When natural gas is combusted, formaldehyde is formed as an intermediate product as methane is converted to CO2 during combustion. Formaldehyde is regulated by the U.S. EPA as a hazardous air pollutant (HAP) under National Emission Standards for Hazardous Air Pollutants (NESHAP) regulations, and both turbines and reciprocating engines are listed source categories where EPA is required to develop regulations. NESHAPs have been adopted for natural gas-fired combustion turbines and reciprocating internal combustion engines (RICE), with initial regulations in 2004 that included a 91 parts...
When natural gas is combusted, formaldehyde is formed as an intermediate product as methane is converted to CO2 during combustion. Formaldehyde is regulated by the U.S. EPA as a hazardous air pollutant (HAP) under National Emission Standards for Hazardous Air Pollutants (NESHAP) regulations, and both turbines and reciprocating engines are listed source categories where EPA is required to develop regulations. NESHAPs have been adopted for natural gas-fired combustion turbines and reciprocating internal combustion engines (RICE), with initial regulations in 2004 that included a 91 parts per billion (ppb) standard for new turbines at “major source” facilities. However, the Turbine NESHAP was “stayed” by EPA as the agency considered whether natural gas-fired turbines should be regulated (i.e., whether those turbines would be “delisted” or removed from the rule). In response to a legal challenge regarding EPA’s failure to meet Clean Air Act mandated schedules, EPA recently indicated that it plans to initiate a required periodic review of the Turbine NESHAP and that review will also address the delisting request. The “residual risk and technology review” (RTR) for the Turbine NESHAP will likely be conducted in 2018. Revisions to the regulation may be proposed when that review process is complete.
Formaldehyde is ubiquitous (e.g., naturally formed through atmospheric chemistry even if not directly emitted), and there is also the potential that atmospheric levels and atmospheric chemistry are not adequately understood. Earlier pipeline industry testing of turbine formaldehyde emissions using refined methods indicated exhaust formaldehyde below 100 ppb and near the method detection limit. Anecdotal data from that test program showed ambient levels comparable to turbine exhaust in some cases, with naturally occurring emissions from an adjacent corn field resulting in ambient concentrations higher than formaldehyde exhaust levels. Evidence of “high” ambient formaldehyde levels (relative to turbine exhaust) may provide context and a counterargument to restrictive formaldehyde regulations.
Understanding turbine formaldehyde emissions as compared to ambient levels is challenged by the ability to measure formaldehyde concentrations less than 100 parts per billion (ppb). Extractive Fourier Transform Infrared (FTIR) methods were developed for combustion exhaust formaldehyde measurement. However, measuring the ultra-low levels from turbines, commensurate with the NESHAP standard, will likely pose challenges. This project measured ambient formaldehyde levels using FTIR testing for comparison to the NESHAP standard. Significant challenges for conducting such measurements are apparent, which presents technical questions related to the feasibility of implementing emissions tests for the Turbine NESHAP standard.