Pulverized coal-fired boiler and pulverized coal burning method

Abstract

A pulverized coal-fired boiler efficiently supplies air to a central part of a furnace and the neighborhood of a furnace wall, thereby promoting mixture with combustion gas, and reducing both NOx and CO. The main after air ports are structured so as to jet air having a large momentum for enabling arrival at the central part of the furnace, and the sub-after air ports are structured so as to jet air having a small momentum to the neighborhood of the wall face of the furnace, and a sectional center of each of the sub-after air ports is within a range from 1 to 5 times of a caliber of the main after air ports from a sectional center of each of the main after air ports.

1 . A pulverized coal-fired boiler, comprising:
 a furnace for composing a pulverized coal-fired boiler,   a plurality of burners arranged on an upstream side of a wall face of the furnace for supplying and burning pulverized coal of fuel and air in the furnace,   a plurality of after air ports for supplying after air arranged on a downstream side of the wall face of the furnace installed above an installation position of the burners, and   main after air ports for supplying a large amount of air and sub-after air ports for supplying a small amount of air installed in the plurality of the after air ports, wherein:   the sub-after air ports are arranged at a position of the wall face of the furnace on an upstream side of the main after air ports and right below the main after air ports, and   a distance from the sectional center of the sub-after air ports to the sectional center of the main after air ports is set within a range from 1 to 5 times of a caliber of the main after air ports.   
     
     
         2 . A pulverized coal-fired boiler, comprising:
 a furnace for composing a pulverized coal-fired boiler,   a plurality of burners arranged on an upstream side of a wall face of the furnace for supplying and burning pulverized coal of fuel and air in the furnace,   a plurality of after air ports for supplying after air arranged on a downstream side of the wall face of the furnace installed above an installation position of the burners, and   main after air ports for supplying a large amount of air and sub-after air ports for supplying a small amount of air installed in the plurality of the after air ports, wherein:   the sub-after air ports are arranged at a position of the wall face of the furnace on a downstream side of the main after air ports and right above the main after air ports, and   a distance from the sectional center of the sub-after air ports to the sectional center of the main after air ports is set within a range from 1 to 5 times of a caliber of the main after air ports.   
     
     
         3 . The pulverized coal-fired boiler according to  claim 1 , wherein a momentum of main after air supplied from the main after air ports is set so as to be within a range from 3 to 20 times of a momentum of sub-after air supplied from the sub-after air ports. 
     
     
         4 . The pulverized coal-fired boiler according to  claim 1 , wherein the main after air ports have a vena contracta composed of an outside diameter of a flow path contracting toward an air jet port for jetting main after air into the furnace and are structured so as to permit the jetted air to flow in a direction of a central axis of the main after air ports. 
     
     
         5 . The pulverized coal-fired boiler according to  claim 1 , wherein the sub-after air ports have a structure of enlarging toward the air jet port for jetting sub-after air into the furnace, are formed in a multi-tube structure on a concentric axis, and are structured so as to jet a straight flow from a flow path at a center and supply a rotational flow from an outer periphery thereof. 
     
     
         6 . The pulverized coal-fired boiler according to  claim 1 , wherein the main after air ports are structured so as to permit the jetted air to flow in a direction of a central axis of the main after air ports and the sub-after air ports are structured so as to jet a straight flow in a parallel direction with a central axis of the sub-after air ports and jet a rotational flow from an outer periphery thereof. 
     
     
         7 . The pulverized coal-fired boiler according to  claim 1 , wherein a mechanism for controlling an air flow rate is installed in both the main after air ports and the sub-after air ports. 
     
     
         8 . The pulverized coal-fired boiler according to  claim 1 , wherein the main after air ports and the sub-after air ports are arranged respectively in a common window box installed on the wall face of the furnace for externally receiving after air. 
     
     
         9 . The pulverized coal-fired boiler according to  claim 1 , wherein a set of one of the main after air ports and one of the sub-after air ports is made, and at least one set thereof is connected to the same window box, and a plurality of the window boxes are installed side by side on the wall face of the furnace in one direction. 
     
     
         10 . The pulverized coal-fired boiler according to  claim 1 , further comprising:
 a plurality of oxygen concentration detectors for detecting an oxygen concentration in a combustion space of the furnace and a controller for individually adjusting air flow rates of a plurality of main after air ports and sub-after air ports on the basis of signals detected from the oxygen concentration detectors, wherein on the basis of signals detected from the plurality of oxygen concentration detectors, when the oxygen concentration at a central part of the furnace is identified to be low, the air amount of the sub-after air ports is decreased, and when the oxygen concentration in the neighborhood of the furnace wall is identified to be low, the air amount of the sub-after air ports is increased.   
     
     
         11 . A pulverized coal-fired boiler, comprising:
 a furnace for composing a pulverized coal-fired boiler,   a plurality of burners arranged on an upstream side of a wall face of the furnace for supplying and burning pulverized coal of fuel and air in the furnace,   a plurality of after air ports for supplying after air arranged on a downstream side of the wall face of the furnace installed above an installation position of the burners, and   main after air ports for supplying a large amount of air and sub-after air ports for supplying a small amount of air installed in the plurality of the after air ports, wherein:   the main after air ports are installed at even intervals in a horizontal direction of the furnace, and the sub-after air ports are installed at even intervals in a horizontal direction of the furnace,   the sub-after air ports are arranged at a position of the wall face of the furnace on an upstream side of the main after air ports and right below the main after air ports, and   a distance from the sectional center of the sub-after air ports to the sectional center of the main after air ports is set within a range from 1 to 5 times of a caliber of the main after air ports from a sectional center of each of the main after air ports.   
     
     
         12 . A pulverized coal-fired boiler, comprising:
 a furnace for composing a pulverized coal-fired boiler,   a plurality of burners arranged on an upstream side of a wall face of the furnace for supplying and burning pulverized coal of fuel and air in the furnace,   a plurality of after air ports for supplying after air arranged on a downstream side of the wall face of the furnace installed above an installation position of the burners, and   main after air ports for supplying a large amount of air and sub-after air ports for supplying a small amount of air installed in the plurality of the after air ports, wherein:   the main after air ports are installed at even intervals in a horizontal direction of the furnace, and the sub-after air ports are installed at even intervals in a horizontal direction of the furnace,   the sub-after air ports are arranged at a position of the wall face of the furnace on a downstream side of the main after air ports and right above the main after air ports, and   a distance from the sectional center of the sub-after air ports to the sectional center of the main after air ports is set within a range from 1 to 5 times of a caliber of the main after air ports from a sectional center of each of the main after air ports.