Cake moisture

Eor evaluation of flocculants for pressure belt filters, both laboratory-scale filters and filter simulators are available (52,53) in many cases from the manufacturers of the full-scale equipment. The former can be mn either batchwise or continuously the simulators require less substrate and are mn batchwise. The observed parameters include cake moisture, free drainage, release of the cake from the filter cloth, filter blinding, and retention of the flocculated material during appHcation of pressure. 

Vacuum filters are usually simulated with a Buchner funnel test or filter leaf test (54). The measured parameters are cake weight, cake moisture, and filtration rate. Retention aids are usually evaluated using the Britt jar test, also called the Dynamic Drainage Jar, which simulates the shear conditions found on the paper machine and predicts performance (55). 

Although filtratioa rates can be much faster with flocculants, the final cake moisture is often higher ia a flocculated cake (60—63). Ia coatrast, usiag flocculants optimized for filtration, coal, and other mineral slurries can be dewatered to moisture contents significantly lower than the untreated cake (64—68). The advantages of rapid filtration rates can also be preserved. Flocculants that provide better filtration tend to form floes having the foUowiag characteristics (65) ... 

Fig. 6. Effect of acrylate content on coal refuse filter-cake moisture (59) (—), the effect on a longer chain flocculant (mol wt of 8 )...

Vacuum or Pressure The vast majority of all continuous filters use vacuum to provide the driving force for filtration. However, if the feed slurry contains a highly volatile hquid phase, or if it is hot, saturated, and/or near the atmospheric pressure boiling point, the use of pressure for the driving force may be required. Pressure filtration might also be used where the required cake moisture content is lower than that obtainable with vacuum. 

Feed Slurry Temperature Temperature can be both an aid and a limitation. As temperature of the feed slurry is increased, the viscosity of the hquid phase is decreased, causing an increase in filtration rate and a decrease in cake moisture content. The limit to the benefits of increased temperature occurs when the vapor pressure of the hquid phase starts to materially reduce the allowable vacuum. If the hquid phase is permitted to flash within the filter internals, various undesired resiilts may ensue disruption in cake formation adjacent to the medium, scale deposit on the filter internals, a sharp rise in pressure drop within the filter drainage passages due to increased vapor flow, or decreased vacuum pump capacity. In most cases, the vacuum system should be designed so that the liquid phase does not boil. 

Pretreatment Chemicals Even though the suspended solids concentration of the slurry to be tested may be correct, it is frequently necessary to modify the sluriy in order to provide an acceptable filtration rate, washing rate, or final cake moisture content. The most common treatment, and one which may provide improvement in all three of these categories, is the addition of flocculating agents, either inorganic chemicals or natural or synthetic polymers. The main task at this point is to determine which is the most effective chemical and the quantity of chemical which should be used. 

There are a number of commercially available surfactants that can be employed as an aid in filter cake moisture reduction. These reagents can be added to the filter feed sluriy or to the filter cake wash water, if washing is used. Since these reagents have a dispersing effect, flocculation may be required subsequently Typical moisture reduc-... 

Cake Moisture Results on a wide variety of materials have shown that the following factor is very useful for correlating cake moisture content data ... 

Coal Slurries - Two component treatments prove to be effective on a commercial scale for coal slurry flocculation. The use of encapsulated floccuiant suspended in a counter charged floccuiant provides the robusmess of traditional dual component systems, but with additional performance advantages, which include reduction in filter cake moisture content and an increased throughput rate. Figure 5 illustrates the typical filter cake moisture content obtained by a conventional treatment system compared to the encapsulated treatment system using coal tailings as the substrate. 

Application Filter area, m2 Slurry feed characteristics % solids pH t/hr Wash ratio (wt/wt based on dry solids) Solubles recovery % Final cake moisture %... 

What problems exist (circle those which apply) erosion, corrosion, capacity, efficiency, blinding, crystal breakage, cake moisture, other ... 

The effect of incubation temperature, initial cake moisture, and olive oil supplementation on lipase production was evaluated following a two-level experimental plan. The range of study of the variables was chosen based on previous results of the our group (2,7,10). 

Run No. Cake Moisture, percent Average Chloride Concentration in Scrubber Liquor, percent Scrubber Feed Scrubber Discharge Comments... 

FIGURE 14.13 Correlating factor for cake moisture content and air rate (Example 14.6). 

The following conditions and specifications are assumed slurry contains 40% solids by weight solute in the liquid is 2% final cake moisture is 25% wash ratio (wash volume per void volume) is 1.5 ... 

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