Combustion and Emission Performance of a Hog Fuel Fluidized Bed Boiler With Addition of Tire Derived Fuel

Salt-laden hog fuel (wood waste) is burnt in a fluidized bed boiler converted from a travelling grate boiler to generate steam for a specialty paper mill. The converted boiler has a design capacity of 156 t/h of steam from hog and actual generation has varied from 76 to 107% of the design capacity. The conversion has resulted in more stable operation, more complete combustion, less ash production, reduced boiler maintenance, and lower fossil fuel consumption. Tire derived fuel (TDF) is used as a supplementary fuel. With an energy content of 33 GJ/t for TDF, as compared to 8 GJ/t for wet hog, addition of 2–5% TDF by weight increased the bed temperature by an average of 55°C, stabilized and improved the combustion of low quality hog and high moisture content sludge. The impact of TDF addition was studied in detail. Stack emissions were tested and bottom and fly ash samples were analyzed. Although TDF contains 1% zinc and 5 to 7% steel wire, addition of TDF did not affect total particulate emissions from the boiler. SO₂ emissions were increased due to the high sulfur content of TDF (1.6%). A good correlation was obtained from the test results, showing that the addition of TDF resulted in a reduction in both the total formation and the stack emissions of dioxins and furans.