Question

Gas Turbine Compressor 2 Combustor 3 4 5 Steam Turbine Econ Boiler Superht 11 Heat Recovery Steam Generator 12 14 Condenser Cooling Water cweCW Pum 13 Pump Qc Figure 1. Combined cycle power plant

Both simple Rankine and Brayton cycles produce a net power of 200MW. Air enters the compressor at 100kPa, 25°C. The compressor pressure ratio is 12.0, and the turbine inlet temperature is 1127°C. The turbine and compressor each have isentropic efficiencies of 90.0%. Heat addition is from a thermal reservoir with a temperature of 1127°C. Heat rejection is to a thermal reservoir at an ambient temperature of 25°C. The HRSG is a set of large heat exchangers having, on one side, a gas which enters hot (state 4) and leaves at a lower temperature (state 5); and, on the other side, water which enters as a liquid (state 14) and leaves as a superheated vapor (state 11).

In a HRSG, there are generally at least three heat exchangers: the economizer, which heats the fluid from the inlet water temperature to a saturated liquid at the steam generator pressure (6MPa); the boiler, which accomplishes phase change from the saturated liquid state to the saturated vapor state; and the superheater, which increases the temperature of the vapor above the saturation temperature to the outlet condition.

Based on the table and figure above, determine the pressure, temperature, and enthalpy in each state (states 1, 2, 3, 4, 11, 12, 13, 14). As an approximation, use a cold air standard model (i.e. constant specific heats evaluated at 25°C). Assume that the environment temperature is 25°C.

Answer 1