Second law analysis of a natural gas-fired steam boiler and cogeneration plant

A second law thermodynamic analysis of a natural gas-fired steam boiler and cogeneration plant at Rice University was conducted. The analysis included many components of the plant including piping, valves, boilers, turbines, piping specialties and various other pieces of equipment. Typical steady state plant operating conditions were determined based on available trending data and the resulting conditions are representative of the bulk of the plants operating hours. The exergy destruction from individual components in the plant was calculated based on these operating conditions to determine the true system losses. The largest source of exergy destruction within the plant was found to be the gas turbine system under typical operating conditions. Recommendations for efficiency improvement based on the analysis are discussed. The addition of a back pressure steam turbine to the system is shown to improve the overall system efficiency from 21% to 22.4% while increasing the plant power generation capacity by 9.8%. A reduction in the plant steam header pressure in conjunction with the addition of the steam turbine improved the overall system efficiency to 23%, while increasing plant power generation by 12%. In addition, a first law thermodynamic analysis was performed and first and second law efficiencies are compared for several components.\u2