A very brief overview of the design steps involved follows:
1. Prepare TBP distillation and equilibrium flash vaporization curves
of the crude to be processed. Several methods are available for
converting TBP data to EFV curves.
2. Using crude assay data, construct TBP curves for all products
except gas and reduced crude. These are then converted to ASTM
and EFV curves by Edmister,5 'Maxwell,'6 or computer methods.
3. Prepare material balance of the crude distillation column, on both
volume and weight bases, showing crude input and product output.Also plot the physical properties, such as cut range on TBP and
LV%, mid vol% vs. SG, molecular weight, mean average boiling
point, and enthalpy curves for crude and various products.
4. Fractionation requirements are considered next. Ideal fractionation
is the difference between the 5% and 95% points on ASTM distillation
curves obtained from ideal TBP curves of adjacent heavier
and lighter cuts. Having fixed the gaps as the design parameter, the
ideal gap is converted into an actual gap. The difference between
the ideal gap and actual gap required is deviation. Deviation is
directly correlated with (number of plates x reflux).
5. The deviation or gap can be correlated with an F factor,7 which is
the product of number of plates between two adjacent side draws
offstream and internal reflux ratio. Internal reflux is defined as
volume of liquid (at 600F) of the hot reflux below the draw offplate
of the lighter product divided by the volume of liquid products (at
600F) except gas, lighter than the adjacent heavier products. This
implies that the reflux ratio and the number of plates are interchangeable
for a given fractionation, which holds quite accurately
for the degree of fractionation generally desired and the number of
plates (5-10) and reflux ratios (1-5) normally used. The procedure
is made clear by Example 1-1.
1. Prepare TBP distillation and equilibrium flash vaporization curves
of the crude to be processed. Several methods are available for
converting TBP data to EFV curves.
2. Using crude assay data, construct TBP curves for all products
except gas and reduced crude. These are then converted to ASTM
and EFV curves by Edmister,5 'Maxwell,'6 or computer methods.
3. Prepare material balance of the crude distillation column, on both
volume and weight bases, showing crude input and product output.Also plot the physical properties, such as cut range on TBP and
LV%, mid vol% vs. SG, molecular weight, mean average boiling
point, and enthalpy curves for crude and various products.
4. Fractionation requirements are considered next. Ideal fractionation
is the difference between the 5% and 95% points on ASTM distillation
curves obtained from ideal TBP curves of adjacent heavier
and lighter cuts. Having fixed the gaps as the design parameter, the
ideal gap is converted into an actual gap. The difference between
the ideal gap and actual gap required is deviation. Deviation is
directly correlated with (number of plates x reflux).
5. The deviation or gap can be correlated with an F factor,7 which is
the product of number of plates between two adjacent side draws
offstream and internal reflux ratio. Internal reflux is defined as
volume of liquid (at 600F) of the hot reflux below the draw offplate
of the lighter product divided by the volume of liquid products (at
600F) except gas, lighter than the adjacent heavier products. This
implies that the reflux ratio and the number of plates are interchangeable
for a given fractionation, which holds quite accurately
for the degree of fractionation generally desired and the number of
plates (5-10) and reflux ratios (1-5) normally used. The procedure
is made clear by Example 1-1.
