Microstructural Properties of Fly Ashes from Oklahoma and Wyoming Coals and their Blends
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MICROSTRUCTURAL PROPERTIES OF FLY ASHES FROM OKLAHOMA AND WYOMING COALS AND THEIR BLENDS JOAKIM G. LAGUROS* AND S. R. GOLLAHALI** *University of Oklahoma, 202 W. Boyd, Norman, OK 73019, USA **University of Oklahoma,
865 Asp, Norman,
OK 73019,
USA
ABSTRACT Blending of different types of coals is an economical method of utilizing locally available lower quality coals. Four blends of Wyoming/Oklahoma coal were prepared (100:0, 90:10, 75:25, 0:100) and burned in a laboratory furnace in a diffusion flame of a mixture of propane and nitrogen in air. Flame temperatures ranged from 1419 K for Oklahoma to 1626 K for Wyoming coal. The higher temperatures indicate better boiler utility, more oxidation, less free carbon, more and better quality fly ash. These observations conform well with the SEM evaluations which indicated that as the amount of Wyoming coal increased, the matrix contained densely populated glassy spherical particles. The SEM data on cured paste samples indicated that the Wyoming fly ash showed a better tendency to crystal (presumably ettringite) formation, followed by the blends of 90% Wyoming-lO% Oklahoma and 75% Wyoming-25% Oklahoma. The least amount of crystal formation was observed in the fly ash of 100% Oklahoma coal. These effects are extremely pronounced in the early curing stages.
INTRODUCTION Class C high-calcium fly ash is being used widely in Oklahoma. Its utilization, primarily in highway construction projects, is the result of research studies during the last two decades. Its effectiveness resides with its capability to stabilize expansive Oklahoma soils derived from shales [1], to replace cement in concrete [2] and to cement/strengthen aggregate road bases [3]. This fly ash has been entirely produced from Wyoming coal. Recently, however, for economical reasons, it has become mandatory to utilize locally available lower quality high sulfur Oklahoma coals by blending them with Wyoming coal. The present study reports on the laboratory findings of burning coal blends and on the properties of fly ash so produced.
PREPARATION OF COAL BLENDS
Two types of coal were used: Wyoming coal which is subbituminous and low in sulfur, and Oklahoma coal which is bituminous and high in sulfur content. Coal samples having compositional characteristics given in Table I were first crushed with a hammer to an approximate size of 2 to 5 mm. Then they were ground to fine powdered form with a laboratory-scale pulverizer. The pulverized coal was then sorted into different size ranges using the U. S. standard sieves and a mechanical shaker. The samples of individual coals were prepared by mixing the required amounts of known size coals to have a size distribution shown in Table II. The blends were prepared by mixing individual coals in the required weight proportion (Table III). The blend was again run through the sieve of the largest size on the shaker so that compositional uniformity as well as size distribution was achieved. This sample was then placed in the coal feeder.
Mat. Res. Soc. Symp. Proc. Vol. 245. t19
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