PED Categorization for sulphur at 190 °C (fluid physical state?)

[FPPE]

Hi,

I have a doubt regarding PED categorization for sulphur with a design temperature equal to 190 °C.
Below the data for categorization:

Pdes = 1.08 bar
Tdes = 190 °C
Fluid hazard group = 1

Fluid physical state = G (?)

For PED:

(i) gases, liquefied gases, gases dissolved under pressure, vapours and also those liquids whose vapour pressure at the maximum allowable temperature is greater than 0,5 bar above normal atmospheric pressure (1 013 mbar) within the following limits:
— for fluids in Group 1 with a volume greater than 1 L and a product of PS and V greater than 25 bar·L, or with a pressure PS greater than 200 bar (Annex II, table 1).
(ii) liquids having a vapour pressure at the maximum allowable temperature of not more than 0,5 bar above normal atmospheric pressure (1 013 mbar) within the following limits:
— for fluids in Group 1 with a volume greater than 1 L and a product of PS and V greater than 200 bar·L, or with a pressure PS greater than 500 bar (Annex II, table 3).

How much is the vapour pressure of sulphur according to PED? If we consider it as gas, we have PED category III, if we consider it as liquid we have PED category I.

Thank you in advance

 

[XL83NL]

The PED doesnt define the vapour pressure of your substance. You should look that up and use that as you me staring point.

What’s the vapour of your substance at the design temperature? That will determine if it’s considered a gas or liquid.

Do you have access to a chemical substances database to look up such data?

Huub
- You never get what you expect, you only get what you inspect.

 

[georgeverghese]

Perry Chem Engg Handbook 7th edn, table 2-7 on page 2-60 list vapor pressure of liquid sulphur to be 1mmHg abs at 184degC, and 5mmHg abs at 223degC. Melting point 118degC at atmospheric pressure. So this would be the vapor pressure of γ - sulphur (otherwise commonly called plastic sulphur) which is the allotrope of liquid sulphur which exists at temperatures above 150degC.
1013mbar = 760mmHg

 

[FPPE]

XL83NL, no, I don't have access to database.
Thank you georgeverghese, so for PED sulphur at 190 °C is liquid, correct?

 

[georgeverghese]

It sure is at 190degC - melting point 118degC at 1atm abs

 

[FPPE]

Sorry, I'm a bit confused. From what design temperature is sulphur considered gaseous for PED?

 

[XL83NL]

This is what the PED says. Stick to this rule and you should be good. Do it otherwise and you might get questions

gases, liquefied gases, gases dissolved under pressure, vapours and also those liquids whose vapour pressure at the maximum allowable temperature is greater than 0,5 bar above normal atmospheric pressure (1 013 mbar) within the following limits

Huub
- You never get what you expect, you only get what you inspect.

 

[georgeverghese]

At 190degC, plastic sulfur is part liquid / part gas. As an analogy, it is like water at 50degC, say. There is some vapor above the liquid, and its vapor pressure is low. Liquid water turns into all gas / steam at above 100degC when its vapor pressure exceeds 101kPa abs.

If you can keep oxygen out of the system, then at atmospheric pressure, molten liquid sulfur boils at about 450degC.

The cutoff between (i) and (ii) in this PED is at a vapor pressure of 1013 + (0.5*1000) = 1513mbar abs.

At 184 degC, liquid sulfur vapor pressure is = (1/760) * 1013 = 1.3mbar abs << 1513 mbar abs, so this falls under clause (ii) classification. At 190degC, it will still be within the clause (ii) limit.

 

[FPPE]

Thank you very much georgeverghese!
Fully understood, have a nice day!

 

[MortenA]

@ FPPE,

You can find many PED category calculator on the net e.g. this:

https://www.hpivs.ie/ce-certification-2/ped/pressure-vessel-calculator

I would think that liquid sulphur is liquid group 1. If your pressure is in absolute bars then its not covered by PED

--- Best regards, Morten Andersen

 

[CuMo]

I assume you're categorising a vessel per the PED so if you set your vessel's design pressure (MAWP) and temperature to "184 degC, liquid sulfur vapor pressure is = (1/760) * 1013 = 1.3mbar abs" as per georgeverghese's comment above
I would probably agree.

But if you're designing your vessel for say 2 bar abs /some safety margin above operating conditions/ - then you're making the assumption that there will be vapour present at pressure higher than 1513 mbar abs and then clause (i) would apply (worst case).

So I'd double check the above if I were you.