Flue gas purifying device

Abstract

An object of the present invention is to provide a flue gas purifying device that can suppress leakage of ammonia and can efficiently decrease nitrogen oxides in flue gas. The object is achieved by including: an exhaust pipe that guides flue gas discharged from an internal combustion engine; a urea-water injecting unit that injects urea water into the exhaust pipe; a catalyst unit that includes a urea SCR catalyst that promotes a reaction between ammonia produced from injected urea water and nitrogen oxides and a support mechanism arranged inside of the exhaust pipe on a downstream side to a position where urea water is injected in a flow direction of the flue gas to support the urea SCR catalyst; an ammonia-concentration measuring unit that measures an ammonia concentration in flue gas at a measurement position in a region where the SCR catalyst is arranged; and an injection control unit that controls injection of urea water based on a measurement result acquired by the ammonia-concentration measuring unit.

1 . A flue gas purifying device that reduces nitrogen oxides contained in flue gas discharged from an internal combustion engine, the device comprising:
 an exhaust pipe that guides flue gas discharged from the internal combustion engine;   an ammonia supplying unit that supplies ammonia into the exhaust pipe;   a catalyst unit that includes an SCR catalyst that promotes a reaction between supplied ammonia and the nitrogen oxides and a support mechanism arranged inside of the exhaust pipe to support the SCR catalyst in the exhaust pipe, and is arranged on a downstream side to a position where the ammonia is supplied in a flow direction of the flue gas;   an ammonia-concentration measuring unit that measures an ammonia concentration in flue gas at a measurement position in a region where the catalyst unit is arranged; and   an injection control unit that controls supply of ammonia performed by the ammonia supplying unit based on a measurement result acquired by the ammonia-concentration measuring unit.   
     
     
         2 . A flue gas purifying device that reduces nitrogen oxides contained in flue gas discharged from an internal combustion engine, the device comprising:
 an exhaust pipe that guides flue gas discharged from the internal combustion engine;   a urea-water injecting unit that injects urea water into the exhaust pipe;   a catalyst unit that includes a urea SCR catalyst that promotes a reaction between ammonia produced from injected urea water and the nitrogen oxides and a support mechanism arranged inside of the exhaust pipe to support the urea SCR catalyst in the exhaust pipe, and is arranged on a downstream side to a position where the urea water is injected in a flow direction of the flue gas;   an ammonia-concentration measuring unit that measures an ammonia concentration in flue gas at a measurement position in a region where the catalyst unit is arranged; and   an injection control unit that controls injection of urea water performed by the urea-water injecting unit based on a measurement result acquired by the ammonia-concentration measuring unit.   
     
     
         3 . The flue gas purifying device according to  claim 2 , wherein the ammonia-concentration measuring unit detects an ammonia concentration at a position included in a region of from a position where a concentration of nitrogen oxides at a time of maximum load of the internal combustion engine when nitrogen oxides in flue gas are reduced in a state with ammonia being input excessively into the urea SCR catalyst becomes either a concentration at an inlet of the urea SCR catalyst at a time of minimum load of the internal combustion engine or a concentration half a concentration at the inlet of the urea SCR catalyst at the time of maximum load of the internal combustion engine, whichever higher, to a position where the concentration of nitrogen oxides at the time of maximum load of the internal combustion engine becomes a theoretical concentration of nitrogen oxides that can be denitrated with an ammonia concentration of 10 ppm, of a region of the catalytic unit in which the urea SCR catalyst is arranged, in a flow direction of flue gas. 
     
     
         4 . The flue gas purifying device according to  claim 2 , wherein
 the urea SCR catalyst in the catalyst unit includes a first catalyst and a second catalyst that is arranged on a downstream side to the first catalyst in a flow direction of the flue gas, and the catalyst unit further includes a connecting pipe for connecting the first catalyst and the second catalyst,   the ammonia-concentration measuring unit is arranged in the connecting pipe, and   the measurement position is in the connecting pipe.   
     
     
         5 . The flue gas purifying device according to  claim 2 , further comprising a particulate-matter reducing unit arranged between the urea-water injecting unit and the internal combustion engine to reduce particulate matters contained in the flue gas. 
     
     
         6 . The flue gas purifying device according to  claim 1 , further comprising a nitrogen-oxide-concentration measuring unit that measures a concentration of nitrogen oxides in flue gas at the measurement position.