A.5 Drying module
B.4.1 Entrainment in ‘A’ pans
Aspen Plus® block: PANA-ENT
Description: Determines the flow rate of entrainment in the ‘A’ pans. Before entrainment can be calculated, the entire pan calculation must be done first (crystallisation and evaporation). This is necessary to determine the composition of the mother liquor of the ‘A’ massecuite when it exits the pans. The entrainment values are then calculated based on the ratios of the components in the mother liquor. The outputs manipulate the initialised values for the separation coefficients in the block which handles the entrainment separation (ENT-A). Calculator blocks PANB-ENT and PANC-ENT are based on the same principles. Variables:
1. S – Calculated variable: Pure sucrose solubility. It is a function of tc.
2. (SW)satpure – Calculated variable: Sucrose-to-water ratio (another way of expressing
solubility). Also just a function of tc.
3. Non-sucrose in mother liquor – Input variable: Flow rate of non-sucrose in A-INV
stream (kg/h).
4. Feed to ‘A’ pans – Input variable: Mass flow rate of A-TOTAL stream (kg/h).
5. Water in – Input variable: Mass flow rate of water in A-INV stream in kg/h (after
inversion).
6. Water in mother liquor – calculated variable: Water in massecuite out from ‘A’ pans.
Function of Dry substance, Water in and Flow of feed to ‘A’ pans.
7. NSWml– Calculated variable: (Non-sucrose)-to-water ratio in the ‘A’ mother liquor.
Function of Non-sucrose in mother liquor and Water in mother liquor.
8. Sat. Coeff. (SC) – Calculated variable: The saturation coefficient of mother liquor when
the massecuite leaves the ‘A’ pans. Function of A, B0, B1, C and NSWml.
9. Sucrose in feed – Input variable: Flow rate of sucrose in A-TOTAL stream (which
would leave in the mother liquor if no crystallisation occurred).
10. (SWmol)impure – Calculated variable: Sucrose-to-water ratio in an impure solution
(mother liquor). Function of Sucrose in feed and Water in mother liquor.
11. (SWmol)satimpure– Calculated variable: The sucrose-to-water ratio for a saturated impure
solution. Function of Sat. Coeff. (SC) and (SW)sat pure.
12. SS actual – Calculated variable: The current supersaturation (before crystallisation has
13. Sucrose required – Calculated variable: The amount of sucrose which would be left in
the mother liquor to give the desired supersaturation (SS required). Function of SS actual, SS required and Sucrose in feed.
14. Crystal in – Input variable: Flow rate of crystals in A-INV stream in kg/h (comes from
magma).
15. Sucrose in (suc+cryst) – Calculated variable: Sucrose in feed added to Crystal in. 16. Sucrose entrained – Calculated variable: Entrainment parameter multiplied by Sucrose
in (suc+cryst).
17. Sucrose into separator – Input variable: Flow rate of sucrose in A-INV stream (kg/h).
18. Sucrose sep. coeff. – Output variable: The fraction of sucrose fed to block ENT-A which
ends up in the A-ENT stream (The fraction which is not entrained). Function of Sucrose into separator and Sucrose entrained.
19. Sucrose sep. – Calculated variable: Sucrose entrained divided by Sucrose required
(Sucrose entrained as a fraction of the sucrose out of the pan in the mother liquor of the ‘A’ massecuite).
20. Water sep. – Calculated variable: Sucrose sep. multiplied by Water in mother liquor
(The ratios of entrainment are calculated based on the ratios which the components are present in the mother liquor of the ‘A’ massecuite).
21. Water sep. coeff. – Output variable: The fraction of water fed to block ENT-A which
ends up in the A-ENT stream (The fraction which is not entrained). Function of Water in and Water sep.
22. Non-suc sep. – Calculated variable: Sucrose sep. multiplied by Non-sucrose in mother liquor.
23. Non-suc sep. coeff. – Output variable: The fraction of non-sucrose fed to block ENT-A
which ends up in the A-ENT stream (The fraction which is not entrained). Function of
Non-sucrose in mother liquor and Non-suc sep. Constants:
A, B0, B1 and C: Constants in the saturation coefficient (SC) equation. Parameters:
1. tc: Exit temperature of massecuite from ‘A’ pans.
2. Dry substance: The fraction which is not water in the massecuite from ‘A’ pans.
Calculations:
Pure sucrose solubility:
𝑆= 64.447 + 0.08222𝑡𝑐 + 1.6169 × 10−3𝑡
𝑐2− 1.559 × 10−6𝑡𝑐3 − 4.63 × 10−8𝑡𝑐4
Sucrose-to-water ratio (pure solution):
(SW)puresat = 𝑆
100 −𝑆
(Non-sucrose)-to-water ratio:
Water in mother liquor = Feed to ‘A’ pans−water in
Dry substance − Feed to ‘A’ pans−Water in
NSWml= Non − sucrose in mother liquor Water in mother liquor
Saturation coefficient:
Sat. Coeff. (SC)=𝐴×NSWml+𝐵0−𝐵1×𝑡𝑐+ (1 −𝐵0+𝐵1×𝑡𝑐)exp (−𝐶×NSWml)
Sucrose-to-water ratio (impure solution):
(SWmol)impure = Sucrose in feed
Water in mother liquor
Sucrose-to-water ratio (saturated impure solution):
(SWmol) impure sat
= (SW)puresat ×Sat. Coeff. (SC)
Supersaturation: SS actual = (SWmol) impure (SWmol) impure sat
Sucrose required to meet specified exit supersaturation condition:
Sucrose required = SS required
SS actual × Sucrose in feed
Total sucrose feed (including crystals):
Entrainment:
Sucrose entrained =Entrainment × Sucrose in (suc + cryst)
Sucrose sep. coeff.= 1 − Sucrose entrained
Sucrose into separator
Sucrose sep.= Sucrose entrained
Sucrose required
The ratios of entrainment are calculated based on the ratios which the components are present in the mother liquor of the ‘A’ massecuite:
Water sep.= Sucrose sep. × Water in mother liquor
Water sep. coeff.= 1 −Water sep.
Water in
Non − suc sep.= Sucrose sep. × Non − sucrose in mother liquor
Non − suc sep. coeff.= 1 − Non − suc sep.
Non − sucrose in mother liquor
B.4.2 Crystallisation in ‘A’ pans
Aspen Plus® block: PANA-CX
Description: Determines the extent of crystallisation in ‘A’ pans. The crystallisation of sucrose in the ‘A’ pans is based on Solid-Liquid-Equilibria. The calculation follows the algorithm of Starzak (2015 and 2016a).
Calculator blocks PANB-CX and PANC-CX are based on the same principles. Variables:
1. S – Calculated variable: Pure sucrose solubility. It is a function of tc.
2. (SW)satpure – Calculated variable: Sucrose-to-water ratio (another way of expressing
solubility). Also just a function of tc.
3. Non-sucrose in mother liquor – Input variable: Flow rate of non-sucrose in A-INV
stream (kg/h).
4. Feed to ‘A’ pans – Input variable: Mass flow rate of A-TOTAL stream (kg/h).
5. Water in – Input variable: Mass flow rate of water in A-INV stream in kg/h (after
inversion).
6. Water in mother liquor – calculated variable: Water in massecuite out from ‘A’ pans.
7. NSWml– Calculated variable: (Non-sucrose)-to-water ratio in the ‘A’ mother liquor.
Function of Non-sucrose in mother liquor and Water in mother liquor.
8. Sat. Coeff. (SC) – Calculated variable: The saturation coefficient of mother liquor when
the massecuite leaves the ‘A’ pans. Function of A, B0, B1, C and NSWml.
9. Sucrose in feed – Input variable: Flow rate of sucrose in A-TOTAL stream (which
would leave in the mother liquor if no crystallisation occurred).
10. (SWmol)impure – Calculated variable: Sucrose-to-water ratio in an impure solution
(mother liquor). Function of Sucrose in feed and Water in mother liquor.
11. (SWmol)satimpure– Calculated variable: The sucrose-to-water ratio for a saturated impure
solution. Function of Sat. Coeff. (SC) and (SW)satpure.
12. SS actual – Calculated variable: The current supersaturation (before crystallisation has
occurred. Function of (SWmol)impureand (SWmol)satimpure.
13. Sucrose required – Calculated variable: The amount of sucrose which would be left in
the mother liquor to give the desired supersaturation (SS required). Function of SS actual, SS required and Sucrose in feed.
14. Sucrose into A-Pan-CX – Input variable: Mass flow rate of sucrose in A-ENT stream in
kg/h (flow rate of sucrose into reactor block where crystallisation is modelled)
15. Sucrose conversion – Output variable: The fraction of sucrose in the feed which is
crystallised. Sets the conversion of block A-PAN-CX. Constants:
A, B0, B1 and C: Constants in the saturation coefficient (SC) equation. Parameters:
1. tc: Exit temperature of massecuite from ‘A’ pans.
2. Dry substance: The fraction which is not water in the massecuite from ‘A’ pans.
3. SS required – Exit supersaturation of ‘A’ massecuite.
Calculations:
Pure sucrose solubility:
𝑆= 64.447 + 0.08222𝑡𝑐 + 1.6169 × 10−3𝑡𝑐2− 1.559 × 10−6𝑡𝑐3 − 4.63 × 10−8𝑡𝑐4
Sucrose-to-water ratio (pure solution):
(SW)puresat = 𝑆
(Non-sucrose)-to-water ratio:
Water in mother liquor= Feed to ‘A’ pans−water in
Dry substance − Feed to ‘A’ pans−Water in
NSWml = Non − sucrose in mother liquor
Water in mother liquor
Saturation coefficient:
Sat. Coeff. (SC)= 𝐴×NSWml+𝐵0−𝐵1×𝑡
𝑐 + (1 −𝐵0+𝐵1×𝑡𝑐)exp (−𝐶×NSWml)
Sucrose-to-water ratio (impure solution):
(SWmol)
impure =
Sucrose in feed
Water in mother liquor
Sucrose-to-water ratio (saturated impure solution):
(SWmol) impure sat
= (SW)puresat ×Sat. Coeff. (SC)
Supersaturation: SS actual = (SWmol) impure (SWmol) impure sat
Sucrose required to meet specified exit supersaturation condition:
Sucrose required = SS required
SS actual × Sucrose in feed
Sucrose conversion:
Sucrose conversion = Sucrose into A − Pan − CX − Sucrose required
Sucrose into A − Pan − CX