Question

We add superheat and reheat to the cycle above. Steam enters the first turbine stage at 8 MPa, 480oC, and leaves at 0.7 MPa. It is reheated to 440oC and enters the second turbine stage, where it is expanded to 0.008 MPa. Saturated liquid leaves the condenser at 0.008 MPa. The turbines and pump again have isentropic efficiencies of 85%, and the plant has 100 MW net power.

Find:

a) (6 points) Draw a system diagram and label all the components. Number the flow, starting with a 1 at the pump inlet.

b) (6 points) Draw a T-s diagram for the isentropic and actual process.

c) (6 points) The mass flow rate of the working fluid (steam). Compare to the answer you got in problem I. Is it less, the same or greater?

d) (6 points) The actual thermal efficiency of the cycle. Compare to the answer you got in problem I. Is it less, the same or greater?

e) (6 points) Calculate the mass flow rate of the cooling fluid (assume subcooled water with a Cp of 4.184 kJ/kgK) ) if this cooling fluid enters the condenser at 15oC and leaves at 25oC.

Answer 1

System diagrams, T-s diagrams, calculations of mass flow rates, and thermal efficiency are involved in the analysis of a reheat-regenerative steam cycle with added superheat to improve efficiency.

Step-by-step explanation:

The analysis of a reheat-regenerative steam cycle with superheat added to improve cycle efficiency. The points in the cycle often start with the inlet to the pump and are numbered sequentially around the cycle. The student is tasked with drawing a system diagram, and a T-s diagram, calculating the mass flow rate of the working fluid, determining the actual thermal efficiency of the cycle, and calculating the mass flow rate of the cooling fluid in a steam power plant.

Drawing a System Diagram

Point 1: Pump inlet. Point 2: Pump outlet/Boiler inlet. Point 3: Boiler exit/First turbine inlet. Point 4: First turbine exit/Reheater inlet. Point 5: Reheater exit/Second turbine inlet. Point 6: Second turbine exit/Condenser inlet.

Point 7: Condenser exit (saturated liquid)/Pump inlet completing the cycle.

Each component like the pump, boiler, turbine stages, reheater, and condenser should be labeled accordingly.

Mass Flow Rate and Thermal Efficiency

The mass flow rate of steam can be determined using energy balance and the given net power output. The actual thermal efficiency will take into account the actual conditions as opposed to the ideal isentropic processes.

Cooling Fluid Mass Flow Rate Calculation

For the cooling fluid that enters the condenser at 15°C and leaves at 25°C, the mass flow rate can be calculated using the formula for heat transfer: Q = m × Cp × ΔT, where m is the mass flow rate, Cp is the specific heat capacity, and ΔT is the temperature change of the cooling fluid.