R&T 2007 - CO2 Issues - Halsey Cascade
Transcript of R&T 2007 - CO2 Issues - Halsey Cascade
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Issues and Answers for CO2Compressors
INDUSTRIAL REFRIGERATION CONSORTIUM
RESEARCH TECHNOLOGY FORUM
FEBRUARY 8-9, 2007, MADISON, WI
77The Pyle Center, 702 Langdon St. Madison, WI
thh
Annualnnual
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Why CO2 ?
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BASIC FUNDAMENTALS OF
CO2 SYSTEMS
• CO2 cascade system uses CO2 on low
side with compressor
• Compressor discharges to cascade
condenser
• Condense CO2 and boil ammonia or
halocarbon
• Indirect CO2 systems use CO2 as “brine”
with conventional 2-stage system
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R717
CO2
+30 oC [+86 oF]
-12 oC [+10 oF]
-15 oC [+5 oF]
NH3 - CO2 cascade system
-40 oC [-40 oF]
CO2-evaporator
CO2 compressor
CO2 - receiver
CO2 -R717 Heat exchanger
-40 oC [-40 oF]
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R717
CO2
NH3 - CO2 brine system
CO2-R717 Heat exchanger
CO2-evaporator
-45 oC [-49 oF]
-40 oC [-40 oF]
-40 oC [-40 oF]
CO2 - receiver
-40 oC [-40 oF]
+30 oC [+86 oF]
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CO2R717R404aRefrigerant
276636ft/sVelocity
4.20.440.31psip
358Diameter – Inch
2-1/2”1-1/22-1/2Diameter - Inch
Wet
return
line
Liquid
line
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CO2R717R404aRefrigerant
5112367ft/sVelocity
4.250.440.3psip
246Diameter – Inch
1-1/23/41-1/2Diameter - Inch
Dry
suction
line
Liquidline
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Relative
displacement
CO2R717R404aRefrigerant
1.09.26.5
91840590CFM
Required
compressor
swept volume
(45 TR @ -58F
and +10F)
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Swept volumes CO2 vs. NH3
GEA FES 180GLB
572 CFM
10.4 / 62.2 psia
51.8 psi
6
GEA Grasso 55HP
76 CFM @ 1150 RPM
145 / 504 psia
359 psi
3.5
- 40 F / 32 F
Cap = 50 TR
Pressure Suct. / Disch.
Pressure differential
Pressure ratio
GEA FES 290GLB
917 CFM
5.9 / 42.2 psi (a)
36.3 psi
7.15
GEA Grasso 65HP
91 CFM @ 1150 RPM
98 / 383 psi (a)
285 psi
3.9
-58 F / 14 F
Cap = 45 TR
Pressure Suct. / Disch.
Pressure differential
Pressure ratio
NH3CO2Running Conditions
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CO2 COMPRESSOR
Application
Considerations
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Compressor Concerns:
Low Pressure Ratio
High Pressure Difference
High Design Pressure
High Shaft Torque
Shaft Seal Design
Design Concerns
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Controls
• Pressure ratio can be below
2:1(300/150), and typically runs 3:1
(360/120). An ammonia system
pressure ratio is 5:1 (200/40) or even
20:1 (200/10).
• Pressure difference is high from suctionto discharge (can be 250-300 psi
differential)
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Controls
• Casing design pressure is high. CO2compressors must be designed for at
least 31 bar/g (450 psig). [Some
compressors are now designed for 50
bar/g (725 psig). Ammonia compressors
only require 20-28 bar/g (300-400 psig)].
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Controls
• Shaft torque is high relative to CFM.
Small compressor must have enough
strength in shaft to resist torsional failure
• Shaft seal design is based on high
pressures, even when operating at or
near suction
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System Concerns:
Water in system
Design Pressure
System shutdown
Oil selection
Component selection
Controls
Design Criteria
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If water is
present in CO2systems, water
reacts with CO2and creates
Carbonic acid.
The
concentration is
depending on
the water content
Strong acid
Water in CO2 Systems
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Heavy corrosion
in a steel pipe
from a CO2production
system caused by
Carbonic acid.
Corrosion will not
take place in a
well maintained
CO2 refrigeration
system.
Water in CO2 Systems
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Principle diagram: CO2-NH3 cascade system
CO2Evaporator
Liquid
CO2 receiver
CO2Compressor
Dry suction
CO2 - NH3heat exchanger
”High” water
concentration”Low” water
concentration
Water in CO2 Systems
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Principle diagram: CO2-NH3 cascade system
CO2Evaporator
Liquid
CO2 receiver
CO2Compressor
Dry suction
CO2 - NH3heat exchanger
Filter drier
Moisture indicator
Water in CO2 Systems
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Design pressure depends on:
• Pressure during operation
• Pressure during “stand still”
• Temperature requirements for defrosting
• Pressure tolerances for safetyvalves (10 – 15 %)
Design Pressure
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R717
CO2
Controlling the
pressure during
”stand still”
System Shutdown
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
-40 -20 0 20 40
Temperature
V
o l u m e c h a n g e
[ %
CO2
R134a
R717
Relative liquid volume
Reference: -40 [oC] / [
oF]
[oC]
-40 32 104-4 68 [oF]
System Shutdown
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• High affinity to water
• Long term stability of oil
• ”Clean” refrigerant system required
• Oil separation and returnsystem
• Long term oil accumulation in
e.g. evaporators
Challenge
• Simple
(system requirements like HCFC
/ HFC )
• Special demand:
• Oil drain from low temperature
receiver ( oil density lower than
CO2 -opposite NH3)
Oil return system
• No special requirements
(system requirements like HCFC / HFC )
• Special demand:
• High filtration demanded
– Two-stage coalescing
filters – 0.05 ppm
– Three-stage - .01 ppm
Oil separation system
High affinity to water LowHydrolysis
High (miscible)Low (immiscible)Solubility
POEPolyol-ester oil
(Ester Oil)
PAOPoly-alpha-olefin oil
(Synthetic Mineral Oil)
Oil type
Oil Selection
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• Due to the relatively small vapor volume of the
CO2 system and large volumetric refrigeration
capacity, the CO2 system is relatively sensitive
to capacity fluctuations.
Controls
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CO2Experiences and
References
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GEA 65HP endurance test
in laboratory
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Field Test CO2/NH3 Cascade
Systems
Page 305 plate freezers with -58 F CO2 as secondary refrigerant
Ocean 7, Trawler (indirect
system)
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CO2 as secondary refrigerant for coolingapplications(150 TR)
-9 / -11
2 %
2-1/2”
2-1/2”
+18.5 / +8.5
9 %
8”
8”
+16
0.3 %
2”
6”
Temperatures (°)
Cir. pump power
(%)
Diameter supply
Diameter return
CO2GlycolNH3(Direct)
Comparison
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• Replacing existingfreezing plant: – CO2 –NH3 cascadeinstallation
– Two separate freezingsystems each 170 TR at -58F
– Two CO2 duo pack GrassoD-7 screw compressors witheconomizer
– Two NH3 duo pack GrassoM-2 screw compressors witheconomizer
– 23 plate freezers
Dirk Dirk, Trawler (direct system)
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First CO2/NH3 Project with
Pistons: CO-OP Vaxjö
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CO2/NH3 cascade system
Complete “factory”
built cascade system
incl. :
- 2 x Grasso 45HP -
CO2- 2 x Grasso 410 -
NH3- Cascade H.E.
- Surge drum
- Standstill coolingcircuit
- 2 xCO2 pumps
- Water cooled cond.
- Power panel
- PLC control
Distribution Center “CO-OP”
Vaxjö, Sweden
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CO2/NH3 cascade system
Process:
Cold storage
Running conditions:
T evap. - 49 F
T cond. +28 F
Running hours:
> 3000
Distribution Center “CO-OP”
Vaxjö, Sweden
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CO2/NH3 Cascade System withScrews