Pilot-scale NOx and SOx removal from boiler emission using indirect plasma and chemical hybrid process

The pilot-scale simultaneous NO_x and SO_x removal from boiler emission was performed using an indirect plasma and a chemical hybrid process. The flue gas flow rate was in the range of 450-1,470 Nm³/hr, the gas temperature of 280 °C, and NO_x concentration of 30 ppm for city gas firing, and 70 ppm of NO_x and 35 ppm of SO_x for heavy oil firing, respectively. The radical injection by the indirect plasma was demonstrated to be extremely effective for NO oxidation especially when the flue gas temperature is in the range of 300 °C where NO_x is generated at this temperature. The produced NO₂ was further reduced to N₂ and nontoxic and water soluble Na₂SO₄ by Na₂SO₃ chemical scrubber. For the case of oil firing boiler SO₂ was simultaneously adsorbed by NaOH solution. The NO_x removal efficiency for gas firing exceeds 90% but 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 SO₂ was in the range of 85-90% The NO_x removal efficiency was evaluated by the ratio of the radical flow rate by the indirect plasma to the primary flue gas flow rate, specific energy density, and Na₂SO₃ concentration and chemical flow rate. Finally, the quality of disposed water was investigated and proved to be disposable.