Numerical investigation on the influence of nozzle–organization–mode of split burner on flow field distribution and combustion characteristics of a 300‐MWe subcritical down‐fired boiler

In order to establish an efficient air‐regulating solution as varying overfire air (OFA) and recommend an appropriate OFA ratio for a 600‐MWe W‐shaped flame furnace equipped with the proposed cascade‐arch‐firing low‐NOx and high‐burnout configuration (CLHC), four air‐regulating solutions were established by respectively adjusting the air into secondary air, tertiary air, and hopper air or proportionally varying the air into the three jets in a uniform distribution form, which were labeled in turn as SA, TA, HA, and UD, respectively. After the efficient air‐regulating solution fixed, four OFA ratios of 15%, 17.5%, 20%, and 22.5% were evaluated. Among the four air‐regulating solutions, only UD develops symmetrical combustion. An order of TA < HA < SA < UD in the final performance indexes enables UD as the efficient air‐regulating solution as varying OFA. A symmetrical flow field and combustion pattern develop at the former three OFA ratios. The excessive OFA ratio of 22.5% achieves a severely deflected flow field and asymmetric combustion. Increasing the OFA ratio generates a decrease‐to‐increase trend in burnout and a continuous decrease trend in NOx emissions. Consequently, the 20% setting is preferred as an appropriate OFA ratio, showing the best low‐NOx and high‐burnout accomplishment. The improvement in both burnout and NOx emissions as opening OFA to deepen air staging is attributed to the improved symmetrical combustion and the strengthened OFA penetration in the upper furnace.

Section: Methodsmentioning

confidence: 99%

Section: Air-regulating Solutions Ofa Ratio Setups and Simulation Met...mentioning

confidence: 99%

High‐burnout and low‐NO_x combustion characteristics in a 600‐MW_e W‐shaped flame furnace: Air‐regulating solution selection as varying overfire air and impact of the overfire air ratio

Wang

Zhao

et al. 2023

“…Subsequently, an improved version of the MIMSCT (i.e., performing a further burner nozzle layout optimization to fit for different down-fired furnace types) was popularized in several furnaces. [15][16][17] Ma et al 18 proposed a low-NO x art for a 600-MW e directflow-burner furnace via rearranging burners and introducing OFA to deepen air staging, finally gaining NO x levels of about 800 mg/m 3 (6% O 2 ) while worsening burnout a little. Chen et al 19 achieved a similar low-NO x accomplishment in a 600-MW e swirl-flow-burner furnace by altering the burner arrangement and using a separated OFA form.…”

Section: Introductionmentioning

confidence: 99%

“…For a multiple‐injection multiple‐staging combustion technology (MIMSCT) focused on high NO x generation plus asymmetric combustion, 14 its first industrial‐size trial in a 600‐MW e boiler achieved a moderate low‐NO x performance, that is, NO x production at 867 mg/m 3 (6% O 2 ) plus carbon content in fly ash at 5.4%. Subsequently, an improved version of the MIMSCT (i.e., performing a further burner nozzle layout optimization to fit for different down‐fired furnace types) was popularized in several furnaces 15–17 . Ma et al 18 proposed a low‐NO x art for a 600‐MW e direct‐flow‐burner furnace via rearranging burners and introducing OFA to deepen air staging, finally gaining NO x levels of about 800 mg/m 3 (6% O 2 ) while worsening burnout a little.…”

Section: Introductionmentioning

confidence: 99%

Strengthening low‐NO_x combustion with flue gas recirculation in a 600‐MW_e down‐fired furnace

Liu

Kuang

et al. 2022

For a down-fired furnace using a cascade-arch-firing low-NO x and highburnout configuration (CLHC, which includes flue gas recirculation and is taken as a strengthened low-NO x combustion solution), the gas/particle flow, coal combustion, and NO x emissions were investigated at various flue gas recirculation (FGR) ratios of 5%, 10%, 15%, and 20% (labeled as settings of FGR = 5%, 10%, 15%, and 20%, respectively). The aim was to disclose the FGR role on the strengthened low-NO x combustion characteristics and meanwhile obtain an available FGR ratio. With increasing FGR, although the downward flame penetration increased continuously, the large local high-temperature zone favoring combustion in the furnace shrunk. Increasing FGR lowered gas temperatures and strengthened the reductive atmosphere in the downstream of the reburning zone to restrain combustion and meanwhile weaken the NOreduction effect of reburning. Trends of the final performance indexes with the FGR ratio showed that NO x production increased continuously, while burnout loss generally undergone an increase-to-decrease trend. In view of the above findings and the gained optimal furnace performance (i.e., NO x emissions of 530 mg/m 3 at 6% O 2 accompanied by carbon content in fly ash at 5.28%), low FGR levels such as FGR = 5% with a hot-air dilution in FGR should be preferred for the CLHC furnace where FGR is used to deliver the fine pulverizedcoal particles for reburning. In comparison to an advanced in-service low-NO x art, the CLHC reduced further NO x production by 41.4% while remained a high burnout achievement except a limited increase in CO emission.

“…Due to the rich reserves of low‐volatile coals and a large proportion of these coals in total coal consumption for thermal power generation, W‐shaped flame furnaces have popularized well in China since the first import from Britain in the late 1980s 3 . However, actual operations have shown that there exist universal problems of late coal ignition, unstable combustion, asymmetric combustion, high burnout loss (carbon content in fly ash above 8%), severe slagging, and high NO x emissions (conventionally higher than 1,100 mg/m 3 at 6% O 2 ) 4–6 . Accordingly, various investigations or solutions have been reported via the methods referred to real‐furnace measurements, lab‐scale cold‐modeling experiments, and numerical simulations 7 …”

Section: Introductionmentioning

confidence: 99%

Impact of the upper/lower furnace depth ratio on the strengthened low‐NO_x combustion performance in a two‐stage W‐shaped flame furnace

Zhao

Kuang

Liu

et al. 2021

For achieving the strengthened low‐NOx combustion plus high burnout in W‐shaped flame furnaces, a cascade‐arch low‐NOx and high‐burnout configuration (CLHC) is realized by positioning two burner layers in a 600 MWe furnace. The gas/particle flow, combustion, and NOx emission characteristics in the furnace are numerically evaluated at four upper/lower furnace depth ratios of CW = 0.458, 0.500, 0.529, and 0.558 (CW signifying the furnace throat shrinkage level) so as to disclose the impact of the furnace throat shrinkage level on the overall furnace performance and meanwhile establish an available CW setup. Increasing CW initially updates but then deteriorates the low‐NOx combustion performance. At the narrowest CW = 0.485 setup, the gained slightly asymmetric combustion shows relatively lower burnout loss but higher NOx emissions, while the widest CW = 0.558 setup forms severely asymmetric combustion with apparently raised carbon in fly ash but relatively lower NOx emissions. At moderate setups of CW = 0.500 and 0.529, a symmetrical combustion pattern develops, showing the low‐NOx and high‐burnout performance characterized as NOx emissions of 700–707 mg/m3 (6% O2) and carbon content in fly ash of 5.4–5.5%. In comparison to CW = 0.500, the larger downward flame penetration, higher flame fullness, and lower CO emission at CW = 0.529 suggest that a reasonable upper/lower furnace depth ratio prefers CW = 0.529. Compared with a currently advanced low‐NOx combustion technology, the CLHC lowers again NOx emissions by about 200 mg/m3 (6% O2) while maintaining high burnout, which confirms the CLHC's availability.