Development of Light-Weight Aggregate Production Process from Coal Ash with a Shaft Kiln (Part 3)

One t/d test plant facilities of the shaft kiln for calcination of coal ash pellets is designed and constructed. Experimental studies are carried out with this test plant to examine the relationship between reactor behavior and product properties and to clarify the technical problems of the shaft kiln necessary to attain the stable operation. It is found that the most important factor is smooth movement of the pellets supllied from the top of the kiln. Steady and smooth discharge of the pellets could be achieved by applying a forced discharger like a ram feeder. The maximum temperature level of the moving bed in the shaft kiln is governed by not only operational conditions but green pellet composition such as carbon and moisture content. The position of the maximum temperature is affected by an air flow rate as well as discharge rate. The calcined pellets are tested according to JIS A 5002 (Light-weight concrete for structure) and Anouncement No. 13 of Environmental Agency (Industrial Waste Disposal Regulation) and tested properties satisfy the specification and regulation values. Especially, the compressive concrete strength shows 550kgf/cm2 which is about 40% stronger than that of JIS value. Conceptual design of a 50t/d pilot plant and cost estimation of the developed process are performed based on the studies conducted up to now. In case of a 1000t/d plant, production cost is estimated under 3000yen/m3.