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Assalam o alaikum,
Friends,
Can i collect naphtha directly from de-propanizer bottom and store it in a storage tank with out keeping it pressurized?? Since the light ends are v.low in amount and can be flared via PSV.
Is it practised any where world wide to keep naphtha unpressurized and unflashed and directly stored??? Appreciate your field experience and prompt response



Thanks and Regards,
Jady

[kkala]

I have seen naphtha from floating roof (FR) tanks feeding a desulphurization unit in a local refinery ; after treatment and cooling, it returned to another FR tank.
Generally FR tanks can accept petroleum products of vapor pressure lower than 13 psia (11 psia according to others) at max storage temperature (usually being max ambient temperature). See http://www.cheresour...s-vapour-losses. Naphtha can be stored in FR tanks, on the condition that it fulfills this condition.
Not being familiar with depropanizer operation, "light ends are v.low in amount and can be flared via PSV" and "keep naphtha unpressurized and unflashed and directly stored" may indicate conditions of vapor pressure higher than 13 psia, under which atmospheric storage is not safe, even in floating roof tanks. This may be due to high naphtha temperature; or even to gases contained in it according to a non equilibrium status, needing "degassing" before storage.
I have not seen liquids called naphtha stored anywhere else but in FR tanks in local refineries. Nevetheless naphtha has a lot of grades (sg~0.60 - 0.75, per wikipedia); vapor pressures higher than 13 psia at max ambient temperature cannot be excluded for some grades of light naphtha.
This is indicated by Fig. 8-7 of Nelson's "Petroleum Refinery Engineering". At 100 oF (38 oC) vapor pressure of 13.8 psia can be found in the boundary between gasolines (sg~0.71-0.77, per wikipedia) and natural gasolines (typical sg=0.67, per wikipedia). Light naphthas (sg~0.60-0.66) could have vapor pressure higher than 13 psi at 100 oF, not being suitable for FR tank storage.