Unique piping design reduces beverage bottler's electric energy bill

Modern aluminum low-friction piping offers potential savings of $58,068 per year.

By Hank van Ormer and Paul Johnson

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A beverage bottling plant had three oil-cooled rotary screw compressors as its primary air supply. One 150-hp class, 750-acfm at 100 psig at 129 kW unit served as base load with two 75-hp class, 360-acfm at 100 psig at 63 kW units as trim compressors.

The average flow during production demand was 700 acfm at 105 psig with peaks to 820 acfm. Production ran 85 hours per week or 4,420 hours per year. Sanitation ran 35 hours per week or 1,820 hours per year. Non-production ran 48 hours per week or 2,496 hours per year. (Compressed air was required during the weekends.)

The schematic shown here reflects the basic equipment layout and design. The base load 150-hp class unit feeds a 3-in. copper header from the end and the two 75-hp class trim units come in with 90° entry to the 3-in. header from two opposing sides creating a “dead head.”

The air demand during sanitation was 450 acfm or less at 110 psig, and the weekend use averaged 277 acfm with peaks to 410 acfm depending on what maintenance and repair programs were being implemented.

The schematic shown here reflects the basic equipment layout and design. The base load 150-hp class unit feeds a 3-in. copper header from the end and the two 75-hp class trim units come in with 90° entry to the 3-in. header from two opposing sides creating a “dead head.”

The problem

When the 150-hp compressor was able to run base load during production, everything was fine. Usually during the first hour of the production shift, the demand would exceed 150-hp supply, the first trim unit (No. 2) would come on, and the 150-hp unit would now short cycle and average about 50% to 60% load (375 acfm to 450 acfm). The trim unit and the base load unit now run all the time at mostly part load. The plan was for the trim unit to come on line, add air as required, unload, and then turn off. The peak load occurs less than 10% of the time.

According to plant management, after reviewing a proposal for a new VSD controlled compressor (100-hp class) that “would probably” correct the problem, called in an independent compressed air consulting company, Air Power USA, of Pickerington, Ohio, to review the entire situation.

– Hank van Ormer and Paul Johnson

Planned operating cfm/kW profile for 4,420 hours per year:
150-hp: 129 kW x 4,420 hours = 570,180 kWh
75-hp: 63 kW x 4,420 hours x .10 = 27,846 kWh
Planned total kWh = 598,026 kWh x .10 kWh = $59,803/year

The actual operating profile
150-hp: 120 kW x .85 = 109.7 kW
109.7 kW x 4,420 = 484,874 kWh
63 kW x 4,420 x .90 = 250,614 kWh
Actual total kWh = 685,488 kWh x .10 kWh = $68,549/year

The sanitation shift used a steady 450-acfm and this was effectively supplied by the 150-hp class unit:

  • 45 acfm at 60% flow
  • 88% power = 129 x .88 x 2114 kW x 820 hrs/year = 206,606 kWh
  • Planned and actual electrical energy operating cost = $20,661/yr
  •  (206,606 kWh x $.10 kWh)

The weekend shift average of 277 acfm demand only calls for one 75-hp class compressor; however, two units are on almost all the time. As soon as the random demand exceeds the 360 acfm available from one unit, the second unit comes on and both units short cycle at 50% to 60% load. They never reach full blow down and idle therefore, the design idle kW of 20 kW is only 41 kW in the unload short cycle; it was 63 kW at full load. At 50% load as running, you have:

Unit 2: 360 acfm at 63 kW at 2,496 hours x .5 = 78,624 kWh
0 acfm at 41 kW at 2,496 hours x .5 = 51,168 kWh

Unit 3: 360 acfm at 63 kW at 2,496 hours x .5 = 78,624 kWh
0 acfm at 41 kW at 2,496 hours x .5 = 51,168 kWh

Actual total electrical operating energy cost = $25,998/year
(259,984 kW x $.10 kWh)

Total annual operating electrical energy cost = $112,507/year
(259,984 kWh + 206,606 kW + 658,488 kWh = 1,125,078 kWh x $.109 kWh)

According to plant management, after reviewing a proposal for a new VSD controlled compressor (100-hp class) that “would probably” correct the problem, called in an independent compressed air consulting company, Air Power USA, of Pickerington, Ohio, to review the entire situation.

The actual electrical operating energy cost far exceeded the projected cost when the system was upgraded and the compressors had to run at a higher pressure of 108 to 110 psig to deliver 80 to 85 psig to the operating system which also did not equal the design criteria. The compressors, controlled by an OEM supplied central air management system, did not seem to be optimizing the compressor alignment relative to the demand.

According to plant management, after reviewing a proposal for a new VSD controlled compressor (100-hp class) that “would probably” correct the problem, called in an independent compressed air consulting company, Air Power USA, of Pickerington, Ohio, to review the entire situation. Air Power USA Inc. (www.airpowerusainc.com) does not sell equipment nor participate in the sale of equipment and installation. As a consulting company, they offer project management and systems design in addition to energy audit and rebate assessment.

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