Optimization

Technology trends in process energy efficiency

Today's monitoring and control systems are making it easier to relentlessly reduce energy cost per unit production.

By Paul Studebaker, editor in chief, Control

With oil and gas prices down, and energy, for the moment, apparently cheap and plentiful, it might be tempting to put energy efficiency on the back burner. But experience shows that's a bad strategy for both short-term profits and longer-term competitiveness: like reliability, energy efficiency requires constant vigilance and unending efforts to improve.

The connection between reliability and energy efficiency is more than a simile. "Increasing utilization with less shutdown time means more productivity per hour, which reduces energy per pound," says Michael Tay, Pavilion product manager, Rockwell Automation. "Shutdowns and startups themselves tend to waste energy, losing it during cool-downs and wasting it bringing equipment back up to temperature."

Better control also can boost efficiency. "Overprocessing wastes energy—we want to be like Goldilocks, ‘just right,' not over distilling or over-drying, then using extra product to make weight," Tay adds. "Optimization through simulation and modeling can reveal waste and present non-intuitive opportunities to save energy dollars. We had a case where the customer had never vented steam, but could be reducing their energy bill by generating more of their own electricity if they vented steam."

Even something as apparently simple as selecting refrigeration or air compressors for a given distribution of loads can be an opportunity. "You know you want to run compressors at 100% for best efficiency, but what if you need the output of 1 1/2 compressors?" Tay asks "Do you run two compressors at 75% or one at 100% and one at 50%? It's a non-linear, dynamic situation. The operator can't figure it out, but simple controls with a mathematical model can do it."

An increasingly powerful tool is a monitoring system—dashboard—that can help you manage energy-intensive systems. "People are developing leading process indicators (LPIs) on major energy elements such as heater efficiency, steam and exchanger efficiency to bring attention to deviations and problems," says Mike Brown, process application consultant, Honeywell. "They can drill down to identify the reasons, and—very important—bring them directly to the attention of the people who have the responsibility to get them working well."

When you see a train or distillation tower routinely using too much energy, it's typically a control problem, Brown says. "Advanced process control [APC] is good for running at the limits, so it's good to include energy in the control application. We're moving APC algorithms from a separate computer into the DCS—we can now do full-blown multivariable control in the DCS. This lets us take on challenges like fired heaters, which couldn't be run fast enough and robust enough in an outside computer. We're also developing applications for network optimization—to optimize things like hydrogen balance, fuel gas and steam across multiple units."

But while you strive for plant-wide optimization, don't ignore the basic blocking and tackling that helps keep creeping inefficiencies at bay. "We see two potential areas for significant gains," says Hilton Hammond, product marketing manager, Fluke. "The first is around process efficiency, where evolving industry standards such as ISO 50001 are providing insights into the next level of savings. And second, systematic waste associated with motor efficiencies, disturbances, exceeding peak demands, harmonics and systemic issues—issues users need to get their heads around and mitigate." In short, process waste and plant equipment systemic waste.

"On the systemic side, things are always changing," says Frank Healy, product manager, Fluke. "We have to use data logging, not spot checks, to keep an eye on harmonics and imbalance, and find dynamic situations where machines are hooked up or operated in ways that are raising costs and wasting energy."

There's no doubt that it's often tough to make inroads on something like energy efficiency that often seems optional. But it can make a huge difference. "In refining, energy averages 54% of the cost of operations, ranging from 82% in the worst plants to 18% in the best," Brown says. "Today, if you walk down the hallway in operations, there's a corkboard with energy efficiency plotted once a month. We want to shift to timely, proactive behavior where if something goes wrong, you can easily see it and do something about it—you can have the right person take care of it, quickly and efficiently."