API Comments

on

RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

The following is a preliminary tabulation of startup and shutdown and other separate operating 

scenarios where the normal RMACT 1 and 2 requirements cannot be met. Inability to comply with 

normal requirements associated with other regulations, preventive maintenance, and with malfunctions 

is not included in this tabulation.

RMACT 1

Process Vents

Requirement: Control Group 1 vents at all times.

Situation: During shutdown of equipment, process vents generally can continue to be 

controlled until the control is no longer effective. For most types of controls a point is 

reached where the vent no longer has adequate pressure to reach the control. For 

combustion controls, a point can be reached where the inert content of the process 

vent is so high that sending it to combustion can be unsafe and/or upset the operation 

of the combustion device. For other types of controls, control efficiency can fall below 

required levels at very low vent stream flows.

Recommendation: As has been done in the Polymer and Resins 1 NESHAP for flares 

(see §63.485(w)), provide an exception from the control requirements for situations, 

during shutdown periods, where the process vent has inadequate pressure to reach the 

control device or is no longer a process vent (i.e., contains <50 PPM HAP). Expand this 

exception to include all types of control devices, when that emission limit cannot be 

achieved due to the process vent flow, pressure, or composition. 

RMACT 2

Fluid Catalytic Cracking (FCC)

Each FCCU features its own unique configuration and operating envelope that impacts 

emissions. Partial burn and full burn refer to the combustion mode of the regenerator 

of an FCCU. A partial burn unit operates with limited oxygen in the regenerator and has 

CO levels of 3% to 6% out of the regenerator. Partial burn units complete the 

combustion of the flue gas (including CO) downstream in a CO boiler. Because of these 

high levels of CO when the CO boiler is not available (versus the 500 ppm normal 

operation limit), averaging is not an effective way of addressing startup and shutdown 

emissions for partial burn CO emission limits. A full burn unit operates with excess 

oxygen to ensure complete combustion and has CO levels of about 10-100 ppm out of 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 2

the regenerator during normal operation. Full burn units are generally not equipped 

with CO boilers. 

1. FCC Regenerator Vent - General Startup and Shutdown

Requirement: 500 ppm CO (hourly avg.)

Situation: High temperature is required to fully combust CO into CO2. In normal 

operation, the required heat is derived from the combustion of coke. From a cold 

startup, FCC’s use a natural gas fired heater to heat the regenerator to about 600 – 800 

°F. We discuss the fired heater operation separately in the next item. These auxiliary 

burners and regenerator internals are not designed to heat the regenerator to 

temperatures required to start the FCC unit cracking reactions (>1000F). Torch oil1

Recommendations: 1. CO limits should not apply when torch oil is being combusted

during startup or shutdown.

is 

needed to heat the regenerator beyond the capacity of the auxiliary burner. Thus, 

during a typical start-up, and during some shutdowns and standby operations of an FCC 

unit, there is a period of time when torch oil is added to the regenerator to facilitate the 

unit heat-up to operating temperature. Upon the addition of feed to the unit, catalytic 

coke will start to burn in the regenerator along with the torch oil. Feed ramp up is fairly 

quick, during which time the torch oil is backed out during normal startups, but can be 

longer if refractory repairs were made because of the need to raise temperatures slowly 

so as not to damage the new refractory. The period of torch oil addition (i.e. the period 

when the bed temperature is relatively low) results in increased CO during the start-up 

period.

2. If there must be a limit, follow the Consent Decree (CD) model and make the 500 

ppm limit a short-term limit that excludes periods of SU/SD and add a long-term limit 

that includes periods of SU/SD (i.e., 365-day average). 

Requirement: Opacity (6 minute rolling avg.), PM emissions, 500 ppm CO (hourly avg.), 

e.g., 80 ppm NOx (7-day avg.), e.g., 50 ppm SO2 (7-day avg.)

 1

 “Torch oil” is a term which is usually applied to gas oil that is burned in FCC regenerators, to supply necessary heat 

requirements during startup, shutdown, or feed-outage conditions, when coke is not being produced in the reactor. Typically, 

it is injected through dedicated nozzles which discharge into the dense catalyst bed of a regenerator. 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 3

Situation: Prior to introducing feed into an FCC unit hot air is used initially to heat up 

the regenerator. The hot air is typically supplied from a natural gas fired air-preheater 

that is only used for start-up. If refractory repairs were made, a refractory dry-out is 

required and the regenerator temperature must be raised slowly (e.g., at a rate of 50 –

100F/hr) to prevent water from damaging the refractory. Emissions from the 

regenerator vent during this time are from the air heater.

Recommendation: Clarify that the FCC regenerator emission limits are only applicable 

when hydrocarbon is being fed to the unit and that combustion exhaust used to heat an 

FCC during start-up are subject to combustion source limits, not FCC regenerator limits.

2. FCC Regenerator Vent - General Startup and Shutdown – Full Burn Units

Requirement: 500 ppm CO (hourly avg.)

Situation: For full burn FCC units, there is a relatively short period of time during 

startup when the unit operates in partial burn mode resulting in an additional period of 

higher CO. This partial burn period can result from heat imbalances during this 

transition state or may be required for safety because operation at regenerator 

temperatures high enough for complete combustion while establishing catalyst 

circulation or introducing feed can result in exceeding metallurgical temperature limits. 

The unit is inherently unstable as feed is being put into the unit. It is a balancing act that 

requires operators to manually balance heat consumed to vaporize the feed and sustain 

the cracking reaction as additional feed is being put on the unit with the heat being 

brought into the reactor from the regenerator via catalyst circulation, which is a 

function of regenerator operating conditions. This is an extremely complex operation 

with numerous variables that operations must manage until the unit can be lined out.

Recommendation: For full burn FCC’s CO limits should not apply until feed and full burn 

operation is stable and normal heat balance can be maintained.

3. FCC Regenerator Vent - General Startup and Shutdown – Partial Burn Units

Requirement: 500 ppm CO (hourly avg.)

Situation: For a partial burn unit, the required CO boilers add an additional step to unit 

start-up. Additional time is required from the point that the regenerator enters partial 

burn until the time the flue gas is all routed through the CO boiler(s). The CO boiler(s) 

must be brought up separately from the regenerator to protect them from swings of the 

regenerator flue gas quality during the start-up process, which can result in temperature 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

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excursions, damage to CO boiler internals and/or trip of the CO boiler(s). A CO boiler 

trip must be avoided because it could ultimately lead to a refinery shutdown due to a 

drastic decrease in steam production (a very large proportion of the refinery’s steam 

supply is typically provided by the CO Boilers), resulting in excess emissions at other 

units, significant flaring, production loss, and potentially equipment damage.

Since the regenerator flue gas initially bypasses the CO boiler, the CO is not further 

combusted. Once the regenerator is stable, the flue gas is added to the CO boilers and 

CO emissions drop to normal levels. Prior to lining up the regenerator flue gas to the CO 

boiler, the unit is operating in a mode with higher CO emissions for a short period of 

time. 

Recommendation: For partial burn FCC units, CO limits should not apply until the CO 

boiler(s) operation is stable and all regenerator gas is routed to the boiler(s).

4. FCC Regenerator Vent - Hot Standby

Requirement: Opacity (6 minute rolling avg.), PM emissions, 500 ppm CO (hourly avg.), 

e.g., 80 ppm NOx (7-day avg.)

Situation: There are operational situations where it is necessary to remove feed from an 

FCC unit to accommodate unit repairs, respond to an upstream or downstream 

malfunction or maintenance outage, and/ or to delay full startup due to downstream 

issues. Although processing is stopped, the FCCU maintains temperature by burning 

torch oil, which can result in higher CO and NOx emissions during this period of 

operation. PM/Opacity will also be higher for FCC units with ESP PM controls, since, as 

discussed below, it is unsafe to operate the ESP during torch oil firing. A standby mode 

of up to 7 – 10 days presents fewer safety risks and total environmental emissions than 

a complete FCCU shutdown and minimizes production losses. 

The ability to operate in hot standby mode allows the FCC to stay ready for startup 

when otherwise it would have to go through a full cold shutdown with catalyst removal, 

which adds days to the downtime, operationally intense startup/shutdown activities, 

potential unit damage due to thermal cycles, and potential for increased emissions. This 

is an extremely important operation that is routinely employed, and the impact should 

not be underestimated. In addition to minimizing overall emissions, this operation 

minimizes the time to get products (e.g. gasoline) to the public. Further, it doesn’t 

introduce reliability issues inherent with cold shutdowns that could result in even 

further delays in returning to production.
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 5

One refinery reports that during a recent hurricane the refinery experienced numerous 

unit shutdowns associated with lost utilities and hurricane related damage. The refinery 

was able to recover the FCC unit and establish stable operations in hot standby ready 

for startup. However, downstream units were not prepared for startup. Consequently, 

the FCCs idled in this condition until downstream facilities were brought back on line. 

Being able to stay in hot standby meant the FCC did not have to go through a cold 

shutdown while refinery resources were dedicated to recovering other units. Other 

refineries report similar situations, riding out hurricanes with the FCC unit in hot 

standby, thereby allowing the refineries to get gasoline back to the public faster than if 

the FCC units had to go through a cold shutdown and restart. 

Recommendation: Exclude the “hot standby” operating mode from the regenerator 

emission limits.

5. FCC Regenerator Vent - CO Boiler Shutdown

Requirement: 500 ppm CO (hourly avg.)

Situation: For FCC units with a single CO boiler, it is sometimes necessary to operate 

partial burn FCC units when the CO boiler is down for inspection or, in particular, for

repair. During such times the CO limit cannot be met. We discuss the reasons why the 

FCC unit needs to continue to operate during these times in the previous item.

Recommendation: For partial burn FCC units do not apply the CO emission limit when 

the CO boiler is out of service for inspection or maintenance.

6. FCC Regenerator Vent - Wet Gas Scrubber (WGS) Control

Requirement: Wet gas scrubber operating parameters, e.g., 80 ppm NOx (7-day avg.), 

e.g., 50 ppm SO2 (7-day avg.)

Situation: Many FCC units monitor wet gas scrubber operating parameters as 

surrogates for opacity and PM, because the normally required COMS are not functional 

in a wet gas environment. The WGS gas/liquid ratio and delta P requirements may not 

be able to be met during the initial startup period due to low regenerator gas flow; 

similarly on shutdown, at some point the regenerator flow will drop off as feed is 

removed.
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 6

NOx and SO2 may be above the RMACT 2 limits on startup for FCC units equipped with 

LoTOx controls since the ozone generation and routing to the WGS may not happen 

until after the FCC unit is fully operational at stable feed rates. Ozone cannot be sent to 

the vent until there is enough NOx and SO2 in the flue gas to assure that the ozone is 

reacting (NOx) or being scavenged (SO2) into scrubber solution and not just being 

emitted to atmosphere. 

Recommendation: For FCC units with wet gas scrubbers do not apply operating 

parameter limits during startup or shutdown. For FCC units using LoTOx controls do not 

apply the NOx or SO2 limits until ozone generation has been started and routed to the 

regenerator vent.

7. FCC Regenerator Vent - Selective Catalytic Reduction (SCR) Control

Requirement: e.g., 80 ppm NOx (7-day avg.)

Situation: At many FCC units, SCR controls have been installed to reduce NOx. SCR 

controls use a NOx reduction catalyst along with ammonia injection to reduce NOx. The 

required ammonia injection cannot commence until the SCR reaches operating

temperature (nominally 600+ °F). This results in an unavoidable delay in controlling the 

NOx and resultant higher short term NOx emissions. In addition, for a partial burn FCC 

unit, the regenerator flue gas must bypass the CO boiler(s) during start-up because the 

SCR needs to be protected from potential regenerator catalyst carryover. If the SCR is 

plugged, this will reduce the overall NOx reduction efficiency during normal operation. 

Additionally, for FCC Units with more than one CO boiler, the NOx limit cannot be 

achieved when one CO Boiler is out-of-service, because at the reduced FCC unit rate 

there is inadequate heat for maximum SCR efficiency.

Recommendation: NOx emission limits must not apply to FCC units with SCR control 

unless the SCR unit is at operating temperature, ammonia injection is at normal levels, 

and all regenerator gas is routed to the SCR unit. (Note: This is a general issue for all 

SCR NOx controls.) Some CDs allow an annual average approach, but it is unclear if that 

would work in every case.

8. FCC Regenerator Vent - Electrostatic Precipitator (ESP) Control

Requirement: Opacity (6 minute rolling avg.), PM emissions, 500 ppm CO (hourly avg.)

Situation: On FCC units equipped with an ESP, the ESP must be powered off or 

bypassed, during an FCCU and/or CO Boiler startup and shutdown. In fact, many FCC

units have critical safety instrumentation which automatically shuts down the ESP in 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

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case of unusual operations or equipment malfunctions, such as loss of circulation 

differential pressure, air blower trip, high ESP inlet temperatures, and other similar 

types of issues. 

During startup and shutdown operations of the FCC unit, the regenerator flue gas may 

become combustible from either direct torch oil firing, from high levels of CO and/or 

with the unintentional introduction of hydrocarbon into the regenerator. For this 

reason and, at a minimum, the ESP should be OFF/Bypassed for the steps of torch oil 

firing and feed introduction/removal, as well as transitory operations (e.g. CO Boiler

malfunction or shutdown, other FCCU process upsets or equipment failures). There is a 

similar point in the SD process where fresh feed rates are unstable and/or torch oil is 

fired where similar precautions must be taken.

Because the ESP must be operating in order to meet PM and opacity limits, but for 

safety reasons, the ESP should be powered off or bypassed during FCC startup and 

shutdown operations, imposing a PM or opacity limit during such periods forces owners 

and operators to choose between compliance and safety to employees and equipment. 

In all cases, safety concerns are paramount and following proper safety procedures 

should not result in a potential non-compliance of an emission limit.

Recommendation: PM and opacity limits cannot apply during periods when 

regenerator offgas cannot be safely routed to the ESP.

9. FCC Regenerator Vent - Cyclone Controls

Requirement: Opacity (6 minute rolling avg.), PM emissions

Situation: During startup and shutdown of FCC units, gas flows are not always adequate 

for cyclones to work properly and thus opacity and PM limits can be exceeded. Startup 

operations require passing through transient operations that are not ideal for cyclone 

performance. This will impact opacity. This is especially apparent during catalyst 

addition. There is also a fair amount of unit variability as air and catalyst levels are 

varied during startup operations.

Recommendation: PM and opacity limits cannot apply during periods when 

regenerator offgas flow is below cyclone minimum design flow.
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

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10. FCC Regenerator Vent - Feed Hydrofiner Outages

Requirements: e.g., 80 ppm NOx (7-day avg.), 50 ppm SO2 (7-day avg.)

Situation: Approximately 45% of FCC units in industry are using catalyst additives to 

meet EPA Consent Decree requirements. In the majority of these applications, the FCC 

feed is hydrotreated in an upstream Cat Feed Hydrotreater (CFH) to remove impurities 

and improve feed quality. The majority of limits established through the Consent 

Decree process have a short-term limit on a 7-day rolling average and a long-term limit 

on a 365-day rolling average. However, the CD recognizes that the operation of the 

FCCU feed hydrotreater is integral in complying with this short term limit, and thus the 

CDs include an exemption from the short term limits provided that the FCCUs comply 

with good air pollution control practices for minimizing emissions consistent with an 

approved plan.

It is a common industry practice to change catalyst in the CFH unit while the FCC 

continues to operate. Under this scenario, refiners may not be able to meet the shortterm limit without adding expensive, redundant hydroprocessing capacity. The EPA will 

need to consider the capital costs associated with installing such redundant capacity for 

use for only short periods and the cost of adding wet gas scrubbers to units without 

them. 

Recommendations: 1. A much more reasonable approach is to provide short-term 

exemptions of any 7-day rolling average limit during periods of startup, shutdown, or 

malfunction of the CFH, including CFH catalyst change-out or turnaround periods. The 

EPA rulemaking could accomplish this by requiring facilities to prepare a CFH Outage 

Plan, outlining the specific steps to be taken to minimize FCCU emissions during this 

period.

2. If there must be a limit, follow the CD model and exclude periods of SU/SD from the 

short term limits and add a long-term limit that includes periods of SU/SD (i. e., 365-day 

average).

Sulfur Plants

1. Catalyst sulfidation

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: During startup, the Claus System (and “SCOT” unit, if present) must be 

warmed up and the tail gas catalyst must be activated (i.e., sulfided) before full H2S 

removal can occur. Sulfiding must be done at low temperatures to avoid catalyst 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 9

damage. During these low temperature periods there can be incremental slip of reduced 

sulfur from the unit or to the tail gas incinerator, resulting in high SO2 or TRS until the 

reactors are activated and on temperature.

Recommendations: 1. Follow the NSR CD model of having a short-term limit that 

excludes SU/SD emissions and a long-term limit that includes SU/SD (e.g., 365-day

average).

2. Establish an allowable mass of SO2 from each SRU for SD – justified by the unit’s 

design.

2. Sulfur flashing

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: In some SRP configurations, during startup, the gas from the Claus System 

must bypass the tail gas unit and vent directly to the incinerator. The sulfur in the line 

can solidify and cause a high temperature flash which can send excess sulfur to the 

incinerator and cause the SO2 limit to be exceeded.

Recommendations: 1. Follow the NSR CD model of having a short-term limit that 

excludes SU/SD emissions and a long-term limit that includes SU/SD (e.g., 365-day

average).

2. Establish an allowable mass of SO2 from each SRU for SD – justified by the unit’s 

design.

3. Hot sweep

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: During some shutdowns, high temperature natural gas and air or oxygen 

must be added to the Claus System during hot sweep to ensure sulfur stays in liquid 

form. Measurement of O2 in the convert outlets becomes unreliable under these 

conditions and can result in is too much O2. If there is too much O2, there is a potential 

for burn off of sulfur in the catalyst bed creating excess sulfur to the incinerator. 
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 10

Similarly, if the shutdown is not for total catalyst replacement, the unit must be 

operated as close to stoichiometric as possible because excess air will result in the 

combustion of sulfur within the reactors that could lead to an Incinerator excursion or 

excessive temperatures within the catalyst bed that could result in catalyst and/or 

equipment damage. Due to system and control variability this operation can result in 

running air deficient. An air deficient operation can result in soot formation (i.e. 

incomplete combustion) that will result in reactor plugging thereby reducing unit 

capacity or in the reduction (i.e. deactivation) of the Tail Gas Catalyst which can

substantially impact sulfur recovery efficiency. 

Recommendations: 1. Follow the NSR CD model of having a short-term limit that 

excludes SU/SD emissions and a long-term limit that includes SU/SD (e.g., 365-day

average).

2. Establish an allowable mass of SO2 from each SRU for SD – justified by the unit’s 

design.

4. Hot strip prior to shutdown

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: During shutdown, there is holdup of sulfur in catalyst, vessels, piping and 

ductwork that needs to be removed for inspection and maintenance. A portion of this 

sulfur can be transferred to sulfur pits, but additional sulfur can only be removed by 

combusting (“burning”) it following shutdown of tail gas units (because excess oxygen 

can damage the tail gas units). The amount of sulfur held up depends in part on the 

configuration of the Claus unit, with some units having lesser ability to route sulfur to 

pits. These incidents have been reported to EPA in Acid Gas/Tail Gas incident reports 

required under refiner’s NSR consent decrees. 

Recommendations: 1. Follow the NSR CD model of having a short-term limit that 

excludes SU/SD emissions and a long-term limit that includes SU/SD (e.g., 365-day

average).

2. Establish an allowable mass of SO2 from each SRU for SD – justified by the unit’s 

design.
API Comments on RMACT 1 and 2 Startup and Shutdown and Special Operating Scenarios 

April 10, 2012 Page 11

5. Single train refinery shutdown

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: Single train refineries are required to have total refinery shutdowns on 

occasion. For these facilities, all acid gas sources are taken out of service, and, in turn, 

all Claus trains have to be taken out of service (i.e., no acid gas feed available). In these 

instances, the Claus unit(s) are shutdown in conjunction with the shutdown of acid gas 

producing units. During the Claus unit shutdown, the tail gas unit remains in service 

prior to introducing oxygen to the Claus reactor. By design, the tail gas unit generates 

acid gas, which is normally routed back to the front of the Claus reactor. When the first 

of multiple Claus units is shutdown, this tail gas (acid gas) can be routed to another 

operating Claus unit. Eventually, however, the final Claus unit is being shutdown, with 

no Claus unit to receive the acid gas and the gas must be purged to the atmosphere. 

These incidents have been reported to EPA in NSR CD Acid Gas/Tail Gas incident reports.

Recommendations: 1. Follow the NSR CD model of having a short-term limit that 

excludes SU/SD emissions and a long-term limit that includes SU/SD (e.g., 365-day

average).

2. Establish an allowable mass of SO2 from each SRU for SD – justified by the unit’s 

design.

6. Hot nitrogen sweep

Requirement: 250ppm SO2 (12-hr avg.) at the incinerator outlet or 300 ppm TRS (12-hr 

avg.) and 10 ppm H2S (12-hr avg.)

Situation: When the sulfur plant is not operating (no feed), a hot nitrogen sweep is 

maintained. The CEMS can register > 250 ppm during this situation, due to residual 

sulfur in the unit or interference from the hot nitrogen.

Recommendation: Be clear that SO2 limit only applies when the SRP is operating with

acid gas feed to the unit and not when it is in hot standby mode.