Device and method for reducing nitrogen oxide (NOx) emission by recycling exhaust gas of chain-grate boiler

The invention relates to a device for reducing nitrogen oxide (NOx) emission by recycling exhaust gas of a chain-grate boiler. The device comprises a forced draught blower (1), a chain-grate boiler system (2), an induced draft fan (3), a primary recycling fan (4) and a chimney (6). An outlet of the induced draft fan (3) is connected to an inlet of the chimney (6) and an inlet of the primary recycling fan (4). The fire grate face of the chain-grate boiler system (2) is divided into a pre-ignition area (211), a high temperature flame area (212) and a burnout area (213), and the areas are correspondingly provided with air inlet pipes (221, 222 and 223). The primary recycling fan (4) is connected to the air inlet pipe (221) of the pre-ignition area (211) through an air hose. The invention further provides a method for reducing NOx emission by the device. The characteristic that the oxygen content of the exhaust gas exhausted by the boiler is low is used for recycling, and thus NOx emission is effectively reduced.