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The filter is assembled as two chambers separated by filtration media.T he Lower Chamber is a Vacuum Nutsche and acts as the filtrate receiver. The Upper Chamber is the Glovebox, supported on 3 independent legs with casters, set so that it can stand over the lower chamber. A self contained hydraulic system is used to lift the Lower Chamber so that a seal is made between them. The top of the filter incorporates two D-shaped viewing windows of clear laminated tempered safety glass. This allows the Operator to see into the Upper Chamber to control the feed and filtration process, and to manipulate the filter cake using the Gloves and Scoop. The Product Chute is positioned to enable the Operator to scoop up the cake and deliver it to receiving containers. The side wall of the Upper Chamber incorporates an insulated Jacket to the maximum slurry depth. Heating or cooling during filtration and subsequent drying is aided by circulation a heat transfer fluid through this jacket. The Lower Chamber acts as the filtrate receiver. It is fitted with a Sight Glass to that the Operator may monitor the rate of extraction of filtrate. The outer periphery of the upper rim of this Lower Chamber is fitted with an O-ring Seal, of a suitable elastomer, which provides a liquid and vacuum tight seal between the chambers when they are brought together. Preparation for Filtration The most commonly used media is a relatively lightweight (polyester) top cloth combined with a heavier (cotton) backing cloth, but a wide range of media can be accommodated. With the Lower Chamber standing on its own set of 3 casters, and apart from the Upper Chamber, the filter media can be installed. The Filter Support Grid, resting in the Lower Chamber, supports the Filter Plate so that it is level with the upper rim of this chamber. The cloths are placed over the Filter Plate, which has 10mm diameter perforations. The Filter Clamp Ring fits over the cloths and the Filter Plate to hold them in position. This ring is a push-fit; there are no screws for fixing bolts within the filter. Two pairs of standard Dry Box Gloves are fitted to the Glove Ports ‘I’ and secured using the Glove Clamp Rings. Scoops of appropriate material for the substances being processed and the filter finish may be placed inside the filter. The Lower Chamber is rolled into position between the legs of the Upper Chamber. The spacing of these legs has been designed to allow this manoeuvre! Within the shrouding of each leg is a hydraulic cylinder; these three cylinders are connected to the Hydraulic Hand Pump. Operating this pump lowers the piston rods to engage in the Lower Chamber Lifting Lugs. The action of the Hydraulic Hand Pump is now reversed and lifts the Lower Chamber some 50mm to mate with the Upper Chamber. The Swing Bolts are then raised into position and tightened to secure the filter during operation. The two Product Chutes ‘H’ terminate in sanitary fittings and may be blanked off with caps. The assembled filter may be rolled into position for filtration. The Filtration Process There are four flanged process connections in the top of the filter and three flanged process connections to the Lower Chamber. Nozzles that are not in use must be closed off with valves or blank flanges. The Nozzle ‘A; is used to exhaust the filter to the facilities Vent Line. When required, an inertisation media, typically nitrogen, is admitted to the filter by Nozzle ‘D’ – for a period prior to commencing filtration. The Operator ensures a small positive pressure of nitrogen in the filter throughout the process by observing the pressure in the Gloves. Slurry is admitted via Nozzle ‘B’ to the level of the top of the Jacket, some 20mm below the Product Chute. Filtrate is extracted from the base of the Lower Chamber via Nozzle ‘G’. (To avoid any electrical requirement in the area, a pneumatically operated variable speed diaphragm pump is typically employed.) The Operator can adjust the rate of filtrate extraction by observing Sight Glass ‘L’ Periodically the Operator should admit more slurry to the filter. During this phase of operation, the filtrate extraction will maintain vacuum conditions in the Lower Chamber. If the filtration requires other than ambient temperature, an appropriate heat transfer fluid is supplied to the jacket via nozzles ‘J’ and ‘K’. If the process scheme requires the filter cake to be washed, solvent may be admitted through the Wash Inlet Nozzle ‘C’. The Operator may manipulate the cake using the Glove and Scoop to assist in reslurrying the solids or to manipulate the cake to ensure effective drainage. As the end of the filtration cycle is reached, vacuum may be applied via Nozzle ‘E’, (just below the Filter Plate) to suck the maximum amount of liquid out of the cake. As necessary, the nitrogen flow via Nozzle ‘D’ must be increased to maintain the small positive pressure in the Upper Chamber. Drying If the positive flow of nitrogen, (or other media) is now applied through Nozzle ‘F’, (just below the Filter Plate), drying by volatilisation of solvents from the cake can be accomplished in the filter. Connections to the Upper Chamber, other than the Vent Nozzle ‘A’, should now be closed. The Jacket temperature should be increased to the maximum – within the filter’s range – which can be tolerated by the product. Periodically the Operator may manipulate the cake to ensure exposure of all moist cake to the drying gas. Discharge of Filter Cake Suitable receiving containers are connected to the Product Chute. For example, a flexible plastic sack, supported in a shipping drum, may be taped to the chute. The Operators use the Gloves and Scoops to discharge the filter cake down the Product Chute into the receiving containers. When completed, with the flow of nitrogen still maintaining a positive pressure, the container may be sealed off and disconnected from the filter. Cleaning After use, appropriate solvents may be admitted through the Wash Inlet Nozzle ‘C’ to wash out the filter. An option, often selected, provides 360° C.I.P. Spray Ball fitted to Nozzle ‘C’. The hydraulic system is now used in the reverse manner to that previously outlined to lower the Lower Chamber. With the Lower Chamber rolled out, the Operator may find it more comfortable to sit on a small stool under the Upper Chamber to complete Cleaning. The Gloves and Scoops should remain installed and treated as part of the filter. |
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