Advantages of Predictive Energy Management

Kevin Grider, General Motors

General Motors’ 20/20 sustainability commitment includes reducing energy and carbon intensity 20 percent by 2020. To support this commitment, one of the energy-reduction opportunities being pursued at the Marion Metal Center (MMC) in Marion, Indiana, is the identification and repair of compressed air and steam leaks.

MMC is a stamping operation that utilizes large volumes of compressed air to counterbalance the weight of press slides, blanking operations, process weld cells and various plant support activities. The 62-year-old facility has 2.2 million square feet and a powerhouse that supplies steam heat and compressed air to the entire plant. With the combined efforts of the predictive maintenance and energy management personnel, a process was developed that engaged the workforce and is on track to meet the plant’s targeted goals.

The Waste

Steam/compressed air leaks could be found in boilers, compressors, heating units, steam traps, fans, supply lines, hose reels, process equipment and maintenance equipment. These leaks were not addressed until they were obvious or necessary and plant personnel were interested in improving reliability and reducing energy consumption and costs.

The Cost

The cost of a compressed air leak can be calculated using the following formula:

Leak Cost/Year = Leak Rate (cubic feet per minute or cfm) x (kilowatts/cfm) x 8,760 hours x cost/kilowatt hours (kWh)

For the leak rate, use equipment that can measure flow from the leak, calculate or estimate the size of the leak, and then utilize one of the many charts available on the internet. Please note that employing an online calculator to determine the leak rate will still require the pressure and leak size, as well as possibly the temperature, humidity, etc.

Kilowatts (kW) equal the power consumption of the compressor at the time of obtaining the cfm used in the denominator.

Cubic feet per minute (cfm) should equal the compressed air flow rate at the time of obtaining the kW used in the numerator.

For cost/kWh, take an average cost calculated using the total cost and kWh from a utility invoice.

What Can Be Done?

A leak repair process was developed to tackle waste and reduce consumption at MMC. The reliability and maintainability (R&M) team, predictive maintenance technicians (PdMs), and energy conservation engineer (ECE) proposed purchasing a new ultrasound unit that would support this initiative.

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During this time, the PdMs were trained and certified in airborne ultrasound, and the process began to utilize the equipment effectively. Leak types had to be identified, pinpointed, quantified, tagged, reported, repaired and verified. The results also had to be compiled. Dedication to the new technology required buy-in, interest and support. Cross-training of skilled trades personnel was necessary to provide additional support. Preventive maintenance (PM) routes and schedules were developed, and inspections began. Airborne ultrasound coupled with infrared imaging offered the ability to hear and see anomalies in the predictive curve before they became obvious or failure occurred.

Technologies and Tools

Electromagnetic radiation (infrared) was used to take thermal images of anomalies. Ultrasound was utilized to capture sound files on the anomalies. Computerized maintenance management software (CMMS) and leak log software were also employed. This software allows proper reporting, with findings entered on worksheets and attached to corrective maintenance work orders in the CMMS.

The CMMS also enables repairs to be scheduled or parts to be ordered when necessary. Repairs remain on a backlog until completed. A “leak repairs completed report” is created in the CMMS daily and sent to PdM for verification of the repairs. Follow-up work orders are generated if the problems are not corrected. Leak log software tracks the repairs and tallies the results.

The Gains

Since implementing the leak repair process in 2015, MMC has repaired 620 air leaks and reduced its compressed air consumption by 2,586 cfm. This has generated a savings of $337,379. The carbon footprint reduction included 9,269 pounds/kWh of sulfur dioxide (SO2), 10,338 pounds/kWh of nitrogen dioxide (NO2), and 16,245 pounds/kWh of carbon dioxide (CO2).

The costs to repair the leaks increased from $14,700 in 2016 to $45,580 in 2017, before dropping to $30,845 in 2018. MMC received incentive rebates for 75 percent of these costs totaling $68,343. This rebate program is evaluated annually by the utility and is contingent upon regulatory commission approval.

In addition to the reductions and associated savings, MMC was presented as best practice to GM’s Energy and Carbon Optimization (ECO)team. MMC was also recognized by the Indiana Department of Environmental Management as an environmental stewardship program member for its energy conservation efforts. In 2017, MMC received the Energy Star award from the U.S. Environmental Protection Agency for lowering its greenhouse gas emissions and reducing energy intensity by 14.5 percent within two years.

Proving and Sustaining the Process

To prove and sustain its process, MMC regularly performs energy audits, verifies all repairs, maintains its PM schedules and monitors the volume of flow in the system. The plant also maintains a history in its maintenance software and keeps a leak log for compiling results.

Predictive Energy Management

Predictive energy management (PEM) is a proactive process of identifying and mitigating energy waste. At MMC, energy waste was identified with compressed air and steam leaks. A process was then developed and set into motion.Net reductions of leak waste have been substantial, and the results are proven. However, with the vibration that is created from stamping operations and the scope of the facility, this process must continue to be sustained.

This article was previously published in the Reliable Plant 2019 Conference Proceedings.

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