CIBO, May 2, 2014 – Page 1

Changes Needed to the Boiler MACT and GACT Startup and Shutdown Provisions

CIBO strongly agrees with EPA that work practices are the correct approach for 

applying a standard to boiler and process heater startup and shutdown periods. 

However, the definitions of startup and shutdown must be revised in order to 

accommodate the practical and safety aspects of starting up and shutting down these 

units and to ensure achievability of the standards. The following points summarize why 

these changes are necessary. 

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

pollution control type and configuration, and fuel firing mechanism. EPA should 

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

and proper operation of certain units. The act of supplying heat, steam, or 

electricity, which defines the end of startup in the current rule, does not represent 

the functional end of the startup period. The startup definition and procedures 

must ensure that the equipment is brought up to normal operating conditions in a 

safe manner, and startup ends when the boiler/process heater and its controls 

are fully functional.

 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. If EPA incorporates a “load plus time” type of threshold 

similar to MATS into the MACT/GACT rules to define the end of startup, it should 

vary by unit design, it should accommodate units that operate at low load or 

standby conditions, and there must also be a mechanism by which a facility can 

establish unit-specific startup criteria and document those criteria in a sitespecific startup plan if it is not technically feasible for them to meet the load plus 

time threshold in the rule. 

 Information gathered from CIBO members in an informal survey indicates that on 

a cold startup, fluidized bed boilers can take up to 26 hours to reach stable 

conditions after reaching 25% load, pulverized coal boilers can take up to 5 hours 

to reach stable conditions after reaching 25% load, and stoker and hybrid 

suspension grate type units can take up to 8 hours to reach stable conditions 

after reaching 25% load (although the majority of units responding can reach 

stable conditions within 4 hours). Circulating fluidized bed boilers need adequate 

time to establish stable bed conditions such as reaching the temperature and 

pressure necessary for stable operation and to calcine the limestone in the bed 

to begin achieving acid gas control within the bed. Although we only received 3 

responses on bubbling fluidized bed units, it appears from that limited feedback 

that the time required for this design to achieve stable operation after 25% load is 

more similar to pulverized coal units. Liquid units can typically achieve stable 

operation within 4 hours of reaching 25% load. On a hot startup, responses 

indicate that fluidized bed boilers can take up to 13 hours to reach stable 

conditions after reaching 25% load, pulverized coal boilers can still take up to 5 

hours to reach stable conditions after reaching 25% load (especially for units that 

come online with a clean fuel and transition to solid fuel), and stoker and hybrid 
CIBO, May 2, 2014 – Page 2

suspension grate type units can take up to 4 hours to reach stable conditions 

after reaching 25% load. 

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

specifically listed as exempt must either fire clean fuels during startup or engage 

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

or process heater. The list of clean fuels should be expanded. There are fuels 

other than those listed in the rule that should qualify as clean fuels to be fired 

during startup prior to engaging any control devices that are not exempted.

 ESPs must be included in the list of exempted air pollution controls that must be 

started as expeditiously as possible. An ESP cannot safely be engaged until a 

certain flue gas temperature and/or oxygen level is reached. EPA recognizes 

this in the current rule for other control devices. Many units have a safety 

interlock that prevents the ESP from operating if the oxygen level is above 10%.

 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 

shutdown has not occurred and therefore a startup cannot occur. There are 

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.

More information and examples are provided in the attached table.
CIBO, May 2, 2014 – Page 3

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 include all Other Gas 1 

fuels, biodiesel, fuels that meet the HCl, Hg, TSM 

limits through fuel analysis, and other clean fuels as 

determined by permitting authorities. Provide 

adequate length of time for startup period to cover 

transition from startup fuel to solid fuel. (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 boiler or process heater 

has continuously maintained a steam production rate 

of at least 25% of maximum steam or heat output at 

normal operating pressure for a certain number of 

continuous hours1after a cold startup or a certain 

number of continuous hours hour after a hot restart 

and when all control devices are in stable operation or 

when the boiler or process heater is operating above 

an alternate minimum operationally stable output flow 

rate and pressure for a minimum time, as specified in 

a site-specific start-up plan. This would also apply to 

units sharing a common control device that start up at 

separate times (separate startup period occurs for 

each unit).

For units sharing a common control device that are 

starting up sequentially, startup ends either when the 

last boiler or process heater to start has continuously 

maintained a steam production rate of at least 25% of 

maximum steam or heat output at normal operating 

pressure for a certain number of continuous hours 

after a cold startup or a certain number of continuous 

hours after a hot restart and when all control devices 

are in stable operation or when the last boiler or 

process heater is operating above an alternate 

minimum operationally stable output flow rate and 

pressure for a minimum time, as specified in a sitespecific start-up plan. 

 

1 The time to reach stable conditions following 25% load will vary based on design, per our discussion on page 1 of this document. 
CIBO, May 2, 2014 – Page 4

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 the Table 3, item 5 list of 

exempted air pollution controls that must be started 

as expeditiously as possible. 

Startup ends either when the boiler or process heater 

has continuously maintained a steam production rate 

of at least 25% of maximum steam or heat output at 

normal operating pressure for a certain number of 

continuous hours after a cold restart or a certain 

number of continuous hours after a hot restart and 

when all control devices are in stable operation or 

when the boiler or process heater is operating above 

a minimum operationally stable output flow rate and 

pressure for a minimum time, as specified in a sitespecific start-up plan. This would also apply to units 

sharing a common control device that start up at 

separate times (separate startup period occurs for 

each unit). 

For units sharing a common control device that are 

starting up sequentially, startup ends either when the 

last boiler or process heater to start has continuously 

maintained a steam production rate of at least 25% of 

maximum steam or heat output at normal operating 

pressure for a certain number of continuous hours 

after a cold startup or a certain number of continuous 

hours after a hot restart and when all control devices 

are in stable operation or when the last boiler or 

process heater is operating above an alternate 

minimum operationally stable output flow rate and 

pressure for a minimum time, as specified in a sitespecific start-up plan.
CIBO, May 2, 2014 – Page 5

Controls Scenario Potential Compliance Issue Suggested Solution

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 entire period is considered 

startup, even if you reach the minimum load 

threshold. If, for example, the end of startup is 25% 

load plus 8 hours, the unit has to be over 25% for 8 

continuous hours.

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 should accommodate the 

scenario where fuel feed is reinitiated before the unit 

ceases to supply steam. Facilities need to be able to 

call it a shutdown, even if fuel supply is restored. 

Facilities should not be forced to take the boiler down 

fully before reinitiating a startup – this would be 

uneconomical and could result in more emissions. 

The end of this period is a hot restart, and then the 

startup work practices would apply until certain load 

and time conditions are met. Could revise end of 

shutdown definition: “Shutdown ends when there is 

both no steam or heat being supplied and no fuel 

being combusted in the boiler or process heater or

when startup is initiated by reintroducing fuel to the 

boiler or process heater after fuel feed has been 

halted.”
CIBO, May 2, 2014 – Page 6

Controls Scenario Potential Compliance Issue Suggested Solution

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 shutdown, even if we get 

fuel back; emissions will be greater if we have to 

complete a shutdown before we can start back up. 

The end of this period is a hot restart, and then the 

startup work practices would apply until certain load 

and time conditions are met. Could revise end of 

shutdown definition: “Shutdown ends when there is 

both no steam or heat being supplied and no fuel 

being combusted in the boiler or process heater or

when startup is initiated by reintroducing fuel to the 

boiler or process heater after fuel feed has been 

halted.”

ESPs must be included in the Table 3, item 6 list of 

exempted air pollution controls that are not required to 

be operated during shutdown. 

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 being fired in this case 

means fuel being fed to the combustion unit.
CIBO, May 2, 2014 – Page 7

Controls Scenario Potential Compliance Issue Suggested Solution

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 address this in the rule, or 

if EPA would advise facilities to submit a request for 

alternate monitoring and establish different operating 

scenarios, such as an alternate operating limit with 

fewer units in operation. This is similar to the 

question of whether operating parameters must be 

maintained if a unit burns gas for an extended period 

of time and emissions controls for PM, HCl, Hg are 

not needed. This is probably covered under a request 

to permit alternate operating scenarios as well. 

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 threshold can’t be 

accommodated by a standby unit, the following types 

of concepts could be incorporated into the permit to 

identify the end of startup:

 The unit is firing its primary fuel for a period of 

time adequate to provide stable and noninterrupted 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.