Power Cycles
I1) Assume that the MSU cogeneration system is operating as described in the Engaged in Thermodynamics Background Information and as shown in the idealized process diagram below. The turbine inlet has a pressure of 150 psig and is a saturated vapor. The exit has a pressure of 50 psig. Condensate which is returned from the buildings to the condensate holding tank is at 10 psig and can be considered a saturated liquid. At its operating condition of 40,000 lbm/hr the turbine/generator combination generates 434 kW of electrical power. The generator can be assumed to have an efficiency of 97%.

a) Calculate the steam turbine isentropic efficiency at 40,000 lbm/hr.


b) If the cogeneration system is operating at a mass flow rate of 40,000 lbm/hr and the demand for steam in the campus buildings is 50,000 lbm/hr at 10 psig, determine the total required heat input to the boilers in Btu/hr. (Reality Check) (Full Page Version)

Picture of the Boiler that Connects With the Rest of the Cogen. Cycle

Power_Cycle

I2) The overall thermal or cogeneration efficiency is defined as the total work output plus the heat recovered (i.e. the process heat), divided by the total heat input. However, this is not a good measure of value since electrical and mechanical energy are often more valuable than thermal energy. A more useful measure is the net thermal efficiency which is defined as the total work output, divided by the total heat input minus the heat recovered. Considering the MSU cogeneration process as described in the previous question, calculate the overall thermal efficiency and the net thermal efficiency. (Reality Check) (Full Page Version)

Picture of the PRV Valves that Reduce the Pressure from State Points 3 (50 psig) - 4 (10 psig)

Power_Cycle