Flame-Shaping Electric Fields Could Make Power Plants Cleaner

ClearSign’s pollution-reducing technology could help power plants burn less fuel and make more money.

Conventional pollution reduction equipment is too expensive to be adopted in many places.

A Seattle company called ClearSign Combustion has developed a trick that it says could nearly eliminate key pollutants from power plants and refineries, and make such installations much more efficient. The technique involves electric fields to control the combustion of fuel by manipulating the shape and brightness of flames.

Flame shaper: A nearly invisible flame is rendered far brighter and larger using electric fields.

The technology could offer a cheaper way to reduce pollution in poor countries. And because ClearSign’s approach to reducing pollution also reduces the amount of fuel a power plant consumes, it can pay for itself, the company says. The need for better pollution controls is clear now in China, where hazardous pollution has been shutting down schools and roads this week.

The company claims that its technology could reduce fuel consumption by as much as 30 percent. Some outside experts say that in practice the likely improvement would be far less, possibly only a few percent, although even that would still result in large savings.

Much of the pollution from a power plant is the result of problems with combustion. If parts of a flame get too hot, it can lead to the formation of nitrogen oxides, which contribute to smog. Similarly, incomplete burning, which can result from the poor mixing of fuel and air, can form soot (see “Cheaper, Cleaner Combustion”).

ClearSign uses high-voltage electric fields to manipulate the electrically charged molecules in a combustion flame. This can improve the way air and fuel mix together, and can spread out a flame to prevent hot spots that cause pollution.

The idea of using electricity to shape flames has been around for decades. But conventional approaches typically involve plasma, and the plasma needs large amounts of energy. ClearSign says its technology only uses one-tenth of 1 percent of the energy in the fuel that a power plant consumes. It works using electrodes within the flame. The electrode produces high voltages that influence the movement of ions; by varying the voltage, it’s possible to control the way the flame forms. The technology is particularly effective at reducing smog-forming NOx emissions, carbon monoxide, and soot.

“There’s been interest in electric fields for some time, but nothing with as strong an effect as they’ve demonstrated,” says Michael Frenklach, a professor of mechanical engineering at the University of California, Berkeley.

In addition to reducing pollution, the technology can improve the efficiency of a power plant or a refinery in several ways. Improved mixing of fuel and air means less fuel is wasted by incomplete combustion; the technology can also improve heat transfer from the flame to the water in a boiler, so less fuel is needed to make steam, which is used to drive turbines in a power plant. But the biggest potential for fuel savings could be in reducing or eliminating the need for conventional pollution controls, which can consume significant amounts of energy, and can be expensive.

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