1. Photo Courtesy of GPU International
A view of the GPU International 80 MW natural gas fired plant adjacent to the Syracuse University campus in Syracuse NY
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2. Components of a Vapor Power Plant
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3. Rankine Cycle Overall Performance: Turbine: Pump: Boiler:
Condenser (1 side):
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4. Rankine Idealizations
Processes 1-2, 3-4: Isentropic
Processes 2-3, 4-1: Isobaric
Saturated liquid at State 3
Reversible Pump Work Equation:
For Incompressible Fluids Only!
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5. Principal Device Analysis:
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6. Principal Device Analysis:
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7. Cycle Performance Parameters
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8. Improving Cycle Performance
One key is in the pressures:
Each method increases cycle thermal efficiency!
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9. Example problem
In a Rankine cycle the steam leaves the boiler and enters the turbine at 4MPa, 400C.
The condenser pressure is 10 kPa. Determine the cycle efficiency and the effect
of boiler pre and temp on cycle efficiency.
p1=4000; {t1=400}; p2=10 { test the effect of boiler pre on efficiency and boiler temp on efficiency and exit quality}
h1=enthalpy(steam,p=p1,t=t1)
s1=entropy(steam,p=p1,t=t1)
h2=enthalpy(steam,p=p2,s=s1); x2=quality(steam,p=p2,s=s1)
h3=enthalpy(steam,p=p2,x=0)
s3=entropy(steam,p=p2,x=0)
h4=enthalpy(steam,p=p1,s=s3)
wt=h1-h2
wp=h4-h3
eff=(wt-wp)/(h1-h4)
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10. Improving Cycle Performance
Superheat and Reheat protect the turbine, and increase TH.
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11. Example problem
Take a reheat cycle utilizing steam. The turbine inlet is 4MPa, 400C and after
expansion to 400kpa the steam is reheated to 400c again. Then the steam expands in
a LP turbine to 10kpa. Determine the cycle efficiency.
p1=4000; t1=400; p2=10 ; {pr=400 }; tr=400 { reheat cycle}
h1=enthalpy(steam,p=p1,t=t1)
s1=entropy(steam,p=p1,t=t1)
h2=enthalpy(steam,p=pr,s=s1); x4=quality(steam,p=p2,s=s3)
h3=enthalpy(steam,p=pr,t=tr)
s3=entropy(steam,p=pr, t=tr)
h4=enthalpy(steam,p=p2,s=s3)
wt=h1-h2+h3-h4
h5=enthalpy(steam,p=p2, x=0)
s5=entropy(steam,p=p2,x=0)
h6=enthalpy(steam,p=p1,s=s5)
wp=h6-h5
eff=(wt-wp)/q
q=h1-h6+h3-h2 { reheat has lot of advantages, eff increases with reheat pressure, exit quality increases }
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12. Improving Cycle Performance
Adding an Open Feedwater Heater (with pump).
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13. Example problem on regneration
Consider the regenerative cycle using steam. Steam leaves boiler at 4000kpa, 400c. After
Expansion to 400kpa some steam is bled off to an open heater at 400kpa. The rest of
Steam is expanded to 10kpa in a condenser. The exit of the heater is at sat liq. Find the cycle eff.
p1=4000; t1=400; p2=10 ; pr=400
h1=enthalpy(Steam,P=p1,T=t1)
s1=entropy(Steam,P=p1,T=t1)
h2=enthalpy(Steam,P=pr,s=s1); x4=quality(Steam,P=p2,s=s3)
h3=enthalpy(Steam,P=p2, s=s1)
s3=s1
h4=enthalpy(Steam,P=p2,x=0)
wt=h1-h2+ (1-m1)*(h2-h3)
h5=enthalpy(Steam,P=pr, s=s4); s4=entropy(Steam, P=p2, x=0)
h7=enthalpy(Steam, P=p1, s=s6)
h6=enthalpy(Steam,P=pr, x=0); s6=entropy(Steam, P=pr, x=0)
h2*m1+(1-m1)*h5=h6
wp=(1-m1)*(h5-h4)+m1*(h7-h6)
eff=(wt-wp)/q
q=h1-h7
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14. Improving Cycle Performance
Adding a Closed Feedwater Heater.
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