate can be filtered per day in the rotary drum ... 

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