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Titolo:
Physicochemical transformations of coal particles during pyrolysis and combustion.
Autore:
Alonso, MJG; Borrego, AG; Alvarez, D; Kalkreuth, W; Menendez, R;
Indirizzi:
CSIC, Inst Nacl Carbon, E-33080 Oviedo, Spain CSIC Oviedo Spain E-33080CSIC, Inst Nacl Carbon, E-33080 Oviedo, Spain UFRGS, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil UFRGS PortoAlegre RS Brazil BR-91501970 BC01970 Porto Alegre, RS, Brazil
Titolo Testata:
FUEL
fascicolo: 13, volume: 80, anno: 2001,
pagine: 1857 - 1870
SICI:
0016-2361(200110)80:13<1857:PTOCPD>2.0.ZU;2-3
Fonte:
ISI
Lingua:
ENG
Soggetto:
REACTIVITY; MACERALS; BEHAVIOR;
Keywords:
pyrolysis; combustion; rank; macerals; coal; optical microscopy;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Engineering, Computing & Technology
Citazioni:
17
Recensione:
Indirizzi per estratti:
Indirizzo: Borrego, AG CSIC, Inst Nacl Carbon, Francisco Pintado Fe 26 Ap 73, E-33080Oviedo, Spain CSIC Francisco Pintado Fe 26 Ap 73 Oviedo Spain E-33080 Spain
Citazione:
M.J.G. Alonso et al., "Physicochemical transformations of coal particles during pyrolysis and combustion.", FUEL, 80(13), 2001, pp. 1857-1870

Abstract

The pyrolysis and combustion behaviour of a set of 11 Canadian coals with different ranks (lignite to low volatile bituminous) and maceral compositions has been investigated by TGA techniques. Temperature programmed heating of the coals was carried out both under nitrogen and under air, and the weight loss rates occurring in the two experimental conditions were compared in the whole temperature range studied (100-1000 degreesC). Results showed that the pyrolysis curves of the coals do not match at all with any specificfeature of the corresponding combustion profiles, and that the temperatures of initiation of both processes are very different in the low-rank end (higher initiation temperatures for pyrolysis), to become similar only for coal ranks of similar to0.8% vitrinite reflectance and above. This contradicts existing theories which state that coal combustion under TGA conditions is a three-stage process, namely volatiles release, vitrinite combustion andinertinite combustion. The processes leading to the weight loss rates occurring in the early stages of combustion were also investigated, with special emphasis in the temperature interval where no substantial weight losses had occurred yet in either a combustion or a pyrolysis experiment. This was done by heating the coals to 300 degreesC in the TGA under air, and then switching the gas flow to nitrogen and allowing the sample to further devolatilise until 1000 degreesC. Also, partly burnt and/or pyrolysed samples wereobtained from the TGA and characterised by optical microscopy techniques. It was observed that the volatile yields of all the coals were substantially reduced as a consequence of their initial heating under air. Besides, evidences of melting and thermal annealing in the inner core of burning coal particles were noticed to occur at lower temperatures than in pyrolysing particles. This was attributed to a sealing effect of the oxidation rim formedin the early stages of combustion, which might give rise to a higher pressure build-up in the inner part of burning particles, thus enhancing the likelihood for condensation reactions to take place in the newly formed metaplast. As combustion profiles are commonly used to infer about combustion behaviour of coals, much care should be exercised in interpreting them, since even in a pure vitrain, two rather than one single material will be involved in the measured weight losses, and, more, these materials will often display fairly different reactivities. (C) 2001 Elsevier Science Ltd. All rights reserved.

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Documento generato il 12/08/20 alle ore 20:51:47