Diego Curti - Fuchs Lubrificanti - VANTAGGI DEI LUBRIFICANTI SINTETICI NEI SISTEMI DI REFRIGERAZIONE OPERANTI CON AMMONIACA

XV EUROPEAN CONFERENCE MILANO 7th-8th JUNE 2013 CSG

Latest Technology in Refrigeration and Air ConditioningUnder the Auspices of the PRESIDENCY OF THE COUNCIL OF MINISTERS

Advantages of synthetic

refrigeration oils for ammonia

refrigeration systems

Christian Puhl

Wolfgang Bock

FUCHS EUROPE Schmierstoffe GmbH

Diego Curti

FUCHS LLUBRIFICANTI S.p.A.



• Ammonia (NH3) as a refrigerant

• Compressor oils for ammonia systems

• Requirements for compressor oils for ammonia systems

• Applications of synthetic oils for ammonia systems

• Conclusion

Content



Ammonia as refrigerant

Refrigerant Ammonia:

•Excellent thermo dynamic

characteristics: High COP

(Coefficient of Performance)

•Low energy costs

•Low price of the refrigerant

•High discharge temperature: two

stage compressor (piston), large oil

coolers (screw)

•Toxic and flammable - special safety

regulations (e.g. secondary loop)

BeverageFood Industry

ChemicalIndustry

Ships

Airconditioning



Lubricants for NH3 systems

The refrigeration oil which is notmiscible with NH3, is trasportedback to the compressor or is drainedoff at the evaporator

Lubricants according to DIN 51503,Group KAA (not miscible)

Conventional ammonia refrigeration system (high refrigerating capacity): Flooded Evaporation

In addition: polyalkylene glycols (PAG)Group KAB = miscible with NH3

Attention•Hightly hygroscopic: can cause problems in the lubricating gap especcially in combination with aluminium components

•Danger of wear problems due to high volumes of dissolved / evaporating NH

3



Open reciprocating pistonCompressors with oil pump /Centrifugal lubrication

LubricantsISO VG 32 - 68

Open screw compressorsOil-injected

LubricantsISO VG 46 - 68

Main viscosity grade for NH3

ISO VG 68

Viscosity grade for NH3 lubricants

Photo: GEA GRASSO

Photo: BOCK



Lubricants for ammonia

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH3

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

DIN 51503 – Group KAA:Not miscible with NH3

( )

Mineral Oils

Hydro-treated Mineral Oils

Alkylbenzene Oils

Polyalfaolefins (PAO)

Synthetic Hydrocarbons

Polyalkilene glycols (PAG) DIN 51503 – Group KAB:Miscible with NH3



Lubricants for ammonia:

Mineral Oils and Hydro-treated Mineral Oils

Mineral Oils (naphthenic)Chemical Structure:

Mainly naphthenic hydrocarbons (cycloalkanes)

Refining process:

Conventional solvent extraction and dewaxing (removal of long-chain paraffins)

Hydro-treated mineral oils (HC/Hydrocrack oils)Chemical Structure:

Iso-paraffinic hydrocarbons

Refining process:

Hydrocracking (saturation, removal of sulfur, denitration.) and isodewaxing(linear hydrocarbons � branched hydrocarbons)




Synthetic base oils

Synthetic base oils:

- Are produced by chemical synthesis

- Have a more homogenous composition than mineral oils

- Do not contain impurities based on sulfur or nitrogen

Alkylbenzenes

Polyalphaolefins (PAO)

Synthetic hydrocarbons

CH3

CH3CH3CH3CH3

e.g.: PAO




Requirements

� High thermal and chemical stability

�Good elastomer compatibility

�Good lubricity

�Excellent low-temperature flowability

�Low evaporating loss / low oil consumption



Thermal and chemical stability for NH3

lubricants

…a thermally and chemically stable oildoesn‘t look like this…!



NH3 lubricants stability with

ammonia (DIN 51538)

Test:

The oil sample is exposed to a

continuous ammonia/air gas stream

bubbling through the fluid; test

temperature: 120°C, test duration: 7d.

Catalyst: steel coupon

Analyses after the test

Analyses after the test (total base number, appearance, …)

and of the steel coupons (appearance)



Increase in total base numbers(mg KOH/g)

Naphthenic mineral oil 0,08

Synth. hydrocarbons 0,05

PAO 0,04

Conventional Mineral Oil (ISO VG 68) 0,20

Increase of “ total base number - TBN”

The higher the increase in total base number the higher is the

amount of critical reaction / aging products

NH3 lubricants stability with

ammonia (DIN 51538)



Stability with ammonia (DIN 51538):

appearance of the oil

PAOMineral Oil Conventional

Mineral Oil(ISO VG 68)

No deposits

No discoloration

Deposits

Dark coloration

Synth Hydrocarbons

No deposits

Slight discoloration



Stability with ammonia (DIN 51538):

appearance of the steel coupons

Mineral Oil

No discoloration Dark coloration

PAOSynth HydrocarbonsConventional

Mineral Oil 68)

Slight discoloration

Selected mineral oils show good results with regard to chemical stability / stability with ammonia. Synthetic oils show excellent results



Compatibility of ammonia lubricants with

elastomer / sealing materials

Moderate swelling of the sealing material (5-20% volume increase) means that oil leakage

will not occur

Mineral oils, hydro-treated mineral oils and synthetic hydrocarbons are suitable

PAO: have to be checked with CR (clorobutadiene – caoutchouk)



Sealing material:CR � Chloroprene

Neoprene®

Test conditions:Storage in oil,

7 days at 100°C

Compatibility of ammonia lubricants with

elastomer / sealing materials



Solubility of ammonia in different lubricants

amount of NH3

in “non-soluble NH3

oils”

Mineral Oils: 2,9%

Synth Hydrocarbons:

2,2%

PAO: 2,1%

1,7 2,0 2,3 2,6 2,9Ammonia - solubility [%]

@ 20°C

Synthetic hydrocarbons and PAOLess ammonia dissolved in the oil � lower dilution � lower

viscosity reduction of the oil

� better stability of the lubricating film in the compressor



Viscosity-Temperature-Behaviour - VI

68

7,4

62

9,1

68

10,5

-10

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Kin

. V

isco

sity / m

m²/s

Temperature /°C

VI V at 40°C V at 100°C

Mineral Oils 58 68 7,4

Synth Hydrocarbons 124 62 9,1

PAO 142 68 10,5

Synthetic hydrocarbons and PAOhigh Viscosity Index VI� lower viscosity

reduction at higher temperature � better wear protection in the lubricating gap



Low-temperature flowability – without

refrigerant

0

2000

4000

6000

8000

10000

12000

14000

16000

-35 -30 -25 -20 -15 -10 -5 0

kin.

Vis

cosity

[mm

²/s]

Temperature [°C]

PAO

SynthHydrocarbons

MIneral OilsHydrotreated

Mineral Oils

Synthetic hydrocarbons and PAOcompared to mineral oils / hydro-treated mineral oils, viscosity increases less at

low temperature

� better flowability at low temperature (in the evaporator)



Low temperature flowability: Pourpoint

(DIN ISO 3016) - without refrigerant

Synthetic hydrocarbons and PAOSuitable for extremely low evaporating temperatures (< -45°C)

Plate heat exchangers (small diameters) can be used, and there is no risk

of channels being blocked by the oil

Pourpoint: lower temperature at which the oil is still flowable

MInerl Oils-39°C

Synth Hydrocarbures-48°C

PAO-57°C

MIneral OilsHydrotreated

ISO VG 68-42°C

-60 -55 -50 -45 -40

PourPoint - Temperature/°C



Determination of the flowability of lubricants:

U-Tube-Test (DIN 51568) - without refrigerant

Mineral Oils

Alkylbenzenes

PAO

Synth Hydrocarbons

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0

Ve

loc

ity

/ (m

m/m

in)

T/°C

5

10

15

Synthetic hydrocarbons and PAOSignificantly better low temperature flowability than mineral oils and alkylbenzenes

Preferable for low evaporating temperatures



Lubricant loss in the compressor

Lubricant in the refrigeration system

0

2

4

6

8

10

12

Ev

ap

ora

tio

n lo

ss

[%

]200 225 250 275 300 325 350 375 400 425 450 475 500 525 550 575 600

Temperature [°C]

Mineral oil ISO VG 68

PAO

Gas-chromatographic investigations – evaporation loss:

comparison mineral oil – PAO

At high thermal stress: highly volatile

compounds (in general of low viscosity)

evaporate / get into the system

� oil loss in the compressor and

increase in viscosity

No highly volatile compounds � no oil loss in the compressor, viscosity remains

stable



0

0,1

0,2

0,3

0,4

0,5

SynthHydrocarbons

PAO, Mineral OilsHydrotreatedISO VG 68

Mineral OilsNaphthenicISO VG 68

Ev

ap

ora

tio

n lo

ss

/ %

Synthetic hydrocarbons and PAOlower evaporation loss than naphthenic mineral oils � low top-up oil

consumption, high oil lifetime

Evaporation loss:according to DIN 51581-1at 150°C / 1h / 0,8 bar

Lubricant loss in the compressor

Lubricant in the refrigeration system



NH3

lubricants for food industry

Example:

NH3 refrigeration system /

24MW / screw compressors

Changeover from Mineral Oil to

PAO

Special PAOs

No oil sludge, no deposits, no lacquers in

screw compressors (Frick & GEA Grasso)

� compressor service intervals increased by 50%

No bearing wear

Reduction of deposits in filters and oil separators

� service intervals increased by 100%

Faster oil removal when defrosting the system

�better oil management

Lower top-up oil consumption

� considerably reduced service and maintenance

costs



Conclusion

In general, standard lubricants based on naphthenic mineral oils / hydro-treated

mineral oils are suitable for application in ammonia refrigeration systems

Synthetic lubricants based on PAO or synthetic hydrocarbons offer different

benefits compared to mineral oils

Lower NH3 solubility + better viscosity-temperature-behaviour

� better lubricating properties

Lower Pourpoints and better low-temperature flowability

� for low evaporating temperatures (< -45°C)

Lower evaporation loss: reduced oil loss in the compressor

� lower oil consumption

Higher chemical and thermal stability allows to increase service intervals

for filters, oil separators and compressors

� lower maintenance and service costs

Business

Diego Curti - Fuchs Lubrificanti - VANTAGGI DEI LUBRIFICANTI SINTETICI NEI SISTEMI DI REFRIGERAZIONE OPERANTI CON AMMONIACA