Fuel Does Impact SCR Catalyst Life and Performance - Hot Topic February 11

Power plants are increasingly using multiple fuel sources. The greenhouse gas concerns are leading to more co-firing of biomass. There was lots of discussion on the subject yesterday and insightful answers from the two speakers.

Mike Cooper of SCR Tech CoaLogix summarized the situation like this:

Ø  Major fuel types lead to unique but predominant modes of SCR catalyst deactivation.
 

Ø  Two broad deactivation modes

o   Physical / mechanical

o   Poisons
 

Ø  Most deactivation modes can be reversed by applying appropriate regeneration methods.

o   Some heavy metal poisoning cannot be easily reversed, i.e. chromium.
 

Ø  Chemical analysis of catalyst surface and bulk by XRF is the preferred method to characterize accumulation of fuel born deactivation agents.

Participants were concerned about the phosphorous poisoning but were reassured that it is reversible via the regeneration process. The contribution of the vanadium in pet coke to an increase in SO₂ oxidation is another concern.

All initiatives have to be evaluated based on the total environmental benefit. Mike explained that some catalyst is collecting as much as 20,000 ppm of arsenic. The McIlvaine calculation would therefore be that a ton of catalyst would capture 40 pounds of arsenic. Keep in mind that the raw quantities of metal toxics are tiny. The average 300 MW power plant only emits 100 pounds of mercury and will have to reduce this to 10 lbs/yr. This opens up a whole new series of questions. How does the deNOx process impact the fate of toxic pollutants?  Do some end up in the scrubber wastewater instead of the air (mercury to mercury chloride) or in the flyash, or in the catalyst? Alternatively, could the catalyst create compounds which leave the stack (sulfuric acid)?  With toxic metals being a new major issue this series of questions has to be addressed.

Noel Rosha of CERAM offered the following conclusions relative to fuel impacts.

• Combustion optimization to reduce boiler NO_x increases the potential for catalyst deactivation due to phosphorus.
• Cyclone boilers may have more negative impact than PC-fired units.
• Catalyst deactivation due to phosphorus is site specific.
• Less existing knowledge base as compared to other known catalyst poisons (arsenic).
• Catalyst must be designed and managed with consideration of combustion practices.

CERAM has experience with a number of types of biomass including seed corn. This material is high in phosphorous and causes problems. Since there is likely to be a large use of corn stalks and cobs to make cellulosic ethanol, Noel was asked whether these other corn parts would be equally high in poisonous compounds. He indicated that they would not and would be similar to grasses in composition.

The Bios, Abstracts and Photos can be viewed as follows: BIOS, PHOTOS, ABSTRACTS - FEBRUARY 11, 2010.htm

The individual slides are located in our NO_x Decision Tree as follows:

MIKE COOPER – SCR TECH (CoaLogix)

NOx Continuing Decision Process For: Products

Fuel Impacts on SCR Catalyst, presented by Mike Cooper, SCR Tech. Hot Topic Hour February 11, 2010.

http://www.mcilvainecompany.com/NOx_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Mike Cooper - SRC Tech (CoaLogix).pdf

NOEL ROSHA - CERAM

NOx Continuing Decision Process For: Products

Catalyst Deactivation by Phosphorus from PRB Coal and Biomass, presented by Noel Rosha, CERAM. Hot Topic Hour February 11, 2010.
http://www.mcilvainecompany.com/NOx_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Noel Rosha - CERAM 2-11-10.pdf