Filtration constant flow

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 ... 

A slurry of CaC03 in water at 25°C containing 20% solids by weight is to be filtered in a plate-and-frame filter. The slurry and filter medium are tested in a constant pressure lab filter that has an area of 0.0439 m2, at a pressure drop of 338 kPa. It is found that 10 3m3 of filtrate is collected after 9.5 s, and 5 x 10 3 m3 is collected after 107.3 s. The plate and frame filter has 20 frames, with 0.873 m2 of filter medium per frame, and operates at a constant flow rate of 0.00462 m3 of slurry per second. The filter is operated until the pressure drop... 

Once filling is complete, filtration begins [Fig. 22.3(b)]. Treated brine is pumped into the vessel at the desired flow rate through an automatic control valve. The flow of brine is from the outside to inside of the filter candles. Filtrate clarity is achieved immediately no recycling of flow is required. As the filtration proceeds at constant flow, solids accumulate as a filter cake on the outside surface of the filter socks. While... 

In practice, it is sometimes possible to incorporate moving blades in the filter equipment so that the thickness of the cake is limited to the clearance between the filter medium and the blades. Filtrate then flows through the cake at an approximately constant rate and the solids are retained in suspension. Thus the solids concentration in the feed vessel increases until the particles are in permanent physical contact with one another. At this stage the boundary between the slurry and the cake becomes ill-defined, and a significant resistance to the flow of liquid develops within the slurry itself with a consequent reduction in the flowrate of filtrate. 

The simulations shown in Figs. 3.10 and 3.12 were made for the following operating conditions 1, for the monodimensional model, the filter was considered to be composed of three identical membranes with a 0.5 m surface, the minimum permeate flow was imposed at 3.8 x 10 m /s, the initial value of the filtration constant ko = 33 x 10 m /m bar 2, in the second case, a 10 m long, 0.075 m high and 0.15 m wide filter was analyzed with a constant permeate flow rate while keeping the initial value of the filtration constant. A concentration of 10 kg/m was used for the fresh suspension. 

Relation (4.283), obtained by coupling Eq. (4.282) and (4.280), presents the time derivation results in (4.284). Replacing the term dCgg/dt in (4.284) by (4.280) results in the famous Mint model equation (4.285). Relations (4.286) and (4.287) are the most commonly used univocity conditions of this model (i) before starting fdtration, the bed does not contain any retained solid (ii) during filtration, the bed is fed with a constant flow rate of suspension, which has a constant concentration of solid. ... 

In the Mint model, we have to take into account the following considerations (i) the initial filtration coefficient Xq, which is a parameter, presents a constant value after time and position (ii) the detachment coefficient, which is another constant parameter (iii) the quantity of the suspension treated by deep filtration depends on the quantity of the deposited solid in the bed this dependency is the result of the definition of the filtration coefficient (iv) the start of the deep bed filtration is not accompanied by an increase in the filtration efficiency. These considerations stress the inconsistencies of the Mint model 1. valid especially when the saturation with retained microparticles of the fixed bed is slow 2. unfeasible to explain the situations where the detachment depends on the retained solid concentration and /or on the flowing velocity 3. unfeasible when the velocity of the mobile phase inside the filtration bed, varies with time this occurrence is due to the solid deposition in the bed or to an increasing pressure when the filtration occurs with constant flow rate. Here below we come back to the development of the stochastic model for the deep filtration process. 

In the pharmaceutical industry, most of the critical membrane filtration operations, such as sterile and virus filtration, are performed in the direct flow filtration mode where a feed solution passes directly through a membrane. As the solution passes through the membrane, particles are retained by size exclusion or adsorption. Direct flow filtration can be operated under constant flow or constant pressure modes. 

Filtration is a special example of flow through porous media, which was discussed in Chap, 7 for cases in which the resistances to flow are constant. In filtration the flow resistances increase with time as the filter medium becomes clogged or a filter cake builds up, and the equations given in Chap. 7 must be modified to allow for this. The chief quantities of interest are the flow rate through the filter and the pressure drop across the unit. As time passes during filtration, either the flow rate diminishes or the pressure drop rises, In what is called constant-pressure filtration the pressure drop is held constant and the flow rate allowed to fall with time less commonly, the pressure drop is progressively increased to give what is called constant-rate filtration. 

This equation indicates that at a constant differential jnessure across the membrane, flow rate will decrease as the effective filtration area becomes clogged by particles. Experiments are normally performed, therefore, at constant differential pressure (usually in the range of 30-50 psig) but with a diminishing flow rate, or at a constant flow rate obtained by progressively increasing the differential pressure across the membrane. 

Control blood (freshly drawn and not exposed to the biomaterial discs) should exhibit a constant flow rate, while blood from the parallel-disc exposure should produce an exponential filtration curve (Equation 4) from which the effective concentration of microemboli can be determined from a semilog plot of flow rate vs. time. 

For a few industrial filtrations, the filter is upplied by a positive-displacement pump, which is practically a constant-flow-rate device. Such a pump feeds the filter at a pressure which is steadily increasing during the filtration. Equation 12.32 shows that for constant k and negligible a the pressure increases linearly with time, because the cake thickness increases linearly with time, ... 

As in flat-sheet filtration, the constant flow rate of the bottle filler dictates the nnmber of cartridges to nse. It has been calculated that three 30-inch cartridges (Alter surface of 1.8 m each, flow rate 720 Fh) are required to supply a bottling line operating at 3000 bottles/h or 2250 1/h. Filter membranes must be used for several weeks, or even months, before they become completely blocked in order to make this system cost-effective. 

We have discussed the equipment and the preparation of the slurry. In this section we will discuss the filtration technique itself. There are two basic types of packing techniques under constant pressure and using constant flow. Both techniques have bwn used successfully for hard particles, such as silica-based packings. However, in a constant-pressure technique, the initial flow rate is... 

A corrprehensrve consideration of the selection processes has been publMred elsewhere [Purchas and Wakeman, 1986]. Here the cake formation time (fiberability), level of production required, filtrate clarity specification, dge proportions (if any), operational modes (constant pressure, constant flow rates, etc.) are all taken, inter aha, into the... 

The target bich removes particles fi-om the liquid stream is the surfiice area of the bed media. If solids are deposited this sur ce area increases and, therefirre, the filtration constant should increase with time. However, pores within the bed will become increasingly clogged leading to straightening of flow channels with a consequent... 

It is not pos le to provide values for the filtration constants, as these are dependent on the material to be ered, the flow conditions, fihration history, etc. They must be assessed by laboratory and pilot-scale tests. 

Favre E. (1993) Constant flow-rate filtration of hybridoma cells snspensions. J. Chem. Technol. Biotechnol., 58 107-112. 

Yet such contradictory results make it somewhat difficult to decide which of these observations made in vitro represents the true in vivo situation. Two different theories remain. One proposes that the rise in systemic blood pressure is associated with a constriction of the afferent arterioles sufficient to maintain the capillary pressure, the renal blood flow, and the glomerular filtration constant. In contrast, a drop in systemic arteriolar blood pressure is accompanied by a... 

The Data Analysis module of FDS facilitates the interactive analysis of constant pressure and constant flow filtration, jar sedimentation and piston press (expression) tests the procedures are computer software implementations of the analysis techniques described in Chapter 4. Data obtained at the laboratory, pilot and even full scale can be analysed in a consistent manner... 

Constant pressure filtration ylV vs. Vf Constant flow filtration t vs. Afy Constant pressure expression — AL/AVt vs. t Jar sedimentation vs. t... 

If the suspension were a clean liquid, all the parameters in equations 9.1 and 9.2 would be constant, resulting in a constant flow rate for a constant pressure drop and the cumulative filtrate volume would increase linearly with time, as shown in Figure 9.4. 

A key feature of the RO process is cross-flow filtration. While some water is passing through the membranes there is a constant flow of water flushing the rejected salts away from the membrane surface. The ratio of these two flows is determined by the design recovery rate, the product flow divided by the feed flow. This is an important design factor that should be determined by the membrane manufacturer. Most manufacturers have special computer programs to calculate the maximum recovery rate based on a feedwater analysis. 

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