Application And Experimental Study Of The Central-Fuel-Rich Swirl Coal Combustion Burner In A 300-MW Utility Boiler

In China, electricity is generated mainly by coal combustion. The central-fuel-rich swirl coal combustion (CSCC) burner has the advantages of high combustion efficiency, stable flame, low NOx emission, less slagging and high-temperature corrosion on the water-cooled wall. Experiments were performed to investigate the combustion characteristics of CSCC burners of a 300-MW wall-fired utility boiler burning with bituminous. The eight enhanced ignition-dual register burners (EI-DRB) in the bottom row of the furnace were retrofitted to the CSCC burners. The experiments consisted of two parts: the cold-flow experiments in pilot scale test facilities modeling from these two types of burners, the full-scale aerodynamic field and combustion experiments of these two types of burners in the utility boiler.The both results of pilot-scale and full-scale cold flow field experiments show that with EI-DRB burner, the central recirculation zone does not exist in the near-burner region when the outer secondary air vane angle is set to 45°. It is the main reason why the boiler can not be stably operated without auxiliary fuel oil at a low load. When the vane angle is set to 30°, there is a stable central recirculation zone in the near-burner region. It is advantageous for the pulverized coal ignition and combustion, but disadvantageous for the lessening of slagging and high-temperature corrosion on the side wall.Through the cold-flow experiments, the effects of the outer secondary air vane angle, the outer secondary air ratio and the primary air ratio on the central recirculation zone size and the divergent angle of CSCC burner were obtained.And though the full-scale combustion experiments, the effect of the outer secondary air vane angle and coal-feed rate on the combustion characteristics of CSCC burner in the near-burner region were presented. The results show that when the outer secondary air vane angle of CSCC burner is set to 45°, the size of the central recirculation zone and the divergent angle are appropriate. It can prevent the jet flows issuring from the adjacent burners from interfering, and makes the coal ignite in time and burn stably, and can also reduce the NOx formation. For CSCC burners, local mean CO concentrations, gas temperatures and their rate of increase are higher and mean concentrations of O2 and NOx along the jet in the burner region are lower compared to EI-DRB burners. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. For CSCC burners in the bottom row, the combustion efficiency of the boiler increases from 96.73% to 97.09%, and NOx emission decreases from 843.55 to 727.67 mg/m3 at 6% O2 compared to EI-DRB burners and the boiler operates stably at 110 MW without auxiliary fuel oil. Thus, the CSCC burners can improve the flame stability when the boiler operates at a low load, and can also reduce the NOx emission and prevent the side water-cooled wall from slagging and high-temperature corrosion.