1. Design Guidelines of Crude Oil Distillation Units
Ref.1: Y.A. Liu et al, Petroleum Refinery Process Modeling, Wiley-VCH, 2018 , Chapter 2.
Ref.2: R.N. Watkins, Petroleum Refinery Distillation, Gulf Publishing Company, 2nd ed., 1979, Chapter 2.

2. Crude Oil Distillation Design guidelines
The first step in designing the atmospheric distillation column is the column pressure. The minimum pressure is the lowest permissible pressure in the reflux drum. The practical range is 0.2 to 1.0 psig. The design pressure drop across the condenser should be set to 5 psi. The allowable pressure drop for trays will be in the range of 0.1 to 0.2 psi per tray. Most atmospheric towers have 25 to 35 trays between the flash zone and the tower top. So a pressure drop of 3 to 6 psi can be assumed between the flash zone and the tower top. A pressure drop of 5.0 psi between the flash zone and the furnace outlet is recommended.

3. Crude Oil Distillation Design guidelines
Recommended ranges for the number of ideal trays in various sections of the atmospheric tower are given in the following Table. Notice that for hydrocarbon distillation, the overall stage efficiencies (Eo) are 50–90%. For absorption processes, the range is 10–50% NIdeal trays = Eo× NActual trays
Separation section
Number of trays
Overall zone efficiency
Light naphtha to heavy naphtha
6 to 8
0.6
Heavy naphtha to kerosene
4 to 6
0.5
Kerosene to diesel
3 to 4
Diesel to atmospheric gas oil
0.4
Atmospheric gas oil to flash zone
0.3
Flash zone to column bottom
1 to 2
0.2
Steam and reboiled stripping sections

4. Crude Oil Distillation Design guidelines
Volumetric flow of petroleum fractions can be estimated from TBP curve of crude oil based on TBP cut points as shown in the following Table:
Petroleum fraction
TBP cut points (oF)
Light ends
IBP-100
Light straight run (LSR)
Naphtha
Kerosene
Diesel
Atmospheric gas oil (AGO)
Light vacuum gas oil (LVGO)
Heavy vacuum gas oil (HVGO)
Vacuum residue
1000-FBP

5. Crude Oil Distillation Design guidelines
The relationship between TBP cut points of petroleum fractions and whole TBP curve of petroleum fractions are shown in the following Figure.

6. Crude Oil Distillation Design guidelines
TBP overlap is defined as (TBP EP of light fraction)-(TBP IP of heavy fraction)

7. Crude Oil Distillation Design guidelines
The recommended specifications for petroleum fractions, ASTM D86 at 95% point, and (5-95) gap are shown in the following Tables:
Petroleum fraction
ASTM D86, 95% (oF)
LSR
Naphtha
360
Kerosene
520
Diesel
620
Atmospheric gas oil (AGO)
Petroleum fraction
(5-95) gap (oF)
Naphtha - LSR
≥ 30
Kerosene - Naphtha
Diesel - Kerosene
≥ 0
AGO - Diesel
-10 to -20

8. Crude Oil Distillation Design guidelines
The required flowrate of steam in side strippers and main column can be estimated based on the following guideline: lb of steam/bbl of product = 8 to 10 The original purpose of adding pump-around circuits was to reduce vapor and liquid traffic at the top section of the column. Without pump-around circuits, all condensation heat has to be removed from the condenser, which results in a large vapor flowrate at the top trays.

9. Crude Oil Distillation Design guidelines
The presence of the pump-around circuit decreases the number of effective ideal trays. The effect can be even more detrimental to separation if the flowrate of a pump-around circuit is increased. These effects can be compensated to a certain extent by increasing the steam rate in the side strippers. Another solution is to increase the number of trays. However, with the constant total number of trays, the relationship between heat recovery and steam consumption can be incorporated into the design procedure.