SYNOPSIS: - H2S desulfurization capacity was compared between the sorbents of 0.59/0.84 mm particle size prepared from iron oxide minerals, i. e. ochers, red clays and iron ores. Reactions were carried out using a packed-bed microreactor with a 0.5 % H₂S-20 % H₂-N₂ gas mixture at the condition of; temperature 500°C, GHSV 10, 000 h^-1, pressure 1.4 kgf/cm². Among the sorbents tested, ochers showed remarkably high capacity. Observations of sulfided sorbent particles by secondary electron microscopy (SEM) together with the measurements of surface area, Fe₂O₃ crystallite size and pore size distribution led to the conclusions as in the followings;
1) Under the reaction condition utilized, the capacity is strongly controlled by intraparticle diffusion. Only a little influence was observed of the surface area and/or the Fe₂O₃ crystallite size.
2) Pore size distribution is an important factor governing the capacity, namely, the larger the macropore volume, the higher the capacity. However, it is the most critical whether or not the dense layer of pyrrhotite is formed on the outer surface of sorbent particles in the course of desulfurization.
3) Examination by SEM revealed that no such dense layer was formed for the sorbents prepared from ochers, while it was clearly seen for the other sorbents. This is very likely the reason of the markedly high performance exhibited by ochers.

View full abstract

Fly ashes E and G those discharged from a same pulverized coal combustion boiler were classified into two components, such as smaller fly ash particle under 38, a m and larger fly ash particle above 125 μm. The carbon cotained in both components were separated from fly ash by using the Ultrasonic Oil Agglomeration method. Properties of separated carbons were investigated by applying the X-ray diffraction, SEM (Scanning Electron Microscope), EDX (Energy Dispersive X-Ray Micro Analyzer) and TGA (Thermogravimetric Analysis). Following results are obtained.
(1) The carbon remains in the larger fly ash as the unburned char, and that cotained in smaller fly ash are carbon black and rock carbon.
(2) Significant differences of the carbon contents and their properties between the fly ashes E and G are found. The carbon content in smaller components of fly ash G is fairly greater than that in smaller components of fly ash E, although the coal G shows a good combustibility.
These observations of the properties of carbon containing in fly ash present significant informations on the for rational operation and control in the process of pulverized coal combustion process.

View full abstract

In order to increase the extract yield of coal and decrease the loss of extraction solvent due to the condensation between the solvent molecules, Wandoan, Wabamun and Illinois No.6 coals were kneaded with a half amount of solvent such as tetralin prior to supercritical extraction of coal. The solvent added coals were swollen during preheating process, and then extracted with a supercritical solvent such as toluene under pyrolysis condition. As a result, the extract yield of Wandoan coal was remarkably increased and the condensation of toluene was suppressed. Wandoan coal swollen with a hydrogen-donor solvent including nitrogen, such as tetrahydroquinoline and piperidine, gave a high extract yield over 88 wt% during extraction with supercritical toluene. However, these solvents were also taken into the residue in fairly mass. The extract yield was further increased by raising the extraction temperature above 653 K which was the temperature giving the maximum extract yield in the usual supercritical extraction without swelling. The effect of solvent addition was more significant for a coal having a higher solvent swelling property, in the order of Wabamun < Wandoan<Illinois.

View full abstract