May 29, 2020
In the previous blog, it was highlighted that the power cost contributes major part in the life cycle cost of the compressed air. It's like an iceberg whose depth below sea level, if ignored may sink your ship filled with earnings similar to Titanic.
So, it is important to keep your ship of earnings away from the iceberg with hidden losses while making buying decisions for compressed air. Let’s sail through with our air experts, to keep this cost at minimum level by discovering solutions to reduce power cost for useful production.
In any industry, air consumption varies between fixed load to intermittent demand i.e. fluctuating demand. This situation depends on application process and distribution of air. So, it is recommended to have good understanding of air demand pattern in your plant.
Around 88% of all the industrial pneumatic application have fluctuating demand profile and the below image explains the pattern of air demand in any industry.
Today such profiles are normally catered by a compressor which are designed for peak requirements. If the choice of compressor is a fixed speed, then it will be modulating between a minimum and maximum pressure which also called load and unload pressure respectively. These machines normally operate with a fixed output and go to idle run to adapt to lower demands and hence they may not be the right choice to save energy. While doing so the fixed speed machine faces three major pit falls.
These can make serious dents in the ship increasing the power consumption by 35%. Remember every drop saved is an extra buck earned!
In traditional compressors with generic comtroller, the motor will continue to run for a fixed amount of time (e.g. 6 min for 45kW) at each switch-over to unload. This is to meet the limitations on motor starts per hour (e.g. 10st/h for 45kW).
On the other hand, the new generation of control principle and intelligent machine learning is used to study the air consumption pattern and the running parameters of the compressor, which anticipates these idle zones. The starts/stops of the motor are utilized through an algorithm to delay the 2nd stop based on a shorter idle zone, thus saving idle running time. This is called Delayed Second Stop(DSS) and the adjacent image show how this works. The DSS algorithm will stop the motor as soon as possible after a switch -over to no load.
The DSS-algorithm can realise an important reduction on the no-load running time in conditions of intermittent operation with prolonged stop periods. The result is a net savings of 10% over traditional load-unload compressors.
This is a major step in insulating the compressor from limited starts and stops. A normal compressor uses a star/delta starter or a DOL (Direct on-line) starter, both have a higher starting current hence limiting the no. of starts for the motor and increasing the starting power consumption as well.
Using soft starter or a variable frequency drive (VFD) enables the compressor with smooth starting and hence the machine can start and stop ‘n’ number of times. The hidden benefit is also downsizing the back up electrical equipment like generators, transformers or UPS systems.
Every time the compressor unloads or stops, it has to depressurize otherwise the pressure inside the compressor may vent through suction taking all the oil with it. Hence this compressed air is vented out slowly through a blow-off valve and thus wasting the power consumed to generate it .
This blow-off is the deepest part of the iceberg, also a big hole in our ship of earnings, which is difficult to calculate. A comprehensive Airscan (power audit) can be conducted to bring more insights on potential savings.
A true VSD compressor stops in pressurized condition, avoiding blow-off and can start ‘n’ no. of times without having to run in idle condition.
So, we have seen, Power Cost = Load + Unload + Blow-off
If the pneumatic applications are varied and the air is distributed into various departments or machines from a single source, then mostly the usage would be fluctuating as shown in the above video.
Hence, the recommended solution is to have variable speed drive (VSD) compressor. It plugs all these holes in the ship and makes it ready for long voyage of profitable productivity with 50% earnings.
Stay tuned for our next blog in this series to know how these earning opportunities can be availed from the VSD compressor!