Calculate the increase in thermal efficiency due to the introduction of a regenerating dearator in the Rankine-cycle power plant of Exercise 7.5. The plant operates at the optimal pressure (the extraction pressure that makes the thermal efficiency maximum). Figure 7.9c shows the process flow diagram of the system. The second feedwater pump has the same isentropic efficiency as the first. Assuming that the nominal net power output of the power plant is 120 MW and that it operates at nominal power for 8000 hours per year, how many more kWh per year does it deliver if compared to the power plant of Exercise 7.5? With a value of the kWh that is typical of your location, what is the value of the extra electrical energy due to the more efficient cycle configuration?
Exercise 7.5
Calculate the thermal efficiency of a simple steam power plant implementing the superheated cycle configuration. Superheated steam enters the turbine at 10 MPa and 680 K. The pressure in the condenser is kept at 0.1 MPa, as the discharged thermal energy is used for district heating. Assume that the water state at the feedwater pump inlet is saturated. The isentropic efficiency of the pump is 0.6, while that of the turbine is 0.87.
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