Reasonable Progress (RP) Four-Factor Analysis of Control Options 

For 

Plum Creek Manufacturing/Columbia Falls Operations 

I. Source Description 

 Owner/Operator: Plum Creek Manufacturing 

 Source Type: Steam Generating Unit/Process Heat 

 RP Emission Sources: Hog Fuel Boiler - 1973 Riley-Union stoker boiler type UO 

field erected rated at 292 MBtu/hr 

 

 Two (2) - Line 1 MDF Dryer Sander Dust Burners - 1986 

and 2006 Coen burners rated at 50 MBtu/hr each 

 Line 2 MDF Dryer Sander Dust Burner - 2001 Coen burner 

rated at 85 MBtu/hr 

Plum Creek Manufacturing’s Columbia Falls Operation consists of a sawmill, planer, plywood, 

and medium density fiberboard (MDF) processes. This Reasonable Progress analysis focuses on 

four emitting units at the Columbia Falls Operation, listed above. The Riley-Union boiler (boiler) 

is used as a load-following steam generator for the dry kilns, plywood press, log vats, and MDF 

platen press. The boiler has sander dust burners downstream of the spreader-stoker grate that are 

capable of supplementing 10% of the heat rate capacity of the boiler. These sander dust burners 

are normally fired with sander dust, but have the ability to fire natural gas during sander dust 

shortages and during startup. The boiler exhausts to a dry electrostatic precipitator (ESP) 

installed in 1993. 

The Line 1 MDF dryers include two direct-contact dryers, a core fiber dryer and a face fiber 

dryer. Each dryer is provided heat by one Coen sander dust burner. The Line 1 fireboxes are 1⁄4 

the size of the Line 2 firebox reducing the capacity of the Line 1 dryers to employ staged 

combustion. The Line 1 dryer exhausts combine with the Line 1 press vents and metering bin 

baghouse exhausts before being controlled by a wet ESP installed in 1995 before emitting to the 

atmosphere through two 80 foot stacks. 

The Line 2 MDF dryers are direct-contact dryers. The flue gas from the combustion chamber 

provides heat for the first and second stage dryer lines. The design of the Line 2 Coen burner 

employs staged combustion, with a rich zone followed by a lean zone reducing peak flame 

temperature thereby reducing thermal NOx emissions. The Line 2 dryer exhausts to a Venturi

scrubber installed in 2001 before emitting to the atmosphere through three 40 foot stacks. 
Reasonable Progress Evaluation of Nitrogen Oxide (NOx) Emissions

Step 1: Identify All Available Technologies 

Selective Catalytic Reduction (SCR)

SCR utilizes a nitrogen based reagent (usually ammonia) injected in the flue gas to enhance the 

reduction reaction of NOx over a metal based catalyst to nitrogen and water. Some of the reagent 

injected will not react with the flue gas and will be emitted (this is referred to as ‘ammonia slip’),

however low levels of ammonia slip are associated with properly operated SCR. NOx emission 

reductions associated with SCR on a variety of source categories can be as high as 95%. The 

optimal temperature range for most SCR catalyst ranges from 600 degrees Fahrenheit to 800 

degrees Fahrenheit (Plum Creek 2011 Response, page 5). The level of control possible is 

dependent on the catalyst, the temperature of the reaction, the amount and location/s of reagent 

injected, exhaust gas constituents that prevent the desired reaction, and the ability to control the 

system during changes to the combustion and flue gas characteristics. 

Regenerative SCR (RSCR)

 RSCR uses a regenerative thermal oxidizer (or waste heat transfer system) to bring cool exhaust 

gas back up to the temperature required for SCR catalyst to be effective at reducing NOx to 

nitrogen and water. RSCR is a good option for exhaust gas that has constituent that may require 

removal prior to introduction into the catalyst (to prevent fouling or plugging), such as high 

particulate matter (PM) concentrations in the exhaust. 

Selective Non-Catalytic Reduction (SNCR)

SNCR involves the injection of a nitrogen reagent (ammonia or urea) in the hot combustion zone 

(1600 to 2100 degrees Fahrenheit) to reduce NOx to nitrogen and water without the use of a 

catalyst. Levels on control may vary widely based on case specific conditions including 

injection temperature and residence time, mixing characteristics of the flue gas and reagent, and 

constituents of the exhaust gas that may reduce the desired reduction of NOx. 

SNCR/SCR Hybrid

This hybrid approach involves injecting the reagent (ammonia or urea) into the combustion 

chamber (which is a higher temperature zone than traditional SCR injection). This provides an 

initial reaction that is similar to SNCR systems. A catalyst is placed downstream to further the 

reduction of NOx and any reagent that remains. 

Combustion Controls

Staged Combustion

Staged combustion can be achieved through a wide variety of methods and techniques, but in 

general always creates a fuel rich zone followed by a fuel lean zone. This reduces the peak flame 

temperature and the generation of thermal NOx. 

Fuel Staging

Fuel staging is a technique that utilizes 10% to 20% of the total fuel input downstream from the 

primary combustion zone. The fuel in the downstream secondary zone acts as a reducing agent 

reducing NO emissions to N2. Natural gas or distillate oil are usually used in the secondary 

combustion zone. 
Low NOx Burners (LNB)

LNB stage the combustion process by injecting fuel in a rich state and injecting excess air 

surrounding the fuel rich area to complete combustion and reduce the peak flame temperature. 

LNB are often employed with separated overfire air or overfire air (SOFA or OFA) to further 

ensure complete combustion. 

Overfire Air (OFA)

OFA is a technique in which some combustion air is diverted from the burner to a location 

downstream from the burner and flame front. This creates a staged combustion with a rich 

combustion zone followed by a lean combustion zone, lowering the overall flame temperature 

and thereby, thermal NOx emissions. 

Low Excess Air (LEA)

LEA reduces NOx generation by reducing the amount of air available for combustion thereby 

reducing flame temperature and NOx. 

Flue Gas Recirculation (FGR)

FGR reduces NOx emissions by reintroducing a portion of the unit’s exhaust into the combustion 

zone, reducing the available oxygen and reducing the combustion zone temperature. 

Optimization/Tuning

Optimum combustion conditions (including air/fuel ratio adjustments) reduce the 

generation of all pollutants except for water, CO2, and N2 (which are maximized under 

ideal combustion conditions). Automated, or intelligent, controls include sensors and 

software to optimize the air/fuel ratio (ECR Nov 2011, page 4; WRAP Report) in order to 

maximize the energy recovered from the burning of the fuel and minimize the pollutants 

produced. Plum Creek utilizes intelligent controls (ECR Nov 2011, page 4; 2011 Plum 

Creek Response Document). 

Step 2: Eliminate Technically Infeasible Options 

SCR

SCR catalysts may be fouled or plugged by exhaust gas that contains high concentrations of PM, 

as is the case with the combustion of wood, biomass, or hog fuel. To prevent the premature 

failure of the catalyst the PM must be removed from the exhaust stream prior to the SCR. 

Boiler: In this case the exhaust from the boiler’s ESP will not meet the minimum temperature 

required for SCR (without reheat). Since the PM loading is too high for high dust SCR prior to 

PM controls; and the gas is too cool after the PM control equipment for a low dust SCR 

(downstream of the ESP), SCR is considered to be technically infeasible for the boiler. 

(2) Line 1 Sander Dust Burners & Line 2 Sander Dust Burners: All of the sander dust burners 

have the same issues associated with the implementation of SCR as the boiler. PM loadings are 

too high for a hot/high dust SCR, and temperatures are too cool following PM control unless 

reheat is utilized. In addition to these issues, the dryer burners are all direct contact dryers. 

Therefore, any ammonia in the gas stream from a hot/high dust SCR would have the potential to 

stain or darken the wood product. Plum Creek has stated that this is unacceptable from a product 
quality standpoint. Therefore SCR is considered technically infeasible for the sander dust burners 

as well. 

SNCR

Boiler: The boiler exhaust does not pass over Plum Creek’s product and as such the discussion 

below regarding ammonia fouling of the wood products does not apply to the boiler. However, 

Plum Creek has stated that the boiler is used as a load following boiler. Plum Creek believes that 

the level of variability of the boiler will have a detrimental effect on the ability of a SNCR 

system to reduce NOx emissions without high levels of ammonia slip. However it may be 

possible through the use of an intelligently designed injection grid and robust plant data 

acquisition and control equipment to successfully apply SNCR, therefore we have not considered 

it to be technically infeasible for the boiler. 

(2) Line 1 Sander Dust Burners & Line 2 Sander Dust Burners: The exhaust from the Line 1 and 

Line 2 sander dust burners act as direct contact heat sources for the drying processes at the 

facility. The use of SNCR would require injection of the reagent prior to the dryers introducing 

ammonia to the product lines. Plum Creek has stated that contact with ammonia may result in 

reduced product quality. Additionally, ammonia may affect the curing of any formaldehyde 

based resins used in the wood products. High levels of ammonia reduce the cellulosic structure 

of the wood allowing it to be permanently shaped, however compressive strength is reduced. 

Space constraints are also a consideration since there is not sufficient residence time at the 

required temperatures in the exhaust stream prior to the location where the exhaust comes into 

contact with the wood products. Therefore, there is a likelihood that the conversion of the 

ammonia reagent may not be sufficiently completed before the exhaust enters the dryers, making 

product quality a concern (as stated above). For these reasons SNCR is not considered to be 

technically feasible for the Line 1 and Line 2 sander dust burners. 

SNCR/SCR Hybrid

Boiler: Since the PM concentrations in the exhaust of the boiler would require the PM controls 

to precede the catalyst section of the hybrid system, reheat would be required. RSCR is 

considered to be feasible without firebox/SNCR injection, therefore SNCR/SCR Hybrid systems 

are not examined further. 

(2) Line 1 Sander Dust Burners & Line 2 Sander Dust Burners: Since the PM concentrations in 

the exhaust of the sander dust burners would require the PM controls to precede the catalyst 

section of the hybrid system, reheat would be required. RSCR is considered to be feasible 

without firebox/SNCR injection, therefore SNCR/SCR Hybrid systems are not examined further. 

Fuel Staging

Boiler: The boiler already employs fuel staging by having a stoker grate for a majority of the 

heat input followed by sander dust burners downstream of the grate. Therefore further fuel 

staging is considered infeasible for the boiler 

(2) Line 1 Sander Dust Burners: The two (2) Line 1 MDF dryer sander dust burners have a 

combustion chamber that is too small to accommodate fuel staging. Therefore fuel staging is 

considered technically infeasible for the Line 1 and Line 2 sander dust burners. 
Line 2 Sander Dust Burners: The Line 2 MDF dryer sander dust burner utilizes staged 

combustion. Further modification of the combustion chamber would be required to utilize fuel 

staging, however space constraints would make the expansion infeasible. Also, further NOx

reductions would not likely be realized since the staged combustion design has already reduced 

thermal NOx to the extent possible. 

Staged Combustion

Boiler: The boiler is a stoker boiler with sander dust burners downstream from the stoker. In 

order to create a further staged combustion process (and lower flame temperature) the energy 

density must be reduced in the combustion fuel. This means that more volume would be 

required to accommodate the current heat rate. In addition to the space constraint it is unlikely 

that the current design could further stratify the rich and lean combustion zones (either through 

decreased under-fire air, or increased OFA) due to the minimum air flow needed to cool the 

stoker grate and maintain an even heat release rate. See also Step 2 for the OFA option. 

(2) Line 1 Sander Dust Burners: The two(2) Line 1 MDF dryer sander dust burners have a 

combustion chamber that is 1⁄4 the volume of the Line 2 MDF dryer sander dust (Coen) burner. 

Staged combustion techniques increase the volume (or size) of the flame front for a given heat 

input rate, therefore it would be necessary to reduce the overall heat input of the burners to 

achieve lower flame temperatures and thereby realize the NOx reduction achievable with staged 

combustion techniques. A reduction in the heat rate to the Line 1 burners would result in 

insufficient heat being sent into the drying process. 

Line 2 Sander Dust Burners: The Line 2 MDF dryer sander dust burner utilizes staged 

combustion, therefore further staging would not be technically feasible without complete 

replacement. 

Low NOx Burners (LNB)

Boiler: LNB are not feasible for spreader-stoker boilers since they do not utilize burners for a 

majority (90% in this case) of the heat input. Sander dust burners are located downstream from 

the stoker grate, however their small size may restrict the ability to create conditions necessary 

for a LNB. For LNB technology to be effective, the rich zone must precede the lean zone. In 

this case the secondary combustion zone burners would not have sufficient space to 

accommodate a larger flame front characterized by LNB technology. Additionally, lowering the 

flame temperature at that location may negatively affect the function of the secondary 

combustion zone which could result in increased emissions of some pollutants. 

(2) Line 1 Sander Dust Burners: As stated above in the Step 2 discussion of staged combustion, 

there is insufficient combustion chamber volume to implement LNB design for the (2) Line 1 

sander dust burners. Therefore LNB are considered to be technically infeasible for the (2) Line 1 

sander dust burners without increasing combustion chamber volume or decreasing the heat input 

rate (which would affect Plum Creek’s ability to successfully operate the wood product dryers). 

Line 2 Sander Dust Burners: LNB (or staged combustion) is a technique that was designed into 

the Line 2 (85 MBtu/hr) Coen sander dust burner, therefore further staging, or LNB 

configuration is considered technically infeasible.
OFA

Boiler: In order to implement OFA on the boiler further modifications would be required to add 

OFA ports. The OFA ports would need to be installed at the same location as the current sander 

dust burners. Additionally, installation of OFA ports will increase the size/volume of the flame 

front, in turn increasing flame impingement on the boiler walls, which may lead to tube failure. 

Flame impingement may also increase quenching of the flame thereby increasing emissions 

associated with incomplete combustion. The reducing atmosphere of the rich primary zone may 

also result in accelerated corrosion of the furnace and grate corrosion and overheating may occur 

in stokers as primary air flow is diverted to OFA ports. Although further OFA is considered 

technically infeasible, some level of staged combustion is a technique already utilized through 

fuel staging (by use of the downstream sander dust burners). Therefore further staging of the 

combustion process through OFA (or other techniques) is technically infeasible without 

increasing the boiler volume or decreasing the heat input rate. 

(2) Line 1 Sander Dust Burners: As is discussed above there is insufficient combustion chamber 

volume to implement OFA on the Line 1 burners without decreasing the heat input rate. The 

reduced heat input rate would prevent the dryers from operating as designed, and therefore make 

OFA technically infeasible for the Line 1 burners. 

Line 2 Sander Dust Burners: The Line 2 burner already employs staged combustion therefore 

further staging through the use of OFA is technically infeasible. 

Low Excess Air (LEA)/FGR

Boiler: The boiler is a stoker boiler that operates on the principle of creating an even release of 

heat across the entire grate. In order to achieve optimal conditions, sufficient air flow is required 

from beneath the grate. In addition sufficient air flow is needed to keep the grate and parts 

exposed to combustion material below their maximum operating temperatures. For these reasons 

LEA is not considered technically feasible for the boiler. 

FGR is a technique having multiple mechanisms for reducing NOx, one of which being that it 

reduces the available oxygen since some exhaust gas replaces oxygen rich ambient air. Undergrate air flow may be maintained with FGR, but in order to prevent high loss on ignition and 

increased pollutant emissions associated with incomplete combustion (and the LEA condition) 

the volume of the boiler’s combustion chamber would likely need to be increased to maintain the 

current steam rate and overall heat release rate. Since the boiler is space constrained, and because 

FGR causes a LEA condition and LEA is considered technically infeasible for the boiler, FGR 

has also been considered to be infeasible for the boiler. 

(2) Line 1 Sander Dust Burners & Line 2 Sander Dust Burners: LEA is considered to be 

technically infeasible for the sander dust burners because sander dust suspension burners require 

high levels of air in order to fluidize the solid fuel. Poor operation of the burners would result 

with LEA since high excess air conditions are found under the conditions necessary to sustain 

stable combustion. The Line 1 and Line 2 dryers are all suspension burners and therefore LEA is 

considered technically infeasible for these sources. 

FGR is a technique having multiple mechanisms for reducing NOx, one of which being that it 

reduces the available oxygen since some exhaust gas replaces oxygen rich ambient air. Since 
FGR causes a LEA condition and LEA is considered technically infeasible for the (2) Line 1 and 

Line 2 sander dust burners, FGR has also been considered to be infeasible for the (2) Line 1 and 

Line 2 sander dust burners. Additionally FGR may require additional combustion chamber 

volume to accommodate the same heat input while maintaining a reduced flame temperature. 

Step 2 Summary:

All other control options are considered to be technically feasible. The following table 

provides a summary of what controls may be considered technically feasible for each unit 

Emission Unit

Boiler Two (2) Line 1 Sander 

Dust Burners

Line 2 Sander Dust 

Burner

Feasible 

Controls RSCR 

RSCR RSCR 

SNCR 

Optimization/Tuning Optimization/Tuning Optimization/Tuning

Step 3: Evaluate Control Effectiveness of Each Remaining Technology 

It is important to note that NOx emissions from wood and bark are low when compared

with fossil fuel NOx emissions (on the order of 0.1 - 0.35 lb/MBtu expressed as NO2). 

Thermal NOx generated is less than for fossil fuels due to the low combustion 

temperatures. Fuel bound nitrogen conversion to NOx is dependent on conditions 

including excess air, air staging, heat release rate, and fuel sizing and moisture content. 

Studies have found NOx to vary inversely with fuel moisture content. Smaller fuel 

particles have been known to generate higher NOx emissions because of their increased 

heat release rate (faster burn rate). Fuel NOx emissions can be significantly reduced by 

reducing the available oxygen in the early stages of combustion. (Kitto, John B. and 

Steven C. Stultz Ed. Steam: Its Generation and Use, Ed. 41, The Babcock & Wilcox 

Company, 2005). 

 RSCR

RSCR achieve equivalent reductions to SCR and perhaps higher reductions due to the 

pretreatment of the exhaust gas to remove PM. 70-95% reduction is commonly cited for 

SCR systems on a wide variety of emission units. However, the use of western biomass 

poses several challenges that may reduce the ability to control NOx. Babcock Power is 

currently the only manufacturer of RSCR systems. They believe that for a unit firing 

western wood based fuel the probable removal efficiency would be in the range of 70% 

to 80% (see Babcock Power technical memos). For this analysis we have assumed that a 

75% reduction would be achievable based on emissions data from several operating wood 

fired boilers with the Babcock Power RSCR. 

 Selective Non-Catalytic Reduction (SNCR)

While NOx reductions of 70% are possible in ideal conditions, often 30% - 50% reductions are 

achieved to maintain acceptable levels of reagent consumption and ammonia slip. For stoker 

boilers the proper temperature range occurs in the convection pass cavities, making application, 
especially on retrofits, more challenging. For these applications NOx reduction may be limited to 

20%-30% reduction. Plum Creek claims that the load following nature of the boilers would 

prohibit the use of SNCR since temperature fluctuations would be too great to maintain the 

necessary temperature range and residence time. However, it is possible to utilize complex 

intelligent controls to determine the appropriate injection location and rate. We recognize that the 

rapidly changing dynamics may reduce the level of control achievable by SCNR, in addition to 

the fact that the system is a retrofit system. Considering these factors Plum Creek believes that 

SNCR applied to the boiler would be able to achieve a 35% reduction of NOx emissions. 

 Optimization/Tuning

Optimum combustion conditions (including air/fuel ratio adjustments) for reducing thermal NOx

generation have been identified as an option that can reduce NOx emissions by 20 - 30% from a 

boiler that is not equipped with intelligent controls that include sensors and software to optimize 

the air/fuel ratio (ECR Nov 2011, page 4; WRAP Report, Roseburg EC/R 11/16/2011). Plum 

Creek utilizes intelligent controls (ECR Nov 2011, page 4; 2011 Plum Creek Response 

Document). 

Step 4: Evaluate Factors and Present Determination 

Factor 1: Cost of Compliance 

Note: no costs have been analyzed for optimization/tuning since Plum Creek already follows 

these practices. Therefore optimization/tuning has no further cost associated with its 

implementation and has not been included in the cost table below. Also, no cost information was 

presented to EPA for RSCR although cost estimates were presented for SCR. Therefore we have 

generated cost ranges by utilizing data for a similar facility being examined through the 

Reasonable Progress process (specifically cost presented for the SolaGen sander dust burner at 

Roseburg Forest Products). 

Unit Control 

Type and 

Control 

Efficiency

NOx

Potential 

Emissions 

(tpy)

NOx

Reduced 

via 

Control 

(tpy)

Capital Cost 

($)

Annual

Cost 

($/year)

Average Cost 

Effectiveness 

($/ton 

reduced)

Boiler RSCR 

(75%) 587 

440 $3,556,9671$748,097 $1,700 

SNCR 

(35%) 

205 $617,709 $294,377 $1,436 

Line 1 

Sander 

Dust 

Burners 

(2) 

RSCR 319 240 $3,556,9671 $748,097 $3,117 

Line 2 

Sander 

Dust 

Burner 

RSCR 200 150 $3,556,9671 $748,097 $4,987 

 

1

 Cost estimate from Roseburg Reasonable Progress Analysis for the SolaGen sander dust burner 
Factor 2: Time Necessary for Compliance 

 RSCR

EC/R presented information to EPA, separately from the information presented by Plum 

Creek that indicates that Babcock Power Inc. believes that systems can be operational 

within eight months from the time an order is made. No information was presented by 

Plum Creek that would indicate the time necessary to place the order or the timeframes 

necessary to bring the equipment off-line to accommodate the retrofit. However, it is 

appropriate to assume that the process could be completed within eight months to one 

year. 

 SNCR (Boiler Only)

No information was presented for the time necessary to install and operate a SNCR at 

Plum Creek’s operations. However, information was provided for RSCR, which is 

applicable to the time that might be required for SNCR. Since RSCR includes much of 

the equipment needed for SNCR, with additional equipment (the catalyst for instance), 

we have assumed that SNCR could be installed within a similar timeframe to that quoted 

for RSCR. Therefore, we believe that SNCR could be installed and operational within 8 

months to one year. 

 Optimization/Tuning

All units are already tuned for optimal efficiency and to minimize the units emissions 

profile. It is assumed that no further time would be required to operate the units 

optimally. 

Factor 3: Energy and Non-Air Quality Impacts 

 RSCR

RSCR requires the reheat of the flue gas either through a heat exchanger that utilizes 

plant waste heat, and/or through direct reheat of the flue gas through the use of additional 

combustion or electrically powered heating elements. Although specific estimates of 

resources needed to operate RSCR on the Columbia Falls units we have examined 

estimates presented for a similar source (Roseburg Forest Products) to illustrate the 

approximate quantity of resources needed to run a RSCR system. 

Ammonia Natural Gas Electricity Steam

RSCR usage 

per system

300,000 

to 

400,000 

gal/year 

2 million 

scf/year 

to 

9.7 million 

scf/year 

930,000 - 5.4 

million 

kWh/year 

42.5 - 125 lb/hr 

or 

186 - 548 

tons/year 

Additionally SCR catalysts and likewise RSCR may have the potential to emit ammonia (as 

ammonia slip) and generate nitrous oxide (a powerful GHG) if not operated optimally. Catalysts 

must be disposed of, presenting a cost. However many catalyst manufacturers provide a system 
to regenerate or recycle the catalyst reducing the impacts associated with spent catalysts. In 

addition to these considerations, there are issues associated with the production, transport, 

storage, and use of ammonia. However, the regularity with which ammonia is handled has 

reduced the risks associated with its transport, storage, and use. 

SNCR

As with RSCR there are issues associated with ammonia, electricity, and compressed air. EC/R 

presented cost calculations for SNCR that presented the following rate of use of reagent (as 

Urea) 

Reagent 

(Urea)

Electricity Steam

Boiler SNCR 

System

165 tons/year 

or 

69,740 gallons 

Urea 

solution/year 

204,108 

kWh/year 

51.4 lb/hr 

or 

225 tons/year 

As with RSCR some level of ammonia slip will be present, which is dependent on the amount of 

reagent injected, and the level of control that is desired. Higher levels of control are associated 

with greater ammonia slip. Whether urea or ammonia is used there are impacts associated with 

the production, transport, storage, and use of these chemicals. If urea is utilized there will be 

GHG emissions associated with its hydrolysis prior to its use at a NOx reagent. 

Factor 4: Remaining Useful Life 

Plum Creek’s 2011 response document indicates that the useful life of their equipment is as 

follows: 

Boiler - 10 years 

(2) Line 1 Sander Dust Burners - 10 years 

Line 2 Sander Dust Burner - 10 years