Process Cuts Down Pollution by Diesels, Coal-Fired Plants

A new way to remove pollutants from the exhaust gases of diesel motor vehicle engines and from the smokestacks of coal-burning power plants has been developed by government scientists at Sandia National Laboratory in Livermore, Calif.

The process uses a relatively inexpensive nontoxic chemical that combines with the pollutants to form harmless nitrogen, carbon dioxide and water vapor.

The technique could sharply reduce both photochemical smog and acid rain, which result from these pollutants, according to its developer, chemist Robert A. Perry of Sandia’s Combustion Research Facility. His report appears in today’s issue of Nature, a British science journal.

The process has been tested only in the laboratory, but a prototype emission-control device for diesel cars, buses and trucks could be ready within five years, Perry said.

“This invention has exciting potential for both pollution control and the greater use of cleaner, efficient diesel engines in industry and on the road,” said U.S. Energy Secretary John S. Herrington, whose department hired AT&T; Technologies Inc. to operate New Mexico-based Sandia National Laboratories.

Used in Pools

The process uses cyanuric acid, a white granular material that has been used for nearly 30 years to prevent chlorine in swimming pools from escaping into the air too rapidly, thus extending chlorine’s disinfectant effect.

Perry’s technique is designed to control a family of pollutants called oxides of nitrogen, or NOx, that are produced when organic fuels like gasoline, diesel fuel and coal are burned.

Once released, NOx forms particulates that degrade air clarity and combines with water vapor in the air to form nitric acid, a key component of acid rain. One of the oxides of nitrogen also reacts with oxygen in the presence of sunlight to produce ozone, a primary source of photochemical smog.

NOx in automobile exhaust is controlled by catalytic converters, which reduce about 80% of it to harmless nitrogen. But cars account for only 27% of the estimated 21.7 million tons of NOx in the air in the United States each year; factories, power plants and trucks account for much of the rest.

Catalytic converters are not used on diesel engines because they do not work well in the presence of the high levels of oxygen that are required to prevent formation of soot in the diesel motors. If NOx from diesel exhaust can be significantly reduced, however, air quality in the South Coast basin would be greatly improved: About 600,000 heavy trucks and buses produce as much NOx as the estimated 13 million cars in the area, according to Bill Sessa of the state Air Resources Board.

Could Be Breakthrough

Effective NOx controls have been installed only on the newest power plants and stationary emission sources, and their effectiveness on coal-burning plants is reduced by sulfur in the coal.

“If this process could be used on a variety of sources of nitrogen oxides, then it would be a breakthrough in environmental control,” said Jeff Alson of the emission-control division of the U.S. Environmental Protection Agency.

Ron Ketchum of the South Coast Air Quality Management District added, “If you could remove all the NOx in the South Coast basin, you would increase visibility greatly and would have no (smog) problem.”

The new process relies on a simple chemical reaction that can be initiated either by passing exhaust gases over the solid chemical or by injecting it into the exhaust stream.

“It’s a pretty safe molecule,” said Bud Rakestraw of Monsanto Co., its primary producer.

When solid cyanuric acid is heated to temperatures above 675 degrees Fahrenheit, it passes directly into the gaseous state and reacts immediately with NOx in the exhaust, converting it to harmless compounds.

This process removed more than 99% of the NOx in the exhaust of a single-cylinder diesel engine, according to Perry and Sandia chemist Dennis L. Siebers.

$1 a Pound

Perry calculates that one pound of cyanuric acid, which sells for less than $1, would last about 500 miles in a conventional diesel truck.

Much work remains to be done before the process can be used in vehicles, however. Engineers, Perry noted, will have to determine the best way to inject the chemical into the exhaust stream, develop devices that could be attached to cars and trucks and test the performance of a potential emission control device under driving conditions.

A control device for power plants would probably take even longer to develop, he said.

Because Sandia does not do such development work, the U.S. Department of Energy has relinquished its patent on the process to Perry, although it retains the rights to a royalty-free license. Perry will leave Sandia to form a private company to carry out the engineering development.