Ethanol Tank Venting 1

[EthanolBlending83]

Hi, I'm building 3 ethanol storage tanks, and need some advice for venting design.
The tanks were design by API 650 without internal floating roof.
The designer required a PVR valve to keep the tank isolated from water vapor in air. The site is very humid we reach normally 80 - 90% RH trouhg the year (tropical site).
I'm the contractor and I need to run warranties for the installation and I'm concerned about the fuel long term quality due to water vapor inbreathing.
API RP 1626 suggest to use flame arrestors and dessicant media on the inbreathing pipe to keep dew point as low as possible.

Am I on the right track?

Thank you!

EthanolBlending83

 

[gr2vessels]

Flame arrestor is mandatory, if you want to keep the tank safe. The inbreath can be controlled via your suggestion of a larger dessiccant package, sized to minimize the pressure drop and potentially creating vacuum. Alternativelly, an even better solution is the N2 blanketting, but a bit costly.

 

[IFRs]

Why not full contact floating roofs?

 

[jamesbanda]

I guess they are madatory for your application.. but please see this tread..

Treat FA's with care and maintain properly..Some comments

> are you sure putting an FA in a relief path (upstream) is acceptable.. ?

> this seems incorrect to me.. i've only seen them on the discharge of reliefs but that is in pressure service.. not low pressure tanks..

> And, in the location drawn to maintain the FA you need to maintain the tank.. do you want to do this often?

http://www.eng-tips.com/viewthread.cfm?qid=306451

 

[MJCronin]

Related comments...

http://www.ast-forum.com/ast_forum_tree.asp?master=8701

 

[mfelzien]

EthanolBlending83

Check to see what if any affect the water vapor would have on this volume of ethanol due to in-breathing. Use a liquid seal material that simply isolates the ethanol from atmosphere. So a layer of inert liquid/solid that floats on the ethanol and to slow the evaporation and prevent dangerous explosion limits.

A polyethylene layer that acts as physical boundary between the EtOH and H2O as in a floating roof type is a solution. This was done with several cryogenic propane tanks I worked with. To prevent evaporation your vents could have seal pots on them and you could design then to act as flame arrestors, and saving the client money.

What about the vapor recovery system available? VRSs' are common in the petroleum industry.
You might consider a dry source of gas that could eliminate water vapor contact during breathing. Determine the LEL/UEL and see if that gas could act as your blanket gas. Assuring the mixture above your tanks are within safe LEL/UELs.

 

[EthanolBlending83]

Thank you everybody for your great advice.
In my case the customer rejected the internal floating roof in the beginning of the project. And his design team turned to P/V valve. Gas blanketing is out of budget so for us is not an option.

The information about flame arresters supplied is very helpful thank you. The choice of a liquid barrier is very interesting I am going to do some research to evaluate the cost. In general terms seems very good.
I'll let you know of the final results.