DENITRATION TREATMENT OF EXHAUST GAS

摘要

PURPOSE: To prevent the precipitation of a solid in an aq. urea spray nozzle by adjusting the mixing ratio of an aq. urea raw soln. and water corresponding to the concn. of NOx in exhaust gas by a controller and holding the concn. of urea to a value supplying urea in an amt. necessary for reducing the concn. of NOx in the exhaust gas to a set value. CONSTITUTION: Spray urea aq. solution N supplied to a urea aq. solution spray nozzle 6 through a urea aq. solution supply pipe 8 is prepared by mixing the urea aq. raw soln. N1 stored in a urea aq. raw soln. tank 12 and water W stored in a water tank 14 by a mixing valve 16. The mixing valve 16 is controlled on the basis of the detection signal from an engine output detector 17 through a controller 18 to adjust the concn. of urea of spray urea aq. solution N supplied to the urea aq. solution spray nozzle 6 and, even when the load of an engine is low, the flow rate of water W is increased so that spray urea aq. solution N flows to the nozzle 6 in a predetermined flow rate.