EPA-R2-73-186
March 1973 Environmental Protection Technology Series
Regeneration Chemistry
of Sodium-Rased
Double-Alkali Scrubbing Process
Office of Research and Monitoring
National Environmental Research Center
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
-------
EPA-R2-73-186
Regeneration Chemistry
of Sodium-Based
Double-Alkali
Scrubbing Process
by
Dean C. Draemel
Program Element No. LA2013
Control Systems Division
National Environmental Research Center
Research Triangle Park, N.C. 27711
Prepared for
OFFICE OF RESEARCH AND MONITORING
NATIONAL ENVIRONMENTAL RESEARCH CENTER
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
March 1973
-------
ABSTRACT
Reactions of Ca(OH)2, CaCO3, and limestone with the aqueous (Na+,
SC>3, HSOj, SDH system were studied. Concentrations and stoichiometries
typical of those for sodium-based double-alkali scrubbing systems were used.
The reactions were studied in a stirred, nitrogen-purged glass reaction vessel
immersed in a constant-temperature bath. The objectives were to study
various reactions of importance in the sodium-based double-alkali process
and to define possible operating modes for the process.
Results indicate desirable operating ranges and may be used to support
engineering design of pilot-scale double-alkali scrubber systems.
111
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CONTENTS
Section PaSc
I Conclusions '
II Recommendations 3
III Introduction 5
Background 5
Reasons for Performing Work 5
Approach and Objectives 5
IV Procedure 7
Plan of Investigation 7
Equipment 1
Materials and Techniques 7
V Results and Discussion II
Reactions Between Lime and Sodium Sulfite Solutions 11
Reactions Between Lime and Sulfite-Bisulfite Solutions 12
Reactions Between Calcium Carbonate and Sulfite-Bisulfite-
Sulfate Solutions 13
Reactions Between Calcium Hydroxide and Sulfite-Sulfate Solu-
tions 18
Reactions Between Calcium Hydroxide and Sulfite-Sulfate Solu-
tions - Checks on Analytical Results and Implications 22
Reactions Between Limestone and Sulfite-Bisulfite-Sulfate
Solutions 26
Calcium Ion Concentrations in Scrubber Solutions 27
VI Acknowledgements ^
VII Appendices 31
Appendix A. Double-Alkali Process Literature Study and Refer-
ences 33
Appendix B, Experimental Data and Results 35
Appendix C, Equilibrium Caustic Formation, Ca(OH)2 -
Na2 SO4 Solutions 37
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FIGURES
No.
1 Batch Apparatus for Studying Chemistry of the Double-Alkali
System 8
2A Runs 54-57-Batch Experiments-CaCO3/NaHSO3, Na2SO3,
Na2SO4-SO3= vs Time at -v 5 wt % Na2 SO4 H
2B Runs 58-61-Batch Experiments-CaCO3/NaHSO3, Na2SO3,
Na2 SO4 -SO3 vs Time at 'v 10 wt % Na2 SO4 '5
2C Runs 62-65-Batch Experiments-CaCO3/NaHSO3, Na2SO3,
Na2SO4-SO3 vs Time at ^ 20 wt%Na2SO4 16
3 Runs 66-71-Batch Experiments-Ca(OH)2/Na2SO3, Na2SO4-
OH-vsTime 19
4 Runs 48-53-Batch Experiments-Ca(OH)2/Na2SO3, Na2SO4-
OH"vs Time 21
5 Runs 67, 70, 72, and 73-Special Experiments-Ca(OH)2/Na2SO3,
Na2SO4-Checks on Analytical Results-SO^ vsTime 24
6 Runs 67, 70, 72, and 73-Special Experiments-Ca(OH)2/Na2SO3,
Na2 SO4 -Checks on Analytical Results-OH"vs Time 25
TABLES
No.
\ Batch Experiments C;i(OH)2/Na2SO3 11
2 Butch Experiments - Ca(OH)2/NaHSO3, Na2SO3, Na2SO4 12
3 Batch Experiments CnCO.,/NaHSO3 , Na2SO3 , Na2 SO4 17
4 Special Experiments Stirrer Speed Effect on CaCO3/NaHSO3,
Na2S03,Na2S04 18
5 Batch Experiments-Ca(OH)2/Na2SO3, Na2SO4 20
6 Batch Experiments-Ca(OH)2/Na2SO3, Na2SO4 20
7 Batch Experiments-Ca(OH)2/Na2SO3, Na2SO4-Supplemental
Calculations 20
8 Batch Experiments-Ca(OH)2/Na2SO3, Na2 SO4-Checks on
Analytical Results and Implications 23
9 Batch Experiments-Limestones/NaHSO3, Na2 SO3, Na2 SO4 .... 26
VI
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SECTION I
CONCLUSIONS
1. The reactions between CaCO3 or lime-
stone and the Na+, SO3=, HSO3", SO4= system
are dependent on HSOJ and SO^ concentra-
tion, 864 concentration (ionic strength),
CaCO3 particle size, and agitation level. Other
factors have lesser effects.
2. Bisulfite neutralization with CaCO3 or
limestone requires roughly 2 hours for 90
percent of the reaction to occur. CaCO3 uti-
lization ranged from 90-40 percent with stoi-
chiometry 1.0 and from 66-40% with stoi-
chiometry 1.5. both at a total initial sulfite
(HSO3 + SOJ) level of 0.088M. In general,
higher bisulfite concentrations (0.055M vs
0.022M) are neutralized more rapidly, provid-
ing better utilization of CaCO3 or limestone.
Increasing sulfate levels appears to suppress
bisulfite neutralization as indicated by the
range of CaCO3 utilizations.
3. Lime reacts with sulfate in the presence
of limited sulfite up to an equilibrium hy-
droxide level of roughly 0.14M OH~ (Appen-
dix C). The reaction with sulfite is suppressed
at higher sulfate levels. The decrease in the
extent of the reaction between lime and sul-
fite with increasing sulfate implies that sulfate
regeneration is possible even in the presence
of sulfite ion concentrations in excess of that
necessary to produce ^ 0.14M hydroxide ion
concentrations.
4. Higher sulfate levels appear to suppress
both the neutralization of bisulfite and the
precipitation of sulfite with limestone or lime.
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SECTION II
RECOMMENDATIONS
On the basis of batch test results and sim-
ilar studies done by other organizations, a
continued effort to characterize the double-
alkali system and to develop it through a pilot
plant or small-scale demonstration is sug-
gested. The proposed double-alkali program
should be carried on as planned.
Additional batch tests should be conducted
to define ranges of possible operation to help
define oxidation effects in the system and to
develop more complete data on the chemical
system. Small-scale continuous-scrubber
systems should be built and operated to prove
operating capabilities and to study the inte-
grated system in its entirety. If all results are
favorable, a pilot plant or small-scale demon-
stration should complete the program.
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SECTION III
INTRODUCTION
BACKGROUND
REASONS FOR PERFORMING WORK
In the development of sulfur oxide (SOX)
control processes the double-alkali process has
emerged as a promising second-generation,
regenerable SOX scrubbing process. Little
research and development work has been
done on the process and much of what has
been done would not apply to the double-
alkali process as it is conceived for the U.S. A
brief literature study of the process is in-
cluded as Appendix A.
The double-alkali process involves circulat-
ing a clear liquor solution of a soluble alkali
salt (Na4", K*, or NH^") with scrubbing taking
place by absorption and reaction to form the
bisulfite from the sulfite. The spent scrubbing
liquor is then treated with limestone and/or
lime to remove solid sulfite (and possibly sul-
fate') and to regenerate the scrubbing liquor.
Major goals of this program arc to regen-
erate active sodium from the sulfate and lo
determine methods of controlling steady state
sulfate levels in the process. Oxidation and
consequent sulfate problems (scaling poten-
tial, chemical costs, and water pollution
potential) are serious problems in many
proposed SO2 control processes. The double-
alkali process appears to have great versatility
and should be applicable to both industrial
and utility boilers.
An experimental program was initiated to
study the process chemistry for a double-
alkali flow scheme using low concentration
(0.01-0.05M) scrubbing solutions of sodium
and regeneration using both limestone and
lime. It was felt that, although the system
appeared promising, there was insufficient
data available to warrant a development pro-
gram without preliminary research. The pro-
gram planned consists of three phases. Phase I
willstudy the chemistry of both the scrubber
and possible regeneration schemes. The bulk
of this work will consist of in-house batch
reactor experiments designed to study specific
reactions and combinations of reactions.
Phase II will involve the operation of a small
bench-scale scrubber system to study steady
state operating modes, oxidation, and solids
characteristics. This work will be conducted
both in-house and on contract. Phase III will
involve the operation of a pilot-scale closed-
loop system to characterize feasibility, eco-
nomics, and operating behavior of the
process. The in-house and contract work
conducted during the first two phases will
support and aid planning of the pilot-plant
test program.
APPROACH AND OBJECTIVES
The study discussed here concerns Phase I
of the program, the laboratory investigation
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of double-alkali regeneration chemistry. Batch system. The hatch tests wore carried out
tests were carried out in which simulated under an N2 purge in a gl;iss vessel submerged
scrubber effluent solutions were treated with in a constant-temperature bath.
limestone to convert the bisulfite to sulfite.
Simulated solutions from this limestone treat- The objectives of this work were to study
ment step were then treated with lime to the effects of concentration, stoichiometry,
precipitate sulfite and sulfate and return reactant composition, and temperature on
active sodium (NaOH) to the scrubbing reaction rates and reactant utilizations.
-------
SECTION IV
PROCEDURE
PLAN OF INVESTIGATION
An experimental program was carried out
to study the chemistry of the scrubber and
possible regeneration schemes. The study in-
volved laboratory-scale batch tests for specific
reactions and the construction and operation
of a bench-scale continuous-scrubber system.
The objectives in carrying out these studies
were to generate detailed data on the chemi-
cal system of the double-alkali process and to
provide an in-house background for the devel-
opment of a double-alkali process program.
constant-temperature bath and the vessel was
purged with nitrogen. When both solutions
reached the desired temperature, they were
poured together in the 3-liter reaction vessel.
Mixing of the solution and nitrogen purging
of the vessel were maintained throughout the
run.
Sampling was carried out by pipetting out
60-70 ml of the mixture and filtering to re-
move the solids; wet chemical analysis was
carried out immediately. Samples were taken
from the reaction vessel after 15 or 30
minutes, after 1 hour, and after 3 hours from
the time the solutions were poured together.
EQUIPMENT
A sketch of the experimental apparatus is
shown in Figure I. Batch reactor experiments
were carried out in a 3-liter three-neck flask
suspended in a circulating, constant-tempera-
ture bath. The reaction vessel was equipped
with a variable-speed, propeller-type stirrer, a
thermometer, and a nitrogen purge line.
Samples were taken through the nitrogen
purge port. The purge was necessary to pre-
vent oxidation of the sult'ile-nisulfile solu-
tions to sulfate.
The dry calcium carhoiialc or calcium
hydroxide was mixed will) roughly half of the
water and placed in the reaction vessel. This
mixture was stirred and the temperature
monitored. The sodium salts were dissolved in
the rest of the water and placed in a separate
vessel. This vessel was placed in the
MATERIALS AND TECHNIQUES
The following reagents were used
batch experiments:
l.Na2SO3-ACS grade. 98.9%
Fisher Scientific (anhydrous)
2. Na2SO4-ACS grade, -v99.9%
Fisher Scientific.
3.Na2S2Os Analytical reagent.
minimum ;iss;iy. Mallincrodl
drite ol N;i I ISO, ).
4. CaCO, ACS, 99% minimum
Allied Chemical.
ACS, -\,99.5%assay, M
5. *C:i(Oin2 Ki-agent, «M%
MC&U.
in the
assay.
.
assay.
(anhy-
assay.
assay.
* Lime mentioned in the text is always hydrated lime
orCa(OH)2.
-------
IMMERSION
HEATER
INSULATED
CONSTANT-
TEMPERATURE
BATH
00
STIRRER
THERMOMETER
ii
N2 PURGE
OK)
REACTION
VESSEL
Figure I. Batch apparatus for studying chemistry of the double-alkali system.
8
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Analytical procedures used for the liquid
phase were:
1. Hydroxide-Titrate filtered sample
with 0.1N HC1 to phenolphthalein
endpoint.
2. Sulfite-Add excess of standard 0.1N
iodine solution (KI-KIO3) to sam-
ple. Back-titrate the excess iodine
with standard 0.05N sodium thio-
sulfate solution to the starch end-
point.
3. Total Sulfur--Oxidize the sample sul-
fite species with an amount equal to
the sample volume of 3% hydrogen
peroxide. Dilute this solution to
100 ml with distilled water. Treat a
portion of this sample with Rexyn
101H resin and let stand for rough-
ly 5 minutes. Titrate a filtered por-
tion of this liquid to a thorin end-
point with Ba(CIO4)2 solution.
4. Calcium-Acidify to dissolve solids
(for solids analysis only). Adjust
the pi I to 12 or 13 with NaOM or
KOI1. Titrate with LOT A to lirio-
chrome Blue Black endpoint.
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SECTION V
RESULTS AND DISCUSSION
The batch tests were conducted in sets of
runs which were planned to study various
reactions involved in double-alkali regenera-
tion chemistry. These sets of runs are dis-
cussed separately in the following sections.
REACTIONS BETWEEN LIME AND
SODIUM SULFITE SOLUTIONS
Runs 1-7 were conducted to compare in-
house experimental techniques and results
with results found by other researchers. The
results of these first runs are presented in
Table 1.
The sulfite levels charged in these experi-
ments correspond to a high sulfur coal. These
concentrations are much higher than those
proposed for the actual double-alkali scrub-
ber/4 ) but they are the same as those used by
researchers at Arthur D. Little, Inc.<5> Slight-
ly less lime was charged than would be neces-
sary for complete conversion, but the reaction
is equilibrium limited so excess lime is pres-
ent. The sulfite and hydroxide levels recorded
in the table are those analyzed after 1 hour.
Run 4 was conducted at 100°F and the rest
of the runs at 150°F to check the tempera-
ture effect on the rate and equilibrium.
The reaction
Ca(OH)2
2NaOH
has an equilibrium rate constant given by
A2(OH-)
A (S03=) 7so= [SO,]
Table 1. BATCH EXPERIMENTS-Ca(OH)2/Na2SO3
Run
1
2
3
4
5
6
7
Temp °F
150
150
150
100
150
150
150
Ca(OH)2
0.466
0.25
0.95
0.25
0.466
0.466
0.466
Reactants
Na2S03
0.50
0.25
1.0
0.25
0.50
0.50
0.50
charged, g
H2O
50
50
50
50
50
50
50
:
moles
Additional
Additives
None
None
None
None
Fe***
Flyash
Few, Flyash
Analysis
g moles/liter
(1 hour sample)
OH" SOj
0.81 0.19
0.45 0.053
1.14 0.58
0.44 0.054
0.77 0.18
0.79 0.18
0.85 0.19
=^==^=^=
(OH-
(S03
Equilibrium
rate
constant
3.5
3.8
2.2
3.6
3.3
3.5
3.8
2
Results of
others*5)
3.4
4.6
23
-------
The activity coefficient, 7, will be concentra-
tion dependent. The values for the equilib-
rium based on concentrations measured will
give
K
-12
7SO= IOH-]
IS03=]
These values are calculated in Table 1 and
compared to the values found by researchers
at Arthur D. Little, Inc. The equilibrium
values calculated for [OH~]2/[SO=] agree
quite well with values shown in the Arthur D.
Little work. The differences may be due to
the time required for the completion of the
reaction. The Arthur D. Little report stated
that the reaction was essentially complete
after 1 hour; in-house data indicated only 95
percent completion after 1 hour. The equilib-
rium values for [OFTp/CSOj] calculated
after 3 hours of reaction time agree within ± 5
percent of the values found by the Arthur D.
Little researchers. The decrease in the equilib-
rium constant with concentration confirms
the Arthur D. Little analysis regarding sulfite
ion activity coefficient decrease with concen-
tration increase, and hydroxide ion activity
increase with concentration increase. Runs 2
and 4 indicate little, if any, effect from
temperature. The concentration effect shown
in runs 1. 2, and 3 appears to be significant.
Runs I, 5. 6, and 7 may be used to deter-
mine the effect on the reaction from the
presence of corrosion products (Fe4*1") and/
or flyash solubles. As shown in Table 1, values
of [OH~12/[SO3=1 for these runs are the same
within the experimental error. This "same-
ness" shows little, if any, effect from either
Fe14* or flyash solubles on rate or equilibrium
concentrations.
REACTIONS BETWEEN LIME AND SUL-
FITE-BISULFITE SOLUTIONS
A second set of runs (45-47) was con-
ducted in which the reactions between lime
and both sulfite and bisulfite in the presence
of sulfate were studied:
Ca(OH)2 + 2NaHSO3^ ^ CaSO3 +
Na2SO3 + 2 H2O (2)
The data for these runs are shown in Table
2. Sufficient lime was charged to convert all
of the bisulfite to sutfite and react further
with roughly half of the resultant total sulfite.
These runs were done at three levels of
Na2SO4, corresponding roughly to 5, 10, and
20 wt % solutions. These tests were meant to
show the effects of sulfate buildup in the
scrubbing solutions on sulfite and bisulfite
Table 2. BATCH EXPERIMENTS-Ca(OH)2/NaHSO3, Na2SO3, Na2SO4
(Runs at 150°F)
Run
45
46
47
Ca(OH)2
0.350
0.360
0.42
Reactants
l\la2SO
0.18
0.19
0.22
charged, g rnoles
3 Na2S04 H20
0.35
0.74
1.70
50
50
50
IMaHSOa
0.34
0.35
0.40
Analysis, g moles/liter
(3-hour sample)
Total S OH' SO3=
0.5680 0.3111 0.2424
0.9425 0.3770 0.2181
1.8298 0.4636 0.2567
12
-------
reaction with lime. At these relatively high
concentrations. ;i siiuill effect from ionic
strength would he expected. As was men-
tioned in the previous section, the equilibrium
ratio [OH~]2/tSOj] should be affected by
ionic strength, temperature, and reactant con-
centration. There was, however, insufficient
lime present in these runs to allow equilib-
rium concentrations equivalent to those in
Table 1 to be attained. The fractional reaction
of the sulfite is roughly the same for all three
runs. The slight increases in initial sulfite and
hydroxide make these results hard to inter-
pret because of the strong concentration
dependence discussed earlier for reaction (1).
Additional runs will be conducted and dis-
cussed following Table 4. The utilization of
lime in the runs shown in Table 2 approached
100 percent as indicated by final 863 and
OH~ levels. The utilization was calculated as
follows:
The two reactions (1,2) proceed concur-
rently. The bisulfite neutralization
would be expected to go to completion
relatively rapidly, considering the rise in
pH. Reaction (1) with the sulfite would
then proceed to some set of equilibrium
concentrations. A sample calculation for
run 45 follows to show lime utilization.
Initial concentrations are:
Ca(OH)2 = 0.39 moles/liter,
SOJ = 0.20 moles/liter, and
HSO3" = 0.374 moles/liter.
After complete bisulfite conversion by
reaction (2), concentrations would be:
Ca(OH)2 = 0.203 moles/liter,
SOj = 0.387 moles/liter, and
HSOj = 0 moles/liter.
The final SO3= concentration indicates
further reaction between lime and
An additional 0.145 moles/liter of
reacts with the Ca(OH)2 - (intermediate
SOJ - final 803) = (0.387 - 0.242 moles/
liter) = 0.145 moles/liter. This would
indicate a final OH" concLMitration of
0.290 moles/liter by reaction (1). This is
in fairly close agreement with the final
OH~ concentration measured of 0.31 1
moles/liter. Overall utilization of
Ca(OH)2 would be:
[Ca(OH)2 for HSO3" + Ca(OH)2 for SO3=]
[initial Ca(OH)2 ]
[0.187 moles/liter + 0.145 moles/liter]
0.390
= 0.85 or 85% Ca(OH)2 utilization.
REACTIONS BETWEEN CALCIUM CAR-
BONATE AND SULFITE-BISULFITE-SUL-
FATE SOLUTIONS
The third set of runs (54-65) was con-
ducted to study the reactions between cal-
cium carbonate and sulfite-bisulfite solutions
at different sulfate levels. The emphasis on
these runs was to study simulated scrubber
solutions with low (less than 0.055M) sulfite
and bisulfite concentrations. These low con-
centrations represent a mode of scrubber
operation that appears very promising for
future development work.
The results of batch tests 54-65 are shown
graphically in Figures 2A, 2B, and 2C, and in
Table 3. These tests were conducted to study
the reaction between CaCO3 and simulated
scrubber effluent solutions from a dilute
scrubber liquor operating mode. CaCO3 stoi-
chiometries of 1.0 and 1.5 were used. Two
sulfitc-bisulfitc levels were studied at three
different sodium sulfate concentrations corre-
sponding roughly to 5, 10, and 20 wt % solu-
tions: Figure 2A is for runs 54-57 with a sodi-
um sulfate level of roughly 5 wt %; Figure 2B
13
-------
0.08
0.06
* I
cP
0.02
0.0
OK1
Reaction Between Bisulfite & Calcium Carbonate
2
TIME, hours
Figure 2A. Runs 54-57 - batch experiments - CaCO3/NaHSO3, Na2 SO3, Na2 SO4 - SOj vs time at ~5 wt % Na2 SO4 .
-------
0.08
0.06
0.04
"w
o
co
0.02
RUN NO.
100%
58
-59
100%*
* Reaction Between Bisulfite & Calcium Carbonate
0.0
2
TIME, hours
Figure 2B. Runs 58-61 - batch experiments - CaCO3/NaHSO3, Na2SO3, Na2S04 - SOa vs time at ~ 10 wt % Na2SO4.
-------
0.08
0.06
- e 0.04
o
tst
0.02
0.00
Reaction Between Bisulfite & Calcium Carbonate
2
TIME, hours
o%*
64
65
100%*
62,63
RUN NO.
62
A 63
64
Figure 1C. Runs 62-65 - batch experiments - CaCO3/NaHSO3 , Na2 SO3 , Na2 SO4 - SOf vs time at ~ 20 wt % Na2 SO4 .
-------
Table 3. BATCH EXPERIMENTS-CaCO3/NaHSO3. Na2SO3, Na2SO4
(Allrunsat150°F)
Run
54
55
56
57
58
59
60
61
62
63
64
65
Reactants charged, g
CaCO3
0.01
0.015
0.03
0.045
0.01
0.015
0.03
0.045
0.01
0.015
0.03
0.045
Na2SO3
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.02
NaHS03
as
Na2S2Os
0.02
0.02
0.06
0.06
0.02
0.02
0.06
0.06
0.02
0.02
0.06
0.06
moles
Na7S04
0.33
0.33
0.33
0.33
0.60
0.60
0.60
0.60
1.60
1.60
1.60
1.60
H20
50
50
50
50
50
50
50
50
50
50
50
50
SOl analysis, g moles/liter
1/2 hr
0.0301
0.0311
0.0780
0.0725
0.0297
0.0282
0.0804
0.081 1
0.0274
0.0284
0.0756
0.0712
2hr
0.0273
0.0318
0.0694
0.0605
0.0294
0.0273
0.0782
0.0757
0.0266
0.0269
0.0749
0.0701
3hr
0.0247
0.0287
0.0580
0.0488
0.0292
0.0254
0.0612
0.0452
0.0259
0.0260
0.0753
0.0676
is for runs 58-61 with a sodium suifate level
of roughly 10 wt %; and Figure 2C is for runs
62-65 with a sodium suifate level of roughly
20 wt %. The bisulfite conversion reaction is:
CaCO3 + 2 NaHSO3 > CaSO3 +
Na2SO3 + H2O + CO2. (3)
The horizontal lines in the figures bracket
the range of sulfite concentrations possible
corresponding to zero and 100 percent reac-
tion between the bisulfite and the calcium
carbonate. As a general trend, the reactions
with CaCOj stoichiometry of 1.5 proceeded
further and faster (lower line in each pair of
lines, indicating more complete HSOJ conver-
sion) than those with stoichiometry of 1.0.
With initial bisulfite concentrations of
0.022M, roughly 60 percent reaction occurs
after 3 hours at all levels of suifate. With bi-
sulfite levels of 0.066M it appears that the
reaction is suppressed at higher suifate levels
(i.e., less HSO3 conversion per unit time).
Reactant (CaCO3) utilization (or bisulfite
conversion) at 1.0 stoichiometry ranges from
90-40 percent with increasing suifate. At 1.5
stoichiometry, bisulfite conversion ranges
from 100-64 percent (limestone utilization of
66-40 percent) with increasing suifate. Addi-
tional runs with different sizes of limestone
have been conducted and will be discussed
later (see Table 9). In general, at a 0.066M
bisulfite level greater reactant utilizations are
possible than at a 0.022M bisulfite level. This
implies a tradeoff between reaction rate, uti-
lization, and sulfite-bisulfite level. Sulfite-
bisulfite level in turn affects required liquor
rate for a given SO2 removal and steady state
concentrations.
Additional runs were conducted to check
reproducibility of this data. A different brand
of ACS grade CaCO3 was used. Better re-
actant utilization was noted in all runs.
Coulter Counter particle size analysis showed
the second brand of CaCO3 to be of finer
size. The following paragraph and the Table 9
discussion give more detail.
17
-------
Table 4. SPECIAL EXPERIMENTS-STIRRER SPEED EFFECT ON CaCO3/NaHSO3,
Na2S03,Na2S04
(All runsat150°F)
Stirrer
speed, rpm
1300
BOO
400
CaCO3
0.045
0.045
0.045
Reactants
NaHSOj
0.06
0.06
0.06
charged, g
Na2SO3
0.02
0.02
0.02
moles
Na2 S04
0.33
0.33
0.33
H20
50
50
50
SO3 analysis, g moles/liter
1/2 hr
0.0619
0.0671
0.0660
1 hr
0.0481
0.0517
0.0651
3hr
0.0388
0.0421
0.0566
Indications are that the reaction is diffu-
sion limited by the CaCO3. A check on this
hypothesis was made by repeating run 57 at a
number of different stirrer speeds. The results
of these runs are shown in Table 4. A signifi-
cant reduction in rate was noted at the re-
duced stirrer speeds. Lower bisulfite conver-
sions (i.e., higher total sulfite analysis) is
noted especially after I and 3 hours of
reaction time. At the lowest stirrer speed,
complete suspension of the solids was not
maintained. This would be expected to reduce
the extent of the reaction with time. The
general trend of reduced rate with reduced
stirrer speed is obvious even though slight
settling did occur at the lowest agitation level.
REACTIONS BETWEEN CALCIUM HY-
DROXIDE AND SULFITE-SULFATE SOLU-
TIONS
Batch tests 66-71 are shown graphically in
Figure 3. Table 5 shows the initial charges and
results lor these runs. These If sis were con-
iliu U'cl ID .study I IK' iviii'lioii |K-|Wlli Irvrls nl siilliU- IIMIIIM ami O.O.VSM)
lite lii^hi-sl i iHuviilialiiMi i»l Na:SO4 appears
(u suppress OH formal ion. Additional in-
formation on this reaction can be obtained
from Figure 4 and Table 6. The figure and
data are from runs 48-53. The difference be-
tween the two sets of runs is: for runs 48-53,
an amount of Ca(OH)2 equivalent to the total
sulfate level was used; for runs 66-71, an
amount of Ca(OH)2 equivalent to a 0.1 5M
equilibrium hydroxide concentration was
used (from 1/5 to 1/30 the amount in runs
48-53). The results of runs 48-53 show that
all the curves for OH~versus time show slight-
ly higher OH" concentrations than the corre-
sponding curves for runs 66-71 and follow the
same pattern for OH~ formation vs sulfite-sul-
fate levels. The reaction between Ca(OH)2
and Na2SO4 consists of
Ca(OH)2
Na2SO4
2NaOH.
CaSO4
(4)
A detailed analysis of the data provides an
explanation for the somewhat unusual be-
havior of the OH"vs time curves with respect
to initial sulfite-sulfate levels. Table 7 shows
some additional calculalions for these reac-
tions. The lahlc also shows react a ills charged,
fiiuil SO; aiul OH, Oil hum reaction willi
SO;, MIX! (HI limn IIMI linn with S(»7 h
appeals tlnil at Ingh Millalr a>iKTiilia(iniii>.
sullile is ivlalivi-ly imtvaclcil ;illiM- .1 lumrv
The calculation of OH from reaction with
SOj and OH" from reaction with SO4 is done
-------
£9
I .^ ..-*
. "."₯ T 70
'W
W\~ _ - 68
V ."""...» 67
! Tf
o
I -
2
TIME, hours
QlOl *".*"." - 66
£F""
.<
- ,/
0.08
RUN NO.
0.06J- 6G
A 67
68
69
V 70
0.04
" 71
Figures. Runs 66-71 - batch experiments - Ca(OH)2/Na2SO3 , Na2SO4 - OFT vs time.
-------
Tables. BATCH EXPERIMENTS-Ca(OH)2/Na2SO3, Na2SO4
(Runs at 150°F)
Run
66
67
68
69
70
71
Reactants charged.
Ca(OH)2
0.07
0.07
0.07
0.07
0.07
0.07
Na2SO3
0.01
0.01
0.01
0.05
0.05
0.05
g moles
Na2SO4
0.33
0.60
1.60
0.33
0.60
1.60
H2O
50
50
50
50
50
50
OH analysis, g moles/liter
1/4 hr
0.0750
0.1007
0.0964
0.1214
0.1171
0.0976
1 hr
0.0982
0.1086
0.1061
0.1244
0.1232
0.1074
3hr
0.1049
0.1147
0.1159
0.1269
0.1232
0.1135
Table 6. BATCH EXPERIMENTS-Ca(OH)2/Na2SO3. Na2SO4
(Runsat150°F)
Run
48
49
50
51
52
53
Ca(OH)2
0.33
0.70
1.60
0.33
0.70
1.60
Reactants charged.
g moles
Na2SO3 Na2SO4
0.01
0.01
0.01
0.05
0.05
0.05
0.33
0.60
1.60
0.33
0.70
1.60
H2O
50
50
50
50
50
50
OH analysis, g moles/liter
1/2 hr
0.0902
0.1251
0.1098
0.1317
0.1348
0.1098
1 hr
0.1024
0.1256
0.1171
0.1342
0.1378
0.1195
3hr
0.1037
0.1244
0.1195
0.1366
0.1384
0.1232
Table?. BATCH EXPERIMENTS-Ca(OH)2/Na2SO3, Na2SO4 -SUPPLEMENTAL CALCULATIONS
Run
48
49
50
51
52
G:»
ee
67
68
69
70
71
Reactants charged.
Ca{OH)2
0.33
0.70
1.60
0.33
0.70
I. («)
O.O/
0.07
0.07
0.07
0.07
0.07
g moles
Na2S03 Na2S04
0.01
0.01
0.01
0.05
0.05
0.01.
U.UI
0.01
0.01
0.05
0.05
0.05
0.33
0.60
1.60
0.33
O./O
I. (30
0.33
0.60
1.60
0.33
0.60
1.60
H20
50
50
50
50
!50
I.O
50
50
50
50
50
50
Analysis after 3 hours
g moles/liter
OH" SO 3
0.1037 0.0091
0.1244 0.0116
0.1195 0.0116
0.1366 0.0066
0.1384 0.0125
o.m? ii.o?:iii
0.0927 O.OO'oti
0.1147 0.0099
0.1159 0.0079
0.1269 0.0067
0.1232 0.0119
0.1135 0.0231
Calculated
From SO3
0.0966
0.0865
0 0(i:iB
-
0.0968
0.0850
0.0628
OH" values
F rom SO^
0.0400
o.o5ia
0.0591
-
0.0301
0.0382
0.0507
20
-------
to.
0.15
0.13
g 0.11
0.09
..A-
:*
2
TIME,hours
.52
51
.49
53
50
48
RUN NO.
48
A 49
50
T 52
X 53.
Figure 4. Runs 48-53 - batch experiments - Ca(OH)2/Na2SO3, Na2SO4 - OH vs time.
-------
only for runs with an initial SO3 concentra-
tion of 0.055 moles/liter because of the ex-
tremely small changes seen in runs with initial
SO3 concentrations of 0.01 1 moles/liter.
A sample calculation (using run 69) for
OH" generated from reaction with SO3 and
from reaction with SO| follows:
Initial concentrations charged were:
Ca(OH)2 = 0.078 moles/liter.
Na2SO3 = 0.055 moles/liter, and
Na2SO4 = 0.366 moles/liter.
Final concentrations measured were:
OH" = 0.1 269 moles/liter, and
= 0.0066 moles/liter.
suppression of the reaction with sulfite may
mean that higher sulfite levels may be used in
a scrubber without precluding the regenera-
tion of inactive Na2SO4 to active NaOH by
the use of lime.
One additional fact should be noted from
Table 7. Comparing runs 51-53 and 69-71
indicates that increased Ca(OH)2 to Na2SO3
stoichiometry does not affect the amount of
SOI reacted (OH" from SO3). Increasing
Ca(OH)2 to Na2SO4 stoichiometry signifi-
cantly changes the amount of SO^ reacted
(OH" from SOa)- This effect can be seen by
noting the similarities in the values of OH"
from SOJ for runs 51-53 and 69-71 and the
differences in the OH" from SO^ values be-
tween these same sets of runs.
Thus, from reaction (1):
OH" = 2[SO3 initial - SO3 final]
= 2[0.055 moles/liter - 0.0066
moles/liter]
= 0.0968 moles/liter.
The OH levels observed imply at least
some reaction with sulfate. Total sulfur
measurement did not give usable results.
Arthur D. Little, Inc. had similar difficulty in
some of its work.
The final OH concentration measured was
0.1269 moles/liter. Thus, it can be assumed
that the difference between OH~ from reac-
tion (1) and the final OH" concentration is
due to reaction (4). Therefore, the OH" from
reaction (4) is:
(°H"final' OH from reaction (1)1
= (0.1269 moles/liter - 0.096K moles/
liter |
= 0.0301 molos/liU-r.
Two effects arc obvious. First, as sulfale
concentration increases, the reaction with
sulfate also increases. Second, as ionic
strength (sulfate concentration) increases, the
reaction with sulfite is suppressed, as indi-
cated earlier. This result is important in that
higher ionic strength (higher SO^ levels)
favors the reaction of lime with sulfate. The
The following section discusses two addi-
tional runs and supports implications from
the data on runs 66-71 and 48-53.
REACTIONS BETWEEN CALCIUM
HYDROXIDE AND SULFITE-SULFATE
SOLUTIONS-CHECKS ON ANALYTICAL
RESULTS AND IMPLICATIONS
Two additional runs were made: one as a
blank on sulfite; the other as i\ blank on both
sulfite and sulfate. These runs were conducted
to show the accuracy of the experimental
methods and to support the implications
given by the data discussed following Table 4.
Table 8 lists reactants charged and analytical
results for these runs (72 and 73) along with
two previously discussed regular runs (67
22
-------
Tables. BATCH EXPERIMENTS - Ca(OH)2/Na2SO3, Na2SO4 - CHECKS ON ANALYTICAL
RESULTS AND IMPLICATIONS
(Runsat 150°F)
Run
67
70
72
73
Reactants charged, g moles
Ca(OH)2
0.07
0.07
0.07
0.07
Na2SO3 Na2SO4
0.01 0.60
0.05 0.06
0.60
H20
50
50
50
50
SOa analysis
g moles/liter
1/4 hr 1 hr 3 hr
0.0103 0.0103 0.0103
0.0165 0.0131 0.0122
0.0008 0.0006 0.0006
0.0016 0.0016 0.0016
OH analysis
g moles/liter
1/4 hr 1 hr 3 hr
0.1028 0.1080 0.1110
0.1190 0.1241 0.1248
0.0317 0.0323 0.0305
0.1086 0.1086 0.1116
and 70). Figures 5 and 6 show the analysis for
SO^ and OH" respectively, as a function of
time for these runs (67, 70, 72, and 73). The
lowest line in Figure 6 shows a hydroxide ion
background level corresponding to the equi-
librium dissolution of calcium hydroxide
when no sulfite or sulfate is present for re-
action. The lower two lines in Figure 5 show
the background SO^ level in the presence of
sulfate only and with neither sulfite nor
sulfate present. From the measured OH'and
SOj levels in the blank runs (72 and 73) and
the measured OH" and SOj levels in the two
regular runs (67 and 70) used for comparison,
it is inferred that from 25 to 72 percent of
the calcium hydroxide is reacted with the
sulfate in the presence of these low sulfite
concentrations. The amount reacted depends
on both initial sulfite-sulfate ratio and
concentration. A sample calculation showing
the rationality of this inference is given
below.
Comparing runs 72 and 73 shows an
equilibrium OH" concentration cor-
responding to the solubility of Ca(OH)2
,0.1116
in run 7_ versus the reaction ol
moles/liter of Ca(OH)2 (by reaction (4))
with the sulfate in run 73. Run 70 shows
n 3-hour OH" concentration appreciably
higher than for run 73 where no sulfite
was present. There are two competing re-
actions in run 70 (1,4). The change in
sulfite generates 0.0856 moles/liter of
hydroxide.
2[so3= initia, -so; fina,i
= 2 [0.055 moles/liter - 0.0122 moles/liter ]
= 0.0856 moles/liter OH"
The final hydroxide ion concentration
in run 70 of 0.1248 moles/liter implies
an additional reaction of lime with
sulfate.
l°H final ~ OH from sulfite reaction^
= [0.1248 moles/liter
- 0.0856 moles/literl
= 0.0392"moles/liter OH"
Thus, the fraction of the lime which
reacts with the sulfate is
fime reacted with sulfate
total initial lime
0.0392 moles/liter
2
0.077 moles/liter
= 25.4%
23
-------
0.014
0.012
0.010
CO
O
in
0.002
0.000
^
I
RUN NO.
67
A 70
72
70
67
73
72
2
TIME, hours
FigureS. Runs 67, 70, 72, 73 - special experiments Ca(OH)2/Na2 SO3 , Na2SO4 - checks on analytical results SO^ vs time.
-------
0.13
0.11
0.09
0.07
to
0.05
0.03
70
.. 57,
73
RUN NO.
67
A 70
72
73
72
TIME, hours
Figure 6. Runs 67, 70, 72, 73 - special experiments - Ca(OH)2/Na2SO3, Na2SO4 - checks on analytical results - OH'vs time.
-------
The same reasoning can be applied to
runs 66-71 and 48-53 to show that, in
the presence of the low sulfite levels
studied, significant reaction of the
calcium hydroxide with sulfate does
occur. Overall utilizations of calcium
hydroxide with the simulated scrubber
solutions (runs 66-71) amounted to
69-83 percent after 3 hours of reaction
time.
REACTIONS BETWEEN LIMESTONE AND
SULFITE-BISULFITE-SULFATE SOLU-
TIONS
determined by Coulter Counter analysis. The
Coulter Counter results indicate th;it the
"Fredonia fine" stone was 50 percent by mass
less than 6/J, and 90 percent by mass less than
22/j. The "Fredonia coarse" stone was 50
percent by mass less than I2ju, and 90 percent
by mass less than
Table 9 lists the reactants charged and the
resultant total sulfite concentrations analyzed
as a function of time. Runs were conducted at
a sulfate level corresponding to roughly 10 wt
% Na2SO4 in solution. Two bisulfite con-
centrations (0.02 and 0.06 g moles charged)
were studied for each stone with limestone
stoichiometries of 1 .0 and 1 .5.
Runs were conducted with two grinds of
Fredonia limestone (representing the stones
being used at the Shawnee wet limestone test
facility) to compare the effect of particle size
on bisulfite neutralization with limestone.
The two grinds, "Fredonia fine" and
"Fredonia coarse," were processed through an
1 8-mesh screen to remove lumps. The particle
size distribution of these two stones was
Three-hour total sulfite levels indicate
slightly higher reaction rates with the finer
stone. Differences might be considered almost
insignificant, although the small magnitude of
the difference in size of the two stones is
probably responsible for the slight differences
in reaction rates. Results shown in Table 4,
indicating the effect of stirrer speed, imply
that the reaction is diffusion limited by the
Table 9. BATCH EXPERIMENTS - LIMESTONES/NaHSO3, Na2SO3, Na2SO4
Run
74
75
76
77
78
79
80
81
CaC03
Fredonia
fine
0.01
0.015
0.03
0.045
Fredonia
coarse
0.01
0.015
0.03
0.045
Reactants
NaHSO3
0.02
0.02
0.06
0.06
0.02
0.02
0.06
0.06
charged, g
Na2SO3
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.02
moles
Na2SO«
0.60
0.60
0.60
0.60
0.60
0.60
0.60
0.60
H20
50
50
50
50
50
50
50
50
Total SO3 analysis
g moles/liter
1/2 hr
0.0188
0.0174
0.0548
0.0562
0.0177
0.0127
0.0562
0.0547
1 hr
0.0158
0.0165
0.0441
0.0412
0.0138
0.0116
0.0487
0.0446
3hr
0.0116
0.0123
0.0402
0.0403
0.0185
0.0130
0.0443
0.0405
26
-------
CaCO3. The slightly increased rate with the
finer limestone supports this implication.
Very fine and very coarse ('vlOju vs 100^)
stones should be compared to amplify the
slight differences seen in these runs. The rates
and utilizations of reactants using natural
limestone compare favorably with those using
reagent grade CaGO3.
CALCIUM ION CONCENTRATIONS
SCRUBBER SOLUTIONS
IN
Calcium ion concentrations in related
scrubber solutions are of prime importance to
thJs study. A number of calcium ion deter-
minations were done but, by themselves, were
felt to have little value. The most revealing
method of studying Ca*1" concentrations and
related SOj and SOJ concentrations is to
operate a small-scale continuous-scrubber
system and measure concentrations of interest
at steady state conditions. A followup to the
batch tests reported in this study will consist
of runs on a small, continuous double-alkali
scrubber. Actual operating conditions will be
closely simulated and steady state concentra-
tions will be determined for the important
components of the scrubber solutions. Special
attention will be given to Ca**, SOj, and SO^
concentrations at various points of interest in
the scrubber loop.
27
-------
SECTION VI
ACKNOWLEDGEMENTS
Assistance is gratefully acknowledged to time spent in conscientious effort on the
J. H. Abbott for his counsel and advice experimental work and to R. E. Valentine for
throughout, along with many reviews of the assistance in preparing this report. All are
material generated. Thanks and credit are also members of this Division's Research Labora-
due to J. W. Rives and B. E. Daniel for much tory Branch.
29
-------
SECTION VII
APPENDICES
Page No.
A. Double-Alkali Process Literature Study and References 33
B. Experimental Data and Results 35
C. Equilibrium Caustic Formation in Ca(OH)2-Na2SO4 Solutions 37
at 120°F
31
-------
APPENDIX A
DOUBLE-ALKALI PROCESS LITERATURE
STUDY AND REFERENCES
1. Borgwardt, R.H. "Experiments on the Precipitation of CaSO3 from
Bisulfite Solution with CaSO3>" EPA draft (June 1972).
2. Frazier, J.H. "A System for Removal of Sulfur Oxides from Industrial
Boiler Flue Gases," General Motors Plant and Environmental Engineering
Section, Illinois State Association paper, National Association of Power
Engineers, Chicago, Illinois, Nov 11, 1970.
3. Johnstone, H.F., H.J. Reade, and H.C. Blankmeyer. "Recovery of
Sulfur Dioxide from Waste Gases," Industrial and Engineering Chemistry,
pp. 101-109, vol. 30, No. 1, Jan 1938.
4. Kaplan, N. "A Study of Double Alkali Scrubbing of Sulfur Dioxide
from Flue Gases," EPA internal publication (Mar 1972).
5. Arthur D. Little, Inc. "Sulfur Dioxide Control Process Study - Sodium
Scrubbing with Lime Regeneration," report to State of Illinois Institute for
Environmental Quality, 1972.
6. Mascarello. J., J. Auclair, R. Hamlin, and C. Peleclier. "Sulfur Oxides
Removal from Flue Gases The Pilot Unit of the Saint-Ouen EDF Station,"
Proceedings of the A merican Power Conference, 31(1969).
7. Phillips, R.J. "Sulfur Dioxide Emission Control for Industrial Power
Plants." paper, Second International Lime/Limestone Wul Scruhhitii/
Symposium, Nov 8-12, 1971.
8. Potts, J.M., J.E. Jordan, M.C. Nason, J.A. Campbell, and A.V. Abies.
"Removal of Sulfur Oxides from Waste Gases - Alkali Limestone Process,"
TV A monthly report, Dec 1971.
9. Potts, J.M., A.V. Slack, and J.D. Hatfield. "Removal of Sulfur Dioxide
from Stack Gases by Scrubbing with Limestone Slurry: Small-Scale Studies
33
-------
at TVA," paper, Second International Lime/Limestone Wet Scrubbing
Symposium, Nov 8-12, 1971.
10. Rawa, R.T. "SO2 Control for Small Boilers," Pollution Engineering,
pp. 22-23, Jan-Feb 1972.
11. Wen. C.Y. (W. Va. University). EPA Contract EHS-D-71-20, Wet
Scrubber Study: Venturi Scrubber and Turbulent Bed Contactor, 1970-72.
1 2. "KiiriMui Flue Gas Dcsulfurization Process," Environmental Protection
and Industry (EPI). pp. 28-31, Mar-Apr 1972.
34
-------
Appendix B. EXPERIMENTAL DATA AND RESULTS
(All runs at 150°F unless otherwise noted)
Reactants charged
Run Ca(OH)2
1 0.466
2 0.25
3 0.95
4s 0.25
5 0.466
6 0.466
7 0.466
45 0.35
46 0.36
47 0.42
48 0.33
49 0.70
50 1.60
51 0.33
52 0.70
53 1.60
54
55
56
57
57-2
57-3
57-4
58
59
60
61
62
63
64
65
CaC03
0.01
0.015
0.03
0.045
0.045
0.045
0.045
0.01
0.015
0.03
0.045
t
0.01
0.015
0.03
0.045
Na2S03
0.50
0.25
1.0
0.25
0.50
0.50
0.50
0.18
0.19
0.22
0.01
0.01
0.01
0.05
0.05
0.05
0.01
0.01
0.02
0.02
0.02
0.02
0.02
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.02
, g moles
NaHSOj
0.34
0.35
0.40
0.02
0.02
0.06
0.06
0.06
0.06
0.06
0.02
0.02
0.06
0.06
0.02
0.02
0.06
0.06
Na2SO4
0.35
0.74
1.70
0.33
0.60
1.60
0.33
0.70
1.60
0.33
0.33
0.33
0.33
0.33
0.33
0.33
0.60
0.60
0.60
0.60
1.60
1.60
1.60
1.60
H2O Other
50
50
50
50
50 Few
50 Flyash
50 Few, Fly-
50 ash
50
50
50
50
50
50
50
50
50
50
50
50
50 400 rpm
50 800. rpm
50 1300 rpm
50
50
50
50
50
50
50
50
S03 analysis
g moles/liter
1/2 hr
0.1935
0.0508
0.5792
0.5900
0.1776
0.1832
0.2081
0.2587
0.2344
0.2535
0.0153
0.0111
0.0106
0.0076
0.0179
0.0384
0.0301
0.0311
0.0780
0.0725
0.0660
0.0671
0.0619
0.0297
0.0282
0.0804
0.0811
0.0274
0.0284
0.0756
0.0712
1 hr
0.1875
0.0535
0.5861
0.0543
0.1769
0.1797
0.1922
0.2537
0.2256
0.2642
0.0096
0.0106
0.0116
0.0076
0.0178
0.0327
0.0273
0.0318
0.0694
0.0605
0.0651
0.0517
0.0481
0.0294
0.0273
0.0782
0.0757
0.0266
0.0269
0.0749
0.0701
3hr
0.1865
0.0494
0.5924
0.0535
0.1653
0.1852
0.1685
0.2424
0.2181
0.2567
0.0091
0.0116
0.0116
0.0066
0.0125
0.0236
0.0247
0.0287
0.0580
0.0488
0.0566
0.0421
0.0388
0.0292
0.0254
0.0612
0.0452
0.0259
0.0260
0.0753
0.0676
OH~ analysis
g moles/liter
1/2 hr
0.7978
0.4431
1.125
0.4278
0.7728
0.7686
0.8723
0.2933
0.3721
0.4331
0.0902
0.1251
0.1098
0.1317
0.1348
0.1098
1 hr
0.8125
0.4480
1.141
0.4382
0.7978
0.7905
0.8466
0.2989
0.3721
0.4514
0.1024
0.1256
0.1171
0.1342
0.1378
0.1195
3hr
0.8175
0.4634
1.169
0.4452
0.8052
0.8064
0.7820
0.3111
0.3770
0.4636
O.I 037
0.1244
0.1195
0.1366
0.1384
0.1232
-------
Appendix B (Cont'd). EXPERIMENTAL DATA AND RESULTS
Run
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
Reactants charged
Ca(OH)2 CaC03
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
Fredonia
fine
0.01
0.015
0.03
0.045
Fredonia
coarse
0.01
0.015
0.03
0.045
, g moles
Na2S03 NaHS03
0.01
0.01
0.01
0.05
0.05
0.05
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.02
0.02
0.02
0.06
0.06
0.02
0.02
0.06
0.06
Na2S04
0.33
0.60
1.60
0.33
0.60
1.60
0.60
0.60
0.60
0.60
0.60
0.60
0.60
0.60
0.60
H20
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
S03 analysis
g moles/liter
1/4 hr 1/2 hr
0.006
0.0454
0.0008
0.0016
0.0188
0.0174
0.0548
0.0562
0.0177
0.0127
0.0562
0.0547
1 hr
0.006
0.0099
0.0093
0.0096
0.1320
0.0311
0.0006
0.0016
0.0158
0.0165
0.0441
0.0412
0.0138
0.0116
0.0487
0.0446
3hr
0.0056
0.0099
0.0079
0.0067
0.1190
0.0231
0.0006
0.0016
0.0116
0.0123
0.0402
0.0403
0.0185
0.0130
0.0443
0.0405
OH~ analysis
g moles/liter
1/2 hr 1 hr
0.0750 0.0982
0.1007 0.1086
0.0964 0.1061
0.1214 0.1244
0.1171 0.1232
0.0976 0.1074
0.0317 0.0323
0.1086 0.1086
3hr
0.1049
0.1147
0.1159
0.1269
0.1232
0.1135
0.0305
0.1116
OJ
"Run at 100 F
-------
APPENDIX C
EQUILIBRIUM CAUSTIC FORMATION
IN Ca(OH)2-Na^O7SOLUTIONSa
(at 120°F)
O
\-
0.2
0.15
0.1
o
£ 0.05
00
5
O
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
SODIUM CONCENTRATION, gm. moles/liter
Reproduced from reference 7.
37
-------
BIBLIOGRAPHIC DATA ' Report No. 2.
SHEET EPA-R2-73-186
4. Title and Subtitle
Regeneration Chemistry of Sodium-Based
Double -Alkali Scrubbing Process
. Author(s)
Dean C. Draemel
. Performing Organization Name and Address
EPA, Office of Research and Monitoring
NERC/RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
2. Sponsoring Organization Name and Address
EPA, Office of Research and Monitoring
Washington, D. C. 20460
3. Recipient's Accession No.
March 1973
6.
8' Performing Organization Kept.
No.
10. Project/Task/Work Unit No.
21 ACX 38
11. Contract/Grant No.
NA
13. Type of Report & Period
Covered
Final
14.
IS. Supplementary Notes
16. Abstracts
The report gives the results of a study of the reactions of calcium hydroxide,
calcium carbonate, and limestone with the aqueous (sodium, sulfite, bisulfite, and
sulfate) system. Concentrations and stoichiometries typical of those for sodium-
based double-alkali scrubbing systems were used. The reactions were studied in a
stirred, nitrogen-purged glass reaction vessel immersed in a constant-temperature
bath. The objectives were to study various reactions of importance in the sodium-
based double-alkali process and to define possible operating modes for the process.
Results indicate desirable operating ranges and may be used to support engineering
design of pilot-scale double-alkali scrubber systems. Appendices include
experimental data, references , and theoretical discussions.
17. Key Words and Document Analysis.
Air Pollution
*Desulfurization
Flue Gases
Washing
Chemical Reactions
Sodium Inorganic Compounds
Alkalis
Regeneration (Engineering)
Limestone
17b. Identifiers/Open-Ended Terms
Air Pollution Control
Stationary Sources
*Double-Alkali Process
Sodium/Calcium Process
Throwaway Process
17o. Descriptors
Sulfur Compounds
Reaction Kinetics
17e- COSATI Fie Id/Group
13B
18. Availability Statement
Unlimited
19. Security Class (This
Report)
20. Security Class (This
Page
UNCLASSIFIED
21. No. of Pages
43
22. Price
FORM NTIS-35 IREV. 3-72)
USCOMM-DC M9sa-P72
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