Fuel efficiency from new Atlas Copco portable compressor

Atlas Copco's new DrillAir range of compressors - which are used to power specialist drilling rigs - provide higher volumes and pressures and have lower fuel consumption than the company's previous range.

The company's Portable Power division said the XRVS 617 and 647 and the XRXS 567 and 607 models use 4% less fuel, equivalent to a cost saving of €144000 over 10 years (based on a consumption rate of 1l/hr, cost of €1/l).

It's easy to understand why reducing drilling cost was the primary design objective of the new range, which can deliver 606-630 l/sec at 25 bar and 566-591l/sec at 30 bar. Division product manager, large compressors Gathuru Mburu said operating costs are more than 85% of total compressor life-cycle costs, and that fuel costs are more than 80% of those. Drillers' primary interest, according to Mr Mburu, has switched from revenue growth to reducing cost.

Equally significant and more immediate, said Mr Mburu, is improved drilling performance using the compressors, because of their 7% higher free air delivery. The Kenyan-born, UK-trained manager said, "Drillers now want deeper and wider holes, faster, and lots of air to remove cuttings at the bottom."

Atlas Copco said approximately 75% of compressors of this size in the UK go to market through rental. Although rental penetration elsewhere is much less, it is growing.

The company tested its new unit, using the same drill rig, new tools, and same drilling settings, against a competitor's. It said its new 25 bar model powered drilling at 710 mm/min, 24% faster, and the 30 bar model at 930 mm/min, 60% faster, than the competitor's.

Instrumental to delivering the benefits of improved performance and energy efficiency is a new screw element, common in the four models of the range. Atlas Copco strived to reduce air leakage from the unit, an objective achieved by stiffening the female rotor to limit its distortion as the male rotor compresses air against it.

The net result, says Atlas Copco, is a wider optimum operating range, and less energy required to compress air. One measure of efficiency is specific energy requirement (SER), or energy per litre of compressed air. Atlas Copco has been steadily reducing that measure of performance. It said from 1995 to 2003 it achieved a 3-5% improvement in SER, from 2000 to 2006 a 3%, and today's news is: the DrillAir line delivers a 5-6% reduction.

The new screw element imparts 15% lower, compared to the earlier design, axial forces on its bearings. Couple that reduced load with improved, direct delivery of lubricating oil to the bearings, and the new compressors should easily give the 12000-15000 hour service lives Atlas Copco said are typical for portable applications.

Also increasing service life is the new range's Oiltronix V2 system, with a new valve, controller, and sensor, to keep the temperature of lubrication oil just above the dew point. Oiltronix is an option on the 25 bar and standard on the 30 bar models.

Preventing water droplet formation is a critical function: Atlas Copco said that ambient conditions of 35º C and 70% humidity equate to a 5% water concentration in lubrication oil. Its studies show that a 1% concentration reduces bearing life by 40%.

Between the screw element and the Cat C18 Acert T3 diesel engine that powers the range is a gear box, a different box for each model. The gear box converts 429 kW of engine power into the four, optimised combinations of air flow and pressure that comprise the range. Fuel efficiency is additionally enhanced by the FuelXpert device, which matches engine speed to partial air demand.

Atlas Copco provides the compressors in five mount options. For single-site use are skid and support (the smallest, at 6555 kg and 4.56 m by 2.25 m by 2.44 m in size) mount versions and a 7200 kg, two-axle wagon mount with 975 l fuel tanks capable of 25 km/hr.

Anticipating, perhaps, the growing use of compressors for drilling on multiple sites, such as in Scandinavia currently for drilling holes for geothermal heating, the company also builds a tandem-axle, 8310 kg, EU trailer version. It is capable of 90 km/hr and has 1550 l fuel tanks. For the US is a version capable of the same speed but having the smaller tank and an external fuel connection.

Helping keep track of the compressors, wherever they might be, is Atlas Copco's Cosmos feature. It links the units via mobile phone networks to provide remote access to operating information and diagnostics. The system also sends text and e-mail, and users can optionally supplement it with a handheld, wireless remote control.