520
The Chemistry and Technology of Petroleum
19.3.2.4 Shell Two-Stage Fluid-Bed Catalytic Cracking
Two-stage fluid catalytic cracking was devised to permit greater flexibility in shifting product
distribution when dictated by demand. Thus, feedstock is first contacted with cracking catalyst in
a riser reactor, that is, a pipe in which fluidized catalyst and vaporized feedstock flow concurrently
upward, and the total contact time in this first stage is on the order of seconds. High temperatures
470°C–565°C (875°F–1050°F) are employed to reduce undesirable coke deposits on catalyst without
destruction of gasoline by secondary cracking. Other operating conditions in the first stage are a
pressure of 16 psi and a catalyst/feedstock ratio of 3:1–50:1, and volume conversion ranges between
20% and 70% have been recorded.
All or part of the unconverted or partially converted gas oil product from the first stage is then
cracked further in the second-stage fluid-bed reactor. Operating conditions are 480°C–540°C
(900°F–1000°F) and 16 psi with a catalyst/oil ratio of 2:1–12:1. Conversion in the second stage varies between 15% and 70%, with an overall conversion range of 50%–80%.
19.3.2.5 Universal Oil Products Fluid-Bed Catalytic Cracking
This process is adaptable to the needs of both large and small refineries. The major distinguishing
features of the process are (1) elimination of the air riser with its attendant large expansion joints,
(2) elimination of considerable structural steel supports, and (3) reduction in regenerator and in
airline size through use of 15–18 psi pressure operation.
19.3.3 movIng-Bed ProCesses
19.3.3.1 Airlift Thermofor Catalytic Cracking (Socony Airlift TCC Process)
This process is a moving-bed, reactor-over-generator continuous process for the conversion of heavy
gas oils into lighter high-quality gasoline and middle distillate fuel oils. Feed preparation may
consist of flashing in a separator to obtain vapor feed, and the separator bottoms may be sent to a
vacuum tower from which the liquid feed is produced.
The gas-oil vapor-liquid flows downward through the reactor concurrently with the regenerated
synthetic bead catalyst. The catalyst is purged by steam at the base of the reactor and gravitates into
the kiln, or regeneration is accomplished by the use of air injected into the kiln. Approximately
70% of the carbon on the catalyst is burned in the upper kiln burning zone and the remainder in
the bottom-burning zone. Regenerated, cooled catalyst enters the lift pot, where low-pressure air
transports it to the surge hopper above the reactor for reuse.
19.3.3.2 Houdresid Catalytic Cracking
Houdresid catalytic cracking is a process that uses a variation of the continuously moving catalyst
bed designed to obtain high yields of high-octane gasoline and light distillate from reduced crude
charge.
Residua, ranging atmospheric residue to vacuum residua including residua high in sulfur or
nitrogen, can be used as the feedstock, and the catalyst is synthetic or natural. Although the equipment employed is similar in many respects to that used in Houdriflow units, novel process features
modify or eliminate the adverse effects and catalyst and product selectivity usually resulting when
metals (such as nickel, vanadium copper, and iron) are present in the fuel. The Houdresid catalytic
reactor and catalyst-regenerating kiln are contained in a single vessel. Fresh feed plus recycled gas
oil is charged to the top of the unit in a partially vaporized state and mixed with steam.
19.3.3.3 Houdriflow Catalytic Cracking
This is a continuous, moving-bed process employing an integrated single vessel for the reactor and
regenerator kiln. The sweet or sour feedstock can be any fraction of the crude boiling between
The Chemistry and Technology of Petroleum
19.3.2.4 Shell Two-Stage Fluid-Bed Catalytic Cracking
Two-stage fluid catalytic cracking was devised to permit greater flexibility in shifting product
distribution when dictated by demand. Thus, feedstock is first contacted with cracking catalyst in
a riser reactor, that is, a pipe in which fluidized catalyst and vaporized feedstock flow concurrently
upward, and the total contact time in this first stage is on the order of seconds. High temperatures
470°C–565°C (875°F–1050°F) are employed to reduce undesirable coke deposits on catalyst without
destruction of gasoline by secondary cracking. Other operating conditions in the first stage are a
pressure of 16 psi and a catalyst/feedstock ratio of 3:1–50:1, and volume conversion ranges between
20% and 70% have been recorded.
All or part of the unconverted or partially converted gas oil product from the first stage is then
cracked further in the second-stage fluid-bed reactor. Operating conditions are 480°C–540°C
(900°F–1000°F) and 16 psi with a catalyst/oil ratio of 2:1–12:1. Conversion in the second stage varies between 15% and 70%, with an overall conversion range of 50%–80%.
19.3.2.5 Universal Oil Products Fluid-Bed Catalytic Cracking
This process is adaptable to the needs of both large and small refineries. The major distinguishing
features of the process are (1) elimination of the air riser with its attendant large expansion joints,
(2) elimination of considerable structural steel supports, and (3) reduction in regenerator and in
airline size through use of 15–18 psi pressure operation.
19.3.3 movIng-Bed ProCesses
19.3.3.1 Airlift Thermofor Catalytic Cracking (Socony Airlift TCC Process)
This process is a moving-bed, reactor-over-generator continuous process for the conversion of heavy
gas oils into lighter high-quality gasoline and middle distillate fuel oils. Feed preparation may
consist of flashing in a separator to obtain vapor feed, and the separator bottoms may be sent to a
vacuum tower from which the liquid feed is produced.
The gas-oil vapor-liquid flows downward through the reactor concurrently with the regenerated
synthetic bead catalyst. The catalyst is purged by steam at the base of the reactor and gravitates into
the kiln, or regeneration is accomplished by the use of air injected into the kiln. Approximately
70% of the carbon on the catalyst is burned in the upper kiln burning zone and the remainder in
the bottom-burning zone. Regenerated, cooled catalyst enters the lift pot, where low-pressure air
transports it to the surge hopper above the reactor for reuse.
19.3.3.2 Houdresid Catalytic Cracking
Houdresid catalytic cracking is a process that uses a variation of the continuously moving catalyst
bed designed to obtain high yields of high-octane gasoline and light distillate from reduced crude
charge.
Residua, ranging atmospheric residue to vacuum residua including residua high in sulfur or
nitrogen, can be used as the feedstock, and the catalyst is synthetic or natural. Although the equipment employed is similar in many respects to that used in Houdriflow units, novel process features
modify or eliminate the adverse effects and catalyst and product selectivity usually resulting when
metals (such as nickel, vanadium copper, and iron) are present in the fuel. The Houdresid catalytic
reactor and catalyst-regenerating kiln are contained in a single vessel. Fresh feed plus recycled gas
oil is charged to the top of the unit in a partially vaporized state and mixed with steam.
19.3.3.3 Houdriflow Catalytic Cracking
This is a continuous, moving-bed process employing an integrated single vessel for the reactor and
regenerator kiln. The sweet or sour feedstock can be any fraction of the crude boiling between