Modeling of a 27 MW Combined Cycle Cogeneration Plant With Central Cooling Facility

This paper describes the modeling of a 27 MW combined cycle cogeneration plant with 10,000 tons chilled water central cooling facility. The cogeneration plant is designed to provide heating, cooling and electricity from a single fuel source viz., natural gas, though the gas turbines do have an inbuilt dual fuel combustion system. The topping cycle of the combined cycle cogeneration plant consists of two gas turbines each producing 11 MW of electric power at full load. The energy of the exhaust gases from these gas turbines is then utilized to generate steam in two heat recovery steam generators. The heat recovery steam generators are duct fired using natural gas to meet the peak steam load. In the bottoming part of the combined cycle, the steam from the heat recovery steam generators is expanded in a backpressure steam turbine to supply steam to the campus at about 963 kPa, generating an additional 5.5 MW of electric power in this process. There is no condenser wherein the campus acts as a sink for the steam. The central cooling facility is designed to supply 10,000 tons of chilled water out of which 3800 tons is supplied by two steam driven centrifugal chillers, which utilize a part of the steam supplied to the campus and the remaining by the centrifugal electric chillers. The combined cycle cogeneration plant along with the central chilled watercooling facility is modeled in a commercially available flexible cogeneration software package. The model is built based on the design data available from design manuals of gas turbines, heat recovery steam generators, backpressure steam turbine and centrifugal chillers. A parametric study is also done on the model to study the effect of different parameters like fuel flow rate, temperature etc on the output of the turbine and efficiency of the plant. Modeling of the inlet air-cooling of the gas turbine using an absorption chiller and electric chiller is also presented. Finally the paper discusses these results.