To investigate the gas/particle flow

coal combustion and NO_x emission characteristics of the firstly-imported 600 MW supercritical MBEL W-shaped flame boiler(developed by Mitsui Babcock Energy Limited Corp.)

cold gas/particle flow experiments were performed within a 1:40-scaled model furnace by varying the staged-air ratio and industrial-size measurements were carried out at designed full load

respectively.The results show that

at all three staged-air ratios(even with staged-air fully closed)

a deflected gas/particle flow field developed

with the downward gas/particle flow near the front wall penetrating deeper than that near the rear wall.The gas/particle flow rapidly inclined towards the furnace central part as it proceeded and therefore reversed ahead of time.The converged upward gas/particle flow deflected towards the front-half furnace zone

resulted in a strong recirculation zone appearing below the rear arch.A three-stage gas/particle slippage phenomenon developed and varied clearly between the front-and rear-half furnace parts.Increasing the stage-air ratio deteriorated the flow-field deflection.Accordingly

asymmetrical combustion appeared in the real-furnace atmosphere

where gas temperatures and combustion status were respectively higher and better in the rear-half furnace part than in the front-half furnace part.The particularly low gas temperatures and lots of unburnt coal particles in the front-half furnace part

local hightemperature zone in the rear-half furnace part

and low air-staging conditions finally generated a poor furnace performance characterized by low burnout rate(carbon in fly ash of 8.5%) and high NO_x emissions(1 467 mg/m~3 when φ(O_2)=6%).