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American Forest & Paper Association and American Wood Council Position 

Paper on Changes Needed to the Boiler MACT and GACT 

Startup and Shutdown Provisions 

(July 2014) 

Executive Summary 

AF&PA and AWC strongly agree with EPA that work practices are the correct 

compliance mechanism for startup and shutdown periods in the area and major source 

boiler rules. The work practice standards that EPA originally proposed for periods of 

startup and shutdown required an owner/operator to minimize periods of startup and 

shutdown following unit-specific procedures. However, the current definitions of startup 

and shutdown and the required work practices must be adjusted in order for facilities to 

be able to safely comply with the Boiler MACT and GACT rules. The following points 

summarize why changes are necessary. 

• The appropriate procedures for startup and shutdown vary by unit design, 

pollution control type, fuel firing mechanism, and integration with plant processes. 

EPA should not set a “one size fits all” work practice standard to cover the 

diverse population of units included in the industrial, commercial and institutional 

(ICI) boiler and process heater source category. Such an approach would result 

in definitions of startup and shutdown that are overly long for some units and too 

short for others. 

• Work practice standards generic enough to encompass all ICI units and address 

the safety and other operational concerns put forward by owners and operators 

may not amount to anything more than general duty requirements in the end. By 

contrast, facilities currently have unit-specific protocols for startup and shutdown 

that take into account the boiler design, type of fuel fired, how the fuel is fired, the 

pollution control equipment in place and its operational constraints, and other 

operational factors, such as the requirements for heating up ancillary equipment 

and ductwork. These unit-specific protocols focus on both safety and 

environmental considerations. 

• The requirement to engage control devices by the end of a defined startup 

period, rather than when the minimum operating temperature or gas flow 

requirements of the control device are met, can lead to damaged control 

equipment, particularly when the end of startup is defined in a generic manner 

that may not be appropriate to a particular installation. 

• Startup procedures ensure that equipment is brought up to normal operating 

conditions in a safe manner. Startup ends when the boiler/process heater and its 

controls are fully functional. 

• There is an energy efficiency incentive to minimize the time spent in startup. 

When units are starting up, the processes being served cannot operate optimally. 

Therefore, boilers and process heaters are started up as expeditiously as 

possible. Similarly, increasing boiler load during startup is dependent upon the 

process start-up/operational status as well, limiting the speed of startup in many 

circumstances. This means that the duration of boiler startup is dependent upon 

startup of other process components which are site-specific. 
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• The act of supplying even minimal quantities of steam or heat “for any purpose” 

should not define the end of startup. EPA has acknowledged in the preamble to 

the current rule that “these boilers and process heaters should be considered to 

be operating normally at all times during which steam of the proper pressure, 

temperature, and flow rate is being provided to a common header system or 

energy user(s) for use as either process steam, heat, or for the cogeneration of 

electricity [78 FR 7146]. And yet, EPA has promulgated a definition that, by not 

stipulating that the steam supplied be of the proper temperature, pressure, and 

flow, would have startup end before normal operation is achieved. 

• Because there is such diversity in the designs and operating modes of the boilers 

and process heaters being regulated by the major and area source rules, there is 

not a single load threshold or time period that would represent the functional end 

of startup for all units (we understand that CIBO has submitted some information 

based on a member survey that shows startup times by unit and unit type vary 

greatly). If EPA incorporates a “load plus time” or “maximum total startup time” 

type of threshold into the MACT and GACT rules to define the end of startup, the 

time should vary by unit design and a mechanism should also be provided by 

which a facility may establish unit-specific startup criteria and document those 

criteria in the site-specific monitoring plan. 

• A “load plus time” threshold to delineate periods of startup from normal operation 

does not address boilers that operate in standby mode for long periods of time. 

For these types of units, a maximum startup time (unit-specific and included in 

the site-specific monitoring plan or varying by unit type/design) is more 

appropriate. 

• Under the current rule, units equipped with control devices that are not 

specifically identified in Table 3 to Subpart DDDDD of Part 63 as exempt must 

engage the controls when coal, biomass, or residual oil is first introduced into the 

boiler or process heater. ESPs must be included in the list of exempted air 

pollution control devices because an ESP cannot be safely engaged until a 

certain flue gas temperature and/or oxygen level is reached. Table 3 of Subpart 

DDDDD must be amended to include ESPs among the listed controls that must 

be started as expeditiously as possible during startup. 

• Under the current rule, boilers and process heaters must use one or a 

combination of listed clean fuels when starting up. The list of clean fuels should 

be expanded. For example, gaseous fuels meeting the “other gas 1” 

classification, biodiesel, dry (<20% moisture) biomass, and fuels that meet the 

TSM, HCl, and Hg emissions limits through fuel analysis are fuels that should be 

permissible for use as clean startup fuels. 

• The shutdown definition currently states that shutdown begins when fuel is no 

longer being fired. The definition should be revised to accommodate units firing 

solid fuels on a grate or in a fluidized bed combustor where the residual material 

in the unit keeps burning after fuel feed to the unit is stopped. EPA has already 

indicated in guidance that they consider fuel “being fired” to mean that fuel is 

being fed. EPA should make this clear in the rule. 

• EPA has indicated through guidance that if a shutdown is not completed to the 

point of both no fuel being fired and no steam or heat being supplied, then a 
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shutdown has not occurred and therefore a startup cannot occur. This does not 

accommodate situations where solid fuel feed is lost where the feed can be 

restored before a complete shutdown takes place. The rule must take these 

periods into account so operators can have certainty in designing monitoring and 

recordkeeping systems and in determining compliance when these events occur. 

The shutdown definition should therefore be modified to say that shutdown ends 

EITHER when no steam or heat is being supplied and no fuel is being combusted 

in the boiler or process heater OR when startup is initiated by reintroducing fuel 

to the boiler or process heater after no fuel has been fed for at least 1 hour, 

whichever comes first. 

The following sections and the attached table provide more detail. 

Background 

In the recent Part 63 major and area source boiler/process heater rules, EPA 

established standards that apply at all times, including periods of startup and shutdown 

when work practice standards are to be followed. EPA correctly acknowledged the 

infeasibility of demonstrating compliance with numeric standards during the transient, 

non-steady state periods of startup and shutdown. Industry strongly agrees with EPA 

that work practices are the correct approach for applying a standard to industrial boilers 

and process heaters during startup and shutdown periods. 

The work practice standards that EPA originally proposed for periods of startup and 

shutdown required an owner/operator to “minimize periods of startup and shutdown 

following the manufacturer’s recommended procedures, if available. If manufacturer’s 

recommended procedures are not available, sources must follow recommended 

procedures for a unit of similar design for which manufacturer’s recommended 

procedures are available.” [76 FR 15642].

The work practice standards were subsequently revised in order to require “more than a 

general duty to reduce emissions” [76 FR 80615]. Definitions of startup and shutdown 

were proposed in order to clarify which periods of operation are subject to work practice 

standards and when numeric standards would apply. The problem since has been to 

arrive at definitions that encompass all units included in the diverse ICI Boiler and 

Process Heater category. 

EPA has already acknowledged that there are design differences amongst boilers and 

process heaters by establishing subcategories with different requirements. EPA should 

continue to acknowledge the differences amongst units by explicitly allowing facilities to 

establish and comply with unit-specific startup and shutdown practices as an alternative 

to generic work practices. Work practice standards generic enough to encompass all 

ICI units are not likely to amount to anything more than general duty requirements. By 

contrast, facilities currently have unit-specific protocols for startup and shutdown that 

take into account the boiler design, type of fuel fired, how the fuel is fired, the pollution 

control equipment in place and its operational constraints, and other operational factors, 

such as the requirements for heating up ancillary equipment and ductwork. These unitspecific protocols focus on safely starting up the unit while minimizing emissions. EPA 

should allow facilities to comply with unit-specific startup criteria that are documented in 

an enforceable site-specific plan (e.g., the site-specific monitoring plan already required 

by the rule). 
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The requirement for control devices to be fully engaged by the end of startup can lead 

to damaged control equipment, particularly when the end of startup is defined in a 

generic manner that may not be appropriate to a particular installation. Startups of 

many types of control equipment are dependent on a variety of physical conditions, 

including minimum temperature and flow requirements. Thus, startup times are specific 

to the installation. Establishing the end of startup based on an across-the-board load 

threshold, load plus time threshold, or total time threshold could force many operators to 

choose between noncompliance and risking control equipment damage and increased 

emissions, because such operators will be unable to start the emissions control 

equipment safely by the end of “startup” as EPA may define it. For instance, ESPs are 

typically not energized until the exhaust (and ESP internal equipment) is above the 

appropriate moisture dew point. If an ESP is energized when moisture levels are high, 

there is a high potential for fouling of the ESP plates which will reduce collection 

efficiency. Excess sparking, which can also occur due to fouling, can cause a fire or 

explosion. 

EPA should not set a work practice standard that is fundamentally incompatible with the 

operation of certain units. It is technologically impossible for some units, even top 

performers, to start their emissions control equipment any sooner in the startup process 

without risking equipment damage and creating environmental concerns. EPA should 

likewise not define the end of startup as the shortest time any particular unit in a design 

subcategory can reach stable operation because that unit will not be representative of 

the design and operation of all the units in that subcategory. 

Facilities cannot be rushed to complete startup and shutdown periods and compromise 

the safety of personnel and equipment. It is critical that the startup and shutdown 

definitions and the associated work practices be structured to allow safe operation, and 

it is critical that facilities understand and have a clear path to compliance with the 

requirements. 

Revision to the Definition of Startup 

EPA has revised the startup and shutdown definitions from those proposed in 

December 2011, where startup and shutdown periods were based on load, agreeing 

with commenters that, 

“...load conditions separating periods of startup and shutdown from periods 

of normal operation can be unit-specific and therefore presupposing certain 

load conditions in the definitions of periods of startup and shutdown is not 

appropriate” [78 FR 7146]. 

As a result, the January 31 and February 1, 2013 rules define startup as: 

“either the first-ever firing of fuel in a boiler or process heater for the 

purpose of supplying steam or heat for heating and/or producing electricity, 

or for any other purpose, or the firing of fuel in a boiler after a shutdown 

event for any purpose. Startup ends when any of the steam or heat from 

the boiler or process heater is supplied for heating, and/or producing 

electricity, or for any other purpose.” [40 CFR §63.7575 and §63.11237] 

The phrase “supplying... for any other purpose” is too restrictive because it implies that 

even using the heat that is generated when fuel is first combusted to safely pre-heat 

and protect important process equipment during the normal startup cycle will trigger the 

end of the regulatory “startup,” even though functionally startup has clearly not ended. 
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All boilers must gradually heat up to prevent damage to the boiler pressure parts and 

refractory, and the period of time that is required varies depending upon boiler design. 

Some processes are designed such that downstream equipment receives heat and/or 

steam when fuel is being burned during startup of the boilers or process heaters. For 

example, steam generated during startup that is not yet of the proper quality to be fed to 

a steam turbine or the designated process may be used to heat trace or preheat piping 

runs. Preheating is necessary to avoid the excessive thermal stresses that result in 

stress corrosion cracking. Stress corrosion cracking drastically reduces equipment 

longevity and negatively impacts the ability to operate safely. Yet, if the act of supplying 

low grade steam during startup for heat tracing or preheating was to define the end of 

startup, then the low grade startup steam would most likely be vented until the 

necessary steam pressure and steam temperature are reached for process use or 

electrical generation, and electrical heat tapes or another energy source would be used 

to warm piping, increasing energy use unnecessarily. 

EPA has acknowledged in the preamble to the current rule that “these boilers and 

process heaters should be considered to be operating normally at all times during which 

steam of the proper pressure, temperature, and flow rate is being provided to a common 

header system or energy user(s) for use as either process steam, heat, or for the 

cogeneration of electricity [78 FR 7146]. And yet, EPA has promulgated a definition 

that, by not stipulating that the steam supplied be of the proper temperature, pressure, 

and flow, would have startup end before normal operation is achieved. The act of 

supplying even minimal quantities of steam or heat “for any purpose” should not define 

the end of startup. 

Above all, the boiler/process heater operator’s primary concern during startup is safety. 

The startup procedures must ensure that the equipment is brought up to normal 

operating conditions in a safe manner. Startup functionally ends when the 

boiler/process heater and its controls are up to the proper operating temperature and 

pressure, and are fully functional. The procedures and the time necessary to complete 

a startup are site specific, and vary by boiler fuel, design, and control technique. They 

also depend on variables such as how long the unit has been shut down and can be 

affected by unexpected equipment problems during startup of the boiler or the process it 

supports, ambient conditions, natural fuel variability, and required testing of new or 

replacement equipment or components during startup. Therefore, the definition of the 

end of startup should be revised to indicate that it occurs when safe, stable operating 

conditions are reached, after emissions controls are properly operating. 

Safe, stable operating conditions should be defined on a unit-specific basis, as the 

various designs and operational modes of the myriad boilers and process heaters 

subject to the rules make establishing a standard threshold for all units impossible. 

Conversations with both operators and vendors have confirmed that a one size fits all 

approach is not workable for all situations. We understand EPA’s desire for a “bright 

line” that defines the end of startup, but not all situations can be accommodated with 

this approach. Therefore, if EPA adds a load and/or time type of threshold to the 

startup definition, facilities with units that cannot safely or practically accommodate that 

common threshold must have the option to implement a site-specific plan that, takes 

into account their specific operational and safety constraints, and provides criteria for 

the end of startup on a unit-specific basis. 

The following types of concepts could be incorporated into the site-specific monitoring 

plan to define the end of a startup period: 
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• The unit is firing its primary fuel for a period of time adequate to provide stable 

and non-interrupted fuel flow, stable and controlled air flows, and adequate 

operating temperatures to allow proper fuel drying and air preheat as applicable. 

• Emissions controls are in service with operating parameters such as flow rates 

and temperatures being controlled and stable. 

• The unit is supplying steam to a common header system or energy user(s) at 

normal operating conditions including pressure and temperature, and is above 

the minimum operational stable output flow rate, as applicable to the unit. 

• For stoker units, when the grate reaches an adequate level of coverage with solid 

fuel based on visual observation and stability of air, fuel, and steam flow rates. 

Boiler and process heater operators have a financial incentive to minimize the time 

spent in startup. When units are starting up, they are not operating in the most efficient 

mode and the process being served cannot operate optimally. Therefore, boilers and 

process heaters are started up as expeditiously as possible, but safety concerns cannot 

be ignored, and proper procedures must be followed. In order to be practically 

implementable, the startup definitions in the Boiler MACT and Boiler GACT rules and 

the startup work practices in the Boiler MACT rule must take these facts into account 

and must be revised to accommodate the technical issues discussed here. 

Reconsideration of Startup and Shutdown Definitions in the MATS Rule 

Industry is following with keen interest EPA’s current reconsideration of the definitions of 

startup and shutdown under the Mercury and Air Toxics Standards (MATS). While EPA 

has recognized in the MATS rule the operational constraints of certain pollution control 

equipment during startup, certain controls will not be fully functional and reducing HAP 

emissions when EPA currently defines “startup” as ending in the MATS rule. Many 

concepts raised by MATS commenters apply to units covered under the Industrial Boiler 

MACT and GACT rules. In fact, the comments on the need for unit-specific definitions 

and work practices are even more pertinent to the industrial boiler rules since the 

designs of industrial, commercial, and institutional boilers and process heaters vary 

more widely than the designs of utility boilers. 

The Proposed MATS rule reconsideration states that some commenters on that rule 

have requested that the end of startup be changed to four hours after 25 percent load is 

first reached, or 12 hours after first electricity generation, whichever occurs first. See 78 

Fed. Reg. 38004. EPA alternatively proposes to define the end of startup at coal-fired 

EGUs as occurring at 25 percent of nameplate capacity plus three hours, or the start of 

electricity generation plus six hours, whichever comes first. See 78 Fed. Reg. 38005. 

These proposed definitions are appropriate for some EGUs, but are too restrictive for 

others due to site-specific factors, and it would be impossible to establish such a 

threshold for industrial boilers and process heaters that would accommodate all sizes 

and designs. 

As the widely divergent comments on the MATS rule demonstrate, finding a single 

appropriate definition of the end of startup that accounts for all boilers in any 

subcategory continues to challenge EPA. The highest degree of flexibility would be 

provided by EPA addressing the wide variations among boilers by revising the startup 

definition to allow facilities to determine the minimum stable operating load or other 

relevant operating parameter with emissions controls at a stable operating condition on 

a unit-specific basis and include the minimum stable operating load or operating 
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condition and the proper procedures to follow during startup and shutdown in the sitespecific monitoring plan. Establishment of the minimum stable operating load or 

operating condition on a site-specific basis is analogous to setting other boiler and 

control device operating parameter limits on a site-specific basis, which EPA does 

routinely in the Boiler MACT and GACT rules. 

Minimum Stable Load, Range of Operation, and Normal Operating Load 

EPA has adopted a source-specific approach to setting lower boundaries of operation in 

other regulatory programs. (See 40 CFR Part 75 Appendix A, Section 6.5.2.1.) Such 

an approach could be used to establish and document a minimum safe, stable load for 

unit operation that would delineate the difference between periods of startup and 

shutdown and periods of normal operation. 

Under Section 6.5.2.1 of Appendix A to Part 75, the owner or operator of an affected 

source identifies the low, mid, and high load levels of each unit based on the unit’s 

operating history. The owner or operator is required to determine the number of 

operating hours at each load level over the previous 4 operating quarters and calculate 

the percentage of time spent at each load level in each quarter. 

Normal operating load, as defined in Paragraph 6.5.2.1(d) of Appendix A to Part 75, is 

designated by the owner or operator as the most frequently used load based on the 

analysis of historical load data. Paragraph 6.5.2.1(e) of Appendix A to Part 75 requires 

the owner or operator to report the upper and lower boundaries of the range of 

operation for each affected unit in the required site-specific monitoring plan. The owner 

or operator is also required to indicate, in the monitoring plan, the load level designated 

as normal and the two most frequently used load levels. The monitoring plan must be 

updated whenever the normal load level and two most frequently used load levels are 

redesignated. 

Similar to the Part 75 procedures, a unit-specific minimum stable load could be 

determined for units subject to Subpart DDDDD. The minimum stable load would be 

based on an analysis of unit operating data and would delineate periods of stable 

operation from the transient periods associated with startup and shutdown. The 

minimum stable load for each unit would be designated in the site-specific monitoring 

plan required under §63.7505(d). 

Operation of Boilers in Standby Mode 

At larger facilities with multiple boilers, some of the site boilers may be maintained in 

standby mode. When in standby, a boiler is in a state of operational readiness at a low 

stable load, frequently below 25%. This practice provides continuity because as 

process demands increase, or the capacity of the load-carrying boilers decreases, the 

standby boiler can be brought online quickly to fill steam demands. When operating in 

standby mode, a boiler subject to the emission limits in Tables 1 or 2 or 11 through 13 

to Subpart DDDDD of Part 63 (and thus subject to the startup and shutdown work 

practice standards of Table 3), would typically be combusting clean-burning liquid or 

gaseous fuels but could be combusting solid fuel or heavy liquid and employing 

emissions controls. 

When EPA proposed a definition of startup and shutdown incorporating a 25% load 

threshold, a number of commenters requested that EPA provide clarity on how the 

requirements would apply to units operating in standby mode at load levels below the 
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proposed threshold. If EPA is to adopt a “load plus time” threshold to delineate between 

periods of startup, shutdown, and normal operation, the same lack of clarity remains. 

In the December 2012 response to comments document for the reconsidered major 

source Boiler MACT rule (EPA-HQ-OAR-2002-0058-3846), EPA provided the following 

incomplete response to comment EPA-HQ-OAR-2002-0058-3510-A1, excerpt 117. 

“The EPA believes that the revised definitions adequately address units 

operating in standby mode and that such units should not be exempt from the 

startup and shutdown provisions of the final rule because??” 

All other comments regarding standby mode refer back to this incomplete response. 

Industry respectfully disagrees that the revised definitions adequately address units 

operating in standby mode. Furthermore, EPA appears to have misunderstood the 

concern – it was not that standby units should be exempted from startup and shutdown 

work practices, but that the regulations should not define startup and shutdown such 

that units operating in standby, which only exceed the operating threshold intermittently 

and may not reach 25% load during startup, are perpetually in a state of startup or 

shutdown. 

EPA’s revised definition of startup should take these units into account by either 

allowing a site-specific definition of the startup procedures required to reach minimum 

stable operating load or a maximum amount of time for startup for these units. 

Clean Fuels Requirement Under MACT 

The current work practice standard in Boiler MACT requires facilities to either start up 

on clean fuels or engage control devices prior to burning fuels not listed as clean fuels 

(except for the listed exempt control devices, which must be engaged as expeditiously 

as possible). At some facilities, the use of clean fuels prior to engaging control devices 

will require installation of dedicated burners to fire these fuels and installation of fuel 

delivery and or storage facilities, both of which may be impracticable to install on a sitespecific basis. In addition, operation and maintenance of burners that are infrequently 

used may be very problematic. For example, natural gas burners that are installed on 

biomass boilers may be prone to buildup of fly ash deposits on critical flame sensors 

and plugging of the burners. In addition, fuel actuator valves can malfunction due to 

infrequent operation. Maintenance and inspection of these components can be 

problematic given the infrequency of access and the problems associated with startup 

on a clean fuel, especially after unplanned outages. In some situations the periodic 

operation and maintenance of these systems has been so problematic that such burner 

systems have been decommissioned despite the strong desire of the operator to have 

the ability to fire a backup fuel in the event of loss of the primary fuel. 

Additionally, due to the nature of the fuels, the air flow rates, air flow distribution, and 

the overfired air configuration are completely different for a natural gas burner than a 

stoker or fuel cell boiler burning biomass. Unless a boiler is designed to burn natural 

gas and biomass at the same time, it may be impractical to install natural gas as a startup fuel. 

In addition to the operational difficulties associated with use of clean fuels, it should be 

noted that EPA did not consider the added cost and burden of requiring clean fuel 

combustion for startup in situations where controls are not engaged prior to burning 

solid fuel or heavy liquid. First, clean fuels may not be universally available in sufficient 

quantities. Use of listed clean fuels to start up results in increased capital and operating 
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costs for many facilities and in the increased use of non-renewable fossil fuels; these 

fuels are in many cases more expensive than a unit’s primary operating fuel and require 

different infrastructure to accommodate (which may not be available, depending on 

location and other factors). In many cases the boilers must be retrofitted with systems 

to burn the alternative fuels such as natural gas when startup may only occur a few 

times per year. This represents a significant expense for a very limited amount of use. 

Furthermore, many facilities would be required to obtain permit modifications prior to 

making this change to their boilers. 

The requirement in the March 2011 MACT rule to establish startup procedures that 

minimize emissions and to train operators made more sense from an operational safety, 

cost, GHG emissions, and sustainability perspective. 

Expansion of the List of Clean Fuels Under MACT 

The list of clean fuels, as written, is too narrow. The list should be expanded to include 

all gaseous fuels meeting the “other gas 1” classification. Biodiesel should also be 

added to the list, as distillate oil is sometimes a biodiesel blend. Fuels that meet the 

TSM, HCl, and Hg emission limits using fuel analysis should be added to the list of 

clean fuels. Dry biomass (<20% moisture content) should also be added to the list of 

clean fuels for units operating with a mechanical collector (i.e., multiclone). Dry 

biomass is included in EPA’s definition of “clean cellulosic biomass” and will burn 

cleaner than other solid fuels. It is a clean fuel for startup because it exhibits low HCl, 

Hg, and CO emissions due to its chloride, mercury, and moisture content. Therefore it 

is a reasonable work practice for solid fuel boilers to burn only dry biomass as clean fuel 

during startup. Permitting authorities should have the flexibility to approve other clean 

fuels that EPA may not have considered (e.g., other renewable fuels). 

Time to Properly Engage Pollution Control Devices Under MACT 

Under the current rule, certain pollution controls do not have to be engaged immediately 

upon startup, but are required to be engaged “as expeditiously as possible.” We 

recommend modifying this provision to take into account safety and protection of 

process equipment and pollution controls, as well as to recognize that some pollution 

controls are engaged gradually. Accordingly, we recommend revising the text to “as 

expeditiously as possible in a manner consistent with the manufacturer’s 

recommendations or standard industry practices”, to take into account worker safety 

and protection of the control device and other equipment that could be impacted by 

improper operation or failure of the pollution control system. 

Under the current rule, units equipped with an ESP must either fire “clean fuels” 

throughout startup or engage the ESP when feeding of coal, biomass, or residual oil into 

the boiler or process heater begins. However, ESPs have operating constraints that 

dictate that they be included in the list of air pollution controls that must be started as 

expeditiously as possible. An ESP cannot practically be engaged until the flue gas 

temperature exceeds the moisture and acid dew points, and the oxygen level in the 

device is low enough to avoid a fire or explosion of combustible materials in the device. 

Some manufacturers recommend that such temperatures be maintained for several 

hours to ensure adequate heating of the equipment. Premature starting of this 

equipment will lead to short-term stability problems that could result in unsafe conditions 

and longer term degradation of ESP performance due to fouling, increased chances of 

wire damage, or increased corrosion within the chambers. In certain processes, the 

length of time spent in startup prior to engaging control devices may require several 
10 

hours to reach the stable conditions necessary to avoid risks associated with explosions 

and fires associated with ESP sparking. Vendors providing this equipment incorporate 

these safety and operational concerns into their standard operating procedures.1

Commenters on the MATS reconsideration have echoed our concerns. They stated 

that ESPs at coal-fired units must be de-energized at all times when the flue gas 

temperature may be below the acid dew point. The ESP also must be de-energized 

during the firing of startup fuels until coal firing results in volatile gas concentrations that 

are below levels that would pose an explosive hazard in the ESP. According to 

commenters, one ESP manufacturer recommends that the ESP remain de-energized 

during startup until flue gas temperatures within the ESP remain above 200 degrees 

Fahrenheit for two hours. 

During periods of startup, combustion begins as fuel is introduced and an ESP cannot 

be engaged until its equipment has been adequately warmed up and the requisite fuel 

gas temperature is reached. As the control device is heated up, additional fuel is added 

until the ESP (and other equipment) meets its design temperature and normal fuel firing 

rates are resumed. Some ESPs have safety interlocks (oxygen sensors and alarms) 

that shut down the ESP or prevent startup of the ESP at high flue gas oxygen levels to 

avoid a fire or explosion in the unit. The oxygen level in flue gas is typically high during 

startup, so the ESP may not engage due to these safety controls until more stable 

operating conditions are reached. Additionally, some units which currently have clean 

fuel startup burners or igniters cannot burn enough clean fuel to achieve the 

temperature, moisture, and/or oxygen levels necessary for safe operation of the ESP. 

Therefore, ESPs must be included in the list of air pollution controls that must be started 

as expeditiously as possible. 

Definition of Shutdown 

The shutdown definitions in the MACT and GACT rules also need to be revised. The 

current definition is: ‘‘Shutdown means the cessation of operation of a boiler or process 

heater for any purpose. Shutdown begins either when none of the steam and heat from 

the boiler or process heater is supplied for heating and/or producing electricity, or for 

any other purpose, or at the point of no fuel being fired in the boiler or process heater, 

whichever is earlier. Shutdown ends when there is both no steam or heat being supplied 

and no fuel being fired in the boiler or process heater.’’ 

The definition is problematic for units firing solid fuels on a grate or in a fluidized bed 

combustor where the residual material in the unit keeps burning after fuel feed to the 

unit is stopped. In this case, fuel is still burning (which is not considered “being fired” if 

EPA makes a regulatory change to confirm the statement in their Boiler MACT 

“Questions and Answers2

” document indicating that the intended meaning of firing is 

feeding fuel) in the unit despite the fact that load reduction is occurring, additional fuel is 

not being fed, and the shutdown process has clearly begun. The shutdown definition 

should be revised to state that “shutdown begins either when none of the steam and 

heat from the boiler or process heater is supplied for heating and/or producing electricity 

or when fuel is no longer being fed to the boiler or process heater. Shutdown ends 

when there is both no steam or heat being supplied and no fuel being combusted in the 

 

1

 See Appendix I of AF&PA’s August 23, 2010 comments on the June 4, 2010 proposed rule for an 

excerpt of an ESP operational manual. 

2 http://www.epa.gov/ttn/atw/boiler/boilermactqanda.pdf, question 57. 
11 

boiler or process heater or when startup is initiated by reintroducing fuel to the boiler or 

process heater after no fuel has been fed for at least 1 hour, whichever comes first.” 

Note also that the terms “supplying” and “or for any other purpose” are too open-ended 

and could be read to mean that steam and heat supplied for uses within the boiler itself 

will delay onset of the shutdown period. Many boilers use steam to drive rotating 

equipment such as feedwater pumps, preheat feedwater, and operate de-aerators. 

Some of these uses, e.g., operating feedwater pumps and preheating feedwater, begin 

in the early stages of starting a boiler and continue until the boiler is cooled down. 

These terms in effect limit the use of energy during shutdown periods for these 

purposes. As a result, an operator may be motivated to use less efficient and more 

expensive electrical power where feasible. Efficient and cost effective internal uses of 

steam and heat for operating the boiler should not be discouraged by definitions that 

unnecessarily limit the duration of the startup and shutdown periods and that may 

require costly retrofits to boilers with no commensurate environmental benefit. 

Conclusion 

As supported above and in the attached table, the startup and shutdown definitions and 

work practices should be revised to improve clarity and more fully address industry’s 

operational and safety concerns. The changes should acknowledge the wide variety of 

boiler designs covered by these standards and the fact that a one-size-fits-all approach 

is not workable.
12 

Controls Scenario Potential Compliance Issue Suggested Solution 

Any Startup on clean fuel, 

engage non-listed controls prior to adding solid fuel. 

May be an issue with clean fuel availability. May have CO issue with transition from gas or liquid fuel to solid fuel, may not be an issue for 30-day average depending on compliance margin. 

Expand list of clean fuels to biodiesel, fuels that meet the fuel analysis, and other clean permitting authorities. Providstartup period to cover transfuel. (as defined below) 

Wet Startup on solid fuel Shouldn’t be an issue for operating parameter 

monitoring – can start wet controls prior to startup (depending on design of wet controls, may not be able to meet operating parameter limits instantaneously, but should be able to meet 30-day average). Need to address units that share a common control device that startup separately. Could have issues meeting 30-day rolling CO CEMS limit if enough time is not given for startup. Need to differentiate between cold startup (need more time) and hot restart (need less time). 

Startup ends either when the continuously maintained a st25% of maximum steam or hpressure for a certain numbe

cold startup or a certain numafter a hot restart and when operation or when the boiler above an alternate minimum flow rate and pressure for a a site-specific start-up plan. sharing a common control detimes (separate startup perioFor units sharing a common up sequentially, startup ends process heater to start has csteam production rate of at leor heat output at normal openumber of continuous hours number of continuous hours control devices are in stable boiler or process heater is opminimum operationally stable for a minimum time, as specplan. 

3 The time to reach stable conditions following 25% load will vary based on design, per our discussion earlier in this docum
13 

Controls Scenario Potential Compliance Issue Suggested Solution 

Dry Startup on solid fuel Can’t startup ESP until certain flue gas temperature 

and oxygen level are reached. NFPA 85- Boiler and Combustion Systems Hazards Code, 2011 Edition, Section 6 Multiple Burner Boilers (firing oil, gas, or PC) requires purging of precipitators prior to initial firing to prevent a precipitator spark from igniting an explosive mixture of unburned fuel. Manufacturer and operating company procedures may include a requirement to be operating on main burners with adequate flue gas temperature and low enough oxygen levels prior to ESP energization to limit potential ignition of unburned fuel by a precipitator spark. Need time within the “startup” period for the combustion unit firing primary fuel(s) and all exempted air pollution controls to reach stable operating conditions relative to the start of steam or process heater output to the distribution system. Need to get better definition of end of startup if heat or steam is immediately supplied upon ignition of fuel. Need to address units that share a common control device that start up separately. Could have issues meeting 24-hour block opacity or 30-day rolling CO CEMS limit if enough time is not given for startup. Need to differentiate between cold restart (need more time) and hot restart (need less time) 

ESPs must be included in thexempted air pollution controexpeditiously as possible. Startup ends either when the continuously maintained a st25% of maximum steam or hpressure for a certain numbecold restart or a certain numbhot restart and when all contoperation or when the boiler above a minimum operationapressure for a minimum timestart-up plan. This would also common control device that (separate startup period occFor units sharing a common up sequentially, startup ends process heater to start has csteam production rate of at leor heat output at normal openumber of continuous hours number of continuous hours control devices are in stable boiler or process heater is opminimum operationally stable for a minimum time, as specplan. 

Any Unit begins startup, 

reaches a certain minimum stable load, then there is an equipment problem that results in “failed startup.” 

All of the above. Need to be sure that this ent

startup, even if you reach the for example, the end of startthe unit has to be over 25% f
14 

Controls Scenario Potential Compliance Issue Suggested Solution 

Wet Lose solid fuel feed, takes 

time to get auxiliary fuel going to boiler or there is no auxiliary fuel available. Sometimes wet fuel can cause high O2 conditions, which will trip the ESP, which will trip the fuel feed. Sometimes there are problems with the equipment used to supply the solid fuel that cause loss of fuel feed. 

Losing fuel feed would trigger a shutdown – however, shutdown as EPA currently interprets would not be completed if the unit continues supplying useful steam until fuel feed is restored. We can’t classify these periods as malfunctions in all cases and these periods are not normal operation. We need to be able to call them shutdown, or we don’t know how to set up recordkeeping because we don’t have certainty on how to classify these periods. Operating parameters would probably be okay on a 30-day rolling average basis. Whether or not there was an issue meeting 30-day rolling CO CEMS limit if this is not shutdown would depend on compliance margin and length of event. 

The shutdown definition showhere fuel feed is reinitiated supply steam. Facilities neeshutdown, even if fuel supply not be forced to take the boila startup – this would be unemore emissions. The end oand then the startup work pracertain load and time conditioof shutdown definition: “Shutno steam or heat being suppcombusted in the boiler or pris initiated by reintroducing fuheater after fuel feed has be

Dry Lose solid fuel feed, takes 

time to get auxiliary fuel going to boiler or there is no auxiliary fuel available. Sometimes wet fuel can cause high O2 conditions, which will trip the ESP, which will trip the fuel feed. Sometimes there are problems with the equipment used to supply the solid fuel that cause loss of fuel feed. 

Losing fuel feed would trigger a shutdown – however, shutdown as EPA currently interprets would not be completed if the unit continues supplying useful steam until fuel feed is restored. Also, NFPA 85 Boiler and Combustion Systems Hazards Code, 2011 Edition, Section 6 Multiple Burner Boilers (firing oil, gas, or PC) requires tripping of electrostatic precipitators as part of a master fuel trip (MFT) to prevent a precipitator spark from igniting an explosive mixture of unburned fuel. We can’t classify these periods as malfunctions in all cases and these periods are not normal operation. We need to be able to call them shutdown, or we don’t know how to set up recordkeeping because we don’t have certainty on how to classify these periods. Could have issues meeting 24-hour block opacity or 30-day rolling CO CEMS limit if this is not shutdown, depending on compliance margin, type of unit, length of event. 

Need to be able to call it a shback; emissions will be greatshutdown before we can staperiod is a hot restart, and thwould apply until certain load Could revise end of shutdowwhen there is both no steam fuel being combusted in the when startup is initiated by reor process heater after fuel fESPs must be included in thexempted air pollution controoperated during shutdown. 
15 

Controls Scenario Potential Compliance Issue Suggested Solution 

Any Begin shutdown upon 

halting fuel feed to the boiler. For some designs, there is still fuel burning in the boiler. 

Current definition says “Shutdown begins either when none of the steam and heat from the boiler or process heater is supplied for heating and/or producing electricity, or for any other purpose, or at 

the point of no fuel being fired in the boiler or process heater, whichever is earlier.” This could be interpreted that shutdown does not begin unless no fuel is burning or no steam/heat is being supplied. In some boiler designs, fuel continues to burn after fuel feed stops. 

EPA should clarify that fuel bfuel being fed to the combus

Wet More than one unit vents to 

a wet control device, one unit shuts down, the other unit stays operating. 

For some wet control designs, the pressure drop depends on the flow through the scrubber. If only one unit is operating, the operating parameter limits established during the performance test with both units in operation may not be achievable. 

Not sure if there is a way to aEPA would advise facilities to monitoring and establish diffesuch as an alternate operatinoperation. This is similar to toperating parameters must bgas for an extended period ofor PM, HCl, Hg are not needunder a request to permit altwell. 
16 

Controls Scenario Potential Compliance Issue Suggested Solution 

Any – low load/ standby unit 

A unit operates for many hours in standby mode, less than 25% load, either burning clean fuels or burning solid fuels with emissions controls in service. 

How to define the end of startup to accommodate a unit that operates in a low-load mode after initial “ignition” (e.g., it never reaches 25% load). Facilities should not have to increase load above 25% just to reach the defined end of startup. 

Where a 25% load+time threby a standby unit, the followiincorporated into the permit t

• The unit is firing its p

adequate to provide flow, stable and contoperating temperatuand air preheat as a

• Emissions controls a

parameters such as being controlled and 

• The unit is supplying 

system or energy usconditions including is above the minimuflow rate, as applicab

• For stoker units, whe

adequate level of covisual observation ansteam flow rates.