Properties of pure fluids and mixtures, multi phase equilibria, process simulation, software
Excel / Matlab application example : dew point, bubble point, cricondentherm, cricondenbar, critical point
Prode Properties has specific methods which permit to calculate dew points, bubble points, equilibrium points at specified phase fraction (vapor, liquid, solid **) and pressure (or temperature), typical applications include hydrocarbons dew point (HDP, HCDP), cricondentherm, cricondenbar of natural gas mixtures from gas analysis.
Prode Properties can calculate up to 5 equilibrium points along a line with specified phase fraction, in addition there are specific methods for calculating directly Cricondentherm, CricondenBar and Critical points. With Prode Properties you can do this in Excel, Matlab or any compatible application including custom software, this example shows how to use these methods in Excel.
First step: define the stream (components, compositions etc.)
Properties includes a Stream editor which permits to access all informations (as compositions, operating conditions, models, options) for all streams which you need to define, to access the Stream editor from Excel Properties menu select Edit Properties
The Stream editor includes several pages, from the first page you can select a stream (Properties can store all the streams required to define a medium size plant) solve a series of flash operations and see the resulting compositions in the different phases, in this page select the stream you wish to define, for example the first.
In the second page you can define a new composition or modify an existing composition, in this example we define C1 0.7 CO2 0.15 H2S 0.15 as molar fractions
In the third page you can define the package (thermodynamic models and related options) , here we define API Soave Redlick Kwong.
The fourth page provides access to BIP (Binary Interaction Parameters) for the different models, you can enter specific values or click on "Load BIPs" button to get the predefined BIPs from databank.
Finally we must save the new data, in the first page click on "Save" button, note that you can redefine the name of the stream as you wish (editing the cell near the button "Save"), you can define / modify many streams following the procedure described.
Once defined the stream you may wish to define the units which we wish to utilize in our problem, in stream editor go then to the "Units" dialog
here you can select the units which you need for a specific problem, in this example for the pressure (first row) select Bar.a , notice that unit for temperature is K (but you can set the units which you prefer) then click on Ok button to accept new values and leave the Properties editor.
Now you are ready to use Properties for calculating all the properties which you need, however there is still a last thing to do if you do not wish to lose all data when leaving a Excel page, precisely to save data to a file, to save data to a file from Excel Properties menu select "Save a Archive"
then select the file "def.ppp" if you wish that Properties utilizes this data as default (this is the normal , recommended option), differently set a different name (you can for example define different names for different projects) but you will need to load that specific Archive before to make calcs for that project and since Excel reloads Properties with any new page this may result tedious...
Properties saves on the file also the units of measurement so you can define different streams and different units in different projects.
Now you can calculate all the properties which you need with the units which you prefer for all the streams defined in that project.
Second step: calculate properties in Excel cells.
Prode Properties includes methods for calculating critical points and equilibrium points at specified conditions, see the paragraph Methods for thermodynamic calcs in operating manual for the details.
Suppose we wish to calculate a equilibrium point near the critical point for the mixture defined in stream 1, to get the first critical point pressure we enter the macro =StrPc(1,1) where (1,1) refers to the stream 1 and first critical point detected, we enter this macro in B1, in B2 we enter the macro =StrTc(1,1) to calculate the critical temperature in the same way, in cells B3 and B4 we enter the macros = StrCBp(1) for CricodenBar pressure and = StrCTt(1) for CricodenTherm temperature, with this data we have a plot of the whole phase envelope.
Note that Prode Properties includes methods to plot the phase envelope directly in Excel, go to the page Phase envelope to investigate this option.
Now we wish to calculate two equilibrium points on the dew line (the red line in phase envelope) at pressure of 89 Bar.a (remember that maximum value is the CricondenBar pressure which is 89.09 Bar.a), we use the method
double t = PfPF(integer stream, double p, double pf, int state, int n)
In cell B1 we define a value for the equilibrium pressure (89 Bar.a) , then in cells B2, B3 we enter the macros
where the first value (1) is the stream , the second (cell B1) represents the pressure, the third (0) is the phase fraction (with 0 we specify 0% liquid or a point on dew line, the same would be by setting the state as gas and phase fraction as 1.0) the fourth (1) is the state (in Properties 0 = gas, 1 = liquid, 2 = solid) and the last is the required position (we require the points 1-2 along the dew line)
If we change the value of equilibrium pressure the procedure calculates the new equilibrium temperatures
Now a more elaborate example, we define a stream with the mixture Methane 0.999 n-Butane 0.001
The phase envelope for this mixture shows up to four saturation point pressures at the same temperature
Observe the dew line, the red line below the critical point, there are up to three different equilibrium points at the same temperature (the area around 190 K), if you add the saturation point on the bubble line (black line) we have a total of four saturation point pressures at a given temperature, to calculate the points on the dew line we use the method:
double p = PfTF(integer stream, double t, double pf, int state, int n)
In cell B1 we define a value for the equilibrium temeperature (190.208 K) , then in cells B2, B3, B4 we enter the macros
where the first value (2) is the stream which we defined, the second (cell B1) represents the temperature, the third (0) is the phase fraction (with 0 we specify 0% liquid or a point on dew line, the same would be by setting the state as gas and phase fraction as 1.0) the fourth (1) is the state (in Properties 0 = gas, 1 = liquid, 2 = solid) and the last is the required position (we require the points 1-3 along the dew line)
If we change the temperature the procedure recalculates equilibrium pressures
you may wish to test the method LfTF(), enter the macro
where 2 is the stream, B1 represents the temperature and 0 is the (liquid) phase fraction, notice that you?ll get the same values as for the first equilibrium point in PfTF(), by changing the specification we can use the method LfTF() to calculate the point on bubble line
where 1 is the specification (100% liquid) for a point on the bubble line , but of course you get the same result with the method:
where the third value (1) is the phase fraction (with 1 we specify a 100% fraction) the fourth (1) is the state (in Properties 0 = gas, 1 = liquid, 2 = solid) and the last is the required position for the point.
Calculate properties in Matlab.
From Matlab command line you can call the methods in Prode Properties by typing the names, for example to calculate equilibrium temperatures at specified pressures
>> ans = 14.975
>> ans = 36.511
in Matlab (as In Excel) you can access the Properties editor from menu associated with the figure.
Prode Properties, technical features overview (Windows version)