3 replies to this topic

[Kevinyun]

Hi everyone

 

I am currently working on a project and I am stuck on vent sizing. 

The parameters are:

 

Flow out of tank is 250kg/min via a pump

The tanks capacity is 600L

The outlet pipe size has yet to be determined but will either be 1,2 or 3 inches

The vent will be open to atmosphere

The material of the tank is stainless steel

 

How would I go about and calculate the vent size? Is that enough information?

 

API 2000 seems to not be helpful as the content in the tank is water and not petroleum

 

Vent sizing was never covered when I studied Chemical Engineering and I am in desperate need of some help.

 

Regards

 

Kevin

[fallah]

Kevin,

 

I think the 3rd post in below link would response to your query:

 

http://www.cheresour...nk-vent-sizing/

[mansari]

API-2000 provides guidelines for in-breathing and out-breathing, with reference to boiling and flash point specification (table 1A and 1B), where outbreathing requirement for more volatile liquids is almost 2 m3/h for every m3/h liquid coming in. This requirement is only 50% for less volatile liquids.

 

Though water is a non volatile liquid, if we apply 1:2 ratio, it will be very safe. Therefore for 250 kg/min or 15 m3/h, you may size your vent for a maximum outflow of 30 m3/h of air. Since pressure drop in the vent line should not be more than the tank design pressure (as also mentioned by Fallah in his earlier post), you have an available limit of 2.5 psig if your water tank is designed on API-650. Please check the data sheet of your tank.

 

Now you can calculate the vent size at the flow rate of 30 m3/h of air taking a vent pipe length of 1 m which is open to atmosphere. Quick calculations reveal that 1 inch size would be adequate as it gives a velocity of 17 m/s (55 ft/s) with a pressure drop of 0.185 bar per 100 m of straight pipe ( 0.8 psi/100 ft) or only 0.00185 bar for a 1 m pipe spool. You can revalidate these quick, "back of the envelope" calculations by using appropriate software

 

Hope this should help you

[shafi83]

Hi,

We manufacture basket filters. Many customers specifies VTA against vent size on the DS. Can I apply same sizing principle of the tanks? If yes, is below is the correct method

 

Going through earlier discussion in this forum, vent size can be done as follows.

1. Find total inbreathing (Qin=Pump outflow+ thermal shrinkage) and total out breathing (Qout= Pump in flow+ thermal expansion) flow using method given in Understanding Atmospheric Storage Tanks "by Siddhartha Mukherjee,Chemical Engineering, April 2006. 
2. Find sonic velocity(Vs= Sqrt(kgRT/MW)
3. Min. Area of the vent pipe (Amin.)= (Qin/Qout-which ever is higher) divided by Vs.
4. Also I found that pressure drop in the vent pipe should not be more than pressure rating of the vessel.
5. Going through Norsok standard P-001, 5th Edition, I found that pressure drop in atmospheric vent line should be <0.005bar.

 

Thank you