Liquid ring Vac pump - water in the exhaust

[Boiler1]

Hi All,

I’ve got a set of liquid ring vacuum pumps operating on 24/7/365 basis with periodic duty/stand by rotations. There is a dedicated separator tank looped with each pump to maintain the water seal during operation. These separator tanks are vented through the common exhaust header with the fan. We recently noticed a large amount of seal water accumulated in the exhaust header.
Its unclear how did the seal water find its way from the separator tank into exhaust ?

The system is designed as follows:
The separator tank exhaust intake is at the top of the tank
The exhaust suction pressure is 4-5 “Water at the intake, whilst the top water level in the tank is 20 “Water below exhaust intake. The high water level is alarmed and the over flow pipe is in place to insure the max water level ( no alarms, no overflow detected)

As there was no way for the water in the tank to reach the exhaust intake – is it possible that pump starts/stops have been trickle splashing water into the exhaust that eventually accumulated in the duct?
Could evaporation ( + condensation in the exhaust ) be the cause ? The water temperature is relatively low – around 55 degF.
Has anybody got similar experiences?

Regards

 

[LittleInch]

Got a drawing / section view?

Is there a demister pad on the exhaust?
what is the residence time of the air in the separator tanks?
External air temperature?

we can't see your piping design so is there a chance of small water accumulation over time?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

One of your separators has issues (either baffle or pad is damaged), or temps are too high, or one of your pumps is passing way more water than it should.
First figure out which unit it is.
The check the pump performance.
Then fully inspect the separator.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TiCl4]

For issues like this, we need some kind of drawing to evaluate a few of the possible options.

Is the vapor/water mixture coming into the tank above the normal liquid level? If so, what is the top outlet nozzle vent velocity of each separator? Do you have a demister pad?

High velocities at the outlet nozzle could be causing entrainment. Do a quick check of your max vapor velocity with the Souders Brown eqn (usually in the ~3 m/s range for atmospheric separators, as far as I remember). Is it possible the vapor load has increased, invalidating previous design?

 

[pierreick]

Hi,
What is the benefit of this fan? A schematic with altimetry will be useful to support. Never seen fan on the discharge line (vent) of a separator of liquid ring pumps.
Make sure the size of the separator is adequate.
Pierre

 

[georgeverghese]

Assuming all operating parameters are within normal operating ranges, the separator demister pad may be fouled/partially blocked or corroded.
Small amounts of seal water entrainment into the separator vapor exit is inevitable even with clean well operating demister. Since you have a common suction fan on separator exit, this fan suction header must not be pocketed and must free drain back into one or more of these separators, else condensed liquids will pool at the low points in the suction header piping pockets. Intermittent liquid slugs from these pockets into the fan can cause mechanical damage to the bearings etc, and also result in erratic suction header pressure.

 

[Boiler1]

Hi All,

Apologies for delayed response. We have borescopped the separators on all the pumps and it turns out one of the pumps is circulating significantly more water when in operation. I mean - much more! The other pumps are working as expected with seldom droplets being pulled into exhaust.
At least we know the likely source of the water.
There's actually no de-misting pad on any of the separators which doesn't help either.
Not sure what would cause one pump to circulate more water

 

[LittleInch]

Water flow through the pump is controllable an should be set to be sufficient to maintain temperature within limits.

Has someone just opened up the water valve?

Time to read the pump manual....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
Consider reading this document from SIHI about liquid ring vacuum pump, in particular section 5.
Good Luck
Pierre