May 28, 2008

Shutdown Learning - Ejectors

An ejector, is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of any motive fluid to velocity energy which creates a

low pressure zone that draws in and entrains a suction fluid and then recompresses the mixed fluids by converting velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry.

The diagram below is a typical ejector. It consists of a motive fluid inlet nozzle and a converging-diverging outlet nozzle. Water, air, steam, or any other fluid at high pressure provides the motive force at the inlet

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So in this shutdown when we opened one of the ejectors, we made following observations. Typically in our complex most of the ejectors are used on main equipments for creating vacuum, thus they are normally steam ejectors pulling vacuum from reactor & finally condensing all the steam in downstream condensers.

So this picture shows some corrosion around the throat & nozzle however it seems to be within normal limits in steam service. The important part is that the tip of nozzle is not corroded and the location of nozzle in the downstream pipe is at required location so it seems to be working fine.

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Anonymous said...

I don't understand how you separate the motive fluid from the inlet fluid at the outlet.

For example: I want to use air as a motive fluid to move natural gas. But if they mix, it will become diluted or possibly explosive.

How is the motive fluid supplied (compressor?) and recycled?

Great blog. Thank you for publishing your work.

profmaster said...

Generally ejectors are used to create vacuum using steam as motive fluid. SO they do not require separation bcoz mostly water vapors are evacuated.

Even if you want to separate them you can But may not be economical. I will suggest to use dry pumps as mentioned in my other articles for the recovery of process fluid, bczo they discharge at ~ atmospheric pressure so by simple CW condensation you can recover it.

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