Lessons from FCC history
Detailed catalyst data collected over 15 years reveal shifts in FCC yields in response to changing market conditions, and provide a marker for future unit operations.
Jacqueline Pope, Melissa Clough and Alexis Shackleford
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Understanding the evidence of past activity is vital to the future of refining operations. Aggregated data paint the macroeconomic trends that have driven the industry. BASF regularly analyses equilibrium catalyst (Ecat) samples from over 200 fluidised catalytic cracking (FCC) units in refineries globally to monitor key parameters including surface area, contaminant metals, and activity. In addition, the company has operating data snapshots from over 250 FCC units. From these two sets of data, global and regional trends can be extracted and evaluated in order to understand market drivers and industry needs. This article will cover 15 years of Ecat trends in the industry, while focusing on both Ecat properties and ACE testing data. Operating data are also explored and juxtaposed against Ecat trends for clarification. The data analysed in this article represent the historical turbulence that has rocked the FCC industry, from changing economics to varying feedstocks and global raw material pricing shocks. The data also highlight the need for ever changing technology in both catalysts and hardware design.
Over the years, technology advances, crude slates, and economics have changed how refineries operate their FCC units. First, hardware changes such as advanced feed nozzles, riser termination devices, and stripper efficiency improvements represent significant changes to operations. Major innovations have also impacted the FCC catalyst, such as using zeolite-based catalysts, which show improved performance compared to the original amorphous FCC catalysts. Also, new matrix materials are now being utilised by refiners for improved coke selectivity, bottoms cracking, and metals passivation. Economic drivers are also affecting refineries. One example of this is the declining gasoline demand in Western Europe, which has impacted how refiners in this region operate their FCC units. Increasing demand for petrochemical feedstocks from heavy oil sources has also led to a change in operating strategies. This article examines Ecat trends and operating data trends over the past 15 years. Ecat trends are explored and segregated based on global region, while operating trends are segregated based on type of operation (for instance, residual feed and gasoil feed).
Feed changes have impacted refineries globally, for example tight oil crudes in North America and heavier crudes in Asia. In this article, nickel (Ni) and vanadium (V) content is used as a marker for residual feed (resid) and gasoil feed processing. Resid units are defined as having greater than 3000 ppm Ni + V content on Ecat. Conversely, gasoil units are defined as having less than 3000 ppm Ni + V. As Figure 1 shows, in recent years, especially 2013 and after, the percentage of units processing resid feed is greater than gasoil feed according to Ecat data benchmarking. This trend is in stark contrast to 2002 when units processing resid feed represented less than 40%. This is a significant increase in the number of refineries that have shifted to resid feeds in the past 15 years, which impacts catalyst selection, hardware, and unit operations of the refinery.
Feed Concarbon is the measure of the coke forming tendencies of the hydrocarbon feed. To confirm the division of resid versus gasoil units based on metals, feed Concarbon data, provided by the refineries, were examined. The data in Figure 2 suggest a good divide between gasoil and resid units using the above definitions. Resid units have higher Concarbon (average ~2 wt%), as expected due to higher contamination, while gasoil units’ average Concarbon is ~0.5 wt%. There has been a slight increase in resid feed Concarbon in recent years from a global perspective, which is a result of heavier crudes being processed.
Data presented in this article are representative of refineries across the globe. The trends are compiled from 2002-2016 and represent global averages. Importantly, shifts in averages require large moves globally and are indicative of market pressures and opportunities. Further, a shift in the data requires a change across a region as opposed to minor regional (or refinery specific) changes. In order to differentiate between regional market differences, the Ecat trends presented here are broken into the global regions of North America, Latin America, Europe Middle East and Africa (EMEA), and Asia. The first half of this article focuses on Ecat properties, while the second half looks at ACE testing at constant conditions.
Equilibrium catalyst benchmarking analyses
Equilibrium catalyst properties
Rare earth, designated REO for rare earth oxide, is a key component of an FCC catalyst. REO improves zeolite stability, imparts higher activity, and changes the selectivity of the catalyst toward higher gasoline at the expense of liquefied petroleum gas (LPG). REO is also incorporated into some FCC additives. In 2010, the rare earth crisis started after China limited its REO exports, which affected REO prices globally. During this time, the REO content of Ecats around the world dropped significantly due to the high cost of the raw material. Even when REO prices stabilised in 2012, levels did not reach historical levels. Specifically, the data in Figure 3 show that the average REO content in 2015 was 2.2 wt%, while the historical maximum was 2.6 wt% (black dotted line). This suggests that there was, and to some extent still is, an economic incentive to operate with lower REO.
Looking at regional trends, North America operates at the highest REO content. This is due to a number of reasons, the most important being that North America is a gasoline driven market, serving both the domestic and Latin American demands via exports. Asia has one of the lowest REO content globally, partially driven by the incentive for petrochemicals.
The total surface area (TSA) trend, shown in Figure 4, also suggests significant differences regionally. Activity directly correlates to TSA, with a higher TSA leading to a higher activity catalyst. North America has the highest TSA globally, with Asia in direct contrast. In 2011, a significant jump in TSA occurred as a response to make up for the lower REO content previously discussed. The jump in TSA was an attempt to boost catalyst activity.
Activity (see Figure 5) relates to both REO and TSA. In North America, a large number of refiners utilise feed hydrotreaters, which remove contaminants from the feed such as sulphur (S) and nitrogen (N). Due to lower contaminants in the FCC feed, catalyst activity can remain high. Coupled with the highest TSA and REO, North America shows the highest Ecat activity during the time frame studied. This is due to, in part, the processing of tight oils, which require higher activity for heat balance purposes. On the contrary, Asia has the lowest TSA and REO, thus the lowest Ecat activity.
Operating data can also give a good indication of how refiners are responding to market drivers. Refiners can change the riser outlet temperature (ROT) to achieve a change in conversion. A lower ROT leads to lower conversion, all else being equal. If a refiner wants to maintain the same conversion while lowering ROT (see Figure 6), there is more dependence on catalyst activity or catalyst to oil (cat/oil) ratio. The global trend shows that refiners have lowered the ROT in recent years; however conversion has remained relatively steady, or even increased. This suggests that the activity of the catalyst is steadily increasing as well as the cat/oil ratio. Another reason refiners might reduce ROT is to avoid downstream constraints, such as wet gas compressor limitations.
Another important trend is the cat/oil ratio. The cat/oil ratio shown in Figure 7 exhibits an increase in recent years. This increase takes place due to a significant global drop in regenerator temperature of 73°F (23°C) from 2009 to 2012, while the feed rate and feed preheat temperature have remained fairly constant. As Figure 6 shows, even with ROT decreasing, conversion remained the same, resulting from the increase in cat/oil. This increase in cat/oil ratio also coincides with the drop in catalyst activity after the REO crisis began in 2010.
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