Method of and Apparatus for Selective Catalytic NOx Reduction in a Power Boiler

Abstract

A method of selective catalytic NO X reduction in a power boiler and a power boiler with selective catalytic NO X reduction. Fuel is combusted in a furnace of the boiler and a flue gas stream that includes NO X is generated. The flue gas stream is conducted from the furnace along a flue gas channel to a stack. The flue gas stream is cooled in a heat recovery area, including an economizer section, arranged in the flue gas channel. At least a portion of the NO X is reduced to N 2 in an NO X catalyst arranged in the flue gas channel downstream of the economizer section. The flue gas is further cooled, and heated air is generated in a gas-to-air heater arranged in the flue gas channel downstream of the economizer section and upstream of the NO X catalyst. The gas-to-air heater may be a tubular air heater or a heat exchanger with a recirculating heat transfer fluid.

1 . A method of selective catalytic NO X  reduction in a power boiler, the method comprising the steps of:
 (a) combusting fuel in a furnace of the boiler and generating a flue gas stream that includes NO X ;   (b) conducting the flue gas stream from the furnace along a flue gas channel to a stack;   (c) cooling the flue gas stream in a heat recovery area, including an economizer section, arranged in the flue gas channel;   (d) reducing at least a portion of the NO X  to N 2  in an NO X  catalyst arranged in the flue gas channel downstream of the economizer section; and   (e) further cooling the flue gas and generating heated air in a gas-to-air heater arranged in the flue gas channel downstream of the economizer section and upstream of the NO X  catalyst.   
     
     
         2 . The method according to  claim 1 , wherein the gas-to-air heater is connected to an air flow to provide heated air to be conducted as secondary air to a burner arranged in the furnace. 
     
     
         3 . The method according to  claim 1 , further comprising an additional air heater arranged in the flue gas channel downstream of the NO X  catalyst. 
     
     
         4 . The method according to  claim 3 , wherein the gas-to-air heater and the additional air heater are connected in parallel to an air flow. 
     
     
         5 . The method according to  claim 4 , further comprising the step of controlling the flow of air entering into the gas-to-air heater on the basis of the load conditions of the power boiler. 
     
     
         6 . The method according to  claim 4 , further comprising the steps of measuring the temperature of the flue gas entering into the NO X  catalyst, and controlling the flow of air entering into the gas-to-air heater on the basis of the measured temperature. 
     
     
         7 . The method according to  claim 1 , wherein the gas-to-air heater is a tubular air heater. 
     
     
         8 . The method according to  claim 1 , wherein the gas-to-air heater is a heat exchanger with a recirculating heat transfer fluid. 
     
     
         9 . A power boiler with selective catalytic NO X  reduction, the boiler comprising:
 (a) a combustor for combusting fuel in a furnace of the boiler so as to generate a flue gas stream including NO X ;   (b) a flue gas channel for conducting the flue gas stream from the furnace to a stack;   (b) a heat recovery area, including an economizer section, arranged in the flue gas channel for cooling the flue gas stream;   (d) an NO X  catalyst arranged in the flue gas channel downstream of the economizer section for reducing at least a portion of the NO X  to N 2 ; and   (e) a gas-to-air heater arranged in the flue gas channel downstream of the economizer section and upstream of the NO X  catalyst for further cooling the flue gas and for generating heated air.   
     
     
         10 . The power boiler according to  claim 9 , wherein the combustor for combusting fuel comprises a burner, and the gas-to-air heater is connected to an air channel for conducting the heated air to the furnace as secondary air adjacent to the burner. 
     
     
         11 . The power boiler according to  claim 9 , further comprising an additional air heater arranged in the flue gas channel downstream of the NO X  catalyst. 
     
     
         12 . The power boiler according to  claim 11 , wherein the gas-to-air heater and the additional air heater are connected in parallel to an air channel. 
     
     
         13 . The power boiler according to  claim 9 , further comprising a controller for controlling the flow of air entering into the gas-to-air heater on the basis of the load conditions of the power boiler. 
     
     
         14 . The power boiler according to  claim 9 , further comprising a temperature gauge for measuring the temperature of the flue gas entering into the NO X  catalyst, and a controller for controlling the flow of air entering into the gas-to-air heater on the basis of the measured temperature. 
     
     
         15 . The power boiler according to  claim 9 , wherein the gas-to-air heater is a tubular air heater. 
     
     
         16 . The power boiler according to  claim 9 , wherein the gas-to-air heater is a heat exchanger with a recirculating heat transfer fluid.