Press belts

Filtrate drain ° water, compressed header sludge feed header 

Limit switches Moving pressing plate Curtains 

The vertical filter press is a very effective unit, fully automatic in operation, though somewhat expensive. It occupies less floor space than a horizontal filter press of the same filtration area. 

Belt presses (or press belts or double belt presses as they are equally usefully known), as their name implies, use the pressure of a belt on a mass of wet solids to dewater the solids. They are not filters, because they work by squeezing liquid out of a sludge, but they can be important adjuncts to filters. They work by accepting a reasonably stiff feed suspension onto a continuous lower belt, which carries the wet mass under an upper belt that is pressed down on to the lower one by a series of rollers. 

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Other designs squee2e the cake between two permeable belts or between a screw conveyor of diminishing diameter, or pitch, and its permeable enclosure. The available filters which use mechanical compression can be classified into four principal categories, ie, membrane plate presses, tube presses, belt presses, and screw presses. 

Continuous Compression Filters. The variable chamber principle appHed to batch filtration, as described before, can also be used continuously in belt presses and screw presses. 

Originally designed for the continuous filtration of conditioned sewage sludges, as were most of the filter belt presses available, the Manor Tower press is increa singly used for the treatment of paper mill sludge, coal, or flocculated clay slurries. 

A belt press commonly uses two belts of woven material. Fmit mash is deposited on, and spread out evenly between, the two belts which converge and press the mash between them. The belts wrap around a series of successively smaller cylinders or pass between rollers (less efficient) for the pressing action. Juice yield for the wraparound belt press is 72%, and increases to 92% with secondary water addition (15). 

Expression Dewaterings of Fibrous Materials. Fibrous materials are frequently dewatered in belt-filter, screw, disk, and roU presses and in batch pot and cage presses. Table 1 Hsts appHcations of screw, roU, and pot presses. Screw and high pressure belt presses are continuous and have replaced batch pot and cage presses in most appHcations. Traditionally, however, batch presses have been used for squee2ing cocoa butter from cocoa beans, which require pressures up to 41 MPa (6000 psi) (39). A description of many types of batch presses is included in Reference 40. 

Fig. 7. Sohds content of sludges dewatered by C, soHd bowl centrifuge VF, vacuum filter BP, belt press FP, filter press, and DFP, diaphragm filter press...

Belt Presses Belt presses were fiiUy described in the section on filtration. The description here is intended to cover only the parts and designs that apply expression pressure by a mechanism in adchtion to the normal compression obtained from tensioning the belts and pulling them over rollers of smaller and smaller diameters. The tension on the belt produces a squeezing pressure on the filter cake proportional to the diameter of the rollers. Normally, that static pressure is calculated as P = 2T/D, where P is the pressure (psi), T is the tension on the belts (Ib/hnear in), and D is the roller diameter. This calculation results in values about one-half as great as the measured values because it ignores pressure created by drive torque and some other forces [Laros, Advances in Filtration and Separation Technology, 7 (System Approach to Separation and Filtration Process Equipment), pp. 505-510 (1993)]. 

Juice yield % Horizontal presse Belt presse... 

Patzelt, R.R. and Hassick, D.E., Dewatering of steel-mill sludges by belt-press filtration, Section 13—Steel and Foundry Wastes, in Proceedings of the 39th Industrial Waste Conference, Purdue University, 469-485, 1984. 

For filter belt presses and centrifuges, resistance to shear and mechanical pressure is the most important parameter. In general, floes produced by charge patch neutralization are stronger than those produced by inorganic salts alone. 

Such treated sludge makes an excellent organic fertilizer that can be applied directly to lawns and agricultural fields or it can be dewatered by means of belt presses. Here, the sludge is passed between rollers that squeeze out most of the water and leave the organic material as a semisolid sludge cake. This cake is easy to stockpile, distribute, and spread on fields with traditional manure spreads. 

Belt presses can be continuously fed with mash. Their output is high, ranging from 2 to 6 t/h. Modern filter belt presses achieve high yields. Because of their rapid operation (juice extraction times of about 4 min) there is little oxidation. 

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