How it Works

ECO-SO2 – SO2, Hg, PM Removal


The ECO-SO2 system is installed downstream of a power plant’s existing electrostatic precipitator or fabric filter, which removes the majority of the ash particles.

  1. Absorber Vessel – saturates and cools the flue gas; removes SO2 and oxidized mercury; and concentrates the fertilizer co-product
  2. Wet Electrostatic Precipitator – removes acid aerosols, air toxics, and fine particulate matter.



Click here to launch a Flash animation of the ECO-SO2 Process Flow.

Click here to download a PDF of the ECO-SO2 Process Flow.

As shown in the process flow diagram, in the ECO-SO2 configuration, the ECO® technology is supplied as two-stage emission removal process consisting of an ammonia absorber column and a tubular, vertically oriented wet electrostatic precipitator (wet ESP). The ammonia absorber column captures SO2 and oxidized mercury from the flue gas. After exiting the absorber, the flue gas enters the wet ESP, which collects acid aerosols, air toxics, and fine particulate matter. Next the ash is filtered, and the captured mercury is removed from the scrubbing liquor by a treated activated carbon adsorption bed, which isolates the mercury for separate disposal. The fertilizer co-product processing facility then crystallizes the liquid fertilizer into a high value, crystalline product.

Valuable Fertilizer Co-Product
The ECO process consumes an ammonia-based reagent and generates an ammonium sulfate fertilizer co-product, which is a safe, stable product. 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. Ammonia can be supplied to the ECO process in anhydrous, aqueous or urea forms to meet site-specific requirements.

Integrates Proven Technologies
The ECO process integrates proven technologies, but with innovative changes. Of significance is ECO’s ability to simultaneously remove SO2 and other emissions in a single absorber vessel, its unique process chemistry, and the utilization of an integral wet ESP.

Ammonia-based scrubbing for SO2 control, as is used in our ECO-SO2 and ECO 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.

Select from the downloadable PDFs below:

ECO-SO2 Simplified Diagram
ECO-SO2 Process Flow