The driving forces behind these applications are the need for gasoline, the lack of
demand for bottom of the barrel, and the increase in demand for light olefins and
aromatics. The technologies for each of these process configurations are reviewed in turn.
Gas Oil Cracking Technology Features
Reaction Technologies
All of the reaction systems offered today consist of a feed injection system, reactor
riser, riser termination device, and sometimes vapor quench technology. Each
licensor approaches the design with different equipment and configurations.
The feed injection system is probably the most important part of the reaction
system since it provides the initial contacting between the oil and catalyst. A good
system must vaporize the feed quickly, quench the hot catalyst as fast as possible,
and provide plug flow of the hydrocarbons and catalyst. Other features are important but are beyond this limited description.
The hot-regenerated catalyst generally comes to the feed riser either through a
wye (Y) section or a J-bend depending on the proximity of the regenerated catalyst
standpipe and the feed riser (see Fig. 7). Feed nozzles are usually located from 10 to
30 f. downstream of the base of the riser. Since raising the nozzles increases the
back pressure on the regenerated catalyst slide valve, lift gas may be incorporated to
control the pressure balance and minimize the backmixing of the catalyst. The lift
gas is normally light gas from the product recovery section and adds to the load in
the main fractionator and wet gas compressor. Steam is sometimes substituted
either whole or in part to reduce the processed gas but can cause some catalyst
deactivation if the regenerator temperature gets too high.
The feed injection systems (Fig. 8) employed by the various licensors all use
different nozzle designs. Oil pressure and dispersion steam rates vary by both
licensor and application. Typical oil pressure drops and dispersion steam rates are
30–150 psi and 1–7 wt% and depend on the type of feedstock processed, i.e.,
vacuum gas oils or residual feeds (BP >1,050
C (565
C)).
The feed injection systems being offered by the licensors are shown in Fig. 8.
These all consist of two fluid nozzles that mix an oil feed and steam and
distribute them across the riser cross-sectional area. Differences exist in the
methods of contacting the steam and oil, in the amount of steam and pressures
used, and in the tip design. Refiners are concerned about both performance and
reliability when choosing a system.
Reactors are vertical pipes that are generally straight and are about 100 f. long.
The diameters at each end are controlled to give adequate lift to the catalyst.
Velocities of 20–30 ft/s at the base and 50–65 ft/s at the vapor outlet are typical
with vapor residence times of about 2 s based on the vapor outlet velocity. Bends in
the riser pipe do not change the vapor residence time but increase the catalyst
residence time (or slip) and usually result in poorer oil/catalyst contacting. Riser
inserts have been offered that reportedly reduce backmixing in the riser.
Fluid Catalytic Cracking (FCC) in Petroleum Refining
273
demand for bottom of the barrel, and the increase in demand for light olefins and
aromatics. The technologies for each of these process configurations are reviewed in turn.
Gas Oil Cracking Technology Features
Reaction Technologies
All of the reaction systems offered today consist of a feed injection system, reactor
riser, riser termination device, and sometimes vapor quench technology. Each
licensor approaches the design with different equipment and configurations.
The feed injection system is probably the most important part of the reaction
system since it provides the initial contacting between the oil and catalyst. A good
system must vaporize the feed quickly, quench the hot catalyst as fast as possible,
and provide plug flow of the hydrocarbons and catalyst. Other features are important but are beyond this limited description.
The hot-regenerated catalyst generally comes to the feed riser either through a
wye (Y) section or a J-bend depending on the proximity of the regenerated catalyst
standpipe and the feed riser (see Fig. 7). Feed nozzles are usually located from 10 to
30 f. downstream of the base of the riser. Since raising the nozzles increases the
back pressure on the regenerated catalyst slide valve, lift gas may be incorporated to
control the pressure balance and minimize the backmixing of the catalyst. The lift
gas is normally light gas from the product recovery section and adds to the load in
the main fractionator and wet gas compressor. Steam is sometimes substituted
either whole or in part to reduce the processed gas but can cause some catalyst
deactivation if the regenerator temperature gets too high.
The feed injection systems (Fig. 8) employed by the various licensors all use
different nozzle designs. Oil pressure and dispersion steam rates vary by both
licensor and application. Typical oil pressure drops and dispersion steam rates are
30–150 psi and 1–7 wt% and depend on the type of feedstock processed, i.e.,
vacuum gas oils or residual feeds (BP >1,050
C (565
C)).
The feed injection systems being offered by the licensors are shown in Fig. 8.
These all consist of two fluid nozzles that mix an oil feed and steam and
distribute them across the riser cross-sectional area. Differences exist in the
methods of contacting the steam and oil, in the amount of steam and pressures
used, and in the tip design. Refiners are concerned about both performance and
reliability when choosing a system.
Reactors are vertical pipes that are generally straight and are about 100 f. long.
The diameters at each end are controlled to give adequate lift to the catalyst.
Velocities of 20–30 ft/s at the base and 50–65 ft/s at the vapor outlet are typical
with vapor residence times of about 2 s based on the vapor outlet velocity. Bends in
the riser pipe do not change the vapor residence time but increase the catalyst
residence time (or slip) and usually result in poorer oil/catalyst contacting. Riser
inserts have been offered that reportedly reduce backmixing in the riser.
Fluid Catalytic Cracking (FCC) in Petroleum Refining
273