Answer Happy

Problem 2) Duct Burner An engineer believes that the system in Problem 1 will be enhanced with a duct burner. Assume the duct burner increases the gas temperature into the HRSG to 1600°F. You may assume that the gas turbine and duct burner are fueled with natural gas with a lower heating value of 20,200 Btu/lbm. For stoichiometry determinations, you may approximate natural gas as pure methane (CH4). a) For the gas turbine, determine the mass AF ratio and the oxygen "wet" concentration (%) in the exhaust before the duct burner. b) Determine the additional fueling (Btu/hr) needed for the duct burner, and the oxygen "wet" concentration (%v) in the exhaust after the duct burner. c) Complete problem 1, part "c" for this case with a duct burner. For each plot, show both the original and these newer results. Comment on the effects of the duct burner case relative to no duct burner for these conditions. d)
Problem 1) Cogeneration System Analysis This problem considers the following gas turbine and steam turbine cogeneration system. The gas turbine exhaust exits at 930°F with a flowrate of 149 lb/sec. The gas turbine requires a fueling rate of 201x106 Btu/hr, and produces 20.5 MW of electrical power. The exhaust gas is used in an unfired HRSG to produce steam at 100 psia, 600°F. Water enters the HRSG at 100 psia, 230°F. This steam is expanded in a steam turbine (nst = 86%) to a pressure of 40 psia. The 40 psia steam is used in a heating process until a saturated liquid state is reached. You may assume a specific heat for the exhaust gases of 0.25 Btu/lb-R. The minimum allowed exhaust gas temperature is 350°F, and the minimum pinch-point temperature difference is 25°F. 1 WET Air Fuel GT Exh Water in 31 Heating Process x=0 a) Determine the maximum possible steam flow rate (lb/s), and the total electrical power (kW), the electrical efficiency (%), the heating rate (Btu/hr), the overall cogeneration efficiency (%), and the pinch-point temperature difference (°F). b) Supply a T-s diagram with the 100 psia and 40 psia lines. Overlay the exhaust gas temperature change. c) For this part, the steam is at 600°F and different pressures. Determine and plot the following quantities as a function of steam pressure (100 psia - 1000 psia): steam flow rate (lb/s), steam turbine electrical power (kW), electrical efficiency (%), overall cogeneration efficiency (%), the heating rate (Btu/hr), the exhaust gas exit temperature (°F) and the pinch-point temperature difference (°F). Hint: be sure and check that the pinch point temperature difference is at or greater than the minimum for each pressure. (Note: problem 2 will ask for these same plots with data for cases using a duct burner. You may supply a single set of plots that satisfy both problems 1 and 2). d) Supply a T-s diagram with the 1000 psia and 40 psia lines. Overlay the exhaust gas temperature change. e) Comment on the effects of increasing the steam pressure (all else constant) for these conditions.