Single-particle combustion of two biomass chars

In order to assess the combustion reactivities of chars produced from the pyrolysis of woody and herbaceous biomass, we have subjected particles of Southern pine and switchgrass chars to two sets of combustion experiments. In the first, a dilute stream of biomass char particles (nominal size, 75–106 μm) is burned in a laminar flow reactor at 12 mole % O 2 and a mean gas temperature of ∼1600 K. In situ optical measurements reveal that at a given residence time in the early stages of char conversion, biomass char particles burn over a much wider temperature range (∼450 K) than coal particles (∼150 K) and that the biomass char particle temperatures span the entire range of the theoretical limits (from the slowest burning inert particles to the fastest burning diffusion-controlled particles). As biomass char conversion proceeds, however, mean particle temperatures decrease, and particle temperature distributions narrow-consequences of the preferential removal of more reactive carbon as well as a number of physical and chemical transformations of the inorganic constituents of the chars (vaporization, surface migration and coalescence, and incorporation into silicate structures). Kinetic parameters for median particles taken at the early stages of char conversion indicate that biomass chars are somewhat less reactive than low-rank lignites and subbituminous coals, somewhat more reactive than high-rank low-volatile bituminous coals, and comparable in reactivity to high-volatile bituminous coals. In the second set of combustion experiments, individual biomass char particles are suspended on an inert mesh and suddenly subjected to a hot 6 mole % O 2 environment. Video images of reflected light and near-infrared emission for a number of pine and switchgrass char particles demonstrate the heterogeneity of the biomass chars in terms of both the sequence of morphological changes and the temperature-time histories of the particles as they undergo combustion.

[1]  F. McTaggart,et al.  Reactions of carbon with atomic gases , 1959 .

[2]  D. Tillman The combustion of solid fuels and wastes , 1991 .

[3]  Philip L. Walker,et al.  Gas Reactions of Carbon , 1975 .

[4]  R. C. Neavel,et al.  Behaviour of calcium as a steam gasification catalyst , 1982 .

[5]  Robert H. Hurt,et al.  Residual carbon from pulverized coal fired boilers: 1. Size distribution and combustion reactivity , 1995 .

[6]  F. Roberts Proceedings of the Fourth Conference on Carbon, University of Buffalo, 1959 : Pergamon Press, London, 1960. xii + 778 pp. £7. 10s , 1961 .

[7]  M. Field,et al.  Measurements of the effect of rank on combustion rates of pulverized coal , 1970 .

[8]  P. Walker,et al.  THE IMPORTANCE OF ACTIVE SURFACE AREA IN THE CARBON-OXYGEN REACTION1,2 , 1963 .

[9]  B. Stanmore,et al.  The combustion characteristics of char from pulverized bagasse , 1992 .

[10]  Larry L. Baxter,et al.  Spectral emittance measurements of coal particles , 1988 .

[11]  R. J. Quann,et al.  A scanning electron microscopy study of the transformations of organically bound metals during lignite combustion , 1986 .

[12]  R. Hurt,et al.  Evolution of char chemistry, crystallinity, and ultrafine structure during pulverized-coal combustion☆☆☆ , 1995 .

[13]  J. Moulijn,et al.  Nature, activity and stability of active sites during alkali metal carbonate-catalysed gasification reactions of coal char , 1983 .

[14]  R L Hirsch,et al.  Catalytic Coal Gasification: An Emerging Technology , 1982, Science.

[15]  Anthony V. Bridgwater,et al.  Developments in direct thermochemical liquefaction of biomass: 1983-1990 , 1991 .

[16]  Robert H. Hurt,et al.  Structural and compositional transformations of biomass chars during combustion , 1995 .

[17]  Robert H. Hurt,et al.  Reactivity distributions and extinction phenomena in coal char combustion , 1993 .

[18]  E. W. Thiele Relation between Catalytic Activity and Size of Particle , 1939 .

[19]  P. Walker,et al.  Reactivity of heat-treated coals in air at 500 °C , 1973 .

[20]  E. Wicke,et al.  Transportvorgänge und Oberflächenreaktionen bei der Verbrennung graphitischen Kohlenstoffs , 1956 .

[21]  P. Walker,et al.  Effect of lignite pyrolysis conditions on calcium oxide dispersion and subsequent char reactivity , 1983 .

[22]  Nancy Y. C. Yang,et al.  single Droplet Combustion of Biomass Pyrolysis Oils , 1994 .

[23]  W. Degroot,et al.  Kinetics of gasification of Douglas Fir and Cottonwood chars by carbon dioxide , 1984 .

[24]  E. Wolf,et al.  FTIR studies of potassium catalyst-treated gasified coal chars and carbons , 1983 .

[25]  W. Smith,et al.  The Oxidation of Graphitized Carbon Black. , 1956 .