I love reading mysteries, and trying to figure out "whodunnit" before the author reveals the answer. So imagine the satisfaction I get from solving real-life mysteries!
One memorable occasion occurred several years ago when I was asked to help a pulp and paper mill figure out why paper brightness was occasionally missing its target at seemingly random intervals, resulting in rejection of several tonnes of paper each time. A few months before this, the mill was an early adopter of a "data historian" system, capturing and storing online data at various points within the process periodically. This allowed me to analyze data from my desktop.
I asked my contact, a process engineer at the mill, to send me selected data in Excel format from both the pulp mill and the paper machine for the period about twelve hours before each brightness failure event. The mill had a peroxide bleach system to brighten the pulp in a bleach tower for about two hours, and the brightened pulp was then sent to the paper machine within 1-2 hours.
I opened the data files and began to read the clues. There appeared to be no deviation from standard procedures and there was no variation in unbleached brightness. Each occurrence of paper rejection was similar: a sudden drop in brightness of 1 to 3 points, then a gradual rise back up to the target brightness. When the magnitude of drop was larger, the time to recover was also longer.
My Eureka moment occurred when I saw that, in each case, 3 to 4 hours prior to the paper brightness event, the flow of pulp and bleach was stopped to the top of the bleach tower. This is a normal occurrence, especially when the paper machine is down and the bleach tower is full. I asked the engineer to check the bleach chemical pumps the next time flow to the bleach tower was stopped. And I got an excited call the next day, telling me that they had discovered that caustic soda (one of the ingredients of the bleach formula) was still trickling into the tower when the caustic pump was supposedly turned off. This was causing a very high pH in the pulp at the top of the tower, resulting in yellowing of the exposed pulp. As this dark slug of pulp proceeded through the papermaking process it was causing a brightness drop at the paper machine, the magnitude being related to the amount of time the pulp flow to the bleach tower was stopped. The caustic pump was fixed and the problem was solved!
This mystery would have been very difficult to solve without the data historian, which today is a commonplace tool in the industry. While most facilities use this tool effectively for tracking their process, there is often untapped potential for process improvement hidden in the data. And solving mysteries!
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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. Carbon credits
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. Lean manufacturing