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Outputs from the Model

Based on the model, 70 MW of power would be unavailable for 0.46% or

  • 40.5 hours p.a. On average, this situation would occur on 2.6 occasions p.a. The main items that had scope to reduce this downtime (or improvement potential) were as follows:
  • 1. Single HRSG 8 hours p.a; all 3 HRSGs 16.2 hours p.a.
  • 2. Single GT 8.3 hours p.a, all 3 GTs 17.2 hours p.a.
  • 3. Single Alternator 1 hour p.a., all 5 Alternators 4.2 hours p.a.
  • 4. Motor driven BFW pump 0.52 hours p.a.
  • 5. Turbine driven BFW pump 0.45 hours p.a.

Note that once the first item in a set, such as GT was improved, there are diminishing returns with the second and third GTs.

Recommendations Made to Project Team

Sensitivity studies showed that the fourth BFW pump contributed only

0.005% to the system availability. It was also clear that a second steam turbine driven alternator would have been considerably cheaper than having the third GT-HRSG combination. This would also have improved the steam balance. However, the GTs had already been ordered in advance, due to the long procurement lead time. Canceling the order would be very costly. At this stage, the lead time for procuring a condensing steam turbine was unacceptably high. However, we discovered that the project team was planning to order a complete LM 2500 GT as an uninstalled insurance spare, in addition to the spare rotor which was already on order.

We recommended that they cancel the order for the fourth turbine driven BFW pump and not proceed with the order for a spare LM 2500 GT. These two actions would save the project US$6 million. In addition, operating and maintenance costs for the fourth BFW pump would be eliminated. These savings made the project viable. The benefit to cost ratio was 20:1 based on just the capital cost reductions. The real benefit was, however, the knowledge that the project would confidently meet its functional requirements in spite of the reduction in investment.

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