Vapor Power Cycles

Abstract

Vapor (or Rankine) power cycles are by far the most common basis for the generation of electricity in large fixed plant operations. They were one of the first developed for steam engines and have been adapted to many applications. They have also been modified in a number of ways to improve their thermal efficiency and better utilize combustible fuels.

Problems

Problem 15.1

Rework Example 15.3 assuming a turbine efficiency of 90%.

Problem 15.2

Rework Example 15.6 with two reheaters. The pressure of the first reheater should be 250 psi, and the second reheater pressure should be 62.5 psi. Assume both reheat to 1500 °R.

Problem 15.3

Rework Example 15.11 with an open feedwater heater and a closed feedwater heater with the drain cascaded backward. Assume the open reheater operates at the lower pressure.

Problem 15.4

Rework Example 15.11 with two closed feedwater heaters with the drains pumped forward.

Problem 15.5

Rework Example 15.11 with a 90% efficient turbine.

Problem 15.6

A power plant is to be operated on an ideal Rankine cycle with the superheated steam exiting the boiler at 4 MPa and 500 °C (one superheater and no feedwater heaters). Calculate the thermal efficiency and the quality at the turbine outlet if the condenser pressure is (a) 20 kPa, (b) 10 kPa, and (c) 8 kPa.

Problem 15.7

Coal with a heating value of 2500 Btu/lbm is used to provide energy to the working fluid in a boiler which is 85 % efficient. (The working fluid acquires 85 % of the energy available from the coal.) Determine the minimum mass flux of coal in lbm/hr that would be necessary for the turbine output to be 100 MW. The pump receives water at 2 psia, in the simple Rankine cycle, and delivers it to the boiler at 2000 psia. Superheated steam leaves the boiler at 1000 °F (one superheater and no feedwater heaters).