Thermal Engineering / GEA Power Cooling, Inc.
HYBRID COOLING SYSTEMS AND AIR COOLED CONDENSERS Dr. Luc De Backer, Vice President of Technology
EPRI Workshop on Advanced Cooling Technologies: Preparing for a Water Constrained Future
Thermal Engineering / GEA Power Cooling, Inc.2
Introduction
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Major purpose of cooling system = reject heat duty (from steam condensation) to the atmosphere
Important note:
Steam turbine output is directly related to the capacity of the cooling system which is a function of the ambient temperature (DBT for dry cooling; WBT for wet cooling)
remember for later.
steam
condensate
Steam Turbine
Steam condensation heat duty
Generator
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Cooling system performance & ambient conditions
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1. Wet Cooling Systems:If WBT � than CWT � which results in BP � and output �
2. Dry Cooling Systems:If DBT � than BP � and output �
Since performance wet cooling depends on WBT while performance dry cooling depends on DBT, the steam generator output is larger for wet systems since WBT ≤
DBT
3. Hybrid Cooling Systems: intermediate performance
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Steam tubine back pressure and generator output
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-13-12-11-10
-9-8-7-6-5-4-3-2-10123
1.5 2.5 3.5 4.5 5.5 6.5 7.5
LP Turbine Exhaust Pressure (inch HgA)
Δ o
utpu
t (%
)
3 %
1 inch
BP ⇒ kW
Design: 3.1 in Hg 100 % output
Design point
Δ BP = 1 inch
Δ output = -
3%
Wet cooling systems can
reach lower BP than dry cooling
systems
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Classification of Cooling Systems
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Plume AbatedEnhanced Dry
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Make-up water requirements & Investment cost
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WATER NEED COST
WET HIGH LOW
DRY LOW HIGH
HYBRID INTERMED. OPTIMIZED
Make-up water requirements & initial investment cost
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Dry cooling systems: the ACC
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Coryton 750 MW Combined Cycle (England)
Steam Duct
Steam Header
Heat Exchanger bundles
Heat exchanger bundles can be compared with car radiator
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ACC: 2-stage condensation process
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WINDWALL
STEAM DISTRIBUTION HEADER
CONDENSATE TANK
VACUUM SYSTEM
PARALLEL FLOW MODULE
STEAM IN
COUNTERFLOW MODULE
AIR MOVING SYSTEM
FIN TUBE BUNDLES
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Air Cooled Condenser: K-bundles
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•Steam & Condensate travel in parallel
•70-80% of steam is condensed in the K’s
•Any air in system is purged to “D” bundles
Condensate Collector
Steam Header
Stea
m
Cond
ensa
teAir Flow
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Air Cooled Condenser: D-bundles
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Stea
m
Cond
ensa
teAir Flow
•Steam & Condensate travel in opposite directions
•Final 20-30% of steam condensed
•Any air in the system is removed at the top of “D” bundles by vacuum system
•Condensate always warmed by steam (Minimizes sub- cooling and avoids freezing of the tubes)
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Hybrid cooling systems: the PAC system
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Best available hybrid cooling technology to use the make-up water optimally !
4 cell MDCT15 cell ACC
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What is a Parallel Condensing System (PAC)
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“A synergy of established cooling technologies”
DRY COOLING SYSTEM WET COOLING SYSTEM
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What is a Parallel Condensing System (PAC)
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The result is a Parallel Condensing System:
SSC and ACC are condensing the steam in parallel
Steam turbine
Cooling tower
steam
ACC
condensate
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Design of hybrid cooling systems (PAC):
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Design of Parallel Condensing Systems:• Not enough water for wet cooling # acre-foot per year limit• Cost optimization: minimize dry section as much as possible• m’make-up
for wet section has to be integrated over 1 year
1st
step: analysis of climatic data for the site• DBT & WBT occurrence in number of hours per year• This kind of info is not available in the ASHRAE handbook• Can be found in Engineering Weather Data (by NCDC)
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PAC systems: climatic data and control
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050
100150200250300350400450500550600650700750800850900950
-26
/ -30
-25
/ -21
-20
/ -16
-15
/ -11
-10
/ -06
-05
/ -01
00 /
0405
/ 09
10 /
1415
/ 19
20 /
2425
/ 29
30 /
3435
/ 39
40 /
4445
/ 49
50 /
5455
/ 59
60 /
6465
/ 69
70 /
7475
/ 79
80 /
8485
/ 89
90 /
9495
/ 99
DBT range (deg F)
Num
ber o
f hou
rs p
er y
ear
-40-30-20-10010203040506070
MC
WB
(deg
F) Control hybrid:
•
m’evap
controlled by **MDCT capacity (fans)• low DBT: ACC only•
DBT ⇒ both MDCT **& ACC in operation•
Monitor m’make-up
to **stay below spec limit
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PAC system design
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ACC selection
Within waterLimit?
PAC designconditions
ACC performance
Engineering weather data
DBT MCWB
ACC duty SSC duty
Aux dutyMDCT duty
Evaporation
Make-uprequirement
Other plantusers
No
# Hours
YesOK
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Make-up water requirements wet cooling
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m’drift 0.0005 % - 0.001 % of water flow rate @ inlet tower
m’make-up
= m’evap
+ m’blow-down
+ m’drift
m’blow-down function of # cycles of concentration (COC)
COC
COC -
1It is easily shown that: m’make-up
= m’evap
Climatic data input: m’evap
is function of WBT & RHrefer to next slide
Water losses should be compensated by make-up water:
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Evaporation rate as function of WBT & RH
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20 %
40%
60%
80%100%
1.0%
1.1%
1.2%
1.3%
1.4%
1.5%
1.6%
1.7%
1.8%
30 °F 40 °F 50 °F 60 °F 70 °F 80 °F
WBT
Evap
orat
ion
to w
ater
flow
ratio
WBT
Evap
RH
Evap
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Performance of PAC systems
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Example (Comanche): reduced BP in summer with PAC
ACC ONLY
PAC
0123456789
10
60 65 70 75 80 85 90 95 100DBT (deg F)
BP
(inch
HgA
)
Reduced turbine BP results in increased power plant output
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Differences between PAC and PA tower
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Major advantages PAC systems compared to PA towers:• If 100 % duty can be handled by the dry section in winter NO PLUME !
• Water consumption can be matched to the amount of water available water savings is not limited to 20 % like for plume abated cooling towers
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Conclusions
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1. If there is no water available for the power plant cooling system, than an ACC is the way to go (high investment + perf.↓
@ hot ambient).
3. If there is some water available, but not enough for a wet cooling tower than a hybrid cooling system may be the most economical choice.
4. PAC systems are used more and more in the power industry, because it is a combination of established cooling technologies.
2. If a very limited amount of water is available, air inlet spray cooling can be used to enhance the ACC performance at dry and hot conditions.
5. Although PA towers may save some water when the dry section is involved, the water savings are rather limited (max. 20 %).
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Hybrid Cooling Systems and ACC’s
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QUESTIONS ?
