Exhaust system for power generating apparatus

Abstract

An exhaust system for a power generating apparatus comprising a heat source for combusting a fuel in air to produce power, which exhaust system being adapted to receive a flowing exhaust gas and comprising a catalyst system for treating the exhaust gas, which catalyst system comprising a first oxidation catalyst and a second catalyst, wherein the first oxidation catalyst is positioned downstream from the heat source so that the flowing exhaust gas contacts the first oxidation catalyst before the second catalyst.

1 . An exhaust system for a power generating apparatus comprising a heat source for combusting a fuel in air to produce power, which exhaust system being adapted to receive a flowing exhaust gas and comprising a catalyst system for treating the exhaust gas, which catalyst system comprising a first oxidation catalyst and a second catalyst, wherein the first oxidation catalyst is positioned downstream from the heat source so that the flowing exhaust gas contacts the first oxidation catalyst before the second catalyst. 
     
     
         2 . The exhaust system of  claim 1  comprising a heat recovery steam generator (HRSG). 
     
     
         3 . The exhaust system of  claim 2 , wherein the HRSG comprises HRSG tube bundles and the first oxidation catalyst is positioned to receive the flowing exhaust gas upstream of any HRSG tube bundles. 
     
     
         4 . The exhaust system of  claim 2 , wherein the HRSG comprises HRSG super heater tube bundles and the first oxidation catalyst is positioned to receive the flowing exhaust gas downstream of the HRSG super heater tube bundles. 
     
     
         5 . The exhaust system of  claim 1  comprising a middle oxidation catalyst disposed in a second block and positioned to receive the flowing exhaust gas downstream of the first oxidation catalyst disposed in a first block and upstream of the second catalyst. 
     
     
         6 . The exhaust system of  claim 1 , wherein the catalyst system comprises an ammonia injection apparatus (AIG) disposed downstream from the first oxidation catalyst and adapted for injecting ammonia into a flowing exhaust gas. 
     
     
         7 . The exhaust system of  claim 1 , wherein the second catalyst comprises an oxidation catalyst. 
     
     
         8 . The exhaust system of  claim 7 , comprising a selective catalytic reduction (SCR) catalyst for reducing oxides of nitrogen with ammonia reductant. 
     
     
         9 . The exhaust system of  claim 8 , comprising an ammonia slip catalyst positioned to receive flowing exhaust gas downstream from the SCR catalyst. 
     
     
         10 . The exhaust system of  claim 6 , comprising a mixing section disposed downstream of the ammonia injection apparatus and adapted for mixing injected ammonia with the flowing exhaust gas. 
     
     
         11 . The exhaust system of  claim 1 , wherein the second catalyst comprises an SCR catalyst in combination with an ammonia slip catalyst. 
     
     
         12 . The exhaust system of  claim 11 , wherein the second catalyst further comprises an oxidation catalyst. 
     
     
         13 . A power generating apparatus comprising: a heat source for combusting a fuel in air to produce power and a flowing exhaust gas comprising carbon monoxide (CO) and hydrocarbons (HC); and an exhaust system according to  claim 1  for receiving and treating the flowing exhaust gas prior to the exhaust gas being released to atmosphere. 
     
     
         14 . The power generating apparatus of  claim 13 , wherein the first oxidation catalyst is positioned in a high temperature zone, wherein the high temperature zone has a temperature of from 427° C. (800° F.) to 621° C. (1150° F.) when the power generating apparatus is at full load, and wherein the second catalyst is positioned in a low temperature zone, wherein the low temperature zone has a temperature of from 260° C. (500° F.) to 427° C. (800° F.), when the power generating apparatus is at full load. 
     
     
         15 . The power generating apparatus of  claim 13 , wherein the first oxidation catalyst is optimized to promote CO and VOC oxidation and NOx reduction during a start-up phase of the power generating apparatus. 
     
     
         16 . The power generating apparatus of  claim 13 , wherein the second catalyst is optimized to promote CO and VOC oxidation and NOx reduction after a start-up phase of the power generating apparatus. 
     
     
         17 . The power generating apparatus of  claim 13 , wherein the second catalyst comprises an oxidation catalyst. 
     
     
         18 . The power generating apparatus of  claim 13 , wherein the second catalyst comprises an SCR catalyst in combination with an ammonia slip catalyst. 
     
     
         19 . The power generating apparatus of  claim 13 , wherein the second catalyst further comprises an oxidation catalyst. 
     
     
         20 . A method of treating an exhaust gas emitted from power generating apparatus comprising a heat source for combusting a fuel in air to produce power and a flowing exhaust gas, which exhaust gas comprising carbon monoxide and hydrocarbons, the method comprising: contacting the exhaust gas with a first oxidation catalyst in a high temperature zone and subsequently contacting exhaust gas exiting the first oxidation catalyst with a second catalyst in a low temperature zone, wherein the high temperature zone has a temperature of from 427° C. (800° F.) to 621° C. (1150° F.) when the power generating apparatus is at full load, and the low temperature zone has a temperature of from 260° C. (500° F.) to 427° C. (800° F.), when the power generating apparatus is at full load. 
     
     
         21 . The method of  claim 20 , wherein the first oxidation catalyst is positioned to promote CO and VOC oxidation and NOx reduction during a start-up phase of the power generating apparatus. 
     
     
         22 . The method of  claim 20 , wherein the second catalyst is positioned to promote CO and VOC oxidation and NOx reduction after a start-up phase of the power generating apparatus. 
     
     
         23 . The method of  claim 20 , wherein the second catalyst comprises an oxidation catalyst. 
     
     
         24 . The method of  claim 20 , wherein the second catalyst comprises an SCR catalyst in combination with an ammonia slip catalyst. 
     
     
         25 . The method of  claim 24 , wherein the second catalyst further comprises an oxidation catalyst.