Pilot-Scale $\hbox{NO}_{\rm x}$ and $\hbox{SO}_{\rm x}$ Removal From Boiler Emission Using Indirect-Plasma and Chemical Hybrid Process

Pilot-scale simultaneous NO
_x
and SO
_x
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 Nm
³
/h, the gas temperature was 280°C, the NO
_x
concentration was 30 ppm for city-gas firing, and both NO
_x
and SO
_x
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 NO
_x
is generated at this temperature. The produced NO
₂
was further reduced to N
₂
and nontoxic and water-soluble Na
₂
SO
₄
by a Na
₂
SO
₃
chemical scrubber. For the case of oil-firing boiler, SO
₂
was simultaneously adsorbed by NaOH solution. The NO
_x
removal efficiency for gas firing exceeds 90%, but the NO
_x
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 SO
₂
was in the range of 85%-90%. The NO
_x
removal efficiency was evaluated by the ratio of the radical flow rate to the primary flue-gas flow rate, specific energy density, Na
₂
SO
₃
concentration and chemical flow rate. Finally, the quality of disposed water was also investigated and proved to be disposable.