Steam Jet Ejector

Steam jet ejector is a device for producing vacuum which is achieved by using a high pressure motive steam. The primary advantages of steam jet ejector are simplicity of operation, no mechanical drive and has no moving parts.

Typically steam jet ejector has three parts ; the jet nozzle(2), the suction chamber (3) and the diffuser (4, 5, 6). The figure 1 illustrates basic operation principle of the steam jet ejector.

The high pressure steam is supplied in steam chest (1), and expanded through jet nozzle (Converging & diverging nozzle causes the velocity up to mach number 3.0 or 4.0) and them motive stream injected into a suction chamber. The suction chamber has the lowest static pressure (approximately equivalent to the suction pressure Ps). The suction fluid enters into the suction chamber(3) and is mixed with motive steam in the diffuser inlet (4). Kinetic energy of motive steam is transferred to the suction fluid through diffuser throat (5). Motive steam & suction fluid mixtures are converted the velocity energy to the pressure energy (recompressed to the discharge pressure Pd) through diffuser outlet (6).

Fluid & Thermal Engineering research has produced numerous improvements in steam jet ejector design and test results. Right figure illustrates suction capacity which calculated by computer at entrance of diffuser. Suction capacity at right figure is 55kg/hr which corresponds to minimum value to the curve. Sometimes there is no minimum value, in this case, eddy current occurs and suction capacity decreases suddenly (By professor Ueda)

Steam jet ejectors are used in field

• Steam power plants : Vacuum pump for surface condenser
  
• Petrochemical : Distillation, deodorization plants
  
• Synthetic fiber : Polymerization of polyester fiber
  
• Food : vacuum dryer
• Paper : Thermo Compressor
  
• Ship building : Crude oil stripping pump
  
• LPG Terminal : jet condenser
  
• Steel industry : Degassing unit for RH, DH, TD, LD
  
• Environmental : Thermo Compressor
  
• Pharmaceutical : Frozen dryer

Motive Fluid

• Steam < 2.0kg/cm2 abs
  
• Air < 1.0kg/cm2 abs
  
• Water < 3.0kg/cm2 abs
  
• LPG < 4.0kg/cm2 abs
  
• Compressed gas

Fluid & Thermal Engineering's is the leading company for innovative, high performance of steam ejector for process industries. The design, production, test facilities create and environment for the manufacture of customer satisfaction and creative the value of customer.

Steam Jet Ejector

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. Left figure illustrates four stage steam jet ejector with inter/after condenser, two stage steam ejector with intercondenser & water ring vacuum pumps.

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 : Water ring vacuum pump

Single stage steam ejector A single steam ejector is used for ultimate suction pressure 10kPA(75Torr) and normal suction pressure up to 15kPa(120Torr). Discharge pressure is mostly equivalent to the atmospheric pressure, for exhaustign 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 ejector are used for suction pressure 20kPa(150Torr) or below, and the ultimate suction pressure is up to 2kPa(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(38Torr) or below, 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 25Torr), 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 0C 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 jecket the jet nozzle and diffuser.
5th stage steam ejector Five stage and siz stage steam ejector are commonly used for special process and space research field, and vacuum metallurgy process such as RH-OB 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)

Steam jet Ejector

Direct contact or barometric condenser Direct contact condensers are constructed to effect condensation of steam and other condensable vapors by means of direct contact with the cooling water. There are two principle types, of counter flow and parallel flow of condensable vapor and cooling water.

Shell and tube(surface) condenser

Shell & tube type condenser do not mix process vapor and cooling water, so there is no contamination of the cooling water. Below figure illustrations of shell & tube type heat exchanger is specially adapted for condensing on ether the shell and tube side. If the fouling is minor, shell side condensing is better, else condensing vapor is extremely fouled, so, tube side condensation is better for easy mechanical cleaning Tube bundles are adapted fixed type, u-tube type & floating head type tube sheet.