By Ron Marshall for the Compressed Air Challenge
A rice, grain and oil seed processor was having pressure problems in the various facilities at their manufacturing complex. The site had a central compressed air system that fed air through a network of pipes supplying six separate buildings. As the complex expanded, the compressed air load increased and eventually the pressure started to sag, which was negatively affecting production—even getting so low that finished product was being destroyed.
A compressed air scoping study was done and found that the 100-psi rated compressors were set at their maximum pressure, yet the farthest facility at the end of the line was receiving only 50 psi. Data logging showed a very significant pressure differential across some undersized air dryers and filters at the compressor room. In addition, the pressure differential across the 2-in. steel piping network, a radial feed, was about 30 psi. The site air demand had grown, but the distribution system had not changed.
The plant manager did the obvious thing and set out to improve his piping, upgrading to 4-in. size and looping the network for improved pressure differential. At the end of it, he expected a pressure improvement of slightly less than 25 psi.
Another data logging was done after the work was completed. This found that the pressure had improved by only 8 psi even though the piping capacity was greatly improved and the pressure drop across the air dryers had been reduced by upgrading capacity. This was quite unexpected!
What the plant manager did not know was that by improving the pressure in the entire plant, they had caused an increase in compressed air flow to every unregulated compressed air consumer on the system due to an increase in artificial demand. Artificial demand is the increase in air flow caused by increasing the pressure to an unregulated compressed air end user. Typically, a 1 psi rise in pressure to an unregulated demand increases the consumption by about 0.9%.
As the pressure improved, the increased flow reached a level where the capacity of all the running compressors was exceeded, causing the compressor discharge pressure to drop, rather than fully boosting the plant pressure. The average compressor discharge pressure reduced by about 20 psi, reducing the compressor power consumption, but not giving the plant the boost in pressure they were expecting.
In future, the plant will be regulating the end uses that do not need full pressure and repairing leaks. Some significant projects are planned to eliminate inappropriate uses which will also reduce compressed air consumption to the point that plant personnel expect full expected pressure can be achieved.
Learn more about artificial demand in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.
Dave says
Cool story but I’m really curious to know the end result.
Did regulating the end use and leaks really fix the problem?