A jet blower is an ejector operating at, or near, atmospheric pressure with a very low compression ratio, generally less than 1:2. It is designed to move a large amount of gas across a small pressure differential. Whereas pressure differentials of standard steam jet ejectors are usually measured in inches of Hg, pressure differentials of jet blowers are measured in inches of H2O (“in. w.c.”). Jet blowers are either steam or air operated.
Stainless steel jet blowers are found in pulp and paper mills in “NCG scavenging systems”, and are used instead of mechanical fans. They are used to collect “noxious” gases from various sources at slightly below atmospheric pressure and boost them through a flame arrestor to an incinerator at slightly above atmospheric pressure. Steel jet blowers find their greatest application in the power industry as turbine gland ejectors.
Because the pressure differentials are so comparatively small, it is possible to use low pressure motive steam (e.g. 50 psig or less). Since we custom design our “BL” series ejectors, it is still possible to achieve high efficiencies (low motive to suction ratios). Jet blowers are “subcritical flow devices”. It is possible to maintain suction and discharge pressures, and to vary the suction capacity by throttling the motive steam pressure (and consequently the motive steam flowrate). Suction capacity decreases roughly as the square of the motive steam flowrate decreases. However, it has been found that increasing the motive steam flowrate above design does not increase the suction flowrate substantially.J