Hydrocarbon Processing - October 2022 - 25

Special Focus Plant Safety and Environment
Q. JIANG, H. SHA and H. SONG, SINOPEC Research Institute
of Petroleum Processing, Beijing, China; S. CUI, J. ZHOU
and D. CAO, SINOPEC Refining Department, Beijing, China;
H. CHEN, SINOPEC Science & Technology Department, Beijing,
China; S. WANG, Y. ZHANG and L. YANG, SINOPEC Qingdao
Refining & Chemical Co. Ltd., Qingdao, China; and T. WANG,
F. KONG and S. WANG, SINOPEC Catalyst Co. Ltd., Beijing, China
An economic evaluation for SOx
refining and petrochemical industry. SOx
) removal has been a global trend in the
reduction additives
from the FCC regenerator
and wet gas scrubbers (WGSs) are the two most widely used
methods to reduce SOx
(FCC) flue gas in addition to feedstock hydrorefining. SOx
duction additives can remove SOx
flue gas with low cost, high efficiency and flexibility. In theory,
flue gas SOx
to achieve SOx
on the application of a proprietary SOx
-reduction additivea
emissions from fluid catalytic cracking
recould
be reduced to an extremely low level if the
proportion of additives was not limited.
However, in a practical FCCU, refiners must consider how
reduction in the most economical way. Based
in
25 different FCCUs with WGSs, the economic benefits of the
application of the SOx
-reduction additive were evaluated and
the most cost-effective ways to use the additive under different
regeneration conditions were predicted.
The cost of SOx
WGSs. The main reaction in WGSs is SO2
additives vs. the cost of caustic in
+ 2NaOH = Na2SO3
+ H2O, so a linear relationship exists between the apparent consumption
of caustic and sulfur dioxide (SO2
tain range of SO2
and that of the SOx
-reduction additivea
) removal in a cerconcentration.
The efficiency of additives to
captured by additive per unit mass].
is P2, then the break≤
1/64 × 40 × 2/30% × P1
(1)
capture SO2 is determined by what is called the pick-up factor
[(PUF): the mass of SO2
Assuming that the unit price of caustic with 30 wt% NaOH is
P1
even point of additive can be calculated as follows (Eq. 1):
1/PUF × P2
PUF ≥ 0.24 × P2/P1
than to consume caustic in WGSs when the PUF of the additive
was greater than 0.24 × P2
Therefore, it would be more economical to use SOx
/P1
additives
kg SO2/kg additive. It should be
)
capture-the benefits of sulfur
noted that the actual cost savings would be even higher since
the simplified model did not consider sulfur trioxide (SO3
capture-it is generally believed that the additive is more
effective than WGSs in SO3
recovery, the cost of treating high-salt wastewater and the WGS
plant investment.
FIG. 1. The relationship between the PUF of the proprietary and the
regenerator outlet SO2
concentration under different excess oxygen
conditions.
Hydrocarbon Processing | OCTOBER 2022 25
emissions reduction
from FCC regenerator flue gas using an additive
Sulfur oxides (SOx
S) in the reactor. A good SOx
Prediction of PUF and maximum cost savings. The PUF
is closely related to the properties of SOx
additives and the operating
conditions of FCCUs. The additive properties lie in
effective magnesium oxide (MgO) utilization, the ability to
promote the conversion of sulfur (S) compounds to SO3
in the
regenerator, and the ability to reduce sulfate to hydrogen sulfide
(H2
-reduction additive should also
balance the high reactant accessibility and low attrition index.
The operating conditions are embodied in the following
aspects. Flue gas excess oxygen content is the decisive factor
to some extent because it determines the conversion of S compounds
to SO3
in the regenerator. The initial SOx
determines the mass transfer force so that higher SOx
concentration
concentration
results in a higher PUF. Increasing the catalyst circulation
rate increases the availability of fresh metal oxides for SOx
Hydrocarbon Processing - October 2022

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