Horizontal belt continuous filter

Another type of horizontal belt vacuum filter uses reciprocating vacuum trays mounted under a continuously traveling filter cloth. The trays move forward with the cloth as long as the vacuum is appHed and return quickly to their original position after the vacuum is released. This overcomes the problem of friction between the belt and the trays because there is no relative movement between them while the vacuum is being appHed. The mechanics of this filter are rather complex, and the equipment is expensive and requires intensive maintenance. A range of solvents can be used. Widths up to 2 m and areas up to 75 m are available. The cloth can be washed on both sides. 

Scale-Up on Rate Filtration rates calculated from bench-scale data shouldbe multiplied by a factor of 0.8 for all types of commercial units which do not employ continuous washing of the filter medium and on which there is a possibility of filter-medium bhnding. For those units which employ continuous filter-medium washing, belt-type drum and horizontal units, the scale-up fac tor maybe increased to 0.9. The use of this scale-up fac tor assumes the following ... 

Agitated/Monoplate Nutsche Filter/Dryer Horizontal Plate Filter/Dryer Continuous Equipment Rotary Drum Filter Centrifugal Filter Horizontal Belt Filter... 

Rapid filtering 0.1-10 cm/sec gravity pans horizontal belt or top feed drum continuous pusher type centrifuge... 

TABLE 11.12. Sizes of Commercial Continuous Vacuum Filters (a) Horizontal Belt Filters ... 

Horizontal-Belt Filter This filter consists of a slotted or perforated elastomer drainage belt driven as a conveyor belt carrying a filter fabric belt (Fig. 18-141). Roth belts are supported by ana pass across a lubricated support deck. A vacuum pan, aligned with the slots in the elastomer belt, forms a continuous vacuum surface which may include multiple zones for cake formation, washing and final dewater-... 

In some drum filters, blinding of the medium can be amehorated by a continuous removal of the cloth during rotation, with back-washing. Again, this produces a loss of available filtration area on the drum. Figure 11.8 this effect is not present in horizontal belt filters. 

The horizontal belt is a continuous filter with an endless cloth supported on a perforated belt (see Figure 1.23). The belt and cloth are driven around two rollers and across a sequence of evacuated suction boxes at linear speeds up to 0.5 m s The feed suspension is introduced at one end of the filter and deliquored to produce a cake. The length of the filter, which can be in excess of 60 m, is arranged to allow adequate cake formation as well as the... 

The two equipment simulation modules provide calculation sequences for more than 20 types of vacuum and pressure filters, potentially involving combinations of cake formation, compression, gas deliquoring and washing. Batch filters include single and multi-element leaf filters, filter presses and diaphragm and tube presses while continuous filters include the horizontal belt, drum, disc, table and tilting pan filters. The user is able to define filter... 

In Section 7.1 the principal features of common continuous filter cycles are described, while Section 7.2 presents the equations required to model these cycles. Section 7.3 provides detailed example calculations for the horizontal belt filter and the rotary drum filter as these are representative of typical continuous cycles. Section 7.4 shows how computer simulations can be used to examine in detail the effects of process variables on... 

In this section the horizontal belt filter and the rotary drum filter are chosen to illustrate the level of detail that can be achieved when the design equations and procedures outlined in Section 7.2 are used to size and predict the performance of continuous filters. 

Simulations provide the potential to investigate the performance of a filter over a range of process conditions, an ability to ask what if questions and ideally negate the need to perform costly sequences of experiments. To illustrate what can be achieved for continuous filters the horizontal belt filter cycle has been chosen. It is noted that any of the filters shown in Table 7.1 can be simulated using the equations and procedures presented throughout the earlier parts of this chapter. To aid the simulation process, the Filter... 

Another possibility is to enclose only the working, top part of die horizontal belt in the pressure vessel and to pass the belt through the sides of the vessel. Inevitably, the operation has to be intermittent because the belt cannot be dragged over the support surface with the pressure on and, also, the entrance and exit ports for the belt must be sealed during operation to prevent excessive losses of air. The movement of the belt is intermittent, therefore, and is synchronized with decompression in the vessel. This means that the whole of the vessel volume must be depressurized in every cycle and this is wasteful there is also the inevitable down-time involved but there are no problems with discharging the cake because this is done at atmospheric pressure. Strictly speaking, such filters do not fall in the scope of this review because the movement is not continuous, and they are only briefly reviewed in the following. 

Multicompartment drum filters range in size from about 1 sq. metre to over 100 sq. metres they are widely used in mineral and chemical processing, in the pulp and paper industry, and in sewage and waste materials treatment. Despite their uneven wash distribution and frequently high run-off (as the filter surface is not horizontal), many 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 drum for a brief period and can thus be washed on both sides. 

These problems do not exist in the horizontal belt filter, of which in the last few years quite a number of very successful machines have been introduced. This filter is basically constructed as an endless belt so it does not have the same dead time factors, is not affected by differences between cake formation and drying time, and in all cases presents a far better washing surface than a rotary filter (see Figure 17.11). If one wishes to take cake washing to the ultimate efficiency then one must consider countercurrent washing, which is virtually only possible on a belt filter or any other type of filter which has a continuous horizontal filter surface such as, for instance, the rotary tipping pan (see Figure 17.12). 

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