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By now, virtually every industrial process in the world is under automatic control, so the logical next step is advanced process control (APC). APC has already been implemented in many facilities, albeit with varying degrees of success. But when APC works, the results can be nothing short of spectacular.Dr. James Ford, senior consultant at Maverick Technologies, says that Maverick engineers recently implemented a set of model-based controls for BASF in Geismar, La. "The application was on a series of fixed-bed catalytic reactors in which the reaction was highly exothermic while the catalyst was very heat-sensitive," Ford explains (See Figure 1).
"The temperature had to be kept high enough to promote the reaction, but just a short high-temperature excursion could rapidly deactivate this very expensive catalyst. Several APC algorithms were used to implement the solution in a Foxboro DCS. The project was very successful, especially at controlling the reactor temperature profile during bed catalyst changes," concludes Ford.
"The controls implemented by Maverick outperform the best of my operators, even with me at the console instructing them exactly how to handle a change-out," says David A. Weatherford, technologist at BASF. "They saved us a lot of money in terms of catalyst cost and paid back the investment in a couple of months."
Enterprise Products in Houston, Texas, is an energy company that operates pipelines, 25 natural gas processing plants, 20 NGL and propylene fractionators, and import/export terminals. "When I took on my new role, I didn't think I'd be able to justify replacing advanced regulatory controls, which I'd developed and supported over a four-year period," says Tom Lyndrup, a staff engineer in the Advanced Process Control group. "But two years later, that's exactly what I am doing."
With some success, he adds, especially in projects where APC replaces existing controls. "In some cases, 24 hours after a new APC routine was started up, we achieved significantly higher total production than the day before, despite a change in feed composition that normally results in lower rates." For more on what Enterprise Products is accomplishing with APC, see the story, "Justifying APC."
Terrance Chmelyk, manager of process solutions at system integrator Spartan Controls in Burnaby, British Columbia, Canada, installed an Emerson Process Management energy management system (EMS) at a cogeneration facility in a pulp and paper mill.
Such an application poses many problems that can't be handled well by conventional controls. "The sale price of electricity may change based on the time of day, the month of year, the market price of power and/or the current rate of power production," he explains. "Other complicating factors include variable fuel costs and availability, dynamic unit efficiencies, fluctuating mill heat requirements and many production-rate-limiting process constraints."
The energy management system employs facility-specific business models based on model-predictive control (MPC), linear programs and advanced energy metering to continually manage the energy contract and determine the optimum operating parameters to maximize profitability.
"The integrated EMS is able to achieve almost 6.5% improvement in overall cogeneration profitability, or about $3000 per day," he says. "Based upon a typical 350-day operating year for the plant, we'd expect that profits could be over $1million per year due to a real-time optimized plant."
Chmelyk continues, "The open-loop operational strategies that existed before saw the human operators make very infrequent changes to unit processes and didn't consider the changing efficiencies or economic models. This is very typical of most cogeneration operations, and the complexity and number of combinations are very difficult for a human operator to process on a real-time basis. In contrast, the integrated EMS with closed-loop control of the boilers and pressure reducing valves is able to make real-time adjustments to find the optimal combinations minute by minute."
Tom Kinney, product manager at Invensys Operations Management, says, "MPC [model-predictive control] moves the operating process closer to multiple constraints simultaneously to realize the maximum profit from an operating unit. Units typically pay for themselves within six months and equip companies for ongoing financial, productivity, quality or other strategic advantages." Table 1 lists the benefits of APC.
Given these success stories, why isn't APC implementation more widespread?
If you saw the movie "Moneyball" or read the book, you probably remember Billy Beane telling Scott Hatteberg how easy it would be for him to switch from catcher to first base. For confirmation, Beane looks to infield coach and colleague Ron Washington, who doesn't miss a beat when he tells Hatteberg, "It's incredibly hard."