Stack Emission Tests Results from Existing and New High Temperature Fluidized Bed Municipal Sludge Incinerators Operating in us and Ontario

In 2011, EPA has released the new MACT (Maximum Achievable Control Technology) emission limits for the high temperature fluid bed municipal sludge incinerators. All existing and new fluid bed municipal sludge incinerators have been mandated to be in compliance with the new MACT emission limits by March 2016. The new MACT emission limits are currently the most stringent emission limits in the world for fluid bed municipal sludge incinerators in terms of particulate matter, acid gas, heavy metals and mercury emissions. For the new fluid bed incinerators, new stack mercury emission limit is 1 μg/dscm (microgram per dry standard cubic meter or 0.001 mg/dscm) at 7% Oxygen. For the existing fluid bed incinerators, new stack mercury emission limit is 37 μg/dscm (microgram per dry standard cubic meter or 0.037 mg/dscm) at 7% Oxygen.One of the major upgrades to be in compliance with the new MACT emission limits is the addition of mercury removal system to the existing air pollution control equipment to meet the new mercury emission limits in stack. In some cases, a wet electrostatic precipitator (WESP), caustic injection system and NOx removal system are added to meet the new metals, particulate matter (PM), acid gases and NOx emission requirements.There are two different mercury removal systems currently available in the market for retrofitting the existing fluid bed municipal sludge incinerators. First one is based on the fixed carbon bed adsorber technology and the second one is based on the sorbent polymer composite (SPC) technology. Fixed carbon bed adsorbers can be installed as part of the new air pollution control system to meet 0.001 mg/dscm (milligram per dry standard cubic meter) mercury emission limit as required in the newly installed incineration system. Fixed carbon bed adsorbers can remove not only mercury, but also dioxin and furan from the flue gas. SPC modules can be installed on the existing incineration systems to meet 0.037 mg/dscm mercury emission limit. SPC modules are employed to remove only mercury from the flue gas without removing any dioxin and furan. However, dioxin and furan emissions from municipal sludge fluid bed incinerators are typically low usually meeting the MACT emission limits on both pollutants without requiring any post combustion treatment. SPC (Sorbent Polymer Composite) modules cannot be incorporated into the new incineration system design to meet the 1 μg/dscm mercury emission limit required by MACT for the new incinerators. This is mainly due to this technology not having high mercury removal efficiency compared to fixed carbon bed system. SPC modules can only be installed on the existing fluid bed incinerators. SPC modules can not be used to remove dioxin and furan from the flue gas to meet the MACT limits for new fluid bed incinerators.In this technical paper, stack emission test results from several existing and new fluidized bed incinerators operating in the US and Ontario (CA) are being compared to MACT emission limits to determine the overall effectiveness of the air pollution control system installed on each incinerator. In addition, stack emission test results from existing and new installations are being reviewed to determine the effectiveness of mercury removal of the fixed carbon bed compared to SPC modules.Results indicated that retrofitted plants were meeting the MACT emission limits on mercury. For new incineration systems in US, it was necessary to have a fixed carbon bed adsorber to be able to meet 1 μg/dscm mercury emission requirement in stack. Fixed bed process resulted in extremely high removal efficiency (>95%). For an existing incineration system in US, results indicated that having SPC modules installed as part of APCS (Air Pollution Control System) was sufficient to meet the 37 μg/dscm mercury emission requirement. SPC modules resulted in mercury removal efficiency, which was higher than 70%. Based on the operating data from these installations, fixed carbon bed adsorbers were difficult to operate compared to SPC modules. However, fixed carbon bed technology had a higher mercury removal efficiency. In addition, based on the results, for the potential future incineration projects in Ontario (CA), having SPC modules installed after the wet scrubber would be enough to meet the mercury emission limit in stack (70 μg/drcm, microgram per dry reference cubic meter – drcm @ 11% Oxygen). This is mainly due to higher mercury emission limits in Ontario, Canada. SPC technology can be used on new fluid bed incinerators in Ontario, Canada to meet the higher mercury emission limit. In US, existing plant mercury emission requirement per MACT is 37 μg/dscm, which is significantly lower than the Canadian requirement for new incineration systems (70 μg/drcm).