A tire manufacturer used air cooled lubricated screw compressors to feed the production machinery in their medium-sized plant. The plant is located in an extremely hot climate. Over the years, some of the air compressors at the plant reached the end of their useful life and were replaced. Because the production demand was growing, the plant management decided to increase the total capacity of their system.
Previously the plant used three compressors sized 75, 55, and 30 kW to feed their compressed air to the production machinery. To gain enough spare capacity to protect against compressor failure, a smaller compressor was replaced with a larger 90 kW unit. The plant quickly noticed that whenever this new large compressor was running near full load, it would overheat. Therefore, they adjusted the pressure settings so a smaller compressor operated at full load, while the large unit ran in load/unload with very low duty, reducing the heat it produced.
A compressed air auditor monitored the system to assess its efficiency; when the data was analyzed, the 90-kW compressor was found to be running at extremely poor efficiency. About half of its energy consumption was consumed in the unloaded state.
The auditor recommended base loading the large compressor so it would carry the full plant load, allowing the small compressor to remain off. Unfortunately, the overheating problem returned when this strategy was applied.
After some investigation the auditor noticed that, while the 90-kW compressor had a very large opening for ventilation at the top of its enclosure, the ducting had to be reduced substantially to fit the ventilation ducts leading away from the compressors. After some questioning, the auditor found that the ducting used for the new compressor was the same size as was used for the previous 30-kW compressor. This caused a significant restriction in air flow when used with a much larger compressor—and made the compressor run very hot. The plant is currently changing the ducting so efficient compressor operation can return.
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Filed Under: Pneumatic Tips