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To solve the problem of high NOx emission of 600‐MWe boilers in power plants, we established a cold gas–solid modeling testbed scaled by 1:5 for two‐channel overfire air (OFA). A phase‐Doppler anemometer was used to measure the characteristics of the outlet flow field of the two‐channel OFA under different OFA rates. We also verified the industrial feasibility of this testbed under loads of 300 and 600 MWe. The influence of the OFA rate on the divergence angle of the outlet jet was small: When the OFA rate was increased from 15% to 35%, the divergence angle only increased by 2.2°. The attenuation of the axial velocity of the outlet jet increases with increasing OFA rate. For OFA rates of 15% and 25%, the jet penetration depth was between 1.5d and 2.5d (where d is the cone diameter of the OFA model in the cold‐flow experiments). When the OFA rate was 35%, the jet penetration depth was between 2.5d and 3.5d. The jet maintained about 17% O2 concentration at 1.4 m (about 11d) in the furnace under different boiler loads, and the concentration of emitted NOx increased with decreasing load. Based on these findings, we propose the use of two‐stage OFA: The jet at the outlet of the first‐stage OFA ports should have a larger jet‐divergence angle, and the other stage should have a larger jet‐penetration depth to realize full mixing with the flue gas and to ensure high burnout and low NOx emission. [ABSTRACT FROM AUTHOR]

Coal and coal char thermal degradation in a CO2 atmosphere is particularly important to understand and model as a rate‐determining step in the gasification process. The work presented here aims to provide a global kinetic model that accurately represents the thermal degradation of Sanxing (SX) coal and coal char under a CO2 atmosphere and to determine the kinetic parameters of the thermal degradation. In the work presented, a novel approach has been used that involves a triple‐Gaussian DAEM that simultaneously considers the primary pyrolysis, secondary pyrolysis, and the process of newly generated char gasified by CO2. The result of the model shows accurate reproduction of the thermal degradation behavior of SX coal and chars and provides significant information about the relative occurrence of the three steps. For SX coal and Char500, the residual error of the triple‐Gaussian DAEM is approximately 0.35 to 0.22 times that of the double Gaussian DAEM. For Char850, the ratio is lower, approximately 0.12 times that of the double Gaussian DAEM. This indicates that the triple‐Gaussian DAEM is more suitable for describing the thermal degradation of chars acquired at high temperatures (500–850°C) under a CO2 atmosphere. [ABSTRACT FROM AUTHOR]

To enhance the rapid switching ability of the boiler load and reduce NOx emissions, a new combustion system was implemented in a 600‐MWe wall‐fired boiler with swirl burners. This system included two levels of overfire air (OFA) and low NOx combustion technology. Industrial tests were conducted at 300‐, 450‐, and 600‐MWe loads before and after the retrofitted. These tests included measuring flue gas and furnace temperatures with thermocouples and analyzing local gas concentrations using a gas analyzer. The research results indicate that under conditions where the OFA ratio exceeds 30%, the burner exhibits good ignition performance at different loads. At the 600‐MWe load, the nitrogen oxides (NOx) emissions were reduced by 55% compared to before the retrofit. After the retrofit, the flame center inside the furnace of different loads was located at the height of 33.36 m, the first and second‐stage cooling water quantities were slightly higher, the reheat cooling water quantity was greatly reduced after the retrofit, and contributes to the boiler's safe operation. Under different load conditions after the retrofit, the gas temperature near the sidewall was below 850°C, and the O2 concentration near the sidewall was above 5%, effectively suppressing sidewall high‐temperature corrosion and slagging. [ABSTRACT FROM AUTHOR]

Low NO x burners and air staging technology are the most economic and effective means of reducing NO x emissions from coal-fired furnaces. However, it is difficult to significantly reduce NO x emissions through air-staged combustion in the furnace without reducing the boiler efficiency. The aim of this work was to study the effect of the inner secondary air cone length of a centrally fuel-rich swirl coal combustion burner on combustion and NOx characteristics using a 0.5 MW laboratory furnace with air-staging. Gas temperature and concentrations of gaseous species (O2, CO, and NO x) were measured in the primary combustion and burnout zones for different inner secondary air cone lengths. It was found that the inner secondary air cone length had significant effects on NO x emissions, unburned carbon content in the fly ash, and ignition performance of the burner. As the inner secondary air cone length increased, the unburned carbon content in the fly ash level increased, NO x emissions decreased, and pulverized-coal ignition occurred later. The optimized results provide an important reference for engineering design. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The asymmetric upper furnace configuration effect (mainly relied on the short upper furnace and large boiler nose) and unreasonable burner designs are taken as potential major factors that favoring the asymmetric combustion formation in down-fired boilers. To determine the boiler nose's role in this aspect and weaken the boiler nose's effect, two boiler nose's depth shrunk settings of C L = 0.199 and 0 were compared with the large design setup C L = 0.298 within a 600 MW e supercritical down-fired boiler. Numerical simulations on coal combustion were carried out for all three settings, plus full-load industrial-size measurements at the boiler's design setup. The boiler's design setup shows badly asymmetric combustion with poor burnout and high NO x emissions, corresponding to its reported, severely deflected gas/particle flow field. Shrinking boiler nose attains limited improvements (such as shortening the front/rear downward coal/air penetration difference, redirecting a little the upward gas flow towards the upper furnace central part, and shrinking the gas-flow stagnation zone below boiler nose), but unfortunately, essentially fails to change the flow-field deflection pattern and meanwhile decreases the gas fullness in the upper furnace's top zone to generate a potential threat on steam parameters. The absence of effective improvements in asymmetric combustion and apparently shortened flame penetration finally develop a worsened burnout, decreased O 2 at the furnace outlet, and lowered NO x emissions as C L decreased. Findings in this work thus exclude boiler nose as a potential major factor that favoring the formation of flow-field deflection and asymmetric combustion and meanwhile, provide useful information that under the circumstances with a short upper furnace aggravating the asymmetric upper furnace configuration effect, a relatively large boiler nose should be used for maintaining (i) the boiler nose's suppression effect on the upward gas flow and (ii) gas fullness in the upper furnace's top zone. [ABSTRACT FROM AUTHOR]