395
Introduction to Refining Processes
asphaltic oil, can cause sediment formation in the unrefined feedstock or in the products, thereby
complicating the refinery process (Mushrush and Speight, 1995, 1998).
15.3 EARLY PROCESSES
Distillation was the first method by which petroleum was refined. In the early stages of refinery
development, when illuminating and lubricating oils were the main products, distillation was
the major and often the only refinery process. At that time gasoline was a minor, but more often
unwanted, product. As the demand for gasoline increased, conversion processes were developed
because distillation could no longer supply the necessary quantities of this volatile product.
The original distillation method involved a batch operation in which the still was a cast-iron
vessel mounted on brickwork over a fire, and the volatile materials were passed through a pipe
or gooseneck that led from the top of the still to a condenser. The latter was a coil of pipe (worm)
immersed in a tank of running water. Heating a batch of crude petroleum caused the more volatile,
lower-boiling components to vaporize and then condense in the worm to produce naphtha. As the
distillation progressed, the higher-boiling components became vaporized and were condensed to
produce kerosene, the major petroleum product of the time. When all of the possible kerosene had
been obtained, the material remaining in the still was discarded. The still was then refilled with
petroleum and the operation repeated. The capacity of the stills at that time was usually several barrels (bbl) of petroleum (1 bbl = 42 U.S. gal = 34.97 imperial gallons = 158.9 L of petroleum). It often
required 3 days or even more to run (distill) a batch of crude oil.
The simple distillation as practiced in the 1860s and 1870s was notoriously inefficient. The
kerosene was more often than not contaminated by naphtha, which distilled during the early stages,
or by heavy oil, which distilled from the residue during the final stages of the process. The naphtha
generally rendered the kerosene so flammable that explosions accompanied that ignition. On the
other hand, the presence of higher-boiling constituents adversely affected the excellent burning
properties of the kerosene and created a great deal of smoke. This condition could be corrected
by redistilling (rerunning, please see Section 17.5.2) the kerosene, during which process the more
volatile fraction (front-end) was recovered as additional naphtha, while the kerosene residue (tail)
remaining in the still was discarded.
The 1880s saw the introduction of the continuous distillation of petroleum. The method employed a
number of stills coupled together in a row (battery), and each still was heated separately and was hotter
than the preceding one. The stills were arranged so that oil flowed by gravity from the first to the last.
Crude petroleum in the first still was heated so that a light naphtha fraction distilled from it before the
crude petroleum flowed into the second still, where a higher temperature caused the distillation of a
heavier naphtha fraction. The residue then flowed to the third still where an even higher temperature
caused kerosene to distill. The oil thus progressed through the battery to the last still, where destructive
distillation (thermal decomposition; cracking) was carried out to produce more kerosene. The residue
from the last still was removed continuously for processing into lubricating oils or for use as fuel oil.
In the early 1900s, a method of partial (or selective) condensation was developed to allow a more
exact separation of petroleum fractions. A partial condenser (van Dyke tower) was inserted between
the still and the conventional water-cooled condenser. The lower section of the tower was packed
with stones and insulated with brick so that the heavier less volatile material entering the tower condensed and drained back into the still. Non-condensed material passed into another section where
more of the less volatile material was condensed on air-cooled tubes, and the condensate was withdrawn as a petroleum fraction. The volatile (overhead) material from the air-cooled section entered
a second tower that also contained air-cooled tubes and often produced a second fraction. The
volatile material remaining at this stage was then condensed in a water-cooled condenser to yield a
third fraction. The van Dyke tower is essentially one of the first stages in a series of improvements
that ultimately led to the distillation units found in modern refineries, which separate petroleum
fractions by fractional distillation.
Introduction to Refining Processes
asphaltic oil, can cause sediment formation in the unrefined feedstock or in the products, thereby
complicating the refinery process (Mushrush and Speight, 1995, 1998).
15.3 EARLY PROCESSES
Distillation was the first method by which petroleum was refined. In the early stages of refinery
development, when illuminating and lubricating oils were the main products, distillation was
the major and often the only refinery process. At that time gasoline was a minor, but more often
unwanted, product. As the demand for gasoline increased, conversion processes were developed
because distillation could no longer supply the necessary quantities of this volatile product.
The original distillation method involved a batch operation in which the still was a cast-iron
vessel mounted on brickwork over a fire, and the volatile materials were passed through a pipe
or gooseneck that led from the top of the still to a condenser. The latter was a coil of pipe (worm)
immersed in a tank of running water. Heating a batch of crude petroleum caused the more volatile,
lower-boiling components to vaporize and then condense in the worm to produce naphtha. As the
distillation progressed, the higher-boiling components became vaporized and were condensed to
produce kerosene, the major petroleum product of the time. When all of the possible kerosene had
been obtained, the material remaining in the still was discarded. The still was then refilled with
petroleum and the operation repeated. The capacity of the stills at that time was usually several barrels (bbl) of petroleum (1 bbl = 42 U.S. gal = 34.97 imperial gallons = 158.9 L of petroleum). It often
required 3 days or even more to run (distill) a batch of crude oil.
The simple distillation as practiced in the 1860s and 1870s was notoriously inefficient. The
kerosene was more often than not contaminated by naphtha, which distilled during the early stages,
or by heavy oil, which distilled from the residue during the final stages of the process. The naphtha
generally rendered the kerosene so flammable that explosions accompanied that ignition. On the
other hand, the presence of higher-boiling constituents adversely affected the excellent burning
properties of the kerosene and created a great deal of smoke. This condition could be corrected
by redistilling (rerunning, please see Section 17.5.2) the kerosene, during which process the more
volatile fraction (front-end) was recovered as additional naphtha, while the kerosene residue (tail)
remaining in the still was discarded.
The 1880s saw the introduction of the continuous distillation of petroleum. The method employed a
number of stills coupled together in a row (battery), and each still was heated separately and was hotter
than the preceding one. The stills were arranged so that oil flowed by gravity from the first to the last.
Crude petroleum in the first still was heated so that a light naphtha fraction distilled from it before the
crude petroleum flowed into the second still, where a higher temperature caused the distillation of a
heavier naphtha fraction. The residue then flowed to the third still where an even higher temperature
caused kerosene to distill. The oil thus progressed through the battery to the last still, where destructive
distillation (thermal decomposition; cracking) was carried out to produce more kerosene. The residue
from the last still was removed continuously for processing into lubricating oils or for use as fuel oil.
In the early 1900s, a method of partial (or selective) condensation was developed to allow a more
exact separation of petroleum fractions. A partial condenser (van Dyke tower) was inserted between
the still and the conventional water-cooled condenser. The lower section of the tower was packed
with stones and insulated with brick so that the heavier less volatile material entering the tower condensed and drained back into the still. Non-condensed material passed into another section where
more of the less volatile material was condensed on air-cooled tubes, and the condensate was withdrawn as a petroleum fraction. The volatile (overhead) material from the air-cooled section entered
a second tower that also contained air-cooled tubes and often produced a second fraction. The
volatile material remaining at this stage was then condensed in a water-cooled condenser to yield a
third fraction. The van Dyke tower is essentially one of the first stages in a series of improvements
that ultimately led to the distillation units found in modern refineries, which separate petroleum
fractions by fractional distillation.