EPA has proposed a maximum achievable control technology (MACT) standard for combustion turbines (CTs). The CT MACT rule (Subpart YYYY of Part 63) is designed to limit the emissions of hazardous air pollutant (HAP) emissions from plant sites that are categorized as major sources. EPA has identified formaldehyde, toluene, benzene, and acetaldehyde as HAP emissions from CTs, with formaldehyde being the HAP emitted in largest quantity.
In the proposal, EPA has identified several subcategories. Emergency and limited use CTs are exempt from the MACT limits, as well as any CTs that combust landfill or digester gas. Other CTs will establish compliance in two ways: (1) by demonstrating compliance with a 43 ppbdv (at 15% O2) emission limit for formaldehyde during annual compliance tests or (2) by demonstrating 95% reduction of CO emissions continually using CEMS. The option to demonstrating compliance with the 43 ppb formaldehyde limit, is only available for "uncontrolled" sources. If a source has an oxidation catalyst for CO control, 95% reduction must be determined. In the preamble to the Subpart YYYY proposal, EPA indicates that most new CTs with lean premix (low NOX) burners should be able to meet the 43 ppb formaldehyde limit without additional control, but diffusion flame type burners would likely require the installation of an oxidation catalyst.
Existing CTs with diffusion-flame type burners are not required to meet the new limits, but new or reconstructed diffusion-flame units must meet the new limits, presumably including oil burners on lean premix CTs since oil burners do not operate in lean premix mode. If a CT with diffusion-flame type burners (or a lean premix unit without a NOX limit) can demonstrate compliance with 43 ppb formaldehyde limit without installing an oxidation catalyst, additional testing, monitoring, or documentation may be required.
The proposed rule is rife with problems. The basis for the emission limits are questionable and based on scant data. Test methods for accurately measuring such low levels of formaldehyde have not been established. Problems exist for trying to measuring CO reductions, particularly at the low levels anticipated. For combined-cycle units, the Subpart YYYY only applies to the turbine emissions--any duct burners would not be covered under the subpart--although it would seem impossible to separate these emissions for the purpose of determining compliance.
A copy of the proposed CT MACT rule is available from our FTP Library. EPA solicits comments on the proposed rule by February 28, 2003.
RMB Consulting &