Development and operation results of low NOx high efficiency coal fired new CUF boiler

In response to recent demands for effective use of energy and increased awa reness of environmental protection, MHI has developed a new CUF boiler capa ble of ensuring a low NOx emission and burning coal stably at a low air rat io. III the CUF type boiler, its burner is installed at the four surroundin g walls having high radiative intensity and the fuel and the air are inject ed slightly downwards to be fired while they are made to swirl over the ent ire furnace. Because this boiler type is excellent in fuel ignitability and can maintain a sufficient fuel residence time in its reduction zone, its d evelopment has always been oriented towards combustion of hard-to-burn coal s such as anthracite. In the CUF boiler newly developed, those features hav e been adopted towards low NOx and high efficiency. For further decrease of the NOx level, optimum conditions of the burner location and the fuel inje ction direction were found out using a 1/15 scale cold model test, which ma de it possible to achieve coal firing at a lower NOx and higher efficiency than ever. Based on these results, a CUF boiler of evaporation 350 t/h was made and this boiler has successfully been operating. Combustion state in t he furnace has been found very stable and operation of this boiler using a low air ratio of excess O-2 about 1% is made available. Comparison with the conventional boiler of the same scale shows that there is the effect of NO x decrease by about 30% on a basis of the same unburned carbon ratio in ash .