Tank Venting - Connection To Exhaust Air System

Dear all,

I'm currently working on the design of an atmospheric storage tank that as per client's request will be venting to a closed exhaust air system. One of the designs that was proposed is shown in the attached sketch: A pipe (2 inches diameter) is connected directly to the exhaust air system and ends roughly at the same height as the top edge of the nozzle (4 inches diameter) of the tank. A small "roof" (a 6x2 1/2 reducer) is put over this connection point in order to prevent any dirt from falling into the tank.

The problem I see is that during pump-out (0.2 ft³/s) a vacuum is created inside the tank, and as air is continuously flowing through the vent to the exhaust air system as well I don't really know how to calculate the vacuum. I don't think the regular pressure drop calculation methods used for line sizing are applicable here, so the only reliable calculation method that I can think of is CFD.

Does anyone else have an idea how to calculate this?

Kind regards

Philipp

Hello,

I've never seen such device. Could you please show us photo?

Hello,

 

I've never seen such device. Could you please show us photo?

I'm afraid not, it's just an idea that the client came up with, they don't actually have any of those in their existing plant, and it's not a device that can be bought anywhere (I think), it would simply be cobbled together from pipe fittings during construction. The closest thing you could compare it to is a draft hood that is used in the exhaust line of a gas fired water heater. I suppose we will just have to convince our client that connecting a tank with such a vacuum rating to an exhaust system with a lower pressure without a venting device that is properly designed and constructed is a really bad idea.

I was thinking a Pressure Vacuum Relief Valve (PVRV) would be good for this. Size the PVRV based on the maximum possible outflow from the tank.

A Restriction Orifice (RO) at the outlet to the exhaust air system would be useful too. Restrict the max air flow going into that exhaust line.

I think the one in the picture below can be suitable. The pressure side connect to the exhaust air system. This should allow the PVRV to close back when the pressure goes too low, such as below -0.04psig. If somehow it does goes too low, the vacuum side will draw air from the atmosphere to prevent it going far below -0.04psig.

Edited by thorium90, 29 August 2019 - 09:37 PM.

Yes, a "pipe-away" pressure/vacuum vent would work nicely in this case

Hi,

The system described is similar to what is used in lab to collect fumes . Multiple "hoods" connected to an header .

BTW I used similar device over a manhole of a reactor to collect fume of methanol . Header was connected to a scrubber.

My experience

Breizh