Batch Distillation Main Window
This window is used to supply the input data for a batch distillation column.
Usage
Number of Theoretical Stages
This entry is the integer number of theoretical stages in the unit. No other data may be entered until this is defined. The minimum number of stages is two. There is no limit on the maximum number of stages. Stages are always numbered from the top down. The condenser is always defined as stage one. The stillpot is defined as the highest numbered stage.
If you change the number of stages in the unit, you will have to redefine all data which refers to specific stage numbers including pressure or liquid holdup profiles, output reports and segment start or stop conditions.
Maximum Simulation Time
When the calculated time reaches this value, all calculations will stop. Note, this is the simulated distillation time and not the elapsed computer time.
Batch Cycle Time
The Batch Cycle Time is necessary to relate the charge and product amounts of the batch unit to stream flow rates in the continuous flow sheet. Practically, product amounts are divided by the Batch Cycle Time to get product stream flows. There is no reconciliation of charge amounts with feed stream flows.
If you do not enter the Batch Cycle Time, it will default to the cumulative (simulated) batch operation time. If the cumulative time is still zero when the unit simulation stops, the Maximum Simulation Time will be used.
Note, unless the batch unit is connected to other units in a continuous flow sheet, stream flows and the Batch Cycle Time are of no interest. When product draws from the batch still feed into a steady-state flow sheet, they are withdrawn on a time-scale that ensures a steady flow of product consistent with the steady-state simulation. Conversely, an accumulator End Cut instantaneously transfers the entire contents of the accumulator to its product stream.
Calculated Condenser Phase
Users may choose between Vapor-Liquid or Vapor-Liquid-Liquid equilibrium based on the need for VLLE calculations in the condenser. The default is Vapor-Liquid equilibrium (VLE). If the user changes to Vapor-Liquid-Liquid, the condenser defaults to the first available VLLE thermodynamics set declared in the Thermodynamic systems Window. If no VLLE thermo is defined in the Thermodynamic Section, an error condition occurs and the Thermodynamics Systems window turns red.
Print Options Button
The Batch Distillation - Print Options window offers several different options for creating both summary and time-profile reports. Reports are written to the output report file. The user creates a report by selecting from lists of features to include in each report. Reports can be produced for different combinations of times, component ranges and column stages. The desired reports must be defined before performing the calculations.
Plot Options Button
Two types of plots are available on the Batch Distillation - Plot Options window; trend graphs and snapshots. Use the Plot Options button to select the information to be stored for creating plots A snapshot shows the instantaneous conditions at the end of a particular policy, or may be time-averaged over a specified time period. A trend graph plots changing conditions over a specified time period using a specified time interval between plot points. These help visualize the progress in selected time intervals during batch distillation calculations.
Initial Pressure Profile Button
The pressure must be defined for all stages in a column. Several options for supplying the stage pressures are provided in the Batch Distillation - Pressure Profile window.
Condenser Button
Batch distillation units always have a condenser. The condenser options, including partial, mixed, bubble point, and subcooled, are provided in the Batch Distillation - Condenser window. Additionally, the condenser supports options to model it using a simple heat-exchanger that can be configured by the user.
Liquid Holdup Button
The liquid holdup must be defined for the condenser and for all column trays in the Batch Distillation - Liquid Holdup window. Liquid holdup may be defined separately for each tray in the column.
Global Stop Criteria Button
When any of the conditions defined in the Batch Distillation - Global Stop Criteria window, such as maximum or minimum amounts, purities or temperatures, are met, all policy segments which are currently executing are terminated. Unless the condition specifies that another policy segment should then be started, the simulation is terminated. If no global stop criteria are defined, the simulation will stop when the Maximum Simulation Time is reached.
Thermodynamic Systems Button
The Batch Distillation - Thermodynamic Systems window is used to specify the system used for the batch distillation calculations. Different thermodynamic systems may be used for individual sections of the column.
Calculation Options Button
Several options are specified in the Batch Distillation - Calculation Options window. These include tolerance and maximum step size for the integration, the rigor of the liquid density calculation, and the calculation interval for the enthalpy balance. Defaults are supplied for all options in this window.
Reboiler Button
The reboiler optionally may be modeled as a simple heat exchanger. This button opens the Batch Distillation - Reboiler HX window that allows configuring the heat exchanger model. U-value, area, tolerance, and the thermodynamic method system may be specified in this window.
Overall Operating Policy
The overall operating policy defines the operation of the unit. It is defined in one (or more) sub-policies. Each row in the table defines one sub-policy. Each sub-policy consists of one or more policy segments. Each segment defines one of several actions such as Distill, Charge, or Draw, Also, the user may specify the next segment to be executed. If the next segment is not defined, the next segment (sequentially in the table) will be executed.
The Overall Operating Policy table of the main Batch Distillation window requires at least one sub-policy to be defined. The first row in the table must include the initial charge to the still pot. The entries in each row of the table include:
Identifier: The policy segment identifier may be up to 12 characters and must be unique. A default identifier is generated if none is supplied by the user.
Initiation Type: Each policy segment must be defined as sequential or non-sequential. The main calculation is a series of sequential segments. Non-sequential segments may run in parallel to the sequential calculations to define additional charges, draws or dynamic controllers.
Segment: Press the Enter Data button to open the Batch Distillation - Policy Segment window to define the actions and conditions for the policy segment.
How to get to this window
Access the PRO/II Batch Distillation window by double clicking the batch distillation icon laid down on the Process Flow Diagram.
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