Ill. Admin. Code tit. 35, § 217.164
Emissions Limitations
Effective Apr 23, 202549 Ill. Reg. 6355AUTHORITY: Implementing Sections 9.9 and 10 and authorized by Sections 27 and 28.5 of the Environmental Protection Act [415 ILCS 5/9.9, 10, 27 and 28.5].POLLUTION CONTROL BOARD
a) Except as provided for under Section 217.152, on and after January 1, 2015, no person shall cause or allow emissions of NOx into the atmosphere from any industrial boiler to exceed the following limitations. Until July 1, 2025, compliance must be demonstrated with the applicable emissions limitation on an ozone season and annual basis. On and after July 1, 2025, compliance must be demonstrated with the applicable emissions limitation on a 30-day rolling average basis.
Fuel Emission Unit Type and Rated Heat Input Capacity (mmBtu/hr) NOx Emissions Limitation (lb/mmBtu) or Requirement Before July 1, 2025 Natural Gas or Other Gaseous Fuels Industrial boiler greater than 100 0.08 Industrial boiler less than or equal to 100 Combustion tuning Distillate Fuel Oil Industrial boiler greater than 100 0.10 Industrial boiler less than or equal to 100 Combustion tuning Other Liquid Fuels Industrial boiler greater than 100 0.15 Industrial boiler less than or equal to 100 Combustion tuning Solid Fuel Industrial boiler greater than 100, circulating fluidized bed combustor 0.12 Industrial boiler greater than 250 0.18 Industrial boiler greater than 100 but less than or equal to 250 0.25 Industrial boiler less than or equal to 100 Combustion tuning Fuel NOx Emission Unit Type and Rated Heat Input Capacity (mmBtu/hr) Limitation (lb/mmBtu) or Requirement On and after July 1, 2025 Natural Gas or Other Gaseous Fuels Industrial boiler greater than 50 0.08 Industrial boiler less than or equal to 50 Combustion tuning Distillate Fuel Oil Industrial boiler greater than 50 0.10 Industrial boiler less than or equal to 50 Combustion tuning Other Liquid Fuels Industrial boiler greater than 50 0.15 Industrial boiler less than or equal to 50 Combustion tuning Solid Fuel Industrial boiler greater than 50, circulating fluidized bed combustor 0.10 Industrial boiler greater than 250 0.15 Industrial boiler greater than 50 but less than or equal to 250 0.20 Industrial boiler less than or equal to 50 Combustion tuning b) For an industrial boiler combusting a combination of natural gas, coke oven gas, and blast furnace gas, the NOx emissions limitation must be calculated using the following equation:
NOx emissions limitation for period in lb/mmBtu = 
Where:
= 0.084 lb/mmBtu for natural gas 
= the heat inpu of natural gas in Btu over that period 
= 0.144 lb/mmBtu for coke oven gas 
= the heat input of coke oven gas in Btu over that period 
= 0.0288 lb/mmBtu for blast furnace gas 
= the heat input of blast furnace gas in Btu over that period
(Source: Amended at 49 Ill. Reg. 6355, effective April 23, 2025)