Toshikazu Tsumura

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.

Reducing the minimum load and NOx emissions for lignite-fired boiler by applying a stable-flame concept

For the purpose of improving the load range and NOx emission level of lignite-fired power plants, a new combustion technology, called NR-LE burners (NOx Reduction-Load Extension), has been developed in co-operation between Babcock-Hitachi and Fortum. A single-burner combustion test was performed in Japan with this new NR-LE type burner using Czech lignite. Adapting the flame-stabilization ring and a special additional air-nozzle resulted in achieving a stable flame, which enables: - The burner minimum load to be less than 50% (Boiler load: 30-40%) - Low NOx emissions of less than 200 mg/m3 (6% O2, dry base) The first commercial full-scale application of the NR-LE burner was by the IPP power producer in the Czech Republic (Sokolovska Uhelna, a.s. at Vresova Unit2 boiler with steam parameters 325 t/h, 535 °C, 13.5 MPa). The commissioning test runs of the new burners were carried out during September to October 2001. The boiler is now in commercial operation, with (i) a 30% minimum load without supplementary fuel, and (ii) lower NOx emission levels.

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%.