Checklist for Energy Efficiency in Compressed Air System
Compressed air leakage of 30 – 40 percent is not uncommon. Carry out periodic leak tests to estimate the quantity of leakage.
Reduce compressor delivery pressure, wherever possible, to save energy.
Ensure air intake to compressor is not warm and humid by locating compressors in well-ventilated area or by drawing cold air from outside. Every 4°C rise in air inlet temperature will increase power consumption by 1 percent.
Clean air-inlet filters regularly. Compressor efficiency will be reduced by 2 percent for every 250 mm WC pressure drop across the filter.
Keep compressor valves in good condition by removing and inspecting once every six months. Worn-out valves can reduce compressor efficiency by as much as 50 percent.
Install manometers/PTs across the filter and monitor the pressure drop as a guide to replacement of element.
Minimize low-load compressor operation; if air demand is less than 50 percent of compressor capacity, consider change over to a smaller compressor or reduce compressor speed appropriately (by reducing motor pulley size) in case of belt driven compressors or even replace gear-set.
Consider the use of regenerative air dryers, which uses the heat of compressed air to remove moisture.
Fouled inter-coolers reduce compressor efficiency and cause more water condensation in air receivers and distribution lines resulting in increased corrosion. Periodic cleaning of intercoolers must be ensured.
Compressor free air delivery test (FAD) must be done periodically to check the present operating capacity against its design capacity and corrective steps must be taken if required.
If more than one compressor is feeding to a common header, compressors must be operated in such a way that only one small compressor should handle the load variations whereas other compressors will operate at full load.
The possibility of heat recovery from hot compressed air to generate hot air or water for process application must be economically analyzed in case of large compressors.
Consideration should be given to two-stage or multistage compressor as it consumes less power for the same air output than a single stage compressor.
If pressure requirements for processes are widely different (e.g. 3 bar to 7 or 10 bar), it is advisable to have two separate compressed air systems.
Provide extra air receivers at points of high cyclic-air demand which permits operation without extra compressor capacity.
Retrofit with variable speed drives in big compressors, say over 100 kW, to eliminate the `unloaded’ running condition altogether.
Keep the minimum possible pressure range between load and unload pressure settings.
Automatic timer controlled drain traps wastes compressed air every time the valve opens. So frequency of drainage should be optimized.
Check air compressor logs regularly for abnormal readings, especially motor current cooling water flow and temperature, inter stage and discharge pressures and temperatures and compressor load-cycle.
Install equipment interlocked solenoid cut-off valves in the air system so that air supply to a machine can be switched off when not in use.
Present energy prices justify liberal designs of pipeline sizes to reduce pressure drops. Compressed air piping layout should be made preferably as a ring main to provide desired pressures for all users.
A smaller dedicated compressor can be installed at load point, located far off from the central compressor house, instead of supplying air through lengthy pipelines.
All pneumatic equipment should be properly lubricated, which will reduce friction, prevent wear of seals and other rubber parts thus preventing energy wastage due to excessive air consumption or leakage.
Misuse of compressed air such as for body cleaning, agitation, general floor cleaning, and other similar applications must be discouraged in order to save compressed air and energy.
Pneumatic equipment should not be operated above the recommended operating pressure as this not only wastes energy bus can also lead to excessive wear of equipment’s components which leads to further energy wastage.
Pneumatic transport can be replaced by mechanical system as the former consumed about 8 times more energy. Highest possibility of energy savings is by reducing compressed air use.
Pneumatic tools such as drill and grinders consume about 20 times more energy than motor driven tools. Hence they have to be used efficiently. Wherever possible, they should be replaced with electrically operated tools.
Where possible welding is a good practice and should be preferred over threaded connections.
On account of high pressure drop, ball or plug or gate valves are preferable over globe valves in compressed air lines.