Capacities pressure filters

The fundamental case for pressure filters may be made using equation 10 for dry cake production capacity Y (kg/m s) derived from Darcy s law when the filter medium resistance is neglected. Eor the same cycle time (same speed), if the pressure drop is increased by a factor of four, production capacity is doubled. In other words, filtration area can be halved for the same capacity but only if is constant. If increases with pressure drop, and depending how fast it increases, the increased pressure drop may not give much more capacity and may actually cause capacity reductions. 

Drum Filters. The rotary dmm filter, also borrowed from vacuum filtration, makes relatively poor use of the space available in the pressure vessel, and the filtration areas and capacities of such filters cannot possibly match those of the disk pressure filters. In spite of this disadvantage, however, the pressure dmm filter has been extensively developed. 

Each filter has demonstrated the capacity to filter the full brine flow of 195 m3 h 1. The pressure drop through the filter medium is measured and monitored continuously. Typically, it is nearly constant over a 2-h filtration at 195 m3 h 1. Back-pulse cleaning restores the initial pressure drop from cycle to cycle, with only a slow increase over time. After 12 months running time, the initial pressure drop at the beginning of the filter cycle had increased by 0.6 bar. The filter membranes were chemically cleaned with 5 % hydrochloric acid. After a cleaning time of 2 h the filter was started again and the pressure drop was less than 0.1 bar greater than that of new filter socks. 

Max. Possible Air Capacity Pressure Drop (Clean Filter)... 

Should cake bridging occur between leaves in pressure filters, unequal pressures on the leaves can cause severe warping. The amount of filter aid that can be added without bridging can be calculated from the cake capacity of the filter (area times cake thickness. 

Pressure filters are operated in the range of 30-60 psi and some times up to 100 psi. In contrast to vacuum filters, pressure filters normally operate in batch mode. The rate of cake buildup in batch operation is slow in comparison with continuous drum filters. The time required to dump the cake and clean and reassemble a pressure filter is called dead time. It is a significant element in determining the capacity of a pressure filter. 

The THF filtrate, which also contains cyclohexane soluble vehicle, was concentrated by roto-evaporation to remove the THF, 5 mL of THF was added back to the slurry, and this THF slurry was dripped into 150 mL of stirred cyclohexane. The flask that contained the concentrated THF solution was sonicated with 10-30 mL of cyclohexane in order to clean it thoroughly. Since the filter/holder has a capacity of 100 mL, only two-thirds of the 150-mL cyclohexane suspension was added. Approximately half of the cyclohexane suspension in the filter/holder was pressure-filtered to allow addition of the remaining suspension. Five hundred mL of cyclohexane was then added to reservoir R, and the sample was pressure-filtered. The residue was then removed, vacuum-dried, and weighed. Since the THF-insoluble material was also cyclohexane-insoluble, combining the weight of the THF-insoluble residue and the insoluble residue obtained from the cyclohexane filtration allows the calculation of a cyclohexane solubility value. The results from the modified procedure on one sample will thus give both THF and cyclohexane solubility values. The modified pressure-filtration procedure takes 2 to 2 1/2 hours. 

The suitability of a filtration process can be assessed in a small laboratory pressure filter with a filter area of about 20-50 cm and a capacity of 0.3-1 L, in which various metal and plastic filter materials can be tested (Figure 2.3.10-1). The pore width is about 10-100 jum. The filter should be heatable and coolable.The experiment is evaluated in terms of the applied gas differential pressure AP, the filter area A, the filtrate volume V, the final filter cake height H, and the filtration time t until gas breakthrough according to Equation (2.3.10-1). 

The horizontal plate filter is a pressure filter with a number of horizontal circular drainage plates in a stack in a cylindrical shell. A filter cloth or paper is placed on each plate. Filter aid may be applied if necessary. Filtration is continued until the cake capacity of the unit is reached or the filtration rate becomes too slow owing to cake resistance. Pressure drop across the filter medium is generally designed for SO lb,/in.. Cake may be washed or air-blown prior to manual removal. This type of filter is flexible and easily cleaned or sterilized, but it has a high labor requirement. 

Figure 1.28 Photographs, with permission from Pope Scientific, of a 0.15 m capacity pressure Nutsche filter assembled (/eft) and disassembled showing the filter medium and sealing arrangements right). A schematic of the typical pressure Nutsche filter cycle is shown in Figure 6.1.

The fundamental case for pressure filters may be made using the following equation for dry cake production capacity, T(kgm s ), derived from Darcy s law when the filter medium resistance is neglected (for the full derivation see appendix I in Svarovsky ) ... 

A further obvious distinction is between vacuum filters (negative pressure) and pressure filters (positive pressure) (see Figure 17.7). As the vacuum filters are limited to a maximum practical pressure differential of about 6.8—8.2 x lO Nm (10 to 12 p.s.i.), theoretically they have a lower capacity. Since most pressure filters, however, rely on a thicker cake and, therefore, a greater cake resistance, the net result is not always so much in favour of pressure filtration. It is important, therefore, actually to check these figures and not assume higher throughput with a higher pressure. 

The electrochemical cell was scaled up to a volume of 23 L, exhibiting the capacity to treat 6 m of wastewater per day. Electrodes of parallel aluminum plates were used, incorporating potential for polarity inversion in order to avoid incrustation. Based on the pilot unit results, the clarifier was modified with internal conduits serving as transition zones to turn turbulent to laminar flow and enhance electroflocculation. Sludge from sedimentation and electroflotation was sent to a conditioning tank and then to a horizontal plate pressure filter to produce a dry filter cake. Clear effluent was filtered... 

Among others, these include those aheady mentioned above, viz. the precoat fdter [11,12], dewaxing fdter [13], single-cell high-capacity vacuum filter [14], compact fdter, pressure-belt drum fdter and so on. 

Place 80 g, of hydroxylamine sulphate (or 68-5 g. of the hydrochloride), 25 g. of hydrated sodium acetate, and 100 ml. of water in a 500 ml. flask fitted with a stirrer and a reflux water-condenser, and heat the stirred solution to 55-60°. Run in 35 g (42 nil,) of -hexyl methyl ketone, and continue the heating and vigorous stirring for ij hours. (The mixture can conveniently be set aside overnight after this stage.) Extract the oily oxime from the cold mixture twice with ether. Wash the united ethereal extract once with a small quantity of water, and dry it with sodium sulphate. Then distil off the ether from the filtered extract, preferably using a distillation flask of type shown in Fig. 41 (p. 65) and of ca, 50 ml, capacity, the extract being run in as fast as the ether distils, and then fractionally distil the oxime at water-pump pressure. Collect the liquid ketoxime, b.p. 110-111713 mm. Yield, 30-32 g. 

Dissolve I ml. of benzaldehyde and 0-4 ml. of pure acetone in 10 ml. of methylated spirit contained in a conical flask or widemouthed bottle of about 50 ml. capacity. Dilute 2 ml. of 10% aqueous sodium hydroxide solution with 8 ml. of water, and add this dilute alkali solution to the former solution. Shake the mixture vigorously in the securely corked flask for about 10 minutes (releasing the pressure from time to time if necessary) and then allow to stand for 30 minutes, with occasional shaking finally cool in ice-water for a few minutes. During the shaking, the dibenzal -acetone separates at first as a fine emulsion which then rapidly forms pale yellow crystals. Filter at the pump, wash well with water to eliminate traces of alkali, and then drain thoroughly. Recrystallise from hot methylated or rectified spirit. The dibenzal-acetone is obtained as pale yellow crystals, m.p. 112 yield, o 6 g. 

The main advantage of HGMS is high efficiency of separation even at relatively high dow rates and minimum pressure drops across the filter. The capital cost is very high, and only large installations are attractive economically because capacity increases with the square of the diameter of the canister while the weight of copper conductor increases linearly with diameter. 

---