Industrial Utility Efficiency

# Optimizing Vacuum Generators in Case Packers and Palletizers

This glass container plant is very large and very well laid out with a very apparent “culture of quality.” They run (14) IS machines and inspection lines on four furnaces.

Currently the plant has three basic air systems: low-pressure air (52 psig); high pressure air (100 psig) and oil free instrument air (100 psig). The low-pressure air averages about 21,700 scfm with peaks to about 25,000 scfm. The high-pressure air system and the instrument air system average about 4,000 scfm at 100 psig with peaks to less than 4,800 scfm.

Annual plant electric costs for compressed air production, as operating today, are \$3,050,625 per year. If the electric costs of \$27,811 associated with operating ancillary equipment such as dryers are included the total electric costs for operating the air system are 3,078,436 per year.

These estimates are based upon a blended electric rate of \$0.085 /kWh. The high and low-pressure air systems operate 8,760 hours per year. The load profile of this system is relatively stable during all shifts for both systems. This was a complete supply and demand-side system assessment. The supply-side audit involved shutting off old air compressors and purchasing newer more efficient air compressors and dryers. The demand-side audit involved finding ways to improve the piping and reduce compressed air consumption. Due to space limitations, this article will focus on some demand-side actions taken. Although the low-pressure leak audit yielded 287 cfm in demand reductions and the high-pressure leak audit yielded 22 cfm in demand reductions, this article will focus on other lesser-known project areas where a plant can reduce compressed air consumption. ### The Existing Compressed Air System Low Pressure: The low-pressure air supply is comprised of mostly old centrifugal air compressors. There are five TA18s with aftercoolers, four TA50’s without aftercoolers, one small TA2000 150 hp centrifugal and a newer (2011) TA6000 1,250 hp centrifugal with an aftercooler. Specific power ranges from 6.49 scfm/kW (\$114.67 /scfm / year) on the TA2000 to 7.62 scfm/kW (\$97.76/scfm/year). This is a 14-15% variance in basic air production efficiency. Most units appear to be in relatively good working order and well maintained. High Pressure: The high-pressure system is comprised of newer small centrifugals and single-stage rotary screws. There are two TA2020, 250 hp centrifugals, two older TA975 single-stage, lubricant cooled rotary screws, and four single-stage, lubricated rotary screws. All units are water-cooled and installed in a very hostile operating environment in the basement. Specific power ranges from 4.66 scfm/kW (\$146.66 /scfm / year) on the rotary screw compressor and 5.45 scfm/kW (136.50 /scfm / year) on one of the centrifugals. This is a 14-15% variance in basic air production efficiency. These units appear to be well maintained, but they are operating in a very harsh environment.

Instrument Air System: The “oil free” air for the instrument air system is supplied by three Joy WGOL-9 single-stage, double-acting reciprocating compressors. These units are very old and are applied at 100 psig discharge pressure which, even though it’s within their rating, will cause excessive premature wear of rings, seal etc. Their optimum operating discharge pressure is really around 70-75 psig.

### Project #2: Replace Air Vibrators

Air vibrators are used to keep product or packaging moving or separated – e.g., keeping lids separated prior to sealing. If a plant employs air vibrators that use about 10 cfm each, they will require about 2.5 hp or more to produce the same as a similar electric vibrator, which might use about 0.25 hp input energy. Air vibrators can almost always be replaced with electric except in foundry sand mold operations.

 List of Air Vibrator Retrofits Location Qty Usage (%) Air Flow (cfm) Savings (cfm) Scale 6 / Outlet #2 1 100 15 15 Scale 1 / Oulet #2 1 100 15 15 Scale 2 / Soda Ash 1 100 15 15 Scale 7 / Cullet 1 50 15 8 TOTAL 4 60 cfm 53 cfm

### Conclusion

The system assessment at this plant realized significant demand-side reduction opportunities. Both the high-pressure and low-pressure systems saw their air flows reduced. This was then leveraged into savings through modifications to the supply side of the system.