Pilot-scale studies on NOx removal from flue gas via NO ozonation and absorption into NaOH solution

Abstract

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.

Research on products of simultaneous removal of SO2 and NOx from flue gas by ozonation and alkaline absorption

“…There were no changes in concentration of SO 2 due to ozone addition [12], what is consistent with the literature data [19]. However, it is well known, that the oxidation of sulfite ion in aqueous medium with ozone plays an important role in the conversion of SO 2 to sulfate in the atmosphere [13].…”

“…The pilot plant was located in Wrocław CHP which provided flue gas from the OP-430 boiler for testing at a rate of 200 m 3 /h. The earlier studies have mainly been devoted to examination of the NO x removal from flue gas by the ozonation method [12]. The effect of prolonged residence time on the effectiveness of NO x removal and the characteristic of products were investigated by adding an oxidation reactor 220 dm 3 in volume in front of the absorber.…”

“…The effectiveness of aftertreatment for SO 2 , CO and NO x was very good (cf. [12,20]). CO and SO 2 were not detected in the exhaust gas from the absorber and the concentration of nitrogen oxides in the treated flue gas was also very low (Table 4).…”

Research on products of simultaneous removal of SO2 and NOx from flue gas by ozonation and alkaline absorption

“…The oxidation of NO 2 to N 2 O 5 requires more time since the reactions (3) and (4) are slower than reaction (1), and further increase the demand for ozone, which in theory is X NO = 1.5, but in practice it is always higher. However, thanks to this it is possible to reduce NO x in the exhaust gas to a dozen mg/m 3 , which was confirmed by the results of removing nitrogen oxides from flue gases in a pilot plant described elsewhere [12].…”

Numerical Simulation of O3 and NO Reacting in a Tubular Flow Reactor

“…Commercialisation of this method has met some economic obstacles, mainly because ozone production is expensive due to oxygen demand and high energy consumption (Jakubiak and Kordylewski, 2012). Further studies are necessary in order to reduce the costs of ozonation by optimisation of ozone use.…”