Oxidation system stops landfill methane odors
The Century Sanitary Landfill in Broward County, Fla., operates one of the nation’s largest landfill gas-to-energy plants. About 9 million standard cubic feet per day of landfill gas, collected from 300 wells on the site, feed gas turbine generators to produce electricity.
After Hurricane Andrew struck in August 1992, Broward residents deposited debris and waste from the massive reconstruction projects, changing the nature of the landfill gas. The level of hydrogen sulfide increased to as much as 5,000 ppm, creating severe odors.
Additionally, sulfur dioxide forming in the gas turbine caused serious corrosion. To alleviate these problems and remain in compliance with air pollution regulations, the landfill needed to remove the hydrogen sulfide before it entered the gas turbines.
To accomplish that, the landfill selected the ARI Lo-Cat hydrogen sulfide oxidation system from U.S. Filter, Schaumburg, Ill. Within the system, landfill gas first enters a counter-current flow, absorber column. The hydrogen sulfide-contaminated air flowing up through the column contacts a counter-current flow of water solution containing chelated ferric ions. The solution absorbs the hydrogen sulfide, causing it to react with the ferric ion to produce iron ions and elemental sulfur. An aerating tank with baffles and a settling tank help complete the deodorizing process.
Since start-up, the landfill has been in compliance with all sulfur dioxide air pollution regulations. Hollow plastic balls in the absorber column remain in constant motion, virtually eliminating sulfur dioxide formation in the turbines and thereby reducing equipment maintenance.
Testing has shown that the elemental sulfur produced by the process is nonhazardous. That allows the sulfur from the dewatering system, containing 60 percent solids, to be sent back to the landfill.