At one period in my career, I was working at a paper mill where I had a lot of projects that depended on the mill running.
I needed live data to analyze so that I could tweak the process. When the mill took a few weeks of market downtime, most of my projects were on hold. What was I to do?
One of my responsibilities was energy management. The boiler wasn't running, and there was no steam being generated, but one form of energy still running was the air compressors. Compressed air is one of the least efficient forms of energy, and an average system can lose 30% of its compressed air through leaks.
A paper mill's compressors can usually be found tucked away in a corner of the basement, complete with air dryer systems to remove water vapour and prevent condensation in the line. During events that use a lot of compressed air, such as a paper machine break, a lot of this air gets used in a short time. For this reason, there is usually a storage tank to provide a reservoir of compressed air. In my mill it was a huge riveted cast iron tank built in the 1920s to supply four paper machines, only two of which were still running. If your data historian records air pressure, it's useful to look at the time trend and see how often there is a significant dip in air pressure. If it's a very rare event, you probably have too much compressor capacity and are spending most of your money feeding air leaks.
When a paper mill is shut down, it's a very quiet place – and a perfect time to carry out a compressed air leak survey!
I took a notebook and a camera, and started my survey. Over a couple of days, I found about 75 leaks, simply by using my ears to find the hissing sources. For each leak, I recorded the location, estimated the hole size, and took a picture, circling the leak location later when I printed out the photos. The largest leak (or at least the loudest, since I couldn't actually see it) was hidden behind a nest of pipes in a basement ceiling.
The US EPA's Energy Star program publishes a useful brochure which enables the calculation of air leak costs using hole size, air pressure and electricity cost. I plugged in my numbers and found that fixing all these leaks would easily pay for most of my annual salary. Of course, there would be costs for repairing the leaks, and then a decision would have to be made to turn off a compressor or put it in reactive mode in order to actually get savings, but after a leak survey, you'll have all the data to justify such a decision.
So next time you have some machine downtime in your mill, take a walk with your camera and notebook, and see if you can justify your salary!
Martin Fairbank has worked in the forest products industry for 31 years,
including many years for a pulp and paper producer and two years with
Natural Resources Canada. With a Ph.D. in chemistry and experience in
process improvement, product development, energy management and lean
manufacturing, Martin currently works as an independent consultant,
based in Montreal. He is also an author, having recently published
Resolute Roots, a history of Resolute Forest Products and its
predecessors over the last 200 years.
Martin Fairbank Consulting
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