Incinerator Air Emissions
MSD operates sludge incinerators at two locations: Mill Creek and Little Miami plants. In 2000, MSD installed a fluidized bed incinerator at the Little Miami treatment plant, designed to handle all sludge produced at this facility. The equipment proved so efficient and clean that MSD made plans to replace the six multi-hearth incinerators that were built at Mill Creek in the late 1950s and 1980s. MSD is now completing the installation of three new fluidized bed incinerators at the Mill Creek wastewater treatment facility.
The original Mill Creek units were fueled with natural gas and fuel oil. Typically, two of the six were in operation at an average feed rate of 1.6 dry tons per hour. These older incinerators burned digested sludge, which had to be heated to remove volatile organic compounds. This system cost MSD $2 million a year in natural gas.
The new Mill Creek incinerators started operation in the mid to late 2010. They cost $75 million to permit and construct, and are anticipated to save about $1 million in fuel costs a year. The new incinerators burn undigested sludge, which means the incinerators can be self-fired by the thermal energy contained in the waste being burned. The old incinerator building will be demolished, and the Mill Creek digesters will be decommissioned.
The rated capacity of the three new incinerators is 4 dry tons per hour each, for a total of 12 dry tons per hour. When operating continuously, they can be autogenous, or self-fueling. This feature will dramatically reduce fuel consumption and air emissions, including GHG emissions.
The figure above shows the average incinerator air emissions in 2009, before the new incinerators came on line. We anticipate the future air emissions will be significantly improved, once data from the new units is available. All regulated pollutants were below regulated limits in 2009. We experienced instances in operating conditions when opacity fell below permit limits, percent oxygen in stack gas went above permit limits, and scrubber pressure drop went below the permit limit.