**7. Conclusions**

92 Efficiency, Performance and Robustness of Gas Turbines

Fig. 9. Variation of hourly total cost and excess revenue at different electricity selling rate

Total Cost

0 2 4 6 8 10 12 14 16 18 20 22 24

**hour [hr]**

0 2 4 6 8 10 12 14 16 18 20 22 24

Eq. 60 Eq. 62

**hour [hr]**

Annual operating cost

\$/kWh \$/y \$/y \$/y \$/y 0.07 1,154,780 1,835,038 -1,013,600 +141180 0.1 1,154,780 1,835,038 -166,821 + 987,962 0.15 1,154,780 1,835,038 1,244,978 + 2,399,758 Table 4. Annual net profits out of retrofitting a cooling system to a GT, HITACHI FS-7001B

Annual net profit for the first 3 years

Revenue

profitability

Annual net profit for the fourth year

Annuity-for Chiller, coil and maintenance

Cels= 0.07

Cels = 0.15 [\$/kW h]

Cels = 0.10

0

200

400

600

**Hourly Total Cost [\$], Revenue [\$]**

800

1000

1200

at Yanbu for different product tariff and 3 years payback period

Revenue

Revenueeff

Fig. 10. Effect of irreversibility on the revenue, *Cels* = 0.07 \$/kWh

0

100

200

300

**Revenue (\$/h)**

400

500

600

Electricity selling rate *Cels*

There are various methods to improve the performance of gas turbine power plants operating under hot ambient temperatures far from the ISO standards. One proven approach is to reduce the compressor intake temperature by installing an external cooling system. In this paper, a simulation model that consists of thermal analysis of a GT and coupled to a refrigeration cooler, exergy analysis and economics evaluation is developed. The performed analysis is based on coupling the thermodynamics parameters of the GT and cooler unit with the other variables as the interest rate, life time, increased revenue and profitability in a single cost function. The augmentation of the GT plant performance is characterized using the power gain ratio (PGR) and the thermal efficiency change term (TEC).

The developed model is applied to a GT power plant (HITACHI FS-7001B) in the city of Yanbu (20o 05" N latitude and 38o E longitude) KSA, where the maximum DBT has reached 50oC on August 18th, 2008 The recorded climate conditions on that day are selected for sizing out the chiller and cooling coil capacities. The performance analysis of the GT shows that the intake air temperature decreases by 12 to 22 K, while the PGR increases to a maximum of 15.46%. The average increase in the plant power output power is 12.25%, with insignificant change in plant thermal efficiency. The second law analysis show that the exergetic power gain ratio drops to an average of 8.5% with 6% maximum decrease in thermal efficiency.

In the present study, the profitability resulting from cooling the intake air is calculated for electricity rates between 0.07 and 0.15 \$/kWh and a payback period of 3 years. Cash flow analysis of the GT power plant in the city of Yanbu shows a potential for increasing the output power of the plant and increased revenues.
