Boiler Plant

Table 26-18 Annual Cost Data for Base Case.

Table 26-17 Excerpt from 4-Hour Simulation Model for Base Case.

The study team assumed that the facility will opt to have one of the existing boilers kept warm for standby purposes at all times when operating cogeneration systems. For any period where the cogeneration system is providing 100% of the export steam demand, the simulation imposes a minimum steam load on the existing boiler plant of 2,000 lbm/h (907 kg/h).

Simulation Results

Tables 26-18 through 26-20 show the annual cost data for each area of plant operations modeled by the simulation. There is one table for the base case and one for each of the cogeneration plant configurations.

Table 26-21 summarizes the project capital cost and annual operating costs and savings for each of the two cogeneration configurations, as well as the base case representing existing conditions. These values show the gas turbine system to offer slightly superior potential economic performance based on simple payback. This is due to a combination of reasons, including:

• Smaller unit size of gas turbines and their resulting ability to operate at lower loads that will leave the larger reciprocating engines idle.

• Higher utilization of recovered thermal energy from the gas turbine cogeneration plant. The reciprocating engine system is limited by the lack of low-tempera-

ture thermal loads, resulting in the need to dump heat using a radiator under certain conditions. The gas turbine cogeneration system evaluated does provide a good match of electrical and thermal capacities for the projected facility loads. In the absence of a more sizable low-temperature load for the reciprocating system, the gas turbine-based system will continue to offer better load matching and project economics for the facility.

It is interesting to note that in this case, two general rules of thumb are broken. While gas turbine systems are generally assumed to have a higher capital cost and lower maintenance cost than reciprocating engines, the reverse was true in this case. The gas turbine system proved to be less costly on a capital cost basis and have a slightly higher annual maintenance cost. This underscores the important point that rules of thumb cannot be relied upon when making significant investment decisions.

Moreover, as with most system application analyses, the results are largely dependent on site-specific conditions. When comparative economic performance results are close for two or more options, it is clear that modest changes in site conditions, operating loads, or other factors could alter system selection decisions. For this reason, sensitivity analyses are often performed to evaluate the degree to which such modest changes would impact expected economic performance. Since energy conserva

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