Matching Compressors to Production Demands

How does your facility stack up?

IS THIS WHERE YOU ARE?

1. Operating multiple rotary screw or centrifugal compressors, ALL featuring some form of inlet throttle modulating control.
2. When production shift ends and maintenance shift takes over, are all production compressors just left running in case maintenance personnel need air.
3. No means of compressor performance testing. Delivery output is determined using visual inspection or power draw at full load as performed by either the maintenance personnel or the supplier's rep.
4. Plant leaks might be excessive but addressing leaks is not a priority because maintenance personnel believe there are more important needs to fill and leak mitigation is not a concern.
5. Mentality is evident that since air is available and easy to use and deliver, it is used for menial applications such as blowing dust or water off of product, machine bearing cooling, optical scanning equipment cleaning, cooling personnel, etc.

THIS IS WHERE YOU WANT TO BE!

1. Multiple compressor installation is under control of a programmed PLC sequencer or equivalent. Any compressor running "unloaded" for long periods of time should be shut down automatically.
2. Air Leak monitoring is part of PM (Preventive Maintenance) program and maintenance and planning departments see that leaks get monthly attention and ACCOUNTABILITY.
3. An load flow meter or other flow testing device is installed so maintenance staff can carry out a performance test at least quarterly to confirm compressors are producing rated air, and controls are allowing proper delivery of air into the system.
4. Heatless desiccant air dryer purging is under full control of a RELIABLE dew point monitoring system, delaying unnecessary tower purge swings during periods of reduced air consumption.

An Example of Multiple Compressor Sequencing

Sequencing: refers to the order in which compressors are brought on and off line to satisfy system air demand.

Current Operation:

Time	Days/week	Required Flow	Leak Volume	Compressor On
1st Shift	5	2,500-2,800	400	A & B & C
2nd Shift	5	2,000-2,200	400	A & B
3rd Shift	5	700	400	B
Sat. & Sun.	2	400	400	C

Leak costs: 400cfm is roughly equivalent to 100hp which over a year will cost:
100hp * .746kW/hp * 8760 hrs/yr * $.06/kWh = $39,200 per year

• If just half of the leaks were repaired, the total Third Shift load would be just 500cfm and Unit C could be run instead of Unit B.
• If a dedicated small (perhaps 5hp) compressor were installed to handle the sprinkler and instrumentation loads, Unit C could be turned off each weekend.

Current Operation:

Time	Days/week	Required Flow	Leak Volume	Compressor On
1st Shift	5	2,300-2,600	200	A & B
2nd Shift	5	1,800-2,000	200	A & C
3rd Shift	5	500	200	C
Sat. & Sun.	2	0	0	None

• A multi-compressor PLC based sequencer could be installed at this facility to accomplish the above tasks for less than $5,000.

For additional information or assistance, contact Kelly Beiermann, Nebraska Public Power District.

Note: We encourage requests from Nebraska customers. Businesses outside of Nebraska will be directed to their utility for further information.

Source: Airometrix Mfg., Inc. 1999-2003