line of the vessel. Piping to the pump should be sized for a 0.25 psi/100 f. pressure
drop, while the discharge piping from the pump may be reduced to meet a pressure
drop of 2.5–4.0 psi/100 ft.
The Side Streams and Intermediate Reflux Sections
There are generally two or three side streams in the atmospheric crude distillation
unit. There may be one more, but a total of three side streams is the norm. The unit
that is going to be developed as an example in this work has three side streams.
These are as follows:
• Kerosene
• Light gas oil
• Heavy gas oil
With three side streams there will be usually two pumparound sections. The
purpose of these pumparound sections is to create the proper internal reflux to that
section of the tower below the location of the respective pumparound.
The pumparound takes suction from a drawoff tray in the tower. Usually this tray
is also a product drawoff. The pump delivers the pumparound stream through a heat
exchanger where it is cooled before returning it to a location in the tower about two
to three trays above the drawoff tray. This cooling liquid flowing down the tower to
the drawoff tray acts as an internal condenser. The hot vapors rising up the tower
through the drawoff tray contain the side stream product, some internal overflow,
and the vapor phase of all the lighter products and their overflow. This particular
side stream product and overflow is selectively condensed by the cold pumparound.
It enters the drawoff tray where the product quantity and pumparound leave the
tower, and the remaining condensate overflows to the tray below the drawoff. This
overflow material is the internal reflux stream, and its quantity determines the
fractionation between this lighter side stream product and the heavier side stream
product drawn from the tower at some point below.
The Side Streams
Side streams are withdrawn from selective and specially designed trays in the main
tower. Each stream is usually combined with the respective pumparound as
described earlier. When withdrawn from the tower, the product is in equilibrium
with the total vapor rising through the drawoff tray. Consequently the product
liquid will contain entrained light ends which will affect the required product
properties such as flash point and its ASTM distillation. To correct this, the side
stream product is steam stripped in a separate trayed stripping column. This
arrangement is shown in Fig. 8.
The side stream from the main tower is routed to a distributor over the top tray of
the stripping column under level control. The stripping column contains four
stripping trays. Steam is introduced below the bottom tray and flows up the tower
142
D.S.J. Jones
drop, while the discharge piping from the pump may be reduced to meet a pressure
drop of 2.5–4.0 psi/100 ft.
The Side Streams and Intermediate Reflux Sections
There are generally two or three side streams in the atmospheric crude distillation
unit. There may be one more, but a total of three side streams is the norm. The unit
that is going to be developed as an example in this work has three side streams.
These are as follows:
• Kerosene
• Light gas oil
• Heavy gas oil
With three side streams there will be usually two pumparound sections. The
purpose of these pumparound sections is to create the proper internal reflux to that
section of the tower below the location of the respective pumparound.
The pumparound takes suction from a drawoff tray in the tower. Usually this tray
is also a product drawoff. The pump delivers the pumparound stream through a heat
exchanger where it is cooled before returning it to a location in the tower about two
to three trays above the drawoff tray. This cooling liquid flowing down the tower to
the drawoff tray acts as an internal condenser. The hot vapors rising up the tower
through the drawoff tray contain the side stream product, some internal overflow,
and the vapor phase of all the lighter products and their overflow. This particular
side stream product and overflow is selectively condensed by the cold pumparound.
It enters the drawoff tray where the product quantity and pumparound leave the
tower, and the remaining condensate overflows to the tray below the drawoff. This
overflow material is the internal reflux stream, and its quantity determines the
fractionation between this lighter side stream product and the heavier side stream
product drawn from the tower at some point below.
The Side Streams
Side streams are withdrawn from selective and specially designed trays in the main
tower. Each stream is usually combined with the respective pumparound as
described earlier. When withdrawn from the tower, the product is in equilibrium
with the total vapor rising through the drawoff tray. Consequently the product
liquid will contain entrained light ends which will affect the required product
properties such as flash point and its ASTM distillation. To correct this, the side
stream product is steam stripped in a separate trayed stripping column. This
arrangement is shown in Fig. 8.
The side stream from the main tower is routed to a distributor over the top tray of
the stripping column under level control. The stripping column contains four
stripping trays. Steam is introduced below the bottom tray and flows up the tower
142
D.S.J. Jones