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cracking process gradually retards along the riser due to the reduction in activity
caused by the inevitable deposition of coke on the catalyst surface.
The spent catalyst falls down the cyclone diplegs into the stripper. In the stripper,
high-pressure steam displaces the remaining hydrocarbons adsorbed on the catalyst’s surface. An efficient catalyst stripper design provides intimate contact between
the catalyst and steam. It is important to minimize the amount of hydrocarbon
vapors carried over to the regenerator, but not all the hydrocarbon vapors can be
displaced from the catalyst pores in the stripper. A fraction of them is carried with
the spent catalyst into the regenerator. Improper stripping can cause high regenerator temperatures and high hydrogen content on coke. The stripped catalyst enters
the regenerator through the spent catalyst standpipe (SCSP). The flow of the catalyst
to the regenerator is controlled by the spent catalyst slide valve (SCSV). The opening of the valve depends upon the level of the catalyst in the stripper.
The catalyst entering the regenerator contains 0.5–1.5 wt% coke. This coke
blocks the pores and active sites on the catalyst. In the regenerator, heated air is used
to fluidize the catalyst and burn off this coke and regenerate the catalyst. The combustion of coke provides the heat energy required to crack heavy hydrocarbons in
the riser. This combustion can be partial or complete, i.e., excess air supplied. There
are cyclones to separate the catalyst from the resulting flue gasses; the catalyst trickles down the diplegs into the regenerated catalyst standpipe (RCSP), whereas the
flue gas escapes from the top of the regenerator. The flow of the catalyst in the RCSP
Fig. 8 Schematic of riser–reactor–regenerator [34]
A. R. Khande et al.
cracking process gradually retards along the riser due to the reduction in activity
caused by the inevitable deposition of coke on the catalyst surface.
The spent catalyst falls down the cyclone diplegs into the stripper. In the stripper,
high-pressure steam displaces the remaining hydrocarbons adsorbed on the catalyst’s surface. An efficient catalyst stripper design provides intimate contact between
the catalyst and steam. It is important to minimize the amount of hydrocarbon
vapors carried over to the regenerator, but not all the hydrocarbon vapors can be
displaced from the catalyst pores in the stripper. A fraction of them is carried with
the spent catalyst into the regenerator. Improper stripping can cause high regenerator temperatures and high hydrogen content on coke. The stripped catalyst enters
the regenerator through the spent catalyst standpipe (SCSP). The flow of the catalyst
to the regenerator is controlled by the spent catalyst slide valve (SCSV). The opening of the valve depends upon the level of the catalyst in the stripper.
The catalyst entering the regenerator contains 0.5–1.5 wt% coke. This coke
blocks the pores and active sites on the catalyst. In the regenerator, heated air is used
to fluidize the catalyst and burn off this coke and regenerate the catalyst. The combustion of coke provides the heat energy required to crack heavy hydrocarbons in
the riser. This combustion can be partial or complete, i.e., excess air supplied. There
are cyclones to separate the catalyst from the resulting flue gasses; the catalyst trickles down the diplegs into the regenerated catalyst standpipe (RCSP), whereas the
flue gas escapes from the top of the regenerator. The flow of the catalyst in the RCSP
Fig. 8 Schematic of riser–reactor–regenerator [34]
A. R. Khande et al.