Vacuum contactors

With the availability of 3.3 and 6.6 kV vacuum contactors the control of HT motors up to 6.6 kV systems has now become easier and economical, compact and even more reliable. For 11 kV. systems, vacuum as well as SF (Sulphur hexafluoride) breakers can be used. The HT motor s switching and protection through a vacuum contactor provides a replica of an LT system. The earlier practice of using an HT OCB, MOCB, or an air blast circuit breaker for the interruption of an HT circuit is now a concept of the past. 

The latest practice for up to 6.6 k V motors is to use an HT load break, fault-making isolator in conjunction with the appropriate type and size of HRC fuses, a vacuum contactor and a motor protection relay. The contactors... 

Prelorius, R.E. and Eriksson. A.J., Field studies of switching surge generation in high voltage vacuum contactor controlled motors , IEEE Conference Publication 210. 54-64 ( 1982). 

Heat Sensitivity. The heat sensitivity or polymerization tendencies of the materials being distilled influence the economics of distillation. Many materials caimot be distilled at their atmospheric boiling points because of high thermal degradation, polymerization, or other unfavorable reaction effects that are functions of temperature. These systems are distilled under vacuum in order to lower operating temperatures. For such systems, the pressure drop per theoretical stage is frequently the controlling factor in contactor selection. An exceUent discussion of equipment requirements and characteristics of vacuum distillation may be found in Reference 90. 

Multistage porous diffuser contactors, which involve a single application of an ozone-rich gas stream and application of fresh ozone gas to second and subsequent stages with off-gases recycled to the first stage. Eductor-induced, ozone vacuum injector contactors, which include total... 

These gas transfer membranes or membrane contactors employ microporous polypropylene hollow fiber membranes arranged in a modular design. Oxygenated water flows on the shell side of the hollow fibers, and a strip gas (such as nitrogen) or a vacuum is applied to the inside (lumenside), with the hollow fibers acting as a support medium for intimate contact between the water and gas phases. 

In the process (Figure 8-10), the preheated feedstock (which may be whole crude, atmospheric residuum, vacuum residuum, or bitumen) is injected into a stream of fluidized, hot catalyst (trade name ArtCat). Complete mixing of the feedstock with the catalyst is achieved in the contactor, which is operated within a pressure-temperature envelope to ensure selective vaporization. The vapor and the contactor effluent are quickly and efficiently separated from each other and entrained hydrocarbons are stripped from the contaminant (containing spent... 

For small U and C values, the discharge resistor may be permanently connected to the capacitor. In the example given above, the resulting power loss would be 10 kW. Consequently, a discharge switch shall be fitted which automatically closes the discharge circuit. For pressurized apparatus, a single-pole vacuum tube (contactor type) may be used. Its open position is achieved by a pneumatically actuated drive, the closed position should be maintained by the atmospheric air pressure, and, if necessary, by an additional helical spring. 

Contactor Circuit breaker Vacuum circuit breaker... 

Many modifications of the three types of contactors just discussed have been developed in an effort to reduce costs, reduce pressure drop, equalize vapor flow through each contactor, increase plate efficiencies, or, in general, improve the operating performance of the tower. An example of this for modification of bubble-cap towers is the old Uniflux tray originally developed by Socony-Vacuum, which consisted of a series of interlocking S-shaped sections which were assembled in the form of tunnel caps with slot outlets on one side only. Segmental downcomers, similar to the downcomers in conventional bubble-cap columns, were provided. The vapors issued from the Uniflux caps in... 

Figure 2.6 schematically illustrates sections of a typical semiconductor ultrapure water (UPW) production process in a semiconductor plant. The water circuit consists of two main sections (1) makeup (or central) system and (2) polishing loop, which provides water at the point of use. There are multiple locations in such a water process where membrane degassing could be needed as shown in the figure. Reverse osmosis is mostly used in makeup line as the primary purification means in such processes. In the past, large and inflexible vacuum towers were frequently used after RO to remove dissolved gases, such as O2, N2, and CO2. Membrane contactors are the norm today for replacement or supplement to vacuum towers in makeup lines, as shown in Figure 2.6. 

FIGURE 2.7 Relative system sizes of vacuum tower and membrane contactors. 

FIGURE 13.10 Scheme of the MHS[FLM-PV] multimembrane hybrid system (1) cation-exchange membranes, (2) FLM, (5) vacuum system, (6) pervaporation unit, (7) pervaporation membranes, (8) contactor, (9) feed solution, (10) stripping solution. (From Wodzki, R. and Szczepanski, P., J. Mem. Sci., 197, 297, 2002. With permission.)... 

Once the absorbent exits from the contactor, it can be regenerated in another membrane contactor unit both by stripping with vacuum or by sweep and by heating. Figure 38.5 reports a simplified scheme for an absorber-desorber flow sheet with the desorber operating under vacuum. 

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