DUAL SO2-NOX CONCENTRATION REDUCTION BY CALCIUM SALTS OF CARBOXYLIC-ACIDS

The simultaneous removal of SO2 and NOx by calcium salts of carboxylic acids was evaluated in a laboratory-scale furnace in atmospheres containing 2,000 ppm SO2, 1,000 ppm NO, 3% O-2, and 12% CO2 at gas temperatures between 550 and 1,250 degrees C (825 and 1,425 K) with a residence times of 4 s in an isothermal zone. The salts studied included calcium formate (CF, Ca(COOH)(2)), calcium acetate (CA, Ca(CH2COOH)(2)), calcium propionate CP, (Ca(CH2CH2COOH)(2)) and calcium benzoate (CB, Ca(C6H4COOH)(2)). Maximum reductions in SO2 concentration due to the formation of CaSO4 were recorded as follows: 60% for CP, 55% for CF, 35% for CA, and 18% for CB at gas temperatures in the neighborhood of 950 degrees C and at a Ca/S molar ratio near 2.8. With the organic portion of the injected salts acting as secondary fuel for NOx control, maximum NOx concentration reductions were 88% for CP, 65% for CB, 22% for CA and less than 10% for CF at gas temperatures near 950 degrees C at bulk equivalence ratios (actual to stoichiometric organic fuel-to-air ratio) that varied between 0.5 for CF and 2.1 for CB. A recently constructed, narrower furnace increased the gas flow velocities and the particle dispersion in the gas. Therein, at residence times as low as 1 s, CP achieved simultaneous SO2 and NOx removal of over 80% at gas temperatures greater than or equal to 950 degrees C. The addition of an oxidizing zone following the carboxylic acid sorbent injection zone affected the overall SO2-NOx removal according to the stoichiometry of the sorbent injection zone. When this zone was: (1) fuel-lean, the overall SO2 removal improved; (2) stoichiometric, the overall SO2 removal was not affected; and (3) significantly fuel-rich, the overall SO2 removal worsened. Under most conditions, the overall reduction of NOx was not affected by the oxidizing zone. At temperatures below 800 degrees C, Ca either was retained as CaCO3 or remained bound to the organic compounds in the sorbents. At temperatures between 950 and 1,150 degrees C, increasing amounts of CaO were found. The composition of the calcined sorbent and the availability of Ca was used to interpret the results of a cenosphere sulfation model. The sorbent sulfation kinetics were found to be bounded by those of pure CaO and pure CaCO3.