Industrial Utility Efficiency

# Inappropriate-Use Assessment Saves 1,881 scfm

### Audit of the Month

 Where: United States Industry: Food & Beverage Issues: Compressor Efficiency, End Uses Audit Type: Supply and Demand Side
 System Assessment Win/Win Results Reduction in Energy Use: 5,870,564 kWh Reduction in C02 Emissions: 4,186 metric tons Equivalent C02 for Homes: 586 cfm Equivalent C02 for Vehicles: 861 vehicles Approximate Annual Savings: \$364,211 Investment: \$435,800 Energy Rebate: 0 Simple ROI: 14.4 months
 Compressor System Before Assessment Operating Hours: 8,760 hours Power Cost kW/h: \$0.06 Avg. Air Flow: 5,068 scfm Avg. Compressor Discharge Pressure: 88-98 psig Avg. System Pressure: 72 psig Input Electric Power: 1,318 kW Compressed Air Specific Power: 3.85 scfm/kW Annual Energy: 11,545,680 kWh Electric Cost per Unit of Air: \$137.00 per scfm per year Annual Compressor Energy Cost: \$692,740 Annual Dryer Energy Cost: \$43,016
 Compressor System Before Assessment Operating Hours: 8,760 hours Power Cost kW/h: \$0.06 Avg. Air Flow: 3,187 scfm Avg. Compressor Discharge Pressure: 85 psig Avg. System Pressure: 80 psig Input Electric Power: 647 kW Compressed Air Specific Power: 4.9 scfm/kW Annual Energy: 5,675,116 kWh Electric Cost per Unit of Air: \$103.08 per scfm per year Annual Compressor Energy Cost: \$328,529 Annual Dryer Energy Cost: \$0

This factory currently spends \$735,757 annually on the electricity required to operate the compressed air system at its plant. The group of projects recommended in the system assessment will reduce these energy costs by an estimated \$364,211 (49% of current use). Estimated costs for completing the recommended projects total \$435,800. This figure represents a simple payback period of 14.4 months. ### Current System Description This is a relatively large operation with ten production lines. The compressed air system is supplied compressed air by several generations of mostly Joy (Cooper Cameron) compressors and two 1995-era Ingersoll Rand 300-hp class units. The Joy units include two 1975-era, 500-hp class machines, two 1985-era, 450-hp class machines, and one 2000-vintage 200-hp compressor. These compressors are well applied and apparently very well maintained and monitored on their central data acquisition system. The air is water-cooled after-cooled and then goes to four blower purge dryers on the 2nd Floor. During our site visit, all the dryers were working well with their dewpoint demand control engaged and working. Pressure dewpoints were always at –40_F or lower. The plant runs 24 hours a day, 7 days a week, almost all 365 days a year. There are two planned shutdown days every year. For calculating usage, we have agreed to use 8,760 hours per year. The new negotiated power cost from the plant’s utility provider is 6 cents per kWh. ### Measurement Actions Taken The following actions were taken to establish baseline measures for flow and pressure: 1. Temperature readings were obtained on all units using an infrared surface pyrometer. These were observed and recorded to correlate to the unit’s performance, load conditions and integrity. 2. Critical pressures including inlet and discharge were measured with calibrated digital calibrated vacuum and pressure test gauges with an extremely high degree of repeatability. 3. The input kW and other pertinent electric operating data on all units was taken from the plant’s very effective operating data monitoring systems. 4. The same basic measurement activity was carried out for system pressure using a similar, high-caliber Ashcroft test gauge. 5. Air flows (scfm) were measured and logged with a thermal mass, heated, wire-type flow meter with data fed to the plant’s monitoring system. We were able to capture this data from the plant’s monitoring system. ### Establishing the Cost of Compressed Air During our site visit, the air compressor units performed very well, spending very little time in blow-off. However, there are seven air compressors and usually three units carry the plant – two are at idle and two are not running, waiting to come on in the auto hot start “ready” mode. The air system operates 8,760 hours per year. The load profile (air demand of this system) is relatively stable during all shifts. Overall system flow ranges from 4,000 scfm during production to 5,000 scfm. The system pressure runs from 68 to 73 psig in the headers during production. Actual electrical demand of the air compressors was measured at 1,318 kW while producing 5,068 scfm of compressed air. The blended electric rate is \$0.06/kWh and the facility operates 8760 hours per year. Annual plant electric costs for compressed air production, as operating today, are \$693,161 per year. This equals a “cost of compressed air per year”, of \$136.69 per scfm.

If the electric costs of \$43,106 per year associated with operating ancillary equipment such as dryers are included - the total electric costs for operating the air system are \$736,177 per year.

### The INAPPROPRIATE USES of 1,881 scfm

The System Assessment recommends both supply-side and demand-side modifications. Due to space limitations, we will only detail the demand-side action plans in this article. The summary of the supply-side recommendations is:

1. Installing a new, more-efficient, base-load centrifugal air compressor to carry the load of the factory. The existing units will be shut-off and used as back-ups. The new air compressor will have a compressor-control system allowing the factory to benefit from the air useage-reduction projects outlined in the demand-side recommendations.
2. Replace the current blower-purge desiccant dryers with a new heat-of-compression air dryer. Existing dryers will be shut-off and used as back-ups.

The Demand-Side Assessment identifies several ways to reduce the compressed air demand (scfm) in the factory. It is critical to note that the energy-savings documented will only be realized if the new air compressor with the load-adjusting compressor-control system is installed. The demand-side actions are:

1. Repair 218 tagged compressed air leaks for 908 cfm in savings
2. Place automatic shut-off valves on laser cooler units for 150 cfm in savings
3. Reduce blow-off and open-blows for 401 cfm in savings
4. Make vacuum generator adjustments for 62 cfm in savings
5. Eliminate Pneumatic air amplifiers for 360 cfm in savings
 *Savings are dependent upon the installation of the new air compressor which has the capacity-control system required to translate reductions in air use into lowered electric costs.

### Conclusion

This case study is a perfect example of a factory which “did not have any issues” with compressed air. Plant pressure was stable, air quality was good, and production was never affected by compressed air. The only issue was that they were paying \\$364,211 more than necessary in electricity costs to power the compressed air system! A thorough supply- and demand-side system assessment was the solution.