Enhanced NO_x Reduction with SO_2 Capture under Air-Staged Conditions by Calcium Magnesium Acetate in an Oil-Fired Tunnel Furnace

摘要

The technique of combustion modification by air staging (over-fire air) for the control of NO_x emissions is currently implemented in many coal-fired power stations. This paper presents results from a new process involving the injection of calcium magnesium acetate (CMA), which can reduce SO_2 and at the same time enhance NO_x reductions above those achievable by air staging alone. The experiments were performed in a 3.5m long, horizontal tunnel furnace with an internal diameter of 500 mm operated at 80 kWth by firing gas-oil. The organic content of CMA behaves like a fuel, and the Ca content calcines principally to CaO for acid gas capture in the furnace at temperatures greater than 1000℃. The solubility of CMA in water means that concentrated solutions can be sprayed into the furnace as a fine mist, giving the possibility of intimate mixing with combustion gases. The concentration of fuel nitrogen in the fuel could be easily modified by varying the amount of dopant (quinoline) injected into the oil feed to simulate typical levels of NO_x emission. SO_2 concentrations were set by injecting SO_2 gas into the combustion air. NO_x reduction studies were performed at staging levels which created near-burner zone stoichiometries (λ_(nbz)) of 1.18 (3% O_2 dry) at 0% staging to 0.64 at 46% staging. Over this range of staging levels, the injection of CMA improved the reduction of NO_x by a further 25—35% for an initial NO_x level of 450 ppm at an overall stoichiometry of λ_1 = 1.18. The effect of CMA on NO_x reduction was more apparent at lower levels of staging because of higher initial NO_x levels. The near-burner zone (nbz) stoichiometry was 0.64 at this condition. SO_2 reductions were studied up to a Ca/S ratio of 2.25, where reductions in the region of 80% were achieved for initial levels of 940 ppm.