&EPA
United States
Environmental Protection
Agency
"Air
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
February 2002
Hazardous Air Pollutant
Emissions from
Mercury Cell Chlor-Alkali Plants
Background Information Document
for Proposed Standards
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NATIONAL EMISSION STANDARDS FOR
HAZARDOUS AIR POLLUTANTS
FROM MERCURY CELL CHLOR-ALKALI PLANTS
Background Information Document
for Proposed Standards
Emission Standards Divis
U.S. Environmental Protection Agenc*
Region 5, Library (PL- 1 2 J)
77 West Jackson Boulevard, 12th Floor
Chicago. II 60604-3590
u.s. E!;V:RC;;;;ENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Researcn Triangle Par'-:, North C
January 2002
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DISCLAIMER
This report has been reviewed by the Emission Standards Division
of the Office of Air Quality Planning and Standards, EPA, and has
been approved for publication. Mention of trade names or
commercial products is not intended to constitute endorsement or
recommendation for use.
11
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TABLE OF CONTENTS .
page
1.0 INTRODUCTION : . . . . 1-1
1.1 INTRODUCTION 1-1
1.2 STATUTORY BASIS 1-1
1.3 BACKGROUND ON SOURCE CATEGORY 1-3
2.0 INDUSTRY CHARACTERIZATION 2-1
2.1 INTRODUCTION 2-1
2.2 MERCURY CELL CHLOR-ALKALI INDUSTRY PROFILE .... 2-4
2.3 MERCURY CELL CHLOR-ALKALI PROCESS DESCRIPTION . . . 2-6
2.3.1 Mercury Cell Operation 2-7
2.3.2 Product Chlorine Purification 2-11
2.3.3 Brine Preparation System 2-12
2.3:4 Product Caustic Purification ....... 2-13
2.3.5 'By-Product Hydrogen Cleaning 2-14
2.3.6 Wastewater Treatment 2-15
2.4 DESCRIPTION OF MERCURY RECOVERY PROCESSES .... 2-16
2.4.1 Mercury Thermal Recovery Units 2-18
2.4.2 REMERC™ Units 2-21
2.4.3 Batch Purification Still 2-22
2.5 REFERENCES 2-2 6
3.0 EMISSION SOURCES AND CONTROL TECHNIQUES 3-1
3.1 INTRODUCTION 3-1
3.2 BY-PRODUCT HYDROGEN STREAM 3-2
3.3 END-BOX VENTILATION SYSTEM AND END-BOX VENTILATION
STREAM 3-3
3.4 MERCURY THERMAL RECOVERY UNIT OFF-GAS 3-7
3.5 FUGITIVE EMISSIONS AND CELL ROOM VENTILATION . . . 3-7
3.6 VENT CONTROL TECHNIQUES AND SYSTEMS 3-9
3.6.1 Condensation 3-S
3.6.2 Absorption 3-11
3.6.3 Adsorption 3-12
3.6.4 Vent Control Systems 3-13
3.7 EMISSION CONTROL TECHNIQUES FOR FUGITIVE EMISSION
SOURCES 3 — 2""'
3-27
4.C PEGULATOrY ALTERNATIVES ................ 4-1
4.1 INTRODUCTION ................... 4-1
4.2 STATUTORY AUTHORITY ................ 4-1
4.3 REGULATORY ALTERNATIVES .............. 4-2
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TABLE OF CONTENTS
(continued)
5.0 ENVIRONMENTAL AND ENERGY IMPACTS '..... 5-1
5.1 INTRODUCTION 5-1
5.2 BASELINE MERCURY EMISSIONS 5-2
5.3 OVERALL IMPACTS ESTIMATION METHODOLOGY 5-3
5.4 PRIMARY ENVIRONMENTAL IMPACTS 5-5
5.4.1 Fugitive Emissions 5-5
5.4.2 By-Product Hydrogen Streams and End-Box
Ventilation System Vents '5-9
5.4.3 Mercury Thermal Recovery Unit Vents .... 5-9
5.4.4 All Emission Sources 5-11
5.5 ENERGY IMPACTS 5-14
5.6 SECONDARY IMPACTS 5-16
5.6.1 Secondary Air Pollution Impacts . : . . . 5-16
5.6.2 Water Pollution Impacts 5-17
5.6.3 Solid Waste Impacts 5-18
5 . 7 SUMMARY OF ENERGY AND SECONDARY-
ENVIRONMENTAL IMPACTS 5-19
5.8 REFERENCES 5-21
6.0 COST IMPACTS 6-1
6.1 INTRODUCTION 6-1
6.2 OVERALL IMPACTS ESTIMATION METHODOLOGY 6-2
6.2.1 Cost Impacts for Fugitive Emission Sources . 6-4
6.2.2 Control Cost Impacts for Point Sources . . . 6-4
6.2.3 MR&R Cost Impacts for Point Sources . . . 6-10
6.3 CONTROL COST IMPACTS 6-11
6.4 MR&R COST IMPACTS 6-12
6.4.1 MR&R Cost Impact for Fugitive Sources . . 6-12
6.4.2 MR&R Cost Impacts for Point Sources . . . 6-19
6.5 ESTIMATE OF TOTAL ANNUAL COSTS AND COST PER UNIT
EMISSION REDUCTION 6-22
6.6 REFERENCES
n —,'
IV
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TABLE OF CONTENTS
(continued)
7.0 RATIONALE FOR SELECTING THE PROPOSED STANDARDS .'.... 7-1
7.1 INTRODUCTION 7-1
7.2 SELECTION OF THE SOURCE CATEGORY 7-1
7.4 SELECTION OF THE FORM OF THE STANDARDS ...... 7-4
7.5 SELECTION OF THE BASIS AND LEVEL OF THE PROPOSED
STANDARDS FOR EXISTING SOURCES 7-6
7.5.1 By-Product Hydrogen Streams and End-Box
Ventilation System Vents 7-7
7.5.1.1 Emission Limit for Plants With End-Box
Ventilation Systems. 7-9
7.5.1.2 Emission Limit for Plants Without End-Box
Ventilation Systems 7-18
7.5.2 Sources of Fugitive Mercury Emissions . . 7-21
7.5.3 Mercury Thermal Recovery Unit Vents . . . 7-31
7.5.3.1 Emission Limit for Oven Type Mercury
Thermal Recovery Unit Vents 7-38
7.5.3.2 Emission Limit for Non-Oven Type Mercury
Thermal Recovery Unit Vents 7-43
7.6 SELECTION OF THE BASIS AND LEVEL OF THE PROPOSED
STANDARDS FOR NEW SOURCES '. 7-50
1.1 SELECTION OF THE TESTING AND INITIAL COMPLIANCE
REQUIREMENTS 7-53
"7.8'. SELECTION OF THE CONTINUOUS COMPLIANCE
REQUIREMENTS 7-58
7.9 SELECTION OF THE NOTIFICATION, RECORDKEEPING, AND
REPORTING REQUIREMENTS 7-63
7.10 REFERENCES 7-64
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LIST OF FIGURES
Figure 2-1. Mercury Cell Chlor-Alkali Process Flow Diagram . 2-8
LIST OF TABLES
TABLE 2-1. PROFILE OF MERCURY CELL CHLOR-ALKALI PLANTS . . . 2-5
TABLE 3-1. POINTS ROUTED TO END-BOX VENTILATION SYSTEMS . . 3-4
TABLE 3-2. BY-PRODUCT HYDROGEN CONTROL SYSTEMS AT
MERCURY CELL CHLOR-ALKALI PLANTS . . 3-14
TABLE 3-3. END-BOX VENTILATION CONTROL SYSTEMS AT
MERCURY CELL CHLOR-ALKALI PLANTS 3-15
TABLE 3-4. THERMAL RECOVERY UNIT CONTROL SYSTEMS AT
MERCURY CE.LL CHLOR-ALKALI PLANTS 3-16
TABLE 3-5. CHARACTERISTICS OF THE PACKED TOWER SCRUBBERS USED IN
MERCURY CELL CHLOR-ALKALI VENT CONTROL SYSTEMS FOR MERCURY
CONTROL 3-20
TABLE 3-6. CHARACTERISTICS OF THE MOLECULAR SIEVE ADSORBERS USED
IN MERCURY CELL CHLOR-ALKALI VENT CONTROL SYSTEMS . . 3-22
TABLE 3-7. CHARACTERISTICS OF THE CARBON ADSORBERS USED IN "
MERCURY CELL CHLOR-ALKALI VENT CONTROL SYSTEMS .... 3-24
TABLE 4-1. REGULATORY ALTERNATIVES FOR MERCURY EMISSION SOURCES
AT MERCURY CELL CHLOR-ALKALI PLANTS 4-5
TABLE 5-1. REGULATORY ALTERNATIVES FOR EXISTING MERCURY EMISSION
SOURCES AT MERCURY CELL CHLOR-ALKALI PLANTS ....... 5-4
TABLE 5-2. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES FOR FOR BY-PRODUCT HYDROGEN STREAMS
AND END-BOX VENTILATION SYSTEMS AT PLANTS WITH END-BOX
VENTILATION SYSTEMS 5-24
TABLE 5-3. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES FOR BY-PRODUCT HYDROGEN STREAMS AT
PLANTS WITHOUT END-BOX VENTILATION SYSTEMS FOR HYDROGEN BY-
PRODUCT STREAMS AND END-BOX VENTILATION SYSTEMS . . . 5-25
TABLE 5-4. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES FOR MERCURY THERMAL RECOVERY UNIT
VENTS AT PLANTS WITH SUCH UNITS . . - 5-E
TABLE 5-5. ESTIMATED COMBINED MERCURY EMISSIONS FROM BY-PRCDUCi
HYDROGEN STREAMS AND END-BOX VENTILATION SYSTEM VENTS AT
REGULATORY ALTERNATIVE LEVELS 5-1C
TABLE 5-6. ESTIMATED MERCURY EMISSIONS FROM MERCURY THERMAL
RECOVERY UNIT VENTS AT THE REGULATORY ALTERNATIVE
LEVELS 5-26
TABLE 5-7. ESTIMATED PRIMARY ENVIRONMENTAL IMPACTS OF REGULAIOF.i
ALTERNATIVES FOR POINT SOURCES 5-2n
TABLE 5-8. ESTIMATED ANNUAL ENERGY AND SECONDARY ENVIRONMENTAL
IMPACTS FOR REGULATORY ALTERNATIVES FOR ALL
EMISSION SOURCES 5-20
vi
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LIST OF TABLES
(continued)
TABLE 6-1. REGULATORY ALTERNATIVES FOR EXISTING MERCURY EMISSION
SOURCES AT MERCURY CELL CHLOR-ALKALI PLANTS 6-3
TABLE 6-2. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES FOR BY-PRODUCT HYDROGEN STREAMS AND
END-BOX VENTILATION SYSTEMS AT PLANTS WITH END-BOX
VENTILATION SYSTEMS 6-32
TABLE 6-3. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES F^R BY-PRODUCT HYDROGEN STREAMS AT
PLANTS WITHOUT END-BOX VENTILATION SYSTEMS 6-33
TABLE 6-4. ASSUMED CONTROL SYSTEM ENHANCEMENTS
FOR MERCURY THERMAL RECOVERY UNIT VENTS AT PLANTS WITH SUCH
UNITS TO MEET THE REGULATORY ALTERNATIVES 6-7
TABLE 6-5. ESTIMATED CAPITAL CONTROL COST IMPACTS OF REGULATORY
ALTERNATIVE I FOR POINT SOURCES " 6-34
TABLE 6-6. ESTIMATED ANNUAL CONTROL COST IMPACTS OF REGULATORY
ALTERNATIVE I FOR POINT SOURCES 6-35
TABLE 6-7. ESTIMATED CAPITAL CONTROL COST IMPACTS OF REGULATORY
ALTERNATIVE II FOR POINT SOURCES • 6-36
TABLE 6-8. ESTIMATED ANNUAL CONTROL COST IMPACTS OF REGULATORY
ALTERNATIVE II FOR POINT SOURCES 6-37
TABLE 6-9. ESTIMATED COST IMPACTS OF REGULATORY ALTERNATIVE II
FOP FUGITIVE EMISSION SOURCES •. 6-17
TABLE 6-10. ESTIMATED CAPITAL MR&R COST IMPACTS OF
REGULATORY ALTERNATIVES FOR POINT SOURCES 6-21
TABLE 6-11. ESTIMATED ANNUAL MR&R COST IMPACTS OF
REGULATORY ALTERNATIVES FOR POINT SOURCES 6-23
TABLE 6-12. ESTIMATE: TOTAL ANNUAL COST IMPACTS OF REGULATORY
ALTERNATIVE I FOR ALL MERCURY EMISSION SOURCES .... 6-24
TABLE 6-13. ESTIMATED TOTAL ANNUAL COST IMPACTS OF REGULATORY
ALTERNATIVE II FOR ALL MERCURY EMISSION SOURCES . . . 6-25
TABLE 6-14. ESTIMATED COST PER UNIT MERCURY EMISSION REDUCTION
CF REGULATORY ALTERNATIVES FC? MERCURY CELL
CHLOR-ALKALI PLANTS 6-36
TA2LE 7-1. BY-PRODUCT HYDROGEN STREAM AND END-BOX VENTILATION
SYSTEM VENT MERCURY EMISSIONS FOR PLANTS WITH END-BOX
VENTILATION SYSTEMS ' 7-11
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1.0 INTRODUCTION
1.1 INTRODUCTION
This background information document (BID) provides
information relevant to the proposal of national emission
standards for hazardous air pollutants (NESHAP) . for limiting
mercury emissions, from mercury cell chlor-alkali plants._ The
standards are being developed according to section 112(d) of
Title III of the Clean Air Act (CAA) as amended in 1990.
Chapter 2 presents a description of the mercury cell chlor-
alkali industry and process. Chapter 3 discusses the techniques
used to control mercury emissions from the mercury emission
sources at mercury cell chlor-alkali plants. Chapter 4 describes
the regulatory alternatives considered by the Environmental
Protection Agency (EPA) for proposal. Chapters 5 and 6 discuss
tne estimation of environmental and energy impacts and cost
impacts, respectively, of the regulatory alternatives on the
inaustry. Chapter 7 presents the detailed rationale behind the
selection of tne proposed NESHAP.
1.2 STATUTORY BASIS
Section 112 of the CAA contains EPA's authorities for
reducing emissions of hazardous-air pollutants (HAP). Section
112 ' c'' '6.! reajires the EPA to list source cateaories and
1-1
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subcategories assuring that sources accounting for not less than
90 percent of the aggregate emissions of each of seven specific
bioaccumulative pollutants (including mercury) are subject to
standards under subsection 112(d)(2) or (d)(4) of the CAA.
Section 112(d) requires the Administrator to promulgate
regulations establishing emission standards for each category or
subcategory of major sources and area sources of HAP listed in
section 112(c). Section 112(d)(2) specifies that emission
standards promulgated under the section shall require the maximum
degree of reductions in emissions of the HAP subject to
section 112 that are deemed achievable. This level of control is
referred to a§ maximum achievable control technology (MACT).
These regulations are often termed "technology-based" standards
because they 'are based on 'the degree of emissions control
achievable through the application of technologies that the best
performing sources ir. the particular source category are using.
These technologies may include equipment or process design,
chemical substitution, collection and treatment of emissions,
worx. practices, ana other measures.
For area sources determined to present a threat cf adverse
effects to human health or the environment, standards or
requirements that represent generally available control
technologies (GACT) or management practices to reduce HAP may be
promulgated, in lieu of establishing standards based on MACT.
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I
I The minimum level allowed for NESHAP established under
• . section 112(d)(2) is referred to as the MACT floor (section
112(d) (3)). For new sources, the MACT floor cannot be less
I stringent than the emission control that is achieved in practice
_ by the best-controlled similar source. The MACT floor for
* existing sources must be at least as stringent as the average
I emission limitation achieved by the best-performing 12 percent of
existing sources in the category or subcate'gory (or the best-
I • ' performing 5 sources for categories or subcategories with fewer
I than 30 sources).
In developing MACT, control options that are more stringent
1
I than the floor may also be considered. Standards more stringent
I than the fleer may be established based on the consideration of
cost of achieving the emissions reductions, any non-air quality
I health and environmental impacts, and energy impacts.
Secticr. 112 ;o' •'4 ' provides fcr consideration of health
* thresholds with an arrple margin of safety. Certain other
I sections cf. section 112 require the EPA, in addition to
technology-based standards, to evaluate risk to public health and
I the environment in Determining whether other control measures are
I appropriate.
1.3 BACKGROUND ON SOURCE CATEGORY
I As previously noted, section 112(c)(6) of the CAA requires
the EPA to list source categories and subcategories assuring that
^~ accounting fcr not less than 90 percent of the aggregate
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emissions of each of seven specific bioaccumulative pollutants
(including mercury) are subject to standards under subsection
112(d)(2) or (d)(4) of the CAA. It was estimated that chlor-
alkali production sources contribute around 5^ percent of the
total nationwide anthropogenic stationary source category mercury
emissions (63 FR 17838), and over 25 percent of the total
nationwide anthropogenic stationary source category mercury
emissions from non-combustion sources.
1-4
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2.0 INDUSTRY CHARACTERIZATION
I
1
I
I
_ 2.1 INTRODUCTION
Chlorine is a essential chemical building block, ranking
I . among the top ten by volume of all chemicals produced in the"
United States.^ According to the Chlorine Institute, a trade
1 . association that represents North American chlorine producers,
I chemicals production is the largest use sector (35 percent) for
the chlorine produced in North America. This is followed by
I plastics production (28 percent); solvents production
I (18 percent) for metalworking, dry cleaning, and electronics;
pulp and' paper bleacning (14 percent); and water/wastewater
I purification (5 percent).
Chlorine producers are identified by Standard Industrial
• Classification (SIC) code 2812 - Alkalies and'Chlorine3 and North
3 American Industry Classification System (NAICS) code 325181 -
Alkalies ar.d Chlorine Manufacturing.^
I The majority of chlorine is produced by electrolysis
i involving three technoloqies, namely diaphragm cells, mercury
cells, and membrane cells. With these methods, an electric
1 current is passed through a salt solution (brine), causing the
dissociation of the salt and resulting in the generation of
cnicrine gas and an alkaline solution (caustic soda, or sodiun
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hydroxide, and caustic potash, or potassium hydroxide). These
saleable chemicals are viewed as co-products, hence the
?
designation of the production methods as "chlor-alkali"
processes. Like chlorine, caustic soda is used in a diverse
range of processes. This includes pulp and paper, detergent,
textiles (particularly, rayon), pigments, petroleum,
Pharmaceuticals, and sodium hypochlorite (bleach) production.^
Hydrogen gas is also produced as a by-product of chlor-alkali
processes. The hydrogen is primarily used on-site, either as
fuel for boilers or as high-purity raw material for other
chemical production. By-product hydrogen is also released to the
atmosphere when supply exceeds demand.
Aside from the three chlor-alkali processes, chlorine is
also produced as a co-product or by-product in four other types
of processes. The first is an electrolytic process involving
molten salts rather than a salt solution (Downs sodium process).
The second is an electrolytic process that uses hydrogen chloride
(HC1) as a raw material instead of salt (Uhde HC1 decomposition
process). The third process is non-electrolytic and involves
chlorine as a cc-product of potassium nitrate production (nitric
acid/salt process). The fourth is the electrolytic primary
magnesium production process.
In 1997, there were 43 chlorine production plants operating
in the United States.6 The majority of the plants, 38 in all,
used diaphragm, mercury, and/or membrane cells. Seven plants
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used a combination of two types of chlor-alkali cells and one
plant used all three types of cells. Of the remaining chlorine
production plants, three plants used magnesium production
process, and one plant each used the Downs sodium, Uhde HC1
decomposition, and nitric acid/salt process.
While chlorine'is produced in various types of processes,
the focus of this document and the corresponding EPA regulatory
action is mercury emissions, which only occur from chlor-alkali
production using jnercury cell technology. Therefore,' this
chapter characterizes mercury cell chlor-alkali plants as an
industry (Section 2.2), the mercury cell chlor-alkali production
facilities (Section 2.3) at tnese plants, and mercury recovery
facilities (Section 2.4) that are co-located with mercury cell
chlor-alkali production facilities. Unless specified otherwise
in this chapter and in subsequent chapters of this background
information document, the information presented originated from
Section 114 questionnaires and supplementary clarifications
(including performance test reports), '" site
visits,y/1^'lx'l^'1J and meetings with industry
representatives. -^' ~^z > 1C:' ^< -"-^
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2.2 MERCURY CELL CHLOR-ALKALI INDUSTRY PROFILE
There are twelve mercury cell chlor-alkali plants currently
operating in the United States.3 Table 2-1 presents'basic
information about each plant, specifically the owner and
location, the year mercury cell chlor-alkali production
started,1^ the number and types of mercury cells, and the annual
amount of chlorine produced.20 The twelve plants are owned and
.operated by eight different companies. Occidental Chemical
Corporation, Olin Corporation, and PPG Industries, Incorporated
own and operate .multiple plants (three, two, and two plants,
respectively). ASHTA Chemicals, Incorporated, HoltraChem
Manufacturing Company, Pioneer Chlor-Alkali Company,
Incorporated, Vulcan Materials Company, and Westlake CA&O
Corporation each own and operate one plant. The plants are
located in ten states: Louisiana and Texas (two plants each), and
Delaware, Georgia, Kentucky, Maine, Ohio, Tennessee, West
Virginia, and Wisconsin (one plant each).
The ages of the plants vary, as mercury cell chlor-alkali
production started in 1938 at the oldest plant and in 1970 at tne
newest plant. As such, new mercury cell chlor-alkali production
facilities have not been constructed in 'over thirty years. This
a At the time of printing of this document, one plant
(HoltraChem Manufacturing Company's Orrington, Maine plant] had
closed (in September 2000), and one plant (Westlake CA&O
Corporation's Calvert City, Kentucky) had indicated it wculc
convert tc membrane cell technology by the end of 20nl . Hov:eT.Ter,
both plants were considered in developing the proposed NE3HAF.
2-4
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TABLE 2-1. PROFILE OF MERCURY CELL CHLOR-ALKALI PLANTS
Plant
Owner
ASHTA
HoltraChem
Occidental
Occidental
Occidental
Olin
Olin
Pioneer
PFG
FFG
Vulcan
West la ke
Plant Location
Ashtabula, OH
Orrington, ME
Muscle Shoals,
AL
Delaware City,
DE
Deer Park, TX
Augusta, GA
Charleston, TN
St. Gabriel, LA
Lake Charles, LA
Martinsville, WV
Port Edwards, WI
Calvert City, KY
Year
Chlorine
Production
via Mercury
Cell Chlor-
Alkali
Process
Started3
1963
1967
1952
1965
1938
1965
1962
1970
1969
1958
1967
1966
Make/Model and
Number of
Mercury Cells
Olin E-ll, 24
De Nora 24H5, 24
De Nora 12x3,
116
De Nora 18x4, 88
De Nora 18x6, 52
Olin 510, 60
Olin 510, 58;
Olin 812, 48
Uhde 300-100, 52
De Nora 48H5, 70
Uhde 20 sq. m,
54
De Nora 24H5, 24
De Nora 24H5, 36
Nationwide Total
Chlorine
Produced by
Mercury Cell
Chlor-Alkali
Process
(Megagrams per
year)b
43,110
65,860
127,322
132,450
88,146
108,210
238,592
173,274
234, 056
66,225
71, 092
111, 041
1,459, 379
^Except 'for the two r PG plants, the year specified is when the plant was
built. The two PPG plar.tr did net initially use mercury cells when chlorine
production commenced (194"' for PPG's Lake Charles, LA plant and 1943 for FPG's
New Kartinsville, WV plant).
bThe values specified for Occidental's Deer Park, TX plant, PPG's Lake
Charles, LA plant, and FFG's New Martansvilie, WV plant do not include all
chlorine produced at the site, as diaphragm cells are co-located with the
rrercury cells at the site. Tne ^otal chlorine production capacities of these
plants are 348,672, 1,156,792, and 359,566 Megagrams per year, respectively
! Source: 195^ Directory cf Cneirticai Producers: United States of America, SRI
International).
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is largely due to the development of membrane cell technology.
Historically, one of the reasons for selecting mercury cell
technology over diaphragm cell technology was the quality of
caustic produced, both in terms of purity and strength. In fact,
the production of rayon fiber evolved to depend on the
availability of the high-purity mercury cell grade caustic soda,
which came to be kno'wn as rayon grade caustic soda. When
membrane cell technology was developed, it became the preferred
method, as high purity caustic soda could be produced with a
lower energy consumption per unit of caustic product.21
The nationwide chlorine production resulting from the use of
mercury cell technology is 1,460,674 Megagrams (1,608,672 tons)
per year. These plants also produce over 450 million standard
cubic meters (16 billion standard cubic feet) of hydrogen
annually.
2.3 MERCURY CELL CHLOR-ALKALI PROCESS DESCRIPTION
The central unit in the mercury-cell chlor-alkali chlorine
production process is the mercury cell, which consists of an
electrolyzer, a decomposer, one or mere end boxes, a mercury
pump, and other components linking the electrolyzer and
decomposer. While each mercury cell is an independent production
unit, numerous cells are connected electrically in series to form
a cell circuit. Mercury cells are situated in a cell room and
typically arranged in two rows separated by a center aisle. The
cell rocrr, generally designates a two-story structure in which
2-6
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mercury cells are housed on the upper floor. The lower floor is
the site of various process and housekeeping functions. The cell
^
room is more fully discussed as a source of fugitive mercury
emissions in Chapter 3, Section 3.5.
Section 2.3.1 describes the general operation in and around
the mercury cell. Sections 2.3.2 through 2.3.6 provide general
descriptions of ancillary operations. Figure 2-1 presents a
simplified flow diagram of the mercury cell chlor-alkali process.
2.3.1 Mercury Cell Operation
A typical mercury cell measures about 15 meters (about
50 feet) in length and 1.5 meters (about 5 feet) in widthb and
holds about 3,600 kilograms (around 8,000 pounds) of mercury.
The number cf cells at a given plant ranges from 24 to 116 and
averages 56. The most prevalent cell make is DeNora
(seven plants), followed by Olin (three plants), and Uhde (two
plants).' Every plant uses cells made by only one manufacturer,
and only Olin's Charleston, Tennessee plant utilizes more than
one cell model. Also, Occidental's Delaware City, Delaware plant
uses the same cell model throughout its cell room but loads half
of the cells with more mercury. DeNora cells (all cell models)
are generally run with the highest amount of mercury, followed by
Uhde and Olin cells. The amount of mercury held by a cell is
largely a function of the cross-sectional area of the
' The dimensions cited are dimensions of the electrolyzer,
the Israest comconent of the mercurv cell.
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electrolyzer, in which the depth of the mercury layer (on the
order of one centimeter) is much smaller than the length and
width. Thus, because DeNora cell electrolyzers have the greatest
length on average (widths vary to a much lesser extent), DeNora
cells can be considered the largest, followed by Uhde and Olin
cells.
A mercury cell involves two distinct reactions, which occur
in separate vessels. The electrolyzer produces-chlorine gas, and
the decomposer produces hydrogen gas and caustic solution. The
electrolyzer can be described as an elongated, shallow steel
trough enclosed by side panels and a top cover. The decomposer
is a four to five-feet high cylindrical vessel located at the end
of the cell and is usually oriented vertically (PPG's New
Martinsville, West Virginia plant has horizontal decomposers).
The electrolyzer and the decomposer are typically linked at the
ends by an inlet end bcx and an outlet end box.
A shallow stream, of liquid mercury flows continuously
between the electrolyzer and the decomposer. The mercury enters
the cell at the inlet end box and flows down a slight grade to
the outlet end bcx, where it flows out of the electrolyzer into
the decomposer. After being processed in the decomposer, the
mercury is pumped back up to the inlet end box.
Saturated brine (sodium chloride solution or potassium
chloride solution) is fed to the electrolyzer via the inlet end
box ar.a flows toward the outlet end bcx on top of the mercury
-------
layer. The brine and mercury flow under dimensionally stable
metal anodes, typically made of a titanium substrate with a metal
catalyst, that are suspended in the electrolyzer top. The
mercury serves as the cathode in the cell.
Electric current applied between the anode and the mercury
(Hg) cathode causes a reaction producing chlorine (C12) at the
anode and.a sodiumimercury (Na:Hg) amalgam at the cathode. If
sodium chloride (NaCl) brine is"used, the overall electrolytic
reaction is as follows:
..Na+ + Cl" + Hg - Na:Hg + ^ C12 1
The reaction is essentially the same for potassium chloride (KC1)
brine except that potassium is substituted for sodium in the
chemical equation. The chlorine gas is collected at the top of
the electrolyzer and transported to a gas purification and
usually to liquefaction units, as described in Section 2.3.2.
The sodium mercury amalgam ultimately exits via the outlet end
box and enters the decomposer. The brine, whose salt content ha-~
been partially depleted in the reaction, also exits the cell at
the outlet end box and is transferred to a brine preparation
system, as described in Section 2.3.3.
The decomposer functions as a packed bed reactor where the
mercury amalgam is contacted with deicnized water in the presence
of a catalyst. The amalgam reacts with the water (H20) ,
regenerating elemental mercury and producing caustic and hydrogen
(H-V| . The overall decomposer reaction is as follows:
2-10
-------
Hg:Na + H20 - Na+ + OH" + ** H2 T + Hg
Again, potassium is substituted for sodium if the plant is
j
producing potassium hydroxide (KOH) rather than sodium hydroxide
(NaOH). The caustic and mercury are separated in a trap at the
end of the decomposer. Prior to transfer to ancillary treatment
operation (as described in Section 2.3.4), the caustic stream
exiting each decomposer is may be passed through a caustic
basket, a fixture containing a serrated funnel that breaks the
stream into droplets so that electric current is not conveyed.
The hydrogen is also transferred to an ancillary treatment
process (as described in Section 2.3.5), and the mercury is
pumped back to the inlet end of cell.
2.3.2 Product Chlorine Purification
Individual chlorine streams are collected under vacuum from
each mercury cell electrolyzer and fed into a header system
leading out of the cell room. The chlorine then undergoes
condensation, mist elimination, and absorption (drying).
Initially, the chlorine is routed to one or more indirect
contact heat exchangers. Next, it is passed through a wet
demister. The condensates from cooling and mist elimination may
be fed to the brine preparation system. The average
concentration of mercury (in its elemental form) in chlorine at
this point and for the remainder of the treatment process ranges
from 0.002 to 0.1 ppm, with a mean value of about 0.03 ppm.
Subsequently, the cnlorine encounters a series of countercurrent
2-1:
-------
sulfuric acid towers to remove water vapor-, followed by a dry
demister to remove entrained acid. Finally, the chlorine gas is
purified, and further cooling, compression, and liquefaction
operations may be conducted to obtain liquid chlorine.
2.3.3 Brine Preparation System
Brine flows in a continuous loop between the mercury cells
and brine preparation system, which provides clean, saturated
brine to the mercury cell chlor-alkali process. Eight mercury
cell chlor-alkali plants use sodium chloride brine, two use
potassium chloride brine, and two plants use both types of brines
in different mercury cell circuits. Due to contact of brine and
mercury, mercury is present in the brine system in its molecular
form as dissolved mercuric chloride. The average mercury
concentration ranges from 3 parts per million (ppm) to 25 ppm,
with a mean value of about 14 ppm.
In the brine loop, an individual brine stream to a mercury
cell passes through the cell and leaves the cell room (via a
•brine header) with a reduced salt content. This stripped brine
is acidified with hydrochloric acid and, then, purified of
chlorine. The chlorine vapor stream generated is fed to the
chlorine product header for treatment. 'After dechlorination, the
brine is resaturated with raw sodium chloride or potassium
chloride. An important function of the brine preparation system
is the removal of impurities, such as calcium, magnesium, iron,
aluminum, strontium, nickel, molybdenum, manganese, copper,
2-12
-------
chromium, lead, and vanadium, that may be introduced in the raw
salt. The presence of these elements can adversely affect
mercury cell efficiency, as they amalgamate with mercury to form
mercury "butters." Accordingly, caustic solutions and sodium
carbonate are added to raise pH, depress metal solubility, and
form metal precipitates. The resulting slurries are filtered to
produce brine muds. Altnough such muds are designated hazardous
wastes ("K071") in accordance with EPA's solid waste
classifications (40 CFR part 261, subpart D), the muds are
"delisted" at some mercury cell chlor-alkali plants (due to their
low mercury content) so that they may be disposed of in an
industrial landfill, rather than at a hazardous waste facility,
Subsequently, the brine is acidified to remove excess caustic,
subjected to heat exchange for temperature adjustment, and
returned to the mercury cells as clean saturated brine.
2.3.4 Product Caustic Purification
Eight mercury cell chlor-alkali plants produce sodium
hydroxide, two produce potassium hydroxide, and two plants
produce both caustic solutions. Because the mercury cell chlor-
alkali process produces a caustic solution that is 50 percent by
weight sodium hydroxide or potassium hydroxide in t'he decomposer
reaction, the treatment process mainly involves mercury removal.
The average concentration of mercury (found in its elemental
form) in the caustic stream leaving the decomposer ranges from
;t 3 pprr, to 15 ppm, with a mear. value of 10 pprn. The streams
-------
from the decomposers are combined into a caustic header. Then
the caustic may undergo cooling to condense entrained mercury
prior to filtration. Five plants use candle filters with carbon
pre-coat only, while two plants use another material in addition
to carbon for the candle filters. Four plants use candle filters
with a cellulose-based material. Two plants use plate filters
with carbon pre-coat (one of these two plants uses both plate and
candle filters with carbon pre-coat). The average mercury
content of caustic product ranges from 0.02 ppm to 0.2 ppm, with
a mean value of 0.08 ppm.
2.3.5 By-Product Hydrogen Cleaning
Hydrogen_exiting a decomposer contains vaporized mercury.
Accordingly, each decomposer is equipped with an adjacent cooler
through which the hydrogen stream is routed to immediately
condense mercury and return it to the mercury cell (this'is true
for all but one mercury cell chlor-alkali plant, which does not
have initial coolers associated with each decomposer). Most of
these coolers are indirect contact devices, including shell and
tube, plate-and-frame, radiator-type, U-tube, and double-pipe,
cooling jacket exchangers. Two plants use direct contact packed
bed, counter-current coolers. The temperature at the decomposer
outlet ranges from 160 degrees Fahrenheit(°F) to 260°F, with a
mean of 209°F and a median of 220°F. Most plants have an
individual cooler associated with each decomposer. The
temperature of the hydrogen stream after passage through
-------
individual coolers ranges from 70°F to 200°F, with a mean of
135°F and a median was 130°iT.
After initial cooling, the streams are collected into a
common header. The hydrogen is then purified of mercury via
various combinations of condensation, mist elimination,
absorption, and adsorption. This is further discussed in
Section 3.2, as the by-product hydrogen stream is a point source
of mercury emissions.
2.3.6 Wastewater Treatment
In the mercury cell chlor-alkali process, various aqueous
liquids containing mercury are generated and must be treated to
remove mercury. These wastewaters can originate from a variety
cf sources.
Water from washdowns, cleanup activities, and liquid mercury
collection, as well as end-box wash waters, are channeled to
wastewater treatment via open-air drains and the cell room sump.
Brine is occasionally purged to wastewater treatment to remedy
the buildup of metallic impurities. Alternatively, slurries from
the purification of saturated brine (if they are not filtered as
part of brine system; may be fed to wastewater treatment. From
caustic treatment, the waters involved in periodic regeneration
of the mercury filters (i.e., caustic filtration "backwash") are
generally fed to wastewater treatment. Waters from absorbers
(absorption is discussed in Section 3.6.2, as a mercury emission
cor.trcl technoloav' mav also be routed to wastewater treatment.
-------
The wastewater treatment method most commonly used by
mercury cell chlor-alkali plants was developed in the 1970's and
is highly dependent on pH. The method entails three'broad steps.
First, sodium hydrosulfide is added to wastewaters, which
contains both elemental mercury and mercury compounded as
mercuric chloride, -to form mercuric sulfide. Next, the mercuric
sulfide is removed via precipitation and filtration, resulting in
wastewaters separated from a mercuric sulfide filter cake.
Lastly, the dissolved mercury in the wastewaters is removed via
carbon adsorption. The treated wastewaters may be then be
released in accordance with plant discharge permits. The
mercuric sulfide filter cake is a designated hazardous waste
("K106") in accordance with EPA's solid waste classifications
(40 CFR part 261, subpart D). "K106" wastes may be treated on-
site to recover elemental mercury, as described in Section 2.4,
prior to disposal.
2.4 DESCRIPTION OF MERCURY RECOVERY PROCESSES
Most mercury cell chlor-alkali plants recover elemental
mercury from mercury-containing wastes. The types of waste
processed include "K106" wastes and "D009" wastes. As previously
discussed, "K106" wastes are sludges from wastewater treatment
filtration. "D009" wastes are general mercury-containing waste
solids that exceed the toxicity characteristic for mercury,
according to EPA's solid waste classifications (40 CFR part 261,
subpart C). "D009" wastes are categorized as either debris or
2-16
-------
non-debris. "D009" debris are those greater than about 2^ inches
in any one dimension, such as hardware, tools, and protective
gear. "D009" non-debris include graphite from decomposers, cell
room sump sludges, and other small solids. Additionally, spent
carbon media from carbon adsorbers (adsorption is discussed in
Section 3.6.3, as a mercury emission control technology) are also
processed.
Of the twelve mercury cell chlor-aDcal'i plants, nine plants
have mercury recovery processes on-site. Six plants have mercury
thermal recovery units, two plants have REMERC™ units, and one
plant has a batch purification still.
Collectively, the nine plants process about 1,044 Megagrams
(1,55C tons) of wastes per year, with the annual waste throughput
ranging 'from over 3.2 Megagrams (3.5 tons) to 454 Megagrams
(500 tons) and averaging about 157 Megagrams (173 tons). The
percentages of total waste processed by type of mercury recovery
unit are 85.6 percent for mercury thermal recovery units,
14.2 percent for PEMFRC™ units, and 0.2 percent for the batch
purification still.
The amount cf mercury recovered annually for the nine plants
totals about 56 Megagrams (61 tons). The percentages of mercury
recovered by type of mercury recovery unit are 89.7 percent for
mercury thermal recovery units, 4.6 percent for REMERC™ units,
and 5.7 percent for the batch purification still. The remainder
-------
of this section discusses mercury thermal recovery units,
REMERC™ units, and the batch purification still.
2.4.1 Mercury Thermal Recovery Units
A mercury thermal recovery unit designates the retort(s)
where mercury-contain:ng wastes are heated to volatilize mercury
and the mercury recovery/control system (control devices and
other equipment) where the retort off-gas is cooled, causing
mercury to condense and liquid mercury to be recovered.
Six plants conduct thermal recovery (retorting) in a mercury
thermal recovery unit. These units can be classified into oven
type units and non-oven type units, based on the type of retdrt
(furnace) used. Discussed below are descriptions and operating
characteristics of the thermal recovery units, focusing on the
retorts used, which include three basic designs: batch oven
(three plants), rotary kiln (two plants), and single hearth (one
plant). The recovery/control systems of all the units are less
differentiated and are further discussed in Section 3.6, since
the mercury thermal recovery unit vent, where treated off-gas is
discharged to the atmosphere, is a point source of mercury
emissions.
There are three plants, all owned and operated by
Occidental, that each have a mercury thermal recovery unit with
batch oven retorts. The Delaware City, Delaware plant operates
five evens, the Muscle Shoals, Alabama plant operates three
evens, and the Deer Park, Texas plant operates two ovens. The
-------
batch ovens are D-tube retorts, which are so named because each
resembles an uppercase letter "D" on its side. Pans are filled
with waste, typically around 10 cubic feet, and then placed into
an oven. After inserting three or four pans, the oven door is
closed and the retort is heated to about 1,000°F. The residence
time varies from about 24 to 48 hours, depending on the type of
waste being processed. While retorting, the oven is kept under a
vacuum and the mercury vapors are pulled into the mercury
recovery/control ^system. After the cycle is completed, the unit
is allowed to cool and the pans are then removed. Retorting at
all three plants is conducted between 6,000 to 7,000 hours per
year. The amounts of waste processed and the amounts of mercury
recovered range frorr 90 to almost 300 tons per year and from 3 to
20 tons per year, respectively.
PPG's Lake Charles, Louisiana plant and Olin's Charleston,
Tennessee plant each have a mercury thermal recovery unit with a
rotary kiln retort. The rotary kilns are long, refractory-lined
rotating steel cylinders in which the waste charge to be treated
flows counter-current: to hot combustion gases used for heating.
Wastes to be treated are conveyed into a ram feeder, which
inserts a waste charge into the kiln at regular intervals,
typically about every 5 minutes. Each is fired with natural gas
and is heated to 1,300°F and above. The rotation of the kiln
provides for mixing and transfer of the waste to the discharge
ena. The resiaence time is about 3 nours. The aas stream
-------
leaving the kiln passes through an afterburner, where the
temperature is increased to 2,000°F to complete combustion
reactions involving sulfur and carbon, and then to a' mercury
recovery/control system. Over 300 tons per year and around 500
tons per year are processed in each unit, and over 12 tons per
year and about 1.0 tons per year of mercury are recovered
Vulcan's Port Edwards, Wisconsin plant has a mercury thermal
.recovery unit with a single hearth retort. This retort is
comprised of a vertically-mounted refractory lined vessel with a
single hearth and a rotating rabble. Waste is charged onto the
hearth through a charge door by way of a conveyor. Once charged,
the conveyor is withdrawn, the charge door is closed, and the
heating or treatment cycle begins. The waste is stirred by the
rabble rake, which turns continuously, and is heated to around
1,350°F. The residence time, which ranges according to waste
type, is typically much longer than for rotary kilns. Like the
kilns, the retort off-gas passes through an afterburner, where
'the temperature is increased to 2,000°F to complete combustion
reactions involving sulfur and carbon, and then to a mercury
recovery/control system. The amount of waste processed in, and
the amount of mercury recovered by, the 'unit are considered
confidential business information by this plant.
Thus, three plants have batch oven retorts, and three plants
have non-oven (rotary kiln and single hearth) retorts. Both
"K106" and "D009" wastes are processed in all six retorts. As
2-20
-------
indicated above, there are differences between the two types
related to operating temperature and residence time. Oven
retorts have lower operating temperatures and substantially
longer residence times. This is related primarily to the more
efficient waste mixing and heating achieved in kilns.
Additionally, oven retorts typically have volumetric flow rates
around 100 scfm, which is an order of magnitude lower than non-
oven retorts, which have flow rates around 1,000 scfm.
2.4.2 REMERC™ Units
REMERC™ units involve liquid-phase operations and produce
.no discharges to the air. Moreover, the process is used to
recover mercury from "K106" wastes only. REMERC™ units are
operated at Pioneer's St. Gabriel, Louisiana plant and Westlake's
Calvert 'City, Kentucky plant, which are both based on a
proprietary design developed by Universal Dynamics.
REMERC7''' unirs are operated in batch mode, with following
steps: (1) leaching mercuric sulfide and metallic mercury from
the "K106" sludge^* with sodium hypochlorite, sulfuric acid, and
brine to form dissolved mercuric chloride; (2) thickening the
leach product to separate low mercury content solids from mercury
rich liquids; (3) subjecting the solids to filtration and washing
to obtain final treated "K106" muds*; and (4) subjecting the
liguid solution containing mercuric chloride to cementation, or
reaction with metallic iron, to precipitate elemental mercury.
At Kestlake's Calvert City, Kentucky plant, this last step is
2-21
-------
forgone, and the mercuric chloride solution is sent to the brine
preparation system for eventual recycling of mercury back to the
mercury cells.
One plant processes 18.2 Megagrams (20 tons) per year of
"K106" wastes, while the other plant processes about
182 Megagrams (200 tons) annually. The annual amount of mercury
recovered.is 0.27 Megagrams (0.3 ton) and 2.3 Megagrams
(2.5 tons), respectively.
2.4.3 Batch Purification Still
At PPG's Ne.w Martinsville, West Virginia plant, a batch
purification still is physically located within a cell room and
involves indirectly heating a small volume of material with a
high mercury concentration. This contrasts with mercury thermal
recovery units, which heat large volumes of low mercury-content
wastes.
This plant operates the batch purification still an average
of seven times each year. Only end-box residues, which are heavy
metal impurities amalgamated with mercury, are processed for
mercury recovery. During a batch run, a vacuum pump is activated
to achieve a vacuum before heating commences. During this
startup period, evacuation vapors are routed through two
identical carbon adsorption beds, one located before the vacuum
pump and one located after the pump. Then, the residues are
heated to a temperature of about 320 degrees Celsius (600 degrees
Fahrenheit) and held at that temperature for 24 to 36 hcurs ir
2-2;
-------
order to volatilize mercury. The mercury is then recovered in a
receiving tank via a total condenser. The plant recovers about
3.2 Megagrams (3.5 tons) per year of mercury in this manner.
2.5 REFERENCES
1. Kirk-Othmer Encyclopedia of Chemical Technology. Fourth
Edition. Volume I. New York, John Wiley & Sons,
Incorporated. 1991. p. 938.
2. Chlorine Institute. Chlorine Does a World of Good
(Pamphlet). Washington DC.
3. Executive Office of the President, Office of Management and
Budget. Standard Industrial Classification Manual - 1987,
Springfield,' Virginia. National Technical Information
Service. 1987. pg. 132.
.4. United States Census Bureau, North American Industry
Classificaticn System - United States 1997.. Accessed
through website .
January 30, 2000.
5. Pioneer Chlor-Alkali Company. Accessed through website
. June 27, 2000.
6. Economic Analysis of Air Pollution Regulations: Chlorine
Industry. Prepared by Research Triangle Institute for
Aaiysha Khursheed, U.S. Environmental Protection Agency,
August 2000.
7. Memorandum. B^atia, K. , McCutchen, J., and Norwood, P.,
EC/R Incorporated, tc Rcsario, I., U.S. Environmental
Protection Agency. Summary of Section 114 Responses from
Mercury Cel_ Cnlor-Alkali Facilities. January 20, 1999.
8. Memorandum. Ehatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Envircnr.er.ial Protection Agency. Compilation of
Clarifications to Section 114 Responses from Mercury Cell
Chlor-Alkali Plants. January 19, 2001.
9. Memorandum. Bnatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site
Visit Report for Clir. Chemicals, Charleston, Tennessee Site.
August 17, 1998.
10. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Rosaric, I., U.S. Environmental Protection
-------
Agency. Site Visit Report for OxyChem's Facility in
Delaware City, Delaware. October 4, 2001.-
11. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site
Visit Report-for Pioneer Chlor-Alkali Company's St. Gabriel,
Louisiana Plant. June 21, 1999.
12. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site
Visit Report for PPG Industries, Lake Charles, Louisiana
Site. August 25, 1999.
13. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Rosario, I., U.S. Environmental Protection
Agency. Site Visit Report [for Vulcan Chemicals' Facility
in Port Edwards, Wisconsin]. May 11, 1999.
14. Memorandum. Bhatia, K., McCutchen, J., and Norwood, P.,
EC/R Incorporated, to Rosario, I., U.S. Environmental
Protection Agency. Summary of April 2, 1998 Meeting between
the EPA and the Chlorine Institute. April 9, 1998.
15. Memorandum. Bhatia, K., McCutchen, J., and Norwood, P.,
EC/R Incorporated, to Rosario, I., U.S. Environmental
Protection Agency. Summary of April 14, 1998 Meeting
between the EPA and the Chlorine Institute. April 24, 1998.
16. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency.
Summary of July 29, 1999 Meeting between the EPA and the
Chlorine Institute. August 10, 1999.
•17. Memorandum. Bhatia, K. , and Norwood, P., EC/R Incorporate,
to Rosario, I., U.S. Environmental Protection Agency.
Summary of the March 30, 2COO Meeting between the EPA and
the Chlorine Institute. April 6, 2000.
18. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of the August
7, 2001 Meeting between the EPA and' the Chlorine Institute.
August 14, 1999.
19. Reference 6.
2C. Memorandum. Bhatia, K., EC/R Incoporated, to Rosaric, I.,
U.S. Environmental Protection Agency. Background on Data
Used to Determine and Assess Regulatory Alternatives for By-
Product Hydrogen Streams and End-Box Ventilation Systerr.
Vents. June 25, 2001.
2-24
-------
21. Olin Chemicals, Incorporated, Chlor-Alkali Division.
Accessed through website
. June 27, 2000.
-------
3.0 EMISSION SOURCES AND CONTROL TECHNIQUES
3.1 INTRODUCTION
As stated in Chapter 2, four types of mercury emission
sources may be present at a mercury cell chlor-alkali plant: by-
product hydrogen streams, end-box ventilation system
vents, mercury thermal recovery unit vents, and fugitive emission
sources. Section 3.2 briefly describes the by-product hydrogen
stream as the combined stream, prior to control. Section
3.3 discusses inputs to plant end-box ventilation systems and
describes the stream, prior to control. Section 3.4
characterizes the mercury thermal recovery unit vents.
Section 3.5 briefly describes fugitive emissions and cell room
ventilation.
Mercury cell chlor-alkali plants are limited to emitting
2,300 grams per day of mercury to the atmosphere under the
"National Emission Standard for Mercury" (40 CFR part 61,
subpart E, §61.50 et. seq.),° hereafter referred to as the
part 61 NESHAP. To control mercury emissions from point sources,
mercury cell chlor-alkali plants employ a variety of
=This regulatory program was originally set forth at 38 FR
8826, April 6, 1973; and amended at: 40 FR 48302, October 14,
1975; 4" FR 24704, June 8, 1982; 49 FR 35770, September 12, 1984;
5C FR 46294, November 7, 1985; 52 FR 8726, March 19, 1987; and,
53 FR 36972, September 23, 1988.
-------
technologies, which are described in Section 3.6. As an
alternative to measuring ventilation emissions from the cell room
to demonstrate compliance, the part 61 NESHAP allows'an owner or
operator to assume a ventilation emission value of 1,300 grams
per day of mercury provided that the owner/operator adheres to a
suite of approved design, maintenance, and housekeeping
practices.-'- All twelve mercury cell chlor-alkali plants carry
.out these eighteen practices instead of measuring mercury
emissions from the cell room ventilation system. Section 3.7
provides specific examples of the implementation of these and
other plant practices for limiting fugitive mercury emissions.
3.2 BY-PRODUCT HYDROGEN STREAM
The by-product hydrogen stream, which is a point source of
mercury emissions, is the by-product hydrogen gas from each
mercury cell decomposer that is manifolded and treated in the
hydrogen system before being burned as fuel, transferred to
another process as raw material, or discharged directly to the
'atmosphere. At the twelve mercury cell chlor-alkali plants, the
temperature of the by-product hydrogen stream at the inlet to the
control system ranges from 85 °F to 200 °F, with a mean of 132°F
and a median of 124°F. The mercury composition of a stream at
the median stream temperature would be no higher than the
saturation concentration of 142 milligrams per cubic meter
(mg/m-) (at 125°F). The volumetric flow rate of the stream
upstream, of the control system ranges from 930 standard cubic
3-2
-------
feet per minute (scfm) to 5,064 scfm, with a mean of 2,721 scfm
and a median of 2,535 scfm.
3.3 END-BOX VENTILATION SYSTEM AND END-BOX VENTILATION STREAM
The vent of the end-box ventilation system, which .evacuates
the head spaces of mercury cell end boxes and other vessels and
equipment to the atmosphere, is also a point source of mercury
emissions, when such a system is present at a plant. Ten of•the
twelve mercury cell chlor-alkali plants 'have end-box ventilation
systems. The eighteen practices referenced in the part 61 NESHAP
require maintaining end boxes of mercury cells under negative
.pressure by a ventilation system, unless the end boxes are
equipped with fixed covers which are leak-tight. The practices
also require each submerged mercury pump, which is used in a
mercury pump tank for moving mercury regenerated in the
decomposer back to the inlet'end of the mercury cell, have a
vapor outlet connected to the end-box ventilation system.
Further, an aqueous layer is required to be maintained (at a
temperature below its boiling point) over mercury in both inlet
and outlet end boxes (unless they are closed) and over mercury in
tanks associated with submerged mercury pumps. Occidental's
Muscle Shoals, Alabama plant and Deer Park, Texas plant both have
closed end boxes and have in-line mercury pumps with associated
pump coolers and, thus, do not have end-box ventilation systems.
Inputs to end-box ventilation systems at the ten mercury
cell chlcr-alkali plants with these systems differ due to
-------
different plant equipment designs. Table 3-1 identifies the
points routed to the end-box ventilation system at each of the
ten plants.
TABLE 3-1. POINTS ROUTED TO END-BOX VENTILATION SYSTEMS
\
Plant
Owner /Location
HoltraChem
Orringtcn, ME
Pioneer
St. Gabriel, LA
OxyChem
Delaware City, CE
Vulcan
Port Edwards, WI
PPG
Lake Charles, LA
Westlake
Calvert Cizy, KY
Oiin
Charleston, TK
Oiin
Augusta, GA
PPG
N a r r i cr1"1 , /.
ASKTA
Ashtabula, OH
Make,
Number
of
Mercury
Cells
DeNora,
24
Uhde,
52
DeNora,
88
DeNora ,
24
DeNora,
70
DeNora,
36
Oiin,
106
01 in,
60
Uhde,
54
Oiin,
24
Ventilated Points
to
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x
o
m
T)
c
4J
a)
4J
3
O
4-1
0)
•H
C
M
X
X
X
£*1
rH
C
O
to
cu
X
0
pa
•o
H
4J
0)
r-H
C
M
X
•^
o
to
0
X
o
m
TD
-P
0)
4J
o
X
X
CO
A;
C
tO
0)
m
w
(0
S
X
o
CO
1
c
CJ
X
X
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-------
Both inlet and outlet end boxes are ventilated at four
plants. Only inlet end-boxes are ventilated at one plant, as the
aqueous and brine layers above mercury amalgam in the outlet end
boxes are believed to sufficiently limit the evaporation of
mercury. Only outlet end-boxes are ventilated at five plants,
for the following reasons: (1) three plants have Olin cells,
which do not have inlet end boxes; (2) one plant has closed inlet
end boxes; and (3) one plant does not ventilate inlet end boxes
due to safety concerns with hydrogen gas (this plant has closed
end boxes, and although the plant is thus not required to do so,
it operates outlet end boxes under negative pressure).
At the three plants with Olin cells, submerged pumps within
mercury pump tanks or sumps are ventilated. For the remaining
plants, DeNora cr Uhde cells are not designed with submerged
pumps. The plants with DeNora cells, however, do ventilate a
section of piping preceding the in-line pump, which is referred
to as the pump seal leg cr loop.
End-box wash water (from the aqueous layer maintained over
mercury in end boxes cr pump tanks; may be held in tanks prior to
wastewater treatment. At five plants, end-box wash water tanks
are also ventilated. Other miscellaneous ventilated points
include the caustic tank/header, cell room sump (via an opening
in the sump cover), and graphite treatment system. Regarding
tnis last point, in whicn graphite removed from decomposers is
reactivated v.'itr. a rolvrdate comround, the need for ventilation
-------
arises due to mercury embedded in the graphite that is vaporized
when a vacuum is exerted to impregnate molybdate. This point is
i
not reported by more plants, as most add molybdate s6lution
directly into the decomposer.
As discussed above, in inlet and outlet end boxes and in
tanks associated with submerged mercury pumps that are
ventilated, mercury is covered by an aqueous layer. Also
discussed above was the ventilation of end-box wash water tanks,
caustic tanks/headers, and a cell room sump, points in which
mercury is inherently found beneath an aqueous layer. Thus, the
end-box ventilation stream is never saturated with mercury, as
air and liquid mercury are always separated by an aqueous layer
and cannot attain equilibrium.
At the ten mercury cell chlor-alkali plants with an end-box
ventilation system, the volumetric flow rate of the end-box
ventilation stream upstream of the control system ranges from
202 scfm to 4,500 scfm, with a mean of 1,492 scfm and a median of
•779 scfm. The stream temperature upstream of the control system
ranges from 89°F to 158°F, with a mean of 118°F and a median of
11C°F. The mercury concentration of the stream at this point
ranges from A mg/m3 (for the 89°F streamy to 200 mg/m3 (for the
158°F stream). The mercury concentration of a stream at 120°F
(before the control system) was reported as about 7 mg/m". These
values indicate a wide range in the degree of saturation of end-
box ventilation streams, from about 6 percent to 41 percent.
3-6
-------
3.4 MERCURY THERMAL RECOVERY UNIT OFF-GAS
The vent of the mercury thermal recovery unit, in which
mercury-containing wastes are heated in retort(s) to volatilize
mercury and the resulting retort off-gas is cooled to condense
mercury for recovery as a liquid, is a point source of mercury
emissions, when such a unit is present at a plant. Six mercury
cell chlor-alkali'plants have thermal recovery units on-site'. Of
these six plants, three plants have oven type units and three
plants have non-oven type units, as discussed in Chapter 2,
Section 2.4.1. The average volumetric flow rate of the gas
.stream upstream of the recovery/control system (i.e., the retort
off-gas) is not known for all oven-type units. For non-oven type
units, the average retort off-gas flow rate ranges from 700 scfm
to 1,250 scfm, with a mean of 1,008 scfm and a median of
1,075 scfm. The temperature of the off-gas ranges from 600°F to
850°F, with a mean and median of 725°F, for oven-type units and
from 1,850°F to 2,100°F, with a mean of 1,983°F and median of
2,_000°F for non-o-en units.
3.5 FUGITIVE EMISSIONS AND CELL ROOM VENTILATION
The majority of fugitive mercury emission sources at a
mercury cell chlor-alkali plant are associated with cell rooms,
which are structures in which mercury cells are situated and many
process and housekeeping functions are carried out. Cell rooms
bring together mercury, a large electrical load, and hot
production equipment. Accordingly, most fugitive mercury
-------
emission sources at mercury cell chlor-alkali plants are
associated with cell rooms. Fugitive mercury emissions are the
result of mercury released to air from various process events.
The opening of a mercury cell for cleaning or other maintenance
results in mercury vapor released to the cell room environment.
Hydrogen/mercury vapor leaks from decomposers as well as other
portions pf hydrogen systems, particularly upstream of hydrogen
headers, and mercury volatilization during liquid mercury leaks
or caustic leaks also result in such emissions. In both cell
rooms and waste storage areas, mercury volatilized from liquid
mercury spilled as part of operational or maintenance activities
also contributes to fugitive mercury emissions. Mercury may also
volatilize from a liquid mercury accumulation situated on a
surface exposed to the air or beneath an aqueous layer in an open
container or trench. Liquid mercury exposed to the atmosphere
evaporates a rate depending on temperature, air flow, and other
variables .
Cell room.s are ventilated in order to dissipate heat evolved
by mercury cells and to reduce worker exposure to mercury vapor
in the cell room environment. All cell rooms are ventilated
along the length of the cell room roof, either by way of roof
monitors or cupolas or through static or mechanically driven
ventilators. Cell rooms in warm climates tend to also be
ventilated through openings in the cell room walls. Due to these
conditions, the reliable measurement of mercury emissions from
3-8
-------
most cell rooms would be costly, owing to the need to measure
both mercury vapor concentration and air flow rate at apertures
with sophisticated equipment. The measurement of mercury
emissions from mercury-containing waste storage areas is also
impracticable, as these are usually located in several places
throughout a plant, many of which are open areas. Not
unexpectedly, emissions data o^ cell room emissions are very-
limited and are non-existent for waste Storage areas.
3.6 VENT CONTROL TECHNIQUES AND SYSTEMS
To control mercury emissions from point sources, mercury
cell chlor-alkali plants employ a variety of technologies,
including condensation, absorption, and adsorption, and
combinations of these technologies. These control systems are
described in tnis section. Specifically, condensation is
discussed in section 3.6.1, followed by absorption in 3.6.2 and
adsorption in 3.6.3. Section 3.6.4 discussed the specific
applications and combinations of these technologies at mercury
cell chlor-alkali plants.
3.6.1 Condensation^-' -1
Condensation is a technique in which a pollutant in a gas
stream is separated from the remaining gas components through
saturation fcliowec. cy a phase change. Condensation of the
pollutant actually occurs at its dew point, when the partial
pressure of the pollutant in the gas stream equals its vapor
pressure at the operating temperature.
-------
The change from gas to liquid can be achieved by lowering
the temperature of the mixture and/or increasing its pressure.
Temperature reduction is used most often, as gas compression
tends to be more expensive. When a hot gas stream contacts a
cooler medium, heat is transferred from the hot gas mixture to
the cooler medium, thereby lowering the average kinetic energy of
the gas (i.e., lowering of gas temperature). Hence, gas
molecules are slowed and the distance between them reduced such
that van der Waals forces between molecules cause the formation
of liquid.
Condensation devices, or condensers, may be of two types':
(1) direct contact, in which the cooling medium and gas
stream/condensate are combined, and (2) indirect contact, in
which the cooling medium and gas stream (including condensate)
are separated by some sort of surface (hence, the synonymous
designation of a surface condenser).
The pollutant removal efficiency of a condenser with fixed
coolant flow rate and temperature depends on the following
parameters: (1) volumetric flow rate of gas stream, (2) inlet gas
stream temperature, (3) pollutant concentration in gas stream,
(4) absolute gas stream pressure, (5) gas stream moisture
content, and (6) pollutant properties, including heat of
condensation, heat capacity, and vapor pressure.
3-10
-------
3.6.2 Absorption4'5
Absorption is a technique in which a pollutant in a gas
stream (the solute) is separated from the remaining gas
components through diffusion and dissolution into a non-volatile
liquid solution (the solvent). Mass transfer occurs due to the
difference in the concentration in the gas (high) and the
concentration in the liquid (low, below the equilibrium
concentration). This physical absorption may be followed by
chemical reaction between the absorbed pollutant and solvent,
which enhances the rate of absorption. The rate of absorption
is, however, typically limited by the diffusion rate.
Absorption devices, which are also called absorbers or
scrubbers, are most corrmonly packed towers that contain packing
material's providing a large surface area to maximize gas-liquid
contact. The gas stream to be treated is introduced near the
bottom of the tov.-er ar.c contacts a liquid scrubbing solution
flowing countercurrently from the top of the column. Aqueous
liquids are the mcst common solvents for inorganic pollutants.
Mist eliminators are passive devices generally found at the tops
of packed tower scrubbers. Mist eliminators provide surface area
on which residual droplets or mosts in the exiting gas stream may
coalesce and fall back into the column.
For an absorber, pollutant removal efficiency depends on
operational and design parameters such as: (1) pollutant
concentrations in inlet gas and solvent, (2) pollutant
-------
diffusivity in the gas and in the solvent and equilibrium
solubility in the solvent (which are temperature dependent),
(3) gas and solvent flow rates, (4) density and viscosity of the
gas and the solvent (which are temperature dependent), and
(5) operating pressure, (7) properties of packing elements (i.e.,
surface to volume ratio), (8) height of packing (based on the
operating.conditions and the equilibrium relationship between
pollutant and solvent), and (9) dimensions of the absorber
column.
3.6.3 Adsorption6'7
Adsorption is a technique in which a pollutant in a gas •
stream (the adsorbate) is separated from the remaining gas
components through adhesion at the surface of solid particles
(adsorbent). Unbalanced forces at the adsorbent surface that are
stronger than intermolecular forces between the pollutant gas
molecules cause the retention (van der Waals attraction) of the
pollutant on the solid surface. This physical adsorption may be
followed by chemiscrption, or chemical reaction between the
pollutant and solid. Whereas pollutants physically adsorbed may
be desorbed to regenerate the adsorbent, chemisorption is
generally not reversible.
Many adsorbents are amorphous in the sense that they have a
non-uniform internal structure. The most common amorphous
adsorbent is activated carbon, typically obtained by heating ccal
or coconut/nut shells anaerobically to obtain particle surface
3-12
-------
activity. Activated carbons may be impregnated with elements to
promote chemical adsorption properties. Adsorbents with a
crystalline internal structure are generally termed as molecular
sieves, which are useful for adsorption of particular species.
In all cases, the adsorbent is chosen for its large surface area
relative to its mass.
Adsorbers,•or adsorption devices, are most commonly vessels
with a stationary (fixed) carbon bed. The pollutant removal
efficiency of. an ^adsorber is a function of the gas stream
temperature and volumetric flow rate, inlet pollutant
concentration in the gas stream, and the condition of the carbon
bed. Since a key factor determining collection efficiency is the
length of time the gas in contact with the adsorbent, carbon bed
depth and sorbent particle size are important design
considerations. A significant operational consideration is the
frequency at which the adsorbent is replaced in a non-regenerable
adsorber, since the adsorption capacity decreases over time as
adsorbent particle surfaces are saturated and breakthrough is
approached.
3.6.4 Vent Control Systems
The technologies discussed in the previous sections are
often combined into a mercury control "system" for a particular
vent. Tables 3-2, 3-3, and 3-4 show by-product hydrogen
stream, end-box ventilation system, and mercury thermal recovery
-------
TABLE 3-2. BY-PRODUCT HYDROGEN CONTROL SYSTEMS AT
MERCURY CELL CHLOR-ALKALI PLANTS
Plant Owner/
Location
ASHTA
Ashtabula, OH
HoltraChem
Orrington, ME
Occidental
Muscle
Shoals, AL
Occidental
Delaware
City, DE
Occidental
Deer Park, TX
01 in
Augusta, GA
Olin
Charleston,
TN
Pioneer
St. Gabriel,
LA
PFG
Lake Charles,
LA
FFG
Natrium, WY
Vulcan
^ O 2T *i — G W £ ZT Q S /
WI
Kestlake
Calvert City,
KY
By-Product Hydrogen Stream Control System
Temperature
at final
cooling
outlet ( F)
<70
•68
• 46
55
75
46
50
79
<58
<70
n/a (cooling
not used;
9C
Demister
used?
Yes - one
Yes - two,
one between
the two
coolers and
one after
second cooler
No
No
No
Yes- - one
Yes - one
No
Yes - two
No
Nc
Yec - one
Finishing device
Molecular Sieve
Adsorber
Carbon Adsorber
(carbon impregnated
with iodine and
potassium iodide)
Series carbon
adsorbers (carbon
impregnated with
iodine and
potassium iodide)3
Two series carbon
adsorbers (sulfur
impregnated carbon)
Molecular sieve
adsorber
Molecular sieve
adsorber
Molecular sieve
adsorber
Molecular sieve
adsorber
Packed tower
scrubber (depleted
brine)
Packed tower
scrubber
(chlorinated brine)
Carbon adsorber
(salfur
imoreanated)
Finishing device
•
Carbon adsorber
(carbon
impregnated with
potassium iodide]
Carbor. adsorber
(sulfur
impregnated)
/"* _ ^ V- - ^ --~-~^.--v
^ d i- *- '~ i * a '^ i ^ ^ ^ 'o ^
(sulfur
impregnated }
Two parallel
carbon adsorbers
a Due to the presence of two mercury cell circuits, there are two hydrogen
control systeirs. Circuit 1 is operated with two identical series adsorbers,
while circuit 2 is operated with' three series adsorbers.
3-14
-------
TABLE 3-3. END-BOX VENTILATION CONTROL SYSTEMS AT
MERCURY CELL CHLOR-ALKALI PLANTS
Plant
Owner/
Location
ASHTA
Ashtabula,
OH
HoltraChem
Orrington,
ME
Occidental
Delaware
City, DE
Olin
Augusta, GA
Olin
Charleston,
TN
Pioneer
St.
Gabriel, LA
PFG
Lake
Charles, LA
PPG
N a t r i uir. , KV
Vulcan
Port
Edwards, KI
West lake
Calvert
City, KY
End-Box Ventilation Control System
Temperature
at outlet of
last cooling
device ( F)
<90
95
60
46
40
n/a (cooling
not used,
inlet temp is
89)
<63
67
n/a (cooling
not used,
inlet temp is
110)
n/a (cooling
not used,
inlet ter;c is
90:
Demister
used?
No
Yes - one
Yes - one
No
Yes - one
Yes - one
Yes - one
No
No
No
Finishing
device
Molecular sieve
adsorber
Packed tower
scrubber
(chlorinated
brine)
Packed tower
scrubber
(aqueous sodium
hvoochlorite)
-------
TABLE 3-4. THERMAL RECOVERY UNIT CONTROL SYSTEMS AT
MERCURY CELL CHLOR-ALKALI PLANTS
Plant Owner/
Location
Occidental
Muscle Shoals, AL
Occidental
Delaware City, DE
Occidental
Deer Park, TX
, Olin
Charleston, TN
PPG
Lake Charles, LA
Vulcan
Port Edwards, WI
Thermal Recovery Unit
Recovery/Control System
Temperature
at outlet of
last cooling
device ( F)
100
69
80
50
57
80
Finishing device
Carbon adsorber
(iodine impregnated)
Carbon adsorber
Two series carbon
adsorbers (sulfur
impregnated)
Two parallel carbon
adsorbers (sulfur
impregnated)
Two series carbon
adsorbers (sulfur
impregnated and
activated carbon)
Packed tower
scrubber
( rhl or •> natpri hrinp)
3-16
-------
unit control systems at mercury cell chlor-alkali plants. In
these control systems, condensers are used as initial control
!
devices, upstream of absorption and adsorption "finishing"
control devices. Packed tower scrubbers are used in several vent
control systems. Molecular sieve adsorbers are used in some by-
product hydrogen and end-box ventilation control systems. Carbon
adsorbers are used in many by-product hydrogen and thermal
recovery unit vent control systems.
A primary factor influencing the overall performance of
these control systems is the temperature to which initial
coolers/chillers/condensers/heat exchangers cool the gas stream
prior to entering finishing control devices. Because of the
volatile nature of elemental mercury, temperature has a direct
effect on the concentration of mercury vapor that can exist in a
gas stream. For example, the concentration of mercury vapor that
could exist in a gas stream at 50°F is 5 mg/m3, while the maximum
(saturation) concentration at 85°F is 30 mg/rrr, a six-fold
increase. At 100°F, the concentration could potentially be over
50 mg/rrr . 8
In by-product hydrogen stream control systems, the hydrogen
gas temperature reduction effected by initial cooling devices
ranges from 18 percent tc 66 percent, with a mean of 47 percent
and a median of 53 percent. For initial cooling devices in end-
box ventilation control systems, the temperature reduction of the
ventilation air stream ranges frcm 4C percent to 64 percent, with
-------
a mean and median of 52 percent. In thermal recovery/control
systems, the temperature reduction of the retort off-gas by
initial control devices (primarily but not limited to
coolers/chillers/condensers/heat exchangers) ranges from
89 percent to 91 percent, with a mean and median of 90 percent,
for oven-type units and from 96 percent to 98 percent, with a
mean and median of 97 percent, for non-oven units.
In the packed tower scrubbers used for mercury control in
this industry, chlorinated brine (also referred to as depleted
brine), or aqueous sodium hypochlorite solution are used as the
liquid scrubbing medium. In the former case, the source of the
liquid scrubbing medium is spent brine from mercury cells, which
is maintained in a narrow pH range so that chlorineb and water
molecules in the solution react to form hypochlorous acid and
hydrogen chloride. These reaction products are vital to the
absorption mechanism, as hypochlorous acid and the elemental
mercury in the gas stream to be treated initially react, and
hydrogen chloride reacts with the resulting intermediate species
to form mercuric chloride, a form of mercury more amenable to
dissolution. With this mechanism, the absorbed mercury may be
recycled directly into the mercury cell process with the return
of the scrubber effluent to the brine system and, subsequently,
the mercury cells, causing dissociation of the mercuric chloride
tChlcrine would normally be removed from the spent brine as
part of brine preparation, hence the term "chlorinated brine"
used by one plant.
3-18
-------
into mercury cations and chlorine anions followed by reduction of
the mercury cations at the cell cathode. With the use of sodium
hypochlorite scrubbing liquid, the solution is formed using two
chlor-alkali products, namely chlorine and sodium hydroxide. The
resultant hypochlorite anions in the solution are used to
chemically absorb elemental mercury in the gas stream to be
treated, as both, mercurous chloride (a slightly soluble species)
followed by mercuric chloride (a more so'luble species) .
Table 3-5 presents characteristics of packed tower scrubbers used
in mercury cell chlor-alkali vent control systems.
The molecular sieve adsorbers used in by-product hydrogen
and end-box ventilation control systems are part of PuraSiv®
systems originally developed and supplied by Union Carbide
Corporation. PuraSiv© systems consist primarily of two adsorber
beds, containing a proprietary molecular sieve media, that
alternate operation such that while one is treating the gas
stream, the other is either being regenerated' or waiting to be
placed on-line, depending on the lengths of the adsorption and
regeneration cycles. Bed regeneration is accomplished by heat-
stripping, specifically by diverting a portion of the treated
strearr. at an elevated temperature through_the spent bed in order
to volatilize mercury held by the molecular sieve adsorbent.
This is followed by bed cooling as well as recycling of the
regeneration gas into the control system for treatment.
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Table 3-6 presents characteristics of molecular sieve adsorbers
used in mercury cell chlor-alkali vent control systems.
Carbon adsorbers used in by-product hydrogen and thermal
recovery unit control systems are fixed bed, non-regenerable
units and contain carbon media impregnated with sulfur, with
potassium iodide, or with both iodine and potassium iodide.
Differences in mercury removal efficiency between these types of
carbon adsorbents are not significant, provided that a sufficient
ratio is maintained between mercury loading to the adsorber and
the carbon adsorbent available for adsorption.^ Certain product
specifications may preclude the use of a particular impregnated
adsorbent, such as customer applications that cannot tolerate
residual sulfur in by-product hydrogen with the use of sulfur-
impregnated carbon adsorbent. Table 3-7 presents characteristics
of carbon adsorbers used in mercury cell chlor-alkali vent
control systems.
3.7 EMISSION CONTROL TECHNIQUES FOR FUGITIVE EMISSION SOURCES10
Techniques practiced by mercury cell chlor-alkali plants to
limit fugitive mercury emissions can be classified as design
(equipment) specifications, operational practices, and diagnostic
practices.
Examples of aesigr. specifications observed include using
vessels in liquid mercury service that have a cone shaped bottom
with a drain valve or other design that readily facilitates
mercury collection and using piping in liquid mercury service
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-------
that has smooth interiors. Examples of operational practices
include keeping decomposers closed and sealed (except for
maintenance) and maintaining decomposer covers in good condition,
allowing decomposers to cool before opening, either removing all
visible mercury from an internal part from a decomposer or
containing the part prior to transport to another work area, and
washing down tne area around the decomposer with water on a
routine basis and cleaning up mercury spilled after maintenance.
Many of the diagnostic practices observed by mercury cell
chlor-alkali plants are routine inspections, including regular
and directed inspections for equipment problems, for leak
detection, and for liquid mercury accumulations and spills.
Examples of visual inspections include checking for amalgam seal
pot covers not securely in' place, for caustic leaks, and for
accumulated mercury beads beneath decomposers. Inspecting for
hydrogen/mercury vapor leaks from decomposers may involve visual
or auditory methods or mercury vapor analyzer, combustible gas
meter, or other instrumentation. Following the inspections,
necessary operational and maintenance activities woula be
performed (i.e., cell shutdown, containment of caustic leaks, and
wash down of area and clean up of exposed liquid mercury).
The routine measurement of mercury vapor levels in the cell
room environment is another diagnostic practice observed by
mercury cell chlor-alkali plants. Such measurements are
typically conducted using mercury vapor analyzers or a wet.
3-26
-------
chemical assembly (permanganate impingers) at fixed locations, in
order to establish normative levels. Readings higher than a
certain level trigger follow-up activities such as more directed
diagnostics to pinpoint mercury vapor leaks and washdowns.
3.8 REFERENCES
1. Review of National Emission Standards for Mercury. EPA-
450/3-84-014a. U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina. December 1984.:
2. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards'Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001) .
Chapter 8. February 1996.
3. Buonicore, A. and Davis, W., eds. 1992. Air Pollution
Engineering Manual. Van Nostrand Reinhold, New York, NY.
4. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001) .
Chapter 9. February 1996.
5. Reference 3.
6. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001) .
Chapter 4. February 1996.
7. Reference 3.
8. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Calculation of
Saturation Mercury Concentration. November 19, 1998.
9. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information Gathered on Impregnated Carbons for Mercury
Removal. May 25, 2000.
10. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Rosario, I., U.S. Environmental Protection
Agency. Database Analysis of Chlorine Production Mercury
Housekeeping Measures. July 28, 1999.
-------
-------
4.0 REGULATORY ALTERNATIVES
4.1 INTRODUCTION
This chapter presents the regulatory alternatives considered
for national emission standards for hazardous air pollutants
(NESHAP) for limiting mercury emissions from mercury cell chlor-
alkali plants. Section 4.2 provides background on the statutory
authority of these NESHAP, and Section 4.3 presents the
regulatory alternatives considered. This chapter does not
include details on the development of these alternatives. These
details, along with the rationale behind the selection of the
regulatory alternatives for proposal, are provided in Chapter 7.
4.2 STATUTORY AUTHORITY
Section 112 (d' cf the Clean Air Act (CAA) requires that
emission of hazardous air pollutants (HAP) from listed stationary
sources be regulated by establishing national emission standards.
The statute requires that standards established reflect the
ma Fimum degree cf reduction in HAP emissions, taking into
consideration the cost of achieving such emissions reductions,
any non-air quality health and environmental impacts, and energy
impacts. These standards are referred to as the maximum
achievable control technology, or MACT, standards.
-------
Section 112(d)(3) of the CAA requires'that the standards
established 'be no, less stringent than a defined minimal level of
control. This minimal level is referred to as the "MACT floor."
For new sources, the minimal level of control
. . . shall not be less stringent than the emission control
that is achieved in practice by the best controlled similar
source, as determined by the Administrator.
For existing sources in the same category or subcategory,
•the minimal level of control is specified as
. . . the average emission limitation achieved by the best
performing 12 percent of the existing sources (for which the
Administrator has emissions information) ... in the
category or subcategory for categories or subcategories with
30 or more sources, or ... the average emission limitation
achieved by the best performing 5 sources (for which the
Administrator has or could reasonably obtain emissions
information) in the category or subcategory for categories
or subcategories with fewer than 30 sources.
"Average" is defined to mean a measure of central tendency,
whether it be the arithmetic mean, median, or mode, or some other
measure based on the best measure decided on for determining the
central tendency of a data set (59 FR 29196).
Once the minimal (floor) level of control is determined,
Section 112(d)(2) requires that the maximum degree of reduction
in emissions of HAP be determined, taking into consideration
options that would achieve greater emission reductions.
4.3 REGULATORY ALTERNATIVES
The mercury cell chlor-alkali plants currently in the U.S.
each operate a mercury cell chlor-alkali process in whicn mercury
cells (and ancillary operations) are used to manufacture chlorine
4-2
-------
and caustic as co-products and hydrogen as -a by-product. Six
plants have mercury thermal recovery units in which mercury-
containing wastes are heated to recover liquid mercuty. For the
purpose of developing regulatory alternatives, mercury cell
chlor-alkali plants were separated into those operations
associated with the. production of chlorine and caustic and those
associated with mercury recovery.
As discussed in Chapter 2, there may be up.to four types of
mercury emission sources at a mercury cell chlor-alkali plant:
(1) hydrogen by-product streams, (2) end-box ventilation system
vents, (3) mercury thermal recovery unit vents, and (4) fugitive
emission sources. The hydrogen by-product streams and end-box
ventilation system vents are unique to chlorine production
operations, and the mercury thermal recovery unit vents are
unique to recovery operations. Fugitive emissions occur from
both production and recovery operations.
Regulatory alternatives were developed for the emission
source types cited above. Specifically, regulatory alternatives
were developed for mercury emissions from: (1) hydrogen by-
prodact streams and end-box ventilation system vents at plants
with end-box ventilation systems, (2) mercury emissions from
hydrogen by-product streams at plants without end-box ventilation
systems (that is, those plants with "closed" end-boxes), (3) oven
type mercury thermal recovery unit vents, (4) non-oven type
mercury thermal recovery unit vents, and (5) fugitive emission
-------
sources. Section 7.5.1 provides an explanation of the
development of separate regulatory alternatives for hydrogen by-
product streams and end-box ventilation system vents, and
Section 7.5.3 provides an explanation of the development of
separate alternatives for mercury thermal recovery unit vents.
Table 4-1 presents a summary of the regulatory alternatives
for mercury emission sources at mercury cell chlor-alkali plants.
For existing sources, Regulatory Alternative I represents the
minimum level of control, or the MACT floor. Regulatory
Alternative II represents a level of control identified above
this minimum floor level. For new sources, the single
alternative represents the only alternative identified, which in
each case is at least equivalent to the "best controlled similar
source."
4-4
-------
TABLE 4-1. -REGULATORY ALTERNATIVES FOR MERCURY EMISSION SOURCES
AT'MERCURY CELL CHLOR-ALKALI.PLANTS
Emission Source Group
Regulatory
Alternative I
(MACT Floor)
Regulatory
Alternative II
Existing Sources
Fugitive Emission Sources
Hydrogen By-Product
Streams/End-Box Ventilation
System Vents8
Hydrogen By-Product Streamsb
Oven Type Mercury Thermal
Recovery Unit Ver.ts
Non-Oven Type Mercury Thermal
Recovery Unit Vents
Part 61 Housekeeping
Procedures
0.14 gram mercury
emitted per Megagram
chlorine produced
0.10 gram mercury
emitted per Megagram
chlorine produced
c
3 milligrams mercury
erritted per dry
standard cubic meter
of exhaust
Enhanced Work
Practices
0.067 gram mercury
emitted per Megagram
chlorine produced
0.033 gram mercury
emitted per Megagram
chlorine produced
23 milligrams
mercury emitted per
.dry standard cubic
meter of exhaust
4 milligrams mercury
emitted per dry
standard cubic meter
of exhaust
New Sources
Hydrogen Ey-Product Streams,
End-Box Ventilation System
Vents, and Fugitive Er.iS£_cn
Sources at Operations Producing
Cr.Iorine
Prohibition of mercury emissions
Oven Type Mercury Thermal
Recovery unit '. er.ts
1
on-Oven Type Mercury Tnermal
Recovery Unit Vents
Fugitive Emission Sources at
23 milligrams mercury emitted per dry
standard cubic meter of exhaust
4 milligrams mercury emitted per ary
stanaard cubic meter of exhaust
Enhanced Work Practices
c Data were only available for the plant with the best performing control
system en ~:e ever type- rrercury thermal recovery ar.it vents.
-------
5.0 ENVIRONMENTAL AND ENERGY IMPACTS
5.1 INTRODUCTION
This chapter presents the environmental and energy impacts
of the existing source regulatory alternatives described in
Chapter 4 for the mercury cell chlor-alkali industry.
Environmental and energy impacts were estimated on a plant-by-
plant basis and then summed for the estimated nationwide annual
.impacts. Environmental impacts include primary impacts, or
reductions of mercury air emissions, as well as secondary
impacts, or alterations in the nature or amount of air pollution
(other than mercury), water pollution, and solid waste. Energy
impacts pertain to changes in electricity consumption.
As discussed in Chapter 4, Section 4.1, it is assumed that
no new mercury cell chlcr-alkali production facilities will be
built in the United States (U.S.). In addition, it is
anticipated that nc new mercury recovery facilities will be built
at mercury cell chlcr-alkali plants in the U.S. in the near
future. Therefore, no new or reconstructed source impacts were
estimated.
Baseline mercury air emissions are discussed in Section 5.2.
The overall methodology for estimating impacts of implementing
the existing source regulatory alternatives is summarized in
-------
Section 5.3. Primary environmental impacts, energy impacts, and
secondary environmental impacts are discussed in Sections 5.4,
5.5, and 5.6, respectively. Details on impacts calculations may
be found in a separate technical memorandum.
5.2 BASELINE MERCURY EMISSIONS
As discussed in Chapter 3, Section 3.1, the part 61 Mercury
NESHAP (40 CFR part "61, subpart E, §61.50 et. seq.)* limits
mercury emissions from a mercury cell chlor-alkali plant to 2,300
grams per day (grams/day). If a suite of eighteen approved
design, maintenance, and housekeeping practices^ are followed,
the rule allows the assumption of a 1,300 grams/day emission 'rate
from the cell .room ventilation system. This effectively creates
a mercury emission limit of 1,000 grams/day for the point sources
(vents) of mercury at a plant, namely by-product hydrogen streams
end-box ventilation system vents, and mercury thermal recovery
unit vents. Therefore, the nationwide level of annual baseline
mercury emissions allowed by the part 61 Mercury NESHAP is
10,074 kilograms per year (kg/yr) (22,209 pounds per year,
Ib/yr). This was simply calculated by multiplying 2,300 grams
per day by 365 days per year and by 12 plants. Of the 10,074
kg/yr total, fugitives account for 5,694 kg/yr (12,553 Ib/yr) and
point sources collectively make up 4,380 kg/yr (9,656 Ib/yr).
aThis regulatory program was originally set forth at 38 FR
8826, April 6, 1973; and amended at: 40 FR 48302, October 14,
1975; 47 FR 24704, June 8, 1982; 49 FR 35770, September 12, 1984;
50 FP 46294, November 7, 1985; 52 FR 8726, March 19, 19£~; and,
53 FR 36972, September 23, 1988.
5-2
-------
For the point sources of mercury, mercury cell chlor-alkali
plants reported annual mercury vent emissions that were lower
than the level allowed in the part 61 Mercury NESHAP: The
nationwide reported mercury emissions for points sources were
estimated to be about 933 kg/yr (2,057 Ib/yr). Summing this
value with 5,694 kg/yr (12,553 Ib/yr) of fugitive mercury
emissions, the nationwide annual actuals baseline emissions total
about 6,627 kg/yr (14,610 Ib/yr).
5.3 OVERALL IMPACTS ESTIMATION METHODOLOGY
Table 5-1 shows the existing source regulatory alternatives.
Regulatory Alternative II is more stringent than Regulatory
Alternative I for by-product hydrogen streams, end-box
ventilation system vents, non-oven type mercury thermal recovery
unit vents, and fugitive emission sources. As discussed in
Chapter 4, Regulatory Alternative I represents the MACT floor
level of control for these emission sources, while Regulatory
Alternative II represents a beyond-the-floor level.
The primary environmental impacts are based on the
differences in the baseline emissions and the mercury emissions
that would occur upon implementation of the regulatory
alternative. For estimating secondary environmental and energy
impacts for point sources, the control system enhancements needed
to meet the emission limits associated with the regulatory
alternatives were assumed, considering actual existing vent
-------
TABLE 5-1. REGULATORY ALTERNATIVES FOR EXISTING MERCURY EMISSION
SOURCES AT MERCURY CELL CHLOR-ALKALI PLANTS
Emission Source Group
Fugitive "mission Sources
Hydrogen ByrProduct
"Streams /End-Box Ventilation
System Ventsa
Hydrogen By-Product Streams*1
Oven Type Mercury Thermal
Recovery Unit Vents
Non-Over. Type Mercury Thermal
Recovery Unit Vents
Regulatory
Alternative I
(MACT Floor)
Part 61 Housekeeping
Procedures
0.14 gram mercury
emitted per Megagram
chlorine produced
0.10 gram mercury
emitted per Megagram
chlorine produced
c
5 milligrams mercury
emitted per dry
standard cubic meter
of exhaust
Regulatory
Alternative II
Enhanced Work
Practices
0.067 gram mercury
emitted per Megagram
chlorine produced
0.033 gram mercury
emitted per Megagram
chlorine produced
23 milligrams
mercury emitted per
dry standard cubic
meter of exhaust
4 milligrams mercury
emitted per dry
standard cubic meter
of exhaust
At plants with end-box ventilation systems.
b At plants with no end-box ventilation systems (i.e., with closed end boxes)
c Data were only available for the plant with the best performing control
system on the oven type mercury thermal reco\ery unit vents.
5-4
-------
controls. Tables 5-2, 5-3, and 5-4 present the enhancement
assumed for each vent at each mercury cell chlor-alkali plant to
meet the regulatory alternatives. Background information on
these assumptions may be found in a separate technical
o
memorandum.J
5.4 PRIMARY ENVIRONMENTAL IMPACTS
The implementation of Regulatory Alternative II for fugitive
emission sources and the implementation of Regulatory Alternative
I or Regulatory Alternative II for point sources would result in
lower mercury emissions released to the air. These mercury
.emissions reductions are discussed below for fugitive emission
sources, by-product hydrogen streams'and end-box ventilation
system vents, and mercury thermal recovery unit vents.
5.4.1 Fugitive Emissions
For fugitive emission sources, Regulatory Alternative I
represents a level cf control that is currently required at every
plant. Therefore, there would be no associated additional
reduction in fugitive mercury emissions.
Regulatory Alternative II represents a compilation of the
most stringent work practices applied in the industry. Hence,
every plant will likely need to enhance its existing housekeeping
program in some manner. While a decrease in fugitive mercury
emissions is expected, it is not possible to quantify the
reduction. Therefore, no reduction in mercury fugitive emissions
is attributed to Reaulatorv Alternative II.
5-:
-------
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-------
TABLE 5-4. ASSUMED CONTROL SYSTEM ENHANCEMENTS TO MEET THE
REGULATORY ALTERNATIVES FOR MERCURY THERMAL RECOVERY UNIT VENTS
AT PLANTS WITH SUCH UNITS
Plant Owner
Occidental
Occidental
Occidental
Olin
PPG
Vulcan
Plant Location
Muscle Shoals, AL
Delaware City, DE
•Deer Park, TX
Charleston, TN
Lake Charles, LA
Port Edwards, WI
Assumed Enhancement to
Meet Regulatory
Alternative I
Assumed Enhancement
to Meet Regulatory
Alternative II
replace existing carbon adsorber with new,
larger adsorber
none
replace existing carbon adsorber with new,
larger adsorber.
more frequent
replacement of carbon
in existing adsorber
none
none
more frequent
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in existing adsorber3
none
none
aRefers to more frequent carbon replacement than that assumed to meet
Regulatory Alternative I.
5-8
-------
5.4.2 By-Product Hydrogen Streams and End-Box Ventilation System
Vents
The Regulatory Alternative I includes an emission limit of
0.14 gram mercury emitted per Megagram chlorine produced (g Hg/Mg
C12) for plants with end-box ventilation systems and an emission
limit of 0.10 g Hg/Mg C12 for plants without end-box ventilation
systems. For each plant, the emissions level at this MACT floor
level was calculated by multiplying the annual chlorine
production (in Mg) by either 0.14 or 0.10 g Hg/Mg C12' and
converting to kg. The same calculation was performed for
.Regulatory Alternative II (using either 0.067 g Hg/Mg C12 for
plants with end-box ventilation systems or 0.033 g Hg/Mg C12 for
plants without end-box ventilation systems). Table 5-5 presents
combined' by-product hydrogen stream and end-box ventilation
system vent mercury emissions at Regulatory Alternatives I and II
and the estimated mercury emission reductions from combined
actual baseline emissions at each of the levels. '
5.4.3 Mercury Thermal Recovery Unit Vents
Regulatory Alternative I for mercury thermal recovery unit
vents includes mercury emission limits of 23 milligrams per dry
standard cubic meter (mg/dscm) for oven type vents and 5 mg/dscrc-
for non-oven type vents. For each plant, mercury emissions at
the regulatory alternative level were calculated by multiplying
either 23 or 5 mg/dscm by the reported vent exhaust flow rate and
5-9
-------
TABLE 5-5.. ESTIMATED COMBINED MERCURY EMISSIONS FROM BY-PRODUCT
HYDROGEN STREAMS AND END-BOX VENTILATION SYSTEM VENTS AT
REGULATORY ALTERNATIVE LEVELS
Plant
Owner /Location
ASHTA~. '
Ashtabula, OH
HoltraChem
Orrington, ME
Occidental
Muscle Shoals,
AL
Occidental
Delaware City,
DE
Occidental
Deer Park, TX
Olin August,
GA
Olin
Charleston, IN
Pioneer St .
Gabriel, LA
PPG Lake
Charles, LA
FPG Natrium,
WV
Vulcan Port
. Edward, WI
West lake
Calvert City,
FY
Chlorine
Production
(Megagrams
per yr)
43,110
.65,860
127,322
132, 450
88, 146
108,210
238, 592
173, 274
234, 056
66,225
T-, 092
111, 041
Nationwide Totalsd
Combined
Actual
Baseline
Emissions3
(kilograms
per year)
147.4
4.4
4.2
10.1
15.4
122.9
204 .1
19.1
74 .5
48.2
-L '~J . ^
73.4
734 .3
At Regulatory
Alternative I
(kilograms per year)
Annual
Emissions*3
6.2
' 4.4
4.2
10.1
9.2
15.6
34 .3
19.1
33.7
9.5
10.2
16. C
172.4
Emission
Reductions
from
Actual
Baseline
141.2
0.0
0.0
0.0
6.2
107.3
169.8
0.0
40.8
38.7
0.3
57.4
561.9
At Regulatory
Alternative II
(kilograms per year)
Annual
Emissions0
2.9
4.4
4.2
8.8
2.9
7.2
15.9
11.6
15.6
4.4
4 .7
7.4
90.1
Emission
Reductions
from
Actual
Baseline
144.5
0.0
0.0
1.3
12.5
115.7
188.2
7.5
58. 9
43.8
c £
6£ . C
644 .2
aThese oaseline emissions are based on annual vent mercury emission releases
reported by the plants. Part 61 NESHAP, of potential-to-emit, baseline
emissions are not shown, since only a value of 365 kg/yr for all point sources
at a plant is available (i.e., NESHAP baseline emissions specifically for by-
product hydrogen streams and end-box ventilation system vents canr.ct be
determined).
Emissions are calculated by multiplying the emission limit (either 0.14 or
CMC z Rg/I?g Cl:' by the annual chlorine production and dividing by I,*"1??.
""Emissions are calculated by multiplying the emission limit (eitner 0.067 or
0.033 g Hg'/Mg C12) by the annual chlorine production and dividing by 1,000.
GTotals may net always appear tc be the SJIT. of values shown due tc rcur.aing.
5-10
-------
the annual operating time and employing appropriate unit
conversions. The same calculation was performed for Regulatory
Alternative II, using either 23 mg/dscm for oven type vents or
4 mg/dscm for non-oven type plants. Table 5-6 presents the
mercury thermal recovery unit vent emissions at the regulatory
alternative levels and the estimated mercury emission reduction
from actual baseline emissions at each of the levels.
5.4.4 All Emission Sources
Table 5-7 summarizes the estimated primary environmental
impacts of the regulatory alternatives for point sources as the
total reductions in mercury air emissions in units of kilograms
per year. The estimated nationwide reduction in mercury
emissions with Regulatory Alternative I for point sources is
arouno. 4., 045 kg/yr (a 92.3 percent reduction) from the vent part
61 NESHAP (or potential-to-emit) baseline level and around
598 kg/yr (a 64 percent reduction) from the actual baseline
level. The estimated absolute reduction in mercury emissions
also represents total reductions for all sources (fugitives and
point sources) witn Regulatory Alternative I, since, by
definition there is no emission reduction associated with the
MACT floor level of control for fugitive emission sources
(overall estimated percentage reduction values are 40 percent
from the part 61 NESHAP baseline level and 9 percent from the
actual baseline level). Tnus, total mercury emissions
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-------
corresponding to Regulatory Alternative I would be 6,029 kg/yr
(13,292 Ib/yr).
The estimated nationwide reduction in annual mercury
emissions with Regulatory Alternative II for point sources is
around 4,133 kg/yr (a 94.4 percent reduction) from the vent part
61 NESHAP (or potential-to-emit) baseline level and around
686 kg/yr-(a 74 percent reduction) from the actual baseline
level. The estimated absolute reduction in annual mercury
emissions again represents total reductions for all emission
sources with Regulatory Alternative II. As previously discussed,
it is not possible to quantify the reduction in fugitive mercury
emissions, although a decrease is expected with the level of
control associated with Regulatory Alternative II. The overall
estimated percentage reduction values are 41 percent reduction
from the part 61 NESHAP baseline level and 10 percent from the
actual baseline level. Thus, total mercury emissions
corresponding to Regulatory Alternative II would be 5,941 kg/yr
(13,098 Ib/yr).
5.5 ENERGY IMPACTS
Regulatory Alternative I for fugitive emission sources
represents a level of control that is currently required at every
plant, as discussed in Chapter 4, Section 4.5. Therefore, there
would be no associated energy impacts. The implementation of
Regulatory Alternative II for fugitive emission sources would be
likely to cause every mercury cell chlor-alkali plant tc enhance
5-14
-------
its existing housekeeping program in some manner, as discussed in
Section 5.4.1. However, only the additional electrical power
consumed by new monitoring equipment assumed for plant cell rooms
could be quantified and, thus were attributed to observing the
Regulatory Alternative II work practices.
The implementation of the regulatory alternatives for point
sources would result in increased energy consumption. This
increase was estimated as the additional electrical (fan) power
per year expended in conveying gas streams through new carbon
adsorbers and new packed scrubbers at a plant (see Tables 5-2,
5-3, and 5-4). Specifically, device costing procedures detailed
in the OAQPS Control Cost Manual4 were used to compute the energy
requirement of a carbon adsorber or packed tower scrubber system
fan as the product of the stream flowrate, calculated pressure
drop through the vessel, and various factors accounting for units
conversions and assumed efficiencies; the hourly energy
requirement was then multiplied by the number of operating hours
per year to give the annual power consumption. The additional
electrical power per year consumed by new monitoring equipment
for plant vents was also included.
The estimated nationwide annual energy impacts of Regulatory
Alternative II for fugitive emission sources are about 53
thousand kilowatt-hours per year (kW-hr/yr). The estimated
nationwide annual energy impacts of Regulatory Alternative I and
-------
Regulatory.Alternative II for point sources are about 1,362
thousand and about 1,724 thousand kW-hr/yr, respectively.
5 . 6 SECONDARY IMPACTS
Regulatory Alternative I for fugitive emission sources
represents a level of control that is currently required at every
plant, as discussed in Chapter 4, Section 4.5. Therefore, there
would be no associated secondary impacts. The implementation of
•Regulatory Alternative II for fugitive emission sources would be
likely to cause every mercury cell chlor-alkali plant to enhance
its existing housekeeping program in some manner, as discussed in
Section 5.4.1. However, only secondary air pollution impacts
could be quantified and were attributed to observing the
Regulatory Alternative II practices.
The implementation of regulatory alternatives for point
sources would result alterations in the nature or amount of air
pollution (other than mercury), water pollution, and solid waste
attributed to mercury cell chlor-alkali plants. These are
separately discussed below.
5.6.1 Secondary Air Pollution Impacts
Indirect air pollutant emissions could result from the
production cf electricity required to operate new finishing
devices (see Tables 5-2, 5-3, and 5-4) and new monitoring
equipment for plant vents as well as new monitoring equipment for
plant cell rooms.
5-16
-------
Electricity production was assumed to be entirely from coal
combustion to correspond to a worst-case estimate. The
combustion of hydrocarbons yields carbon dioxide (C02) , water,
and particulate matter (PM); incomplete combustion generates, in
addition, carbon monoxide (CO) and sulfur dioxide (SO2) . All
types of combustion in air yield nitrogen oxides (NOX) , with more
generated during incomplete combustion. Accordingly, secondary
air emissions estimates were developed for these pollutants,
using the following emission factors: 1.9 Ib NOX per thousand kW-
hr, 4.25 Ib S02 per thousand kW-hr, 702 Ib CO2 per thousand kW-
'hr,5 0.078 Ib CO per thousand kW-hr, and 0.081 Ib PM per thousand
kW-hr.6
The estimated nationwide secondary air impacts for all
pollutants combined are about 17 Megagrans per year (19 tons per
year) for Regulatory Alternative II for fugitive emission
sources. The estimatec1 nationwide secondary .air impacts for all
pollutants combined are about 438 Megagrams per year (483 tons
per year) and abo-.t 554 Megagrams per year (611 tons per year)
for Regulatory Alternative I and Regulatory Alternative II for
point sources, respectively.
5.6.2 Water Pollution Impacts
The implementation of the regulatory alternatives for point
sources could result in an increased amount of mercury-containing
waters from the heightened use of packed tower scrubbing. This
increase was estimated as the total wastewater generated per year
5-r
-------
by five new packed tower hypochlorite scrubbers installed on end-
box ventilation system vents to meet Regulatory Alternative I.
For Regulatory Alternative II, this increase was estimated total
wastewater generated annually by the five new packed tower
hypochlorite scrubbers installed to meet the MACT floor level and
operated to give higher performance and two new packed tower
hypochlorite scrubbe'rs (see Tables 5-2 and 5-3) . Specifically,
the gas absorber costing procedure detailed in the OAQPS Control
Cost Manual^ was used to compute the annual volume of wastewater
as the product of the calculated scrubbing liquid flow rate
through the column, the fraction of scrubbing liquid wasted, 'and
number of operating hours per year.
The estimated nationwide annual water pollution impacts of
Regulatory Alternative I and Regulatory Alternative II for point
sources are about 1.2 million liters (320 thousand gallons) and
about 1.8 million liters (466 thousand gallons), respectively.
5.6.3 Solid Waste Impacts
The implementation of the regulatory alternatives for point
sources could result in an increased amount of mercury-containing
solid wastes due to the heightened use of'-carbon adsorption.
This increase was estimated as the amount of spent carbon
generated per year by seven new non-regenerative impregnated
carbon adsorbers installed and three existing non-regenerative
carbon adsorbers in which the carbon would be replaced more
freauently to meet Reaulatorv Alternative I. For Reaulatorv
5-18
-------
Alternative II, this increase was estimated as the amount of
spent carbon generated per year by a 25 percent higher carbon
charge in five of the seven new carbon adsorbers installed to
meet the MACT floor level, still more frequent replacement in two
existing carbon adsorbers, and three new carbon absorbers (see
Tables 5-2, 5-3, and 5-4). Specifically, the carbon adsorber
costing procedure in the OAQPS Control Cost Manual® and
appropriate modifications were used to compute the carbon charge
based on a optimum mercury-to-carbon ratio (see Chapter 6,
Section 6.3).
The estimated nationwide annual solid waste impacts of
Regulatory Alternative I and Regulatory Alternative II for point
sources are about 25 Megagrams (26 tons) and about 34 Megagrams
(38 tons), respectively.
5.7 SUMMARY OF ENERGY AND SECONDARY ENVIRONMENTAL IMPACTS
Table 5-8 summarizes the estimated nationwide energy impacts
and secondary environmental impacts of the regulatory
alternatives for all emission sources.
-------
TABLE 5-8. ESTIMATED ANNUAL ENERGY AND SECONDARY ENVIRONMENTAL
IMPACTS FOR REGULATORY ALTERNATIVES FOR ALL EMISSION SOURCES
Nationwide Impacts Regulatory Regulatory
Alternative I Alternative II
Energ", electrical power
consumed (kiloWatt-hours per 1,361,716 1,776,162
year
Secondary air pollution,
additional pollutants
emitted (kilograms per year)
NOX
" S02
C02
CO
PM
Water pollution, additional
mercury-contarrinatea 1,212,768 1,763,001
wastewater (Liters per year)
Solid waste, additional
spent carbon media 23,206 34,043
(kilograms per year)
1, 180
2,629
433,971
48
50
1,540
3,430
566,053
63
66
5-20
-------
5.8 REFERENCES
1. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. -Impacts Calculations
for Mercury Cell Chlor-Alkali Plant NESHAP Regulatory
Alternatives. December 14, 2001.
2. Review of National Emission Standards for Mercury. EPA-
450/3-84-014a. U.S. Environmental Protection Agency.
Research Triangle Park, North Carolina. December 1984.
3. Memorandum.. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Background on Vent
Control System Enhancements to Meet Regulatory Alternatives
for Existing Mercury Emission Sources at Mercury Cell Chlor-
Alkali Plants. September 26, 2001.
4. OAQPS Control Cost Manual (Fifth Edition), EPA,'Office of
Air Quality Planning and Standards, Emission Standards
Division, February 1996 (EPA 453/B-96-001).
5. Data from EPA's Acid Rain program
«www.epa.gov/acidrain/score97/es1997.html».
6. Data from EPA's National Pollutant Emission Trends Update,
1970-1997 on EPA's TTN CHIEF site ().
7. Reference 4.
8. Reference 4.
-------
-------
6.0 COST IMPACTS
6.1 INTRODUCTION
This chapter presents the cost impacts of implementing the
existing source regulatory alternatives described in Chapter 4
for the mercury cell chlor-alkali industry. Total annual cost
impacts were estimated on a plant-by-plant basis and then summed
for the estimated nationwide total annual cost impacts.
As discussed in Section 7.6, it is assumed that no new
•» mercury cell chlor-alkali production facilities will be built in
the United States (U.S.). In addition, it is anticipated that no
new mercury recovery facilities will be built at mercury cell
chlor-alkali plants in the U.S. in the near future. Therefore,
no new or reconstructed source impacts were estimated.
Costs incurred by a plant in complying with a standard
consist of emissions control costs and monitoring, recordkeeping,
and reporting (MR&R! costs. The former are associated with the
purchase, installation, and operation of pollution control
devices, while the latter pertain to monitoring emissions or the
performance cf control measures, keeping records of required
information, and submitting required reports.
Each of these cost categories may be divided into capital
and annual costs. Capital costs represent the one-time purchase
of equipment. Annual costs, which are recurrent, are the sum of
-------
direct and indirect costs. Direct costs tend to vary with the
level of emissions or production and include costs of raw
materials, utilities, waste treatment and disposal, maintenance
materials, replacement parts, and operating, supervisory, and
maintenance labor. Indirect costs are independent of the level
of emissions or production and include property taxes, insurance,
and administrative charges. Indirect costs also include the
.capital recovery cost, or capital cost "annualized" over the life
of the equipment. The sum of direct and indirect costs minus
annualized capital costs correspond to operating and maintenance
(O&M) costs.
The over-all methodology for estimating cost impacts of
implementing the existing source regulatory alternatives at
mercury cell chlor-alkali plants is summarized in Section 6.2.
Control and MR&R cost impacts estimated for fugitive sources and
point sources (vents) are discussed in Sections 6.3 and 6.4,
respectively. Total cost impacts for all mercury emission
'sources and estimated cost per unit of mercury emission reduction
are discussed in Section 6.5. Details on impact calculations may
be found in a separate technical, memorandum.-'-
6.2 OVERALL IMPACTS ESTIMATION METHODOLOGY
Table 6-1 shows the existing source regulatory alternatives.
Regulatory Alternative II is more stringent than Regulatory
6-;
-------
TABLE 6-1. REGULATORY ALTERNATIVES FOR EXISTING MERCURY EMISSION
SOURCES AT MERCURY CELL CHLOR-ALKALI PLANTS
Emission Source Group
Fugitive Emission Sources
Hydrogen By-Product
Streams/End-Box .Ventilation
System Vents3
Hydrogen By-Product Streamsb
Oven Type Mercury Thermal
Recovery Unit Vents
Non-Oven Type Mercury Thermal
Recovery Unit Vents
Regulatory
Alternative I
(MACT Floor)
Part 61 Housekeeping
Procedures
0.14 gram mercury
emitted per Megagram
chlorine produced
0.10 gram mercury
emitted per Megagram
chlorine produced
c
5 milligrams mercury
emitted per dry
standard cubic meter
of exhaust
Regulatory
Alternative II
Enhanced Work
Practices
0.067 gram mercury
emitted per Megagram
chlorine produced
0.033 gram mercury
emitted per Megagram
chlorine produced
23 milligrams
mercury emitted per
dry standard cubic
meter of exhaust
4 milligrams mercury
emitted per dry
standard cubic meter
of exhaust
At plants
end-ocx ventilation systems
1 At plants with nc end-bcx ventilation systems (i.e., with closed end boxes)
c Data were only available for the plant with the best performing control
system on the oven type mercury thermal recovery unit vents.
c- .
-------
Alternative. I for by-product hydrogen streams, end-box
ventilation system vents, non-oven type mercury thermal recovery
i
unit vents, and fugitive emission sources. As discussed in
Chapter 4, Regulatory Alternative I represents the MACT floor
level of control for these emission sources, while Regulatory
Alternative II represents a beyond-the-floor level.
"6.2.1 Cost Impacts for Fugitive Emission Sources
Regulatory Alternative I for fugitive emission sources
represents a level of control that is currently required at every
plant. Thus, the.re would be no associated cost impacts.
Regulatory Alternative II represents a compilation of the most
stringent work practices applied in the industry. These work
practices consist largely of monitoring and inspection
requirements, and costs incurred in implementing them are most
appropriately classified as MR&R cost impacts.
6.2.2 Control Cost Impacts for Point Sources
Control system enhancements, considering existing vent
controls, were assumed in order to estimate control cost impacts,
for point sources to meet the emission limits associated with the
regulatory alternatives. Tables 6-2, 6-3, and 6-4 present the
enhancement assumed for each vent at each mercury cell chlor-
alkali plant to meet the regulatory alternatives. Background
information on these assumptions may be found in a separate
technical memorandum.
6-4
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6-6
-------
TABLE 6-4. ASSUMED CONTROL SYSTEM ENHANCEMENTS
FOR MERCURY THERMAL RECOVERY UNIT VENTS AT PLANTS WITH SUCH UNITS
TO MEET THE REGULATORY ALTERNATIVES
Plant
Occidental
Occidental
Occidental
Olin
PPG
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Muscle Shoals,
AL
Delaware City,
Deer Park, TX
Charleston, TN
Lake .Charles,
Port Edwards,
Assumed Enhancement
to Meet Regulatory
Assumed
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new, larger adsorber
none
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more frequent
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carbon in existing
none
none
more frequent
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none
none
aRefers to more frequent carbon replacement than that assumed to
meet Regulatory Alternative I.
c-
-------
Generally, the main type of enhancement assumed was the
addition of a new,, final control device. The devices included
>
non-regenerative adsorbers with an impregnated carbon media
suited for mercury removal for by-product hydrogen stream and
mercury thermal recovery unit control systems and packed tower
hypochlorite scrubbers for end-box ventilation control systems.
For a vent control system having an existing carbon adsorber but
not meeting the emission level associated with a regulatory
alternative, it was assumed that either more frequent replacement
of the carbon (with first switching to an impregnated carbon
media in some cases) or replacement of the existing adsorber with
a new, larger adsorber would be necessary.
For estimating control cost impacts of Regulatory
Alternative I for point sources at all twelve plants, seven out
of ten plants with end-box ventilation systems were assumed to
enhance their by-product hydrogen streams and/or end-box
ventilation syster controls as follows: (1) two plants would need
to install new carbon adsorbers on their by-product hydrogen
streams (one plant would be replacing an existing adsorber with a
new, larger adsorber), (2) one plant would need to install a nev.;
packed scrubber on its end-box ventilation system vent, .'3' one
plant would need to change the type of carbon in its existing
adsorber (to an impregnated carbon) and then, replace the carbon
more frequently than its current practice (this plant wou. ci also
need to add a nev; packed scrubber on its end-box ventilation
-------
system vent), and (4) three plants would need to install a new
carbon adsorber on their by-product hydrogen stream and a new
packed scrubber on their end-box ventilation system vent. One of
two plants without end-box ventilation systems was assumed to
enhance its by-product hydrogen stream controls by replacing the
carbon in its existing adsorber more frequently than its current
practice. Three out of six plants with thermal recovery units
were assumed to enhance their mercury thermal recovery unit
controls as follows: (1) two plants with oven type units would
need to replace their existing carbon adsorbers with new, larger
carbon adsorbers, and (2) one plant with a non-oven type unit
would need to replace the carbon in its existing carbon adsorber
more frequently than its current practice.
For estimating control cost impacts of Regulatory
Alternative II for point sources at all twelve plants, it was
assumed that all seven plants with end-box ventilation systems
enhancing their controls for by-product hydrogen streams and/or
end-box ventilation system vents to meet Regulatory Alternative I
would undertake the same types of control measures with the
following additional enhancements: (1) a 25 percent higher carbon
charge would be used in the five new carbon adsorbers, (2) carbon
replacement frequency wou^d be further increased in one existing
carbon adsorber, and (3) the five new packed scrubbers needed
would be designed and operated more efficiently. Two additional
plants with end-box ventilation systems were assumed to install
-------
new packed.scrubbers, for a total of nine affected plants for
meeting Regulatory Alternative II for combined by-product
hydrogen streams and end-box ventilation system vents (for plants
with end-box ventilation systems). The plant without an end-box
ventilation system enhancing its controls to meet Regulatory
Alternative I for by-product hydrogen streams (by replacing the
carbon in its existing adsorber more frequently than its current
practice) was assumed to need to replace its existing carbon
adsorber with a new, larger carbon adsorber. Since there is a
single level of control for oven type mercury thermal recovery
unit vents in both regulatory alternatives, the assumptions
previously discussed for meeting Re.gulatory Alternative I apply
to meeting Regulatory Alternative II for these vents. The one
plant assumed to enhance its non-oven mercury thermal recovery
unit controls to meet Regulatory Alternative I would further
increas-e carbon replacement frequency in its existing carbon
adsorber.
6.2.3 MR&R Cost Impacts for Point Sources
As part of the regulatory alternatives for point sources,
continuous compliance with emission limits would be demonstrated
through the monitoring of mercury concentration in the vent
exhaust streams (as an indicator of control system performance',
Accordingly, the MR&R cost impacts for point sources were
estimated based on the installation and operation and maintenance
6-10
-------
(including repeat performance testing) of a mercury concentration
continuous monitoring system (CMS) for each vent at a plant.3
6.3 CONTROL COST IMPACTS
Emission control costs are associated with the purchase,
installation, and operation of pollution control equipment. As
discussed in Section 6.2.1, no control cost impacts were
associated with fugitive emission sources. Control cost impacts
for point sources were estimated based on assumed vent control
system enhancements needed to meet Regulatory Alternative I and
Regulatory Alternative II (Section 6.2.2), respectively.
Capital and annual costs for new carbon adsorbers were
estimated using the EPA carbon adsorbers spreadsheet^ and
procedures detailed in the EPA OAQPS Control Cost Manual.5 As
the former focuses on regenerative systems with activated carbon,
modifications were made to accommodate non-regenerative devices
with impregnated carbon media for mercury removal. Capital and
annual costs for new packed scrubbers were estimated based on the
EPA gas absorbers spreadsheet" and procedures detailed in the EPA
OAQPS Control Cost Manual.'1
Costs for replacing carbon in existing adsorbers were
estimated based on the replacement frequency needed to meet an
appropriate optimum mercury-to-carbon ratio among plants with
existing carbon adsorbers. In calculating this ratio for each
plant, the mercury concentration at the inlet of the carbon
adsorber and stream flow rate were multiplied and unit
6-11
-------
conversions applied for the mercury loading in milligrams of
mercury per minute. This value was then multiplied by operating
time per year, divided by the mass of carbon in the adsorber, and
multiplied by the existing carbon media replacement frequency (in
years) to yield the quotient of mercury mass to carbon mass.
Tables 6-5 and 6-6 present the estimated, capital cost and
annual co'ntrol cost impacts, respectively, for implementing
Regulatory .Alternative I for point sources. The nationwide
annual control cast impact is estimated to be $743,482.
Tables 6-7 and 6-8 present the estimated capital cost and
annual control cost impacts, respectively, for implementing
Regulatory Al'ternative II for point sources. The nationwide
annual control cost impact is estimated to be $1,026,508.
6.4 MR&R COST IMPACTS
The MR&R cost impacts for fugitive sources and point sources
are discussed below.
6.4.1 MR&R Cost Impact for Fugitive Sources
As discussed in Section 6.2.1, there are no estimated cost
impacts for Regulatory Alternative I for fugitive emission
sources. As part of Regulatory Alternative II for fugitive
emission sources, cell room inspections and associated
recordkeeping would be conducted at specified frequencies Trie
measurement of mercury vapor levels in the cell room, in order to
detect elevated levels and enable prompt corrective aoticr., would
also be conducted. Additionally, recordkeeping would bt
6-12
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associated with the routine washdown of surfaces where liquid
mercury accumulates, as well as for the storage of mercury-
containing wastes. Regulatory Alternative II ccst impacts for
fugitive emission sources were estimated as costs of these
additional monitoring, inspections, recordkeeping, and reporting
activities.
Table 6-9 presents these estimated MR&R cost impacts. The
capital MR&R cost impact for fugitive mercury emission sources
was estimated based on one cell room mercury monitoring system
for each plant. _A vendor quotation of about $31,8008 per system
TABLE 6-9. ESTIMATED COST IMPACTS OF REGULATORY ALTERNATIVE II
FOR FUGITIVE EMISSION SOURCES
MR&R For Work Practices
Annualized Capital Cost
for Mercury Monitoring
System
Labor Cost for
Monitoring,
Inspections, and
Recordkeep. ng
Utility Cost for
Mercury Monitoring
System
Cost of Replacement
Parts for Mercury
Monitoring System
Total3
Annual Costs
Per Plant
$7,870
$61, 336
$180
$624
$70, 010
Nationwide
Annual Costs
$94,442
$736,037
$2, 155
$7,488
$840, 122
a Totals may not appear to be the sum of the values shown due to
6-1"
-------
was multiplied by 1.08 to account for taxes and freight, and then
by 1.61 to account for direct and indirect installation costs,
based on the estimation methodology in the EPA CAQPS Control Cost
Manual.^
The annual MR&R cost impact for fugitive mercury emission
sources.was estimated.as the sum of the annualized capital cost
of each cell room mercury monitoring system, plus operation and
maintenance costs. The O&M costs consist of labor costs for
monitoring, inspections, and recordkeeping, utility costs for
mercury monitoring systems, and costs of replacement parts for
•these systems. The labor hour burden for each plant was
approximated as an additional 3.75 technical labor hours per day,
consisting of the following: (1) 0.1 hour per day for
recordkeeping for washdowns, (2) 0.5 hour per day for measuring
and recording cell room mercury vapor levels, (3) 1.5 hours per
day for twice daily inspections for vessel and process equipment
problems, as well as for hydrogen/mercury vapor leaks at
decomposers and at equipment up to the hydrogen header, (4) an
equivalent of 0.07 hour0 per day for monthly inspections for
cracks, spalling, or other deficiencies in cell room floor?,
(5) an equivalent of 0.04 hours per day for semiannual
inspections for cracks, spalling, or other deficiencies in eel-
room pillars and beams, (6) 1.25 hours per day for daily cell
room inspections for caustic leaks, liquid mercury spills anc
accumulations, and liquid mercury leaks, (7) an equivalent cf
6-18
-------
0.04 hours per day for quarterly inspections for hydrogen/mercury
vapor leaks in the hydrogen system, from the the hydrogen header
to the last control device, and (8) 0.25 hours per day for
recordkeeping for handling and storage of mercury-containing
wastes. An hourly compensation value of $34.44 for technical
labor was obtained from the U.S. Bureau of Labor Statistics10 and
multiplied by a factor of 1.3 to account 'for overhead
expenditure. The labor hour burden was then extrapolated to
365 days per year at a technical labor rate of $44.77 per hour.
Utility costs for a mercury monitoring system were estimated as
the product of the device power consumption of 500 Watts,H
continuous operation for 8,760 hours per year, and energy cost of
$0.04 per kiloWatt-hour. ^ Replacement part costs for a mercury
monitoring system were estimated based on monthly changeout of a
$2 device sample filter and annual changeout of sampling valve
tubes at a cost of S6CO.^^ Thus, the estimated annual cost
impact of Regulatory Alternative II for fugitive sources is
$70,010 for each plant, and the nationwide annual cost impact is
$840,122 .
6 . " . 2 MR&R Cost Impacts for Point Sources
As stated in Section 6.2.3, MR&R cost impact's for point
sources were estimated based on a mercury concentration CMS for
each plant vent. An average vendor quotation of about $9,760-^
per CMS was multiplied by 1.08 to account for taxes and freight,
and then by 1.61 to account for direct and indirect installation
-------
costs, based on the estimation methodology in the EPA OAQPS
Control Cost Manual.^ This value for cost per CMS was then
multiplied by the number of vents at the plant, on which
individual CMS would be installed. Table 6-10 presents the
estimated capital MR&R cost impacts of implementing the
regulatory alternatives for point sources.
The annual MR&R cost impact for point sources was estimated
as the sum of the annualized capital cost of vent mercury
concentration CMS plus operation and maintenance costs. The O&M
costs consist of labor costs for monitoring, inspections
(including calibrations), and recordkeeping, CMS utility costs,
CMS replacement part costs, and annualized vent performance test
costs. The labor hour burden for each plant was approximated as
an additional 0.54 technical labor hours per day, consisting of
the following: (1) 0.5 hour per day for daily vent monitoring and
recording of CMS data, averages, and deviations, and (2i the
equivalent of 0.04 hour per day for semiannual CMS inspections
and calibrations and recording of results. As previously done,
the labor hour burden was then extrapolated to 365 days per year
at a technical labor rate of $44.77 per hour. Utility costs for
a CMS were estimated as the product of the device power
consumption of 40 Watts, -^ continuous operation for 8,760 hc^rs
per year, and energy cost of $0.04 per kiloWatt-hour.1 '
6-20
-------
TABLE 6-10. ESTIMATED CAPITAL MR&R COST IMPACTS OF
REGULATORY ALTERNATIVES FOR POINT SOURCES
Plant Owner
ASHTA
HoltraChem
Occidental
Occidental
Occidental'-
Olin
Olin
Pioneer
FPG
PPG
Vulcan
Westlake
Location
Ashtabula, OH
Orrington, ME
Muscle Shoals, AL
Delaware City, DE
Deer Park, TX
Augusta, GA
Charleston, TN
St. Gabriel, LA
Lake Charles, LA
Natrium, WV
Port Edwards, WI
Calvert City, KY
Nationwide Total3
1
Number
Df Vents
2
2
2
5
2
2
4
2
3
2
3
2
Total Capital MR&R
Cost
$33,937
$33,937
$33,937
$84,841
$33,937
$33,937
$67,873
$33, 937
$5C, 905
$33, 937
$50, 905
$33, 937
$526, 016
Total may not appear to be the sum of the values shown due to rounding.
-------
Replacement part costs for a CMS were estimated based on monthly
changeout of a $2 device sample filter.18 Table 6-11 presents
the estimated annual MR&R cost impacts for implementing the
regulatory alternatives for point sources.
6.5 ESTIMATE OF TOTAL ANNUAL COSTS AND COST PER UNIT EMISSION
REDUCTION
Tables 6-12 and 6-13 present the estimated total annual cost
impacts of the regulatory alternatives for all mercury emission
sources (i.e., fugitive emission plus point sources) at each
plant and on a nationwide basis. The total estimated annual cost
•impact of Regulatory Alternative I for all mercury emission
sources at a plant ranges from $20,689 to $251,053, and the
estimated nationwide total is $1,033,041. The estimated total
annual cost impact of Regulatory Alternative II for all plant
mercury emission sources ranges from $90,699 to $374,549, and the
estimated nationwide total is $2,156,189.
Table €-14 shows the estimated cost impact per un:t of
estimated mercury emission reduction (see Chapter 5, Table 5-7)
for the regulatory alternatives for point sources. Using
estimated reductions from the baseline level of emissions allowed
by the part 61 Mercury NESHAP, this computes to about S255
per kilogram ($116 per pound) of mercury for Regulator-;
Alternative I for point sources. For Regulatory Alternative II,
the cost per unit of mercury emission reduction for point sources
is about $318 per kilogram ($144 per pound) of mercu*-;, . Tr.e
6-22
-------
TABLE 6-11. ESTIMATED ANNUAL MR&R COST IMPACTS OF
REGULATORY ALTERNATIVES FOR POINT SOURCES .
Plant Owner
ASHTA
HoltraChem
Occidental
Occidental
Occidental
Olin
Olin
Pioneer
1 PPG
PPG
•Vulcan
West lake
Location
Ashtabula, OH
Orrington, ME
Muscle Shoals, AL
Delaware City, DE
Deer Park, TX
Augusta, GA
Charleston, TN
St . Gabriel, LA
Lake Cnarles, LA
Natrium, WV
Port Edwards, WI
Calvert City, KY
Nationwide Total0
Annuali zed
Capital
MR&R Cost
$4,832
$4,832
$4,832
$12,079
$4,832
$4,832
$9, 664
$4, 832
$7,248
$4,832
$7, 248
54, 832
$74, 593
MR&R O&M
Cost
$15,857
$15,857'
$15,857
$26,308
$15,857
$15,857
$22,824
$15,857
$19,341
$15,857
$19,341
$15,8.57
$214, 666
Total Annual
MR&R Cost
$20,689
$20,689
$20,689
$38,387
$20,689
$20, 689
$32,488
$20, 689
$26,589
$20,689
$26,589
$20, 689
$289, 559
-------
TABLE 6-12. ESTIMATED TOTAL ANNUAL COST- IMPACTS OF
REGULATORY ALTERNATIVE I FOR ALL MERCURY EMISSION SOURCES
Plant Owner
ASHTA
HoltraChem
Occidental
Occidental
Occidental
Olin
Olin.
Pioneer
PPG
PPG
Vulcan
Wes tlake
Location
Ashtabula, OH
Orrington, ME
Muscle Shoals, AL
Delaware City, DE
Deer Park, TX
Augusta, GA
Charleston, TN
St. Gabriel, LA
Lake Charles, LA
Natrium, WV
Port Edwards, WI
Calvert City, KY
Nationwide Total0
Total
Annual
Control
Cost
$57,992
$0
$120,339
$0
$55,272
$51,890
$114,998
$0
$36,785
$41,530
$26,314
$238, 364
$743, 482
Total
Annual
MR&R Cost
$20,689
$20,689
$20,689
$38,387
$20,689
$20,689
$32,488
$20, 689
$26,589
$20, 689
$26, 589
$20, 689
$289,559
Total
Annual Cost
$78,681
$20,689
$141,028
$38,387
$75,961
$72,579
$147,486
$20, 689
$63, 3^4
$62,219
$52, 903
$255, 053
$1, 033, 041
Totals may not appear to be the SUIT, of the values shown due to rounding.
6-24
-------
TABLE 6-13. ESTIMATED TOTAL ANNUAL COST IMPACTS OF
REGULATORY ALTERNATIVE II FOR ALL MERCURY EMISSION SOURCES
Plant Owner
ASHTA
HoltraChem
Occidental
Occidental
Occidental
Olin
Olin
Pioneer
PFG
PPG
Vulcan
WestlaKe
Location
Ashtabula, OH
Orrington, ME
Muscle Shoals, AL
Delaware City, DE
•• Deer Park, TX
• Augusta, GA
Charleston, TN
St. Gaoriel, LA
Lake Charles, LA
' Natrium, WV
Port Edwards, WI
Calvert City, KY
Katicnuide Total0
Total
Annual
Control
Cost
$62,809
$0
$120,339
$26,304
$181,507
$55,329
$134,786
$40, 872
$40, 872
$53, 178
$26, 664
$283, 850
$1, C26, 508
Total
Annual MR&R
Cost
$90,699
$90,699
$90,699
$108,397
. $90, 699
$90,699
$102,498
$90,699
$96,599
$90, 699
$96,599
$90, 699
$1, 129, 681
Total Annual
Cost
$153,508
$90,699
$211,038
$134,701
$272,206
$146,028
$237,284
$131, 571
$137,471
$143, 877
$123, 264
$374, 549
$2, 156, 189
Totals may nor appear to be the sum of the values shown due to rounding,
6-25
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difference in estimated point source cost impacts divided by the
difference in estimated vent mercury emission reductions at the
two alternatives, is approximately $3,200 per kilogram ($1,450
per pound) of mercury.
Using estimated reductions from the actuals baseline, the
cost per unit of.mercury emission reduction computes to about
$1,727 per kilogram ($783 per pound) of mercury for Regulatory
Alternative I for point sources. For Regulatory Alternative II,
the cost per unit of mercury emission reduction for point sources
is about $1,918 per kilogram ($870 per pound) of mercury. The
difference in estimated point source cost impacts divided by the
difference in estimated vent mercury emission reductions at the
tvc alternatives, is approximately $3,200 per kilogram ($1,450
per pound) of mercury.
-------
6.6 REFERENCES
1. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Impacts Calculations
for Mercury Cell Chlor-Alkali Plant NESHAP Regulatory
Alternatives. December 14, 2001.
2. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Background on Vent
Control System Enhancements to Meet Regulatory Alternatives
for Existing Mercury Emission Sources at Mercury Cell Chlor-
Alkali Plants. September.26, 2001.
3. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information Gathered on Continuous Mercury Emission
Measurement., July 27, 2001.
4. U.S. Environmental Protection Agency. CO$T-AIR Control Cost
Spreadsheets. July 1999. Accessed through website:
.
5. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001).
Chapter 4. February .1996.
6. Reference 4.
7. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001^ .
Chapter 9. February 1996.
8. Reference 3.
9. U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Emission Standards Division. OAQPS
Control Cost Manual, Fifth Edition (EPA 453/B-96-001/ .
Chapter 2. February 1996.
10. U. S. Government, Bureau of Labor Statistics. TaLIe 2,
Civilian workers, by occupational and industry grout , Merer;
2000. Accessed through website:
. January 3, 2001.
11. Reference 3.
12. U.S. Energy Information Administration, Departme-.L of
Energy, Washington, D.C. Electricity Industrial Sector
6-28
-------
Prices (Average of monthly prices for 1998). Accessed
through website: . April 19,
2000.
13. Reference 3.
14 . Reference 3.
15. Reference 9.
16. Reference 3.
17. Reference 12.
18. Reference 3.
6-2!
-------
-------
7.0 RATIONALE FOR SELECTING THE PROPOSED STANDARDS
7.1 INTRODUCTION
This chapter provides the detailed rationale for the
selection of the national emission standards fo,r hazardous^air
pollutants (NESHAP) regulatory requirements that we are proposing
to reduce mercury emissions from mercury cell chlor-alkali
plants. Section 7.2 discusses the selection of the source
category, Section'7.3 discusses the selection of the affected
sources and emission points, and Section 7.4 discusses the
selection of the form of the standards. The basis and level for
the proposed standards for existing and new sources are presented
in Sections 7.5 and 7.6, respectively. Tnis is followed by
discussions on the selection of testing and initial compliance
requirements in Section 7.7, continuous compliance requirements
in Section 7.8, and notification, recordkeeping, and reporting
requirements in Section 7.9. Section 7.10 lists references.
7.2 SELECTION OF THE SOURCE CATEGORY
i
Tne chlor-alkali production source category was among the
categories and subcategories of major and area sources listed for
regulation under Section 112 (c) (6) of the Clean Air Act (CAA)
(63 FR 17838, April 10, 1998), to assure that sources accounting
for net less than 90 percent of tne aggregate mercury emissions
-------
nationwide are subject to standards under Section1 112(d). We
;
'estimate that the chlor-alkali production source category
accounts for over 5 percent of all stationary source emissions of
mercury and over 25 percent of the emissions from stationary non-
combustion sources. The source category is comprised of
43 facilities engaged in the manufacture of chlorine and caustic
in~electrolytic cells.-'- Cell types employed include the
diaphragm cell, membrane cell, '-and mercury cell. Of these, only
the mercury cell subcategory has the potential to emit mercury.
Mercury emissions occur at process vents and as fugitive
emissions from the cell room and other areas. Therefore, this
rulemaking focuses only on mercury cell chlor-alkali plants.
For the 1997 base year of the maximum achievable control
technology (MACT) analysis, twelve facilities employed mercury
cells. We are aware that one of the twelve facilities ceased
operations permanently in September 2000. Nonetheless, we
considered it to be part of the source category for the
development of MACT standards since it was in operation in 1997,
which is the base year of the analysis.
7.3 SELECTION OF THE AFFECTED SOURCES AND EMISSION POINTS TO 51
REGULATED
For the purposes of implementing a NESHAP, an affected
source is defined to mean the stationary source, the grour cf
stationary sources, or the portion of a stationary source, that
is regulated by a relevant standard or other requirement
7-2
-------
established under Section 112 of the CAA. An affected source
specifies the group of unit operations, equipment, and emission
points that are subject to the standard. Under each relevant
standard, we designate one or more affected sources for the
purpose of implementing that standard. We can define an affected
source as narrowly as a single piece of equipment or as broadly
"as all~e~q~uipment at a plant site.
We decided to separate the unit operations and emission
points related to the production of chlorine and caustic from the
unit operations and emissions points related to mercury recovery-
Mercury cell chlor-alkali production facilities include a number
of integrated operations dedicated to the production, storage,
and transfer of product chlorine, product caustic, and by-product
hydrogen. In contrast, mercury recovery facilities are
operations dedicated to the recovery of mercury from mercury-
containing wastes. These operations are independent of the
chlor-alkali process and are thus not integral to production. As
a result, the proposed rule addresses emissions from two separate
affected sources: mercury cell chlor-alkali production facilities
and mercury recovery facilities.
Unit operations and emission points grouped within the
mercury cell chlor-alkali production facilities affected source
are by-product hydrogen streams, end-box ventilation system
vents, and fugitive mercury emissions associated with cell rooms,
hydrogen systems, caustic systems, and storage areas for mercury-
-------
containing wastes. As described previously in Chapter 3, each is
a potentially significant source of mercury .emissions. Chlorine
purification, brine preparation, and wastewater treatment
operations are believed to have low mercury emissions to the air.
Accordingly, the proposed rule contains no requirements for these
operations.
Unit operations and emTssToh points grouped within the
mercury recovery facilities affected source include all mercury
thermal recovery unit vents and fugitive mercury emissions
associated with mercury-containing waste storage areas. Chemical
mercury recovery and recovery in a batch purification still are
believed to have low mercury emissions to the air. Accordingly,
the proposed rule contains no requirements for these operations.
Therefore, the proposed rule contains requirements for four
basic emission sources. These are (1) hydrogen by-product
streams, (2) end-box ventilation system vents, (3) mercury
thermal recovery unit vents, and (4) fugitive emission sources.
7.4 SELECTION OF THE FORM OF THE STANDARDS
Section 112 of the CAA requires that standards be specified
as numerical emission standards, whenever possible. However, if
it is determined that it is not feasible to prescribe or enforce
a numerical emission standard, Section 112(h) indicates that a
design, equipment, work practice, or operational standard may be
specified.
7-4
-------
With the exception of standards for fugitive emission
sources, we are proposing numerical emission limits for all other
mercury emission sources. Specifically, the proposed standards
include numerical emission limits for by-product hydrogen
streams, end-box ventilation system vents, and mercury thermal
recovery unit vents.
Most fugitive mercury emission sources at mercury cell
chlor-alkali plants are associated with cell rooms and storage
areas for mercury-containing wastes. Cell rooms are ventilated
in order to dissipate heat evolved by mercury cells and to reduce
worker exposure tp mercury vapor in the.cell room environment.
All cell rooms are ventilated along the length of the cell room
roof, either by way of roof monitors or cupolas or through static
or mechanically driven ventilators. Many are also ventilated
through openings in the cell room walls. These conditions make
the reliable measurement of mercury emissions from most cell
rooms extremely difficult, if not totally impracticable, due to
the number of openings needed to be sampled concurrently and the
low flow of air through individual openings.
The measurement of mercury emissions from mercury-containing
waste storage areas is also impracticable, as these are usually
located in several places throughout a plant, many of which are
open areas.
Not unexpectedly, emissions data on cell room and waste
storage emissions are very limited, as in the case of cell rooms,
-------
or non-existent, as in the case of waste storage areas. As such,
we believe that it is not feasible to either prescribe or enforce
numerical emission.limit(s) for fugitive mercury emissions from
cell rooms and waste storage areas. Consequently, the proposed
standards address fugitive emission sources at mercury cell
chlor-alkali plants through the establishment -of work practice
•
"standards".
7.5 SELECTION'OF THE BASIS AND LEVEL OF THE PROPOSED STANDARDS
FOR EXISTING SOURCES
Section 112 of the CAA establishes a minimum baseline or
"floor" for MACT standards. For new sources, the standards for a
source category or subcategory cannot be less stringent than the
emission control that is achieved in practice by the best-
controlled similar source. The standards for existing sources
may be less stringent than standards for new sources, but they
cannot be less stringent than the average emission limitation
achieved by the best-performing 12 percent of existing sources
for categories and subcategories with 30 or more sources, or the
average emission limitation achieved by the best-performing
5 sources for categories or subcategories with fewer than
30 sources for.which the Administrator has emissions information.
After the floor has been determined for a category or
subcategory, we must set MACT standards that are technically
achievable and no less stringent than the floor. Such standards
must then be met by all sources within the category or
7-6
-------
subcategory. The regulatory alternatives selected for new and
existing sources may be different because of different MACT
floors, and separate emission limits may be established for new
and existing sources.
We generally determine the MACT floor and then consider
beyond-the-floor control options. Here, we consider the
achievable reductions in emissions of HAPs (and possibly other
pollutants that are co-controlled), cost and economic impacts,
energy impacts, and other non-air environmental impacts. The
objective is to achieve the maximum degree of HAP emission
reduction without incurring unreasonable cost or other impacts.
The remainder of this section discusses the proposed
standards for mercury emission sources at existing sources.
Specifics on the environmental and energy impacts cited in this
section may be found in Chapter 5, and specifics on costs may be
found in .Chapter 6.
7.5.1 By-Product Hydrogen Streams and End-Box Ventilation System
Vents
The fundamental unit in the mercury cell chlor-alkali
process is a mercury cell. The by-product hydrogen stream and
the end-box ventilation system vent represent the mercury
emission point sources that originate from a mercury cell.
Hydrogen gas is incidentally produced as a result of the
catalyzed reaction of sodium/mercury amalgam and deionized water
to produce caustic in a decomposer. The end-box ventilation
-------
stream is a collection of vapors from head spaces of end boxes
and possibly other vessels, including pump tanks and seal legs,
wash water tanks, and caustic tanks and headers. The mercury
content of the by-product hydrogen stream and the end-box
ventilation stream, prior to control, is a direct function of the
design of the mercury cell. As discussed in Section 2.3, ten
different mercury cell models are used by the twelve mercury cell
chlor-alkali plants. Given these differences in cell design and
their effect on potential vent mercury emissions, we opted to
develop a cell-wide standard for mercury emissions from both
•points.
Given the large variation among the plants in terms of
production that was shown in Table 2-1 (the largest plant
produces over five times as much chlorine as the smallest) and
mercury emissions .potential, we concluded that any equitable
assessment of MACT should account for this disparity. We
selected the actual amount of chlorine produced by weight as thf
uniform parameter for our analysis for the following reasons:
(1) chlorine is the primary product generated; (2) chlorine
production can be accurately determined; and (3) chlorine and
hydrogen are generated in the same stoichiometric quantities,
that is one molecule of hydrogen is produced for each rr.clecu LC c:
chlorine produced.
We then considered the fact that two plants do not have end-
box ventilation systems, as discussed in Chapter 3. Both plants
7-8
-------
operate cells with closed end boxes. Consequently, there is no
need for end-box ventilation and therefore no end-box ventilation
system emission point. Next, we examined whether the mercury
cells at the ten plants equipped with end-box ventilation systems
could be reconfigured with closed end boxes. We concluded that
the use of an end-box ventilation system is an inherent feature
of the original design of a cell, and that it is not technically
feasible to eliminate end-box ventilation systems at these
plants. We h-ave, therefore, decided to distinguish plants with
end-box ventilation systems and plants without these systems for
purposes of establishing MACT.
Accordingly, we are proposing, for plants with end-box
ventilation systems, a single emission limit for mercury
emissions from all by-product hydrogen streams and mercury
emissions from all end-box ventilation system vents, in units of
mass of .mercury emissions per mass of chlorine produced. For
plants without end-box ventilation systems, we are proposing an
emission limit for mercury emissions from all by-product hydrogen
streams, also in units of mass of -mercury emissions per mass of
chlorine produced.
7.5.1.1 Emission Limit for Plants .With End-Box Ventilation
Systems. In order to establish MACT for the combined mercury
emissions from by-product hydrogen streams and end-box
ventilation system vents, we relied on estimates of annual
rrercury emissions for each vent and information on annual
-------
chlorine production provided by the ten plants with end-box
ventilation systems. A total of twenty mercury emission
estimates were provided, one emission estimate for all by-product
hydrogen streams and one emission estimate for all end-box
ventilation system vents at each of the ten plants. A summary of
each emission estimate and its basis is shown in Table 7-1. ^
Of the twenty emission estimates, fourteen (six for by-
product hydrogen streams and eight for end-box ventilation system
vents) are based "on stack tests performed in accordance with
established EPA reference methods specific to chlor-alkali
plants. These include Method 101 for the determination of
particulate and gaseous mercury from air streams (i.e., end-box
ventilation system vents) and Method 102 for the determination of
mercury in hydrogen streams. We obtained and reviewed copies of
all available test.reports and determined that the tests were
conducted correctly.
Six emission estimates (four for by-product hydrogen stria;:-
and two for end-box ventilation system vents) are basea or.
periodic measurements of mercury concentration in the vent
streams. These methods, which are all very similar, irv-.-jvc
pulling a gas sample through impingers containing potassij;-
permanganate solution, followed by cold vapor atomic a;:c^,:pt^cr.
analysis in a laboratory setting. These methods are adaptations
of EPA Method 101A and Method 102. One difference is thai
sampling for these methods is not isokinetic, which is rc-ou^rea
7-10
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for valid Method 101A and 102 tests. Although generally
desirable, isokinetic sampling is not critical for gases and fine
particulate, such as mercury vapor and condensate that is
believed to comprise most of the mercury in these exhaust
streams. Based on our review of the sampling and analytical
procedures employed in these methods, we believe that this
""potassium permanganate rion-isokihetTc" methods are capable of
producing measurements of reasonable accuracy. As such, we
believe that they provide reasonably accurate results consistent
with what would otherwise be obtained with the EPA reference test
methods. Our conclusion is that these data represent the best
information available on mercury emissions from these vents, and
that they are appropriate for use in establishing MACT.
The MACT floor was calculated as follows. For each plant,
we divided the sum of the reported annual mercury emissions from
all by-product hydrogen streams and end-box ventilation system
vents by the ar.nual chlcrir.e prcauct. ion. The chlorine production
values used are largely representative of actual annual chlorine
production levels. We then ranked the plants from lowest to
highest emitters for combined normalized mercury emissions. The
i
resulting plant-specific values are shown in Table 7-1. The
normalized mercury emission values range from 0.067 grams Hg/Mg
C12 to 3.42 grams Hg/Mg Cl:. We should note that the lowest
value, 0.067 grams Hg/Mg C12| is from the plant that closed
permanently in September 2000 (Hcltrachem in Orrington, Maine).
-------
Nonetheless, we believe that it is appropriate to retain it in
the pool of existing sources used to determine existing source
MACT. This plant closure is a recent event, and prior to
closure, the plant was the lowest-emitting and best-performing
source. The average (mean) of the best (lowest) five normalized
values results in a floor value for existing sources of
~CT.14~~grams Hg/Mg C12.
Of the ten plants with by-product hydrogen streams and end-
box ventilation systems, we project that seven would need to
install additional controls or upgrade existing controls to meet
the 0.14 grams Hg/Mg C12 floor level. We assume that the plant-
specific actions that were shown in Table 5-2 could reduce
mercury emissions at least to the 0.14 gm Hg/Mg C12 floor option.
We estimate that the total installed capital control costs
needed to meet the existing source MACT floor to be about
$660,000. We estimate total annual control costs, including
costs for labor, materials, electricity, capital recovery, t£..xes,
insurance, and administrative charges (excluding costs for
monitoring, reporting, and recordkeeping), to be about $570,000
per year. Mercury emission reductions against actual emissions,
as represented by the emission estimates in Table 7-1, would
total 556 kg/yr (1,225 Ibs/yr). Mercury emission reductions
against the potential-to-emit baseline, as represented by the
allowable emissions under the part 61 NESHAP, would total over
3,400 kg/yr (over 7,500 Ibs/yr) . The associated annua i cos" per
7-14
-------
unit of mercury emission reduction values would be approximately
$465 per pound (actuals baseline) and under $80 per pound
(potential-to-emit baseline), respectively.
Water pollution impacts, due to the increased use of packed
bed scrubbers involving aqueous hypochlorite scrubbing solution
on end-box ventilation systems, are estimated to total
1.2 million liters (320 thousand gallons) of additional
.wastewater. Impacts on solid waste, due to increased use of
carbon adsorption for by-product hydrogen streams, are estimated
to total 17 Mg/yr (19 tons/yr) of mercury-containing spent
carbon. Energy requirements are estimated to total an additional
878 thousand kilowatt-hours per year (kW-hr/yr). Estimated
secondary air pollution impacts due to heightened energy
consumption total 282 Mg/yr (311 tons/yr), with carbon dioxide
emissions comprising 99 percent of the estimate.
We . then examined beyond-the-floor MACT options. We selected
the lowest normalized value among the ten plants, namely
'0.067 grams Hg/Mg C12 assigned to Holtrachem in Orrington, Maine,
as a beyond-the-floor option. This corresponds to 0.05 grams
Hg/Mg CI2 from the by-product hydrogen stream, which is
controlled by a condenser coupled with a molecular sieve
adsorber, and 0.017 grams Hg/Mg Cl: from the end-box ventilation
system vent, which is also controlled by a condenser coupled with
a molecular sieve adsorber. It is our understanding that
molecular sieve technology for mercury vapor emission control is
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no longer commercially available. ^ We, thus, acknowledge some
uncertainty associated with the achievability of this level of
control. However, we believe that other technologies and
operating practices exist that can achieve this level of
emissions control.
Due to the very low volumetric flow rates associated with
both by-product hydrogen streams and end-box veritTlation system
vents (typically less than 5,000 scfm and 4,500'scfm,
respectively) , we believe that the retrofit of control equipment
to reduce mercury emissions is both practical and reasonable. We
project that the nine plants with emissions above
0.067 grams Hg/Mg C12 could install additional controls or
upgrade existing controls to meet the 0.067 grams Hg/Mg C12
beyond-t'he-f loor option, as was shown in Table 5-2.
In evaluating regulatory options that are more stringent
than the floor, we must consider the cost of achieving such
emission redaction, and any non-air quality health and
environmental impacts and energy requirements. The beyond-the-
floor option would result in an additional 65 kg/yr (143 Ib/yr)
of total mercury emission reductions (a 48 percent incremental
reduction from the floor option) . The incremental installed
capital costs are estimated to total around $210,000, -?nd ^he-
incremental annual costs are estimated to total around $150,000
per year. The incremental cost per unit of incremental mercury
emission reduction is $L'00 per pound.
7-16
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The incremental water pollution impacts are estimated to
total 550 thousand liters (145 thousand gallons) of additional
wastewater. The incremental solid waste impacts are estimated as
5.1 Mg/yr (5.6 tons/yr) of mercury-containing .spent carbon in
total. The incremental energy impacts are estimated as
110 thousand kW-hr/yr in total. The incremental secondary air
pollution impacts are estimated to total 35 Mg/yr (39 tons/yr),
with carbon dioxide emissions comprising 99 percent of the
estimate.
We believe the additional emission reduction that would be
•achieved by the beyond-the-floor option is warranted. Further,
we believe that the incremental costs of achieving such emission
reduction, as well as incremental non-air environmental impacts
and energy requirements, are reasonable for mercury. Therefore,
we selected the 0.067 grams Hg/Mg C12 beyond-the-floor option as
MACT for plants with end-box ventilation systems.
If comments are received on the proposed rule that lead us
to conclude that tnis level of control is unachievable, we retain
the option of setting the standard at the next lowest normalized
emission value. Accordingly, we have evaluated the impacts of an
alternative 0.076 grams Hg/Mg C12 mercury emission limit for
plants with end-box ventilation systems.
We project that the eight plants with baseline emissions
greater than 0.076 grams Hg/Mg C12 would need to install new
controls or upcrade existina controls to meet this level. This
7-1
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would result in an additional 65 kg/yr (143 Ib/yr) of total
mercury emission reductions (a 41 percent incremental reduction)
from the floor option. We assume the same plant-specific actions
as those assumed to meet the 0.067 grams Hg/Mg C12 value, given
the small difference in emission reductions at the two levels.
The incremental installed capital costs are estimated to total
"arbuhd"$197, 000, and the" incremental annual costs "are estimated
to total around $125,000 per year. The incremental cost per unit
of incremental me-rcury emission reduction is $875 per pound.
The incremental water pollution impacts are estimated to
total 317 thousand liters (84 thousand gallons) of additional
wastewater. The incremental solid waste impacts are estimated as
5.1 Mg/yr (5.6 tons/yr) of mercury-containing spent carbon in
total. The incremental energy impacts are estimated as
105 thousand kW-hr/yr in total. The incremental secondary air
pollution impacts are estimated to total 34 Mg/yr (37 tons/yr),
with carbon dioxide emissions comprising 99 percent of the
estimate.
7.5.1.2 Emission Limit for Plants Without End-Box
Ventilation Systems. In order to establish MACT for mercury
emissions from by-product hydrogen streams for the twc plants
without' end-box ventilation systems (Occidental in Muscle Shells,
Alabama and Occidental in Deer Park, Texas), we used estimates of
annual mercury emissions from by-product hydrogen streams and
information en actual chlorine production provided by th', tv,1?
7-1!
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plants for 1997.6 Both emission estimates are based on periodic
measurements of mercury concentration in the vent streams
obtained using potassium permanganate non-isokinetic methods,
which we believe provide reasonably accurate results consistent
with what would otherwise be obtained with EPA reference test
methods, as discussed in Section 7.5.1.1.
For each plant, we divided the reported" annual mercury
emissions from by-product hydrogen streams by the annual chlorine
production. The normalized values are 0.033 grams Hg/Mg C12 for
Occidental/Muscle Shoals and 0.17 grams Hg/Mg C12 for
Occidental/Deer Park. Although there are fewer than five sources
from which to constitute a MACT floor, we opted to take the
average (mean) of the two normalized values, resulting in 0.10
grams Hg/Mg C12 as the floor value for existing sources. We
assume that Occidental/Deer Park could reduce mercury emissions
to the 0.10 gn\ Hc/K.g Cl: fleer option by replacing the carbon in
its existing carbon adsorbers on by-product hydrogen streams more
frequently than current practice. No capital costs are
associated with meeting this level, as more frequent carbon media
replacement was estimatea as only a recurring (annual) cost of
$13,000 per year. Mercury emission reductions against actual
emissions would total 6 kg/yr (14 Ibs/yr). Mercury emission
reductions against the potential-to-emit baseline, as represented
by the allowable emissions under the part 61 NESHAP, would total
over 600 kg/yr (over 1,300 Ibs/yr). The associated annual cost
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per unit of mercury emission reduction values would be
approximately $940 per pound and under $10 per pound,
respectively. With the assumption of more frequent carbon media
replacement at Occidental/Deer Park, there are no associated
secondary air pollution, water pollution, and energy impacts.
Estimated solid waste impacts, due to increased use of carbon
adsorption", total 1.0 Mg/yr (l~.l tons/yr).
We then examined beyond-the-floor MACT options. We selected
the lowest normalized value among the two plants, namely
0.033 grams Hg/Mg C12 assigned to Occidental/Muscle Shoals, as a
'beyond-the-floor option. This corresponds to th-is plant's by-
product hydrogen stream controlled by a condenser coupled with a
carbon adsorber.
As stated above, we believe that the retrofit of control
equipment to reduce mercury emissions is quite practical and
reasonable largely due to the low volumetric flow rates
associated with by-product hydrogen streams. For.purposes of
estimating impacts, we assumed that Occidental/Deer Park would
replace its existing carbon adsorber with a new, larger adsorber
to meet the 0.033 grams Hg/Mg C12 level.
In evaluating regulatory options that are more stringent
than the floor, we must consider the cost of achieving kj.cL
emission reduction, and any non-air quality health and
environmental impacts and energy requirements. The beyond-the-
flcor option would result in an additional 6 kg/yr (14 ^b'-;r :. f
7-20
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total mercury emission reductions for the two plants (a
47 percent incremental reduction from the floor option). The
incremental installed capital costs are estimated to total around
$182,000. The incremental annual costs are estimated to total
around $126,000 per year. The incremental cost per unit of
incremental merc.ury emission reduction is approximately $9,000
"per pound. There are no associated incremental water pollution
.impacts. The estimated incremental solid waste impacts total an
additional 5.3 Mg/yr (5.8 tons/yr) of mercury-containing spent
carbon. The incremental energy impacts are estimated as
252 thousand kW-hr/yr in total. The incremental secondary air
pollution impacts are estimated to total 81 Mg/yr (89 tons/yr),
with carbon dioxide emissions comprising 99 percent of the
estimate.
We believe the additional emission reduction that would be
achieved by the beyond-the-floor option is warranted. Further,
we believe that the incremental costs of achieving such emission
'reduction, as well as incremental non-air environmental impacts
and energy requirements, are reasonable for mercury. Therefore,
we selected the 0.033 grams Hg/Mg C12 level as MACT for plants
without end-box ventilation systems, which is approximately half
the level selected for plants with end-box ventilation systems.
7.5.2 Sources of Fugitive Mercury Emissions
As explained above, we have determined that work practice
standards provide the most appropriate approach for addressing
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fugitive me'rcury emissions at mercury cell chlor-alkali plants.
Every mercury cell chlor-alkali plant is currently subject to the
part 61 NESHAP and implements the design, maintenance, and
housekeeping practices referenced in the NESHAP to control
fugitive cell room emissions. We believe that these existing
requirements represent the MACT floor for existing mercury
fugitive emission ""sources. Since these floor requirements are
currently observed at each existing plant, a standard based on
this floor level -of control would not be expected to reduce
mercury emission^ from current levels, or- produce any associated
cost, non-air environmental, or energy impacts.
We then examined beyond-the-floor options. We noted that
many of the existing work practice requirements are general in
nature and non-specific relative to the frequency and scope of
inspections, as well as recordkeeping and reporting. We decided
that clarification and elaboration on these general practices was
warranted to make them more explicit and to improve assurance of
compliance. Accordingly, we initiated a thorough examination of
specific measures employed across the industry to limit fugitive
mercury emissions.
In the summer of 1998, we conducted site visits, lasting
from one to four days each, to five mercury cell chloi-alkali
plants to observe and document their design, operational,
maintenance, housekeeping, and recordkeeping
practices.7'8'9'10'11 The five plants were selected t-_ provide a
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broad representation of ownership (the five plants are owned by
five different companies) and different mercury cell models
(mercury cells made by all three manufacturers and of varying
sizes are represented). We also selected plants in different
areas of the United States to account for geographical
variations, such as climate. In addition to the site visits, we
obtained current standard operating procedures for mitigating
sources of fugitive mercury emissions from all twelve plants. We
used this knowledge and information to develop a detailed
compilation of practices currently used across the industry to
'control fugitive mercury emissions.^
We used this compilation to identify explicit practices for
each individual plant area, equipment type, and inspection
procedure, and assembled them as beyond-the-floor work practice
requirements. We feel that the resulting work practice standards
represent the most stringent practices applied in the industry.
The types of enhancements from the MACT floor level
requirements that are included in the beyond-the-floor option may
be generally classified in three categories. First, the beyond-
the-floor requirements add considerable specificity. The
equipment and areas to be inspected are identified, along with
the required frequency of the inspections and the conditions that
trigger corrective action. Response time intervals for when the
corrective actions must occur are also included. Second, some
types cf inspections are required at more frequent intervals than
7-23
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required by the part 61 NESHAP (e.g., inspecting decomposers for
hydrogen leaks once each 12 hours rather than once each day) .
Third, the beyond-the-floor option includes additional
requirements not included in the floor level. The two most
obvious examples of this are the detailed recordkeeping
procedures and reporting provisions, which are more fully
deveTopecf'than those in the part 61 NESHAP",and" the requirements
for storage of'mercury-containing wastes.
Also included in the beyond-the-floor option is a
requirement for owners and operators to develop and implement a
'plan for the routine washdown of accessible surfaces in the cell
room and other areas. All plants currently wash down cell room
surfaces regularly. However, due to plant-specific
considerations, we are uncomfortable with issuing a specific set
of requirements for washdowns that would apply at all plants. As
a result, the beyond-tne-floor option establishes the duty for
owners or operators to prepare and implement a written plar. for
washdowns and identifies elements to be addressed in the plan.
Although washdowns are an ongoing practice at all plants, we
believe that including such a requirement'in the beyond-the-flocr
option will elevate the importance of washdowns as part of an
overall•approach to reducing cell room fugitive emissions.
As a final element of the beyond-the-floor option, we
considered the extent to which measurement of ambient mercury
levels in the cell room air should be incorporated. C
7-24
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all mercury cell chlor-alkali plants periodically monitor mercury
vapor levels at the cell room floor plane, in keeping with
Occupational Safety and Health Administration (OSHA) standards
for worker exposure to mercury. Typically, on a daily basis, a
plant operator measures and records the mercury vapor level in
the cell room. Some plants use technologies that measure the
mercury vapor level at a single point, such as portable mercury
vapor analyzers based on ultraviolet light absorption or gold
film amalgamation detection. Plant operators using these
technologies take readings at specified locations in the cell
roorr. Other plants utilize procedures that provide an aggregate
reading, such as chemical absorption into potassium permanganate
solution followed by separate cold vapor atomic absorption
analysis in a laboratory setting. This composite sample is most
often obtained by a plant operator walking through the cell room
with a small sampling pump.
When a mercury vapor level above the OSHA personal exposure
limit is measured, plant operators require the use of respirators
in the area. They also take action to determine and eliminate
the cause of the elevated mercury level.
Giver, the fact that all plants conduct cell room mercury
vapor measurements, we determined that it was appropriate to
include requirements tc conduct cell room monitoring as a means
tc identify and correct situations resulting in elevated mercury
levels (and obviously, increased mercury emissions) as part of
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the beyond-the-floor option for fugitive mercury emission
sources. We considered basing such a program on periodic
measurement, which would correspond to the programs currently in
place at mercury cell chlor-alkali plants. We also considered
basing such a program on the continuous measurement of mercury
vapor levels in the upper portions of the cell room. We are
aware of technologies, including extractive, cold vapor
spectroscopy systems and open-path, differential optical
absorption spectroscopy systems, designed for such continuous
monitoring applications.
Upon consideration of the benefits of periodic versus
continuous monitoring of the cell room mercury vapor levels, we
selected continuous monitoring as part of the beyond-the-floor
option monitoring program for the following reasons. First, we
believe that continuous monitoring would identify hydrogen leaks
or other situations that result in elevated mercury levels in the
cell room much more promptly than periodic monitoring. If
periodic monitoring was conducted on a daily basis, hours could
pass before such a leak was detected. We also believe that the
continuous monitoring of mercury vapor levels during maintenance
activities would provide information to help plant operators
refine and improve such maintenance activities to reduce mercury
emissions.
Finally, we believe that the monitoring on the cell rcorr
floor plane could fail to detect hydrogen leaks, or other
7-26
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situations .resulting in mercury vapor leaks, that may occur at
higher elevations. Continuous monitoring in the upper portion of
the cell room would provide a representation of all areas of the
cell room at all levels.
Therefore, we have included a program involving the
continuous monitoring of mercury vapor levels in the cell room as
part of the beyond-the-floor option. We envision the basic
•elements for this program to be'as follows. Each owner or
operator would be required to install a mercury monitoring system
in each cell room and continuously monitor the elemental mercury
concentration in the upper portion of the cell room. The type of
technology, whether an extractive, cold vapor spectroscopy system
or an open-path, differential optical absorption spectroscopy
system, would be at the discretion of the owner or operator,
provided that performance criteria, such as a minimum detection
limit, were met. A sampling configuration would be specified to
acquire a composite measurement representative of the entire cell
room air. For example, the sampling configuration may involve
sampling at least three points along the center aisle of the cell
room and above the mercury cells at a height sufficient to ensure
representative readings.
Fcr each cell room, the owner or operator would need to
establish an action level, which would be based on preliminary
monitoring to determine normal baseline conditions. The onset
anc deration of this preliminary monitoring would be specified,
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as well as'guidelines for setting the action level. Continuous
monitoring would commence after a specified time period following
establishment of the action level and its documentation in a
notification to us. A minimum data acquisition requirement would
be established, such as a requirement to collect and record data
for at least a certain percent of the time in any six-month
period.
Actions to correct the situation as soon as possible would
be required when measurements above the action level were
obtained over a defined duration, such as a certain number of
'consecutive measurements or an average over a certain time period
above the /action level. If the elevated mercury vapor level was
due to a maintenance activity, the owner or operator would need
to keep records describing the activity and verifying that all
work practices related to that maintenance activity are followed.
If a maintenance activity was not the cause, then inspections and
other actions would need to be conducted within specific time
periods to identify and correct the cause of the elevated mercury
vapor level.
In evaluating whether to establish the beyond-the-floor
option as MACT, we looked at the incremental impacts on
emissions, cost, energy, and other non-air effects. Relative to
emissions, we firmly believe that although we are unable to
actually quantify the reductions expected with the implementation
of the beyond-the-f loor option, substantial reductions w ;-uio
7-2!
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nonetheless occur. We know from experience and inference that
the added scrutiny inherent in the suite of. beyond-the-floor
practices will of necessity result in fewer fugitive emissions.
In considering the cost impacts of the beyond-the-floor option,
we attempted to estimate the cost associated with the equipment
needed to carry out cell room monitoring as well as increased
demand for labor and overhead needed to fully implement the
proposed monitoring, inspection, recordkeeping, and reporting
activities. We estimate the total installed capital costs needed
to meet the beyond-the-floor option for fugitive mercury
emissions to be around $663,000. We estimated the total annual
costs to be around $840,000, consisting of about $94,000 for
annualized capital expenditure on mercury monitoring systems,
about $736,000 per year for labor for monitoring, inspections and
recordkeeping, about $2,100 per year for mercury monitoring
system utilities, and about $7,500 for mercury monitoring system
replacement parrs. We are unable to estimate increases in
wastewater associated with washdown and clean-up activities for
liquid mercury spills and accumulations as well as increases in
solid waste, since these would be highly plant-specific. Energy
requirements for mercury monitoring systems are estimated to
total an additional 53 thousand kW-hr/yr. Estimated secondary
air pollution irrpacts due to heightened energy consumption total
17 Mg/yr (19 tons/yr), with carbon dioxide emissions comprising
99 percent of the estimate.
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We believe the additional emission reduction that would be
achieved by the beyond-the-floor option is warranted and that the
estimated incremental costs to meet this level are reasonable.
Therefore, we are selecting the beyond-the-floor work practice
standards as MACT for fugitive mercury emission sources.
With regard to the cell room monitoring program, we
acknowledge that there are uncertainties associated with the use
of mercury monitoring systems for continuous monitoring that can
only be addressed through actual field validation. In the
preamble for the proposed rule, we are specifically requesting
comment on the feasibility of using such systems, for continuous
monitoring to prompt corrective actions for elevated mercury
vapor levels in the cell room. We are also requesting comment on
the detailed elements of the cell room monitoring program, which
we are unable to delineate in its entirety at this time.
Following publication of the proposed rule, we will involve
the public in defining this program. Specifically, we wilo. enzer
into a joint effort' with industry, monitoring instrument
suppliers, and other interested parties, to detail the elements
and requirements of this program. We will take additional
appropriate rulemaking steps as necessary to fully implement chis
program', including assuring opportunity for industry ana t.ne
public to comment.
7-30
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7.5.3 Mercury Thermal Recovery Unit Vents
Nine of the twelve mercury cell chlor-alkali plants have
mercury recovery processes. Six of the nine plants operate a
thermal recovery unit, in which mercury-containing wastes are
heated and the resulting mercury-laden off-gas is cooled and
treated for mercury removal prior to being discharged to the
atmosphere. Two plants recover mercury with a chemical process
and one plant recovers mercury in a purification still; in both
cases, mercury air emissions are believed to be low.
In establishing MACT for mercury thermal recovery units, we
obtained information from all six plants with these units. ^' ^-^
Each plant provided descriptions of its thermal recovery
operation, including tne types of wastes processed and the
control devices applied. Where available, plants also provided
results of performance testing or periodic sampling, and an
estimate of their mercury emissions . ^' ^°' •*-'' -*-°
Each of the six plants operates one or more retorts (as part
of its mercury thermal recovery unit) in which mercury-containing
wastes are heated to a temperature sufficient to volatilize the
mercury. The off-gas containing mercury vapor is then cooled in
the mercury recovery/control system, causing the mercury to
condense to liquid. The liquid mercury condensate is then
collected from recovery devices for reuse in the mercury cells.
The primary emission source is the mercury thermal recovery unit
vent, where off-gas that has passed through the recovery/control
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system is discharged to the atmosphere. Retorts used include
three basic designs: batch oven (three plants), rotary kiln (two
plants), and single hearth (one plant).
The batch ovens are D-tube retorts, which are so named
because each resembles an uppercase letter "D" on its side. Pans
are filled with waste, typically around 10 cubic feet, and then
placed into an oven. After inserting three or four pans, the
oven door is closed and the retort is indirectly heated to about
1,000°F. The residence time varies from about 24 to 48 hours,
depending on the type of waste being processed. While heating,
'the oven is kept under a vacuum and the mercury vapors are pulled
into the mercury recovery/control system. After the cycle is
completed, the unit is allowed to cool and the pans are then
removed.
The rotary kilns are long, refractory-lined rotating steel
cylinders in which the waste charge to be treated flows counter
current to hot combustion gases used for heating. Waste? tc be.
treated are conveyed into a ram feeder, which inserts a waste
charge into the kiln at regular intervals, typically about every
five minutes. Each is directly fired with natural gas and is
heatec, to over 1300°F. The rotation of the kiln provides for
mixing and transfer of the waste to the discharge end. The
residence time is about 3 hours. The gas stream leaving the kiln
passes through an afterburner, where the temperature is increase::
7-32
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to around 2,000°F to complete combustion reactions involving
sulfur and carbon, and then to a mercury recovery/control system.
The single hearth retort is comprised of a vertically-
mounted, refractory lined vessel with a single hearth and a
rotating rabble. Waste is charged onto the hearth through a
charge door by way of a conveyor. Once charged, the conveyor 'is
withdrawn, the charge door is closed, and the heating or
treatment cycle begins. The waste is stirred by the rabble rake,
which turns continuously, and is heated to around 1,350°F. The
residence time, which ranges according to waste type, is
typically much lo-nger than for rotary kilns. Similar to rotary
kilns, the gas stream leaving the hearth retort passes through an
afterburner, where the temperature is increased to around 2,000°F
to complete combustion reactions involving sulfur and carbon, and
then to a mercury recovery/control system.
As noted above, there are several important differences
between the oven retorts, and the non-oven (rotary kiln and
single hearth) retorts related to operating temperature and
residence time. There are also significant differences in the
volumetric flow rates produced by the oven and the non-oven
retorts. Oven retorts typically have volumetric flow rates
around 100 scfm, which is an order of magnitude lower than flow
rates for non-oven retorts.which are around 1,000 scfm.
Together, these differences can have a material impact on mercury
concentration, mass flow rate cf mercury, and ether factors that
7-3:
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influence mercury loadings to the recovery/control system. After
evaluation of these technical and operational differences between
oven retorts and non-oven retorts, and their potential effect on
emissions characteristics and control device applicability, we
are proposing to distinguish between retort types for the purpose
of establishing MACT.
With the exception of the plant with a single"hearth retort
that is controlled with a scrubber as the final control device,
the recovery/control system at each plant consists of
condensation and carbon adsorption. The 'amount and type of
carbon adsorbent used in the fixed bed, non-regenerative carbon
adsorbers varies among the five plants. One plant uses activated
carbon, one uses iodine-impregnated carbon, and three use sulfur-
impregnated carbon. We believe that each type is effective in
removing mercury, provided the adsorbent is replaced at a
frequency appropriate to prevent breakthrough.
In contrast, the plant with the single hearth retort
utilizes a chlorinated brine packed-tower scrubber for final
mercury control. In this scrubber, elemental mercury vapor is
removed by chemically reacting with the chlorinated brine
solution to form mercuric chloride, a non-volatile mercury salt
which is readily soluble in aqueous solutions. The resulting
scrubber effluent is returned to the brine system, causing the
absorbed mercury to be recycled back to the mercury cells.
Performance data (i.e., outlet concentration) for this orine
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scrubber system shows that the effectiveness is comparable to
that of the condenser/carbon adsorber systems used at .the other
1 Q
five plants. *-y
While examining the performance capabilities of the
condenser/carbon adsorber systems, we identified several factors
that influence performance. We believe that a primary factor
affecting mercury recovery and control is the temperature to
which retort off-gas is cooled prior to entering the final
control device. Because of the volatile nature of elemental
mercury, temperature has a direct effect on the concentration of
'mercury vapor that can exist in a gas stream. For example, the
concentration of mercury vapor that could exist in a gas stream
at 50°F is 5 mg/m3, while the predicted concentration at 85°F is
30 mg/m3, a six-fold increase. At 100°F the concentration could
potentially be over 50 mg/m3. 0
A key factor relative to the performance of carbon adsorbers
is contact time. As noted previously, we believe that generally
each of the carbon adsorbents presently used in the industry can
effectively collect mercury vapor. However, it is essential for
optimum performance that the contact time between the gas stream
tc be treated and the carbon adsorbent be long enough to allow
for maximum adsorption. Consequently, design and operational
factors such as carbon bed depth, sorbent particle size, and gas
velocity have an appreciable impact on collection efficiency.
Another key ccnsiaerati:n is the frequency at which the adsorbent
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is replaced, since the adsorbing capacity of any sorbent
decreases as saturation and breakthrough are approached.
In assessing potential formats for a numerical emission
limit we considered a limit on emissions in a specified time
period, a limit normalized on the amount of wastes processed, and
an outlet mercury concentration limit. The amounts and types of
*
wastes processed at each plant" and among plants vary
considerably. We believe, generally, that mercury emissions from
the thermal recovery unit vent are proportional to the amount of
mercury-containing wastes processed and the amount of mercury
'contained in these wastes. Therefore, we concluded that limiting
emissions over a specified time period would unfairly impact
plants that process larger amounts of wastes and/or wastes that
contain more mercury. A mercury emission limit normalized on the
amount of wastes processed would eliminate this inequity.
However, given the wide variation in the mercury content of
different types of wastes and the varying mix of waste types
processed at different plants, we concluded that setting and
enforcing such an emissions limit is impractical.
Several factors influence the concentration of mercury in
the thermal recovery unit vent exhaust. The most significant
include' the mercury content of the wastes being processed and trie
volumetric flow rate through the system. Volumetric flow rate is
dependent on process rate, fuel usage, and the volume of
combustion gas generated. The mercury concentration may also
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vary depending on the stage of the heating cycle. The mercury
content of the exhaust stream leaving the condenser(s) or other
type of cooling unit should remain relatively constant, provided
that the outlet temperature is constant and the residence time is
sufficient. Depending on the effectiveness of the carbon
adsorber or brine scrubber, the mercury concentration would be
further reduced. As a result, we conclude that concentration at
the outlet of the final control device is the most meaningful and
practical measure of the combined performance of each element of
the mercury recovery/control system. Therefore, we selected
concentration for.-the format of the MACT standard for mercury
thermal recovery units.
Finally, we evaluated how, or if, the proposed regulation
should address different waste types; that is, should different
emission limits be set for different waste types or should one
limit be set for the waste type shewn to be the highest emitting.
We analyzed all the available data but were unable to ascertain
any relationship between the type of waste (K106, D009 debris, or
D009 non-debris) being treated during testing or sampling and the
outlet mercury concentration measured across all plants.21 AS a
result, we are proposing an outlet mercury concentration limit
that is neutral tc the type of waste being processed. This
analysis also influenced our decision on the proposed
requirements for performance testing. We are proposing that
testing be conducted during conditions representative of the most
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extreme, relative to potential mercury concentration, expected to
occur under normal operation. While we would have preferred that
the proposed rule specify the type of waste to be processed
during testing, our inability to discern a relationship between
waste type and outlet mercury concentration across plants caused
us not to do so. Therefore, the proposed rule obligates owners
and operators to process mercury-containing wastes~that result in
the highest vent mercury concentration during performance
testing.
In summary, our review and analysis of all the available
information on mercury thermal recovery units leads us to the
following conclusions:
(1) Separate MACT emission limits should be developed for
oven type and non-oven (rotary kiln and single hearth) type
mercury thermal recovery units.
(2) These emission limits should not distinguish among
waste types processed.
(3) Concentration is the appropriate format for the
numerical emission limits.
The following describes how we selected the proposed
emission limits for oven type and non-oven type mercury thermal
recovery units.
7.5.3.1 Emission Limit for Oven Type Mercury Thermal
Recovery Unit Vents. There are three plants that use even
retorts. All are owned and operated by the same company
7-3!
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(Occidental Chemical). The Occidental Plant in Delaware City,
Delaware operates five ovens, the one in Muscle Shoals, Alabama
operates three ovens, and the one in Deer Park, Texas operates
two ovens. Thermal recovery at all three plants is conducted
between 6,000 to 7,000 hours per year. The amounts of waste
processed and the amounts of mercury recovered range from 90 to
almost 300 tons per year and from 3 to 20 tons per year,
respectively. At all three plants, the mercury-laden off-gas
leaving the retort is cooled and treated for particulates and
acid gases in a wet scrubber with caustic solution, followed by
further cooling in a condenser. The cooled gas is then routed
through one or more fixed-bed, non-regenerative carbon adsorbers
before being discharged to the atmosphere. We conducted an
evaluation of the mercury "recovery/control systems at all three
plants considering the condenser outlet temperature and the
amount of carbon in the beds. This evaluation indicated that the
Delware City plant is the best-controlled of the-three plants. 2
Occidental/Delaware City provided mercury emissions data
(periodic sampling results) over three years. 3 The Occidental
plants in Muscle Shoals and Deer Park were unable to provide
reliable emissions data. Therefore, data from the Delaware City
plant were used to establish MACT. Since an emission limit based
on the best controlled plant would obviously be more stringent
than tne floor level, the selection of a level associated with
the best performing recovery/control system for this retort type
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clearly meets our statutory requirement regarding the minimum
level allowed for NESHAP.
Occidental/Delaware City has five ovens and two separate
(but identical) mercury recovery/control systems. One,
designated as Stack 1, treats the exhaust gas from three ovens
while the second, designated as Stack 2, services two ovens.
TogetherV the five ovens process about" 90 Ifbris of mix waste
annually, and recover about 3 tons of mercury per year. Each
system is comprised of a wet scrubber and condenser, which cool
the exhaust gases to around 70°F, followed by a carbon adsorber
•with about 700 pounds of activated carbon. The volumetric flow
rate of the exhaust stream ranges from about 10 scfm to 110 scfm
and averages about 40 scfm.
The data from Occidental/Delaware City consist of bimonthly
measurements for 1997, 1998, and 1999 on each stack. Samples
were collected at a single point using a potassium permanganate
non-isokinetic method, which we believe provides reasonably
accurate results consistent with what would otherwise be oDtained
with EPA reference test methods, as discussed in Section 7.5.1.1.
Sampling times ranged from one-half to one hour in duration.
Waste processed during sampling included all three basic waste
types.
Each data set for the two stacks at Occidental/Delaware City
is comprised of 70 data points. Each data set appears to have at
least three unrepresentative high data points. We believe the*.
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each of these six points is an outlier. In an attempt to affirm
this judgment, we evaluated the data by way.of.Rosner's Test/ an
established statistical method for evaluating the probability
that data points at the extreme ends of a sample might be so
unrepresentative as to be considered statistical outliers and
thus rejectable. The results of applying Rosner's Test to each
"data set affirmed our conclusion thai: "the" three highest data
points in each data set are indeed statistical outliers, and that
all six points should be rejected and dismissed from further
consideration. Our evaluation of the amended data sets,
'containing 67 data points for each stack, is as follows.
Lacking any evidence to the contrary, we assumed that all
the remaining data points in the Stack 1 and Stack 2 data sets
are representative of the full range of normal operating
conditions for both recovery and control. Based on the fact that
the stacks are associated with essentially identical retort
operation and mercury recovery/control systems, we combined the
stack data into one data base of 134 data points. This decision
is strongly supported by the similarities between the two data
sets including measures of center and variability.
We are proposing that performance tests for mercury thermal
recovery units be conducted under the most challenging
conditions, which we are defining as the processing of wastes
that result in the highest mercury concentration in the vent
exhaust. Each oerformance test would consist of at least three
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runs, and the average concentration measured would be compared
with the emission,limit to determine compliance. Given our
inability to establish a discernible correlation between waste
type processed and emissions, and our obligation to set standards
that are achievable under the full range of normal acceptable
operating conditions,. we chose to set the standard based on the
average~of the three highestr^ihdividual data points" in the
combined data base for Occidental/Delaware City. The result is
23 mg/dscm as the- proposed mercury concentration emission limit
for oven type units.
Due to the very low volumetric flow rates associated with
oven type mercury thermal recovery unit exhaust streams
(typically less than 300 scfm), we believe that the retrofit of
control equipment to reduce mercury emissions is both practical
and reasonable. For purposes of estimating the impacts of the
proposed emission limit, we assumed that the Occidental plants in
Muscle Shoals, Alabama and Deer Park, Texas would need to install
carbon adsorbers that are larger than their existing units to
meet the 23 mg/dscm level. The total installed capital control
costs are estimated to be around $217,000, and the total annual
control costs are estimated to be around $163,000 per year.
Estimated mercury emission reductions against actual baseline
emissions would total 33 kg/yr (74 Ibs/yr). The associated
annual cost per unit of mercury emission reduction would be
approximately $2,200 per pound.
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Impacts on solid waste, due to increased use of carbon
adsorption, are estimated total 5.2 Mg/yr (5.7 tons/yr) of
mercury-containing spent carbon. Energy requirements are
estimated to be an additional 473 thousand kW-hr/yr. Estimated
secondary air pollution impacts due to heightened energy
consumption are 152 Mg/yr (168 tons/yr), with carbon dioxide
emissions "comprising 99 percent of~the estimate".
7.5.3.2 Emission Limit for. Non-Oven Type Mercury Thermal
Recovery Unit Vents. As noted previously, three plants operate
retorts other than oven-type retorts. The mercury
recovery/control systems operated at the two plants with rotary
kiln retorts (PPG in Lake Charles, Louisiana and Olin in
Charleston, Tennessee) consist of direct contact cooling,
particulate and acid gas scrubbing, condensation, and carbon
*
adsorption. The mercury recovery/control system at the plant
with a single hearth retort (Vulcan in Port Edwards, Wisconsin)
employs a chlorinated brine scrubber as the final control device.
The following are more detailed descriptions of these
recovery/control systems, the emissions data available, and our
approach to determining MACT for non-oven type units.
7\t PPG/Lake Charles, over ?00 tons of waste are processed
annually, and over 12 tons of mercury are recovered. In addition
to processing waste generated at this site, wastes from other
sites are also processed in this rotary kiln unit. The off-gas
frcn the rotary kiln is routed to a direct contact water quench
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tower and a direct contact condenser, followed by a caustic
packed-tower scrubber which has an outlet temperature of around
57°F. Subsequently, the stream is routed througn filtration
equipment for particulate collection and two carbon adsorbers
(which are used in series) containing a total of 6,000 pounds of
sulfur-impregnated carbon, which is replaced about every
2^ years. The volumetric flow rate of the e^chaust~stream ranges
from about 490 scfm to 990 scfm and averages about 720 scfm.
Daily, personnel at this plant measure the mercury
concentration at the outlet of the last carbon bed using a
'company-developed procedure derived from an Occupational Safety
and Health Administration (OSHA) method for determining worker
exposures in the workplace. A personal air sampler is used to
pull a 1 to 2 hour sample from the carbon adsorber exhaust at a
rate of around 0.2- liters/minute through a small tube containing
about 200 milligrams of molecular sieve media. The sample is
recovered from the media through digestion in small amounts of
nitric and hydrochloric acids. The mercury content is determined
by atomic absorption analysis. Data were submitted by PPG/Lake
Charles for 1997, 1998, and 1999. When submitting these data,
the company cautioned that although the routine sampling with tr>~
modified OSHA procedure produces credible information 01. relative
changes in performance, it does not produce accurate information
on actual mercury releases.^4 Specifically, we believe the data
obtained using this method are biased low. 5 -phe average
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measured mercury concentration for PPG/Lake Charles is an order
of magnitude lower than averages for Vulcan/Port Edwards and
Olin/Charleston, and the minimum measured value is two orders of
magnitude lower than the minimum values for the Vulcan and Olin
plants.26,27 It j_s our conclusion that data from PPG are
unsuitable for standard setting, as they understate emissions .and
thus"overstate the performance of the mercury" recovery/control
system.
The rotary kiln unit at Olin/Charleston processes around
500 tons of waste per year and recovers about 10 tons of mercury.
This plant processes wastes generated on-site, as well as wastes
from other sites. Similar to the unit at PPG/Lake Charles
discussed above, the vapor stream from the kiln is routed to a
direct contact water quench tower and then to a venturi unit and
caustic packed-tower scrubber. This is followed by a indirect
contact condenser ana two carbon adsorbers in series. The outlet
temperature of the condenser is around S"70?. Each carbon
adsorber contains 1,000 pounds of sulfur-impregnated carbon,
which is replaced about every 2^ years. The volumetric flow rate
of the exhaust stream ranges from about 310 scfm to 1,560 scfm
and averages about 720 scfm. Concentration measurements are made
monthly using a potassium permanganate non-isokinetic method,
which we believe provides reasonably accurate results consistent
with what would otherwise be obtained with EPA reference test
methcos, as discussed in Section 7.5.1.1. Data were provided for
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each month in 1998. The measured mercury concentrations range
from 1.4 mg/m3 to ,6.0 mg/m3, with a mean of 2.8 mg/m3.28
At Vulcan/Port Edwards, the off gas from the single hearth
retort is routed through a direct contact water quench tower, a
venturi scrubber, then to a caustic packed-tower scrubber with an
outlet temperature of around 80°F. As noted previously, the
"'final control device is a chlorinatecf brine packed-tower
scrubber. Mercury control is accomplished by chemically
absorbing mercury- from the gas stream and converting it to
mercuric chloride, which is soluble in aqueous solutions. The
resulting scrubber effluent is recycled back to the mercury cells
with the brine. The volumetric flow rate of the exhaust stream
ranges from about 590 scfm to 2,030 scfm and averages about
1,100 scfm.
Personnel at Vulcan/Port Edwards conduct monthly
measurements of the mercury concentration in the brine scrubber
exhaust gas. The measurement method used is a potassium
permanganate non-isokinetic method, which we believe provides
reasonably accurate results consistent with what would otherwise
be obtained with EPA reference test methods, as discussed in
Section 7.5.1.1. Data were provided for 1997, 1998, and 1999.
The measured mercury concentrations range from 0.2 mg/m1 tc
10.8 mg/m3, with a mean and median value of 1.6 and 2.2 mg/mj,
respectively.
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In addition, a separate Method 101 stack test was conducted
in October 1998. The test consisted of three two-hour sample
runs in accordance with Method 101 test procedures. The results
compare favorably with the monthly periodic measurements cited
above, enhancing our belief that the potassium permanganate
method provides reasonably accurate results that can be used in
setting MACT.30
In establishing the MACT floor and subsequently MACT, we
focused on the two plants (Vulcan/Port Edwards and
Olin/Charleston) •• for which we have credible emissions data. As
•noted above, the data from Vulcan consists of 3 years of monthly
measurements. There are 35 data points. We examined these data
and noticed what appear to be two unrepresentative high data
points, one at 10.8 mg/m3 and the other at 6.7 mg/m3. We
evaluated whether the two points are outliers and should be
rejected. In an attempt to affirm this judgment, we again used
Rosner's Test. The results support our ' conclusion that the two
data points are outliers, and thus should be dismissed. We
believe that the remaining 33 data points are representative of
the full range of normal operating conditions, including
reasonable worst-case circumstances, for both recovery and
control at the Vulcan plant. The data from Olin/Charleston
includes 12 monthly measurements conducted in 1998, each lasting
between 30 to 60 minutes in duration. There are no apparent
outliers in the Olin data.
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Although there are fewer than five sources from which to
constitute a MACT floor, we opted to take the mean of Vulcan/Port
Edwards data and Olin/Charleston data as the MACT floor option
for existing sources. We averaged the three highest
concentration data points for each plant (3.9 mg/dscm for Vulcan
and 5.4. mg/dscm for Olin) and took the mean of the two plant
^averages (5 mg/dscm) as the floor value. " ~~
Of the three plants with non-oven type mercury thermal
recovery unit vents, we project that only Plant H would need to
upgrade existing controls to meet the 5 mg/dscm floor level. We
•project that PPG/Lake Charles would not need to upgrade its
existing controls to meet the floor level. We assume that
Olin/Charleston could reduce mercury emissions to the floor level
by replacing the carbon in its existing carbon adsorbers more
frequently than current practice. No capital costs are
associated with meeting this level, as more frequent carbon media
replacement was estimated as only a recurring (annual; ccst cf
$1,200 per year. Mercury emission reductions against actual
baseline emissions would total about 2 kg/yr (5 Ibs/yr) for the
three plants. The associated annual cost per unit of mercury
emission reduction would be approximately $240 per pound. With
the assumption of more frequent carbon media replacement at
Olin/Charleston, there are no associated secondary air pollution,
water pollution, and energy impacts. Estimated solid waste
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impacts, due to increased use of carbon adsorption, total
0.09 Mg/yr (0.1 tons/yr).
We then examined beyond-the-floor MACT options. A direct
comparison of the data for Vulcan/Port Edwards and
Olin/Charleston indicates that the emission levels recorded at
the Vulcan plant are about half that recorded at the Olin plant.
The mean and median values recorded by Vulcan are 1.2 and
0.7 mg/m3, 31 respectively, while the same values by Olin are 2.8
and 1.9 mg/m3, ^2 respectively. The highest monthly value
recorded at Vulcan is 4.3 mg/m3, while the highest value recorded
at Olin is 5.9 mg/m3. Given the better performance (lower
emissions) recorded at the Vulcan plant, we used the data from
Vulcan to establish a beyond-the-floor option. We averaged the
three highest values for Plant D, for a beyond-the-floor value of
4 mg/dscm.
Due to' the very low volumetric flow rates associated with
non-oven type mercury thermal recovery unit exhaust streams
(typically less than about 2,000 scfm), we believe that the
retrofit of control equipment to reduce mercury emissions is both
pnct^cal and reasonable. For purposes of estimating impacts, we
assumed that Olin/Charleston could further increase its carbon
replacement frequency to meet the 4 mg/dscm level. We assume
that PPG/Lake Charles would not need to upgrade its existing
controls to meet the beyond-the-floor level.
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In evaluating regulatory options that are more stringent
than the floor, we must consider the cost of achieving such
emission reduction, and any non-air quality health and
environmental impacts and energy requirements. The beyond-the-
floor option would result in an additional 6 kg/yr (13 Ibs/yr) of
total mercury emission reductions (a 10 percent incremental
"reduction from the floor option). The incremental annual costs
are estimated to total around $5,800 per year. The incremental
cost per unit of .incremental mercury emission reduction is
approximately $450 per pound. The estimated incremental
environmental and energy impacts are an additional 0.4 Mg/yr
(0.5 tons/yr) of solid waste in the form of mercury-containing
spent carbon.
We believe the additional emission reduction that would be
achieved by the beyond-the-floor option is warranted. Further,
we believe that the incremental costs of achieving such emission
reduction, as well as incremental non-air environmental impacts
and energy requirements, are reasonable for mercury. Therefore,
we selected 4 mg/dscm as MACT for non-oven type mercury thermal
recovery unit vents.
7.6 SELECTION OF THE BASIS AND LEVEL OF THE PROPOSED STANDARDS
FOR NEW SOURCES
Section 112(d)(3) of the CAA specifies that standards for
new sources cannot be less stringent than the emission control
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that is achieved in practice by the best-controlled similar
source, as determined by the Administrator.
In the case of mercury cell chlor-alkali production
facilities, of the 43 chlor-alkali production facilities in
operation in the U.S. at the time of this analysis, 32 use cell
technologies other than mercury (23 use diaphragm cells and 9 use
membrane cells).' "As explained ^further below, we consider^tHese
chlor-alkali facilities using non-mercury cell technology to be
"similar sources," and, as such, a suitable basis for the
standard for new source MACT. Such a standard would effectively
eliminate mercury emissions from new source chlor-alkali
production facilities.
The impact of such a standard would be negligible given that
in terms of cost, economic-and air and non-air environmental
impacts, we don't believe that a new mercury cell chlor-alkali
plant would otherwise ever be constructed. No new mercury cell
chlor-alkali plant has been constructed in the U.S. in over
30 years, and we have no indication of any plans for future
construction.33,34 jn addition, we believe that any future
demand for new or replacement chlor-alkali production capacity
would be met easily through the construction of new production
facilities that do not use or emit mercury. Consequently, we
believe it is appropriate to consider non-mercury cell facilities
as similar sources and the prohibition of new mercury cell chlor-
alkali production facilities achievable. Accordingly, we are
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proposing a.prohibition on mercury emissions for new source MACT
for mercury cell chlor-alkali production facilities. We are not
proposing any initial and continuous compliance requirements
related to this emission limit, as we believe they are
unnecessary, since the emissions prohibition effectively
precludes the new construction or reconstruction of a mercury
"cell"chlor-ancaTi productioh~facility.
As highlighted in the previous discussion on the selection
of standards for existing sources, the emission levels achieved
by the best-controlled sources at thermal recovery processes were
.selected as the proposed existing source MACT levels for mercury
recovery facilities. These best levels of control for point
sources are 23 milligrams of total mercury emitted per dry
standard' cubic meter of exhaust from an oven type mercury thermal
recovery unit vent, and 4 milligrams of total mercury emitted per
dry standard cubic meter of exhaust from a non-oven type mercury
thermal recovery unit vent. For fugitive emission sources, the
best level of control identified is the work practice standard
represented in the beyond-the-floor option selected for the
proposed rule for existing sources.
In the case of mercury recovery facilities, we know of three
plants that employ low emitting mercury recovery processes.
These processes include chemical mercury recovery used at two
plants and recovery in a batch purification still used at a thira
plant. Unlike thermal recovery units, however, which are capar.L
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of treating a variety of waste types, the chemical recovery and
the purification still processes have limited application. Both
are suitable to treating only certain waste types, K106 wastes
for chemical recovery and end-box residues for purification
still. Plants using these non-thermal recovery processes
transfer their remaining wastes off-site for treatment, which
"typically involves thermal recovery. " Giverr this "TimitatTonT"we
do not believe that these non-thermal recovery processes qualify
as a suitable basis for new source MACT. Consequently, for new
source MACT for mercury recovery facilities, we are proposing
numerical mercury emission limits consistent with that achieved
by the best similar sources, 23 mg/dscm for oven type thermal
recovery unit vent and 4 mg/dscm for non-oven type thermal
recovery, units.
7.7 SELECTION OF THE TESTING AND INITIAL COMPLIANCE REQUIREMENTS
We selected the proposed testing and initial and continuous
compliance requirements based on requirements specified in the
NESHAP General Provisions (40 CFR part 63, subpart A). These
requirements were adopted for mercury cell chlor-alkali plants to
be consistent with other part 63 NESHAP. These requirements were
chosen to ensure that we obtain or have access to- sufficient
information to determine whether an affected source is complying
with the standards specified in the proposed rule.
The proposed rule requires initial and periodic compliance
tests for determining compliance with the emission limits for by-
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product hydrogen streams and end-box ventilation system vents,
and the emission limits for oven type and non-oven type mercury
thermal recovery unit vents. The proposed rule requires the use
of published EPA methods for measuring total mercury.
Specifically, the proposed rule allows the use of Method 101 or
101A (of Appendix A of 40 CFR part 61) for end-box ventilation
~sy¥teitr^vent"s and mercury thermal IrecoVeTy^liiTr^nts and
Method 102 for. by-product hydrogen streams. Methods 101 and 102
were developed in the 1970s specifically for -use at mercury cell
chlor-alkali plants. Although Method 101A was developed to
measure mercury emissions from sewage sludge incinerators, it is
appropriate for use for end-box ventilation system vents and
mercury thermal recovery unit vents.
The NESHAP General Provisions specify at §63.7(e)(3) that
each test consist of three separate test runs. The proposed rule
adopts this requirement. Further, the proposed rule requires
that each test run be at least 2 hours long. This is the
duration specified in Method 101 and referenced in Methods 101A
and 102.
In the stack test data that were provided to us, there were
numerous incidents where the results were reported as "less than"
a certain level. We believe that this is primarily related to
the sensitivity of the analytical instrument (that is, the
absorption spectrophotometer) used to measure the amount of
mercury in the collected sample. Method 101 states tnat the
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absorption spectrometer must be the "Perkin Elmer 303, or
equivalent, containing a hollow-cathode mercury lamp and the
optical cell ... ." It is our understanding that this
particular model is no longer commercially available, and that
newer, more sensitive absorption spectrophotometers are
available.^5 we considered whether it was necessary to specify,
"either" In~th~e proposed rule or through a""modification to the test
method, that Perkin Elmer 303 did not have to be used. We
concluded that the "or equivalent" language contained in
Method 101 allows for the use of newer, more sensitive
instruments and as a result, adding rule language or amending
Method 101 was unnecessary.
Even with the 2-hour minimum test run period and the
clarification that newer, more sensitive absorption
spectrophotometers are allowed to be used, we remain concerned
that quantifiable results of mercury emissions may not be
obtained during performance tests. As a result, the proposed
rule includes a requirement that the amount of mercury collected
during each test run be at least 2 times the limit of detection
fc_ the analytical method used. This will assure that a reliably
quantifiable amount of mercury is collected for each test run.
The emission limits ^or by-product hydrogen streams and end-
box ventilation system vents are in the form of mass of. mercury
emissions per mass of chlorine produced. Therefore, criteria for
the measurement of chlorine production during performance testing
-------
are also necessary. It is our understanding that instrumentation
used to measure actual chlorine production, as well as the
location and frequency of measurement, varies from plant to
plant. Types of instruments used include rail car weigh scales,
weigh cells on liquid storage tanks, and gas flow meters.
Calibration procedures for these instruments are plant-specific
and dependent ori~the ±nvorveme"irtr~o"f~third-partiBs~c"onc"e'rneii with
quantifying actual chlorine production for bill-ing and other
purposes. Moreoyer, at a given plant, an accurate value for
actual chlorine production based on these measurements is
generally obtained at the end of an operating month, when mass
balance calculations are performed to verify measurements.36'37
For a compliance test run on the order of several hours, we
therefore needed to rely on some other reasonable indicator of
chlorine production. All mercury cell chlor-alkali plants
measure the electric current through on-line mercury cells, also
known as the cell line load or cell line current load, with a
digital monitor that provides readings continuously. This cell
line current load measurement can be used in conjunction with a
theoretical chlorine production rate factor to obtain the
instantaneous chlorine production rate. The theoretical factor
is based on a statement of Faraday's Law, that 96,487 Coulombs
(Faraday's constant, where a Coulomb is a fundamental unit of
electrical charge) are required to produce one gram equivalent
weight of the electrochemical reaction product (chlorine;. It is
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our understanding that chlorine production-calculated in this
manner would differ from the actual quantity produced at the
plant by about 3 to 7 percent, due to electrical conversion
efficiency and reaction efficiency determined by equipment
characteristics and operating conditions. We consider this
degree of variability acceptable.
We therefore stipulated in the"proposed "rule that the cell
line current load be continuously measured during a performance
test run and that measurements be recorded at least every
15 minutes over the duration of the test run. We further
specified equations for computing the average cell line current
load and for calculating the quantity of chlorine produced over
the test run.
In addition to the requirement to conduct performance tests
to demonstrate compliance with the emission limits, owners or
operators would be required to establish a mercury concentration
operating limit for each vent as part of the initial compliance
•demonstration. Then, at least twice a permit term (at mid-term
and renewal), they would conduct subsequent compliance
deTcnstrations and at the same time reestablish operating limit
values. The proposed rule requires that' these me'rcury
concentration operating limits be determined directly from the
concentration monitoring data collected concurrent with the
initial performance test.
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For the work practice standards, initial compliance is
demonstrated by documenting and certifying that the standards are
;
being met or will be met, by submitting a Washdown Plan, and by
certifying that the plan is being followed or will be followed.
This approach assures initial compliance by requiring the owner
or operator to submit a certified statement in the Notification
"of "Cbmplianc e" Status" ~r~e portv " ""
7.8 SELECTION OF THE CONTINUOUS COMPLIANCE REQUIREMENTS
For each of the proposed emission limits, which consist of
the limits on mercury emissions from hydrogen streams, end-box
ventilation systems, and thermal recovery units, we considered
the feasibility and suitability of continuous emission monitors
/
(CEM) as the means of demonstrating continuous compliance. While
we were unable to identify any mercury cell chlor-alkali plant
currently using a mercury CEM on any vent, we did determine that
there are mercury CEM commercially available that may be suitable
for use at mercury cell chlor-alkali plants. ° To date, most of
the development work on mercury CEM has focused on the
development of monitors for the continuous measurement of mercury
air emissions from either coal-fired utility boilers or hazardous
waste incinerators. Most mercury CEM are extractive monitors
which extract a continuous or nearly continuous sample of gas
then transfer the gas to an instrument for spectroscopic analysis
by way of either cold vapor atomic absorption or cold vapor
atonic fluorescence.
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These cold vapor techniques have similar limitations. Both
detect mercury vapor only in its elemental form. To measure
other forms of mercury vapor (e.g., oxidized/incrganic/divalent
mercury, such as mercuric chloride), the sampled gases 'must first
pass through a converter which reduces any non-elemental mercury
vapor present to the elemental form prior to analysis. None of
the available monitors based^on^the cold vapor"techniquers^are
capable of measuring particulate or non-vapor phase mercury,
since the sample gas must be filtered to remove any particulate
matter present prior to conversion and analysis. This would
.include elemental mercury condensed on particulate matter and any
mercury compounds in particulate form. Monitors that are capable
of measuring total vapor phase mercury range in price from
$50,000 to $80,000. Simpler monitors that measure only elemental
mercury vapor average about $10,000.
For the proposed emission limits for by-product hydrogen
streams and end-box ventilation system vents, which are expressed
in grams of mercury per megagram of chlorine produced, we
evaluated two options: (a) continuous compliance against the
proposed gram per megagram standards, and (b) continuous
compliance against plant and vent specific operating limits
expressed in terms of concentration. In addition to monitoring
mercury concentration, the first option would require continuous
monitoring of volumetric flow rate and a continuous, or at least
periodic, measurement of chlorine production. The operating
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limits for the second option would be set at the time that
initial compliance with the emission limit is demonstrated.
Since the predominant form of liquid mercury in mercury
cells and other production facilities is elemental, we assumed
that the mercury contained in the vent gas from either by-product
hydrogen streams or end-box ventilation system vents is similarly
T:alfgeXy~~iTj^The"elemental ~vap~of~~form:Thus,^lrhe"~s"impler', less
expensive monitors for measuring elemental mercury vapor only
should be suitable.
We concluded that monitoring only elemental mercury
.concentration provides a simpler, less expensive, and more
reliable alternative to demonstrating continuous compliance than
monitoring against the gram per megagram standards. As a result,
we are proposing that continuous compliance for by-product
hydrogen streams and end-box ventilation system vents be
demonstrated through the continuous monitoring of elemental
mercury concentration in the vent exhaust.
To the best of.our knowledge, mercury contained in the
exhaust gas of thermal recovery units, both oven and non-oven
types, should exist as both vapor (elemental or non-elemental)
and fine particulate matter. As highlighted above, none of the
currently available monitors are capable of measuring particulate
mercury. Consequently, continuous monitoring to demonstrate
continuous compliance with the total mercury concentration limit
would not be possible.
7-60
-------
Similar to the by-product hydrogen streams and end-box
ventilation system vents, we also considered the feasibility and
usefulness of monitoring vapor phase mercury, specifically the
elemental form. We concluded that the continuous monitoring of
elemental mercury vapor as a surrogate to the total mercury
emission limit using the simpler of the available monitors,
~provides"a~h acceptable and cost-eTfective;~"means'; of tYacTcincg ~
relative changes in emissions and control device performance.
Therefore, as proposed for by-product hydrogen streams and end-
box ventilation system vents, we are proposing for oven type and
non-oven type mercury thermal recovery units that continuous
compliance be demonstrated through continuous monitoring of
elemental mercury concentration against an applicable
concentration operating limit established as part of the initial
compliance demonstration.
Another important aspect of continuous compliance is the
time period over which continuous compliance is determined. One
option would be an instantaneous period, where any measurement
outside of the established range (that is, above the established
concentration limit) would constitute a deviation. More
commonly, the average of the monitoring data over a specified
time period, for example an hour, is compared to the established
limit.
While mercury cell chlor-alkali production facilities are
generally operated continuously, there are process fluctuations
-------
that impact emissions. Mercury recovery facilities are operated
intermittently, depending on the amount of mercury-containing
*,
waste to be treated and other factors. We believe that an
averaging period is necessary for both situations. We considered
a daily averaging period and concluded that daily averaging would
accommodate process variations while precluding avoidable periods
~of~Eigh~emissions. "Therefore,we a re "proposing a~daily averaging
period for demonstrating continuous compliance.
We also considered how to address monitoring data collected
during startups, shutdowns, and malfunctions. We believe that it
is important to continue to monitor the outlet mercury
concentration during startups, shutdowns, and malfunctions to
minimize emissions and to demonstrate that the plant's startup,
shutdown, and malfunction plan is being followed. However, as
provided for in the NESHAP General Provisions (40 CFR part 63,
subpart A), we do not believe that the data collected during
these periods should be used in calculating the daily average
values. The emission limits were developed based on normal
operation, and the performance tests will be conducted during
representative operating conditions. Therefore, the inclusion ~f
monitoring data collected during startups, shutdowns, and
malfunctions into the daily averages would be inconsistent with
the data used to develop the emission limits and subsequently,
the mercury concentration operating limits.
7-62
-------
While we did not identify situations in the mercury cell
chlor-alkali industry where elemental mercury concentration is
being continuously monitored, we believe that continuous
elemental mercury concentration monitoring devices are available
for use at mercury cell chlor-alkali plants. We recognize that
the transfer of this monitoring technology to applications at
mercury~ceTl chlor-alkali "planTs~wi"IX"inT:roduc~e~"unceftainTie~s "
that can only be addressed through actual field demonstration.
We are specifically requesting comment on the technical
feasibility of using continuous elemental mercury concentration
monitors for indicating relative changes in control system
performance. We are also requesting comment on the proposed
specifications for these devices.
Continuous compliance- with the proposed work practice
standards for the fugitive emission sources would be demonstrated
by maintaining the required records documenting conformance with
the standards and by maintaining the required records showing
•that the Washdown Plan was followed.
7.9 SELECTION OF THE NOTIFICATION, RECORDKEEPING, AND REPORTING
REQUIREMENTS
We selected the proposed notification, recordkeeping, and
reporting requirements ba^ed on requirements specified in the
NESHAP General Provisions (40 CFR part 63, subpart A). As with
the proposed initial and continuous compliance requirements,
these requirements were adapted for mercury cell chlor-alkali
7-63
-------
plants to be consistent with other part 63 national emission
standards.
7.10 REFERENCES
1. Economic Analysis of Air Pollution Regulations: Chlorine
Industry. Prepared by Research Triangle Institute for
Aaiysha Khursheed, U.S. Environmental Protection Agency.
August 2000.
2. Seavey, D. and S. Young. "Holtrachem to shut down plant."
~"Bangor~lMa~iher Daily "News". August 23 r~2 00OY
3. Reference 1.
4. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Background on Data
Used to Determine Regulatory Alternatives for By-Product
Hydrogen Streams and End-Box Ventilation System Vents. June
25, 2001.
5. Memorandum. Bhatia, K. and Norwood, P. EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency.
Availability of Molecular Sieve Adsorption Productions for
Mercury Cell Applications. August 24, 1999.
6. Reference 4.
7. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Fosario, I., U.S. Environmental Protection
Agency. Site Visit Report for Oxychem's. Facility in
Delaware City, Delaware. October 4, 2001.
8. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site-
Visit Report for Olin Chemicals, Charleston, Tennessee Site.
August 17, 1998.
9. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site
Visit Report for PPG Industries, Lake Charles, Louisiana
Site. August 25, 1999.
10. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Rosario, I., U.S. Environmental rin-t-iJtic*
Agency. Site Visit Report [Vulcan Chemicals Facility in
Port Edwards, Wisconsin]. May 11, 1999.
7-64
-------
11. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated,
to Rosario, I., U.S. Environmental Protection Agency. Site
Visit Report for Pioneer Chlor-Alkali Company's St. Gabriel,
Louisiana Plant. June 2, 1999.
12. Memorandum. McCutchen, J. and Norwood, P., EC/R
Incorporated, to Rosario, I., U.S. Environmental Protection
Agency. Database Analysis of Chlorine Production Mercury
Housekeeping Measures. July 28, 1999.
13. Memorandum. Bhatia, K., McCutchen, J., and Norwood, P.,
EC/R Incorporated, to Rosario, I., U.S. Environmental
"Protection Agency. Summary bf~Section "114 Respofises^Trom
Mercury Cell Chlor-Alkali Facilities. January 19, 1999.
14. Memorandum. Bhatia, K. and Norwood, P., EC/R Incorporated.
Compilation of Clarifications to Section 114 Responses from
Mercury Cell Chlor-Alkali Plants. January 19, 2001.
15. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information on Mercury Thermal Recovery Unit at Occidental's
Delaware City, Delaware Plant. June 25, 2001.
16. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information on Mercury Thermal Recovery Unit at Olin's
Charleston, Tennessee Plant. June 26, 2001.
17. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information on Mercury Thermal Recovery Unit at PPG's Lake
Charles, Louisiana Plant. June 27, 2001.
18. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of
Information on Mercury Thermal Recovery Unit at Vulcan's
Port Edwards, Wisconsin Plant. June 28, 2001.
19. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Background on Vent
Control System Enhancements to Meet Regulatory Alternatives
for Existing Mercury Emission Sources at Mercury Cell Chlor-
Alkali Plants. September 26, 2001.
20. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Development of
Mercury Vapor Concentration Versus Temperature Equation.
November 19, 1998.
7-65
-------
21. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Relationship Between
Type of Waste Processed and Periodic Mercury Concentration
Sampling Results for Mercury Thermal Recovery Units. June
29, 2001.
22. Reference 18.
23. Reference 14.
24. Facsimile. Smith, T., PPG Industries, Inc., to Norwood, P.,
EC/R Incorporated. RE: Request for PPG TRU Emissions Data
ancTAnalysis "Procedures: ' June 1T8, ~2000 .
25. Memorandum. Riley, G., U.S. Environmental Protection
Agency, to Rosario, I., U.S. Environmental Protection
Agency. Review of NIOSH Mercury Procedure 6009. November
2, 2000.
26. Reference 15.
27. Reference 17.
28. Reference 15.
29. Reference 17.'
30. Compliance Test Report for the Determination of Mercury
Emissions from the Hydrogen Stack, Retort Stack, and the
Fume Stack. .Vulcan Chemicals, Port Edwards, Wisconsin.
October 1998.
31. Reference 17.
32. Reference 15.
33. Review of National Emission Standards for Mercury. EPA-
450/3-84-014a. U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina. December 1984.
34. Letter from Smerko, R., Chlorine Institute, Washington,
D.C., to Document Control Officer, Office of Pollution
Prevention and Toxics, U.S. Environmental Protection Agency,
Washington, D.C. October 15, 1999.
35. Teleccn. Hartmann, A., EC/R Incorporated, to Terr.,
PerkinElmer. Information on atomic absorption
spectrophotomers for EPA Method 101. June 22, 1999.
7-66
-------
36. Memorandum. Norwood, P., EC/R Incorporated, to Rosario,
I., U.'S. Environmental Protection Agency. Chlorine
Production Measurement Techniques. November 16, 2001.
37. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Summary of the August
7, 2001 meeting between the EPA and the Chlorine Institute.
August 14, 2001.
38. Memorandum. Bhatia, K., EC/R Incorporated, to Rosario, I.,
U.S. Environmental Protection Agency. Information Gathered
on Continuous Mercury Emission Measurement. July 27, 2001.
-------
APPENDIX A.
EVOLUTION OF THE BACKGROUND INFORMATION DOCUMENT
The purpose of this study was to develop a basis for
supporting proposed national emission standards for hazardous air
pollutants TNESHAP) for mercury~~ernissions~"from m~ercury~celT""""
phlor-alkali plants. To accomplish the objectives of this
program, technical data were acquired on the following aspects of
the mercury cell chlor-alkali industry: (1) the mercury cell
chlor-alkali process that produces chlorine and caustic,
(2) processes that are used to recovery mercury from wastes
generated in the mercury cell and related processes, (3) mercury
emissions from the mercury cell and mercury recovery processes,
(4) methods for reducing mercury emissions, (5) methods to
monitor the performance of control devices in reducing mercury
emissions, and (6) housekeeping and work practices to reduce
mercury emissions. The bulk of the information was gathered from
the following sources:
1. Technical literature;
2. Plant visits;
3. Industry representatives;
4. The Chlorine Institute, which is a trade organization
representing chlor-alkali manufacturers; and
5. Equipment vendors.
A-l
-------
Significant events relating to the evolution of the
background information document are itemized in Table A-I
A-2
-------
TABLE A-l. EVOLUTION OF THE BACKGROUND INFORMATION DOCUMENT
Date
Company, Consultant, or
agency/location
Nature of action
4/10/98
U.S. Environmental
Protection Agency
Chloralkali production
listed as source of
mercury emissions in
section 112 (c) (6)
emission inventory
4714A9~8
The Chlorine Institute
"Meeting "bet we eh the
EPA and the Chlorine
Institute to discuss
plans for the
development of a
mercury standard for
mercury cell chlor-
alkali plants.
5/4/98 -
5/7/98
Olin Chemicals, Charleson,
TN
Plant visit to gather
information on mercury
housekeeping
procedures techniques,
the mercury cell
process, and mercury
control techniques.
5/26/98
5/29/98
Occidental Chemical,
Delaware City, DE
Plant visit to gather
information on mercury
housekeeping
procedures techniques,
the mercury cell
process, and mercury
control techniques.
6/10/98
-6/12/98
Vulcan Materials,
Port Edwards, WI
Plant visit to gather
information on mercury
housekeeping
procedures techniques,
the mercury cell
process, and mercury
control techniques.
A-3
-------
TABLE A-l.
EVOLUTION OF THE BACKGROUND INFORMATION DOCUMENT
(continued)
Date
Company, Consultant, or
agency/location
Nature of action
6/22/98
6/25/98
Pioneer Chlor-Alkali,
St. Gabriel, LA
Plant visit to gather
information on mercury
housekeeping
procedures techniques,
the mercury cell
prpcejss>, and mercury
control techniques.
6/26/98
PPG Industries,
Lake Charles, LA
Plant visit to gather
information on mercury
housekeeping
procedures techniques,
the mercury cell
process, and mercury
control techniques.:
9/1/98
ASHTA Chemicals (Astabula,
OH!),
Holtrachem (Orrington, ME),
Occidental Chemical
(Delaware City, DE, Deer
Park, TX, and Muscle Shoals,
AL) ,
Olin (Charleston, TN and
August, GA),
Pioneer Chlor-Alkali (St
Gabriel, LA),
PPG Industries (Lake
Charles, LA and New
Martinsville, WV), Vulcan
Chemicals (Port Edwards,
WI), Westlake (Calvert City,
KY)
Section 114
information request.
1/19/99
EC/R Incorporated
Summary of Section 11^
Responses from Mercury
Cell Chlor-Alkali
Facilities.
A-4
-------
TABLE A-l.
EVOLUTION OF THE BACKGROUND INFORMATION DOCUMENT
(continued)
Date
Company, Consultant, or
agency/location
Nature of action
2/99 -
5/99
ASHTA Chemicals (Astabula,
OH),
Holtrachem (Orrington, ME),
Occidental Chemical
(Delaware City, DE, Deer
Park, TX, and Muscle Shoals,
AL) ,
Olin (Charleston, TN and
August, GA),
Pioneer Chlor-Alkali (St
Gabriel, LA),
PPG Industries (Lake
Charles, LA and New
Martinsville, WV), Vulcan
Chemicals (Port Edwards,
WI), Westlake (Calvert City,
KY)
Follow-ups to section
114 responses.
5/99 -
7/99
Bacharach; Mine Safety
Appliances; PerkinElmer;
Arcadis, Geraghty & Miller;
Emission Testing Services,
Inc.; CHEMTEX
Requests for
information related to
mercury test methods
and analytical
equipment.
7/29/99'
The Chlorine Institute
Meeting between the
EPA and the Chlorine
Institute to discuss
XXX
8/99
Union Carbide, Linde
Requests for
information on
molecular sieves
W17/99
The Cnlorine Institute
Comments and
information regarding
MACT floor
determination and
thermal treatment
units.
a /no
The C^crin ^ Institute
Information regarding
RCRA rules applicable
to mercury-cell
facilities.
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TABLE A-l.
EVOLUTION OF THE BACKGROUND -INFORMATION DOCUMENT
(continued)
Date
Company, Consultant, or
agency/location
Nature of action
6/8/00
The Chlorine Institute
Documents regarding
housekeeping and work
practice standards.
6/8/00
and
"6723700
The Chlorine Institute
Letters providing
information related to
mercury recovery""
thermal treatments
units and emissions
7/00
Lake Shore, Process Control
Systems, Sigma-Aldrich,
Perkin-Elmer, Dwyer
Instruments, Uehling
Instrument Company, Princo
Instruments, Davis
Instruments, Universal Flow
Monitors
Information requests
for parametric
monitoring cost data.
7/00
EcoChem Analytics, Aldora,
ST:
Requests for cost and
other information on
mercury continuous
monitoring devices
3/00 -
Occidental Chemical
(Delaware City, DE, Deer
Park, TX, and Muscle Shoals,
AL) ,
Olin (Charleston, TN), PPG
Industries (Lake Charles,
LA, Vulcan Chemicals (Port
Edwards, WI)
Requests for
additional testing,
monitoring, and other
information on r.ercury
thermal' recovery units
A-6
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TECHNICAL REPORT DATA
(Please read Instructions on reverse before completing)
1. REPORT NO.
EPA-453/R-02-007
2
4. TITLE AND SUBTITLE
Hazardous Air Pollutant Emissions from Mercury Cell Chlor-Alkali
Plants Background Information Document for Proposed Standards
7 AUTHOR(S)
Heather Brown, Phil Norwood, and Iliam D. Rosario
9 PERFORMING ORGANIZATION NAME AND
U.S. Environmental Protectk
Office of Air Quality Plannin
Research Triangle Park, NC
ADDRESS
>n Agency
ig and Standards
27711
12 SPONSORING AGENCY NAME AND ADDRESS
Director
Office of Air Quality Planning and Standards
Office of Air and Radiation
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
3. RECIPIENTS ACCESSION NO.
5. REPORT DATE
February 2002
6 PERFORMING ORGANIZATION CODE
8 PERFORMING ORGANIZATION REPORT NO
10 PROGRAM ELEMENT NO
II CONTRACT/GRANT NO
13 TYPE OF REPORT AND PERIOD COVERED
Final
14 SPONSORING AGENCY CODE
EPA/200/04
15 SUPPLEMENTARY NOTES
ESD Work Assignment Manager: Iliam D. Rosario. C439-02. 919-541-5308
16 -ABSTRACT
This background information document (BID) provides information relevant to the proposal of national
emission standards for hazardous air pollutants (NESHAP) for limiting mercury emissions from mercury cell
chlor-alkali plants. The standards are being developed according to section 1 12(d) of Title III of the Clean
Air Act (CAA) as amended in 990.
17
a • DESCRIPTORS
Air Pollution
Chlorine Production
Mercury
Chlor-Alkali Plants
Regulations
18 DISTRIBUTION STATEMENT
Release Unlimited
KEY \\ ORDS A\D DOCUMENT ANALYSIS
b IDENTIFIERS OPEN ENDED TERMS c COSATI Field Group
Air Pollution control
19 SECURITY CLASS iRcp<,n, ' 1\ NO OF PAGLS
Unclassified
20 SECURITY CLASS (t'agei 22 PRICE
Unclassified
EPA Form 2220-] (Re^ 4 7?) PREVIOUS EDITION IS OBSOLETE
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U.S. Environmental Protection
Region 5, Library (PL-12J)
7? West Jackson Boulevard, 12th Floor
Chicago.lt 60604-3590
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