The paper presents results of experimental studies on removal of NOx from flue gas via NO ozonation and wet scrubbing of products of NO oxidation in NaOH solutions. The experiment was conducted in a pilot plant installation supplied with flue gas from a coal-fired boiler at the flow rate 200 m3/h. The initial mole fraction of NOx,ref in flue gas was approx. 220 ppm, the molar ratio X = O3/NOref varied between 0 and 2.5. Ozone (O3 content 1÷5% in oxygen) was injected into the flue gas channel before the wet scrubber. The effect of the mole ratio X, the NaOH concentration in the absorbent, the liquid-to-gas ratio (L/G) and the initial NOx concentration on the efficiency of NOx removal was examined. Two domains of the molar ratio X were distinguished in which denitrification was governed by different mechanisms: for X ≤ 1.0 oxidation of NO to NO2 predominates with slow absorption of NO2, for X >> 1.0 NO2 undergoes further oxidation to higher oxides being efficiently absorbed in the scrubber. At the stoichiometric conditions (X = 1) the effectiveness of NO oxidation was better than 90%. However, the effectiveness of NOx removal reached only 25%. When ozonation was intensified (X ≥ 2.25) about 95% of NOx was removed from flue gas. The concentration of sodium hydroxide in the aqueous solution and the liquid-to-gas ratio in the absorber had little effect on the effectiveness of NOx removal for X > 2.

The influence of ozone injection mode on the effectiveness of nitrogen monoxide oxidation to nitrogen dioxide by ozone in a flow reactor was investigated experimentally in laboratory apparatus. Nitrogen monoxide was diluted to the mole fraction 100 ppm in air which served as the carrier gas flowing through the tube of the diameter D = 60 mm into which ozone was injected. The effects of a number of ozone injecting nozzles and their configuration on the effectiveness of NO oxidation were examined. In the closest vicinity from the injection site the counter-current injection mode appeared to be superior to the co-current injection mode, but in areas located further from the injection site both injection systems were almost equally effective.

Abstract:The results of experimental investigations on the removal of NO x from gases applying ozone as the oxidizing agent and the absorption of higher nitrogen oxides in the sodium hydroxide solutions are presented. The experiment was conducted using a pilot plant installation with the air fl ow rate 200 m 3 /h, being a prototype of a boiler fl ue gas duct and a FGD scrubber. It was shown that in the range of [NO ref ] = 50 ÷ 250 ppm the mechanism of NO ozonation depends on the molar ratio X = O 3 /NO ref : for X ≤ 1.0 oxidation of NO to NO 2 predominates and NO 2 is poorly absorbed, for X >> 1.0 NO 2 undergoes further oxidation to N 2 O 5 , which is effi ciently absorbed in the scrubber. The stoichiometric molar ratio of complete conversion of NO into N 2 O 5 is X = 1.5, in these studies to reach the effectiveness η ≥ 90% the molar ratio X was much higher (2.75).

A process capable of NO x control by ozone injection gained wide attention as a possible alternative to proven post combustion technologies such as selective catalytic (and non-catalytic) reduction. The purpose of the work was to develop a numerical model of NO oxidation with O 3 that would be capable of providing guidelines for process optimisation during different design stages. A Computational Fluid Dynamics code was used to simulate turbulent reacting flow. In order to reduce computation expense a 11-step global NO -O 3 reaction mechanism was implemented into the code. Model performance was verified by the experiment in a tubular flow reactor for two injection nozzle configurations and for two O 3 /NO ratios of molar fluxe. The objective of this work was to estimate the applicability of a simplified homogeneous reaction mechanism in reactive turbulent flow simulation. Quantitative conformity was not completely satisfying for all examined cases, but the final effect of NO oxidation was predicted correctly at the reactor outlet.

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