Compressed Air Case Studies

Compressed air is widely used in all aspects of industry. It is non- hazardous, readily available, can be stored easily and is a convenient source of power for a range of machines and tools.

Compressed air at Wyeth Medica, Newbridge, Co.Kildare.

However, it is not cheap to operate. Approximately 10% of all electrical power in industry is employed in compressing air. Over its lifetime the operating cost of a compressed air plant will be many times its initial purchase and ongoing maintenance costs. Typically, the life cycle costs of a compressed air system can be broken down in Table 1 as follows:-

Typical on-site savings have been estimated to be up to 30% of the energy input to the compressor. These savings are achievable through initially selecting the most efficient type of compressor, ensuring the correct air system design and ongoing efficient operation and good maintenance. It includes maximising the use of the latest technologies available and also ensuring that attention is paid to the simple measures of good housekeeping and primarily, keeping leakage rates to a minimum.

The Annual Self Audit and Statement of Energy Accounts Scheme is operated by the Irish Energy Centre for the largest energy consumers in the industrial sector in Ireland. Participation in the scheme is voluntary with member companies committing to annual energy savings targets, regular audits of their energy consumption, and the publication of an annual statement of their achievements. The Irish Energy Centre provides support to the membership by helping in the preparation of annual statements and also through workshops, seminars, newsletters and site visits, and by providing information on specific approaches to energy efficiency.

As part of the scheme, the Irish Energy Centre contracted Air Technology Ltd., U.K. to conduct comprehensive energy audits of the compressed air facilities at Carbery Milk Products, Ballineen, Co. Cork and at Wyeth Medica, Newbridge, Co. Kildare.

THE AUDIT
The audits were measurement based and covered all areas of the air systems. The aim of the audits was to identify economies in the rational use of compressed air through the on-site measurement of compressor efficiency, air demand pattern and air quality. The audits also made recommendations for improving system efficiency and outlined a strategy for reducing overall compressed air costs.

The audits were carried out over the course of a week with little or no disruption to the operation of the individual sites.

On both sites, rotary screw compressor efficiency was tested to ISO 1217 Annex C, which assesses the compressor in terms of its output and its power consumption; and centrifugal compressor efficiency was tested to ASME PTC10. The test results showed that it is essential that compressors are correctly maintained if they are to operate at their designed output and performance level. Regular monitoring of compressor operation will help to alert maintenance staff when performance is below standard.