Storage Alternatives for High-Calcium Fly Ashes
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STORAGE ALTERNATIVES FOR HIGH-CALCIUM FLY ASHES CAROL L. KILGOUR, KENNETH L. BERGESON and SCOlT SCHLORHOLTZ Department of Civil and Construction Engineering, Iowa State University, Ames, IA 50011 Received 24 November, 1988; refereed ABSTRACT One of the major problems currently restricting the utilization of high-calcium (ASTM Class C) fly ashes in Iowa is lack of adequate storage space. High-calcium fly ashes are self-cementitious and are generally not economically reclaimable once they have been exposed to water (i.e., the environment). Since the on-site silo storage capacity of a given power plant is normally only about one or two weeks of overall generating capacity (assuming nearly full load), the fly ash industry is hard-pressed to meet the demand for fly ash during the peak construction months. This paper presents some early research findings concerning the storage alternatives available for these high-calcium fly ashes. A simple pan agglomerator, requiring only the addition of a water spray was used to produce fly ash pellets. Since the method required minimal energy input the process would be expected to be economically feasible for field production. Laboratory produced pellets appeared strong and durable and would be expected to withstand field handling without significant degradation. The pelletization process did not appear to result in a loss of reactivity for either the air-dried or water-cured pellets. This is highly important for potential use in Portland cement concrete or soil stabilization. INTRODUCTION The current utilization of fly ash in the construction industry of Iowa is approximately 25%. The remaining 75% is wasted or disposed of in sanitary landfills. It must be disposed of primarily because the physical facilities for volume storage do not currently exist, nor is it economically fea-
sible. If the technology for outside stockpile storage of Class C ashes could be developed, landfilling costs could be saved and the processed ash could be used for future construction. The purpose of this paper is to present some early research findings concerning the storage alternatives -available for these high-calcium fly ashes. Since the introduction of equipment for producing pellets from the powder of raw materials and ores in the steel-making process, pan pelletizing as a granulating technology has found applications in various fields. Hall et al. [1], and Fuerstenau et al. [2,3] used such a pan agglomeration process in the production of fly ash pellets for disposal by internment with overburden. Studies to be presented in this paper have focused on using a simple pan agglomeration technique to produce fly ash pellets that can be stockpiled for later use. EXPERIMENTAL METHODS Materials High-calcium fly ashes from the Ottumwa and Lansing power plants were selected for the initial pelletization study. The coal source for both plants is a low sulfur subbituminous coal from the Powder River Basin near Gillette, Wyoming. Ottumwa Generating Station produces -80,000 tons of high calcium fly ash per year,
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