Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
If the oil filtering arrangements in the plant are correct, so that particles are being removed, any Si reported in the lube oil is in principle harmless. Although some OEMs limit Si in used oil to 300 ppm, others explicitly state that the Si content of used oil has no limit (ref 4).
4. Lubricating oil formulation routes
Based on the above, Shell Lubricants have defined the following targets for the newly developed lubricant for gas engines burning biogas:
• Suitable for biogas from any source, including biomass, manure, sewage and landfill.
• Able to handle the contaminants that these different types of biogas may contain.
• Ash content to be compliant with latest OEM requirements. • Significantly longer oil life than internal and external benchmarks, where the internal benchmark is Shell Mysella MA.
• Highest level of engine protection at given fuel quality. • Suitable for use in engines equipped with exhaust gas catalyst.
The lubricants technology team at Shell’s Marine and Power Innovation Centre in Hamburg has been tasked with formulating the new oil. The following approach has been used to develop a series of candidate formulations:
• Retardation of oxidation and nitration processes. Slower oxidation directly contributes to longer oil life. In addition however, less BN will be required to neutralize the acids that are the result of the oxidation/nitration reactions, and more BN will be available to neutralise acidic compounds from the fuel gas. This also contributes to longer oil life.
• As high as possible BN, in order to maximize the alkalinity reserve of the oil and extend oil life on gases that contain acidic species.
• Minimise the contribution of oil to deposit formation, by limiting the ash producing additives to 0.6% and by applying a base oil and additive combination that is highly resistant to oxidation and carbonization.
For this reason the candidate oils have been formulated with severely processed Grp II base oils. This has also been recognized by one of the leading OEMs who explicitly prefers Grp II based lubricants for their engines running on biogas (ref 5).
In this paper we will compare three of the candidate formulations, each of them based on a distinctly different additive technology. Table 1 provides the main characteristics of these three formulations and of the internal benchmark Shell Mysella MA (Oil E):
5. Experience in the field
Following laboratory bench tests and in-house engine tests, the candidate oils have been tested in the field. Trial engine was a GE-Jenbacher J312 GSC21 installed on a landfill site. The installation was not equipped with fuel gas cleaning, but the fuel acidity was relatively mild. An exhaust gas cleaning catalyst was installed. Details of the installation are given in Appendix 1.
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From these characteristics, Oil D looks most attractive because of its high BN in combination with low ash. The table also shows that the BN in Oil C and Oil D is provided by additives that produce less ash than the BN additives in Oil E.
Figure 3. Test site.
5.1. Comparison of oil life of the candidate oils The results of the oil analysis results are presented in appendix 2. The two most important charts are replicated here in figure 4 and 5, and show the oxidation and BN trends of the three candidate oils.
Figure 4. Oxidation trends of three candidate oils.
The rate of oil oxidation, which is leading over the nitration in this lean burn engine, is very similar for the three candidate oils. Even after 2000 running hours the oxidation is below 10, which proves the excellent oxidative stability of the candidates.
Table 1. Main characteristics of three candidate oils compared with internal benchmark.
26 LUBE MAGAZINE NO.124 DECEMBER 2014 PART 2 in the next edition of Lube Magazine, February 2015
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