Kazuhiro Kumabe

Coal gasification with a subcritical steam in the presence of a CO2 sorbent: products and conversion under transient heating

Pulverized Taiheiyo coal (Japanese subbituminous coal) was gasified with steam in the presence of CO2 sorbent (Ca(OH)2) under relatively high pressure (approximately 20 MPa; subcritical condition) using a tubing-bomb microreactor (TB reactor). The transient characteristics in the conversion of coal and the formation of gaseous products during the gasification were investigated. During initial heating period, 40–50 wt.% of the coal initially loaded was rapidly converted to gas or tar. In the presence of Ca(OH)2, the yield of gaseous products was apparently increased owing to the catalytic effects of Ca(OH)2 on coal gasification. No CO2 was observed in the produced gas at any soaking time in the gasification with Ca(OH)2, suggesting that CO2 sorption by Ca(OH)2 took place effectively under high-pressure conditions. A rigid agglomeration of char and CO2 sorbent was observed at relatively high temperature, which is attributed to the formation of melts of the CO2 sorbent.

Direct Quantitative Analysis of Arsenic in Coal Fly Ash

A rapid, simple method based on graphite furnace atomic absorption spectrometry is described for the direct determination of arsenic in coal fly ash. Solid samples were directly introduced into the atomizer without preliminary treatment. The direct analysis method was not always free of spectral matrix interference, but the stabilization of arsenic by adding palladium nitrate (chemical modifier) and the optimization of the parameters in the furnace program (temperature, rate of temperature increase, hold time, and argon gas flow) gave good results for the total arsenic determination. The optimal furnace program was determined by analyzing different concentrations of a reference material (NIST1633b), which showed the best linearity for calibration. The optimized parameters for the furnace programs for the ashing and atomization steps were as follows: temperatures of 500–1200 and 2150°C, heating rates of 100 and 500°C s−1, hold times of 90 and 7 s, and medium then maximum and medium argon gas flows, respectively. The calibration plots were linear with a correlation coefficient of 0.9699. This method was validated using arsenic-containing raw coal samples in accordance with the requirements of the mass balance calculation; the distribution rate of As in the fly ashes ranged from 101 to 119%.

Microstructural Modification of AZ91 Magnesium Alloy Using Friction Stir Processing and Carbon Fibers

The microstructure of cast magnesium (Mg) alloy, AZ91, was modified by a friction stir process (FSP) technique. FSP was applied to AZ91 plate with a narrow slit, in which carbon fibers (CFs) were filled. The rotating FSP tool consisting of probe and shoulder could modify the microstructure of the material by sever plastic deformation (SPD) and simultaneously disperse CFs into the matrix. Microstructural observation revealed that sever stirring of material by a tool resulted in the grain refinement due to the dynamic recrystallization and distribution of CFs into the stir zone (SZ). The distribution was not uniform depending on the plastic flow in the SZ, but any worm-hole defects were not formed. Hardness of FSPed AZ91 in the SZ was higher than the as-casted AZ91 because of the grain refinement and distribution of hard CFs.