5 Vacuum pan

Continuous vacuum pans have been successhiUy developed for raw sugar crystallization, and are widely appHed in South Africa, AustraHa, South America, and the United States. Continuous crystallizers, developed for beet sugar manufacture, are being adapted for use in cane sugar factories. 

Crystallization batches range from 30,000 to 60,000 Hters for each pan. Continuous centrifugals are typically used for second, third, and affination steps continuous vacuum pans are less common but are used in the U.S. for intermediate strikes. Most horizontal batch crystallizers have been replaced by continuous units, and all are designed for controlled cooling of the massecuite to maintain supersaturation. 

Anhydrous a-dextrose is manufactured by dissolving dextrose monohydrate in water and crysta11i2ing at 60—65°C in a vacuum pan. Evaporative crysta11i2ation is necessary to avoid color formation at high temperatures and hydrate formation at low temperatures. The product is separated by centrifugation, washed, dried to a moisture level of ca 0.1%, and marketed as a very pure grade of sugar for special appHcations. 

Freeze drying has also been carried out at atmospheric pressure in fluid beds using circulating refrigerated gas. Vacuum-type vibrating conveyors, rotating multishelf dryers and vacuum pans can be used as can dielectric and microwave heating. 

Euter, n. udder, ev., abbrev. of eventuell. evakuieren, v.t. evacuate, empty, exhaust. Evakuienmgskessel, m. vacuum boiler, vacuum pan. 

VACUUM PANS AND EVAPORATORS FOR SALT, SUGAR, milk, etc. 

Despite these qualifications copper and its alloys are used extensively and successfully in much chemical equipment. Uses include condensers and evaporators, pipelines, pumps, fans, vacuum pans, fractionating columns, etc. Tin-bronzes, aluminium-bronzes and silicon-bronzes are used in some circumstances because they present better corrosion resistance than copper or brasses. 

MASSECUITE A mechanical mixture of crystals in mother liquor (molasses or heavy syrup), produced in a vacuum pan. The suspension of sugar crystals in mother liquor produced during the early stages of crystallization. 

PAN/VACUUM PAN Equipment used for controlled crystallization of sugar solutions by boiling under a vacuum. 

Continuous vacuum filters, 16 657 Continuous vacuum pans, for raw sugar crystallization, 23 449 Continuous veno-venous hemodiafiltration (CWHD), 26 832... 

Anhydrous alpha dextrose may be obtained by drying the hydrate in a stream of warm air.6 For a very pure grade of the anhydrous product a better method is used which consists of crystallizing from solution in a vacuum pan at a temperature above 50°C.1314 This temperature is the hydrate-anhydrous transition point. Dextrose from the first crystallization of the starch conversion liquor is dissolved in water to give about a 60 % solution which is treated with a small quantity of activated carbon... 

Typical pilot-plant BDH results are shown in Table 24.4. The brine that was treated in this case was made up with vacuum pan salt to a concentration of approximately 10% w/w, which is the concentration employed for regeneration of the SAC ion-exchange softener unit. Included in the table is the entrained volume of feed solution (i.e. feed void) which is displaced from the bed prior to regeneration on each cycle. The feed void would normally be recycled to the feed tank and processed in subsequent cycles. 

Table 24.4 BDH brine softening results dilute vacuum pan salt.

Table 24.5 shows the results obtained in treating a saturated solution of vacuum pan salt which would be more typical of that required for primary treatment in the chlor-alkali industry. Note that the higher feed concentration did not adversely affect the removal efficiency, even considering the higher hardness concentration. Complete hardness removal was obtained with 99% recovery of the NaCl values. 

Brines are also cone, by evaporation under reduced press., i.e. in what are called vacuum fans heated by steam, and specially designed to eliminate difficulties arising from the tendency of the brine to deposit a hard scale or crust of calcium salts. In some cases, the magnesium salts are first precipitated as magnesium hydroxide, Mg(OH)2, by the addition of milk of lime, and the calcium sulphate subsequently removed by precipitation as carbonate by the addition of ammonium carbonate liquors. The decanted liquor is then cone, in vacuum pans. 

In those countries where fool is cheap, and especially in those manufactories where-staam is employed, cither ob a motive power for the mill, or the vacuum pan— afterwards-, to be described—or for other purposes,... 

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