Optimizing Catalyst Regeneration with an In Situ Oxygen Probe0 pages

Application Data Sheet

Power

Optimizing Catalyst Regeneration
with an In Situ Oxygen Probe
Optimizing the Performance of the
Catalytic Cracking Process Through
Better Gas Analysis

Catalytic crackers have long been utilized to extract additional
gasoline from heavier components resulting from the distillation
process. The distillation process is the physical separation of a
MIXTURE of different molecules, based upon the different boiling
points of these molecules. The catalytic cracking process splits
larger hydrocarbon molecules into lighter and higher value
components such as gasoline by using a catalyst, which aids the
reaction or "cracking" process. The cracking process produces
carbon, or coke, which remains on the catalyst particle, reducing
its effectiveness over time. Fluidized Catalytic Cracking Units
(FCCU) will continuously route coked catalyst into a regenerator
unit where oil remaining on the surface of the catalyst is stripped
off with steam or solvent. The catalyst is then sent into the
regenerator, where air is introduced to burn the coke off of the
hot catalyst, usually in suspension. There are many different
variations in the regeneration process, including the Continuous
Catalyst Regenerator (CCR) process.
The regeneration of catalyst frequently becomes a bottleneck
that limits the throughput of the catalytic cracking process, so
optimizing this process is important.

Complete Burn Regeneration
A complete burn regeneration process burns all of the coke off,
and the resulting flue gases are routed through gas-cleaning
equipment, and then to a smokestack. Oxygen is measured in
the flue gas resulting from the coke burn-off to maximize the
coke removal, and throughput. This may take place at the top
of the regeneration tower, and under pressure, or after a turboexpander that recovers energy and results in lower pressures
closer to the smokestack (see Figure 1). In-situ zirconiumoxide oxygen analyzers can be utilized to measure the flue
gas O2 resulting from regeneration in either location. Pressure
affects the analyzer readings, so a pressure balancing system is
recommended for pressures above 2 PSI.

Figure 1 - Typical Regenerator with Integral Combustor Section
To Fractionation
O2 Probe Mounted
in Duct Work
or Stack
Combustor-style
Regenerator

Open Riser
System

Flue Gas

Combustor
Riser
Hot-Catalyst
Circulation

Feed

Catalyst
Cooler

Air

Lift Media

Partial Burn Regeneration
A partial burn regeneration process endeavors to volatize,
or outgas the coke, and produce CO gas that is then burned
in a separate CO boiler. Some coke is also burned in this
process, and one goal is to control the CO-to-CO2 ratio in the
regeneration off-gases in order to maximize the burn-off, and
hence the throughput. An extractive analytical system utilizing
gas chromatographs or Infra-red process analyzers is typically
used to measure and control the CO and CO2 ratios. Refer to
Application Note PGC_ANO_Refining_Improving_Catalytic_
Cracking_Vapor for a detailed description of these measuring
systems.

Oxygen Enrichment Improves
Throughput (see Figure 2)

Enriching the air used in the regeneration process can increase
the coke burn-off rate. Many refineries will mix pure oxygen with
the air used for regeneration, resulting in a mixture of 21 to 25 %
O2, which increases the efficiency of the regeneration process.
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