How Much FCC Catalyst Should You Add Per Day?
By Richard Grove and Adrian Humphries
FCC catalyst addition rate is determined by metals control and the desired catalyst activity level. The optimal rate depends on feed quality, unit constraints, and the economic tradeoff between catalyst cost and product value.
Becht’s Fun with FCC Catalyst series takes a conversational look at how catalyst choices shape FCC performance. From tweaking frequency to test strategy and cost trade-offs, each post aims to spark debate and share real-world insights – because great ideas often start with great discussions.
Key takeaways
- FCC catalyst addition rate is driven by metals accumulation in the catalyst.
- Catalyst activity targets directly influence how much fresh catalyst is required.
- High metals levels increase coke and dry gas yield and degrade catalyst performance.
- Alternative coke sources often reduce product value and increase operating cost.
- Increasing fresh catalyst addition can improve heat balance and unit economics.
What determines FCC catalyst addition rate?
Fresh catalyst addition rate is one of the most discussed – and debated – topics in FCC operation. Globally, fresh addition rates range from less than 0.1 lbs/bbl for hydrotreated light feeds to more than 1.0 lb/bbl for heavy resids or high metals operations.
For simplicity, we will examine two key drivers that determine fresh catalyst addition rate:
- Metals control
- Activity target
Let’s focus on the easier one first – metals control.
Metals control
Keeping ECAT metals near or below target is very important in units running heavier or high-metal feeds. Typically nickel, vanadium, sodium, calcium, and iron are key variables to monitor, but other metals can also have a significant impact on how the unit runs. It is important to review all metals reported on your ECAT analysis and, more importantly, to monitor trends over time. Trends are often far more informative than any single data point.
As metals increase, coke and dry gas yields generally increase as well. High iron can negatively impact fluidization by lowering apparent bulk density (ABD) and may hinder diffusion through pore blocking, often resulting in poor bottoms upgrading. High vanadium can directly attack the zeolite structure. Be sure to discount vanadium associated with SOx control additives, as this vanadium is typically non-mobile.
Historical operating data should be used to establish appropriate upper metal limits, recognizing that these limits are highly unit-specific. Look for correlations between metals levels and key indicators such as dry gas yield, regenerator temperature, and ECAT activity. If metals exceed established limits, increasing fresh catalyst addition and/or adding purchased ECAT may be necessary to bring metals back under control.
Activity target
In addition to metals control, catalyst addition rate is strongly influenced by the desired activity target. If purchased ECAT is routinely added, the fresh-to-ECAT ratio should be adjusted to maintain activity within an optimal range. If activity is trending low, reduce ECAT addition and increase fresh catalyst. If activity is high, the opposite may be appropriate. In most cases, the goal is to adjust activity to maximize catalyst circulation while minimizing regenerator temperature.
Catalyst addition strategies for low-metals FCC units
If you have “clean” feed, your ECAT metals may not be a significant player in your fresh catalyst addition scheme. The main areas you are trying to control are overall catalyst health and unit heat balance. Clean feeds typically produce less coke, which can make it challenging to maintain regenerator temperature above the lower operating limit. In these cases, some units attempt to minimize fresh catalyst addition and compensate by introducing alternative coke sources.
For some units, a misguided perception is that fresh catalyst should only be added to replace losses, with other methods used to supply the additional coke required. The most common options for making up this coke include:
- Torch oil
- Reduced stripped steam
- Bottoms recycle
Each of these alternatives is discussed in more detail below.
Torch oil
If torch oil is routinely being added to a unit that minimizes catalyst adds, it should be called a “croaker,” not a cracker! A croaker is a blend of an FCC unit (where catalytic reactions are the dominant driver) and a coker (where there is 100% thermal cracking). Thermal cracking results in higher dry gas yield and lower olefinicity of FCC products. Torch oil will also decrease ECAT activity, requiring the use of even more torch oil!
Torch oil is also often the most expensive option. For example, assume an FCC feed value of $100/bbl and a torch oil rate of 500 bpd is being used to maintain regenerator temperature. This represents $50,000 per day of feed being burned with no product yield other than coke.
Now compare that to fresh catalyst addition. Even assuming a conservatively high catalyst cost of $5,000 per ton, adding an incremental 2 tons per day to increase activity from 72 to 75 would cost approximately $10,000 per day. In many cases, this increase in activity can generate $50,000 or more per day in additional liquid product value. In this simplified example, increasing catalyst addition improves heat balance while delivering a net economic benefit of roughly $40,000 per day.
An additional benefit of increasing fresh catalyst addition is the corresponding withdrawal of older catalyst from the unit. As catalyst ages, particles tend to become rounder and denser, making them more easily retained by cyclones. Over time, the zeolite continues to dealuminate and collapse, ultimately leaving behind dense, low-activity material that contributes primarily to thermal cracking rather than catalytic conversion.
Many units have been able to operate for extended periods with minimal catalyst addition and no torch oil. However, in these cases, catalyst circulation and product yields typically degrade over time as the inventory becomes increasingly dominated by aged, low-activity material.
Reduced stripping steam
Adjusting stripping steam is often an easy operational lever and can be a viable option, provided catalyst withdrawal is still occurring. It is important to remember that reducing stripping steam sends reaction products – not just bottoms – to the regenerator. Small, controlled adjustments can be effective, but this approach should be evaluated to ensure it remains the lowest-cost option available.
Bottoms recycle
A third option is to recycle bottoms back to the reactor. Bottoms recycle primarily increases coke and dry gas yields and can be effective, provided the economic penalty associated with bottoms destruction is lower than the cost of fresh catalyst addition.
For example, if bottoms are valued at $50/bbl and 200 bpd must be recycled to generate sufficient coke, the resulting economic penalty is approximately $10,000 per day – roughly equivalent to adding 2 tons per day of catalyst at a conservative cost of $5,000 per ton.
If the unit is already operating at minimum bottoms, additional recycle may require shifting LCO into the bottoms pool to maintain rundown velocity. In those cases, increased fresh catalyst addition is often the more favorable option.
Final thoughts
There is no universal “correct” catalyst addition rate. The optimal rate depends on feed quality, metals loading, unit constraints, heat balance, and overall economic objectives.
In high-metals units, fresh catalyst addition is often driven by metals control and activity maintenance. In low-metals units, the decision becomes more nuanced. While alternative coke sources can be useful tools, they do not replace the catalytic benefits of fresh catalyst and often come with higher long-term costs.
In many cases, increasing fresh catalyst addition is the most effective and economical way to maintain heat balance, protect catalyst inventory quality, and sustain unit performance.
If you’d like to learn more, reach out to connect with one of our FCC subject matter experts. We’re always glad to discuss catalyst addition strategies and help optimize unit performance. Have an FCC topic you’d like us to cover in a future blog? Let us know – your ideas help shape our content and ensure we’re addressing the challenges that matter most to you.
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