The recent NOx State Implementation Plan calling for substantial reductions in NOx emissions continues to be debated. In a recent market analysis completed by McIlvaine Company, U.S. power plants are likely to spend an estimated $48 billion on advanced emission controls over the next 20 years. An estimated $22.5 billion will be spent on "scrubbers" to reduce fine particulate, hazardous air pollutants, and sulfur dioxide; $13 billion for "selective catalytic reduction" to control NOx; and $12.5 billion for additional technology to control other pollutants, including mercury.
The interest in discovering a better way to control emissions from combustion sources has engineers and scientists drawing on information from a variety of studies and disciplines to create high-tech solutions. Most recently, at the Air & Waste Management Association conference in Salt Lake City, Chang Yul Cha from the University of Wyoming, Charlie T. Carlisle from CHA Corporation, and Joseph D. Wander of Tyndall Air Force Base presented their findings from a Small Business Innovation Research project.
Their study investigated the feasibility of using a novel filter device (in which microwave energy is applied to destroy pollutants in a catalyst bed) to control unwanted combustion by-products in diesel engine exhaust gases. The microwave-based cleanup process for diesel engine exhaust gases has the potential to significantly reduce the cost of removing airborne pollutants from the exhaust of combustion processes. These pollutants include nitrogen oxides (NOx), carbon monoxide (CO), particulate matter less than 10 microns (PM10), products of incomplete combustion (PICs), volatile organic compounds (VOCs), and other hazardous air pollutants (HAPs).
Currently, no single device is available for simultaneous removal of NOx, CO, VOCs, and PM10 from oxygen-rich exhaust gases. Two methods for NOx reduction currently available are selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR). In both SNCR and SCR (processes originally developed for large, coal-fired power plants), a chemical reducing agent, commonly anhydrous ammonia or urea, is injected into the exhaust gas stream as it exits the combustion chamber. The costs of implementing and operating these processes are quite high, and emissions of small amounts of unreacted ammonia are likely. Furthermore, the service conditions of non-steady-state operations are ill-suited for SNCR and SCR processes.