Filtration equipment rotary drum

Other important separation techniques such as pressure-leaf filtration, centrifugation, rotary drum filtration and others all require technology very specific to the equipment and cannot be generalized in many instances. 

A precoated rotary drum vacuum filter is the only filtration equipment from which extremely thin filter cakes can be positively and continuously removed in a semi-dry state. 

Filtration. Filtration can include filter presses, rotary drum vacuum filters (RDVF), belt filters, and variations on synthetic membrane filtration equipment, such as filter cartridges, pancake filters, or plate and frame filter presses. These processes typically operate in a batch mode when the filter chamber is filled up or the vacuum drum cake is exhausted, a new batch must be started. This type of filtration is also called dead-end filtration because the only fluid flow is through the membrane itself. Due to the small size of cells and their compressible nature, typical cell cakes have low permeability and filter aids, such as diatomaceous earths, perlite, or other mined materials are added to overcome this limitation. Moreover, the presence of high solids and viscous polymeric fermentation byproducts can limit filtration fluxes without the use of filter aids. 

Various types of filtration equipment are available commercially and can be operated in batch, semicon-tinuous, or continuous modes. Among the commonly used types are the plate and frame filter, rotary drum filter, leaf filter, plate filter, and tray filter. Apart from the plate and tray filters, all other are enclosed and therefore are easy to work with when sterility of the solids is an important issue. Moreover, all these filters are examples of dead-end filters. Cross-flow filtration is mostly used in the purification stage through membranes with very low pore sizes and is discussed later. 

Raw fermentation broth is an example of a large volume production. Rotary drum vacuum filters (RVF s) have traditionally been found in this service. Slow-settling materials or more difficult filtrations with large scale production requirements are typical applications for this type of equipment. For an overview of filter selection versus filtering rates, see Table 3, which is excerpted by special permission from Chemical Engineering/Deskbook Issue, February 15, 1971, by McGraw Hill, Inc., New York, NY 10020. 

The process system consists of two long-tube vertical evaporators, a draft-tube baffled crystallizer, a rotary-drum vacuum filter, and a direct-heat rotary dryer. Also, pumps are needed to move the solution from evaporator 1 to evaporator 2, to recycle the filtrate from the filter to the crystallizer, and to move the magma from the crystallizer to the filter and a heat exchanger is needed to heat the recycle filtrate. However, the purchase costs for the three pumps and the heat exchanger are not considered here because examples for these types of equipment are presented in Section 16.5. For the equipment considered here, assume fabrication from stainless steel, with a material factor of 2 for the ratio of stainless steel cost to carbon steel cost. For the process, using the following size factors and the equations in Table 16.32, the estimated f.o.b. equipment purchase costs at a CE index of 394 are included in the following table. 

Rotary drum vacuum filters are a widely used piece of equipment for this filtration step, due to its simple operation and low investment costs. The drum is typically precoated (e.g., with diato-maceous earth, sUica, perlite) to improve the process performance [7]. Additional filter aid is often added to improve the filtrate qnality hence, the amount of slndge generated from this unit operation is relatively large. Several other filtration devices such as filter automates and cross-flow filtration devices are also nsed for the filtration. One of the benefits of the latter is that they can be operated withont addition of filter aids and thus, the amount of generated sludge can be reduced. 

Equipment for vacuum filtration (a) continuous rotary drum, and (b) rotary disc. 

This equipment consists of a horizontal axis revolving drum. The surface of the drum is segmented, with compartments fitted with drainage pipes leading inside the drum to a common manifold and a rotary valve located at one end of the drum. A filter medium is attached to the external surface of the drum. When the drum is mounted with part of its surface in a tank of slurry, the application of a vacuum behind the filter medium pulls the filtrate through. The solid material is retained on the filter surface and, as the drum turns slowly past a knife, is dislodged into a collection hopper for disposal or further treatment. 

A simple rotary-filter system consists of a rotary filter and auxiliary equipment such as a cort ressor, a filtrate receiver, a filtrate pump, a vacuum punp, and a separator-silencer, as shown in Figure 6.10. Auxiliary equipment usually runs 25 to 40% of the filter cost [25]. When solids deposit on the drum, air and filtrate are drawn into the filtrate receiver, which is a gas-liquid separator. After... 

A rotary filter (Figure 11.10) consists of a cylindrical drum covered with a perforated sieve which supports a filter cloth. The drum rotates around its horizontal axis at adjustable speed, in a tank equipped with an agitating device to homogenize the liquid and keep the filtration adjuvant in suspension during preparation of the filter layer. Diatomaceous earth may be used, but perlite also gives good results at lower cost. A vacuum, created inside the drum by a vacuum pump, draws tlie liquid in. A layer of filtration adjuvant is deposited on the drum during each... 

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