تجزیه و تحلیل حساسیت برای بهبود ظرفیت یک نیروگاه سیکل ترکیبی (100-600 MW)

Power improvement of a combined cycle power plant using inlet air cooling was analyzed in this paper. The corresponding CC capacities in a range of 100–600 MW were examined. The CC performance can be improved by decreasing an inlet air temperature and humidity to 15 °C (ISO) and 100% RH before entering air compressor of a gas turbine (GT). All year ambient temperature in Bangkok is normally higher than 15 °C. This research used a steam absorption chiller (AC) to cool intake air to the desired temperature level and no storage unit was needed. The CC uses a cooling tower (CT) for cooling purpose. In the 400 MW power plant as an example, it could increase the power output of the GT by 9.32% and the CC by 5.8%, while the ST power decreased by 3.42% annually, as some steam was supplied to the AC. In the economical analysis, the payback period (PB) will be in the range of 0.68–0.94 years, internal rate of return (IRR) 29–176%, and net present value (NPV) 116.5–154.63 MUS$. Additionally, sensitivity analysis concerning economic performance and environmental impact of the plants were also studied.

Boonnasa et al. [1] analytically demonstrated an improvement of the CC (336 MW) of the Electricity Generating Authority of Thailand (EGAT, south Bangkok) by cooling the inlet compressor air of a GT using an AC with a chilled water storage. Cooling inlet air will increase air mass flow rate then increase the power output. It could increase the power output of a GT by about 10.6% and the CC 6.24% annually. Furthermore, Ameri et al. [2] could improve power of the new GT plant (16.6 MW) by about 11.3%. Mohanty et al. [3] observed 11% increases in power of the GT in Bangkok. Both used an AC without cooling water storage to solve their problem. Their systems had no ST unit. Recently Thailand produced 134,826.72 MW h of electrical energy of which 69,937.09 MW h was produced by private enterprises in 2005 [4]. The energy production will be increased gradually each year. Nowadays, the Thai government wants to promote small and medium enterprises (SMEs) which need electricity for their business. Moreover, it is a state policy to purchase the access electricity from private power producers [5]. In order to assist many independent power producers (IPPs) in Thailand and those having a similar climate to improve their existing power units, we simulated the CC improvement with various capacities: 100, 200, 300, 400, 500 and 600 MW using AC as in [1] but no cooling water storage was included. The analysis investigated both techniques and economics which can provide an appropriate solution for a business people. Environmental impacts as well as the influence of an interest rate, NG cost on economical performances were also investigated. Statistical data of hourly ambient temperature and relative humidity in 2005 were used in this study.

Fig. 8 shows the technical and economical analyses based on minimum, maximum and mean climatic data. It represents the worst, mean and best cases respectively. The worst case was occurred when ambient temperature is minimal so that the PB was increased. So the users will see three possibilities before making a decision to select the appropriate unit for their companies. In the above figure NPV increases linearly with a plant capacity. IRR increases gradually near the 600 MW plant capacity. The PB is between 0.68 and 0.94 y which will make the investment decision more interesting. The produced condensate is higher during the hot season than during the cold season due to more humidity in summer. Increases in cooling load, capacity improvement, chilled water supply, NG consumption and steam for AC during 9:00–22:00 are based on the national demand curve and ambient temperature. Sensitivity analysis and plant CO2 emission results will be used as guidelines for the investor of a CC plant project, particularly, one who works at some places located in hot climatic zone such as Thailand.