2 March 2009

The US Environmental Protection Agency (EPA) proposed national emission standards for hazardous air pollutants (NESHAP) for stationary reciprocating internal combustion engines (RICE) that are not already covered by earlier EPA regulations. The proposed rule would set emission limits for engines that:

  • are located at “area sources” of air toxics emissions;
  • have a site rating of less than or equal to 500 hp, are located at “major sources” of air toxics emissions, and were constructed or reconstructed before June 12, 2006;
  • have a site rating of greater than 500 hp, are located at “major sources” of air toxics emissions, and were constructed or reconstructed before December 19, 2002.

These engines are used at facilities such as power plants and chemical and manufacturing plants to generate electricity and power pumps and compressors. They are also used in emergencies to produce electricity and pump water for flood and fire control. “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”.

The proposed rule limits emissions of hazardous air pollutants by introducing emission standards for carbon monoxide and/or formaldehyde. Engine owners and operators can meet the limits by installing aftertreatment controls. The EPA expects that owners or operators of existing “rich-burn” engines, which burn natural gas, gasoline or other fuels, would install a non-selective catalytic reduction (NSCR) systems to meet the proposed emission limits.

The proposed rule considers two aftertreatment options for existing diesel engines:

  1. Oxidation catalysts (OC)—a technology that can achieve significant (up to 90%) air toxics reductions from diesel engines, but can only reduce fine particle pollution by about 25-30%.
  2. Catalyzed diesel particulate filters (CDPF), which can reduce air toxics and fine particle emissions (including black carbon) from diesel engines by over 90%.

Owners or operators of existing engines would be required to:

  • install emission control equipment that would limit air toxics emissions by up to 90%,
  • perform emissions tests to demonstrate engine performance and compliance with rule requirements, and
  • use ultra-low sulfur diesel fuel in non-emergency engines with a site rating greater than 300 hp.

The EPA is soliciting comments on the proposal, including comments on the feasibility of using CDPF’s on existing stationary diesel engines, and the control of fine particles as a surrogate for air toxic metals. The final rule is to be adopted by February 10, 2010.

Emissions from most existing engines covered by the proposal still remain unregulated by the EPA. Emissions from certain categories of existing stationary engines (at major sources of air toxics emissions) were regulated in June 2004 and in January 2008. In June 2006, EPA finalized emission standards for new stationary diesel engines.

Source: US EPA (Proposed rule | Fact sheet)