How it Works
ECO® – NOX, SO2, Hg, PM Removal
The ECO® system is installed downstream of a coal-fired power plant’s existing electrostatic precipitator (ESP) or fabric filter, which removes the majority of the ash particles resulting from coal combustion. The ECO technology treats the power plant’s flue gas in three process steps to achieve multi-pollutant removal of sulfur dioxide (SO2), nitrogen oxides (NOX), oxidized mercury, and fine particulate matter.
- ECO Reactor – oxidizes pollutants, which are removed downstream
- Absorber Vessel – saturates and cools the flue gas; removes SO2, NO2, and oxidized mercury; and concentrates the fertilizer co-product
- Wet Electrostatic Precipitator (Wet ESP) – removes acid aerosols, air toxics, and fine particulate matter.
Valuable Fertilizer Co-Product
The ECO process consumes an ammonia-based reagent and generates a valuable ammonium sulfate fertilizer co-product. Ammonium sulfate has competitive advantages over many existing supplies of nitrogen and sulfur fertilizers including its safe, stable form; ease of production and transportation in various forms (liquid, crystalline, granular); and compatibility with existing fertilizer application equipment and warehouse capabilities. Ammonium sulfate is highly valued for its sulfur and nitrogen content and commands a significant price premium per unit nitrogen over urea and ammonia fertilizers.
In 2005, the Electric Power Research Institute (EPRI) commissioned the engineering firm, Burns & McDonnell, to perform an independent study regarding a process reliability analysis for full-scale applications of the ECO technology at coal-fired utility power plants. The analysis was based on the preliminary design of an ECO system for a 650-MW pulverized coal-fired unit. The study, completed in September 2005, indicated the ECO equipment is at least as reliable as conventional pollution control equipment, predicting better than 99 percent availability.
Integrates Proven Technologies
The ECO process integrates proven technologies, but with innovative changes. Of significance is ECO’s ability to simultaneously remove NOX, SO2 and other emissions in a single absorber vessel, its unique process chemistry, and the utilization of an integral wet ESP.
The ECO reactor is similar to gas reactors used in large industrial ozonators for water purification and disinfection, but the ECO reactor does not generate ozone due to the relatively high temperature of the treated flue gas.
Ammonia-based scrubbing for SO2 control, as is used in our ECO and ECO-SO2 processes, is an existing technology that has been used in other industrial applications for decades. Compared to ammonia scrubbing processes deployed by other suppliers, Powerspan’s ammonia scrubbing technology incorporates a number of innovative changes to the earlier process, improving the system’s performance and cost-effectiveness for large applications.
For example, the ECO absorber vessel is similar in scale and structure to absorber vessels used in wet flue gas desulfurization systems. However with ECO’s unique process chemistry, a smaller tower—approximately two-thirds the size of a conventional wet scrubbing system—and lower liquid flowrates are required, resulting in a lower cost scrubbing system.
The integral wet ESP is similar to wet ESPs used in other applications. Wet ESPs have been used successfully in industrial applications to collect acid aerosols for over 50 years, particularly in metallurgical plants and in sulfuric acid manufacturing. Wet ESPs have shown to be efficient collectors of fine particulate matter and hazardous air pollutants such as mercury.