Seeking help with question 10 in the 2018 case study for the Chemical Engineering major
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10. In a certain steam power plant, the steam flow rate entering the steam turbine is 1680 kg/h, with a temperature of 430°C and a pressure of 3.727 Mpa (H=3280 KJ/kg, S=6.92 KJ/kg·K). The steam expands adiabatically through the turbine to perform work; after doing this work, the pressure of the waste steam is 0.1047 Mpa and its temperature is 60°C (H=2620 KJ/kg, S=8.02 KJ/kg·K). Given that the atmospheric temperature is 25°C, and neglecting any changes in kinetic and potential energy, what is the thermal efficiency (%) of the steam passing through the turbine? A 78.9 B 66.8 C 87.6 D 50.2
I’m not sure about one thing: W=ΔU-Q and ΔH=ΔU+Δ(PV). According to your solution, ΔU=ΔH, so why is that?
For the calculation of shaft work, refer to textbooks on chemical thermodynamics, which provide specific formulas for this purpose.
How is 461.05 calculated, expert?
Ideal work (Wid) = 1680 * (2620 – 3280) – 1680 * 298.15 * (8.02 – 6.92) = -1.66E6 KJ/h; Q = 0, Ws = M(H2 – H1) = 1680 * (2620 – 3280) = -1.11E6; Efficiency = 1.11 / 1.66 = B