Staging of ejectors becomes necessary for economical operation as the absolute suction pressure decreases. Based upon the use of auxiliary equipment, two and three-stage ejectors can either be condensing or non-condensing types. Four, five, and six-stage units can also be non-condensing, but are usually condensing types.
Principle of Operation
Two-Stage Steam Jet Ejectors have the same general field of application as the single stage units. They handle both condensable and non-condensable gases or vapors, as well as mixtures of the two. The general operating range is between 5″ Hg. abs. and 3 mm Hg. abs. Depending on conditions, however, a single-stage unit may be more economical at the top of the range and a three-stage unit near the bottom.
Applications
Principle of Operation
Three-Stage Ejectors are recommended for applications where a two-stage unit will not provide low enough suction pressure economically. Applicable range is from 26 mm Hg. abs. to 0.8 mm Hg. abs. but economics might dictate use of a Two-Stage Ejector at the upper part of the range and a Four-Stage Ejector at the lower end.
Three-Stage Condensing Steam Jet Ejectors consist of a booster ejector, a booster condenser, and a Two-Stage Ejector consisting of a high-vacuum ejector, intercondenser, and low vacuum ejector. In some applications another condenser (after-condenser) can be used at the low vacuum ejector discharge.
Applications
Principle of Operation
Four, Five and Six-Stage Steam Jet Ejector units are used for applications where required suction pressures are beyond the range of the ejectors previously described. Generally, suction pressure ranges are as follows:
Four-stage units consists of (1) a primary booster ejector; (2) a secondary booster ejector; (3) a high vacuum ejector; (4) a low vacuum ejector; and (5) usually two condensers—one after the secondary booster ejector and the other between the high vacuum and low vacuum ejectors. The condenser between the high and low vacuum ejectors is sometimes omitted, depending upon application requirements. Direct contact or surface condensers, arranged barometrically or at ground level, can be used.
The four-stage is similar to the three-stage unit except that another booster ejector is added. In the four-stage, the primary booster is steam-jacketed to prevent build-up of ice on the diffuser internal bore.
The five and six-stage units are similar in appearance to the four-stage ejector except that additional booster ejectors are added. While four, five, and six-stage ejectors are usually condensing types for reasons of efficiency and operating economy, it is possible to employ non-condensing types.
Applications
