ERTC 2023
Reducing environmental impact of FCCs with wet gas scrubbers by using SO x additives
ANdrew hubbell citgo, brandon burns shell energy and chemicals and victor batarseh w.r. grace & c0
Introduction Over the last 80 years, the FCC has played a critical role in the refining industry and continues to adapt to shifting industry conditions. The next opportunity to dem- onstrate the flexibility of the FCC is to re-optimise the unit to reduce its carbon intensity. Grace remains committed to sup- porting the industry with creative solutions to drive the highest profitability operation while minimising the FCC’s environmental footprint. The case studies below exam- ine Grace’s collaboration with refiners to maintain environmental compliance for SO x emissions in a more cost-effective and sus- tainable manner. SO x reduction additives have long been used in the FCC to limit SO x emissions to the atmosphere in units without wet gas scrub- bers (WGSs). Units with WGSs typically do not require SO x additives to maintain regu- latory compliance. However, they can be implemented to offset caustic usage, reduc- ing operating expenses and limiting the life- cycle CO₂e (carbon dioxide equivalent) of operating the FCC while also converting waste streams to usable products. In these case studies, lifecycle CO₂e reduction is achieved by limiting the amount of NaOH being produced, shipped to, and utilised by the FCC WGS. The waste avoidance described here is driven by the additive capturing the sulphur, which would be wastewater-dissolved solids and redirecting it to generate ele- mental sulphur. A full-burn FCC at CITGO Lemont’s refinery and a partial-burn FCC at a Shell refinery on the US Gulf Coast are examined here. Case Studies In both case studies, the first step to imple- menting SO x additives for WGS caustic reduction was to understand the caustic consumption without using additive. To do this, multivariable linear regressions were developed to predict additive-free caus- tic consumption from parameters, includ- ing feed sulphur mass flow rate. For both cases, close alignment between actual and predicted caustic consumption confirms a good fit for the regression model. Utilising a combination of the baseline data and Grace’s proprietary SO x additive performance model, an evaluation was con-
tive in partial burn, significant sustaina- bility benefits are still realised through a reduction in lifecycle CO₂e emissions and waste avoidance. Operation without SO x additive requires greater amounts of caustic to be produced, then shipped to the refiner, and treated as total dissolved solids in wastewater plants. Additional details on data and calculations associated with the lifecycle CO₂e changes in the system when considering this switch from caustic to a combination of caustic and SO x additive are shown in Table 1 . This analysis confirms that implement- ing Grace’s EMISSCIAN TM SO x additive for WGS caustic reduction at both the CITGO Lemont and Shell US Gulf Coast FCCs not only provided significant Opex reduc- tion but also reduced the Scope 3 carbon emissions associated with operating the FCC and diverted sulphur from a waste stream to the sulphur plant, creating a sell- able product. Annualised CO₂e reduction totals were substantial at more than 8,100 tons combined between the two FCCs, which equates to saving the emissions from com- busting 135.5 million standard cubic feet (MMSCF) or 140,300 million BTUs of nat- ural gas. Conclusions Evaluation of the activities at CITGO and the Shell refinery show that implementing SO x additive for WGS caustic abatement has the potential to deliver sustainabil- ity benefits in addition to Opex reduction. The sustainability benefits include a reduc- tion in Scope 3 emissions associated with caustic production and transportation as well as converting the sulphur destined for waste into a usable product in both full- and partial-burn FCC units. Implementing Grace’s SO x additive, EMISSCIAN, allows refiners to achieve these benefits while also minimising SO x emissions compliance Opex by delivering the highest flue gas sul- phur reduction per pound of additive across a variety of applications. Grace remains dedicated to continually investing in the development of novel solutions and man- ufacturing capabilities to better serve its customers.
Primary analysis
CITGO Lemont FCC
Shell US Gulf FCC (partial burn)
(full burn)
SOx additive usage (lbs/day)
510
400
Caustic usage and delivery reduction
Usage, 11.8 (dry sT/day) Deliveries, 1.1 per day
21.3% (combined)
SOx additive deliveries (deliveries/day)
0.01 16.3
0.01
6.1
Lifecycle CO
2e reduction (tons/day)
Annualised lifecycle CO 2e
reduction (tons/year)
5,959
2,230
Other impacts Waste sulphur converted into sellable product (tons/day) Waste sulphur converted into sellable product (tons/year)
9.5
4.2
3,461
1,536
SOx additive to cement kiln (lbs/day)
510
400
Table 1 Summary of sustainability benefits associated with implementing SO x additive in combination with WGS caustic at CITGO
additive was compared to the actual caus- tic usage with SO x additive, and the gap between actual and predicted caustic con- sumption signifies the reduction achieved with the additive. The refinery averaged 510 lb per day of SO x additive usage and 11.8 dst per day of caustic reduction, realising net SO x control Opex savings of $2.5-3.5 million per year (annualised after excluding a period of unu- sual operation during turnarounds at other process units). This was calculated assum- ing a $1,000 per dst caustic price. The deep partial-burn Shell US Gulf Coast FCC examined here is a residual fluid catalytic cracking unit (RFCC) that typically operates at ~100,000 barrels per day with a 22.5 feed API and sulphur content of 0.7-1.1 wt%. This FCC rou- tinely operates with flue gas CO between 5-7 vol%. Grace collaborated with Shell, leveraging unit data and Grace’s proprie- tary model to identify the optimum caustic reduction to minimise SO x emissions com- pliance operating expenses. Due to operation in partial burn and lim- ited oxygen availability for oxidising SO₂ to SO₃, SO x additive is less effective in this unit than the full-burn FCC studied in the previous case study. As a result of partial-burn operation and other unit parameters, the target caus- tic reduction for maximising Opex sav- ings was 20-25% at the Shell refinery. Implementation of 400 lb per day of SO x additive, preblended with fresh catalyst, drove a 21.3% caustic reduction. This resulted in $0.5-1.0 million per year in sav- ings, assuming a $1,000 per dst caustic price. Despite the challenges for SO x addi-
ducted to determine the optimal balance between additive usage and WGS caustic required to minimise total emissions com- pliance operating expenses. This type of analysis demonstrates that there is a wide range of SO x additive rates over which oper- ating expenses (Opex) can be reduced. The full-burn CITGO Lemont FCC unit typically processes 60,000 barrels per day of feed with an API of 18 and sulphur content of 2.5 wt%. For this operation, the Implementing EMISSCIAN SOx additive not only provided significant Opex reduction but also reduced Scope 3 emissions associated with the FCC unit’s WGS consumes ~24.5 dry short tons (dst) of caustic (NaOH) per day. The CITGO Lemont and Grace teams collaborated to develop a comprehensive analysis to help set SO x additive rates throughout the year as caustic pricing, feed quality, and feed rates shifted. The evaluation revealed additive rates ranging from 400 to 700 lb per day maxim- ised the total SO x compliance Opex savings by appropriately balancing SO x additive and WGS caustic. The same regression model utilised to describe caustic usage without
Contact: victor.batarseh@grace.com
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