Lubricating Oils for Refrigeration Compressors

Transcription

1 Lubricating Oils for Refrigeration Compressors This specification has been revised to detail our preferred oils, and describes the background and detail for the available alternatives, particularly for ammonia and CO 2 plant. Guidance on oil brands approved by the compressor manufacturers has been added. The preferred lubricants for various combinations of refrigerant, compressor type and operating conditions are given in the tables. Design staff must note that the oil type should be considered before ordering compressors and then it shall be clearly stated on the order. It is not acceptable to write an oil type on a compressor order unless the compressor manufacturer has previously agreed to it or has expressly agreed to it for that application. Oils of the same basic type and viscosity can usually be mixed but this is best avoided, even if the base stock is the same the additive package will be different between different manufacturers. CPI CP can be used to replace Castrol 2293 and the alkylbenzene CPI oils can be mixed with Esso Zerice S oils. Never top-up a system with a different oil type (base stock) unless agreed with the technical department. It is very important to specify Esso Zerice S type oil for the specified applications listed because Esso sell their mineral oil called Zerice, which is similar to Shell Clavus mineral oil. Zerice S type oil can be recognised because it is a clear, colourless liquid and does not have an oily appearance. For certain retrofit applications e.g. Isceon 49, improved solubility and oil return can be achieved with a single compressor oil change. The polyolester lubricant is soluble in mineral or alkylbenzene remaining in the system. Staff must note the need to keep POE and PG oils free from moisture, these oils shall be bought in containers that can be used up one a day or so. In addition these oils should not be charged to the compressor until we are ready to charge refrigerant. Design Managers must ensure that the oil supplier and product selected for the system is clearly stated in the notes section of the Diagram of Connections. For application outside the specified temperature ranges or with alternative refrigerants which are not listed please refer to the technical department. October 2002 Page 1 of 5

2 mmonia Screw Compressor pplications Mineral Oils We no longer use mineral oils on new ammonia plant due to its generally poorer characteristics including stability, pour point, viscosity index and life. There is evidence that the changing sources of base stock oils has resulted in a deterioration in the characteristics of mineral oils for ammonia refrigeration applications, including the formation of black sludge in the compressor. PO Oils We have used Castrol 2293 (ISO 32 grade) PO (polyalfaolefin) with a lot of success. It is a very high quality synthetic oil with good stability, high viscosity index and low pour point. The direct CPI equivalent is CP Castrol 2294 is the ISO 68 grade PO oil we have used on some Sabroe machines as Sabroe never accepted the lower viscosity oil. good alternative to the above is CP which is a ISO 32 grade PO with seal additive to prevent seal shrinkage. CP is the ISO 68 grade alternative including the seal additive. We have used alternative oils in the last few years to avoid the problems related to O ring shrinkage which has caused leaks and necessitated expensive repairs due to this known problem (high aniline point of the oil which causes O ring shrinkage) with PO oil. PO lkylbenzene Mix gain this is a high quality synthetic oil and can be considered to have good life expectancy and viscosity characteristics. The pour point tends to be slightly higher than the equivalent pure PO oils but it has the advantage that the alkylbenzene in the mix counteracts the O ring shrinking effect of the PO. Some compressor manufacturers have specified a PO & B mix for some time. We understand that the Sabroe branded oil currently marketed for use on ammonia applications is this type of oil. It is also one of only a few oils Grasso recommend for use with ammonia. We have had some good success with this oil and have no particular reservations over using it in any ammonia application Hydro-treated Mineral Oils Hydro cracking is a more intensive method of producing mineral oil, we can consider these oils as highly refined mineral oils with improved characteristics. Users changing from mineral oil to hydro-treated mineral oils have reported good results. We have used both Reflo 68 and CP with good results on chill plant. The pour point of these oils is around -40 C so they are best avoided for plant where the evaporating temperature is below -35 C and under no circumstances should they be used in LPR cold store or blast freezer systems. Howden ll of the above oils except some of the PO/B mixes are approved by Howden. However, Howden compressors have given us most O ring and shaft seal leakage problems. We must ensure that the oil type is agreed with Howden before compressors are ordered as they sometimes change the O ring and shaft seal specification dependant on the oil type, in addition they don t always pay attention when we write the oil type on our compressor order! October 2002 Page 2 of 5

3 Grasso Unfortunately Grasso no longer accept the use of oils on ammonia plant screw compressors other than Reflo 68, Mobil SHC 326 and CPI CP Special acceptance for particular oils in particular applications can be sought before ordering the compressor but use of Grasso machines with pure PO, if accepted at all, will require special (HNBR) O rings with additional cost and extended delivery. Sabroe Sabroe no longer offer their compressor warranty on new screw compressors on ammonia applications with oils other than their own unless specifically agreed at time of order. CO 2 pplications This section has been included for general guidance, particularly for sales staff. ll oils selections for CO 2 applications will be referred to the technical department, to ensure best use of recent experience, until further notice. Compressor manufactures including Grasso and Howden have good experience of using PO oil in CO 2 applications, the latter for many years in process gas compression applications. PO oil is not miscible with CO 2 and will float on top of the refrigerant so the oil separation system needs special consideration (to ensure very high efficiency) as does the means of separating oil carried over from the compressor pack. Our preferred oil is CPIs CP as it is a PO but it will also resist O ring shrinkage. Grasso have approved this oil for use with their screw compressors on CO 2. Use of CP also means that we can put the same oil in the CO 2 compressors and ammonia compressors on a cascade plant. It would obviously be an advantage to use a miscible oil with CO 2 and we have some experience with POE which satisfies this requirement, but our tests were not conclusive. Unfortunately there is little industry experience of this refrigerant and oil combination so we will not use it in the near future except in a development application. October 2002 Page 3 of 5

4 Refrigerant Compressor Type Evaporating Pressure ( C) Oil Supplier Oil Brand / Product Oil Type / Viscosity R22 R403a (Isceon 69S) R403b (Isceon 69L) R413 (Isceon 49) Open reciprocating (1) >+10 C (and all Grasso recips CPI CP E* lkyl-benzene/100 regardless of evap pressure) Esso Zerice S100 lkyl-benzene/100 <+10 C (not Grasso recips) CPI CP E* lkyl-benzene/68 Esso Zerice S68 lkyl-benzene/68 Semi-hermetic recips (1) ll conditions CPI CP E* lkyl-benzene/46 Esso Zerice S46 lkyl-benzene/46 Screws (1) ll conditions CPI CP E* lkyl-benzene/100 Esso Zerice S100 lkyl-benzene/100 R134a Recips inc Grasso not or Bitzer Castrol SW 68* Polyolester / 68 Mobil EL 68 Polyolester / 68 Bitzer recips Castrol SW32 Polyolester / 32 Bitzer BSE32 Polyolester / 32 recips Mobil rtic 22 cc Polyolester / 32 ICI Emkarate RL32CF Polyolester / 32 ll screws ll conditions Consult Technical Department R404 R407a R407b R507 Recips inc Grasso not or Bitzer >-40 C <0 C >-15 C <+15 C Castrol SW 68* Polyolester / 68 Mobil EL 68 (2) Polyolester / 68 Castrol SW 100* Polyolester / 100 Mobil EL 100 (2) Polyolester / 100 Bitzer recips ll Castrol SW32 Polyolester / 32 Bitzer BSE32 Polyolester / 32 ll Mobil rtic 22 cc Polyolester / 22 ICI Emkarate RL 32CF Polyolester / 32 Bitzer screws ll Bitzer BSE 170 Polyolester / 170 Other screws ll conditions Consult Technical Department (1) Consult technical department for new plant or check approval of oil brand/product with compressor manufacturer (2) Not Grasso compressors October 2002 Page 4 of 5

5 Refrigerant Compressor Type Evaporating Pressure ( C) Oil Supplier Oil Brand / Product Oil Type / Viscosity R717 Reciprocating > -30 C CPI CP * Hydro-treated mineral / 68 Petro Canada Reflo 68 Hydro-treated mineral / 68 Esso Zerice 68 Mineral / 68 <-30 C Consult Technical Department Howden Screws ll except below CPI CP * PO with seal Castrol 2294 PO / 68 Mobil SHC224 PO / 32 CPI CP * PO with seal additive / 32 Castrol 2293 PO / 32 Mobil SHC224 PO / 32 Grasso Screws ll except below CPI CP * PO with seal Mobil SHC 326 PO / B mix / 68 Petro Canada Reflo 68 Hydrotreated Mineral 68 CPI CP * PO with seal Mobil SHC 326 PO / B mix / 68 Bitzer ll except below CPI CP * PO with seal Castrol 2294 PO / 68 Mobil SHC224 PO / 32 CPI CP * PO with seal additive / 32 Castrol 2293 PO / 32 Mobil SHC224 PO / 32 Other Screws ll Consult Technical Department R744 ll Compressors ll conditions Consult Technical Department PO *Preferred choice Date Issue Originator DTF DTF DTF E MG October 2002 Page 5 of 5