5 replies to this topic

[clarence]

Hi, I came across this problem in Himmelblau's book prescribed for my material and energy balance course.

Question:
100 mol/minof a binary mixture A and B are separated in a 2-stage (serial) process. In the first stage, the liquid and vapour flow rates exiting from the stage are 50 mol/min each. The liquid stream is passed through a second separator that operates at the same temperature as the first stage, adn the respective exit streams of liquid and vapour from the second stage are each 25 mol/min. The temperature for each stage is the same and at that temperature, the vapour pressures for A and B are 10kPa and 100kPa respectively.

Treating the liquids and vapours as ideal, determine:
(a) The compositions of all the streams in teh process.
( the pressure in each stage.

Thanks in advance to anyone who can point me to a start point, as I have been scratching my head and pulling my hair over this question.

Cheers!

[abhi_agrawa]

Clarence,
I believe that if your read Himmelblau carefully, you will see that the procedure for doing the isothermal flash calculations is there. However, I am attaching the relevant equations in the pdf file. You need to solve those equations to get what you are looking for. However, I suggest you go though Himmelblau for a better understaning of the Flash calculation, specially for multi-component mixtures.

-abhishek

Attached Files

•  LaTeX1.pdf   28.21KB   86 downloads

[clarence]

Hi, i have tried solving the problem using an equation solver, but it returns an error message stating that the equations are inconsistent - which means that the problem is underspecified or overspecified in some way. I've been trying for a couple of hours, and I've checked my workings which are ok, and in line with what i've learnt in class and from himmelblau's book.

would appreciate any additional help on the same problem.

cheers.

[process equipment]

Hi,

You can also try " Chemical engineering thermodynamics" of Smith ,van Ness and try to solve with mathCad..

Cheers

[abhi_agrawa]

Clarence,
For a binary mixture, you do not need to solve very complex equation. The above set of equations can be reduced to the equations attached with this. Have a look. Now you jave 3 simple equations and 3 variables. Your system is neither underspecified nor overspecified. Before askeing the software to solve equation for you, it is a good habit to do a degree of freedom analysis and ascertain whether the system is correctly specified. Also, it is good to have a look at your equations, before giving then to the solver, and try to simplify the system.
Hope this helps,
-abhishek

Attached Files

•  LaTeX2.pdf   33.19KB   49 downloads

[chemsep05]

What Equation Solver did you use?

I would suggest using MathCad, or you can try Chemsep, you can get a free version online that should be able to handle these flash calculations