Other Gas Power System Applications Helium is used in a combined cycle power plan...

Other Gas Power System Applications

Helium is used in a combined cycle power plant as the working fluid in a simple closed gas turbine serving as the topping cycle for a vapor power cycle. A nuclear reactor is the source of energy input to the helium. Figure P9.94 provides steady-state operating data. Helium enters the compressor of the gas turbine at 200 lbf/in.², 180°F with a mass flow rate of 8 x 10⁵ lb/h and is compressed to 800 lbf/in.² The isentropic efficiency of the compressor is 80%. The helium then passes through the reactor with a negligible decrease in pressure, exiting at 1400°F. Next, the helium expands through the turbine, which has an isentropic efficiency of 80%, to a pressure of 200 lbf/in.² The helium then passes through the interconnecting heat exchanger. A separate stream of liquid water enters the heat exchanger and exits as saturated vapor at 1200 lbf/in.² The vapor is superheated before entering the turbine at 800°F, 1200 lbf/in.² The steam expands through the turbine to 1 lbf/in.² and a quality of 0.9. Saturated liquid exits the condenser at 1 lbf/in.² Cooling water passing through the condenser experiences a temperature rise from 60 to 90°F. The isentropic pump efficiency is 100%. The helium is modeled as an ideal gas with k = 1.67. Stray heat transfer and kinetic and potential energy effects can be ignored. Determine

(a) the mass flow rates of the steam and the cooling water, each in lb/h.

(b) the net power developed by the gas turbine and vapor cycles, each in Btu/h.

(c) the thermal efficiency of the combined cycle.