Research On600MW Supercritical Coal-fired Boiler Operating Characteristics

The problem that the coal actually used by utility boiler is poor and seriously deviates from designed-coal exists widely in current China, which is seriously affecting the economy and safety of the units. In this paper, several problems in a600MW supercritical utility boiler are studied, including the temperature of reheat steam and output of coal pulverizing system is low, the combustion is not stable and the burnout is poor. An improvement scheme aiming at operation adjustment and structural modification is carried out based on the analysis of structure and operation characteristic of once-through boiler. TGA experiments on coal actually used, numerical simulations of boiler process, thermodynamic calculation of heating surfaces and pulverizing system performance calculation are done in this research.Results of TGA experiments confirm that the fire and burnout index of actually used coal is worse even than the general anthracite, which is the root cause of problems in utility boiler. According to the result of numerical simulations, temperature of flue gas at the exit part increases when burners upswing, while the conversion rate of carbon particles decreases. In addition, we put forward simulations on combustion status under different operating conditions such as change of burner level and account of perimeter air,and compare the result with that under design-coal. Effects of moisture, HGI,ash content and volatile matter in coal on pulverizing system performance and account of air are given by pulverizing system calculation. Compared with design-coal, coal actually used has lower HGI and Vdaf, higher Aar and Mar, which leads to the poor performance of pulverizer. For design-coal and the existing blended coal, ventilation and drying capability of pulverizer are big enough to avoid powder plugging. Boiler thermodynamic calculation provides super-heater and re-heater area that should be changed for different re-heater renovation scheme.All research results above will be helpful to the operation optimization and modification of boiler units.