Compressed air- the 4th Utility:


Compressed air, also referred to as the "4th Utility" (after electricity, water & steam) is one of the major energy consumption utility in any industry. Various estimates indicate that about 4,000-5,000 MW is consumed nation wide by the compressors and its related accessories & support systems. It is a well-known fact that of the life cycle cost of any compressor, 85-90% is towards energy and only 10-15% towards initial investment & maintenance.


Hence, the design and selection of the right compressor assumes great significance while setting up your air system. It is very important on the part of each one of us using compressed air to understand a simple fact that "Air is free but compressed air is not!"


Compressed air is a key utility in the Textile industry, both the segments of Natural & Man-made textiles. Compressed air is more or less required at every stage of manufacturing particularly large volume of air is required for integrated cotton textile industries having Airjet Looms & as well in the Polyester yarn industries. Compressed air is a very critical requirement in the PFY valued added segment such as Texturing.


Compressed air is one of the most expensive utilities, but more often than not, this fact is not understood. Unlike the other utilities, many users find it difficult to measure their cost per cfm. Primarily, it should be understood that the compressed air consumes 3 - 4 times more power as compared to electrical energy (say for e.g. a pneumatic tool of 1 hp would consume compressed air equivalent to 3 times more power than a 1 hp electric tool). However, compressed air being highly versatile in nature, it makes many industrial operations more effective in terms of high productivity and safety and hence, cannot be replaced


A major opportunity lies here...


  • The US Department of Energy (DOE) has determined that air compressors are one of the largest users of electricity in industry
  • Although at one time the DOE considered electric motors as the largest user of electricity, savings through improved electric motor efficiency are dwarfed by those available through improving the compressed air system design and operation
  • On a very conservative estimate, the average energy savings potential in a compressed air system could easily vary from a minimum of 15% to as high as 30%!
  • This means about 1,000 1,300 MW can be saved annually at the national level; amounting to phenomenal savings of Rs. 1,800 2,000 crores in the energy cost every year!



This makes it an obligation on our part to our Nation and the Society to look at this very critical utility with due amount of respect so as to maintain and run it in the most efficient manner

Which Compressor suits my requirement?

Air compressors are mainly classified in two types based on their construction & operation:


  1. Positive displacement (Reciprocating & Rotary compressors)
  2. Dynamic type (Centrifugal & Axial flow compressors)


Air compressors are also classified in to lubricated & non-lubricated type; the latter delivering oil-free quality air which is again very critical for better productivity and long & trouble-free operation of the downstream system components and point-of-use equipment / tools.

 

While there are different types of compressors, all compressor types theoretically operate more efficiently with multi-staging, whereby the final discharge pressure is achieved over 2 or 3 compression stages as against a single compression stage. Multi-stage compression saves energy by cooling the air between stages, reducing its volume and thereby the work required for compressing it. In spite of this, many industrial compressors are still purchased as single-stage due to lower capital costs, which goes to show the ignorance of the compressed air costs. Single-acting reciprocating compressors are generally air-cooled and available in the smaller hp sizes (1 hp to 50 hp). However, such compressors are generally less efficient than the other types. Double-acting reciprocating compressors are generally water-cooled and with multi-stage versions are usually considered to be the most efficient air compressors (100 hp to 250 hp). These however, come with high initial & installation costs and higher maintenance as well.


Screw compressors are available as oil-flooded (lubricated) single or multistage (generally from 15 hp to 500 hp) but have lower operating efficiencies at part-loads and also high unload power, which could become the key factors in reducing your operating efficiencies. However, incorporating VFD (variable frequency drive) or HPM motor (hybrid permanent magnet; as in the latest Nirvana compressors of Ingersoll-Rand) would make these compressors efficient throughout the operating range. For more details visit our exclusive Nirvana web site http://air.irco.com/nirvana/index.htm for visit to a live demo Pl email to airsolutionsindia@irco.com.


Three stage centrifugal compressors available in the market would give much higher efficiencies generally 10-15% more than the two stage positive displacement types. Moreover, features like 100% oil-free air, constant pressure, high turndown abilities with good part-load efficiencies, nil wear & tear, much lower maintenance costs have made this compressor very popular with all users. These are available from 250 hp to 5,000 hp and upward as well. In fact, for many large textile units who have been using positive displacement technology for the last 5-10 years or above can ideally look to incorporate the centrifugal technology, which will have payback of less than 2 years in most cases.


The Air System:


The compressed air system mainly consists of:

  • Supply side
  • Distribution &
  • Demand side


When we talk about conservation of energy the emphasis has to be in all these three areas of the compressed air system, each of which, if ignored can bring your overall air system to low efficiency levels.


Encon in compressed air system starts from sizing & selection of compressors. The ratio of actual air consumption in a plant to the maximum air demand is known as the load factor. The load factors play a vital role in estimating the total compressed air requirement at the design stage. The load factor can be determined with the help of properly evaluated air system study (air audit) or recommendation of competent consultant or equipment manufacturer. Having done this basic work, taking "a systems approach" for overall evaluation or design in making the decision with regards to compressed air system. As such the compressed air system has following six major sub systems


  1. Air compressors
  2. Controls
  3. Air Quality
  4. Storage
  5. Distribution
  6. Demand (consumption)

 

Many industries often either ignore or overlook the following:


  • Improper compressors control
  • Pressure losses in transmission and distribution
  • Overlooking air leakages
  • Condensate management
  • Air quality (in terms of pressure fluctuation, moisture, contamination from piping system)
  • Use of higher air pressure than is required by the point-of-use
  • Conservative approach towards maintenance.


The various studies & audits carried out in US & European countries & in India reveal that on an average only 55-65% of energy consumed in the compressed air system is actually used for the production. The balance 35-45% is wasted in terms of artificial demand, pressure drop, leakages & improper usage. This very fact is an "alarm-bell" for every industry to have a relook at their compressed air systems. Remember..."Air is free but compressed is not!"


Air requirement in the textile industry can be segregated under Low Medium Large volume consumers. Typically power looms, process house & ginning mills required low air between 30-500 cfm. Denim spinning, medium PFY industries require medium air between 500-1,500 cfm. Large polyester yarn integrated plants, texturing units & integrated cotton textiles may require anywhere between 2,000-40,000 cfm


Air quality is one of the major concerns & high quality air requirement is essential in integrated textile units. However, the preparatory segments such as ginning mills, spinning mills & process units can use lubricated compressors with well-designed air filtration system. The annual operating cost of compressed air in medium to large textile industries may normally range anywhere between Rs. 30 Lacs to 500 Lacs.


The possible saving opportunities in the textile industries are,


  1. Migration to new technology air compressors in old installations / plants, for example considering 2-stage rotary or 3-stage centrifugal compressors instead of existing old reciprocating or single-stage screw compressors
  2. Proper evaluation on the performance of air treatment requirement such as dryers, filters & FR units installed near points-of-use
  3. Properly evaluating pressure requirement of different processes and if required segregation of low & high-pressure consumers
  4. System pressure optimization for unregulated consumers
  5. Evaluating usage of waste heat from compressors (use of waste heat recovery systems for use in boiler make-up or hot water application)
  6. Re-look at distribution & storage to minimize the pressure drops
  7. Optimize air consumption & pressure for cleaning air application (this is one of the largest wastage in most of the textile industries)
  8. Have effective controls on the operation of the compressors for better optimization & sequencing
  9. Effective leakage management program & designated team for the same

 


Six steps to optimize your Air System

Demand Side

1.  Establish your correct air needs for the points-of-use (Flow & Pressure)

Distribution Side

2.  Establish the leakage in your system and proactively manage the same

3.  Analyse the System Capacitance & optimize the same

4.  Track the pressure profiles across the plant to match the supply & demand and also minimise the pressure drops

Supply Side

5.  Evaluate the health of the compressors and the support systems

6.  Optimise the controls to match the system dynamics


Note: A detailed system audit done through a professional consultant can help in achieving the above objectives


Ingersoll-Rand is one of the leading manufacturers of all types of air compressors such as Air-cooled reciprocating type, air and water cooled Rotary screw type, large reciprocating & centrifugal compressors. Ingersoll rand also cater to all associated equipments & accessories used in the compressed air system.


Ingersoll-Rand is also focusing aggressively to assist various industries & in particularly the textile towards "Encon in compressed air system". Compressed air system is not static but is a dynamic system. The need and requirement keep changing or fluctuating like the demand of textile in this highly dynamic market. Reducing the operating cost has become very essential and there is a potential of reducing energy cost in compressed air by 10-50% in most of the Industries. Ingersoll Rand can support any textile industries interested in reducing their energy costs in compressed air by conducting a compressed air Audit. Before we conclude the last reminder but not least, "Air is free but compressed air is not!!".


About the Author


The author is Manager-Solutionizing (Industrial Technologies), Ingersoll Rand (India) Limited.