Problem 8.1 - A 10 MPa Steam Power Plant with an Open Feedwater Heater

Consider the steam power plant with an open feedwater heater operating under the conditions shown in the following diagram:

Carefully draw the complete cycle above on the pressure-enthalpy [ P-h ] diagram provided below, indicating clearly all 9 stations on the diagram.

Using the conditions shown on the diagram above and values obtained from the Steam Tables :

• a) determine the enthalpy values at all nine stations. Indicate these values on the axis of the P-h diagram above and check them for feasibility.

• b) determine the mass fraction [y] of steam bled from the turbine set at station (2). [y = 0.207]

• c) determine the thermal efficiency [η _th ] of this power plant. (You may neglect the pump work for this evaluation.) [39%]

• d) Consider the condition that the throttling valve is completely shut off, and that the state at station (9) is reduced to 10 MPa, 40C. Determine the thermal efficiency [η _th ] under this condition. [35%]

Note : Justify all values used and derive all equations used starting from the basic energy equation for a flow system, and basic definition of thermal efficiency of a heat engine.