13 replies to this topic

[f2386]

Dear Sirs,

 

This is my first post in this forum. I highly appreciate if you can help to clarify my questions regarding the kerosene storage tank as follow:

 

In my refinery, there is a tank to store kerosene rundown from CDU/KTU with flash point min     + 38^oC. The kerosene is then used to blend diesel.

 

The kerosene tank has an internal floating roof, but no circulation vents or inerting system. The maximum operating temperature is approximately 38^oC (see attached file). But the tank temperature can be lowered maximum 35^oC by reducing kerosene rundown temperature.

 

So

 

1. Is that safe to store the kerosene with lower flash point but still higher than the tank operating temperature in that tank? And what is safe margin of kerosene flash point above tank operating temperature that should be maintained because I suspect that the temperature of space between floating and fix roof would be higher than the tank operating temperature?

 

2. If the kerosene flash point is reduced lower than the tank operating temperature, does the tank need any modifications such creating circulation vents or inerting? Could you help to calculate the circulation vents or Nitrogen requirement for blanketing in those case.

 

Thanks,

Attached Files

•  8474L-051-PDS-TK-5114-013-C.pdf   275.38KB   101 downloads
•  Multicases Report_Pi_Data_2013.xlsx   78.37KB   54 downloads

[AlertO]

hi f2386

 

Flash point is used to classify the liquid type for tank design (See NFPA 30). Each fluid class has different requirements for tank design. You have to ensure that your different products are the same fluid class. For the temperature, if the fluid temperature is not higher than the design temperature, it will be OK. Only venting devices you may need to check the rate between your existing design and new operations.

 

inert blanketing is required for many reasons e.g. product degration, tank corrosion and other hazards, but for floating type, the product is not directly contacted to the atm so the blanketing is not required.

 

Hope this may help you

[f2386]

Hi AlertO,

 

Thank you for your reply. But in my refinery other internal floating roof tanks with low flash point have inerting system for safety as attached document.

 

Regards,

Attached Files

•  Inerting tank.pdf   91.17KB   91 downloads

[AlertO]

Thanks f2386 for giving me more information. if my understanding is correct, the blanketing at your storage aims to ensure that the concentration of product vapor in tank space is below the LEL. (wait other to confirm this again). Anyway, the fire protection device which is refered to flash point is normally flame arrestor.

[fallah]

f2386,

 

For FP<38 C, as in the case you attached to post no. 3, the free vent on the fixed roof should be terminated by a FA. If it not to be terminated by a FA, the space between floating roof and fixed roof of an IFR should be blanketed by an inert gas, as for mentioned case has been performed.

Edited by fallah, 18 April 2014 - 12:25 AM.

[f2386]

Dear fallah,

 

Thanks for your consultation, but my No 3 post is just an illustration to show that in my refinery case this tank has flash point lower than operating temperature then it is inerted for safety.

 

Can you review my original questions in post No1 and give your advices.

 

Thanks,

[fallah]

f2386,

 

In the case attached to your first post, the stored fluid is class II as per NFPA 30 and has a FP>40 C i.e. higher than relevant operating temperature (40 C). Then, as can be seen in relevant data sheet, FA and blanketing with an inert gas hadn't been used...

[f2386]

Hi fallah,

 

Many thanks for your comments, but that is existing design and we are now exploring the opportunity to lower the kerosene flash point to maximize diesel production and the questions arise as I mentioned in post No 1.

 

Regards,

[fallah]

Many thanks for your comments, but that is existing design and we are now exploring the opportunity to lower the kerosene flash point to maximize diesel production and the questions arise as I mentioned in post No 1.

 

 

f2386,

 

Then, my post no.5 might be the reply to your query for new conditions.

[f2386]

Dear Fallah,

 

Thanks for the advices.

 

But in my opinion, the flame arrester is used to prevent the passage of the flame through the vents. However, is it safe to install only flame arrestors for eliminating the inside tank fire/explosion hazards without applying other safety methods such as inerting or crearting circulation vents in case the tank is storing a flammable liquid and operating temperature is higher than liquid flash point then space between internal floating roof and fixed roof can create an explosive mixture.

 

Regards,

[oscarsender]

Flash point is a physical property of a chemical. You cannot change it unless you change the chemical or its composition.

[f2386]

Dear oscarsender,

 

Thank for your reply on the query.

 

Kerosene runs down from distillation column therefore its flash point depends on the kero/naph cut-point. The lighter kero/naph cut-point the lower kerosene flash point. That's why a safety concern has arisen.

 

Regards,

[f2386]

Dear all,

 

No one further can share your experience/advice on my query?

 

Any experience or advice is highly appreciated.

 

Thanks,

[narendrasony]

f2386,

 

I think you are  left with no other option : Use either circulation vents or inert (N2/ Ar / CO2) blankating. There is  option of using Argon also in place of N2. Experienced members may throw more light on this option. I think circulation vents will be much easier, but there are concern over its efficacy compared to inerting.

 

http://www.eng-tips.....cfm?qid=320379

 

In my view, open vent (not circulation vent) flame arrestor will also be required with circulation vents.

 

Regards

Narendra