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Show based on a 2.5% sulfur coal with a baseline emission level of 3.8 Ib/106 Btu. It should be noted that the S02 emissions represent almost 84% of the NOx and S02 pollutant tonnage emitted. Thus, by providing nominal reductions from a large baseline, the lime portion of the sorbent provides a significant contribution to the overall pollutant reduction. COMPARISON WITH ALTERNATIVE TECHNOLOGIES In order to assess the relative cost effectiveness of the lime-urea hydrate technology, the current study also evaluated the retrofit costs of alternative technology combinations for the reduction of NOx emissions. The alternative technology costs were not developed independently, but were based upon published values or methodologies for determining the retrofit costs. The only adjustments to the costs were to insure that the comparisons were based on similar unit operating characteristics (e.g. unit size, capacity factor, and plant remaining life). The alternative technologies examined in the current study consisted of the following NOx reduction technologies: o Low NOx Burners (LNB); (Emmel, et aI., 1988), o Reburning (REB); (Farzan and Maringo, 1989), and o Selective catalytic Reduction (SCR); (Robie et aI., 1989). In addition, lime-urea hydrate (LUH) in combination with low NOx burners was evaluated. The capital and O&M costs associated with this technology combination were assumed to be the sum of the individual technology costs. Although not strictly true, the magnitude of any adjustments was felt to be within the accuracy limitations of a non site-specific study. As each of these technologies are also at different stages of development and/or demonstration, the contingency factors used in developing their estimated cost of implementation were evaluated differently. A summary of the factors used in the different economic assessments Is shown in Table 3. One should note, that this approach is not always favorable to newer technologies when compared with established technologies, but is intended to take into account unforeseen costs. To the extent that these costs do not materialize as the process is developed, the estimated cost can be reduced through reduced contingency factors. A comparison of the results, as applied to a 100 MW unit, is shown in Figures 6 and 7. The capital costs ($/kW) and levelized costs (mills/kWh) are presented as a function of the percent baseline emissions reductions of NOx' As one might expect, the capital costs, as well as the levelized costs increase dramatically with greater pollutant emission reduction requirements. It should be noted, however, that pOints beneath the curve represent more cost effective approaches relative to points above the curve for a specified level of NOx reduction. -15- |
