Energy Efficient Compressors Making Compressed Air System Energy Efficient

Author / Editor: S Raghunandan / Dominik Stephan

In this era of energy efficiency, there is huge scope for saving energy through compressed air systems. New as well as existing systems can give better results with the help of few energy conserving steps. Here are some ways to save energy and ultimately cost, through these systems.

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Centac — Oil-free centrifugal compressors - A tradition of proven reliability, ultimate efficiency and unrivaled productivity
Centac — Oil-free centrifugal compressors - A tradition of proven reliability, ultimate efficiency and unrivaled productivity
(Picture: Ingersoll-Rand India)

Compressed air, is widely acknowledged as the ‘4th Utility’ after electricity, natural gas and water. However, it is one of the major energy consuming utilities in any industry. Estimates indicate that compressed air accounts for 10–30 per cent of the total power consumed in different industries. As a result, it proves to be a very expensive source of energy with the actual output being only 10 to 15 per cent of the input power. This makes compressed air systems an important cost center for improving the productivity of the overall plant.

Even in a compressed air system in which the owner does not see any energy efficiency issues, there is a great opportunity for saving and reducing operating cost. Such a compressed air system can significantly be overpowered with a more energy efficient system.

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85% Costs for Compressors are Energy–Related

Additional Information
The Energy Checklist
Six Steps to Optimize your Air System

Demand side – Establish correct air needs for the points-of-use (flow & pressure)

Distribution side – Establish the leakage in your system and proactively manage it; analyse the system capacitance and optimize it; track the pressure profiles across the

plant for supply - demand mismatch and minimize the pressure drops

Supply side – Evaluate the health of each compressor and the support systems; optimize controls to match the system dynamics

For an average 10-year life cycle cost of any compressor, more than 85 per cent is incurred towards energy and only 10–15 per cent towards initial investment and maintenance. The target thus, should be a bigger pie i.e. greater energy cost. An optimistic 10–20 per cent reduction in energy osts could have a major positive impact in an organization’s operating margin and can significantly increase return on investment.

All over the world, majority of compressed air systems are not energy efficient. As a system owner, one has a great opportunity to improve operating margins and reduce costs. As such, any productivity enhancement project in the organization must consider compressed air systems as one of its key constituents.

Hannover Messe 2012
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Normally in a compressed air system, saving opportunities can include:

  • A. Supply side – 10–2 per cent
  • B. Distribution side – 6–8 per cent
  • C. Demand side – 4–6 per cent

These figures increase depending on the type of the industry as well as on the condition of the existing compressed air system.

Discover Opportunities in the Existing Compressed Air System

A preliminary assessment of the system from a critic’s point of view will give the owner an idea of the hidden opportunities that exist within the system. Globally, research has shown that with an energy efficient compressed air system, operating costs can be reduced by 20–50 per cent of current levels or more! To operate a 500 CFM compressor round the clock at 100 PSIG pressure, the power cost alone will be approximately `30 lakhs per annum, at `4 per kWh energy tariff. This cost and energy can be saved in cases where the system:

  • Is running unloaded for extended hours or frequently loading and unloading
  • Is running at a pressure higher than 100 PSI, unless it is a specific industry demand
  • Has a single network for various applications
  • Has high ΔP across cleaning instruments like dryers, filters, etc.
  • Emits significant hissing sound, which indicates leakage
  • Is dependent on manual controls, which indicates absence of cascading settings
  • Does not have any effective regulation at the point of usage

Other factors that affect energy efficiency compressed air systems are:

Capacity deterioration due to inadequate maintenance or if age of the compressor is normal. However, this may result in operating two compressors, in a situation where an existing single compressor can meet the demand, with necessary modification or overhauling.

Pressure plays an important role in the compressed air system. Often pressure is maintained at a very high level than required to avoid problems down the line. However, for every one bar that one over–pressurizes the system, energy expenses increase by seven 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 required compressed air. An 1/8” orifice can drain out 23.8 CFM or `1.2 lakhs. (Refer to the table 1). Many compressed air systems also have unregulated flow, i.e. there are no pressure regulators at the point of use. The consumption of air reduces at low pressure and increases at higher pressure.

The effect this can have is seen when the load-unload press band is high. More air is drawn when the compressor is near unloading press and consumption reduces near load pressure. For example a machine consuming 23.8 CFM at 90 PSIG will start consuming 31.6 CFM at 125 PSI, resulting in more air drawn from the compressors. (Refer to table 1)

TABLE 1: LEAKAGE RATES: (Specific power assumed – 18 KW/100 CFM)Potential savings PA – Rs. 1.20 Lacs PA(1 leak x 23.8 cfm x 0.18 KW/CFM x 7000 hrs/PA x `4/Kmh)
TABLE 1: LEAKAGE RATES: (Specific power assumed – 18 KW/100 CFM)Potential savings PA – Rs. 1.20 Lacs PA(1 leak x 23.8 cfm x 0.18 KW/CFM x 7000 hrs/PA x `4/Kmh)
(Source: CAC)

Compressed Air Energy Audits

Specific compressed air energy audits are becoming increasingly relevant as organizations realize the opportunities for cost savings. Results of such audits are as high as 30 per cent of the existing power cost. Such audits act like a health check for compressed air systems, exploring opportunities for major or minor improve-ments, identifying inefficiencies in the system or opportunities to avoid wastage.

It is important to understand that compressed air systems are dynamic and their need and requirement keeps fluctuating. Hence re-auditing or health checks are required periodically. Its time industries started making regular audits a part of their maintenance schedules.

Additional Information
Energy Audits
Making Compressed Air System Energy Efficient

Supply side audits – Efficiency of individual compressors and complete system, sizing of compressors and peripheral system w.r.t. demand, fluctuation in loading patterns, system capacitance - supply side.

Opportunities - energy saving products in supply side.

Demand side audits – Establish accurate peak and average demand, capacity required for major air consumers, optimum press for such consumers, pressure segregation, pressure profile across plant, System capacitance - demand side, leakage quantification, improper usage of air.

Opportunities - Energy saving products in demand side.

System audits – Complete study of supply and demand side.

Audits are primarily designed to cover these:

  • Air compressors
  • Controls
  • Air quality
  • Storage
  • Distribution
  • Demand (consumption

How to turn an Energy Audit Into Actual Money for Your Company

Compressed air audits can be a supply side audit or a complete system audit. In supply side audits opportunities explored are limited to the supply side, i.e. compressors and the peripheral systems for improving the quality of air and reducing costs. Complete system audits study the complete system, i.e. generation, distribution and usage of air. A demand side audit can be performed to establish the new demand or for designing a new system. (Refer to Box1)

Centac — Oil-free centrifugal compressors - A tradition of proven reliability, ultimate efficiency and unrivaled productivity
Centac — Oil-free centrifugal compressors - A tradition of proven reliability, ultimate efficiency and unrivaled productivity
(Picture: PROCESS India)

Essentially, these audits help in reducing operating cost, improving productivity, iImproving air quality and eliminating problems associated in production and also in minimizing or eliminating future capital costs.

With compressed air being one of the 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.

* The author is Product Manager - Air Treatment & System Solutions; Global Product Management, Industrial Technologies of Ingersoll-Rand India