Pulverized coal-fired boiler and pulverized coal burning method

A pulverized coal-fired boiler comprising:

• a furnace 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 air arranged on a down stream 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 airports and right above the main after airports, or
• the sub-after airports 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 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,
• 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, and an air flow rate adjustment mechanism is installed on an after air supply duct for supplying after air, and the air flow rate adjustment mechanism is arranged in secondary and tertiary air supply ducts for supplying secondary and tertiary air for combustion to the burners so as to independently supply air to the burners,
• wherein a pulverized coal flowmeter for measuring a pulverized coal amount of fuel conveyed to a plurality of burners is installed in a flow path for conveying pulverized coal to the burners and a controller for adjusting secondary and tertiary air amounts for combustion to be supplied to the burners on the basis of the pulverized coal amount measured by the pulverized coal flowmeter, is installed.