BATCHFRAC Main Window

This window is used to supply the input data for a BATCHFRAC 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 still pot 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 Policy Run time

When the calculated time for each policy reaches this value, calculations will stop for that policy. Note that this is the simulated distillation time and not the elapsed computer time. Default for maximum simulation time is 10 hours.

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. Default for batch cycle time is 1 hour.

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 When product draws from the batch still feed into a steady-state flow sheet, they are withdrawn on a time-scale that ensures a steady flow of product consistent with the steady-state simulation.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 Dump instantaneously transfers the entire contents of the accumulator to its product stream.

Calculated 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 no VLLE thermo is defined in the Thermodynamic Section, an error condition occurs and the Thermodynamics Systems window turns red.

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 BATCHFRAC- Pressure Profile window.

Condenser... Button

BATCHFRAC units always have a condenser. The condenser options, including partial, mixed, bubble point, and sub cooled, are provided in the BATCHFRAC- Condenser window.

Products... Button

All the products are specified in the BATCHFRAC- Products window. BATCHFRAC unit must have at least two products, a Main Accumulator product leaving accumulator at condenser and column contents leaving the still pot. Optionally, Unit may also have Overhead vapor leaving the top tray, Draw products from any stage known as Side Accumulator products and Dump products to dump the accumulator contents.

Heaters & Coolers... Button

Any stage may have a heat source or sink as described in the Heaters/Coolers Window.

Calculation Options... Button

Several options are specified in the BATCHFRAC- Calculation Options window. These include tolerance and maximum step size for the integration. Defaults are supplied for all options in this window.

Initial Estimates... Button

Initial estimates for stage temperatures and compositions may be provided as described in the BATCHFRAC Initial Estimates Window. Users may supply their own values for the initial profile values. Additionally, two initial estimate generators, Bubble and Linear, also are available. These built-in algorithms allow PRO/II to supply initial values using estimation techniques.

Thermodynamic Systems... Button

The BATCHFRAC- Thermodynamic Systems window is used to specify the system used for the BATCHFRAC calculations. Different thermodynamic systems may be used for individual sections of the column.

Liquid Holdup... Button

The liquid holdup must be defined for the condenser and for all column trays in the BATCHFRAC- Liquid Holdup window. Liquid holdup may be defined separately for each tray in the column.

Print Options Button

The BATCHFRAC- 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, column stages and accumulators. The desired reports must be defined before performing the calculations.

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, and the segments will be executed sequentially as specified in the table.

The Overall Operating Policy table of the main BATCHFRAC 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.

Policy Type: Each policy segment must be defined as Total Reflux, Standard or Both type. The main calculation is a series of sequential segments. First policy should be of type Total Reflux or Both.

Note: Calculations for Total Reflux type policy are not marched in time, but run till such time where compositions of each stage do not change with further iterations. Hence for all Total Reflux type policies, the elapsed time is zero like in Batch_Distillation unit op.

Segment: Press the Enter Data button to open the BATCHFRAC- Policy Segment window to define the actions and conditions for the policy segment.

How to get to this window

The PRO/II BATCHFRAC window is accessed by double clicking the BATCHFRAC icon laid down on the Process Flow Diagram.

$image\SML_LINE.gif$