The dirty business of ‘CLEAN’ COAL
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the coal’s byproducts, which include mercury, nitrogen oxides and sulfur. High sulfur content is the reason Illinois coal fell out of favor when the federal government placed limits on the acid rain-causing emissions in 1990. With the Energy Center’s technology, sulfur would no longer be a problem and Illinois coal could make a full rebound, project supporters say.

The process of transforming coal into syngas is called “gasification” and is the first part of the project’s “integrated gasification combined cycle” (IGCC) system. Before the gas enters the “combined cycle” phase, it is further refined through a process called “methanation,” becoming chemically identical to natural gas, or methane. During methanation, the carbon dioxide (CO2) is removed and captured. The remaining gas is then burned in the same manner as natural gas, using two turbines to harness its energy, doubling its capacity to produce electricity and completing the “combined cycle” process.

Using about 150 megawatts of electricity each year just to keep it running, the Energy Center would annually consume about 1.59 million metric tons of Illinois coal to produce upwards of 700 megawatts of electricity, enough energy to power about 600,000 homes. It would also produce about 3.45 million metric tons of CO2 each year.

But not all of that CO2 would be released into the atmosphere, as happens with conventional power plants. Tenaska plans to capture more than half of the greenhouse gas, about 1.9 million metric tons. What to do with it is still a toss-up. Options include sending it down an as-yet unrealized pipeline, selling it for enhanced oil recovery, and sending it down a more than 5,600-foot-deep well, where it would be stored locally in the 60,000-square-foot Mount Simon Sandstone, a super salty water-bearing rock formation that’s topped by a 200-foot-thick layer of impervious shale. After 30 years of injection, Tenaska’s Mount Simon CO2 plume would span about 8.2 miles.

Illinois State Geological Survey (ISGS) scientists, who are now conducting studies at Archer Daniels Midland’s future geologic sequestration site in Decatur, are confident that the technique will have no adverse effects on the environment. They cite the depth of the wells, the rock layers’ properties and the non-toxicity of carbon dioxide – qualities of Decatur’s site that would likely ring true for Tenaska’s Taylorville site, as they are both above the same geologic formations. Although the buried CO2 would cause asphyxiation if released in large quantities without ventilation, director of the ISGS Advanced Technology Initiative Robert Finley says that even if CO2 found a way to the surface – a highly unlikely event considering the multiple layers of impervious rock – it would exit the earth in insignificant amounts and be greeted by plenty of fresh air to whisk it away. Finley adds that the country has used similar procedures for decades for storing explosive natural gas, taking it in and out as needed.

But Clayborn says carbon sequestration is still too new. “You just don’t know until it’s been underground for awhile,” she says, adding that Taylorville’s project, which could inject up to 3.41 million metric tons of CO2 each year, would be three times the size of the Decatur site.

And even with carbon capture, the Energy Center would still send 1.55 million metric tons of CO2, the equivalent of that produced by about 296,000 cars, into the air each year. That portion of the project’s CO2 is released after the coal becomes identical to natural gas and is burned as in any other natural gas power plant, without any carbon capture technology.

In 2007, all Illinois power plants, both natural gas and coal-fired, combined to emit about 98.9 million metric tons of CO2.

Tenaska says that the Taylorville Energy Center’s presence would result in dirtier plants closing down and a decreased use of their electricity, which comes with more CO2 emissions than the Taylorville Energy Center’s electricity would. As a result, the