Product category:
Lubricants
News Release from: Kluber Lubrication GB | Subject: Synthetic air compressor oil formulations
Edited by the Engineeringtalk Editorial
Team on 05 July 2002
Lubrication provides significant energy
savings
Advanced synthetic air compressor oil formulations can outperform commonly used mineral-oil-based compressor fluids not only in terms of service life but also in energy saving.
Approximately 5TWh of electrical energy is literally "blown into the air" by air compressing units in Germany each year This inefficient use of energy results in costs of more than Eur 500 million per year
This article was originally published on Engineeringtalk on 10 Apr 2008 at 8.00am (UK)
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In this article we try to prove that a remarkable reduction of energy consumption can be achieved by the use of well formulated air compressor oils.
An advanced synthetic air compressor oil formulation is able to outperform commonly used mineral-oil-based compressor fluids not only in terms of long service life but also in energy saving.
As we are facing rising energy consumption, increasing costs and a limitation of resources, it makes sense to have a closer look at air compression, which is one of the most important means of energy transport used in industry and trade.
According to a study by the US Department of Energy, approximately 8.6 % of overall industrial energy consumption is to be attributed to air compression.
Taking as a basis the 200TWh consumed by German industry each year, the share of air compression amounts to 17TWh.
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If we assume a reduction potential of 30%, which is not unrealistic, we find that at present approximately 5TWh worth Eur 500 million is blown into the air for nothing.
The extent to which energy costs dominate operating costs is shown using the example of a screw-type compressor.
Energy costs consume a massive 72-77%, capital costs 18-23% and maintenance costs 3-5%, leaving a nominal figure of less than 1% for compressor oils.
(The compressor is assumed to run 4kh per year, with electricity costs of Eur 0.05/kWh, 5% interest on capital and a 5-year depreciation period).
In compressors, energy consumption is the factor with the biggest reduction potential, and consequently most efforts to cut down on costs are focused on this aspect.
Besides much-discussed measures such as the use of optimised control systems, the installation of energy regeneration systems and the prevention of line leakage, there is another simple and straightforward way of effectively reducing a compressor's demand for energy: the use of special synthetic compressor oils.
The tasks to be fulfilled by compressor oils are manifold.
They are expected to protect against wear, reduce friction, dissipate heat, seal parts, protect against corrosion, reduce noise, separate off air and water etc.
As synthetic compressor oils have a better viscosity temperature behaviour, better low-temperature characteristics, a lower tendency to residue formation, lower evaporation rates and lower friction coefficients than mineral oils, they can meet these requirements considerably better.
A synthetic compressor oil specifically formulated for its job should reduce friction in the compressor and improve the sealing of gaps, hence increasing the compressor's volumetric efficiency as well as reducing its energy consumption.
The pertinent literature and several publications by various companies speak of an energy reduction potential of 2 to 7%.
A differentiation is made between piston and screw-type compressors: since there is a higher percentage of frictional forces in piston compressors, their energy reduction potential is generally regarded as higher than that of screw-type compressors.
There is a lack of measurement results backing these estimated figures, which is why a test was made on an operating compressor, which is described in the following.
This test was made with the intention to compare a high-quality synthetic compressor fluid with a mineral oil based compressor oil in long-term use in a screw-type compressor.
The compressor chosen for this test was a commonly used air-cooled screw-type compressor with a belt drive connecting it to an electric motor.
When operating at full load, the motor outputs 125kW at a speed of 1500rev/min.
The maximum attainable volume flow is 1118Nmü/h.
The compressor is connected to the compressed air system and is subject to normal demand fluctuations.
Only one compressor was used for the test so as to prevent the result from being influenced by unit-specific differences.
The two compressor oils used are commonly found in the market and widely used.
Following the test setup and the data of eleven test points were recorded and processed in a PC.
These data comprised: pressure difference at the intake filter; intake temperature; electric power consumption of the compressor; compressor shaft speed; temperature of compressed air before oil separator; pressure after compressor; pressure difference at oil separator; oil injection temperature; temperature of air fed into compressed-air system; system pressure; and volume flow.
Ambient conditions in the compressor room such as ambient temperature, air pressure and relative air humidity were measured by mechanical high-precision instruments (barometer, horsehair hygrometer and mercury thermometer) and recorded at the beginning of each measurement.
In a first step, the compressor system was thoroughly inspected and then cleaned, which is a simple task if a suitable cleaning fluid is used.
The cleaning fluid is added to the compressor oil with a concentration of 10%.
It has to remain in the compressor for approximately 60 to 100 operating hours before the oil is exchanged.
During this time, the compressor can be operated normally.
Then the oil-fluid mixture was removed and air filter, oil filter and oil separation cartridges were replaced.
In this state the compressor was filled with the first test medium, i.e the mineral compressor oil.
A first test cycle was started, and after 5000 operating hours the system was once again cleaned as described above, filters replaced and the compressor subsequently filled with a synthetic compressor oil.
The viscosity of both test oils was as prescribed by the compressor manufacturer.
For both oils, data were recorded after 300, 600, 1000, 2000, 4000 and 5000 operating hours, which took one year each.
For each measurement, data were recorded on three successive days and averaged in order to even out disproportionate fluctuations.
Simultaneous with the recording of data, oil samples were taken and their condition analysed.
The infra-red spectrum was determined as well as the oil's viscosity at 40C, its neutralisation number, water content and the nature and percentage of foreign matter contained.
The most important parameter determined was power consumption per compressed standard volume (kWh/Nmü).
With this result, the power consumption attained with different compressor oils can be compared directly.
Right from the start of the test, the synthetic compressor oil showed a better specific performance than the mineral-oil-based product.
This difference in performance became gradually less pronounced until 2200 operating hours.
After that point, the advantages of the synthetic product became more and more apparent.
The standard volume flows developed in a similar pattern.
Actually, between 1200 and 2200 operating hours, volume flow figures attained by the mineral oil were even slightly better than those of the synthetic oil.
After that, however, the volume flow was up to 5% higher with the synthetic product than with the mineral oil.
Why power consumption values of both oils are so close together between 1000 and 2000 operating hours has not been found out.
The reason may lie with different additive reaction speeds or differences in the oils' shear behaviour.
An energy consumption that is on average 3% higher means for a driving power of 125kW that 18,750kWh is additionally required over 5000 operating hours.
Looking at it the other way round, at an electricity cost of Eur 0.05/kWh, savings of around Eur 1000 are attained through the use of a synthetic compressor oil.
The mineral oil's shorter service life, which incurs additional costs due to the necessity of an oil change after 3000 operating hours at maximum, has not even been taken into account in this consideration: used oil analyses have shown that the mineral oil bears clear signs of ageing after 2000 operating hours.
The synthetic compressor oil was inspected after 5000 operating hours.
There were also certain signs of ageing, however the oil was still perfectly fit for further use.
While, when looking simply at the purchasing prices, synthetic compressor oils are three to six times more expensive than mineral oils, the situation looks different when considering overall costs.
This is illustrated by another example from compressor operation in practice.
A screw-type compressor with oil injection in a standard factory environment has a power input of 125kW and works for 6.5kh per annum.
The annual energy requirement would therefore stand at 812,500kWh.
However by using the synthetic lubricant there is an initial energy saving of approximately 5% which at Eur 0.06/kWh equates to a Eur 2436 saving per compressor.
In addition to this the oil consumption, disposal and labour costs are also reduced by approximately 50%.
Besides other advantages, for instance longer oil change intervals, higher oxidation stability, better low temperature characteristics and higher resistance to thermal stress, synthetic compressor oils also help to reduce energy costs.
The test described in this paper has shown that an energy cost reduction between 3 and 5% can be attained in comparison with mineral compressor oils for operation above 2kh.
For all applications, an overview of overall costs should be made, which shows the cost savings possible with the use of a suitable synthetic compressor oil. Request a free brochure from Kluber Lubrication GB ...
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