Cake washing continuous filters

The trend in the use of deep bed filters in water treatment is to eliminate conventional flocculators and sedimentation tanks, and to employ the filter as a flocculation reactor for direct filtration of low turbidity waters. The constraints of batch operation can be removed by using one of the available continuous filters which provide continuous backwashing of a portion of the medium. Such systems include moving bed filters, radial flow filters, or traveling backwash filters. Further development of continuous deep bed filters is likely. Besides clarification of Hquids, which is the most frequent use, deep bed filters can also be used to concentrate soflds into a much smaller volume of backwash, or even to wash the soflds by using a different Hquid for the backwash. Deep bed filtration has a much more limited use in the chemical industry than cake filtration (see Water, Industrial water treatment Water, Municipal WATERTREATiffiNT Water Water, pollution and Water, reuse). 

In apphcations where the fraction of fine particles in the soHds of the feed slurry is low, a simple and relatively cheap vacuum filter can yield cakes with moisture contents comparable to those discharged by pressure filters. Vacuum filters include the only truly continuous filters built in large sizes that can provide for washing, drying, and other process requirements. 

Despite their theoreticaUy poor washing performance, due to uneven wash distribution and excessive mn-off because the filter surface is not horizontal, many multicompartment dmm filters continue to be used as cake washing filters. Effective washing of the filter cloth can be done only with the belt discharge type, where the cloth leaves the dmm for a brief period and can thus be washed on both sides. 

The Artisan continuous filter operates at pressures from 150 to 200 kPa, it allows washing by iajection of washflquid after the initial filtering stages, and the sizes available range from 0.3 to 19 m. Abrasive wear on the cloth is claimed to be eliminated by the thin protective layer of cake on the medium. 

Preparation of Intermediate Compound 2-Methyl-3-o-Tolyl-6-Sulfamyl-7-Chloro-4(3H)-Quinazoiinone Set up a 5-liter 3-necked flask fitted with a stirrer, condenser and a drying tube. To a stirred mixture of 100 g (0.342 mol) of powdered 4-chloro-5-sulfamyl-N-acetylanthranilic acid, 40.2 g (0.376 mol) of o-toluidine and 2.0 liters of dry toluene was added dropwise, over a period of 15 minutes, 21.7 ml (34.1 g) (0.248 mol) of phosphorus trichloride. The mixture was then refluxed for 10 hours. The solid turned somewhat gummy towards the latter part of the first hour. The mixture then became more free flowing as heating was continued. Let stand overnight. The yellow solid was filtered, washed with toluene and dried. The toluene filtrate was discarded. The dried solid was triturated with 1.5 liters of 10% sodium bicarbonate, filtered and the cake washed with water. The filtrate on acidification yielded 11.5 g of the starting acid. The damp product was dissolved in 4,5 liters of 95% ethanol and the solution treated with charcoal and filtered. On cooling filtrate yielded 69.5 g (55.5%) of the title compound, MP 271.5° to 274°C. 

A suspension of 10.7 g LAH in 100 mL anhydrous THF was placed under an inert atmosphere, stirred, and treated dropwise with a solution of 10 g 1-(3-indolyl)-2-nitropropene-1 in anhydrous THF over the course of 2.5 h. The reaction mixture was brought to reflux temperature, held there for 2 h, and then returned to room temperature. The excess hydride was destroyed with an aqueous THF solution (80 mL of 25% solution) and there was then added 10 mL of 50% NaOH. There was added 150 mL Et20, and the stirring was continued until no more solids formed. The reaction mixture was filtered and the filter cake washed with 150 mL Et20. The filtrates and washings were combined, dried over 2 , and the solvent removed under... 

The chilled oil-naphtha solution containing crystallized wax and the filter aid is then filtered by means of a continuous vacuum filter or an intermittent pressure leaf filter. Increased dewaxed oil yields are realized by applying a cold naphtha displacement wash to the wax cake on the filter. The pour point of the dewaxed oil is usually 25° to 35° F. higher than the filtering temperature. 

The naphtha is recovered from the dewaxed oil solution in conventional distillation equipment. The wax cake containing the filter aid is discharged from the dewaxing filter into a heated vessel, where the wax is taken into solution and the inert filter aid settles to the bottom in the form of a concentrated slurry. The aid separated from the wax solution is slurried with kerosene and this slurry is filtered on a continuous filter at a temperature sufficiently high to flash off water adsorbed on the aid. The dried and recovered aid on the filter is subjected to a chilled naphtha wash to displace the kerosene and cool the aid, which is then recycled to the chilled oil-naphtha mixture. Recovery of the aid in this manner permits its re-use indefinitely. 

The wax cake is washed continuously and automatically on the filter with cold solvent to displace any retained oil solution. By control of the conditions of solvent composition, dilution, and the manner in which the cake is deposited on the filter, the displacement wash becomes very effective in producing wax of very low oil content. 

Ultrafilters can be used to permit sequential washing and filtering, after which the filter cake is redispersed into suspension, or continuous hollow-fibre ultrafiltration can be used to accomplish the same result (see Figure 7.6). 

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