Synthetic chars for the study of ash vaporization

Abstract

Synthetic chars have been produced in order to facilitate the study of ash vaporization mechanisms. The synthetic chars are glassy carbons produced by the polymerization of furfuryl alcohol. Simple minerals are added to the polymer prior to curing in order to generate chars for which the ash thermodynamics are known. Although simple glassy carbons generally have low surface areas, the surface area can be increased by two orders of magnitude by adding carbon black to the polymer. The resulting pore structure substantially alters the way the char burns. Ash vaporization from synthetic chars containing 1 to 4 micron quartz inclusions was studied in an externally heated laminar flow reactor. The fraction of the quarts ash vaporized varied from 0.3 to 33 percent for combustion in a 1600 K furnace in gases containing 40 to 100 percent oxygen in nitrogen. Calculated particle temperatures were between 2200 K and 2900 K. Quartz in the synthetic char appeared to be vaporized directly rather than by reduction to SiO as previously reported for cool chars. The vaporization rates were below those predicted for SiO₂ vapor equilibrium at the char surface, but above those predicted when the diffusional resistance within the char was taken into account.

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