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-------
RESEARCH REPORTING SERIES
Research reports of the Office x>f Research and Development U S
"<^
>_> -j. —o "«••-' i-^n.o\_a.uuaj.y pxcinneci to
transfer and a maximum interface in related fields.
3.3TG Z
The seven series
1.
2.
3.
4.
5.
6.
7.
Environmental Health Effects Research
Environmental Protection Technology
Ecological Research
Environmental Monitoring
Socioeconomic Environmental Studies
Scientific and Technical Assessment Reports (STAR)
Interagency Energy-Environment Research and Development
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Pr"ram
is to assure the rapid development of domestic energy supplies in ™
environmentally-compatible manner by providing the necessary
^s
techno?™? f effects; assessments of, and development of, control
ranee if T"87 SyStemS' and intesrated assessments of a wide
range of energy-related environmental issues
-------
EPA-600/7-76-0341
December 1976
ENVIRONMENTAL CONSIDERATIONS OF SELECTED
ENERGY CONSERVING MANUFACTURING PROCESS OPTIONS
Volume XII
CHLOR-ALKALI INDUSTRY REPORT
EPA Contract No., 68-03-2198
Project Officer
Herbert S., Skovronek
Industrial Pollution Control Division
Industrial Environmental Research Laboratory - Cincinnati
Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO, 45628
For sale by the Superintendent of Oocnments, U.S. Government Printing Office, Washington. D.C. 20402
-------
DISCLAIMER
R, ^TT0" haS been reviewed by the Industrial Environmental
publication A^^ ?t Environmental Protection Agency, and approved for
~f7 f IZ .Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
nor ^^a mcm.j.uu or trade names or commercial products constitute
ment or recommendation for use.
11
-------
FOREWORD .
When energy and material resources are extracted, processed, converted,
and used ?he related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol meSods be used. The Industrial Environmental Research Laboratory -
Cincinnati (IBRL-Ci) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and
economically.
This study, consisting of, 15 reports, identifies promising i
processes and practices in 13 energy- intensive industries which, if imple-
mented over the coming 10 to 15 years, could result in more effective uti-
iLation of energy resources. The study was carried out to assess the po-
tentiarenvironmlntal/energy impacts of such changes and the adequacy of
existing control technology in order to identify potential conflicts with
Environmental regulations and to alert the Agency to areas^where its activi-
ties and policies could influence the future choice of alternatives. The
results will be used by the EPA's Office of Research and Development to de-
nne those areas Wherewisting pollution control technology suffices where
current and anticipated programs adequately address the areas identified by
the contractor, and where selected program reorientation seems necessary
Specific data will also be of considerable value to individual ^searchers
as industry background and in decision-making concerning project selection
and direction? The Power Technology and Conservation Branch of the Energy
Systems-Environmental Control Division should be contacted for additional
information on the program.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
111
-------
EXECUTIVE SUMMARY
^ chlor-alkali industry is a large and relatively mature segment of
the inorganic chemical industry. In this series of 13 industry studies, the
chlor-alkali industry ranked eleventh in terms of both purchased energy usage
and potential for viable process changes having significant energy and
effluent consequences.
Chlorine and caustic are coproducts of brine electrolysis. There are
several dozen important U.S. producers of these chemicals, although the top
four producers account for nearly 60% of total production. Current (1974)
production levels for these chemicals are on the order of 11 to 12 million
tons each. The diffuse end use markets are expected to lead to an average
demand growth of approximately 5 to 6 percent per annum over the next decade.
Chlor-alkali plants and production technology have a history of slow
evolution in the United States. During the next 15 years, several significant
changes are expected. Among the more important are the conversion from exist-
ing _ graphite electrodes to dimensionably stable anodes (DSA), the development
of ion-exchange membrane technology and the replacement of deposited asbestos
diaphragms with stabilized asbestos diaphragms. No new mercury cell plants
are expected to be built because of inherent problems with pollution and
high electrical energy requirements.
The effect of these and other changes over the long run will be to reduce
average energy consumption for the industry by 15 percent or more per ton of
product. None of the process changes are expected, in themselves, to create
any new pollution hazards, but rather they are expected to further reduce the
level of industry effluents. For example, the already small volume of chlo-
rinated organic waste associated with the use of graphite anodes will be
eliminated, as will the solid waste from spent anodes and diaphragms. The
introduction of DSA technology will reduce the amount of gas vented from the
chlorine liquefaction system.
Basic research needs in the industry center around further reduction in
process wastes, further reduction in energy requirements and further decoupling
of chlorine and caustic production to allow a closer supply/demand balance for
each. It is recommended that research, development, or demonstration efforts
be directed at promoting the work already underway in these areas.
This report was submitted in partial fulfillment of contract 68-03-2198
by Arthur D. Little, Inc. under sponsorship of the U.S. Environmental
Protection Agency. This report covers a period from June 9 1975 to
February 9, 1976.
iv
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APPENDIX B - CHLOR-ALKALI GLOSSARY
TABLE OF CONTENTS
iii
FOREWORD lv
EXECUTIVE SUMMARY vi
List of Figures vii
List of Tables - ix
Acknowledgraents xii
Conversion Table
1
I . INTRODUCTION
A. BACKGROUND ,
B. CRITERIA FOR INDUSTRY SELECTION £
r CRITERIA FOR PROCESS SELECTION f
Si S™ION OF CHLOR-ALKALI INDUSTRY PROCESS OPTIONS 4
II FINDINGS, CONCLUSIONS AND RECOMMENDATIONS 6
9
III. INDUSTRY OVERVIEW
9
A. DESCRIPTION
1. Industry Sectors
2. Plant Characteristics ^
3. Type of Integration
B. ECONOMIC OUTLOOK
1. Historical Trends and Projected Growth 15
2. Technical and Economic Life of Manufacturing ^
Facilities
TV COMPARISON OF CURRENT AND ALTERNATIVE PROCESSES 20
20
A BASIS FOR SELECTING PROCESSES
B. COMPARISON OF PRESENT PROCESS WITH ALTERNATIVES ^
1. Base Line Process - Graphite Anode Diaphragm Cell 21
2. Current Effluent Situation ^
3. Modified Anodes 4g
4. Modified Diaphragms
5. Comparison of Mercury and Diaphragm Cells ^
V IMPLICATIONS OF POTENTIAL INDUSTRY CHANGES 61
61
A. PROBABLE CHANGES 61
B. ENVIRONMENTAL IMPLICATIONS
APPENDIX A - INDUSTRY STRUCTURE 66
77
v
-------
LIST OF FIGURES
Number
Page
IV-1 Diaphragm Cell Process
22
IV-2 Mercury Cell Process
53
a 3 - . armo™ 1 10-7C ^
vi
-------
LIST OF TABLES
Number Page
1-1 Summary of 1971 Energy Purchased in Selected Industry
Sectors 3
II-l Comparison of Base Line and Alternative Processes 7
III-l U.S. Chlorine Producers and Capacities (short tons per
day - 1974) 9
III-2 U.S. Caustic Soda Producers and Capacities (short tons
per day - 1974) 10
III-3 1974 U.S. Chlorine Demand Pattern 11
III-4 1974 U.S. Caustic Soda Demand Pattern 12
III-5 Chlor-Alkali Industry: Trends and Projections 1967-75
(In millions of dollars except as noted) 14
III-6 U.S. Chlorine Production, Trade, and Apparent Consumption,
1955-74 (Millions of Short Tons) 16
III-7 U.S. Caustic Soda Production, Trade, and Apparent Consumption,
1955-74 (Millions of Short Tons) 17
III-8 U.S. Soda Ash Production, Trade, and Apparent Consumption,
1955-74 (Millions of Short Tons, 100% Na2CC>3) 18
IV-1 Waste Streams From Diaphragm Cell Process 23
IV-2 Estimated Production Cost of Chlorine and Caustic Soda 26
IV-3 Raw Waste Loads From Mercury Cell Process Based on a
Survey of 21 Facilities (lb/1000 Ib chlorine) 30
IV-4 Wastewater Treatment Cost Estimates - Diaphragm Cell Chlor-
Alkali (1000 ton/day capacity - 360 days/year) 35
IV-5 Wastewater Treatment Cost Estimates - Mercury Cell Chlor-
Alkali (1000 ton/day capacity - 360 days/year) 36
vii
-------
LIST OF TABLES (Cont.)
Number
IV-6 Chlorine Emissions Form Liquefaction Blow Gases in
Diaphragm- and Mercury-Cell Plants 40
IV-7 Estimated Production Cost of Chlorine and Caustic Soda 45
IV-8 Power Savings Effected by Stabilized Diaphragm in H-4
DSA Cells 49
IV-9 Estimated Energy Savings With Advanced Ion Exchange
Membrane Cell 51
IV-10 Waste Streams From Modern Mercury Cell Process 54
IV-11 Estimated Production Cost of Chlorine and Caustic Soda 57
IV-12 Energy Comparison of Mercury and Diaphragm Cells 59
V-l Environmental Implications of Changes in Diaphragm Cells 62
A-l SIC 2812 Alkalies and Chlorine, Distribution of
Establishments 68
A-2 SIC 2812 Alkalies and Chlorine, Distribution of Plant Sizes 69
A-3 SIC 2812 Alkalies and Chlorine, Distribution of Plant Ages 70
A-4 SIC 2812 Alkalies and Chlorine, Distribution of Processes 71
A-5 SIC 2812 Alkalies and Chlorine, Distribution of Production 72
A-6 Chlorine Production Routes - U.S. and Canada 73
A-7 Chlorine Capacity and Production in the United States 74
A-8 U.S. Soda Ash Producers and Capacities (short tons per
year - 1973) 75
A-9 U.S. Caustic Potash Producers and Capacities (short tons
per year - 1973) 76
A-10 U.S. Sodium Bicarbonate Producers and Capacities (short
tons per year - 1973) 76
viii
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ACKNOWLEDGMENTS
This study could not have been accomplished without the support of a
zreat number of people in government agencies, industry, trade associations
!nd universities! Although it would be impossible to mention each individual
-uld like Jtake this opportunity to acknowledge the particular
by
support of a few such people.
Dr Herbert S. Skovronek, Project Officer, was a valuable resource to us
throuzhout the study. He not only supplied us with information on work
presently being done in other branches of EPA and other government agencies
Starved as an indefatigable guide and critic as the study Prog««d His
advisors within EPA, FEA, DOC, and NBS also provided us with insights and
perspectives valuable for the shaping of the study.
During the course of the study we also had occasion to contact many
e
tial nature or was supplied to us with the understanding that it was not to
credited Therefore, we extend a general thanks to all those whose comments
were valuable to us for their interest in and contribution to this study.
^
Mr. James I. Stevens, Environmental Coordinator; and Ms. Anne B.
Administrative Coordinator.
Members of the environmental team were Dr. Indrakumar L. Jashnani,
Mr. Edmund H. Dohnert and Dr. Richard Stephens (consultant).
• Within the individual industry studies we would like to acknowledge the
contributions of the following people.
Iron and Steel: Dr. Michel R. Mounier, Principal Investigator
- -- Dr. Krishna Parameswaran
Petroleum Refining; Mr. R. Peter Stickles, Principal Investigator
~~ ~ Mr. Edward Interess
Mr. Stephen A. Reber
Dr. James Kittrell (consultant)
Dr. Leigh Short (consultant)
IX
-------
j?ulp and Paper;
Olefins:
Ammonia:
Aluminum:
Textiles:
Cement:
Glass:
Chlor-Alkali:
Phosphorus/
Phosphoric Acid;
Primary Copper:
Fertilizers;
Mr. Fred D. lannazzi, Principal Investigator
Mr. Donald B. Sparrow
Mr. Edward Myskowski (consultant)
Mr. Karl P. Pagans
Mr. G. E. Wong
Mr. Stanley E. Dale, Principal Investigator
Mr. R. Peter Stickles
Mr. J. Kevin O'Neill
Mr. George B. Hegeman
Mr. John L. Sherff, Principal Investigator
Ms. Nancy J. Cunningham
Mr. Harry W. Lambe
Mr,
Ms.
Dr.
Mr.
Mr.
Mr.
Richard W. Hyde, Principal Investigator
Anne B. Littlefield
Charles L. Kusik
Edward L. Pepper
Edwin L. Field
John W. Rafferty
Dr. Douglas Shooter, Principal Investigator
Mr, Robert M. Green (consultant)
Mr., Edward S., Shanley
Dr, John Willard (consultant)
Dr.. Richard F, Heitmiller
Dr, Paul A. Huska, Principal Investigator
Ms. Anne B. Littlefield
Mr, J. Kevin O'Neill
Dr. D. William Lee, Principal Investigator
Mr, Michael Rossetti
Mr, R. Peter Stickles
Mr, Edward Interess
Dr, Ravindra M. Nadkarni
Mr. Roger E. Shamel, Principal Investigator
Mr, Harry W. Lambe
Mr,, Richard P. Schneider
Mr. William V. Keary, Principal Investigator
Mr. Harry W. Lambe
Mr, George C, Sweeney
Dr, Krishna Parameswaran
Dr. Ravindra M. Nadkarni, Principal Investigator
Dr, Michel R. Mounier
Dr, Krishna Parameswaran
Mr. John L. Sherff, Principal Investigator
Mr. Roger Shamel
Dr. Indrakumar L. Jashnani
-------
(SI) CONVERSION FACTORS
To Convert From
Acre
Atmosphere (normal)
Barrel (42 gal)
British Thermal Unit
Centipoise
Degree Fahrenheit
Degree Rankine
•T-t «_
Foot
3
Foot /minute
3
Foot
T?rt n 4-
Foot
Foot/sec
2
Foot /hr
Gallon (U.S. liquid)
Horsepower (550 ft-lbf/sec)
Horsepower (electric)
Horsepower (metric)
Inch
Kilowatt-hour
Litre
Micron
Mil
Mile (U.S. statute)
Poise
Pound force (avdp)
Pound mass (avdp)
Ton (assay)
Ton (long)
Ton (metric)
Ton (short)
Tonne
To
2
Metre
Pascal
3
Metre
Joule
Pascal-second
Degree Celsius
Degree Kelvin
Metre
o
Metre /sec
3
Metre
2
Metre
Metre/sec
2
Metre /sec
3
Metre
Watt
Watt
Watt
Metre
Joule
o
Metre
Metre
Metre
Metre
Pascal-second
Newton
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Multiply By
4,046
101,325
0.1589
1,055
0.001
t° = (tl -32)71.8
C r
fcK = tR/1'8
0.3048
0.0004719
0.02831
0.09290
0.3048
0.00002580
0.003785
745.7
746.0
735.5
0.02540
6
3.60 x 10
-3
1.000 x 10
-6
1.000 x 10
0.00002540
1,609
0.1000
4.448
0.4536
0.02916
1,016
1,000
907 . 1
1,000
Source: American National Standards Institute, "Standard Metric Practice
Guide," March 15, 1973. (ANS72101-1973) (ASTM Designation E380-72)
xi
-------
I. INTRODUCTION
A. BACKGROUND
Industry in the United States purchases about 27 quads* annually, approxi-
mately 40% of total national energy usage.** This energy is used for chemical
processing, raising steam, drying, space cooling and heating, process stream
heating, and miscellaneous other purposes.
In many industrial sectors energy consumption can be reduced significantly
by better "housekeeping" (i.e., shutting off standby furnaces, better thermo-
stat control, elimination of steam and heat leaks, etc.) and greater emphasis
on optimization of energy usage. In addition, however, industry can be expected
to introduce new industrial practices or processes either to conserve energy
or to take advantage of a more readily available or less costly fuel. Such
changes in industrial practices may result in changes in air, water or solid
waste discharges. The EPA is interested in identifying the pollution loads of
such new energy-conserving industrial practices or processes and in determin-
ing where additional research, development, or demonstration is needed to
characterize and control the effluent streams.
B. CRITERIA FOR INDUSTRY SELECTION
In the first phase of this study we identified industry sectors that have
a potential for change, emphasizing those changes which have an environmental/
energy impact.
Industries were eliminated from further consideration within this assign-
ment if the only changes that could be envisioned were:
• energy conservation as a result of better policing or "housekeeping,"
• better waste heat utilization,
• fuel switching in steam raising, or
• power generation.
After discussions with the EPA Project Officer and his advisors, industry sec-
tors were selected for further consideration and ranked using:
*1 quad = 1015 Btu
**purchased electricity valued at an approximate fossil fuel equivalent of 10,500
Btu/kWh
-------
• |uantitative criteria based on the gross amount of energy (fossil
fuel and electric)- purchased by industry sector as found in U.S
Census figures and from information provided from industry sources
The chlor-alkali industry purchased 0.24 quads out of the 12 14
quads purchased in 1971 by the 13 industries selected' for study
or y% of the 27 quads purchased by all industry (see Table 1-1) .
• Qualitative criteria relating to probability and potential for
process change, and the energy and effluent consequences of such
changes .
In order to allow for as broad a coverage of technologies as possible we
t;r= - —
elevP°?hth? baS±S °f ^±S rankln§ method> the chlor-alkali industry appeared in
eleventh place among the 13 industrial sectors listed. PP^area in
C. CRITERIA FOR PROCESS SELECTION
dnrMIn thlS Study We have focused on identifying changes in the primary pro-
duction processes which have clearly defined pollution consequences. In select-
t?ons ofthe ^A" ^6d ^ ?** ^^ ™ ^ «»»"«ed the needs and limita-
tions of the EPA as discussed more completely in the Industry Priority Report
y epor
comnlri I™ C°al>ex±st±^ in abundant reserves in the United States in
comparison to natural gas. Moreover, pollution control methods resulting in
Ce °f this
e^h^CTeTtl0nibaV! ^^ lnClUded W±th±n the SC°Pe °f this study- nal
emphasis has been placed on process changes with near-term rather than long-
term potential within the 15-year span of time of this study.
to excluding from consideration better waste heat utilization
**i !-• -t. P°rr Seneration> and fuel switching, as mentioned above, cer-'
tain options have been excluded to avoid duplicating work being funded under
other contracts and to focus this study more strictly on "procLs changes "
Consequently, the following have also not been considered to be within the
scope of work:
• Carbon monoxide boilers (however, unique process vent streams yield-
ing recoverable energy could be mentioned);
• Fuel substitution in fired process heaters;
• Mining and milling, agriculture, and animal husbandry;
2
-------
TABLE 1-1
SUMMARY OF 1971 ENERGY PURCHASED IN SELECTED INDUSTRY SECTORS
SIC Code
In Which
Industry Sector
1. Blast furnaces and steel mills
2. Petroleum refining
3. Paper and allied products
4. Olefins
5. Ammonia
6. Aluminum
7. Textiles
8. Cement
9. Glass
10. _Alkalies and chlorine
11. Phosphorus and phosphoric
acid production
12. Primary copper
13. Fertilizers (excluding ammonia)
1015 Btu/Yr
, 3.49(1)
2.96(2)
1.59
0.984(3)
0.63(4)
0.59
0.54
0.52
0.31
0.24
0.12(5)
0.081
0.078
Industry Found
3312
2911
26
2818
287
3334
22
3241
3211, 3221, 3229
2812
2819
3331
287
(1)
(2)
(3)
Estimate for 1967 reported by FEA Project Independence Blueprint, p. 6-2,
USGPO, November 1974.
Includes captive consumption of energy from process byproducts (FEA Project
Independence Blueprint)
Olefins only, includes energy of feedstocks: ADL estimates
(4) Ammonia feedstock energy included: ADL estimates
estimates
Source: 1972 Census of Manufactures, FEA Project Independence Blueprint, USGPO,
November 1974, and ADL- estimates.
3
-------
• Substitution of scrap (such as iron, aluminum, glass, reclaimed
textiles and paper) for virgin materials;
• Production of synthetic fuels from coal (low- and high-Btu gas
synthetic crude, synthetic fuel oil, etc.); and
• All aspects of industry-related transportation (such as transporta-
tion of raw material).
D. SELECTION OF CHLOR-ALKALI INDUSTRY PROCESS OPTIONS
^ Within each industry, the magnitude of energy use was an important crite-
rion in judging where the most significant energy savings might be realized
since reduction in energy use reduces the amount of pollution generated in the
energy production step. Guided by this consideration, candidate options for
in-depth analysis were identified from the major energy consuming process
steps with known or potential environmental problems.
After developing a list of candidate process options, we assessed
subjectively
• pollution or environmental consequences of the process change,
• probability or potential for the change, and
• energy conservation consequences of the change.
Even though all of the candidate process options were large energy users
there was wide variation in energy use and estimated pollution loads between '
options at the top and bottom of the list," A modest process change in a manor
energy consuming process step could have more dramatic consequences than a
more technically significant process change in a process step wliose energy
consumption is rather modest. Process options were selected for in-depth anal-
ysis only if a high probability for process change and pollution consequences
in the lesser energy-using process steps was perceived.
Because of the time and scope limitations for this study, we have not
attempted to prepare a comprehensive list of process options or consider all
economic, technological, institutional, legal or other factors affecting imple-
mentation of these changes. Instead we have relied on our own background
experience, industry contacts, and the guidance of the Project Officer and EPA
advisors to choose the following processes (or process elements) for considera-
tion' in the chlor-alkali industry:
• dimensionally stable anodes - conventional and expandable,
• diaphragm cell synthetic membrane,
• mercury cell,
• power recovery from sodium-mercury amalgam,
-------
• regeneration of chlorine from spent hydrogen chloride,
• production of caustic soda from soda ash,
• bi-polar electrolytic cells,
• multi-effect evaporation, and
• natural versus synthetic soda ash.
From this listing, we chose the first three for detailed analyses,
because the options or modifications are considered to be the most likely
to have a significant impact on overall energy consumption in the chlor-alkali
industry over the next five to ten years. The other six options either have
relatively small energy consequences and would therefore be implemented for
other reasons, or have important shortcomings as substitutes for current
technology.
-------
II. FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS
The chlor-alkali industry is large, mature, and growing at a rate
averaging 5-6% per year. Since the plants are long-lived and the rate of
equipment renewal is low, changes are implemented gradually and considerable
time passes before a significant portion of industry capacity is affected by
change.
During the next 15 years the following evolutionary changes in the
industry are expected, in approximately the order listed:
• Existing graphite anode plants will be converted to dimensionally
stable anode (DSA) cells,
0 Deposited asbestos diaphragms will be replaced with stabilized
asbestos diaphragms,
• New plants will use combinations of expandable DSA type cells or
wide DSA's with stabilized asbestos diaphragms,
« Microporous membranes will supersede the use of asbestos in new
plants and probably be used for some existing plant
modernizations,
• Mercury cells, which expose the industry to considerable risk in
the form of plant maloperation or accidents and which use more
energy (combining both electrical and thermal forms) than the
newest DSA/ modified diaphragm cells, will be slowly phased out
over the next ten years, and
® Perfection of the ion exchange membrane cell will enable it to
economically replace mercury cells in existing mercury cell plants.
The effect of these changes will be a reduction of 15% or more in the
average energy consumed by the industry per ton of product. Although the
present environmental problems of the industry, with the exception of mercury
cell plants, are comparatively minor, these changes will ease existing prob-
lems as shown in summarized form in Table II-l. The already small volume of
chlorinated organic waste associated with the use of graphite anodes will be
eliminated, as will the solid graphite waste from spent anodes. Traces of
lead in wastewater arising from the lead used to set the graphite will also be
eliminated. Stabilized asbestos diaphragms will greatly reduce solid asbestos
waste from spent diaphragms and essentially eliminate asbestos fibers in waste-
water. Polymer membranes, either microporous or ion exchange, will eliminate
all asbestos from the plant. Higher purity cell gas from DSA cells reduces
the amount of gas necessarily vented from the chlorine liquefaction system.
-------
TABLE II-l
COMPARISON OF BASE LINE AND ALTERNATIVE PROCESSES
Cell Anode
Cell Cathode Diaphragm
Environmental Factors
Pollution Control Costs
($/Ton of Chlorine)
Comments
Energy Factors
Consumption per Ton of Product
Electrical kWh
Fuel 106 Btu
Total 10 Btu
Comments
Process Economics
Fixed Investment (10 $)
Pollution Control and Operating
Costs ($/Ton of Chlorine)
Base Case
Graphite
Deposited
Asbestos
0.64
3274
6.21
40.58
56.4
116.01
Standard DSA
Deposited Asbestos
0.55
Waste graphite and
hlorinated hydro -
arbons eliminated,
educed tail gas
olume . Lead ef f lu—
nt eliminated.
3151
5.01
38.10
Improved electrode
reduces resistance
voltage effects.
54.2
107.65
Process Changes
a
Wide DSA
Stabilized Asbestos
0.55
Same as Std DSA but
waste asbestos easier
to remove from
effluent.
2826
5.01
34.68
Closer electrode
spacing reduces
54.5
104.03
DSA
Microporous
Membrane
0.50
Same as Std DSA
but asbestos
eliminated from
process.
, 2826
5.01
34.68
Same as wide
DSA.
54.5
103.53
DSA
Ion Exchange
Membrane
0.50
Same as DSA -
microporous mem-
brane plus elimina-
tion of inorganic
salt purge from
evaporator section.
3363
0.91
36.22
Production of high
strength caustic
power use, reduces
fuel use.
57.2
109.38
Modern
Mercury Cell*
DSA
Hg
3.60
3716
0.56
39.53
58.20
138.08
*Although this is not a process change in the same sense as the others displayed on
this table, it was discussed in this report and is therefore included in this summary table.
Source: Arthur D. Little, Inc., estimates and industry data.
-------
In summary, none of these process changes in themselves are expected
to create new environmental problems. On the contrary, the changes are
expected to further reduce the amount of pollution generated by the industry.
Consequently, it is recommended that any research, development, or demonstra-
tions effort be oriented toward accelerating and evaluating the introduction
of the newer, less polluting, and energy conserving technology.
-------
III. INDUSTRY OVERVIEW
.A. DESCRIPTION
In terms of both production volume and level of energy consumption, the
most important segment of the U.S. chlor-alkali industry consists of some 30
manufacturers (see Tables III-l and III-2) who electrolyze crude salt brine
to form sodium hydroxide (caustic soda, or caustic) and chlorine. Chlorine
and caustic are coproducts, with about 1.1 tons of caustic soda (100 percent
basis) produced for each ton of chlorine. Of the 11 million short tons of
chlorine produced in the United States in 1974, over 95% was made with caustic
soda as the coproduct. The balance was produced as a coproduct of potassium
hydroxide, or sodium metal, or was regenerated from byproduct hydrogen chloride.
Because it is difficult to store large quantities of chlorine except in the
form of end products, the production of caustic soda is closely tied to the
demand for chlorine.
TABLE III-l
U.S. CHLORINE PRODUCERS AND CAPACITIES
(short tons per day - 1974)
Producer Capacity
Alcoa 470
Allied 1,650
BASF Wyandotte 1,550
Diamond Shamrock 3,200
Do" 11,000
DuPont 940
Ethyl 640
FMC 790
Goodrich 30Q
Hooker 2,680
Kaiser 535
Linden Chlorine 460
Mobay 200
Monsanto 250
Olin ,... 1,625
Pennwalt 950
PPG 3,330
Shell
375
Sobin 310
Stauffer ggQ
Vulcan , 3-75
Paper Companies 590
Other 1,180
TOTAL 34,480
Source: Chemical Profiles, Schnell Publishing Co., New York.
-------
TABLE III-2
U.S. CAUSTIC SODA PRODUCERS AND CAPACITIES
(short tons per day - 1974)
Producer Capacity
Alcoa . 520
Allied ...... 1,760
BASF Wyandotte 1,780
Diamond Shamrock 3,420
Dow 12,000
Ethyl 200
FMC 860
Linden Chloride 510
Goodrich 330
Hooker 2,840
Kaiser . 590
Monsanto 275
Olin 1,820
Pennwalt 935
PPG Industries 3,660
Shell 410
Sobin 340
Stauffer 1,080
Vulcan 445
Paper Companies 760
Other 51Q
TOTAL 35,045
Source; Chemical Profiles, Schnell Publishing Co., New York.
10
-------
Approximately 75% of U.S. chlorine is used in the production of other
chemical products, the most important of which are vinyl chloride plastics,
chlorinated solvents, and fluorocarbons. That portion of chlorine not used
as a raw material is used chiefly in the pulp and paper industries and in water
treatment (see Table III-3). Of the 10 million tons of caustic soda consumed
in the United States in 1974, nearly 85% was used by various sectors of the
chemical and allied products industry. Among the most important uses of caustic
are those in pulp and paper processing, the production of miscellaneous organic
chemicals, and neutralization of spent acid wastes in several industry sectors
(see Table III-4).
1. Industry Sectors
Broadly defined, the U.S. chlor-alkali industry includes manufacturers not
only of chlorine and caustic, but also of sodium carbonate (soda ash), sodium
bicarbonate, and caustic potash. The latter three chemicals are not treated in
detail in this study, either because of their small production volume (sodium
bicarbonate and caustic potash represented less than 1% of total chlor-alkali
shipment in 1974), or because changes in energy requirements associated with
expected changes in technology are small and decreasing relative to chlorine and
and caustic soda (such as in the case of soda ash).*
TABLE III-3
1974 U.S. CHLORINE DEMAND PATTERN
Thousands of
of short tons Percent
ORGANIC CHEMICALS
One-Carbon Compounds 1,620 15
Two-Carbon Compounds 3,220 29
Three-Carbon and Above 600 6
Cyclic Compounds 510 5
Oxygen-Containing Compounds 1,120 .10
SUBTOTAL 7,070 65
NON-ORGANIC
Inorganic Chemicals 1,270 12
Pulp & Paper 1,460 13
Water Treatment 540 __5_
SUBTOTAL 3,270 30
TOTAL DEMAND (includes unspecified) 10,930 100
Source: Arthur D. Little, Inc. estimates, based on industry contacts.
*The replacement of synthetic soda ash facilities with natural soda ash facili-
ties results in nearly a 50% reduction in process energy requirements per
unit of production. (We have not included consideration of energy requirements
for delivery of the product to major markets because transportation aspects
were specifically excluded from the scope of this study.)
11
-------
TABLE II1-4
1974 U.S. CAUSTIC SODA DEMAND PATTERN
Thousands of
short tons,
100 percent NaOH
Percent
INORGANIC CHEMICALS
Brine Treatment
Alumina
Sodium Hypochlorite
SUBTOTAL
ORGANIC CHEMICALS
Phenols & Dyes
Caustic Scrubbing
Neutralization
Misc. Organics
SUBTOTAL
CELLULOSE PROCESSING
Pulp & Paper
Rayon
Cellophane
SUBTOTAL
SOAP & CLEANERS
PETROLEUM REFINING
MISC. & UNIDENTIFIED
TOTAL DOMESTIC DEMAND
NET EXPORTS
TOTAL DEMAND
294
515
241
1,050
535
590
1,333
1,996
4,545
2,177
309
238
2,724
600
352
629
9,809
1,019
10,828
10
41
25
6
3
6
9
100
Source: Arthur D. Little, Inc., estimates, based on industry contacts.
12
-------
In terms of 1974 production volume, chlorine and caustic accounted for
approximately 80% of chlor-alkali industry production. Estimated 1974 ship-
ment value was approximately $1 billion, with an estimated 13,000 workers
(see Table III-5).
In 1967, synthetic soda ash production accounted for nearly 75% of total
soda ash output. Since then, pollution problems have resulted in the closure
of some synthetic soda ash plants and the construction of several natural soda
ash plants in Wyoming and California. In 1974, production of natural soda ash
exceeded production of synthetic soda ash; by 1980, new and expanded natural
soda ash facilities are expected to provide about 75% of total output.
Producers of chlorine and caustic may be segmented on the basis of
production process. Approximately 70% of U.S; chlorine and caustic produc-
tion is via the diaphragm cell; approximately 25% via the mercury cell;
and 5% via the Down's cell or as a byproduct in the manufacture of mag-
nesium, potassium hydroxide, and potassium nitrate. The technology for
both mercury and diaphragm cells was developed in the United States in the
1890's and, although many refinements have been made to increase efficiency
and reduce pollution, the technology has remained basically the same. Both
cells produce comparable grades of chlorine, but the mercury cell produces
a more concentrated caustic solution of higher purity than that obtained
from the diaphragm cell. A comparison of energy consumption by the two
cells is complicated by the fact that the mercury cell requires more
electrochemical energy but less heat (for evaporation) to produce a com-
mercial concentration of aqueous caustic soda.* Although both cells con-
tribute to environmental pollution in various ways, the 1970 discovery of
mercury in fish gave rise to considerable concern over continued use of
mercury cell technology. This concern has already lead to a 90% reduction
in mercury effluents, but contamination of the environment by mercury and
other heavy metals remains a matter of concern.
®
Non-electrolytic chlorine production, such as by the Kel-Chlor process,
is a small but growing source of the chemical. The process, however,
does not represent alternative technology for the electrolytic process,
because the chlorine output represents "recycled" chlorine which is gener-
ally being recovered from a waste stream of HC1. In addition, non-electro-
lytic chlorine production produces no coproduct caustic soda and the
demand for caustic would need to be met by an additional, independent
process.
2. Plant Characteristics
A summary of statistical information relating to the number, age,
size and location of U.S. chlor-alkali plants is presented in Appendix A.
In 1972 (the last year for which detailed information is available), a
total of 67 establishments produced chlorine, while 59 produced caustic.
*Details of this comparison are presented in Chapter IV.
13
-------
TABLE III-5
CHLOR-ALKALI INDUSTRY: TRENDS AND PROJECTIONS 1967-75l
(In millions of dollars except as noted)
Industry: 3
Value of shipments
Total employment (000)
Production workers (000)
Value added
Value added per production
worker man-hour ($)
Product :^
Value of shipments
Value of imports
Value of exports
Production (000 short tons)
"Sodium carbonate, synthetic
Chlorine gas5
Chlorine, liquid
Caustic soda, liquid
Caustic soda, dry
Sodium bicarbonate
Caustic potash
1967
720
19
13
419
16.44
623
6
36
4,849
7,680
3,936
7,690
565
122
175
1970
660
15
11
362
16.91
638
5
55
4,393
9,710
4,521
9,382
564
143
175
1971
676
14
10
360
18.38
706
7
73
4,128
9,317
4,571
9,074
544
121
186
1972
803
13
10
437
23.10
801
9
81
4,310
9,873
4,919
9,583
475
122
176
19732
841
13
10
821
14
79
3,838
10,302
5,200
10,250
459
125
188
19742
1,000
13
- 10
975
18
108
3,600
11,000
5,600
11,600
500
125
190
Percent
Increase
1973-74
19
o
0
19
29
37
-6
7
8
13
9
0
1
19752
1,130
1,100
22
125
3,700
11,600
5,900
11,800
525
J £. J
130
192
Percent
Increase
1974-75
13
i n
-LU
13
22
1 A
J-D
3
5
R
J
2
C.
_>
A
*•+
i
1 Does not include natural soda ash.
Estimated by Bureau of Domestic Commerce (BDC).
Value of all products and services sold by the Chlor-
Alkali Industry (SIC 2812).
Value of shipments of chlor-alkalies made by all industries.
Includes quantities converted to liquid.
n.a. = Not available.
Source: U.S. Industrial Outlook 1975. U.S. Depart-
ment of Commerce, Bureau of Domestic
Commerce, from Bureau of the Census,
Bureau of Labor Statistics, BDC.
-------
Approximately 60% of U.S. chlorine and caustic plants are 5 to 30 years
old. Approximately 10% are less than 5 years old, while approximately 30%
are more than 30 years old. In terms of production volume, plants built within
the last five years account for a proportionately larger share of total
production, because of their much larger size.
Plant sizes vary from as little as 10 tons per day for older plants, up
to 1200 tons per day for plants built in the 1970's. The average plant size
(1974) is approximately 900 tons per day.
The distribution of plant locations is heavily weighted toward the
states of Texas (with 12) and Louisiana (with 10). Together, these two
states account for about 60% of U.S. chlorine production. Other states
having more than three chlor-alkali establishments are Alabama and Michigan,
New York, Ohio, and Washington. As may be expected, the largest plants
tend to be located in those states having the greatest number of plants.
Plant distribution by process is detailed in Appendix A. A review of
this information shows that the highest concentration of mercury cells is in
Alabama, Louisiana, and New York, while the highest concentration of diaphragm
cells is in Louisiana, Michigan, and Texas.
3. Type of Integration
The U.S. chlor-alkali industry exhibits characteristics of both vertical
and horizontal integration to varying degrees — generally in proportion to
the overall size of the producing companies. Although the degree of integra-
tion varies widely from company to company, in terms of vertical integration,
the average company in the industry consumes captively approximately 60% of its
production. In terms of horizontal integration, the average company depends
on chlor-alkali products for approximately 10-15% of its sales. These average
figures may be misleading, because captive consumption may reach 100% in some
cases and horizontal integration may be nonexistent in other cases.
B. ECONOMIC OUTLOOK
Although several serious threats to future chlorine demand can be identi-
fied, the long-range prospects for the U.S. chlor-alkali industry appear to be
reasonably favorable.
1. Historical Trends and Projected Growth
Historical levels of U.S. production, trade, and apparent consumption
of chlorine, caustic and soda ash are presented in Tables III-6, III-7 and
III-8. U.S. chlorine production volume has traditionally reflected the
performance of the U.S. economy. On the basis of a healthy economy between
1955 and 1968, apparent*U.S. consumption of chlorine grew at an average
annual rate of 6.3% during the period. However, since 1968, because of the
economic slowdown of 1970-71 and recent capacity constraints, annual
chlorine consumption increases have averaged only 4.3%. With the addition
of significant new industry capacity in late 1974 and early 1975, U.S.
15
-------
TABLE III-6
U.S. CHLORINE PRODUCTION, TRADE, AND APPARENT CONSUMPTION, 1955-74
(Millions of Short Tons)
Year
Production
Imports
Exports
Apparent Consumption
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
3.42
3.79
3.95
3.60
4.35
4.64
4.60
5.14
5.46
5.95
6.52
7.20
7.68
8.44
9.38
9.76
9.35
9.87
10.30
10.62
0.01
0.02
0.01
0.01
0.02
0.03
0.02
0.03
0.02
0.02
0.04
0.07
0.06
0.04
0.03
0.03
0.04
0.04
0.05
0.08
0.04
0.04
0.04
0.03
0.03
0.03
0.03
0.04
0.04
0.04
0.04
0.02
0.04
0.04
0.03
0.02
0.01
0.01
0.01
0.02
3.39
3.77
3.92
3.58
4..34
4.64
4.59
5.13
5.44
5.93
6.52
7.25
7.70
8.44
9.38
9.77
9.38
9.90
10.34
10.68
Source; Production from U.S. Department of Commerce, Current Industrial
Reports Series M28A, and Import and Export Statistics from
U.S. Department of Commerce, FT110, FT125.FT410.
16
-------
TABLE III-7
U.S. CAUSTIC SODA PRODUCTION, TRADE, AND APPARENT CONSUMPTION, 1955-74
(Millions of Short Tons)
Year Production Imports Exports Apparent Consumption
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
3.915
it. 227
4.336
3.993
4.748
4.972
4.914
5.486
5.814
6.389
6.831
7.596
8.398
8.868
9.917
10.141
9.667
10.270
10.541
10.87
small
small
small
0.004
0.002
0.002
small
small
small
0.001
0.003
0.009
0.018
0.039
0.040
0.063
0.076
0.105
0.135
0.12
0.228
0.264
0.291
0.209
0.247
0.239
0.228
0.202
0.321
0.496
0.420
0.430
0.565
0.646
0.814
1.062
1.216
1.202
1.034
1.14
3.687
3.963
4.045
3.788
4.503
4.735
4.686
5.284
5.493
5.894
6.414
7.175
7.851
8.261
9.143
9.142
8.527
9.172
9.779
9.85
Source: Production from U.S. Department of Commerce, Current
'~ Industrial Reports Series M28A, and Import and Export
Statistics from U.S. Department of Commerce, FT110, FT125,
FT410.
•17
-------
TABLE III-8
U.S. SODA ASH PRODUCTION, TRADE, AND APPARENT CONSUMPTION, 1955-74
(Millions of Short Tons, 100% Na_CO )
Production
Year
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
Source
Synthetic
4.907
4.998
4.659
4.324
4.904
4.558
4.516
4.607
4.682
4.948
4.926
5.071
4.849
4.596
4.540
4.393
4.298
4.310
3.838
3.503
Natural
.689
.655
.677
.627
.715
.790
.785
.978
1.119
1.275
1.494
1.738
1.748
2.043
2.513
2.688
2.857
3.129
3.632
4.030
: Production from U.S.
Total
5.596
5.653
5.336
4.951
5.619
5.348
5.301
5.601
5.797
6.223
6.420
6.809
6.597
6.639
7.053
7.081
7.155
7.439
7.470
7.533
Department
Imports
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
Neg.
.035
Exports
.185
.225
.178
.128
.173
.170
.140
.152
.184
.276
.277
.346
.304
.288
.324
.336
.437
.480
.425
.552
of Commerce, Current
Apparent
Consumption
5.413
5.376
5.121
4.845
5.462
5.163
5.197
5.403
5.627
5.920
6.179
6.548
6.244
6.463
6.688
6.753
6.747
6.947
7.008
7.016
Industrial
Reports series M28A, and Import and Export statistics from
U.S. Department of Commerce, FT110, FT125, FT410.
18
-------
chlorine production should _not be capacity-constrained in the foreseeable
future. Between 1974 and 1980 U.S. chlorine demand is expected to grow
at an average annual rate of about 5%, bringing total 1980 demand to a level
of approximately 15 million tons.
Historic demand growth for caustic soda has been somewhat below that
of chlorine, averaging about 5.3% since 1955. Growth in demand for caustic
is typically less affected by economic factors than is that of chlorine.
However, because the production of caustic soda is closely tied to chlorine
production, its supply is a function of chlorine" demand levels. This
relationship has lead to situations of both over- and under-supply as the
demand for chlorine has fluctuated above and below demand for caustic.
In the most recent economic slowdown (1974/75), drastically reduced levels
of chlorine demand led to extreme tightness in domestic caustic soda
markets. Future U.S. demand growth for caustic is expected to be at an
average annual rate greater than 5%. Total U.S. apparent consumption in
1980 is forecast at approximately 15 million tons.
The rate of demand growth for soda ash has been the lowest of the
three major chlor-alkali chemicals. Demand for caustic shows little cor-
relation with the U.S. economy. As shown in Table III-8, domestic apparent
consumption has grown at an average rate of only about 1.5% per annum since
1955. This slow rate of growth is due in part to the replacement of soda
ash by caustic soda in some applications. Assuming a continuation of the
current strong demand for soda ash by glass manufacturers, the outlook for
domestic consumption is for continued slow growth but at a more rapid
average rate of 2.5 to 3% per annum. The more rapid growth rate to 1980
is also a reflection of slower loss of markets to caustic soda. Estimated
1980 U.S. consumption will be approximately 8 million tons.
2. Technical and Economic Life of Manufacturing Facilities
As already indicated, nearly 30% of U.S. chlorine plants are more than
30 years old and are still using essentially the same technology as was
developed near the turn of the century. However, plants that are this old
have been rebuilt in almost every case, because average cell life is on
the order of 20 years. Even without rebuilding, a 5% average annual growth
implies that half of industry capacity existing in 1990 will have been
built after 1975.
19
-------
IV. COMPARISON OF CURRENT AND ALTERNATIVE PROCESSES
A. BASIS FOR SELECTING PROCESSES
The caustic-chlorine industry in the United States is a large, mature
part of the chemical industry with 34,000 tons per day of installed chlorine
capacity as of January 1975. All but 5.3% of this capacity is represented by
salt brine electrolysis plants, with diaphragm cells accounting for 69.9% and
mercury cells 24.8%. The size and maturity of the industry result in process
changes being evolutionary, rather than radical, and in a rather long time
being required before process changes or alternative processes have a sig-
nificant impact on the entire industry.
Over the history of the industry, process changes have been primarily
those that reduce cost by improving energy efficiency. The energy intensity of
the electrolytic processes has always made power cost a major expense, and has
promoted efforts to mitigate very high capital intensity by developing larger
and more efficient cells and plants. Current large increases in the cost of
energy have provided a major impetus to accelerate development of energy-
reducing techniques. However, from our knowledge of the industry, and through
discussions with the major companies in the industry, we believe that most of
the process changes to be implemented during the next five years will consist
of incremental energy-saving techniques rather than radical step changes.
To focus our efforts on the most likely changes in the industry, we
selected the following for detailed analysis:
• The use of dimensionally stable anodes (DSA) to replace graphite
anodes; and
• The use of modified diaphragms to provide improved cell electrical
characteristics and permit a more concentrated caustic to be
produced, with reduced energy for evaporation.
There are several variations of these two categories, which we have analyzed
to assess their probable degree of implementation.
As was mentioned before, the mercury cell process accounts for about
25% of present chlorine production but, because of environmental problems
associated with mercury, its use is declining.* To help determine whether
*For most plants, the industry rapidly developed techniques to comply with
EPA requirements at acceptable cost levels, but there has been considerable
difficulty in complying, on a constant and affordable basis, with OSHA reg-
ulations. In addition to plant changes, compliance with OSHA regulations
involves drastic changes in employee assignments and work habits which are
difficult for management to enforce.
20
-------
or not research to improve the environmental aspects of the mercury cell
process is desirable (as it certainly would be if the process used less
energy), we compared the relative energy consumption of that process with
the diaphragm cell process.
B. COMPARISON OF PRESENT PROCESS WITH ALTERNATIVES
1. Base Line Process - Graphite Anode Diaphragm Cell
We selected the graphite anode diaphragm cell process as a basis for
judging the energy and environmental effects resulting from process changes.
The diaphragm process represents over 65% of U.S. chlorine capacity and,
even though conversion to the use of dimensionally stable anodes is rapidly
taking place, the graphite anode version of the process is still a basis of
industry comparison.
Although not used as a basis for comparison, the mercury cell process
is fully discussed later in this section. The waste effluent aspects of both
processes are also presented.
a. Process Description
As shown schematically in Figure IV-1, the major raw material for the
diaphragm cell process is a nearly saturated solution of sodium chloride made
up by dissolving purchased solid salt in water or brine, or (much more
commonly in the U.S.) by injecting water into an underground salt structure.
The crude brine must be purified before it is suitable for use as a feed to
the cells. This is carried out by adding sodium carbonate, often produced at
the plant by treating cell liquor with flue gas, and dilute caustic soda (cell
liquor) to raise the pH to 10 or 11. Heavy metals and magnesium are^ pre-
cipitated as hydroxides and calcium as the carbonate. A flocculating and
settling aid is usually added to aid in the settling of the precipitates which
are then filtered from the brine. The waste sludge is generally sent to a
lagoon. This stream and other wastes are described in Table IV-1. The brine
is then heated and brought to saturation by the addition of pure salt recycled
from the caustic evaporator system. The pH is adjusted to about 6 with
hydrochloric acid to remove excess alkalinity, which would form hypochlorites
and chlorates in the cell, before the brine is introduced to the electrolytic
cells.
In the cells the brine is electrolyzed to produce chlorine,' caustic soda
and hydrogen:
2 NaCl + 2 H20 -* C12 + 2 NaOH + H2
21
-------
ROCK SALT
OR
SOLAR SALT
RECOVERED SALT - 2ND
SLUDGE:
CA, Mg, Fe
AL (S04)
-W1
RECOVERED SALT - 1ST
CELL LIQUOR
EVAPORATION
HEAT EX-
CHANGE WITH
PURIF. BRINE,
PROCESSING.
FUEL, OR
TO ATM.
CHLORINATED
HYDROCARBONS
Figure IV-1. Diaphragm Cell Process
22
-------
TABLE IV-1
WASTE STREAMS FROM DIAPHRAGM CELL PROCESS
Stream Source and Comments
1 Sludges from brine purifica-
tion, amount-& nature de-
pends upon salt purity
Materials from rebuilding
electrolytic cells
Housekeeping operations,
equipment cleaning
Recycled salt from evapora-
tors is washed to dissolve
sodium sulfate so that it
can be purged
Diluted sulfuric acid from
chlorine drying towers
Final vent scrubber after
normal removal of chlorine
from tail gas and other
vents. Dilute caustic aoda
used as absorbent.
Product chlorine purifica-
tion
Components
Mg(OH)2
CaC03
Iron & other
metal hydroxides
Total
Filter Aid
NaCl
Water
Concrete & graphite
rubble
Asbestos fibers
NaCl
NaOH
Lead
Copper
Water, approx.
Na SO,
NaOH
NaCl
Water, approx.
H-SO,, 93 to
70% *
NaOCl
NaHC03
Water, approx.
Quantity
lbs/1000 Ib Cl,
15
0.2
3
45
3
0.4
50
5
0.04
< 0.01
600
10
20
50
150
35
to 10
1
3
40
Chlorinated organics
of unspecified nature
0.45
Normal Disposition
Sent to lagoon
Landfill dump
Sent to lagoon or sewered
Sent to lagoon or neutralized
and put into receiving water
where allowable
Sold for use or for recon-
centration
Sent to lagoon or sewered
Drummed for disposal by
incineration or landfill
Source: Arthur D. Little, Inc., estimates and "Assessment of Industrial Hazardous Waste Practices,
Inorganic Chemicals Industry," U.S. Environmental Protection Agency, Contract 68-01-2246, 1975.
-------
Chlorine is formed at the graphite anode, bubbles to the top of the cell,
and is removed by the chlorine header. The cathode is a hollow plate
made of iron mesh with a deposited asbestos layer, or diaphragm on the
outside. The sodium ion migrates to the cathode where hydroxyl ion and
hydrogen are formed:
2Na+ + 2H20 + 2e~ -> H2 + 20H~ + 2Na+
Thus, a solution containing 10-11% NaOH is generated in the cathode
compartment.
The purpose of the diaphragm is to hinder back-migration of hydroxyl
ions to the anode area where they would react with the chlorine, ultimately
forming chlorates and thereby reducing cell current efficiency.
The hydrogen from the top of the cathode is piped from the cells, cooled
to remove water and then, depending on circumstances, burned for fuel, sold,
or flared. The disposition of the hydrogen depends on specific local
conditions. If a local industrial gas market exists, the hydrogen is often
sold to a company for purification, bottling, and distribution. Large plants
can economically install the added equipment for the safe burning of hydrogen
(up to about 50% of total fuel), in the steam boiler, or can use it as a
chemical synthesis material. Of course, the latter use involves entering a
new business with major capital expenditures. Small operators, as well as
many intermediate sized plants, must vent the hydrogen, either entirely or
that in excess of possible sales.
The cell liquor withdrawn from the cathode still contains about 13-15%
salt, because only 50% of the salt is decomposed at optimum cell operating
conditions. This liquor is concentrated in steam-heated, multi-effect
evaporators (usually triple effect) to produce a 50% caustic soda product
which contains about 1% salt. The remaining salt crystallizes out during
concentration and is centrifuged from the caustic and recycled for brine
saturation.
For those very few applications which require a "salt-free" caustic,
such as rayon, diaphragm cell caustic can be purified by any one of several
proven techniques. The most common is an anhydrous ammonia extraction
process which removes chlorates and a number of other minor inorganic salt
impurities along with the sodium chloride.
To control the buildup of sulfate ions in the salt recycle (introduced
as one of the major impurities in the feed salt or brine) and thus in the
brine system, a small purge stream is taken at the point of maximum sulfate
concentration. Where allowable this stream, after neutralization, is sewered
or put into a river or ocean. If such disposal is not allowable it is
lagooned.
24
-------
The wet chlorine from the cells is cooled to remove water, dried in
sulfuric acid scrubbers, then compressed and liquefied. The presence of
small amounts of air (in-leaks from the chlorine duct system) and other
inert gases results in a residual gas containing about 35% Cl2 after
liquefaction. This tail, or blow gas, can be used to make bleach or burned
to form hydrogen chloride. Systems for its recovery as chlorine are also
available.
In the chlorine drying towers 98-104% sulfuric acid (or oleum) is used
in a countercurrent fashion to remove water vapor from the chlorine. The
spent acid from the first tower is about 70% H SO, and the disposal technique
used depends on specific conditions at the site. It-is often returned to
processors for refortification, or sold for uses such as fertilizer manufacture
that can use a dilute, impure acid. Only in unusual instances must it be
wasted by neutralization and lagooning.
In the cells, the graphite anodes are gradually consumed by side
reactions involving oxygenated compounds which form carbon monoxide by
reaction with the graphite and by chemical attack on the organic binder. The
graphite particles which are formed tend to clog the diaphragm on the
cathode. Both of these effects increase the electrical resistance of the
cell. As the graphite is consumed, the surface area of the anode decreases,
increasing current density, and its distance from the cathode increases. As
the diaphragm is plugged its electrical resistance, as a result of decreased
ion passage, increases. Thus power consumption per ton of product gradually
increases and at some point the cell is removed from the circuit and rebuilt.
The debris from cell rebuilding, asbestos diaphragm material, anode stubs, and
concrete cell bodies is disposed of through landfill dumping.
The reactions between chlorine and the organic materials in the graphite
anode lead to the formation of volatile chlorinated organic materials
of rather indefinite composition. Thus, in addition to the problems associated
with physical disintegration of the anode, the chemical attack produces
impurities in the chlorine which must be removed and safely treated for
disposal, generally by incineration with acid fume absorption or by acceptable
landfill operations.
b. Cost of Production
Based on a modern large plant with a capacity of 1000 tons of chlorine
per stream day, the cost of production is estimated to be $84.04 per ton of
chlorine, as shown in Table IV-2. Coproduced with this chlorine would be
1.055 tons of caustic soda per ton of chlorine, or 380,000 tons/year. As is
normal in the industry, in this estimate all costs are placed on chlorine, or
as it is often expressed, the costs are on an electrochemical unit (ECU) basis.
The ECU is one ton of chlorine plus the coproduced caustic, or in this case
2.055 tons of product. This estimate is based on 360 stream days per year,
normal for the industry, and current costs for labor and materials on the U.S.
Gulf Coast.
To the production cost, which includes depreciation on an 11-year
straight-line basis, we have added an amount equal to 20% of the fixed invest-
ment to allow for a minimum pre-tax return, or $31.33/ton, and pollution
control cost of $0.64/ton to arrive at a total of $116.01 per ton of chlorine
or ECU. ~ 25 .
-------
TABLE IV-2
ESTIMATED PRODUCTION COST OF CHLORINE AND CAUSTIC SODA
Process:
Annual Production:
Stream Days/Year:
Plant Location:
Electrolysis of Brine, Graphite Anode Diaphragm Cell
360,000 Tons Chlorine
380,000 Tons Caustic Soda (100% basis as 50%)
360
U.S. Gulf Coast
Depreciation Period: 11 years (IRS Guideline)
Fixed Investment:
$56,400,000
Variable Costs
Salt (100% as brine)
Misc. Chemicals
Graphite Anodes
Diaphragm Material
Cell Rebuilding Supplies
Power
Fuel for Steam (Gas)
H2 Fuel Credit
Cooling Water Circ.
Process Water
Semi-Variable Costs
Operating Labor
Supervision
Labor Overhead
Maintenance
Fixed Costs
Plant Overhead
Local Taxes & Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (Pretax)
Pollution Control
TOTAL
Units Used or
Annual Basis
tons
pounds
$/Unit
Units/Ton
of Chlorine
$/T Cl,
kWh
106 Btu
106 Btu
103 gal
103 gal
42 men 12,000/yr
8 foremen 18,000/yr
1 superintendent 25,000/yr
35% of Labor & Supervision
5% of Investment
70% of Labor & Supervision
1.5% of Investment
9.0% of Investment
20% of Investment
See Table IV-5
2.00
0.80
0.80
0.20
0.75
0.012
0.70
0.70
0.02
0.25
1.75
1.0
7.0
1.0
1.0
3274.0
9.15
2.94
40.0
1.9
3.50
0.80
5.60
0.20
0.75
39.29
6.40
(2.06)
0.80
0.48
55.76
1.40
0.40
0.07
0.66
7.83
10.36
1.31
2.35
14.26
17.92
8476T
31.33
0^64
116.01
Source: Arthur D. Little, Inc. estimate
26
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The total estimated fixed investment is $56.4 million, including the
process units themselves and all necessary auxiliary facilities. Power gener-
ation is not included. (The capital investment for pollution control is esti-
mated to be $355,000 as described later in Chapter IV, Section 3.2, Table IV-5.)
We assumed that plant location allows solution mining of an underground
salt bed resulting in a unit cost of $2.00 per ton of salt. Purchased solid
salt would be much more expensive, about $12.00/ton delivered.
c. Energy Usage
Energy costs, both power at 1.2<:/kWh (utility company published rates
show ranges of 1.05 to 1.4c/kWh at Gulf Coast locations for large loads) and
net fuel at 70
-------
The relative amount of electrical energy and thermal energy for boiler
fuel can be varied to a limited degree. The fuel requirements listed above
are for a cell liquor caustic concentration of 140 grams per liter, which is
normal for this type of cell. By operating at higher cell liquor concentra-
tions, up to about 160 grams per liter, the steam for concentration can be
reduced about 10-12%, but cell current efficiency decreases and power con-
sumption increases. The rates used are about optimum for a graphite anode
cell. These rates result in a total energy consumption of 40.58 x 106 Btu/
ton as shown below:
106 Btu/ton
Electrical Power (3274 kWh) (10,500 Btu/kWh) 34.37
Boiler Fuel 9.15
Total 43.52
Hydrogen Credit (2.94)
Net Total 40.58
2. Current Effluent Situation
a. Water Pollution
"Water pollution regulatory constraints imposed upon the _chlor-alkali
industry are mainly the result of Sections 304(b) and 306 of the Federal
Water Pollution Control Act, as amended. The Act provides for the Environ-
mental Protection Agency to issue effluent limitations guidelines applicable
to the point source discharge of industrial wastewater. For specific
industry categories, the effluent limitations guidelines are based on
technical studies commonly referred to as the EPA Development Documents.
The function of the Development Document is to characterize the industry,
describe the sources of water pollution, the wastewater characteristics,
control technology currently in use, suggested permissible effluent levels,
recommended technology for their attainment, and cost estimates for the
implementation of such technology. For this study, general information on
the sources'of wastewater, wastewater characteristics, treatment technology,
and treatment cost estimates has been extracted from the Development Document
pertaining to the chlor-alkali industry.*
(1) Sources of Wastewater
The diaphragm cell process for the manufacture of chlorine and caustic
soda or caustic potash usually has the following raw wastes emanating from
the process:
^Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Major Inorganic Products Segment of the
Inorganic Chemicals Manufacturing Point Source Category, U.S. Environ-
mental Protection Agency, March 1974. EPA-440/l-74-007-a
28
-------
a A solution of sodium hypochlorite and sodium bicarbonate from
the scrubbing of chlorine tail gases (about 7.5 Ib of dissolved
solids/1000 Ib of chlorine produced);
• Chlorinated organics from the liquification of chlorine gas
(about 0.7 lb/1000 Ib of chlorine produced);
• Brine wastes from the brine purification system (about 12.2 Ib
of dissolved solids/1000 Ib of chlorine produced);
• Spent sulfuric acid from the chlorine drying process (about 4.2 Ib/
1000 Ib of chlorine produced);
• Weak caustic and brine solution from the caustic evaporators
using barometric condensers (about 9.5 Ib of dissolved solids/
1000 Ib of chlorine produced); and
• Weak caustic and brine solution from the caustic filter washdown
(about 37.5/lb of dissolved solids/1000 Ib of chlorine produced).
Lead is sometimes present in the effluent as a result of cracks around
protective resin seals which encase underlying lead mountings. Currently,
over 30% of the industry is using anodes (DSA) which eliminate the lead
discharge. Industry representatives state that another 30% are seriously
considering conversion.
The mercury cell process for the manufacture of chlorine and caustic
soda or caustic potash usually has similar wastes to the diaphragm cell
process - the notable exception is the additional presence of mercury in
the wastewater due to losses of mercury from the process. Based on a survey
of 21 facilities, the Development Document sets forth a typical raw waste-
load for the mercury cell process, which is shown in Table IV-3.
(2) Effluent Limitations
Based on the findings and recommendations presented in the Development
Document, the Environmental Protection Agency has published "Effluent
Limitations Guidelines for the Chlor-Alkali Industry."* The Effluent
Limitations Guidelines will serve as the basis for the issuance of actual
specific discharge permits and will directly influence the type of technology
to be implemented and its associated costs.
The Effluent Limitations Guidelines sets forth three treatment levels:
• Best Practicable Control Technology Currently Available
(BPCTCA) - to be implemented by 1977;
• Best Available Technology Economically Achievable (BATEA) - to be
implemented by 1983; and
^Federal Register, March 12, 1974
29
-------
TABLE IV-3
RAW WASTE LOADS FROM MERCURY CELL PROCESS
BASED ON A SURVEY OF 21 FACILITIES
(lb/1000 Ib chlorine)
Waste
Purification Muds
(CaC03 8 Mg (OH)2)
NaOH
NaCl
KC1
H2S04
Chlorinated Hydrocarbons*
Na2S04
Cl£ (as CaOCl2)
Filter Aids
Mercury
Carbon, Graphite
Mean
16.5
13.5
211
16
0.7
15.5
11
0.85
0.15
20.3
Range
0.5 - 35
0.5 - 32
15 - 500
0-50
0 - 1.5
0 - 63
0-75
0-5
0.02 - 0.28
0.35 - 340
*Depends markedly on grade of chlorine produced.
Source: "Development Document for Effluent Limitations Guidelines and
New Source Performance Standards for the Major Inorganic Products
Segment of the Inorganic Chemicals Manufacturing Point Source
Category", U.S. Environmental Protection Agency, EPA-440/l-74-007a,
March, 1974.
30
-------
» New Source Performance Standards - which apply to new plants
constructed before 1983 and to major changes in existing
plants.
The effluent limitations are given in terms of kg of pollutants per 1000 kg
of product (equivalent to Ibs per 1000 Ib of product), and are specified
both for maximum daily levels and maximum 30-day averages. The effluent
limitations are as follows:
e Diaphragm Cells - The effluent limitations restrict the discharge
of total suspended solids and lead, and place restrictions on pH.
BPCTCA Level (1977)
Effluent 'Limitations
Effluent
Characteristics
Maximum for
any 1 day
Average of Daily
values for 30
consecutive
days shall not
exceed -
Total Suspended Solids
Lead
pH
Metric units (kg per 1,000 kg of product)
0.64 0.32
.005 .0025
Within the range 6.0 to 9.0
BATEA Level (1983)
There shall be no discharge of process wastewater pollutants to navigable
waters.
New Source Performance Standards
Effluent
Characteristics
Effluent Limitations
Maximum for
any 1 day
Average of daily
values for 30
consecutive
days shall not
exceed -
Total Suspended Solids
Lead
pH
Metric units (kg per 1,000 kg of product)
0.64 0.32
.00008 .00004
Within the range 6.0 to 9.0
31
-------
Mercury Cell - The effluent limitations restrict the discharge
of total suspended solids, mercury, and place restrictions on pH.
BPCTCA Level (1977)
Effluent
Characteristic
Effluent Limitations
Maximum for
any 1 day
Average of Daily
values for 30
consecutive
days shall not
exceed -
Total Suspended Solids
Mercury
PH
Metric Units (kg per 1,000 kg of product)
0.64 0.32
.00028 .00014
Within the range 6.0 to 9.0
BATEA Level (1983)
1. There shall be no discharge of process wastewater pollutants into
navigable water.
2. A process wastewater impoundment-which is designed, constructed
and operated so as to contain the precipitation from the 25-year,
24-hour rainfall event as established by the National Climatic
Center, National Oceanic and Atmospheric Administration for the area
in which such impoundment is located - may discharge that volume of
process wastewater which is equivalent to the volume of precipita-
tion that falls within the impoundment in excess of that attribut-
able to the 25-year, 24-hour rainfall event, when such event occurs.
New Source Performance Standard
Effluent
Characteristic
Effluent Limitations
Maximum for
any 1 day
Average of Daily
values for 30
consecutive
days shall not
exceed -
Total Suspended. Solids
Mercury
PH
Metric units (kg per 1,000 kg of product)
0.64 0.32
.00014 .00007
Within the range 6.0 to 9.0
-------
(3) Control Technology
For both the mercury cell and diaphragm cell categories, the BPCTCA
limitations require the control of specific pollutants, lead and mercury,
from the wastewater prior to discharge, while the BATEA limitations for both
categories prohibit the discharge of process wastewater pollutants. In
complying with these limitations, the chlor-alkali industry will have to
implement both end-of-pipe treatment of wastewater and various degrees of
waste recovery and internal wastewater recycle.
The Development Document recommends a number of wastewater treatment
and pollution abatement measures that are believed to enable the industry
to comply with the various effluent limitations. These measures are
summarized below:
• Diaphragm Cells
BPCTCA Level (1977)
1. Asbestos and cell rebuilding wastes are filtered or settled
in ponds then land dumped;
2. Chlorinated organic wastes are incinerated or land dumped;
3. Purification muds from brine purification are returned to salt
cavity or sent to evaporation pond/settling ponds; and
4. Weak Caustic (brine solution from the caustic filters) is
partially recycled.
BATEA Level (1983)
Same as BPCTCA, plus
1. Waste sulfuric acid is reused or sold;
2. The hypochlorite waste is catalytically treated and reused or
recovered;
3. All weak brine solution is recycled; and
4. Conversion to stable anodes.
No specific technology has been recommended for the New Source Per-
formance Standards, but one can reasonably conclude that the BPCTCA
level in conjunction with a high level of recycle would be sufficient.
• Mercury Cells
BPCTCA LeVel (1977)
1. Cell rebuilding wastes are filtered or placed in settling pond,
then used for landfill;
33
-------
2. Chlorinated organic wastes are incinerated or placed in containers
and land dumped;
3. Purification muds from brine purification are returned to brine
cavity or sent to evaporation/settling ponds;
4. Brine waste streams are partially recycled; and
5. Mercury effluent is recovered and reused by curbing, insulation and
collection of mercury containing streams, then treatment with sodium
sulfide. The precipitated mercuric sulfide is converted back to
mercury for reuse.
BATEA Level (1983)
Same as BPCTCA plus
1. Waste sulfuric acid is reused or recovered;
2. The hypochlorite waste is catalytically treated and reused or recovered;
3. All weak brine solutions are recycled.
(4) Pollution Abatement Costs
Since compliance with the BPCTCA and BATEA effluent limitations can
entail many combinations of end-of-pipe wastewater treatment, wastewater
recycle, and in-process changes, the actual costs incurred will vary greatly
among specific plants. Furthermore, there are various stages of pollution
abatement measures already in-place, thus further complicating an estimate
of the cost of compliance.
To reduce these complexities, the Development Document makes use of a
cost model and considers the following four treatment levels:
Level A - Base level practices followed by most of the industry and
exceeded by exemplary plants;
Level B - Treatment and control practices at the average exemplary
plant;
Level C - The best technically and economically feasible treatment
and control technology; and
Level D - Complete waterborne waste elimination.
The cost model considers a 1000 ton/day (chlorine basis) mercury cell
plant and a 1000 ton/day (chlorine basis) diaphragm cell plant for the
purpose of cost estimates. The cost estimates are shown in Tables IV-4 and
IV-5. In each case treatment level B corresponds to BPCTCA and level D to
BATEA. Note these levels are cumulative in that D includes A through C.
34
-------
TABLE IV-4
WASTEWATER TREATMENT COST ESTIMATES
Diaphragm Cell Chlor-Alkali (1000 tons/day capacity - 360 days/year)
Treatment Level
Capital Investment
Variable Costs
Operating & Maintenance
Energy & Power
Total Variable Cost
Fixed Costs
Depreciation @ 9.1%
Taxes & Insurance @ 1.5%
Total Fixed Cost
Total Annual Cost
Return on Investment @ 20%
Total
Total per Unit ($/ton chlorine)
Wastewater
Electrical (kwh/yr)
Thermal (106 Btu/yr)
Total Energy Equivalent (10 Btu/yr)
Total per Unit (10 Btu/ton chlorine)
A
$32,000
13,500
nil
$13,500
?,900
500
$3,400
$16,900
$ 6,400
$23,300
$0.065
Treatment
nil
nil
nil
B
$46,700
122,500
1,000
$123,500
4,200
700
$4,900
$128,400
$ 9,300
$137,700
$0.38
Energy Consumption
83,300
875
0.0024
C
$355,000
122,500
1,000
$123,500
32,300
5,300
$37,600
$161,100
$ 71,000
$232,100
$0.64
83,300
875
0.0024
D
$1,076,000
122,500
1,000
$123,500
97,900
16,100
$114,000
$237,500
$215,200
$452,700
$1.26
83,300
875
0.0024
Notes: 1. Costs derived from EPA Development Document and adjusted to fit specific cases.
2. Costs for the treatment levels are cumulative, i.e., D includes A + B + C.
3. Costs have been adjusted to the 1975 level using the Engineering News Record
Construction Cost Index.
4. Level A - Settling pond.
Level B - Chlorinated hydrocarbons to disposal pit* + sulfuric acid to sales,
neutralization of sodium hydroxide and brine returned to system.
Level C - Installation of chlorine burning hydrochloric acid plant for
chlorine tail gas. Hydrochloric acid value is assumed to be equal
to variable costs.
Level D - Non-contact cooling substituted for barometric condensers (rough
estimate).
5. Total annual cost includes cost of on-site sludge disposal. Total sludge
generation = 1,350 TPY (dry basis).
35
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TABLE IV-5
WASTEWATER TREATMENT COST ESTIMATES
Mercury Cell Chlor-Alkali (1000 tons/day capacity - 360 days/year)
Treatment Level
B
Capital Investment $1,736,000 $1,736,000 $2,434,000 $2,604,000
Variable Costs
Operating & Maintenance 354,000 354,000 388,000 411,000
Energy & Power-
Electricity @ $0.012/kwhj ^^ ^^ ^^ ^^
Fuel @ $0.70/10 Btu \
Total Variable Cost $371,000 $371,000 $418,200 $508,000
Fixed Costs
Depreciation @ 9.1%
Taxes & Insurance @ 1.5%
Total Fixed Cost
Total Annual Cost
Return on Investment @ 20%
Total
Total per Unit ($/ton chlorine)
Wastewater
Electrical (kwh/yr)
Thermal (10 Btu/yr)
Total Energy Equivalents (10 Btu/yr)
Total Per Unit (10 Btu/ton chlorine)
158,000
26,000
$184,000
$555,000
$347,200
$902,200
$2.51
Treatment Energy
1,420,000
14,910
0.041
158,000
26,000
$184,000
$555,000
$347,200
$902,200
$2.51
, Consumption
1,420,000
14,910
0.041
221,000
36,500
$257,500
$675,700
$486,800
$1,162,500
$3.23
1,420,000
18,800
33,710
0.094
237,000
39,000
$276,000
$784,000
$520,800
$1,304,800
$3.62
1,420,000
114,200
129,110
0.359
Notes: 1. Costs derived from EPA Development Document ;md adjusted to fit specific cases.
2. Costs for the treatment levels are cumulative, i.e., D includes A + B + C.
3. Costs have been adjusted to the 1975 level using the Engineering News Record
Construction Cost Index.
4. Level A - Reduction of mercury to less thnn 1 x 10 kg/kkg
Level B - Reduction of mercury to less than 7 x 10 kg/kkg
Level C - Level B + catalytic conversion of sodium hypochlorite to sodium
chloride
Level D - Level C + evaporation and reuse of sodium chloride. No effluent
except cooling water. Dry Inn sulfuric acid to other use
on concentration.
5. Total annual cost includes cost of on-wllr shul^e disposal. Total sludge
generation = 8,360 TPY (dry basts).
36
-------
b. Solid Waste
Solid wastes emanating from the chlor-alkali industry are the result of
both the purification of raw materials and the actual production processes
themselves.
Common to both the mercury-cell process and the diaphragm-cell process^
are solid wastes resulting from the purification of brine. Process constraints
require that calcium, magnesium and sulfates be largely removed prior to
electrolysis. Such removal is generally accomplished by precipitating the
calcium and magnesium out of solution with caustic and soda ash. Sulfates
are sometimes removed by adding barium chloride to form insoluble barium
sulfate. The precipitated compounds are removed from the brine after they
settle as a sludge. The brine is usually further purified by filtration, and
often there are various filtration wastes such as spent filter precoat
materials and filter aids. As long as satisfactory process operation makes
it necessary to remove calcium and magnesium from the brine by precipitation,
such wastes will be generated.
Principal sources of solid waste from the mercury cell process are:
• brine purification sludges and filtration wastes,
• used graphite cell anodes and mercury-contaminated graphite from
the decomposers, and
• cell lining material and general industrial trash.
The disposal of solid waste from chlor-alkali plants using mercury
cells presents certain problems because of the necessity for preventing
mercury contamination. Mercury is adsorbed into the brine purification
sludges and into the graphite used in the decomposers. The mercury is
normally removed from the sludges by careful washing and is then precipitated
as the sulfide from the wash water. The sulfide is subsequently reduced to
metallic mercury for reuse. Mercury can be recovered from graphite by
either roasting (retorting) or chemical leaching.
Principal sources of solid waste from the diaphragm cell process are:
• brine purification sludges and filtration wastes,
• deteriorated concrete cell hoods,
• asbestos from the cell diaphragms,
• used graphite cell anodes,
• mastic used in the bonding of carbon anodes,
• lead from cell bottoms, and
• general industrial trash.
37
-------
The contact of chlorine with the hydrocarbon-based mastic can pro-
duce small quantities of chlorinated hydrocjarbons.
A number of plants in the industry are taking steps to use- anodes that
eliminate the discharge of lead. Lead, asbestos, and chlorinated hydro-
carbons are generally considered hazardous, and careful control measures are
necessary for environmentally acceptable land disposal.
An estimation of the quantity of land-destined hazardous waste from the
chlor-alkali industry is as follows:*
Tons Per Year to Land Disposal
Hazardous Constituents
Hazardous in Total Stream Total Waste Stream
Constituents (dry basis) .(dry/wet basis)
Asbestos, chlorinated 7,700 63,000/120,000
hydrocarbons, lead,
mercury
Industry production in 1974 was 10.62 million tons of chlorine, so total dry
solid waste is only 0.006 ton/ton of chlorine. The disposal cost of this
material is very small, averaging about $10/ton of dry waste, or 6<:/ton of
chlorine.
c. Atmospheric Emissions
Atmospheric emissions of chlorine, carbon dioxide, carbon monoxide,
residual gas, or hydrogen occur from diaphragm- and mercury-cell plants in
amounts that depend largely upon plant design and operation. If liquid
chlorine is not produced (as in a paper mill plant), the plant will have no
"blow gas," resulting from liquefaction and will have, therefore, no chlorine
emissions from this source. Where liquid chlorine is produced, emissions vary
according to the waste treatment system employed and the chlorine content of
the blow gas.
For safety and health reasons, operating procedures are established to
minimize the potential for "fugitive emissions." Consequently, the atmo-
spheric emission points, except for accidental occurrences, are usually known
and efforts are made to control the emissions as discussed in the following
sections.
(1) Chlorine Emissions
• Blow Gas - When a chlorine-cell gas is compressed and cooled to
produce liquid chlorine, noncondensable gases saturated with
chlorine vapor are produced at the discharge of the condenser.
^Assessment of Industrial Hazardous Waste Practices, Inorganic Chemicals
Industry, U.S. Environmental Protection Agency, Contract 68-01-2246, 1975.
38
-------
These gases are commonly called blow gas, sniff gas, or tail
gas. The amount of chlorine emitted to the atmosphere from blow
gas varies with operating conditions and the type of recovery
equipment through which the stream is processed. Emissions
vary with plant capacity, concentration of chlorine in the blow
gas, percentage of inerts in the cell gas, and according to
whether air is injected before the chlorine condenser to pre-
vent an explosive mixture in the vent gas.
Table IV-6 shows ranges of concentrations and the amounts
of chlorine that may be emitted if the emissions are uncontrolled
and when various types of scrubbers are used to remove chlorine.
A typical range for the diaphragm cells is 2,000 to 10,000 Ib
of chlorine in the blow gas per 100 tons liquefied, or 1 to 5%
of the product. Mercury-cell installations usually require more
air dilution because more hydrogen is contained in the cell gas.
The usual range of chlorine in the blow gas is 4,000 to 16,000 Ib
of chlorine per 100 tons of chlorine liquefied, or 2 to 8% of
the product.
The value of this chlorine is significant and, for this
reason, all but the smallest plants have for many years recovered
such chlorine by either burning with hydrogen to make hydro-
chloric acid or by caustic scrubbing to produce bleach. Pro-
prietary processes are also available for solvent absorption of
the chlorine (one using carbon tetrachloride) and subsequent
recovery of the material as elemental chlorine.
It is common practice to operate at condensing pressures and
temperatures that represent an economic optimum. When there is
no use for chlorine in the blow gas, and chlorine must be neu-
tralized , it becomes economical to condense at higher pressures
or lower temperatures, or both, to reduce the chlorine in the
blow gas. If useful byproducts can be made, or if the chlorine
in the blow gas is recycled or recovered in some other manner, it
will usually be more economical.to allow the percentage chlorine
in the blow gas to increase in lieu of operating at relatively
high pressures or low temperatures, or both.
The high operating costs encountered when chlorine in the
blow gas must be neutralized and discarded have caused consid-
erable attention to be directed to methods of recycle or recovery.
This is particularly true for gas streams with large concentra-
tions of carbon dioxide, since this compound also reacts with
and consumes alkali.
Abnormal operating conditions that increase the quantities
of chlorine in the blow gas are given below.
39
-------
TABLE IV-6
CHLORINE EMISSIONS FORM LIQUEFACTION BLOW GASES
IN DIAPHRAGM- AND MERCURY-CELL PLANTS
Type Chlorine Concen- Emissions Factor,
of trations in Lb Chlorine/100 Tons
Control Exhaust^ Vol % Chlorine Liquefied
None 20 to 50 2,000 to 16,000
Water Absorber 0.1 to 4.5 25 to 1,090
Caustic or Lime
Scrubber 0.0001
Source: Environmental Protection Agency, Atmospheric Emissions, from
Chlor-Alkali Manufacture, January,1970 (Air Pollution Control
Office Publication No. AP-80)
40
-------
Operating above rated capacity - Cell manufacturers specify for
a particular cell an upper current limit or cell load that
determines the rate of chlorine, caustic, and hydrogen pro-
duction. As technical and operating improvements have been made,
cell ratings for both new and existing cells have increased. If
existing chlorine condensing facilities are inadequate for the
expanded plant production resulting from such improvements, the
percentage of chlorine in the blow gas will increase and positive
pressure may occur in the cell headers, resulting in chlorine
emissions in the cell room.
Startup and shutdown - During chlorine plant startup, air is
present in chlorine lines and equipment and liquefaction effi-
ciencies are low, so that large amounts of blow gas are generated.
A new cell circuit may require 8 to 24 hours to attain steady
operating conditions at full load. Normally, when a cell circuit
is started up, every effort is made to maintain continuous opera-
tion; at times, however, entire circuits may be shut down for
major repairs or for economic reasons. To minimize the excess
air in the chlorine system at -startup, liquid chlorine is fre-
quently evaporated into the chlorine headers.
Vents from Returned Tank Cars, Ton Containers, and Cylinders -
Occasionally, water and other liquids are present in returned
tank cars. To ensure a clean empty car before reloading, it is
common practice to apply suction to returned tank cars, as well
as to cylinders and ton containers, to remove any liquid chlorine
remaining in the vessel before inspection and cleaning. The
amount of chlorine thus removed Varies considerably, but averages
about 450 pounds for a 55-ton tank car. The recovered chlorine
is usually sent to the chlorine handling system, although some
plants send the chlorine to a caustic scrubber to avoid upsetting
their cell operation.
Vents from Storage Tanks, Process Transfer Tanks, and Tank Cars
During Handling and Loading of Liquid Chlorine - A common method
of transferring chlorine involves the use of air padding. After
the transfer it is necessary to vent the air, which now contains
a relatively small concentration of chlorine, because the trans-
fer is normally completed before equilibrium conditions can be
reached. The amount of chlorine in the vented air varies consid-
erably and is greater at higher temperatures. It depends also
upon the shape of the vessel, the time required for transfer,
and the number of transfers made.
Quantities of chlorine are flushed out with the padding air
during the loading of shipping containers with liquid chlorine.
Data show that the chlorine flushed out varied from 110 to 6,000
41
-------
pounds per 100 tons of chlorine liquefied, with an average of
1,700 pounds. Chlorine removed during tank car loading operations
is transferred to other plant uses, returned to the process, or
treated in a scrubber.
In many newer plants, submerged pumps are used for the trans-
fer of liquid chlorine. Although pumps eliminate the loss of
chlorine attendant with air padding, emergency venting is neces-
sary for pump repair and general maintenance. These emergency
vents are usually connected to a caustic scrubber. It is good
practice to use small pump tanks that can be isolated from large
storage tanks for servicing. This practice greatly reduces emis-
sions during pump repair.
Another method of transfer is to apply suction on the receiver
or vessel to which a transfer is to be made and connect the dis-
charge from the compressor to the vessel containing the chlorine
that is to be transferred. This is somewhat similar to transfer
by means of air, except that neither tank requires any venting.
Emergency Vents - Chlorine seals and other sources of infrequent
emissions are usually connected to an emergency scrubber, although
in other cases these emissions are vented to the atmosphere. In
either case, alarms and electrical tie-in connections are usually
provided to permit prompt shutdown or changes in operating pro-
cedures to limit the duration of the emission.
Cell room chlorine header seals - Seals on chlorine headers, pro-
vided to prevent back pressure at the cells, are usually vented
to the cell house or to the outside atmosphere. Although in an
emergency they must handle the full capacity of the cells con-
nected to the header, the seals blow infrequently and for short
periods. In certain locations seals are piped to a lime or caustic
scrubber designed to absorb all the cell chlorine produced.
Compressor seals - The shaft seals on liquid-seal chlorine com-
pressors are usually piped so that a stream of sulfuric acid is
fed into the compressor. Carbon-ring reciprocal compressors
usually have a double stuffing box vented to a caustic scrubber
or to the suction of the compressor. This effectively prevents
emissions to the atmosphere.
Storage tanks - The tank vent line is usually connected to a dis-
posal scrubber. The relief connection from the safety valves
may be vented to the atmosphere or to an emergency scrubber.
Air Blowing of Depleted Brine in Mercury-Cell Plants - Recycled
brine in mercury-cell plants is saturated with chlorine. This
brine is usually vacuum treated, air blown, or both, to remove
residual chlorine before resaturation. Concentrations of chlorine
-------
encountered in the vent gas are usually low and economic recovery
in a water or carbon tetrachloride absorber cannot be obtained.
Consequently, such gases are normally used for in-plant purposes
such as water chlorination, or they are sent to lime or caustic
scrubbers for disposal or vented to the atmosphere. Although
air blowing of depleted brine is common, it is by no means uni-
versal. For example, certain plants air blow and retreat only
a 5-10% sidestream, and several plants dispense with this proce-
dure entirely.
• Mercury-Cell End Boxes - On certain mercury cells the discharge
end box is constructed with a removable cover for servicing.
End boxes are connected to a common suction header to prevent
chlorine gas from entering the cell room when the covers of the
end boxes are opened. Chlorine in the exhaust header is usually
neutralized with lime or caustic.
(2) Other Emissions
Carbon monoxide forms a small part of the inerts in cell gas, amount-
ing to 0.02% by volume and appearing in the same relative amounts in the
blow gas. Assuming a 20-fold increase in carbon monoxide concentrations
because of liquefaction of the chlorine, the carbon monoxide concentration
in the blow gas would be 0.40% by volume.
The use of mercury in mercury-cathode cells produces some mercury
vapor, which is emitted during cell operations. The trend toward the use
of higher-strength amalgams and, therefore, lower mercury requirements has
minimized mercury vapor emissions. Modern cells with steeper bottom slope,
vertical decomposers, higher-strength amalgam, and increased current den-
sites have reduced mercury inventory to slightly less than 90,000
pounds for a 100-tpd chlorine plant, about half that required by older
plants. With the newer cells, daily mercury losses have decreased from
0.6 pound to less than 0.3 pound per ton of installed daily chlorine
capacity. The usual range of mercury losses for typical plants in the
United States has been given as 30-40 pounds per 100 tons of chlorine pro-
duced. European sources indicate that some 3% of the mercury lost is
emitted to the surrounding atmosphere.
The weak (about 10-15%) sodium hydroxide solution is evaporated in a
double or triple effect evaporators followed by a washing filter. The con-
centrated 50% solution is sold as such or further concentrated. The vapors
from evaporators represent an emission source. These, however, are con-
densed in barometric condensers, so that the only atmospheric emissions
are inert gas (air) and some steam from jet eductors.
43
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3. Modified Anodes
a. Dimensionally Stable Anodes (PSA)
To eliminate the problems associated with the graphite anode, the
industry has long worked on developing a non-consumable anode. These efforts
led to the successful 1968 introduction, by De Nora in Italy, of the first
commercial DSA. The anode consists of an expanded titanium metal sub-
strate coated with precious metal/rare earth oxides. These were initially
developed for mercury cells but were quickly introduced to the diaphragm
cell process. In the United States they are produced and licensed by the
Electrode Corporation, a joint venture of De Nora and Diamond Shamrock.
The DSA has numerous advantages which result in power savings (direct
current at the cell) of up to 20% and labor savings from reduced maintenance
on the cells. Chlorine quality is also improved since reactions with the
graphite and organic binders is eliminated. This leads to a reduction in
tail gas and in the chlorinated organics removed in the chlorine purifica-
tion system. These materials, a mixture of rather indefinite composition,
are now drummed for acceptable land fill disposal or incinerated. Elimina-
tion of these materials, plus elimination of the need to handle waste
graphite anodes, reduces pollution problems.
Power savings result from a number of effects, the major one being the
fact that anode-cathode spacing remains constant throughout use as does
anode area. Thus, cell voltage does not increase rapidly with time. There
is a small increase as the anode coating deactivates, which indicates a
need for recoating, but the change is small compared to that experienced
with graphite. A reduction in cell voltage also results from the fact
that the chlorine bubbles formed on the anode are smaller and release more
readily, so that less of the anode is covered with gas, which increases
effective area and reduces resistance. The electrode overvoltage effects
are also reduced with the coating used.
The user of the electrode has the operating option of running his
plant, after installation of DSA, at the same current loading to produce
the same amount of chlorine with less power per ton, or to increase current
loading to produce more chlorine but at an increased consumption of power
per ton of chlorine. Because capital costs and energy costs are both of
major significance, the optimum lies between the two extremes.
Table IV-7 shows the estimated cost of producing chlorine in a 1000-tpd
plant on the Gulf Coast. The cost plus a 20% pretax return and pollution con-
trol cost, per ton of chlorine or ECU, is $8.35/ton, less than that shown in
Table IV-2 for the graphite anode plant under the typical balance of operating
conditions used here. Power consumption has been reduced by 123 kWh/ton (3.7%)
and steam consumption, expressed as fuel, by 1.2 x 10& Btu/ton (13%). The
latter reduction is brought about by operating the cells at a cell liquor
concentration of 160 g/1* of caustic, instead of 140 g/1 for graphite. Opera-
tion of the DSA at 140 g/1 would decrease power use, but would eliminate the
fuel savings.
*Customary unit used in industry, therefore not expressed in English units.
44
-------
TABLE IV-7
ESTIMATED PRODUCTION COST OF CHLORINE AND CAUSTIC SODA
Process:
Annual Production:
Stream Days/Year:
Plant Location:
Depreciation Period:
Fixed Investment:
Electrolysis of Brine, DSA Diaphragm Cell
360,000 tons of Chlorine
380,000 tons of Caustic Soda (100% basis as 50%)
360
U.S. Gulf Coast
11 years (IRS Guideline)
$54,200,000
$/Unit
Variable Costs
Salt (100% as brine)
Misc. Chemicals
Diaphragm Material
Cell Rebuilding Supplies
Power
Fuel for Steam (Gas)
H£ Fuel Credit
Cooling Water Circ.
Process Water
Anode Royalty
Semi-Variable Costs
Operating Labor
Supervision
Labor Overhead
Maintenance
Fixed Costs
Plant Overhead
Local Taxes & Insurance
Depreciation
TOTAL PRODUCTION COST
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used or
Annual Basis
tons
kWh
106 Btu
106 Btu
103 gal
103 gal
34 men 12,000/yr
4 men 18,000/yr
1 superintendent 25,000/yr
35% of Labor & Supervision
4% of Investment
70% of Labor & Supervision
1.5% of Investment
9.1% of Investment
20% of Investment
See Table IV-4
Units/ton
of Chlorine
2.00
0.80
0.05
0.03
0.012
0.70
0.70
0.02
0.25
1.75
1.0
1.0
1.0
3151.0
7.95
2.94
40.0
1.9
$/ton
3.50
0.80
0.05
0.03
37.81
5.56
(2.06)
0.80
0.48
5.20
52.17
1.13
0.20
0.07
0.49
6.02
7.91
0.98
2.26
13.67
16.91
76.99
30.11
0.55
107.65
Source: Arthur D. Little, Inc. estimate
45
-------
Other savings result from elimination of graphite costs, reduction
in rate of diaphragm renewal (no plugging from graphite particles) and
labor savings, because less cell rebuilding is needed, and in new plants
fewer, larger cells are used. A modern DSA cell would be rated at 150,000
amperes compared to 80,000 for the largest graphite anode cells. The
smaller number of cells also reduces the number of bus connections and
bus losses tend to decrease.
The power and energy use breakdown for the typical plant of Table IV-7
is as follows:
kWh/ton
DC to Cell 2774
Busbar Losses 30
Total DC Power 2804
AC Power at 97% Efficiency 2891
Auxiliary Process Power 250
Power for Plant Auxiliaries 10
Total AC Power 3151
Added Power for Environmental Control 0.23 (Negligible)
Steam Use Ib/ton Cl,,
Evaporators 5447
Miscellaneous Plant Uses 700
Total 6147
Fuel equivalent at 1100 Btu/lb steam and
85% boiler efficiency 7.94 x 106 Btu/ton
Byproduct hydrogen fuel credit (2.94) x 10^ Btu/ton
Net fuel requirement 5.01 x 10^ Btu/ton
(Compare with tabulation on page 28 for graphite anode process)
46-
-------
Under present commercial arrangements, the DSA are leased by Electrode
Corporation to the user and recoated by Electrode Corporation. The user
pays an initial fee, included in the plant investment cost shown in Table
IV-7, plus a running royalty calculated as shown below.
For a power cost under 10 mills per kWh the royalty in dollars per
ton of chlorine is:
3.00 + 200 (power cost, $/kWh)
Above 10 mills per kWh the royalty is:
4.00 + 100 (power cost, $/kWh)
This schedule results in a royalty of $5.20/ton at the power rate of 1.2c/
kWh used here. Thus, under the operating conditions used, the royalty
exceeds the power savings but the user still has a significant cost reduc-
tion. This reduction is sufficient so that it is expected that the entire
industry, with the exception of a few small plants, will soon be using
DSA cells. All new capacity is being based on DSA-equipped cells.
b. Expandable DSA
The distance between the anode and the asbestos-coated cathode is one
factor in determining cell voltage and power consumption. The closer the
spacing the less the power consumption. With normal, rigid DSA a
"working" space must be allowed to assemble the cell without scraping
asbestos from the cathode as it is inserted. The expandable DSA is con-
structed so that the outer faces can be moved outward after the cell is
assembled to allow working room for assembly and then inward for reduced
spacing.
The result of this change is a reduction of about 325 kWh per ton of
chlorine (about 10%) compared to the "standard" DSA configuration. This
change has no effect on environmental considerations over the normal DSA
unit.
Royalty arrangements for the expandable anode will split the power
savings with the user, presumably on a basis to provide an incentive for
their use, but specific charges are not yet known.
•47
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4. Modified Diaphragms
In addition to the significant changes in anodes, some major improve-
ments are being introduced for diaphragms which have beneficial effects for
both power consumption and environmental matters. The three most signifi-
cant are discussed here in order of commercial status.
a. Polymer Modified Asbestos
This concept uses a polymer-treated asbestos diaphragm which is baked
into place on the cathode. Whereas the normal deposited diaphragm swells
in use (increasing electrical resistance, cell voltage, and power consump-
tion), the modified diaphragm does not. It is also possible to use a
thinner diaphragm to further reduce resistance.
Use of the diaphragm has a minor environmental benefit in that the dis-
carded material, at the time of cell rebuilding, is in stabilized pieces
instead of loose asbestos fibers. Thus, disposal is easier and safer,
because the fibers resist dispersion.
Another benefit of the stabilized diaphragm is that wider DSA anodes
may be used since swelling does not occur. This reduction in anode-cathode
spacing can accomplish significant power savings, comparable to those
achieved with the expandable anode. Based on the configuration used by
Hooker for the H-4 cells, the savings compared to the standard DSA are
shown in Table IV-8.
A baking oven and facilities would add about $300,000 to the capital
cost of a plant, but added material costs are essentially offset by longer
diaphragm life.
As noted in the table, the cell liquor concentration is 150 g/1 for
this comparison. At higher levels, the power savings would be slightly
reduced because of reduced current efficiency. The reduction in savings
may approximate 30-50 kWh/ton.
b. Polymer Membranes
A number of groups are developing microporous teflon-type polymer
membranes, successfully demonstrated to date on laboratory/pilot-scale cells,
which would replace the asbestos diaphragm entirely. Such thin membranes
would give an energy performance equivalent to the stabilized asbestos with
the "extra wide" anode shown in Table IV-8. They would have the added advan-
tage of a much longer life and would eliminate the environmental issues
associated with handling and disposal of asbestos.
The restraint on commercialization of the membranes has been the devel-
opment of means for large-scale manufacture with good control of both pore
size and total porosity. It is expected that these problems will be solved
within the next few years.
48
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TABLE IV-8
POWER SAVINGS EFFECTED BY STABILIZED DIAPHRAGM IN H-4 DSA CELLS
Diaphragm Type
Anode Width
Standard
(1)
DC Power, kWh/ton chlorinev ' 2731
Decrease from standard, kWh/ton
AC Power at 97% Eff.,. kWh/ton
Power Cost Savings 1.2£/kWh, $/ton
Added Capital Costs at 24.5%
Net Savings, $/ton
(2)
1
! tandard
2613
118
122
1.46
0.20
1.26
Wide
2525
206
212
2.54
0.20
2.34
I
Extra Wide
2459
272
280
3.36
0.20
3.16
(1) Differs slightly from that used elsewhere since caustic concen-
tration is 150 g/1.
(2) 20% capital recovery, 3% maintenance, 1.5% taxes and insurance.
Source: Hooker Chemical Company and Arthur D. Little, Inc.
-------
The use of microporous membranes is expected to have little effect on
plant investment. The higher first cost of the membranes would be offset
by the elimination of the present facilities for depositing asbestos and its
handling,
c. _Ion_E_xchange Membranes
There is growing interest in the use of ion-exchange membranes with
high electrical conductivity and high ion-transfer rates, such as du Font's
Nafion (TM) , to separate the anode and cathode compartments of the cell.
These membranes would only allow transfer of positive ions to the cathode,
and prevent transfer of negative ions to the anode, thus allowing produc-
tion of a very pure, salt-free caustic similar to that from the mercury
cell.
In the operation of such cells, the partially depleted brine is
recycled for resaturation and pure water is fed to the cathode, similar to
the arrangement used for mercury cells. At present, the cell units are
small, such as the 45-ton-per-day unit being installed in Canada, and out-
put caustic strength is limited to about 10% NaOH. This type of unit is
well suited for replacing mercury cells in applications such as pulp mills
that use a dilute caustic.
Work now underway would make this type of cell of much broader inter-
est, because it may be possible to produce a cell capable of producing
25 to 40% caustic directly from the cell. As shown in Table IV-9, the
potential energy savings over the graphite anode or DSA diaphragm cell
could be significant. As shown earlier, the energy consumption for efflu-
ent control, 0.23 kWh/ton of chlorine, is negligible for these processes.
From an environmental viewpoint, the cell represents an improvement
over the graphite anode/asbestos cell in the same manner as would the
microporous membrane. The following waste streams generated by the
graphite-anode/asbestos cell would be eliminated:
lb/1000 Ib C12
Asbestos fibers 0.4
Graphite anode stubs 0.8
Evaporator purge stream
Caustic soda 20.
Salt 50.
Water 150.
In common with other cells using DSA, the 0.45 lb/1000 Ib C12 of
chlorinated hydrocarbons would also be eliminated.
-------
TABLE IV-9
ESTIMATED ENERGY SAVINGS WITH ADVANCED ION EXCHANGE MEMBRANE CELL
Cell Type
Anode
Standard
Ion Exchange
Caustic concentration from cell 10.5%
Product caustic concentration
Energy use, DC power to cells
only, kWh/ton C12
AC power at 97% efficiency
Evaporator steam fuel input
106 Btu/ton C12
As Compared to Graphite Anode
Power savings, kWh/ton
f fn \
Power as 10 Btu/ton '
Fuel savings, 10 Btu/ton
Net Savings, 10 Btu/ton
As Compared to DSA
Power savings, kWh/ton
Power as 10 Btu/ton
(2)
Fuel savings, 10 Btu/ton
Net savings, 10 Btu/ton
(1) ADL estimates
(2) At 10,500 Btu/kWh
Graphite
10.5%
50%
2894
2880
8.24
DSA DSA
11.5% 25%
50% 50%
2774 2880(1)
2860 2969
7.05 4.79
-89
- 0.93
3.45
2.52
-109
- 1.14
2.26-
DSA
40%
50%
2980(1)
3070
0.91
-192
- 2.01
7.33
5.32
-212
- 2.23
6.14
1.12
3.91
Source: Industry data and Arthur D. Little, Inc.
51
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At the present state of development (producing 10% caustic which
must be concentrated), plant costs are more expensive than normal plants.
The ability to produce a higher-strength caustic will probably make them
competitive.
5. Comparison of Mercury and Diaphragm Cells
To assist in providing information useful in predicting the relative
viability of the mercury cell process in the United States, we have
examined the process carefully and carried out an analysis of its energy
requirements relative to the diaphragm cell. To keep the comparison real-
istic and valid for new plants that could be constructed, we have based the
comparison on existing improvements which would be used in the modern design
of either type of plant. Thus, for the mercury-cell basis we have used one
equipped with dimensionally stable anodes and compare it with the similarly
equipped diaphragm cell. Future, but developed, improvements for each are
also considered.
a. Process Description
The mercury cell, although many variations exist, is usually a long,
very slightly sloped trough, either rubber lined or bare steel, containing
the flowing brine being electrolyzed. The cathode is a thin layer of metal-
lic mercury completely covering and flowing down the bottom of the trough
under the brine. The trough is covered, and projecting down through the
top cover are many anodes, originally graphite but now DSA's. Chlorine is
produced at the anodes, mixed with some hydrogen from the cathode, particu-
larly if heavy metals are in the brine, and leaves the cell through the
chlorine ducts to the drying and liquefaction system, which are exactly the
same as for diaphragm cells. However, caution must be used to control the
hydrogen content to prevent the explosive formation of hydrogen chloride in
the cells or in the chlorine system.
At the mercury cathode, the sodium ion is discharged to form a dilute
sodium amalgam. As shown in Figure IV-2, this amalgam leaves the cell and
flows to the decomposer, a graphite-packed tower. Here, the amalgam is
contacted with .demineralized water to form a 50% caustic soda solution,
mercury, and hydrogen.
2 Na:Hg + 2 H 0 + 2 NaOH + H + 2 Hg
The sodium-free mercury is pumped back to the front end of the cell for
reuse.
Because the caustic is formed outside of the cell it is salt-free, and
can be kept iron-free since it does not have to be pumped through an evapora-
tor system. It must, however, be treated for mercury removal, and even after
treatment is not regarded as suitable for food or photographic chemical
uses. The various waste streams are shown in Figure IV-2 and their disposition
is given in Table IV-10.
52
-------
SOLID SALT:
ROCK,SOLAR
OR EVAPORATOR
BRINE
RESATURATION
DEPLETED BRINE
,. CONC. CONTROL
BRINE
PURIFICATION
HC.f'J-
pH
SOLID
SLUDGE:
CaCOs
Mg(OH)2
HEAVY
METALS
(SULFATES)
Hg
WASTE
MERCURY CELL
ELECTROLYSIS
NaHg
(3
LU
3
Sf.
a.
UJ
Z
E
o
i
u
WEAK BRINE
Hg
Hg REMOVAL
1 SYSTEM
DECOMPOSER
SPENT
H2S04
SCRUBBER
LIQUOR
DECHLOR
INATION
2-STAGE
TO
DISPOSAL
MERCURY-
FREE
SLUDGE
1
FLOOR
WASHING
&
Hg MAT'L
S(
PUF
STR
— »-
50% NaOH
<30 ppm NaCI
MERCURY
REMOVAL
WASTE
H2O •
50% CAUSTIC
SODA
VENTILATION
AIR
Figure IV-2. Mercury Cell Process
53
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TABLE IV-10
WASTE STREAMS FROM MODERN MERCURY CELL PROCESS
Source and Comments
Precipitated impurities from
brine contain adsorbed soluble
mercury removed by water wash-
Ing
Wasted sludges from brine
purification
Rubber cell linings, decom-
poser graphite packing, etc.
from cell rebuilding opera-
tions
Quantity
lbs/1000 Ib Cl.
Hydrogen from decomposer con- Mercury vapor
tains mercury vapor at
equilibrium pressure of mer-
cury temperature
Components
Complexed & ionic
mercury in aqueous
solution
CaCCL
Mg
-------
The hydrogen from the decomposer is dried, treated for mercury removal
by refrigeration to condense the bulk of the mercury followed by carbon
adsorption and then can be burned for fuel, sold, or vented.
In the mercury-cell process the only water losses from the brine are
in the vapor leaving with the chlorine, as no evaporators are involved.
Thus, the brine leaving the cell (only about 11-12% decomposed as compared
to 50% in the diaphragm cell), is recirculated and must be resaturated with
solid salt. Before resaturation the chlorine-saturated brine is acidified
and air blown to remove chlorine and chlorates that would interfere with
brine purification.
Because of the much lower percentage decomposition in the cell the
brine purification system must handle about four times the volume handled
in a diaphragm-cell plant. Otherwise, purification is handled in much the
same way using a carbonate and caustic treatment to remove heavy metals and
calcium. The sludges, precipitated under controlled conditions to minimize
mercury adsorption, must be treated for mercury removal before disposal.
This is done by thorough water washing on a filter with the filtrate sent
to the water treatment area for sulfide treatment. Some plants use barium
chloride addition to precipitate sulfate ions, others purge part of the
brine to control sulfate buildup. Even though the volume of brine passing
through the purification system is much larger than for the diaphragm cell,
the volume of waste discharged is essentially the same. The amount of brine
sludge is determined by the amount of impurities in the feed salt, not by
the total volume treated.
The mercury sulfide obtained by treatment of the various waste streams
is retorted, as discussed in Section IV.B.2, to recover the mercury for
for reuse:
HgS + 02 -> Hg + S02
This recovery operation is sometimes carried out at the chlorine plant, but
the sulfide is often sent to an outside company for mercury, recovery. The
EPA* has sponsored work on this recovery and advanced commercial technology
has been developed and used in Europe by Uhde and others.**
Mercury Recovery from Contaminated Waste Water and Sludges, Georgia-Pacific
Corp., 1974, EPA Project No. 12040 HDU.
?J?
European Chemical News, August 4, 1972, p. 22.
55
-------
b. Cost of Production
Based upon a 1000 ton/stream day chlorine plant located on the U.S.
Gulf Coast, we estimate that the fixed investment would be $58.2 million
plus an added $3.6 million for mercury inventory. The latter amount is
shown separately because it is regarded as non-depreciable for tax purposes
but is normally amortized. About $2.6 million is required for investment
in effluent treatment equipment as shown earlier in Table IV-5.
Using purchased solid salt at $12/ton delivered, and with power at
1.2<:/kWh, the production cost is estimated to be $100.13/ton, as shown in
Table IV-11. The anode royalty for the DSA's is the same as for a diaphragm
cell, $5.20/ton of clorine at this power cost. Again all costs are based
on chlorine or the ECU. Inclusion of a minimal pretax return on investment
of 20% of plant cost plus mercury cost per year, or $34.33/tons, and effluent
treatment costs of $3.62/ton (Table IV-4) increases the total to $138.08/
ton or ECU.
Power consumption, excluding effluent treatment, is 3712 kWh per ton of
chlorine, derived as shown below:
kWh/ton
DC power at cells 3221
Bus bar losses 65
Total DC power 3286
AC at 97% Efficiency 3387
Process use (chlorine system, Hg & brine pumps) 315
Auxiliary use 10
Total AC power 3712
Only a nominal amount of steam is used, 550 Ib/ton, requiring a fuel
input of 0.72 x 10& Btu at 1100 Btu/lb of steam and a boiler efficiency of
85%. The hydrogen produced, 10.7 x 103 SCF or 2.94 x 106 Btu/ton of chlorine,
the same as for the diaphragm cell, cannot be fully utilized since it
exceeds the heat requirements of the process. For safety reasons, only
about 50% of the boiler fuel can be hydrogen, so that 0.36 x 10^ Btu can be
used, leaving an excess of 2.58 x 10^ Btu/ton to be flared or used else-
where. The net fuel purchases are reduced to 0.36 x 10^ Btu/ton.
The ability' to sell all or part of the hydrogen is a site-specific
issue and depends on the local supply/demand balance for hydrogen. In
most cases only modest amounts can be sold, if any. Revenue from hydrogen
sales do not enter into the basic economics of a caustic chlorine plant,
since such revenues are insignificant compared to those from the two major
products.
56
-------
TABLE IV-11
»
ESTIMATED PRODUCTION COST OF CHLORINE AND CAUSTIC SODA
Process:
Annual Production:
Stream Days/Year:
Plant Location:
Depreciation Period:
Fixed Investment:
Mercury Inventory:
Electrolysis of Brine, DSA Mercury Cell Process
360,000 tons of Chlorine
380,000 tons of Caustic Soda (100% basis as 50%)
360
U.S. Gulf Coast
11 years (IRS Guideline)
$58,200,000
$3,600,000
Variable Costs
Salt (solid)
Misc. Chemicals
Hydrochloric Acid
Cell Rebuilding Supplies
Mercury
Power
Fuel for Steam
H2 Fuel Credit
Excess H2 Fuel
Cooling Water Circ.
Process Water
Anode Royalty
Semi-Variable Costs
Operating Labor
Supervision
Labor Overhead
Maintenance
Fixed Costs
Plant Overhead
Local Taxes & Insurance
Depreciation
TOTAL PRODUCTION COST
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used or
Annual Basis
tons
pounds
—
pounds
kWh
106 Btu
106 Btu
106 Btu
103 gal
103 gal
$/Unit
12.00
0.80
0.40
0.15
4.08
3712.0
0.70
0.70
_
0.02
0.25
_
Units/ton
of Chlorine
1.70
1.0
30.0
1.0
0.25
0.012
0.72
0.36
2.58
16.4
0.4
-
$/ton C10
20.40
0.80
1.20
0.15
1.02
44.54
0.50
(0.25)
-
0.33
0.10
5.20
29 men 12,000/yr
4 foremen 18,000/yr
1 superintendent 25,000/yr
35% of Labor & Supervision
4% of Investment
70% of Labor & Supervision
1.5% of Investment
9.1% of Investment
20% of Investment including Mercury
See Table IV-4
73.99
0.97
0.20
0.07
. 0.43
6.47
0.87
2.43
14_._70
18.00
100.13
34.33
3.62_
138.08
Source: Arthur D. Little, Inc. estimates
57
-------
As shown earlier in Table IV-5, effluent treatment adds 4 kWh per ton
of chlorine to the power consumption and requires an added 0.32 x IO6 Btu/
ton of chlorine. This heat, in the form of steam, requires a fuel input of
0.41 x 10 Btu. As discussed before, 50% of this can be derived from hydro-
gen so that net added fuel to be purchased is increased by 0.2 x 106 Btu/
ton and excess hydrogen decreased by the equivalent of 0.21 x 106 Btu/ton.
Including these adjustments, total energy requirements are:
Total AC Power 3716 kWh/ton
Total fuel 1.13 x io6 Btu/ton
Hydrogen Used as Fuel (0.57 x IO6 Btu/ton)
Net Fuel Requirement 0.56 x IO6 Btu/ton
c.
Comparison of Energy Consumption With Diaphragm Cell
^In view of the decline of the use of mercury cells for chlorine pro-
duction, largely because of the understandable reluctance of the industry
to risk the consequences of a plant mishap or maloperation, even though
present techniques allow normal operation within all current regulations,
it is desirable to analyze the energy efficiency of the process. If it
offered energy advantages over the alternative cells, means could be
studied to encourage its use.
In Table IV-12 the energy consumption of the mercury-cell process,
both electrical and thermal, is compared with the presently used DSA/
asbestos diaphragm cell and with the newer expandable anode or stabilized
asbestos/wide anode diaphragm cells. A comparison is also made with the
ion-exchange membrane cell, but this is to be considered approximate
because of the unavailability of detailed data for this cell.
To allow properly for the total energy use, total electrical power has
been converted to thermal energy by using 10,500 Btu/kWh, the U.S. average
heat rate in public utility generating plants. The fuel value credit for
hydrogen has been shown first, most realistically, for what can be safely
used in the plant, and secondly as the total available assuming possible
use in other processes.
If all hydrogen can be used, the modern mercury-cell plant uses about
2-3% less energy than the typical DSA/diaphragm plant, assuming solid salt
is available for feed. However, if solid salt for plant feed must be pro-
duced from brine or solution-mined salt, salt production would require
5.6 x.106 Btu/ton of chlorine, making the diaphragm cell clearly advan-
tageo'us. As discussed in the process description, the mercury-cell process
requires a solid salt feed since only 11-12% of the salt in the brine fed
to the cell is decomposed per pass and no water, except for vapor in the
chlorine and purges, is removed from the system.
58
-------
TABLE IV-12
Electrical Energy kWh/ton Cl
DC to cells
Bus & other losses
Total DC
AC at 97% Efficiency
Process AC
Auxiliary AC
Total Power
Thermal Energy, 10 Btu/ton
Evaporator steam
Misc. Plant Uses
Total
Electrical as Thermal Equiv.
Total Energy Use
Credit for Hydrogen Usable
Net Total
Hydrogen Not Usable
Total giving Allowance
for all Hydrogen
(5)
SON OF MERCURY
Mercury
DSA
01 111
3221 3221
65 65
3286 3286
3387 3387
315 315
10 14
3712 3716
0.72 1.13
0.72 1.13
38.98 39.02
39.70 40.15
iP__._36) (0.57)
39.34 39.58
2.58 2.37
AND DIAPHRAGM
DSA
Standard*- '
2774
30
2804
2891
250
10
3151
7.05
0.90
7.95
33.09
41.04
(2.94)
38.10
0
CELLS
Wide or
Expanded DSA
Stabilized
Diaphragm(3)
2459
30
2489
2566
250
10
2826
7.05
0.90
7.95
29.67
37.62
ll-ii)
34.68
0
Ion
Exchange
(40% NaOH)<4
2980
30
3010
3103
250
10
3363
0.91
0.90
1.81
35.31
37.12
(0.90)
36.22
2.04
36.76 37.21
38.10
34.68
34.18
(1)
(2)
(3)
(A)
(5)
Plant excluding effluent control
Plant including effluent control
Includes effluent control
Estimated from limited available data, includes effluent control
10,500 Btu/kWh
Source: Industry data and Arthur D. Little, Inc. estimates
59
-------
However, the mercury cell - compared with the available technology that
would be used in new plants, the expandable DSA or stabilized asbestos plus
wide anode - uses 6% more energy. Comparisons based on crediting only usable
hydrogen place the mercury cell at a strong disadvantage in all cases.
The advantage of the diaphragm cell from an energy viewpoint is
increased if quadruple-effect evaporators, at higher capital cost, are
used instead of the customary triple-effect evaporators. These would
reduce energy use for evaporator stream by 20% or 1.4 x 106 Btu per ton of
chlorine for the DSA diaphragm cells. Since steam use is small for the ion-
exchange membrane, a quadruple-effect evaporator would not likely be
considered.
From this comparison one may conclude that further development of
mercury cell technology is not likely in the U.S.
60
-------
V. IMPLICATIONS OF POTENTIAL INDUSTRY CHANGES
A. PROBABLE CHANGES
During the next 15-year period it is expected that the electrolytic
chlorine-caustic soda industry will adopt a number,of evolutionary changes
that will lead to a 15% or greater reduction in energy requirements. This
saving will result from a gradual conversion of major existing plants to
the use of dimensionally stable anodes and stabilized or microporous polymer
membranes and from the probable fact the newly constructed plants will
take advantage of improved anode geometry as well as the newer types of
diaphragms to achieve slightly greater energy savings.
We do not expect to see any new mercury cell plants constructed in the
United States for two reasons. First, the risk of violating EPA and OSHA
regulations through plant accidents, transient conditions, and the like is
unacceptable to management. Second, the new developments in diaphragm-type
cells provide a lower-cost, more energy-efficient process. In the near
future, perhaps within five years, when the ion-exchange membrane cell has
been perfected to the point where it can produce a strong caustic, we expect
existing mercury-cell plants to convert, gradually, to this process. The
process produces a pure, salt-free caustic, equal or superior to that from
a mercury cell, particularly in that it contains no mercury, and its closed
brine system fits with the existing system and system capacity in mercury-
cell plants. Such conversions are now being carried out in Japan and
Canada, even though production of high-strength caustic without evaporation
is not now deemed commercial practice.
B. ENVIRONMENTAL IMPLICATIONS
At the present time, the industry, at least by comparison with others
and excluding mercury cells, does not have severe environmental problems.
Liquid effluents contain non-toxic inorganic salts and precipitates that can
be lagooned and the supernatant water reused in the plant system to a major
extent. However, a small amount of lead and copper salts and asbestos
fibers are in these wastewater streams and are of major environmental con-
cern from a long-range viewpoint. Probable process changes, although
undertaken for energy-conservation motives, will also ease some of these
environmental issues.
Table V-l summarizes the preceding discussions of the process changes
expected to take place in the diaphragm-cell process for chlorine/caustic
soda manufacture and the environmental implications of these changes. The
energy consumption in the form of electrical power, thermal energy and the
total, expressed as equivalent thermal energy for each process, is also
shown. The waste streams are numbered to key into the base process flow-
sheet, Figure IV-l and Table IV-1, presented earlier.
61
-------
TABLE V-l
ENVIRONMENTAL IMPLICATIONS OF CHANGES IN DIAPHRAGM CELLS
Anode
Diaphragm
Base Case
Graphite
Deposited
Asbestos
Process Changes
Waste Stream Quantities (lb/1000 Ib chlorine)
1.
2.
3.
Brine Sludges
Inorganic Salts
Filter Aid
Water
(1)
Cleaning
4.
5.
Cell Rebuilding Materials
Concrete Rubble
Graphite Rubble
Asbestos Fibers
Housekeeping, Equipment &
Salt
Caustic Soda
Lead
Copper
-Water
Salt Purge from Evaporators
Sodium Sulfate
Caustic Soda
Salt
Water
Sulfuric Acid (Chlorine Drying)
Dilute Sulfuric Acid
6. Final Vent Scrubbers
Sodium Hypochlorite
Sodium Bicarbonate
Water
7. Chlorine Purification
Chlorinated Organics
8. Polymer Membranes
Energy Use Per Ton of Chlorine or ECU
Electrical kwh
Thermalv
Total")
106 Btu
106 Btu
18
0.2
45
1
2
0.4
SO
5
0.04
< 0.01
600
10
20
50
150
10-35
1
3
40
0.45
0
3274
6.21
40.58
Fuel Value of Hydrogen not Used 10 Btu
(1) Mg(OH)2, CaC03, iron and other metal hydroxides, sodium chloride.
(2) Net after maximum use of hydrogen (limited to 50% of total fuel).
(3) Electrical converted to thermal at rate of 10,500 Btu/kwh.
Source: Table IV-1 and Arthur D. Little. Inc., estimates.
DSA-STD DSA-Wtde DSA
Deposited Stabilized Microporous
Asbestos Asbestos Membrane
000
0.2 0.2 0
40 40 40
44 4
000
480 480 480
0.9 )
36 j
. - 0 - 0 - 0
0 0 < 0.05
3151 2826 2826
5.01 5.01 5.01
38.10 34.68 34.68
000
DSA
Ion Exchange
Membrane
0
0
40
3
0
480
0
, 0
0
- 0
< 0.05
3363
0.91
36.22
0
62
-------
Brine sludges are the impurities in the salt used as raw material
which must be removed to allow proper electrolytic cell operation. These
are in the form of inorganic salts, calcium carbonate and magnesium hydrox-
ide being the principal compounds, but smaller amounts of iron and other
heavy metal basic compounds are also present. The sludges are dewatered by
filtering and, because of their gelatinous nature, some filter aid, such as
diatomaceous earth, is used and is present in the waste cake. Salt is pres-
ent because the mother liquor is a saturated brine and cake washing on the
filter does not completely remove all mother liquor. The amount of sludge
is directly related to the crude salt purity and for all practical purposes
is not influenced by any of the process changes considered.
Cell renewal gives rise to a number of wastes which include the con-
crete cell bodies themselves, graphite anode stubs, and waste asbestos from
spent diaphragms. It is not expected that any of the process changes will
in themselves change the life expectancy of the cell body. Thus, the
amount of concrete rubble sent to landfill will remain the same.
Conversion from the use of graphite anodes to DSA, in any of its varia-
tions, completely eliminates the use of graphite and this waste stream.
Use of DSA reduces asbestos waste from renewal of the diaphragms since with
the absence of graphite particles, they need renewal only about half as often.
Conversion to either microporous polymer membranes or ion-exchange membranes
completely eliminates the use of asbestos from the process. Both of these
membranes are expected to have long lives, perhaps five years, and so as
shown in item 7 of Table V-l, the volume of waste they will cause is esti-
mated to be very small, less than 0.05 lb/1000 Ib chlorine.
Plant housekeeping and flushing of equipment for maintenance gives rise
to waterborne effluents as shown in item 3 of the table. Since the DSA-
equipped cells require much less frequent renewal, there is less washing
involved and it is estimated that the volume of this stream and the con-
tained salt and caustic soda will be reduced to at least 80% of its normal
amount. The ion-exchange membrane cell may produce a 40% caustic, as com-
pared to a 10-12% from the other cells, so less evaporative equipment is
needed which would lead to a further reduction in caustic in this waste
stream.
As' discussed, the anodes in the graphite-anode diaphragm cells are set
in lead to provide electrical connections. The lead is protected from the
corrosive solution in the cell by a layer of mastic, but some attack of the
lead does occur. When cells are cleaned or rebuilt, small amounts of the
corroded lead dissolve into the washwater and form part of the effluent.
The DSA-equipped cells do not use lead for imbedding and forming electrical
connections so that lead in the effluent is eliminated.
Copper compounds, less than 0.01 lb/1000 Ib chlorine, get into the
wastewater since the cell house atmosphere contains enough chlorine to cause
some corrosion of the copper bus bars and cell connections. The process
changes we envision would not alter to any appreciable degree the amount of
copper contained in this waste stream.
63
-------
In the part of the plant concentrating the 11-12% caustic from the
cells up to 50%, a purge stream is taken to eliminate sodium sulfate from
the system. This stream also contains some sodium chloride and caustic
soda. Since the amount of the purge is determined by the sulfate content
of the raw material salt or brine, as long as the process allows the sulfate
to flow through the cell into the catholyte (dilute caustic on the cathode
side of the diaphragm), there will be no change in this stream. In the ion-
exchange membrane cell, however, the sulfate ions do not pass through the
membrane; only the positive sodium ions are transferred to the cathode side
of the membrane, which is supplied with deionized water. For this reason,
the caustic solution leaving the cell is very pure, containing only insigni-
ficant amounts of materials other than sodium hydroxide and no evaporator
purge is needed for the salt recycle, since there is none, or to meet pro-
duct purity specifications.
The quantity of spent sulfuric acid discharged from the chlorine drying
system depends on the moisture content of the chlorine gas after it is
cooled, and is not influenced by any of the process changes considered here.
This spent acid is normally sold for use where dilute acid can be used, or
is returned to the supplier for reconcentration or fortification. Only
under unusual conditions is it discharged as a waste stream.
The chlorine gas from the cells in graphite-anode-equipped cells con-
tains carbon oxides derived to a major extent from reactions of various
impurities in the brine with the graphite and air as impurities. Air enters
the system through leaks, because the chlorine headers are kept under a
slight negative pressure to prevent leakage of chlorine into the cell room
atmosphere. The presence of these inerts results in a residual gas leaving
the chlorine liquefaction equipment and following supplementary chlorine
recovery processing which does contain, although primarily inerts, some
chlorine. This stream is scrubbed with caustic soda to remove chlorine
before the inerts are vented and the chlorine is converted to sodium hypo-
clorite. Carbon dioxide, also removed by the scrubbing, is converted to
sodium bicarbonate. The use of DSA-equipped cells will increase the cell
gas purity and decrease the volume of inerts and chlorine associated with
the inerts. It is estimated that a 10% reduction, or perhaps as much as 20%,
can be achieved in the final vent scrubber effluent volume.
The graphite anodes, which contain organic binders, also give rise to
some chlorinated organics which leave the cell in the chlorine gas. These
are removed from the chlorine after liquefaction to meet high-purity chlorine
specifications. As mentioned, they are normally drummed for subsequent
incineration or landfill disposal. Conversion to DSA eliminates the graph-
ite from the process and essentially eliminates the formation of chlorinated
organics in the process.
64
-------
Although mercury-cell plant operators have developed processes to,.
enable them to comply with EPA limitations on water effluents (7 x 10 lb/
100 lb chlorine for new source standards), and discharges to the atmosphere
can be held to reasonable levels, the fact that this process has no energy
advantage over the newer types of diaphragm cells, and that industry is
not spending funds to develop further improvements in mercury cells, is
expected to limit its use to existing plants. It is probable that some
plants will convert.to the diaphragm-cell process, particularly when the
ion-exchange membrane type is further developed, and thereby achieve a
reduction in the total amount of mercury discharged to the environment by
the chlorine industry.
We conclude that these expected process changes, which could cause a
15% reduction in the energy used to produce a ton of chlorine, do not result
in any increased environmental problems. In fact, a reduction in the
volume of waste streams and pollutants is expected.
65
-------
APPENDIX A
INDUSTRY STRUCTURE
The tables and figures in this Appendix augment and complement the
information presented in Chapter III, Industry Overview.
Figure A-l shows the location of operating chlorine and alkali plants
in the United States and Canada as of 1/1/75.
Tables A-l through A-5 present details of the U.S. chlor-alkali indus-
try by state for number of establishments, plant size, plant age, production
process and production volume.
Table A-6 gives historic data on U.S. and Canadian production processes
from 1946 to 1974.
Table A-7 presents a record of U.S. chlorine capacity and production
from 1951 through 1974.
Finally, Tables A-8 through A-10 list U.S. producers and capacities
for soda ash, caustic potash and sodium bicarbonate.
66
-------
N DAKOTA \ MINNESOTA
Figure A-l. Operating Chlorine and Alkali Plants in the United States and Canada -
January 1, 1975
-------
TABLE 4^-1
SIC 2812 ALKALIES AND CHLORINE, DISTRIBUTION OF ESTABLISHMENTS
EPA .. , .
Number of
Re8ionEstablishments
IV Alabama
X Alaska
IX Arizona
VI Arkansas
IX Cali f ornia
VIII Colorado "~~
I Connecticut
III Delaware ~
T7 FloridI
V Georgia
IX Hawaii
V Illinois ~
V Indiana
IV' Kentucky
vl Louisiana
III Maryland
V Michican
V Minnesota
VII Missouri
VII Nebraska
Ix Nevada
I . New, Hampshire
II New Jersev
IV North Carolina'
VIII North Dakota
I Rhode" Island
VIII South Dakota
X Washington
III West Virciinia
V Wisconsin
^ Region -I
i ,
VII
vTfi
Source: "Assessn
Inorgani
EPA Cont
28121
Chlorine
4
i
1
i
3
1
_
2
9
1
4
i
i
2
2
4
1
3
11
1
1 4
4
3
2
67
1
7
f!
n
20
1
5
tent of In
c Chemica
ract No.
281 22
Synthetic
Sodium
Carbonates
2
1
1
-
3
2
dus trial H
Is Industr
5^-01-2246
28123
Sodium
Hydroxide
4
1
3
1 ,
1
2
o
1
, 4
1
2
3
1
o
4
3
1
4
_ — ,
13
18
1
2
azardous V
y," Final
, 1975.
28124 '
Other
Alkalies
2
1
1
1
1
1
3
1
1
2
15
4
2
/aste T?rac
Report Sfc
2812
as a
Whole
" 4
1
1
3
1
1
2
10_
4
1
1
3
3
1
1 _
3
2
__ 1
16 "
22
1
tices,
F-104C,
6S
-------
EPA
TABLE A- 2
Sir 9R19 AT.KAT.TF.S AND CHLORINE. DISTRIBUTION OF PLAN SIZES
Plont Size,
n Daily Capacity (metric tons)
IV Alabama
X Alaska
IX Arizona
VI Arkansas
IX California
VIII Colorado
I Connecticut
III Delaware
IV Florida
IV Georoia
IX Hawaii
X Idaho
V Illinois
V Indiana
VII Iowa
VII Kansas
IV Kentucky
VI Louisiana
I Maine
III Marvland
I Massachusetts
V Michigan
V Minnesota
IV Mississiooi •
VII Missouri
VIII Montana
VII Nebraska
IX Nevada
I New Har.oshire
II New Jerscv
VI New Mexico
II New York
IV . North Carolina
VIII North Dakota
V Ohio
VI Oklahoma
X Oreqon
III Pennsylvania
I Rhode Island
IV South Carolina
VIII South Dakota
IV Tennessee
VI Texas
VIII Utah
I Vermont
III Viroinia
X Washington
III West Virginia
V Wisconsin
VIII Kvoning
TOTAL
A Reqion I
II
III
IV '
V
VI
VII
VIII
IX
X
28121
Chlorine
A
n
B
1
I
1
1
1
1
1
1
R
1
2
i
i
r
3
l
2
1
2
/
1
4
1
1
2
5
1
3
1
3
R
4
1
54
1
7
4
1?
fi
•1
1
5
j
2
2
4
4
28122
Synthetic
Sodium
Carbonates
A •
.
n
n
c
i
I
1
i
4
1
2
1
L)
1
]
1
1
1
C
1
/
1
1
28123
Sodium
Hydroxide
A
0
B
1
1
1
1
1
1
/
1
2
2
C
4
1
2
1
1
i
6
n
4
l
L
2
1
2
1
'/
1
4
n
l
4K
1
4
4
11
ti
1 3
1
1
• 5
U
5
1
4
i
281 24
Other
Alkalies
A
.
, .....0 ._
B
1
1
1
1
1
1
7
2
1
1
2
1
C
2
1
1
2
1
1 -
8 I
2
1
3
1
1
KEY: A = 0-9 metric tons; B = 10-99 metric tons; C
D = 1000 & over
100-999 metric tons;
Source: "Assessment of Industrial Hazardous Waste Practices,
Inorganic Chemicals Industry," Final Report SW-104C
EPA Contract No. 68-01-2246, 1975.
69
-------
TABLE A-'3
SIC 2812 ALKALIES AND CHLORINE, DISTRIBUTION OF PLANT AGES
EPA
Region Plant Age (years)
IV Alabama
A Alaska ^
IX Arizona
. VI Arkansas
IX California
VIII Colorado
I Connecticut
III Dolawaro
IV Florida
IV Georgia
IX Hawaii
X Idaho
V Illinois
V Indiana
VII Iowa
VII Kansas
VI Louisiana
Hi Maryland
I Massachusetts
V Michigan
V Minnesota
IV Mississippi
VII Nebraska
I New Hampshire
II New Jersey
VI New Mexico
IV North Carolina
VI Oklahoma
X Oregon
III Pennsylvania
I Rhode Island
IV South Carolina
IV Tennessee
VIII Utah
Hi Virginia
X Washington
III West Vircrir.ia
V Wisconsin
VIII Wvoming
TOTAL
,EPA Region I
Fi "*
lYJ r-
—
__
28121
Chlorine
A
•)
j—
— r~
~
1 8
— 1 —
1
1
B
4
~T~
"""O"*"
~T~
• *
1
2
5
1
1
2
~r~
i
~3
1
2
_A
2
i
40
1
"~3~
I
13
9
~
"1
c
1
2
2
~
•3
1
1
~~4
__
2
1
19
~r~
2
1
3
/.
28122
Synthetic
Sodium
Carbonate
A
0
B
2
2
~~2
C
1
2
1
_i_
2 '
1
1
7
1 '
_3
28123
Sodium
Hydroxide
A
2
1
1
"I —
J
_J
R
4
T^
I
J
o
j
2
5
1
_J
_j
5
~i —
2
w~
1
2
i]
•7
10
_J
_J 1
C
2
h-T—
_1_
_J_
_j
4
~T—
2
~r~
T?~
T~
2
_!_
3
2
28124 ,
Other
Alkalies
A
1
_J
2
]
1 •
B
1
1
J
J_
1
1
1
7
'2
2
C
1
-11
_J_
1
2
0
1
3
KEY: A = less than 5; B = 5 to 30; C = Over 30
Source: "Assessment of Industrial Hazardous Waste Practices,
Inorganic Chemicals Industry," Final Report SW-1Q4C
EPA Contract No. 68-01-2246, 1975.
70
-------
TABLE A-4
SIC 2812 ALKALIES AND CHLORINE, DISTRIBUTION OF PROCESSES
\
EPA Pfocess Types,
Re 2 ion No. \( Facilities
IV Alabama .
X Alast-a
IX Arizona
VI Arkansas
IX California
VIII Colorado
I Connecticut
III Delaware
IV Florida
IV Georaia
IX Hawaii
X Idaho
V Illinois
V Indiana
VII Iowa
VII Kansas
IV Kentucky
VI Louisiana
I Maine
III Maryland
I Massachusetts
V 'Michiqan
V Minnesota
IV Mississipoi
VII Missouri
VIII Montana
VII Nebraska
IX Nevada
I New Hamnshire
II Hew Jerscv
VI New Mexico
II Hew York
IV North Carolina
VIII North Dakota
V Ohio
VI Oklahoma
X Oreaon
III Pennsylvania
I Rhode Island
IV South Carolina
. VIII South Dakota
IV Tennessee
VI Texas
VIII Utah
I Vermont
III Virginia
X Washinqton
III West Virginia
V Wisconsin
VIII Wvoninq
TOTAL
EPA Region I
II
III
IV. .
• V
VI
VII
VIII
IX
X
J8121
Chlorine
A
I
2
1
^
2
3
1
1
3
1
1
2
2
2
?R
1
4
3
10
3
"5
2
R
—i —
1
1
7
4
1
1
2
1
2
1
1
R
1
2
2
17
3
3
3
7
15
1
2
3
£-
1
•
1
1
1
1
•i
1
1
1
2
>
2
2
2
1
L
Synetheic w
Sodium ^
Carbonote *>
F
2
1
1
1
1
]
2
1
7
1
3
.1
G
1
1
1
_2
•i
1
7
'1
28123
Sodium
ydroxide
A
2
1
2
;>
i
i
i
.
l
i
2
2
2
1
26
1
2
3
in
3
S
2
1
7
4
1
1
1
'i
2
1
1
8
1
2
2
1,
37
2
3
4
7
H
2
3
<-
1
1
1
28124
Other
Alkalies
1
1
1
1
9
2
2
3
1
1
1
1
2
1
1
H
1
1
1
4
—
-
J
3
1
]
1 1
1
A = Mercury Cell; B = Diaphragm Cell; C = Down's Cell; D = HCI Process;
E = NOCI Process; F = Solvay Process; G = Bicarbonate Process;
H = Potassium Carbonate Process^ I = Ammonium Carbonate Process
Source: "Assessment of Industrial Hazardous Waste Practices,
Inorganic Chemicals Industry," Final Heport SW 104C,
EPA Contract No. 68-01-2246, 1975.
71
-------
TABLE A-5
SIC 2812 ALKALIES AND CHLORINE, DISTRIBUTION OF PRODUCTION
EPA Annual Production
Region 103 metric tons
IV Alabama
X Alaska
IX Arizona
VI Arkansas
IX California
VIII Colorado
I Connecticut
III Delaware
IV Florida
IV Georgia
IX Hawaii
X Idaho
V Illinois
V Indiana
VII Iowa
VII Kansas
IV Kentucky
VI Louisiana
I Maine
III Maryland
I Massachusetts
V Michigan
V Minnesota
IV Mississ.ipoi
VII Missouri
VIII Montana
VII Nebraska
IX ' Nevada
I New Hampshire
II New Jersev
VI New Mexico
II Mew York
IV North Carolina
VIII North Dakota
V Ohio
VI Oklahoma
X Oregon
III Pennsylvania
I Rhode Island
IV South Carolina
VIII. South Dakota
IV Tennessee
VI -Texas
VIII Utah
Vermont
III Virginia
X Washington .
Ill West Virginia
V Wisconsin
VIII Wyoming
TOTAL
EPA Region I
II .
Ill
IV
V
VI
VII
VI 1 1
IX
X
28121
Chlorine
320
15
130
180
32
73
200
2.600
65
510
46
48
240
460
71
260
130
330
4,non
73
17
330
590
76
nrooo
65
700
740
1 inn
880
6r600
73
73
63
460
28122
Synthetic
Sodium
Carbonates
960
*
. 750
1,000
790
770
A40
4,400
irooo
1,500
ir?on
640
28123
Sodium
Hydroxide
345
17
150
190
59
80
220
2.700
72
560
53
260
140.
78
25Q
110
290
2,000 ,
18
310
&5Q
88
8,600
72
400
820
i i no
'960
4,700
80
70
420
28124
Other
Alkalies
100
25
55
23
0
9
0
30
0
6.6
250
9
25
170
85
f, &
2812
as a
Whole
760
32
300
370
150
150
440
6.300
140
1,800
46
100
500
1,600
150
1.300
240
0
620
6 300
73
35
600
1_,2QO
160
64Q
24,000
140
2, 100
.1.500
7 400
3^400
13 000
150
7QQ
130
840
Source: "Assessment of Industrial Hazardous Waste Practices,
Inorganic Chemicals Industry," Final Report SW-1Q4C,
EPA Contract No. 68-01-2246, 1975.
72
-------
TABLE A-6
CHLORINE PRODUCTION ROUTES - U.S. AND CANADA
Year
1946
1956
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
Per Cent of Total Installed Capacity
Diaphragm
Cells
43.0
44.3
46.0
45.0
36.0
33.2
37.3
43.2
42.7
39.9
39.5
53.2
64.5
Canada
Mercury
Cells
57.0
55.6
54.0
55.0
64.0
66.8
62.7
56.8
57.3
60.1
60.5
46.8
35.5
All Other
_
-
-
-
_
.
.
-
-
_
-
-
United States
Diaphragm
Cel Is
88.6
81.6
76.2
74.1
72.2
71.2
69.7
69.8
68.1
69.2
69.6
69.8
72.4
71.8
69.9
Mercury
Cel'ls
4.3
12.4
18.5
20.8
23.0
24.2
26.5
26.7
28.6
27.9
.27.2
27.2
24.2
24.6
24.8
All Other
7.1
6.0
5.3
5.1
4.8
4.6
3.8
3.5
3.3
2.9
3-2
3.0
3.4
3.6
5.3
Source: 1946 : "Diaphragm vs Amalgam Cells for Chlorine-Caustic Production"
by R.B. MacMullin, Chem. Industries. July 1947.
1956 onward : Chlorine Institute as of July 1 of year Indicated.
Source: The Chlorine Institute Inc.
73
-------
TABLE A-7
Col
CHLORINE CAPACITY AND PRODUCTION IN THE UNITED STATES
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Year
1951
1952
1953
1954
1955
1956
1957
1958
1959
I960 •
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
197*
Capaci ty
short
Tons/Day
5,937
6,800
8,200
9,750
10,150
10,300
13,960
14,405
14,697
15.503
16,404
17,245
18,939
21 ,216
23,238
25,124
28,276
29,131
28,588
29, 643P
30,310
Short Tons
2,517,913
2,608,690
2,797,279
2,903,723
3,421,107
3,797,702
3,947,688
3,604,538
4,347,118
4,636,939
4,600,791
5,142,876
5,464,080
5,945,215
6,517,079
7,204,372
7,679,868
8,444,459
9,375,906
9,763,702
9,352,437
9,873,371
10,303,471P
GAS PRODUCTION
Change from Previous Year
Tons
433,752
90,777
188,589
106,444
517,384
376,595
149,966
(343,130)
742,580
289,821
(36,148)
542,085
321,204
481,135
571,864
687,293
475,496
764,591
931,44?
387,796
(411,265)
520,934
430,100
Percent
20.81
3.61
7.23
3.81
17.85 '
1 1.00
3-95
(8.69)
20.60
6.67
(0.78)
11.82
6.24
8.29
9.62
10.54
6.60
9.96
11 .03
4.14
(4.21)
5.57
4.36
Average
Tons/Day
6,898
7,128
7,664
7,955
9,373
10,376
10,816
9,875
1 1,910
12,123
12,605
14,090
14,967
16,244
17,855
19,705
21 ,041
23,072
25,687
26,750
25,623
26,976 ,
28,229
Avg. Tons/Day
Highest Month
7,409(Dec.)
7,433(Jan.)
7,853(Apr.)
8,389(0ct.)
10,270(Nov.)
11 ,016(Dec.)
1 1 ,066(Sep.)
11 ,179 (Nov.)
12,555(Nov.).
!2,8l2(Mar.)
13,713(Nov.)
l4,731(Nov.)
15,733(Nov.)
17,007(Dec.)
19,173(Dec.)
20,650(Dec.)
22,491 (Nov.)
23,908(Dec.)
27,212(Dec.)
27, 795 (Oct.)
27,17S(Dec.)
28, 063 (Nov.)
Percent
Liquef led
46.6
50.3
53.0
54.6
54.8
55.5
52.9
55.5
51.4
51.7
53-9
53.9
53.5
52.5
53-5
53.3
51.2
50.0
46.7
45.4
47.9
49.8
50.8
LIQUID PRODUCTION
Short Tons
1,173,753
1,311 ,981
1 ,483,048
1 ,584,796
1,875,552
2,105,888
2,090,190
2,000,318
2,233,329
2,398,031
2,478,007
2,755,162
2,920,127
3,120,201
3,484,312
3,852,763
3,935,754
4,219,468
4,381 ,076
4,428,972
4,476,242
4,918,461
5,238,808
Average
Tons/Day
3,211
3,584
4,063
4,341
5,138
5,753
5,726
5,480
6,119
6,552
6,789
7,548
8,000
8 ,525
9,546
10,555
10,783
11,529
12,003
12,134
12,264
13,438
14,353
Price
Tank Cars
Cents/Lb.
2.70
2.70
2.70-2.93
2.93
2.93-3-05
3-05-3.15
3.15
3.15
3.15
3.15-3.25
3.25
3.25
3.25
3.25
3.25
3.25
3.35-3.45
3.45-3.65
3.65-3-75
3-75
3.75
3.75
SOURCE: Column 1 (Jan. 1 of year indicated) : Chlorine Institute
Column 2 for years 1923-1941 : "Chlorine in World War II", R.T. Baldwin, Armed Forces Chem. Jour.
(Oct. 1948)
Columns 2,6 6 8 for years 1942 : Current Industrial Reports, Series M28A, U.S. Dept. of Commerce
onwa rd
Column 8 for years 1914 through 1940 : Biennial Census of Manufacturers - "Made for Sale" [pulp industry not included].
Column 10 : Oi 1 , Paint & Drug Reporter thru 1971; Chemical Marketing Reporter 1972 onward.
Notes: Revisions are current to Dec. 74. Gas figures include amounts liquefied. Figures in parentheses are negative.
Columns 3,4,5,7 and 9 are computed by the Institute from columns 2 and 8 [Basis 365 or 366 days].
Legend: P - Preliminary; R - Revised from previous report; NA - Not Available.
Source: The Chlorine Institute Inc.
-------
TABLE A-8
U.S. SODA ASH PRODUCERS AND CAPACITIES
(short tons per year - 1973)
Producer
Allied
Allied
Allied
BASF
Diamond Shamrock
FMC
Kerr-McGee
01 in
PPG
Stauffer
Stauffer
Location
Baton Rouge, La.
Green River, Wyo.
Syracuse, N.Y.
Wyandotte, Mich.,
Painesville, Ohio
Green River, Wyo.
Trona, Calif.
Lake Charles, La.
Corpus Christi, Tex.
Green River, Wyo.
Westend, Calif.
Synthetic/Natural
S
N
S
S
S
N
N
S
S
N
N
Capacity
785,000
1,100,000
1,000,000
800,000
800,000
1,750,000
160,000
375,000
270,000
1,450,000
160,000
TOTAL
Source: Chemical Profiles, Schnell Publishing Co. Inc., New York.
75
-------
TABLE A-9
U.S. CAUSTIC POTASH PRODUCERS AND CAPACITIES
(short tons per year - 1973)
Producer
Capacity
Allied, Syracuse, N.Y 35,000
Diamond, Delaware City, Del 27,000
Diamond, Muscle Shoals, Ala 60,000
Hooker, Niagara Falls, N.Y. 53,000
Monsanto, Sauget, 111 60,000
Pennwalt, Calvert City, Ky 25,000
PPG, Corpus Christi, Tex 10,000
Sobin Chemicals, Niagara Falls, N.Y. ... 35.000
TOTAL 305,000
Source: Chemical Profiles, Schnell Publishing Co. Inc., New York.
TABLE A--10
U.S. SODIUM BICARBONATE PRODUCERS AND CAPACITIES
(short tons per year - 1973)
Producer Caj>acjLty_
Church & Dwight, Green River, Wyo 100,000
Church & Dwight, Syracuse, N.Y 100,000
Diamond Shamrock, Painesville, Ohio ... 28,000
BASF Wyandotte, Wyandotte, Mich 36'000
TOTAL 264>000
Source:
Chemical Profiles, Schnell Publishing Co. Inc., New York.
76
-------
APPENDIX B
CHLOR-ALKALI GLOSSARY
Brine - An aqueous salt solution.
Rustic - Characterized by the presence of hydroxyl ions in solution.
Common name for sodium hydroxide.
Electrolysis - Decomposition by means of an electric current.
Ion Exchange - A reversible chemical reaction between a solid and a fluid
by means of which ions may be interchanged from one substance to another.
f*ff Gas ~ The exhaust or tail gas effluent from the chlorine liquefaction
and compression process in a chlor-alkali plant. -nquetaction
77
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/7-76-0341
3. RECIPIENT'S ACCESSIONING.
4. TITLE AND SUBTITLE
ENVIRONMENTAL CONSIDERATIONS OF SELECTED ENERGY CON-
SERVING MANUFACTURING PROCESS OPTIONS. Vol. XII.
Chlor-alkali Industry Report
5. REPORT DATE
December 1976 issuing date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
Acorn Park
Cambridge, Massachusetts 02140
10. PROGRAM ELEMENT NO.
EHE624B
11. CONTRACT/GRANT NO.
68-03-2198
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S". Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA-ORD
is. SUPPLEMENTARY NOTES Vol_ m_Xi. EPA-600/7-76-034c through EPA-600/7-76-034k, and VIII-
XV, EPA-600/7-76-034m through EPA-600/7-76-034o, refer to studies of other industries
as noted below; Vol I, EPA-6QO/7-76-034a is the Industry Summary Report and VII.
16. ABSTRACT EPA-600/7-76-Q34b is the Industry Priority Report. ! '
This study assesses the likelihood of new process technology and new practices being
introduced by energy intensive industries and explores the environmental impacts of
such changes.
Specifically, Vol. XII examines options in the chlor-alkali industry relating to
diaphragm and mercury cell technology, including dimensionally stable anodes,
ion-exchange membranes and stabilized asbestos diaphragms in terms of relative
process economics and environmental/energy consequences.
Vol. III-XI and Vol. XIII-XV deal with the following industries: iron and steel,
petroleum refining, pulp and paper, olefins, ammonia, aluminum, textiles, cement'
glass, phosphorus and phosphoric acid, copper, and fertilizers. Vol. I presents the
overall summation and identification of research needs and areas of highest overall
priority. Vol. II, prepared early in the study, presents and describes the overview
of the industries considered and presents the methodology used to select industries.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Energy, Pollution, Industrial Wastes,
Sodium Hydroxide, Chlorine
Manufacturing processes'
Energy Conservation
Chlor-alkali,
environmental impact
13B
8. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
90
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
78
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