Johnson Matthey Emission Control Technologies

EPA NESHAPS

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Do You Have the Right Catalyst to Meet the EPA’s NESHAPS for Your Gas Compressor Engines

The EPA recently finalized national air toxics standards for existing stationary reciprocating spark-ignited engines. This new rule sets limits for hazardous air pollutants (HAP) such as acrolein, formaldehyde, acetaldehyde, methanol and benzene from existing gas engines. Also known as the National Emission Standards for Hazardous Air Pollutants (NESHAPS), it specifically targets the reduction of formaldehyde. For all types of HAPs, the rule targets the reduction of CO, as a representative surrogate.

Gas engines are commonly used for gas compression, power generation and pumping. A very large population of these engines may already have catalytic converters installed to reduce NOx, CO and HC. If the engine is a rich burn engine (or stoichiometric engine), the catalytic converter contains a precious metal catalyst, which will convert all three pollutants simultaneously. This is known as a 3-Way catalyst. The 3-Way catalyst is also referred to as NSCR (non-selective catalytic reduction). If the engine is a lean burn engine, the catalytic converter would contain a precious metal catalyst that will reduce CO and HC and is known as a 2-Way catalyst. The 2-Way catalyst is also referred to as Oxidation Catalyst.

Since HAPs are essentially HC’s or hydrocarbons in nature, both 3-Way NSCR and 2-Way Oxidation Catalyst will convert HAPs. However, since 3-Way catalysts are formulated to maximize the reduction of NOx and 2-Way catalysts are formulated to maximize the reduction of CO, they may not be the most effective in reducing formaldehyde or the other HAPs.

The NESHAPS affects existing spark ignited (SI), Reciprocating Internal Combustion Engines (RICE) that are located at area sources or that have a site rating ≤ 500 BHp and are located at major sources of hazardous air pollutant emissions. A major source is defined as any stationary source or group of stationary sources located within a contiguous area and under common control that emit or has the potential to emit ≥ 10 TPY (tons per year) of a single HAP or ≥ 25 TPY of two or more HAPs. An area source is defined as not a major source. This rule is in effect from October 19, 2010 with compliance by October 19, 2013. The rule is summarized in Table 1.

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