Effect of hot water treatments on coal conversion is reviewed. Hot water treatments of coal contain treatent with hot steam, subcritical and supercritical water in the absent and presence of CO gas. The results of coal model compounds are also included.
Property assessment of the hydro-gasified char was undertaken. The char was pre-pared using a high-pressure drop tube reactor under hydrogen atmosphere and rapid pyrolysis conditions. For comparison purposes, another type of char was also prepared under N2 atmosphere (N2-char). From the results, the coal conversion was found to increase with increasing pressure in the case of the hydro-gasified char but decreased in the case of N2-char. The char reactivity decreased slightly with an increase in pressure for the hydro-gasified char but remained almost constant for the N2-char. Generally, hydrogasified char was more reactive than the N2-char at lower pyrolysis pressures, but the tendency reversed as pyrolysis pressure increased. Results also show the depend-ency of the reaction rate constant on pressure to be proportional to the 1/4th power of the total pressure at 1, 273K. The hydrogasified char was found to have an activation energy of 68 kJ/mol. As for the effect of hydrogenation on the particle surface area, results showed that the surface area increases with an increase in the pyrolysis pres-sure. Further, it was found that, as the pyrolysis pressure increases, more pores are made but with smaller pore diameters. On the other hand, upon increasing H2/coal feed ratio, the coal conversion was found to increase while char reactivity decreased. The corresponding effect was not observed from the N2-char thus exhibiting the so called “rapid carbon” of about 15‰ at H2/coal ratios greater than 1.0. Comparison of char from this work to that from a relatively larger equipment (ca. 2.5 ton/day) revealed that the chars' properties are quite similar in many ways and that drop tube results can serve as useful indicators in the scale-up of the hydrogasification process.
The properties of limonite ores in Australia were examined by using powder XRD, Mossbauer spectroscopy and TGA, compared to hematite or pyrite are in relation to the catalytic activity in the direct coal liquefaction. It was found that one limonite (YY) deposited in Yandi mine of BHP Iron Ore, that is called Yandi Yellow, con-sisted of only α-FeOOH with no hematite from the analysis in XPD and Mossbauer spec-troscopy. The H2O/Fe (mol/mol) ratio, which was calculated from the weight loss in TGA, varied from 0.06 for hematite to 0.60 for limonite (YY) depending on the hematite content in limonite ore. Results of preliminary pulverization tests using a planetary mill showed that limonite (YY) could be easily pulverized to sub-micron particle size with a small abrasion of medium ball. The coal conversion in the liquefaction of Yallorn coal was increased with an increase in H2O/Fe ratio of limonite catalyst. It appeared tha H2O/Fe ratio could be one of the most important factors to select the better catalyst among limonite ores. The crystallite size of pyrrhotite (Fe1-xS) formed during the coal liquefaction with limonite (YY) catalyst was smaller than that with other limonite cata-lysts. The residual catalytic activities of CLB-THFI, recycled to the reactor through the bottom recycle mode in BSU experiments, was slightly decreased compared to the fresh catalyst due to a slightly increase in the crystallite size of pyrrhotite. It was con-cluded that limonite (YY) could be advantageously used as a catalyst raw material in the commercial plat for coal liquefaction, due to the low cost of catalyst preparation with finely pulverization as well as a high liquefaction activities to obtain a high oil yield.
Properties and liquefaction activities of Ni containing Soroako limonite ores, deposited in the upper layers of nickel mine, Sulawesi Island in Indonesia, were examined by comparing with those of Yandi Yellow limonite in Australia. It was found that Soroako limonite consisted of mainly a -FeOOH and Al (OH) 3, containing 1.0-2.0wt‰ of Ni, Cr, Si and a small amount of Mg and Co on the dry basis. Results of the wet pulverization test with a process solvent by using an agitated mill showed that Soroako limonite could be easily pulverized to sub-micron particle size as well as Yandi Yellow. The finely pulverized Soroako limonite catalyst exhibited a high liquefaction activity in the liquefaction of Indonesian Banko coal, compared to Yandi Yellow catalyst. It appeared that Soroako limonite could be transformed into smaller crystallite size of pyrrhotites (Fe1-XS) by the addition of elemental sulfur, leading to high catalytic activity. The agglomeration or crystal growth of pyrrotites may be suppressed by Al-O-Fe strong interaction between FeOOH and Al (OH) 3. Results of TEM-EDX analysis indicated that Ni could be coexisted with Fe and S in the used catalyst. It suggested that Ni could be located near the Fel_xS structure, leading to the promotion effect on the liquefaction activity. Soroako limonite can be used advantageously in a commercial plant as a cata-lyst raw material for the liquefaction of brown coal in Indonesia.
The mass and cooling-rate dependences of degree of supercooling was evaluated for disodium hydrogenphosphate dodecahydrate, which is used in long-term, supercooled thermal energy storage (Super-TES). Super-TES stores thermal energy at temperatures lower than the melting point of the phase-change material, which reduces heat loss from the storage system. From the theoretical analysis for homoge-neous nucleation, the degree of supercooling is dependent on the mass of the material and independent of the cooling rate of the material. From the results of the experi-ments, we found that the degree of supercooling of the hydrate decreases monotonically with increasing mass. The measured degree of supercooling is about one half of that calculated by the homogeneous theory, which indicates that the crystallization of the hydrate in Super-TES is initiated not by homogeneous nucleation but by heterogeneous one. We also found that the degree of supercooling increases monotonically with increasing cooling rate of the hydrate because of the time lag of heat transfer in the hydrate. For practical condition in Super-TES, however, the influence of the cooling rate is negligible.