Two-stage Steam Ejectors
Steam ejectors are based on the ejector-venturi principal and operate by passing motive steam through an expanding nozzle. The nozzle provides controlled expansion of the motive steam to convert pressure in to velocity which creates a vacuum with in the body chamber to draw in and entrain gases or vapors. The motive steam and suction gas are then completely mixed and then passed through the diffuser or tail, where the gases velocity is converted in to sufficient pressure to meet the predetermined discharge pressure.
Steam ejectors are used in a variety of applications in the process, food, steel and petrochemical industries. Typical duties involve filtration, distillation, absorption, mixing, vacuum packaging, freeze drying, dehydrating and degassing. Ejectors will handle both condensable and none condensable gas loads as well as small amounts of solids or liquids.
Staging of ejectors is required for more economical operation when the required absolute vacuum level is reduced. Two-stage steam ejectors generally cover vacuum ranges between 3mm HgA to 130mm HgA, however depending up on actual operating conditions a Single Stage may be more economical if at the upper limit of the operational envelope, or a Three Stage Ejector System if conditions are at the lower end.
Two-stage steam ejectors consist of a primary High Vacuum (HV) Ejector and a secondary Low Vacuum (LV) Ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure.
Two-stage steam ejectors is Condensing type. Condensers can be used as inter-condensers, and after-condensers, all of which help to reduce the gas load being passed on to the next ejector stage. This helps to reduce motive steam consumption and also allows smaller ejectors to be used with in the system.
In condensing steam turbine systems, Two-stage steam ejectors has function to extract air and other non-condensing gases from the sealed condenser, and in such way to maintain vacuum which corresponds to ratio of cooling water quantity, cooling water temperature and cooling surface.
- No Moving Parts – Steam ejectors are exceedingly simple and reliable. There are no moving parts to wear or break in a basic ejector.
- Low cost – Units are small in relation to the work they do and cost is correspondingly low.
- Versatile – Various piping arrangements permit adapting to environmental conditions.
- Easy to Install – Relatively light in weight, ejectors are easy to install, and require no foundations. Even multi stage units are readily adaptable to existing conditions.
- Corrosion and erosion resistant – Because they can be made of practically any workable material, or coated with corrosion-resistant materials, ejectors can be made highly resistant erosion and corrosion.
- High vacuum performance – Ejectors can handle air or other gases at suction pressures as low as 3 microns HgA.
- Condenser air removal.
- Vacuum packaging.
- Decarbonating brewery water.
- Water treating by degasifying.
- Used in degassing molten steel.
- Perfume concentration.
- Sea water deaeration and desalination.
- Crude tower distillation.
- Geothermal gas extraction.
- Chemical processing.
Materials of Construction
- For jet ejectors: cast iron, steel, stainless steel, Low alloy steels
- For condensers: steel, stainless steel, bronze or other special alloys.
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