Apr-2019

FCC metals trapping additive trial (TIA)

The Parkland refinery in Burnaby, British Columbia has consistently high levels of feed metals going to the FCC. In the past, high levels of fresh catalyst addition supplemented with purchased Ecat were used to alleviate the effects of the feed metals.

Adam Toenjes, Parkland Refining
Todd Hochheiser and Heather Blair, Johnson Matthey

Article Summary

In an effort to find a more effective solution, Parkland enlisted Johnson Matthey to carry out a trial of the separate particle metals trapping additive, Cat-Aid. This article will discuss the results seen when this additive was used, and the unusual way that the Parkland refinery was able to take advantage of the benefits. 

Feed metals are a common problem facing FCC unit operators. High metal feedstocks are often more economically favourable, making the effects necessary to mitigate. Metals such as vanadium and iron enter the unit with the feed and cause catalyst poisoning. The result of this poisoning leads to increased delta coke which results in loss of conversion, increased slurry yield, and increased dry gas production. There are several commonly used ways to mitigate metals poisoning including increasing fresh catalyst addition rate, adding flushing Ecat, or incorporating a metals trap into the fresh catalyst. Burnaby, like many other refineries, had been using flushing Ecat to mitigate feed vanadium and iron effects.

Burnaby’s FCC processes a feed with a very high vanadium and iron content. The vanadium forms vanadic acid, H3VO4, inside the regenerator. The acid is very destructive to FCC catalyst zeolite and promotes dehydrogenation reactions. The iron can block the catalyst pores by forming a dense nodular ‘glassy’ shell on the catalyst surface. This shell inhibits diffusion of both feed into the catalyst and products exiting the catalyst, limiting normal FCC hydrocarbon reactions.

ACE testing was conducted prior to the commercial trial to reduce the risk and help with the management of change process. This testing showed positive results with injection of Cat-Aid and significantly eased the decision-making process. A three-phase trial was then conducted to evaluate the effectiveness of Cat-Aid in the Burnaby FCC.

After an initial 10 wt% base load, the overall trial lasted 80 days, allowing time to evaluate savings by reducing fresh catalyst additions, maintaining constant catalyst additions with lower feed quality, and reducing flushing Ecat addition rate.

Delta coke reduction
Feed contaminants result in increased delta coke. Since Cat-Aid mitigates the impact of both vanadium and iron poisoning, delta coke is reduced. At Burnaby, Cat-Aid was found to reduce delta coke by an average of 0.08 wt% (see Figure 1).

The Burnaby FCC operates a catalyst cooler in the FCC regenerator. The catalyst cooler duty is adjusted to maintain a constant regenerator temperature. Feed and riser temperatures are also relatively steady which in turn maintains a constant cat/oil ratio of about 6.3. At constant cat/oil, a reduction in delta coke will show up as a direct reduction in coke yield. The reduction in coke yield at constant feed quality is 0.51 wt% of feed.

Coke yield = Delta coke × cat/oil
Base case: Coke yield = 0.95 wt% × 6.3 = 5.99 wt%
Cat-Aid trial: Coke yield = 0.87 wt% x 6.3 = 5.48 wt%

The heat balance and coke yield are dependent on catalyst cooler duty. For the 0.51 wt% coke yield reduction, catalyst cooler steam production was reduced by 13.0 Mlb/hr. The lower catalyst duty allows more operational flexibility and reduces dependence on the catalyst cooler for stable FCC operation.

Liquid volume yield increase
Coke yield has a direct effect on liquid volume yield. Figure 2 shows a clear increase in liquid volume yield of 0.8 vol% when Cat-Aid was used. To validate the observed yield increase of 0.8 vol%, the coke yield reduction was cross-checked against it. Based on the coke yield reduction of 0.51 wt%, the expected liquid volume increase was 0.6 vol%. Additionally, Cat-Aid reduced dry gas yield. The total liquid yield increase of 0.8 vol% is comprised of 0.6 vol% from coke yield reduction and 0.2 vol% from dry gas reduction.
 
Iron poisoning impacts
Prior to beginning the trial, iron nodules were observed on Burnaby’s Ecat. After Cat-Aid was well established in the FCC, Ecat was examined again under a scanning electron microscope. A clearly visible difference was observed on the catalyst at equal iron levels of 0.9 wt% (see Figure 3). The change in surface morphology significantly improved the catalyst selectivity and activity.
 
Catalyst activity impact
Ecat MAT activity increased by 0.5-1.0 wt% with Cat-Aid due to mitigation of vanadium and iron poisoning. Cat-Aid shows MAT activity as a function of Ecat vanadium comparing base case and trial data. Activity is strongly dependent on Ecat vanadium level which is observed in almost all FCC units. The Cat-Aid metals trap reduced the deactivation of the base catalyst by subjecting it to fewer contaminant metals.

Operating expense reduction
Due to the magnesium component of Cat-Aid, Burnaby was able to completely stop the use of SOx additive. The efficiency of Cat-Aid was not as high as the SOx additive, but the concentration was much greater. The refinery was therefore able to meet the original trial goals and reduce both flushing and fresh catalyst addition rates.

Conclusions
Cat-Aid greatly increased FCC profitability at Burnaby by trapping unwanted metals and in turn decreasing delta coke, decreasing hydrogen and dry gas, increasing liquid volume yield, mitigating iron poisoning effects, increasing catalyst MAT activity, and allowing for reduction in SOx additive and reduction in fresh and flushing Ecat additions.

The economic flexibility options provided by Cat-Aid were wide ranging. Parkland was able to reduce catalyst addition rate, SOx additive use, and process lower quality feeds while increasing liquid volume yield. The additive can also be used to increase feed rate and residue processing or improve yield slate with improved liquid volume yield. Cat-Aid provided additional operational flexibility and debottlenecked several FCC constraints. Parkland was able to take advantage of the reduction in delta coke by optimising the FCC heat balance and allowing the FCC to operate in a less constrained mode as can be seen in the results of this trial.

This short case study originally appeared in PTQ's Technology In Action feature - Q1 2019 issue.

For more information: Todd.Hochheiser@matthey.com