Filtration time

If ah of the nonfiltration operations are grouped together into a downtime, assumed to be fixed and known, an optimum filtration time in relation to p can be derived by optimizing the average dry cake production obtained from the cycle. Eor constant pressure filtration and where the medium resistance R and the specific cake resistance are constant, the fohowing equation appHes ... 

When the medium resistance R is smah compared with the specific cake resistance (, the second term in the above equation becomes negligible and the optimum filtration time becomes equal to downtime p. For any other case, p is always greater than p. It fohows, therefore, that the filtration time... 

The operating cycle is seldom less than two hours, and several sets of frames can be operated in rotation. The cake thickness should be more than 3 mm, 9 mm being a typical value. Sluicing of the cake with a jet of compressed air has been used to permit thinner cakes and shorter filtration times. The leaves are spaced sufficiendy far apart that there is always clearance between the finished cakes. 

This expression shows the relationship between filtration time and filtrate volume. The equation is applicable to both incompressible or compressible calces, because at constant AP the values and x are constant. For constant AP, an increase in the filtrate volume results in a reduction in the filtration rate. If we assume a definite filtering apparatus and set up a constant temperature and filtration pressure, then the values of Rf, r , fi and AP will be constant. We now take note of the well-known filtration constants K and C, which are derived from the above expressions ... 

We now turn attention towards the ease of eonstant-rate filtration. When sludge is fed to a filter by means of a positive displaeement pump, the rate of filtration is nearly constant, i.e., dV/dx = constant. During constant-rate filtration, pressure increases with cake thickness. As sueh, the principal filtration variables are pressure ind filtrate volume, or pressure and filtration time. Integrating the filtration equation for a constant-rate process, we find that the derivative dV/dx ean simply be replaeed by V/x, and we obtain ... 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

This expression can be represented graphically in dimensionless form to simplify its use. It is generally expressed as the so-called filtration number , defined as follows E, = /iR, / 2APT3 jr x . The filtration number, E, is dimensionless and varies from zero at Rf = 0 to a large value when there is an increase in the viscosity of the sludge and Rf or a decrease in pressure drop, auxiliary time, specific cake resistance and the ratio of cake volume to filtrate volume. It may be assumed in practice that F(, = 0 to 10. If washing and drying times are constant and independent of filtration time, they may be added directly to the auxiliary time. In... 

The filtration time corresponding to total pore blockage, when Ap->°o may be estimated from ... 

Filtration and Separation. .. in terms of filtrate volume with time as well as dry cake yield with filtration time. Both are outputted in tabular form suitable for importing into a. .. http //www.filtration-and-separation.com/ [More Results From www.filtration-and-separation.com]... 

Calculate the total filtration time of both steps and the volumes of filtrate, cake and separated slurry. Assume for these calculations that the operation is performed without any washing and dewatering stages. 

The system described in question 4 has an auxiliary time of = 1800 sec. Determine the total filtration time at constant pressure drop, cake thickness and filtrate volume. 

The filtration time of 20 m of a suspension in a filter press is 2.5 hours. Determine the approximate washing time of the cake for 2 m of water, assuming that the washing rate is 4 times less than that of filtration at the end... 

Calculate the required filtration time for 10 Liters of liquid through 1 m of filter area if tests have shown that 1 Liter of filtrate is obtained after 2.25 min. and 3.2 Liters after 14.5 min. from the start of the process. 

Using the filtration constants determined from the above question, determine the filtration time of a 5 m CaCOj suspension containing 5 % solids on the filter with 10 m area. The cake wetness is 40% and the solids density is 2,200 kg/m The density of the liquid is 1,000 kg/m Also determine the final filtration rate after 2 hrs. of operation. 

As a batch filtration proceeds, so the rate of filtrate collection decreases due to the increased cake thickness. While operation with thin filter cake results in a higher instantaneous filtration rate, however, it also requires more frequent dismantling of the filter and discharge of the filter cake. There is thus an optimum balance between filtration time and down time. 

Thus for the optimal operation of a bateh filter, the filtration time and the down time are equal. In praetiee t > t due to eloth resistanee, whieh is negleeted in this simple analysis. 

Consider the ease of eonstant pressure with negligible eloth resistanee. The filtration time is given by r/iv... 

Therefore in order to reduee filtration time any of the following measures ean be adopted... 

Sinee filter eake is deposited in one revolution before removal, the filtration time per revolution is effeetively Henee... 

API Filtration. A filter press is used to determine the wall building characteristics of mud. The press consists of a cylindrical mud chamber made of materials resistant to strongly alkaline solutions. A filler paper is placed on the bottom of the chamber just above a suitable support. The filtration area is 7.1 ( 0.1) in.-. Below the support is a drain tube for discharging the filtrate into a graduate cylinder. The entire assembly is supported by a stand so that a 100-psi pressure can be applied to the mud sample in the chamber. At the end of the 30-min filtration time volume of filtrate is reported as API filtration in milliliters. To obtain correlative results, one thickness of the proper 9-cm filter paper, Whatman No. 50, S S No. 5765, or the equivalent, must be used. 

A 30 ml sample of broth from penicillin fermentation is filtered in the laboratory on a 3 cm2 filter at a pressure drop of 5 psi. The filtration time is 4.5 minutes. Previous studies have shown that the filter cake of Penicillium chrysogenum is significantly compressible with S = 0.5. If 500 litres of fermentation broth from a pilot plant have to be filtered in 1 hour, what size of filter is required for a pressure drop of 10 psi and 5 psi Neglect the resistance of the filter medium. 

Equation (7.3.1.5) was modified as the second part is neglected, so the filtration time per unit volume is ... 

In the multi-purpose batch chemical plant context, continuous utilization of multiple unit operations on-plant is extremely difficult and rarely achieved. In addition, for many batch chemical operations, it is not uncommon for there to be long reaction times, extended periods of time at reflux, extended filtration times, drying times, and so on. Each... 

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). 

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