Abstract: The coal-blend combustion using different types of coals in coal fired power plants is of great significance to the secure and economic operation of the unit. By taking account of the testing on the 350 MW supercritical bituminous coal boiler in a power plant, the positive impacts of lignite blending such as reducing unit price of standard coal, improving boiler efficiency and reducing NO_x emission are analyzed and verified and consequentially better economic benefits have been obtained. The optimal air distribution scheme under different loads is explored through combustion testing with blended coal. The on-line monitoring for the boiler CO concentration is proposed and the impact of burnout air flow ratio on low nitrogen combustion and boiler efficiency is also investigated, such that the CO concentration is generally maintained around 200 mg/m³ and the ratio of burnable air at the range of 7.0%~13.0%, which can be used as a reference to resolve the contradiction between low NO_x combustion and combustion efficiency. Moreover, comprehensive improvement measures have been taken such as improving the smoothness of the boiler's cold hopper, which effectively relieved the coking problem of the heating surface of the boiler and the results sound satisfactory. In summary, this paper has provided reference for coal blending as well as energy saving and emission reduction of utility boilers.

Key words: utility boiler, blended coal combustion, energy-saving and emission-reduction, coking and slagging, application of defocus