CO2 Presentation LAM 2003 06

CO2Refrigerant for Industrial Refrigeration

Part I - Sub-critical refrigeration cycles

Prepared byNiels P Vestergaard

Content - Part IØ HistoryØ FactsØ Refrigeration cycles with CO2

§ Transcritical§ Subcritical

§ Cascade systems§ DX – systems§ Pump circulating systems

Ø CO2 compared with R717 & R134aØ Safety valvesØ OilØ Design pressureØ Why CO2

Ø RegulationØ Components for CO2

CO2 cooling

Climate change

Kyoto Protocol

Environment

Saving energy

Cooling

CO2 for Industrial refrigeration

History

1850 199319601920 ----------1930

The peak of utilizingCO2 as refrigerant

Reinvention of CO2-refrigeration technology(G. Lorentzen)

CO2 CompressorApprox. 1900

HistoryCO2 utilized as refrigerant in sub- and supercritical refrigeration systems

Proposal to use CO2as a refrigerant(Alexander Twining,British patent)

HistoryMarine refrigerant systems registered at Lloyds in London

Source: S.A. Andersen ”Køleanlæg i skibe og på land” 1971In 1970 S. Forbes Pearson, UK made an general view over the most commonused refrigerant used in marine refrigeration systems registered at Lloyds inLondon

CO2

Facts

CO2(Carbon Dioxide / R744)

• Natural substance

• Refrigerant classified as non-toxic and non- flammable fluid

• Concentration in the atmospheric air approx. 0,04% (volume)

Refrigerationcycles with

CO2

CO2 look like all the otherrefrigerants, but …….

Log p,h-Diagram of CO2

1

10

100

1000

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Temperature (Deg.C)

Pres

sure

(bar

)

Liquid

Solid

Vapour

Supercritical

CO2 Phases

Triple point5.2 bar

- 56.6 Deg.C

Critical point

73.6 bar

31. Deg.C

1

10

100

-200 -100 0 100 200 300 400 500

Enthalpy (J)

Pres

sure

(bar

)

Supercritical

Solid - Vapour vapour

Liquid - vapour

Liquid

Solid

Solid -Liquid

- 78,4 Deg.C

Log p,h-Diagram of CO2

73,6

+31 Deg.C

Criticalpoint

- 56,6 Deg.C5,2

Triple(freezing)

point

NOYESNONOToxic

1-32601300Global Warming Potential (GWP) *

73.631.1

113132.4

37.372

40.7101.2

Critical pressure in bar°C

5.18-56.6

0.06-77.7

0.028-100

0.004-103

Triple point in bar°C

NO(YES)NONOFlammable or explosive

0000Ozone Depletion Potential (ODP) *YESYESNONONatural substanceCO2NH3R404aR134aRefrigerant

CO2 properties compared with various refrigerants

* prEN 378-1 (2003)

10 bar (-40 Deg.C)

35 bar (0 Deg.C)

Subcritical refrigeration procesExample –10/35 bar

10 bar (-40 Deg.C)

65 bar (25 Deg.C)

Subcritical refrigeration procesExample –10/65 bar

Transcritical(supercritical)refrigeration

process

90 bar

Supercritical refrigeration process

26,5 bar (-10 Deg.C)

90 bar

Supercritical refrigeration processGas cooling

26,5 bar (-10 Deg.C)

95 Deg.C35 Deg.C Gas cooling

Residential CO2 heatpumpapplication for hot waterproduction

CO2 Automotiveaircondition application

1

1,5

2

2,5

3

70 75 80 85 90 95 100 105 110

Compressor outlet pressure [bar]

CO

P

Max

100 bar

100 bar,COP = 2,46

90 bar,COP = 2,51

90 bar

COP = (∆hEVAP*m )/ (∆hComp-is*m)

∆hComp-is

80 bar

80 bar,COP = 1,72

∆hEVAP

35 oC

Supercritical refrigeration procesInfluence of compressor outlet pressure

Supercritical CO2 heat pumps

Patents:A number of patents has to be taken intoconsideration

Sub critical refrigerationprocess, e.g.

• Cascade system• DX systems• Pump circulating systems

R717

CO2

+30 Deg.C (12 bar)

-20 Deg.C (1,9 bar)

+30 Deg.C

-20 Deg.C-15 Deg.C

-40 Deg.C

Pres

sure

Enthalpy

-15 Deg.C (23 bar)

-40 Deg.C (10 bar)

Pres

sure

Enthalpy

CO2

R717

Principal diagram717 - CO2 cascade system

-40 Deg.C

CO2-evaporator

CO2 compressor

CO2-receiver

CO2-R717 Heat exchanger

R717

CO2

-45 Deg.C (0,5 bar)

-40 Deg.C (10 bar)

+30 Deg.C

-45 Deg.C

-40 Deg.C

-40 Deg.C

Enthalpy

Enthalpy

Pres

sure

Pres

sure

+30 Deg.C (12 bar)

CO2

R717

Principal diagram717 - CO2 brine system

-40 Deg.C


CO2-receiver

CO2-evaporator

R717

CO2

+30 Deg.C (12 bar)

-20 Deg.C (1,9 bar)

-15 Deg.C (23 bar)

-40 Deg.C (10 bar)

+30 Deg.C

-20 Deg.C

-40 Deg.C

-40 Deg.C

Pres

sure

Pres

sure

Enthalpy

Enthalpy

CO2

R717

+8 Deg.C

+8 Deg.C (43 bar)

Principal diagram717 - CO2 cascade system with CO2hot gas defrosting

-15 Deg.C


CO2 compressor

CO2 defrostcompressor

CO2-receiver

CO2-evaporator

Principal diagram CO2 cascade system with 2temperature levels (e.g supermarket refrigeration)

R717,R404, R134a,….

CO2

Pump circulating system

DX system

+30 Deg.C

-12 Deg.C-7 Deg.C

-7 Deg.C

-20 Deg.C

CO2 applicationCO2 compared with R134a and R717

111[K]∆T

250250250[kW]CapacityWet return lineCO2R717R134aRefrigerant

9,423,012,6[m/s]Velocity0,36600,03750,0263[bar]∆p

26099982968[mm2]Area

583661[mm]Diameter

0,80,80,8[m/s]VelocityLiquid line

33101221331941[mm2]Area

65125202[mm]Diameter

CO2Smallpipediameter!

Leqv = 50 [m]Pump circ.: ncirc = 3Evaporating temp.: TE = -40 [Deg.C]

Wet return / Liquid linesWet reurn

Liquid

CO2Area -Liquid

line44%

Area -Wet

returnline56%

R717

Area -Wet

returnline92%

Area -Liquid

line8%

R134aArea -Liquid

line9%

Area -Wet

returnline91%

111[K]∆T

250250250[kW]CapacityWet return lineCO2R717R134aRefrigerant

9,423,012,6[m/s]Velocity0,36600,03750,0263[bar]∆p

26099982968[mm2]Area0,80,80,8[m/s]VelocityLiquid line

33101221331941[mm2]Area

CO2Liquidfraction ishigh

Leqv = 50 [m]Pump circ.: ncirc = 3Evaporating temp.: TE = -40 [Deg.C]

Wet return / Liquid linesWet reurn

Liquid

111[K]∆T

250250250[kW]CapacityDry suction lineCO2R717R134aRefrigerant

17,642,923,3[m/s]Velocity0,36630,03750,0261[bar]∆p

9753531089[mm2]Area352137[mm]Diameter


1956707519413[mm2]Area5095157[mm]Diameter

Dry suction / Liquid lines

CO2Smallpipediameter!

Leqv = 50 [m]Evaporating temp.: TE = -40 [Deg.C]Condensing temp.: TC = -15 [Deg.C]

Dry suction

Liquid

111[K]∆T

250250250[kW]CapacityDry suction line

CO2R717R134aRefrigerant

17,642,923,3[m/s]Velocity

0,36630,03750,0261[bar]∆p

9753531089[mm2]Area


1956707519413[mm2]Area

CO2

Area -Dry

suctionline67%

Area -Liquid

line33%

R134

Area -Dry

suctionline95%

Area -Liquid

line5%

R717

Area -Dry

suctionline95%

Area -Liquid

line5%

CO2Liquidfraction ishigh

Leqv = 50 [m]Evaporating temp.: TE = -40 [Deg.C]Condensing temp.: TC = -15 [Deg.C]

Dry suction / Liquid linesDry suction

Liquid

250250250[kW]Capacity

CO2R717R134aRefrigerant

1,08,813,1[-]Compressor capacity relative12410921628[m3/h]Compressor capacity

Evaporating temp.: TE = -40 [Deg.C]Condensing temp.: TC = -15 [Deg.C]

CO2Compressorshave highcapacity

Compressor capacityCompressor

333[m]High "h"CO2R717R134aRefrigerant

0,885,2114,91[oC]Pump inlet pressure - ∆t0,3290,2030,418[bar]Pump inlet pressure - ∆p

CO2Sub cooling (∆t)is small

Liquid pumpPumpe

h

Pump

0,1

1

10

100

1000

10000

-50 -40 -30 -20 -10 0 10 20 30 40

Temperature [oC]

[kg/

m3]

CO2 Vapour [m3/kg]

CO2 Liquid [m3/kg]

R134a Vapour [m3/kg]

R134a Liquid [m3/kg]

R717 Vapour [m3/kg]

R717 Liquid [m3/kg]

log Density - R134a - R717 - CO2

CO2Density differencebetween liquid andvapour is small

Density - CO2

0

200

400

600

800

1000

1200

1400

-50 -40 -30 -20 -10 0 10 20 30 40

Temperature [Deg.C]

[kg/

m3 ]

CO2 Liquid

CO2 Vapour

100

300

500

700

900

1100

1300

1500

-50 -40 -30 -20 -10 0 10 20 30 40temperature [oC]

[kg/

m3]

CO2Liquid-vapour[m3/kg]

R134aLiquid-vapour[m3/kg]

R717Liquid-vapour[m3/kg]

Difference between liquid and vapour density

F

F = ( density liquid – density vapour)

liquid

Vapour

SUMMARYCO2 application:

• Pipe dimensions in CO2 systems are small

• Due to very small vapour volume, CO2 systems are verydynamic

• Liquid pumps in CO2 systems are sensitive to capacitychanges (low sub cooling & gas bobbles are difficult toget rid of at high temperatures.)

• Compressors with big capacity steps can createproblems (small vapour volume).

• Frequency converters are an obvious possibility !

Safety valves

CO2

1

10

100

-200 -100 0 100 200 300 400 500

Enthalpy (J)

Pres

sure

(bar

)

Supercritical

Solid - Vapour

vapour

Liquid - vapour

Liquid

Solid

Solid -Liquid

73,6

- 56,6 Deg.C5,2

- 78,4 Deg.C

+31 Deg.CSafety valves

Safety valve 20 barliquid

Safety valve 20 barliquid

78% solid CO2 atthe triple point

Safety valve 35 barvapour

Safety valve 35 bar

0% solid CO2 at thetriple point

Safety valve 50 barvapour

Safety valve 50 bar

5% solid CO2 at thetriple point

Designpressure

Design pressure is depending of:

• Pressure during operation• Pressure during ”stand still”:• Temperature requrements for

defrosting• Pressure tolerances for safety

valves (10 – 15 %)

R717

CO2

Controlling thepressure during”stand still”

Saturated pressure CO2

CO2

20

25

30

35

40

45

50

55

60

-30 -20 -10 0 10 20Design temperature (Deg.C)

Pres

sure

(bar

) Design pressure (bar-g): Ps + 15 %

"Saturated"pressure (bar-a)

Ps + 10% (bar-g)

PS 50

PS 40

PS 25

Practical limit: PS ≥ Psaturated +15%

Design pressurePressure peaks 5%

Saturated pressure10%Safety valve

Design pressure

CO2 and oil

§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 thanCO2 -opposite NH3)

Oil return system

§No special requirements(system requirements like HCFC / HFC )

§Special demand:§High filtration demanded§Multistage coalescing filters§Active carbon filter

Oil separation system

High affinity to waterLowHydrolysis

High (miscible)Low (immiscible)Solubility

POEPolyol Ester Oil

PAOPolyalfaolefin(Synthetic Mineral Oil)

Oil type

Common used oil type in CO2 systemsCO2 and oil

Why CO2 ?

HouseholdCompressors

ApplianceControls

IndustrialRefrigeration

Petro-Chemical

Refrigeration and Air Conditioning

R717R600a R134a R1270R410

• All valves are suitable for Ammonia• All valves are in steel• ”Big” valves in small quantity• Requirements for type approvals,

traceability etc.

Danfoss IndustrialRefrigeration A/S

Commercial/Supermarket

SVA-HS

• Small valves made ofe.g. brass, copper

• Valves are NOTapplicable for Ammonia

• Large quantity

CO2

IndustrialRefrigeration

Commercial/SupermarketCO2 – Drivers

Why CO2 ?

EnvironmentPhase out CFC, HCFC: Change to CO2(ODP (Ozone Depletion Potential), GWP (Global Warming Potential) )

SafetyIncreased restrictions on toxic/flammable refrigerants (e.g.requirements for systems with big R717 charge)

Cost• Reduced running cost due to increased

efficiency (compressor efficiency, heat transfer)• Reduced cost on refrigerants.• Reduced size on components.

E

E

E E

CO2componentsfor industrialrefrigeration

High pressure components - CO2

CO2Refrigerant for Industrial Refrigeration

Part II - Properties, compatibility & chemical reactions

Prepared byFinn Broesby Olsen &Niels P Vestergaard

Content - Part IIØ Safety aspects with CO2

Ø Chemical reaction with water and other impurities in CO2 systemsØ Removing water from CO2 systems

§ Filter driersØ Water (moisture) in CO2 systems

§ Solubility§ Moisture indicators

§ Cascade systemsØ How can water penetrate into CO2 systemsØ Compatibility with metal, elastomere

Safety aspectswith CO2

CO2(Carbon Dioxide / R744)

• Natural substance

• Refrigerant classified as non-toxic and non- flammable fluid

• Concentration in the atmospheric air approx. 0,04% (volume)

Safety Aspects of CO2

Carbon dioxide replaces air, and causes lack of oxygen. At presence of sufficient oxygen, CO2 has a narcotic effect at strongerconcentration. With smaller amounts, CO2 has a stimulating effect on the respiratory center. Due to the acidic characteristics of CO2, acertain local irritating can appear, particularly on the mucous membrane of nose, throat and eyes as well as induce coughing. The symptomsassociated with the inhalation of air containing carbon dioxide are, with increasing carbon dioxide concentrations.

The data, valued for adults with good health, are as follows:

§ 0,04% Concentration in the atmospheric air

§ 2% 50% increase in breathing rate

§ 3% 10 Minutes short term exposure limit; 100% increase in breathing rate

§ 5% 300% increase in breathing rate, headache and sweating may begin after about an hour

(Com.: this will tolerated by most persons, but it is physical burdening)

§ 8% Short time exposure limit

§ 8-10% Headache after 10 or 15 minutes. Dizziness, buzzing in the ears,blood pressure increase,

high pulse rate, excitation, and nausea.

§ 10-18% After a few minutes, cramps similar to epileptic fits, loss of con-sciousness, and shock

(i.e.; a sharp drop in blood pressure) The victims recover very quickly in fresh air.

§ 18-20% Symptoms similar those of a stroke.

(source: AGA Gas Handbook)

Chemical reaction withwater and other impurities

in CO2 systems

If water ispresent in CO2systems, waterreacts with CO2and createsCarbonic acid.

Theconcentration isdepending onthe water content

Strong acid

Water in CO2 systems

Water in CO2 systemsHeavy corrosion in a steelpipe from a CO2 systemcaused by Carbonic acid.

Corrosion will not take placein a well maintained CO2refrigeration system.

X-ray defraction:

Crystal structure analysis ofthe steel pipe.


With very highconcentration of water inCO2 systems, the CO2gas hydrate can beperformed. CO2 gashydrate looks like ice,but exists also at highertemperatures

The CO2 gas hydrate cancreate problems in e.g.filters

CO2 gas hydrate - CO2(H2O)8

Ammonia in CO2 systems

• The solid substance Ammonium Carbamate is formed immediately ifCO2 gets in contact with ammonia.

• Ammonium Carbamate is a corrosive substance (white powder)

• Ammonium Carbamate will dissolve, if it is heating up to a temperaturehigher than approx. 60 Deg. C

• If oxygen is present in CO2 system, it will react with the PAO oil•Oxygen can be present e.g. from corrosion in tubes

• Organic Acid and Water are generated

• The Organic Acids from oxidation are relatively strong acids

PAO Polyalfaolefin Oil in CO2 systems(Synthetic Mineral Oil)

PEO Polyol Ester Oil in CO2 systems

• If water is present in CO2 system, it will react with Ester oil•Organic Acid and Alcohol are generated

• The Organic Acid is relative weak acid

Removing water from CO2systems

Filter drier in CO2 systems

Desiccant core absorbingwater from refrigerant(Molecular Sieves)

Filter mat collecting solidcontaminants

Molecular Sieves in CO2 systems

CO2 penetrates through the micropores unlike other refrigerants likeR134a. If water is present, it will also penetrate through the microporesand throw CO2 out, due to difference in polarity of water and CO2.

CO2 driers with Molecular Sieves are very efficient.

Refrigerantmolecules andmicropore sizein Zeolite LTA

Molecular Sieves water uptake in CO2 systems

Molecular Sieves water uptakeCO2 /R134a systems

CO2 R134a

The efficiency of the molecular sieves with CO2 and R134a are almost identical

Water (moisture) in CO2

Water Solubility in Refrigerants.Liquid Phase

(Y-Axis Linear)

0

500

1000

1500

2000

2500

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [oC]

mg

of w

ater

/kg

refr

iger

ant [

ppm

]

Water Solubility in Refrigerants. Gas Phase(Y-Axis Linear)

0

200

400

600

800

1000

1200

1400

1600

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [oC]

mg

of w

ater

/kg

of re

frig

eran

t [pp

m]

CO2

CO2

R134aR134a

0

200

400

600

800

1000

1200

1400

1600

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature [oC]

mg

of w

ater

/kg

of re

frige

rant

[ppm

]

CO2

NH3 R134a

R22

R404A

Water Solubility in Refrigerants. Gas Phase(Y-Axis Linear)

CO2

0102030405060708090

100

-50 -40 -30 -20 -10 0 10 20

Temperature [oC]

mg

of w

ater

/kg

of re

frig

eran

t[p

pm]

CO2 + H20 gas Phase

CO2 +ICE

CO2 +Water

Danfoss Sight Glass SGN in CO2

01020

30405060

708090

100

-50 -40 -30 -20 -10 0 10 20

Temperature [oC]

mg

of w

ater

/kg

refr

iger

ant [

ppm

]

”Wet”

”Dry”


CondenserEvaporator

CO2 system with filter drier and indicator

Filter drier Moisture indicator

How can water penetrate into a CO2 system?ØThe pressure of CO2 systems is always above the atmospheric

pressure; therefore there are not the same risks, as e.g. in NH3systems, that air / water penetration into a leaking CO2 system,however permeation of water into the system is still possible.


Ø When charging CO2, there are different specifications of CO2. Someof them allow relative high amounts of water.

ØCO2 is treated as a very safe refrigerant, and is therefore handledwithout following the normal safety requirements. If a system isopened up, air can penetrate into it, and the moisture can condenseinside the tubes. If the system is not evacuated properly, some watermay well be retained.

ØBy charging lubricant (oil) to the compressor.

ØBy decomposition of oil

Ø CO2 is compatible with almost all common metallic materials, unlikeNH3. There are no restrictions from a compatibility point of view, whenusing copper or brass.

CO2 compatibility with metal and polymers

Ø The compatibility of CO2 and polymers is much more complex. BecauseCO2 is a very inert and stable substance, the chemical reaction withpolymers is not critical.

Ø The main concern with CO2 is the physiochemicaleffects, such as permeation, swelling and the generation of cavities andinternal fractures. These effects are connected with the solubility anddiffusivity of CO2 in the actual material.

Ø The compatibility of CO2 and polymers can be sensitive.

CO2 compatibility with metal and polymers

Ø CO2 penetrates into polymers, but has difficulties to get out fast.

Ø CO2 pressure, temperature and pressure change are important factors

But !

Ø In sub-critical CO2 refrigeration the pressure is relative low (< 50 bar)and further more pressure changes take place relative slow.Experience has shown that standard CR O-rings can be used with CO2,under these conditions.

Ø CO2 is a natural non-toxic/non-flammable substance

Ø CO2 is a relative unreactive refrigerant

Ø All reaction involving CO2 need water to take place.

Ø The acceptable water content in CO2 systems is much lowerthan in other refrigeration systems

Ø Water, oxygen, oxides, oil, contaminants and system metalsare the most important chemical reactants. Also in systemswith CO2.

SUMMARY

Thank youfor attention!

Questions ?

Documents

CO2 Presentation LAM 2003 06