An EPA decision to reopen the comment period on a proposed definition of “startup and shutdown” of fossil fuel-fired electric generating units (EGUs) shows that the Agency and industry still have significant ground to cover before reaching agreement on this perpetually controversial provision.  In the current action, the EPA is again requesting feedback on when startup ends and related issues.  Clarity here is essential since the termination of startup marks the point in which EGU operators must shift from complying with work practice standards to meeting numerical emissions limits.

Work practice standard

The current action affects the Agency’s February 2012 mercury air toxics standard (MATS) and New Source Performance Standards (NSPS) for steam EGUs.  In those standards, the EPA included work practice standards for hazardous air pollutants and particulate matter  emissions during periods of startup and shutdown.  The work practice standard included the requirement to use certain clean fuels during such periods when the temperatures and air flow in EGUs may not be sufficient to effectively engage air pollution control devices (APCDs). 

However, since this provision appeared in the final rules without having been previously proposed, the EPA agreed to reconsider the provision, thereby allowing public comment.  Accordingly, in November 2012, the Agency proposed to define the end of startup as being “when the EGU generates electricity that is sold or used for any other purpose (including on-site use), or the EGU makes use of thermal energy (such as heat or steam) for industrial, commercial, heating, or cooling purposes…whichever is earlier.”

APCD not online

In response, industry commenters stated that the generation of electricity should not mark the end of startup.  The commenters noted that electricity generation may begin when the boiler’s steam load is as low as 10 percent of nameplate capacity.  At this point, the commenters stated that startup fuel is still being burned, but many major components of the EGU, particularly APCDs, may be neither online nor fully functioning.  For example, an EGU may be generating electricity but the temperatures may be too low to make effective use of electrostatic precipitators (ESPs); in other words, compliance with numerical emissions limits may not be possible even though electricity is being generated.  Some commenters contended that operating an ESP at the wrong temperatures to meet emissions limits may create a safety risk.

In general, the industry commenters requested that the EPA move the end-of-startup definition further along in the operational process.  For example, commenters asserted that the startup period involves, and in some cases must involve, co-firing of both startup and primary fuels.  The commenters also argued that in its proposal, the EPA did not adequately account for the operational differences among different types of EGUs.  For example, commenters stated that the startup process for supercritical pulverized coal EGUs is different from that of subcritical EGUs.  Commenters also recommended that the EPA expand its definition of clean fuels that may be applicable during startup. 

Other issues

The EPA is requesting comment on the definition of startup, including when startup ends, along with the following issues:

• The use of default diluent gas cap values during periods of startup and shutdown;
• How to calculate startup/shutdown emissions when multiple affected EGUs share a common stack; and
• The use of a default electrical production rate value to calculate output-based emissions limits during startup and shutdown hours where the electrical load is zero.

Additional comments on the November 2012 EGU MATS and NSPS proposal must be received by the Agency by August 26, 2013.

EPA’s announcement reopening the comment period on the proposal was published in the June 25, 2013, FR.