The invention discloses a W 
flame boiler adopting circulating 
flue gas type slit-type direct-flow pulverized 
coal burners, and relates to the technical field of boiler 
combustion. The W 
flame boiler solves the problems that an existing W 
flame boiler is high in 
NOx emission concentration, poor in 
combustion stability, high in 
fly ash combustible matter content, overtemperature of a 
water cooling wall of a lower 
hearth, large in wall temperature deviation and 
slag bonding. According to the W flame boiler, the plurality of direct-flow pulverized 
coal burners are symmetrically arranged on a front arch and a rear arch with the center line of a 
hearth as the center, thin pulverized 
coal airflow nozzles are arranged on the sides close to the 
water cooling walls, main circulating 
flue gas nozzles are arranged on the sides, close to the center lines of the direct-flow pulverized coal burners, of thick pulverized coal 
airflow nozzles and the thin pulverized coal 
airflow nozzles, secondary air nozzles are arranged on the sides, away from the center lines of the direct-flow pulverized coal burners, of the thick pulverized coal airflow nozzles and the thin pulverized coal airflow nozzles, and outer circulating 
flue gas nozzles are arranged on the sides, close to the 
water cooling walls in the width direction of the 
hearth. The W flame boiler is used for reducing 
NOx emission of a hearth outlet, enhancing stable 
combustion and 
burnout of pulverized coal, reducing overtemperature and thermal deviation of the water cooling walls of the front wall and the rear wall of the lower hearth, and preventing 
slag bonding of the water cooling walls.