Question

Problem 2_Skills: Setup, T-s, mass and energy balances A steam power plant operates on the reheat regenerative Rankine cycle with a closed feedwater heater. Steam enters the turbine at 8 MPa and 500°C at a rate of 15 kg/s and is condensed in the condenser at a pressure of 20 kPa. Steam is reheated at 3 MPa to 500°C. Some steam is extracted from the low-pressure turbine at 1.0 MPa, is completely condensed in the closed feedwater heater (x3 0), and pumped to 8 MPa before it mixes with the feedwater at the same pressure. Assuming that both the turbine and the pumps operate isentropically, determine (a) the temperature of the steam at the inlet of the closed feedwater heater, (b) the mass flow rate of the steam extracted from the turbine for the closed feedwater heater, (c) the net power output, and (d) the thermal efficiency. Assume that the two exit streams from the closed FWH are at the same temperature Mass fraction y is defined as the fraction of the mass flow rate through the boiler which is bled from the turbine and going through state 8 (that is y -m /m, same as f in our text). The value of y is unknown High-P turbine Low-P Turbine Boiler 0FWH Mixing chamber P II PI Part 1: Drawing T-s diagrams based on the hardware schematic Identify all the devices that substantially change pressure How many different pressures are present in the system? Group state numbers by pressure On a T-s Diagram sketch the saturation lines. Sketch gently all relevant constant pressure lines 1. 2. 3. 4. Which states can be fixed right away (i.e., two independent intensive properties are 5. How can you find the remaining states? Are there any processes with a property that is 6. Connect all the states in the flow sequence. Indicate flow direction with arrows. known)? For example, P and T, or P and x. Mark these states on the T-s diagram constant? For example, entropy? Sketch these processes and mark the final states Indicate heat and work terms leaving the system defined as the circulating steam in entire plant.

Answer 1