PILOT-SCALE NOx AND SOx REMOVAL FROM BOILER EMISSION USING RADICAL INJECTION AND CHEMICAL HYBRID PROCESS

The pilot-scale NOx and SOx simultaneous removal from boiler emission was performed using radical injection and chemical hybrid process. The radical injection is often called as indirect plasma (or remote plasma) and air radicals are produced at room temperature with less than 1/10 of the flue gas flow rate. The flue gas from the boiler was in the range of 450~1,470 Nm/hr, the gas temperature of 280C, and NOx concentration of 30 ppm for city gas, and 70 ppm of NOx and 35 ppm of SOx for heavy oil, respectively. The radical injection was demonstrated to be extremely effective for NO oxidation especially when the flue gas temperature is in the range of 300C where NOx is rather generated at this temperature range. The produced NO2 was further reduced to N2, and nontoxic and water soluble Na2SO4 by Na2SO3 solution in the 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 NOx removal efficiency for oil firing was in the range of 60% due to the lack of radicals and ozone concentration with the pulse power supply used. 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 by the indirect plasma to the primary flue gas flow rate, specific energy density, and Na2SO3 concentration and chemical flow rate. Scrubbing solution was chemically analyzed and it is confirmed that the waste solution can be disposed outside of the plant.