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This `Popcorn' Can Stop Acid Rain Before It Starts


Developments to Watch

THIS `POPCORN' CAN STOP ACID RAIN BEFORE IT STARTS

To keep coal-fired power plants from belching chemicals that cause acid rain, emissions are bubbled through vats of limestone sludge before they even reach the smokestack. Although effective in removing sulfur dioxide, the vats don't catch nitrogen oxide, another acid-rain villain. And the method requires costly equipment that is frequently clogged by sludge and corroded by acid by-products.

Engineers at Northeastern University may have a cheaper way to capture acid-rain culprits: spraying a patented combination of calcium carbonates and magnesium carbonates into the combustion chamber of the plant. When particles hit the right temperature, they "pop" like popcorn. Popping increases the surface area of the particles, which maximizes their ability to absorb sulfur dioxide. Another benefit: When the "popcorn" pops, it releases acetone, which reacts with nitrogen oxide and turns it into harmless nitrogen. A harmless chalky residue, gypsum, is left behind. The acetone used to produce the carbonates is costly. But inventors Yiannis Levendis and Donald Wise are working on extracting acetone from sewage and other organic waste. That could reduce the price from $500 a ton to less than $100.EDITED BY RUTH COXETER


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