Thickening increases the solids content of the sludge in preparation for dewatering. Waste Activated Sludge (WAS) is collected in Thickener Tank and pumped to thickening centrifuges, which Thickening Centrifugeseparate the liquid content of the sludge in a similar way to how the spin cycle of a washing machine removes water from clothes. Thickened WAS (TWAS) flows by gravity to blend tanks, where it is mixed with the raw sludge from primary treatment tanks.
Dewatering increases the sludge's solids content to about 28 per cent total solids in preparation for incineration. TWAS and Dewatering Centrifugeprimary sludge are collected in the blend tanks and pumped to dewatering centrifuges. Dewatered cake is conveyed by an inclined screw conveyor into collection silos. Centrate flows by gravity to centrate tanks and is pumped back to the head of the plant for treatment. Polymer is added to the blended sludge feed to increase efficiency.
Fluid Bed Incinerators:
The dewatered solids are pumped from the collection silos to the fluid bed incinerators.
Fluid Bed IncineratorCombustion air is fed into the windbox at the base of the incinerator. Dewatered cake and supplementary fuel (fuel oil or natural gas), if necessary, is pumped into the fluidized sand bed. Water is evaporated and most of the solids combustion is processed within the sand bed. Final combustion occurs above the bed in the freeboard section with exhaust gases exiting at 700 - 900 degrees Celsius.
The air pollution control system consists of a quenching unit, impingement Air Pollution Controlscrubber and a multiple, fixed venturi scrubber. The quenching unit reduces the exhaust gas temperature and most of the ash and gaseous pollutants are collected in a slurry and flow by gravity to the ash tanks. The impingement scrubber and fixed venturi further reduce the temperature of the exhaust gas and remove the rest of the ash and gaseous pollutants. Cleaned and cooled exhaust is discharged to the atmosphere. Dedicated emissions monitoring systems provide a continuous check on emissions leve
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