Enter flowsheet parameters

Fractionation parameters can be directly entered into grid for each cut. Each cut requires three fractionation parameters:

• ECP - the effective cut point

• Stripping FI - the stripping fractionation index showing the amount of heavy component in the lighter stream

• Rectifying FI - the rectifying fractionation index showing the amount of light component in the heavy stream.

When using the ECP/SI separation model, Stripping FI and Rectifying SI are replaced by Bottom SI and Top SI, respectively.

Values for the ECP and FIs can be directly entered in the grid for each cut point. Alternatively to set a cut point as perfect double-click on a cut point and select Perfect from the drop-down menu. This replaces commercial fractionation with perfect cutting, setting the cut point between the streams to the value entered for the ECP.

Tower parameters can be entered manually entered, or calculated by Process Model Manager Reference Manual from test run data. To use Process Model Manager Reference Manual to calculate the parameters open the Tower Fitting dialog by clicking the icon for the required distillation unit. Each distillation unit in the system must be fitted separately using its own set of test run data (Tower fitting).

Each cut requires four pieces of information:

• Product name: The name of the product stream between the previous cut point and the cut point entered in the ECP field.

• ECP: The effective cut point of the product. This corresponds to the "cut point" between this product and the next. Notice that the final product, the residue product, has no ECP. The temperature unit for ECP is governed by the default unit setting for Boiling Point (Unit Manager).

• Stripping and Rectifying FIs: Parameters indicating the quality of the separation at that cut point (the fractionation index). The values may range between 0.5 and 20, with higher values indicating more efficient separation. The values correspond to the number of theoretical plates in the separation. Stripping governs the amount of light components in the heavy product at a separation, while rectifying governs the amount of heavy components in the lighter product. The option "perfect" is also available, corresponding to perfect separation. This can be found by double clicking in the cell and choosing Perfect from the combo box.

When using the ECP/SI separation model, Stripping FI and Rectifying SI are replaced by Bottom SI and Top SI, respectively.

The term ECP is defined as the effective cut point of a stage of the separation. A molecule having a boiling point equal to the ECP is equally partitioned between the product stream boiling just above that temperature and the product stream boiling just below that temperature. For example a distillation unit may have two adjacent streams, diesel and atmospheric residue. The ECP of the lower boiling diesel stream is calculated as the boiling point of a molecule which is equally separated between the diesel and atmospheric residue. The boiling point of this molecule is not dependent on the composition of the crude being analysed - it only depends on the conditions found within the distillation unit. Hence the ECP is not crude dependent.