Vacuum pump application

[Vertigo123]

Dear all,

My first post here, what a great forum! I would like to ask the advice of the fellow engineers here about a problem.

I am currently examining the possibility of using a liquid ring vacuum pump for extraction of VOC laden air through a carbon bed before discharge. I understand that this is not really the real application of a vacuum pump but I am not given the budget to purchase a new extraction fan etc.

The problem I face now is that the spare pump that I have is too large, even with a suction pressure of ca. 800 mbara, my flowrate (from pump curve) is still around 140m³/h. This would cause my gas flow to reach sonic velocity (1 inch line). Is there any way I could reduce this flowrate to say, 40 m³/h but yet retain a certain degree of negative pressure at the suction side? All inputs are greatly appreciated!

Thanks!

 

[d23]

Vertigo123

Is speed control of your back-up pump a possibility?

 

[Vertigo123]

Hi d23,

Thanks for the response, I think I made a mistake of saying spare pump. Actually I meant that the pump that I am only given a spare from some other process

I only have the pump characteristics for 2 pump speeds but I will try to do some calculations to predict the flowrate at lower rpms.

Thanks!

 

[ccfowler]

Since you are apparently stuck with only available equipment, you have little choice but creativity. Liquid ring vacuum pumps can be considered to be positive displacement devices with volumetric flow (at the suction) being proportional to shaft speed. As long as the pump is operated within its speed range capabilities, you should be able to reduce the flow rate fairly readily. The temperature of the circulating water will control the level of vacuum that the pump can effectively draw.

Get as much information as possible about the specific pump to determine the range of your options.

Is the water for the liquid ring to be once through and wasted to a treatment facility, or is it to be recirculated through a cooling heat exchanger? If it is to be recirculated, be sure to have plenty of heat dissipation capacity.

 

[Vertigo123]

ccfowler,

Thanks for the response! I will be using the affinity laws to try and get the required flowrate by varying shaft speed. As for the circulating liquid, I will be using a once-through system, for there are no heat exchangers available to me too. Will be doing some calculations to get some idea of how much make up water is required...

Cheers!