Startup and Shutdown Scenarios for Solid Fuel Boilers
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 4 continuous hours after a cold startup or 1 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 4 continuous hours after a cold startup or 1 hour 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 site-specific start-up plan.  
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 4 continuous hours after a cold restart or 1 hour 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 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 4 continuous hours after a cold startup or 1 hour 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 site-specific start-up plan.
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 4 hours, the unit has to be over 25% for 4 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."
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.
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.  

For reference- Subpart DDDDD definitions:
    Startup means 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.
Shutdown means the cessation of operation of a boiler or process heater for any purpose. Shutdown begins either when none of the steam from the boiler 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 no steam and no heat being supplied and no fuel being fired in the boiler or process heater.
From Table 3:
5. An existing or new boiler or process heater subject to emission limits in Table 1 or 2 or 11 through 13 to this subpart during startup
You must operate all CMS during startup.
For startup of a boiler or process heater, you must use one or a combination of the following clean fuels: natural gas, synthetic natural gas, propane, distillate oil, syngas, ultra-low sulfur diesel, fuel oil-soaked rags, kerosene, hydrogen, paper, cardboard, refinery gas, and liquefied petroleum gas.
   
If you start firing coal/solid fossil fuel, biomass/bio-based solids, heavy liquid fuel, or gas 2 (other) gases, you must vent emissions to the main stack(s) and engage all of the applicable control devices except limestone injection in fluidized bed combustion (FBC) boilers, dry scrubber, fabric filter, selective non-catalytic reduction (SNCR), and selective catalytic reduction (SCR). You must start your limestone injection in FBC boilers, dry scrubber, fabric filter, SNCR, and SCR systems as expeditiously as possible. Startup ends when steam or heat is supplied for any purpose.
   
You must comply with all applicable emission limits at all times except for startup or shutdown periods conforming with this work practice. You must collect monitoring data during periods of startup, as specified in § 63.7535(b). You must keep records during periods of startup. You must provide reports concerning activities and periods of startup, as specified in § 63.7555.
6. An existing or new boiler or process heater subject to emission limits in Tables 1 or 2 or 11 through 13 to this subpart during shutdown
You must operate all CMS during shutdown.
While firing coal/solid fossil fuel, biomass/bio-based solids, heavy liquid fuel, or gas 2 (other) gases during shutdown, you must vent emissions to the main stack(s) and operate all applicable control devices, except limestone injection in FBC boilers, dry scrubber, fabric filter, SNCR, and SCR.
   
You must comply with all applicable emissions limits at all times except for startup or shutdown periods conforming with this work practice. You must collect monitoring data during periods of shutdown, as specified in § 63.7535(b). You must keep records during periods of shutdown. You must provide reports concerning activities and periods of shutdown, as specified in § 63.7555.

