Batch Distillation - Policy Segment

Use this window to specify the elements of a policy segment. At least one policy segment action is required in each policy segment.

Usage

Initiations

It is possible to execute a policy segment more than once. For example, assume a segment is specified to start whenever the amount of a component in the stillpot falls below a certain value. If the Initiation selection is "Single", the segment starts only when the start condition is met for the first time. If "Multiple" is selected, it starts every time the condition is met.

Initiation Criterion

This is a rarely-used specification, for defining exceptional reasons to start a policy segment. It is not needed for the usual series of sequential policy segments.

If the policy segment is specified as sequential on the Batch Distillation Main Window, the text for the Initiation Criterion will read Start After Policy Segment Identifier. Clicking on Identifier allows choosing another sequential policy segment. If there is no Start condition in the Action/Condition table, the current policy segment is inserted into the sequence after the chosen policy segment. More usefully, if there are Start conditions in the table, the current policy segment will start after the end of the chosen segment; but only if at least one of the Start conditions is fulfilled.

For a non-sequential policy segment, the text for the Initiation Criterion reads "Start With Policy Segment Identifier". Again, clicking on Identifier only allows choosing a sequential policy segment. The non-sequential segment will start simultaneously with the chosen segment.

Action/Condition

Each policy segment must contain at least one of the following: Charge, Draw, Distill, End Cut, or Go To.

Select the desired Action/Condition from the drop down list; then click on the text under Description to open the appropriate definition window. The selections available are:

Start: Start Conditions are usually for non-sequential policy segments, where they define when to start the segment. When a number of conditions are supplied, the segment starts when any of them are met. Start is not allowed when Initiation Criterion Start With Policy Segment is active.

In a sequential policy segment with Initiation Criterion Start After Policy Segment declared, the Start option may supply additional conditions to be satisfied. The present segment will not start unless one of any Start Conditions has been met.

Charge: Specify Charges for the unit. Charges may be instantaneous or continuous, and may apply to any stage of the column. Only the stillpot allows Instantaneous charges. Continuous charges may be made to any stage except the condenser.

Draw: Specify Draws for the unit. Draws may be instantaneous or continuous. Only the stillpot and accumulator allow Instantaneous draws. Continuous draws may be taken from any stage (but not from the accumulator). Note that dumping the contents of the accumulator is an End Cut rather than a draw.

Distill: Specify the Distill actions for the unit. This indicates when distillation is actually taking place. Only one Distill action is allowed in a policy segment.

Control: Specify a dynamic controller which varies the reflux ratio to meet a temperature or purity specification. Only one dynamic controller is allowed in a policy segment.

Run Until: Specify Run Until Conditions which define conditions for ending the policy segment. The segment terminates when any of the conditions is satisfied.

End Cut: Ends a cut. End Cut dumps the contents of the accumulator into a defined product at the end of the policy segment. Only one End Cut is allowed in a policy segment if bulk phase holdup is given. Two End Cuts can be given if Individual (L1, L2) phase holdups are given.

Go To: Specify a Go To to identify the sequential policy segment which will be executed when this segment ends. Only one Go To is allowed in a policy segment. If this is omitted, the next sequential segment in the Overall Operating Policy table on the Batch Distillation Main Window will be executed.

Pressure Profile: Specify different Pressure Profile for this policy which defines pressures to be used for the policy segment.

How to get to this window

The Batch Distillation - Policy Segment window is accessed by pressing the Enter Data button in the Overall Operating Policy table on the Batch Distillation Main Window. You should ensure that the policy segment is defined correctly as sequential or non-sequential before accessing this window.

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