| Staging of Ejectors |
| In an Ejector system, where temperature and pressure permit, a number of ejector stages are used in series with condensers between the stages to condense the load and motive fluids. Since Ejectors are a fixed-capacity devices, according to the process load and pressure control, various parallel-series arrangements of Ejectors are used.
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There are mainly two types of ejector systems on basis of their stages : |
| Single Stage Ejector Systems |
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Multi Stage Ejector Systems |
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Single Stage Ejector Systems : |
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Vacuum approximately up to 60 TORR is easily produced from just a few meters of water draft using Single Stage Vacuum Systems. These are the simplest systems, used with or without pre-condensers.
Thermo compressors (recompression boosters) are single-stage Ejectors which are designed to convert low pressure steam to a high pressure and temperature. Thermocompressors are generally used to increase the efficiency of heaters, dryers or evaporators. |
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Multi Stage Ejector Systems : |
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Multi Stage Ejector Systems have same field of operation and working as the single stage ejector systems. Multi stage ejector systems are recommended for application where single stage ejector systems can not give reasonably low vacuum suction pressure.
Pre condenser, intermediate condenser and after condenser may be used as per the requirement of the system to lower the steam load. According to their working range multi stage ejector system divided in mainly three types which are as following. |
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- Multi stage, non condensing ejector system
- Multi stage condensing ejector system
- Multiple-stage non-condensing Ejectors followed by multiple-stage condensing ejectors
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| • Multi stage, non condensing ejector systems : |
Multi-stage, non-condensing ejectors are used when an application requires a pressure lower than what the single-stage ejectors could develop. These types of ejectors require more motive steam than an individual single-stage ejector so that they could handle the load of the preceding stages. In this type of ejector system discharge of first stage ejector is directly connected with suction of second stage ejector without providing any condenser.
These systems are used when we have to achieve low absolute pressures (10-50 TORR).These systems have an advantage of low purchase and installation cost. |
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| • Multi stage, condensing ejector systems : |
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In a Multi stage condensing ejector system, inter-condensers are connected between the ejector stages to condense steam and vapour from preceding stages, and cooling air and non-condensible vapour to reduce the load to succeeding stages.These systems are designed for low absolute pressures (5 to 100 TORR).
Inter-condensers can be of two types which can be arranged at either barometric height or the ground level:
a) Direct Contact Condensers
b) Shell and Tube type Condensers
If a multi-stage-condensing ejector has a large amount of condensable vapours to handle, a booster condenser is connected after a condenser and a two-stage ejector to handle the amount of condensable vapour to compress it at the atmospheric pressure.
If a system produces smaller condensable loads, a single inter-condenser is used to condense the vapours after the ejectors.
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| • Multiple stage non condensing ejectors followed by multiple stage condensing ejectors: |
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This type of system employs as many as six stages of ejectors to achieve maximum vacuum. It is used when extremely low absolute pressure is to be achieved. (.001 to 5 TORR)
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