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Compressing the cost of air

Compressed air has an important role to play in a multitude of drilling applications, from tunnelling to exploration, and geothermal heating to water-well drilling. Often, the most efficient way to generate compressed air on site is to use a portable compressor that will provide a reliable air source for the duration of the job; however, generating the high volumes and air pressures demanded by such applications can be an expensive business, especially as fuel costs continue to rise.

Choosing a compressor with the correct combination of features can help to reduce fuel consumption and deliver the correct air pressure, to ensure that drilling contractors can complete the project on time and within budget. This concept has been put in to action through the development of CompAir’s new high-pressure TurboScrew C range, which is now being used successfully in numerous drilling applications around the world.

Analyse the cost of ownership

Before purchasing a new compressor, it is advisable to undertake a full lifetime cost analysis. For example, for a conventional portable compressor operating over ten years for a typical 10,000 operating hours (OH), the initial purchase price may equate to as little as 15% of the overall cost of ownership.

Service and maintenance costs are estimated at around 20% of the overall cost, meaning that by far the highest expense – more than half of the overall cost in fact – is the fuel required to operate the compressor.

Using average figures from a conventional compressor, fuel consumption can be as much as 42L/h, which at a cost of €1/L over 10,000 OH can be more than €400,000 during the lifetime of the machine – far outweighing the initial purchase price. It soon becomes apparent therefore, that any steps that the operator can take to reduce fuel consumption will impact significantly on ownership costs and lead to a more profitable operation.

Assess your requirements

The criteria for selecting a new compressor should, however, not be based on fuel consumption alone. There are other factors to consider, such as the minimum air pressure required by the application and the ease with which the unit can be transported between sites, so it is advisable to be familiar with all aspects of the compressed-air requirements first.

It is essential that the compressor is correctly sized for the application, and is neither undersized and incapable of producing the required air pressure nor oversized and generating air unnecessarily.

Reducing fuel consumption

A key area to consider is the compression element design and whether it has been engineered to save energy, while still producing the high air pressure required.Compared to conventional compressors, CompAir’s new high-pressure TurboScrew machines, launched early this year, deliver up to 30% better fuel efficiency with no loss in pressure, helping site managers to reduce both the cost of diesel used and the frequency with which the unit needs to be refuelled.

Providing air pressures of up to 24bar, the units feature CompAir’s bi-turbo technology with a light-weight and compact Cummins engine. The turbo-chargers power a CompAir screw compressor unit, with the addition of an engine exhaust-gas turbine to pre-compress the inlet air before it enters the compressor chamber, enhancing the shaft power by 14%.

A conventional diesel engine, with a turbocharger would lose up to 8% energy as radiant heat, 22% for cooling water and up to 30% as exhaust. In contrast, by reusing 5% of what would normally be wasted exhaust energy and converting it to motive power to create compressed air, CompAir has been able to increase both efficiency and flow performance.

Part load operation

It is worth considering that a compressor will not always operate at 100% full load as there may be peaks and troughs in demand during drilling. Typically, the compressor may run for a quarter of the time at 100% load, a quarter at 67% part load and another quarter at 33% part load, spending the remainder of the time idle.

Operating at part load and running idle are generally much less fuel efficient, so careful examination of a compressor’s free air delivery and the associated costs should be carried out to ensure the unit chosen is best suited to requirements.

For example, CompAir has engineered its TurboScrew machines to run at just 1,000rpm when idle in offload mode; equivalent to turning down the fuel consumption by up to 58% when there is no requirement for air on site. Compared to a conventional compressor, this equates to a fuel saving of around 12L/h.

Ease of use

Choosing a portable compressor that is easy to manoeuvre is, without question, a key requirement for many contractors. Users will need to consider not just how easy it is to tow the compressor between sites, but also the affect that this will have on the towing vehicle’s fuel consumption.

It has long been a challenge for manufacturers to develop a lightweight machine with smaller dimensions, which can deliver the higher air pressures of 20bar, and above, required by drilling applications. As a result, contractors usually have to make a compromise; either choose a small compressor with a lower air pressure or a large machine that is costly to transport.

With the CompAir units, each machine weighs less than 3.5t, meaning it can be towed with no need for air brakes, is easier to site in hard-to-access areas and will help to save diesel costs.

Harald Wenzel is product manager for portable compressors at CompAir
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