6 replies to this topic

[chemic]

Hi,

Can the ejectors (steam or water)be used for pumping water from vacuum tanks that is being maintained at 0.2 bar(a)?

elaborating the above question:

I need to pump water from Hotwell tank to the storage tank (maintained at atmospheric pressure), The Hotwell tank is maintained at a pressure of 0.2 bar(a).

Can I use ejectors(using steam or liquid as motive fluid), (by having a suction lift) for pumping water from hotwell to storage tank?

Do the NPSH calculations apply for these Ejector systems?

thanks,

Edited by chemic, 27 August 2009 - 01:35 PM.

[daryon]

I'm not sure if you can use ejectors for this, i think you probably can. But can't you use centrifugal pump with low NPSH requirements?

On a project I've just finshed working on we bought a steam turbine with a vacuum condenser. The condenser operates at 0.21 bar (abs), and has a hotwell where the steam condensate collects. The condensate was pumped from the hotwell back to the boiler feed tank. The pumps were discharging at 6 barg and the NPSH required 1.17m, which was acheieved by elevating the condenser. Pump minimum flow was around 8 m³/h and max flow 39 m³/h.

You should check and see if you can get a pump suitable for your application, it will save you having to design an ejector system.

[ankur2061]

Hi,

Can the ejectors (steam or water)be used for pumping water from vacuum tanks that is being maintained at 0.2 bar(a)?

elaborating the above question:

I need to pump water from Hotwell tank to the storage tank (maintained at atmospheric pressure), The Hotwell tank is maintained at a pressure of 0.2 bar(a).

Can I use ejectors(using steam or liquid as motive fluid), (by having a suction lift) for pumping water from hotwell to storage tank?

Do the NPSH calculations apply for these Ejector systems?

thanks,

Chemic,

I haven't heard of any application of ejectors for pumping liquids. Thermocompression ejectors are definitely used for pumping/transferring gas but not liquids. However, ejector design and application is a very specialized field and the knowhow is limited to a few manufacturers. Why don't you contact one of the manufacturers and find out about the suitability to your application. Some of the renowned manufacturers are:

'Graham Mfg Co ', 'Croll-Reynolds', GeA Jet Pumps' & 'JetVac'.

Hope this helps.

Regards,
Ankur.

[chemic]

Ankur,

Just for your info,

We do have water and steam jet ejectors, used as syphon where the suction pipe is dipped, to pump liquids from the tank usually maintained at atmospheric pressure.

But in my case the tank is maintained at a pressure of 0.2 bar(a), also the existing vertical centrifugal pumps frequently cavitate due to insufficient head and I don't have any provisions for further increasing head.

The alternative may be either to have a lower NPSHr pumps or to install a ejector system (HP Water) by providing a suitable suction lift.
The question here is how to arrive at a suitable suction lift for these tanks maintained at vacuum.

regards,
chemic

[djack77494]

The question here is how to arrive at a suitable suction lift for these tanks maintained at vacuum.

It will be hard to achieve suction LIFT when starting with vacuum conditions. I think you will need to locate whatever device you use, ejectors or pumps, below the liquid level in your hotwell. NPSH calcs will tell you if you are in danger of flashing going into the pumping device, and should apply to ejectors the same as pumps. In any case, you should contact one of the vendors of this equipment to get their input. They should know the answers to these questions.

[hollerg]

Just what NPSHa do you have availible?
Could the issue be vortexing letting gas/vapor into the pump suction?

Of course pump vendors will proposal with slower, larger casing pumps (lower NPSHr), oversized inlet lines, perhaps an inducer or even a slow multi stage pump. If an inducer is not an option, It often is cheaper to install a low head pump ahead of your current pump, boosting the liquid into that pump's suction.

If you have a large pressure drop in a control valve or your impeller is significantly less than a full sized impeller, I would investigate switching to a VFD, and operate the existing pump at a lower speed. The pump vendor ought to be able to predict if that reduction in impeller speed (and NPSHr) will mitigate the problem.

One last thought is to raise the liquid inventory, if you have excess elevation in your barametric pipe lines.

Edited by hollerg, 10 September 2009 - 11:02 PM.

[Dineshchem]

Hi,

Can the ejectors (steam or water)be used for pumping water from vacuum tanks that is being maintained at 0.2 bar(a)?

elaborating the above question:

I need to pump water from Hotwell tank to the storage tank (maintained at atmospheric pressure), The Hotwell tank is maintained at a pressure of 0.2 bar(a).

Can I use ejectors(using steam or liquid as motive fluid), (by having a suction lift) for pumping water from hotwell to storage tank?

Do the NPSH calculations apply for these Ejector systems?

thanks,

Yes definetely NPSH will play the role but it would be not feasible to use ejector for lifting the water from 0.2 bar .