Parallel steam ejectors

[hanon]

May two parallel steam ejectors work properly in a Vacuum unit? The system consists of three pairs of 2 parallels ejector. Each stage is compounded by a common pipe which is divided into two ejectors. The discharges of both are again mixed and go to the condenser of this stage. It can not be ran with both ejector at the same time because it looses vacuum. One is designed for 2/3 of the total load and the other for 1/3 of the load. May it work?. Are there any hydraulic limitation? What could be the cause of this problem? Any suggestion or technical reference are welcome.

Thanks, hanon

 

[ash9144]

Parallel ejectors should work properly if properly designed and installed. Do they both work individually?

You may want to look at the downstream configuration, such as discharge pipe too small causing back pressure or condenser undersized and overloaded. Also check that you can get enough steam to run both simultaneously.

 

[0707]

In principle there is nothing wrong with well design parallel steam ejectors. If something is not working properly check the following:

If the flanges of the ejectors are equal maybe they were wrongly mounted after a maintenance operation it has already happen!

Check the threads of the ejector nozzles for steam leaks through the threaded connection. Remove deposits from the suction chamber and make sure it is not cracked, rusted, or corroded. Shine a small light through the diffuser to make sure it is completely free from scale and is not pitted, grooved, or cut. After all stages and intercondensers have been cleaned, the throat diameters or the nozzles and diffusers should be measured as accurately as possible. Compare these with the original dimensions of the throat diameters, supplied by the manufacturer, to determine wear.
If either diameter is larger than the original equipment specifications, calculate both original and present throat areas, and determine the percentage increase in areas. If the percentage increase is greater than 7%, the nozzle or diffuser will have to be replaced before satisfactory operation can be expected.

luis marques

 

[katmar]

If each of the ejectors work according to their design specs when operated individually, but they do not work when operated in parallel then I would suspect either the inter-stage condensers or the steam supply. Did the two ejectors ever work correctly together, or has the problem been there from the beginning?

The condensers could be fouled, or it could be a cooling water capacity problem. If the condenser cannot cope with the combined load it will raise the back pressure on the ejector and you will not get the performance.

Similarly, if the steam supply is not adequate to supply the two ejectors simultaneously they will not operate according to spec. It could be a fundamental piping error, or just a dirty strainer. A pressure gauge at the steam nozzle will quickly let you know if this is the cause.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[hanon]

These eyetors are located in the top part of a vacuum unit. The load is basically constant independently of using one or both in parallel. The parallel eyector was installed in a revamp of the unit but it has never got to work toghether with the high capacity one. The condensers are working properly and it is supposed to be designed to work with both ejector. Some trial have been unsuccesful and a huge loose in the tower vacuum have been reached, so for the moment we are not planning to do more test if we don´t konw the exact cause of the problem. Is there any kind of test to overview the source of the trouble?.

Hanon