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• What adjustments would you consider in your FCC unit, in order to increase dynamic activity?

  Feb-2022

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Answers

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• Nieves Álvarez, MERYT Catalysts & Innovation, nalvarez@meryt-chemical.com

  Dynamic Activity, proposed by Mott5⁽¹⁾, is calculated to indicate the FCC conversion characteristic of VGO fraction derived from hydroprocessing.

  Dynamic Activity is defined as follows:

  Dynamic activity

  Where:

  Second Order Conversion

  (1) The conversion here is the sum of coke, light gases and gasoline, divided by the weight of feedstock.
  (2) Relative cracking efficiency of the feed can be quantified by examining the Dynamic Activity using the same equilibrium catalyst.
  (3) The Dynamic Activity indicates improvement of FCC conversion in converting the feed, you could make some laboratory test (MAT/ACE/Pilot Units), to compare different commercial catalyst with the same feed.
  (4) If FCC unit is downstream of HDT/MHC, you could test the changes on Residue’s characteristic of HDT/MHC taking some lab test in MAT/ACE/Pilot Unit, with same equilibrium catalyst in order observe how deactivated are the HDT/MHC catalyst with Time.

  Hydrogenation of FCC feedstock results in higher FCC conversion. Polyaromatic compounds are preferentially adsorbed on FCC catalyst surfaces, where they react to form coke. Hence, a reduction in polyaromatics contents reduces the coke-deposit, leaving more catalytic sites available for selective cracking reactions.

  In other words, polyaromatics hydrogenation causes increase of FCC conversion and therefore an increase in Dynamic activity

  When MHC / HT experiment significant catalyst deactivation, the Dynamic Activity of FCC catalyst diminish, producing more coke and less value products.

  One form to increase again the Dynamic activity in FCC, is increasing operation temperature in HDT/MHC unit, but this will produce a reduction in the lifetime of the HDT /MHC catalyst. A technical economical evaluation will be necessary to take the better decision, total benefits between HDT/MHC/FCC and HDT/MHC catalyst cost.

  On the other hand, you could evaluate an FCC catalyst change, to use a better catalyst (higher dynamic activity) for the new HDT/MHC Residue characteristics. This action required more time and constant catalyst changes and maybe in the interim your losses could increases

  The aging rates in HDT/MHC catalyst depend of desulfurization, denitrogenating, hydrocracking and improvement of FCC conversion characteristic, for MHC operation were much greater than those for HT operation

  Coke deposition is generally accepted to be the main cause of catalyst deactivation in hydroprocessing experiments), Coke precursors responsible for the deactivation are presumably resins, asphaltenes, polycyclic aromatics, and heterocyclic atoms. The fact that catalyst deactivation seems to be primarily a function of the hydrocracking conversion level suggests that coke. Precursors, formed in the mild hydrocracking reaction, play an important role, and that coke precursors in the feedstocks are less important.

  Another alternative could diminish the bottom of VGO when HDT/MHC catalyst diminish his lifetime.
   
  1 Mott, R. W., Oil & Gas J., 85, (4), 73 (1987).

   

  Mar-2022

• Eelko Brevoord, Catalyst Intelligence, brevoord@catalyst-intelligence.com

  The catalytic contribution to conversion is catalyst activity multiplied by the catalyst-to-oil ratio. The latter is very much dependent on the heat balance in the unit, and thus, the tendency of the catalyst to form coke and increase regenerator temperature. In an attempt to quantify the equilibrium catalyst characteristics, the dynamic activity was introduced as a measure, being (conversion / (100-conversion)/coke yield). It is measured at constant conditions in a laboratory test. The catalyst activity can obviously be increased by increasing the fresh catalyst activity or by increasing the catalyst addition rate, but the coke yield in the test will then increase as well. Consequently the dynamic activity will not increase as much as the catalyst activity, limiting its impact in the commercial unit.

  The dynamic activity can be increased by:
  - Moving to a more coke selective catalyst
  - Increasing catalyst activity
  - Reducing contaminants on catalyst, such as nickel, vanadium and sodium, or move to a more metal resistant catalyst
  - Switching to a test feed, which is easier to crack (more hydrogen content, lower nitrogen, CCR, etc.)

  Note that in he commercial unit, dynamic activity as measured in a test, does not tell the full story. Factors of importance are:
  - Catalyst strippability, which usually improves if the catalyst has a better accessibility and lower surface area
  - Capability of the catalyst to selectively convert heavy components in the feed in a very short time at which the reaction takes place in the reactor riser

  The catalyst-to-oil ratio can also be increased by adapting other variables then catalyst quality, such as:
  - Improve the feed dispersion, for instance by optimising the riser steam rate
  - Reduce feed temperature, increase reactor temperature
  - Install a catalyst cooler

   

  Feb-2022

• manoj katakdaunde, Shell, manoj.katakdaunde@shell.com

  Dynamic Activity is simply defined as Conversion per unit of coke yield. To increase dynamic activity in the unit, following moves are suggested depending on the constraints on the unit:

  Increase conversion at the same coke yield
  - Reformulate to higher Z/M catalyst to increase catalyst activity
  - Switch to a different family of catalyst providing better conversion or lower delta coke or both
  - Increase fresh catalyst addition rate
  - Increase severity (conversion) on the unit while maintaining the same coke burn such as adding more air to regenerator assuming the air blower is not constrained   

  Decrease coke yield at the same conversion
  - Operational changes to reduce heat demand on unit such as increase feed preheat
  - Reduce feed contaminants such as metals and con-carbon
  - Improve feed atomisation using dispersion steam, if possible
  - Improve stripping using stripping steam, is possible
  - Switch to full burn or swallow partial burn if operating in deep partial burn
  - Reduce the usage of sour water or recycles to the riser, if being used
  - Use Hydrotreated feed if available

  Increase conversion while decreasing coke yield
  - Combination of moves mentioned above

  Feb-2022