Step 5. The calculation is complete when V/L calculated is equal to V/L assumed.
An answer within 5 % is usually acceptable. If the calculated V/L assumed is not
within this limit, make another assumption for V/L and repeat steps 2, 3, and
4. For this second assumption try 5, or 0.5, or 0.05, whichever is most
appropriate.
Step 6. If there is still no agreement between assumed and calculated V/L, plot the
two trial points (assumed V s calculated) on log graph paper. Draw a straight line
through these two points and note where on this line assumed V/L = calculated
V/L. This value is the next assumed V/L. Repeat the calculation steps 2–4 using
this value; this usually completes the calculation. If it does not then check that
the conditions for the flash are within the boiling point and condensing point for
the feed.
In the example below, it is desired to determine the amount of vapor and liquid
and their compositions in a feed to a fractionator at 112 psig and 300
F (Table 9).
Note the components NP260–NP382 are pseudo components having
mid-boiling points of 260
F, 300
F, 340
F, and 382
F respectively. K for these
components are based on their vapor pressure and system pressure relationship.
Predicting the EFV Curve from TBP Data. For crude oils and complex mixtures
such as the heavy products, the equilibrium vaporization curve can be calculated
from the TBP curve using empirical methods given by Edmister or Maxwell. In this
work the EFV is based on the method by Maxwell in his book Hydrocarbon Data.
This method has been described in the section “Developing the TBP Curve and the
Equilibrium Flash Vaporization (EFV Curve from the ASTM Distillation Curve” of
this chapter.
References
W.C. Edmister, Applied Hydrocarbon Thermodynamics (Gulf Publishing, Houston, 1961)
C. Good, et al., Oil & Gas Journal, (Pennwell Publishing, Tulsa, 1944)
J.B. Maxwell, Data Book on Hydrocarbons (D. Van Nostrand, London, 1968). 1950, 9th Printing
Thrift, Oil & Gas Journal, (Pennwell Publishing, Tulsa, 1961)
Introduction to Crude Oil and Petroleum Processing
51
An answer within 5 % is usually acceptable. If the calculated V/L assumed is not
within this limit, make another assumption for V/L and repeat steps 2, 3, and
4. For this second assumption try 5, or 0.5, or 0.05, whichever is most
appropriate.
Step 6. If there is still no agreement between assumed and calculated V/L, plot the
two trial points (assumed V s calculated) on log graph paper. Draw a straight line
through these two points and note where on this line assumed V/L = calculated
V/L. This value is the next assumed V/L. Repeat the calculation steps 2–4 using
this value; this usually completes the calculation. If it does not then check that
the conditions for the flash are within the boiling point and condensing point for
the feed.
In the example below, it is desired to determine the amount of vapor and liquid
and their compositions in a feed to a fractionator at 112 psig and 300
F (Table 9).
Note the components NP260–NP382 are pseudo components having
mid-boiling points of 260
F, 300
F, 340
F, and 382
F respectively. K for these
components are based on their vapor pressure and system pressure relationship.
Predicting the EFV Curve from TBP Data. For crude oils and complex mixtures
such as the heavy products, the equilibrium vaporization curve can be calculated
from the TBP curve using empirical methods given by Edmister or Maxwell. In this
work the EFV is based on the method by Maxwell in his book Hydrocarbon Data.
This method has been described in the section “Developing the TBP Curve and the
Equilibrium Flash Vaporization (EFV Curve from the ASTM Distillation Curve” of
this chapter.
References
W.C. Edmister, Applied Hydrocarbon Thermodynamics (Gulf Publishing, Houston, 1961)
C. Good, et al., Oil & Gas Journal, (Pennwell Publishing, Tulsa, 1944)
J.B. Maxwell, Data Book on Hydrocarbons (D. Van Nostrand, London, 1968). 1950, 9th Printing
Thrift, Oil & Gas Journal, (Pennwell Publishing, Tulsa, 1961)
Introduction to Crude Oil and Petroleum Processing
51