Compressed air control system cuts energy costs

An award-winning compressed air control system developed and launched in Finland three years ago is now delivering energy savings and productivity gains to UK companies. Angela Himus reports.

Half of the energy produced in Europe is consumed by industry, and generating compressed air accounts for 8-10% of all industrial electricity consumption. But according to Leicester-based Sarlin Ltd, an average 10-30% of this energy is wasted through poor compressor control and leakage. And wasted energy is only part of the problem. An unstable compressed air network pressure disrupts plant productivity leading to costly raw material and production losses.

To overcome these problems, Sarlin-Hydor Oy, Sarlin’s Finnish parent, part of the multi-national Sarlin Group, developed an intelligent control system which varies the pressure settings according to air demand, thus avoiding pressure fluctuations. Winner of the ‘Eco-Design’ category of the 1998 European Better Environment Awards for Industry, the Sarlin ‘Balance’ compressed air control system not only achieves energy savings of 10-30%, with a guaranteed pay-back of less than one year, but the system also improves productivity and product quality by reducing plant disruption and optimising raw material consumption. In some paper and steel mills, these indirect benefits are estimated to be at least ten times those of the direct energy savings.

Typical systems

Industrial multi-compressor systems typically feature individual controls, mainly consisting of one to four adjustable pressure switches. Depending on the discharge pressure level, a compressor runs either loaded or unloaded. The pressure will vary somewhat as a result.

To guarantee the supply of compressed air in changing production situations, the pressure of compressed air systems is kept higher than the actual air demand of the processes and machinery being supplied. This, however, means energy losses.

The Sarlin Balance control system is based on a software algorithm and microprocessor-based industrial logic developed as a result of actual measurements of compressor efficiency. With some 400 ‘air audits’ under its belt, the company has found that the average energy wastage is about 30% but it has been found to be as much as 70% in extreme situations where leakage plays a key role.

The Balance control unit monitors the network pressure and the discharge pressures of the compressors. The central unit processes the measurement results. By using these processed results and a database of actual measurement based on practical experience, the software is able to maintain the pressure at an adequate level, while keeping compressor capacity as low as possible.

The pressure level required and the deviation allowed are set at the interface. To achieve an efficient solution to controlling air compression plants the system uses real-time measurements of both the system behaviour and the tuning of the controls. The interface settings should preferably be made by someone with a good understanding of compressed air systems and experience in tuning their conditions. Operating sequences can also be set to equalise compressor run times.

The Sarlin Balance includes a comprehensive fault diagnostic system which prevents any drop in pressure if, for instance, a failure occurs, in the logistics or sensors. The basic Sarlin Balance module can be used for up to eight compressors. The number of basic modules, and thus the number of controlled compressors, is not restricted.

Balance is supplied as a turnkey package which starts with an ‘Air Audit’ to show how the system is operating at the moment. If the current control system proves to be inefficient, the Air Audit report will calculate the guaranteed energy savings which Balance compressor management would achieve.

Since the first installation at the Enso Oy Tainionkoski paper and board mill in Finland in 1995, Balance has been installed in over 111 plants world wide. Raychem, the Swindon-based manufacturer of specialist wire and cable products, is one of the first UK companies to see the benefits of Balance, since its launch into the UK market last year. Raychem’s Air Audit identified several areas for improvement including significant pressure fluctuations across its compressed air system which was costing the company £72,000pa on electricity. Installation of the Balance control system has reduced Raychem’s electricity bill by £12,000pa, paying for itself within a year and providing a stable network pressure independent of the air consumption.

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