Ejectors direct-contact

Wlien ejectors pull non-condensables and other vapors from a direct contact water condenser (barometric, low level jet, deaerator) there is also a release of dissolved gases, usually air, from water. This air must be added to the other known load of the ejector. Figure 6-22 presents the data of the Heat Exchange Insdtute [10] for the amount of air that can be expected to be released when cooling water is sprayed or otherwise injected into open qqae barometric or similar equipment. 

Condensers and vacuum pumps will be needed for evaporators operated under vacuum. For aqueous solutions, steam ejectors and jet condensers are normally used. Jet condensers are direct-contact condensers, where the vapour is condensed by contact with jets of cooling water. Indirect, surface condensers, are used where it is necessary to keep the condensed vapour and cooling water effluent separate. 

The main factor accounting for lack of reliable attainment of sterility in autoclaves has been entrapped air acting as a barrier to direct contact between stetun and product. Thus the main thrust for technological advances in steam sterilization has been concerned with improved effectiveness of removal of air from the chamber and its contents. Advanced high vacuum autoclaves have evolved from downward-di lacetnent types by the addition of condensors, vacuum pumps, and ejector systems to assist in air removal. 

Heuristic 46 For pressures down to 10 torr and gas flow rates up to 10,000ft /min at the inlet to the vacuum system, use a liquid-ring vacuum pump. For pressures down to 2 torr and gas flow rates up to 1,000,000 ft /min at the inlet to the vacuum system, use a steam-jet ejector system (one-stage for 100 to 760 torr, two-stage for 15 to 100 torr, and three-stage for 2 to 15 torr). Include a direct-contact condenser between stages. 

For most steam ejector applications, direct contact condensers between stages were frequently used. For vacuum steam stripping, use shell and tube condensers with refrigerant at -8 to -12 °C upstream of the booster ejector with interstage dry condensers plus a liquid ring vacuum pump. 

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

In dry compressors, shaft end seals are generally one of five type.s. These are labyrinth, restrictive ring, mechanical contact, liquid film, and dry gas seal. The labyrinth type is the most simple but has the highest leakage. The labyrinth seal is generally ported at an axial point between the seals in order to use an eductor or ejector to control leakage and direct it to the suction or a suitable disposal area. Alternatively, a buffer gas is used to prevent the loss of process gas. Appendix D presents a calculation method for use with labyrinth seals. 

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