Hello everyone. I wanted to ask a few questions related to different types of storage tanks used in refinery and nitrogen blanketing.
Part 1: Types of storage tanks
Many websites say that:
1) Fixed roof is for diesel, kerosene, residual fuel oil, etc.
2) External floating roof is for crude oil, gasoline, naptha, etc.
3) Internal floating roof is for aviation fuel, etc.
4) Bullets are for propylene, propane, butane, etc.
5) Underground tanks are for naptha, superior kerosene oil, motor spirit, etc.
On what basis is this decided that a certain product is to be stored in a certain type of tank? Are bullets used for propylene, propane, butane, LPG, etc because large volume of those products are obtained from cracker and they have to be maintained at high pressure because their vapor pressure is also high? Also, my reasoning is that floating roof is probably used for volatile material with high vapor pressure at ambient temperature because of which large volumes could breathe out through the breather valve if they were stored in fixed roof. Is that correct? (Also do we use breather valves in floating roof storage tanks?) And my last question is that on what basis do we decide whether to use internal floating roof or external floating roof?
Part 2: Nitrogen blanketing
I could not understand how nitrogen blanketing actually works (see image attached). Do we push the vapors of the liquid stored out to the atmosphere? Wouldn't that be hazardous? Or do we push the air out of the empty storage tank during startup and then when the liquid is pumped in we take nitrogen out via that control valve that vents to atmosphere? And why is a siphon breaker sometimes provided on vent to atmosphere lines and what exactly is a siphon breaker?
One more small question, why do we ground storage tanks? I know it's to prevent the liquid stored from catching fire if flammable and exploding but where is the static electricity coming from and where does it get accumulated?
Sorry for my beginner level questions and thank you in advance.
Image link: https://cdn1.imggmi....fe6427-full.png
Edited by traineeprocessengg, 14 March 2019 - 12:03 PM.