Kouichi Miura

Factors affecting the reactivity of coal chars during gasification, and indices representing reactivity

Literature data for the rate of gasification of coal chars with oxygen, CO2 and steam have been reviewed to clarify the factors controlling this process. Based on steam gasification data for 95 chars from 68 coals whose carbon contents ranged from 65.0 to 93.7%, the gasification rates of the chars from lower rank coals (C 80%) were controlled by the intrinsic reactivity of the coal, which is related to active sites in the coal matrix associated with carbon atoms bonded to heteroatoms, nascent sites, dangling carbon atoms, edge carbon atoms, etc., The number of active sites can be estimated from the amount of chemisorbed oxygen at around 100 °C. Highly dispersed metals such as Ca, K, Na and Mg act as catalysts for gasification, and the degree of dispersion of the metals can also be estimated from the amount of chemisorbed oxygen or CO2. The selectivity of the steam gasification is related to the catalytic action of the coal minerals. Finally, the problems associated with employing the chemisorbed oxygen as a reactive index are discussed.

Correlation of gasification reactivities with char properties and pyrolysis conditions using low rank Canadian coals

Abstract During the flash pyrolysis and flash hydropyrolysis of coals performed at relatively low temperatures (around 650 °C) to maximize liquid product yields, a large amount of char is obtained. It is expected that this char will be gasified to produce synthesis gas or to generate electricity. In this work the gasification rates of chars produced by flash pyrolysis or flash hydropyrolysis of different Canadian coals were measured to investigate the effects of pyrolysis conditions on char reactivity. Gasification measurements were made by the temperature programmed reaction (TPR) method in an air atmosphere. Data obtained were analysed using the Bhatia-Perlmutter model to obtain gasification rate parameters. These were used to represent char reactivity. In all cases, reactivity of a char decreased as the severity of the pyrolysis step increased. Several char properties such as pore surface area, amount of chemisorbed oxygen and residual volatile matter were measured in addition to the proximate and ultimate analyses to see if one or more of these properties would serve as a reactivity index. The amount of chemisorbed oxygen was found to be the best index.

EXAMINATION OF MACROMOLECULAR NETWORK OF COAL BY DIFFERENTIAL SCANNING CALORIMETRY

Publisher Summary This chapter explores the macromolecular network of coal by differential scanning calorimetry. It describes the properties of five coals used in a study described in the chapter. These coals were ground into the particles of less than 74 μm in diameter and were then dried in vacuo at 110°C for 24 h before use. Four solvents, namely, tetralin (Tet.), 1-buthanol (1-BuOH), ethanol (EtOH), and quinoline (Q) were used for the swelling. Tetralin was mainly used because of its nonpolarity. The swelling of coal was performed by simply mixing coal and solvent by the ratio of 1 to 0.6 by weight in a closed tube. It was performed at 30°C for 24 h for the polar solvent and was performed at 100 to 220°C for 1 h under 1 MPa of N 2 for the nonpolar solvent. The chapter presents the swelling ratio of Taiheiyo (TC) coal treated with tetralin and that of the vacuum-dried coal against the swelling temperature. It was found that TC began to swell at around 70°C and seemed to reach an equilibrium swelling ratio of ca. 1.35 over 150°C.

MEASUREMENT OF OXYGEN CHEMISORPTION ONTO COAL CHARS AND CARBON BY USE OF MASS SPECTROMETRY

Publisher Summary This chapter discusses the measurement of oxygen chemisorption on to coal chars and carbon by using mass spectrometry. The concept of active surface area (ASA) in the gasification of carbon is presented, a number of works have been performed to measure the ASA rationally and to relate it to reactivity and mechanism of the gasification reaction. ASA, however, has been measured at temperatures much lower than the actual reaction temperatures, which makes it difficult to examine the gasification reaction in relation to the ASA. For Coal-Dem, oxygen starts to be adsorbed at ca. 300°C, and the value of chemisorbed oxygen n0 exceeds 10 mol/kg-fixed carbon at the peak; however, the peak comes earlier than that of the gasification rate. On the other hand, oxygen starts to be adsorbed from as low as 200°C, but the maximum n0 value is much smaller for Coal-Dem-Ca. For Coal-Dem-Na, oxygen uptake starts from 250°C or so, and the gasification rate is almost in parallel with the change of n0.