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Following the completion of the CFD model and operating case studies, an injection design model is developed to simulate and optimize the TIFI injector array. Best candidate solutions are then modeled with CFD, coupled with injector placement and flows. Figure 4 shows the optimized injector placement for Drake Unit 7. There are 22 injectors distributed through 4 levels and 6 feed manifolds. Chemical streamlines from the bottom level of injectors also are shown in Figure 4.
Figure 5 shows TIFI chemical coverage in the radiant and convective zones of the unit, and Figure 6 shows a cross-sectional concentration profiles entering the superheat pendants. Green and light blue shades indicate more concentrated coverage of the targeted surfaces. Figure 6 shows that in addition to good coverage in the ash hopper, good chemical distribution is evident around the bull nose and into the superheat pendants. Figure 6 shows good uniform coverage across the superheat pendants, with a slightly higher concentration bias toward the bottom of the pendants. During the PRB test burns conducted
Figure 7 shows the timeline of the successful fuel flexibility trials conducted with the Fuel Chem TIFI program. As indicated, the PRB blend was increased from the previous average of about 10 percent up to 30 percent, and soon to 50 percent with the start-up of the slag control program. PRB blend was maintained at 50 percent for at least 4 months during the 5-month trial.
Overall, thermal absorptions across the waterwalls and the secondary superheat circuits are shown across the operating load range in Figures 8 and 9, respectively. In these graphs, baseline operation with Colorado coal is shown in blue. Heat transfer performance for the 5-month operation with PRB blends and TIFI slag control is indicated by the red data points. These trends show that heat transfer performance could be maintained with TIFI, together with good combustion practice and soot blowing measures as implemented by the Drake operations team.
Efficient combustion practice and slag management procedures also have allowed the unit to maintain design steam temperature, even with PRB blends up to 50 percent, as shown in Figure 10.
Figure 11 presents superheater attemperator spray flow time trends for the Colorado coal baseline and 30-50 percent PRB blends with TIFI. The time periods are 5 months in 2008 (baseline) and 5 months in 2009 (PRB with TIFI). Again, blue and red data points are used to distinguish between baseline operation and PRB operation. Gaps in the data occurring in March are scheduled outages (6 weeks in 2008, 11 days in 2009). This graph shows that superheat spray flow rates during PRB operation with TIFI were generally similar, if not slightly below baseline operation.
This finding indicates that heat transfer distributions in the unit were not substantially upset with the fuel switch. The drop in spray flows seen following the March 2008 outage was primarily the result of refurbishment and return to service of the top high pressure feedwater heater. This allowed a slight reduction in furnace firing and furnace exit gas temperature.