Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN: 9781259696527
Author: J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher: McGraw-Hill Education
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Chapter 8, Problem 8.1P
Interpretation Introduction
Interpretation:
The thermal efficiency of the cycle and the turbine efficiency for the simple power plant shown should be determined.
Concept introduction:
The steam power plant has the turbine operating adiabatically with the given inlet steam pressure and temperature. We used the values shown in the figure to determine the thermal efficiency and turbine efficiency. Turbine efficiency is determined to be the ratio of enthalpy change in the process to the enthalpy change in the reversible process while thermal efficiency is obtained by taking the ratio of energy released by the system to the heat applied to the system.
Expert Solution & Answer
Answer to Problem 8.1P
The thermal efficiency of the cycle is determined to be 31.1 % and the turbine efficiency is 79 %.
Explanation of Solution
Given information:
The basic cycle for a steam power plant is shown by Fig. 8.1.
Suppose the turbine operates adiabatically with inlet steam at 6800 kPa and 550°C, and the exhaust steam enters the condenser at 50°C with a quality of 0.96. Saturated liquid water leaves the condenser, and is pumped to the boiler. Neglecting pump work and kinetic- and potential-energy changes, we need to determine the thermal efficiency of the cycle and the turbine efficiency.
Turbine efficiency is determined to be the ratio of enthalpy change in the process to the enthalpy change in the reversible process while thermal efficiency is obtained by taking the ratio of energy released by the system to the heat applied to the system.
Calculation:
Turbine efficiency is given by the formula
Where
Here
We know that
We know that
Enthalpy of steam after neglecting work done is
Therefore, the turbine efficiency is
And the thermal efficiency of the cycle is
Conclusion
The thermal efficiency of the cycle is determined to be 31.1 % and the turbine efficiency is 79 %.
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Students have asked these similar questions
use the integral method if you can, thank you!
2. A single-effect evaporator is concentrating a feed solution of organic colloids from 5 to 50 wt
%. The solution has a negligible boiling point elevation. The heat capacity of the feed is cp
.
4.06 kJ/kg K and the feed enters at 15.6 °C. Saturated steam at 101.32 kPa is available for
heating, and the pressure in the vapor space of the evaporator is 15.3 kPa. A total of 4536 kg/h
of water is to be evaporated. The overall heat-transfer coefficient is 1988 W/m². K. What is
the required surface area in m² and the steam consumption?
A mixture with 4% n-pentane, 40% n-hexane, 50% n-heptane, and 6% n-octane is to
be distilled at 14.7 lb/in² (1 atm.) with 98% of the hexane and 1% of the heptane
recovered in the distillate. If the liquid feed is a saturated liquid (i.e., q = 1). Calculate
i.) The product compositions, ii.) The top and bottom temperature iii.) Minimum
reflux ratio (Rm), iv.) Minimum theoretical plates and v.) Actual plates when the
reflux ratio is 2Rm.
Table 1: Component boiling point and molar mass
Component
Boiling point
n-C5
97°F
n-C6
156.2°F
n-C7
209.1°F
n-C8
258.1°F
Molar mass
72.2
86.2
100.2
114.2
Hint: Since 1% of heptane is specified to be recovered in the distillate, 99% of
heptane is to be recovered in the bottom.
Chapter 8 Solutions
Introduction to Chemical Engineering Thermodynamics
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