Model-based advanced process control helps create energy efficient plants

If cost weren't a factor, numerous technologies could be tapped to create the most energy-efficient plant. The latest furnaces, boilers, or co-generation equipment could be installed. The facility could have solar panels or geo-thermal heating. A new distributed process control system (DCS) could be deployed.




But that's not today's reality.


The economic reality dictates that manufacturers must be as energy-efficient as they can, largely with the assets that exist. As John Nesi, VP of market development for Rockwell Automation , a vendor of plant automation systems, acknowledges, "We are in a phase of Draconian cutbacks in terms of capital expense."


Still there are technologies that make existing assets more energy efficient, says Nesi. These include advanced process control (APC), a class of software that optimizes real-time plant-floor processes; variable speed control, which allows gears and motors to adjust speed efficiently; and energy monitoring software.


According to Allen Avery, an analyst with Dedham, Mass.-based analyst firm ARC Advisory Group , "Technology is an enabler, but improved energy management is mainly a matter of people, processes, and organizational commitment."


The value of APC

Advanced process control uses software to model how multiple variables interact during a process, and integrates with automation hardware such as programmable logic controllers (PLC) or DCSs to control the process optimally. APC projects historically have been aimed at throughput, but APC can also optimize energy use.


To deploy APC, plant testing is typically used, whereby incremental inputs from the control layer are fed into the software to build a model.


"We start by building models of how a process works," says Mike Tay, manager of sales engineering with Pavilion , a Rockwell Automation division that offers APC. "It's a virtual plant that you can then optimize to achieve various goals, such as minimum cost, energy, or emissions."


Fonterra Cooperative Group , an Auckland, New Zealand-based dairy products manufacturer, has used APC for more than a decade.


"We have a track record for APC projects where people in the business understand what it can do and what it can deliver to the business," says Tristan Hunter, manager of Fonterra's advanced process control group.


An early project was aimed at improved boiler operation at Fonterra's Waitoa plant in New Zealand. The site has several spray driers that make a range of powdered products. The coal-fired boilers that supply high-pressure steam to the driers were exhibiting unwanted variability, so in 1997, the company deployed Pavilion's Model Predictive Control APC solution to, as Hunter explains it, "run the boilers smarter."


More specifically, APC reduces variability and minimizes excess oxygen in the flue gas of the boilers, as well as reducing variability in the high pressure steam supply. The project cut oxygen variability in the boiler's flue gas by up to 50 percent, while high-pressure steam variability was reduced by at least 60 percent. What's more, the steadier operation brought close to a 4-percent reduction in coal consumption.


To work well, APC needs a solid control foundation, Hunter warns.


"Your existing control systems need to be running well," he says. "You need to review the instrumentation, the calibration, and the tuning of the low-level loops. When APC is running, the plant needs to respond reliably to what the control moves are."


Over the years, Fonterra has established an APC group of 10 people who deploy projects with help from Pavilion. With this expertise, says Hunter, projects can be better aligned with corporate goals, rather than focused on immediate pain points. "We are now aligning more with the strategy of our business, looking where we are headed in the next two to three years," says Hunter.


Beyond basic control

At Yara Belle Plaine , a manufacturer of ammonia, granular urea, and urea ammonium nitrate (UAN) products used in agricultural products, APC is saving energy by achieving consistent, cleaner operations. Located near Belle Plaine, Saskatchewan, Canada, the company deployed Honeywell International 's Profit Controller APC solution for the nitric acid processing unit within the plant.


The unit or "plant" feeds UAN production within the site. The APC solution optimally controls the amount of NOx emissions leaving the plant's combustor while minimizing the consumption of the combustor's fuel gases.


Since deploying APC in November of 2007, combustor fuel consumption has dropped by up to 5 percent, NOx emissions have been held at 200 parts per million, and methane emissions dropped 25 percent.


"The benefits have held up," says Rob Harkness, controls supervisor for Yara Belle Plaine. "We've consistently kept the 3-percent to 5-percent improvements in fuel reduction."


Yara Belle Plaine is upgrading its DCS to Honeywell's latest Experion PKS system, but APC goes a step beyond DCS in that it's able to model and control multiple variables without operator intervention. The APC integrates with DCS, but runs on its own server.


"APC technology can take a whole plant into consideration," says Harkness. "It looks at all the critical elements, where typically with conventional control, you'd have one input, one controller, and one output—or possibly a cascade control arrangement. But with APC, it takes in numerous measurements throughout the plant and works with all of them to optimize the entire process—not just one part of the process."


Why energy reduction is everyone's business


Attention surrounding the metric for energy intensity—i.e., energy consumed per unit of product produced—is especially high among process manufacturers, with Fortune 500 firms like DuPont and Dow Chemical elevating their energy programs to board-level importance.


Avery, the ARC analyst, says, "The sheer amount of energy that process manufacturers use is startling . . . "For some it's higher than that of many small countries, but the payoff when [an energy management] program is adopted top to bottom in an organization can be equally surprising."


Allen says a recent ARC study found that companies in the forefront of the energy management movement treat it like a continuous improvement program.


"It requires involvement at all levels of the plant, with everyone aligned around it," Allen says. "You have to give them visibility, the tools, and the authority to make a difference. Technology can clearly play a role in this."


Advanced process control, decision support, and real-time performance management software were the top three areas of technology investment among companies identified as energy-management leaders in the ARC survey.


"In tough economic times like now, vendors should focus on helping customers understand how these technologies can assist them in energy reduction," Allen says.


A comprehensive energy assessment of plant operations to determine where and how much energy is consumed is the starting point for any energy-management effort. ARC found that the vast majority of the companies it identified as leaders have performed an energy assessment. These companies also perform audits more regularly and at shorter intervals than their peers.


Energy management is worthy of being a core tenet in managing the business, "as the potential payoff is huge," Allen states. Underscoring the point, one process manufacturer ARC spoke with claimed energy savings of $7 billion over 12 years.


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