22 February 2010

The US Environmental Protection Agency (EPA) has issued a final emission regulation for existing stationary diesel engines. The rule will reduce emissions of toxic air pollutants—such as formaldehyde, acetaldehyde, acrolein, methanol and other air toxics—from several categories of previously unregulated stationary engines.

The rule is applicable to following categories of diesel engines:

  • used at “area sources” of air toxics emissions and constructed or reconstructed before June 12, 2006,
  • used at “major sources” of air toxics emissions, have a site rating of less than or equal to 500 hp, and constructed or reconstructed before June 12, 2006,
  • used at “major sources” of air toxics for non-emergency purposes, have a site rating of greater than 500 hp, and constructed or reconstructed before December 19, 2002.

“Major sources” of air toxics are defined as those that emit 10 short tons per year of a single air toxic or 25 short tons per year of a mixture of air toxics. “Area sources” are those sources that are not “major sources”.

EPA chose to select formaldehyde to serve as a surrogate for hazardous air pollutants (HAP) emissions from stationary engines. In addition, the EPA has determined that carbon monoxide (CO) is an appropriate surrogate for formaldehyde. Since testing for CO emissions has many advantages over testing for HAP emissions, the emission standards have been finalized in terms of CO (as volumetric concentrations).

The affected stationary diesel engines must comply with CO emission limits or must be fitted with emission controls, such as diesel oxidation catalysts, to reduce CO emissions by 70%. The emission standards are:

  • For non-emergency engines above 500 hp: 23 ppm CO or 70% CO emission reduction,
  • For non-emergency engines between 300 and 500 hp: 49 ppm CO or 70% CO emission reduction,
  • For non-emergency engines between 100 and 300 hp at major sources: 230 ppm CO.

The rule also requires the use of ultra-low sulfur diesel fuel for stationary non-emergency engines greater than 300 hp with a displacement of less than 30 liters per cylinder. The regulation will be fully implemented by 2013.

The regulation includes a number of other provisions, including work practices for engine operators. Stationary engines above 300 hp must also be equipped with closed or open crankcase filtration system in order to reduce metallic HAP emissions.

While the regulation does not mandate the emission control technology, the EPA designed the standards based on the capabilities of the diesel oxidation catalyst (DOC) rather than the catalyzed diesel particulate filter (CDPF). The agency said it does not have any data that shows that CDPFs provide greater reductions of HAP emissions than oxidation catalysts on stationary engines, and CDPFs are approximately four times as costly as oxidation catalysts.

The EPA proposal, published in March 2009, also included requirements for spark ignited (SI) stationary engines which are not included in the adopted rule. The SI engine regulation has been postponed and will be subject of a separate rule to be finalized in August 2010.

An emission rule for new stationary engines was adopted in June 2006.

Source: US EPA