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As refiners prepare for summer operations, optimizing FCC units becomes crucial. Operators may need to run poorer quality feeds at maximum capacity while optimizing FCC products to maximize refinery profitability. Higher ambient temperatures and cooling water constraints push FCC units to their limits.

Optimizing FCC Units

When optimizing FCC units, remember to include equilibrium catalyst (ecat) activity. Operations and engineers often focus on riser outlet temperature (ROT) and catalyst-to-oil ratio (CTO) when optimizing between capacity and severity. Lowering ROT can maximize feed rates at the expense of conversion, but adjusting catalyst activity can re-optimize these concessions.

Catalyst Activity

Catalyst activity, measured by vendors, indicates conversion percentage of a standard gas oil sample. Ketjen's Fluidized Standard Test (FST) provides this key variable. Catalyst activity can be adjusted by changing the catalyst addition rate (CAR) or the formulation of fresh catalyst. Both options have pros and cons depending on unit goals.

Commercial Examples

Optimizing ROT and Ecat Activity: A refiner reduced ROT during summer and increased catalyst activity to improve selectivity. This strategy optimized slurry yields while lowering ROT to maximize feed and limit dry gas production.

This first, classic example focuses on a refiner who reduced ROT during the summer to manage constraints but also increased catalyst activity to counter the lower ROT to improve selectivity. The graph below shows how catalyst activity was increased to offset the reduction in ROT.

The analysis of the ecat (via Ketjen’s FST test) shows that the 650F+ yield improved with the activity of the catalyst, while dry gas yield remained relatively flat. This is the case because dry gas yield is significantly impacted more by ROT. This strategy allowed the refinery to achieve optimal slurry yields at the FCC unit while lowering ROT to maximize feed and limit dry gas production.

Impact of Poor Catalyst Addition System Reliability: Unreliable catalyst addition rates led to deteriorating catalyst activity, resulting in increased slurry yield and decreased C4 olefin yield. This example highlights the importance of maintaining a reliable catalyst addition system.

In our second example, optimization did not go as planned. This FCC maintains a consistent feed diet and operation, allowing it to optimize around margins and constraints. Unfortunately, catalyst addition rates were impacted by loader/addition system reliability. As a result, the normal circulating catalyst activity of 72-74 slowly deteriorated through the year due to unstable addition rates, reaching as low as 69.

Poor catalyst addition reliability led to less catalyst selectivity at similar operating conditions, which resulted in an increase of +2 vol% slurry and a decrease of 0.5 vol% C4 olefin yield between 73 and 70 catalyst activity.

This example serves as an important reminder to maintain a healthy catalyst addition system. While disappointing, this data helps justify regularly scheduled maintenance to improve the reliability of the additional system or the need to implement a capital project to replace the loader.

Higher Activity with Less Rare Earth: Switching to Ketjen's ACTION+™ formulation allowed a refiner to achieve improved operating conditions with lower rare earth levels, enhancing flexibility without sacrificing yields and selectivity.

In our final example of attempts to optimize catalyst activity, we turn to a refiner who chose to switch their catalyst to an ACTION+™ formulation. Historically, the easiest and most direct way to increase FCC catalyst activity without adding operating cost is to add rare earth to the zeolite. Unfortunately, this approach leads to lower olefinic LPG and reduced gasoline octane due to increased hydrogen transfer. As a result, refiners are often forced to compromise, balancing activity, olefin selectivity, and catalyst cost.

Ketjen’s innovative ACTION+™ platform incorporates our bottoms upgrading matrix (MT-20) with our zeolite stabilization system (ZT-500), which allows lower rare earth levels on zeolite without sacrificing activity and butylene selectivity. In this example, the FCC was able to improve operating conditions, specifically running at lower ROT and regenerator bed temperature.

This allowed more flexibility on unit constraints, such as WGC and air blower limits. However, the yields and selectivity were not sacrificed to get these better operating conditions, as shown in the accompanying tables displaying C4 olefin and slurry yields.

This example illustrates the importance of not solely looking at catalyst activity as an optimization handle but also catalyst technology and formulation as part of the overall optimization strategy. The advantage of changing the activity of your fresh catalyst via re-formulation is that addition rates will not be impacted.

Summary

FCC optimization is key to refinery profitability. Including catalyst activity and formulation in optimization strategies is crucial. Maintain a healthy catalyst addition system to ensure reliability and consider re-formulation to adjust activity without impacting addition rates. The experts at Ketjen are available to help you determine the optimized target for your catalyst activity and reach your FCC goals.