1

MEMORANDUM

To: David Putney, U.S. Environmental Protection Agency (EPA) , OAQPS

From: David Green, RTI

Date: October 31 , 2011

Subject: Draft MACT Floor Analyses for the Primary Aluminum Production Source Category

This memo describes the data and calculations supporting the proposed MACT floor determination s for Primary Aluminum Reduction Plants, beyond the floor analyses, and the estimated impacts of these options. MACT floors were established for the following three previously unregulated hazardo us air pollutant (HAP) sources at primary aluminum plants:

1

. Polycyclic o rganic m atter (POM) e missions from p rebake p otlines

2

. Carbonyl s ulfide (COS) e missions from p rebake and Soderberg p otlines

3

. POM e missions from existing p itch s torage t anks

POM Emissions from Prebake Potlines

MACT Floor Determination

Limited data were available for emissions of POM from prebake potlines because these emissions are not regulated under the 1997 NESHAP, and no testing of these emissions has been done in recent years. Primary POM emissions are presently controlled with dry alumina scrubber/baghouse systems which also control total fluoride (TF). With regard to secon dary emissions from vents in the roof of the potrooms, typically there are no add

- on control devices (with the exception of one facility that operates a wet roof scrubber). However these emissions are limited to some degree by minimizing the opening of
the pots and , thereby, maximizing the potline fume capture efficiency.

MACT floors for existing prebake potlines were determined for emissions of POM from prebake potlines using test data cited in the Technical Support Document for the 1997 NESHAP (Primary

A luminum Industry: Technical Support Document for Proposed MACT Standards, US EPA, July 1996). This report included estimates of POM/TF ratios for the sum of primary and secondary emissions from prebake potrooms of various types. The ratio applicable to c en ter

- w orked p rebake one (CWPB1)

p otlines and s ide

- w orked p rebake (SWPB) potlines is 0.3 whereas the ratio applicable to CWPB2 and CWPB3 potlines is 0.5. Using these ratios and TF emissions reported in calendar year 2010 , POM emissions were estimated for currently operating prebake potlines. These data are shown in Table 1. The

MACT f loor for existing sources is calculated based on the average emissions of the 5 best performing facilities plus an amount to account for var iability. This accounting for variability is usually accomplished by using the 99

- percent u pper p rediction l imit (UPL)

. The next step in the MACT floor analysis was to account for data variability in the c alculat ions of the applicable MACT floor limit s for the subcategories using the data’s 99% upper prediction limit (UPL)

. Specifically, the MACT floor limi t was determined as the UPL calculated with the Student’s t

- test using the “ TINV ” function in Microsoft
Excel software. The UPL approach has also been us ed in other EPA rulemakings (e.g., NESHAP for Portland Cement, NSPS for Hospital/Medical/Infectious Waste Incinerators, NESHAP for Industrial, Commercial, Institutional Boilers and Process Heaters , and NESHAP for Electric Generating Units ) to2

account for variability in emissions data for a specified level of confidence

. The level of confidence represents the level of protection afforded to facilities whose emissions are in line with the best performers. For example, a 99% level of confidence means that a f acility whose emissions are consistent with the best performers has one chance in 100 of exceeding the floor limit

. A prediction interval for a single future observation (or an average of several test observations) is an interval that will, with a specifie d degree of confidence, contain the next (or the average of some other pre

- specified number of ) randomly selected observation (s) from a population. In other words, the upper prediction limit estimates
what the upper bound of future values will be, based up on present or past background samples taken

. The UPL consequently represents the value at which we can expect the mean of future observations for
the HAP emissions to fall within a specified level of confidence, based upon the results of an independent sam ple from the same population

. This method accounts for the point

- to

- point variability in
the data set

. The form of the UPL equation differs somewhat depending upon the number of data points and data distribution to which it is applied. Attachment B includes a flow diagram that summarizes the UPL approaches used. To th is end, the data sets were evaluated for each HAP to ascertain whether the data were normally distributed, or fit another type of distribut ion ( e.g. , log normal distribution )

. According to the Central Limit Theorem (Durrett, 1996), when a data set includes 15 or more sources, the UPL is based on the assumption that the data fit a normal distribution. The C entral L imit T heorem states that regardless of the shape of the original distributi on, if the distribution has a finite mean ( μ ) and variance ( σ2 ), the sampling distribution of the mean approaches a normal distribution with a mean of (μ) and a
variance of σ2/N as N, the sample size, increases 1 (Durrett, 1996)

.
The facility averages of es timated POM emissions were used to calculate the 99% UPL for the POM
MACT emissions limits applicable to prebake potlines

. Only 2 facilities have CWPB2 and CWPB3 type potlines. Each of those facilities has 4 currently operating potlines. Only 1 facility has SWPB potlines and only 2 of those potlines are currently operating. Therefore, the 99

- percent UPL for the POM
emissions from CWPB1 facilities is based on inter

- facility variability (i.e., the variability between CWPB1 type facilities) whereas the 99

- percent UPL for the POM emissions from CWPB2, CWPB3 and
SWPB facilities is based on intra

- facility variability (i.e., the variability between potlines located w ithin the same production facility )

.

Using the methods described above, t he calculated POM MACT f loor emission limits for existing prebake potlines are 0.6 2 pounds POM per ton of aluminum produced (lb /ton Al ) , 1.3 (lb /ton Al ) , 1.26 (lb /ton Al ) , and 0. 65 ( lb /ton Al ) for CWPB1 , CWPB2, CWPB3 and SWPB potlines , respectively . T he
lowest of these POM standard s [i.e., 0. 62 (lb /ton Al ) ] is proposed as the MACT floor emission limit for all new prebake potlines

.

Impacts at MACT Floor Level

Particulate emissions from prebake potlines are currently well controlled via the associated controls (e.g., dry alumina scrubbers, wet scrubbers and baghouses ) . Therefore, we expect that all prebake facilities presently in operation would be able to compl y with the POM MACT floor emission limits without any additional controls. An estimated 50% of the TF emissions from the Primary Aluminum Production source category is in particulate form and it is expected that much of the POM from this
source category is also in particulate form at the exhaust temperatures of control device stacks ( typical ly
less than 180 degrees Fahrenheit (°F)) and potroom vents ( typical ly less than 100 °F) . While no
additional control costs would be expected to comply with the MACT f l o or limits , the proposed rule

1 Durrett, R. Probability: Theory and Examples. Cambridge. (1996).3

w ould require periodic demonstration s of compliance with the appropriate POM emission limit

. Assuming compliance testing would be required for each potline once every five years and that t his
demonstration can be made either by 1) summing the results of emission tests on the primary control system exhaust and the secondary (roof vent) emissions or, 2) summing the results of an emission test on the primary control system exhaust and the estimated secondary emissions ( based on t he secondary emissions exhaust volume, the secondary TF emission rate and the ratio of POM to TF present in the primary control system exhaust , we estimate that the 12 prebake type facilities w ould need to conduct performance tests for POM emissions from p rebake potlines on 45 prebake potlines every 5 years at an
estimated cost of $10,000 per test

, for an average annual cost of $ 7

, 5 00 per prebake facility or $ 90, 000 total annual cost for the industry

.

Beyond the Floor Analys i s

It is estimated that more than 2/3 of the potline POM emissions are emitted as secondary emissions (i.e., emitted through the roof vents). Since secondary POM emissions are comprised of high

- volume, low

concentration emissions stream s , additional control s are e stimated to be very e xpensive. A cost estimate was prepared for the installation of wet roof scrubbers on a Soderberg plant, which has considerably higher POM emissions. It was estimated that capital costs would be $42 million and total annual costs (including capital recovery ) would be $13.1 million. POM reductions of 40 tons per year were estimated for this system. However , since prebake facilities have much lower POM emissions, emissions
reductions of no more than about 15 tons per year of POM would be expected for prebake f acilities

. Therefore, we estimate a cost

- effectiveness of approximately $ 800,000 per ton of POM for installation
of wet roof scrubbers on a prebake plant

.

COS Emissions from Potlines

MACT Floor Determination

Carbonyl sulfide (COS) is emitted from potlines at primary aluminum manufacturing facilities . Sulfur
present as an impurity in anodes is emitted either as SO 2 or COS. Industry representatives have reported
that most (an estimated 90%) of the sulfur is converted to COS in the bath, with most (an estimated 90%) of the COS oxidizing to SO 2 in the pots and associated hooding and ductwork before it is emitted
from the control device stack . COS is not well controlled by the existing control d evices used for potline emissions (typically dry alumina scrubbers and wet scrubbers). Anodes are produced for prebake
facilities (which represent all but one of the currently operating primary aluminum facilities ) from a
paste comprised of pitch and coke. Available data 2

, 3 and information submitted by industry indicates that essentially all of the sulfur in prebake electrodes originates in the coke, and that the sulfur present in the pitch is lost in the anode production process. R ecent COS emission test d ata are limited, and inadequate
for calculating a COS emission limit directly

. Primary aluminum production facilities estimate their
COS emissions based on the sulfur content of anode coke, the coke content of the anodes, the mass of anode consumed per ton of aluminum produced, and a fractional sulfur to COS conversion rate (reported by industry to range from 4. 5 to 1 0 % . T he remain ing sulfur is converted to SO 2

.

EPA sent an information collection request (ICR) to the primary aluminum production companies in April, 2011 which included requests for data on the typical sulfur content of coke used in anode production, the range of anode coke sulfur contents over the last year or the last twelve months , and

2 Hay, S. J. The Formation and Fate of Carbonyl Sulfide (COS) Gas in Aluminum Smelting. Ph. D Thesis. University of Aukland. Aukland, New Zealand. (2002)

3 Hay, S. J. The Influence of Dry Scrubber Alumina and Hu midity on COS Smelter Emissions. Light Metals, p. 289

- 296. (2002)4

information on the methods used to estimate COS emissi ons . Typical anode coke sulfur contents and
fractional sulfur to COS conversion rates were provided by 9 operating primary aluminum facilities

. W e used an industry average anode coke content of 78% and anode consumption rate of 0.57 tons of green anode per ton of aluminum produced

. These industry average values were provided by The Aluminum Association (a trade group for primary aluminum companies) . These data were used to calculate estimated facility wide COS emission s

. COS emissions were calculated on the basis of the lowest (4.5%) and highest (10 % ) reported sulfur to COS conversion rate s. The facilities were ranked in ascending order of estimated COS emissions

. Data used in the analysis are summarized in Table 2. The
COS emissions are calculated as a faci lity wide monthly average since the facilities track their anode coke sulfur content levels on a monthly average basis and each aluminum production facility ha s only one paste production facility that supplies the anode paste for all of the ir potlines.

Th e 5 facilities with the lowest estimated COS emissions were designated as the best performing
facilities for existing source COS MACT floor determination. Using the 99% UPL method to account for variability , we calculate that t he MACT floor limit for exist ing facilities is 3.9 lb COS per ton of aluminum produced. The COS MACT floor for new sources was calculated based on the emissions of the top performing facility. Using the 99% UPL method to account for variability , we calculate that t he
MACT floor limit for new facilities is 3.1 lb COS per ton of aluminum produced.

Impacts at MACT Floor Level

It is expected that all primary aluminum production facilities presently in operation would be able to compl y with the existing source COS MACT floor emission limi t without any additional controls. The owner or operator will be required to demonstrate compliance on a monthly basis via a mass balance equation with 3 variables: anode consumption rate, aluminum production rate, and anode coke sulfur

content. However, t he owner or operators of the affected facilities already monitor all 3 variables. Therefore, w e estimate that there would be n o emission reductions or cost impacts due to th e proposed
COS MACT floor limit

. However, industry representatives have indicated that they expect the sulfur content of available petroleum coke to increase in the future due to changes in refinery operations. Therefore, it is possible that compliance costs will increase. Industry repre sentatives provided the following documents to support their position:

1

. The Minerals, Metals & Materials Society, 2004. “ A Preview of Anode Coke Quality in 2007 ,” Franz Vogt, Robert Tonti, Maia Hunt, Les Edwards. pp. 489 through 493.

2

. The Minerals, Metals & Materials Society, 2011. “Analysis on the Market Developing Conditions of Prebaked Carbon Anodes for the Aluminum Industries,” Guanghui Lang, Chunyu Fu, Ronald Logan, Yan Li. pp. 163 through 166.

3

. The Minerals, Metals & Materials Society, 2009. “Use of Sho t Coke as an Anode Raw Material” Les Edwards, Franz Vogt, Mike Robinette, Ric Love, Anthony Ross, Marilou McClung, RJ Roush, William Morgan. pp. 985 through 990

.

4

. McCloskey 6 th Petcoke Conference, May 2008

. “Petcoke and its role within the aluminum industry ,” Calvin Graham. pp. 1 through 99.

Based on the submitted information, it is possible that lower sulfur content anode coke will increase in price in the future and that the MACT floor COS emission limits will , therefore, result in future costs to the prim ary aluminum industry.5

Beyond the Floor Analyses

In regard to beyond the floor analyses for COS emissions, we considered COS emission limits of 3.5 lb COS per ton of aluminum produced and 3.1 lb COS per ton of aluminum produced. Based on current
anode c oke cost data, we estimate that the limits of 3.5 lb COS per ton of aluminum produced and 3.1 lb COS per ton of aluminum produced would impose annual costs of approximately $2 million on two facilities and $13 million on 5 facilities, respectively. We predict these options would reduce COS emissions by 52 tons per year and 224 tons per year, respectively, and result in cost effectiveness of $ 35,000 per ton and $ 57,000 per ton, respectively. Again, based on the submitted information referenced
in the MACT floor discussion above, it is possible that the costs cited in this paragraph for the listed beyond the floor options will increase in the future.

POM Emissions from Existing Pitch Storage Tanks

MACT Floor Determination

The MACT f

loor for control of POM emissions from existing pitch storage tanks was determined based on the responses to the April, 2011 ICR sent to primary aluminum production companies. When an ICR

response was not available

, the type of control equipment was determined from a review of the facility
Title V operating permit. The reported control equipment and estimated efficienc ies are summarized in
Table 3 . Of the 12 facilities operating existing pitch storage tanks, four had some type of controls in place and two additional facilities may have had some type of controls in place. Of the five best
controlled facilities ’ tanks , the median of the estimated control efficiencies is 95%, represented by a fume capture and return syst em accompanied by a charcoal scrubber. The MACT floor for existing pitch storage tanks was proposed on this basis. This is equivalent to the MACT floor for new pitch storage
tanks in the 1997 NESHAP.

Impacts at MACT Floor Level

We estimate that eight fac ilities would be affected by this standard and would need to add controls, at a n annual cost of approximately $ 2 0

, 979 per facility or $167,836 for the industry

. There are no available data on pitch storage tank emissions. Potential emissions were estimated on the basis of vapor displacement during loading. These calculations assumed anode paste was comprised of 22% pitch (the industry average value provided by The Aluminum Association) , a pitch specific gravity of 1.25 and

vapor pressure equal to that of oxidized asphalt at 300 °F (estimates based on available data) and 35% HAP content of methylene chlorid e extractable matter and an average HAP molecular weight of 250 (based on testing conducted at the Kaiser

- Tacoma Soderberg facility) . Estimated emission reductions by facility are summarized in Table 4.

Beyond the Floor Analys i s

The cost effectiveness of control at the MACT floor level is approximately $ 10 8

, 000 per ton of HAP. A

non

- contact, single stage, refrigerated, water cooled condenser system was considered as a beyond the floor option for POM emissions from existing pitch storage tanks. The cost of such a system was estimated at $184,000 per facility, per year, and would affect an additional 2 facilities. The associated incremental reduction of POM emissions from the industry was estimated at 0.1 tons per year, resulting in an estimated cost effectiveness of $ 26 million per ton of HAP

.6 

### Attachment A : Table s

Table 1: Estimated POM emissions from operating prebake potline facilitie s

Facility Name Potline Type Reported facility average

TF e missions (lb/ton Al) Estimated facility average
POM e missions (lb/ton Al)

Alcoa

– Wenatchee Works CWPB1 1.76 0.53

Alcoa

– Warrick Operations CWPB1 1.46 0.44 a

Noranda Aluminum CWPB1 1.38 0.41 a

Alcoa

– Massena Operations (aka Alcoa

– Massena West) CWPB1 0.97 0.29 a

Alumax of South Carolina (aka Alcoa

– Mt. Holly) CWPB1 0.77 0.23 a

Rio Tinto Alcan CWPB1 0.56 0.17 a

Ormet Primary Aluminum CWPB2 2.5 1.3 b

Century Aluminum of

K entucky CWPB3 1.83 0.91 c

Intalco Aluminum SWPB 1.34 0.40 d

a These are the top 5 performers used to establish the existing source POM MACT floor limit for CWPB1 potlines.

b The variability applied in the development of the existing source POM MACT floor limit for CWPB 2 potlines was obtained from estimated POM emissions from this facility of 1.3, 1.1, 1.5 and 1.1 lb POM/ton of aluminum.

c The variability applied in the develop ment of the existing source POM MACT floor limit for CWPB 3 potlines was obtained from estimated POM emissions from this facility of 1.01, 0.86, 0.81 and 0.99 lb POM/ton of aluminum.

d The variability applied in the development of the existing source POM MA CT floor limit for CWPB 3 potlines was obtained from estimated POM emissions from this facility of 1.01, 0.86, 0.81 and 0.99 lb POM/ton of aluminum.7

Table 2: Estimated COS and SO2 emissions

Facility n ame Plant c apacity (ton Al/year) Anode c oke

s ulfur c ontent COS e missions

(lb COS/ton Al) SO2 e missions

(lb SO2/ton Al)

Alcoa

– Warrick Operations 340,600 1.94 % 2.59 a 31.74

Noranda Aluminum 325,000 2.00 % 2.67 a 32.72

Alumax of South Carolina (aka Alcoa

– Mt. Holly) 246,900 2.13 % 2.84 a 34.85

Century Aluminum of KY 269,000 2.20 % 2.93 a 35.99

Alcoa

– Massena Operations (aka Alcoa

– Massena West) 137,788 2.41 % 3.21 a 39.43

Reynolds Metal Company (aka Alcoa

– Massena East) 143,299 2.45 % 3.27 40.09

Alcoa

– Wenatchee Works 202,823 2.60 % 3.47 42.54

Intalco Aluminum 306,439 2.80 % 3.73 45.81

Rio Tinto Alcan 216,051 2.80 % 3.73 45.81

a These are the top 5 performers used to establish the existing source COS MACT floor limit.

Note: %S to COS ranged from 4.5% to 10% and averaged 8%

%S to SO2 ranged from 90% to 95.5% and averaged 92%8

Table 3: MACT floor determination for existing pitch storage tanks

Facility Name Equipment Estimated

c ontrol

e fficiency Notes

Lake Charles Carbon (Alcoa anode plant) Water cooled condenser 99% Condition in Title V permit

Intalco Aluminum Fume capture and return system, condensing tank, carbon bed 95%

Alcoa

- Wenatchee Works Fume capture and return system, scrubber, carbon filter 95%

Alumax of South Carolina (aka Alcoa

- Mt. Holly) TIGG adsorber (carbon filter) 95% No estimate of efficiency in ICR response or Title V permit

Rio Tinto Alcan Two tanks, one empty, not necessarily connected NS No estimate of efficiency in ICR response or Title V permit

Alcoa

- South Plant Three tanks, one empty, not necessarily connected NS No estimate of efficiency in ICR response or Title V permit

Alcoa

- Warrick Operations Two tanks, no controls 0%

Alcoa

- Massena Operations (aka Alcoa

- Massena West) Two tanks, no controls 0%

Century Aluminum of KY Three tanks, no controls 0% BACT analysis estimated costs of control at $18 k

- $ 22 k

/ton POM

Noranda Aluminum Two tanks, no controls 0%

Columbia Falls Aluminum Two tanks, no controls 0% Based on permit conditions

Century Aluminum of WV No controls 0% Based on permit conditions (installation in 1997)

Ormet Primary Aluminum Not operating any pitch storage tanks, no controls on tanks NA Possibly have empty tanks, using dry pitch, or buying anodes

Reynolds Metal Company (aka Alcoa

- Massena East) No active tanks on site NA Possibly have empty tanks

Alcoa

- Rockdale Operations No tanks NA Plant uses dry pencil pitch

Notes: The estimate of control efficiency for the Alumax of South Carolina facility was obtained from the
document EPA/625/6

- 91/014 "Handbook: Control Technologies for Hazardous Air Pollutants."

NS = Not specified. There may be some control achieved

- but no estimate of the e fficiency was made.

NA = Not applicable (i.e., since there are no pitch storage tanks on site).9

Table 4: Estimated emissions reductions from control of HAP emissions from pitch storage tanks

Facility Name Plant Capacity (ton Al/year) HAP Controlled (ton HAP/year)

Rio Tinto Alcan 216, 051 0.1 77

Alcoa

– South Plant 237,000 0. 19 4

Alcoa

– Warrick Operations 340,600 0.2 78

Alcoa

– Massena Operations (aka Alcoa

– Massena West) 137,788 0. 11 3

Noranda Aluminum 325,000 0.2 66

Century Aluminum of K entucky 269,000 0.2 20

Century Aluminum of West Virginia 187,400 0.1 53

Columbia Falls Aluminum 185,200 0. 15 1

Total: 1,898,039 1. 55210 

## Attachment B : MACT Floor Flow Chart