Latent Heat For Multi-component Hydrocarbon Liquid

[knapee]

Dear Sir/Madam

Could any pro kindly explain to me the rigorous Hysys method to calculate the latent heat of vaporization of mixture posted on the following webiste.

http://webwormcpt.blogspot.com/2008/06/determine-latent-heat-and-maximum.html

The confusing step is following adapted from that website

STEP 2a : Determine liquid volume (Vl0) and vapor volume (Vv0) which will be defined by the physical vessel dimension and piping volume. Calculate liquid volume (Vl0) and vapor volume (Vv0) consider liquid level in the vessel is at maximum liquid level (L0) and piping vapor & liquid volume.

STEP 2b : Adjust the inventory (vapor mass and liquid mass) in the vessel until you achieve the vapor
volume (Vv0) and liquid volume (Vl0).

HYSYS : Copy stream 2 to stream 4. Copy stream 3 to stream 5. Mix stream 4 & 5 into stream 6. ADJUST stream 4 Mass Flow to obtain Stream 6 Vapor Actual Volumetric Flow to Vv0. ADJUST stream 5 Mass Flow to obtain Stream 6 Liquid Actual Volumetric Flow to Vl0.

STEP 3 : Bring the the system to Relieving pressure (Pr0=121% of Pset). By maintaining system volume at V0 (=Vv0+Vl0). The system is at relieving condition. The temperature at this point is Tr0.

HYSYS : Define a new stream 7 with a BALANCE unit (mole balance only). Set Stream 7 pressure at Pr0. ADJUST stream 7 temperature until Overall Actual Volumetric Flow to V0 (=Vv0+Vl0).

STEP 4 : Next step is further input heat (Q1) to achieve 1-2 deg C above Tr0 but maintain pressure at Pr0. Normally the total volume (V1) at this point potentially higher than V0.

HYSYS : Flash stream 7 in VESSEL V-101 into Vapor outlet, stream 6 and Liquid Outlet stream 11. Attach a heat stream (Q-100) into V-101. SET stream 8 temperature 1-2 degC above stream 7.



In Bechtel, the usual approach is to take the top tray liquid at relief pressure and estimate the enthalpy change required to flash increasing amount of vapor. If small amount water is present, the latent heat will drop off rapidly.

Could any expert kindly explain to me this calculation step of Latent Heat for multicomponent liquid mixture more physical intuitively ? Or provide me a solved example Aspen Plus file (.apw) or PRO \II for this multi-component mixture?


Greatly appreciated any positive response.

Thanks you so much.

Regards,

 

[CMA010]

This rigorous Hysys method you describe seems rather cumbersome and complicated. If you have Aspen or PROII, why not make a flash or heating/cooling curve of your mixture?

 

[rense]

the basic procedure for simulating the discharging conditions under external fire has been discussed in several papers, I have a copy of a presentation at Chemputer's conference 1994 from Prode, if you are able to find a copy of Prode Calculator (the programmable process calculator discussed in the paper) it should include the code which you can then easily convert.
For multicomponent mixtures the procedure is iterative, the direct integration method permits to evaluate the properties of discharging fluid and flud in the vessel at the different conditions as composition changes.
You can put all in Excel and use a process library or a simulator for thermodynamics.
Not difficult but from your questioning I would guess you prefer something ready to use ;-))