## Latent heat of vaporization

## Latent heat of vaporization

(OP)

Hello,

Is it possible to have latent heat of vaporization of Nitrogen at 1 atm and 25 deg.C, despite that nitrogen in vapor phase?

If the answer is no than why ASPEN, during simulation, shows latent heat of vaporization for Nitrogen.

Need help regarding in this case.

Many Thanks.

shiplu48

Is it possible to have latent heat of vaporization of Nitrogen at 1 atm and 25 deg.C, despite that nitrogen in vapor phase?

If the answer is no than why ASPEN, during simulation, shows latent heat of vaporization for Nitrogen.

Need help regarding in this case.

Many Thanks.

shiplu48

## RE: Latent heat of vaporization

Be sure the thermodynamic and physical property models are set up correctly.

Good luck,

Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

## RE: Latent heat of vaporization

,LatexmanI have Propylene Oxide and Nitrogen and other chemicals in vessel in overpressure case scenario. I have to size PSV for Fire Case (Propylene Oxide and Nitrogen will pass through PSV).

For that I have to determine Required Relieving Capacity by the equation w=q/Hv, where,

w = Required Relieving Capacity

q= heat absorption

Hv= latent heat of vaporization

Hv has to be determined at relieving condition (Relieving T and P). But both Propylene Oxide and Nitrogen are in vapor phase at Relieving condition.

Then how am I supposed to get Hv at vapor phase?

Any suggestion is highly appreciated.

Many Thanks.

shiplu48

## RE: Latent heat of vaporization

= = = = = = = = = = = = = = = = = = = =

P.E. Metallurgy, Plymouth Tube

## RE: Latent heat of vaporization

## RE: Latent heat of vaporization

,srfishAs per your suggestion, section 5 of the Engineering Data Book of the GPSA, I have given look at that section.

I didn't found any equation to calculate W(Required Capacity)without latent heat of vaporization. But it mentions that

"When no better information is available, a conservative minimum value of 50 Btu/lb is typically used".

Will it be appropriate to use 50 Btu/lb for latent heat of vaporization (for any vapor or liquid: specially polymers

that does not have data like latent heat of vaporization ) if no information could be achievable?

Many Thanks.

shiplu48

## RE: Latent heat of vaporization

Good luck,

Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

## RE: Latent heat of vaporization

The set pressure of the PSV 20 barg and relief T is 170 deg C.

PO will be vapor at relieving case.

The problem is that Latent Heat of vaporization have to be determined

at relieving condition. At relieving condition PO and N2 both are vapor.

Then how could we get latent heat of vaporization of vapor phase?!!

Many Thanks

## RE: Latent heat of vaporization

Fire below vessel vaporises the liquid in the reactor, pressurising the vessel. The heat of vaporisation is for the liquid, not the gas phase above it or the whole mixture.

If you've got enough vapour space for the differences in composition to be significant, you'll need to look at the equilibrium composition at relieving pressure to get the gas phase composition, use your sizing equation to determine the number of moles of vapour being generated (or volume), and displace the equivalent from the vapour space. If you really have to sharpen your pencil, this could even be done dynamically.

I can't vouch for how compliant this is with your code of choice and regulator.

Matt

## RE: Latent heat of vaporization

For fluid properties calculation of PSV, would the calculation be performed at the relieving pressure

(corresponding of the saturation temperature) regardless of the relieving temperature and fluid phase?

At section 3.3.2.1.4 of "Guidelines for Pressure Relief and Effluent Handling Systems", it has been

mentioned that all properties should be determined at maximum venting pressure.

Many Thanks.

shiplu48

## RE: Latent heat of vaporization

## RE: Latent heat of vaporization

## RE: Latent heat of vaporization

In reply to mbt22, the mentioned reference book recommend to use relieving pressure for determining all fluid properties.

## RE: Latent heat of vaporization

Talking through what happens inside the vessel to cause this relief case with a colleague may help, starting from a pool fire ignition underneath it at normal operating conditions.

Matt

## RE: Latent heat of vaporization

as said by others, vaporization (latent heat contribute) applies to liquid fractions,

for calculating temperatures inside a vessel protected by a PSV you can solve (in sequence) a series of flash operations (solving at each step heat and mass balance),

there are several posts discussing these aspects,

a software can help (many simulators include specific procedures),

for the initial step see (as example)

http://prodesoftwareapplications.blogspot.com/

## RE: Latent heat of vaporization

Yo came to know the answer in your 6th post.

If you do not have the latent heat of vaporisation input you can take the minimum value 50btu/lb or 27kcal/kg. You will get the maximum relief value. If your design capacity is more then its ok, but if you designed less capacity then it will be a problem. Don't worry do your calculation

Navneet (Process)