Darigold: Compressed Air System Optimization
America's fifth-largest dairy co-op, Darigold has 11 plants in the northwestern United States that produce milk, butter, sour cream, milk powder, and other dairy products. The Sunnyside plant is the company’s largest facility and each day it produces about 530,000 pounds of cheese and 615,000 pounds of powdered dairy products. Compressed air supports production at this plant through control valves, cylinders, positioners, dampers, and pulsing for bag houses. An inefficient distribution system compelled the partner to upgrade its air piping to enable stable system pressure.
MoreThe plant uses two 350-horsepower (hp) air compressors to supply numerous production areas, one fixed speed and one with a Variable Frequency Drive (VFD). Darigold noted that system pressure became elevated to serve production areas deeper in the plant, and large swings in pressure were being seen. For example, pressure at the discharge of the compressors was around 104 Pounds per Square Inch Gauge (PSIG) but demand areas were receiving air at 87 to 97 PSIG. And, because of high demand flows at the end uses, pressure was observed to draw down significantly at times. Darigold was concerned that pressure may have been set higher than needed to accommodate the varying pressures in the plant.
These issues led Darigold to request a Better Plants In-Plant training (INPLT) in 2015 to explore potential improvements and to educate its team, including personnel from other plants, on evaluating compressed air systems. While the training identified several best practices, it also measured pressure losses in piping, and highlighted benefits of improving the air distribution system capacity to accommodate intermittent uses and allow for a lower system pressure, which would reduce energy consumed by the compressors.
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Darigold worked off recommendations from the March 2015 INPLT and replaced an existing 4” header pipe running from the compressors to a storage tank with a 6” header. The shorter pipe diameter hadn’t sufficiently served the system, as engineers recorded air pressure losses starting in the compressor room. Darigold also added a second 4” header pipe parallel to an existing 4” header leading out of the storage tank to supply separate parts of the plant and form a complete loop. This re-configuration was completed in March 2016 and eliminated bottle-necking within the piping, thereby enabling a more stable system pressure.
In addition to supplying the additional compressed air needed, the project also reduced overall energy use by allowing the compressors to run at reduced system pressure. Data logged after the project was completed showed a reduction in system pressure of 10 PSI, with plans to reduce pressure further to 14 PSI. This will translate into annual energy savings of approximately 300,000 kWh and energy cost savings of $15,000, which will yield a simple payback of just over three years.
Before: Showing System Pressure of 104 PSI and 86 PSI at Lowest Point of Use. Wide pressure fluctuations are seen at the farthest distance from the compressor room (teal colored graph)
After: With a system pressure of 100 PSI Leaving Compressor Room, 98 PSI is now seen at the farthest distance with only minor fluctuations. (Further reductions in pressure have been implemented)
The project implementation process served as an opportunity to immerse Darigold employees in the ins-and-outs of compressed air systems. For example, plant engineers took care to analyze air flow requirements to ensure that system piping is adequate to deliver needed pressure to downstream uses. They also consulted flow vs. velocity data to confirm that the system is operating at improved efficiency. Finally, thanks to reduced air pressure, less frequent maintenance requirements for system components is expected.
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