Vaccum in the reactor during stirring - which vacuum pump

[rob5377]

Hello,
I have to propose vacuum pump to keep vacuum in the vessel during stirring to degas the batch. Vacuum in the vessel 0.7 0.8 bar. Capacity of vessel is very small - 115 litres. The vessel + installation will be installed on movable skid. I proposed dry running vacuum pump for that application as it does not need water for liquid ring, but to be honest I am not sure which is better: dry running or liquid ring vacuum pump. I do not even know which is better due to investment costs. Can you give me some advices please?
Robert

 

[rob5377]

Hello,
Correct me if I am wrong.
I assumed that 20% of the vessel will be filled with the vapour. It gives 114 litres x 0.2 =~23 litres. I assumed that I will need 5 minutes to pump vapour out, it gives ca. 5 litres/min. It seems that I may use rather laboratory size vacuum pump than process pump.
I found diaphragm vacuum pump performance data:
Delivery 11.5 l/min ; Vacuum 290 mbar abs. According performance curve at 780 mbara vacuum it has capacity 5 l/min. Am I correct?

 

[Compositepro]

Duoseal pumps are probably the most common and best for your application. The manual will answer more questions than I can.

http://www.welchvacuum.com/pdfs/manual/67-0777R2.9 (DUOSEAL).pdf

There is a lot of physics involved in vacuum degassing. If you mix at one tenth atmospheric pressure, you are not degassing, you are mixing air into the liquid at one tenth of an atmosphere. For your purpose that might be good enough.

 

[quark]

Use the equation Q = (V/t)ln(P0/P1) to calculate the required pump flowrate. P0 is initial vessel pressure and P1 is required vessel pressure (both in absolute terms).

So, your pump capacity would be (23/5)ln(1.013/0.213) = 7.17L/min. Add leakage into the system and evaporation from the batch (incase of volatiles). These are to be added to the flowrate.

However, this is a very small flowrate and diaphragm pump should be OK.