The Anti-Mercury Team
April / May 2010
Volume 8 Number 2
The blue glass bottles that line the windowsills of Henry Pennline’s office at the National Energy Technology Laboratory in Pittsburgh cast a soft, pleasing glow when the sun hit them, which was not often during this long, gloomy winter. “It has a calming effect on me,” the soft-spoken Pennline says with a smile that makes a visitor try to imagine him as anything but calm. “Some people say I need it,” he adds with a chuckle.
Seated across the desk from him is Evan Granite, a researcher Pennline hired as a postdoc in 1996. Their mutual regard becomes evident as they try to reconstruct the timeline. “You came on the scene as a postdoc,” Pennline recalls, “and then, by the time you became a federal employee three years later, you’d done an outstanding study on mercury removal.”
“I was fortunate to have a fantastic researcher as my supervisor,” Granite replies, his voice booming as it sometimes does.
In an effort to defuse the compliment, Pennline turns to the visitor with a grin and says, “I have a good team.”
But the compliments are genuine and, judging by the success these two and their colleagues Mark Freeman, Bill O’Dowd and Rich Hargis have enjoyed, well-deserved. Presented with the daunting challenge of detecting, measuring, and removing mercury from coal-derived flue gas in power plants to meet anticipated environmental regulations in the 1990s, Pennline, Granite and coworkers invented not just one commercial method, but three. The methods are based on technologies as distinct as UV irradiation of an empty quartz tube, a partially activated carbon sorbent taken from a power plant’s coal furnace during normal operation, and a palladium-based sorbent that also removes other toxic pollutants from a fuel gas stream.
One remarkable aspect of their success is the extreme conditions they must deal with. “Flue gas from coal-burning power plants,” says Granite, “is a dirty, moist, particulate-laden stew.” This witch’s brew contains sulfur oxides (SOx), nitrogen oxides (NOx), moisture, hydrochloric acid, fly ash, carbon monoxide, carbon dioxide, unburned hydrocarbons and only 1 part-per-billion (ppb) of mercury. “It’s very difficult to measure 1 ppb—such an infinitesimally small concentration of mercury—in a dirty matrix” like flue gas, Granite says.
So they started off looking at a simpler system. Mercury absorbs and re-emits ultraviolet (UV) light, so they used an instrument consisting of a clear quartz chamber irradiated by UV light, with a photodetector to measure mercury in a pure argon stream. After demonstrating that they could measure mercury at the sub-ppb level, they placed sorbents such as sulfur-promoted or iodine-promoted activated carbon upstream of the detector to see if they would remove mercury from a simulated flue gas. But at this point the system stopped working. When they took it apart, they noticed that the quartz chamber was stained, probably from the sulfur or the iodine, they suspected.
Analysis of the stains, however, revealed them to be mercuric oxide. By accident they had discovered a method of removing elemental mercury from a gas stream using an empty quartz tube and UV radiation. After additional development work, they soon patented the technology and licensed it to Powerspan, a small company in New Hampshire, which demonstrated successful operation at the large bench scale.
Stronger evidence of how these innovators and their colleagues work together emerges when Granite starts describing the second technology, the partially activated carbon taken from an operating coal furnace and placed downstream to remove mercury from the flue gas. They call it the “thief process” because it involves “stealing” carbon from one part of the process to use in another.
Sorbents from the thief process turned out to be as good or better than activated carbon, which had long been the sorbent of choice for mercury removal. But activated carbon has the disadvantage of being expensive to make, ship and store at the power plant. The thief process produces the sorbent at the power plant during normal operations, so it eliminates those expensive steps. A small company called Mobotec (now Nalco-Mobotec) licensed the process, and is currently performing demonstration studies at some major power plants.
Finally, the third technology arose from Pennline’s burgeoning interest in coal gasification—specifically integrated gasification combined cycle (IGCC)—instead of coal combustion. Whereas most power plants burn coal to create steam to drive a turbine that produces electricity, in IGCC coal reacts with oxygen and steam to produce fuel gas or synthetic gas (syngas), which is essentially hydrogen and carbon monoxide. A second reaction produces more hydrogen and the greenhouse gas carbon dioxide. “Because the process takes place at high pressure,” Pennline says, “the CO2 is more highly concentrated than in combustion processes, so it is easier to capture and sequester.” This is a major benefit in reversing global climate change.
“We’re very fortunate,” Granite says. “We really have an easy job—they’re paying us to think. There’s no shortage of pollutants in the world, so if you’re fortunate enough to be paid to think, you’d better be enthusiastic and apply yourself and try to come up with some solutions.”
Timothy Palucka is a writer at the National Energy Technology Laboratory.
Copyright © 2012 | Innovation America