Liquid ring pump sizing

[jeap]

Hi All!

I have designed a system for deareating 170 m3/h of river water from 13 to 0.7 ppm of oxygen. This system consists of a deoxygenation tower (Operating pressure 70 mbara) and a liquid ring pump. I've found that it is necessary to extract abt 6 Kg/h of gas/vapor from the water stream to reach the desired oxygen ppm level.

I sized the liquid ring pump and it shall extract abt of 100 m3/h of attenuated gas. I assume an oversizing factor of 1.5 thus the power of the pump results in abt 6 hp.

Should I consider any grater overdesign factor to overcome air entrance into the system (vg. leak or bubbles coming from the river pumping station)?


My question comes from the fact that the pump I've sized seems very small to me.

I appreciate any comments/experiences.

 

[MikeHalloran]

How much time will it take to pump down the tower from startup conditions?


Mike Halloran
Pembroke Pines, FL, USA

 

[quark]

When you derease the DO from 13ppm to 0.7ppm, you may have to extract about 2kgs out of 170m[sup]3[/sup]/hr of water. So, you already have a buffer of about 4kgs/hr. The density of air is 1.2kg/m[sup]3[/sup] approx. and you have a standard flowrate of 6/1.2 = 5m[sup]3[/sup]/hr. The ACFM will be (1/0.07)*5 = 72[sup]3[/sup]/hr. You already have 38.8% overcapacity, so that shouldn't be a problem.

For leakages, you can consider 0.002lb/ft (of seal length) if the seal is very tight (for ex. welded joints and flanged joints), 0.0067lb/ft if the seal condition is good and 0.0134lb/ft if the seal condition is poor.

6HP for a 100[sup]3[/sup]/hr capacity and 70mBara pump seems to be OK for me and there is no big gap there.

However, you should take advice from the manufacturer regarding the minimum flowrate of noncondensable gases required to avoid cavitation (this depends upon pump). If you assume 4kgs/hr to be water vapor, you have only 33% of noncondensable gases. If this is too tight a flow then bleeding is required and you should add this flowrate to your total flowrate.

Good luck,

 

[Montemayor]

Jeap:

Go to:

http://www.cheresources.com/invision/index.php?showforum=2

and do a search feature for "vacuum" - (without the quotes!) and you will find a thread that has downloadable files that allow you to calculate the air leaks, the pump down capacity required, and other information to design your vacuum system.

 

[jeap]

Dear all,

I forgot to mention that I considered a water temperature of 5ºC as the worst condition for the system.

Well, I downloaded Mr. Montemayor's spreadsheet, it is really useful. For the system configuration I obtained an "air seepage" of 1.5 Kg/h which is within the overdesign I assumed for the pump.

The time to pump down the system is abt 7 minutes which seems ok.

Regarding to the minimun noncondensible flow rate for the pump, mentioned by quark,I was considered a 1" ball valve in the suction of the pump to manually adjust the vacuum pressure under certain conditions. It is not a sophisticated system but, I think it will work. Although, I'm waiting for the supplier's proposal.

I really thank you all!

 

[JoeChem]

Greetings,

I am interested in the vacuum calculation spreadsheet developed by Montemayor. I looked throught the threads in the discussion Forum and could not find any downloadable files...just a bunch of e-mail addresses for Montemayor to forward the sheet. Where did you find it?

JoeChem