The energy efficiency standard adds compressed air specs for the first time, bringing engineers into system design.
A large food manufacturing operation in the U.S. Midwest spends $529,000 annually on energy to operate the compressed air system.
The plant currently has two supply-side systems that operate and feed two different distribution networks at two different pressures. One compressed air system is at 115 psig (medium pressure system) and the low-pressure system is at 30 psig. The compressed air equipment for both systems is located in four areas throughout the facility.
The medium-pressure system has four air-cooled, two-stage, oil- free, rotary screw air compressors. Two air compressors have integrated rotary drum dryers and the other two have external, air-cooled, refrigerated dryers. There is also a single air-cooled, lubricated, rotary screw air compressor. This system supplies the needed compressed air to operate the plant’s production equipment and is located in three different areas.
The low-pressure system has five oil-free, air-cooled, rotary screw air compressors. Three of the air compressors are 125 psig, two-stage units. These units produce 115 psig compressed air which is then regulated down to around 30 psig. The other two are single-stage, oil-free, air-cooled, rotary screw air compressors producing compressed air at 30 psig. One unit has an internal, rotary, heat-of-compression dryer, two have external refrigerated dryers, and one has a water-cooled heat exchanger with a desiccant dryer supplying compressed air to an external building.
Prior to our audit, the plant decided to create a low-pressure compressed air utility room. It purchased two oil-free, 30 psig, centrifugal air compressors and moved the 125 psig units to the medium pressure system. The low-pressure system is for the process of aerating and stirring the ingredient batches in the storage tanks until ready for bottling.
Our firm was invited to examine the demand-side of the compressed air system. We focused on the piping systems and on ways to reduce demand. Due to article space limitations, this audit excerpt focuses on the demand-side reductions identified.
All projected savings in this audit reflect an air compressor control system able to translate demand reduction into energy savings. The system operates 8,400 hours per year and the local electric rate was $0.08 per kWh.
Summary of Demand Reduction Projects
| Project |
Flow Savings scfm |
Power Savings kW |
Energy Savings kWh/yr |
Annual Savings $ |
Estimated Project Cost $ |
| Repair 87 identified and tagged compressed air leaks |
287 scfm |
58.0 |
487,463 |
$39,000 |
$19,000 |
| Install dew point demand control on heatless desiccant dryer |
46 scfm |
9.3 |
78,130 |
$6,250 |
$5,000 |
|
Replace open blows with air saver nozzles and/or auto shut-off controls |
127 scfm |
25.7 |
215,707 |
$17,260 |
$5,000 |
|
Install automatic no-air-loss condensate drains |
3 scfm |
0.6 |
5,095 |
$410 |
$1,200 |
|
TOTAL |
463 scfm |
93.6 kW |
786,395 kWh/yr |
$62,920 |
$30,200 |
Project #1: Compressed Air Leak Survey
A compressed air leak survey was conducted for the plant and 87 leaks were identified, quantified, tagged, and logged. Potential savings totaled 287 scfm for the tagged leaks.
Most of the leaks could not have been found without the use of an ultrasonic leak detector and a trained operator. Leak locating during production time with the proper equipment is effective and often shows leaks that are not there when idle. However, a regular program of inspecting the systems during off-production hours with air powered up is also a good idea. In a system such as this one, some 80% to 90% of the total leaks will be in the use of the machinery, not in the distribution system
Most plants can benefit from an ongoing air leak management program. We recommended that this plant purchase an ultrasonic leak detector and implement a program with maintenance personnel.
| Number of leaks tagged and identified | 87 leaks |
| Air reduction | 287 scfm/yr |
| Annual electric cost savings | $39,000/year |
| Unit cost of leak repairs ($150 materials per leak and $70 labor per leak) | $220 |
| Overall cost of leak repairs | $19,140 |
|
No. |
Location |
Description |
Pressure at Leak (psig) |
Decibel Reading from 6” away (Db) |
Calculated Leak Size scfm |
|---|---|---|---|---|---|
|
1 |
Palletizer |
3/8” Female NPT |
50 |
61 |
3.2 |
|
2 |
Filler Bottle Line |
¼” PPFX Ppt Straight to Solenoid Bank |
50 |
79 |
4.9 |
|
3 |
Labeler |
Regulator Gasket Bad 3/8” In/Out |
50 |
63 |
3.4 |
*All 87 tagged leaks were given this level of description in the above table format to maintenance for repair to be schedule.
Project #2: Install Dew Point Demand Control on Heatless Desiccant Dryer
One of the four areas has a heatless (pressure-swing) desiccant air dryer providing a -40° F pressure dew point. This dryer has a maximum rated flow capacity of 636 scfm. The dryer does not have a purge economizer and is purging the standard 15% of the compressed air to regenerate each tower.
This project involves installing a purge economizer on the unit. We anticipate this project will deliver 46 scfm in savings by reducing the purge rate to 7%.
| Current dryer purge air rate | 15% |
| Current dryer rated capacity | 636 scfm |
| Dewpoint demand control savings | 7% |
| Project flow reduction | 46 scfm |
| Annual energy savings | $6,250/year |
| Estimated project cost | $5,000 |
Project #3: Open Blows
Open blows are devices in which turbulent compressed air blasts straight out of a pipe or tube. This process not only wastes huge amounts of compressed air, but also violates OSHA noise and dead-ended pressure requirements.
Air jets and air flow-inducing nozzles used in place of open blows can reduce noise level, lower compressed air use, and most often improve blow-off operation in both productivity and quality.
We recommend the use of engineered air nozzles for the open blow applications listed in the table.
| Number of open blows to be replaced | 25 |
| Project flow reduction | 127 cfm/yr |
| Annual energy cost savings | $17,260/yr |
| Estimated project cost (25 blows x $200/blow) | $5,000 |
Open Blow Applications
|
Location |
Qty |
Type / Size |
Estimated Current CFM Usage Each |
Utilization |
Net Avg Cfm |
Recommended Action / Nozzle |
New Avg Net CFM Each |
Net Avg CFM Usage |
Est Net Avg Cfm Saved |
| Bucket Feed Clean |
1 |
3/8" Fitting |
30 |
36% |
10.8 |
48008 |
7 |
2.52 |
8.3 |
| Line 3 Filler Dry |
3 |
Wind Jet |
25 |
40% |
30 |
48008 |
7 |
8.4 |
21.6 |
| 1/2 Gallon Filler |
6 |
Wind Jet |
25 |
40% |
60 |
48008 |
7 |
16.8 |
43.2 |
| 1/2 Gallon Filler |
6 |
Silvent |
15 |
40% |
36 |
48008 |
7 |
16.8 |
19.2 |
| 1/2 Gallon Filler |
1 |
2" Venturi |
30 |
40% |
12 |
48008 |
7 |
2.8 |
9.2 |
| Line 1 Labeler |
2 |
Lechler |
5 |
70% |
7 |
48002 |
1.8 |
2.52 |
4.5 |
| Line 2 Labeler |
1 |
Lechler |
5 |
70% |
3.5 |
48002 |
1.8 |
1.26 |
2.2 |
| Line 1 Cap Seal |
1 |
1/4" Poly |
10 |
70% |
7 |
48002 |
1.8 |
1.26 |
5.7 |
| Line 2 Filler |
4 |
Lechler |
15 |
40% |
24 |
48008 |
7 |
11.2 |
12.8 |
|
Totals |
25 |
|
|
|
190.3 |
|
Total |
126.7 |
|
Project #4: Install Automatic No-Air-Loss Condensate Drains
All (but one) identified condensate drains were automatic, no-air-loss condensate drains. These are high quality drains with an internal capacitance tube inside. The only moving part is the drain solenoid.
The exception was one refrigerated dryer that came with a dual-timer electronic drain. This drain should be replaced with a no-air-loss drain.
Dual-timer electronic drains use an electronic timer to control the number of times per hour they open and the duration. In theory, the frequency should be adjusted to ensure that condensate drains open fully and that the open time without water is minimized because compressed air is wasted. But cycles often are not reset from original factory settings, resulting in condensate build-up during the summer and being set wide open during cooler weather. When they fail in “open position,” they blow at a full flow rate of about 100 scfm.
| Air flow (cfm) savings per drain (each) | 3 cfm/yr |
| Total of number of drains | 1 |
| Total compressed air saved | 3 scfm |
| Total annual energy savings | $410/yr |
| Cost of project ($700 materials and $500 installation) | $1,200 |
Conclusion
Manufacturing plants have consistent opportunities to reduce compressed air demand. The projects we repeat at most plants include compressed air leak surveys, heatless desiccant dryer purge economizers, open blows and automatic no-air-loss condensate drains.
For more information on APenergy visit apenergy.com or call 740.862.4112.
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