Swing cuts calculation methods

When using perfect cutting the swing cut calculation method is set automatically to Perfect and cannot be changed. When using perfect cutting the property value for a swing cut can be calculated by inserting the swing cut of the correct width between the upper and lower streams. For example, the naphtha/kerosene cut might be at 200°C, and a swing cut width of 20°C is required. Using perfect cutting a cut of 20°C width is inserted into the scheme, with the centre of the swing cut at 200°C. Therefore the naphtha cut then ends at 190°C, followed by the swing cut of 20°C, and the kerosene cut begins at 210°C. The property values are determined by calculating the property value of this new 190-210°C cut.

When using flowsheet cutting the ECP of the cut is not equivalent to the end point of the stream and it is not possible to directly insert the swing cut into the cutting scheme. Instead the swing cut's properties are calculated by inserting an extra stream into the cutting scheme and modifying the ECPs so that the original cut's ECP is equal to the lower bound of the swing width, and the new cut's ECP is equal to the upper bound of the swing cut.

For example, at the naphtha/kerosene cut of 200°C a swing of 30°C may be required. When using a swing cut the ECP of the cut would be changed to 185°C, and a new cut would be inserted with an ECP of 215°C. To calculate the property of the swing cut the average of the two cut's property values is taken. To calculate the average several different methods are available. By default the method used is Edge Matching Average, as usually swing cuts tend to swing much more to one extreme so it is important to more accurately match the cut's properties at the extreme of the swing cut width.