Chemical looping
gasification (CLG) is an emerging process that
aims to produce valuable chemical feedstocks. The key operational
requirement of CLG is to limit the oxygen transfer from the air reactor
(AR) to the fuel reactor (FR). This can be accomplished by partially
oxidizing the oxygen carrier in the AR, which may lead to a higher
reduction degree of the oxygen carrier under the fuel conversion.
A highly reduced oxygen carrier may experience multiple issues, such
as agglomeration and defluidization. Given such an interest, this
study examined how the variation of the mass conversion degree of
ilmenite may affect the conversion of pine forest residue char in
a fluidized bed batch reactor. Ilmenite was pre-reduced using diluted
CO and then underwent the char conversion at 850, 900, 950, and 975
°C. Our investigations showed that the activation energy of the
char conversion was between 194 and 256 kJ/mol, depending upon the
mass conversion degree of ilmenite. Furthermore, the hydrogen partial
pressure in the particle bed increased as the oxygen carrier mass
conversion degree decreased, which was accompanied by a lower reaction
rate and a higher reduction potential. Such a hydrogen inhibition
effect was confirmed in the experiments; therefore, the change in
the mass conversion degree indirectly affected the char conversion.
Langmuir–Hinshelwood mechanism models used to evaluate the
char conversion were validated. On the basis of the physical observation
and characterizations, the use of ilmenite in CLG with biomass char
as fuel will likely not suffer from major agglomeration or fluidization
issues.
Lightweight geopolymer concrete was synthesized using fly ash as an aluminosilicate source with the addition of a pore-forming agent. The synthesis of a geopolymer was conducted by employing various volume ratios of geopolymer paste to the foaming agent: 1:0.50, 1:0.67, 1:0.75, 1:1.00, 1:1.33, 1:1.50, and 1:2.00, while the ratios of aluminum powder weight percentage to the fly ash weight varied between 0.01 - 0.15 %wt. The results showed that the higher foaming agent content, the lower the compressive strength and density of the geopolymer. The ratio of the geopolymer paste to the foaming agent, 1:1.33 was found to produce the strongest light weight geopolymer whose compressive strength and density were 33 MPa and 1760 kg/m3, respectively. With the addition of 0.01%wt aluminum powder, the geopolymer specimen showed the highest compressive strength of 42 MPa and density of 1830 kg/m3, respectively. X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and FT-IR were utilized to study the effects of foaming agent and aluminum powder addition onto the microstructure, surface morphology, and functional groups of the geopolymer. Both types of synthesized geopolymers have the potential to be developed in terms of compressive strength and density in the future.
Chemical looping combustion (CLC) can be used to convert
biomass
for heat and/or power production while efficiently capturing the produced
CO2. This is possible because the biomass is oxidized by
an oxygen carrier instead of directly by air. However, the ash species
in biomass can interact with the oxygen carrier causing agglomeration
and/or reducing its reactivity. One of the ash elements previously
reported to cause problems is phosphorus and especially in combination
with alkali. In this work, the interaction between a benchmark oxygen
carrier, ilmenite, and a phosphorus model compound, sodium phytate,
was studied up to a temperature of 1100 °C in N2 using
a fixed bed setup. Activated carbon and NaH2PO4 (thermally decomposing to NaPO3) were also used to study
the individual effect of carbon and inorganic Na-phosphate. The CO
and CO2 concentration in the flue gas was measured to monitor
the oxidation of the samples, which showed that ilmenite participated
in the conversion of Na-phytate starting from about 600 °C. Scanning
electron microscopy coupled with energy dispersive X-ray spectroscopy
analysis of cross sections of the ilmenite residues revealed that
Na-phosphate (forming from Na-phytate) penetrates porous ilmenite
particles to a greater extent compared to denser particles, which
may reduce the agglomeration tendencies since a lower amount of sticky
Na-phosphate melt will coat the particle surface. The effect of Na-phytate
on the reactivity of ilmenite was quantitatively determined in a fluidized
bed using 50% syngas or CO in N2. For a loading of 1.5
wt % Na-phytate, the reactivity toward CO decreased to only 20% of
the reference sample. The reason was partly attributed to a decreased
surface area but is likely also due to the formation of less reactive
Na–Fe-phosphates. A compilation of thermodynamic data relevant
for the NaPO3–FeO
x
(x = 1 or 1.5) system shows that NaPO3 can form
a melt containing dissolved iron starting from around 600 °C
and that sodium and phosphorus are present solely in this form above
approximately 930 °C at equilibrium.
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