Chapter 5E

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##### Preliminary product splits

This page is used to determine the preliminary products splits where it is necessary to establish the approximate quantity of the fluids to be produced. The vapor pressure is the primary property used to make this split.

Pc (mixture) = S xi Pvi (5.16)

Where: xi = mol fraction of each component

Pvi = vapor pressure

The normal fractionator can make a reasonably sharp separation between hydrocarbons with different molecular weight. What separation that occurs will depend on the not yet available detailed design of the fractionator. In the making of this preliminary split, Equation 5.17 will prove useful for predicting isomer behavior.

L¢ / L = A (x¢ / x) (5.17)

Where:L = mol of the iso-paraffin in the final mixture

L¢ = mol of the normal paraffin in the final mixture

x¢ = mol fraction of normal paraffin in fractionator feed

x = mol fraction of iso-paraffin in fractionator feed

A = 1.25 for butanes and 1.12 for pentanes

This preliminary split will not check actual plant performance exactly but will be very adequate for planning purposes. In most cases the error should not exceed about 5%.

How do I carry out this calculation?

To carry out the preliminary product spits calculation the Reid Vapor Pressure and the feed mole % of each component in the mixture must be entered into their entry space. To do so use the mouse to click the courser in the entry spaces and input the data. Once the Reid Vapor Pressure and the feed mole % of each component in the mixture has been entered, select Run to execute the solution. An explanation of the solution is listed below.

Column (3) = Feed Moles percent

Column (4) = Liquid flow rates in mole

Column (5) = Liquid in mole %

Column (6) = Liquid volume per 100 moles of feed

Column (7) = Vapor Moles

Column (8) = Vapor Moles %

Please refer to example 5.6 in page 134 of Volume 1.

##### Definitions of the variables and where to obtain the unknown data

Reid vapor pressure is the substitute or surrogate specification used for most crude oil, condensates, and C5+ NGL liquids. This substitute is used because in order to measure true vapor pressure there can be nothing in the test cell except the liquid being tested. In practice this means that any air present at the beginning of the test must be removed before introduction of the sample. This is inconvenient in a field or plant laboratory using operating personnel. If you see RVP after the vapor pressure it is the Reid vapor pressure; if RVP is not shown it is a true vapor pressure, by default.

The component table is a list of the possible compounds along with their symbols to be used with this program. In the far right column titled Feed Mole %, use the mouse to choose the available cell and enter the mole percentage of each component, of the mixture, that is fed into the fractionator. Use the Up and Down arrow keys to move from cell to cell. The total for this column should be 100.00.

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