r&t 2007 - co2 issues - halsey cascade

8/18/2019 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

Page 2

Why CO2 ?


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Page 5

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

Page 6

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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Page 7

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]

Page 8

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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Page 9


5112367ft/sVelocity

4.250.440.3psip

246Diameter – Inch

1-1/23/41-1/2Diameter - Inch

Dry

suction

line

Liquidline

Page 10

Relative

displacement


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

Page 12

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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Page 15

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)].

Page 16

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.


Page 20

Principle diagram: CO2-NH3 cascade system

CO2Evaporator

Liquid

CO2 receiver

CO2Compressor

Dry suction

CO2 - NH3heat exchanger

”High” water

concentration”Low” water

concentration



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Principle diagram: CO2-NH3 cascade system

CO2Evaporator

Liquid

CO2 receiver

CO2Compressor

Dry suction

CO2 - NH3heat exchanger

Filter drier

Moisture indicator


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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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Page 23

R717

CO2

Controlling the

pressure during

”stand still”

System Shutdown

Page 24

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

Page 26

• 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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Page 27

CO2Experiences and

References

Page 28

GEA 65HP endurance test

in laboratory


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Page 29

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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Page 31

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

Page 32

• 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

Page 34

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

Page 36

CO2/NH3 Cascade System withScrews

r&t 2007 - co2 issues - halsey cascade

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