Ill. Admin. Code tit. 35, § 217.141
c) For fuel combustion emission units burning simultaneously any combination of solid, liquid and gaseous fuel, the allowable emission rate shall be determined by the following equation:

Where:
| E | = | allowable nitrogen oxides emissions rate |
| Q | = | actual heat input |
| G | = | percent of actual heat input derived from gaseous fossil fuel |
| L | = | percent of actual heat input derived from liquid fossil fuel |
| S | = | percent of actual heat input derived from solid fossil fuel |
| G + L + S | = | 100.0 |
| Metric | English | |
| E | Kg/hr | 1ls/hr |
| Q | MW | Mmbtu/hr |
| A | 0.023 | 0.003 |
| B | 0.023 | 0.003 |
| C | 0.068 | 0.009 |
d) Exceptions: This Section shall not apply to the following:
No person shall cause or allow the emission of nitrogen oxides into the atmosphere in any one hour period from any existing fuel combustion emission unit with an actual heat input equal to or greater than 73.2 MW (250 mmbtu/hr), located in the Chicago or St. Louis (Illinois) major metropolitan areas to exceed the following limitations:
(Source: Amended at 33 Ill. Reg. 13345, effective August 31, 2009)