vacuum problem 2

[santoshdada]

Dear Friends
i am a maintenance engineer in our plant i faced a vacuum problem in our polymerisation we are using a root pump befor liquid ring pump to boost the vapour medium now problem is that suddnly vacuum changed from 0.00 torr to 13 torr now what may be proabable reason. we took following action

1)complete line cleanig for any chocking

2)leakage checked there is no lekage

after doing all above activity we did not found any improvement

then we change root pump(twin lobe type) both side lube oil(fresh oil P3) as we found temp is high(80 Deg) on both side after that we again started the system then we found 0.00 torr again, now i am not able to uderstand how it happend

we tested the lube oil sample(used one) on our laboratry we found 10% mixing of glycol vapour(pumping medium) on the lub oil

now i fully confused how vacuum break from 0.0 torr to 10.0 torr

is thr any link with lube oil ??

or there are some othe reason?

mixing of glycol indicate there may be lekage from sealing but now how it is working well

plz help me any one from ths field

thx in advance

 

[Latexman]

What do you mean by "both side" in "we change root pump(twin lobe type) both side lube oil"? Did you do anything to the liquid ring pump? What liquid does the liquid ring pump use?

Good luck,
Latexman

 

[crjones]

The fact that you have glycol in the lube seems to say that you had a seal failure. Changing out the booster backs this up.

Between the process seal and the lubricant seal is a vent area. Look at how this area is cleared may give you a clue as to the reason for the jump.

 

[Compositepro]

What vapor is being pumped? You could easily be getting water or other vapor condensing in the piping after the roots pump and draining back into the pump, where it will vaporize again and keep the pressure above 13 torr. Whether this happens or not depends a lot on how much non-condensible gas flows through the pump along with any condensible vapor.

Bleeding some air into the suction of the roots pump may solve your problem. Or place a drain leg in the piping immediately after the pump. That would then require manual draining, or another pump. Or heat trace the piping.

 

[santoshdada]

1)both side oil mean root pump drive and non drive end oil
2)glycol is the medium in liquid ring pump
dear Compositepro (Chemical) how air enjectin will improve vacuum,at what pressure and flow ??
plz note we are already using glycol sprey at the suction of root pump

 

[Compositepro]

When you pump vapors like water or even glycol they will condense when they are compressed. They will condense in the vacuum pump and exit piping. Air flow though a vacuum pump will carry some of these vapors out of the pump. You could think of it as drying air.

You need to understand the concept of vapor pressure and know the vapor presure versus temperature curves for the vapors you are pumping. For example, the vapor pressure of water at 20C is 17.5 torr. As long as liquid water is present it will boil and the pressure will not go lower unil it is gone or it's temperature drops due to boiling. The water vapor that is removed by the pump will condense back into a liquid when the pressure is increased above 17.5 torr. It will also be heated by the compression so it won't actually condense until it cools in the exit piping.

 

[Latexman]

And if you have a contaminate, like water in your EG or EG in your oil, you may need to worry about partial pressures.

Good luck,
Latexman