Sucrose integration into COCO

[jasper]

The enthalpy specification of the heater/cooler equals the difference in feed and product enthalpy (which you can validate, double click the unit, go to balance, select enthalpy).

So for a constant temperature process (e.g. single compound at boiling point) the latent heat is accounted for.

[Farhan]

I have uploaded two files regarding simulation of multiple effect evaporator with 6 stages. Problem statement is explained in the MS WORD file. please guide me through the problem.

[jasper]

The first thing I notice is that your feed pressure in the fsd file does not match your documented feed pressure.

The second thing I notice is that the VL equilibria are not ok, and your entire simulation depends on it. I am just looking at the bottom product of the first flash. Presuming that top and bottom stream pressures match, this is at 356.2 kPa, as in your document. At that concentration, the bubble point is at 148 C, and not very close to your documented 139 C. Unless you get your phase envelope right, this will not work.

I see you use an ideal activity model. I suggest you use a 2 parameter activity model, and fit the coefficients to the dew point temperatures, the data for which you have in your bottom streams.

[Farhan]

u r right feed pressures were not correlating. i have tried it with the same pressures but still it does not give satisfactory results. i have to work on the activity model. i face problem in fixing the interaction parameters. i have already discussed it with u n previous mails. I dont know what to feed in the four boxes like for water/water, water/sucrose, sucrose/water, water/water..

[Farhan]

sucrose is not present in the component list I have defined it by myself. plz have a look at it, is there any major mistake.

[jasper]

I would, for simplicity, select the DECHEMA model (http://cocosimulator.org/index_help.php ... gacity.htm):

fug_water_liquid = x_water * gamma_water * Psat_water(T)

fug_water_vap = y_water * P = P

At equilibrium, liquid and vapor fugacities are equal, also for water:

fug_water_liquid = fug_water_vap

or

x_water * gamma_water * Psat_water(T) = P

Back out the PSat relation for water (from temperature correlations in the TEA setup):

Psat_water = exp(A + B/T + C*ln(T) + D*T^E)

with

A = 98.5149993896
B = -8530.70019531
C = -10.984000206
D = 6.36630011286e-006
E = 2

results an expression in just x_water, T and P:

x_water * gamma_water * exp(A + B/T + C*ln(T) + D*T^E) = P

Now, at the dew points, you know all of these from the bottom streams.

This gives you several expressions for gamma_water.

Now, pick a model for activity coefficient, e.g. Margules.

ln(gamma_water) = [A_water_sucrose + 2 * (A_sucrose_water - A_water_sucrose) * x_water] * (1 - x_water)^2

(see http://en.wikipedia.org/wiki/Margules_activity_model, or http://cocosimulator.org/index_help.php ... tivity.htm)

You really don't care about the activity coefficient of sucrose (it will not appear in the vapor phase with the very high vapor pressure you selected), so each dew point condition gives you an equation in which merely A_sucrose_water and A_water_sucrose are unknown. Pick values that fit all your dew points best.

[jasper]

[Farhan]

can i use other form of antoine equation for ''Psat''.

[jasper]

You cannot capture composition dependence of the dew point temperature in a PSat correlation. More-over, for pure water, the PSat correlation must represent the boiling point of water, which it does reasonably well.

[Farhan]

I have calculated values for A12 (water-sucrose) and A21(sucrose-water). Now for Water-water and sucrose-sucrose can I put value of 1