Dec 182013


A new method for controlling fire could prevent air pollution from forming in the first place

An emerging technology could offer a more efficient way of reducing air pollution from power plants. A Seattle-based company called ClearSign Combustion has demonstrated how to manipulate flames using high-voltage electric fields to prevent pollution from forming in the first place.

Much of the air pollution produced by today’s fossil-fuel power plants is the result of imperfect combustion. Hot spots in a flame increase the reactions between fuel and air molecules and lead to formation of common air pollutants like nitrogen oxides (or NOx, a precursor to smog), carbon monoxide (CO) and particulate matter. Pollutants are commonly scrubbed after combustion and before exhaust gases are released into the atmosphere. Exhaust can be recirculated back into the combustion chamber to burn up any remaining fuel or passed through a chemical process that strips out unwanted compounds (using ammonia and a catalyst)—consuming large quantities of energy in the process. “We need energy. It’s a serious business”, says Michael Frenklach, professor of mechanical engineering at the University of California, Berkeley. “Scientists who are doing combustion research are basically trying to answer the question: How do you do it more effectively?”

Combustion can be improved by manipulating electrically charged particles (ions) in a flame to prevent hot spots—and therefore pollutants—from forming. Earlier this year, engineers at ClearSign Combustion demonstrated how a high-voltage electric field can control the shape and intensity of a flame while using only a small amount of power: less than one tenth of a percent of a furnace’s total power output.

Early test results suggest that controlling combustion with electric fields can lead to improved efficiency, compared with conventional methods. A more uniform flame shape means less fuel is wasted and exhausted as soot whereas more heat is transferred to surrounding surfaces (such as a boiler or heat exchanger for a crude oil treatment process). The biggest energy savings, however, could come from reducing or eliminating the need for conventional postcombustion pollution systems (like ammonia-based catalysts). The company claims its technology can lead to system-wide efficiency improvements up to 30 percent with comparable emissions reductions

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