ChemE 260 Improvements and Non-Ideal Behavior in the Rankine Cycle

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ChemE 260 Improvements and Non-Ideal Behaviorin
the Rankine Cycle

• Dr. William Baratuci
• Senior Lecturer
• Chemical Engineering Department
• University of Washington
• TCD 9 C DCB 9 3 - 6

May 20, 2005
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Improvements on the Rankine Cycle

• Superheat Rankine Cycle
• Almost always used, improves h and turbine
  effluent quality
• Supercritical Rankine Cycle
• Increases h. Not common b/c, for steam, T and P
  are very high materials become very expensive.
• Reheat Rankine Cycle
• Very common way to improve turbine effluent
  quality
• h drops slightly unless regeneration is used as
  well.
• Regeneration Rankine Cycle
• Preheating boiler feed reduces irreversibility of
  heat transfer in the boiler
• Increases h.
• Binary Rankine Cycle
• Not very common. Main advantage is TH gtgt TC
• Big increase in h, but also increases cost to
  build.
• Rankine Cycle with Cogeneration
• Use some of the HP turbine effluent in another
  process.

Baratuci ChemE 260 May 20, 2005
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Superheat Rankine Cycle
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Supercritical Rankine Cycle
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Reheat Rankine Cycle
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Regeneration Rankine Cycle
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Binary Rankine Cycle
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Irreversibilities

• 4 main sources of irreversibilty in a real power
  cycle
• Heat losses to the surroundings
• Effects every process as well as the pipes that
  connect them.
• Fluid friction
• Effects every process as well as the pipes that
  connect them.
• Result is pressure drop. This causes the
  temperature to drop as well in the boiler and
  condenser.
• Mechanical losses (friction rapid expansion
  compression)
• Effects the turbine and the pump the most.
• Causes entropy to increase.
• Subcooling in the condenser
• Necessary to avoid cavitation in the pump.

Baratuci ChemE 260 May 20, 2005
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Irreversibilities on a TS Diagram
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Irreversibilities Lost Work

• From Lesson 8D

• Now, include the effect of direct heat lost to
  the surroundings

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Next Class

• Prepare for Test 2
• After that Test 2
• TCD Ch 5 8
• CB 4.3 4.5 and Ch 5 6
• And then
• Gas Power Cycles
• Air-Standard Power Cycles
• The Brayton Cycle
• Variations on the Brayton Cycle
• Regeneration
• Reheat
• Intercooling
• Regeneration with Reheat and Intercooling

Baratuci ChemE 260 May 20, 2005
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Example Problem

• Net Power, Heat Transfer and hth in an Ideal
  Rankine Cycle with Reheat
• Water is the working fluid in an ideal Rankine
  cycle. The pressure and temperature at the
  turbine inlet are 1200 lbf/in2 and 1000oF,
  respectively, and the condenser pressure is 1
  lbf/in2. The mass flow rate of steam entering the
  turbine is 1.4 X 106 lb/h. The cooling water
  experiences a temperature increase from 60 to
  80oF, with negligible pressure drop, as it passes
  through the condenser. The ideal Rankine cycle is
  modified to include reheat. In the modified
  cycle, steam expands through the first-stage
  turbine to saturated vapor and then is reheated
  to 900oF. If the mass flow rate of steam in the
  modified cycle is the same as in ideal Rankine
  cycle, determine for the modified cycle
• the net power developed, in Btu/h.
• the rate of heat transfer to the working fluid in
  the reheat process, in Btu/h.
• the thermal efficiency.

Baratuci ChemE 260 May 20, 2005
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Example Answers
Baratuci ChemE 260 May 20, 2005