Research on the Burnout of Fujian Anthracite in CFB Boiler

Abstract

Coal property, boiler structural and designing parameters, running parameters of boiler are the main factors which influence the burnout of Fujian anthracite during combustion in CFB boiler. These coal properties and combustion characteristics such as the compact inner structure of particle, the poor combustion reactivity, and the strong thermal fragmentation tendency are the main reason that cause the Fujian anthracite difficult to burnout in CFB boiler. And these operating parameter such as the combustion temperature, the particle size distribution of feeding coal, the flow velocity of flue gas in furnace, the fly ash reburning, the excess air coefficient and the secondary air ratio have also an strong effect on its burnout. By means of improving the boiler structure and designing parameter such as rising the height of furnace, layout of refractory belt, choosing low-medium circulation ratio, employing high separation efficiency cyclone, ect, can also promote the burnout of Fujian anthracite when it combustion in CFB boiler. For those small-medium capacity CFB boiler (capacity ≤ 75 t/h) burning Fujian anthracite, due to its limited height of furnace, it is good to improve the burnout of Fujian anthracite by adjusting the operation parameter of boiler such as employing the mid-coarse size particle in feeding coal, properly rising the excess air coefficient and the secondary air ratio, intensifying the perturbation and penetration capability of secondary air in furnace, increasing the combustion temperature, and reburning the fly ash. In order to get a good burnout result, the running temperature of boiler should be risen to about 1000 °C, and the excess air coefficient is supposed to maintain in 1.25–1.30.