14 replies to this topic

[Ramkumar666]

Hi All,

 

I am searching for gooseneck vent sizing calculations. Following are some details of what I am working on. 

 

The tank  has an 6" gooseneck. I calculated the Inbreathing and outbreathing rates as per API 2000 

 

Inbreathing - 3450 SCFH

 

Outbreathing - 14590 SCFH

 

I want to find out if the 6" gooseneck is adequate to prevent the tank from exceeding its design pressure. This tank is Atmospheric.

 

I would appreciate your help. 

 

Thanks,

[proinwv]

A few comments:

 

1. Flow through a vent will produce losses. This means that the tank will operate at some pressure and vacuum.
2. Sizing can reduce the losses considerably, if the cost is acceptable.
3. The cost of adequate venting should be balanced against the value of human life/health, equipment loss or product loss should inadequate venting cause and accident.
4. Atmospheric tanks may have a pressure and vacuum limitation; those numbers, if available, should be determined.
5. Without (4) above, (1) becomes useless.
6. The calculations for vent losses are not difficult. Publications such as Crane describe them. Since you seem to be unsure of how to approach this there are consultants who would do so for you. You need to accept what is stated above and also have vent vapor properties available to properly calculate the flow losses. (www.ostand.com)

Paul

[Ramkumar666]

Thanks for your response Paul. 

[fallah]

Hi,

 

At first you should calculate sonic velocity of the air at the tank operating conditions by:

v_s =sqrt(kgRT)

Then minimum cross section area of the goose-neck vent line would be obtained by:

Area_min=Q(input/output flowrate)/v_s

The pressure drop in the goose-neck vent line must be lower than the pressure rating of the tank, otherwise size of vent pipe to be increased for compensation. This size increment should be repeated till balancing the pressure drop with tank pressure rating.

[Ramkumar666]

Hi Fallah,

 

Thanks.  Please correct me if I am wrong -

 

K- ratio of specific heat 

g - gravitational constant

R is the Gas Constant ( in my case the gas is air), 

T - temperature of the gas at inlet

[Art Montemayor]

Ramkumar666:

 

No one can tell you what the symbology you list represents.  These symbols can mean a lot of different things - it all depends on what specific equation you refer to and the identified symbols related to it.  No one in his right mind should use an equation or mathematical relationship without a complete, detailed identification of all the math symbols employed in said equation, as well as a full identification of all the units that should be employed in the same equation as they relate to any numerical constants employed.  To do so indicates that one doesn't know what one is doing.

 

Just to give you some examples of how wrong you can be, consider that the symbol "K" can mean the ratio of specific heats as well as a means to identify a resistance coefficient in pipe fittings - or perhaps it stands for the absolute temperature in degrees Kelvin?  The symbol "g" can mean a gauge reading for pressure, etc., etc. ....................etc.

 

I recommend you stop thinking and using general terms and start dealing with specific information and identifications.  Otherwise you open yourself up for generating errors and mistakes in engineering.  I offer this advice after over half a century in the business of engineering.

[Ramkumar666]

Hi Art,

 

Yes, you are right. I was referring to the equation for Sonic velocity Vs = =sqrt(kgRT). 

 

Thanks

[fallah]

 

Thanks.  Please correct me if I am wrong -

 

K- ratio of specific heat 

g - gravitational constant

R is the Gas Constant ( in my case the gas is air), 

T - temperature of the gas at inlet

 

Hi,

 

Correct...

Edited by fallah, 22 January 2019 - 12:32 AM.

[shan]

You have to have the tank max inlet flow rate, max outlet flow rate, tank volume, and temperature change rate to determine if your vent sizing is adequate for the worst case.

[Art Montemayor]

To determine the worst case scenario in a storage tank's pressure-vacuum venting, I agree with Shan.  You need

• the tank's maximum inlet flow rate (for the pressure case); and
• the tank's maximum outlet flow rate (for the vacuum case).

But you don't need the "temperature change rate".  What you need is to identify the maximum temperature existing during the two above cases.  The rate at which the temperature is changing doesn't enter the related equation.  The maximum flow rate does and what is to be taken into account is how high that flow gets - not at what rate.

[shan]

For a large capacity tank, you may not ignore the vapor expansion and contraction due of temperature change rates. 

 

For examples, in very short time a heavy summer thunderstorm will drop the tank temperature significantly or a hot product winter midnight introduction will raise the tank temperature notably.   

Edited by shan, 22 January 2019 - 03:06 PM.

[jaddy]

Hi I hope you have satisfied yourself with you inbreathing and outbreathing relief load. To outbreath 14590SCFH = 390 Nm3/h through a 6" goose neck of 0.5m length (assuming sched 40) you should be ok. 6" for your inbreathing load seems fine as well. 1 mbar dp give me a flow of 860 Nm3/h I did my calcs on a software that we use. You should check calcs at your end.

[jenniferscott]

What is meant by the pressure rating of the tank? If I get a pressure drop in my water storage tank vent of 0.7bar and then the design pressure of my tank is 10mbar would I be ok? Given the tank is at least at atmospheric pressure. 

[fallah]

What is meant by the pressure rating of the tank? If I get a pressure drop in my water storage tank vent of 0.7bar and then the design pressure of my tank is 10mbar would I be ok? Given the tank is at least at atmospheric pressure. 

 

Hi,

 

It's not ok at all...

The 0.7 bar pressure drop in the vent line will build up a pressure higher than 0.7 barg during tank venting which is much more higher than the tank design pressure...

[Chemitofreak]

What is meant by the pressure rating of the tank? If I get a pressure drop in my water storage tank vent of 0.7bar and then the design pressure of my tank is 10mbar would I be ok? Given the tank is at least at atmospheric pressure. 

 

What is the design code used for the tank.

 

If tank is designed as per API 650 then the design pressure should not be exceeded.

 

If it is designed as per API 620 then 10% over pressure can be allowed.

 

Regards,