June 30 Hot Topic was Fuel Impacts on SCR Catalysts (including Biomass)

On June 30 during the Hot Topic Hour, the following speakers discussed the impact of various fuels on catalyst life and performance for different operating parameters, discussed new developments in catalyst formulations directed at improving flexibility and reducing expense and told us how to select the optimum catalyst for various fuels and operating conditions.

Brian Adair, Ph.D, Director of Technology Development at SCR-Tech, LLC a CoaLogix Company, discussed fuel impacts on SCR catalysts from a catalyst management perspective. SCR-Tech has experience with all types of catalyst (honeycomb, corrugated and plate-type) being exposed to all types of coals, blends, temperatures and operating conditions. Its unique perspective seeing all the catalyst types with the different fuels types has led to the following observations:

• Consult your SCR Catalyst Manager to model fuel change impacts on catalyst life and system performance.
   
• Less expensive coal generally “trumps” more frequent catalyst replacement; but total economics and system performance must be evaluated.
   
• Most important factors to determine catalyst type, formulation and geometry are:
   
  • Ash content
  • Sulfur content
  • Arsenic and calcium content
  • Operating temperatures
  • Flue gas velocity
     

John Cochran, President of CERAM Environmental, discussed fuel impacts on the design and performance of SCR catalysts. Catalyst performance, and thereby design, is dependent on many combustion and fuel quality parameters. This is especially evident for PRB coals and Western coals. He concluded that:

• Deactivation rates vary widely dependent on site specifics. Fuel quality, combustion parameters, and boiler duty cycle greatly affect catalyst deactivation rates.
   
• Vanadium-Titania based catalysts all deactivate at the same rate based on site specifics.
   
• Underestimating or aggressive sizing compromises SCR performance and effective catalyst management.
   
  • Risk of early outage for catalyst additions.
  • Risk of deficient performance.
     
• Initial SCR project design should carefully consider reactor potential to determine the risk profile of various proposals. Aggressive catalyst designs can result in operational difficulties and increased cost.

There was a good discussion of catalysts for gas turbines. Bob McGinty of Johnson Matthey observed that the problems of operating at high temperature are more related to the ammonia injection than the zeolite catalyst. At high temperatures the ammonia is converted to NO_x. The advantages of the high temperature catalyst make it attractive even if tempering air is used. The plant is less likely to be shut down by a fan problem.

Mark Buzanowski of Peerless Manufacturing explained the advantages of controlling tempering air and injection at multiple points. The optimum temperature for the oxidation catalyst is higher than for the reduction catalyst. So some air is added prior to the oxidation catalyst and the rest prior to the reduction catalyst.