Coal could satisfy many regions’ energy needs were it not so polluting. For decades, scientists have dreamed of economically extracting the fuel’s energy without releasing huge quantities of CO2 and other pollutants. Researchers at Ohio State University have moved closer to achieving that dream through a novel process called coal-direct chemical looping.
The University’s Clean Coal Research team, led by Professor Liang-Shih Fan, has successfully demonstrated a laboratory power plant that chemically ‘burns’ coal without releasing CO2. The system operates in two stages. First, iron oxide pellets and powdered coal are electrically heated in a chamber, releasing coal gas, which combines with the oxygen of the oxide, turning it into iron. Second, the hot iron moves to another chamber, where it burns in air and so becomes iron oxide again. The heat from the burning iron drives a steam turbine. The oxide returns to the first chamber, where the process is repeated.
The system captures all the CO2 at a purity of 99%, and because the coal ‘burns’ at a lower temperature than in a traditional plant, much less NOx is produced. As in a traditional plant, a standard desulphurisation unit deals with the SOx.
Gary Spitznogle, Director, New Technology Development & Policy Support, American Electric Power, is enthusiastic. “The chemical looping technology promises a future of clean, efficient power plants with very low CO2 emissions”, he says.
The team spent 15 years perfecting the technology before building the current 25kW test unit. Now, with financial support from the US Department of Energy, they plan a 1MW plant with energy company Babcock and Wilcox.
“The recent breakthrough by Professor Fan’s team indicates the potential of this technology,” comments Samuel Tam, Divisional Director Office of Fossil Energy at the US Department of Energy.
Electricity produced by a traditional coal-fired plant with standard carbon capture systems costs about 70% more than electricity produced by a plant without such systems. “Our process would increase the cost by less than half that amount”, says Professor Fan. “That’s well within the target set by the Department of Energy.” – John Fencer
Photo: Jo McCulty / Ohio State University