Pyrolysis and Ignition Characteristics of Pulverized Coal Particles

2000 ◽  
Vol 123 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Masayuki Taniguchi ◽  
Hirofumi Okazaki ◽  
Hironobu Kobayashi ◽  
Shigeru Azuhata ◽  
Hiroshi Miyadera ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fine Particles ◽  
Early Stage ◽  
Radiant Heat ◽  
Volatile Matter ◽  
Combustible Mixture ◽  
Radiant Heat Transfer ◽  
Coal Particles ◽  
Intermediate Size ◽  
Ignition Characteristics

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.

The ignition of clouds of particles in shock-heated oxygen

1967 ◽  
Vol 300 (1460) ◽  
pp. 62-77 ◽  
Keyword(s):  
Radiant Heat ◽  
Volatile Matter ◽  
Radiant Heat Transfer ◽  
Ignition Process ◽  
Particle Ignition ◽  
Ignition Delay Times ◽  
Complex Process ◽  
Coal Particles ◽  
Delay Times ◽  
The Times

The ignition of clouds of coal particles in shock-heated oxygen has been studied. The requisite gas temperatures and pressures for ignition have been measured and have been related to particle ignition temperatures which are dependent on the volatile content of the coal and are in close agreement with the temperatures at which the particles lose volatile matter at an appreciable rate. Ignition delay times for various coals of different size ranges have been measured at oxygen pressures of 1.5 to 30 atm and temperatures of 700 to 1600°K. The experimental results indicate that the influence on the delays of the radiant heat transfer from a previously established flame at the shock-reflecting face is small. Some evidence that ignition is a surface catalysed process is presented. A mechanism for the ignition process is proposed. This relates the ignition delays with the times required to heat the particles solely by conduction to the appropriate particle ignition temperature. This theory is shown to describe the experimental delays satisfactorily. In testing it, similar experiments on completely volatile particles (anthracene) and non-volatile particles (graphite) have been carried out. Ignition of anthracene occurs when the particles approach their boiling point. Ignition of small graphite particles is a more complex process in which the first stage is the heating of the particles by conduction to a temperature just below that of the shock-heated gas. This is followed by a period in which heating due to chemical reaction overtakes heating by conduction.

Radiant Heat Transfer From Isothermal Dispersions With Isotropic Scattering

1967 ◽  
Vol 89 (4) ◽  
pp. 300-308 ◽  
Author(s):  
R. H. Edwards ◽  
R. P. Bobco
Keyword(s):  
Heat Transfer ◽  
Approximate Solutions ◽  
Radiant Heat ◽  
Second Order ◽  
Isotropic Scattering ◽  
Radiant Heat Transfer ◽  
Approximate Methods ◽  
First Order ◽  
Order Solution ◽  
Radiant Transfer

Two approximate methods are presented for making radiant heat-transfer computations from gray, isothermal dispersions which absorb, emit, and scatter isotropically. The integrodifferential equation of radiant transfer is solved using moment techniques to obtain a first-order solution. A second-order solution is found by iteration. The approximate solutions are compared to exact solutions found in the literature of astrophysics for the case of a plane-parallel geometry. The exact and approximate solutions are both expressed in terms of directional and hemispherical emissivities at a boundary. The comparison for a slab, which is neither optically thin nor thick (τ = 1), indicates that the second-order solution is accurate to within 10 percent for both directional and hemispherical properties. These results suggest that relatively simple techniques may be used to make design computations for more complex geometries and boundary conditions.

Sign in / Sign up

Export Citation Format

Share Document