Decarbonize FCCU Catalytically

Written by: Gowri Shankar Jayabalan, Technical Services Consultant, Ketjen Singapore Pte Ltd

Fluid Catalytic Cracking Unit (FCCU), a key conversion unit, is a significant contributor to the overall margin of any refinery. FCCUs are highly profitable carbon rejection machines. For a given feed and catalyst system, the higher the conversion, the higher carbon rejection and higher the net overall CO₂ emission. Given the global and refinery mandates on CO₂ emission reductions, a key challenge for many FCC operators is to lower FCC CO₂ emissions, whilst maintaining margin uplift.

In general, FCC units contribute 20-40% of CO₂ emissions in a refinery. Excluding crude distillation unit furnaces and captive power plants, the FCC unit is the largest contributor of CO2 emissions.

However, there are multiple pathways refiners can take to meet their goal of reducing FCC CO₂ emissions. These are:

• Adjustment/optimization of FCC unit operations
• Utilization of renewable feeds in FCC
• Adopting technology for CO₂ capturing/hardware modification
• Adopting advanced FCC catalyst and additive technologies

For any particular FCCU, a combination of approaches may be needed to reach its decarbonization targets.  In this article, we primarily focus on the application of FCC Catalyst and additive technologies to profitably enable an FCCU’s decarbonization needs.

Catalytic Approaches to Reduce FCCU CO₂ Emissions Ketjen has commercialized the DENALI^TM catalyst family targeted primarily for resid operations, which desire extremely low delta coke and conversion, while delivering excellent bottoms upgrade.  DENALI^TM can be formulated to target specific product profile as desired, be it transportation fuels or light olefins such as propylene and butylene. In the following, we present an illustrative case study that demonstrates how these catalytic benefits can be used to reduce CO₂ emissions. Typical of most Asian FCCUs, an FCC unit processing heavy residue feed,

equipped with two-stage regenerators and a catalyst cooler is considered for this simulation study. Table 1 summarizes the various simulations performed.  

Table 1: CO₂ reduction with DENALI^TM catalyst

Relative to the base case, the lower delta coke and superior activity retention of the DENALI^TM catalyst results in CO₂ reduction of ~ 0.9 wt%, while increasing the conversion by ~ 2.5 vol%. In cases 2 & 3, further optimization of process variables in pursued, with an intent of maintaining the baseline conversion and yield pattern, while allowing further reductions in coke yield and CO₂. Optimization of FCC riser temperature targeting the same base conversion provides ~ 5% reduction, while optimization of catalyst cooler duty targeting the same conversion yields ~ 9.5% reduction. Figure 2 shows relative comparison of the CO₂ reduction versus the margin uplift against the base case and provides an interesting perspective. Application of state-of-the-art catalyst such as DENALI^TM can provide a significant relief in CO₂ reduction at a given conversion level. Furthermore, the flexibility provided by such catalysts enable refiners to thread the needle between their carbon reduction needs and FCC margin requirements, taking into consideration their own specific economics.

Figure 2: CO₂ reduction vs. margin uplift

CO₂ reduction using state of the art ZSM-5 additive: DuraZOOM-MA^TM

An alternative approach for lowering CO₂ is to employ ZSM-5 additives with enhanced activity. Many refiners in Asia operate integrated FCC complexes with downstream petrochemical complexes with a target approach to maximize light olefins yield. While current propylene prices are depressed, the prices are expected to recover in the medium to long term, so in that scenario, they provide an additional degree of freedom for CO₂ reduction.  

At Ketjen, steady improvements have been achieved over years of continuous R&D work, primarily focused on improving the intrinsic activity, stability, and distribution of the components and physical properties of ZSM-5 additives through superior binding technology and optimized manufacturing routes. DuraZOOM-MA^TM is a result of this effort and is expected to deliver a significant boost in C3= yield at the same intake, compared to previous DuraZOOM-HA^TM. Figure 3 illustrates effect in C3= yield with DuraZOOM-MA^TM vs HA^TM at same intake.

Figure 3: Effect of C3= yield with DuraZOOM-MA^TM vs base case ZSM-5 at similar intake

Typically, most refiners increase ROT to maximize C3=, however it results in higher CO₂ emissions. Alternatively, in such a scenario where C3= yields are most desired, an alternate approach could be the employment latest ZSM-5 additive technology such as DuraZOOM-MA^TM Figure 4 illustrates the benefit of applying DuraZOOM-MA^TM compared to alternate carbon intensive approaches such increasing ROT, which results in the same C3= yield at ~3% less CO₂ emissions.

Figure 4: CO₂ reduction at same propylene yield with DuraZOOM-MA^TM vs high ROT approach

Conclusion

Given the global and refinery mandates on CO₂ emission reductions, reducing FCC CO₂ emissions, whilst maintaining margin uplift will remain a critical challenge for many FCC operators. Application of latest catalyst and/or additive technology could be an effective option to consider for achieving a significant reduction in FCC CO₂ emissions while maintaining unit margins. Conducting a commercial unit trial, would help the refiner quantify the actual benefits of CO₂ reduction and unit margins, and will help the refinery operator to define the road map towards CO₂ emissions reduction.