Hydrocarbon Processing - July 2021 - 46

Process Optimization
p
h
h
10
15
20
25
30
30
25
20
15
10
5
-10
-5
5
c
FIG. 6. Three flow patterns in an industrial
FCC standpipe. Point (c) represents the gas
leakage formed and the gas above the slide
valve flowing into the riser, while point (d)
represents the catalyst sealing ability above
the slide valve.
500
450
400
350
300
250
200
200
250
300
350
400
450
500
400
400
d
Pressure difference between C6 and C9 cross-sections
Pressure difference between C6 and C9 cross sections
1. Different catalyst flow patterns
were present in the industrial
FCC standpipe. Dynamic
pressure characteristics could
be adopted to determine the
catalyst flow patterns.
-5
-10
400 450
400 450 500 550 600 650 700 750 800 850 900
Gs, kg × m-2
500
550 600 650
700
Gs / (kgm ×-2 s-1
.
s )
-1
FIG. 8. Relationship curve between Gs
and Δploss
from 247 kg/m3
much less than ρmf
-461 kg/m3
, which was
. In Case 1, catalyst density
above the slide valve was around 461
kg/m3
Catalyst density above slide valve
Catalyst density above slide valve
lyst density dropped to only 247 kg/m3
, which had a strong sealing capacity
to prevent gas leakage from the slide valve.
However, catalyst density decreased gradually
with the reduced Gs
. In Case 4, cata.
Catalyst
flow patterns transformed into
the lean-phase fluidized solids flow, and
the catalyst sealing function disappeared.
Gas leakage was the fundamental reason
for the bottom standpipe pressure reversal.
According to the double flow pattern
500
500
600
600
Gs, kg × m-2
700
700
Gs / (kgm s )
× s-1-2
-1
FIG. 7. Catalyst density above the slide valve
under different operating conditions.
upward and the pressure gradient is still
negative, as shown in the curve in FIG. 6D.
Catalyst density above the slide
valve. For the parallel FCCU, Eq. 1 is
used to calculate the catalyst density
above the slide valve:
A = (6.29Fs × 10-2
)/[Cs
(∆p × ρ)0.5
] (1)
where:
A = Actual catalyst flow area, cm2
Ao
= Full open area of the slide valve
plate = 936.95 cm2
Fs = Catalyst circulation rate, kg/hr
ρ = Catalyst density above the slide
valve, kg/m3
Δp = Pressure drop of slide valve, kPa
Cs
= Flowrate coefficient.
throttling cone, Cs
For the single acting slide valve with a
equals 0.85. According
to TABLE 1 and Eq. 1, catalyst density
above the slide valve under different operating
conditions can be calculated as
shown in FIG. 7.
Within the operating conditions, catalyst
density above the slide valve varied
46 JULY 2021 | HydrocarbonProcessing.com
800
800
900
900
model shown in FIG. 3, pressure in the
bottom standpipe decreased, which suggested
that catalyst density above the slide
valve would be close to ρmf
. In reality, however,
catalyst density above the slide valve
from Case 2 to Case 4 was much less than
ρmf, as shown in FIG. 7. This indicated that
the gas leakage flow pattern had a similar
pressure distribution to the packed-bed
flow in the industrial FCC standpipe.
Pressure loss in standpipe. The average
pressure difference between the
C6 and C9 cross-section was defined as
the standpipe pressure drop loss in kPa
(Δploss
= pC6 - pC9). According to the avand
Gs
erage value of dynamic pressure in FIG. 4,
the relationship between Δploss
was
established as shown in FIG. 8. Within the
operating conditions (Gs
× s-1 to 857.4 kg × m-2 × s-1), there was a
, Δploss = -0.07554Gs
+ 58.51208.
= 435.4 kg × m-2
linear relationship equation between Δploss
and Gs
Takeaway . The dynamic pressure in the
regenerated standpipe was measured at different
operating conditions in a 1-MMtpy
FCCU. Process parameters and pressure
distribution in the standpipe were used to
determine the catalyst flow patterns. The
main conclusions were summarized as:
750
800 850 900
2. Catalyst flow patterns in the
standpipe varied with the
catalyst circulation rate.
Under the low catalyst mass
rate, gas leakage appeared from
the slide valve into the riser,
which was the fundamental
reason for the axial pressure
reversal in the bottom standpipe.
3. Gas leakage reduced the
standpipe pressure drop. A linear
relationship equation between Gs
and pressure loss was expressed as:
Δploss
= -0.07554Gs
+ 58.51208,
which could be used to calculate
the catalyst mass rate.
ACKNOWLEDGMENTS
The authors acknowledge financial support by the
2021 Technical Talents Innovation Foundation Project
of CNPC and the Natural Science Foundation of China.
LITERATURE CITED
Complete Literature Cited available online at
www.HydrocarbonProcessing.com.
PENG WEI is a Senior Engineer
in the FCC division of the
petrochemical branch company of
PetroChina. He has worked in FCC
plant production, management and
technical revamp for 11 yr. He holds
a PhD in chemical engineering from
the China University of Petroleum in Beijing. His
research interests include oil and gas processing and
fluidization technology, among others.
QI HONGWEI is a Senior Engineer
and the Director of the science and
technology department of the
petrochemical branch company of
PetroChina. With more than 30 yr
of experience, he is responsible for
technology management of the fuel
oil system. He also oversees the technical revamp of
many units, including the catalytic cracking, delayed
coking and distillation units. He also has abundant
experience in process optimization.
LIU YANSHENG is a Professor of
chemical engineering at the China
University of Petroleum in Beijing
and is engaged in the distillation
process, equipment development
and application of basic research.
His research interests include
transmission and separation, distillation, equipment
development and fault diagnosis. He has worked in
chemical engineering for more than 30 yr and is
responsible for the technical revamp of several FCCUs,
having abundant experience in debottlenecking the
production process.
ρ, kg × m-3 
  kgm-3
p / kPa
p, kPa
http://www.HydrocarbonProcessing.com http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - July 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - July 2021

Hydrocarbon Processing - July 2021 - Intro
Hydrocarbon Processing - July 2021 - Cover1
Hydrocarbon Processing - July 2021 - Cover2
Hydrocarbon Processing - July 2021 - 3
Hydrocarbon Processing - July 2021 - 4
Hydrocarbon Processing - July 2021 - 5
Hydrocarbon Processing - July 2021 - 6
Hydrocarbon Processing - July 2021 - 7
Hydrocarbon Processing - July 2021 - 8
Hydrocarbon Processing - July 2021 - 9
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Hydrocarbon Processing - July 2021 - 46
Hydrocarbon Processing - July 2021 - 47
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Hydrocarbon Processing - July 2021 - 90
Hydrocarbon Processing - July 2021 - Cover3
Hydrocarbon Processing - July 2021 - Cover4
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