For some of the larger CHP plants, August Storm GmbH & Co. KG has installed an online monitoring system and can, if necessary, react extremely quickly. One of the most important elements of condition monitoring is, and has always been, lubricant analytics. Oil samples are regularly taken from all the gas engines that it maintains and sent to the OELCHECK laboratory for testing. If, in exceptional cases, the samples are taken by the operating company itself and analysed by its oil suppliers, the experts from Spelle offer to check the results as a precaution and advise on measures to be taken based on the analysis results and engine history. Thanks to its longstanding relationship with OELCHECK, August Storm GmbH & Co. KG now has its own database with the results of over 1,500 oil analyses. These are used as reference analyses. This way, the company can offer its customers an even more comprehensive service and the best advice possible when it comes to engine oils and their service lives.
The main aim of the analyses is to ensure that the oil is changed only when it needs to be so that the engine oil is used as extensively as possible. Often a stable trend emerges from just a few analyses which means that subsequent analyses are mainly for monitoring purposes and for detecting any changes in the engine’s operating behaviour early. What is important is that the overall picture in an analysis is consistent. If, however, in the case of a particular type of oil just one single warning value shows a strong level of acidification in the lubricant and therefore prompts and early engine oil change, the engine oil’s acid neutralisation capacity will be questioned. If there is a better suited oil for the type of gas, the type of engine and the operating conditions, then a change will be recommended.
When choosing an engine oil and assessing analysis results during operating time, the following should be considered:
- With gas engines, regardless of whether they operate with natural gas, biogas or special gases, there are always high combustion final temperatures.
- In addition, gas engines for power generation work in continuous operation at full load.
- To increase operational reliability, gas engine oils have to prevent deposits, wear and corrosion.
- In the case of biogas and special gases, the quality of the gas can vary substantially and wear from hydrogen sulphide, impurities and moisture can develop.
In the case of natural gas, contamination from acidic components is lower compared to special gases such as biogas, sewage gas or landfill gas. However, over the last few years, it has become increasingly more common for proportions of various special gases to be mixed in with natural gas when delivered for operations to large CHP plants. These acidic components put considerable strain on engines and oils. If a gas engine oil cannot or can no longer compensate for and neutralise these proportions, natural gas engines, which were able to operate perfectly under clean natural gas operations, can also be heavily affected.
Although some engine manufacturers do not make it a requirement for natural gas, August Storm GmbH & Co. KG take note of the AN (Acid Number or Neutralisation Number), the BN (Base Number) and the initial pH in OELCHECK’s laboratory test results for oils from natural gas engines which have become contaminated with acidic components due to mixing with special gases.
The AN is a measure of the degree of oil acidification. The BN indicates the content of alkaline additives in the oil. It is a significant criterion for determining how many acidic components can still be neutralised and rendered harmless by the oil. Accordingly, the BN should always be higher than the AN.
If an engine oil is loaded with very strong acids, in its laboratory report OELCHECK will also point out the SAN (Strong Acid Number) if it can be measured. In gas engines which operate on biogas or very variable gas qualities, the initial pH provides additional information on the degree of acidification in the gas engine oil.
Conclusion: With the help of OELCHECK analyses, August Storm GmbH & Co. KG has been consistently able to optimise engine oil change intervals and, in doing so, reduce operating costs. By monitoring the trend in the analyses, system faults have often been spotted early so that action could be taken to prevent more serious problems from occurring. And if an engine does suffer some damage, OELCHECK analyses are an important tool for detecting and clarifying the cause.