Dry coolers

The use of dry coolers cannot take advantage of the lower cooling temperatures available by the evaporation of the cooling water, and is limited by the ambient dry bulb temperature, rather than the wet bulb Higher power is therefore required, and a given size compressor will perform less cooling duty. 

Toxic effects have not stopped copper spraying, because toxicities have been far outweighed by good results from disease control. However, toxic effects need more serious study. They may be more noticeable in warm moist coffee regions than in the dried cooler parts. 

Fig. 2. Flow sheet of lecithin producing unit. Crude soybean oil is heated in the preheater, 1, to 80°C, mixed with 2% water in the proportion control unit, 2, and intensively agitated in 3. The mixture goes to a dweUing container, 4, and is then centrifuged after a residence time of 2—5 min. The degummed oil flows without further drying to the storage tanks. The lecithin sludge is dried in the thin-film evaporator, 6, at 100°C and 6 kPa (60 mbar) for 1—2 min and is discharged after cooling to 50—60°C in the cooler, 8. 9 and 10 are the condenser and vacuum pump, respectively.

Superheated steam results when steam is heated to a temperature higher than that which would produce saturated steam. The equiUbrium between hquid and vapor is destroyed, and the steam behaves as a gas. It loses its abiUty to condense into moisture when in contact with the cooler surface of the article to be sterilized. This process resembles dry-heat sterilization more than steam sterilization and, under ordinary time—temperature conditions for steam sterilization, does not produce stetihty. 

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

The coarse calciae cooler operates at 300°C, while the waste-heat boiler cools the gas to 350°C. The tubes ia the boilers have a chain-shaking arrangement operated by paeumatic hammers. Steam productioa is 0.78 kg/kg of dry coaceatrate. The only trouble with dust reported is ia the connection betweea the reactor and waste-heat boiler. It is necessary to cool the gas stream quickly to avoid sulfation, but even so the carry-over calciae coataias oa the order of four times more sulfate than the coarse overflow. In this plant, the composite calciae is 0.1% sulfide and 2.2% sulfate sulfur. 

Citric acid and its salts are used in dry beverage mixes, convenience teas, and cocktail mixes for pH control and flavor, and are used in wine coolers at 0.10—0.55%, combining well with fmity and light flavors. 

There are many chemicals, by lowering suitable as carriers. Their bp is one of the principal criteria in selection. If bp is too low, the compound will evaporate from the dyebath at dyeing temperatures, and will be lost before it is effective in its role as a carrier. It may also steam distill (condense on the cooler parts of the equipment) and cause drips that will spot the fabric. On the other hand, if the bp is too high, the compound cannot be removed from the fabric under normal plant drying conditions and will affect lightfastness of finished goods, leave residual odor, and possibly cause skin irritation to the wearer. 

Trim Coolers Conventional air-cooled heat exchangers can cool the process fluid to within 8.3°C (15°F) of the design dry-biilb temperature. When a lower process outlet temperature is required, a trim cooler is installed in series with the air-cooled heat exchanger. The water-cooled trim cooler can be designed for a 5.6 to 11.1°C (10 to 20°F) approach to the wet-biilb temperature (which in the United States is about 8.3°C (15°F) less than the diy-bulb temperature). In arid areas the difference between diy- and wet-bulb temperatures is much greater. 

Example 5 Cooling and Dehumidification Find the cooling load per pound of dry air resulting from infiltration of room air at 80 F dry-bulb temperature and 67 F wet-bulb temperature into a cooler maintained at. 30 F dry-bulb and 28 F wet-bulb temperature, where moisture freezes on the coil, which is maintained at 20 F. 

Vapors (from drying) are removed at the feed end of the dtyer to the atmosphere through a natural-draft stack and settling chamber or wet scrubber. When employed in simple drying operations with 3.5 X 10 to 10 X 10 Pa steam, draft is controlled by a damper to admit only sufficient outside air to sweep moisture from the cylinder, discharging the air at 340 to 365 K and 80 to 90 percent saturation. In this way, shell gas velocities and dusting are minimized. When used for solvent recovery or other processes requiring a sealed system, sweep gas is recirculated throu a scrubber-gas cooler and blower. 

The plate dryer is limited in its scope of apphcations only in the consistency of the feed material (the products must be friable, free flowing, and not undergo phase changes) and diying temperatures up to 320°C. Applications include speci ty chemicals, pharmaceuticals, foods, polymers, pigments, etc. Initial moisture or volatile level can be as high as 65 percent and the unit is often used as a final dryer to take materials to a bone-dry state, if necessary. The plate dryer can also be used for heat treatment, removal of waters of hydration (bound moisture), solvent removal, and as a product cooler. 

Employing wood chips, Cowan s drying studies indicated that the volumetric heat-transfer coefficient obtainable in a spouted bed is at least twice that in a direct-heat rotaiy diyer. By using 20- to 30-mesh Ottawa sand, fluidized and spouted beds were compared. The volumetric coefficients in the fluid bed were 4 times those obtained in a spouted bed. Mathur dried wheat continuously in a 12-in-diameter spouted bed, followed by a 9-in-diameter spouted-bed cooler. A diy-ing rate of roughly 100 Ib/h of water was obtained by using 450 K inlet air. Six hundred pounds per hour of wheat was reduced from 16 to 26 percent to 4 percent moisture. Evaporation occurred also in the cooler by using sensible heat present in the wheat. The maximum diy-ing-bed temperature was 118°F, and the overall thermal efficiency of the system was roughly 65 percent. Some aspec ts of the spouted-bed technique are covered by patent (U.S. Patent 2,786,280). 

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