vacuum knock out system

[lotus7312]

We have water ring vacuum pump. When we pull vacuum from reactor, organic fumes will come out of the reactor and enter into the vacuum pump water line, which cause contamination issues in my waste water system. We tried to keep the water into a circulation tank without any cooling, but the water became hot very soon. We are trying to use a oil seal vacuum pump, so that the organic fumes will be trapped into the oil. And the organic solvent will be drained once their level is high. Will that affect the vacuum pump performance? Is there any better solution?

 

[pmureiko]

You could use this organic chemical as the liquid ring fluid instead of oil. Eventually you will have to dispose of the oil. This way you can recycle the material that is pulled out of the reactor. The limitation is the vapor pressure of the chemical determines the deepest vaccuum that can be pulled by the liquid ring pump.

A variation is to use another compatible chemical in your plant as the liquid ring fluid if a deeper vaccuum is needed. Compatible means physically and by your plant process.

Liquid disposal & contamination is the biggest drawback of liquid ring pumps. That is why there is such a big effort to use dry vacuum pumps from Busch and Edwards.

 

[quark]

There are chances that the vapors may contaminate the oil. And you will have pump jamming problems because of oil dilution.

Why can't you condense the vapors prior to vacuum pump? Or you can use cooling towers to cool and recirculate the water, provided you don't have any problems with organic vapors polluting air.

Pmureiko has given the best option of dry vacuum pumps but they are very costly.

Regards,

 

[lotus7312]

Pmureiko and quark,
Thank you for your suggestion.
We do have a condenser before the vacuum pump. But there is still some vapors coming out of the reactor.
I will look at the dry vacuum pumps.
Regards

 

[BRT549]

My 2 cents . . . how about the circulating tank with a heat exchanger on the return line to the liquid ring vacuum pump. Cool it as low as you need to maintain the desired vacuum level. Dump the tank when you need to.

Would this organic material get gummy once it condenses? Wonder if it would pass through the dry vacuum pump option and become a problem further downstream?

 

[lotus7312]

We thought about the option of the circulation tank with cooler. But the problem is that once the water is mixed with those organic materials, we have to dispose it as the hazadous waste, which is quite costly.

I looked at the dry vacuum pump. There is a model with built-in downstream cooler, which is able to cool the solvent trapped. I think that might be the best option(I am sure it is expensive too).

 

[chemtiger]

Their advice are all reasonable. But i think it is lack of operation experience. I think the best choice is the combination of mechanical pump and organic ring vacuum pump. The best advantage is that it can avoid blocking and absorbing the waste. I think you can understand, the medium of the ring should be the compound in your process, so that it can be recycled back. I have designed two units with the inlet pressure 1 mmHg.

 

[SASC]

Chemtiger,

I think you are on target.........if there is a trend toward dry vacuum pumps out there, it is a trend to disaster, short and long term. Dry vacuum will not rplace liquid ring....maintenance will have the last word on that one for sure! If vapors are scooting by into the vacuum pump, look toward pouring on more condenser flow. In the end, the avenue of using the seal medium the same as the process compound is a full fledged end to the end answer.

Regards,
SASC

 

[bchoate]

All the posts to this thread have added information for a possible solution. I have a couple of items that may or may not be of any use. Please consider that I do not know what pressure you are using the vacuum system for. Since it a liquid ring pump on water, I'll assume it may be in the neighborhood of 50 - 100 mm Hg.
1) if the precondenser still has vapours coming out of it,
a mechanical blower could be used ahead of the liquid ring
to increase the pressure and improve the operation of the partial condenser. Blowers are more typically used when the working pressure is below 5 mm Hg. MD, Aerzens, and BOC Edwards blowers are sturdy machines.
2) If you are going to consider a 'dry' pump there are two primary designs available. There is a'scroll' or screw pump from Busch or a 'hook & claw' design from Graham or from Nash-Elmo (BOC-Edwards pump). The Nash-Elmo pump is far more economical than the Graham. Dry pumps can tolerate some liquid.
The last question that I might have is about the design of your vacuum precondenser. If that exchanger was designed using B-Jac or HTRI, then it is not likely an optimum design. Either Nash-ELmo or Graham can design the exchanger using inhouse programs for vacuum condensers.
Bill Choate