By Ron Marshall for the Compressed Air Challenge
A spring water bottling plant had a compressor room filled with a complicated piping to connect their four compressors to the two main areas of their plant. The plant personnel had learned a long time ago that supplying the main plant with excessive pressure increased the power consumed by the air compressors and also caused additional artificial demand, where the compressed air consuming equipment uses more flow at higher inlet pressures.
The operating personnel had modified their supply piping so that the pressure supplied to the machines in the bottle blowing area of the plant was about 140 psi, but the remaining areas were running at about 100 psi. The system was split so that only one compressor ran at the higher pressure and the remaining units ran with more efficient lower discharge pressures. In case the high pressure compressor ever failed (or was shut down for maintenance), a system of crossover connections and regulating valves was implemented so that an one of the low pressure compressors could supply the high pressure system in abnormal conditions.
The plant operating personnel were interested in how efficiently their system was running and agreed to have an auditor come in and place data loggers on their system.
When the auditor analyzed the data, he could see that one of the compressors was contributing almost nothing to the compressed air demand, while the others were running inefficiently due to lack of storage capacity. Due to the complexity of the system, it took a while, but eventually it was found that a regulating valve that should have been bypassed in normal condition was preventing the compressed air produced by one of the compressors from entering the system. The valve also prevented the other compressors from seeing a large storage tank, causing the other compressors to cycle rapidly, lowering their efficiency. The isolated compressor still continued to run very lightly loaded because a receiver tank drain and various leaks expelled just enough air to prevent it from turning off.
It is estimated that this compressor wastes about $26,000 worth of electricity at 10 cents per kWh—plus additional maintenance costs!
In designing this system to be very flexible, the piping became too complicated for the operating personnel to easily understand. The plant had no method of monitoring the compressed air system efficiency so they did not realize there was an issue. The plant is currently developing a procedure to make the correct position of all the valves easier to understand. A method of monitoring the loaded and running hours of the compressors to ensure they are running efficiently is also recommended.
Learn more about compressor control in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.
Cheryl Beebe says
$26,000!! This is a prime example of an out of control process. Upfront audit/maintenance/repair costs to fix the issue may be high, but having a more efficient process long term is going to cost much less.