Note: The quantity of overflow in this case is independent of pumparound duties
above it. It is dependent only on the amount of overflash.
Calculate Tower Loading in the Packed Section of Vacuum Towers
As discussed earlier, most modern “dry” vacuum towers use low pressure drop grid
or stacked packing. This packing enhances heat exchange in the tower and of course
permits the tower to operate at very low pressures. Nevertheless, this packing can
become overloaded causing high pressure drop in the tower and poor all-around
performance.
The following discussion describes a general method of evaluating the grid
performance in terms of its pressure drop. Please note this is a quick general method
of estimating tower packing design or performance. Proprietary grid and packing
manufacturers have their own correlations which they use in their design work.
A more detailed examination of packed tower loading is presented in the author’s
2.00
1.00
.10
1.50 1.50
1.00 1.00
0.50 0.50
0.25 0.25
0.10 0.10
L O W E R L O A D L IN E
L O W E R L O A D L IN E
0.05 0.05
UP PE R LO AD LIN E
UP PE R LO AD LIN E
FL O O D IN G LI N E
FL O O D IN G LI N E
PRESSURE DROP PARAMETER
INCHES OF WATER PER FOOT
OF PACKING
1.50
1.00
0.50
0.25
0.10
L O W E R L O A D L IN E
0.05
UP PE R LO AD LIN E
FL O O D IN G LI N E
.010
G
2
FpμL 0.2
e
R
e
ν e
L g
c
.001
.01
.1
1
L
G
1/2
ρ ν
ρ L
10
20
L = Liquid Rate, Lbs/sec., Sq.ft
e L = Liquid Density, Lbs/cu. ft
F P = Packing Factor ≈ a /∈
3
e R = Ratio, Density of Water
Density of Liquid
G = Gas Rate, Lbs/sec., sq.ft
e V = Gas Density, Lbs/cu. ft
g e = Gravitational Conversion Factor − 32.2
m L = Viscosity of Liquid, Centipoise
Fig. 34 Pressure drop through grid in inches of hot liquid per foot height
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
191
above it. It is dependent only on the amount of overflash.
Calculate Tower Loading in the Packed Section of Vacuum Towers
As discussed earlier, most modern “dry” vacuum towers use low pressure drop grid
or stacked packing. This packing enhances heat exchange in the tower and of course
permits the tower to operate at very low pressures. Nevertheless, this packing can
become overloaded causing high pressure drop in the tower and poor all-around
performance.
The following discussion describes a general method of evaluating the grid
performance in terms of its pressure drop. Please note this is a quick general method
of estimating tower packing design or performance. Proprietary grid and packing
manufacturers have their own correlations which they use in their design work.
A more detailed examination of packed tower loading is presented in the author’s
2.00
1.00
.10
1.50 1.50
1.00 1.00
0.50 0.50
0.25 0.25
0.10 0.10
L O W E R L O A D L IN E
L O W E R L O A D L IN E
0.05 0.05
UP PE R LO AD LIN E
UP PE R LO AD LIN E
FL O O D IN G LI N E
FL O O D IN G LI N E
PRESSURE DROP PARAMETER
INCHES OF WATER PER FOOT
OF PACKING
1.50
1.00
0.50
0.25
0.10
L O W E R L O A D L IN E
0.05
UP PE R LO AD LIN E
FL O O D IN G LI N E
.010
G
2
FpμL 0.2
e
R
e
ν e
L g
c
.001
.01
.1
1
L
G
1/2
ρ ν
ρ L
10
20
L = Liquid Rate, Lbs/sec., Sq.ft
e L = Liquid Density, Lbs/cu. ft
F P = Packing Factor ≈ a /∈
3
e R = Ratio, Density of Water
Density of Liquid
G = Gas Rate, Lbs/sec., sq.ft
e V = Gas Density, Lbs/cu. ft
g e = Gravitational Conversion Factor − 32.2
m L = Viscosity of Liquid, Centipoise
Fig. 34 Pressure drop through grid in inches of hot liquid per foot height
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
191