Filters automatic belt

The main features in which the Radford process differs from the batch operation are in thermal dehydration and compounding. Water-wet nitrocellulose on a continuous vacuum belt filter is vacuum-dried followed by hot air transfusion (80°C) to reduce the moisture to less than 2%. After cooling, alcohol is sprayed on the nitrocellulose to a concentration of 15—20%. The alcohol-wet nitrocellulose is then transferred from a surge feeder to a compounder by a continuous weigh-belt along with the other ingredients of the composition, which are also weighed and added automatically. 

The vertical recessed plate automatic press, shown schematically in Figure 15 and described previously, is another example of a horizontal belt pressure filter. Cycle times ate short, typically between 10 and 30 minutes, and the operation is fully automated. The maximum cake thickness is about 35 mm washing and dewatering (by air displacement) of cakes is possible. Apphcations include treatment of mineral slurries, sugar, sewage sludge, and fillers like talc, clay, and whiting. 

User maintenance includes operation where not automatic, cleaning of filters and strainers, attention to oil and lubricant levels, belt tensioning, general cleaning, running standby equipment, and verification of control operation. 

Tower Presses This press is similar to the stacked horizontal diaphragm presses, but only one filter belt is used (Fig. 18-191). The operation is also fully automatic. The primary applications are in chemical, mineral and pharmaceutical industries. The testing method is the same as the diaphragm presses. One important factor in designing a tower press is the sohds need to be able to be cleared from the chamber sed, otherwise leakage will occur in the following filtration cycle. 

Belt presses have the advantage of large capacity and automatic operation. The initial capital cost is also low. They were originally developed in the pulp and paper industry. Any slurry with fibers will do well in a belt press, and high-fiber material can be added to the slurry as a filter aid for belt press operation. Today, in addition to pulp dewatering, the belt press is widely used in wastewater sludge dewatering. 

Fig. 3. Process flowsheet for cellulase production in wheat bran culture [25]. A Submerged seed culture of T. viride, B oil-free compressed air C air filter D inoculum E exhaust air F sample collection G centrifugal pump H automatic wheat bran culture of T. viride I water spray I ammonium sulfate, alcohol and water J conveyor belt J screw conveyor K hopper L extraction column M storage tank centrifuge 0 precipitation P mixing tank Q ion-exchange column R membrane concentrator S spray dryer T filter press U rotary dryer V mixer W cellulase preparation and salt stabilizer... 

Larox automatic pressure filter showing path of filter belt and mechanism of cake discharge. Larox, Inc.)... 

The chambers are then opened hydraulically so that the belt may be moved a distance somewhat greater than the length of one chamber. This action discharges cake from both sides of the filter as shown in Fig. 30.7. At the same time, part of the belt passes between spray no22les for washing. After all the cake has been discharged, the belt is stopped, the chambers are closed, and the filtration cycle is repeated. All the steps are actuated automatically by impulses from a control panel. Filter sizes range from 0.8 m (8.6 ft ) to 31.5 m (339 ft ). The overall cycle is relatively short, typically 10 to 30 min, so that these filters can be used in continuous processes. 

These weaves are frequently, though not exclusively, found in belt filters, either of the vacuum, continuous multi-roll press or of the vertical automatic pressure type. Owing to the interlacing pattern of the threads, it is possible to create fabrics with a measure of a solidity and stability that are ideally suited to filters of the types identified. On the debit side, the cost of weaving such high-density fabrics tends to preclude their use in all but a limited number of niche appUcations. 

Figure 3. Diagrammatic cross section of rotary-drum vacuum filter I - drum 2 - connecting pipe 3 -sender 4 -automatic valve 5, 13 -chambers of automatic valve connected with a source of compressed air 6, 10 -chambers of automatic valve connected with a source of vacuum 7 -endless belt 8 - wash header 9 - guiding roll 11 - tank for suspension 12 -stirring device.

Filter pressing is a cyclic operation. Different designs enable automatic cake removal. One method is to blow the cake off by sending compressed air tiirough the filtrate tubes. Another method is to make the filter cloth a moving belt. After each operation, the belt is shifted to allow the cake to drop off on either side. 

The discharge from the filters is passed to a drying and calcining stage. It is convenient to use a belt conveyor and feed continuously into a tunnel type of furnace. The dried product can then be drummed directly and automatically at the other end of the furnace. 

These are normally chosen for finer particle substrates which require a greater differential pressure (greater than the 14.7psi maximum differential achieved under full vacuum) in order to achieve a practical rate of filtration, or to minimise cake moisture content and again there are many different designs of filter [26, 27], Several employ a batch process such as the common Plate and Frame Filterpress, but can be semi-continuous as in the Automatic Pressure Filter whereby a continuous filter cloth enables feed, discharge and belt washing to be operated in sequence or fuUy continuous pressure belt filters. 

Since compressed air is supplied by a compressor. Great care must be taken to insure certain types of equipment are operating in a safe manner. Safety devices for a compressed air system should be checked frequently. Compressors should be equipped with pressure rehef valves and pressure gauges. The air intakes must be installed and equipped so as to ensure that only clean uncontaminated air enters the compressor. Air filters installed on the compressor intake cilitate this. Before any repair work is done on the pressure system of a eompressor, the pressure is to be bled off and the system locked-out. All compressors must be operated and lubricated in accordance with the manufacturer s recommendations. Signs are to be posted to warn of the automatic starting feature of compressors. The belt drive system is to be totally enclosed to provide protection fiom any contact... 

Combined mono and multifilament fabrics are now available with useful additional characteristics. Thus such a material is used on disc filter segments, which is elastic and so will expand during the blow-back stage to help with cake release. New belt press filters and large automatic filter presses have put tremendous demands on the physical properties of the filter fabrics, which are being met by heavy dense monofilament fabrics. 

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