Influence of the Secondary Air-Box Damper Opening on Airflow and Combustion Characteristics of a Down-Fired 300-MW_e Utility Boiler

Abstract

Experiments with a small-scale furnace for a down-fired pulverized-coal 300-MWe utility boiler were carried out on a single-phase test facility to investigate the influence of different secondary air distributions on the aerodynamic field in the furnace. When the secondary air flux of tier E increased within a suitable range, it did not reverse the fuel-rich flow or shorten the residence time of coal particles in the furnace. Industrial experiments were also performed on a full-scale boiler. The gas temperature distribution along the primary air and coal mixture flow and in the furnace, and gas components such as O2, CO, CO2, and NO x in the near-wall region, were measured with damper openings of the E-tier secondary air box at 0% and 30%. At 0%, ignition of the primary air and pulverized coal mixture was delayed and the gas temperature peak was above the burner arch, with high NO x emission. Increasing the damper opening to 30% provided the oxygen necessary for the initial combustion. This was advantageous for stable combustion and also lowered NO x emissions and carbon content in the fly ash.

Multi-injection multi-staging combustion mechanistic studies and down-fired boiler technology

“…(2) 浓煤粉气流下冲深度小 英巴W火焰锅炉由于炉内流场偏斜, 后墙侧煤粉 气流下冲深度较小. 图5为美国FW 300-MW W火焰锅 炉额定负荷模化工况下不同二次风配比浓煤粉气流竖 直速度的衰减 [39] .…”

“…图 5 美国FW 300-MW W火焰锅炉不同二次风配比浓煤粉 气流竖直速度的衰减 [39] Figure 5 Decay of the vertical-velocity components of fuel rich flow under different secondary air distribution for the FW 300-MW downfired boiler [39]. 流燃烧器内、外二次风角度较大时, 煤粉气流的下冲 深度也较小 [10] .…”

“…分别为8.5% [35] 、11.5% [33] 、7.84% [39] , 煤粉燃尽差. [19,35,45,46] 、超过1400 mg/m 3 (O 2 =6%) [27,33,36] 、2101 mg/m 3 (O 2 =6%) [5,8,39,47] , NO x 排 放浓度高. ; 在靠近喉口位置布置直 流燃尽风.…”

Effects of Near-Wall Air Application in a Pulverized-Coal 300 MWe Utility Boiler on Combustion and Corrosive Gases

“…In the NWA technology, NWA nozzles, that can inject adequate amounts of secondary air to protect water-wall surfaces from high-temperature corrosive gases, are installed. − Most of the previous investigations on the NWA technology were confined to the application in down-fired furnaces . Studies have been carried out on the formation mechanism of high-temperature corrosion and corrosive gas distribution in furnaces. − Through numerical simulation calculations of a 550 MW e tangentially fired furnace, Al-Abbas et al , analyzed the relationship between the CO distributions obtained from simulation and the actual operation condition.…”

Trends of the Flow-Field Deflection and Asymmetric Combustion in a 600 MWe Supercritical Down-Fired Boiler with Respect to the Furnace Arch’s Burner Span

“…In China, down-fired boilers, which are designed especially for firing low-volatile, hard-to-burn fuels (such as anthracite and lean coals), − have been widely imported from North America and western Europe since the 1990s. However, the operation performances of about 200 large-scale units show problems of poor combustion status, , serious slagging, high burnout loss and NO x emissions, − and asymmetric combustion. , Accordingly, various solutions have been proposed such as burning blended fuels to strengthen combustion, − shutting down near-wall burners or exchanging the bias combustion’s burner nozzle location to mitigate slagging, descending wall-air to increase burnout, − and regulating air-staging conditions − or retrofitting combustion system to sharply reduce NO x emissions. − With respect to asymmetric combustion, only Kuang and Li’s group published a series of comprehensive investigations, with major findings containing the following aspects: (i) reporting that the occurrence of in-furnace flow-field deflection results in asymmetric combustion; , (ii) taking the asymmetric furnace configuration effect and unreasonable burner designs as the potential reasons that favor the formation of flow-field deflection and thereafter confirming it by comparing three down-fired boilers’ asymmetric combustion performances; (iii) trying out various primary measures to improve the deflected flow fields, such as decreasing the staged-air ratio, , constructing asymmetric air distribution model, and descending staged air . However, under the circumstances without improvement in the asymmetric upper furnace configuration and unreasonable burner designs, these primary measures show limitations.…”