Figure 8.A-14 shows a Rankine steam cycle in which a double-extraction turbine is used to supply...

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Figure 8.A-14 shows a Rankine steam cycle in which a double-extraction turbine is used to supply both power and process steam for an industrial plant. The energy source for the boiler is natural gas which has a heating value of 50,000 kJ/kg. Thermodynamic data for all points in the cycle are provided in Table 8.A-14. The process steam is supplied at state 4 at 1250 kPa, 280°C at 45 kg/s. All of the process steam is returned as condensate at state 9 and mixed with the condensate from the condenser before the combine flow enters the feedwater heater. The surroundings are at 25°C, 1 atm. 2 3 4 5 6 8 9 Combustion Products m kg/s 96.4 96.4 96.4 45 11.4 40 Boler 92% efficiency 40 40 45 Pump 130 132.7 400 280 160 36.2 30 32 120 Natural gas Pump Figure 8.A-14 Steam plant with a double-extraction turbine Extraction Turbine P kPa 300 3020 3000 1250 Condenser 300 6 6 300 300 Feedwater Heater Table 8.A-14: Property information at each state T h S °C kJ/kg-K 1.635 1.66 6.921 6.932 kJ/kg 546.4 45 kg/s to plant 280°C, 1250 kPa 559.8 3231 3000 2782 2567 125.7 Generator Condensate 120°C, 300 kPa 7.127 8.329 0.4365 134.3 0.4639 503.8 1.528 f.) Determine the rate of exergy destruction in the boiler g.) Determine the rate of exergy destruction in the feedwater heater. V m'/kg 0.00107 0.001071 0.09935 0.1968 0.6506 23.74 0.001004 0.001005 0.00106 e.) Determine the Second-Law efficiency of this plant. Assume that the exergy of the natural gas is equal to its heating value. Figure 8.A-14 shows a Rankine steam cycle in which a double-extraction turbine is used to supply both power and process steam for an industrial plant. The energy source for the boiler is natural gas which has a heating value of 50,000 kJ/kg. Thermodynamic data for all points in the cycle are provided in Table 8.A-14. The process steam is supplied at state 4 at 1250 kPa, 280°C at 45 kg/s. All of the process steam is returned as condensate at state 9 and mixed with the condensate from the condenser before the combine flow enters the feedwater heater. The surroundings are at 25°C, 1 atm. 2 3 4 5 6 8 9 Combustion Products m kg/s 96.4 96.4 96.4 45 11.4 40 Boler 92% efficiency 40 40 45 Pump 130 132.7 400 280 160 36.2 30 32 120 Natural gas Pump Figure 8.A-14 Steam plant with a double-extraction turbine Extraction Turbine P kPa 300 3020 3000 1250 Condenser 300 6 6 300 300 Feedwater Heater Table 8.A-14: Property information at each state T h S °C kJ/kg-K 1.635 1.66 6.921 6.932 kJ/kg 546.4 45 kg/s to plant 280°C, 1250 kPa 559.8 3231 3000 2782 2567 125.7 Generator Condensate 120°C, 300 kPa 7.127 8.329 0.4365 134.3 0.4639 503.8 1.528 f.) Determine the rate of exergy destruction in the boiler g.) Determine the rate of exergy destruction in the feedwater heater. V m'/kg 0.00107 0.001071 0.09935 0.1968 0.6506 23.74 0.001004 0.001005 0.00106 e.) Determine the Second-Law efficiency of this plant. Assume that the exergy of the natural gas is equal to its heating value.

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Solutions Turbines is adiabatic Applying steady flow energy equation is turbine for generator power ... View the full answer