Reasonable Progress (RP) Four-Factor Analysis of Co ntrol 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 - 1 986
and 2006 Coen burners rated at 50 MBtu/hr each

Line 2 MDF Dryer Sander Dust Burner - 2001 Coen bu rner 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 do wnstream of the spreader-stoker grate that are capable of supplementing 10% of the heat rate capac ity of the boiler. These sander dust burners are normally fired with sander dust, but have the a bility 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 dr yers, a core fiber dryer and a face fiber dryer. Each dryer is provided heat by one Coen san der dust burner. The Line 1 fireboxes are 1⁄4 the size of the Line 2 firebox reducing the capacit y 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. T he 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 followe d by a lean zone reducing peak flame temperature thereby reducing thermal NO

x emissions. The Line 2 dryer exhausts to a Venturi scrubber installed in 2001 before emitting to the a tmosphere through three 40 foot stacks.Reasonable Progress Evaluation of Nitrogen Oxide (N O
x ) Emissions

Step 1: Identify All Available Technologies Selective Catalytic Reduction (SCR) SCR utilizes a nitrogen based reagent (usually ammo nia) injected in the flue gas to enhance the
reduction reaction of NO

x 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 w ith properly operated SCR. NO

x emission reductions associated with SCR on a variety of sour ce categories can be as high as 95%. The optimal temperature range for most SCR catalyst ran ges 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 r eaction, 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 ga s characteristics.

Regenerative SCR (RSCR) RSCR uses a regenerative thermal oxidizer (or wast e heat transfer system) to bring cool exhaust gas back up to the temperature required for SCR cat alyst to be effective at reducing NO

x to nitrogen and water. RSCR is a good option for exha ust 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 exhau st.

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 NO

x 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 ch aracteristics of the flue gas and reagent, and constituents of the exhaust gas that may reduce the desired reduction of NO

x .

SNCR/SCR Hybrid This hybrid approach involves injecting the reagent (ammonia or urea) into the combustion chamber (which is a higher temperature zone than tr aditional SCR injection). This provides an initial reaction that is similar to SNCR systems. A catalyst is placed downstream to further the
reduction of NO

x and any reagent that remains.

Combustion Controls

Staged Combustion Staged combustion can be achieved through a wide va riety 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 NO

x .

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 downstrea m secondary zone acts as a reducing agent reducing NO emissions to N 2 . Natural gas or distillate oil are usually used in the secondary
combustion zone.Low NO
x 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 combusti on 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 cr eates a staged combustion with a rich combustion zone followed by a lean combustion zone, lowering the overall flame temperature and thereby, thermal NO

x emissions.

Low Excess Air (LEA)
LEA reduces NO

x generation by reducing the amount of air available for combustion thereby reducing flame temperature and NO

x .

Flue Gas Recirculation (FGR)
FGR reduces NO

x emissions by reintroducing a portion of the unit’s exhaust into the combustion zone, reducing the available oxygen and reducing th e combustion zone temperature.

Optimization/Tuning Optimum combustion conditions (including air/fuel r atio adjustments) reduce the generation of all pollutants except for water, CO 2 , and N 2 (which are maximized under ideal combustion conditions). Automated, or intelli gent, controls include sensors and software to optimize the air/fuel ratio (ECR Nov 20 11, page 4; WRAP Report) in order to maximize the energy recovered from the burning of t he 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 g as 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 wi ll not meet the minimum temperature required for SCR (without reheat). Since the PM loa ding is too high for high dust SCR prior to PM controls; and the gas is too cool after the PM c ontrol equipment for a low dust SCR (downstream of the ESP), SCR is considered to be te chnically 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 implementa tion 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, th e 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 s tated that this is unacceptable from a productquality standpoint. Therefore SCR is considered tec hnically 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 product s 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 NO

x emissions without high levels of ammonia slip. How ever it may be possible through the use of an intelligently design ed injection grid and robust plant data acquisition and control equipment to successfully a pply 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 he at sources for the drying processes at the facility. The use of SNCR would require injection o f 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, h owever compressive strength is reduced. Space constraints are also a consideration since th ere is not sufficient residence time at the required temperatures in the exhaust stream prior t o 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 b efore the exhaust enters the dryers, making product quality a concern (as stated above). For th ese reasons SNCR is not considered to be technically feasible for the Line 1 and Line 2 sand er dust burners.

SNCR/SCR Hybrid
Boiler : Since the PM concentrations in the exhaust of th e boiler would require the PM controls to precede the catalyst section of the hybrid syste m, reheat would be required. RSCR is considered to be feasible without firebox/SNCR inje ction, 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 requir e the PM controls to precede the catalyst section of the hybrid system, reheat would be requi red. 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 downstre am 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 an d 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 e xpansion infeasible. Also, further NO

x reductions would not likely be realized since the s taged combustion design has already reduced
thermal NO

x to the extent possible.

Staged Combustion
Boiler: The boiler is a stoker boiler with sander dust bu rners 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. Th is means that more volume would be required to accommodate the current heat rate. In a ddition 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 h ave 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 (o r size) of the flame front for a given heat input rate, therefore it would be necessary to redu ce the overall heat input of the burners to achieve lower flame temperatures and thereby realiz e the NO

x 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 proces s.

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 NO
x 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. Sand er dust burners are located downstream from the stoker grate, however their small size may rest rict 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 wou ld not have sufficient space to accommodate a larger flame front characterized by L NB technology. Additionally, lowering the flame temperature at that location may negatively a ffect the function of the secondary
combustion zone which could result in increased emi ssions of some pollutants.

(2) Line 1 Sander Dust Burners: As stated above in the Step 2 discussion of stage d combustion,
there is insufficient combustion chamber volume to implement LNB design for the (2) Line 1
sander dust burners. Therefore LNB are considered t o be technically infeasible for the (2) Line 1 sander dust burners without increasing combustion c hamber volume or decreasing the heat input rate (which would affect Plum Creek’s ability to su ccessfully operate the wood product dryers).

Line 2 Sander Dust Burners: LNB (or staged combustion) is a technique that wa s designed into the Line 2 (85 MBtu/hr) Coen sander dust burner, th erefore further staging, or LNB configuration is considered technically infeasible.OFA

Boiler: In order to implement OFA on the boiler further m odifications 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 por ts 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 th e 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 p orts. Although further OFA is considered technically infeasible, some level of staged combus tion 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 combu stion chamber volume to implement OFA on the Line 1 burners witho ut decreasing the heat input rate. The reduced heat input rate would prevent the dryers fr om 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 combusti on therefore further staging through the use of OFA is technical ly 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 o ptimal 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 r educing NO

x , 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 o rder to prevent high loss on ignition and increased pollutant emissions associated with incom plete 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. S ince the boiler is space constrained, and because
FGR causes a LEA condition and LEA is considered te chnically infeasible for the boiler, FGR
has also been considered to be infeasible for the b oiler.

(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 f uel. 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 r educing NO

x , one of which being that it reduces the available oxygen since some exhaust gas replaces oxygen rich ambient air. SinceFGR causes a LEA condition and LEA is considered te chnically infeasible for the (2) Line 1 and

Line 2 sander dust burners, FGR has also been consi dered to be infeasible for the (2) Line 1 and Line 2 sander dust burners. Additionally FGR may re quire additional combustion chamber volume to accommodate the same heat input while mai ntaining a reduced flame temperature.

Step 2 Summary: All other control options are considered to be tech nically feasible. The following table provides a summary of what controls may be consider ed 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 Optimizatio n/Tuning

Step 3: Evaluate Control Effectiveness of Each Rema ining Technology It is important to note that NO

x emissions from wood and bark are low when compared
with fossil fuel NO

x emissions (on the order of 0.1 - 0.35 lb/MBtu expr essed as NO 2 ).
Thermal NO

x generated is less than for fossil fuels due to the low combustion temperatures. Fuel bound nitrogen conversion to NO

x is dependent on conditions including excess air, air staging, heat release rat e, and fuel sizing and moisture content.
Studies have found NO

x to vary inversely with fuel moisture content. Small er fuel particles have been known to generate higher NO

x emissions because of their increased heat release rate (faster burn rate). Fuel NO

x emissions can be significantly reduced by reducing the available oxygen in the early stages o f 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 perha ps 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. Ho wever, the use of western biomass poses several challenges that may reduce the abilit y to control NO

x . Babcock Power is currently the only manufacturer of RSCR systems. Th ey believe that for a unit firing western wood based fuel the probable removal effici ency would be in the range of 70% to 80% (see Babcock Power technical memos). For thi s analysis we have assumed that a
75% reduction would be achievable based on emission s data from several operating wood
fired boilers with the Babcock Power RSCR.

Selective Non-Catalytic Reduction (SNCR)
While NO

x reductions of 70% are possible in ideal conditions , often 30% - 50% reductions are achieved to maintain acceptable levels of reagent c onsumption and ammonia slip. For stoker boilers the proper temperature range occurs in the convection pass cavities, making application,especially on retrofits, more challenging. For thes e applications NO

x 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 fluctuat ions would be too great to maintain the necessary temperature range and residence time. How ever, it is possible to utilize complex intelligent controls to determine the appropriate i njection location and rate. We recognize that the rapidly changing dynamics may reduce the level of c ontrol achievable by SCNR, in addition to the fact that the system is a retrofit system. Cons idering these factors Plum Creek believes that SNCR applied to the boiler would be able to achieve a 35% reduction of NO

x emissions.

Optimization/Tuning Optimum combustion conditions (including air/fuel r atio adjustments) for reducing thermal NO

x generation have been identified as an option that c an reduce NO

x emissions by 20 - 30% from a boiler that is not equipped with intelligent contro ls that include sensors and software to optimize the air/fuel ratio (ECR Nov 2011, page 4; WRAP Repo rt, 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/tunin g 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 cos t table below. Also, no cost information was presented to EPA for RSCR although cost estimates w ere presented for SCR. Therefore we have generated cost ranges by utilizing data for a simil ar facility being examined through the Reasonable Progress process (specifically cost pres ented for the SolaGen sander dust burner at Roseburg Forest Products).

Unit Control

Type and
Control Efficiency NO

x

Potential
Emissions (tpy) NO

x

Reduced
via
Control (tpy) Capital Cost

($) Annual

Cost ($/year) Average Cost

Effectiveness ($/ton reduced)

Boiler RSCR

(75%) 587 440 $3,556,967 1 $748,097 $1,700

SNCR (35%) 205 $617,709 $294,377 $1,436

Line 1
Sander

Dust

Burners (2) RSCR 319 240 $3,556,967 1 $748,097 $3,117

Line 2
Sander

Dust

Burner RSCR 200 150 $3,556,967 1 $748,097 $4,987

1 Cost estimate from Roseburg Reasonable Progress An alysis for the SolaGen sander dust burnerFactor 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. believ es 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 t o place the order or the timeframes necessary to bring the equipment off-line to accomm odate the retrofit. However, it is appropriate to assume that the process could be com pleted 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 S NCR. Since RSCR includes much of the equipment needed for SNCR, with additional equi pment (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 thr ough a heat exchanger that utilizes plant waste heat, and/or through direct reheat of t he 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 Fa lls units we have examined estimates presented for a similar source (Roseburg Forest Products) to illustrate the approximate quantity of resources needed to run a R SCR 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 ha ve the potential to emit ammonia (as ammonia slip) and generate nitrous oxide (a powerfu l GHG) if not operated optimally. Catalysts must be disposed of, presenting a cost. However ma ny catalyst manufacturers provide a systemto 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 regularit y with which ammonia is handled has reduced the risks associated with its transport, st orage, and use.

SNCR
As with RSCR there are issues associated with ammon ia, 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 pre sent, 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 thes e chemicals. If urea is utilized there will be GHG emissions associated with its hydrolysis prior to its use at a NO

x 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