Transcript S.Barnes_progressreport3.ppt

Using Pinch Analysis to Optimize the Heat
Exchanger Network of a Regenerative
Rankine Cycle for an Existing Modern
Nuclear Power Plant
MANE 6980: Third Progress Report
November 21, 2013
Stephanie Barnes
Background
• Millstone Unit III Power Plant
– Regenerative Rankine Cycle
– Consists of a steam generator,
high pressure turbine, three low
pressure turbines, condensers,
six feedwater heaters, feed
pumps
– Condensate is reheated using the
heat exchanger network
(feedwater heaters) to improve
plant efficiency
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Pinch Analysis
• Optimize a power plant by using the
heat energy from the streams, instead
of using external heating and cooling
methods (heat exchanger, furnace,
cooler, etc.), to increase the thermal
efficiency of the plant and minimize
energy costs
Problem Statement
• Analyze a Regenerative Rankine Cycle,
based on the Millstone Unit III heat balance,
using pinch analysis techniques.
• Determine the pinch point and minimum hot
and cold utilities.
• Evaluate retrofit methods and recommend
improvements to the heat exchanger network
to improve plant efficiency.
Methodology
• Data Extraction: Performed a simplified analysis using 7
streams (1 cold from the condenser to the steam generator and
6 hot streams (1 for each feedwater heater in the current
design)).
• Obtain the Heat Capacities, Problem Table, Composite Curves,
and Heat Cascade
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Results
• Determined the pinch point and hot
and cold utility requirements for the
Millstone Unit III heat exchanger
network (HEN), using the problem
table and heat cascade (shown).
• The minimum hot and cold utility
requirements are 1,641 MBtu/hr and
370,852 MBtu/hr, respectively, as
determined by the software and 1,642
MBtu/hr and 371,225 MBtu/hr as
determined by hand calculations.
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Results - Cont.
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
• Shifted Hot and Cold Composite Curves
–
Curves touch at the pinch point
– External Utilities determined by the gaps between hot and cold curves at
the endpoints
Results - Cont.
QuickTime™ and a
decompressor
are needed to see this picture.
• Grand Composite Curve
– Combined Hot and Cold
Composite Curves
– Can determine the
minimum external
utilities (x-axis) and the
associated temperatures
at the endpoints of the
curve.
– Pinch temperature is the
point where net heat
flow is equal to zero.
Results - Cont.
• Determined the optimal minimum
temperature difference between the hot and
cold streams is 50 F based on external utility
requirements.
Delta
Pinch
Minimum Hot Utili ty Minimum
Cold
Tmin (F)
Temperature (F)
(MBtu/hr)
Utili ty (MBtu/hr)
10
486
0
369,210
30
476
0
369,210
40
471
0
369,210
48
467
0
369,210
50
466
1,641
370,852
70
456
19,877
389,088
Results - Cont.
Case
Pinch
Minim um
Hot Minim um
Cold
Temperature (F)
Utili ty (MBtu/hr)
Utili ty (MBtu/hr)
2
466
1,641
370,917
3
466
1,641
370,548
4
447
18,965
366,897
5
447
18,965
366,962
6
447
18,965
366,592
7
447
18,965
366,252
8
465
2,553
349,840
9
467
729
348,016
10
466
1,641
320,096
11
466
1,641
37,228
•
Evaluated 10 additional cases to
determine the effect of the number of
heat exchangers and the supply and
target temperatures on the external
utilities.
•
Case11 provided the most
significant decrease in the cold
utility requirement.
–
–
Deleting the 5th and 6th point
heaters decreased the cold utility
requirement from 370,852
MBtu/hr to 37,228 MBtu/hr, as
determined by the software, while
keeping the hot utility at 1,641
MBtu/hr.
To provide adequate cost
savings, it is recommended that
the 5th and 6th point heaters be
deleted and the exhaust from the
turbines that enters the 5th and 6th
point heaters be directed
elsewhere, such as the main
condenser.
Project Schedule
• Continue to work on the report and analysis based on
advisor’s comments.
Task
Final Report
Date
December 13