This unit operation model simulates crystallization under continuous flow by solvent evaporation. Solvent evaporation lowers the solubility of solute components so crystallize out of the solution occurs.
● Continuous Evaporative Crystallization Procedure
Solvent evaporation can either be based on VLE modeling or user-specified evaporation percentages. For details on the mass balances associated with the evaporation of the solvent based on VLE principles see Flash Evaporation: Modeling Calculations
During crystallization, one or more components will be converted from their soluble forms into their crystallized forms. Initially, the user has to select whether one or multiply components that crystallize. This selection will be used to adjust the controls appearing in the Continuous Crystallization: Crystal. Data Tab
The mass balances for the crystallization design component can be based either on a user specified crystallization yield (yp) or the design component’s solubility curve. If the solubility curve is unknown, the user must specify both the design component yield and the crystallization temperature. In the opposite case, only one of these parameters needs to be specified and the other will be calculated by the program.
The crystallization yield for secondary crystal components (yi) is specified as a function of the crystallization yield of the design component (yp) using the following a second-degree polynomial equation:
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There is additionally, the option to designate a co-crystallization agent for every crystallization that takes place. The co-crystallization agent is considered to be entrapped in the crystals formed according to the mass (or mole) ratio specified.
Energy Balances
A heat of crystallization should be specified for every component that crystallizes. Notice that the heat of crystallization should be negative to denote that the crystallization is exothermic (which is usually the case). SuperPro will calculate the heating duty and the heat transfer agent flowrate required to maintain the crystallization temperature (either set by the user or calculated).
The sizing variable of the evaporator is the heat transfer area, A. In Design mode, the heat transfer area is calculated by:
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eq. (A.296) |
where U is the constant overall heat transfer coefficient, Q is the cooling duty and ΔT is the mean logarithmic temperature difference between feed and the cooling agent.
The equipment purchase cost is calculated as the cost of the heat exchanger with the heat transfer area being the costing variable.
See Vacuum Pump Auxiliary Equipment Calculations.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Continuous Evaporative Crystallization: Oper. Conds Tab
● Solubility Data, see Continuous Cooling Crystallization: Solubility Data Dialog
● Crystal. Data, see Continuous Crystallization: Crystal. Data Tab
● Rigorous Toolbox, see Flash Evaporation: Toolbox Options Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Scheduling, see Operations Dialog: Scheduling Tab
