E^-600/2-76-014
Japuary 1976
Environmental Protection Technology Series
MOLECULAR SIEVE MERCURY CONTROL PROCESS
IK CHLOR-ALKALI PLANTS
industrial Environ mental Research
Office of Research and Development
U.S. Environmental Protectm Agency
Research Triangle Park, North Carolina 27711
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring ' . ; ' ; ;. ,'
5. Socioeconomic Environmental Studies '"' ':
This .report has-been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-014
MOLECULAR SIEVE
MERCURY CONTROL PROCESS
IN CHLOR-ALKALI PLANTS
by
M.Y. Anastas
Battelle Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-1323. Task 17
ROAPNo. 21ADH-008
Program Element No. 1AB014
EPA Task Officer: E.J. Wooldridge
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
January 1976
-------
ABSTRACT
The applicability of the PuraSiv Hg adsorption process to mercury
removal from the hydrogen byproduct and the end-box ventilation streams
from mercury cell chlor-alkali plants was investigated. The investigation
included the analysis of data obtained from testing of a system that is
currently in operation and technical information provided by the system
vendor together with that available in the open literature.
Although the measurements of mercury concentration in the hydrogen
byproduct stream entering the PuraSiv Hg adsorber taken during performance
testing of the control unit appear to be in error, measurements of the
outlet concentration indicate that a concentration less than 60 ppbv may
be achieved.
The economics of the PuraSiv Hg adsorption process were explored.
Available data indicate that the operating costs by this process vary between
0.58 and 0.33 per ton of chlorine produced for plants with capacities between
100 and 750 tons per day.
Mercury removal from the hydrogen byproduct stream may also be achieved
by either adsorption over treated activated carbon or by scrubbing with depleted
brine. Technical and economic data available to the investigator seem to
favor the use of these two processes for mercury control although the data base
thereon is not sufficiently developed to warrant a meaningful comparison.
iii
-------
TABLE OF CONTENTS
Page
INTRODUCTION 1
MERCURY-CELL CHLORINE PROCESS MERCURY AIR EMISSIONS AND CONTROL
ALTERNATIVES . . . 3
Description of the Mercury-Cell Process 3
Sources of Mercury Emissions 6
Mercury Control Technology in Chlor-Alkall Plants 10
TECHNICAL ANALYSIS OF MERCURY CONTROL BY MOLECULAR SIEVE
, ADSORPTION 20
General Description of Molecular Sieves 20
Use of Molecular Sieves for Mercury Removal from Gaseous
Streams 21
Performance of a PuraSiv Hg Mercury Adsorption System .... 22
Factors Affecting Performance of Molecular Sieve Mercury
Control Systems 31
ECONOMIC ANALYSIS 33
Capital Costs 33
Operating and Maintenance Costs 34
Total Annual Costs of PuraSiv Hg Adsorption . . 34
CONCLUSIONS AND RECOMMENDATIONS 37
REFERENCES . 40
APPENDIX A
CALCULATION OF AVERAGE MERCURY CONCENTRATIONS AND AVERAGE DAILY
EMISSIONS IN MOLECULAR SIEVE ADSORBER OUTLET A-l
APPENDIX B
CAPITAL, OPERATING AND MAINTENANCE, AND ANNUAL COSTS OF MERCURY
CONTROL PROCESSES B-l
-------
LIST OF TABLES
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Estimated Mercury Emissions from a 300 TPD Mercury-
Cell Chlorine Plant .
Approximate Material Balance for Molecular Sieve
Adsorption in a 100 TPD Plant
Summary of Test Data Obtained from a PuraSiv Hg Mercury
Adsorption Process
Mercury Emissions from a 200 TPD Mercury-Cell Chlorine
Plant ...
Capital Costs of Cooling/Demisting and PuraSiv Hg
Adsorption
O&M Costs of PuraSiv Adsorption
14
23
30
35
36
Table A-l. Calculation of Average Mercury Concentration for Cycle A-7
Table B-l. Capital Costs of Cooling/Demisting and List of
Equipment
Table B-2. Capital Costs and List of Equipment for PuraSiv Hg
Adsorption
Table B-3. Basis for Computation of Annual O&M Costs
Table B-4. Utility Requirements for Cooling/Demisting in a 100 TPD
Plant
Table B-5. Utility Requirements for PuraSiv Hg Adsorption in a
100 TPD Plant
Table B-6. O&M Cost Components for Cooling/Demisting, $1000
(Curve A, Figure B-2)
Table B-7. Incremental O&M Costs of Cooling/Demisting Attributed
to PuraSiv Hg, $1000
Table B-8. O&M Costs of PuraSiv Hg ($1000) Excluding Incremental
Cooling/Demisting Costs (Curve C, Figure B-2) ....
B-3
B-5
B-7
B-8
B-ll
B-13
B-14
B-15
-------
LIST OF FIGURES
Page
Figure 1. Basic Flow Diagram for Chlor-Alakli Mercury-Cell
Operation 4
Figure 2. Mercury Emission Control by Molecular Sieve Adsorption
from Hydrogen Byproduct Stream . 13
Figure 3. Mercury Control by Activated Carbon Adsorption ... 16
Figure 4. Depleted Brine Scrubbing for Mercury Removal from the
Hydrogen Byproduct Stream 19
Figure 5. Inlet and Outlet Mercury Concentration Profiles for a
Molecular Sieve Adsorber - Cycle 1 24
Figure 6. Inlet and Outlet Mercury Concentration Profiles for a
Molecular Sieve Adsorber - Cycle 2 25
Figure 7. Inlet and Outlet Mercury Concentration Profiles for a
Molecular Sieve Adsorber - Cycle 3 26
Figure 8. Inlet and Outlet Mercury Concentration Profiles for a
Molecular Sieve Adsorber - Cycle 4 .. 27
Figure 9. Inlet and Outlet Mercury Concentration Profiles for a
Molecular Sieve Adsorber - Cycle 5 28
Figure A-l. Effluent Mercury Concentration from PuraSiv Control
Unit - Cycle 1 A-2
Figure A-2. Effluent Mercury Concentration from PuraSiv Control
Unit - Cycle 2 A-3
Figure A-3. Effluent Mercury Concentration from PuraSiv Control
Unit - Cycle 3 A-4
Figure A-4. Effluent Mercury Concentration from PuraSiv Control
Unit - Cycle 4 A-5
Figure A-5. Effluent Mercury Concentration from PuraSiv Control
Unit - Cycle 5 A-6
Figure B-l. Capital Costs of Control of Mercury in the Hydrogen
Byproduct Stream B-4
Figure B-2. Operating and Maintenance Costs for Mercury Control
in Hydrogen Byproduct Stream B-10
vi
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TOPICAL REPORT
on
ENGINEERING ANALYSIS OF THE PURASIV HG
ADSORPTION FOR MERCURY CONTROL IN
MERCURY-CELL CHLORINE PLANTS
to
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH & DEVELOPMENT
ENVIRONMENTAL PROTECTION AGENCY
from
BATTELLE
Columbus Laboratories
INTRODUCTION
Mercury is a hazardous air pollutant that is emitted from three
gaseous streams resulting from the manufacture of chlorine by the mercury-
cell process. These are the hydrogen byproduct, end-box ventilation and
cell-room ventilation air streams. A number of control technologies are
commercially available for the control of the pollutant in the hydrogen
byproduct and end-box ventilation streams. Among these control alternatives
is adsorption of the mercury vapor in the PuraSiv Hg adsorption process
which is designed for recovery of mercury vapor and cyclic regeneration
of the adsorbent. Union Carbide Corporation (UCC), designer of the PuraSiv
Hg process claims that the level of control of the process is such that the
average concentration of mercury in the effluent gas stream is at or below
60 ppbv. The life of the adsorbent is also guaranteed for three years.
In an effort to determine the technical and economic feasibility
of the PuraSiv Hg process in its applicability to the stated purpose, the
U.S. EPA sponsored the study at hand. It is the objective of this study
-------
to determine (1) the technical feasibility of the control system on the
basis of the analysis of data independently obtained from testing of a .
PuraSiv Hg adsorption system currently in operation and from analysis of
information made available by the system vendor and (2) the economics of
the system.
-------
MERCURY-CELL CHLORINE PROCESS MERCURY AIR
EMISSIONS AND CONTROL ALTERNATIVES
Chlorine may be produced by electrolytic methods from fused
chlorides of aqueous solutions of alkali-metal chlorides. (1»2»3»^»5) In
the electrolysis of aqueous solutions of potassium or sodium chloride, chlorine
is produced at the anode, while hydrogen and potassium hydroxide or sodium
hydroxide are produced as a result of processes taking place at the cathode.
This requires that the anode and cathode products be kept entirely separate.
Consequently, many ingenious cell designs have been developed and refined; all
of these have been variations either on the diaphragm cell, or on a cell which
employs mercury metal as an intermediate cathode. Historically, these two processes
(4)
were developed more or less in parallel. In the United States, the mercury
process was an early leader, but shrunk to less than 5 percent of the installed
chlorine capacity in 1946. The use of the mercury cell since, has grown toward
28 percent of the installed U.S. chlorine capacity through 1968. Since then,
there has been a negative trend in the use of mercury cells. Chlorine production
in 1974 amounted to 33,000 tons per day of which 21 to 23 percent were
obtained from mercury cells. During the first three quarters of 1974,
demand for chlorine was high and plants were operating at 95 percent of
capacity or higher. Since then the operating rate has dropped to 83
percent. While the number of mercury-cell chlorine plants have not
increased recently, the introduction of "dimensionally stable" anodes
instead of graphite anodes increased the production of chlorine by mercury
cell processes.
Description of the Mercury-Cell Process
The use of potassium chloride brines for chlorine production is
entirely analogous to that of sodium chloride. The latter will serve as
the basis for the following discussion. The basic process flow sheet for
the production of chlorine and caustic soda is shown in Figure 1.
Sodium chloride may be obtained from brines or seawater. Whatever
the source, solid sodium chloride is the starting material fed to the process.
Purified saturated brine is fed continuously from the main
brine treatment section through the inlet end box to the electrolyzer
-------
BASIC TREATMENT CHEMICALS
(SODA ASH, CAUSTIC LIME,
ACID, CaCL2, ETC.)
SOLID
NaCL FEED
CHLORINE
PRODUCT
CHLORINE
OTHER
I
BRINE
DECHLORINATOR
SPENT BRINE
STREAM
RECYCLE
TREATED
MAIN BRINE
SATURATION,
PURIFICATION, AND
FILTRATION
BRINE
INLET
END-BOX-
END-BOX
VENTILATION SYSTEM'
AQUEOUS
LAYER
STRIPPED
- AMALGAM
END-BOX
VENTILATION SYSTEM
Hg PUMP
AQUEOUS LAYER
L
1
COOLING,
DRYING,
COMPRESSION, AND
LIQUEFACTION
ELECTROLYZER
I
— OUTLET END-BOX
_^.END-BOX
VENTILATION SYSTEM
•**— ' AQUEOUS LAYER
WATER COLLECTION
SYSTEM
END-BOX
' VENTILATION SYSTEM
HYDROGEN GAS
BYPRODUCT '
DECOMPOSER
(DENUDER)
Purified^
Water
AMALGAM
CAUSTIC SODA
SOLUTION
PRODUCT
PROPRIETARY TREATMENT CHEMICALS INCLUDE PRECIPITATORS,
FLOCCULANTS, POLYELECTROLYTES, AND SIMILAR MATERIALS
TION, AND JVCAUSTIC
FIGURE 1. 'BASIC FLOW DIAGRAM FOR CHLOR-ALKALI MERCURY^GELL OPERATION
(8)
-------
where it flows between a stationary graphite (or metal dimensionally
stable) anode and a flowing mercury cathode. The following reactions
take place in the mercury cell:
Anodic half-reaction: 2Cl~(aq) ->• C12(aq) + 2e
C12(aq) * C12(g)
Cathodic half-reaction: 2Na+ + Hg + 2e~ •»• 2Na(Hg)
Overall cell reaction: 2NaCl( j + Hg •*• Cl2(g) + 2NaHg.
The inlet box is a receptacle placed on the inlet and of the electro-
lyzer to provide convenient connections for the feed brine and the stripped
mercury returning from the decomposer. It also serves to keep the incoming
mercury covered with brine. The spent brine is recycled from the electro-
lyzer to the main brine treatment section of the plant; it may also be sent
through a dechlorination step in which it is vacuum treated and/or air blown.
The chlorine gas product formed at the anode leaves the
electrolyzer for further treatment. After cooling, the wet gas is dried
by scrubbing with concentrated sulfuric acid. The spent acid from this
step contains most of the mercury brought along by the wet cell gas. After
compression, the dry chlorine gas at elevated pressure either may be used
directly or may be subjected to a liquefaction step. It is not known whether
there are emissions of mercury to the atmosphere during cleanup of the chlorine
prior to sale.
The sodium amalgam flows continuously from the electrolyzer
through the outlet end box to the decomposer (denuder) where it is made
the anode to a short-circuited graphite or metal cathode (packed bed of
chips) in an electrolyte of sodium hydroxide solution. The outlet box is
a receptacle placed on the outlet end of the electrolyzer to provide a
convenient means to keep the sodium amalgam covered with spent brine and
at the same time to permit the physical separation of the two streams.
Purified water is fed continuously to the decomposer, where it reacts with
the sodium amalgam to produce sodium hydroxide solution as well as byproduct
hydrogen gas according to the following reactions. The following reactions
-------
take place in the denuder:
. ' V ' •'•',:+ f..*,:. •( ' •
Anodic (mercury) half-reaction: 2Na(Hg) -*• 2Na + Hg + 2e
Cathodic (graphite) half- reaction: 2H20 + ,2e~ _ + ,20H~ +:1H
Overall decomposition reaction: : •"
2Na(Hg) + 2H20 -» 2NaOH + HZ( , + Hg.
The high-purity caustic soda generally leaves the decomposer at the con-
centration of about 50 weight percent sodium hydroxide. , ,
The caustic soda solution from the decomposer usually is sent to
a filtration unit. The solid waste from the filter, which: contains the
precoat material, is usually sent to an externally fired retort similar
to that used for the secondary processing of waste mercury. The mercury.
thus recovered is returned to the cell for reuse. .
Filtered caustic solution at a concentration of 50 weight percent
may be concentrated further by evaporation to a 73 weight percent. sodium
hydroxide product. In some instances, this material is heated to drive off
the remaining water in order to produce anhydrous pellets or flakes of solid
sodium hydroxide. : , . - , " •
The byproduct hydrogen gas from the decomposer may be vented .to
the atmosphere, burned as fuel, or used. as a feed material to a process
after removal of the mercury therein. ,.,-...•
Sources of Mercury Emissions ,
The main sources of mercury emissions to the atmosphere from
mercury-cell chlorine plants are
(1) The hydrogen byproduct stream . ;
i ' i ' '
(2) The cell end-box ventilation air stream . ,
(3) The cell-room ventilation air. . • . . .,
The hydrogen byproduct stream leaving the decomposer at 180 iF
and 1 atm is saturated with mercury vapor and will carry unknown .
-------
amounts of mercury in the form of fine droplets which may be an order of
magnitude higher than the saturation value. Most of this mercury may be
removed by cooling in a surface exchanger to 110 F and passing through a
wire-mesh pad mist eliminator. The stream thus treated is saturated with
mercury vapor at 10 ppmv and may contain 3 to 10 times the saturation value
in the form of mercury droplets most of which are 3 micron in diameter
or less. At the 10 ppmv level, the mercury losses will be higher than
5 pounds per day for a 100 ton per day (TPD) plant.
Mercury and mercury compounds leave the cell/decomposer system
in the end-box ventilation air. The volume of ventilation air depends upon
the age of the plant, the type and specific physical configuration of the
cells and end boxes, and the standard operating procedures employed at a
particular location. In some cases, the volume flow rate of end-box
ventilation air may approach or exceed that of the hydrogen produced in
the decomposer. For some new cell modifications currently in operation,
the volume of the end-box ventilation air is usually equal to or less than
that of the hydrogen byproduct stream. In a certain plant the former is about
80 percent of the latter. Because of the wide variations in end-box construction,
it is difficult to specify the emissions. The best current intelligence
indicates that the mercury losses sustained in the untreated end-box
ventilation air range from about 0.1 to 1.2 pounds per 100 tons of chlorine
(4)
produced. These values are reasonable in view of the ranges of temperature,
degree of saturation, and ventilation-air volume to be expected.
The volume of cell-room ventilation air employed varies from
(45}
approximately 100,000 to 1,000,000 cfm for a 100 TPD plant. '' A part
of this air serves to cool the cells and to keep the cell-room temperature
within acceptable limits. The minimum amount of air required for this
purpose varies seasonally with geographic location, cell design, and the
age of the plant. Additional ventilation air is usually required to
remove mercury vapor or compounds from the working environment.
Estimates of the mercury losses, under normal conditions of operation, in
the cell room ventilation air range from about 0.5 to 5 pounds per 100 tons
of chlorine produced for plants of 100 to 150 TPD chlorine capacity. The
mercury emissions from plants larger than 100 to 150 TPD chlorine capacity
apparently are less than would be indicated by a direct proportion based on
increased production capacity. These estimates are consistent with the
-------
approximations obtained by multiplying the ventilation-air volume by the
Q
TLV concentration of 50 mg/m . On this basis emissions of 0.45 pounds/day
for 100,000 cfm and 4.5 pounds/day for 1,000,000 cfm of cell room ventilation
airflow may be expected. Thus, for some plants, the losses of mercury in
the cell room ventilation air may amount to more than the combined losses
in the hydrogen and the end-box ventilation.
Mercury enters the cell-room atmosphere as a result of a number
of operations or conditions:
• End box sampling procedures
• Removal of mercury butter from the end boxes
• Cell maintenance and rebuilding operations
• Other maintenance work which exposes the internal surfaces
of pipes and equipment
• Accidental spills of mercury
• Cell and mercury pump leaks
• Cell failure, and other unusual circumstances.
The number and variety of sources of mercury in the cell room air indicate
that careful plant operation and good housekeeping are essential in order
to minimize the amount of mercury emitted into the cell room air. On the
other hand, it is extremely difficult to completely eliminate the contamination
of the cell room atmosphere with mercury.
Typical emissions of mercury from a 300 TPD mercury-cell chlorine
plant are given in Table 1.
-------
TABLE 1. ESTIMATED MERCURY EMISSIONS FROM
A 300 TPD MERCURY-CELL CHLORINE
PLANT
Mercury
Emission Percent
Steam grams per day of Total
a
Hydrogen-Byproduct^ ' 8,300 89.63
Cell Room Ventilation^ 900 9.72
End Box Ventilation'0^ 60_ 0.65
Total 9,260 100.00
(a) Saturated with respect to both water and mercury
at 110 F and 1 atm. Does not include mercury mist,
Reference (4).
(b) Based on a ventilation rate of 1450 cfm per TPD
chlorine and a TLV of 50 micrograms mercury per
cubic meter at 70 F and 1 atm. Reference (5).
(c) Based on ventilation rate of 8500 scf (60 F and
1 atm.) air per. ton of chlorine and a mercury
concentration that is 1/10 of saturation @ 110 F.
-------
10
Mercury Control Technology in Chlor-Alkali Plants
The national emission standard for mercury from stationary sources,
including mercury-cell chlorine plants, limits the daily emission to 2,300
(9)
grams per day (GMPD). Recently, EPA proposed amendments to this mercury
emission standard which would raise the limit to 3,200 GMPD. ' The 2,300
GMPD limit is divided among the three sources of mercury air emissions such
that 1,300 GMPD may be emitted in the cell-room ventilation air and the
remaining 1,000 GMPD may be emitted in the hydrogen byproduct and end-box
(9)
ventilation streams.
Mercury emission control technology that is currently being employed
(including the molecular sieve adsorption process) is apparently capable of
achieving the 1,000 GMPD limit for both streams in the largest mercury cell
chlorine plants (about 750 TPD). As mentioned earlier, primary cooling and
demisting are a necessary precursor to the other control techniques as it
is capable of reducing the mercury concentration to about 1 ppmv (as vapor).
Other alternatives are reportedly available for reducing the latter concen-
tration to below 50 ppbv. If a daily emission of 500 GMPD is allowed for
the hydrogen byproduct stream in a 750 TPD plant then an adequate level of
mercury control will allow an effluent mercury concentration of about 250 ppbv.
For a 100 TPD chlorine plant, a concentration of about 1.0 ppmv may be allowed.
When preceded by cooling and demisting the control techniques (molecular
sieve and treated activated carbon adsorption and depleted brine scrubbing)
to be discussed below are capable of reducing the time-average mercury con-
centration to below 50 ppbv.
The end-box ventilation stream is usually of the same volumetric flow
rate (or less) as the hydrogen byproduct stream. Furthermore, control schemes
available for the latter are usually also available for the former.
There are several control processes that are potentially available
for control of mercury emissions from the hydrogen byproduct and end-box
ventilation air streams by reducing the vapor concentration from 1 ppmv to 60 ppbv,
These processes are usually preceded by secondary cooling and demisting. The
processes are:
-------
11
• PuraSiv Hg adsorption
• Sulfur- or iodine-impregnated activated carbon adsorption
• Depleted brine scrubbing
• Hypochlorite scrubbing.
Common to all three processes under consideration are two processing
steps prior to mercury vapor adsorption by molecular sieves or sulfur
impregnated activated carbon or scrubbing with depleted chlorinated brine.
The first step is cooling the hydrogen stream from about 180 F to 110 F using
80 F cooling water followed by mercury mist elimination in a wire-mesh pad mist
eliminator. In application of the device for collection of acid mist in sulfuric
acid plants, it has been found capable of removing 99 percent (plus) of particles
of 3 microns in diameter or greater (> 3y ) and 15 to 30 percent of particules
<3y . The concentration of mercury in the stream at this point (no F, 1 atm.)
will be the saturation value of 10 ppmv and (probably) an additional 20 to 30 ppmv
(equivalent) in the form of mercury mist. The second step involves compressing the gas
to 6 psig in a rotary blower followed by cooling to between 55 F and 65 F and passing
it through a tubular type mist eliminator which has a removal efficiency of 99
percent (plus) for particles < 3y in sulfuric acid-mist removal applications.
(13)
Measured values of mercury concentration downstream from such a tubular type
mist eliminator strongly indicate that the particulate removal efficiencies
reported for sulfuric acid mist are applicable for mercury mist since mercury
inlet concentrations that are 5 to 10 percent higher than the vapor saturation
value were observed.
In what follows the first three control technologies listed
above will be described. A flow diagram and approximate material balance
for a 100 TPD plant will be given. The design basis for the cooling/
demisting step will be as follows.
For all processes considered the cooling/demisting step involved
(1) cooling the hydrogen byproduct stream to 110 F at 14.7 psia in the primary
cooler from approximately 180 F, (2) mist elimination in a wire-mesh pad
demister, (3) compression in a rotary blower to 20.7 psia, (4) cooling to
60 F in the secondary cooler, and (5) mist elimination in a tubular-type
eliminator. The pollution control alternatives were assumed to reduce the
mercury concentration of about 1 ppmv, obtained after cooling and mist
elimination, to 60 ppbv.
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12
PuraSiv Hg Adsorption
A process for control of mercury in the hydrogen byproduct stream
(13)
has been developed by Union Carbide Corporation (UCC). The mercury vapor
(about 1 ppm) is removed from these streams by adsorption over a proprietary
adsorbent especially designed for such use.
A typical flow sheet of such a process is given in Figure 2. The
purpose of the two-bed system shown is such that at any time one of the beds
is undergoing adsorption while the other is undergoing regeneration. The
hydrogen byproduct stream is compressed to a pressure between 4 and 8 psig,
cooled to a temperature in the range 50 F to 70 F and passed through a tubular
type mist eliminator and steam heated to a temperature between 90 F and 100 F
before being introduced to the PuraSiv Hg adsorber. Adsorption of the mercury
occurs without a significant rise in temperature.
The concentration of mercury in the effluent is guaranteed by Union
Carbide to be lower than 60 ppbv on the average. Part of the adsorber effluent
(10 to 20 percent of the hydrogen from the decomposer) from the bed in which
adsorption occurs is used to regenerate the other bed. In a dual-bed system
designed for adsorption over a period of 24 hours, regeneration of the loaded bed
is carried out by heating the generation gas to a temperature between 450
to 500 F in an electrical heater and passing it through the bed for about
12 hours. Thereafter, the heater is shut off and the bed undergoes cooling
for about 12 hours. The gas from the bed undergoing regeneration is
cooled before mixing with the hydrogen byproduct stream from the decomposer.
The process can be designed for a turndown ratio of 5:1. The flow
through the rotary blower is the sum of the hydrogen byproduct and the
regeneration gas. Hence for the PuraSiv Hg adsorption process the cooling/
demisting equipment is 10 to 20 percent larger in capacity. The life of the
molecular sieve absorbent is guaranteed by the vendor to be not less than 3
years with effluent discharge of 60 ppbv. This period was used as the design
life for the adsorbent. An approximate material balance appears in Table 2.
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Regeneration
heoter
r
Bypass
Purified
hydrogen
stream
I Note: Adsorber I undergoing
regeneration add adsorber 2
undergoing adsorption.
Adsorber-2
TubuIqr
type mist
eliminator
Secondary
(Brine)
cooler
?C
""^^A^egenerat i <
gas
cooler
Knock-out
drum
sealed
rotary
blower
Primary
(Water)
Wire-mesh cooler
pad mist
eliminator and
seal pot
FIGURE 2. MERCURY EMISSION CONTROL BY MOLECULAR SIEVE
ADSORPTION FROM HYDROGEN BY-PRODUCT STREAM
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TABLE 2. APPROXIMATE MATERIAL BALANCE FOR MOLECULAR SIEVE ADSORPTION IN A 100 TPD PLANT
Stream
Number Description
1
2
3
4
5
6
7
8
9
10
11
12
13
14
(a)
(b)
(c)
Hydrogen Byproduct
from Decomposer
Hydrogen Byproduct
to the First Mist
Eliminator
Mercury and Water
from Separator
Gas to Blower
Mercury and Water
from Knock-out Drum
Gas to Secondary
Cooler
Gas to Tubluar Mist
Eliminator
Liquid Mercury and
Water
Gas to Preheater
Gas to Adsorber
Adsorber Effluent
Purified Gas
Regeneration Gas
Regeneration Gas to
Primary Cooler
Obtained at saturated vapor
At 60 F and 1 atm.
Hydrogen only.
Press
Psia
14.7
14.7
14.7
14.7
14.7
20.7
20.5
14.7
20.4
20.2
19.6
19.6
19.6
14.7
Temperature
F
180
110
110
110
110
110
60
60
60
100
100
100
100
180
conditions only. Extent
Mass
H2, Ibs/hr
234.7
270.0
unknown
270.0
unknown
270.0
270.0
unknown
270.0
270.0
270.0
234.7
35.3
35.3
of entrainment
(a)
Flow Ratev
H20, Ibs/hr Hg,
2207.0
231
unknown
231
unknown
.231
31
unknown
31.0
31.0
28.0
24.4
3.7
8.8 (max.)
not known.
Ibs/day
145.2
7.1
unknown
7.1
unknown
7.1
0.48
unknown
0.48
0.48
0.033
0.028
0.005
0.447
Volumetric
Flow rate,
SCFMOO
1,870
935
--
935
--
935
865
--
865
865
864
751
113
113 C
-------
15
The advantages and disadvantages of utilizing PuraSiv Hg adsorption
may be summarized as follows:
Advantages
1. Guaranteed performance of the ad-
sorption system.
2. Relative ease of operation and
maintenance.
3. The system does not require special
materials of construction. Carbon
steel is used throughout.
4. The recovered mercury is continuously
recycled to the manufacturing
process.
5. Applicable for mercury control in end
box ventilation air as is in the
hydrogen byproduct stream.
Disadvantages
Regeneration gas requirements
tend to limit the value of the
turndown ratio of the system
to a maximum value of 5:1.
Mercury adsorption efficiency
is dependent upon the relative
humidity of the adsorber inlet
gas stream. Control to levels
specified by the vendor is
necessary.
Sulfur-Impregnated Activated Carbon Adsorption
Mercury in the hydrogen byproduct stream can also be removed by
reaction with sulfur, to form mercury/sulfur compounds, in sulfur-impregnated
activated carbon. *• » » ' The temperature-enhanced chemisorption at 100 F
to 110 F takes place in a one- or two-bed system as shown in Figure 3. In
a two-bed system the FRP-lined (fiber glass reinforced plastic) absorbers
are in series with provisions for bypass or reversal of the flow through
the beds. The FRP lining is necessary to prevent vessel corrosion by the
products of reaction that contain sulfur. This scheme is used to effect a
maximum (100 percent) utilization and reliability of the adsorption system.
However, one-bed systems are currently in use. Here a small fraction
of the adsorbent remains unloaded in the "mass transfer zone" and cannot be
used since the emissions after breakthrough may exceed allowable limits.
-------
Tubular
type mist
eliminator
Secondary
(Brine)
cooler
Knock-out
drum
Water
sealed
rotary
blower
Primary
(Water)
Wire-mesh cooler
pad mist
eliminator and
seal pot
Hydrogen
byproduct
stream from
decomposer
FIGURE 3. MERCURY CONTROL BY ACTIVATED CARBON ADSORPTION
-------
17
Minor departures from the cooling/demisting steps reported
('14')
earlier are necessary in this case. Secondary cooling to 50 F and
reheating to 110 F are undertaken. The temperature of adsorption should
be kept below 150 F since H?S formation may occur. Calgon, the vendor of
the adsorbent, reports typical outlet concentrations below 50 ppbv that
may approach 1 ppbv.
A material balance similar to that presented in Table 2 was
performed. The only difference here is the absence of recycle. The hydro-
gen byproduct stream is heated to 100 F before entering the adsorber. A
one-bed design was considered rather than two beds in series since opera-
tional experience indicates that the reliability, length of service, and
(14)
adsorbent requirements are satisfactory for such a design. . Kinetic
considerations seem to dictate the use of an amount of adsorbent that is
sufficient for a 3-year service. Thereafter, the adsorbent may be shipped
to a processor for retorting of the mercury value therein. The loading
capacity of the adsorbent is about 20 pounds of mercury per 100 pounds of
adsorbent. Current designs in operation seem to favor a constant pressure
drop through the bed. This gives a bed depth of about 4 feet. A gas
residence time of 8 seconds in the bed is usually employed.
The projected advantages and disadvantages of utilizing the
treated-activated-carbon adsorption process may be summarized as follows:
Advantages Disadvantages
1. Relative simplicity of equipment 1. A Fiberglas-reinforced-polyester
design and layout. lining of the adsorption vessel
is necessary to prevent corrosion
2. Mercury adsorption to acceptably thereof when sulfur-impregnated
low levels (reportedly 1 ppb) carbon is used.
appears feasible.
3. Ease of equipment operation and
maintenance.
4. It is possible that mercury could be
recovered by retorting the spent
adsorbent, although the economics of
such a recovery operation are unknown.
-------
18
Advantages Disadvantages
Adsorption process applicable to
mercury from end-box ventilation
air as well as removal from the
hydrogen byproduct.
Depleted-Brine Scrubbing
Another method of mercury removal involves scrubbing the
hydrogen byproduct stream first with depleted brine obtained from the
mercury cell and then with 10 percent caustic soda to remove chlorine
vapors picked up in the depleted brine scrubber (Figure 4).' ' ' '
The cooling/demisting treatment steps are the same as before. The gas
is not heated prior to scrubbing. The minimum reported mercury concen-
/Q \
tration in the scrubber effluent is about 10 ppbv. In a current
operation where only depleted brine scrubbing is employed and gas cooling
to 80 F is undertaken (in the summertime) scrubber effluent mercury con-
/io \
centrations of about 30 ppbv have been reported.^ ' The scrubbers are
(2)
usually packed columns with a titanium or rubber lining.
However, for purposes of this study, the hydrogen stream at 60 F
is contacted with depleted chlorinated brine at 100 to 150 F in the brine
scrubber which is operated at an L/G ratio of about 10 to 12 gal per
3
1000 ft . This is followed by scrubbing with 10 percent caustic soda
to remove elemental chlorine that volatilizes into the gas in the depleted
brine scrubber. A reported L/G ratio in the caustic scrubber is of the
order of 20 gal. Depleted brine scrubbing is essentially a closed-loop
process. The mercury is recovered in the brine treatment process and in
the mercury-cell. Caustic scrubbing appears to consume very little caustic
soda because of the reportedly low chlorine concentrations in the gaseous
/I O\
effluent from the depleted brine scrubber. in any case, the caustic
scrubber liquid effluent is utilized in brine treatment.
-------
Depleted brine
to treatment
Depleted brine
from mercury cells
Brine
feed pump
Depleted
brine
scrubber
Caustic
scrubber
T
Tubular
type mist
eliminator
Secondary
(Brine)
cooler
Knock-out
drum
Water
sealed
rotary
blower
Wire-mesh
pad mist
eliminator and
seal pot
Tubular type
mist eliminator
Caustic
feed pump
Purified
Hydrogen
By-Product
Stream
Caustic
return pump
Primary
(Water)
cooler
Dilute
caustic jn.
"
Caustic out
to brine
treatment
Hydrogen
byproduct
stream from
decomposer
FIGURE 4. DEPLETED BRINE SCRUBBING FOR MERCURY REMOVAL FROM
THE HYDROGEN BY-PRODUCT STREAM
-------
20
The projected advantages utilizing depleted brine scrubbing may
be summarized as follows:
Advantages
1. Process streams used to scrub 1.
Mercury and chlorine are ob-
tained from the chlorine/caustic
manufacturing process to which 2.
they are recycled after use.
2. Mercury recovery is instantaneous. 3.
Disadvantages
Mercury removal capabilities are
not proved at the present time.
Corrosion resistant materials of
construction are necessary.
Maintenance requirements are
relatively high because of (1)
above and because of corrosive-
fluid pumping requirements.
TECHNICAL ANALYSIS OF MERCURY CONTROL
BY MOLECULAR SIEVE ADSORPTION
General Description of Molecular Sieves
Zeolites are crystalline hydrated alumino-silicates of the
alkali and alkaline earth elements. Structurally, they are framework
alumino-silicates which are based on an infinitely extending three-
dimensional network of A10, and SiO, tetrahedra linked to each other by
sharing all the oxygens. They may be represented by the general formula:
M2/n°'A1203'xSi02'yH2°
where x is greater or equal to 2 and n is the cation valence.
The framework contains channels and interconnected voids which
are occupied by the cation and water molecules.
. . The term molecular sieve was originated by McBain to define
porous solid materials which exhibit the property of acting as sieves on a
molecular scale.
-------
21
There are 100 types of synthetic zeolites. Only a few have
practical significance. Uncontrolled dehydration irreversibly alters
the framework structure and the positions of the cations such that the
structure collapses. To be used as molecular sieves the structure of the
zeolite after complete dehydration must remain intact.
Adsorption takes place on external surfaces as well as the
internal convoluted surface of the dehydrated microporous zeolite crystal.
Because of the inherent characteristics of the crystal structure of the
zeolite, the adsorption of a guest molecule depends partially upon its
polarity and polarizability.
Use of Molecular Sieves for
Mercury Removal from Gaseous Streams
The adsorption of mercury vapor on zeolite molecular sieves has
been known for a long time now. Earlier work in this area has been
(19)
thoroughly reviewed by Breck. He reports that as early as 1909,
F. Grandjean found that heated chabazite (a Class I, naturally occurring,
molecular sieve with a narrow interstitial channel diameter between 4.89A
and 5.58A) had mercury adsorption capabilities. Barrer and Woodhead^ ^'
concluded that the high adsorption of mercury vapor in air on this zeolite
was due to a chemical adsorption influenced by the presence of oxygen. The
adsorption process was found to be irreversible. However, the adsorption
of mercury under conditions approaching vacuum was reversible and the
capacity (in grams mercury adsorbed per 100 grams chabazite) of the adsorbent
decreased with decreasing temperature. Adsorption data obtained at elevated
temperatures showed (after extrapolation) that the mercury adsorption
/ *2
capacity of chabazite at 70 F was in the range 10 x 10 gms/100 gms.
(21)
Logan studied the adsorption of mercury vapor in hydrogen gas
over a synthetic molecular sieve (Union Carbide's 13X) and over chromic
acid-impregnated silica gel. At a mercury concentration of about 4.0
3 3
mg Hg per m and for breakthrough at a concentration of 0.001 mg Hg/m the
-------
22
capacity of the molecular sieve was found to be of the order of 10 to
10~ gm Hg /100 gm. The results for the molecular sieve suggest that
water vapor did not seem to affect the adsorptive capacity although the
heat of water adsorption caused a 90 F rise in temperature. Furthermore,
physical adsorption was seen to occur since the adsorptive capacity
increased with a decrease in temperature.
As mentioned earlier, a proprietary synthetic molecular sieve,
manufactured by UCC, is commercially available for adsorption of mercury
(22)
vapor from the hydrogen by-product and end box ventilation streams.
The adsorptive capacity of this molecular sieve is orders of magnitude
higher than that of 13X.
Performance of a PuraSiv Hg Mercury
Adsorption System
The PuraSiv Hg adsorption process is guaranteed by the vendor (UCC)
to control the concentration of mercury in the hydrogen byproduct stream to
(22)
a maximum average of 60 ppbv for a period of 3 years. The control
capability claimed for the system was tested by monitoring the mercury con-
centration in the streams influent to and effluent from the adsorption system
(12)
installed on a 200 TPD chlorine plant. The results of the test, carried
out two years after startup of the adsorption system, are summarized in Table
3. The inlet and outlet concentrations are plotted in Figures 5 through 9.
For purposes of this study, a process that is considered applicable
for controlling the mercury content of the hydrogen byproduct stream should be
capable of reducing the concentration of the pollutant to below a time
average of 60 ppbv. This limit has been arbitrarily set since (1) the
vendor of PuraSiv Hg adsorption systems (UCC) claims that such a condition
is met by their system and (2) this limit can probably be achieved by
alternative control technologies, namely, treated activated carbon adsorption
and depleted brine scrubbing.
-------
TABLE 3. SUMMARY OF TEST DATA OBTAINED FROM A PURASIV HG MERCURY ADSORPTION PROCESS
(a)
Adsorber Inlet Conditions
Adsorber Outlet Conditions
Cycle
1
2
3
4
5
(a) Source:
(b) Obtained
Time, hrs
during
24-hr
cycle
0-2
3.5-5.25
6.5-8.5
9.67-11.67
12.5-14.5
15.75-17.75
18.67-20.67
22-24
0-2
3-5
5.75-7.75
9-11
12-14
15-17
18-7.0
21-23
0-1.75
2-3.25
4.25-6.25
7.25-9.25
10.25-12.25
13.25-15.25
16.25-18.25
19.25-21.25
0-2
3-5
6-8
9-11
12-14
15-17
18-20
21-23
0-2
3-5
6-8
9-11
12-14
15-17
18-20
22-24
Reference 12.
Ave. ,
Pressure,
in., Hg
39.2
39.1
39.1
39.2
39.1
39.1
38.8
38.6
38.6
38.5
38.4
38.5
38.5
38.4
38.4
38.4
38.3
38.6
38.6
38.6
39.3
39.4
39.3
39.3
39.4
39.4
39.5
39.7
39.5
39.5
39.7
39.7
39.4
39.4
39.5
39.5
39.4
39.4
39.2
39.1
for mercury vapor pressure
. Ave . , ,
0 Te0p.,(a>
F
72
72
72
72
72
72
71
71
71
71
71
71
71
71
70
72
71
70
70
71
71
71
70
70
71
71
70
70
70
70
71
71
71
71
71
71
71
71
71
71
in mm Hg between
Measured
Ave., ,
Conc.,U;
ppbV
963
938
876
900
1,146
1,219
958
965
976
954
846
841
840
907
992
668
1,053
837
828
707
806
761
878
949
945
727
873
923
787
830
937
1,067
1,243
1,054
1,267
1,176
1,155
1,231
1,058
1,145
32 and 300
Hg
Cone, at,, \
Saturation, '
ppbv
1,397
1,400
1,400
1,397
1,400
1,400
1,346
1,353
1,353
1,357
1,360
1,357
1,357
1,360
1,297
1,426
1,364
1,291
1,291
1,353
1,329
1,326
1,268
1,268
1,326
1,326
1,261
1,255
1.261
1,261
1,316
1,316
1,326
1,326
1,323
1,323
1,326
1,326
1,333
1,336
F. log.nP - -3212.
Flow .
Rate/c)
scfm
2,431
2,412
2,467
2,513
2,461
2,414
2,383
2,386
2,386
2,377
2,354
2,350
2 , 350
2,350
2,285
2.330
2,395
2,334
2,351
2,403'
2,356
2,323
2.325
2,370
2,378
2,382
2,483
2,567
2,515
?.,!>(•?.
2,483
2,446
2,408
2,406
2,397
2,368
2,373
2,324
2,322
2,296
5/T + 8.025,
Ave'(a)
Temp.,
F
95.5
95.5
95.5
95.5
95.5
95.5
96.0
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.0
95.0
95.0
95.0
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
95.5
where T is
Ave . , .
Pressure,13'
in. Hg
38.1
38.1
38.1
38.1
38.1
37.9
38.1
38.1
38.1
38.1
38.1
37.9
36.6
37.9
37.9
37.9
38.1.
39. 3 e
39. 3 e
39.6(e)
38.9
38.9
38.9
38.9
39.1
39.1
39.1
38.9
38.9
3P.9
38.9
38.9
39.1
39.1
39.1
39.1
39.1
38.9
38.9
38.9
°K, Kirk & Othmer
Measured
Cone . ,
ppbv
55.4
3.1
<0.1
0.3
<0.1
1.1
95.9
429.5
57.4
53.6
0.4
0.2
0.2
0.4
26.4
38.6
55.0
1.9
0.4
0.1
0.1
0.2
0.2
8.1
4.7
0.2
0.1
0.1
0.1
0.1
3.6
120.1
37.4
0.2
0.2
0.1
0.1
0.1
11.0
425.9
Flow Rate
to Boiler
Vent."7
scfa
1.466
1.457
1.457
1,452
1,452
1,452
1,452
1,454
1,465
1,466
1,466
1,466
1,357
1,221
1,221
1,349
1,457
1,465
1,466
1,466
1,466
1,414
1.191
1,468
1,459
1,465
1,466
1.467
1,465
1,459
1,457
1.457
1,457
1,457
1,457
1,457
1,457
1.457
1,457
1,457
Encyclopedia of
Chemical Technology, Second Edition, 1967, Volume 13, p 221.
(c) Obtained from Reference 2 but adjusted to standard conditions at 1 atm and 60 F.
(d) Obtained from data on chlorine production reported in Reference 12 and by assuming a factor of 180.16 scfm per ton per hour.
(e) These values are incorrect.
-------
10,000
1000
X)
a.
o.
o
5
O>
X
Cycle:!
Inlet :D
Out let :O
UCC 3-year guaranteed average
outlet concentration
ei
w
PQ
td
M
C/3
OS
CJ
Cd
i
§
PM
Z
O
W
u
o
CJ
H
3
O
O
2
O
8 10 12 14 16
Absorption Cycle Time.hrs
-------
10,000
25
Legend
Cycle: 2
Inlet :D
Outlet : O
FIGURE 6. INLET AND OUTLET MERCURY CONCENTRATION
PROFILES FOR A MOLECULAR SIEVE ADSORBER
1000
Ed
CQ
Oi
O
CO
Q
Ed
td
O.I
I
I
I
I
8 10 12 14 16
Adsorption Cycle Time.hrs
18 20 22 24
Id
I
100
.a
a.
Q.
o
c
o
o
o>
X
UCC 3-year guaranteed average
outlet concentration
10
CO
Id
M
Cn
O
z
O
u
§
O
I
I
H
Ed
J
H
O
1.0
H
Id
z
vD
Cd
3
-------
10,000 r
1000
100
n
CL
o.
o
c
o
o
INLET AND OUTLET MERCURY CONCENTRATION
PROFILES FOR A MOLECULAR SIEVE ADSORBER
Cycle : 3
Inlet : D
Outlet : O
UCC 3-year guaranteed average
outlet concentration
ai
w
to
cm
o
CO
a
Cd
w
u
<
o
CO
u
§
a.
§
o
o
I
o
Di
w
H
w
H
O
Q
H
W
r^
w
8
o.
8 . 10 . 12 , 14 . 16 .
Adsorption Cycle Time, hrs
-------
10,000
FIGURE 8. INLET AND OUTLET MERCURY CONCENTRATION
PROFILES FOR A MOLECULAR SIEVE ADSORBER
Cycle
Inlet
Outlet
4
d
o
1,000
100
.0
a
o.
u
o
,UCC 3-year guaranteed average
outlet concentration
10
-A
\
i.o
O.I
I
I
12 14 16 18
Adsorption Cycle Time, hrs
20
22
24
26 28
-------
10,000
FIGURE 9.
1000 —
100
.a
a.
a.
u
c
o
o
CT
X
28
INLET AND OUTLET MERCURY CONCENTRATION
PROFILES FOR A MOLECULAR SIEVE ADSORBER
Cycle: 5
Inlet: D
Outlet: O
UCC 3-year guaranteed average
outlet concentration
I
8 10 12 14 16
Adsorption Cycle Time, hrs
18
20 22
24
-------
29
UCC's claim was tested through measurements of mercury inlet and
outlet concentrations in a PuraSiv Hg adsorption system used to control
mercury emissions in a 200 TPD plant. With the exception of the third cycle
the measurements of concentration were taken over five characteristic 24-hour
cycles of adsorption. The third cycle was terminated after 22.5 hours
because of an unscheduled plant shutdown. Mercury outlet cycle - average
concentrations were obtained by integration of the profiles given in Figures
5 through 9. The procedure is explained in Appendix A. The amount of
mercury emitted was calculated from this average concentration and the
average hydrogen flow leaving the system. The results are given in Table 4.
Upon inspection of the values of average concentration given in Table 4, it
may be seen that except for the first two cycles, UCC's guarantee of the
outlet concentration was met after 2 years of service. The average concen-
tration was 65 percent higher than the guaranteed 60 ppbv for the first cycle
and 25 percent higher for the second cycle.
The PuraSiv Hg system which was tested on behalf of EPA as a
background to this analysis was operated at mercury levels beyond those
normally expected in a mercury-cell chlorine plant of the stated capacity—
namely 200 TPD. This situation arose as a result of complications caused
by an anticipated expansion of the chlorine-producing capacity of the
(27) ^
plant. As a result, abnormally large quantities of hydrogen were being
recycled. At the time the testing was in progress the hydrogen flow to the
(13)
adsorber was about 2400 SCFM. UCC-recommended design criteria pre-
dicted a flow of about 1700 SCFM. Furthermore, secondary cooling to about
72 F was employed instead of the recommended cooling to 60 F. These two
factors tended to increase the amount of mercury flowing into the adsorber.
Since the hydrogen stream always is saturated with mercury, the increased
flow through the cooling/demisting equipment causes an increase in the
total amount of mercury to the adsorber. It is estimated that about 150
percent more mercury was carried to the adsorber as a result of this mode
of operation.
The PuraSiv Hg system that was the subject of EPA testing reportedly
has been overdesigned with respect to the amount of adsorbent used therein.
Although this has been confirmed by the system designer-UCC, no information
on the system "overdesign" has been made available.
-------
30
TABLE 4. MERCURY EMISSIONS FROM A 200 TPD
MERCURY-CELL CHLORINE PLANT
Number of
24-Hour
Test
Period
1
2
3
4
5
24-Hour
Average
Chlorine
Production,
rate
TPD
194
183
190
198
194
24-Hour
Mercury
Emission,
gm
49.6
35.4
16.3
19.1
26.0
24-Hour
Average
Mercury
Concentration,
ppbv
99
75
33
37
51
-------
31
The results of testing indicate that the guaranteed average mercury
concentration of 60 ppbv was being achieved by the adsorption system after 2
years of operation. However, it was not possible to verify UCC's claim that such
effluent mercury levels could be achieved after 3 years of system operation.
The mercury inlet concentrations obtained from Reference 12 are
too low as a result of experimental error. This is immediately apparent
upon comparison of the data on inlet concentration with the saturation
value at the reported inlet stream temperature and pressure. The measured
value should be higher than the saturation value.
Factors Affecting Performance of
Molecular Sieve Mercury
Control Systems
The performance of the molecular sieve adsorbent used in control
of mercury in the hydrogen stream is affected mainly by (1) the number of
adsorption/regeneration cycles to which it has been subjected and (2) the
concentrations of mercury and water vapors in the influent stream.
The adsorption system design is such that a maximum average
effluent mercury concentration of 60 ppbv is guaranteed for a period of
(22)
3 years. With the passage of time this average concentration of the
effluent is expected to gradually increase from a level which is well
below that guaranteed to one which is close to it. This loss in performance
is directly caused by the gradual, but cumulative, destruction of the micro-
pores of the adsorbent as a result of its exposure to the relatively high
temperature swings between the regeneration temperature of about 500 F and
the adsorption temperature of about 100 F. Investigators of the Bureau of
Mines studied the sulfur dioxide adsorption/desorption characteristics
of UCC synthetic molecular sieve 13X. The adsorption experiments were
carried out at a temperature of 79 F and a total pressure of 26.38 in. Hg
for sulfur dioxide concentrations ranging from 1 to 9 percent by volume.
The space velocity employed was of the order of 400 vol/vol/hr. The
time for complete saturation or loading of adsorbent with sulfur dioxide
-------
32
was a.bout 36 minut.es. The observed loading ranged from 27 to 30 Ib S0_
per 100 Ib adsorbent, being higher for the feed richer in SCL. Desorption
.(or regeneration) for about 2.3 hours was carried out at tmperatures of
about 700 F while the space velocity of nitrogen purge gas was maintained
at 4 vol/vol/hr. A 60 percent drop in the capacity of 13X was observed after
13 cycles of adsorption/regeneration. Thereafter the capacity of the molecular
sieve seemed to stabilize at the lower level. While no independently obtained
information on the long-term effects of cyclic heating (regeneration) is
available for the molecular sieve under consideration, field tests carried
out by UCC indicate a 10 percent loss in loading capacity over a period of
2 years. Two types of loss in activity may occur for the adsorbent. The
first may be a short-term loss taking place during earlier cycles as.observed
for 13X. The second may be a long-term loss as reported by UCC. Both of these,
however, can be anticipated by system design. Analysis of data on effluent
mercury concentration from a molecular sieve adsorption unit indicates that the
design does anticipate this loss in activity as evidenced by cycle
average concentrations that are usually lower than that guaranteed [60 ppbv]
i by UCC. Field tests indicate that a 2-year sieve life is demonstrated.
Unspecified concentrations of water vapor in the gas stream
undergoing adsorption affect the performance of the molecular sieve by
reducing its selectivity toward mercury. The condition of relative humidity
of the hydrogen stream to the adsorber is considered proprietary by UCC.
High water concentrations increase the amount of adsorbent needed to remove
a;given amount of mercury. While no data on the effect of relative
humidity on adsorption capacity are available, it has been found that a
design relative humidity of 50 percent does not adversely affect the
selectivity to the point where "uneconomical" loadings are produced.
-------
33
ECONOMIC ANALYSIS
In this section an evaluation of the economic feasibility of
mercury control by PuraSiv Hg adsorption is developed and discussed.
While a comparison of the capitalized costs of this system with other
potentially available alternatives (treated activated carbon adsorption
and depleted brine scrubbing) would be useful in assessing their economic
feasibility, the lack of an adequate data base on the cost and perfor-
mance of alternative systems does not permit the development of such a
comparison.
Capital Costs
The capital costs of control by PuraSiv Hg adsorption were
generated from data available on actual operating systems and from data
provided by UCC. Where actual economic data were lacking, conceptual
designs based on known process operating characteristics were performed.
(24 25)
In these conceptual designs the module technique recommended by Guthrie '
was used. Briefly, this approach to capital cost estimation involves the
use of "experience" multipliers to obtain the installed costs of major
components of a processing system from known purchased equipment costs.
As explained in Appendix B, the installed equipment costs obtained in
this manner include the costs of foundations, piping, instrumentation,
insulation, and paint. The estimates of capital cost reported would
normally be correct to within a ±30 percent range that is characteristic
(26)
of such estimates. The costs reported are end-of-1974 estimates for
a value of the Marshall and Stevens Index of 398. Where conceptual
designs were necessary (as in the case of cooling/demisting) the capital
costs were estimated for plants of 100 and 750 TPD capacity, this range
representing 87 percent of the mercury cell-chlorine plants.
A conceptual design for the cooling/demisting step was performed
in order to obtain the incremental capital and operating
costs incurred by recycling the regeneration gas in PuraSiv Hg adsorption.
The cost estimates obtained from the conceptual design were about 50
-------
34
(13)
percent lower than those supplied by UCC. The actual cost for a
PuraSiv Hg adsorption system was found to be 70 percent higher than the
estimates reported by UCC for a 750 TPD plant. The estimated
capital costs for cooling and demisting and PuraSiv Hg adsorption are
given in Table 5. Appendix B outlines how they were obtained.
After the addition of the incremental (15 percent) costs of higher
cooling and demisting capacity which is necessary in the case of
PuraSiv Hg adsorption, it was found that the capital costs were in
the range of 853 and 313 dollars per TPD for plants with chlorine
capacities ranging from 100 to 750 TPD.
Operating and Maintenance Costs
The operating and maintenance (O&M) costs include those incurred
annually for (1) operating labor, (2) cooling water, electricity, and
steam, (3) raw materials and chemicals, (4) local property taxes and
insurance, and (5) maintenance labor and materials. Details of the esti-
mated O&M costs for cooling/demisting and PuraSiv Hg adsorption and the
method by which they were obtained are given in Appendix B.
The PuraSiv Hg adsorption process is a mercury recovery
process. Therefore, a credit for mercury recovery was included. Since
primary and secondary cooling are necessary precursors to the adsorption
processes, a mercury credit was not taken for the former. The O&M
costs of PuraSiv Hg adsorption (including costs of additional cooling/
demisting capacity) were found to vary between 0.24 and 0.14 dollars
per ton of Cl_ for plants in the chlorine capacity range of 100 to 750
TPD. A summary of O&M costs is given in Table 6. .
Total Annual Costs of PuraSiv Hg Adsorption
The total annual costs of control by PuraSiv Hg adsorption
consist of the sum of the operating and maintenance costs, adsorbent
replacement costs, and costs incurred for depreciation of the capital
investment over its life. Furthermore, 15 percent of the depreciation
-------
35
TABLE 5. CAPITAL COSTS OF COOLING/DEMISTING
AND PURASIV HG ADSORPTION
Capital Costs, $1000
Cl2 Capacity
TPD
100
250
500
600
750
Thousand
Tons per
Year
34.7
86.7
173.4
208.0
260.0
Cooling/
Demisting
143.0
269.6
435.6
494.1
576.6
Incremental Cooling/
Demisting
Costs Attributed
to PuraSiv HgOO
14.3
26.7
43.6
49.4
57.7
PuraSiv Hg
Adsorption
71.0
107.6
147.4
160.1
177.2
Total
PuraSiv Hg
and Incremental
Cooling/Demisting(b)
85.3
134.3
191.0
209.5
234.9
(a) Obtained by computing the difference in capital costs between a plant of the
stated capacity and another that is 15 percent larger. Thus the incremental
cost at 100 TPD is 5907(100)°-692[ (1.15)0'692- 1].
(b) Total includes PuraSiv Hg adsorption and incremental cooling/demisting at
stated capacity. Depreciation costs computed from numbers in this column
are given in Table 6.
-------
TABLE 6. O&M COSTS OF PURASIV ADSORPTION
Cl Capacity
Thousand
Tons per year
34.7
86.7
173.4
208.0
260.0
Depreciation
$1000)
20.3
37.6
62.9
72.7
86.2
Costs of
PuraSiv Hg
Adsorption
Per Ton
of C12, $
0.58
0.43
0.36
0.35
0.33
(a) Depreciation computed using capital costs in Column 6 of Table 5 assuming
10 year period.
(b) Includes depreciation.
OJ
-------
37
cost of cooling/demisting needs to be added for reasons previously
mentioned.
The capital investment for all processes was depreciated over
a period of 10 years. This is an average equipment life in the chemical
( 26)
process industries. The length of the adsorbent guarantee of 3
years was taken as the life of the adsorbent. Table 6 also gives the variation
with capacity of the annual costs and the costs per ton of chlorine
produced. In the capacity range of 100 to 750 TPD it is seen that the
costs of PuraSiv Hg adsorption per ton of Cl. will vary between $0.58
and $0.33.
CONCLUSIONS AND RECOMMENDATIONS
The data generated from EPA-sponsored tests together with
other available information seem to indicate that PuraSiv Hg adsorption
is effective in the removal of mercury vapor present in concentrations
of the order of 1500 ppbv from the hydrogen by-product stream obtained
in the manufacture of chlorine by the mercury-cell process. Removal
to levels below 60 ppbv was observed in the above-mentioned tests.
There is evidence that sulfur-impregnated activated carbon absorption
and depleted brine scrubbing may be effective in removal of the pollu-
tant from the hydrogen by-product stream. However, testing of the other
systems for performance is believed to be necessary at this time in order
to clearly define those technologies and to establish their capabilities
to decrease mercury concentrations to desirable levels (below 60 ppbv).
Operators and vendors of treated activated carbon control systems claim
that such levels of mercury concentration are easily achievable. Like-
wise the operator of a depleted-brine scrubbing system (in-house design)
claims maximum effluent mercury emissions of 0.03 Ib per day from the
hydrogen generated in a 150 TPD chlorine plant (about 30 ppbv). Apparently
this is being achieved with one-step cooling of the stream to 75 to 80 F.
It also is claimed that chlorine concentration in the gaseous effluent
from the depleted brine scrubber is so. low that caustic scrubbing has
been deemed unnecessary.
When the operator of a mercury-cell chlorine process is faced
with the problem of choosing a mercury control process, the factors which
-------
38
are most likely to influence his decision as to which control process is
most attractive are
(1) Performance
(2) Reliability
(3) Economic feasibility relative to other processes
(4) Ease of operation and flexibility of design.
As to performance, PuraSiv Hg adsorption does seem to achieve
average mercury effluent concentrations lower than 60 ppbv after two
years of operating such an adsorption system. This has been observed in
the testing of a unit designed to control mercury vapor in a 200 TPD
chlorine plant. This has been found to be true from data obtained by
the monitoring of adsorber effluent mercury concentration in three out of
five adsorption cycles. In the two cycles where the guaranteed level of
60 ppbv was not achieved, the departure amounted to 60 percent in the first
and 25 percent in the second. This departure may be attributed to either
operating the adsorption unit at levels above those recommended by the
design value with respect to hydrogen flow rate and to insufficient
cooling of the hydrogen stream prior to mercury adsorption at the time of
testing. Cooling to 71 F was employed instead of the recommended 60 F.
Evidence accumulated from the operators and/or vendors of depleted brine
and treated activated carbon adsorption systems indicates that these
processes are potentially capable of achieving the same level of control
as PuraSiv Hg adsorption.
From available information on the PuraSiv adsorption system, an
availability greater than 95 percent may be inferred. The process involves
a relatively simple equipment layout and the materials of construction are
not highly specialized. Carbon steel is used throughout. The adsorption
system is easy to operate and can be designed in such a manner that a high
degree of automation may be achieved.
In summary, it is concluded that
(1) PuraSiv Hg adsorption is a technically viable
and feasible mercury control alternative of
the end-box and hydrogen by-product streams in
mercury-cell chlorine plants
(2) Depleted brine scrubbing and treated activated
carbon adsorption are potentially feasible mercury
control processes in mercury-cell chlorine plants
-------
39
(3) The economics of PuraSiv Hg adsorption are such
that the total annual costs are in the range of
0.58 to 0.33 dollars per ton of Cl, for plant
capacities in the range of 100 to 750 TPD with
respect to chlorine production. These cost
estimates are based on an adsorbent life of three
years as guaranteed by UCC. The vendors guarantee
of adsorbent life could not be independently
verified. However, in EPA testing of a PuraSiv Hg
system, the adsorbent was found effective after
two years of system operation.
On the basis of this study it is recommended that an engineering analysis
similar to the study at hand be performed for depleted brine scrubbing
and treated activated carbon adsorption.
-------
40
REFERENCES
(1) Shreve, R. N., "Chemical Process Industries", Third Edition, McGraw-
Hill, New York (1967).
(2) Anonymous, "Atmospheric Emissions from Chlor-Alkali Manufacture", A
cooperative study project MCA & PHS, Publ. No. AP 344, EPA
(January, 1971).
(3) Anonymous, "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",
Reported prepared for Office of Air and Water Programs, U.S. EPA,
Publ. No. EPA-440/l-74-007-a (March, 1974).
(4) Stambaugh, E. P. and Hall, E. H., "Topical Report on Basis for
National Emissions Standards on Mercury", to Office of Air Programs,
U.S. EPA, Contract No. EHSD 71-33 (June 15, 1971).
(5) Anonymous, "The Cost of Clean Air, 1974", Final Report to U.S. EPA
by Battelle's Columbus Laboratories under Contract No. 69-01-1538
(January 15, 1974).
(6) Anonymous, "Can Chloride Cutbacks Hold the Price Line?", Chemical
Week (March 12, 1975).
(7) Laubusch, E., The Chlorine Institute, personal communication
(January and February, 1975).
(8) Anonymous, "Control Techniques for Mercury Emissions from Extraction
and Chlor-Alkali Plants", U.S. EPA, Office of Air Programs, Research
Triangle Park, North Carolina, Publ. No. AP-118 (February, 1973).
(9) Federal Register, _38 (66), 8831 (April 6, 1973).
(10) Anonymous, American Metal Market (October 29, 1974).
(11) Anonymous, "Engineering Analysis of Emissions Control Technology for
Sulfuric Acid Manufacturing Processes", Final Report to PHS, US DHEW,
Contract CPA22-69-81 (March, 1970).
(12) Chehaske, J. T. and Cline, J. R., "Testing of a Molecular Sieve Used
to Control Mercury Emissions from a Chlor-Alkali Plant", Report to
EPA, Control Systems Laboratory, Research Triangle Park, North
Carolina, Contract No. 68-02-1406, Task Nc. 3 (January, 1975).
(13) Based on information made available to Battelle's Columbus Laboratories
by Union Carbide Corporation in January and February, 1975.
-------
41
REFERENCES
(Continued)
(14) Istas, L. J., Manager, Engineering, Pennwalt Corporation, Calvert
City, Kentucky, letter to M. Y. Anastas (February 5, 1975).
(15) Cunniff, F. T., Manager - Product Development, Calgon Corporation,
Pittsburgh, Pennsylvania, letter to M. Y. Anastas (March 26, 1975).
(16) Dreibelbis, J. A. and Joyce, R. S., "Method of Removing Mercury
Vapor from Gases", U.S. Patent 3,194,629 (July 13, 1965).
(17) Clapperton, J. A., Manager of Manufacturing Industrial Chemicals,
PPG Industries, Pittsburgh, Pennsylvania, letter to M. Y. Anastas
(February 28, 1975).
(18) Spomer, M., BASF Wyandotte, Port Edwards, Wisconsin, communication
with M. Y. Anastas (April 3, 1974).
(19) Breck, D. W., "Zeolite Molecular Sieves - Structure Chemistry and
Use", John Wiley, New York (1974).
(20) Barrer, R. M. and Woodhead, M., transactions of the Faraday Society,
.44, p 1001 (1948).
(21) Logan, W. R., "Mercury Removal from Hydrogen Gas Streams, Journal
of Applied Chemistry, 1.6_, p 285 (October, 1966).
(22) Collins, J. J., Miller, W. C., and Philcox, J. E., "The PuraSiv Hg
Removal and Recovery", paper presented at the 65th Annual Meeting of
the Air Pollution Control Association, Miami Beach, Florida
(June, 1972).
(23) Martin, D. A. and Brantley, F. E., "Selective Adsorption and Recovery
of Sulfur Dioxide from Industrial Gases by Using Synthetic Zeolites",
U.S. DOI, Bureau of Mines, RI 6321 (1963).
(24) Guthrie, K. M., "Capital Cost Estimating", Chemical Engineering
(March 24, 1969).
(25) Guthrie, K. M., Process Plant Estimating Evaluation and Control.
Craftsman Book Company of America, Solana Beach, California (1974).
(26) Peters, M. S. and Timmerhaus, K. D., Plant Design and Economics for
Chemical Engineers, 2nd Edition, McGraw-Hill, New York (1968).
-------
APPENDIX A
CALCULATION OF AVERAGE MERCURY CONCENTRATIONS
AND AVERAGE DAILY EMISSIONS IN MOLECULAR SIEVE
ADSORBER OUTLET
-------
APPENDIX A
CALCULATION OF AVERAGE MERCURY CONCENTRATIONS
AND AVERAGE DAILY EMISSIONS IN MOLECULAR SIEVE
ADSORBER OUTLET
3
Data on the 2-hour average mercury concentration (in rag per Nm )
in the adsorber outlet obtained from Reference 12 was plotted versus
cycle time on semi-log graph paper. The average concentration as reported
was considered to represent the average time in the interval. A smooth
curve was drawn through the points and extrapolated to both ends of the
cycle, namely, 0 and 24 hours. The extrapolation was such that the cycle
end points of the outlet concentration profile did not exceed the inlet
concentration. Plots of the outlet concentration profiles for cycles
1 through 5 are given in Figures A-l to A-5.
The average concentration was obtained by integration of the
outlet concentration profile according to the expression
f&2
H = _1 H(e)d0 (A-l) .
Vei. ^
Where H is the 2-hour average concentration and Q is the cycle time in hours.
Linear portions of the semi-log plot were fitted to the equation
H(e)=E1010 (A.2) f
Integration of this function gives
ft
I = f 2 H(e)d0 = 2 1;031 (10192 - 1019l) (A-3) . ,
el ' .
Where the curve is not linear it was divided into smaller linear
segments to which the equations given above were applied. The cycle average
concentration was obtained by summing the I's and dividing by the cycle time
of 24-hours. An example calculation is given for cycle 2 in Table A-l. The
3
average concentration obtained was 0.62 mg/Nm „
-------
A-2
o
o
c.
0
o
o
O.I —
0.01 —
0.001
8 10 12 14 16
Hours in Cycle (24 hrs total)
18
20
22
24
FIGURE A-l.
EFFLUENT MERCURY CONG. FROM PURASIV CONTROL UNIT
Date: 24-25, 1975
Cycle: 1
Plant: Sobin - Orrlngton, Maine
-------
A-3
o
8
I
E
6
§
o
0.001
Ave inlet cone. - between
21 and 23 hours
0.01 —
8 10 12 14 16
Hours in Cycle (24 hrs total)
FIGURE A-2. EFFLUENT MERCURY CONC. FROM PURASIV CONTROL UNIT
Date: 25-26, 1975
Cycle: 2 - Adsorber 2
Plant: Sobin - Orrington, Maine
-------
A-4
O'
E
i_
o
c
o>
E
d
c.
O
o
0.001
- extrapolation
O.Ol —
8" 10 " 12 14 16
Hours in Cycle (24 hrs total)
FIGURE A-3. EFFLUENT MERCURY CONG. FROM PURASTV CONTROL UNIT
Date: 26-27, 1975
Cycle: 3
Plant: Sobin - Orrington, Maine
-------
10
A-5
Note: extrapolation
1.0
o
E
t_
o
10
c'
o
o
O.I
0.01
0.001
J—i—ua
8 10 12 14 16
Hours .in Cycle (24 hrs total)
FIGURE A-4. EFFLUENT MERCURY CONG. FROM PURASIV CONTROL UNIT
Date: September 27-28, 1974
Cycle: 4
Plant: Sobin - Orrington, Maine
-------
A-6
10
1.0
o
E
o
o>
u
c
o
O
0.01
0.001
o
2 4 6 8 10 12 14 16
Hours in Cycle (24 hrs total)
FIGURE A-5. EFFLUENT MERCURY CONG. FROM PURASIV CONTROL UNIT
Date: September 28-29, 1974
Cycle: 5
Plant: Sobin - Orrington, Maine
-------
A-7
TABLE A-l. CALCULATION OF AVERAGE MERCURY
CONCENTRATION FOR CYCLE
Segment
1
2
3
4
5
6
7
8
61
0
4
6
8
16
18
20
22
92
4
6
8
16
18
20
22
24
Hl
0.48
0.48
0.006
0.002
0.002
0.06
0.65
3.4
H2
0.48
0.0062
0.0022
0.002
0.06
0.65
3.4
5.5
I
1.920
0.218
0.008
0.016
0.034
0.495
3.320
8.848
El = 14.86
Have = 14.86 =0.62 mg/Nm3
24
-------
A-8
The daily mercury emission was obtained by multiplication of the
average cycle concentration with the total hydrogen gas flow leaving the
process computed from the cycle average chlorine production in tons per
hour. Thus for cycle 2:
Nm [ 70 F and 1 atm] per day
= 7492.0 X (TPD) average
= 7492.0 X 7.64
= 57,240
3
grams Hg per day =H xNm per day
El Vc
= 0.62 *. 57.240
1000
= 35.4
ppbv - Hg =120.65 XHave
= 75
For the other cycles the results are given in Table 3.
-------
APPENDIX B
CAPITAL. OPERATING AND MAINTENANCE. AND ANNUAL
COSTS OF MERCURY CONTROL PROCESSES
-------
APPENDIX B
CAPITAL. OPERATING AND MAINTENANCE..AND.ANNUAL
COSTS OF MERCURY CONTROL PROCESSES
Capital Costs
Where actual economic data were lacking, conceptual designs
based on schematic flow sheets were performed for the mercury removal
processes considered. The capital costs were obtained from sizing
process equipment for a 100 TPD plant and obtaining the Installed costs
(12)
of major equipment using Guthrle's modular technique. ' The
equipment cost for a 750 TPD plant was obtained in a similar manner.
The capital costs for the 100 and 750 TPD cases were fitted to the
equation:
C = A-L (TPD)n (B-l)
The conceptual designs were carried out for cooling/demisting (without
recycle) and molecular sieve and treated activated carbon adsorption only.
The capital costs for depleted brine scrubbing were obtained from published
data(3) and data supplied by PPG.^
Cooling/Demi sting
This step involves the use of five major items of equipment.
The first was cooling of the hydrogen by-product stream from the decomposer
at 180 F to 110 F at a pressure of 1 atm, using 80 F cooling water, in a
shell and tube heat exchanger. The second is a wire-mesh pad mist
separator which in sulfuric acid mist removal applications is capable of
removing nearly 100 percent of mist particles 3 microns in diameter or
larger but removes only 15 to 30 percent of particles less than 3 microns
in diameter. The third item of equipment is a water-sealed rotary blower
followed by a knock-out drum in which pressure of the gas is increased to
about 20.7 psia. The gas is then cooled to 60 F in a shell and tube
exchanger using a chilled brine as coolant. A tubular-type mist eliminator
-------
B-2
which reportedly removes 99+ percent of particles smaller than 3 microns
follows the secondary cooler.
A list of equipment and associated costs appears in Table B-l.
All costs were updated to a Marshall and Stevens installed equipment
index of 398. Unless indicated otherwise all costs were obtained from
Reference 25 in the text. The capital costs obtained for cooling/ demisting
were found to follow relation:
CCD = 5907 (TPD)0'692 (B-2)
where C is the cost in dollars and TPD is the daily chlorine capacity
UD
in tons. This capital cost/capacity relation is graphically displayed
in Figure B-l.
PuraSiv Hg Adsorption
The PuraSiv Hg adsorption system consists of (1) a steam heated
preheater in which the gas to the adsorber is heated to approximately 100 F and
(2) two vessels in which at any given time adsorption of mercury is taking place
in one and regeneration of the adsorbent is taking place in the other.
A portion (15 percent assumed) of the gas leaving the adsorber is heated
to a temperature above 500 F in an electrical heater and routed to the
vessel undergoing regeneration. The gas effluent from this vessel is cooled
to more than 100 F in a shell and tube heat exchanger using 80 F cooling
water. A list of equipment and estimated costs by the Guthrie method
appears in Table B-2.
The costs supplied by UCC rather than those generated through the
conceptual design were used. A linear log-log relation was assumed between
the 100 and 750 TPD cases. This led to the expression:
0
CL-, = 8775 (TPD)U* . (B-3)
Mb '
Because of the recycle of regeneration gas through the
cooling/ demisting module, a 15 percent increase in the capacity of that
unit will be required. Therefore, the capital costs of PuraSiv Hg
adsorption at any plant capacity are those given by Equation B-3 in
-------
B-3
TABLE B-l. CAPITAL COSTS OF COOLING/DEMISTING AND LIST OF EQUIPMENT
Primary Cooler
Wire Mesh Pad
Demister
Rotary Blower
Secondary Cooler
Refrigerator
Tubular Type
Demister
Bare Module Cost
Total Module Cost
(18 percent
contingency)
100 TPD
Cost,
Size $1,000
400 ft2(a) 16
900 cfm 18(b)
900 cfm 12(c)
100 ft2(a) 4
25 ton 45
530 cfm 26(b)
121
143
750 TPD
Cost,
Size $1,000
3,000 ft 62
6,750 cfm 65
6,750 cfm 67(C)
750 ft2 16
187 ton 192
4,000 cfm 85
487
575
(a) Reference 5.
(b) References 4 and 8 in the text.
(c) Reference 26 in the text.
-------
B-4
1000
o
o
o
o
"5
'd
o
o
100
10
10
Cooling/demisting
PuraSiv Hg adsorption
with additional cooling/
demisting included
PuraSiv Hg adsorption only
i I i J_ l _L l i
j i i i i i i i
100
Chlorine Capacity, TPD
1000
FIGURE B-l. CAPITAL COSTS OF CONTROL OF MERCURY IN THE HYDROGEN BYPRODUCT STREAM
-------
B-5
TABLE B-2. CAPITAL COSTS AND LIST OF EQUIPMENT
FOR PURASIV HG ADSORPTION
Major Equipment
Preheater
Adsorber vessels
100
Size
10 ft2
4'd> x 11'
TPD
Cost,
$1000
1
35
750 TPD
Size
75ft2
10"d> x 11'
Cost,
$1000
5
80
(2)
Regeneration gas
heater
Regeneration gas
cooler
Bare module
Total module 18
percent con-
tingency
Cost given by UCC
26KW Nominal 200KW 5
28 ft2 1 213 ft2 10
37 100
44 118
69 175
-------
B-6
addition to the capital costs additional for cooling/demisting. The
cost/capacity relation is displayed in Figure B-l.
Adsorbent requirements for the process are such that a 3-year
replacement is necessary at a cost/capacity variation given by
C = 108 TPD. (B-4)
am
Operating and Maintenance Costs
Operating and maintenance costs include (1) operating labor;
(2) maintenance; (3) utilities including water, electricity, and low
pressure steam; and (4) taxes and insurance. An operating rate of 95
percent (or 8,322 hours per year) was assumed. The values of the above
items used in computing the O&M costs for the various control processes
are summarized in Table B-3.
All processes considered recover mercury. Therefore, a credit
for mercury recovery was included. For PuraSiv Hg adsorption the mercury
is returned immediately and as such can be treated as an annual credit
in this case. For purposes of this study, primary and secondary
cooling are necessary precursors to the adsorption process. The costs
of cooling/demisting, however, affect the adsorption process as it
requires a higher capacity for cooling/demisting because of the recycle
of the regeneration gas stream. Therefore, taking a mercury credit for
secondary cooling/demisting is not feasible.
Cooling/Demisting
Operating labor costs that may be attributed to the mercury
processes for this module were assumed negligible since the operation
of this unit may be considered as an integral part of operating the
manufacturing process. Maintenance requirements were assumed to be 3
percent of capital per year. Taxes and insurance usually amount to
2.5 percent of capital per year.
The utility requirements of this module are detailed in Table B-4
for a 100 TPD plant.
-------
B-7
TABLE B- 3. BASIS FOR COMPUTATION OF ANNUAL O&M COSTS
Cooling/ PuraSiv Hg
Demisting Adsorption
Utilities
Steam. (Ib/hr per TPD) @ 50
-------
B-8
TABLE B-4. UTILITY REQUIREMENTS FOR COOLING/DEMISTING
IN A 100 TPD PLANT
Equipment Duty Utility Rate
Primary boiler 2 MMBtu/hr 80 F, cooling
water 200 gpm
(a\
Rotary blower 37.5hpv ' Electricity 37.5hphr
hr
Refrigerator 62.5hp Electricity 62.5hphr
hr
(a) Reference 5.
-------
B-9
At cooling water costs of 3C/1000 gal, the annual costs of
cooling water are given by:
_$__ _ 200 gpm _ 60 min g „ hrs $0.03 m 3Q
7ea7 100 TPD X TPD X hr X *'J^ yr X 1000 gal JU
The annual costs of electricity at 1.2
-------
B-10
100
o
o
o
o
o
10
Cooling/demisting
PuraSiv Hg adsorption -
incremental cooling/
demisting cost included
PuraSiv Hg adsorption only
I i i i i i
l
i i i i i
10
100
Chlorine Capacity, TPD
1000
FIGURE B-2. OPERATING AND MAINTENANCE COST FOR MERCURY
CONTROL IN HYDROGEN BYPRODUCT STREAM
-------
B-ll
Table B-5. UTILITY REQUIREMENTS FOR PURASIV HG ADSORPTION
IN A 100 TPD PLANT
Equipment
Preheater
Regeneration Gas
Heater
Regeneration Gas
Cooler
Duty
32,000 Btu/hr
90,000 Btu/hr
75,000 Btu/hr
Utility
LP Stream
Electricity
80 F Cooling
Water
Utility Rat(
32 Ib/hr
26 kw
7.5 gpm
(a) On for only 14 hours out of every 24.
-------
B-12
The annual mercury credit amounts to
0.48 Ib per day .,, _. day. $200 = 4 4 TPD
100 TPD X 346'75 yr X TPD X 76 Ib 4'4 TPD*
Therefore, total O&M costs are
O&M = 483 (TPD)0'454 + 13.2 TPD + 1000. (B-9)
The above relationship is graphically displayed in Figure B-2. Components
of the O&M costs shown in this figure are detailed in Tables B-6, B-7, and
B-8 for various C10 capacities.
Total Annual Costs
The total annual costs of PuraSiv Hg adsorption are the sum
of the O&M, depreciation, and adsorbent replacement costs.
-------
B-13
TABLE B-6. O&M COST COMPONENTS FOR COOLING/DEMISTING
$1000 (CURVE A, FIGURE B-2)
ci2.
Capacity
TPD
100
250
500
600
750
Labor (a)
0
0
0
0
0
Utilities
12.3
30.7
61.5
73.8
92.1
Maintenance
4.3
8.1
13.1
14.8
17.3
Taxes and
Insurance
3.6
6.7
10.9
12.3
14.4
Total
20.2
45.5
85.5
100.9
123.8
(a) Operating labor for cooling/demisting was assumed to be part of the
manufacturing costs.
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B-14
TABLE B-7. INCREMENTAL O&M COSTS OF COOLING/DEMISTING
ATTRIBUTED TO PURASIV HG, $1000
TPD
100
250
500
600
750
Labor
0
0
0
0
0
Utilities
1.8
4.6
9.2
11.1
13.8
Maintenance
0.4
0.8
1.3
1.5
1.7
Taxes and
Insurance
0.4
0.7
1.1
1.2
1.4
Total
2.6
6.1
11.6
13.8
16.9
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B-15
TABLE B-8. O&M COSTS OF PURASIV HG ($1000) EXCLUDING
INCREMENTAL COOLING/DEMISTING COSTS
(CURVE C, FIGURE B-2)
TPD
100
250
500
600
750
Labor
1.0
1.0
1.0
1.0
1.0
Utilities
1.8
4.4
8.8
10.8
13.2
Mercury
Credit
0.4
1.1
2.2
2.6
3.3
Maintenance
1.4
2.1
2.9
3.2
3.5
Taxes and
Insurance
1.8
2.7
3.7
4.0
4.4
Total
5.6
9.0
14.2
16.4
18.8
-------
B-16
REFERENCES
(1) Guthrie, K. M., "Capital Cost Estimating", Chemical Engineering
(March 24, 1969).
(2) Guthrie, K. M., Process Plant Estimating Evaluation and Control.
Craftsman Book Company of America, Solana Beach, California (1974).
(3) Anonymous, "Control Techniques for Mercury Emissions from Extraction
and Chlor-Alkali Plants", U.S. EPA, Office of Air Programs, Research
Triangle Park, North Carolina, Publ. No. AP-118 (February, 1973).
(4) Clapperton, J. A., Manager of Manufacturing Industrial Chemicals,
PPG Industries, Pittsburgh, Pennsylvania, letter to M. Y. Anastas
(February 28, 1975).
(5) DeAngelis, P., Sobin Chemicals, Orrington, Maine, communication to
M. Y. Anastas (March, 1975).
(6) Information made available to Battelle's Columbus Laboratories by
Union Carbide Corporation in January and February, 1975.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-76-014
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Molecular Sieve Mercury Control Process in
Chlor-Alkali Plants
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
M.Y. Anastas
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Battelie-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
1AB014; 21ADH-008
11. CONTRACT/GRANT NO.
68-02-1323, Task 17
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 10/74-11/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
. ABSTRACT The y^pf gjves results of an investigation of the use of the PuraSiv Hg
adsorption process to remove mercury from the hydrogen byproduct stream and the
end-box ventilation stream from mercury cell chlor-alkali plants. The investigation
included the analysis of data obtained from testing of a system that is currently in
operation and technical information provided by the system vendor together with that
available in the open literature. Although the measurements of mercury concentra-
tion in the hydrogen byproduct stream entering the PuraSiv Hg adsorber, taken during
performence testing of the control unit, appear to be in error, measurements of the
outlet concentration indicate that a concentration less than 60 ppbv may be achieved.
The economics of the PuraSiv Hg adsorption process were explored. Available data
indicate that the operating costs by this process vary between $0. 58 and $0. 33 per
ton of chlorine produced for plants with capacities between 100 and 750 tons per day.
Mercury may also be removed from the hydrogen byproduct stream either by brine
adsorption over treated activated carbon or by scrubbing with depleted brine. Tech-
nical and economic data available to the investigator seem to favor the use of these
two processes for mercury control, although the data base thereon is not sufficiently
developed to warrant a meaningful comparison.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Mercury (Metal)
Absorbers (Materials)
Chemical Plants
Chlorine
Sodium Hydroxide
Activated Carbon
Brines
Air Pollution Control
Stationary Sources
Molecular Sieves
Chlor-Alkali Plants
PuraSiv Hg Unit
13B
07B
11G
07A
B. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
72
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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