| Abstract | KB  Full paper
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Background, Aim and Scope:
The objective of this paper is to present results of impact assessment efforts applied to the LCI results of the two CCP disposal scenarios previously reported in Paper 1. To assess opportunities for savings in environmental and health impacts relative to each CCP material, this paper expands the two scenarios of 100% CCP disposal and 50% CCP disposal/50% CCP beneficial use considered in Part 1 by also considering the individual beneficial use of 50% of each type of CCP, while the remaining CCPs are still disposed of in landfills and surface impoundments, as well as considering 50% beneficial use of all CCPs generated.
Materials and Methods:
SimaPro 5.1 software (PRé Consultants, Amersfoort, The Netherlands) was used to calculate comparative environmental impacts of all scenarios using the CML 2001 and EDIP 1997 midpoint impact assessment methods and both the Heirarchist and Individualist levels of the Eco-indicator (99) end point method. Trends in the impacts generated by each scenario were compared across global and local environmental and human health impact categories, including global warming, ozone depletion, acidification, smog formation, human toxicity, and ecotoxicity. Finally, a sensitivity analysis considered the effects of disposal option, percentage change in electricity generated, and transportation distance to beneficial use applications on the impact assessment results.
Results:
For each of the impact categories considered, the beneficial use of fly ash, bottom ash, and FGD material resulted in a reduced impact, as compared to disposal of these materials. The beneficial use of boiler slag alone did not decrease impacts. Global warming impacts were reduced by the substitution of fly ash for Portland cement in concrete production, as the production of Portland cement generates large quantities of CO2. However, for the category of global warming, as well as for ozone depletion, smog formation, and acidification, the impact reductions from CCP beneficial use are small, less than 6 percent, as these impacts were shown to be created in greater part by upstream processes, including coal mining, transportation, and combustion. Human toxicity and ecotoxicity categories showed larger but more varied reductions, from 0-50 percent, due to diverting CCPs from landfills and surface impoundments and reducing the emission of metals associated with these stages.
Discussion:
Reductions to global warming, ozone depletion, and smog formation were shown to be due to the substitution of CCPs in place of virgin raw materials in beneficial use applications, especially the use of fly ash in place of Portland cement. On the other hand, reductions in acidification, human toxicity, and ecotoxicity were attributed more to the diversion of CCPs from landfills and surface impoundments, rather than the beneficial use itself. When comparing the beneficial use scenarios, the four impact assessment methods used showed similar trends in reductions for categories of global warming, ozone depletion, acidification, and smog formation. However, results diverged when categories of human toxicity and ecotoxicity were used, due to the lack of consensus among methods as to the classification and characterization of impacts from heavy metal release. Similarly, when assessing the sensitivity of the impact assessment results to changes in assumptions or system boundaries, the human toxicity and ecotoxicity categories were most susceptible to change, while other impact categories had more robust results.
Conclusions:
Impact assessment using the Eco-indicator 99(I), Eco-indicator 99(H), EDIP 97, and CML 2001 methods showed that beneficial use of all CCPs presented opportunities for reduced environmental impacts in the life cycle of coal combusted for electricity generation, as compared to the baseline scenario of 100% CCP disposal.
Recommendations and
Perspectives:
As regulators and electric utilities increasingly consider the viability and economics of the use of CCPs in various applications, this study provides a first-basis LCA of selected beneficial use alternatives. With these initial comparative results, future studies should be directed towards those beneficial uses that promise significant economic and environmental savings, such as the use of fly ash in concrete, to quantify the risk of the escape of currently unknown amounts of CCP contaminants from these applications into the surrounding environment.
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