Latest Low-NO x Combustion Technology for Pulverized-coal-fired Boilers
Kenichi Ochi Kenji Kiyama Hidehisa Yoshizako, Dr. Eng. Hirofumi Okazaki Masayuki Taniguchi, Dr. Eng. OVERVIEW: Hitachi has long been working on the development of low NOx combustion technologies to satisfy the worldwide need for environmental conservation and has devised the world-first concept of “inflame NOx reduction” which has been applied in the field of pulverized coal combustion technology in the HT-NR burner series. Hitachi has developed new technology to lower NOx levels even further by improving the structural design and operation of a two-stage air port system which is used in combination with in-flame NOx reduction. This work has been progressed using a large-scale combustion test facility that simulates actual furnace conditions and through the use of a numerical analysis technique developed in-house. The new technology can lower boiler outlet NOx by 40% for the same level of CO.
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.
Influence of process parameters on nitrogen oxide formation in pulverized coal burners
This paper describes the influence of burner operating conditions, burner geometry and fuel parameters on the formation of nitrogen oxide during combustion of pulverized coal. Main attention has been paid to combustion test facilities with self-sustaining flames, while extensions have been made to full-scale boilers and furnace modeling. Since coal combustion and flame aerodynamics have been reviewed earlier, these phenomena are only treated briefly.