It is estimated that on average there may be one rough vacuum pump for every three compressors installed on a production site. However, in many cases they can be found operating at minimum performance levels in remote areas, which represents an uneconomic burden in terms of energy consumption. This is ironic considering that state-of-the-art air compressors are often found in the very same working environments, operating far more efficiently and located at the actual point of use.
Realising such findings, enlightened plant operators are now warming to the idea that having both compressors and vacuum pumps supplied and serviced by a single air movement specialist makes practical sense. In addition, the technical similarities between rotary screw compressors and oil-sealed rough vacuum pumps is leading more companies to view these two air movement solutions together as a ‘Yin and Yang’ synergy. In practice, this approach confers the benefits of improved operational efficiency, increased uptime and system integrity: plus the reward of long-term energy savings.
For this reason, the air movement industry has focussed its efforts in recent years on developing vacuum pump systems to the same levels of quality and reliability as those of the compressors. The success of this endeavour is clearly demonstrated in the latest generation of oil-sealed rough vacuum pumps, which have evolved to share an air movement synergy with compressors – a breakthrough that is not far short of a technical revolution in comparison to traditional equipment principles and practices.
The GHS VSD+ vacuum pump offers average energy savings of 50% compared with conventional oil-sealed and dry vane vacuum pumps, as well as best in class noise levels and oil retention.
These vacuum pumps are designed from the outset to consistently help production plants become more efficient by lowering the cost of ownership, increasing sustainable productivity and enhancing final product quality.
For a start, efficient, on-site vacuum in a nominal displacement range of up to 900m3/h can now be produced by oil-sealed rotary screw systems that incorporate two screw elements rotating at slow speeds, enabling the pump to run at sound levels as low as 51 dB(A). Such silent operation allows installation close to the point of use with the added benefit of minimum pipework connections and a corresponding reduction in pressure drop energy losses. As an added energy-saving bonus, there are facilities for process heat recovery from individual pump units.
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GHS VSD+ vacuum pump in a production environment. (Polestar Sheffield)
With the latest types of oil-sealed rough vacuum pumps incorporating Variable Speed Drive technology, it is also now possible for users to precisely adapt their vacuum generation requirements to match the demands of their process; leading to a dramatic reduction in total cost of ownership.
In general terms, there is also close parallel between the size and rating of vacuum pump drive motors and those of screw compressors. A distinct advantage of this is that such units fall with the boundaries of the British Compressed Air Society's (BCAS) uniformity of energy reporting initiative − a yardstick which does not apply to other types of vacuum drive systems. The commonality of motors, drive trains and components argues strongly in favour of maintenance programmes designed to cope equally effectively with compressors and vacuum pumps from the same manufacturer and service provider.
Case study: Polestar
The principle is best illustrated by a case study involving Polestar, one of Europe's largest and independent printing companies, which produces 2.5 million high quality catalogues, magazines, brochures and supplements every 24 hours from its £100million, purpose-built production plant.
Ensuring reliability of performance and harnessing advanced technology has always been key to the company's success. A vacuum system plays an essential role within the transfer of work from the presses to the print finishing and bindery operations so, when confronted with the need for major repairs to three existing conventional vacuum pumps, it made sense to re-assess the units' combined operation to establish the potential savings that could be achieved by installing the most advanced, energy efficient replacement.
Already a long-term user of Atlas Copco's fixed-speed and VSD rotary screw compressor solutions, pipework and maintenance services, the company recognised the clear synergies between its compressed air installation and its vacuum generation needs. It was a logical step to trial and install one of Atlas Copco's new generation of intelligent, oil-sealed, plug-and-play, rotary screw vacuum pumps. These are designed from the outset to deliver peak performance at the required pressure while achieving substantial energy savings – up to 50% compared with conventional oil-sealed and dry vane types of unit. The company's three original pumps ran at approximately 20kW an hour. The single GHS VSD+ pump that replaced them was a 15kW unit that operates close to 20% load – just 4kW. On an annual 8,000 hours operation, the estimated energy savings are in the region of £10,000.
Monitoring, measuring and management
Most compressed air users would agree that to get the best return from their capital investment, the monitoring, measuring and management of compressor installations is essential if optimum control, improved productivity and energy efficiency is to be achieved. Conducting energy audits is seen as the definitive approach to identifying trends, establishing how well a system is performing, and installing energy-efficient solutions where needed. This cost-saving approach applies equally well to the new generation of rotary screw vacuum pumps.
Applying simple non-intrusive air audit data logging techniques to vacuum pump systems can help establish a true indication of a system's air use and, ultimately, help to identify any wastage factors such as leakage and pressure drops. These monitoring techniques have been applied to a number of diverse applications throughout industry and as a result of implementing these energy-efficient measures, it is not uncommon to realise operating cost savings of as much as 40%.
It is clear that by looking at all air movement demands collectively, whether for compressed air or vacuum applications, plant operators can achieve considerable improvement in terms of cost and energy-efficiency, plant uptime and system integrity. What is more, the rapid advance in energy-saving technologies promises even greater productivity benefits for the future.
