Removal Of NOx From The Flue Gas By Activated Carbon

The NOx(nitrogen oxides) from combustion of fuels is one of the major air pollutants. It is very harmful to human health and to the environment. The principal processes for NOx control from flue gas that have been commercialized are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) now. The SCR technology has widely applied in commerce, but it consumes a great deal of NH₃ and brings a serious secondary pollution for the leaking of NH₃.The carbons materials such as activated char, activated carbon and activated carbon fibre could be applied in the treatment of NOx. They can be used as sorbent, catalyzer carrier and catalyzer. For example,on condition that oxygen existed,activated carbon could catalytic reduct NOx to N2 with NH₃ at low temperature (<200℃) ;and the char had been used to control the NOx and SO₂ in the flue gas. But the char has low sperific surface, the airspeed was 400h-1 commonly, so the equipment was large. The activated carbon has large sperific surface and low cost,as well as strong mechanical strength and the SCR activity. For reasons above,activated carbon is suitable for the treatment of NOx. It is necessary to study the activated carbon's SCR activity in order to reduce the reactor scale and the investment cost. The activated carbon has been studied as the catalyzer with the NH₃ as the reducing agent. The activated carbon act as carrier carried the complex metal oxide and the reducing agent controlled the NOx. The activated carbon have favorable low temperature SCR activity. The NOx conversion efficiency decreases with the temperature increasing under experimental condition, while increases with the oxygen concentration increasing, but the rate of NOx conversion efficiency increasing was slow when the oxygen concentration was more than 2.5% and the inlet concentration was more than 1050 mg/m3.The reduction efficiency of NOx was more than 88% under the room temperature, 2.5% oxygen concentration, 2000h-1, 1390 mg/m3 NOx, the NH₃/NOx was 1.2. The oxygen promoted the catalyse reaction. The ratio can be enhanced by oxidation the NO to NO₂. The structure analyse of activated carbon's surface showed that the activated carbon with stronger acidity took on better low temperature SCR activity. Its adsorption quantity of the water and NOx was large, and reduced after acid treatment, the SCR activity was enhanced.The effect of the SO₂ was less in the room temperature, The main reason was the reaction between SO₂ and NH₃ which would reduce the NH₃/NOx and decrease the NOx conversion efficiency. Activated carbon could recover its catalytic activity partly after the removal of SO₂ in the reaction gases.