Preface - kmutt

KMUTT Annual Research Abstracts 2005
inlet steam:methane ratio, an SOFC with a
proton-conducting electrolyte (SOFC-H + )
thermodynamically offers higher efficiency than
one with an oxygen ion-conducting electrolyte
(SOFC-O 2− ), the benefit of a lower steam
requirement for the SOFC-O 2− was not taken
into account. Therefore, this study attempts to
consider the benefit of differences in the steam
requirement on the performance of SOFCs
operated with different electrolytes and flow
patterns. The efficiencies under the best
conditions are compared in the temperature
range of 900-1300 K. It is found that the
maximum efficiencies decrease with increasing
temperature and follow the sequence: SOFC-H +
(PF) > SOFC-O 2− (PF) > SOFC-H + (MF) >
SOFC-O 2− (MF). The corresponding inlet
H 2 O:MeOH ratios are at the carbon formation
boundary for the SOFC-O 2− electrolyte, but are
about 1.3-1.5 times the stoichiometric ratio for
the SOFC-H + . It is clearly demonstrated that the
PF mode is superior to the MF mode and that,
although the benefit from the lower steam
requirement is realized for the SOFC-O 2− , the
use of the proton-conducting electrolyte in the
SOFCs is more promising.
IJ-096 COMPARISON OF CARBON
FORMATION BOUNDARY IN DIFFERENT
MODES OF SOLID OXIDE FUEL CELLS
FUELED BY METHANE
Wibul Sangtongkitcharoen,
Suttichai Assabumrungrat, Varong Pavarajarn,
Navadol Laosiripojana, Piyasan Praserthdam
Journal of Power Sources, Vol. 142, No. 1-2,
2005, pp. 75-80
A detailed thermodynamic analysis is
employed as a tool for prediction of carbon
formation boundary for solid oxide fuel cells
(SOFCs) fueled by methane. Three operating
modes of SOFCs, i.e. external reforming (ER),
indirect internal reforming (IIR) and direct
internal reforming (DIR), are considered. The
carbon formation boundary is determined by
finding the value of inlet steam/methane
(H 2 O/CH 4 ) ratio whose equilibrium gas
composition provides the value of carbon
activity of one. It was found that the minimum
H 2 O/CH 4 ratio requirement for which the carbon
formation is thermodynamically unfavorable
decreases with increasing temperature. For
SOFCs with the oxygen-conducting electrolyte,
ER-SOFC and IIR-SOFC show the same values
35
of H 2 O/CH 4 ratio at the carbon formation
boundary, independent of the extent of
electrochemical reaction of hydrogen. In
contrast, due to the presence of extra H 2 O from
the electrochemical reaction at the anode
chamber, DIR-SOFC can be operated at lower
values of the H 2 O/CH 4 ratio compared to the
other modes. The difference becomes more
pronounced at higher values of the extent of
electrochemical reaction.
For comparison purpose, SOFCs with
the hydrogen-conducting electrolyte were also
investigated. According to the study, they were
observed to be impractical for use, regarding to
the tendency of carbon formation. Higher values
of the H 2 O/CH 4 ratio are required for the
hydrogen-conducting electrolyte, which is
mainly due to the difference in location of water
formed by the electrochemical reaction at the
electrodes. In addition, with this type of
electrolyte, the required H 2 O/CH 4 ratio is
independent on the SOFC operation modes.
From the study, DIR-SOFC with the oxygenconducting
electrolyte seems to be the promising
choice for operation.
IJ-097 ENVIRONMENTAL ASSESSMENT OF
POWER GENERATION FROM BAGASSE AT
A SUGAR FACTORY IN THAILAND
Daranee Janghathaikul, Shabbir H. Gheewala
International Energy Journal, Vol. 6, No. 1,
June 2005, pp. 357-366
Bagasse, the waste from sugar
processing, is one of the biomass residues used
as fuel. It can thus be a useful renewable
resource for energy which also promises to
avoid the environmental emissions of power
generation from fossil fuels. Nevertheless, it
should be confirmed that power production from
bagasse is friendly for the environment. Life
Cycle Assessment (LCA) is a very useful tool
for such an evaluation. In this study, the LCA
methodology is used for the environmental
assessment of energy production from bagasse at
Ratchasima Sugar Mill, Thailand. The sugar mill
processes 30,000 tons of sugarcane per day. The
power plant, attached to the sugar mill, is of
cogeneration type. The energy and water balance
show that 272 tons of bagasse can produce 342
tons of steam at 420 o C used in the sugar process
and about 25.5 MWh of electricity. Since the
carbon in bagasse is part of the global carbon
cycle, the CO 2 emission from the combustion of
International Journal