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A histogram showing relative operation across three ranges (or “bins”) of generation is shown in Figure 12 (see online). This graph reveals that with all of the operating measures and slag management tools employed during the 5 month PRB run with TIFI, the station was actually able to slightly increase generation on Unit 7 compared to previous baseline operation. Summing the operating time percentages in the top two bins, we see that the PRB/TIFI run achieved an operating time of 77 percent at or above 130 MW vs. about 59 percent for the baseline period.
Table 1 presents Drake Unit 7 site conditions, together with operating parameters and annual cost summaries for three operating cases:
- Case I: Baseline Operation, Colorado Coal
- Case II: 30 percent PRB/70 percent Colorado, w/o TIFI
- Case III: 50 percent PRB/50 percent Colorado, with TIFI
Averages for coal heating value, delivered price and electric power pricing appear under site conditions. Average operating parameters
Using Case I as the baseline, costs for boiler cleaning and tube leak repairs are added to lost revenue due to forced outages and derates under Annual Cost Impacts. The Annual Fuel Cost row shows the operating cost reductions coming from higher percentages of PRB. In Case III, the savings are offset by the average annual TIFI program cost for Drake Unit 7. The small loss in boiler thermal efficiency resulting from the addition of dilution water and atomizing air in the 22 TIFI injectors is included in unit heat rate and effective fuel consumption. Total savings (compared to Case I) are summarized below these rows. Including the cost of the TIFI program, the station has demonstrated a potential annual operating cost reduction approaching $4.9 million. Effective return on TIFI program investment (ROI) is 4.2 to 1.
With the TIFI program and optimized slag management procedures at Drake Station, the operators were able to blend lower cost Powder River Basin coal with design fuel up to double the percentages achieved previously. Using TIFI, the plant was able to maintain full load generation, better control slagging deposits, show improvements in heat absorption, and reduce attemperator spray flows compared to previous blend trials. Given significant changes in coal market pricing that occurred in late 2009, Drake Unit 7 was returned to 100 percent Colorado design coal and the TIFI system was placed on standby. This status illustrates a key benefit of the minimal capital costs of the TIFI program. Chemical metering, control systems, injection probes and related equipment are provided by Fuel Tech under the program, so there is no need for the plant to carry unused capital equipment during standby periods. As market and operational circumstances shift, the flexibility of the TIFI system allows utilities to quickly leverage the benefits and financial advantages accordingly.