ECN publication
Flame-transformations of coal-pyrite
Published by: Publication date:
ECN 1995
ECN report number: Document type:
ECN-RX--95-037 Other
Number of pages: Full text:
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The flame-kinetics of pyrite (FeS2) particles were studied in alaboratory burner facility. Size and composition of the in-going particles and the flame-products were analyzed with CCSEM, Computer Controlled Scanning Electron Microscopy. The particles, of fifty micrometer size, decomposed in 25 milliseconds into pyrrhotite (FeS), which rapidly melted. There were no further transformations in a reducing flame. In an oxidizing flame, decomposition and melting occurred prior to oxidation with similar rates. The pyrrhotite droplets oxidized to solid iron oxide in 100 ms. This time translates to the characteristic rate for diffusion of oxygen to the droplets. It shows that the expected slow internal transport of reactants in the droplets is not the rate-limiting step. The rapid droplet-side transport is caused by internal flows induced by the surface friction of the gravitational motion of the droplets relative to the combustion gas. At the final stage of oxidation, cenospheres were observed. The standard CCSEM method had classified the cenospheres as small particles which led to a first erroneous conclusion of particle fragmentation. 5 figs., 2 tabs., 1 appendix, 17 refs.

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