Review the graphical quality of the fit

The graphical quality of the fit may be reviewed by using the graph. The graph shows measured and fitted distillation profiles for all of the products. You can zoom into this graph to assess the quality of fit in more detail by clicking and dragging a selection box, and reset the zoom by selecting Reset Scaling from the graph's right-click context menu.

To change the method used for displaying the yield measurements use the X-axis menu. Select either wgt or vol from the second X-axis menu.

To change the measurement unit used to display the temperature use the Y-axis menus. Use the second Y-axis menu to select the required temperature unit.

If you are fitting the whole flowsheet, rather than a single distillation unit, choose from the Distillation Unit drop-down menu the distillation unit for which you want to review the fit quality. If you are fitting a single distillation unit, this drop-down menu will have a single entry.

The Graph Toolbar of the fitting graph has several icons which display different features on the graph:

• - displays the synthesised cumulative yield curve for the crude.

• - displays the synthesised cumulative yield curves for each of the products.

• - displays the distillation measurements converted to TBP.

• - displays the effective cut points between the product streams.

During Distillation Unit Fitting any distillation measurements entered are converted to true boiling point (TBP) before fitting. If the distillation points are shown on the graph the points are shown at the TBP temperature, irrespective of the method used to measure the data. Conversion to TBP is performed using standard ASTM methods. See Distillation correlations.

After fitting the fractionation parameters will update with the calculated effective cut point and fractionation indices for each cut in the system. The effective cut points can be displayed on the graph by selecting the icon on the Fitting Graph Toolbar. The value of the ECP and fractionation indices are explained in Configure the pressure and products for your distillation units in Create a flowsheet.