Urea-based SCR systems gaining steam

Federal, state and local emissions regulations are pushing power plant owners and operators to cut NOx emissions considerably. Selective catalytic reduction, wherein NOx emissions are converted into harmless nitrogen gas emissions by reacting them with ammonia over a catalyst bed, is one of the most common technologies in use.

Anhydrous and aqueous ammonia are often used by power plants equipped with SCR systems. Ammonia in these concentrations, however, is considered a hazardous substance regulated by the EPA and OSHA, and can cause serious injury as a result of accidental spill or over exposure. Urea, on the other hand, is a stable compound commonly found in fertilizer that can be safely transported directly to the power generation site and converted into ammonia, as needed, thereby eliminating the handling and storage risks. Cost differences exist, so a detailed cost-benefit analysis is typically made when deciding between the various ammonia sources.

The urea-to-ammonia (U2A) system manufactured by Wahlco Inc. of Santa Ana, Calif., and developed by EC&C Technologies, offers an alternative to aqueous and anhydrous ammonia SCR systems. The U2A system was first launched in a full-scale demonstration in September of 2000 at the AES Alamitos Steam Station in Southern California and ran for 1,500 hours, complying with NOx regulations and performing successfully in a side-by-side comparison to an existing aqueous ammonia system.

The operation led to a permanent installation of two U2A system reactors at the AES Station in Huntington Beach, Calif., where more than 5,000 hours of operation have accumulated, to date, with availability well over 99.5%. The U2A system automatically adjusts to meet the ammonia needs of the SCR system and is compatible with all types of catalysts. There is no evidence of undesirable side reactions, such as organic or carbon residue.


“The U2A system is proving to be safe, reliable and cost-effective,” said James Clark, president and CEO of Wahlco. “Urea, with an ammonia equivalence of approximately 50%, provides lower operating cost when compared to aqueous ammonia and is a desirable alternative to the high risks of anhydrous ammonia. We are currently working with seven utilities, totaling over 12,000 MW of SCR systems, who have chosen the U2A system for on-site urea to ammonia conversion.”

Wahlco Inc., which manufactures the patented U2A system, shares the exclusive license to supply this system worldwide with Hamon Research-Cottrell.

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