Energy Management in Plastics Processing - Part 11
Compressed Air




A series of energy efficiency worksheets by Dr. Robin Kent for the Carbon Trust to help the plastics industry reduce costs through efficient use of energy.

UK Government Environment and Energy Helpline 0800 585 794

Compressed Air

Compressed air is a convenient and often essential utility, but it is very expensive to produce. In fact, most of the energy used to compress air is turned into heat and then lost. At the point of use, compressed air costs more than ten times the equivalent quantity of electrical power i.e., an equivalent cost of around 50p/kWh. At this price, it should never be wasted and only be used when necessary. Air also needs to be treated to remove moisture, oil and dirt and the higher the quality required, the greater the energy consumed by the treatment system.

The chart below shows the cost of compressor ownership over ten years. In a typical 24 hour day, five and half day week, a 100 kW motor will use energy worth around £30,000 per year, assuming the cost of electricity to be £0.045/unit. At these cost levels, an energy efficient system is highly cost effective, even if it costs slightly more to install.

The cost of compressed air makes it an expensive resource and the way to achieve the best savings is to minimise the demand and then to optimise the supply. Up to 30% savings can be made by inexpensive good housekeeping measures such as making end users aware of the cost of generating compressed air and enlisting their help in reporting leaks.

Compressed air is an expensive resource. Minimise the demand and then optimise the supply.

Minimise the demand

Reduce leakage

A significant amount of energy is wasted through leakage. Typically, leak rates are up to 40% - i.e. 40% of the generating power is wasted in feeding leaks. A 3 mm hole in a system at 7 bar will leak about 11 litres/sec and costs £1,000 per year. In a system with numerous leaks, this cost will multiply rapidly!

Simple leak surveys and maintenance can produce dramatic cost reductions and in some cases, leak reporting and repair has enabled companies to shut down some compressors for all or most of their operating time.

Reduce usage

Compressed air is often misused because everyone assumes itís cheap. Check every application to see whether it is essential or simply convenient.

Optimise the supply

Reduce generation costs

The higher the compressed air pressure, the more expensive it is to provide the air. Twice the pressure means four times the energy cost. The real needs may be lower than you are supplying. In some cases the machine rating is for a 7 bar supply but pressure reducers are fitted inside the machine. What are your real needs? 

Improve distribution

The longer the compressed air pipeline, the greater the pressure loss over the pipeline and the greater the cost of the system.

Reduce treatment costs

Next steps

Compressed air is not free and processors can save at least 30% of the costs of compressed air by simple management systems and maintenance. Start now by contacting the Environment and Energy Helpline for the full set of free information on how to reduce your costs.

"Energy Management" Series.

The "Energy Management" series is designed to give plastics processors an insight into how to manage a valuable resource.

Download the complete series as an Adobe Acrobat file.

Last edited: 11/03/10  

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