Shigeru Azuhata

Pyrolysis and Ignition Characteristics of Pulverized Coal Particles

Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37-74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.

A study of gas composition profiles for low NOx pulverized coal combustion and burner scale-up

A turbulent diffusion flame of pulverized coal was investigated to clarify the relationship between flame structure and NOx emissions. NO was formed in the initial flame zone and was reduced in the fuel-rich, post-flame regions, where HCN and NH 3 were produced probably by the oxidation of coal by H 2 O and CO 2 . Burner scale-up also was examined by conducting parallel experiments in a small-scale combustor and a facility with a 25-fold larger coal feedrate. The performance and the profiles of gas species in the flame of the large-scale furnace were well simulated by the data obtained in a laboratory-scale burner where combustion air inlets were remotely located from the central fuel jet to surpress the transverse mixing of air and coal.

Advanced clean coal technologies

In this paper, the author argues that, although coal may be an interim solution, the development of technologies providing effective use of coal is important to bridge the gap between present and future energy supply situations.

A study of the kinetics of the NH3−NO−O2−H2O2 reaction

The addition of H2O2 to NH3−NO mixtures was found to promote the NO reduction reaction and to initiate it around 500°C. A model of the NH3−NO−H2O2−O2 reaction was investigated to establish the characteristics of the reaction. We evaluated the relative importance of individual elementary reactions based on the experimental results and by comparison with previously reported rate constants. The final model consisted of 21 reactions of 14 species. The results obtained by numerical integration of the differential equations were in good agreement with the experimental ones.

NOx Removal Process by Injection of NH3 and H2O2 in Gas Turbine Exhaust Gas

For the removal of NOx in a gas turbine exhaust gas, the reduction of NOx with NH3 and H2O2 was studied. It was found that the addition of H2O2 very effectively lowers the reduction temperature of NO with NH3 and that more than 90 percent NOx reduction could be attained at 550 C in the absence of O2. However, the NOx reduction rate decreased with increases in the concentration of O2, and NOx reduction was about 40 to 60 percent under gas turbine exhaust gas condition (15 percent O2). In order to attain a high rate of reduction of NOx, a combined reduction process, which consisted of homogeneous gas phase and the catalytic heterogeneous reactions, was also developed. The efficiency of the new process was proved in a pilot plant using half a size model of a 25-MW gas turbine combustor.Copyright

Effect of Volatile and Ash Contents on Flame Propagation Properties for Pulverized Coal Dust Clouds Ignited by Pulsed Laser.

Effect of volatile and ash contents on cloud ignition behaviors were examined for pulverized coal dust clouds, that were suspended in a laminar upward flow and heated by a single-pulsed YAG laser. We compared burning times of volatile matter, flame propagation velocities and lean flammability limits for several coals. The coals contains almost same volatile matter, but different ash. The present results showed that the burning time of volatile matter, flame propagation velocity and lean flammability limit were mainly determined by volatile content. The effects of ash content were small. The maximum flame propagation velocity increased with volatile content. The velocity increased the third as much as when volatile content increased from 10% to 20%.

A Study of Premixed Flames Stabilized by Bluff Bodies for Reducing NOx Emission.

乱流予混合火炎の低NOx化を目的として, 予混合火炎の安定化手法とNOx排出濃度との関連性を検討した.さらに, 予混合火炎中の流速, 温度およびガス組成の分布を測定し, NOxが低減されるときの火炎形状と流れの特徴を調べた.ブラフボディを用いて噴流中心部から外周に向かい伝播する火炎を形成すると, パイロット火炎を用いて形成した円錐型火炎と比較して, 火炎温度が約150K低減され, NOxが約1/3～1/5に低減された.このブラフボディで安定化された予混合火炎中では, 混合気体噴流の内周および外周に燃焼気体が循環する領域が形成され, 噴流と逆流領域の境界に剪断層が形成される.内周側の剪断層では火炎が形成される.外周側の剪断層では, 燃焼気体が噴流中の燃料, 空気を希釈しNOxの発生を抑制する.