Inside VMG | November 2014

Tips and Tricks: Shortcuts Using the Component Splitter

By Chris Arthur-VMG Calgary

This edition of Tips and Tricks is an overview of the features and capabilities of the Component Splitter unit in VMGSim 9.0.

Advanced Features

The Component Splitter is a shortcut unit that distributes components between exit streams according to split fractions assigned to each component. The functionality of the Component Splitter can be tailored using the Advanced and Product Data frames. Within the Advanced frame are drop down lists Calc P Mode and Calc T Mode which determine the relationship of pressure and temperature between the exit streams. 


Selecting All P Equal and All T Equal will separate components but maintain the pressures and temperatures of the feed in both exit streams. Alternatively, other options allow the exit streams to calculate pressures and temperatures from thermodynamic principles. The Product Data frame allows temperatures and vapour fractions of the exit stream to be specified, if required, when the unit is used to represent more than separation of components at constant temperature and pressure


Estimate the Operating Point of a Tower

This example will show how the Component Splitter can be used to help estimate operating parameters of a tower using a sample naptha stabilizer. By specifying the desired separation of an unstabilized naptha feed the Component Splitter can be configured to estimate the stabilizer operating temperature and pressure.

In this example a feed stream was connected to a component splitter and the splits were configured to meet the desired separation. The overhead temperature was set to 40C to represent an air cooled  condenser and VapFrac set to 1 to calculate the dew point condition. The pressure of the bottoms was set to the overhead dew point pressure and VapFrac specified as 0 to find the bubble point temperature. A pressure of 420 kPa and bottoms bubble point temperature of 121°C were calculated. These values were used to specify a distillation column with an operating pressure that allowed for an air cooled condenser to be used, estimates for reboiler temperature as well a mole flow for product streams of the stabilizer.


Separating Components by Group 

In the case of a model containing oil hypotheticals, assigning split fractions to individual components can be time consuming. To quickly assign splits to many components VMGSim 9.0 has the ability to separate components by group. Groups can be configured on the basis of molecular weight or normal boiling point. Each group requires minimum and maximum values, whether molecular weight or normal boiling point, components with properties that lie within these limits will be part of the group and a common split fraction can be assigned. Each group can be applied to all components with corresponding properties or applied to particular hydrocarbon families. There is no limit to the number of groups that can be created.

The following example will separate components generated from a PIONA slate with a boiling point greater than 150°F. The feed stream will then be substituted for analternative component slate and the Component Splitter willmaintain the separation at 150°F.

For the example AssignSplits by Group was selected to reveal the group  rules frames. Reference Property refers to the basis for the rule, in this example Normal Boiling Point forms the basis. The threshold for separation was set to 150°F 

and entered as the Min value. A large number was entered as the upper limit in Max and a split value of 0 was specified for the group. The separation with a threshold of 150°F was maintained by the component splitter when the PIONA component slate was altered.   




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