8 replies to this topic

[mgeorgiadis]

Dear Forum members.

I am not fully understanding concepts of converting tank venting requirements from one pressure/temperature state to another. Moreover, my chemical engineering understanding is poor so please explain in simple terms.

It is my understanding that you perform the calculations for in and out breathing and arrive at a flow rate that is required and then size a vent to achieve no more pressure resistance than what the tank is designed for. But the API-2000 standard cautions that this flow rate for venting is at international standard or normal conditions and must be converted for pressurized tanks.

Can you please explain consequences of this if for example the tank is designed for a small pressure above atmospheric conditions and also the product inside is at a slightly higher temperature than atmospheric. Will the vent need to be sized to handle more or less flow and why? Can you give example to make it clear perhaps?

Thanks in advance

MG

 

extract from API-2000 6th Ed. 2009

The out-breathing requirements in this International  Standard are for air at normal or standard conditions. The user shall correct the out-breathing requirements to normal or standard conditions for heated (insulated) and/or pressurized tanks at pressures greater than 6,9 kPa (1 psi).

[AlertO]

hi

the venting in API 2000 use the volume balance theory. we can not use the flow calculated in the code for pressued storage because that gas flow doesn't represent the actual rate we need.

For example the you may be more clear, if we required the out breathing rate of 1 m3/h at a pressure, we can not provide only 1 Nm3/h because the volume of gas will be reduced at that pressure.

Hope this may help you

[breizh]

Probably good to read , even not updated.

 

Breizh

[mgeorgiadis]

Alerto & Breizh

Both thanks for the answer. I wil read the attachment and come back with further questions if required.

Regards

Michael

[mgeorgiadis]

Ok, I read the paper.  Thank you for sharing it. I found it interesting, but I'm still bursting with questions:

 

I shoud repeat that my chemistry is not my strong point.

 

What I know:

The filling volume rate

The temperature of the filling product

 

Then I calculated an "out-breathing" requirement assuming the air in the tank to be displaced through a vent is at the same temperature as the tank contents. I don't have a pressure in mind yet since my understanding the vent size creates the pressure. For a small vent, for example, pressure will build up if the vent is undersized for the filling rate. For a very large vent (over sized), there is no restriction so there is no pressure. But at this stage the vent size is not determined only I have the requirement for out-breathing.

 

I must size the vent so not to produce a pressure higher than what tank is capable of withstanding. I don't know why is the conversion of this volume of out-breathing required to some standard temperature and pressure?

 

Please explain further.

Michael

[mgeorgiadis]

Please chaps share your ideas with me.

[AlertO]

hi

your question is why the API indicates the breath-in & out rate in the unit of Nm3/h, right?

For my opinion, it 's easy to use because we can ignore some a little deviation of pressure and temperature (but not over the code limit) and we also can find the rate in the code directly which is better than you need to calculate the rate at the actual condition in term of the time saving as well as the error possibility. In addition, volume of gas in Normal / standard condition is also well known by vendor.

[mgeorgiadis]

Hi Alerto

Thanks for the reply. I understand it can be ignored. I see it often is ignored. I want to understand the issue which I don't understand. Maybe your can clarify your reply with some basics because it is still not clear to me

[breizh]

mgeorgiadis,

Consider the search engine (top right) in this forum , key words API 2000 .This should help .

Same with the post attached : http://www.cheresour...lculation-help/

Breizh

Edited by breizh, 03 February 2014 - 08:38 AM.