Revised Best Available Retrofit Technology (BART) Analysis for SO2 at ASARCO Hayden –

Converters 1, 3, 4, and 5 (Revised June 2014) 

I. Source Description

Owner/Operator: ASARCO Incorporated (formerly American Smelting And Refining 

Company), a wholly owned subsidiary of Grupo Mexico S.A. de C. V.

Source Type: Batch –process copper smelting and converting (SIC 3331)

BART Units: Converter #1 (SCC 3-03-005-04)

Converter #3 (SCC 3-03-005-04)

Converter #4 (SCC 3-03-005-04)

Converter #5 (SCC 3-03-005-04)

The Environmental Protection Agency (EPA or we) has updated the BART analysis for 

converters #1 and #3-5 at the ASARCO Hayden Smelter based on additional information 

received by EPA following publication of our proposed BART determination on February 18, 

2014.

1 For a description of the facility and BART Units please see the Technical Support 

Document that accompanied that proposed rulemaking.

II. Baseline Emissions

Our assessment of baseline SO2 emissions from the converters remains unchanged from the 

proposal.

Table I: BART Baseline SO2 Emissions in TPY

Converters

Acid Plant Secondary Capture Uncaptured

SO2 1,034 20,341 1,209

III. SO2 BART Evaluation for the Converters

Step 1: Identify all Available Technologies

EPA initially identified two possible control technologies for controlling SO2 emissions from the 

converters: a double contact acid plant and a wet alkali scrubber. Commenters on EPA’s 

proposal, including National Parks Conservation Association and ASARCO identified a third 

possibility: amine scrubbing (e.g. Cansolv)

Because SO2 emissions captured by the primary capture system are already controlled by a 

double contact acid plant, we evaluated potential upgrades to the existing plant, as well as the 

 

1 79 FR 9318.
possibility of adding a tailstack scrubber to the existing acid plant. For emissions from the 

secondary capture system, we evaluated the use of a double contact acid plant, traditional 

scrubbing, and amine scrubbing. 

Double Contact Acid Plant

A double contact acid plant uses a solid state catalyst to convert SO2 to SO3, which reacts with 

water to form sulfuric acid. Sulfuric acid plants typically are designed to control feed streams 

containing several percent SO2 so the exothermic catalytic reaction can operate autothermally. 

However, acid plants can be designed to process feed streams that contain only a fraction of a 

percent of SO2, although it may be necessary to heat the inlet gas stream or the catalyst. In 1984, 

EPA reported that SO2 conversion rates of 99.8 percent and above can be achieved by double 

contact acid plants operating in steady state.2

There are two types of catalysts used in double contact acid plants. The traditional catalyst uses a 

potassium/vanadium salt mixture on a silica substrate. The other is a cesium promoted catalyst, 

where some of the potassium in a traditional catalyst is replaced with an equal molar quantity of 

cesium. According to Monsanto, the cesium promoted catalyst is more stable, less prone to 

deactivation, and active at lower temperatures. Traditional and cesium promoted catalysts can be 

used in combination, typically in the first and fourth passes of a double contact acid plant.3

As noted above, ASARCO Hayden currently uses a double contact acid plant to control SO2

emissions captured by primary capture system. ASARCO reports that approximately 30 percent 

of the catalyst used in the first and fourth passes is cesium promoted.4

Wet Alkali Scrubbing

Wet alkali scrubbing involves the reaction of SO2 with liquid phase absorbents to yield sulfur 

compounds that can be sold, reprocessed, or discarded. The absorbent can be based on lime

(calcium oxide, CaO) or caustic (sodium hydroxide, NaOH). Wet alkali scrubbing is commonly 

used in many industries for control of SO2. Alkali scrubbing produces sulfite (SO3

2-

) or bisulfite 

(HSO3

-

) salts as a waste product.

Amine Scrubbing

An amine scrubbing system, such as the Cansolv ® system, uses an aqueous amine solution to 

absorb SO2 from gas streams. The process is regenerable, as the amine absorbent is not 

consumed in the process. SO2 absorbed by the process is stripped and introduced to the acid 

plant. 

 

2

“Review of New Source Performance Standards for Primary Copper Smelters,” US EPA, Office of Air Quality 

Planning and Standards, March 1984, EPA 450/3-83-018a.

3 Letter from Jack Garrity, ASARCO to Thomas Webb, EPA, Item #8 (January 25, 2013).

4 Letter from Jack Garrity, ASARCO to Thomas Webb, EPA, Item #7 (January 25, 2013).
Step 2: Eliminate Technically Infeasible Options

According to information provided by ASARCO, double contact acid plants, wet alkali

scrubbing, and amine scrubbing are all technically feasible for the secondary capture system.

5 A 

double contact acid plant is already in use on the primary capture system.

Step 3: Evaluate the Control Effectiveness of Each Remaining Technology

In its July 11, 2013 response to EPA’s June 27, 2013 information request, ASARCO indicated 

that its double contact acid plant, which controls emissions from the primary capture system, was 

capable of recovering 99.81 percent of the SO2 vented to it.6 The expected control effectiveness 

of wet alkali scrubbing and amine scrubbing as well as a double contact acid plant on the 

secondary capture system was provided by ASARCO in the February, 2014 letter from GCT.

These values are as follows:

Control Technology SO2-Reduction Effectiveness

Double Contact Acid Plant 98.81% on primary, 96% on secondary

Wet Alkali Scrubber 90 – 95 %

Amine Scrubber “close to 99%”

Step 4: Evaluate Impacts

Factor 1: Cost of Compliance

We calculated the cost to control SO2 collected by the secondary capture system with an acid 

plant, a wet alkali scrubber, and an amine scrubber. We also calculated the addition of a tailstack 

scrubber to the existing acid plant that controls SO2 collected by the primary capture system.

Double Contact Acid Plant to Control Secondary Capture System

EPA had previously calculated the cost of construction for an acid plant for the secondary 

capture system using an equation published in the1984 review of the NSPS for primary copper 

smelters, page 8-13.

7

In the February, 2014 letter from GCT to ASARCO, some refinements to 

the cost estimate were provided.

We applied a control efficiency of 96 percent, which GCT indicated as possible to ASARCO. 

The emission reduction was applied to the secondary capture system baseline emissions.

Control 

Effectiveness

Tons SO2

Reduced

Capital Cost Annualized 

Capital Cost

Annual 

Variable Cost

Total Annual 

Cost

$/ton SO2

Removed

96% 19,527 $163,242,594 $15,408,946 $18,169,779 $33,578,725 $1,720

 

5 Letter from GCT to Jack Garrity, ASARCO (February 12, 2014).

6 Letter from Jack Garrity, ASARCO, to Thomas Webb, EPA (July 11, 2013).

7 Review of the New Source Performance Standards for Primary Copper Smelters. U.S. EPA, Office of Air Quality, 

Planning, and Standards. March, 1984. EPA 450/3-83-018a
Wet Alkali Scrubber to Control Secondary Capture System

EPA calculated costs of constructing and operating a wet scrubber to control SO2 from the 

secondary capture system based on information from ASARCO.

8

Control 

Effectiveness

Tons SO2

Reduced

Capital Cost Annualized 

Capital Cost

Annual 

Variable Cost

Total Annual 

Cost

$/ton SO2

Removed

90% 18,307 $28,000,000 $2,643,002 $14,000,000 $16,643,002 $909

According to ASARCO, these costs do not include the cost of treating or landfilling sludge that 

is classified as hazardous waste, which it considers likely. If the sludge is hazardous waste, this 

will increase the annual cost by at least $7,000,000.

Amine Scrubber to Control Secondary Capture System

Based on estimates of capital and operating costs for an amine scrubber provided by ASARCO,9

EPA calculated the $/ton of SO2 removed from the secondary capture system. We applied a 

control efficiency of 98.5% for an amine scrubber, which we consider to be reasonable and 

conservative, given that Cansolv has indicated that such a scrubber could achieve “close to 99%”

removal efficiency for this application.10

Control 

Effectiveness

Tons SO2

Reduced

Capital Cost Annualized 

Capital Cost

Annual 

Variable Cost

Total Annual 

Cost

$/ton SO2

Removed

98.5% 20,036 $85,000,000 $8,023,399 $9,300,000 $17,323,399 $865

EPA’s complete cost calculations are available in the docket.11

Wet Scrubber to Control Acid Plant Tailstack

EPA calculated costs of constructing and operating a wet scrubber to control SO2 from the 

existing acid plant tailstack based on information provided by ASARCO.12 In this case we used 

the low-end estimate of operating costs. We also included a sludge hauling fee of $60 per ton and 

assumed one ton of SO2 controlled would result in five tons of sludge.

Control 

Effectiveness

Tons SO2

Reduced

Capital Cost Annualized 

Capital Cost

Annual 

Variable Cost

Total Annual 

Cost

$/ton SO2

Removed

85% 879 $28,000,000 $2,643,002 $9,274,521 $11,917,523 $13,564

 

8 Letter from Jack Garrity, ASARCO, to Thomas Webb, EPA (July 11, 2013); Email from Jack Garrity, ASARCO 

to Geoffrey Glass, EPA (May 19, 2014).

9

Id. 

10 Letter from GCT to Jack Garrity, ASARCO (February 12, 2014).

11 BART Analysis of Control Options for ASARCO Hayden – June 2014.xlsx

12 Letter from Jack Garrity to Thomas Webb (July 11, 2013).
Again, these costs do not include the cost of a booster fan or a modified stack that may be 

needed. Although the calculation includes the cost hauling sludge off site, it does not include the 

cost of treating or landfilling the sludge, which may be classified as hazardous waste depending 

on the metals content. In addition, we note that some of the SO2 that passes through the acid 

plant was emitted by the flash furnace which is not BART eligible.

Factor 2: Energy Impacts

Operation of a sulfuric acid plant at the ASARCO Hayden smelter would require energy to heat 

inlet air from approximately 177° F to 735° F. EPA estimated that this would require a heat input 

of approximately 114 MMBtu/hr and could require 1,200 MMscf of natural gas per year, 

resulting in up to 30 tpy NOx emissions.13 GCT estimated emissions of NOx closer to 40 tons per 

year.14 This assumes 100 percent of the needed heat resulted from natural gas combustion.

Operation of an amine scrubber would require the installation of a boiler capable of producing 30 

tons-per-hour of low quality steam to strip SO2 from the absorbent solution. ASARCO estimated 

this would result in NOx emissions of about 12.5 tons per year.15

Factor 3: Non-air Quality Environmental Impacts

Non-air quality environmental impacts from a second acid plant are not expected to be 

significant given that ASARCO already has the capacity to handle and store the much larger 

quantities of sulfuric acid produced by the primary acid plant.

Addition of a scrubber would result in sludge which would have to be shipped off site to be 

treated or landfilled. Because of metals in the sludge, it may need to be treated as hazardous 

waste.

ASARCO did not identify any significant non-air environmental impacts resulting from 

construction or operation of an amine scrubber.

Factor 4: Remaining Useful Life

The BART-eligible converters have each been in place for approximately 40 years or longer.

Although ASARCO has identified replacement of the existing converters as part of their plan to 

bring the Hayden Area into attainment with the one-hour SO2 NAAQS, ASARCO has not 

committed to removal of these units. Therefore, we have assumed that these units have a 

remaining useful life of at least twenty years. 

 

13 Based on the AP 42 factor for low NOx burners

14 Letter from GCT to Jack Garrity, ASARCO (February 12, 2014)

15 Email from Jack Garrity, ASARCO to Geoffrey Glass, EPA (May 19, 2014)
Step 5: Visibility Impacts

We previously calculated visibility improvements for a 99.81 percent reduction is SO2 emissions 

from the secondary capture system as part of the proposed rulemaking (79 FR 9318, February 

18, 2014).16 The 98.5 percent control efficiency achievable by the amine scrubber is lower than 

the 99.81 percent assumed in our proposal, and yields visibility benefits that are 1.5% 

lower.17 The visibility benefits are so large that this changes makes a negligible difference, and 

does not affect our BART determination.

98th Percentile Visibility (DV)

(2001-2003)

Days Modeled > 0.5 DV

(2001-2003)

Base Amine Scrubber Base Amine Scrubber

Chiricahua NM 1.02 0.14 117 0

Chiricahua WA 1.04 0.15 112 0

Galiura WA 1.76 0.28 239 2

Gila WA 0.69 0.09 52 0

Mazatzal WA 0.88 0.13 73 0

Mount Baldy 

WA

0.66 0.09 40 0

Petrified Forest 

NP

0.68 0.10 43 0

Pine Mountain 

WA

0.67 0.10 42 0

Saguaro NP 1.28 0.18 108 0

San Pedro Parks 

NP

0.44 0.06 13 0

Sierra Ancha 

WA

1.09 0.15 83 0

Superstition WA 1.74 0.27 197 2

Sycamore 

Canyon WA

0.51 0.07 23 0

Conclusion

We identified three possible control strategies to reduce SO2 emissions from the converters :

1. Control of the secondary capture system by a double contact acid plant.

2. Control of the secondary capture system by a wet alkali scrubber.

3. Control of the secondary capture system by an amine scrubber

4. Control of acid tailstack emissions by a wet scrubber.

 

16 79 FR 9318, February 18, 2014

17 See spreadsheet in docket, ASARCO_scaled_benefit.xlsx
Option #4 is ruled out because of cost (> $13,000/ton SO2). Ranking the other three options in 

order of effectiveness:

Control Control 

Effectiveness

Tons SO2

Reduced

Total Annual 

Cost

$/ton SO2

Removed

Incremental Cost 

Effectiveness ($/ton)

Amine Scrubber 98.5% 20,036 $17,323,399 $865

Acid Plant 96% 19,527 $33,578,725 $1,720 -$31,966

Alkali Scrubber 90% 18,307 $16,643,002 $909 $394

Because it would be both more expensive and less effective at removing SO2 compared to an 

amine scrubber, an acid plant for the secondary capture system is an inferior option. Therefore, 

we are ruling out construction of a new acid plant as BART for the secondary capture system. 

With regard to the remaining two options, we note that ASARCO has indicated that it believes 

the secondary gas stream would be “more practically controlled by caustic [alkali] scrubbing” 

than an amine scrubber. However, the cost and control effectiveness estimates provided by 

ASARCO do not support this contention. In particular, while the total annual cost of an alkali 

scrubber is higher than that of an amine scrubber, the amine scrubber is more cost effective on 

$/ton basis due to its higher control effectiveness. We further note that if alkali scrubber sludge 

had to be treated as hazardous waste, which ASARCO had indicated was likely, the total 

annualized cost of an alkali wet scrubber would actually be greater than the total annualized cost 

of an amine scrubber. (According to cost data provided by ASARCO, the annual operating cost 

of an alkali scrubber would be greater than the annual operating cost of an amine scrubber. See 

above.)

Furthermore, an amine scrubber would have greater visibility benefits than an alkali scrubber 

because it would result in lower emission rates. Although the energy usage of amine scrubber 

would be greater, we consider the amount of energy required to be reasonable in light of its 

greater effectiveness. In addition, an amine scrubber would have fewer non-air environmental 

impacts than an alkali scrubber, which would not result in the creation of potentially hazardous

sludge. 

Based on consideration of the five BART factors, we have determined that a level of control 

equivalent to an amine scrubber constitutes BART for the secondary capture system. We express 

the limit in terms of a mass-based control efficiency (i.e. rolling 365-day percent reduction)

because of the high variability in SO2 concentration vented to a control device during batch 

operations. A concentration based limit (e.g. ppm) would allow the owner or operator to 

demonstrate compliance by including in the averaging calculations many hours with low outlet 

concentrations because of low inlet concentrations.

With regard to the primary capture system, we are finalizing our proposed determination that use 

of the existing double contact acid plant constitutes BART. In our proposal, we noted that 

ASARCO had indicated that its double contact acid plant is capable of recovering 99.8 percent of 
the SO2 vented to it.18 In its comments to EPA, ASARCO noted that this figure is an annualized

performance estimate for the acid plant and therefore is not an appropriate basis for setting a 30-day 

rolling average control efficiency.

19 Therefore, we are revising the proposed limit from a rolling 

30-day limit to a rolling 365-day limit.

We are requiring the following as BART for SO2 for the converters :

1. An SO2 control efficiency of 99.8 percent, 365-day rolling average, on all SO2 captured 

by the primary control system. 

2. An SO2 control efficiency of 98.5 percent, 365-day rolling average, on all SO2 captured 

by the secondary control system.

3. Compliance with each SO2 BART limit may be verified either through the use of SO2

CEMS before and after controls in each system or by monitoring acid production and the 

use of outlet SO2 CEMS.

4. Operation and maintenance of primary and secondary capture systems meeting the 

requirements of 40 CFR 63, subpart QQQ, as it applies to Peirce Smith converters. 

 

18 79 FR 9344 (citing Letter from Jack Garrity, ASARCO to Thomas Webb, EPA, July 11, 2013.

19 ASARCO Comment Letter at 13-14 (March 31, 2014).