The Monitor page is primarily used for editing specifications, monitoring
Column convergence, and viewing Column profile plots. An input summary, and a property view of the initial estimates can also be accessed from this page.
Optional Checks Group
The Optional Checks group displays the iteration number, step size, and equi-librium and heat / spec errors during the iteration process. You will also find the following two buttons:
Button Function Input
Summary
Provides a column input summary in the Trace Window. The summary lists vital tower information including the number of trays, the attached fluid package, attached streams, and specifications.
You can click the Input Summary button after you make a change to any of the column parameters to view an updated input summary. The newly defined column configuration appears.
View Ini-tial Estim-ates
Opens the Summary page of the Column property view, and displays the initial temperature and flow estimates for the column. You can then use the values generated by HYSYS to enter estimates on the Estimates page.
These estimates are generated by performing one iteration using the cur-rent column configuration. If a specification for flow or temperature has been provided, it is included in the displayed estimates.
Profile Group
During the column calculations, a profile of temperature, pressure or flow appears, and is updated as the solution progresses. Select the appropriate radio button to display the desired variable versus tray number profile.
Specifications Group
Each specification, along with its specified value, current value, weighted error, and status is shown in the Specifications group.
You can change a specified value by typing directly in the associated Specified Value cell. Specified values can also be viewed and changed on the Specs and Specs Summary pages. Any changes made in one location are reflected across all locations.
Note: New specifications can also be added via the Specs page.
Double-clicking on a cell within the row for any listed specification opens its property view. In this property view, you can define all the information asso-ciated with a particular specification. Each specification property view has three tabs:
l Parameters
l Summary
l Spec Type
This property view can also be accessed from both the Specs and Specs Sum-mary pages.
Spec Status Check Boxes
The status of listed specifications are one of the following types:
Status Description
Active The active specification is one that the convergence algorithm is trying to meet. An active specification always serves as an initial estimate (when the Active check box is selected, HYSYS automatically selects the Estim-ate and Current check boxes). An active specification always exhausts one degree of freedom.
An Active specification is one which the convergence algorithm is trying to meet initially. An Active specification has the Estimate check box selec-ted also.
Estimate An Estimate is considered an Inactive specification because the con-vergence algorithm is not trying to satisfy it. To use a specification as an estimate only, clear the Active check box. The value then serves only as an initial estimate for the convergence algorithm. An estimate does not exhaust an available degree of freedom.
An Estimate is used as an initial “guess” for the convergence algorithm, and is considered to be an Inactive specification.
Status Description
Current This check box shows the current specs being used by the column solu-tion. When the Active check box is selected, the Current check box is automatically selected. You cannot alter this check box.
When Alternate specs are used and an existing hard to solve spec has been replaced with an Alternate spec, this check box shows you the cur-rent specs used to solve the column.
A Current specification is one which is currently being used in the column solution.
Completely Inactive
To disregard the value of a specification entirely during convergence, clear both the Active and Estimate check boxes. By ignoring a specification rather than deleting it, you are always able to use it later if required. The current value appears for each specification, regardless of its status. An Inactive specification is therefore ideal when you want to monitor a key variable without including it as an estimate or specification.
A Completely Inactive specification is ignored completely by the con-vergence algorithm, but can be made Active or an Estimate at a later time.
The degrees of freedom value appears in the Degrees of Freedom field on the Monitor page. When you make a specification active, the degrees of freedom is decreased by one. Conversely, when you deactivate a specification, the
degrees of freedom is increased by one. You can start column calculations when there are zero degrees of freedom.
Variables such as the duty of the reboiler stream, which is specified in the Work-book, or feed streams that are not completely known can offset the current degrees of freedom. If you feel that the number of active specifications is appropriate for the current configuration, yet the degrees of freedom is not zero, check the conditions of the attached streams (material and energy). You must provide as many specifications as there are available degrees of freedom.
For a simple Absorber there are no available degrees of freedom, therefore no specifications are required. Distillation columns with a partial condenser have three available degrees of freedom.
Specification Group Buttons
The four buttons which align the bottom of the Specifications group allow you to manipulate the list of specs. The table below describes the four buttons.
Button Action
View Move to one of the specification cells and click the View button to display its property view. You can then make any necessary changes to the spe-cification.
To change the value of a specification only, move to the Specified Value cell for the specification you want to change, and type in the new value.
You can also double-click in a specification cell to open its property view.
Button Action Add