7 replies to this topic

[mosayef]

dear all,

 

i have questions regarding radiation and dispersion of flare stack that i need to establish near from community...

 

a. if i need to establish a flare stack in onshore near from community for small natural gas facilities, what is the maximum radiation intensity ? i can't find it in API RP 521, is it ok if i set 500 BTU/hr/ft2 as the input for the maximum radiation intensity ? i need to estimate the radius distance from flare stack to community. please point me out if there is a code regulates about this issue

 

b. i dont really understand about the dispersion effect of disposal gas from flare stack, i cant find it in API RP 521. what is the purpose of dispersion study of natural gas ? and why is it needed ? because of Carbon Monoxide gas from incomplete combustion or related with flammability limit ?

 

could you please share the references about this ? i need to know the limitation, so i can estimate the flare stack distance from the community, i have tried to search but it was not good enough, something related with gaussian method, LFL, UFL i guess.

 

thank you very much

Edited by mosayef, 30 May 2015 - 06:40 PM.

[Zauberberg]

First of all, it is not true that guidelines on acceptable radiation intensity are not available in API 521. They are located in the paragraph 5.7 (in the 2014 edition) and related Appendices. You will find there all the information you need with regards to your first question. Try Google also - some earlier revisions might be available on the internet.

 

As for the second question, dispersion study is required for evaluation of hazards when relief occurs without combustion (e.g. in flame lift-off conditions or ignition system failure) and the relief gas gets simply vented from the flare stack. In those cases, it is required to evaluate concentrations of flammable and toxic components around the source of emission, and see if any explosive or toxic clouds can be formed. As you can imagine, possible consequences can be extreme if explosive clouds reach areas where they could ignite and if toxic clouds enter the areas occupied by people.

[mosayef]

First of all, it is not true that guidelines on acceptable radiation intensity are not available in API 521. They are located in the paragraph 5.7 (in the 2014 edition) and related Appendices. You will find there all the information you need with regards to your first question. Try Google also - some earlier revisions might be available on the internet.

 

As for the second question, dispersion study is required for evaluation of hazards when relief occurs without combustion (e.g. in flame lift-off conditions or ignition system failure) and the relief gas gets simply vented from the flare stack. In those cases, it is required to evaluate concentrations of flammable and toxic components around the source of emission, and see if any explosive or toxic clouds can be formed. As you can imagine, possible consequences can be extreme if explosive clouds reach areas where they could ignite and if toxic clouds enter the areas occupied by people.

 

Zauberberg,

 

thank you very much for your respond

 

a.

could you please tell me the name of paragraph 5.7 ? unfortunately i dont have API 521 2104 edition. do you mean the table "exposure time to reach the pain treshold" (Table 8 API 521 1997) and "recommended design thermal radiation for personel" (Table 9 API 521 1997)? could you please tell me the radiation intensity limit for flaring near public area ?

 

if yes, it states in those tables that if the radiation intensity is 500 BTU/hr.ft2, the pain threshold is around 60 second  , and if the maximum limit is at 500 BTU/hr/ft2, personel with appropriate clothing can be continuously exposed. it seems contraditory. because the person cant be continuously exposed if the pain threshold is 60s. maybe for design near public area, i will use  200 BTU/hr/ft2

 

 

b.

thanks for your explanation

could you please tell me the codes that regulate this dispersion issue ? so i can find the limitations

 

thanks

[breizh]

Moyasef ,

Consider the document attached .

Good luck.

Breizh

[Zauberberg]

1- Table 8 from Pierre's attachment shows the relevant radiation levels. There are no reasons to reduce the target radiation arbitrarily. Typical values are 1.58 kW/m² at the plant fence, and this means that any person standing on the other side of the fence during the maximum flare load will not experience any injuries.

 

2- This depends on what are the components of the flare gas. For flammable components, you want to see their distribution at ground level and possibility to get ignited. For toxic components, you would be looking at concentrations at ground level which can cause injuries or death to human population. Each flammable component has defined LEL and UEL numbers, and each toxic component has defined maximum allowable concentrations in air as a function of exposure time. You can find this information in any MSDS or encyclopedia.

[mosayef]

thanks all

Edited by mosayef, 02 June 2015 - 04:00 AM.

[breizh]

Hi ,
Additional info.

Hope this helps

Breizh

Edited by breizh, 04 June 2015 - 07:13 PM.

[mosayef]

thanks breizh