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Process Energy Benchmarking for the Metalcasting Industry


n every energy program, we talk about benchmarking. To know how much we could save by optimizing our process, we need to compare our current performance to benchmarks. The problem is how to determine those benchmarks. The prior column discussed difficul- ties in benchmarking a plant; this column will discuss benchmarking a particular process.

I As an example of the importance of

benchmarking, I worked with a company that bought a new set of heat treat fur- naces. After several years in operation, they had yet to benchmark their energy performance. Te assumption was a new furnace meant great energy performance. It turned out measured energy perfor- mance was extremely poor on these new furnaces. Problems with both scheduling and furnace settings had cost the com- pany hundreds of thousands of dollars over those years. When benchmarking a process, you need to be sure you are comparing the same things. • Some reported numbers might be based on energy used during a single cycle such as melting a batch. Other numbers are based over time such as over a month. Personally, I like energy numbers over a month since it includes inefficiencies like mainte- nance, scheduling problems, weekend shutdown-startup activities, and the variation in shift performance. Tis extra energy is your actual cost in running the fur- nace. Batch numbers gives you performance of your equipment while month data gives you a measure of your process.

• Watch that the benchmark is from the same technol- ogy. Te benchmark for a cold air furnace and a hot air furnace (like a regenera- tive or recuperative) , are vastly different. Electric and natural gas furnaces

have very different numbers.

• Melting furnaces tend to use Energy Intensity numbers such as Btu/ lb. or kWh/t or mJ/t. Heat treat furnaces tend to use Energy Ef- ficiency calculations based on the final temperature. This method is needed since the amount of energy to bring metal to 200F or 1,000F is quite different, even though both may be called “Heat Treat.”

• Watch the denominator. We say Btu per lb. [or kWh/tonne or MJ/ tonne]. Tis may be the pounds ini- tially loaded into the furnace (charge weight), the pounds out of the furnace (pour weight), or it may be the “good pounds out” of the process after scrap and recovery losses (cast weight). My preference is charge weight. Tis tells you the energy performance of the furnace based on heat required to process this total metal. “Good pounds out” includes the influence of recovery within the process. Benchmarking can be internal (us-

ing internal performance) or external (using data from furnaces outside your company). External is better, but sometimes

you just can’t find those numbers or your particular process is unique. To use internal numbers: • Collect energy intensity data from all similar furnaces at a plant and/ or within the company and go back in history as far as you can . . . the

more data the better. Use whatever time period works for the company. For instance, monthly data can be compared.

• Find the first quartile of the data. In most popular spreadsheets, this func- tion is simply “=quartile(range,1)”. Twenty-five percent of the data is less than the 1st Quartile value. Tis is a better number than the average. Us- ing this value as a benchmark means your new goal is a stretch but it can be achieved. Since you are already achieving this goal or better 25% of the time, naysayers can be challenged.

• As improvements are made over time, recalculate the 1st Quartile. Ideally the numbers should improve so your benchmark will move. External benchmark numbers

from an outside authority are best. Te problem is finding these numbers. Some options: • Manufacturers/Vendors—Talk to the vendors from both the equipment you own and competitors. Te numbers from vendors tend to put their prod- ucts in the best light and are often single cycle data versus monthly data, but discuss this point.

• Technical Papers—Read industry technical papers to obtain numbers from different studies. Some num- bers are averages while others are state-of-the-art. Some are based on pounds in (charge weight) and others are based on pounds out (cast weight). Read carefully. Based on your opera-

tions, you may not be able to reach state-of-the-art benchmarks immediately, but gathering this data and comparing to your actual operation allows you to see the possibilities and have a goal for improvements.

Using the first quartile value is a good way to benchmark your metalcasting facility’s performance.

Te final column on this topic will describe an automated method developed by AFS to continuously benchmark and produce manage- ment reports of power utilization for furnace operations.

June 2017 MODERN CASTING | 45

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