Influence of Staged-Air on Airflow, Combustion Characteristics and NO_x Emissions of a Down-Fired Pulverized-Coal 300 MW_e Utility Boiler with Direct Flow Split Burners

Abstract

Cold airflow experiments were conducted to investigate the aerodynamic field in a small-scale furnace of a down-fired pulverized-coal 300 MW(e) utility boiler arranged with direct flow split burners enriched by cyclones. By increasing the staged-air ratio, a deflected flow field appeared in the lower furnace; larger staged-air ratios produced larger deflections. Industrial-sized experiments on a full-scale boiler were also performed at different staged-air damper openings with measurements taken of gas temperatures in the burner region and near the right-side wall, wall heat fluxes, and gas components (O(2), CO, and NO(x)) in the near-wall region. Combustion was unstable at staged-air damper openings below 30%. For openings of 30% and 40%, late ignition of the pulverized coal developed and large differences arose in gas temperatures and heat fluxes between the regions near the front and rear walls. In conjunction, carbon content in the fly ash was high and boiler efficiency was low with high NO(x) emission above 1200 mg/m(3) (at 6% O(2) dry). For fully open dampers, differences in gas temperatures and heat fluxes, carbon in fly ash and NO(x) emission decreased yielding an increase in boiler efficiency. The optimal setting is fully open staged-air dampers.

Low-NOx and High-Burnout Combustion Characteristics of a Cascade-Arch-Firing, W-Shaped Flame Furnace: Numerical Simulation on the Effect of Furnace Arch Configuration

“…Carbon in fly ash and NO x emissions were acquired by sampling fly ash and flue gas at the air preheater exit. More detailed introductory material about the industrial-size measurement methods, measurement errors and uncertainties analysis, and configuration parameters of the water-cooled stainless steel probe, can be found in the literature. ,,,, …”

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

“…但是, 采用国外技术制造的W火焰锅炉一 般燃烧效率较低、易于结渣, 特别是氮氧化物排放普 遍较高, 不能满足环保标准要求 [6,7] . NO [15,16] 、燃烧不稳 [17,18] 、结渣严 重 [19,20] 、炉内偏烧 [21~23] 等问题, 我们通过冷态单相、 气固两相试验、数值模拟以及在300-MW和600-MW 机组锅炉上的工业试验研究, 消化吸收了英国三井巴 布科克(简称英巴) [24,25] 、美国巴布科克•威尔科克斯 (简称美巴) [26,27] 、美国福斯特惠勒(简称美国FW) [28,29] 燃烧技术, 找出了存在这些问题的原因, 提出了W火焰 锅炉多次引射分级燃烧技术 [30~34] . 该技术已被用于4…”

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.…”