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EXAMPLE 10-4 The Ideal Reheat Rankine Cycle Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 15 MPa and 600°C and is con- densed in the condenser at a pressure of 10 kPa. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10.4 per- cent, determine (a) the pressure at which the steam should be reheated and (b) the thermal efficiency of the cycle. Assume the steam is reheated to the inlet temperature of the high-pressure turbine.

EXAMPLE 10-4 The Ideal Reheat Rankine Cycle Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 15 MPa and 600°C and is con- densed in the condenser at a pressure of 10 kPa. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10.4 per- cent, determine (a) the pressure at which the steam should be reheated and (b) the thermal efficiency of the cycle. Assume the steam is reheated to the inlet temperature of the high-pressure turbine.

Introduction to Chemical Engineering Thermodynamics
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:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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How find X6
EXAMPLE 10-4 The Ideal Reheat Rankine Cycle Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 15 MPa and 600°C and is con- densed in the condenser at a pressure of 10 kPa. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10.4 per- cent, determine (a) the pressure at which the steam should be reheated and (b) the thermal efficiency of the cycle. Assume the steam is reheated to the inlet temperature of the high-pressure turbine. Analysis The schematic of the power plant and the T-s diagram of the cycle are shown in Fig. 10-13. We note that the power plant operates on the ideal reheat Rankine cycle. Therefore, the pump and the turbines are isentropic, there are no pressure drops in the boiler and condenser, and steam leaves the condenser and enters the pump as saturated liquid at the condenser pressure. (a) The reheat pressure is determined from the requirement that the entropies at states 5 and 6 be the same: State 6: P₁ = 10 kPa Also, Thus, State 5: X6 0.896 (sat. mixture) $6 = $f + X6Sfg = 0.6492 +0.896(7.4996) = 7.3688 kJ/kg K = h6 = hƒ + xghfg = 191.81 +0.896(2392.1) = 2335.1 kJ/kg T₁ = 600°C P5 = 4.0 MPa S5 = $6 Jh5 = 3674.9 kJ/kg Therefore, steam should be reheated at a pressure of 4 MPa or lower to pre- vent a moisture content above 10.4 percent. 16
Transcribed Image Text:EXAMPLE 10-4 The Ideal Reheat Rankine Cycle Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 15 MPa and 600°C and is con- densed in the condenser at a pressure of 10 kPa. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10.4 per- cent, determine (a) the pressure at which the steam should be reheated and (b) the thermal efficiency of the cycle. Assume the steam is reheated to the inlet temperature of the high-pressure turbine. Analysis The schematic of the power plant and the T-s diagram of the cycle are shown in Fig. 10-13. We note that the power plant operates on the ideal reheat Rankine cycle. Therefore, the pump and the turbines are isentropic, there are no pressure drops in the boiler and condenser, and steam leaves the condenser and enters the pump as saturated liquid at the condenser pressure. (a) The reheat pressure is determined from the requirement that the entropies at states 5 and 6 be the same: State 6: P₁ = 10 kPa Also, Thus, State 5: X6 0.896 (sat. mixture) $6 = $f + X6Sfg = 0.6492 +0.896(7.4996) = 7.3688 kJ/kg K = h6 = hƒ + xghfg = 191.81 +0.896(2392.1) = 2335.1 kJ/kg T₁ = 600°C P5 = 4.0 MPa S5 = $6 Jh5 = 3674.9 kJ/kg Therefore, steam should be reheated at a pressure of 4 MPa or lower to pre- vent a moisture content above 10.4 percent. 16
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