Compressed air is one of the major power consuming equipment in many process industries. Power saving in compressed air can bring significant energy saving.
Let us find ways to improve compressed air system efficiency : –
1.Waste Heat recovery : more than 85% of energy is lost in air compressor as heat. Heat of air compressor can be used to generate hot water like preheating of boiler feed water or for any other heating application typically upto 70 deg C.
Please refer below case study for waste heat recovery in air compressor for further detail
Waste heat can also be used in HOC dryer for production of dry air.
for differnt types of dryer :
2. System load: Air leakages are the most common and many place gets unnoticed due to difficulty in visualizing losses. Proper check for air leakages to be performed in frequent period to identify and eliminate losses. Ultrasonic leak detector shall be useful for identifying air leakages.
3. Right pressure: Delivery pressure of air compressor to be maintained at minimum possible. For eg if consumption air pressure requirement is 4 Kg/cm2, air compressor delivery pressure should not be maintained above 5 Kg/cm2. Pressure losses in distribution system must be minimized to save energy.
Reduction in 1 Kg/cm2 of delivery pressure will reduce air compressor power to 5-6%.
Following ways for reducing distribution losses :-
a. Piping size: under sizing of piping will increase pressure drop across distribution network. Therefore piping size must be designed with minimum distribution pressure loss.
b. Air distribution : Air distribution to be analysed and made proper. Many times it is noted that air distribution keep on increasing and due to uneven pipe sizing pressure drop to particular consumption point gets increased . To compensate pressure drop at consumption point compressor pressure and complete line pressure increased.
c. Low friction piping : low friction piping helps in reducing air pressure drop across distribution system.
d. Correct piping accessories: Globe valves, sharp bends , long piping to be avoided in compressed air piping to minimize pressure drop. Ball valve may be used.
e. “Ring Main” Closed loop piping system to be used for long distance compressed air piping system
4. Air filter pressure drop : observe suction air filter pressure drop and clean it regularly. Every 250mmWC of pressure drop across filter will reduce efficiency of air compressor by approx 2%.
5. Lower inlet air temperature and humidity: Every 4 Deg C of increase in air compressor inlet air temperature will increase power consumption by 1 %. Therefore air compressor to be installed at cool place and under proper shed,
Heat of other nearby machine should not affect increase in suction air temperature. If air cooled machine are installed nearby air compressor vent of hot air should be thrown away from air compressor.
Lower humidity is desirable to maintain compressor efficiently hence equipment like cooling tower air, steam flash and evaporation ponds should be avoided near air compressor installation area.
6. Energy efficient condensate drain : Condensate needs to be removed from air piping and receiver for efficient distribution and life of distribution system. While removing condensate care to be taken for avoiding air loss. Timer based condensate drains are not efficient, hence level based auto drain with zero air leak to be installed in air distribution system.
7. Loading and unloading of compressor and use of VFDs : Loading and unloading of compressor to be checked. if unloading of air compressor is more than 20%, VFD may be explored , for higher than 40% of air compressor unloading right size air compressor to be planned.
8. Right Selection of Air Compressor : Selecting right air compressor is important for energy efficient operation. During selection low specific power consumption machine (kw/cfm) machine to be considered. Based on quality and quantity of compressed air different air compressor technology like screw, reciprocating, centrifugal is available even multistage compressors can be right choice for many application.
9. Separation of lower and high pressure requirement : As air compressor power depends on delivery pressure, Lower and higher pressure requirement should be separated and different air compressors to be used for different pressure application.
For small high air pressure and low volume requirement, air boosters may be explored.