The CEC uses Selective Catalytic Reduction (SCR) to reduce NOx emissions. The previous SCR system injected anhydrous ammonia to react with combustion turbine exhaust gases in the presence of a catalyst to decrease NOx emissions to approximately 3 ppm.
As our communities grow and change, ENMAX Corporation often has to reassess the impacts of our operations. Since the CEC achieved commercial operation in 2003, the residential development around the facility has significantly increased over the last decade, including the construction of Stoney Trail, a high capacity provincial ring road immediately south.
A risk assessment comparing anhydrous ammonia with aqueous ammonia was completed from an emergency response management and land use planning perspective. Following the risk assessment, in 2013 ENMAX Energy decided to change the type of ammonia used at the plant so it could reduce the impact that the unlikely release of ammonia emissions would have on the surrounding communities.
The 99 per cent anhydrous ammonia in the SCR system was replaced with 19 per cent aqueous ammonia, decreasing potential environment and safety release impacts by an order of magnitude while still maintaining NOx emission reduction and compliance to the facility's Alberta Environment and Sustainable Resource Development Approval. Converting to aqueous ammonia reduced the potential worst case emergency response zone from 5.8 kilometers to 360 meters providing a substantial benefit to the public and nearby neighbors. In addition the conversion also decreases potential health impacts to ENMAX personnel and contractors during ammonia transport, handling, storage and use. The CEC is the first facility in Canada to change from anhydrous ammonia to aqueous ammonia for SCR NOx reduction.
The conversion project required several system changes including: enhancing the truck unloading area to collect potential spills during off-loading; reconfiguring the existing storage tank to store the aqueous ammonia; new transfer pumps to move the liquid ammonia from the storage tank to the ammonia flow control unit; and pipe penetration into the Heat Recovery Steam Generator providing flue gas for ammonia vaporization.
"The data from the risk assessment was compelling. By replacing anhydrous ammonia with aqueous ammonia, we could significantly reduce potential impacts to the public, our nearby neighbours and our employees," explained Daryl Balderson, Manager, Environment Health and Safety. "The conversion could also reduce the impact of ammonia on the surrounding environment – there was no cost savings to ENMAX, we did it simply because it was the right thing to do."
The Association of Professional Engineers and Geoscientists of Alberta recognized ENMAX Corporation for their efforts with a Summit Environment and Sustainability Award in 2014.
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