Improving the combustion performance of a 660MWe down-fired utility boiler by adopting high efficiency combustion technologies

To overcome the problem of high carbon content in the fly ash of down-fired utility boilers using low-volatility coals, the combustion system of a 660 MW _e full-scale down-fired boiler was retrofitted with many items: louver concentrators was adopted, the fuel-lean flow is laid near the wall, the F-tier secondary air is modified with an angle of declination of 20°. Industrial experiments were performed using the boiler before and after the retrofit to determine the reconstruction effect. Data are reported for the gas temperature distribution along the primary air and coal mixture flow, furnace temperature, gas compositions (O ₂ and CO) and gas temperatures in the near-wall region. Comparisons between the two cases were made, and the results show that after the retrofit, ignition of the primary air and pulverized coal mixture was brought forward in the boiler. Gas temperatures rose in the fuel-burning zone, and the residence time of pulverized coal in the fuel-burning zone was extended. Thus the quantity of unburned carbon in fly ash and the gas temperature at the furnace outlet decreased, and the boiler efficiency increased.