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From: Lane, Sean [mailto:SLane@CenturyKY.com] 

Sent: Thursday, February 13, 2014 2:51 PM 

To: Putney, David 

Cc: Lane, Sean 

Subject: Comment Regarding Bake Furnaces 

David, 

Per our conversation early last week, be find the attached 

letter containing our comments and request to modify the 

PMACT standard to accommodate the averaging of emissions 

from new and existing baking furnaces ducted to a common 

control device. 

Please contact me if you have questions. 

Thank you. 

Sean T. Lane, CSP, CHMM

Environmental Manager

CenturyALUMINUM of Kentucky

1627 State Route 3543

P.O. Box 500

Hawesville, KY 42348

P - (270) 852-2880

F - (270) 852-2887
Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

1 

February 13, 2014 

Mr. David Putney 

Environmental Engineer 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Sector Policies and Programs Division 

109 T.W. Alexander Drive 

Research Triangle Park, NC 27711 

Mail Drop D243-02 

RE: Comments to Primary Aluminum MACT concerning Carbon Bake Furnaces 

Dear Mr. Putney: 

Century Aluminum of Kentucky (Century), in conjunction with the seven (7) year review of the National 

Emission Standards for Hazardous Air Pollutants for Primary Aluminum Reduction Plants (PMACT) at 40 

CFR Part 63 Subpart LL, formally requests that EPA amend PMACT to establish an alternate emission 

limit for the unique carbon baking units at Century’s Hawesville smelter that have a single common 

control device serving existing and new carbon baking sources. 

Background

Prior to promulgation of the final PMACT on October 7, 1997, Century’s predecessor, NSA, a Division of 

Southwire Company, planned and applied for a Prevention of Significant Deterioration (PSD) Permit for a 

new potline at the Hawesville primary aluminum smelter facility.1

 The original PSD application was 

submitted to the Kentucky Division for Air Quality (KDAQ) in December 1995. Ultimately, a revised PSD 

application was submitted by NSA that included construction of a new carbon bake unit to supplement 

anode production from the two existing anode bake furnaces. The planning and design of the new potline 

and associated support facilities was initiated prior to issuance of the final PMACT, although construction 

pursuant to the PSD Permit was initiated in 1998. 

As a result of the timing of the application for the new potline, NSA did not have an opportunity to provide 

input to EPA on the proposed PMACT standard in 1996 relative to the carbon bake furnace configuration 

at the Hawesville facility or the appropriate emissions standards or compliance monitoring that was 

deemed appropriate for the unique circumstances at the facility. Because the two existing carbon bake 

furnaces were uncontrolled, NSA opted to design a single dry scrubber to control emissions from the two 

existing carbon bake furnaces and the new carbon bake furnace that was authorized by the April 1998 

PSD Permit issued by KDAQ. In essence, by designing a single dry scrubber for all three carbon bake 

furnaces, NSA significantly over-controlled HAP emissions from the two existing carbon bake furnaces as 

compared to the existing source PMACT standard at 40 CFR 63.843(c). 

During development of PMACT, it was never considered or anticipated that there were situations where a 

new carbon baking furnace and existing furnace would be ducted to a common control device. Primary 

Aluminum Industry: Technical Support Document for Proposed MACT Standards (July 1996) (hereinafter 

1

 Century purchased the smelter from NSA in April 2001. 

Attachment 1. p.1 of 6
 

Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

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“TSD”). It was certainly a unique circumstance that as MACT was being promulgated, NSA was in the 

process of designing a new carbon baking unit and a control device sized and intended to also control 

HAPs from its existing carbon baking sources. This allowed NSA to build only one control device that 

provided, on aggregate, more control than required under the final PMACT for each unit separately. In

fact, the rulemaking record demonstrates that EPA determined emission reductions achieved by a single 

dry alumina scrubber would represent MACT for multiple anode bake furnaces at existing source and for 

new sources. TSD at pp. 4-12, 4-13, App. B, Table B-5; Basis and Purpose Document for the 

Development of Proposed Standards for the Primary Aluminum Industry (July 19, 1996) (hereinafter 

“BPD”) at App. B, pp. 3-6; see also 61 Fed. Reg. 50588 (Sept. 26, 1996). 

Following construction of the new carbon bake furnace and fifth potline, NSA contacted EPA Research 

Triangle Park to determine how the recent PMACT compliance standards would apply to the two existing 

and one new carbon bake furnaces that were ducted to a common control device, since emission 

limitations for this configuration were not directly addressed in the proposed and final PMACT preambles 

or the rule development documents. At that time, the informal EPA response was that the issue could not 

be addressed in the short-term through a PMACT rulemaking, but that the issue should be raised with the 

state regulatory authority to explore a compliance demonstration approach based upon use of a formula 

similar to that specified in 40 CFR 63.845(b) for new potroom groups that are added to an existing potline. 

(See Attachment 1). 

After working with KDAQ to develop a compliance demonstration plan for POM for the three carbon bake 

furnaces, KDAQ ultimately approved a compliance demonstration approach as part of the Title V Permit 

that was issued to the facility in 2003. KDAQ approved permit language that established a combined 

permit limit at the outlet of the control device for two (2) existing sources and one (1) new source. These 

limits were established as 0.14 lbs POM / ton Green Anode and 0.14 lbs TF / ton Green Anode. (See 

Attachment 2, 2003 Title V Permit). The Title V permit was reviewed by EPA Region IV without objection. 

It was not until EPA Region IV did a compliance audit in 2008 that Title V Permit language became an 

issue for EPA. Region IV’s contention was that since a combined weighted average emission formula 

was not specifically provided for in PMACT, the limit was not permissible. Century ultimately settled upon 

a solution with Region IV that determined compliance with the respective new and existing source limits 

for the three furnaces separately, but this methodology has proven to be overly burdensome to the facility 

and actually penalizes the facility for efficient furnace and control device operation. 

Concerns with Current Testing Approach

The current testing scenario utilizes the sum of the mass of pollutant loadings in the inlets to the common 

control device along with the mass of pollutants in the outlet of the common control device to obtain an 

overall control system pollutant removal efficiency. This overall efficiency is then applied to the 

uncontrolled emissions from each source to determine a controlled pounds per hour for each furnace. 

The controlled pounds per green ton of emissions is then calculated from the calculated controlled 

pounds per hour. The respective calculated emission rates for the new and existing furnaces are then 

compared to the new and existing source PMACT standards to determine compliance. (See Attachment 

3, excerpt from current Title V Permit.) 

Since implementing this approved compliance demonstration approach, Century has had difficulty on 

occasion in demonstrating compliance with the new source emission limitation of (0.05 # POM/GT) 

through the calculated emissions rate for the new unit. However, on a combined emissions basis, the dry 

scrubber comes close to meeting the new source limit of 0.05 # POM/GT with the long term average of 

0.059 # POM/GT since the year 2000 for all three units. Moreover, on a combined control basis of the 

new and two existing units, emissions of POM and gaseous fluoride are an average 95.7% (POM) and 
Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

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57.9% (TF) lower on an equivalent production basis than the cumulative allowable for the three units 

under PMACT. If Century operated the three furnaces (1 new, 2 existing) with separate control devices 

and at its permitted production capacity (233,000 green tons), the allowable hourly emissions per the 

PMACT would be as follows: 

Furnace 

POM Limitation

(@ 233,000 TPY Production) 

TF Limitation

(@ 233,000 TPY Production) 

lbs/GT lbs/hr lbs/GT lbs/hr

New 0.05 0.44 0.02 0.18

Existing 1 0.18 1.60 0.20 1.77

Existing 2 0.18 1.60 0.20 1.77

Combined NA 3.64 NA 3.72

As previously stated, the three furnaces (1 new, 2 existing) were ducted to a common control device that 

was designed at the time of permit issuance for all three units. The testing since 2000 shows that the 

actual emissions to the environment were as follows: 

Furnace 

POM Total Fluoride*

AVG. 

Emissions 

Max 

Emissions 

AVG. 

Emissions Max Emissions 

lbs/GT lbs/hr lbs/GT lbs/hr lbs/GT lbs/hr lbs/GT lbs/hr

Common 

Exhaust Stack 

0.059 1.200 0.133 2.870 0.006 0.239 0.029 0.730

*lbs/hr emissions only reflect 2011-2013, but are representative of highest emission rate.

Also, under the methodology that Century must now use to demonstrate compliance, there have actually 

been test events where the combined emissions from the stack were measured as being below the 

allowable new source limit, but the new source (Building #3) was calculated as out of compliance with the 

new source limit due to over control of the emissions from the two existing sources.2 This is illustrated by 

the stack test data from May 23, 2011, below. 

Date Stack

(lbs POM/GT) 

Building#1 - Existing 

(lbs POM/GT) 

Building #2 - Existing 

(lbs POM/GT) 

Building #3 - New

(lbs POM/GT) 

2/17/2011 0.05 0.06 0.03 0.054

5/23/2011 0.04 0.02 0.04 0.071

8/25/2011 0.04 0.06 0.06 0.003

6/21/2012 0.13 0.13 0.09 0.172

11/13/2012 0.04 0.05 0.03 0.015

5/31/2013 0.10 0.11 0.12 0.078

8/20/2013 0.06 0.04 0.03 0.091

11/15/2013 0.03 0.05 0.03 0.018

In all stack tests to date, Century’s control system reduces HAP emissions on a combined mass basis 

beyond that required by PMACT had each unit been controlled separately. For example, the allowable 

2

 This may be caused by variability in one or more of the tested parameters or due to the dry scrubber 

receiving variable loading from the existing units and the new furnace. 
 

Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

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emissions of POM of three separate furnaces as shown above would be 3.64 lbs/hr at the permitted 

maximum production rate. Century’s actual worst-case emission rate performance since the beginning of

the PMACT for the three sources ducted to the same control device was 2.87 lbs/hr of POM, and the 

average emissions of POM have been 1.20 lbs/hr. 

Regulatory Support for Proposed Amendments

As aluminum plants in the United States age, they may rebuild their carbon bake sources and 

subsequently may meet the definition of “modified” or “reconstructed”. These modified or reconstructed 

sources can potentially be ducted to a control device that also controls “existing” sources. 

Century believes that there is precedent in the original NESHAP language in 40 CFR Part 63 Subpart LL 

to support its requested amendments. 40 CFR 63.845 was written to allow additional cells to be added to 

an existing potline. 40 CFR 63.845 allows recalculation of the permit limit for potlines based on the

fraction of the potlines total aluminum production capacity that is contained within all modified, 

reconstructed, or new potroom groups and, of course, ducted to a common control device. In the final 

PMACT rule preamble, EPA noted that because there were “many variations in the configuration of 

potrooms and potlines in the industry” establishing limits for both an NSPS and NESHAP could result in

the confusing situation of duplicative emission limits and unnecessary monitoring obligations for potlines. 

As explained in the final rule preamble, 

To resolve this issue a method was devised in the NESHAP to combine the limit 

for the NSPS potroom group with that for the NESHAP potline based on the 

production capacity of the reduction cells that would be subject to each set of 

limits. The result is a single TF emission limit for the entire potline that maintains 

equivalent stringency, and it has the additional advantage of allowing the use of 

the NESHAP potline requirements for monitoring, reporting and recordkeeping to 

avoid unnecessary duplication. 

62 Fed. Reg. 52384, 52394 (Oct. 7, 1997). 

Accordingly, the unique circumstances of the design and operation of the three carbon bake furnaces at

Century’s Hawesville facility justify amending the regulation to create an emission limit for the common 

stack that represents an emission limitation of “equivalent stringency” to PMACT standards as applied on 

a common control basis for a new and existing furnaces. 

As EPA noted in the TSD, several design factors for carbon bake furnaces, such as combustion 

conditions in the flues (temperature, oxygen content, residence time, mixing) affect the quantity of 

hydrocarbons in the flue entering the control device. That in turn can affect the overall control efficiency 

and certainly the ultimate emission rate of POM. Accordingly, the differing flue combustion conditions 

among existing and new anode furnaces result in flue conditions to a common control device that are not 

reflective of a new carbon bake furnace. EPA’s new source MACT determination for POM was based 

upon very limited testing at a single facility with low POM inlet concentrations as compared to other 

facilities. TSD at App. B, B-7. Century is the only primary aluminum facility that is subject to a new 

source MACT standard for an anode bake furnace. Therefore, it is appropriate to allow facilities with

existing and new carbon bake furnaces controlled by a common dry alumina scrubber to determine 

compliance with new source POM standards through a weighted average equivalent emission limit. As 

EPA noted in the proposed PMACT with respect to emissions averaging for existing sources: 

Consistent with EPA policy on regulatory flexibility . . . , the use of emissions 

averaging under this rule should reduce pollution as well as benefit regulated 
 

Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

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entities. Compliance through averaging is expected to achieve somewhat 

greater emissions reductions than would occur without averaging. 

The same rationale applies equally here. 

Establishing an amended emissions standard for the common stack on the three carbon bake furnaces at 

Century's Hawesville facility is further justified by the small universe of primary reduction plants in the 

United States that are subject to PMACT and the considerable variation in the configuration of units at 

those sources.3

 Specifically, Section 112(d)(1) of the Clean Air Act provides that EPA may distinguish 

among classes, types, and sizes of sources within an industrial category in establishing MACT standards. 

That includes such factors as differences in air pollution control technologies and configurations and

opportunities for further pollution prevention. 

Accordingly, Century proposes that the PMACT be modified to include the following language: 

63.844(e) Equivalent Emission Limit for new anode bake furnaces sharing a common control 

device with existing anode bake furnaces. 

(1) This provision applies to new anode bake furnaces ducted to a common control device that is 

shared with one or more anode bake furnaces that elect to be subject to an equivalent emission limit 

established pursuant to this section in lieu of the separate limits under 63.843(c) and 63.844(c). 

(2) On each anniversary date of the start-up of the new source, the following production weighted 

calculations shall be performed: 

EL (TF) = ((EL1 x P1) + (EL2 x P2))/(P1 + P2) 

EL (POM) = ((EL1 x P1) + (EL2 x P2))/(P1 + P2) 

Where: 

EL (TF) = Combined emission limit for Total Fluoride 

EL (POM) = Combined emission limit for Polycyclic Organic Matter 

EL1 = New source emission limit 

EL2 = Existing source emission limit 

P1 = Monthly average new source production 

P2 = Monthly average existing source production 

(3) The owner or operator of a new anode bake furnace that is controlled by a dry scrubber that 

also controls emissions of TF and POM from one or more existing anode bake furnaces shall not 

discharge or cause to be discharged into the atmosphere any emissions of TF or POM in excess of the 

limits established pursuant to paragraph (e)(2) of this section. 

 

3

 The 1996 proposed rule states that, at that time, there were 23 primary aluminum plants in 14 states. 

61 Fed. Reg. 50586, 50587 (Sept. 26, 1996). Of those, 17 used pre-bake technology. Dev. Doc. At pp. 

2-5, 3-20, 3-21. Of the 17, five plants used dry alumina scrubbers (injection type) for control of anode 

bake furnaces. Id. at 3-21. Today there are 8 primary aluminum plants in operation in 5 states. None 

of the remaining plants have bake furnaces that are subject to the new source MACT. 
Century Aluminum of Kentucky ◊ 1627 State Route 3543 ◊ Hawesville, KY 42348 ◊ P - (270) 852-2880 ◊ F - (270) 852-2883 

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* * * * * 

In conclusion, Century believes the unique circumstances of the design and construction of the common 

control device on its new source anode bake furnace at its Hawesville facility justifies amendment of the 

PMACT as part of the seven year review to establish an equivalent common stack control standard. 

Such a standard would be protective of the environment because it would provide for over control of 

HAPs, as compared to the application of individual emission limits to each of the three furnaces. 

Establishment of an equivalent common stack standard would also eliminate the complications of the 

currently approved testing and compliance demonstration method. 

EPA’s favorable consideration of this proposal would be greatly appreciated. Please feel free to contact 

me directly if you have questions or need further information regarding this proposal. 

Sincerely, 

Sean T. Lane, CSP, CHMM 

Environmental Manager 

CC: Danny Carroll, Century Aluminum – Sebree Works 

Jason Young, Century Aluminum – Sebree Works 

Sean Byrne, Century Aluminum – Hawesville 

Jamie Coomes, Century Aluminum – Hawesville 

John Hoerner, Century Aluminum 

Michael Serafini, Century Aluminum 

Chuck Johnson, Aluminum Association 

Sean Alteri, KY Division for Air Quality