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 Conditioning
Under 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)
Beverage
Food Industry
Chemical
Industry
Ships
Air
conditioning

Lubricants for NH3 systems
The refrigeration oil which is not
miscible with NH3, is trasported
back to the compressor or is drained
off 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 NH3

Open reciprocating piston
Compressors with oil pump /
Centrifugal lubrication
Lubricants
ISO VG 32 - 68
Open screw compressors
Oil-injected
Lubricants
ISO 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
CH3 CH3CH3CH3
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 oil
doesn‘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 Hydrocarbons
Conventional
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 2,9
Ammonia - solubility [%]
@ 20°C
Synthetic hydrocarbons and PAO
Less 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.Viscosity/mm²/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
high 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.Viscosity[mm²/s]
Temperature [°C]
PAO
Synth
Hydrocarbons
MIneral Oils
Hydrotreated
Mineral Oils
compared 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
Suitable 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 Oils
Hydrotreated
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
Velocity/(mm/min)
T/°C
5
10
15
Significantly 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
Evaporationloss[%] 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
Synth
Hydrocarbons
PAO, Mineral Oils
Hydrotreated
ISO VG 68
Mineral Oils
Naphthenic
ISO VG 68
Evaporationloss/%
lower evaporation loss than naphthenic mineral oils low top-up oil
consumption, high oil lifetime
Evaporation loss:
according to DIN 51581-1
at 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

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

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