FIGURE 6-10. Operating costs for wet lime/limestone FGD systems with different sulfur content coals.

and $125/kWh, respectively, for magnesium-based systems and $50/kW and $200/kWh, respectively, for sodium-based scrubbers. The variability in operating costs, though, is evident in data reported by Blythe et al. [18] and summarized in Figure 6-10, which shows the total operating costs for various systems for low-, medium-, and high-sulfur coals. Similarly, capital costs for recent LSFO retrofits can vary from $180 to $348/kW [16].

Spray Dry Processes The spray dry process generally has lower capital costs but higher and more expensive sorbent use (typically lime) than wet processes. This process is used primarily for small- to medium-sized plants firing low- to medium-sulfur coals and is preferable for retrofits [16]. For example, Blythe et al. [18] reported total operating costs for lime spray dry processes of $836/kWh compared to $695/kWh for LSFO systems (see Figure 6-10) for low-sulfur coal applications.

Sorbent Injection Processes The sorbent injection process, with a moderate SO2 removal efficiency, has a relatively low capital cost. The capital costs for furnace sorbent injection are approximately $70 to $120/kW [16].

Circulating Fluidized-Bed Processes The circulating fluidized-bed processes have relatively low capital costs, similar to those for the spray dry process. The process also has low to moderate fixed operating costs, but the variable operating costs are relatively high [16].

Regenerative Processes Regenerative processes generally have high capital costs and power consumption [16]. The net variable operating costs are moderate because the processes produce salable by-products; however, the fixed operating costs are substantially higher than other processes.

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