Green Plains started operations in or around September 2008 and currently operates a 100 million gallons per year dry mill ethanol manufacturing facility (the facility) in Bluffton, Indiana. The facility also produces approximately 550 tons per hour of animal feed known as distiller grains. Ethanol manufacturing produces by-products such as Distillers Dried Grains with Solubles (DDGS) and Distillers Wet Grains (DWG).
At the facility, the company uses the dry mill process, where the entire grain kernel is ground into flour. The starch in the flour is converted to ethanol during the fermentation process, creating carbon dioxide and DDGS. The facility includes: four natural gas-fired DDGS dryers (identified as EU029 through EU032), with emissions controlled by recuperative thermal oxidizers (RTOs) and a heat recovery steam generating (HRSG) system (identified as C10 and exhausting to stack S10).
On March 13, 2007, IDEM issued a Federally Enforceable State Operating Permit (FESOP) No. F179-23641-00033 (with conditions) to the facility under the Indiana Enhanced NSR construction permit process. The FESOP limited the facilityÂs NOx emissions to less than 100 tons per year. This permit restricts the RTO/HRSG emissions to 21.20 lbs. NOX per hour. Under the permit, on and after the date of stack test results are available, Green Plains is required to operate the RTOs at or above the 3-hour average temperatures as observed during the latest compliance stack tests. The RTOs