Sucrose integration into COCO

[jasper]

In the PCD manager, select the compound. On the T-correlations tab, select the desired correlation type from the drop down list. This will populate the box below the list with the equation number, temperature range and parameters. Pick the desired shape of the equation. This dropdown list will show the equation shape, including the meaning of the parameters. You can just type values for the parameters; after this you can tabulate and plot the equation output. Alternatively you can fit the values of the parameters to imported data, on the import tab. When done, hit Apply.

[Farhan]

I want to use ''Flash unit operation with energy stream'' as an Evaporator for evaporation of water from Sucrose-Water solution. Kindly guide me whether I can use it as an Evaporator or I have to define my own model or u having a defined model in ''Excel unit operation'' for Evaporator.

[jasper]

I suppose you can simply use the flash. Did you try? Does it give any problems or behaviour that is not expected?

[Farhan]

I have tried the flash unit but the results are not matching with that of experimental and theoretical results/calculations.

[jasper]

In this case I would expect either that

- none of the phase equilibrium calculations match experiment, or
- your experimental evaporator does not operate in phase equilibrium

Are you able to validate your phase equilibrium calculations separately, from different data?

[Farhan]

...

[jasper]

Please enter the flowsheet configuration, select the property package and hit Edit

From the Configure menu, hit compounds. Select sucrose, click Edit.

On the Constants page, please correct the charge. It should be zero.

On the Temperature Correlations page, please select Vapor Pressure (not Antoine Vapor pressure). In the Equation field, select "A" (below <None> all the way at the top). For A, enter, say, 1e10. Something high. Hit OK, OK, close. Solve.

Now, the sucrose is virtually not present in the vapor, due to its high vapor pressure.

Still you find a difference in the amount of water that vaporizes. This implies that in HYSYS you are using different fugacity models either for the vapor phase, or for the liquid phase, or both. You are using ideal gas for the vapor in TEA, and ideal activities. So beyond vapor pressure there are no more adjustable parameters to change the equilibrium, with these models. Which models are you using in HYSYS?

[Farhan]

I have made the changes accordingly, moreover at 1st I was using UNIQUAC model in HYSYS but now I have changed it to Ideal gas for vapor and ideal solution for liquid. Results are now better but still needs improvement. I have got up to 75% success.

[jasper]

Which aspects of the results are not in agreement at this point?

For the ideal gas phase, the water fugacity equals the pressure.

For the liquid phase, the activity coefficient of water results from its mole fraction (given by the mass balances), its activity coefficient (unity, for ideal models) and the water vapor pressure (which you can compare). In addition, there may or may not be a Poynting factor correction in the model you selected, which takes into account the water specific volume (http://cocosimulator.org/index_help.php ... /poynt.htm)

[jasper]

Furthermore, as your specification includes a heat duty term, you may have some differences in the heat of vaporization of water. But I'd be surprised if the differences in water heat of vaporization or water vapor pressure between the two applications are significant.