Flue gas purifying device

Abstract

A flue gas purifying device includes an exhaust pipe that guides flue gas discharged from an internal combustion engine; a catalytic unit that is arranged on a downstream side to the internal combustion engine in a flow direction of flue gas and includes a nitrogen-oxide storage-reduction catalyst that stores nitrogen oxides contained in flue gas and a support mechanism that is arranged in the exhaust pipe and supports the nitrogen-oxide storage-reduction catalyst in the exhaust pipe; a reducing-agent injecting unit that injects a reducing agent to the catalytic unit in the exhaust pipe; a concentration measuring unit that is arranged on a downstream side to the catalytic unit in the flow direction of flue gas and measures a concentration of nitrogen oxides in flue gas having passed through the nitrogen-oxide storage-reduction catalyst; and a control unit that controls whether to inject the reducing agent from the reducing-agent injecting unit based on a concentration of nitrogen oxides measured by the 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;   a catalytic unit that is arranged on a downstream side to the internal combustion engine in a flow direction of the flue gas and includes a nitrogen-oxide storage-reduction catalyst that stores nitrogen oxides contained in the flue gas and a support mechanism that is arranged in the exhaust pipe and supports the nitrogen-oxide storage-reduction catalyst in the exhaust pipe;   a reducing-agent injecting unit that injects a reducing agent to the catalytic unit in the exhaust pipe;   a concentration measuring unit that is arranged on a downstream side to the catalytic unit in a flow direction of the flue gas and measures a concentration of nitrogen oxides in the flue gas having passed through the nitrogen-oxide storage-reduction catalyst; and   a control unit that controls whether to inject the reducing agent from the reducing-agent injecting unit based on a concentration of nitrogen oxides measured by the concentration measuring unit.   
     
     
         2 . The flue gas purifying device according to  claim 1 , wherein the concentration measuring unit continuously measures a concentration of nitrogen monoxide as the concentration of nitrogen oxides. 
     
     
         3 . The flue gas purifying device according to  claim 1 , further comprising a temperature detecting unit that detects a temperature of the nitrogen-oxide storage-reduction catalyst, wherein
 the control unit stores temperature history data thereof detected by the temperature detecting unit, calculates an amount of fuel to be injected from the reducing-agent injecting unit based on the temperature history data and the concentration of nitrogen oxides, and causes the reducing-agent injecting unit to inject a calculated amount of fuel.   
     
     
         4 . The flue gas purifying device according to  claim 1 , wherein the control unit causes the reducing-agent injecting unit to inject the reducing agent when the concentration of nitrogen oxides measured by the concentration measuring unit exceeds a standard value. 
     
     
         5 . The flue gas purifying device according to  claim 1 , further comprising an ammonia-concentration measuring unit that is arranged on a downstream side to the catalytic unit in a flow direction of the flue gas and measures an ammonia concentration in the flue gas having passed through the nitrogen-oxide storage-reduction catalyst, and
 the control unit controls an amount of a reducing agent to be injected based on the ammonia concentration measured by the ammonia-concentration measuring unit.   
     
     
         6 . The flue gas purifying device according to  claim 5 , wherein the control unit calculates time degradation of a storage capacity of the nitrogen-oxide storage-reduction catalyst based on the detected concentration of nitrogen oxides and the detected ammonia concentration and controls an injection timing and an injection amount of a reducing agent based on a calculation result thereof. 
     
     
         7 . The flue gas purifying device according to  claim 1 , further comprising an SCR catalytic unit that is arranged on a downstream side to the catalytic unit in a flow direction of the flue gas, and includes an SCR catalyst that promotes a reaction between the nitrogen oxides and ammonia, and a support mechanism that is arranged in the exhaust pipe and supports the SCR catalyst in the exhaust pipe. 
     
     
         8 . The flue gas purifying device according to  claim 7 , further comprising a post-treatment nitrogen-oxide-concentration measuring unit that is arranged on a downstream side to the SCR catalytic unit in a flow direction of the flue gas and measures a concentration of nitrogen oxides in flue gas having passed through the SCR catalyst, wherein
 the control unit controls injection of a reducing agent by the reducing-agent injecting unit also based on concentration of nitrogen oxides measured by the post-treatment nitrogen-oxide-concentration measuring unit.   
     
     
         9 . The flue gas purifying device according to  claim 7 , further comprising a post-treatment ammonia-concentration measuring unit that is arranged on a downstream side to the SCR catalytic unit in a flow direction of the flue gas and measures an ammonia concentration in flue gas having passed through the SCR catalyst, wherein
 the control unit controls injection of a reducing agent by the reducing-agent injecting unit also based on an ammonia concentration measured by the post-treatment ammonia-concentration measuring unit.