Regulating Low-NO_x and High-Burnout Deep-Air-Staging Combustion under Real-Furnace Conditions in a 600 MW_e Down-Fired Supercritical Boiler by Strengthening the Staged-Air Effect

Abstract

A 600 MW(e) down-fired pulverized-coal supercritical boiler, which was equipped with a deep-air-staging combustion system for reducing the particularly high NOx emissions, suffered from the well-accepted contradiction between low NOx emissions and high carbon in fly ash, in addition to excessively high gas temperatures in the hopper that jeopardized the boiler's safe operations. Previous results uncovered that under low-NOx conditions, strengthening the staged-air effect by decreasing the staged-air angle and simultaneously increasing the staged-air damper opening alleviated the aforementioned problems to some extent. To establish low-NOx and high-burnout circumstances and control the aforementioned hopper temperatures, a further staged-air retrofit with horizontally redirecting staged air through an enlarged staged-air slot area was performed to greatly strengthen the staged-air effect. Full-load industrial-size measurements were performed to confirm the availability of this retrofit. The present data were compared with those published results before the retrofit. High NOx emissions, low carbon in fly ah, and high hopper temperatures (i.e., levels of 1036 mg/m(3) at 6% O2, 3.72%, and about 1300 °C, respectively) appeared under the original conditions with the staged-air angle of 45° and without overfire air (OFA) application. Applying OFA and reducing the angle to 20° achieved an apparent NOx reduction and a moderate hopper temperature decrease while a sharp increase in carbon in fly ash (i.e., levels of 878 mg/m(3) at 6% O2, about 1200 °C, and 9.81%, respectively). Fortunately, the present staged-air retrofit was confirmed to be applicable in regulating low-NOx, high-burnout, and low hopper temperature circumstances (i.e., levels of 867 mg/m(3) at 6% O2, 5.40%, and about 1100 °C, respectively).

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

“…Kuang et al 29 put forward a deep‐air‐standing low‐NO x combustion technology (i.e., multiple‐injection and multiple‐staging combustion technology, abbreviated as MIMSCT) for sharply reducing NO x and improving the severely asymmetric combustion. Its industrial application in a 600 MW e furnace confirmed that, in comparison to the same‐grade MBEL furnace suffering from asymmetric combustion, high carbon content in fly ash of 8.5%, and high NO x emissions of 1,467 mg/m 3 (6% O 2 ), the MIMSCT exhibited superiority in regulating symmetrical combustion and apparently lowering NO x , with NO x levels of 867 mg/m 3 (6% O 2 ) and carbon content in fly ash of 5.4% 30–32 …”

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

“…As mentioned previously, aiming at the compatibility problem of strengthened low-NO x combustion and high burnout, CLHC is developed based on our group’s many years of work on W-shaped flame furnaces and the application experience gained from several stages of the prior MIMSCT. In order to confirm the CLHC’s high-burnout and low-NO x combustion advantages compared with the prior arts, the 600 MW e supercritical MIMSCT W-shaped flame boiler furnace involved in the previous work ,, was selected to perform both industrial-size measurements and numerical simulations at normal full-load operation. The subsequent efforts were devoted to numerical simulations of the gas/particle flow, coal combustion, and NO x formation of the furnace with CLHC.…”

“…The horizontal staged air and inclined OFA (fed into the primary combustion and burnout zones, respectively) are used to regulate the third and fourth stages of airflow injection and deepen the air-staging conditions. This deep-air-staging combustion layout is based on the so-called multiple-injection and multiple-staging combustion technology (MIMSCT), whose detailed description has already appeared in the literature. , Table lists the furnace’s conventional operation parameters mainly in the airflow and fuel supplying at full load.…”

“…By positioning fuel-lean nozzles in the near-wall side, redirecting staged air, and introducing the separated OFA to regulate a novel combustion system for a 600 MW e FW W-shaped flame furnace, Ma et al , found that NO x emissions reduced by 42–50% to achieve levels of about 760 mg/m 3 at 6% O 2 , accompanied by a certain increase in the burnout loss. Based on a multiple-injection and multiple-staging combustion technology (MIMSCT) applied in a 600 MW e supercritical boiler furnace, Kuang et al optimized an accepted furnace performance with NO x emissions of 867 mg/m 3 at 6% O 2 and carbon in fly ash of 5.4%. − Although strengthening further air staging by opening OFA decreased again the NO x emissions to 503–696 mg/m 3 at 6% O 2 , carbon in fly ash surged to 13–15% …”

Online-CPD-Coupled Large-Eddy Simulation of Pulverized-Coal Pyrolysis in a Hot Turbulent Nitrogen Jet

“…On the other hand, coal is the most polluting fossil fuel. Due to increasing environmental concerns, development of clean coal technologies, e.g., low NOx combustion (Kuang et al, 2014;Lv et al, 2010) and oxy-coal combustion for carbon capture and storage (CCS) (Bu et al, 2015), becomes more and more important. To develop clean coal technologies, a comprehensive understanding of pulverized-coal combustion physics is necessary.…”