Excel library for process calc's including distillation

[rense]

thank you Carlo,
which is the formulation used for extended correlations in Prode Properties?

[carlo.stenali]

rense,
the general form of a equation of state (Soave-Redlich-Kwong or Peng-Robinson) is

P = RT/(V-b) - a/(V^2+ubV+wb^2)

(see The Properties of Gases and Liquids by Reid, Prausnitz, Poling)

in Prode Properties the parameters a and b have been calculated to fit experimental data of each pure component,
data includes vapor pressure, enthalpy and volume,
as result you obtain a much better fitting than using the original expressions for alpha correlation,
and with non ideal fluids as water you get much lower errors,
this is a very important factor in phase equilibria and other unit operations.

[mpat]

I think it is of general interest a thread from cheresources about the vapor-liquid-liquid phase envelope in Excel with Prode Properties

Question:
I wish to calculate the phase envelope for different mixtures of hydrocarbons + water including different line fractions,
Prode Properties has a Excel page to calculate vapor-liquid-liquid diagrams,
the page allows to print the bubble line, dew line plus a line with specified phase fraction,
with water the procedure correctly shows as bubble line a vapor-liquid-liquid equilibrium line,
plus the line with specified phase fraction and the water dew line (see attached image)
For my application I need to calculate at least three lines with specified phase fractions,
say 0.25 , 0.5, 0.75
how should I proceed ?

[link Point to another website Only the registered members can access] Answer by Marchem :
differently from other simulators Prode integrates directly with Excel or Matlab,
you have access to all the methods in the library and can modify almost everything by program,
this gives great flexibility and I really appreciate this feature,

in the specific if you look inside the Excel page, VBA code you'll find
this little piece of code

' Original VBA code (prints one line with specified phase fraction)
nrpt = PFLine(stream, 1, pf, pt(0), pp(0), 51)
' nrpt is the effective number of calculated points
ri = 15
For i = 0 To nrpt - 1
Cells(ri + i, ci) = pt(i)
Cells(ri + i, ci + 1) = pp(i)
Next i

here the code calls the method PFLine in the library for calculating the line with specified state and phase fraction
the remaining stuff is the code to write on Excel Cells

you can easily modify this code for including more than one line with specified state and phase fraction

' Modified VBA code (prints three lines with 0.25,0.5,0.75 liq. molar fractions)
pf = 0
For ii = 0 To 2
pf = pf + 0.25
nrpt = PFLine(stream, 1, pf, pt(0), pp(0), 51)
' nrpt is the effective number of calculated points
ri = 15
For i = 0 To nrpt - 1
Cells(ri + i, ci + 2 * ii) = pt(i)
Cells(ri + i, ci + 2 * ii + 1) = pp(i)
Next i
Next ii

I have added the first For (For ii = 0 To 2) to calculate three lines as you wish,
very simple.

Remember to define properly the settings (see the operating manual) ,
these are available under the Tab Models in Properties Editor,
for example you may decide to
-print vapor-liquid; vapor-liquid-liquid; vapor-liquid-solid diagrams
-print all calculated points or stop when crossing dew or bubble lines (default)
-validate points (default) or not etc.

remember that a phase diagram is complex to calculate and may take a lot of time to complete if you add many lines,
you may test different possibilities as for example print all calculated points to see how the phase diagram appears before to customize on your needs.

Prode exposes several methods which you can access from Excel or Matlab,
these are discussed in paragraph "Methods for calculating equilibrium lines in phase diagrams" in Operating Manual,

herebelow the description of PFLine
integer nrpt = PFLine(integer stream,double pf, double *P, double *T, int maxpt)
Given a stream, a state, a specified phase fraction and two arrays (0-maxpt elements) the procedure returns nrpt < maxpt
equilibrium points in specified phase fraction line

the above is C/C++ syntax but you can use different languages as VBA, C#, VB-Net, FORTRAN etc.

[carlo.stenali]

mpat,
thanks for the information,
the utility to calculate vapor-liquid-liquid phase envelope / phase diagram has been included in Prode since the origin,
a interesting point is that you can calculate vapor-liquid-liquid equilibria for many mixtures,
it's not limited to hydrocarbons plus water...

[tinom]

thanks,
with Prode Properties can I print a phase envelope with hydrocarbon's bubble point, hydrocarbon's dew point, water dew point and hydrate formation line ?
This could be useful for us, our simulator doesn't do that.

[carlo.stenali]

yes,
you can include gas hydrate formation conditions in phase diagram,

see the paragraph Methods for Hydrate Phase Equilibria in Prode Properties Operating Manual,

there is a method HPFORM() which allows to calculate a series of equilibrium points,

the method HPFORM() gives three options for hydrate equilibria

1) assume free water present
2) calculate the amount of water present
3) solve as multiphase equilibria including solids as ice

the last gives the most accurate analysis

[STD manager]

Hi
if you want to buy any standard document and do not pay much money
please contact to:
i n t e r n a t i o n a l s t a n d a r d 2 0 1 2 @ g m a i l . c o m
h t t p : / / internationalstandard.blog. com

[cstaff]

I am doing LLE data regression with Prode Properties,
for a specific binary the procedure calculates very different values for NRTL depending from the data set which I enter,
how could I select the best values ?

[dbert]

>I am doing LLE data regression with Prode Properties,
>for a specific binary the procedure calculates very different values for NRTL depending from the data set which I enter,
>how could I select the best values ?

with Prode Properties you can do multiple vapor-liquid, liquid-liquid and solid-liquid data regression and select the best parameters based on calculated errors,
-go on BIPs dialog (see attached image) and select the binary (in the example Water-Ammonia)
go on Regress dialog (see attached image) select model (in the example Peng-Robinson NRTL with Wong-Sandler mi&#236;xing rules) , enter the VLE/LLE/SLE data (or ask the procedure to estimate VLE with UNIFAC) and calculate parameters
-in the output grid notice the data fitting errors, you can easily calculate different datat sets and select that with best match

does this answers your question ?

[cstaff]

thanks dbert,
I have several data sets from DECHEMA,
Prode Properties Data Regression Procedure calculates the parameters for the NRTL model in all cases,
however the calculate values are different for the different data sets,
the reported errors (for X and Y compositions) also are different,
should I select the data set which gives the lowest errors ?

[dbert]

that's a quite common problem in VLE/LLE data regression,
generally I create a data set with different data sets to cover a suitable range of pressures (or temperatures),
the main problem when regressing parameters for a model is to have something which extrapolates nicely when required,
you can verify the results (at different conditions) with a TPXY diagram (there is an Excel page distributed with Prode Properties which does that) .

[cstaff]

thanks dbert,
yes , my problem is to evaluate how NRTL works outside the area where the parameters have been regressed,
I think the TPXY diagram is the tool that I need.