Expo in September focused on control charts as a way to make sure lab equipment is functioning properly. But, he adds, control charts can be useful in other areas, too. “Ethanol laboratories are not the only place where data is collected and analyzed to determine how the process is running,” he says. “That’s also something that’s done in the control room. … It complements doing trends in a DCS, because it’s a way to check your instruments. You can actually use it for the whole process. You could make control charts for the temperature on ferm 2 if you really wanted to.” Hank Britton, director of optimization and advanced control for OpX Control Inc., agrees that control charts are valuable outside the lab. Briton, whose work with ethanol plants involves programming PID control loops and continuous process control,
says control charts can be used in process control for things like measuring fermenter temperatures. “You could plot temperature at a specific time for multiple batches,” he says. He adds that one of his customers did this as a way to see how fermenters were operating. They plotted fermenter temperatures at 12, 18 and 24 hours for different batches. “[They] looked at snapshots for multiple fermentation batches before I did work and then multiple fermentation batches after I did my work,” he says. “You could plot temperature at specific times for those batches to see an improvement.” He also says plotting dryer temperature could be helpful. He said a customer recently complained his dryer was not controlling well. “when I looked at the average absolute error, the absolute value of the deviation from the setpoint as a function of time, it
went up from like a 0.22 to a 0.69,” Britton says. “That increase in an average absolute error indicated to me that something changed in the process.” However, control charts remain most impactful in the lab. And Plack recommends plants use them. “I would highly recommend the use of control charts in the laboratory for all aspects; all tests that they run,” she says. “The big thing is you don’t know what you don’t know. So you really need to watch all of these things because a little bit of a change in an instrument could affect all kinds of operational changes, and then you find out it was because an instrument was not tight enough and that could mean a lot of money to the plant.” Author: Matt Thompson Freelance Writer mthompson@bbiinternational.com
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