Method for removing nitrogen oxides from exhaust gas

Abstract

In an apparatus for selectively reduction-removing nitrogen oxides in exhaust gas in presence of catalyst by spraying aqueous solid reducing agent solution into exhaust gas flowing through a duct to mix the reducing agent into exhaust gas, the present invention prevents nozzle-clogging caused by the reducing agent or its reaction product, permits stable and continuous spraying and uniform mixing of the reducing agent solution into exhaust gas, and thus removes nitrogen oxides at a high efficiency. The nozzle is cooled by supplying at least one of water and gas before supplying the solution into the nozzle. Upon discontinuing supply of the solution to the nozzle, at least one of water and gas is supplied to remove the solution remaining in the nozzle. The solution stored at high concentration is sprayed after diluting it with water in the course of transfer for spraying. A line for supplying water for diluting is added to the line for supplying the solution. On the side peripheral surface of the duct, a nozzle having double-tube structure comprising an inner and an outer tube in which the inner tube tip projects by 1 to 5 mm from the outer tube tip is installed, the solution is supplied into the nozzle inner tube and spray gas is supplied between the inner and outer tubes to spray the solution to exhaust gas.