GENERAL TIPS

• Air compressors generates heat, check to see if the heat can be recovered and used elsewhere in the process/site
• If possible, place the air compressor where the temperature inside the plant is at the lowest (not below freezing). This will decrease the inlet temperature and as a result it will operate more efficiently
• Pneumatic equipment/tools may not be the most efficient to use, look at other electric tools and alternatives that may be more efficient
• Ensure the air compressor system is maintained by qualified specialists that are able to ensure the system is operating at its optimum.
• When purchasing new air compressors, speak to your local supplier and ask them for new energy efficient compressors that would meet the site’s air requirements

IDENTIFY & MINIMIZE COMPRESSED AIR LEAKS

The first and foremost effective way to optimize the compressed air system is to ensure the leaks are minimized. Leave the air compressor on during plant shuts and observe the air consumption, if the consumption is still high, it is an indication that there are a lot of air leaks. Use the ultrasonic sound gun to detect air leaks around the plant. Tag all leaks found and list them in a table and mark off the ones that are fixed. Prioritize and fix the largest leaks first.

ANALYZING THE COMPRESSED AIR SYSTEM FOR SYNCHRONIZATION

Determine the Required Quantity, Quality & Pressure Provided that the air leaks are identified and fixed, contact your local compress air service provider and using a data logger measure the amount of air consumed at different times of the day, week etc. Measure at least 7 days and ensure it is representative of what is normally happening at the site. This will provide the site with the air demand for the site.

NOTE: Too often, low or fluctuating pressure at end uses is misdiagnosed as not enough discharge pressure. Perform a pressure profile, this is a series of measurements of compressed air pressure at different points in the system, and allows identification of system components that are causing excessive pressure drop. Contact your air compressor specialist for more information.

Look at the different uses of air on the site and investigate the required quality of the compressed air that the plant needs. Is the quality requirements of air required being met? Do not over-treat air as it consumes more energy than necessary.

Analyze the Collected Data Look at the minimum and maximum demand of the compressed air demand profile. What are the operating hours, is there consumption during periods where is supposedly no use? Where are the peaks occurring? Where are the troughs occurring and why? Can the peaks be rectified and reduced?

Compressed Air Synchronization (Multiply Compressor Control) After analyzing the data collected, look at whether or not compressed air synchronization is suitable for the system. Systems that are suited to synchronization are the ones with large fluctuations in demand (large differences between the peaks and the troughs); where automated controls can help the system to be more efficient.

Compressed air synchronization typically uses a microprocessor linked together to form a logic of communications, this ensures that the compressors are modulated to the site’s compressed air needs. The aim is to produce the required amount and to avoid excessive production of compressed air. The system monitors the demand for air and coordinates between the air compressors available to run the system as efficiently as possible.

To effectively implement this, the system must match the demand with the compressors operating at its optimum level and take into account fluctuations in demand, available storage and the end source use requirements.

There are different types of controls that are available on the market, investigate the most suitable system for the existing compressed air system/network.

COMPRESSED AIR STORAGE The purpose of the air receiver is to store a predetermined amount of air for use to avoid air pressure drop during peak periods of use. Where large fluctuations of air demand exists a large air receiver is suitable, to allow the use of a smaller air compressor.

Location If the receiver is installed before the dryer, it will provide additional radiant cooling and remove some of the condensate and entrained oil. As a result the dryer will run more efficiently and effectively. However if there is a sudden surge of demand the dryer would be overloaded.

When the receiver is installed after the dryer, a sudden surge of demand will not overload the dryer. However the benefits of having the dryer before the dryer are lost.

One way to resolve the issue is to have air receivers on both sides of the dryer.

Size The approximate size of the primary receiver can be calculated using the following formulae (assuming that the air pumped into the receiver by air compressor/s while air is being drawn from the receiver):

Where:

T = Time allowed for pressure drop to occur (Minutes)
C = Air demand of free air (ft³/min)
P_a = Absolute atmospheric pressure (psia)
P₁ = Initial receiver pressure (psig)
P₂ = Final receiver pressure (psig)

If the air compressor is running while air is being drawn from the receiver, the formulae should be:

Where S is the surplus compressor capacity (ft³/min)

Note: to factor in pressure drops from filters, lines, dryer etc will contribute to the pressure drop.

COMPRESSED AIR TRAPS & DRAINS Ensure manual drains and traps are closed and open only when required.  To ensure the optimal operating conditions, all traps must be maintained on a regular basis.

Manual Operation Typically, manually operated air traps and drains are often left in the permanent open position to discharge condensate from moisture separators, intercoolers, refrigerated dryers and filters. This results in compressed air wastefully leaking into the atmosphere. Ensure manual traps are checked and maintained on a regular basis to ensure its effectiveness. 

Level Operated Mechanical Traps When in working order, these float valve designs are effective in draining out condensate and minimize air leak, however they require a high level of maintenance to ensure it does it get blocked with sediment.

Electronic Solenoid Valves These valves can be adjusted to open at interval and even if there is no condensate, it will open and compressed air is wasted or may not be long enough time for condensate to be discharged.

Air Traps with Reservoirs Ensure to drain the reservoirs on a regular basis to prevent the build up of contaminants which leads to the decrease effectiveness of the trap.

ALTERNATIVES TO COMPRESSED AIR Compressed air is an expensive utility and should be used sparingly, where possible substitutes for compressed air should be considered. Below is a table for the common uses of air and recommended efficient alternatives. 

Source & Further Information:

1. http://www1.eere.energy.gov/industry/bestpractices/pdfs/compressed_air_sourcebook.pdf
2. www.compressedairchallenge.org
3. http://www.p2pays.org/ref/14/13584.pdf