As of January 1, 2018, all rich-burn engines greater or equal to 100 hp are subject to the maximum NOx emission limit of 0.5 g/hp-hr.
The new regulation can be found on pg. 41 of the Air Quality Standard Permit for Oil and Gas Handling and Production Facilities PDF below Table 6: Engine and Turbine Emission and Operational Standards.
The full note reads “After January 1, 2015, regardless of manufacture date, no rich burn engine greater than or equal to 240 hp authorized by this permit shall emit NOx in excess of 0.5 g/bhp-hr. After January 1, 2018, regardless of manufacture date, no rich burn engine greater than or equal to 100 hp authorized by this permit shall emit NOx in excess of 0.5 g/bhp-hr. If an authorization or authorizations is issued for a spark ignited rich burn engine under this standard permit after the applicable date of January 1, 2015 or January 1, 2018, NOx emissions from that engine shall not exceed 0.5 g/bhp-hr, except that the standard permit holder shall have a one year grace period from the date of the initial authorization under this standard permit to comply with the limit of 0.5 g/bhp-hr for NOx. The commission reserves the right to re-evaluate the upgrade requirement if EPA promulgates any standards for existing engines.”
If you would like assistance with engine testing or compliance, contact flatrock at firstname.lastname@example.org or on the website here.