3 replies to this topic

[ankur2061]

Dear Joe Wong,

I was going through your blog at:

http://webwormcpt.bl...nd-maximum.html

where you have explained the calculation of Latent Heat for multicomponent liquid mixture at relieving pressure using rigorous method in HYSYS. However, I am still not clear about the steps. Can you provide a solved example or provide a HYSYS file (.hsc) with solved example for a multi-component mixture.

If the .hsc file cannot be uploaded then upload with a diiffernt extension (say.txt) which I can change back to .hsc or you can send the .hsc file to my mail id:

ankur_2061@hotmail.com

Anticipating your positive response.

Thanks in advance.

Regards,
Ankur.

[ankur2061]

Dear All,

Has anyone developed an excel spreadsheet for calculating the latent heat of a multicomponent crude oil mixture at the relieving pressure for a fire case relief valve.

Appendix A.3 of API STD 521 gives a graph of vapor pressure and latent heat of vaporization of pure single-component paraffin hydrocarbon. Has anyone tried to regress this as an equation and developed as an excel calculation? I would like to approach this as a calculation which would not require to do any simulation.

If any forum member has any idea about such calculations, it would be great if he/she could share it.

Regards,
Ankur.

[serra]

Ankur,
the basic procedure for simulating the discharging conditions under external fire has been discussed in several papers, see for example the attached pdf from Prode, the use of a simulator (or , in this case, a process calculator) and rigorous thermodynamics permits to evaluate the properties of discharging fluid at the different conditions (as composition changes), as alternative you may define the values suggested in API for unknown fluids.
Unfortunately I have lost my copy of Prode Calculator which did include the complete procedure (to convert into a Excel file) and I can't attach the source code, however the details are discussed in the paper.

Attached Files

•  Chempute1994.pdf   51.53KB   416 downloads

Edited by serra, 30 January 2012 - 10:45 AM.

[knapee]

Dear Mr Ankur

I really appreciated the pro like you can bring this up.

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

http://webwormcpt.bl...nd-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,

Edited by knapee, 10 February 2012 - 09:54 PM.