10 replies to this topic

[Jen1982]

Hello everybody,
please I need advice.

I have to calculate or at least estimate electricity consumption of liquid ring pump.

Values which I know are:

Gas capacity: 1521,5 m3/h
Gas suction pressure: -0,573 bar g
(The hole stream properties are avaible in simulation)

Could you give me any recommendation how to get this figure?

Is there analogy with rotary pump? I ve found tables for some range of gas flow rate , but unfortunately my capacity is out of this range.

Next point is the sealing liquid flow rate, is it possible to calculate it (in this case water) or this is the value, which gives a vendor?

Also could you give any information about efficiency of liquid ring pump?

Thank you very much for any hint you can give me.

[ankur2061]

jen1982,

To understand more about vacuum systems in general and liquid ring vacuum pumps (LRVPs)`in particular it is recommended that you study, Chapter 6, Ejectors and Mechanical Vacuum Systems, Applied Process Design, Volume 1 by Ernest`E Ludwig. This will help in strengthening your fundamentals on vacuum systems and LRVPs.

Additionally, have a look at the links below for more details and some calculations on LRVPs:

http://www.ieindia.o...6/techa5cm6.pdf

http://www.travaini....ance Manual.pdf

Hope this helps.

Regards,
Ankur.

[Art Montemayor]

Jen:

What you mean by a “liquid ring pump” I presume to be the conventional machine as I describe in the attached Word document. If that is the case, then:

For the sake of engineering logic and sanity, let’s get some basics understood up front:

• A pump pumps liquid fluids;
• A compressor compresses gases and vapor fluids.

A liquid ring “pump” is NOT A PUMP. It is a rotating, positive displacement gas or vapor compressor that is used to transport gases or vapors or to compress them. In the process of transporting the gases or vapors, it can act as a vacuum “pump” (which is a gross misnomer) and hence the popular nom de plume. Therefore, while it is typically used as a vacuum device, it can also be used as a gas compressor. The function of a liquid ring “pump” is similar to that of a rotary vane “pump” - the difference being that the vanes of the former are an integral part of the rotor and churn a rotating ring of liquid to form the compression chamber seal. This is an inherently low friction machine, with the rotor being the only moving part. Sliding friction is limited to the shaft seals. Liquid ring pumps are typically powered by an induction motor. There is no metal-to-metal contact in the operating components of the machine, so the mechanical design is a very attractive and maintenance-free one.

Therefore, the normal, conventional calculations as made for a positive-displacement compressor should also hold for an LRP (liquid ring pump). However, as you can see by my description of the machine, this is a difficult and complex configuration and therefore, the displacement (which is a variable in the horsepower equation) is not easy to calculate. The displacement is normally known only to the manufacturer. Therefore, what one does in this case is to go directly to the manufacturer of your LRP and get the electrical consumption directly from them.

A true, rotary (centrifugal) pump is certainly NOT analogous with an LRP. Simply study the mechanical design and operational features of both machines and you will quickly find out why.

You normally do not calculate the sealing liquid makeup flow rate. This, again, is normally given by the manufacturer and depends on the application.

The efficiency of the LRP is another item that is obtained directly from the manufacturer.

Attached Files

•  Liquid Ring Pumps.doc   67.5KB   171 downloads

[breizh]

Hi Jen 1982 ,

Attached a paper to support your query .

Hope this helps.
Breizh

[Jen1982]

Hi all,
thank you very much for giving me such a good documents and basic information about this equipment. It helped a lot.

Now I have idea how it works and what are the fundamentals.

Have a nice day.

[jitendraprocess]

Dear sir,

There is no attached paper, so please guide regarding this.

Thanks & Regards

[breizh]

Hi Jiten ,
hope this helps you.
Breizh

[jitendraprocess]

Dear sir,

sorry for late reply.
thank you very much.

[kkala]

Having read this interesting topic, following notes might be of some interest, taken from a water ring pump, having operated in a phosphoric acid evaporation unit of Fertilizers (~1978).
1. Check vacuum required, it might be much lower than reported -0.573 barg = 0.44 bara = 330 mm Hg a. In said evaporation unit it was about 30 mm Hg a. See also http://en.wikipedia.org/wiki/Liquid_ring_pump.
2. Vacuum cannot be lower than the vapor pressure of sealant water, corresponding to its operating temperature. In mentioned unit it was slightly higher, apparently due to upstream air ingression at a rate a bit higher than estimated.
3. Sealant was potable water having passed from activated carbon for chlorine removal. Not having understood why, I assume that intermittent chlorination into potable water had peaks (but to affect vapor pressure?). Anyway, in case of a new vacuum pump, ask required specification of sealant water from supplier.

[mohagheghfard]

Hi,
Can somebody advise how much contamination of H2S or mercaptane components can be removed from a stream gas which is compressed by a liquid ring compressor?
Rgds,

[kkala]

Hi, Can somebody advise how much contamination of H2S or mercaptane components can be removed from a stream gas which is compressed by a liquid ring compressor? Rgds,

Since no answer has been received so far, I dare make a quantitative wild guess. Quite a little of H2S / mercaptane will be retained, if there is no water condensation; a higher percentage will, if there is water condensation. You have mentioned that the gas is compressed, so condensation is possible especially in case of downstream cooling.
Weak evidence for the above makes a fluoride balance, based on measurements (1977) in the mentioned (post No 9) phosphoric acid evaporation unit, operating under vacuum and taking air to ambient through a water ring pump. Big majority of fluorides in gas (HF, SiF4), probably > 95%, was retained in a water spray tower upstream of pump along with condensed water vapor. Fluorides in the water sealant out were comparatively quite little, fluorides in the air out even less.
We were also aware that condensing water vapor in the off gases from phosphoric acid reactor (phosphate rock+H2SO4, off gases 80 oC initially) contributed to a reduction of the off gas fluoride content, probably by 35%.
Mentioned wild guess assumes similar behaviour between H2S / RSR and HF / SiF4 .

Edited by kkala, 15 August 2012 - 04:23 PM.