Apr-2018

Interpreting FCC equilibrium catalyst data

Regular Ecat and fines analysis provides information to support optimum performance from the FCC.

ALEXIS SHACKLEFORD
BASF

Article Summary

As part of best practice in fluid catalytic cracking (FCC) unit monitoring, routine analysis of equilibrium FCC catalyst (Ecat) and fines is vital to maximise profitability and reliability. Ecat and fines analysis provides valuable information on the FCC unit to assess operation, monitor performance, troubleshoot, ensure reliability, and optimise the unit.

BASF routinely analyses Ecat and fines data for units around the world. This article describes the testing and interpretation of the data. BASF data sheets are communicated through email or can be downloaded from the company’s refinery profile website.

Typically, FCC units send one sample of Ecat per week to their catalyst supplier. In addition, fines samples (slurry fines, flue gas fines such as TSS, ESP and scrubber water fines) should be sent monthly at a minimum. All Ecat samples are first decoked (to remove any remaining carbon on the regenerator catalyst) and measured for activity, particle size, physical properties, surface areas, chemical analysis, and yields. These tests provide information about the yield performance (activity and yield selectivities) and fluidisation/retention of the catalyst. While absolute values are useful, trends are equally, if not more, important for monitoring.

Advanced Cracking Evaluation1 (ACE)
BASF introduced ACE testing for standard Ecat evaluation in 2001, replacing fixed bed Micro Activity Test (MAT) units. This is a fluidised laboratory test measuring the catalyst activity, coke, and product selectivities. The ACE unit is run at constant operating conditions with a standard feed so changes seen over time are due only to the catalyst (versus the unit which is impacted by feed slate and operating conditions).

Fluidised activity test (FACT)
The reported Ecat activity is the weight percent (wt%) conversion obtained for the catalyst sample in an ACE unit run with a standard feedstock. Conversion [Conv] is defined as:
100 – Light cycle oil (LCO wt%) – Bottoms (BOT wt%)

For reference:
Kinetic conversion = [Conv] / (100 – [Conv])

Since the in-unit conversion is a function of the FCC process conditions, feedstock properties and catalyst properties, the FACT activity provides a separate evaluation of the catalyst contribution to the unit conversion. Often the term MAT is still used for activity (including FCC SIM programmes) even though all major vendors use ACE testing today.

Each Ecat sample is decoked and screened before being tested. The ACE activity is the carbon-free catalyst activity. The in-unit activity might be lower if the regenerated catalyst contains significant amounts of residual carbon, which will block access to cracking sites. For high carbon on regenerated catalysts (CRC), this drop is significant. At 0.3-0.4 wt% carbon, this can lead to a 1-2 number drop in activity. For Ecat with high CRC, BASF can run as received activity with the carbon on the catalyst for comparison.

What impacts FACT? When fresh catalyst is added to an FCC unit, both the zeolitic and matrix portions deactivate significantly as the catalyst ages. The rate of Ecat deactivation is accelerated with increases in regenerator temperature and moisture, catalyst residence time, and contaminant levels including vanadium (V), alkali metals (sodium [Na], potassium [K]) and alkaline earths (Ca). A rule of thumb: if vanadium + sodium increases by 1000 ppm on Ecat, expect ~2 number decrease in activity. Ecat activity increases with increased fresh catalyst make-up rate and fresh catalyst activity.

Fluidised coke factor (FCF)
FCF provides a measure of the coke selectivity of the equilibrium catalyst adjusted for conversion. Increases in this value can show up as a rise in regenerator temperature and delta coke, often resulting in decreased conversion. Catalyst type will impact the coke factor, but major changes are frequently a result of changing levels of contaminant metals (primarily nickel [Ni] and vanadium) on the Ecat (see Figure 1). A common equivalent metal calculation of nickel + ¼ vanadium – 4/3 antimony (Sb) is used to normalise the dehydrogenation activity of these common metals.

The commercial regenerator temperature is influenced by many factors including operating conditions (feed preheat and reactor temperatures), catalyst activity, feed qualities (1050°F/565°C+ content and Conradson carbon level), and hardware. The FCF helps the refiner to isolate the effect of the catalyst on the regenerator temperature. It must be remembered that the Ecat metals level (which strongly influences the FCF) depends on the feedstock quality and the fresh catalyst make-up rate.

Fluidised dry gas factor (FDGF)
FDGF is the dry gas production (C2 and lighter) adjusted for conversion. Hydrogen product, and therefore FDGF, is strongly influenced by metals contamination (see Figure 2). High dry gas yields take up a significant portion of the wet gas compressor capacity and may limit the FCC capacity.

Fluidised gas factor (FGF)
FGF describes the ‘wet gas’ production (C4 and lighter) adjusted for conversion. Adding ZSM-5 additive or lowering rare earth on the fresh catalyst will increase this value (see Figure 3).