Hydrocarbon Processing - August 2021 - 18

Valves, Pumps and Turbomachinery
teed the emergency switch of the regeneration
slide valve, but the sensitivity to
control the catalyst circulation rate was
poor, and the reaction temperature still
fluctuated. According to the fluidization
theory,2,3
engineers explored the influIt
was found that
/hr)
ence of sensitive aeration gas on the reaction
temperature.
catalyst flow patterns and amplitude of reaction
temperature could be adjusted by
changing the aeration rate (Qa, Nm3
at the C5-C7 nozzles above the regeneration
slide valve. FIG. 8 shows the effect of
Qa on the reaction temperature and the
opening of the regeneration slide valve.
Based on the stability of the reaction
temperature, catalyst flow patterns in the
vicinity of the slide valve were divided into
packed-bed flow, bubbling fluidized flow
and slug flow. In the packed-bed flow, Qa
was only 30 Nm3
/hr. The opening of the
regeneration slide valve was large, around
50%, but the reaction temperature was stable
and the fluctuation was 510°C-515°C.
Reaction temperature increased with
the increase of Qa. When Qa was 60
Nm3
/hr, packed-bed flow varied with
the bubbling fluidized flow. The reaction
temperature increased to 518°C-523°C,
and the opening of the regeneration slide
valve decreased to 40%. The catalyst was
fluidized well in the vicinity of the slide
valve, and the standpipe driving force was
strengthened. When Qa was larger than
90 Nm3
/hr, the reaction temperature and
the opening of the slide valve fluctuated
significantly within the ranges of 510°C-
527°C and 35%-70%, respectively. This
phenomenon indicated that large bubbles
appeared in front of the slide valve, referred
to as the slug flow.
FIG. 9 shows the effect of Qa on the
FIG. 6. Soft coke in grids.
axial pressure distribution in the regeneration
standpipe. The pressure distribution
above the C4 cross-section was not affected
by Qa, but the pressure above the slide
valve increased first, and then decreased
with the increase of Qa, indicating that
the pressure drop of the standpipe and the
catalyst circulation rate in the packed-bed
flow and slug flow were lower than that in
the bubbling fluidized flow. During the
production process, the operating parameters
and catalyst flow pattern should be
adjusted in time, according to the reaction
temperature fluctuation. The packed-bed
flow above the slide valve is suitable for
low-load condition. The bubbling fluidized
flow is suitable for high-load condition,
and the slug flow is the most difficult
to operate. When the reaction temperature
fluctuates greatly, the aeration rate above
the slide valve should be reduced in time.
Takeaway. This article introduced a
double-valve control technology for the
FCCU to realize the online treatment of a
stem fracture in a slide valve, prolong the
operation cycle of the FCCU and avoid
an unplanned shutdown. By adjusting the
aeration rate, the influence of sensitive
aeration gas on the reaction temperature
and the opening of the slide valve was explored,
and stable control of the reaction
temperature was realized.
ACKNOWLEDGMENTS
The authors acknowledge support by the Research
Foundation of the Karamy Campus of the China
University of Petroleum in Beijing (grant number
RCYJ2016B-02-001). The authors also acknowledge
financial support from CNPC's Technical Talents
Innovation Foundation Project (2021).
LITERATURE CITED
1
2
Leung, L. S. and L. A. Wilson, " Down flow of solids in
standpipes, " Powder Technology, Vol. 7, 1973.
Zhao, Z. H. and X. D. Ye , " Chinese FCCU revamp
improves performance, " Oil &Gas Journal, Vol. 99, Iss.
46, 2001.
3
FIG. 7. Double-valve control technology.
530
525
520
515
510
505
500
Reaction temperature
Bubbling
Packed-bed flow
Qa = 30 Nm3/hr
OP% = 50%
20
40
fluidized flow
Qa = 60 Nm3/hr
OP% = 40%
60
Time, min
FIG. 8. Effect of aeration rate on reaction
temperature.
18 AUGUST 2021 | HydrocarbonProcessing.com
80
Slug flow
Qa = 90 Nm3/hr
OP% = 35%-70%
100
120
30
25
20
15
10
5
Pi
C1-C2
C3
C4
C5-C7
C8
200
250
300
p, kPa
FIG. 9. Effect of aeration rate on pressure
distribution.
350
Ps
Po
400
450
LIU YANSHENG is a Professor of chemical engineering
at China University of Petroleum in Beijing. He has
worked in the chemical engineering field for more
than 30 yr and is responsible for the technical revamp
of several FCCUs.
Qa = 60 Nm3/hr
Qa = 90 Nm3/hr
Qa = 30 Nm3/hr
4
Wolschlag, L. M. and K. A. Couch, " Upgrade FCC performance, "
Hydrocarbon Processing, September 2010.
Knight, J. and R. Mehlberg, " Maximize propylene
from your FCC unit, " Hydrocarbon Processing,
September 2011.
GAO RUIBO is a Process Engineer for catalytic
cracking in the petrochemical branch of PetroChina.
He has been engaged in process technology
management of the FCCU for 13 yr, during which time
he has carried out a number of technical renovations
of the FCCU.
PENG WEI is a Process Engineer for catalytic cracking
in the petrochemical branch of PetroChina. He holds
a PhD in chemical engineering from China University
of Petroleum.
Temperature, °C
Elevation, m
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