Steam Jet Ejector - Vacuum System
A typical steam jet ejector system Consistence of one or more steam ejector assemblies with associated ejector condensers arranged to condense vapor discharged from previous ejector stage assemblies as below figures.
- Designations for ejector assembly
Designation for ejector system
- U stage: 4th booster
- V stage: 3rd booster
- W stage: 2nd booster
- X stage: 1st booster
- Y stage: 1st ejector
- Z stage: 2nd ejector
- XY condenser: 1st inter condenser
- YZ condenser: 2nd inter condenser
- ZA condenser: after condenser
- WRVP: Waterring vacuum pump
- Common type of ejector & condenser stage
- Single stage steam ejector
A single stage steam ejector is used for ultim ate suction pressure 10kPa (75Torr) and normal suction pressure up to 15kPa (120Torr). Discharge pressure is mostly equivalent to the atmospheric pressure, for exhausting the following methods are employed. (1) up to silencer and muffler, (2) sealed in hot well or seal pot with pressurized vent, (3) after condenser.
- Two stage steam ejector
Two stage steam ejectors are used for suction pressure 20k Pa (150Torr) or below, and the ultimate suction pressure is up to 2k Pa (15Torr). Two stage steam ejectors include three types; (1) two stage noncondensing ejector: small capacity, (2) two stage ejector with barometric inter condenser : continuous operation and steam consumption per capacity is lowest , (3) two stage ejector with surface inter condenser : eliminates water contamination and product recovery system.
- Three stage steam ejector
Three stage steam ejectors are used for suction pressure 5kPa (38 Torr) or below, and the ultimate suction pressure is up to 0.5k Pa (3.8 Torr).
Three stage steam ejectors are include three types ; (1) three stage non-condensing ejector : small capacity and intermittent service, (2) two stage booster and 3rd ejector with inter condenser : continuous and high vacuum range, (3) three stage ejector with two inter condenser : achieve maximum steam economy. Impossible to condense gas at pressure too low to permit condensation (suction pressure below 25 Torr), with available cooling water.This case consist of vary large 1st stage ( booster), which is always designed to compress the vapors to the condensable pressure.
- Four stage steam ejector
Four stage steam ejector is designed for high vacuum range, suction pressure 0.5kPa (3.8Torr) or below, and ultimate suction pressure in up to 0.07kPa (0.5Torr). The suction pressure is below 4.6Torr, steam saturation temperature is sufficiently below 0 C to freeze moisture in the suction gas and motive steam, thus the forming of ice between jet nozzle and diffuser inlet. The avoid of the ice formation, required steam jacket the jet nozzle and diffuser.
- Five stage steam ejector
Five stage and six stage steam ejector are commonly used for special process and space research field, and vacuum metallurgy process such as RH -O B degassing unit at POSCO. Suction pressure range of five stage steam ejector is 0.01kPa (0.75Torr) to 0.013kPa(0.1Torr). 6th stage steam ejector Suction pressure range of six stage steam ejector is below 0.007kPa (0.05Torr).