Hydrocarbon Processing - January 2021 - 31

Sustainability

Placid Refining Co. refinery was able to effectively manage its
flue gas NOx emissions by using a strategic FCC additive regimen and process variable optimization. NOx emissions were
first decreased by changing the combustion promoter from a
platinum-based promoter to a palladium-based one. Emissions
were further reduced with an NOx reduction additive specifically designed to catalyze the conversion of HCN and NH3 to N2.
Placid Refining operates a 25,000-bpd FCCU. The facility's crude slate is typically composed of Light Louisiana
Sweet and Gulf Coast Sour crudes. The refinery's FCCU feed
comprises 70%-80% gasoil and 20%-30% deasphalted oil.

NOX

N in coke

HCN/NH3
NONOX
N2

1.2

NOx reduction additiveb additions, lb/day

NOx reduction additiveb concentration, wt%

FIG. 4. NOx reduction additiveb mechanism.
200
180
160
140
120
100
80
60
60
20
0

0.8

0.6
0.4
0.2
0
0

60 120 180 240 300 360 420 480 540 600 660 720 780 840
Day

FIG. 5. Proprietary non-platinum additivec addition rate and
concentration.
1.2

0.8

0.6

0.4

0.2

Flue gas NOX, ppm

Case study from the Placid Refining Co. refinery. The

The feed basic nitrogen averages 440 ppm, with a typical API
gravity of 20.9.
In 2010, Placid Refining began initial steps in overall NOx
control by changing from a platinum-based CO promoter to a
proprietary non-platinum promoterc. Removing the platinum
promoter from the FCCU typically results in a 60%-70% reduction in NOx emissions.
In 2015, Placid Refining started analyzing the benefits of
a capital project vs. a non-capital project solution to further
reduce NOx emissions. This was in preparation for a new environmental regulation limiting NOx to a 45-ppm rolling average limit. The proprietary non-platinum additive was trialed
to determine if capital investment could be avoided.
Placid Refining conducted a two-phase trial: 1 wt% concentration followed by 2 wt%. During each phase of the trial, noticeable reductions were observed in the level of NOx emissions.
The trial was successful and proved that Placid Refining would
be able to meet its emissions regulations without capital investment. The proprietary non-platinum additive was stopped after
the trial and reintroduced once the NOx regulation went into

NOx reduction additiveb concentration, wt%

Non-capital investment options. The following are noncapital investment project options to reduce FCCU NOx
emissions:
CO promoter optimization. All CO promoters contribute
to NOx formation. To reduce NOx , the CO promoter addition
rate should be minimized and, if feasible, stopped. If a CO promoter is required, utilizing a non-platinum rather than a CO
promoter is a common first step to lower NOx . Non-platinum
CO promoters typically utilize palladium to catalyze CO oxidation, although other metals can be used.
O2 /CO optimization. The most prominent operating
variable to control NOx is excess oxygen in a full-burn regenerator. Lower excess oxygen contributes to lower flue gas NOx .
In partial-burn operations, NOx emissions are measured at the
CO boiler outlet. Lower flue gas CO results in lower CO boiler
NOx . NOx increases in deep partial burns because the amount
of HCN and NH3 in the regenerator flue gas increases. These reduced nitrogen species are converted to NOx in the CO boiler.
Usually, the lowest NOx formation can be achieved when operating at the crossover point between full burn and partial burn.
Feed nitrogen reduction. Minor changes in feed nitrogen
do not typically have a noticeable impact on NOx formation.
However, major changes in feed nitrogen have shown an impact
on NOx . FIG. 2 is from an FCCU that was able to decrease its
feed nitrogen by an order of magnitude by adjusting gasoil hydrotreater severity. This action allowed the operator to significantly reduce NOx formation. Another method that could significantly decrease feed nitrogen is by changing the feed source,
such as removing residue or coker gasoil from the FCCU feed
stream or changing the crude slate.
Flue gas NH3 injection. Some refiners have successfully
reduced NOx through NH3 injection into the flue gas system.
This is done at a low temperature and without a NOx reduction catalyst system. The injection point is often upstream of
the electrostatic precipitator (ESP), as NH3 also improves ESP
performance. FIG. 3 shows an FCCU that began injecting NH3
upstream of the ESP and was able to achieve a 35% reduction in
flue gas NOx emissions.
NOx reduction additive. NOx reduction additives can be
used to reduce both regenerator flue gas NOx and HCN. These
additives are injected into the regenerator through an additive
addition system. The additives are designed to catalyze the oxidation of HCN to N2 (FIG. 4). The additives are used at 1 wt%-
2 wt% concentration in Ecat and can reduce NOx by up to 40%.
Refiners can also use NOx reduction additives in combination
with other technologies to optimize operating costs.

60 120 180 240 300 360 420 480 540 600 660 720 780 840
Day

FIG. 6. Proprietary NOx reduction additivec reduced NOx emissions.
Hydrocarbon Processing | JANUARY 2021 31

Hydrocarbon Processing - January 2021

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