Duffin Creek Experience Two New Fluid Bed Municipal Sludge Incinerators Equipped With State of the Art Equipment

The Duffin Creek Water Pollution Control Plant (WPCP) is located at 901 McKay Road in the City of Pickering, Ontario, Canada. The plant is jointly owned by the Regional Municipalities of York and Durham. Both regions are experiencing significant population growth. The rated plant capacity has been increased to 630 million liters per day (ML/d) through the completion of the Stage 3 Process Expansion ProjectsDuffin Creek WPCP has a long experience with fluid bed Thermal Oxidizers. Two fluid bed units were built back in the late 1970’s by GL&V. Two, additional reactors built by SUEZ were recently added to provide the facility with a firm solids processing capability of 270 metric dry tonnes per day (MDTPD). Identical to the original systems, the new oxidizers are also equipped with two waste-heat recovery systems producing superheated steam to drive the two steam turbines coupled with two fluidization air blowers. Unit No. 4 fluidization air blower is connected to an electric motor (447 kW) and a steam turbine through a clutch mechanism. Unit No. 3 fluidization air blower is connected to only a steam turbine. A clutch mechanism between the fluidization air blower and the steam turbine enables the switching from turbine to electric motor during normal operation.Once both units are operating at full capacity, the fluidization air blowers are driven by steam turbines during steady state operation. This unique design should be a template for future incineration systems.Both fluid bed units have refractory lined hot wind-box and air distributor inside the reactor. . Each fluid bed unit has the capacity to incinerate 105 MDTPD total solids. Unit No. 4 passed the performance testing in June 2013. Unit No. 3 passed the performance testing in February 2014. Both fluid bed units have satisfied the emission requirements per air permit issued by the Ministry of the Environment and Climate Change (MOECC) including mercury, dioxin, and furan removal.Each fluid bed unit is equipped with a dedicated heat recovery system employing a primary heat exchanger and waste heat recovery boiler. Primary heat exchanger (shell and tube design) is used to preheat the fluidization air to minimize the auxiliary fuel usage during steady state operation. Each unit was designed to be autogenous, with a sludge feedstock composition of 68% volatile, 28% total solids, and 5,560 kcal/kg sludge heat value based on volatile part of dry solids (dry sludge). Based on the feedback from the plant, both units are operating autogenously even with a sludge feedstock content as low as 24%. Flue gas from the fluid bed reactor is passed through a primary heat exchanger and then discharged into a waste heat boiler to generate superheated steam. From waste heat boiler, flue gas is sent to a wet scrubber to remove particulate and acid gas (SO2, HCl). The wet scrubber is not equipped with a caustic injection system. Due to today’s more stringent air requirements, a Kombisorbon mercury-removal system is installed downstream of the multi-venturi wet scrubber to remove mercury, dioxins, and furans. The Kombisorbon system includes a conditioner having a droplet separator to remove free water droplets from the clean flue gas discharged from the wet scrubber. The conditioner also has a heat exchanger to increase the saturated flue gas temperature about 20C above the dew point temperature to prevent moisture formation inside the fixed carbon bed adsorber. Clean flue gas discharged from the wet scrubber flows through the cold side of the conditioner heat exchanger and the steam from the low pressure steam header is used as the heating medium for the hot side of the conditioner heat exchanger. Clean flue gas from the conditioner heat exchanger is sent to Kombisorbon adsorber to remove mercury, dioxins and furans. There is also an ID Fan installed before the stack to maintain vacuum conditions inside the waste heat boiler to prevent any potential flue gas leak into the building. The Kombisorbon adsorber has three layers with the first layer filled with regular carbon and the following two layers filled with activated carbon.The text provides the detailed information on the process, the scope of equipment installed, and the information regarding the performance test results. Mercury-removal technologies available today for fluid-bed sewage-sludge incinerators are also discussed, along with their respective mercury-removal efficiency associated with each mercury removal technology.The successful operation at Duffin Creek WPCP has shown that the improved thermal oxidizer design incorporating enhanced air pollution control and energy recovery systems to reduce the operational expenditures is an economical, environmentally friendly, and cost effective solution for sludge disposal. Duffin Creek WPCP fluid bed units have satisfied the sludge disposal needs of the plant, emission requirements of the Ministry of the Environment and Climate Change (MOECC) and the future growth needs of both Regions.