SBIR-STTR Award

This project's aim is to assess the potential of usingwaste materials from the Atmospheric Fluidized-Bed Combustion(AFBC) process as a source of lime in producing a syntheticaggregate. The basic principle of this combustion process involvesthe burning of coal in a fluidized bed of high calcium or dolomiticlimestone under conditions that calcine the limestone to the oxideform. In the oxide form, the limestone acts as a reagent that cancapture the sulfur oxide gases emmitted in the coal burningoperation. An ash or residue commonly known as spent sorbent orspent-bed material is generated in this process. The residuecontains substantial quantities of calcium compounds, one of whichis in the form of free or unreactive calcium oxide (quic@). Thespent-bed material will be mixed with pulverized coal fly ash andother residuals and processed in a unique fashion to produce theaggregate. The unique aspect involves the use of a vacuum extruderto form a high strength product, which is then aged and crushed toproduce the aggregate. The research will be done in the laboratoryand will involve evaluation of conditioning procedures, mixing ofspent-bed material with fly ash and other residuals, extrusion ina vacuum extruder, crushing and grading of the extruded product,and evaluation of the synthetic aggregate by standard ASTM tests. Two sources of fluidized-bed residuals and two @ of pulverized coalfly ash will be used.Anticipated Results/Potential Commercial Applications as described by the awardee:A synthetic aggregate will be produced that will require little or, no heat in the production process. The potentialapplications are nunwrous and would include use as a coarse and/orfine aggregate in concrete, bituminous mixes, and masonry units;use as a structural fill; and use as a base course material. PhaseII will involve producing the aggregate in a pilot plant anddesigning and conducting field scale demonstration projects.

It is anticipated that technically acceptable lightweight aggregate materials can be produced on a commercial scale from optimum formulations of fluidized bed residuals and Class F fly ash, using one or more of the production techniques demonstrated in Phase I. The technical feasibility and commercial potential for producing synthetic aggregates from fluidizedbed residuals will be demonstrated in Phase II of this project. Bench scale testing will concentrate on optimum formulations of conditioned spent bed material and Class F fly ash and the applicability of pelletizing as well as extruding the optimum blends. Scale_up aggregate production will encompass three different forming techniques: (1) extrusion followed by crushing; (2) pelletizing; and (3) compaction followed by excavation and crushing. At least 50 tons of aggregate will be produced using each of these techniques. The resultant materials will be incorporated into six different end uses, which will be demonstrated and monitored in the field. The most promising opportunities for further commercialization of aggregate production and end use applications will be identified.Anticipated Results/Potential Commercial Applications as described by the awardee:High potential commercial applications are anticipated from use of these aggregates in concrete block, lightweight concrete, reef blocks, lightweight fill, riprap, and stabilized road base.