Filtration tubular filters

The advantages of the tubular filter are that it uses an easily replaced filter medium, its filtration cycle can be interrupted and the shell can be emptied of prefilt at any time without loss of the cake, the cake is readily recoverable in dry form, and the inside of the filter is conveniently accessible. There is also no unfiltered heel. Disadvantages are the necessity and attendant labor requirements of emptying by hand and replacing the filter media and the tendency for neavy solids to settle out in the header chamber. Applications are as a scavenger filter to remove fines not removed in a prior-filtration stage with a different land of equipment, to handle the runoff from other filters, and in semiworks and small-plant operations in which the filter s size, versatility, and cleanliness recommend it. 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

Solvent Crystallization. Two processes, one utilizing acetone (Armour) and the other employing methanol (Emery), are well known. Using the latter, fatty acid is dissolved in 90 percent aqueous methanol in a 1 2 acid/ solvent ratio by the application of heat. The resulting solution is then cooled to H 5°C in a multi-tubular crystallization chamber equipped with scrapers for efficient heat transfer. The crystallized fatty acids are removed by filtration. The filter cake is melted and stripped of any residual solvent to yield the refined stearin fraction, and then the liquid stearin is converted to flakes or powder by a variety of processes, for example, chill roller, and the like. The mother liquor from the filtration is stripped to obtain the olein fraction. The separated stearin and olein fractions have a variety of commercial applications in both the chemical and food processing industries. 

SHEET FILTRATION. Sheet filters consist of a tubular steel chassis or a freestanding filter chassis in which square metal or plastic filter plates are vertically arranged. The filter plates are fluted plates made of ribbed material or tubular frames with perforated plates. 

Candle FilterS Tubular filter elements contained in a matching vessel are known as candle filters. The actual filter vessel may contain one or more filter candles, and may be used as pressure or suction filters for the filtration of liquids and gases. A particular advantage offered is that candles may readily be changed to different types, to suit particular requirements or applications. A typical candle filter is shown in Fig. 11. Materials of candles are selected to fit a particular process. 

A decline in the urinary excretion of uric acid to a level below the rate of production leads to hyperuricemia and an increased miscible pool of sodium urate. Almost all the urate in plasma is freely filtered across the glomerulus. The concentration of uric acid appearing in the urine is determined by multiple renal tubular transport processes in addition to the filtered load. Evidence favors a four-component model including glomerular filtration, tubular reabsorption, tubular secretion, and postsecretory reabsorption. ... 

In water-loaded rats orally administered single doses of 25, 50, 200,350, and 500 mg/kg corn stigma extract, an increase in potassium excretion was observed at doses of 350 and 500 mg/kg. At the 500 mg/kg dose, diuretic activity was observed. In rats administered a single dose of 500 mg/kg of the same extract, glomerular filtration and filtered load decreased without affecting proximal tubular function, sodium, or uric acid excretion (Velazquez et al. 2005). 

FIGURE 58.7 Tubular filter. (From Shirato, M. et al., Filtration— Principles and Practice, eds. M.J. Matteson and C. Orr, Marcel Dekker, New York, pp. 299-423, 1987. With permission.)... 

Polymer-containing solution can be purified and the solvent reused by subjeeting the solution to microfiltration using tubular filters having an average pore diameter of less than 1 pm and a filtration pressure of at least 0.35 MPa. ... 

The advantage of candle filters is that as the cake grows on the tubular elements the filtration area increases and the thickness of a given volume of cake is therefore less than it would be on a flat element. This is of importance where a thick cake is being formed the rate of increase in the pressure drop is less with tubular elements. 

The overall effect in most animals is to stimulate intestinal absorption of calcium with a concomitant increase in semm calcium and a reduction in parathyroid hormone (PTH). Modest hypercalcemia allows the glomerular filtration rate to remain stable and hypercalciuria to occur because of increased filtered load of calcium and reduction of tubular resorption of calcium with reduced PTH. However, with further increases in semm calcium, the glomerular filtration rate decreases, resulting in an even more rapid increase in semm calcium and the subsequent fall in urinary calcium. 

Glomerular filtration rate (GFR) is the volume of plasma-like fluid that is filtered per unit time across the glomerular capillary membranes to enter the tubular space. Filtrate formation is driven by the net filtration pressure that is equal to the capillary hydrostatic pressure diminished by the sum of capillary oncotic... 

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