Clean Burning Coal

At the University of California, Irvine (UCI), within the Lasers, Flames, and Aerosols Laboratory at the Henry Samueli School of Engineering, researchers are seeking to create greener energy sources.

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Dr. John Garman, associate specialist II at UCI, is leading a project with the goal of discovering ways to burn coal more completely and with fewer emissions. More specifically, Garman’s research team focuses on converting coal into energy more efficiently, controlling the residual particulate matter, and, in the process, collect naturally released toxins such as mercury, so that they do not adversely impact the environment.

Garman and his team, in a project partially funded by GE and the National Science Foundation, are seeking to understand the fundamental processes that occur during the final stages of burnout when burning coal, biomass fuel, or a combination of the two.

“Part of what we’re doing is examining the process of char burnout and investigating why a small percentage of unburned carbon remains after combustion,” says Garman. The project also seeks to better understand and potentially minimize mercury emissions, as coal-fired power plants account for 40 percent of all such emissions resulting from human-related activities.

Over the years, Garman had used hardware from Opto 22, of Temecula, Calif., in various automation projects he had been involved in. Garman discovered that his project qualified for an OptoGreen Grant. “These grants are donations of free automation hardware, software, and engineering services to companies, research organizations, educational institutions and government agencies involved in projects that produce, study, promote, source or educate the public on alternative energy, renewable energy, the conservation of natural resources, or environmental responsibility,” explains Arun Sinha, director of business development at Opto.

“For our research, the best way to burn powdered coal is in suspension, so we use small samples (around 40 grams) of pulverized coal, which we feed into a drop tube furnace (DTF), also known as an entrained flow reactor,” says Garman.

This nearly 15-foot tall, column-shaped furnace is designed to produce the very high-temperature reactions needed for investigation of coal and biomass combustion and gasification. Various sample feeding and residence rates are established for the furnace so that the proper environment can be established for experimentation. Through a combination of propane and electric heat, the furnace is raised to a temperature of more than 1200 F.

A sample of pulverized coal is heated to drive off all moisture and then fed into the furnace. As reactions take place, lasers are used to measure particle sizes and temperatures, emissions are carefully monitored and identified, and specialized software is used to calculate the gaseous pollutants such as carbon monoxide and nitric oxide.

Thus far, Garman’s research has led to some interesting observations, such as the fact that carbon burnout varies based on the where the coal sample is injected into the furnace. For example, although particles originating from the upper row injectors on the furnace spend less time in the coal combustor, they have higher carbon burnout compared to particles originating from the lower row injectors. A close look reveals that particles originating from the lowest row injectors circulate around the bottom of the furnace, and although they have longer residence time, the carbon burnout was also lower because these particles avoid the most intense combustion zone, thereby preventing them from obtaining the high temperature needed for complete combustion.

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