617 / 2019-01-20 23:08:15

Effects of burner adjustment and air distribution for a 600MWe subcritical down-fired boiler on NOx emissions and boiler efficiency

down-fired bolier; air distribution; A/B/C-layer secondary-air; F-layer secondary-air; dynamic separator; NOx emission; boiler燾ombustion

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To investigate the NOx爀mission characteristics and the燽oiler爀fficiency during the low-quality blended coal combustion in a 600MWe subcritical down-fired boiler, the experiments of secondary air distribution including A/B/C-layer secondary-air on the arch and F-layer secondary-air in the lower furnace, fuel-lean air,燿ynamic separator爄n double-pressure燿irect燽low燽all爉ill爌ulverizing爏ystem were carried out. The results indicated that the optimum speed of separator showed different values under different loads. When the speed of dynamic separator increased under爃igh爈oad, the pulverized coal became finer, the pulverized-coal燾oncentration decreased, the high velocity of primary air nozzle could affect the initial ignition of pulverized coal flow. Meanwhile, increasing the speed of dynamic separator under low load could lengthen the fuel-rich coal/air downward distance and be爁avorable爁or燽oiler爀fficiency. In experiment the optimum speed of separator was 800rpm-1000rpm under high load, and 1200rpm-1400rpm under low load. The reasonable distribution of secondary air was one of the key technologies of low-quality coal combustion. Secondary air induced into furnace on the arch, including A/B/C-layer secondary-air, just meet the requirement of cooling and incipient combustion, which avoid sending excessive secondary air into catch fire area affected flame stabilization. Main secondary air in the lower furnace, including F-layer secondary-air, induced into furnace by step, which supplying main air for burning in time to ensure the burnout requirement. The F-layer secondary-air could control the爁lame爏hape during combustion, and the爄nconformity爋f爐he secondary air distribution in the front and rear walls would lead to the flame deflection. The secondary air had on-way resistance in the actual operation process. In order to ensure the uniformity of air supply of burner, the C/F-layer secondary-air adopted the arch air distribution mode, Which had high opening value in the middle, low opening value on both sides air distribution characteristics. Through combustion adjustment, the recommended air distribution mode was obtained, which carried爋ut both爐he low NOx爀missions and the爋ptimal boiler燾ombustion economy.