Improved reliability and better energy efficiency
April 20th 2007

During the last decade there have been a number of technical developments by the compressed air industry to help users reduce their cost of generation and use of compressed air. However, the greatest influence on the consumption is still largely down to the user in how the whole system is installed and maintained, and how the compressed air is used on site.

Many of the barriers to improving energy efficiency of a compressed air system are the same as for general energy management. Compressed air is invisible and as long as the supply is continuous and not causing production any problems, energy saving is low on the priority list. Indeed few, if any, on site know the annual cost of using air. Reliability is of paramount importance and fear that energy efficiency measures could compromise reliability of air supply impedes changes.

Two of the largest causes of avoidable waste in a compressed air system are leaks and over-pressurisation. Add to this unregulated and indiscriminate use for low grade duties such as cleaning and cooling, and there’s significant variability and hence a risk to supply reliability – a matter of greater immediate concern for the manufacturing and process industries. However all these can be controlled by the user.

1) Unregulated use

Review what compressed air is used for on site , it is often misused i.e. wasted – just because an air supply is readily available, not because it is the most cost-effective or appropriate method. Processes evolve and production methods change, affecting the way compressed air is used, so review the system and working practices regularly.

2) Compressed air leaks

High compressed air leakage rates persist in many systems - the leak rate on an unmanaged compressed air system can be as much as 40% of the compressor output. The most common sources of leaks are:

• Manual condensate drain valves left open

• Shut-off valves left open

• Leaking hoses and couplings

• Leaking pipes and pipe joints

• Leaking pressure regulators

• Air-using equipment left in operation when not needed.

Compressed air leaks also lead to additional costs through:

Fluctuating system pressure, which can cause air tools and other air-operated equipment to function less efficiently – potentially stalling and affecting production

Reduced service life and increased maintenance of equipment due to unnecessary compressor cycling and running time

Excess compressor capacity.

The fluctuating system pressure brings us round to the second issue:

3) Over-pressurisation: compressed air systems often run at pressures of up to 2 bar above the rated pressure. This is usually to guarantee sufficient air at all times for different production processes. Not only does this consume more energy, it also shortens life of components due to over-pressurisation. A 1 bar reduction in air pressure can reduce generation costs by 6-8%. Over-pressurisation (often referred to as “artificial demand”) is usually indicative of trying to lessen the effect of fluctuating air pressure in the system which causes problems such as production stoppages and variable product quality. Poor maintenance is often responsible for pressure drop in a system where dryers, filter elements and piping have all been neglected. So, why are systems generally over-pressurised although it costs more in terms of electricity? The over-pressurisation cost is usually minimal compared to potential downtime costs should the air supply fall below the required level.

There is a solution to creating a reliable system where the pressure can be lowered without compromising the compressed air supply a paramount requirement for manufacturing and process industries. BCAS has applied for Carbon Trust funding to trial pressure control techniques together with leak reduction programmes. Although the pilot sectors are food and drink and aerospace, if you have an installed capacity of 200kW or more please contact us directly about potential participation. Watch this space for news and updates.

For further information, just  click here.

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