Page 1 of 8 MEMORANDUM

Date: November 16, 2012

Subject: Startup and shutdown provisions

From: William Maxwell, ESG/SPPD/OAQPS

To: EPA-HQ-OAR-2009-0234

The Administrator signed the “National Emissi on Standards for Hazardous Air Pollutants from Coal- and Oil-fired Electric Utility Steam Gene rating Units and Standards of Performance forFossil-Fuel-Fired Electric Utility, Industrial-Commercial-Institutional, and Small IndustrialCommercial-Institutional Steam Generating Unit s,” comprising the NESHAP portion, known as the Mercury and Air Toxics Standards (MATS) and the Utility NSPS, on December 16, 2011, and the final rules were publis hed in the Federal Register on February 16, 2012 (see 77 FR 9304). We proposed different standards for startu p and shutdown by our inclusion of certain default values, which applied on ly during startup and shutdown.

In response to comments on the proposed rule, we finalized work practic e standards to apply during startup and shutdown, as described fu rther below. This t echnical support document describes the provisions fo r startup and shutdown promulgated in the final rule 1 and changes to these provisions to address issues raised in the petitions for re consideration of the final MATS rule and the Utility NSPS.

I. MATS Proposed Rule

In the final rule, we proposed different standa rds for startup and shut down by our inclusion of the default values described below, whic h applied only during startup and shutdown. Specifically, we stated:

To appropriately determine emissions during startup and shutdown and account for those emissions in assessing co mpliance with the proposed emission standards, we propose use of a defa ult diluent value of 10.0 percent O 2 or the corresponding fuel specific CO 2 concentration for calculating emissions in units of lb/MMBtu or lb/TBtu during start up or shutdown periods. For calculating

emissions in units of lb/MWh or lb/G Wh, we propose source owners use an electrical production rate of 5 percent of rated capacity during periods of startup or shutdown. We recognize that there are other appr oaches for determining emissions during periods of startup a nd shutdown, and we request comment on

1 This document uses the terms “the final rul e” and “the rule” to re fer to MATS, though the Utility NSPS incorporates these same provisions w ith regard to the particulate matter standard

for that rule.Page 2 of 8 those approaches. We further solic it comment on the proposed approach

described above and whether the valu es we are proposing are appropriate.

We proposed application of th e respective emission limits du ring periods of startup and

shutdown and use of default values to calculate the emission limits

. The standards that apply at all times other than startup and shutdown are production-based limits, which is why we proposed

the default values. The default values were mean t to account for the fact that during startup and shutdown events, production (in this case the generation of electricity) is by definition

nonexistent.

We received a variety of comments on the propos ed rule concerning th e application of the standards during startup and s hutdown. Many commenters pointed to the lack of data in the record concerning emissions that occur during periods of startup and shutdown. Commenters also asserted that emissions during these pe riods can vary widely during the startup and shutdown of an EGU. Other commenters questioned the feasibility of collecting additional data during such periods and voiced conc erns regarding the reliability of measurements obtained from EGUs during such periods.

II. Final Rule

In response to comments, we established work pr actice standards rather than numeric emissions standards for periods of star tup and shutdown in the final MATS rule. See 77 FR 9380-82.

The final rule required the owners and operators of EGUs to: (1 ) operate using “clean fuels,” which were listed as either natural gas or distilla te oil, or a combination of those, for ignition during startup, (2) vent emissions to the main st ack(s) and operate all c ontrol devices necessary to meet the normal operating standards under th e final rule, with th e exception of those technologies whose operation is te mperature-dependent, when coal , solid oil-derived fuel, or residual oil is fired in the EGU during start up or shutdown, and (3) st art their temperaturedependent control systems appropriately to comp ly with relevant standards applicable during normal operation.

In the proposed reconsideration not ice, the Agency is proposing wo rk practice standards that are substantially the same as the work practice standards established in the final MATS. Specifically, sources must combust clean fuels during periods of startup and shutdown, and coal and oil may

not be combusted in the EGU until certain ai r pollution controls are engaged. The EPA is, however, proposing to revise the definitions of “startup” and “s hutdown,” to add a definition of “clean fuel” and expand the list of “clean fuels, ” and to revise requirements related to the operation of controls.

A. DefinitionsPage 3 of 8 We first address what constitutes startup and shutdown because definitions of these periods are essential to implementation of work practice standards.

1. Startup and Shutdown Periods

In the final rule, we included the follow ing definitions of startup and shutdown:

Startup means either the first-ever firing of fuel in a boiler for the purpose of producing electricity, or the firing of fuel in a boiler after a shutdown event for any purpose. Startup ends when any of the steam from the boiler is used to generate electricity for sale over the gr id or for any other purpose (including on site use).

Shutdown means the cessation of operation of a boiler fo r any purpose. Shutdown begins either when none of the steam from the boiler is used to generate electricity for sale over the grid or for any other purpose (including on-site use) or at the point of no fuel is being fired in the boiler. Shutdown ends when there is both no electricity being generated and no fuel being fired in the boiler.

Petitioners sought clarification re garding these terms as applied to EGUs and stated that the

definitions should be revised to accommodate th e operation of cogeneration units, and did not accurately reflect startup conditions for all affected units, particularly supercritical units. We are proposing to revise the definitions in this reconsideration notice as follows:

Startup means the period in which operation of an EGU is initiated for any purpose. Startup begins with either the first-ever firing of fuel in an EGU for the purpose of producing electricity or useful thermal energy (such as heat or steam) for industrial, commercial, heating, or cool ing purposes, or the firing of fuel for any purpose in an EGU after a shutdown event. Startup ends when the EGU generates electricity that is sold or us ed for any other purpose (including on site use), or the EGU makes useful therma l energy (such as heat or steam) for industrial, commercial, h eating, or cooling purposes (16 U.S.C. 796(18)(A) and 18 CFR 292.202(c)), whichever is earlier.

Shutdown means the period in which cessation of operation of an EGU is initiated for any purpose. Shutdown begins when the EGU no longer generates electricity or makes useful thermal energy (such as h eat or steam) for industrial, commercial, heating, or cooling purposes; or when no coal, liquid oil, syngas, or solid oilderived fuel is being fired in the EGU, whichever is earlier. Shutdown ends when the EGU no longer generates electricity or makes useful thermal energy (such as steam or heat) for industrial, commerci al, heating, or cooling purposes, and no fuel is being fired in the boiler.Page 4 of 8 We maintain that the proposed revised definitions, including the addition of provisions for useful thermal energy, 2 appropriately address the f act that EGUs can provide electricity both for sale and for on-site use, and cogenera tion EGUs can also supply useful thermal energy (such as heat or steam) for industrial, commercial, heating, or cooling purposes. For this reason, we believe

that EGUs should be considered to be operating normally at all tim es electricity is generated for sale or use, and/or useful therma l energy (such as heat or steam) is supplied for a useful purpose.

Some petitioners have asserted that, by defin ition, a supercritical EGU can only achieve its normal operating conditions once the steam reach es supercritical conditions. Because this process requires transition from “subcritical” to “supercritical” conditions, a supercritical EGU has a dedicated startup system to separate steam from water until the unit reaches operating conditions at approximately 30 to 40 percent of full lo ad. Through this comment, the petitioners seem to suggest that for supercritical EGUs the startup period ends only af ter the steam sent to the turbine has no water droplets, which, according to the petitioners, happens at approximately 30 to 40 percent load.

We believe our proposed revised definition of star tup accounts for the operation of supercritical EGUs. Under the revised definition, the startup peri od begins with firing of clean fuel and ends with generation of electricity for any useful pur pose or production of useful thermal energy (such as steam or heat), whichever comes first. Separa tion of steam and water, irrespective of the EGU type – subcritical or supercriti cal – occurs with in this period. 3

Some petitioners asserted that the definition of st artup period and the work practices in the final rule are not accurate because startup extends beyond first generation of electricity, because electricity generation does not mean that the E GU and emission controls have reached a safe or stable normal operating condition, because the con cept of minimum stable load (at which point supplemental fuel is not needed) is relevant relative to efficient, stable, and safe operation of air pollution controls, and because opera tion of all control equipment s hould be tied to the end of the startup in the revised definiti on. As discussed below, we be lieve both the proposed revised definitions of startup and shutdown periods and the proposed revised work practices, which take into consideration potential ope rational constraints of air pol lution control devices (APCDs),

address these concerns.

Per our proposed definition of st artup period, this period ends when an EGU generates electricity that is sold or used for any other purpose (incl uding on-site use) or an EGU makes useful thermal energy (such as heat or steam) for industria l, commercial, heating, or cooling purposes, whichever is earlier. We disagree that the star tup period extends beyond firs t generation of useful electricity, as we believe EGUs are operating in production (not startup) mode when they

2 16 U.S.C. 796(18)(A) and 18 CFR 292.202(c).

3 We understand that a steam turbine should not be exposed to water droplets at its inlet at any load, to prevent blade erosion a nd other problems, and that boiler /turbine systems are designed to prevent this, and we do not consider the proposed definition to be problematic in this regard.Page 5 of 8 generate electricity or produce thermal energy for use.

We also believe that the proposed APCD operation-related work practice requirements accommodate efficient, safe, and stable operation. Moreover, we have carefully designed our definitions and work practice requirements to provide flexibility to EGU owners/operators regarding operation of controls , and therefore we have not tied operation of these more condition-specific controls to loads or specific po ints in the startup period. We also understand

that no technical barrier exists to burning clean fuels for longer portions of startup or shutdown periods. Hence, if needed, an EGU could burn clean fuels until the appropriate flue gas

conditions are achieved to e ngage the required APCDs.

While petitioners suggest that th e concept of minimum stable load (at which point supplemental fuel is not needed) is relevant relative to efficient, stable, and safe operation of air pollution controls, they have not provided data supporting this claim. Moreove r, if an EGU co-fires clean fuels with production fuels (coal, liquid oil, syngas , or solid oil-derived fu el) after the end of its startup period, its emissions will be lower than those generated when it fires only production fuels. Considering these factors, the EPA is not taking any acti ons relative to the concept of minimum stable load asserted by petitioners.

2. Clean Fuels

The final rule required use of “clean fuels,” listed as either natural gas or distillate oil, or a combination of those, for ignition during startup. Petitioners asserted that the finalized work practice standards should include synthetic natural gas, syngas, and ultra-low sulfur diesel (ULSD) as “clean fuels.” Specifically, petitioners referred to the use of synthetic natural gas or diesel fuel for some EGUs and syngas for star tup of integrated gasification combined cycle (IGCC) EGUs affected by this rule. The EPA also understands that propane is used for startup at

some EGUs.

In the proposed reconsideration ru le, we have proposed adding a definition of “clean fuels” and including synthetic natural gas that meets the specification necessary for that gas to be transported in/via a Federal Energy Regulatory Comm ission-regulated pipeline, synthesis gas (syngas) 4 , propane, and ultra-low sulfur diesel (ULSD) to the list of clean fuels noted in the final rule (natural gas and distillate oil). We believe that HAP emissi on reduction benefits associated with burning of clean fuels warr ant utilization of such fuels dur ing startup and shutdown periods. We also note that addition of synthetic natura l gas to the list of clean fuels provides the opportunity for conventional coal-fired EGUs to st artup on synthetic natura l gas if desired. Also, limiting the diesel fuel to the ULSD type will help minimize emissions dur ing period of startup

and shutdown.

4 Synthesis gas (syngas) is gasifier product gas consisting mostly of hydrogen and carbon

monoxide.Page 6 of 8 The proposed definition is below.

Clean fuel means natural gas, synthetic natural gas that meets the specification necessary for that gas to be tran sported on a Federal Energy Regulatory Commission (FERC) regulated pipeline, pr opane, distillate oi l, synthesis gas (syngas), or ultra-low-su lfur diesel (ULSD).

B. Operation During Startup and Shutdown

In the final rule, the EPA required sources to vent emissions to the main stack(s) and operate all control devices necessary to meet the operating st andards that apply at all other times under the final rule (with the exception of dry scrubbers an d selective catalytic re duction (SCR) systems) when coal, solid oil-derived fuel, or residual oi l is fired in the EGU dur ing startup or shutdown.

The EPA stated that it is the re sponsibility of the ope rators of EGUs to start their dry scrubber and SCR systems appropriately to comply with relevant standards applicable during normal operation.

Petitioners stated that IG CC EGUs are fired with syngas, not the fuels listed as “clean fuels” in

the final rule. Petitioners also contended th at the standards need to recognize operating

conditions for fluidized bed com bustion (FBC) EGUs that inject limestone for acid gas control, for most effective control of those gases, as well as operating conditions for selective noncatalytic reduction systems (SNCRs), selective catalytic reduction systems (SCRs), and other systems. We have considered these concerns, and in the propo sed reconsideration notice are proposing to require EGU source owners or operators , when firing coal, solid oil-derived fuel, or residual oil in the EGU during startup and shutdow n, to vent emissions to the main stack(s) and operate all control devices necessary to meet the operating standards that apply at all other times under the final rule (with the exception of limestone injecti on in FBC EGUs, dry scrubbers, SNCRs, and SCRs). Owners and operators of EGUs are responsible for starting limestone injection in FBC EGUs, dry scrubbe r, SNCR, and SCR systems as expeditiously as possible, but, in any case, when necessary to comply with other standards applicable to the source that require operation of the control devices.

1. IGCC Units

The EPA understands that at IGCC EGUs, syngas (primarily a mixture of carbon monoxide and hydrogen) is used as both a clean fuel and the production fuel. We unders tand that syngas is generated in the gasifier of an IGCC EGU and af ter the syngas achieves the desired site-specific composition, it is fired in the combustion turbine as a clean and production fuel. The syngas fired

in the combustion turbine is considered a clean fuel because it is cleaned to remove trace contaminants such as sulfur before its injection in the turbine. We also understand that during the startup and shutdown periods, some or all of th e syngas produced may not be combusted in the turbine. In the proposed reconsideration rule, we are proposing two options for IGCC EGUs for handling syngas not fired in the combustion turbine: (1) syngas must be flared, not vented, or (2)Page 7 of 8 syngas must be routed to duct burners, which may n eed to be installed, and the flue gas from the

duct burners must be routed to th e heat recovery steam generator.

2. Operating Constraints of Certain APCDs

In the proposed reconsideration rule, we also propose to revi se the rule’s work practice requirements to recognize constraints of cer tain EGUs and APCDs. Specifically, after considering petitions that FBC EGUs that inje ct limestone for acid ga s control need to be operated at temperatures at whic h limestone can calcine for most effective control of acid gases 5,

we are proposing to revise the standards to allo w limestone injection to start after appropriate temperatures as specified by the eq uipment manufacturer or installe r have been attained in such EGUs. In addition, we acknowledge operating temper ature constraints of SNCR systems, and we are proposing to revise the standards to allow su ch systems to start as soon as technically possible after the appropriate temperatures as specified by the equipment manufacturer or

installer have been reached. We are also aw are that SNCR and SCR systems with ammonia injection need to be operated within a prescr ibed and relatively narrow temperature window to provide nitrogen oxide (NO X ) reductions 6 and that dry scrubbers also n eed to be operated close to flue gas saturation temperature 7 , and we have addressed these c onsiderations in the proposed work practice requirements.

Some petitioners have asserted that premature us e of ACI, as well as trona and other alkaline

sorbents that are heavier than activated carbon, can lead to de posits on particular matter (PM) control surfaces and potentially cause detrimental impacts on hardware and operation of these controls and create safety con cerns, including fires. Petitioners suggested that sorbent use can only begin when a sufficiently high gas flow rate is achieved in the duct. The EPA has reviewed publicly available information and information submitted in comments to the rule, and we have not found any information supporting the petitioners’ assertions. Moreover, petitioners have not provided data substantiating their assertions. Ther efore, we are not adding specific work practice requirements associated with sorbent (carbon or trona or other alkaline materials) injection.

Further, as discussed in the preamble to the fina l rule, we understand that there may be concerns with acidic and tarry deposits on surfaces of PM controls (ESPs and baghouses) related to firing of heavy (residual) oil, but that such concerns do not exist when EGUs co mbust light (distillate)

oil. 8 Accordingly, with residual fuel oil firing, si te-specific flue gas temperature and oxygen (O 2 )

5 Fluidized Bed Combustion. Simeon Ok a, CRC Press, September 2003, pp. 527-528.

6 NO X Emission Control Options For Coal-Fired Elect ric Utility Boilers. R.K. Srivastava, R.E. Hall, S. Khan, K. Culligan, and B. Lani, Journa l of the Air & Waste Management Association

, 55, September 2005, pp. 1372-1374.

7 Flue Gas Desulfurization: The St ate of the Art. R.K. Srivastava and W. Jozewicz, Journal of the Air & Waste Management Association , 51, December 2001, p. 1680.

8 Coal is fired at sufficiently high temperatures that concerns with condensation causing acidic and tarry deposits are not relevant.Page 8 of 8 concentration thresholds may be relevant to mi nimize condensation of acids and tars and thereby minimize any potential for detrimental impacts on hardware and any safety concerns. The rule’s proposed work practice requirements provide flexibil ity to the operator to take appropriate sitespecific remedial measures, if needed, to addres s this issue. EGU owners or operators have several options to prevent detrimental impacts: (1) using clean startup fuels (e.g., natural gas, synthetic natural gas, syngas, ULSD , or distillate oil) until appropriate flue gas conditions have been reached and then subsequently switching to firing of residual oil; (2) pre-coating the PM

control surfaces 9 with an alkaline powder (e.g., limestone ); (3) installing ch emically resistant bags 10 in fabric filters (FF)s if applicable, or (4) using low-sulfur oils.

The EPA also notes that there are currently ma ny operational residual oil- fired EGUs that are started up with either natural gas or distillate oil. At these EGUs, the transition from the startup fuel, distillate oil or natural ga s, to residual oil is already be ing practiced without unacceptable impacts on APCDs, including PM controls that ar e operated to meet applicable opacity limits. Based on this experience and the options de scribed above, those E GUs where residual oil is used for either a part of the startup period or as the main fuel will also be able to operate their PM controls to meet the rule’s work practice requirements.

We are not aware of any operati onal constraints applicable to operation of wet scrubbers during startup that could cause detrim ental impacts on wet scrubber hard ware or could create safety concerns, and we did not receive comments on this aspect of we t scrubber operation.

We also note that dry sorbent injection (DSI) can be applied across a very broad temperature range and will be engaged when residual oil or coal is fired in an EGU if necessary to comply with HCl requirements. Again, we did not receive comments on this aspect of DSI operation.

In summary, based on the discus sion above, we believe there ar e no constraints with engaging PM controls (ESPs and baghouses), wet scrubbers , and sorbent injection systems (ACI and DSI) when firing coal, solid oil-derived fuel, or re sidual oil in EGUs during startup and shutdown. Owners and operators of EGUs are responsible for starting limestone injection in FBC EGUs, dry scrubber, SNCR, and SCR systems as expediti ously as possible, but, in any case, when necessary to comply with other standards applicable to the sour ce that require operation of the

control devices.

9 Coal Power, May 1, 2007: http://www.coal powermag.com/plant_design/Coal-Plant-O-and-MRiver-Locks-and-Barges-Are-a n-Aging-Workforce-Too_36.html

10 Neundorfer: Lesson #4, p.4-7, Table 4-1: http://www.neundorfer.com/FileUploads/CM SFiles/Fabric%20Filte r%20Material[0].pdf