Dewatering methods

In a study on dewatering methods for peat, displacement dewatering was done using acetone, a polar solvent having a lower heat of vapori2ation than water. Dewatering was improved in terms of both the pressure filtering step and the quantity of heat required. Less heat was required to dry the cake and recover the acetone from the filtrate by distillation (31). 

Dewatering methods are available for most high-water-content virgin and waste biomass. This suggests that the moisture content of such feedstocks can be readily adjusted before conversion. This is not the case, however, because it is often difficult to reduce moisture content to the level desired at reasonable cost. 

A pilot plant study was carried out on "drying-pyrolysis" process in order to put the sludge pyrolysis process with multiple hearth furnace to a practical use. Additional studies were carried out on direct pyrolysis process and incineration process in order to compare these three thermal processings. The samples in this study were 5 dewatered cakes obtained from various sewage treatment plants and from various dewatering methods. The pilot plant for the experiments of this study consisted of a four-shaft indirect steam dryer with a total heating area of 10.1 m, a four hearth furnace with a total hearth area of 1.63 and its incidental facilities. 

Dewatering methods are limited to grain size ranges, as shown in Figure 4.7. The finest treatment zone is labeled electro-osmosis. The electro-osmotic... 

Most municipal waste treatment plants dewater blends of waste-activated and raw primary sludges. A mixture of the two types of sludges facilitates concentration of solids and disposal by conventional dewatering methods. Cationic polymers are widely used in the waste treatment industry as dewatering aids. 

Horowitz, A. J., Ehack, K. A., and Hooper, R. C., A comparison of instrumental dewatering methods for the separation and concentration of suspended sediments for subsequent trace element analysis, J. Hydrol. Process., 2, 163-184, 1989. 

For the food industry, the conunonly used dewatering methods are evaporation, pressure-driven membrane process, and forward osmosis process. Compared with the first two conventional methods, the forward osmosis process can provide several advantages such as low operation pressure and temperature, low energy input, and low deterioration of the food quality. 

Perhaps the princ al area of ignorance in both the filtration and dewat g of precipitates is the effect of crystal morphology. Serious theoretical and practical problems arise in cases where the crystal in ct possesses internal porosity. Liquors bound inade a crystal will be iirposable to remove by normal dewatering methods. Agam, m process cakulaticms and correlations of e qrerimehtal results, uncertainties arise in the vabes of particle doisity fin these materials. 

Some of the worst conditions are met in excavations that have to be taken below the water table (Forth, 2004). In such cases, the water level must be lowered by some method of dewatering. The method adopted depends on the permeability of the ground and its variation within the stratal sequence, the depth of base level below the water table and the piezometric conditions in underlying horizons. Pumping from sumps within an excavation, bored wells or wellpoints are the dewatering methods most frequently used (Bell and Cashman, 1986). Impermeable barriers such as steel sheet piles, secant piles, diaphragm walls, frozen walls and grouted walls can be used to keep water out of excavations (Bell and Mitchell, 1986). Ideally, these structures should be keyed into an impermeable horizon beneath the excavation. 

The compressibihty of many industrial filtration cakes, an unwanted phenomenon in filtration by hydrauhc pressure, may be turned into an advantage by considering mechanical squeezing of the pre-formed cake as an alternative or additional dewatering method. The fact that a cake has a reasonable or high... 

From the press section, the paper goes to the dryer sections. Steam heated or infrared dryers are the most expensive dewatering methods on the paper machine. The dryers willl reduce water in the sheet from 60% to 5-8%. Steam dryers are a series of cylinders over which the paper web passes, while being held to the siuface by felts. Drying also occurs between the cylinders by heated air blown into the gaps. This is known as pocket ventilation. 

Figures. 12 Stress-strain curves of GRC composites produced by the spray-up vacuum-dewatering method (after Aii et al. [46]). (a) Effect of fibre content (fibre length 30 mm) (b) effect of fibre length (fibre content 4% by volume).

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