Page 37 - Fluid Catalytic Cracking Handbook

20 Fluid Catalytic Cracking Handbook

significant levels. Low temperature regeneration was the mode of
operation that was used in the early implementation of the catalytic
cracking process.
In the early 1970s, high temperature regeneration was developed.
High temperature regeneration meant increasing the temperature until
all the oxygen was burned. The main result was low carbon on the
regenerated catalyst. This mode of regeneration required maintaining
in the flue gas, either a small amount of excess oxygen and no CO,
or no excess oxygen and a variable quantity of CO. If there was excess
oxygen, the operation was in a full burn. If there was excess CO, the
operation was in partial burn.
With the advent of combustion promoter, the regeneration tem-
perature could be reduced and still maintain full burn. Thus, intermediate
temperature regeneration was developed. Intermediate regeneration is
not necessarily stable unless combustion promoter is used to assist in
the combustion of CO in the dense phase. Table 1 -2 contains a 2 x 3
matrix summarizing various aspects of regeneration.
The following matrix of regeneration temperatures and operating
modes shows the inherent limitations of operating regions. Regenera-
tion is either partial or complete, at low, intermediate, or high tern-

Table 1-2
A Matrix of Regeneration Characteristics

Operating Region Regenerator Partial Combustion Full Combustion
Combustion Mode Mode
Low temperature (nominally Stable (small Not achievable
1,190°F/640°C) afterburning) O 2,
CO, and CO 2 in
the flue gas
Intermediate temperature Stable (with Stable with
(nominally 1,275 °F/690°C) combustion combustion
promoter); tends to promoter
have high carbon
on regenerated
catalyst
High temperature (nominally Stable operation Stable operation
1,350°F/730°C)