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[Yogesh jain]

This is query for Cone roof API 650 tank (6 m Ht. X 8m dia., Nominal 301 m3 approx.) with Fuel gas (C1=85% + other) as Blanketing gas:

The tank (Crude oil emulsion) is maintained at 80°C. Its vapor space shall have following composition @ 1 kPag (10 mbarg),

Vapour Phase
Mole Fractions
H2O 0.437527702400190
Nitrogen 0.000000000000000
CO2 2.08153672175579e-002
H2S 4.20646954845664e-003
Methane 0.522034254496957
Ethane 7.11671150710042e-003
Propane 3.33527213189730e-003
i-Butane 0.000000000000000
C6* 4.62893953128418e-003

Mainly methane and saturated water vapour & other HC gases.

Is it required to heat the blanket gas also up to 80°C.

Is this the practice to consider blanket gas volume requirement for shrinkage due to phase change also? (API 2000 thermal inbreathing probably not considering it (phase change), please correct my understanding)

The threat with cold (~ 10 - 15°C) blanket gas I felt is condensation of water vapor which may cause excessive blanket gas requirement further, to cover the shrinkage due to condensation.

If any one (Refinery person handling heavy stuff) have idea about such situation and can suggest the method of calculation if not using heated gas?

[Zauberberg]

If you are interested in shrinkage of blanket gas when undergoing temperature change from 10 degC to 80 degC (that is quite high storage temperature), using Charles' Law is more than sufficient as we are in the low pressure region.

V1/T1 = V2/T2, which gives approximately 25% volume shrinkage.

I don't see what kind of phase change you can have in the tank vapor space. The components you have listed can be treated as non-condensables at storage pressure.