A wood products manufacturer had a problem — it was running out of compressed air capacity. Many times a day, the plant pressure would drop and the workers would lose their most critical production line.
Faced with this problem, the Maintenance Manager did a search of the company inventory and found a spare 200-hp compressor. This unit was quickly installed and the plant pressure problems were solved. But the most critical production line needed 110 psi to run at full capacity. Even with the added compressor, they struggled to keep the pressure up, even to 105 psi.
The compressor they had installed was only rated at 100 psi, but could produce higher pressures if it was placed in continuous mode, where the inlet valve modulated to control the flow. However, the Maintenance Manager soon learned that this type of operation came with a price tag.
A compressed air auditor did an assessment of this compressed air system and found that the input energy was very high compared to a normal optimal system. Instead of consuming a normal 18 kW per 100 cfm, this system was producing air while demanding 25 kW per 100 cfm output — about 40% higher than normal.
Measurement instrumentation placed on the system showed that the spare 200 hp compressor was consuming about 80% of its rated power, but on average only producing about 10% of its rated flow! The modulation mode was to blame.
The extra power this compressor consumed was costing about $87,000 per year in extra electrical costs!! Over the last 5 years, the spare compressor had consumed an estimated $440,000 in extra energy costs, more than enough to pay for any new compressors rated for higher pressure.
The compressed air auditor identified further savings potential of $24,000 per year by rearranging the compressors so that one smaller unit was dedicated to the high pressure requirement, allowing all the other compressors to operated at a lower 90 psi plant pressure. A number of leaks and inappropriate compressed air uses were also found that were wasting about $50,000 per year in energy costs.
Plans are in place to refurbish the compressor room to upgrade the compressors to more efficient design, lower the pressure, reduce waste and recover the heat of compression for building heat. These changes will yield significant savings, very quickly paying for the costs of the system upgrade.