Calculation of expansion of hot material cooling in tank

[v8landy]

Hi

I need some urgent help on the following.

We have a 18m3 7bar/full vac rated vessel that has a spring PRV of set pressure 125 psi and 175 l/min rated discharge.

What I need advice on is calculating required discharge rate i.e. is our PRV correct.

Material is introduced into the vessel via vacuum. The main problem comes from the two streams we have, one is vac'ed material that is ambient temperature, the other is vac'ed at ~150 deg c.

I need to check who the pressure will alter as the material cools and can the PRV cope?

I guess worste case senerio would be, when tank is nearly full of ambeint temp material i.e 15m3, we then vac in 3m3 of 150deg c material.

Vac turned off and materials mix and cool and expand.

Thanks

 

[gr2vessels]

More details required;- what material would expand in the tank/vessel that much, to set off the PRV's 125 psi, starting from vacuum or 0 psig?? Obviously, you are handling an existing system, hence this is not an academic question from you;- but it is still unclear, what are you discharging at 125 psi from the 100% full vessel, gas, liquid, polymer foam, fluid butter garlic flavoured?
Please advise..
cheers,
gr2vessels

 

[v8landy]

Hi

I wish it was garlic flavoured butter!

We reprocess and distill all wastes containing solvents, from paints printing inks, vinaly products etc etc.

So receive drums,IBC tankers of MIXED materials.

Stream A is drums vaced into Vessel X. at ambient temp.
Stream B is still base residue x distialtion of mixed material @ ~150 deg C.

You could say that everything below toluene should have been removed.

Above streams (one at a time) are vacced into vessel X, by appying vacuum to vessel X.

We normaly then pressurise vessel x with nitrogen to trasfer to another part of the plant.

But the question is what and when could we lift the PRV.

One thought would be is we have vessel X full nearly full of material at ambient, and then we filled it to 100% with 150 deg c material.

Vacuum is then removed, but we do not trasfer it straight away.

Material cools and expands, will prv blow?

Vessel is ~18m3 3m x 3.5m.

I have already done some calcs, to verify that the current area of the PRV is more than twice required, as per API520

see below cals

Relief Area Calculation to API RP520 (2000) Appendix D


Input Data

Case Toluene

Relief Device Set Pressure 125 psi g
Overpressure permitted 10 %
Proportion of vessel filled 100 %

Vapour MW 92
? 1.2
Temperature 100 oC
Heat input rate 50 kW
Latent heat 351 kJ/kg
Liquid density 867 kg/m3

Two Phase Discharge Rate

Derived Parameters

Mass flow rate of vapour 512.8 kg/hr
?v 31.13 kg/m3
Volumetric discharge rate 16.5 m3/hr
Relieving pressure, Po 1,049,655 N/m2

?o 836.19 kg/m3
vo 0.00120 m3/kg
vvo 0.03213 m3/kg
xo 0.00000
cpl 2647.7 J/kg K
vvlo 0.03097 m3/kg

Omega Value and Critical Mass Flux

Two phase mass flow for relief 13,777 kg/hr
? 6.8 Eqn. D.2
?c 0.91 Figure D.1
GC 10374.58 kg/m2 s


Relief Area

Relief area 0.0003689 m2
0.57 in2

Bursting disc diameter 22 mm
0.85 in