Enhanced NO_x Reduction with SO₂ Capture under Air-Staged Conditions by Calcium Magnesium Acetate in an Oil-Fired Tunnel Furnace

Abstract

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 °C. 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.

Combustion Performance Evaluation of Air Staging of Palm Oil Blends

“…In a fuel staging combustor, the fuel is divided to two or more streams and directed into different locations in the combustion chamber in order to burn the fuel in the primary zone under a lean or a rich condition, which is less conducive to NOx formation compared to a stoichiometric condition . NOx reduction attainable with air or fuel staging usually ranges from 30 to 40% than that resulting from conventional combustors because the most important factor affecting NOx formation is the flame temperature. − In addition, staging decreases the emissions of CO and unburned hydrocarbon due to the longer residence time and the burning of CO and hydrocarbon in the final lean stage…”

Removal of NOx and CO from a Burner System

“…This will then make the primary zone fuel-rich, which is less conducive to NO x formation when compared to stoichiometric conditions. The unburned combustibles from the primary zone are then combusted in the secondary zone (20). The overall stoichiometry may be similar to that of the conventional burners, but the peak flame temperature is much lower in the staged air technique because the combustion process is staged over some distance while heat is simultaneously being released from the flame.…”

Pollutant and Corrosion Control Technology and Efficient Coal Combustion

“…There have been recent technical reports in the literature demonstrating effectiveness of injected additives in the coal stream toward the improvement in inhibition of lignite ash slagging and fouling, coal saving–bed temperature rise– carbon content reduction in fly ash, and steam to fuel ratio on 30 MW th industrial pulverized coal-fired boiler, 5 MWe circulating fluidized bed boiler, and 5 t·h –1 smoke tube boiler, respectively. Other technologies which are based on the injection of the additives in the flue gas pathway, i.e., dry sodium bicarbonate based Airborne process, sulfur trioxide–air mixture based Pentol flue gas conditioning system, and dry sorbent (hydrated lime)/calcium magnesium acetate based injection, , demonstrate reduction in SO x –NO x emissions, resistivity of the electrostatic precipitators (ESP), and emitted acidic gas concentrations, respectively. Moreover, economically driven overconsumption of high quality coal sources has resulted in investigation of technologies concentrating on processing coal waste as a main fuel component in thermal power plants.…”