August 1, 2015
The January 2015 Emissions Monitor featured the article “The Engine Rules: Ten Key Elements” written by Principal Consultants Jeremy Jewel and Shannon Lynn for the Fall 2014 Trinity Consultants Environmental Quarterly. That article noted the voluminous rules and guidance issued by EPA regarding permitting and compliance with the engine rules (e.g., 40 CFR Part 63, Subpart ZZZZ) and provided clarification surrounding several confounding issue. In its summer 2015 Environmental Quarterly Jewel and Lynn have updated their earlier article with several additional elements related to these complex rules and EPA’s interpretation of them. Portions of their update are featured below.
Understanding Rich Burn and Lean Burn…EPA’s Way
Technically (but not regulatorily), the difference between rich burn and lean burn combustion depends on which side of the ideal air-to-fuel ratio (AFR) line the engine operates. The ideal, or “stoichiometric”, AFR for any fuel can be calculated using a simplified combustion chemistry equation and the molecular weights, in pounds per mole (lb/mol), of carbon, C (12); hydrogen, H (1); oxygen, O (16); and nitrogen, N (14). An example for methane, CH4, is shown below.
CH4 + 2O2 + 7.5N2 → 2H2O + CO2 + 7.5N2
In this equation, the methane weighs 16 lb and the air (oxygen plus nitrogen) weighs 274 lb, resulting in an ideal AFR of 17.1. Each fuel has a different stoichiometric AFR. For example, a typical average diesel formulation has an AFR of 14.6. Lambda (the excess air ratio) is often used to discuss combustion generically; λ = 1 represents the stoichiometric AFR for any fuel. Any λ value less than 1 (i.e., for methane, an AFR of less than 17.1) represents rich burn conditions, and any λ value greater than 1 (meaning that more air is present than the stoichiometric AFR) represents lean burn conditions.
Non-certified Parts for Certified Engines
Some engine manufacturers assert that, for certified engines, all maintenance/replacement parts (e.g., spark plugs) must be purchased from the certifying manufacturer or else the certification is voided. While this may be ideal, EPA seems to indicate that it is not required. A 2007 regulatory preamble states that EPA “disallows tampering (including the installation of clearly inadequate replacement components), but EPA does NOT require the use of original OEM parts or certified components when replacing emission-related parts.”
Fire Pump (NFPA) Certifications v. EPA-manufacturer Certifications
Caution should be used when reviewing whether an engine is properly certified for compliance with the engine rules, as more than one certification could be required. The engine rules establish different requirements depending on whether an engine is certified as a National Fire Protection Association (NFPA) fire pump engine. While the requirements for a fire pump engine may be different, purchasing a fire pump does not necessarily preclude the need to purchase an engine that has been certified to meet the emission standards established in the engine rules. An owner/operator of a fire pump engine should ensure that proof of certification to the relevant emission standards as well as the NFPA fire pump certification are readily available (e.g., included on engine nameplate or included in owner’s manual).
It is important to have an individual designated as the expert on stationary engines purchased/operated at a facility. Some engine dealers and manufacturers may claim that facilities can demonstrate compliance with NSPS IIII by purchasing what are known as “flex” engines (described in 40 CFR 1039.625(e)(2)). These standards are less stringent, and they apply only to non-road/mobile engines. EPA has been explicit that “flex engines are not allowed for stationary applications.”
Addressing Related Modeling Issues
While not directly related to NSPS and NESHAP regulations, modeling is a critical element to many air permitting programs. Modeling of engines is often challenging because short, horizontal exhausts result in large fence line concentrations, especially for sources near a fence line, which is also often the case for engines.
Many regulatory authorities allow “quick and easy” screening modeling, but sometimes those models are so conservative that passing is nearly impossible. For the same scenario of engines, a screening model can predict impacts at least 50 percent greater than a refined model, primarily because a screening model adds together the peak impacts for each source. This methodology ignores the likelihood that each source’s peak impact is occurring at different locations and times.
The problem has been exacerbated by the continual ratcheting down of ambient air quality standards. NO2 is the most problematic pollutant when modeling engines. The current National Ambient Air Quality Standard (NAAQS) for NO2 is 188 micrograms per cubic meter (µg/m3) on a 1-hour basis, which is many times more stringent than the annual-average standard that was in place for many years prior to the 2010 update.
What this means to you
Jeremy Jewell and Shannon Lynn review and update 10 key areas of EPA regulations affecting owners and operators of stationary internal combustion engines.
MIRATECH can help
Contact MIRATECH to learn more about cost effective emission compliance strategies for your stationary ICEs.