A food processor purchased a surplus air compressor and dryer at auction for their processing facility. The compressor was much larger than required, but the plant manager had hopes for future expansion. Because the air pipes in the plant run in unheated areas, a surplus heatless desiccant dryer was also purchased.
The dryer has an older style dew point control installed that turns off the dryer regenerating purge—which consumes 25% of the compressors capacity when it is flowing. This typically saves significant power because of the light loading.
It turns out the planned expansion of the plant never happened. Therefore, the average compressed air flow was much lower than the capacity of the compressor, an average of about 7%. A large storage receiver was installed to allow the compressor to turn off between cycles and save power.
An auditor did a plant assessment a few years after the installation and found the compressed air loading was much higher than expected. He found that, over the years, oil contamination had fouled the dryer desiccant because of less-than-optimum filter maintenance. This made it difficult to reach -40° dew point that triggers the control to save purge. The oil had also fouled the dew point sensor on the dryer control, which caused the dryer purge to run constantly. Overall, the auditor calculates that due to the dryer control failure, about 78% of the compressed air produced by the oversized compressor and dryer is being consumed by dryer purge.
The customer is now considering a smaller compressor and more efficient dryer, likely funded partly by a substantial power utility incentive. Plant maintenance practices will also be reviewed.
Learn more about air dryers in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.
By Ron Marshall for the Compressed Air Challenge
Filed Under: Pneumatic Tips