Drying continuous countercurrent

Coconut Flour. Coconut flour is produced from the shredded kernel, dried in a continuous countercurrent drier, and subsequently extracted with solvent to remove the residual oil. The white meal produced contains 25% protein and 65% carbohydrate, as well as various minerals and vitamins (62). This coconut product... 

The basis of the process is to use activated carbon to recover SO2 in a salable form. The process flowsheet and chemistry are summarized in Figure 1. All steps of this dry, cyclic process are performed in continuous, countercurrent, multi-stage fiuidized-bed equipment. In the S02-removal step the carbon catalyzes the reaction of the SO2 with oxygen in the flue gas to form SO3, which is hydrolyzed to sulfuric acid that remains sorbed... 

A continuous countercurrent dryer is to be designed to dry 800 lb of wet porous solid per hour from 140 percent moisture to 20 percent, both on the dry basis. Air at 120°F dry bulb and 70°F wet bulb is to be used. The exit humidity is to be 0.012. The average equilibrium-moisture content is 5 percent of the dry weight. The total moisture content (dry basis) at the critical point is 40 percent. The stock may be assumed to remain at a temperature 3°F above that of the wet-buib temperature of the air throughout the dryer. The heat-transfer coefficient is 12 Btu/ft -h-°F. The area exposed to the air is 1,1 ft per pound of dry solids. How long must the solids remain in the dryer ... 

In Fig. 9.10-5 typical temperature profiles of the gas Tq and the solid Tj are shown for a continuous countercurrent dryer. In the preheat zone, the solid is heated up to the wet bulb or adiabatic saturation temperature. Little evaporation occurs here, and for low-temperature drying this zone is usually ignored. In the constant-rate zone, I, unbound and surface moisture are evaporated and the temperature of the solid remains essentially constant at the adiabatic saturation temperature if heat is transferred by convection. The rate of drying would be constant here but the gas temperature is changing and also the humidity. The moisture content falls to the critical value at the end of this period. 

As another example, the case of air drying was calculated and compared with the complex calculation result obtained by the method introduced in the previous section (Chihara and Suzuki, I9 3a). The case of isothermal operation (Fig. 11.6, solid and open circles) is compared with the results of the continuous countercurrent flow model (solid and broken lines) in Fig. 11.14. Rigorous calculation was done for a throughput ratio of 0.01 and the change in the profiles of the amount adsorbed after adsorption and desorption steps found to be reasonably small. Thus the simple model simulated quite well the cyclic steady state profile of PSA. 

A gas or vapor in a gas can be adsorbed on a solid which is slurried in a liquid. For example, sulfur dioxide can be adsorbed from a mixture with air on activated carbon slurried in water [8]. This procedure was suggested as early as 1910 [25], but interest in it has revived only recently. The reported details thus far are confined to laboratory studies of sparged vessels [73, 88] operated semibatch (gas flow continuous, sluny batch) or cocurrent flow or both [66]. A continuous countercurrent process has been described [4, 27]. The slurry is of course much easier to handle than dry solid, and it has been shown that the capacity of the slurried adsorbent is about the same as for dry solid [73], much larger than that of the liquid solvent alone [96]. 

We wish to estimate the height of a continuous countercurrent isothermal adsorber for drying air at 26.7 C, standard atmospheric pressure, from an initial humidity 0.003 to a final humidity 0.0001 kg H20/kg dry air. The entering gel will be dry. Note-. So-called "dry silica gel must contain a minimum of about 5% water if it is to retain its adsorptive capacity. Moisture measurements as ordinarily reported do not include this.) A gel rate 0.680 kg/m s (500 Ib/ft h) and an air rate 1.36 kg/m s (1000 Ib/ft h) will be used. For the moisture contents expected here, the equilibrium adsorption isotherm at 26.7 C, std atm (see Illustration 11.9), can be taken as substantially straight and described by the expression Y 0.018SJf. 

A continuous countercurrent hot-air turmel drier is to be designed to dry a filter-press cake of coarse crystals of an inorganic substance, insoluble in water. The filter-press cake will be placed on trays 1.0 m long by 0.9 m wide by 25 mm, 20 trays to-a truck, with 50 nun between trays. The tutmel drier will have a cross section 2 m high by 1 m wide. The trays have a reinforced screen bottom, so that drying takes place from both top and bottom of each tray. Production permits introducing one... 

All filters of this type have the distinct advantage of continuous operation and, as a result, the feed and wash liquors may be fed to the equipment at steady rates. Dense, quick settling solids can be handled, and the cake thickness — and the washing and drying times — can be varied independently between quite wide limits. The cake can be flooded with wash liquor, which can be taken away separately and re-used to obtain countercurrent... 

Figure 9.6. Tray dryer arrangements, batch and continuous. Performance data are in Table 9.5. (a) Air flow across the surfaces of the trays, (b) Air circulation forced through the beds on the trays (Proctor and Schwartz Inc.), (c) Continuous drying of trays mounted on trucks that move through the tunnel air flow may be in parallel or countercurrent (P.W. Kilpatrick, E. Lowe, and W.B. Van Arsdel, Advances in Food Research, Academic, New York, 1955, Vol. VI, p. 342).

In the process of Dietzsch Co, a continuous roll of pulp, in the form of a sheet 45cm wide, was passed thru a chamber, countercurrently to the nitric acid fumes and then thru a bath contg coned nitric acid. After washing the resulting NC with water and air-drying, the sheet was coated on one side with an adhesive(such as Vinarol) and made into a cartridge case. It was waterproofed by coating it with a bituminous lacquer mixed with an acetonic soln of NC(Ref 2,pp 7-11)... 

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