The final air permit for the Christian County Generation LLC (CCG) coal gasification project in Illinois shows that this facility would gasify coal to make substitute natural gas (SNG), with the SNG to either be directly sold as a product or used on-site to fuel combined cycle combustion turbines to generate electricity, which would be fed to the grid.
The gasification block would have a nominal daily production capacity of 64 million standard cubic feet of SNG. The power block would have a nominal net electrical output of 602 MW. CCG is a project affiliate of Tenaska, which on April 30 announced receipt of the air permit.
“CCG no longer plans to construct an Integrated Gasification Combined Cycle (IGCC) power plant, which would not have produced SNG, as addressed in a previously issued construction permit,” the final permit, released on May 1 by the Illinois Environmental Protection Agency, said. “Rather, that plant would have only produced electricity, using syngas from the gasification block as fuel for the combined cycle combustion turbines in the power block. The design coal supply for the plant would be Illinois Basin coal. The design feed rate of coal to the gasification block would be 212 tons of coal per hour. The plant would be located in Taylorville. The site is in an area that is currently designated attainment for all criteria pollutants.”
The permit later added: “The affected emissions units for the purpose of these unit-specific permit conditions are the units in the gasification block. In the gasification block, two gasifiers convert coal into a synthesis gas or ‘syngas’. The raw syngas from the gasifiers is then processed to remove contaminants and prepare it for conversion into substitute natural gas (SNG) in the Methanation Unit. The first step in the cleanup of raw syngas is a particulate removal system on each gasifier. Further cleanup of the raw gas then takes place in a gas processing or cleanup train. The gasification block has a single gas cleanup train for the raw syngas output from both gasifiers. In the gas cleanup train, a carbon bed removes mercury from the raw syngas. Sulfur compounds are removed in an Acid Gas Removal (AGR) Unit and sent to the Sulfur Recovery (SR) Unit. In addition to removing sulfur compounds from the raw syngas, the AGR Unit also removes CO2. The SR Unit uses the Claus Process to convert the sulfur compounds recovered from the raw syngas into liquid sulfur, a byproduct from the plant. The tailgas from the SR Unit will normally be recycled backed to the AGR Unit and not vented to the atmosphere.”
Notable is that coal producer Rhino Resource Partners LP (NYSE: RNO) hopes to supply the plant with coal out of a permitted but undeveloped underground mine nearby.
Illinois EPA responds to permit critics
The proposal to issue a permit for the construction of the Taylorville Energy Center (TEC) generated a variety of comments from the public and environmental organizations, IEPA said in a responsiveness summary that accompanied the final permit. These comments were fully considered by the IEPA prior to issuance of the permit.
A major concern raised during the comment period was whether emissions of the plant will be a threat to ambient air quality and public health in Christian County. As part of the application, CCG was required to submit a modeling analysis to determine the impact of the TEC on local ambient air quality. The modeling and subsequent analysis indicate air quality would continue to comply with the National Ambient Air Quality Standards, which have been developed by U.S. EPA to protect public and welfare, the Illinois agency noted.
A related concern was how the Illinois EPA would take into account other sources of emissions in the area and background levels of air quality when evaluating the plant. The ambient air quality analysis looked at other sources of emissions and background levels of pollutants when the analysis indicates that emissions from the plant would be above a very small or “de minimis” level of impact. A preliminary analysis for the plant by itself indicated potential impacts above these levels. This triggered further analysis with modeling of both the emissions of the proposed plant and the emissions of existing sources in the area. This full modeling analysis, which took into account other sources and background air quality, showed that the plant would not threaten current air quality, the agency said.
The permit requires the plant to use Best Available Control Technology (BACT) to control its emissions, as determined on a project-specific basis. As part of its application, CCG was required to review the control techniques that are available and the emission limits that would be achievable with these techniques considering other similar facilities that already use them. The most stringent level of control is selected as BACT unless that is shown to be technically infeasible or accompanied by cost or environmental impacts that would be excessive. The Illinois EPA reviewed the BACT analysis that was submitted to actually determine BACT requirements for the plant and set appropriate condition in the permit requiring use of BACT.
The plant would not be a major source for emissions of hazardous air pollutants. The permit sets stringent limits on emissions of mercury for a plant of its size. The issued permit limits emissions of mercury to 20 pounds per year, a 90% decrease from the level proposed in the draft permit and a fraction of the mercury levels of existing coal-fired power plants.
The plant is being developed with the expectation that it would be able to use carbon capture and sequestration (CCS). The plant would be developed to be a “clean coal facility” under the Illinois Clean Coal Portfolio Standard Law, which would require geological sequestration of CO2. However, the permit does not require sequestration because this technology is not developed enough to be technically feasible when the plant begins operation and during its entire operating life (i.e., as BACT). One of the benefits of the TEC should be to demonstrate the technical feasibility and reliability of CO2 sequestration, the Illinois EPA said.