Abstract
Pilot-scale simultaneous NOx and SOx removal from boiler emission was performed using an indirect-plasma and chemical hybrid process. The flue-gas flow rate was in the range of 450-1470 Nm3/h, the gas temperature was 280°C, the NOx concentration was 30 ppm for city-gas firing, and both NOx and SOx concentrations were 70 and 35 ppm for heavy-oil firing, respectively. Radical injection by an indirect plasma was demonstrated to be extremely effective for NO oxidation, particularly when the flue-gas temperature is in the range of 300°C where NOx is generated at this temperature. The produced NO2 was further reduced to N2 and nontoxic and water-soluble Na2SO4 by a Na2SO3 chemical scrubber. For the case of oil-firing boiler, SO2 was simultaneously adsorbed by NaOH solution. The NOx removal efficiency for gas firing exceeds 90%, but the NOx removal efficiency for oil firing was in the range of 60% due to the lack of ozone concentration with the present pulse power supply. The removal efficiency of SO2 was in the range of 85%-90%. The NOx removal efficiency was evaluated by the ratio of the radical flow rate to the primary flue-gas flow rate, specific energy density, Na2SO3 concentration and chemical flow rate. Finally, the quality of disposed water was also investigated and proved to be disposable.
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