An air supply you can rely on
July 04th 2007

Compressed air is the invisible, invaluable resource for industry and business, and represents one of the best site opportunities for substantial energy and cost savings. BCAS is the UK trade association for compressed air manufacturers, suppliers and users discusses the energy saving opportunities within a typical compressed air system and how these can be made without compromising reliability of supply

The goal of anyone responsible for the compressed air system is to deliver air at the right flow and pressure for the processes required at the lowest cost. The overriding need is to maintain production, hence it is not uncommon to find the system pressure being higher than is needed. The overpressurisation cost is usually dismissed as minimal compared to downtime costs (where the latter cost is more likely to be known). However in a climate of increasing fuel prices,it makes good sense to look at how to reduce costs through reduction of pressure: a 1 bar increase in air pressure can increase generation costs by 6- 8% in terms of energy.

Overpressurisation also incurs additional costs such as:

Shortened service life of equipment

Increased maintenance costs

Higher incidence of leaks in the compressed air system

Over-pressurisation may be present due to the need to overcome pressure drop in the system between the compressor outlet and the point of use. Pressure drop may be due to inherenetly poor design, under-sizing of pipes or poor maintenance. Cutting back on maintenance will incur more cost in terms of energy consumed, as well as decreased service life and reduced reliability of components and equipment.

Another reason for over-pressurisation is the attempt to lessen the effect of fluctuating air pressure in the system. Pressure fluctuations cause problems for production e.g. stoppages and variable product quality. This excess air required by a system’s unregulated uses due to a pressure level in excess of actual production requirements is often referred to as “artificial demand”.

Artificial demand is most often caused by:

• insufficient online kW to meet peak demands

• compressor controls that cannot respond fast

enough to demand fluctuations

• insufficient pipe diameters (causing air flow restrictions)

• air leaks

• a lack of useful storage

Any one or combination of these factors can cause pressure fluctuations that in turn lead to the creation of artificial demand. Air leaks in themselves are typically the largest avoidable source of waste in a compressed air system and should always be addressed as priority to improve reliability of supply. Although more companies are carrying out leak detection,the repair aspect – which is the action which saves the energy, is at best a one-off haphazard activity, at worst not carried out at all.

The solution to creating a reliable system where the pressure can be lowered without compromising the compressed air supply is to separate demand from supply. BCAS has gained Carbon Trust funding to trial flow-pressure control techniques together with leak reduction programmes. These combined approaches can yield pressure reductions of 2 bar. Although the pilot sectors are food and drink and aerospace, if you have an installed capacity of 200kW or more contact BCAS directly about potential participation.

Compressed air systems are by their nature dynamic, so their operation should be under continuous review to ensure they deliver safe, reliable and efficient power. For impartial advice contact BCAS.