Pictures of the Future      Spring 2008

How Lasers Make Coal Burn Better

U.S. start-up Zolo Technologies is working closely with Siemens on optimizing combustion processes in coal-fired power plants in order to make such facilities more efficient and environmentally friendly.

Las Vegas, December 2005. At the Power-Gen international trade fair, Dr. Rainer Speh, technical director for power plant technology at Siemens, meets Henrik Hofvander for the first time. Hofvander, managing director of Zolo Technologies, a Boulder, Colorado start-up, is at the fair to present a new intelligent, laser-based, measuring technology that has already been installed in several coal-fired power plants in the U.S.

The system is being used in boilers that burn a ton of pulverized coal in just 15 seconds at temperatures of up to 1,400 °C. Some of these boilers are up to 100 m in height and more than 10 m in diameter. Failure to achieve optimal distribution of air and coal in such units results in non-homogenous combustion, which lowers efficiency and leads to the accumulation of pollutants such as nitrogen oxides. Before Zolo Technologies came up with its innovation, the exact makeup of the air-coal mixture could only be measured in the flue gas a long way from the combustion zone, and was thus inaccurate.

"Zolo’s measuring technology has made it possible to precisely analyze the combustion process online," says Speh, who immediately recognized the potential the start-up’s technology offered Siemens. That’s because precise measurements of gases like O₂, H₂O, CO, CO₂ and NH₃ enable a power plant’s control system to automatically adjust air and coal flows in a manner that optimizes the combustion process.

Zolo’s realtime measurements are achieved with a laser beam sent through the boiler. Depending on ambient conditions, the gases absorb the laser light at typical wavelengths. Gas concentrations and temperatures can be determined because the level of absorption increases in accordance with the number of molecules present. The Zolo system uses motorized measuring heads that are flange-mounted at various heights on the boiler wall. These probes automatically guide the laser beam inside the boiler, which can expand by as much as one meter when heated. Trajectory guidance is important here because it ensures a line of sight for the laser beam as it travels through the boiler, thus enabling realtime measurements. The measurement data collected is analyzed in an electronic compartment linked to the boiler via fiber optic waveguides. This compartment is where the actual optical measuring devices are housed.

Lower CO₂ Emissions. Zolo Technologies was originally established in 2000 with the idea of offering its system for use with optical telecommunication networks. "But in 2003, we defined a new application area and combined the knowledge we’d already gained with the results of fundamental research at Stanford University on laser-based measurements at high temperatures," Hofvander explains. In January 2007, Siemens and Zolo signed an agreement that included funding from Siemens Venture Capital and the El Dorado Investment Company. This agreement called for the construction of a test installation that would serve as a reference project for Zolo’s measuring technology in combination with control system technology from Siemens. "This investment was very important for us—as was the fact that we were able to get Siemens onboard as a business partner capable of providing integrated solutions for power plants," says Hofvander.

Hofvander believes his company’s measuring technology and the resulting combustion optimization can improve coal-fired power plant efficiency by as much as three percent. Such an increase in the U.S. alone would reduce the amount of coal burned by 30 mill. t per year, and also lower annual CO₂ emissions by 75 mill. t.

"However, it’s not just the improved efficiency that offers power plant operators added utility," says Speh. That’s because burning less coal would also result in lower costs for disposing of ash with excess levels of residual coal. In addition, more accurate measurements would mean fewer temporary plant shutdowns to check boilers. "What’s more, our systems offer huge savings potential for new plant construction," Speh adds. He also believes that online combustion analyses can drastically reduce the time it takes to achieve optimal power plant operation. Other industries could benefit from Zolo’s technology as well, says Speh: "We could also use our intelligent measuring procedure with gas turbines, refineries, and the cement industry, for example."
                                                                                                              Nikola Wohllaib