Air compressors are essential for commercial and industrial applications. Without these machines, manufacturers would not be able to fulfill their needs in the timely manner. With compressed air networks comprising of thousands of such machines, this aspect of business must also be kept in mind while planning to set up the network.
Air compressors and compressed air network
Air compressors are used in industries for a variety of applications to meet process requirements, operate pneumatic tools, and meet instrumentation needs. These are mechanical equipment used to compress and pressurize air. The centralized compressor air network consists of compressors, filter, after cooler, dryer, intelligent electronic control system, receiver tanks, distribution piping, air cylinder nozzle, ejector, etc. The pressurized air is transferred to various points of usage either directly or through receiver tanks. This post provides Energy Conservation Guidelines for air compressors and compressed air network.
1. Management and control
The industry shall undertake the following:
A. Manage and control operations as per the instructions provided by the Original Equipment Manufacturer (OEM). It shall maintain specific power consumption (SPC) of air compressor as specified in below Table.
B. Ensure that the quality of suction air to the compressor is clean, cool, and dry air for optimum performance.
C. Pre-set a minimum generation pressure of compressed air based on plant requirements to optimize the performance. Maintain optimum pressure setting of slightly more than maximum requirement for the plant to compensate envisaged pressure losses in distribution line.
D. Install receiver tanks of sufficient capacities for compressed air storage so as to cater to load demands and process fluctuations without any trouble irrespective of compressor operational status.
E. Use suitable size of air compressor to meet compressed air demands. The industry shall use dedicated air compressors to meet exclusive high or low pressure demands.
F. Install intelligent flow controller for effective compressed air demand management involving multiple compressor operation.
G. Use the most energy efficient compressors to meet base load in case of multi compressor operation.
H. Isolate compressed air distribution lines wherein compressed air is not required for a prolonged time period.
I. Install suitable pressure gauges on discharge side of air compressor pipe line, air receivers, and end-use points to monitor the pressure of the compressed air for estimating pressure losses in distribution lines.
J. Use air blowers or air gun, wherever feasible, to reduce compressed air usage and leakage levels.
2. Measurement and recording
The industry shall measure and record the following:
A. Electricity consumption on daily basis using dedicated energy meter.
B. Discharge pressure and temperature of compressed air and inlet temperature of air on daily basis to evaluate free air discharge (FAD) of individual air compressors to assess the specific power consumption (SPC).
C. Pressure across inlet air filter and record pressure drop. Higher pressure drop will increase electricity consumption (refer Table 5.2). Measure load time and unloading time of the individual compressor on daily basis.
D. Leakage on monthly basis to estimate air leakages and undertake remedial actions to plug off leakages. Some of the common points of leakage in a compressed air system include joints, valves, bends, etc.
3. Maintenance and inspection
The industry shall:
A. Inspect and clean air filters on weekly basis. Replace air filters based on suction air conditions.
B. Avoid moisture carryover in compressed air by draining the accumulated moisture on a daily basis.
C. Check oil level and oil leakage for oil-based compressor system on daily basis.
D. Inspect and remove fouling of inter-cooler and after-cooler to ensure optimum performance air compressors on quarterly basis.
E. Inspect the compressor for vibration and noise level on quarterly basis.
F. Undertake overhauling of air compressors on a periodical basis, as recommended by OEMs.
G. Calibrate instruments and gauges as per the recommendations of the suppliers to ensure reliability and maintain accuracy of data.
4. Necessary measures when installing new facilities
The industry shall consider the following:
A. Undertake demand assessment of compressed air to select a suitable compressed air system based on the existing requirements as well as considering the immediate expansion plans. This includes energy efficient systems, such as in-built VFD, motor with permanent magnet, inverter type air compressor, etc.
B. Select and install air compressors with the lowest SPC while meeting the compressed air demands.
C. Avoid installing oversized air compressors, which may lead to inefficiencies in operation.
D. Install air compressor closer to point of use.
E. Consider the following while designing and installing a compressed air network:
Installing ring main loop header for minimizing pressure losses in compressed air distribution network.
Use seamless metallic pipes or fibre reinforced plastic (FRP) pipe for compressed air lines. Install optimum size piping and increase diameter of pipes whenever a new compressor is added to the system.
Provide a minimum slope of 1 inch for every 10 ft in main header to facilitate moisture drainage. The distance between two drain points shall not exceed 30 metres. Provide adequate auto drain traps and strainers in receiver, main, and branch lines.
Avoid unnecessary bends and turns in distribution network to minimize pressure losses. Take tapings from branches from top of the main pipeline.
Install separate high pressure and low pressure lines.
Use moisture separators to remove moisture before entering pneumatic equipment. The separator is not required if the industry has installed air dryer.
Install dedicated air receiver close to the location wherein intermittent high volume compressed air is required.
Install pressure reduction valves for low pressure applications and boosters for high pressure applications.
G. Meet fluctuations in compressed air demands using VFD-enabled screw air compressors. While using multiple air compressors system, the industry shall use one-inverter type air compressor with a suitable pressure setting to meet the variable load conditions while the other air compressors shall be used in continuous operation to cater to the base load. Use reciprocating compressor for part-load applications.
H. Use centrifugal compressors for meeting high volume air with low pressure applications, wherever feasible.
I. Install air dryers in the distribution line which supplies to dry air usage points only, for example, instrumentation air.
J. Ensure the proper location of air compressors and the quality of suction air as per the recommendation of OEM.
K. Avoid exposure of compressor to direct sunlight or other heat producing units, while ensuring adequate ventilation of air compressor room.
The industry shall:
A. Ensure compressed air leakage within 3% to 10%.
B. Maintain operating SPC within the design range as provided by the OEMs.
The typical specific power consumption levels of different types of air compressors used in the industry are provided in below Table.
Specific energy consumption of air compressor
Source: ENERGY CONSERVATION GUIDELINES FOR MSME SECTOR - BEE
The industry shall assess the specific power consumption using the following formula:
Specific power consumption (kW/cfm)= Electricity Consumption (kW)/Free air discharge (cfm)
Free Air Discharge (FAD) of an air compressor is estimated using the following formula:
FAD = V/t * Pd/Ps * Ti/To
FAD = Free Air Discharge (ft3/min)
V = Volume of air receiver including interconnecting pipes (ft3)
t = Time taken to fill receiver (min)
Pd = Cut-off or final air pressure (kg/cm2)
Ps= Atmospheric air pressure (kg/cm2)
To= Compressed air exit temperature (°K)
Ti = Inlet air temperature (°K)
Leakage test is carried out to quantify the level of air leakage from compressed air network, and is computed as follows:
Leakage rate (%) = Onload time (sec)/ off load time (sec) + Onload time (sec) * 100
Annual energy wastage (kWh) = FAD (cfm) × Leakage rate (%) × SPC (kW/cfm) × Annual operating hours (hour)
Source :- ENERGY CONSERVATION GUIDELINES FOR MSME SECTOR ENERGY by Bureau of Energy Efficiency Ministry of Power, Government of India