Published in: EM India Jan/Feb 2010, p. 42
energy efficiency  |  

Energy conservation in compressed air systems

Compressed air, also called the ‘4th Utility’ is one of the major energy consuming utilities in any industry. Compressed air systems are an important cost centre for improving productivity.

Estimates indicate that compressed air accounts for 10 to 30 per cent of the total power consumed in different industries. This makes compressed air systems an important cost centre for improving the productivity of the overall plant. Thus it is very important for users of compressed air to understand that air is free but compressed air is not! Even in a compressed air system in which the owner does not see any energy efficiency issues, there is a great opportunity for reducing operating cost. For a 10-year life cycle cost of any compressor, more than 85 per cent of the cost is incurred towards energy and only 10 to 15 per cent towards initial investment and maintenance. For a system owner, an optimistic 10 to 20 per cent reduction in energy costs could have a major positive impact in his operating margin, and can significantly increase return on investment. As such any productivity enhancement project in an organisation must consider compressed air system as one of its key constituents. Normally in a compressed air system, saving opportunities can include: • Supply Side – 10 to 12 per cent • Distribution Side – 6 to 8 per cent • Demand Side – 4 to 6 per cent These figures increase depending on the type of the industry as well as the condition of the existing compressed air system. Opportunities in an existing system Globally, research has shown that with an energy efficient system, operating costs can be reduced by 20-50 per cent of their current levels or more. A preliminary assessment of a system from a critic’s standpoint unveils the hidden opportunities that exist. Here are some startling figures… • Operating a 90 KW or (~500 CFM) compressor amounts to about Rs 31 lakhs per annum as running cost. This is equivalent to the cost of 3 new compressors! • A 90 KW compressor unloaded for 4 hours daily means a cost of Rs130000 pa • A 1/8” (3 mm) orifice at 6.5 bar means a loss of Rs.150000 per annum • A 90 KW compressor @ 90 per cent efficiency means a cost of Rs 31Lacs + Rs 350000 pa • Over-pressurising a 90 KW system by 0.5 bar can cost Rs 100,000 pa • A 20 per cent leakage in a 90 KW system means another Rs 630,000 pa • sP in one bend is equivalent to resistance by 100 ft of pipe Other factors that affect energy efficiency in compressed air systems: Capacity deterioration due to inadequate maintenance or the age of the compressors is normal. However this may result in operating two compressors, when the existing single compressor can meet the demand, with necessary modification or overhauling. Pressure plays an important role in a compressed air system. More often than not pressure is maintained at a very high level than required to avoid problems down the line. However for every one bar of over-pressurising the system, energy expenses increase by 7 per cent. So an optimum pressure adequate to meet the demand has to be established and maintained. Leakage in some systems is as high as 50 per cent. This means, of the two identical compressors working, one is catering only to leakage, and another delivering the compressed air. For instance, a 1/8” orifice can drain out 23.8 CFM or Rs 1.2 lakhs from a company. Compressed air energy audits An audit is a complete analysis of the compressed air system with the ‘system’ as the focal point. Specific compressed air energy audits are becoming increasingly relevant as organisations realise that the opportunities for cost savings are as high as 30 per cent of the existing power cost. Such audits are a health check for the system, exploring opportunities for major or minor improvements, identifying inefficiencies in the system or opportunities to avoid wastage. Here it’s important to understand that compressed air systems are dynamic and their needs and requirements keep fluctuating. Hence re-auditing or health checks in compressed air systems are required periodically. It is time that industries started making regular audits a part of their maintenance schedules. Audits are primarily designed to cover air compressors, controls, air quality, storage, distribution and demand (consumption) These audits help to: • Improve productivity • Reduce operating cost • Improve quality (as per process requirement) • Stabilise air pressure • Minimise or eliminate future capital costs Interactive audits At Ingersoll Rand Industrial Technologies, we have seen that such audit processes are often very informative and throw up a lot of learning. Also, it is absolutely essential that users of compressed air systems gain a complete understanding of the audit process. Users need to participate and learn the methodology during such audits apart from just monitoring and implementation. With compressed air being one of the most poorly managed industrial utilities, there is enormous opportunity to change the way it works now. As every industry tries to cut down costs, audits of compressed air systems help in reducing hidden costs and ultimately contribute to increase in revenue. In these trying times we should remember that a rupee spent is a rupee earned. In the end, let’s remember that air is free but compressed air is not!

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