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Background, Aim and Scope:
Currently, only 40%, or 44.5 million metric tons, of coal combustion products (CCPs) generated in the United States each year by electric utilities are diverted from disposal in landfills or surface impoundments for use in various applications. Despite the promising economic and environmental savings from CCP beneficial use, there has been scant attention devoted to assessing the life cycle impacts of CCP disposal and beneficial use, the goal of this two-part study. The objective of this first paper is to present a life cycle inventory of raw material inputs and emissions considering two cases—100% disposal of CCPs to surface impoundments and landfills and 50% CCP disposal/50% CCP beneficial use—and including the stages of coal mining and preparation, coal combustion, CCP disposal, and CCP beneficial use. Six beneficial uses were considered, concrete production, structural fills, soil amendments, road construction materials, blasting grit and roofing granules, and wallboard, chosen for their extent of use by Florida utilities or their general level of acceptance by industry and government.
Materials and Methods:
Primary data for raw material inputs and emissions of all stages considered on the basis of “per 1000 kg coal combusted” were obtained from surveys and site visits of coal-burning utilities in Florida conducted in 2002. Secondary data were obtained from various published sources and from databases available in SimaPro 5.1 software (PRé Consultants, Amersfoort, The Netherlands).
Results:
Results of the surveys administered to Florida utilities revealed that 50 percent of all CCPs produced, or 108 kg per 1000 kg of coal combusted, are diverted for application in a beneficial use; however, the relative amounts sold by each utility is dependent on the process operating parameters, air emission control devices, and resulting quality of CCP. Diversion of 50% of all CCPs to beneficial use applications yields a decrease in the total raw materials requirements (with the exception of gravel and iron) and some emissions to air, water, and land, as compared to 100% disposal.
Discussion:
In general, the greatest reduction of raw materials was attributed to replacing Portland cement with fly ash, using bottom ash as an aggregate in concrete production and road construction in place of natural materials, and substituting FGD gypsum for natural gypsum in wallboard production. The use of fly ash as the cementitious material in concrete production also promised significant reductions in emissions, particularly the carbon dioxide that would otherwise be generated during Portland cement production. Beneficial uses of fly ash and gypsum yielded reductions of emissions to water (particularly total dissolved solids) and emissions of metals to land, although these reductions were small compared to the savings realized by simply diverting 50% of all CCPs from disposal in landfills or surface impoundments.
Conclusions:
This LCI provides the foundation for assessing the impacts of CCP disposal and beneficial use. Beneficial use of CCPs is shown here to yield reductions in raw material requirements and various emissions to all environmental compartments, with potential tangible savings to human health and the environment.
Recommendations and
Perspectives:
Extension of this life cycle inventory to include impact assessment and sensitivity analysis will enable a determination of whether the savings in emissions reported here actually result in significant improvements in environmental and human health impacts.
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