Kunihiro Kitano

Some relationships between coal rank and chemical and mineral composition

Some relationships between coal rank (Cdaf) and the mineral and chemical composition of coals and their high-temperature ashes worldwide were studied. Low-rank coals (Cdaf <75 wt%) are relatively rich in moisture, volatile matter, ash, H, N, O and S, and their ashes are abundant in MgO, CaO and SO3. Coal ashes derived from higher-rank coals demonstrate increased contents of SiO2, Al2O3, Fe2O3, K2O, Na2O and TiO2. It was found that the occurrence, abundance and origin of mineral matter in coal depends on the coal rank to a certain extent. Coals enriched in illite, mica, chlorite, spinel, dolomite, siderite and hexahydrite, and partly in quartz, kaolinite and Fe oxyhydroxides, are of higher rank, while coals with increased contents of montmorillonite, feldspars, zeolite, Al oxyhydroxides, calcite, pyrite, gypsum and Fe, Al and Ba sulfates are of low rank. Higher-rank coals are abundant in ash-forming elements associated with probable detrital minerals, while low-rank coals show enrichment in ash-forming elements associated with probable authigenic minerals and organics. Various processes related to some changes in inorganic matter during coalification are discussed. The metamorphic progression and leaching behaviour of different minerals, phases and elements from low- to high-rank coals have resulted in essential changes in the mineral and chemical composition of coals.

Relations between ash yield and chemical and mineral composition of coals

Abstract Some relations between the ash yield (db) and the mineral and chemical composition of coals and their high-temperature ashes were studied. Low-ash coals ( 2 O and TiO 2 . High-ash coals (> 20 wt%) have increased contents of H, N, O, S and minerals such as quartz, illite, calcite, pyrite and gypsum, while their ashes are enriched in SiO 2 , Fe 2 O 3 and K 2 O. Medium-ash coals (10–20 wt%) have high concentrations of C and Al 2 O 3 (ash basis) and minerals such as kaolinite, mica and siderite, and show the lowest contents of plagioclases and K-feldspars. The low-ash coals are enriched in ash-forming elements associated with probable authigenic minerals and organics, whereas higher-ash coals demonstrate an enrichment in ash-forming elements associated with probable detrital minerals. Various processes related to changes in ash yield and inorganic matter during coalification are discussed. The material supply and leaching behaviour of different minerals, phases and elements during peat formation and conversion to coal as well as the various plant constituents and regional, depositional and paleoenvironmental conditions are responsible for the most essential changes in the mineral and chemical composition or ash yield of coals.

Gasification of hybrid particles of gasification and liquefaction residue of coal.

Hybrid particles of coal ash from gasifier and higher viscous residue and solid pitch from coal liquefaction were successfully produced by two new methods. They were then gasified by steam and oxygen in a fluidized bed under atmospheric pressure. Gasification characteristics of these particles, such as the distribution and yield of gas produced and the carbon conversion, were evaluated as a function of operating variables.

Tar yield in fluidized bed coal gasifier.

Tar yielded in a fluidized bed coal gasifier was analyzed. Taiheiyo coal of size 0.64 and 1.00mm was fed continuously to a 0.083 m diameter fluidized bed and gasified using mixtures of steam and air.Tar Quantity in produced gas decreased rapidly as the bed temperature became higher. Molecular weight of tar became smaller and ratio of methane and ethane in produced gas increased at higher temperature. Tar yield decreased as the tempera-ture of freeboard region just above the bed became higher. But the gas residence time in freeboard region had no effects upon tar yield.