Pilot-scale entrained flow gasification
experiments were carried
out at the 3 MWth LTU Green Fuels black liquor gasification
(BLG) plant, using ∼140 tons of Kraft black liquor (BL) with
a dry solids content of ∼72.5%. Comprehensive mass and energy
balances were performed to quantify process performance under varying
pressure, load, and oxygen/fuel ratio. Carbon conversion efficiency
of the BLG process was 98.3%–99.2% and did not vary systematically
in response to process changes. The unconverted carbon is almost exclusively
present as dissolved organic carbon in the green liquor (GL) stream.
GL is an aqueous solution of sodium carbonate and sodium sulfide used
to recover the inorganic pulping chemicals present in BL for reuse
in the pulp mill. A small fraction of syngas CO is converted to formate
ions dissolved in GL through reaction with hydroxide ions. Unconverted
carbon present in GL solids is insignificant. Syngas produced is subsequently
upgraded to methanol and dimethyl ether (DME) in an integrated fuel
synthesis facility. Concentration of H2 in syngas is not
significantly affected by operating point changes in the domain investigated,
while CO and CO2 concentrations are. Syngas hydrocarbon
concentration values are typically in the single-digit parts per million
(ppm) with the exception of C6H6, which was
present at 16–127 ppm. CH4 is present at 0.5%–1.2%,
with lower concentrations at higher temperatures, and shows good correlation
with C6H6. A quantity of 24%–27% of BL
sulfur ended up in the syngas as 1.5%–1.7% H2S and
64–72 ppm COS. Cold gas efficiencies (CGEs) on a lower heating
value (LHV) basis, when including syngas CH4, were 52%–55%
and decreased at higher temperature. CGEs on an LHV basis, when considering
only H2 and CO with a sulfur-free BL heating value relevant
for catalytic syngas upgrading, were 58%–60% and showed the
opposite temperature dependence. Good mass and energy balance closures
show the figures presented to be reliable. The results obtained from
this study demonstrate process stability at varying operating conditions
and can be further used for techno-economic analysis and design purposes.
Tar and soot in product
gas have been a major technical challenge
toward the large-scale industrial installation of biomass gasification.
This study aims at demonstrating that the formation of tar and soot
can be reduced simultaneously using the catalytic activity of alkali
metal species. Pine sawdust was impregnated with aqueous K2CO3 solution by wet impregnation methods prior to the
gasification experiments. Raw and alkali-impregnated sawdust were
gasified in a laminar drop-tube furnace at 900–1400 °C
in a N2–CO2 mixture, because that creates
conditions representative for an entrained-flow gasification process.
At 900–1100 °C, char, soot and tar decreased with the
temperature rise for both raw and alkali-impregnated sawdust. The
change in tar and soot yields indicated that potassium inhibited the
growth of polycyclic aromatic hydrocarbons and promoted the decomposition
of light tar (with 1–2 aromatic rings). The results also indicated
that the catalytic activity of potassium on tar decomposition exists
in both solid and gas phases. Because alkali salts can be recovered
from product gas as an aqueous solution, alkali-catalyzed gasification
of woody biomass can be a promising process to produce clean product
gas from the entrained-flow gasification process at a relatively low
temperature.
This study addresses the change of char morphology and fuel conversion during pyrolysis in a laminar entrained flow reactor by experiments and particle simulation. Three experimental parameters were examined: reaction temperature (1073 and 1273 K); particle size (125−250, 250−500, and 500−1000 μm); and the length of reaction zone (650 and 1885 mm). The scanning electron microscopic (SEM) images showed that biomass swelled during heating and shrank during initial stage of pyrolysis. Then, char morphology transformed to cenospheres after the plastic stage. The yields of solid residue from the experiments were reasonably predicted by particle simulation. To give a guideline for the design of laminar entrained flow pyrolysis reactors, the required reactor length for complete conversion of biomass was also calculated for the pyrolysis. High reaction temperature, small particles, and slower gas flow were favorable for high fuel conversion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.