Search

For a 300 MWe anthracite- and arch-fired boiler with biased-swirling-secondary-air (BSSA) technology, the distribution law of gas/solid two-phase velocity in the furnace is obtained with the help of a 1:10 cold modeling experiment bench, and the combustion and NOx formation characteristics in the furnace are revealed by numerical calculation. The results show that, with the increase of over-fire air rate, the reflux velocity in the reflux zone under the arch decreases continuously, and when the main air flow from the furnace arch reaches the staged air region from the vent air region, the position of particle flow in the primary air turn upward is advanced, and the utilization rate of the space in the lower furnace will decrease continuously. In the regions of vent air and staged air, when the over-fire air rate increases from 15% to 25%, the maximum vertical velocity decreases by approximately 2 times, and the downward depth of air flow from the furnace arch decreases significantly. When the over-fire air rate is increased from 10% to 25%, the thermal resistance between the primary air of the burner and the high-temperature flue gas in the furnace center increases, the ignition of the primary pulverized coal air flow is advanced, the flue gas temperature in the center of the lower furnace is decreased. As a result, with the increase of over-fire air rate, the combustible content of fly ash increases continuously. Especially, when the over-fire air rate increases from 20% to 25%, the combustible content of fly ash increases significantly. With the increase of the over-fire air rate, the high CO concentration region in the primary combustion zone expands, the reducing atmosphere is strengthened, the formation of NOx is effectively restrained, and the NOx emission concentration at the furnace outlet continues to decreases. In particular, when the over-fire air rate increases from 15% to 20%, the NOx emission concentration decreases greatly. After the swirling secondary air of the arch-fired boiler is biased, the setting of over-fire air rate is recommended to be 20%, and the NOx emission concentration and combustible content of fly ash are 694 mg/m3(O2 = 6%) and 7.32%, respectively. Compared with a traditional swirling arch-fired boiler, the combustible content of fly ash and NOx emission concentration are reduced by 46.8% and 34.1%, respectively. [ABSTRACT FROM AUTHOR]

Taking a 300-MWe arch-fired boiler as the research object, compared with original Babcock & Wilcox (B&W) combustion technology, the flow, combustion and NOx emission characteristics are comprehensively revealed under the novel biased-swirl-secondary-air combustion (BSSAC) technology with the help of cold-modeling experiments and numerical simulations. The results show that, for BSSA combustion technology, the dimensionless downward depth of the air flow from furnace arches is increased by 0.13, and the air flow fullness of whole the lower furnace is improved under the effect of burner secondary air near the water-cooled wall, vent air and staged air being injected step by step. The high-temperature reflux zone and gas reflux velocity under the furnace arch increase significantly, the ignition of primary pulverized coal air flow is advanced, and the combustion path of pulverized coal particles increases. The combustible content of fly ash decreases by 32.4%. At the same time, the ignition process of pulverized coal air flow near the center of the furnace is in a strong reducing and low oxygen atmosphere, and the multi-stage effective air supply is obtained in the downward process of pulverized coal combustion. The NOx emission concentration at the furnace outlet is reduced from 824 to 694 mg/m3 (O2 = 6%). [ABSTRACT FROM AUTHOR]