Abstract
Gasification, among the several thermochemical conversion
processes, possesses great potential in the advanced
utilisation of biomass and wastes as a source for energy
and material production. This work deals with the
characterisation of reactivity and ash sintering in the
gasification of biomass and wastes using thermogravimetry
(TG) as a tool.
The gasification reactivity of biomass fuels depends on
many factors; in particular the catalytic factors play a
large role, and the behaviour is not easy to predict. On
the basis of results obtained experimentally and
information available in the literature, a method was
developed for the characterisation of reactivity and ash
sintering of fuels to be used in fluidised bed
gasification processes, both atmospheric and pressurised.
The purpose was to take into account the complexity of
the phenomena rather than to find systematic correlations
between the various fuel properties and reactivity and
ash sintering, or to determine kinetic parameters. The
observed complexity was the spur to develop a method, one
that would be as simple as possible, to characterise
biomass and solid recovered fuels or wastes intended as
feedstocks for use in gasification while taking into
account the conditions of the process. Thus, the
temperature and pressure ranges, heating rates and
gaseous environment for the thermobalance were selected
so as to be relevant for the conditions existing in
fluidised bed gasifiers, including pressurised
conditions. The temperature maximum was thus 1000 C, and
the heating rate of the fuel sample was adjusted to that
when feedstock enters the reactor. The gaseous
environment was selected so that it would sufficiently
describe that existing in a gasifier.
Solid recovered fuels were selected to represent
waste-based fuels rather than waste as a whole. The
gasification reactivity of solid recovered fuels was
found to be similar to that of paper and higher than that
of wood. Test results showed broad scattering before the
samples were extracted by sample division.
The method also provides information about ash sintering.
The ash is the residue remaining in the thermobalance
after the gasification reactions, which thus represents
the conditions of gasification, even pressurised
gasification. A separate ash does not need to be prepared
in the laboratory. The ash residue can be classified into
three categories: non-sintered ash, partly sintered ash
and totally sintered or fused ash. For some of the
biomasses, ash sintering was much stronger under
pressurised conditions than at atmospheric pressure. The
laboratory findings for ash sintering appeared in various
ways in real scale since several factors affect the ash
depositing in the reactor. Each time sintering (even
weak) was detected in the ash residue of the TG tests,
agglomerates or deposits were found in the reactor.
The results of thermobalance tests on different fuels
were in good correspondence with the behaviour of the
fuels in fluidised bed gasifiers.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
|
Award date | 1 Jul 2006 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-6846-X |
Electronic ISBNs | 951-38-6847-8 |
Publication status | Published - 2006 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- thermogravimetric characterisation
- thermobalance
- biomass
- wastes
- gasification
- fluidized bed gasifiers
- fuel properties
- reactivity
- ash sintering
- solid recovered fuel