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Energy Program
ESA-073-2 Public Report (J.R. Simplot, Nampa) PDF Print E-mail
Written by USDOE Energy Efficiency & Renewable Energy   
Friday, 15 July 2011 10:18

ESA-073-2 Public Report


The JR Simplot plant in Nampa, Idaho, produces frozen potato products, including patties, triangles, and French fries. Potatoes are cleaned, peeled, cut (slices, wedges, fries, or shredded), fried, quick frozen, packaged, and shipped. Primary process equipment includes peelers, cutters, defect removal, fryers, freeze tunnels and packaging equipment. Boilers, air compressors, and 2-stage ammonia refrigeration compressors support the process.

Objective of ESA:

The objective of the ESA is to model your compressed air system using the AIRMaster+ software tool and to use the tool to identify savings from several measures that would improve system efficiency. It is not the objective of the ESA to look at all potential plant improvement opportunities. The JR Simplot plant has an objective to reduce electricity use by 10% and natural gas by 2%, aggressively reduce energy consumption at each of their facilities.

Focus of Assessment:

The focus of the ESA is for plant personnel to understand how the appropriate DOE tool can be effectively applied in the plant. The focus of this ESA is the main compressed air system.

The compressed air system includes 3 compressors: two 150 hp Gardner Denver lubricated screw compressors with turn- valve and unloading controls and one 75 hp Gardner Denver lubricated screw compressor with throttle control. Typically two compressors operate depending on load. One compressor operates during down days. An AirTek twin tower desiccant dryer has an electric heater and dew-point control to improve efficiency and is operating properly. The plant air compressors currently cost approximately $37,000/yr to operate.

The air distribution system has three (3) 650 gallon receivers and one (1) 120 gallon receiver. There is approximately 1750 feet of 2” through 4” header piping throughout the plant that adds an additional 365 gallons of storage capacity. The piping system is efficient with approximately 2 psi drop from the centrally-located compressor room to the far ends of the plant.

Approach for ESA:

  1. Identify and understand the compressed air system(s) and determine priorities for opportunities to pursue.
  2. Identify critical airflows, pressures, end uses, temperatures and other information that will be required for the analysis.
  3. Gather available data and trend logs and develop a list of data that needs to be obtained from other sources or that
    needs to be measured or logged.
  4. Reduce and enter this data into the AIRMaster tool and check for internal consistency, such as with metered energy
    use. Data will be verified and adjusted, if necessary. Team members will enter data into the AIRMaster tool and
    check results for feasibility.
  5. Acquire cost estimates from vendors if possible. Estimate range of improvement costs from previous plant and
    Qualified Specialist experience.
  6. Demonstrate AIRMaster to interested participants.
  7. Complete:
    • Plant Intake Questions
    • Summary Report
    • Software Tool Output
    • Evaluation

General Observations of Potential Opportunities:

Trend logging was added to the three compressors (current in amps) and system pressure, which significantly helped this analysis. The trend data was exported to a spreadsheet and imported into the LogTool for analysis, including AirMaster daytype selection and reduction to hourly averages.

The two compressors with turn valve controls were not operating properly at the time of the site visit. The local air service company ordered parts and installed them the following week. The service company believes that they are now operating properly although both compressors appear to be operating below rated power.

Note what you would expect would be Near Term, Medium Term, Long Term opportunities. See definitions below:

  • Near term opportunities would include actions that could be taken as improvements in operating practices, maintenance of equipment or relatively low cost actions or equipment purchases.
  • Medium term opportunities would require purchase of additional equipment and/or changes in the system such as addition of recuperative air preheaters and use of energy to substitute current practices of steam use etc. It would be necessary to carryout further engineering and return on investment analysis.
  • Long term opportunities would require testing of new technology and confirmation of performance of these technologies under the plant operating conditions with economic justification to meet the corporate investment criteria.

1.    Reduce Air Leaks (savings 0.14% of plant electricity use, 4.6% of compressor use, Near Term)
Situation: Air leaks can be heard at several locations in the plant. We were able to determine the amount of air leaks from the trend log (compressor amps) on a down day. Only the 75 hp compressor was running with no load in the plant except control systems. It was operating at full load at 95 psig, which is approximately 10 psig below the set point pressure. Additional loads caused pressure to drop. We assumed leaks to be approximately 90% of air use on the down day.

Solution: Tag and repair air leaks. An air leak generally costs around $800/year at $0.05/kWh by the time it can be heard. Fixing leaks is generally low cost in both time and materials, with paybacks typically less than one-year

Savings: The plant air system operates 8,760 hours/year. AirMaster calculates savings to be $1,680/yr

2.    Reduce System Pressure (savings 0.07% of plant electricity use, 2.3% of compressor use, Near Term)
Situation: The critical pressure requirement in the packaging department is 85 psig, at which the machines cut out. The goal is to maintain at least 90 psig throughout the plant distribution system. Current minimum pressure in the system is 100 psig. Compressor power and air use (including leaks) are reduced at lower discharge pressure.

Solution: Recommend reducing the discharge pressure at the compressors by 5 psi initially, and more in smaller increments if there are no problems. If a problem arises, consider the cost of resolving the problem versus the savings from reducing pressure. For example, adding a secondary receiver near the end use to meet an intermittent load, or adding a dedicated or booster compressor to satisfy a critical or higher pressure load.

Savings: Savings from reducing system pressure 5 psi are approximately $850/yr

3.    Improve End Use Efficiency (savings 0.02% of plant electricity use, 0.7% of compressor use, Near Term) Situation: A pneumatic diaphragm pump uses approximately 15 scfm to move waste water to an adjacent filter with
approximately 3 feet of elevation.

Solution: Replace the diaphragm pump with an electric pump. We estimated flow and pressure to determine air use from the manufacturer’s specs at approximately 15 scfm. This would require approximately 3 compressor hp to produce. Since electric motors are approximately 10 times as efficient as pneumatic motors, including the compressor efficiency, estimate that the motor would need to be approximately 1/3 hp.

Savings: AIRMaster calculates savings to be approximately $300/yr. We estimated the cost of an electric pump and electric service to be $2,000 for a 6.5 year payback. Don’t recommend this measure due to the payback. It was included as an example of how to calculate savings from replacing less efficient compressed air uses with other methods, such as electric motors, fans, vacuum pumps, or mechanical methods. For example, the plant has several compressed air venturis that pump chemicals for cleanup water.

4.    Use Unloading Controls (savings 1.13% of plant electricity use, 39% of compressor use, Near Term)
Situation: Compressor #3 is the least efficient compressor at part-load, therefore it is base loaded in the AIRMaster proposed system. Compressor #4 has electronic controls with the capability of unloading to approximately 10% of full load compressor power when it operates unloaded for a set period of time. After operating unloaded for another set period of time, the compressor will turn off. However, it will restart immediately if system pressure falls below its reset pressure. After leaks have been reduced AIRMaster calculates that a single 150 hp compressor can provide the required system airflow, allowing one compressor to be turned off.

Solution:I recommend using the existing automatic unloading feature and overrun timer to turn off compressor #4 if it is not needed. This allows significant energy savings from turning a compressor off, while returning to operation immediately and automatically if it is needed.

Savings: Savings from turning off #4 compressor when it is not needed are approximately $14,500, 39% of current air system use.

5.    VSD Compressor (savings 0.09% of plant electricity use, 3.1% of compressor use, Near Term)
Situation: The 75 hp compressor has inlet throttle control, which is the least efficient of compressor control strategies. Throttling compressors are comparably efficient at full load, however, less efficient at part load. Such compressors typically draw 70% of full load power when they are fully throttled, producing no air. We assume that the 75 hp compressor is only used on down days, when it currently operates at full load. However, after reducing leaks by 50% it will operate inefficiently at half load.

Solution: Replace it with, or add, a more efficient compressor at part loads (swing compressor). There are several strategies to achieving this objective. One is a load-unload compressor with adequate storage capacity to avoid short- cycling. Another is a Variable Speed Drive (VSD) compressor. Both operate at similar part load efficiencies.

Savings: Savings are relatively small because the small compressor currently only operates on down days (48/year). However, an efficient swing compressor might find more use as plant loads change in the future. Many utilities now have incentive programs to support system improvements such as this one. AIRMaster calculates savings to be approximately $1,000/yr at a cost of approximately $35,000 before incentives.

Management Support and Comments:

Plant management has recently started a comprehensive corporate energy conservation plan (March 2007). The plan will evolve and become more robust as they move forward.

DOE Contact at Plant/Company: (who DOE would contact for follow-up regarding progress in implementing ESA results...)

Vince Lavorante
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