Extraction height

Because 5.307 in. is a minimum value, increase it by 20% to avoid flooding. Therefore, the design HETS is 6.368 in (0.162 m). From Equation 6.32.6, the extraction height,... 

The countercurrent contact zone height will depend primarily upon the number of stages required ( ) and the column characteristics. The effect of backmixing also increases the column diameter. A reasonable first approximation of extraction height (L) required for agitated columns is ... 

Where = coal extracting height = forced caving height k = swell factor of the forced caving rocks = the threshold free-standing height... 

The heights of a transfer unit ia each phase thus contribute to the overall heights of a transfer unit. Data on values of HTU for various types of countercurrent equipment have been reviewed (1,10). In normal operating practice, the extraction factor is chosen to be not greatiy different from unity, within the range of 0.5—2. 

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Jibutilon theophrasti is a herbaceous annual plant produciag a jute-like fiber. The plant is native to the People s RepubHc of China and is commercially grown ia China and the former USSR. Because of its association with jute ia mixtures and export, it is also called China jute. The plant grows to a height of 3—6 m with a stem diameter of 6—16 mm. After harvesting by hand and defoHation, bundles of the stems are water retted and the fiber is extracted by methods similar to those for jute. The fiber is used for twiae and ropes. 

Cellulose liner material absorbs water and needs to be wet for at least 30 s prior to investing to prevent Uquid from being extracted from the investment. The ceUulose liner bums when heated in air and is eliminated completely from the mold at burnout temperatures of 700°C (123). To ensure retention of the mold within the casting ring, a ceUulose liner should be kept short of each end. For gypsum investments a liner that is 12 mm shorter than the height of the ring should be used. 

The height equivalent to a theoretical stage (HETS) in an extraction tower is simply the height of the tower Zt divided by the number of theoretical stages achieved [Eq. (15-29)]. 

The contribution to the height of a transfer unit overall based on the raffinate-phase compositions is the sum of the contribution from the resistance to mass transfer in the raffinate phase plus the contribution from the resistance to mass transfer in the extract phase divided bythe extraction factor [Eq. (15-31)]. 

At high extraction factors the height of a transfer unit is mostly dependent on the resistance to the transfer of solute from the raffinate phase. 

The mass-transfer coefficients depend on complex functions of diffii-sivity, viscosity, density, interfacial tension, and turbulence. Similarly, the mass-transfer area of the droplets depends on complex functions of viscosity, interfacial tension, density difference, extractor geometry, agitation intensity, agitator design, flow rates, and interfacial rag deposits. Only limited success has been achieved in correlating extractor performance with these basic principles. The lumped parameter deals directly with the ultimate design criterion, which is the height of an extraction tower. 

Mass Transfer As mentioned earlier, spray columns rarely develop more than 1 theoretical stage due to the axial mixing in the column. Nevertheless, it is necesary to determine what column height will give this theoretical stage. It is recommended by Cavers in Lo et al. Handbook of Solvent Extraction p. 323 and p. 327, John Wiley Sons, New York, 1983 that the following equation be used to estimate the overall efficiency coefficient ... 

The general proportions may be varied from one end of the tower to the other to accommodate changing liquid volumes and physical properties. These towers have been used in diameters ranging from a few inches for laboratory work up to 2.4 m (8 ft) in diameter by 12.2 m (40 ft) tall for purposes of deasphalting petroleum. Other commercial services include furfural extraction of lubricating oils, desulfurization of gasoline, phenol recoveiy from wastewaters, and many others. Columns up to 4.5 m in diameter and up to 50 m in height have been constructed. 

Typical data for operation with methyl isobutyl ketone, water, acetic acid four stages 101.6-mm stage height, 152-mm-diameter column extraction, water ketone. 

Pilot tests are usually conducted in 0,075-m diameter columns the column should contain a sufficient number of stages to complete the extraction this may require several iterations on column height,... 

There are a number of the optimal conditions for sorption pointed below volume of extract - 4 ml ratio of aqueous and organic phases is 1 1 cyllindric foampolyurethan (marc - T 25-3,8) with diameter 8 mm, height - 4,5 mm, mass - 0.007 g. Time of full soi ption is 20 min. Completeness of soi ption is determined by spectrophotometric method. 

It is noteworthy that the above rule connects two quite different values, because the temperature dependence of is governed by the rate constant of incoherent processes, while A characterizes coherent tunneling. In actual fact, A is not measured directly, but it is calculated from the barrier height, extracted from the Arrhenius dependence k T). This dependence should level off to a low-temperature plateau at 7 < This non-Arrhenius behavior of has actually been observed by Punnkinen [1980] in methane crystals (see fig. 1). A similar dependence, also depicted in fig. 1, has been observed by Geoffroy et al. [1979] for the radical... 

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