Coarse vacuum

Liquid seal pumps are frequently employed as mechanical pumps in the coarse vacuum range. During the pump s rotation, a water ring forms as a result of centrifugal... 

The equipment for continuous distillation can only separate one stage in the equilibrium diagram. Countercurrent distillation, also called rectification, has found widespread application with normal pressure and coarse vacuum distillation when complex mixtures or components with small relative volatility factor are to be separated. The fundamentals are discussed above (2.1.3.3.2) the technical side will be dealt with here [41-45]. 

Coarse vacuum 1000 to 50 mbar water ring pumps... 

Larger tray pressure drops under coarse vacuum, normal pressure, or overpressure operation are tolerated... 

This type of filling material is particularly useful with normal pressure and under coarse vacuum operation. 

Some who specialize in vacuum technology use the following gradation system for levels of vacuum coarse vacuum (760 to 1 Torr absolute), rough vacuum (760 to 0.001 Torr absolute), high vacuum (10 to 10 Torr absolute), and ultra high vacuum (10 to 10 Torr absolute). To get to any pressure below lO Torr absolute requires more than one vacuum pump. 

For evaporation under coarse vacuum a variety of evaporator types is available. They represent a historical development, and each type has its specific field of application. Some typical evaporator types are described here. 

Working pressures between 80 and 800 mbar abs characterise the coarse vacuum. Water temperatures between 42 and 93 C correspond to these pressures. Most of the watery solutions are evaporated in this range. The evaporator types which are used here are hardly different from those used in the pressure range. 

Exhaust steam processes with liquids, however, are mainly operated in the fine vacuum range down to pressures of 1 mbar. The construction of the evaporators which are used here is very different from that of evaporators working under coarse vacuum. 

Coarse vacuum (vacuum technology) A vacuum in the range of atmospheric to about 10 Torr. Also called a rough vacuum (preferred). See also Rough vacuum. 

The cmde oxide is pressure-leached in a steam-heated autoclave using water or circulating mother hquor. The arsenic trioxide dissolves, leaving behind a residue containing a high concentration of heavy metal impurities and sihca. The solution is vacuum-cooled and the crystallisation is controUed so that a coarse oxide is obtained which is removed by centrifuging. The mother hquor is recycled. The oxide (at least 99% purity) is dried and packaged in a closed system. 

Butyl slurry at 25—35 wt % mbber continuously overflows from the reactor through a transferline to an agitated flash dmm operating at 140—160 kPa (1.4—1.6 atm) and 55—70°C. Steam and hot water are mixed with the slurry in a nozzle as it enters the dmm to vaporize methyl chloride and unreacted monomers that pass overhead to a recovery system. The vapor stream is compressed, dried over alumina, and fractionated to yield a recycle stream of methyl chloride and isobutylene. Pure methyl chloride is recovered for the coinitiator (AlCl ) preparation. In the flash dmm, the polymer agglomerates as a coarse cmmb in water. Metal stearate, eg, aluminum, calcium, or zinc stearate, is added to control the cmmb size. Other additives, such as antioxidants, can also be introduced at this point. The polymer cmmb at 8—12 wt % in water flows from the flash dmm to a stripping vessel operated under high vacuum to... 

When the sohds involved are coarse and fast settling, the vacuum should be applied an instant after the sluriy reaches the surface of the filter medium. 

Slurries of free-filtering sohds that are difficult to suspend are sometimes filtered on a top-feed drum filter or filter-diyer. An example application is in the production of table salt. An alternative for slurries of extremely coarse, dense solids is the internal drum filter. In the chemical-process industiy both top-feed and internal drums (which are described briefly by Emmett in Schweitzer, op. cit., p. 4-41) have largely been displaced by the horizontal vacuum filter (q.v). 

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