March 13, 2008
A good discussion on the status of SCR catalyst technology took place yesterday in our weekly webinar. The timing was appropriate due to the promulgation of the new Ambient Air Quality Ozone Standard on Wednesday. This probably will mean SCR or SNCR at every coal-fired power plant over the next decade.
The vacature of CAMR by the Court last month also means more pressure on catalyst suppliers to provide a product which also oxidizes mercury. However, this same ruling also eliminated the exemption of coal-fired power plants as toxic air emitters. This means that SO3 becomes more important.
There is more pressure to reduce the carbon footprint. Co-firing of biomass in coal-fired boilers is the cheapest way to do that. Most coal-fired boilers in Europe are co-firing. But it creates challenges for catalyst suppliers. However they are up to the challenge and participants learned how these problems are being handled in the 80 minute webinar yesterday.
Tony Favale of Hitachi reported that recent R&D efforts have resulted in addressing major industry concerns including: phosphorous poisoning in catalyst for PRB applications; enhanced mercury oxidation for eastern bituminous applications; and significant mercury oxidation for PRB applications.
Hitachi has developed a new SCR catalyst with high Hg oxidation and low SO2 conversion. TRAC™, Hitachi’s new catalyst, can achieve high Hg oxidation and low SO2 oxidation for power plants burning bituminous coal. This catalyst has achieved 95 percent Hg oxidation at temperatures above 700°F while keeping the SO2 oxidation rate below 0.5 percent. Durability testing at several U.S. installations will be completed soon. For PRB Coal: mercury oxidation greater than 80 percent across the catalyst was obtained in a slip stream reactor after 7,000 hours without additives. HCl concentration in flue gas was very low and flue gas temperature was above 660°F. So, TRAC™ for PRB fuel is now commercially available. The first layer will be installed in May 2008.
Tony says that there are four issues that need to be addressed to minimize catalyst pluggage. They include:
Greg Holscher of CERAM Environmental, Inc. says CERAM has ten U.S. utility high dust references operating with SO2 to SO3 oxidation rates less than 0.50 percent guaranteed. Commercial designs down to <0.30 percent are available. Mercury oxidation is a function of many variables including halogens (more is better), temperature and ammonia distribution. CERAM has developed theoretical models based on experience to predict the effects of biomass. Washing may be required, so you need sufficient mechanical strength (achieved with a wall thickness of 0.8 to 1.0 mm). Potassium, phosphorous and highly alkaline ash can pose both pluggage and deactivation challenges (proper volume and washing solves these issues). During layup periods or outages, the reactor must be filled with dry air (e.g. ≈ 120°F) due to hygroscopic nature of wood ash. Catalyst should be preheated to 250°F before first flue gas is introduced to avoid condensation. Operating at temperatures greater than 700°F can lead to severe deactivation due to high levels of potassium in ash.
Greg was asked whether the SCR oxidizes CO2. He volunteered to research this and subsequently sent us the following answer. The SCR catalyst does not oxidize CO but does convert VOC to 50 percent CO and 50 percent CO2.
The CWLP Dallman Station has a B&W cyclone boiler (80 MW). The SCR was installed in 2003. The unit was co-firing 5 percent seed corn in 2004-05. The seed corn ash was 52 percent P2O5. This equates to adding ≈ 0.5 percent P2O5 to coal. Catalyst design did not account for the biomass co-firing increase in deactivation rate but the unit still met all performance requirements.
Ken Jeffers of Argillon told participants that system guarantees require information about the design and performance of the existing catalyst. Required information about existing catalyst includes:
Geometry:
Activity Testing Data:
The above information is used to determine the rate of catalyst deactivation, to calculate existing activity potential and to develop a catalyst management plan (CMP).
You can view this recording at
http://www.mcilvainecompany.com/EUEC08/EUEC_2008_conference_coverage.htm