The Indiana Department of Environmental Management on Oct. 5 issued a final Title V air permit revision that will allow Indianapolis Power & Light to convert Unit 7 at the Harding Street power plant from coal to natural gas.
The approved change is a modification to Boiler 70 (Unit 7) to enable the unit to use natural gas as its only fuel and discontinue the use of coal and fuel oil. The rated capacity of the unit will increase slightly from 4,123 MMBtu/hour to 4,346 MMBtu/hour as a result of the change. This modification to Boiler 70 will also allow for the removal of the recently permitted storage silo for activated carbon, which will not be constructed and the source is also proposing to install a new 100 MMBtu/hr natural gas fired auxiliary boiler.
Boiler 70 is equipped with low NOX burners, neural net controls, separated over fire air (SOFA), and selective catalytic reduction technology (SCR). These technologies were voluntarily installed. Construction was completed on this unit in 1973.
The Indiana Utility Regulatory Commission on July 29 approved an October 2014 application from Indianapolis Power & Light for certificates of public convenience and necessity related to this coal-to-gas conversion project at Harding Street Unit 7. The commission had previously approved coal-to-gas conversions at Harding Street Units 5 and 6.
The Unit 7 conversion is needed to comply with federally-mandated requirements, including the National Pollutant Discharge Elimination System (NPDES) and the Mercury and Air Toxics Standards (MATS). IPL’s “Compliance Plan” approved July 29 includes the construction of wastewater treatment technologies, operational changes, and use of modified stormwater management practices at its coal-fired Petersburg and Harding Street plants, and the refueling of Harding Street Unit 7.
Harding Street 5 and 6 were among the units targeted to stop using coal because it is not cost effective to add emission controls to these small coal-fired units (106 MW each when coal-fired). The GenerationHub database shows Harding Street Unit 7 at 471 MW (nameplate) and 435 MW (net summer) of capacity.
IPL’s mainstay coal generator will, after these conversions, be the four-unit Petersburg plant. IPL is a unit of AES Corp. (NYSE: AES).