Michio Shibaoka

Microscopic investigation of unburnt char in fly ash

A microscopic method to characterize unburnt char particles in fly ash is proposed. Polished samples of fly ash in epoxy resin to which a few drops of blue pigment have been added are observed by incident light microscopy. The char particles are classified into four types (vesicular, dense, mixed and mineral-rich) and categorized into five volumetric size classes (>106, 106−105, 105−104, 104−103, <103μm3) Percentages of individual types and classes are calculated and can be illustrated diagrammatically. To test the feasibility of the proposed method, eight fly ash samples were analysed. Reasonable relationships between the level of unburnt char, particle size and proportions of char types were recognized. When the total carbon content in a fly ash was high, the proportion of coarse classes was also high, and there was a broad inverse correlation between the total carbon and total percentage of the dense char. The proposed microscopic method may be useful in understanding various technical problems related to coal combustion in pulverized-fuel fired furnaces.

Coal and coal macerals as source rocks for oil and gas

Abstract The role of coals in the generation and migration of hydrocarbons is discussed from the viewpoints of chemistry and petrology. Extract data and considerations of volatile matter and maturity suggests that under geochemical conditions most coals can give rise to oil, as well as gas. A distinction is drawn between release of absorbed oil and formation of hydrocarbons by thermal breakdown of the coal matrix itself. The generation and preservation of oil require not only that suitable lipidic structures be present but that the product oil can escape before being cracked to gas. Exinite, preferably in large discrete particles, is the most oil-prone maceral. Vitrinite can form oil but subsequent migration depends on the availability of cracks and fissures in the coal matrix. The most highly reflecting forms of inertinite (e.g. fusinite) have no inherent capacity to generate oil. Low reflectance inertinite, such as is common in many Australian coals, may have minor source potential. A speculative attempt is made to quantify the oil-generating capacity of coal macerals and mixtures. As a general broad rule, on a weight basis, exinite can produce ten times more oil than vitrinite and a hundred times more than inertinite. Approximate calculations suggest that thermal maturation of coals can account for all the known oil and gas reserves in the Gippsland and Cooper Basins of Australia, even if only 1% of generated hydrocarbons is trapped.

Application of microscopy to the investigation of brown coal pyrolysis

Abstract To examine the influence of calcium on the mechanisms of brown coal pyrolysis and gasification, the morphology of chars from raw and calcium-exchanged Yallourn brown coal was analysed. The chars were obtained by slow pyrolysis in a thermo gravimetric analyser and rapid pyrolysis in fluidized bed reactors operating at atmospheric pressure and at 1.1 MPa. They were examined by optical microscopy to determine reflectance and the percentage of particles that had become plastic during pyrolysis. In addition to confirming calciums inhibiting effect on tar yield, the results from the rapid pyrolysis experiments show that in the presence of calcium, char reflectivity decreases, char H/C ratio increases, and the proportion of particles going through a plastic stage decreases. Calciums inhibition of plasticity development is augmented by high pressure in the fluidized bed reactor. The effects appear to be attributable to the action of carboxylate calcium as a cross-linking agent, leading to the formation of a tighter char structure which traps the organic material that would otherwise be liberated as tar. The presence of Ca also increases the H/C ratio of the chars produced by slow pyrolysis, but the mechanism of pyrolysis differs, since in slow pyrolysis none of the particles showed evidence of plasticity. In slow pyrolysis, calciums influence on char reflectivity depends on the holding temperature, since temperature determines the extents of both coal devolatilization and catalytic transformations. The roles of calcium in these processes and their influence on optical anisotropy and reflectance are discussed.

A new experimental device for pyrolysing coal particles under controlled conditions over a wide range of heating rates

Abstract CSIRO has designed and built a new device for pyrolysing coal under closely controlled conditions over a range of heating rates from 10 −1 to 10 4 °C/s. The coal is placed in a stainless-steel mesh which is heated electrically in a cell under a controlled atmosphere. The heating rate is precisely rectilinear even at the highest or lowest heating rates. The terminal temperature (up to 1000 °C) can be held on a selected plateau for 10 −2 to 10 2 s before the sample cools by simple heat dissipation.

Carbon content of fly ash and size distribution of unburnt char particles in fly ash

Abstract The type and size of unburnt char particles in 13 fly ash samples were determined microscopically. The samples were collected from a power station fired from an inertinite-rich coal seam. The carbon content of the ash samples ranged from 2.3 to 25.3 wt%. When the carbon content in a fly ash was high, the proportion of coarse char particles, in particular > 10 6 μm 3 particles, was also high. These results suggest that the size distribution of the feedstock coal has a major effect on the carbon content of the fly ash.

Microscopic observations of the swelling of a high-volatile bituminous coal in response to organic solvent

Abstract The swelling behaviour of individual coal macerals in response to solvents is thought to be important since it represents an early stage in the disintegration of the coal, which is, in turn, of fundamental importance to coal hydrogenation at elevated temperatures. Therefore, a detailed incident-light microscope study of solvent-treated, polished coal surfaces, involving a new edge-on mode of observation, was undertaken in order to observe the way in which solvents interact with the different coal macerals. This study was carried out on blocks of Bayswater Seam coal, using tetralin, pyridine, and 1:3 maleic anhydride-xylene solutions at temperatures near their respective boiling points. The degree of swelling of the polished coal surface depends on the nature of the organic solvent and the individual coal macerals. Vitrinite and, in some instances, low-reflectance semifusinite exhibit varying degrees of swelling in response to the solvent treatment; whereas exinite and the majority of the inertinite macerals appear to be unaffected by the solvents. Within the vitrinite group the lower-reflectance sub-macerals exhibit the greater degree of swelling. At temperatures of less than 200 °C the ability of the solvents to produce swelling in the coal decreases in the order pyridine → 1:3 maleic anhydride-xylene → tetralin.

Behaviour of vitrinite macerais in some organic solvents in the autoclave

Abstract The various vitrinite macerals differ in their behaviour in vehicle solvents; this probably influences their rate of hydrogenation. In the present study, the expansion of vitrinite macerals in tetralin, naphthalene and decalin was investigated. Small granular samples of a high-volatile bituminous coal were treated with the solvents under hydrogen pressure at high temperatures, and the residual solid materials were investigated microscopically. In tetralin, the expansion behaviour of vitrinite macerals from Bayswater seam coal has been found to depend on (1) the degree of fusinitization, and (2) the degree of gelification of the original plant material. Telinite and desmocollinite formed thin lamellae on expansion, while highly-gelified telocollinite formed relatively coarse plastic particles indicating longer survival under solvent treatment conditions. On treatment with tetralin, vitrinite-semifusinite transition material became slightly plastic, but did not expand. In naphthalene, vitrinite macerals expanded greatly, but became only slightly plastic. Vitrinite macerais did not expand in decalin.

Formation and stability of mesophase during coal hydrogenation 2. Destruction of mesophase

Abstract Vitrinite samples from Australian bituminous coals were hydrogenated in autoclaves without vehicle solvent, and the solid products were examined microscopically. When a vitrinite sample was stirred during hydrogenation, the yields of liquid and gaseous products were high. However, when the samples were not stirred, the yields were low, and the solid products contained a high proportion of mesophase. In a vertical section of a vitrinite sample which was unstirred during hydrogenation, the surface in contact with hydrogen was covered by isotropic material, underlaid by a zone of mixed isotropic and mosaic-textured material. Away from the surface, the proportion of isotropic material decreased. The authors conclude that mesophase is formed from material previously liquefied, more readily under hydrogen-deficient conditions than under conditions in which hydrogen is freely available. Application of this conclusion may increase the efficiency of hydrogenation processes by reducing the deleterious effects of mesophase formation.

Some aspects of the behaviour of tin(II) chloride during coal hydrogenation in the absence of a solvent

Abstract In this application of optical and electron microscopy to the study of catalytic hydrogenation of coal, the coal is regarded as a stationary phase and the catalyst and hydrogen as mobile entities. Sampling was carried out at various stages, in the 320–474 °C temperature range, of the catalytic hydrogenation of a high-volatile bituminous coal (Bayswater seam, New South Wales, Australia) with tin(II) chloride in the absence of a solvent. The behaviour of coal macerals during hydrogenation, the mode of occurrence, morphology and composition of the catalyst, and the distribution of the elements of interest (Sn, CI, Fe, S) in hydrogenated vitrinite are described. The study has shown that both tin and chlorine can enter the coal at the very earliest stages of hydrogenation. Deep penetration of the coal by tin and chlorine takes place with progressive hydrogenation; the extent of the catalyst penetration coincides with the optically-defined hydrogenation zone. Discrete catalyst grains are confined to the hydrogenated zone; these grains do not occur at the active front of hydrogenation. Tin(II) sulphide is the product of the scavenging of sulphur by tin and is the predominant form of the catalyst after the onset of mesophase formation.

The behaviour of inertinite macerals under pulverised fuel (pf) combustion conditions

Abstract The usefulness of the current system of classification of the inertinite group of macerals for understanding the pulverised fuel (pf) combustion process is discussed and questioned. Results to date on the combustibility of inertinite macerals are indecisive, especially as inertinite is mosltly regarded as a single entity. Simulated pf combustion experiments with a laser microreactor revealed that the inertinite macerals yielded a wide diversity of char morphologies. With one-to-one correlations between maceral and char, it was possible to determine which maceral was fusible or infusible (commonly called reactive and inert respectively). The microreactor is being developed to measure the burning parameters of individual maceral particles. For example, the data will show which macerals are slow burning (and by how much) and whether fusibility has any relevance to the speed of char burning.