Roderick Manuzon
The Ohio State University
Although ammonia emissions are not regulated in the U.S., it is a precursor of PM2.5 (particulate matter with 2.5 micron diameter or lower), which is a criteria pollutant regulated under CERCLA* which limits emission to 100 pounds/day. Concerns that high levels of ammonia emitted from large poultry facilities may result in PM2.5 levels exceeding the standard has increased interest in using scrubber to remove ammonia before air is exhausted from a building. This study used a spray- type wet scrubber designed to use a small amount of water, have minimal impact on airflow and reduce ammonia emissions as well as particulates. The effectiveness of the scrubber increases as the mass transfer coefficient increases, droplet size decreases and scrubber height increases. The mass transfer coefficient is affected by the acidity of the solution being sprayed as it increases its reactivity. Smaller droplets increase surface area while the scrubber height affects contact time of the solution with the emitted air. The nozzle type and operating pressure, scrubbing liquid acid concentration, number of nozzles, screens to separate droplets and stages through which the emissions moves were optimized for ammonia scrubbing efficiency using a half scale scrubber prototype. Although theoretical computations indicated that a multi-stage scrubber would improve removal of ammonia, the data were significantly lower than expected due to the interaction of droplets between stages. To mitigate the problems, screens were used to separate the droplets but they decreased the air pressure below acceptable limits and the flow configuration was changed. The optimal system used a mixed-flow design with two counter flow nozzles in the lower stage and two co-flow nozzles in the higher stage with a single screen in between the stages. Additional research is recommended to evaluate the effect of increasing gas retention time inside the scrubber and of reducing droplet size within the multi-stage chambers on reduction of ammonia.
* Comprehensive Environmental Response, Compensation and Liability Act
Discussion:
Harry Hoitink (OSU) noted that he had heard of a system that uses horizontal tubes with a central axle with a disc perforated with small holes. Air flows through the tubes and the disc turns, emitting the liquid into the tube. However, documentation of the effectiveness of the system is not available. Manuzon suggested that it may be similar to a cyclonic wet scrubber. Lingying Zhao (OSU) noted that the challenge in agriculture is the need to process large volumes of air. Large changes in pressure are not acceptable as it affects affordability.
Notes by Mary Wicks
The OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.