screw compressor

TECHNICAL INFORMATION SCREW COMPRESSORS GRASSO SC Types C ... XF LUBRICATING OILS FOR SCREW COMPRESSORS

Refrigeration / Grasso _165520_ti_sc_gbr_1_.doc 1 03.08.2011

1 LUBRICATING OILS FOR SCREW COMPRESSORS

1.1 Lubricating oil selection list Special refrigeration oils must be used for Grasso screw compressors. The selection of the oils de-pends on the chemical properties of the oil, the re-frigerants, the operating conditions of the plant and the required oil viscosity during startup and run. On request with Grasso also different than in the table indicated oils can be used. For refrigeration com-

pressors special refrigeration oils have to be used. The selection depends on the refrigerant, viscosity (at least 7 cSt for oil temperature before entering the compressor), evaporating temperature (pour point) and requirement made of the oil separation behav-iour (flash point, viscosity).

Basis of the lubricating oils and used abbreviations:

M M * AB PAO E PAG

Mineral oil Mineral oil with special treatment (hydrocracked oil) Alkylbenzene Polyalphaolefin Polyolester Polyalkylglycol

Table 1: Lubricating oils for R717 (Ammonia)

(recommended especially if minimum oil carry-over from the oil separator is important)

Manufacturer Type of oil Basis Viscosity at 40°C in cSt

Flash point in °C

Pour point in °C Remarks

CPI CP 1009-68 M* 68 226 -40

Hydrotreated for R717 only

CP 1008-68 M* 64.9 240 -39

Klüber Lubrication

Klüber Summit RHT 68 M* 62 230 -35

Shell Shell Clavus S 681) M* 68 232 -39

Petro-Canada Reflo 68A M* 58 236 -42

TEXACO Capella Premium M*/PAO 67 262 -42

Paramo Mogul Komprimo ONC 68 M* 68 230 -33

TOTAL Lunaria NH 68 M* 68 230 -36

1) Product no longer available.


2 _165520_ti_sc_gbr_1_.doc Refrigeration / Grasso 03.08.2011

Table 2: Lubricating oils for DX Chiller with R717 (Ammonia)


Flash point in °C


CPI CP 412-100 PAG 98 226 -40

Fuchs Fuchs Reniso PG 68 PAG 62 230 -35

Shell Shell Clavus SG 68 PAG 73.5 >250 -48

Mobil Mobil Zerice S32 AB 32 154 -33 Please contact Grasso



Table 3: Lubricating oils for R717 (Ammonia) and R22


Flash point in °C


Castrol Icematic 299 M 56 180 -34 Icematic 2294 PAO 69 233 -60 for R717 only

CPI CP-4600-46 PAO 46 268 -51 for R717 only

MOBIL

Zerice S32 AB 32 154 -33

Zerice S68 AB 68 174 -27 Gargoyle Arctic SHC 226E PAO 68 266 -45 for R717 only

Gargoyle Arctic SHC NH 68 AB/PAO 64 211 -54

Gargoyle Arctic 300 M 68 200 -42

Gargoyle Arctic C Heavy M 46 195 -42

Fuchs

Reniso S68 AB 68 190 -33 Reniso Synth 68 PAO 68 260 -57 for R717 only

Reniso KS 46 M 46 195 -42

Reniso KC 68 M 68 200 -39

Shell

Shell Clavus 46 1) M 44 195 -39

Shell Clavus 681) M 65 205 -36 Shell Clavus G461) M 44 195 -39

for R22 only Shell Clavus G681) M 65 205 -36

Shell Refrigeration Oil S4 FR-V 46 AB 46 180 -42

for R717 only Shell Refrigeration Oil S4 FR-V 68 AB 68 190 -39

Shell Refrigeration Oil S2 FR-A 46 M 46 218 -39

for R22 only Shell Refrigeration Oil S2 FR-A 68 M 68 232 -39

TOTAL

Lunaria NH 46 M 46 226 -36 for R717 only

Lunaria SH 46 PAO 44 252 -51 for R717 only

Lunaria FR 68 M 68 175 -34 for R22 only

Petro-Canada Reflo Synthetic 68A AB/PAO 62 245 -54 for R717 only




Table 4: Lubricating oils for R134a; R404A; R407C; R410A; R507


Flash point in °C


Castrol Icematic SW 68

E 68 250 -39

Icematic SW 220 220 290 -26

CPI

Solest 68

E

64 266 -43

Solest 120 125 262 -27

Solest 220 216 271 -27

Fuchs

Reniso Triton SE 55

E

53 270 -51

Reniso Triton SEZ 80 80 275 -39

Reniso Triton SEZ 100 91 288 -39

Reniso Triton SE 170 170 260 -24 Reniso PAG 220 PAG 220 240 -38 for R134a only

Shell

Shell ClavusR681)

E

64 250 -54

Shell Clavus R 1001) 93 280 -45 Shell Refrigeration Oil S4 FR-F 68 66 230 -42

Shell Refrigeration Oil S4 FR-F 100 94 230 -42

MOBIL EAL Arctic 68

E 68 230 -36

EAL Arctic 100 105 250 -30

TOTAL Planetelf ACD 100FY

E 100 270 -30

Planetelf ACD 150FY 150 272 -36


Hint!

When using high-viscosity oils with high refrigerant solubility after initial fill of the plant a suffi-cient mixture from refrigerant and oil has to be provided before start-up the screw compressor.



Table 5: Lubricating oils for natural gas and hydrocarbon compounds


Flash point in °C

Pour point in °C

Remarks

BP Energol RC-R 68 M 67 234 -30 for natural gas compression

CPI

CP-1515-68

PAG

65 224 For heavy hydrocarbons, where strong dilution or condensation will occur CP-1515-100 103 260

CP-1516-68 62 229 For propane refrigerant plants or volatile hydrocarbons, where the danger of stronger dilution or con-densation does not exist

CP-1516-100 92 260 CP-1516-150 153 260 -34

CP-4601-68 PAO

60 271 For high temperature application and for feed gas control compres-sors for gas turbines CP-4601-100 106 271

CP-9001-68 M

69 241 for feed gas control compressors for gas turbines CP-9001-100 108 260

CP-1507-68 PAG

62 231 For heavy hydrocarbons, for hy-drocarbon cooling applications in range of high pressure/ low tem-perature

CP-1507-100 89 260

MOBIL Glygoyle 11

PAG 85 226 -45

For natural gas and propane Glygoyle 22 177 229 -41

Shell

Comptella Oil S68 M 68 240 For natural gas

Madrela Oil T1) PAG 185 260 -30 For natural gas and propane

Shell Gas Com-pressor Oil S4 PV PAG 190 262 -30 For natural gas and propane

TOTAL Primera LPG 150 PAG 142 280 -48 For natural gas, propane and vola-tile hydrocarbons

Klüber Summit Summit NGSH-100 PAO/ E 140 250 -46

For natural gas, for feed gas con-trol compressors for gas turbines and hydrocarbons




Table 6: Lubricating oils for CO2 application


Flash point in °C


CPI

CP-4600-68

PAO

68 immiscible

CP-4624-46F 46

CP-4624-68F 68

Fuchs

Reniso C 85 E E* 278 complete misci-ble

Reniso C 130 E E* 136 -27

Reniso C 170 E E* 170 -30 attend to the miscibility gap

Shell Clavus SG 68 PAG 73.5 >250 -48 partially miscible only

* During application of Polyolester: t oil inlet ≤ t discharge - 4K

Hint!

When using high-viscosity oils with high refrigerant solubility after initial fill of the plant a suffi-cient mixture from refrigerant and oil has to be provided before start-up the screw compressor.



Table 7: Use of O-ring elastomers in screw compressors depends on refrigerant and lubricant:

Refrigerant Oil

M M* M*/PAO AB E PAO AB/PAO PAG

R717 (ammonia) CR1) CR1) HNBR CR - HNBR CR HNBR

R22 CR - - CR CR - - -

R134a, R404A, R407C, R410A, R507, R23 - - - - HNBR - - -

R290 (propane), R1270 (propylene) - - - - - HNBR - HNBR

R744 (Carbon dioxide CO2) - - - - HNBR HNBR - HNBR

Abbreviations used for the elastomers:

CR Chloroprene (Neoprene caoutchouc)

HNBR Hydrogenated nitrile butadiene caoutchouc 1)shaft seals only with O-rings of HNBR-composition

Hint!

If natural gas and hydrocarbon compounds are used as compression me-dium (Table 5; page 5), please contact Grasso for O-ring elastomer type.

Hint!

• The pour point describes the cold fluidity of an oil and represents a non-guaranteed guide value for the minimum evaporating temperature. [The pour point is defined as the temper-ature at which the fluidity of an oil decreases to an extent that it does not leave a jar within 5 sec under certain conditions.]

• Compressors are equipped with suitable elastomers at the sealing point, which are se-lected dependent on the refrigerant and lubricant. (Table 7; page 7)

• When selecting the type of oil, the compatibility of the sealant material used in the com-pressor for o-rings (elastomer quality) must be taken into consideration in addition to the refrigerant. (Table 7; page 7)

• Not all the listed oil types can be used for an existing compressor. It is absolutely neces-sary to assign the oil grade depending on the elastomer used, even if the refrigerant is the same.

• Oil grades are not always compatible with each other (cannot be mixed).

• Changing from one oil type to another can lead to disruptions in the operation of the com-pressor and to leakages at the sealing points. The compressor manufacturer should al-ways be contacted before changing the oil type.



Caution!

• The lubricant viscosity range downstream of the compressor given in data sheet must always be observed. At the same time, it must be noted that refrigerant/oil combi-nations are possible in which, dependent on the pressure and temperature in the oil separator of the package, the refrigerant dissolves in the oil. This leads to a reduction of the viscosity of the pure oil and to the formation of foam when the solution equilibri-um is altered due to pressure reduction or temperature increase. In this case, the oil must be cooled by a minimum temperature difference, which is calculated in the com-pressor selection programme for the given operating conditions. The compressor may only be operated if the oil entry temperature is complied with in accordance with the compressor selection programme!

• The oil separation behaviour of the types of oil given in the Table can vary greatly (e.g. influence of oil vapour pressure, oil viscosity, solubility, discharge temperature).

TECHNICAL INFORMATION SCREW COMPRESSORS GRASSO SC Types C ... XF LUBRICATING OILS FOR SCREW COMPRESSORS; HINTS FOR SELECTION OF REFRIGERATION OIL


1.2 HINTS FOR SELECTION OF REFRIGERATION OIL The properties of the refrigeration oil have an influence on the operation of refrigerating plants with oil-flooded screw compressors, as it cannot be excluded that residues of the refrigeration oil get into the refrigerant circuit despite the use of highly effective oil separators. For this reason, when selecting the oil the following should also be considered

• a sufficient lubricity of the oil at the bearing points of the screw compressor (minimum oil viscosity with con-sideration of the solubility of refrigerants in oil depending on both the pressure and temperature),

• the vapour pressure of the oil for a proper separation behaviour in the oil separator,

• a sufficient fluidity of the oil at both the evaporating and suction temperature,

• the requirements upon the miscibility of the liquid phases of the refrigerant and the oil (miscibility gap).

The refrigerant used, the operation conditions and the specific plant design all determine the required characteris-tics of the refrigeration oil.

At present, five different base oil brands are used:

1. Mineral oils for ammonia and R22

2. Polyalphaolefins for ammonia and CO2 (R744)

3. Alkyl benzene for ammonia and R22

4. Polyglycol (PAG-oil) for ammonia, CO2 and R134a

5. Ester oil for R 404A, R 134a, R 507 and CO2 as well as other refrigerant blends such as R410A and R407C

Besides the pure base oil components other blends of mineral oil and alkyl benzene or of polyalphaolefin and alkyl benzene can also be used.

The characteristics of the refrigerants regarding the oils mentioned are very different.

Thereby 2 fundamental requirements are needed from the refrigerant and refrigeration oil:

a) Minimum oil viscosity of 7 cSt, maximum 70cSt, at the compressor inlet with consideration for the refriger-ant solubility in oil

and

b) Miscibility of both liquid phases of a certain portion of the oil (approx. 1 to 2 %) and the refrigerant.

Besides the requirement of a sufficient viscosity of the lubricating oil, the discharge temperatures in the compres-sor must be high enough to enable a subcooling of the refrigerant-laden oil by at least 10 K in order to prevent foaming in the compressor in case of decrease in pressure and/or increase in temperature, before the oil gets to the bearing points. The basic requirement b) is not met by mineral oil, alkyl benzene and polyalphaolefin in con-nection with ammonia, as there exists a miscibility gap of 100 %, and neither a solubility of the refrigerant vapour in the oil nor a miscibility of liquid phases is given. Nevertheless these oils are preferably used in NH3-plants. Oil fine separation stages prevent greater portions of the oil from getting into the refrigerant circuit.

The base oil versions mentioned will bring about differing oil carry-over rates as the flash points of the oils cited differ greatly from each other (lowest flash point of alkyl benzene at approx. 160 °C, highest flash point of polyal-phaolefin considerably above 200 °C).

Although the fluidity of the oil is characterized by the pour point indicated by the oil manufacturers, the base oil brands mentioned above feature different VT-characteristics so that at the same initial viscosity of say 68 cSt, there may arise differences in viscosity at low temperatures in the evaporator in the range of approx. 1500 and 20000 cSt at -20°C.



With relation to oils, the refrigerants feature the following properties:

• Ammonia

With the exception of PAG-oil, ammonia is not soluble with other lubricants. However, mechanical intermixing is very intensive so that the oil always carries along ammonia. Due to the low portion of the ammonia the lu-bricity of the oil will not be changed. The miscibility between the liquid phases of oil and refrigerant is not giv-en. For this reason, an efficient oil separation is required.

• HFC (e.g. R134a, R404A, R507)

HFC's possess no chlorine and are not limited in their application. Ester oils are used for these refrigerants. The higher solubility of these refrigerants in ester oil has to be considered when selecting an oil as the initial viscosity of the oil might drastically change due to the refrigerant dissolved in the oil. However, the fluidity of the oil in the evaporator is given due to proper miscibility over a wide range.

The most important properties of the main oil groups are described in the following:

1. Mineral oil

Naphthenic base mineral oils are most suitable for refrigeration systems, but paraffinic base oils are also used. Due to special treatment (dewaxing) paraffinic base oils have more or less the same properties as naphthenic base oils. Mineral oils are characterized by a relatively low miscibility with HCFC’s (e. g. R22) at low temperatures. Mineral oils feature a relatively high viscosity index and a low vapour pressure (higher flash point) whereby oil carry-over is positively affected.

2. Alkylbenzene (also known as alkyl benzole)

Alkyl benzenes represent synthetic oils produced from natural gas. They are characterized by high miscibility with HCFC’s (e.g. R22) even at lower evaporating temperatures. Alkyl benzenes feature higher thermal stabil-ity than mineral oils (use of ammonia in piston compressors). Due to the lower flash point, however, they have a tendency to heavy foaming in the oil separator and to higher oil carry-over. After changing from mineral oil to alkyl benzene it should be recognised that alkyl benzenes have a considerable cleaning effect causing in its turn the filters to clog faster than usual in the time immediately after the oil change.

3. Polyalphaolefins

Polyalphaolefins represent synthetic oils of high chemical and thermal stability. Therefore, they are preferably used in compressors operating at high discharge temperatures e.g. in heat pumps. Polyalphaolefins are also employed in ammonia systems. The very low pour point permits very low evaporating temperatures. The high flash point of the polyalphaolefins leads to smaller oil carry-over rate.

Attention: The high aniline point of polyalphaolefins causes a relatively high shrinkage of O-rings with CR material whereby leakages may occur even at static seals, when mineral oils or alkyl ben-zenes are replaced by polyalphaolefins.

Shrinkage can be avoided is synthetic oil blends comprising polyalphaolefin and alkyl benzene are used. In case of use of pure PAO-oil the Grasso compressors will be equipped with HNBR-O-rings, which do not shrink when in contact with the oil.

4. Ester oils

In contrast to mineral oil, alkyl benzene and polyalphaolefin ester oils are soluble in the new non-chlorinated HFC’s (R 134a, R 404A, R 507 etc.). Therefore, the ester oils are the only lubricants at present which may be used for the HFC’s. Ester oils possess a higher flash point whereby the oil vapour portion from the oil separa-tor and hence the oil carry-over rate are favorably affected. Ester oils are hygroscopic. They absorb water when getting in contact with the atmosphere. For this reason, ester oils have to be stored in closed tanks. Pri-or to oil charging, the compressor has to be thoroughly evacuated.



5. Polyglycol oil

Polyglycol oils are ammonia soluble and very hygroscopic. That’s why the same requirements have to be im-posed as when handling ester oil. When selecting the oil take into consideration the reduction of viscosity caused by the refrigerant dissolved in the oil. Check the fluidity of the oil in the evaporator with consideration of the miscibility between the lubricating oil and refrigerant at the corresponding evaporating temperatures.

PARAMETERS USED FOR OILS:

Specific density

The difference in specific density between the refrigerant liquid and the oil may be of interest for oil return. In this case it should be considered that alkyl benzene has a lower specific density than mineral oil and polygly-col has a higher specific density than mineral oil. The method for specific density measurement is described in DIN 51757.

Viscosity

According to ISO standard 3448 lubricants are classified in viscosity grades indicated as ISO VG numbers. The ISO-no. is a nominal guide value only, i. e. the actual viscosity may vary in certain ranges (DIN 51562). The viscosity indicated refers to 40 °C and to 100 °C.

Viscosity index

The viscosity index gives the relationship between the change in viscosity depending on the temperature (ISO 2909). A high viscosity index means smaller changes in viscosity at temperature changes as compared to a low viscosity index.

Flash point

The flash point indicates at which temperature the vapours escaping from a heated cup may be ignited over a flame. The method of measurement is described in ISO 2592. Oils with high flash point have a low oil vapour pressure. This will enhance the possibilities of oil separation from a compressed gas in the oil separator and reduce the oil carry-over rate from the compressor into the plant.

Pourpoint

The pour point is the temperature at which the fluidity of an oil decreases to an extent that under certain con-ditions it will no more leave a jar within 5 sec. According to ISO 3016, the pour point temperature is 3 % lower than the measured temperature. The pour point is interesting for working oil/refrigerant combinations which are not soluble with each other. Oils having a low pour point can be returned to the suction side more easily than oils having a high pour point. The practice, however, shows that oils may be used even at evaporating temperatures lower than the pour point without any operating problems.

Floc point

The floc point indicates the temperature at which liquid R12 with the addition of 10 % oil will show turbidity by wax particles precipitating from the oil when chilled (method of measurement according to DIN 51351). The floc point is of interest when oil and refrigerant can be mixed. The floc point indicates that an oil contains but a few wax particles and that plants employing HCFC (e. g. R22) can be operated at low evaporating tempera-tures. When wax precipitation from the oil takes place, problems are to be expected at the expansion valve or at the regulating valves. For ester oils a critical solution temperature is given measured with a mixture of 10 % oil and 90 % of R134a. The critical solution temperature is the temperature at which the oil completely precipi-tates from the refrigerant (non-standardized value).

Aniline point

The aniline point indicates the temperature at which the oil concerned shows a homogenous mixture with pure aniline. The aniline point is the measurement of the quantity of unsaturated carbon which can be found in the oil. It is an indication of the compatibility of different sealing materials coming into contact with the oil (method of measurement according to ISO 3977). Most lubricating oils possess a low aniline point. Neoprene and chlo-roprene will swell. For this reason, O-rings have to be replaced after disassembling. Polyalphaolefin has a high aniline point causing neoprene to shrink. (use of HNBR required).



Neutralization number

The neutralization number gives the acid content of an oil and is determined by titration with potassium hy-droxide solution (KOH). The value is given in mg of KOH per g of oil (method of measurement according to DIN 51558). Fresh oils should have a low neutralization number.

Hints for oil change

Prior to changing the oil brand or the manufacturer of an oil, consult the compressor manufacturer for advice to prevent problems in plant operation. In case of incompatible oil brands precipitations from the oil can occur which might lead to problems within the plant (oil filter, lubrication of bearings, oil return not guaranteed). If, however, it should be necessary to employ another type of oil, it is of vital importance to remove all the oil from the plant and to thoroughly clean both the compressor and oil separator (if possible, perform additional scavenging).

Oil selection table

All oils permitted for the Grasso-screw compressors are given in the oil selection table. Depending on the specific conditions of a plant consider the above technical features when selecting an oil.

TABLE: Refrigerant – oil compatibility

Ammonia (NH3)

R22 R134a R404A R407C R410A R507 CO2

Mineral oil (M) x x NO NO NO NO NO NO

Polyalphaolefins (PAO) * NO NO NO NO NO NO *

Alkylbenzene (AB) x x NO NO NO NO NO NO

polyglycol (PAG) * NO NO 1) NO NO NO NO *

Ester oil NO x * * * * * *

M + AB x x NO NO NO NO NO NO

PAO + AB x NO NO NO NO NO NO NO

x = suitable, use of CR-O-rings

* = suitable, use of HNBR O-rings

NO = not suitable

NO 1) = not suitable except refer Table 4 page 4.

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