EPA-650/2-75-065
July 1975
Environmental Protection Technology Series
IDENTIFICATION
OF REGENERABLE METAL OXIDE
S02 SORBENTS FOR FLUIDIZED-BED
COAL COMBUSTION
U.S. Environmental Protection Agency
Office of Re
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EPA-650/2-75-065
IDENTIFICATION
OF REGENERABLE METAL OXIDE
S02 SORBENTS FOR FLUIDIZED-BED
COAL COMBUSTION
by
P. S. Lowell and 'I' B. Parsons
Radian Corporation
P. O. Box 9948
Austin, Texas 78766
Contract Mo. 68-02-1319, Task 10
ROAP No. 21ADD-042
Program Element No. IAB013
EPA Project Officer: P. P. Turner
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D.C. 20460
July 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Centre - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2. ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
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.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-650/2-75-065
11
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TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Objectives 2
1.3 Contents of the Report 3
2.0 SUMMARY AND RECOMMENDATIONS 4
2.1 Summary of Results 4
2.2 Recommendations for Future Work 9
3.0 RESULTS AND CONCLUSIONS 10
3.1 Sorption 10
3.2 Regeneration 12
3.3 Other Considerations 26
3.3.1 Support Materials 26
3.3.2 Heat Transfer 28
4.0 BIBLIOGRAPHY.
5.0 APPENDIX.
29
30
5.1 Technical Note 200-045-10-01a"Thermodynamic
Screening of Dry Metal Oxides for High
Temperature S02 Removal" 31
5.2 Technical Note 200-045-10-02a"The Thermo-
dynamics of Chemical Regeneration of Metal
Oxide S02 Sorbents" 107
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1.0 INTRODUCTION
This report summarizes work done by Radian
Corporation under EPA Contract No. 68-02-1319, Task 10.
The investigation was a theoretical study of the feasibility
of using dry metal oxides as regenerable SOa sorbents dur-
ing fluidized bed combustion. The work was performed from
July through December 1974.
1.1 Background
Direct-contact fluidized bed combustion employs a
granular bed material which does not undergo combustion.
The bed is fluidized by air. Heat exchange surfaces are
immersed in the fluidized bed where the fuel combustion rate
is extremely rapid. Heat exchange occurs in the actual com-
bustion zone between heat transfer surfaces and the fluidized
particles rather than hot combustion gases. The resulting
heat release rate is much greater than in conventional fur-
naces, and boilers utilizing fluidized bed combustion are
expected to be a fraction of conventional boiler size (AN-001).
In addition to savings due to reduction in the boiler
size, fluidized bed combustion offers the potential of provid-
ing efficient reduction in air pollutant emissions. The
fluidized bed may be used to advantage in this respect. While
particulate removal equipment is required, there may be no
requirement for additional stack gas cleaning equipment. Gas-
eous air pollutants NOX and S02 are formed during coal and oil
combustion in conventional furnaces. NOX formation from
thermal fixation of atmospheric nitrogen is anticipated to be
substantially reduced in fluidized bed combustion due to
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relatively higher heat release rates and lower combustion
temperatures. NOX formation from fuel-bound nitrogen is
still possible in fluidized bed combustion processes.
While formation of sulfur dioxide occurs in fluidized bed
combustion, studies have shown that its emission in stack
gas can be prevented by the utilization of limestone as the
granular bed material. Reaction of S02 with the limestone
produces calcium sulfate (AN-001).
There are a number of problems attendant with the
use of limestone as bed material and S02 sorbent. While
limestone is inexpensive and easily obtained in some areas,
there may be other locations at which the mineral is un-
available. In addition, some limestones are known to have
limited kinetic activity. Finally, the calcium sulfate
product must be either discarded as solid waste in a once-
through process or treated to regenerate the calcium oxide
(or carbonate) sorbent. Since the sulfate is thermally
quite stable, heating to decompose it requires prohibitively
high temperatures. Attempts at chemical regeneration with
a reducing agent have identified problems such as sulfide
formation.
1.2 Objectives
The goal of the work described herein was to
identify potential solid S02 sorbents for a fluidized bed
combustion sorption - regeneration process. Candidate
sorbents were to be evaluated theoretically using thermo-
dynamic analysis of the sorption and regeneration reactions.
The objective was to identify metal oxide sorbents which
could be chemically regenerated by reductive decomposition
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to produce a gaseous product containing S02 (or possibly S2).
Two options were investigated. The first was regeneration
directly to the oxide. The second option was a two-step re-
generation process with a sulfide intermediate. The thermo-
dynamic analysis was to employ data and computational tools
developed under an earlier study done for EPA (PA-016).
Because of the screening nature of this study only
a small amount of time could be spent on each potential sor-
bent. Point design conditions were chosen. Process assump-
tions were made. Situations that are based upon different
assumptions can give somewhat different answers. The differ-
ences are calculable and deviations from the results presented
here can usually be quantified.
1.3 Contents of the Report
A brief summary of the results of this analysis
and recommendations for continued investigation are given
in Section 2.0. The approach used for the theoretical study
of sorption-regeneration processes and implications of the
results are discussed in Section 3.0. Section 4.0 is the
Bibliography. Section 5.0, the Appendix, contains the two
technical notes which are the major product of this effort.
Technical Note 200-045-10-Ola, "Thermodynamic Screening of Dry
•Metal Oxides for High Temperature S02 Removal", gives the
complete details of the thermodynamic analysis of the sorption
process. Technical Note 200-045-10-02a, "The Thermodynamics
of Chemical Regeneration of Metal Oxide S02 Sorbents", gives
the detailed methods and results of the identification of
sorbents which can be regenerated by reductive decomposition
of the sulfate.
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2.0 SUMMARY AND RECOMMENDATIONS
Calculations were made to determine the three
following items:
the temperature range in which the sorbent
would pick up SOX,
the temperature range in which the sorbent
could be regenerated by a variety of reduc-
ing gases, and
an estimate of the sulfide forming tendencies
of the sorbents.
A general framework for screening was chosen.
Choices were made for screening criteria. For example, the
sorbent screening basis was the thertnodynamic ability to
reduce SOX to 100 ppm total SOX at one atmosphere. Regenera-
tion was with a gas at one atmosphere pressure containing
no diluents. While different pressures, equipment arrange-
ments, etc., will give somewhat different numbers, no gross
changes are expected as a result of basis changes.
2.1 Summary of Results
Fifty three single and binary metal oxides were
evaluated as candidate S02 sorbents for a fluidized bed
combustion process. The oxides were screened on the basis
of their potential to react with S02 to produce sulfates.
Thermodynamic calculations were made to determine
metal oxides for which the total SOX partial pressure in the
flue gas would be reduced to 100 ppm. Process temperatures
considered were 600 to 1400°C (1100-2550°F). Regeneration
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calculations were made with a reducing gas at one atmosphere
total pressure (with no diluent). Sorption or regeneration
conditions other than these might change the conclusions
slightly. The procedures used are outlined in enough detail
so that these adjustments may be made.
The sorption criteria used were that the sorbent must
be stable enough to sorb 802 but not so stable that regenera-
tion would be difficult. These criteria eliminated the not
stable enough sulfates, e.g., ferric sulfate, and the "too
stable" sulfates, e.g., potassium sulfate. It was found that
sodium,,calcium, strontium, and barium oxides; lithium, sodium,
calcium, strontium, and barium aluminates; lithium and sodium
ferrates; and lithium, strontium, and barium titanates produce
sulfates with the required stability. These compounds are
listed in Table 2-1.
The oxides were further evaluated to identify those
which could be regenerated directly by reductive decomposi-
tion of the sulfate in the temperature range 600-1400°C. Six
reducing agents were considered. They are listed in Table 2-2
in the order of their ability to react with oxygen. Note that
the reducing agents vary both in type (H2 versus C) and
stoichiometry (1 to 4). The sorbents were evaluated to deter-
mine if they could be regenerated or not. Regeneration to
the oxide was considered superior to regeneration to the sul-
fide. Therefore the oxide stability with respect to sulfide
formation was also calculated. Each reducing agent - sulfate
combination was evaluated from 600 to 1400°C.
As a result of this work, processes may be based on
compounds listed in Table 2-3. Sorption and regeneration
processes employing compounds were found to be thermodynamic-
ally favored between 600 and 1400°C. Individual temperatures
depend on the particular oxide-reducing agent combinations.
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TABLE 2-1
POTENTIAL SORBENTS BASED ON SORPTION CRITERIA
Na20
CaO
SrO
BaO
Li2Fe2On
Na2Fe2Oi,
Li2Al204
Na2Al20,
CaAl2Oi»
SrAl2Oi,
BaAl2Oi,
Li2Ti03
SrTi03
BaTi03
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TABLE 2-2
REDUCING AGENTS CONSIDERED
Reducing Agent Gram Atoms
per mole S02 0 Reacted
H2 1.0
CO 1.0
CO + %H2 1.5
C (char) 2.0
CH (coal) 2.5
CH, 4.0
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TABLE 2-3
COMPOUNDS SUITABLE AS A BASIS FOR A
HIGH TEMPERATURE S02 REMOVAL PROCESS
S02 sorption to form the sulfate and regeneration to form
the oxide:
Oxides Ferrates
calcium lithium
sodium
Aluminates
lithium
sodium Titanates
calcium strontium
strontium barium
barium
S02 sorption to form the sulfate and regeneration with
sulfide intermediate:
Oxides Titanates
calcium lithium
strontium strontium
barium
Aluminates
calcium
Ferrates
lithium
sodium
-8-
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2.2 Recommendations for Future Work
The thermodynamic analysis identified a number
of potential sorbents as well as the conditions at which
regeneration to the oxide is predicted. The selection of
materials and conditions on which to base a process should
begin with these. Continued work should include an evalua-
tion of published data on the physical and chemical properties
of these potential sorbents. Data of interest include such
things as melting and softening point, possibility of flux
formation or reaction with ash constituents, piezoelectric
properties, mechanical strength, etc. It is anticipated that
limited data may also be available describing tests of
fluidized bed combustor SOa removal and possibly sorbent
regeneration. These data should also be collected and
evaluated.
Thermodynamic predictions have provided a starting
point for future work which should be primarily experimental
in nature. Preliminary screening experiments to confirm the
predicted sorption and regeneration potentials are suggested
as a first step. The most promising candidates can then be
evaluated further in experiments to define the required
reaction kinetics.
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3.0 RESULTS AND CONCLUSIONS
This section presents a discussion of the results
of a thermodynamic analysis of high temperature S02 sorption
by metal oxides and reductive decomposition of the resulting
metal sulfate. The philosophy of this method of investiga-
tion is described, and the significance and implications of
the results are assessed. Details of methods used in obtain-
ing the results are given in the two technical notes in
Section 5. The sorption step is discussed in Section 3.1,
the regeneration step is assessed in Section 3.2, and other
problems are considered in Section 3.3.
3.1 Sorption
The fifty three metal oxides listed in Table 3-1
were evaluated as candidate SO2 sorbents. The candidates
were selected on the basis of oxide and sulfate stability.
Volatile oxides such as tungstates or molybdates and oxides
whose sulfates decompose at temperatures below 600°C were
not considered. Previous work had indicated that sulfate
is the S02 sorption product in the oxidizing combustion gas
atmosphere.
For an actual process to "go" a driving force
must exist. The driving force can be expressed as the
difference between actual conditions and equilibrium. The
tendency of metal oxide sorbents to form sulfates was eval-
uated by considering the driving force available for SOs
sorption. The available driving force was determined by
comparing the desired partial pressure of 80s in the com-
bustion gas (actual conditions) with the equilibrium S03
vapor pressure over the sulfate. At temperatures where the
S03 vapor pressure of the sulfate is less than the S03 partial
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RADIAN CORPORATION
TABLE 3-1
METAL OXIDES CONSIDERED IN THERMODYNAMIC SCREENING
Li80
NaaO
KaO
BeO
CaO
SrO
BaO
NiO
ZnO
CdO
Ce803
CeOa
LiA103
LisCr04
LiaCra04
LiFeOa
LiaTi03
LiVO,
NaA10a
NaaCr04
NaaCra04
NaFe08
KA10
NaVO,
KFeOa
KVO,
BeAla04
BeCr04
BeCr8 04
BeFea 04
BeTiOg
BeV806
CaAla04
CaCr04
CaCr304
CaFea 04
CaV206
SrAla04
SrCr04
SrCra 04
SrFea 04
SrTi03
SrVa06
04
BaCr04
BaCra 04
BaFe204
BaTi03
BaV303
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pressure in the combustion gas, there is a driving force for
the metal oxide to remove SO 3 from the combustion gas.
The driving force concept is shown in Figure 3-1.
For Sorbent 1 the sulfur oxide could not be completely removed.
Either Sorbent 2 or 3 could remove sulfur oxides down to the
appropriate level. Since the process is cyclical, Sorbent 2
will be thermodynamically easier to regenerate.
The vapor pressure of SO 3 over the metal sulfate
may be calculated from the following equilibrium.
Metal Sulfate -»• S03 + Metal Oxide (3 -la)
MexSO^ + S03 + MexO (3
Table 3-2 lists single and binary metal oxides for
which thermodynamic data indicate sulfate formation is favored
between 600 and 1400°C at combustion gas conditions. The
combustion exit conditions were chosen as 100 ppm total SOX ,
5% 02, and one atmosphere total pressure. These are condi-
tions that are more stringent than the EPA standard of 1.2
pounds SOz /million Btu. The conditions were purposely chosen
for a screening study for a second (or third) generation
process. For details see Appendix 5.1. The oxides listed in
Table 3-2 were evaluated further to identify conditions at
which regeneration could be accomplished.
3.2 Regeneration
While the simplicity of thermal decomposition is
intriguing from a process point of view, Table 3-2 indicates
that the sulfates formed are quite stable and prohibitively
high temperatures would be required. The same conclusion was
reached by Vogel and coworkers (VO-034) for the calcium system.
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Inlet
0)
n
3
to
to
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RADIAN CORPORATION
TABLE 3-2
POTENTIAL SORBENTS' FOR SOy REMOVAL FROM FLUE GASES
Maximum Sorption**
Sorbent* Temperature (°C)
Na20 1380
CaO 1090
SrO I260
BaO 1380
LiAl02 1200
LiFe02 950
Li2Ti03 1200
NaA102 820
NaFe02 1°20
CaAlzO- 950
SrAlzO., 1000
SrTi03 920
BaAlzO., 1000
BaTi03 1000
* Potential sorbents were selected on the basis of the
vapor pressure of SOs over the metal sulfate. If the
SOs vapor pressure was less than the partial pressure
of S03 in the flue gas, then a driving force for
sorption was said to exist. See Technical Note 200-
045-10-Olafor details.
** Conditions other than one atmosphere total pressure,
5% Oz, and 100 ppm SOX would change this maximum
temperature.
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Chemical regeneration as shown in reaction 3-2 was therefore
investigated.
Metal Sulfate + Reducing Agent -»• Metal Oxide + Products
(3-2)
Since the actual mechanism of the reductive decomposition
process is unknown, it is reasonable to choose some set of
steps which are assumed to be at equilibrium and which can
be evaluated using available thermodynamic data. The steps
shown below were convenient for the purposes of this study:
MexS(K •»• S03 + MexO (3-1)
SO3 + Reducing Agent •* Products (3-3)
MexSOi, + Reducing Agent •* MexO + Products (3-2)
The approach was to describe the individual reactions at
equilibrium at various temperatures within the range of
interest. Then the individual results were compared over
the temperature range and the conditions at which the over-
all reaction was feasible were identified. Note that reac-
tion 3-1 had been used in a similar manner for the sorption
step.
The conclusions reached in the regeneration study
are based upon logical but assumed process equipment arrange-
ments and operating conditions. Furthermore, there is an error
associated with the thermodynamic data used. The results,
which are a list of sorbents and suggested operating temperature
ranges, should be considered only as guidelines when making
decisions for further investigations.
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The six reducing atmospheres described in Table
2-2 were considered. The reducing atmospheres are of varying
strength, as indicated in Table 2-2 by their capacity to
react with oxygen.
The reducing agent must react with a very low
concentration of S03. The most efficient use of the reducing
agent occurs when it removes only one gram atom of oxygen
from S03 (S in the +6 oxidation state) to produce S02 (S in
+4 oxidation state). An example of this is reaction 3-4.
S03 + CO -» S02 + C02 (3-4)
Reduction of the 80s sulfur to a lower oxidation state by
production of 82 (oxidation state zero) is efficient only if
elemental sulfur is the desired product. Production of foS
(oxidation state -2) would be less efficient since that would
be a, greater reduction than is required. It could be more
efficient to produce a concentrated S02 stream from the
reducing agent - S03 reaction and to achieve any further
desired change in sulfur oxidation state by treating the
concentrated S02 stream when it is no longer in contact with
the sorbent.
The products of reaction between S03 and the
reducing agents were predicted by calculating the distribu-
tion of products at equilibrium for a number of temperatures
between 600 and 1400°C. Products considered are listed in
Table 3-3.
COS and CS2 are undesirable due to their toxicity.
Table 3-4 shows the major sulfur bearing and other products
formed from reaction between one mole of S02 with each of
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TABLE 3-3
GASEOUS PRODUCTS CONSIDERED
S02 H2 CO
SO3 H20 CO2
H2S 02 CH,,
COS CS2
S2
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RADIAN CORPORATION
TABLE 3-4
MAJOR PRODUCTS OF THE REACTION OF
SO3 WITH REDUCING AGENTS
Sulfur Bearing
Products Other Products
Reactants 600°C 1400°C 600°C 1400°C
S03 + H2 100% S02 100% S02 100% H20 100% H20
SO3 + CO 100% S02 100% S02 100% C02 100% C02
SO3 + CO + H' 83% S02 100% S02 75% C02 63% C02
17% H2S 25% H20 24% H20
6% CH,,
7% CO
SO3 + C + H 50% S02 86% S02 88% C02 66% C02
40% H2S 14% S2 12% H20 16% CH,,
10% S2 9% H20
14% CO
SO3 + C 66% S02 75% S02 100% C02 80% C02
34% S2 25% S2 20% CO
S03 + CH,, 100% H2S 86% S02 50% C02 20% C02
14% H2S 50% H20 40% CH,
40% H20
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the reducing agents. Note that COS and CS2 are not predicted
in significant quantities under these conditions. Variations
in type and excess of reducing agent and total pressure would
be expected to produce different product distributions.
As in the sorption step analysis, the feasibility
of reductive decomposition of metal sulfates with each
reducing agent was assessed by considering the available
driving force. Reducing gas S03 partial pressures were com-
pared to the S03 vapor pressure over the sulfate. At tempera-
tures where the vapor pressure of S03 over the sulfate was
greater than PSQ in the reducing gas, driving force was said
to exist for the sulfate to give up S03 to the reducing gas,
or decompose to the oxide. The regeneration concept is shown
in Figure 3-2. Regeneration Gas A is not as effective as
Regeneration Gas B. Sorbent 1 could be completely regenerated
by either gas, Sorbent 2 by Gas B, and Sorbent 3 by neither
gas.
Minimum temperatures at which such decomposition
would be thermodynamically favored are given in Table 3-5. In
general, Table 3-5 shows that the strongest reducing agents
give the lowest sulfate decomposition temperatures.
The actual path of the reductive decomposition will
depend partly on the equipment and operating conditions
selected. A cocurrent gas solid reactor would be accurately
described by the equilibrium calculations made. A fixed or
moving bed process may be operated so that a large excess of
reducing agent is present at the gas inlet. The reducing
gas is consumed as it moves through the bed. At low stoichi-
ometries, which are desirable from an economic standpoint, the
gas at the outlet approaches an oxidizing atmosphere. A counter-
current gas-solid contactor would provide different reducing
conditions than a cocurrent contactor and would be expected to
produce different products.
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Sulfated Sorbent
Inlet
Sulfated Sorbent
Sulfated Sorbent
FIGURE 3-2 - REGENERATION
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TABLE 3-5
I
ro
MINIMUM TEMPERATURES AT WHICH METAL SULFATES ARE REDUCED BY SIX REDUCING AGENTS*
Temperature (°C)
^•—^.^^ Reducing
Metal"""" — -^^Agents Hydrogen
Sulfates -"-.^^ H2
Na2SO*
CaSO*
SrSO*
BaSO*
Li2SO*
Li2SO*
LijSO*
Na2SO*
Na2SO*
CaSO* +
SrSO* +
SrSO* +
BaSO* +
BaSO* +
+ A120,
+ Fe20s
+ Ti02
+ A120,
+ Fe20,
AlzOs
A120,
Ti02
A120,
Ti02
>1400
1320
>1400
>1400
>1400
1110
>1400
830
1220
1180
1250
1020
1230
1190
Carbon
Monoxide
CO
>1400
1340
>1400
>1400
>1400
1160
>1400
800
1245
1220
1290
1040
1290
1220
Synthesis
Gas
CO + %H,
>1400
1025
1310
>1400
1400
825
1350
670
930
840
900
775
890
910
Coal Char
C/H = 1 C
>1400
960
1240
>1400
960
775
1140
645
875
790
840
735
840
850
>1400
960
1210
>1400
960
785
1140
655
890
800
860
740
850
860
Methane
CHu
>1400
730
1060
>1400
<600
660
<600
670
600
640
<600
630
630
* Minimum temperature for which the vapor pressure of SOj over the metal
sulfate is greater than the partial pressure of SOj in the reducing gas.
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The literature indicates the possibility of
formation of metal sulfides (BO-001) and reduction to the
elemental metal (PO-001) during reductive sulfate decompo-
sition. The formation of metal sulfides would be undesirable
since an additional processing step would be required to
produce the oxide for recycle. Therefore, the possibility
of metal sulfide formation in the reducing gases was con-
sidered. Transition between oxide and sulfide is shown in
reaction 3-5.
MexO + %S2 * MexS + %02 (3-5)
Partial pressures of 62 and 82 over the metal oxide and sulfide
at equilibrium were compared to those in the reducing gases.
The temperature range where PQ2/PS2 is greater in the reducing
gas than over the metal oxide and sulfide at equilibrium was
identified. In that temperature range the oxide is predicted
to be stable. Each oxide was evaluated for the temperature
range for oxide stability with respect to sulfide formation
in each reducing gas. Table 3-6 summarizes the predicted
temperature ranges for oxide stability for each sulfate-
reducing agent combination.
Conditions and reagents for oxide producing and
sulfide producing regeneration processes were identified
using the data from Tables 3-5 and 3-6. Table 3-7 lists
sorbent-reducing agent combinations and temperature ranges
for processes in which oxide formation is predicted. Table
3-8 lists sorbent-reducing agent combinations and temperature
for processes in which sulfide formation is predicted.
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TABLE 3-6
MINIMUM TEMPERATURE OF STABILITY OF METAL OXIDE WITH RESPECT TO
FORMATION OF METAL
SULFIDE IN REDUCING GAS*
Temperature (°C)
*-» Reducing
Metal • — ^Agents Hydrogen
Oxide ^"^-^^^ H2
Na20
CaO
SrO
BaO
LiA102
LiFeOz
AljO,
Ti02
NaAIOz
NaFeOz
CaAl20»
SxAl20»
SrTiOj
BaAljO,
BaTIO,
LizTiOi
970
<600
<600
<600
<600
<600
<600
600-1190
<600
<600
<600
<600
<600
<600
<600
<600
Carbon Synthesis
Monoxide Gas
CO CO + %H2
955
<600
590
700
<600
<600
<600
880-1325
<600
<600
<600
<600
<600
<600
<600
<600
>1400
1250
>1400
>1400
<600
750
<600
>1400
<600
820
740
<600
<600
<600
<600
<600
Coal
C/H = 1
>1400
>1400
>1400
>1400
<600
1100
<600
>1400
<600
1175
1360
<600
<600
<600
<600
<600
Char
C
>1400
>1400
>1400
>1400
<600
975
<600
>1400
600
1030
970-1350
<600
<600
<600
<600
<600
Methane
CH*
>1400
1370
>1400
>1400
<600
890
<600
>1400
<600
980
890
<600
<600
<600
<600
<600
Minimum temperature at which the ratio of oxygen activity to sulfur activity
in the reducing gas is greater than the ratio of oxygen to sulfur activities
at equilibrium for the reaction 2MeO + S2 * 2MeS + 02.
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TABLE 3-7
SORPTION-REGENERATION PROCESSES IN WHICH OXIDE FORMATION OCCURS
Maximum Sorptlon
Temperature
Sorbent (*C)
CaO 1090
LlAlOi 1200
LIFeOi- 950
NaAlO, 820
NaFeOi- 1020
CaAliO. 950
SrAlaO, 1000
SrTiO, 920
BaAl,Ot 1000
BaTIO, 1000
1. Formula Reducing Agent
CH» Methane >
C + Wz Coal
C Char
CO + %H, Synthesis Gas
CO Carbon Monoxide
HI Hydrogen
Temperature Range for
Regeneration with
. Oxide Formation
Reducing Aftent-i («C)
Hi 1320-1400
CO 1340-1400
CO + %H, 1250-1400
CH. 1370-1400
Coal and Char 960-1400
CH» 600-1400
Hi 1110-1400
CO 1160-1400
CO + *Hi 825-1400
Coal 1100-1400
Char (975?) 1020-1400
Methane 890-1400
Hi 830-1400
CO 800-1400
CO + %Hi 670-1400
Coal and Char 650-1400
Methane 600-1400
Ht 1220-1400
CO 1245-1400
CO + %Hi 930-1400
Coal 1030-1400
Char 1175-1400
Methane 980-1400
Hi 1180-1400
CO 1220-1400
CO + *H, 840-1400
Char 970-1350
Coal 1360-1400
Methane 890-1400
Hi 1250-1400
CO 129.0-1400
CO + %H, 900-1400
Coal and Char *850-1400
Methane 640-1400
Ha 1020-1400
CO 1040-1320
Hi 1230-1400
CO + %Hi 1290-1400
Coal and Char 850-1400
Methane 630-1400
H, 1190-1400
CO 1220-1320
One mole of reducing agent per mole
of S0| was assumed.
2. Possibility of Iron sulflde formation not inveatlgate'd due to lack
of thermodynamlc data.
-24-
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TABLE 3-8
SORPTION-RECEHERATIOH PROCESSES IB WHICH SUT.FIDE FORMATION OCCURS
Maximum Sorption
Temperature
Serbenc CO Reduclne Aeentl
CaO
SrO
UTcOi A
HaFeOt A
CaM.,o.
SrTtOi
BaTlOi
LiiTlOi
i. formula
CH.
C + %H,
C
co + w,
CO
H,
1090 CO + Wi
Coal and Char
Hechane
1260 00 * %H,
Coal and Char
Methane
950 Coal
Char
Methane
1020 Coal
Char
Methane
950 Char
Coal
Methane
920 CO
CO* «Hi
Coal and Char
Methane
1000 CO
CO + Wt
Coal and Char
Methane
1200 CO •*• %H,
Coal and Char
Methane
Reducing Agent
Methane •
Coal
Char On? "wle °*
> aoif et so>
Synthesis Gas [
Carbon Monoxide
Hydrogen f
Temperature Range for
Regeneraclon with
SulClde Formation
(•C)
1030-1250
960-1400
725-1370
1310-1400
1240-1400
1060-1400
775-1100
775-1020 (9757)
600-890
875-1030
875-1175
670-980
800-970
800-1360
600-890
1320-1400
775-1400
740-1400
600-1400
1320-1400
910-1400
830-1400
630-1400
1330-1400
1140-1400
660-1400
reducing agent per
was assumed.
2.
'Ul"dC fonMtlon "« investigated due co lack of
-25-
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3.3 Other Considerations
Although the main thrust of this program was devoted
to thermodynamic screening of potential sorbent and regenera-
tion materials, limited consideration was given to support
material and heat transfer requirements. The results of those
considerations are briefly discussed in the following sub-
sections .
3.3.1 Support Materials
The majority of the potential sorbents identified
by thermodynamic screening could not be used in their pure
form but would have to be distributed or dispersed on some
support material. Some of the reasons for supporting the
sorbent materials include:
(1) to increase resistance to sintering,
(2) to increase resistance to poisoning,
(3) to improve thermal conductivity to and
from the sorbent surface and in the
fluidized bed,
(4) to improve the mechanical strength of the
sorbent system and reduce abrasion losses,
and
(5) to provide suitable framework for deposi-
tion of the sorbent resulting in a greater
total surface.
-26-
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One of the questions to be answered in this program was
whether or not supports existed which would be suitable for
use at high temperatures in a fluidized bed. To answer this
question several catalyst carrier manufacturers were con-
tacted (MC-122, FR-110, PE-105). Criteria given to the carrier
manufacturers were that the support should be inert, have high
thermal stability, and have high mechanical strength.
Contacts with the carrier manufacturers indicated
that a wide variety of materials, shapes, sizes, porosities
and structures were available. Low surface area carriers
(less than 3m2/g) such as a-alumina and various refractories
were suggested as being suitable. However, it was the general
conclusion of all manufacturers contacted that definitive
recommendations on support materials could not be made until
more was known about the porosity and surface area requirements.
Porosity, pore structure, and pore size are extremely
important factors in the selection of support materials. The
pore structure of a particular support will be a controlling
factor in the way a sorbent will be deposited. It will also
contribute significantly to the final properties of a finished
sorbent which affect residence time of reactants within the
structure, rate of reaction, useful sorbent surface area, and
the extent of undesirable side reactions. Clearly any future
experimental work on the potential sorbents identified in
this study should be devoted in part to identifying the support
material porosity and surface area requirements.
-27-
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3.3.2 Heat Transfer
In the development of a process it is essential
to make both material and heat balances. The calculations
presented thus far have addressed themselves to the tempera-
ture and pressure at which a process might proceed. It is
also important to assess the heat transfer requirements.
It would be desirable to have the solid from the
sorber pass to the regenerator and come back without involv-
ing a heat transfer step. Should this not be possible, the
amount of heating (or cooling) required must be known. An
estimate was made for the calcium system. This estimate
indicated that the decomposition of the sulfated sorbent is
highly endothermic (requires heat). The reaction of the
evolved S03 with the reducing gas is moderately exothermic
(gives off heat). The amount of heat given off is slightly
dependent on which reducing gas is used. The net effect is
a heat requirement of about 50 Kcal per mole of sulfate
decomposed.
While the calculation of heat requirements is beyond
the scope of this screening study, it does appear as if most
regeneration processes will be endothermic. Heat balances
must be considered in future work.
-28-
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4.0 BIBLIOGRAPHY
AN-001 Anonymous, "Fluidized Bed Steam Generators for
Utilities", Environmental Science and Technology
8(12), 968-70 (1974).
BO-001 Bowen, J. Harry and C. K. Cheng, "Regeneration of
Sulfated Alkalized Alumina", Environmental Science
and Technology 8(8). 747-51 (1974).
FR-110 Fritz, R. C.,. Private Communication, Girdler Chemical
Inc., Catalysts Division, 6006 Bellaire Blvd., Suite
118-5, Houston, Texas, 77036, 18 October 1974.
MC-122 McDowell, Robert G., Private Communication, Norton
Company, Chemical Process Products Division, 3701
Kirby Building, Suite 890, Houston, Texas, 77006,
10 August 1974.
PA-016 Parsons, T. B., Gary D. Schroeder, and David DeBerry,
Applicability of Metal Oxides to the Development of_
New Processes for Removing S02 from Flue Gases, two
volumes, Austin, Texas, Tracor, Inc., 1969.
PE-105 Perkins, J. D., Private Communication, The HarsHaw
Chemical Company, P.O. Box 6813, Houston, Texas,
77005, 14 October 1974.
PO-001 Pohlenz, J. B., "The Shell Flue Gas Desulfurization
Process", presented at the Environmental Protection
Agency Flue Gas Desulfurization Symposium, Atlanta,
Georgia, November 4-7, 1974.
VO-034 Vogel, G. J., et al.. Reduction of Atmospheric Pollu-
tion by_ the Application of Fluidized-Bed Combustion
and Regeneration of Sulfur-Containing Additives. EPA-
R-2-73-253. Argonne, 111., Argonne Nat'l Lab., 1973.
-29-
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5.0 APPENDIX
5.1 Technical Note 200-045-10-Ola
"Thermodynamic Screening of Dry Metal Oxides for
High Temperature S02 Removal", prepared by N. P.
Phillips, 1 May 1975.
5.2 Technical Note 200-045-10-02a
"The Thermodynamics of Chemical Regeneration of
Metal Oxide S02 Sorbents", prepared by Philip S.
Lowell and Terry B. Parsons, 25 April 1975.
-30-
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*• ;'f"-.ifs}"-r&*- •
-.IT. >j:.j 'i'^^fc v
Section 5.1
TECHNICAL NOTE 200-045-10-Ola
THERMODYNAMIC SCREENING
OF DRY METAL OXIDES FOR HIGH
TEMPERATURE S0a REMOVAL
1 May 1975
Prepared by:
N. P. Phillips
-31-
8500 Shoal Creek Blvd./PO. Box 9948/Austm, Texas 787667(512)454-4797
-------
TABLE OF CONTENTS
Page
1.0 INTRODUCTION 33
2.0 METHODS 34
2.1 Selection of Sorbents for Screening 34
2.2 Thermo dynamic Screening 38
3.0 RESULTS 43
4.0 BIBLIOGRAPHY 48
APPENDIX - FIGURES A-l THROUGH A-53 49
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RADIAN CORPORATION
1.0 INTRODUCTION
This technical note presents the results of the
thermodynamic screening of potential metal oxide and mixed
metal oxide sorbents for use as S03 sorbents in high temperature
fluidized bed combustors. Fluidized bed combustion of fossil
fuels for electrical power generation, as all combustion pro-
cesses, generates sulfur oxide emissions. One approach to SOX
removal for this combustion method is injection of limestone
into the combustion zone. In many cases, however, limestone
has been found to be unsuitable for fluidized combustion pro-
cesses. This has been due to either limestone type or process
conditions. Also, there are some locations in which limestone
is not readily available. Therefore, metal oxides and mixed
metal oxides will be evaluated as alternate high temperature
regenerable S0a sorbents to avoid these problems.
In a previous study, a thermodynamic approach was
employed to select potential dry metal oxide sorbents for a
lower temperature S0a removal process (PA-016). The methods
developed during that study were applied to the screening task
involved in the present investigation. These earlier results
are extended to high temperatures, and the fact that SOg is
not the dominant species is accounted for.
-33-
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2.0 METHODS
Although the species actually sorbed during the
sorption process is 802, the relative pressures of SO3 in the
flue gas and over the metal sulfate determine the feasibility
of a metal oxide as an S02 sorbent. The actual mechanism of
reaction is unknown. The S02 is probably catalytically oxi-
dized and reacts with the metal oxide. A generalized reaction
for sulfate decomposition is shown in Equation 1. While
Equation 1 results in formation of the metal oxide plus SO3,
it is equivalent to the decomposition to oxygen and sulfur
dioxide as discussed by Vogel, et al. (VO-034, page 35).
MexSOu * MexO + S03 (1)
For a metal oxide to be an effective sorbent, the
metal sulfate must be stable at the temperature at which sorp-
tion takes place. The degree of sulfate stability is indicated
by the vapor pressure of S03 over the solid sulfate at the
temperature of interest. A potential sorbent will remove
SOX at temperature T if the partial pressure of SO3 in the
flue gas is greater than the vapor pressure of 80s over the
metal sulfate. Comparison of these two partial pressures
over the temperature range of interest (750-1200°C) will be
used as the basis for screening potential metal oxide SO*
sorbents.
2.1 Selection of Sorbents for Screening
The results of an earlier investigation (PA-016) of
a dry metal oxide SOz removal process were used as a starting
point for the sorbent screening task in this study. In the
earlier work, a computerized data base of thermodynamic prop-
erties was compiled for inorganic metal oxides, mixed metal
oxides, sulfates, sulfur oxide gaseous species, and numerous
-34-
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other inorganic compounds. Decomposition behavior as reported
in the literature was also reviewed. Logarithms of the equi-
librium constant (which is numerically equal to the partial
pressure of S03) for reactions of the type shown in Equation
(1) were calculated and plotted as a function of temperature
through 800°C for a number of metal oxides. Analysis of these
earlier results was used as a preliminary screening technique
for high temperature SOS sorbents. The following criteria were
used:
1. Metal oxides whose sulfates decompose
below 600°C were eliminated (PA-016,
T.M. 004-009, Ch. 8 and 16).
2. The oxide itself must be stable at high
temperature (PA-016, T.M. 004-009, Ch. 7).
3. For those oxides whose sulfates are stable
up to at least 600°C, the SO, vapor pres-
sure over the sulfate at 600°C should be
low enough to allow sufficient free energy
available as driving force for S03 sorp-
tion (PA-016, Section 8.2).
4. Potential single metal oxide sorbents were
eliminated from further consideration if
they were not produced in reasonable
quantities (PA-016, T.M. 004-009, Ch. 6).
5. The thertnodynamic data base must contain
standard state heat of formation, absolute
entropy, and heat capacity coefficients
for each species involved in the reaction
in order for log K to be calculated.
-35-
-------
Estimation methods were used to supply
some of the data. Those oxides for which
the necessary information was not avail-
able and could not be estimated were
excluded from further consideration.
6. Binary metal oxides of alkali and alkaline
earth compounds were considered. However,
because of their volatilities, molyb-
dates and tungstates were not included
in the study. In addition, silicates
were not considered because thermodynamic
data for this class of compounds had not
been included in the data base.
Table I shows the results of this initial screening.
Heat capacity data over the temperature range of
interest for the reactants (metal sulfates) and products (metal
oxides plus S03) of the sulfate decomposition reaction are
required to calculate log K. In most cases the range of validity
for the heat capacity coefficients stored in the data base does
not extend to 1400°C, the upper temperature limit in this inves-
tigation. The computer routine used to calculate log K auto-
matically extends the range of the stored heat capacity coef-
ficients; therefore, it was necessary to check the validity of
such extensions. The expected behavior of heat capacity at
high temperature is a gradual increase with increasing tempera-
ture. However, negative values for B, C, or D in the heat
capacity equation shown below may cause a slight decrease at
high temperatures.
C - A + BT + CTa - DT~8 (2)
-36-
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TABLE I
RESULTS OF PRELIMINARY SCREENING OF METAL OXIDES
***
Sulfate Decomposition > 600°C
Li20
Na20
K20
Rb20*
<
Cs20
BeO
MgO*
CaO
SrO
BaO
Sc203*
Sulfate Decomposition < 6000C
Ti02
Zr02
Hf02
V203
Y203 ^
La203
Ce203
Ce02
MnO*
Mn02*
Mn20 3
Fe203
CoO*
NiO
V02
V205
Cr203
CuO
*
Cu20
. «**
Ag20
ZnO
CdO
A1203*
PbO**
Pb02 **
Bi203*
Th02*
FeO
Sn02
U02
Sulfate Decomposition Data Unavailable
Nb205
Ta205
Mo03
WO 3
Re02
Rhx°>
Ir02
PdO
Ga203
Ge02
Sb203
**
***
Indicates oxides eliminated from further consideration on
the basis of S03 partial pressure over the sulfate.
Oxide is very unstable in temperature range of interest,
therefore not considered further.
No heat capacity data available.
-37-
-------
This error would introduce inaccuracies into the log K calcula-
tion. Therefore, a short computer program was written and used
to calculate heat capacity values at 100 degree intervals over
the temperature range from 600 to 1400°C using the coefficients
stored in the data base. This was done for S03 and all can-
didate metal oxides and corresponding sulfates. The only
compound data set requiring revision was that of S03 . This
was accomplished by correlating heat capacity versus temperature
data reported in the literature using a least-squares curve
fitting routine to estimate improved heat capacity coefficients.
2.2 Thermodynamic Screening
As described previously, the free energy available
as driving force for S08 sorption is related to the difference
between vapor pressure of S03 over the sulfate and flue gas
S03 partial pressure. These two were calculated separately and
compared in the final screening analysis.
The flue gas S03 partial pressure is described by
the following equilibrium reaction:
S03 * S0a + J?0a (3)
The equilibrium constant for this reaction may be written
*
aso3
(4)
Thus, the concentrations of S03 and SOS at a given temperature
are a function of the total SOX present (assumed to be 100 ppm
or 10" atm) , the oxygen partial pressure in the flue gas, and
the equilibrium constant at that pressure.
-38-
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The choice of the total SOX partial pressure is
somewhat arbitrary. The following rationale was followed. A
pound of coal will generate 0.45 to 0.6 pound moles of flue
gas. Heating values range from 9000 to 12000 Btu per pound.
To meet an emission regulation of 1.2 pounds SO2/mi11ion Btu
would result in S02 concentrations of 200 to 500 ppm based
upon the above ranges. In setting a goal for second genera-
tion processes it is advisable to look beyond today's
requirements. For this reason 100 ppm was chosen as a basis
with 5% 02 in the flue gas.
Log KI (per mole SO3) was calculated and plotted
from 600 to 1400°C at flue gas oxygen partial pressures of
0.02, 0.03, 0.05, and 0.10 atm. The following expression
was then used to calculate SO3 partial pressures at 50 degree
intervals over the temperature range of interest.
(PSO,)(P0*)%
Log Ki = Log -22* ?J_
PS03
SO3 concentrations derived from the log KI calculations
agreed well with expected values. At 0.05 atm Oa the calcu-
lated SO3 content was 70 ppm at 600°C and 0.5 ppm at 1400°C.
Table II shows the results for the case in which the oxygen
standard state was 0.05 atm.
The second parameter which was calculated was the
vapor pressure of S03 over the metal sulfate. This was
determined by calculating the equilibrium constant for the
sulfate decomposition reaction (Equation 1) for each poten-
tial sorbent over the temperature range of interest. The
equilibrium constant for this reaction is numerically equal
to the partial pressure of S03 if activities of the solid
-39-
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TABLE II
PARTIAL PRESSURE OF S03
IN FLUE GAS
(Total SOX = 100 ppm, 02 = 57., Total Pressure = 1 atm)
Temp.
°C
600
650
700
750
800
850
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
K, =
K* 3
J^
log 10 Ki
-0.32680
-0.01807
0.25752
0.50485
0.72788
0.92987
1.1135
1.2810
1.4344
1.5752
1.7048
1.8243
1.9349
2.0374
2.1326
2.2212
2.3037
*
0.47118
0.95922
1.8093
3.1978
5.3442
8.5088
13.646
19.098
27.189
'37.601
50.676
66.727
86.079
108.99
135.71
166.42
201.23
equilibrium constant
K,
1 + K?
1.47118
1.95922
2.8093
4.1978
6.3442
9.5088
14.646
' 20.098
28.189
38.601
51.676
67.727
87.079
109.99
136.71
167.42
202.23
1.0x10"*
S°3 1 + rf
6.7973x10"*
5.1041x10"*
3.5596x10"*
2.3822x10"*
1.5762xlO"5
1.0517x10"*
6.8278x10"*
4.9756x10"'
3.5475x10"'
2.5906x10"'
1.9351x10"'
1.4765x10"'
1.1484x10"'
9.0917x10"'
7.3147x10"'
5.9730x10"'
4. 9449x10" '
Io8 PS03
-4.1677
-4.2921
-4.4486
-4.6230
-4.8024
-4.9781
-5.1657
-5.3031
-5.4501
-5.5866
-5.7133
-5.8308
-5.9399
-6.0413
-6.1358
-6.2238
-6.3058
for the reaction SO, «• S0a + 0.5 Oa
(0.05)'
-40-
-------
species are equal to one. Log K per mole of S03 was calculated
from thermodynamic data stored in the data base and plotted as
a function of temperature for all metal oxides listed in
Table III. The resulting curve was equivalent to the logarithm
of the vapor pressure of S03 over the sulfate.
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RADIAN CORPORATION
TABLE III
METAL OXIDES CONSIDERED IN THERMODYNAMIC SCREENING
LiaO
Na20
BeO
CaO
SrO
BaO
NiO
ZnO
CdO
Ceaa,
CeOa
LlAlOg
LiaCr04
LiaCra04
LiFeOa
KA10
NaA10a
NaaCr04
NaaCra04
NaFeOs
NasTiO,
NaVOj
KFe08
BeAla04
BeCr04
BeCra 04
BeFes 04
BeTi03
BeV806
CaAla04
CaCr04
CaCra04
CaFea04
CaV206
Sr Ala 04
SrCr04
SrCr8 04
SrFe8 04
SrTi03
SrV806
BaAla04
BaCr04
BaCra 04
BaFea 04
BaTiOa
BaV806
-42-
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3.0 RESULTS
The selection of promising high temperature S0a
sorbents was made on the basis of free energy available as driv-
ing force for sorption. The results of the calculations described
in the preceding section were used for this analysis. The plots
of log K per mole S03 versus T for the various sulfate decom-
position reactions were compared to the plot of log Pqo versus
T for the S03 - SOS equilibrium reaction. Comparison ol the
two plots provides a direct means of determining if the process
is thermodynamically feasible. That is, if the partial pressure
of S03 in the flue gas is greater than vapor pressure of S0a
over the sulfate, sorption will occur. The plots for each
sulfate decomposition are included in the appendix to this tech-
nical note. Also shown on each figure is the plot of log PSQ
versus temperature representing the flue gas S03 partial pressure.
For temperature regions in which the curve of log K
per mole S03 for the sulfate decomposition reaction indicated
(i.e., PSQ over the sulfate) is above the curve of log PSQ
(i.e., partial pressure of S03 in the flue gas), sorption is not
thermodynamically favored. For the region below the log Pqo
curve, the vapor pressure over the sulfate is less than the flue
gas S03 partial pressure. Therefore, SO, could be sorbed from
flue gas in that temperature range. In the example shown in
Figure 1, the portion of the curve above A represents the feasible
sorption range and below A the unfeasible region. Using this
basic criterion, the potential sorbents were screened from 750-
1200° C.
Several other criteria were also employed in the
screening. Very low values of log K for the sulfate decomposi-
tion reaction, say about 6 logarithmic units below the flue gas
-43-
-------
o:
»—
oo
z
o
CJ
01
CD CO
•—i CD
LU
o z:
p LU
o a.
700
800 900 \QOO ]\00 1200 1300
TEMPERflTURE - DEGREES CENTlGRflOE
1400
08 flUG 74
FIGURE 1
Log K Versus T for A Sulfate Decomposition Reaction
-------
SO3 line, indicate stable sulfates. In such cases, although
sorption would occur readily, the oxide might not be suitable
for an S02 removal process because of high energy requirements
for sorbent regeneration. In Figure 1 the portion of the
curve below B is less desirable. There is no sharp cutoff so
judgment is required. One of the purposes of this screening
study is to identify metal oxide - S03 reactions that form
sulfate for which the free energy change is very large. Such
metal oxides would be attractive as sorbents. However, the
energy requirement in the regeneration step would be too
great. This idea is illustrated by comparing Figures 1 and
A-3. Figure 1 shows a sorbent with a relatively small free
energy change (several logarithmic units) for the sulfate
forming reaction. Figure A-3 shows a difference of 10 to 25
logarithmic units between the two S03 partial pressures.
Such a metal oxide would be eliminated from further considera-
tion for the reasons just described.
A relatively gradual increase of log K with respect
to increasing temperature indicates a lower heat of reaction
than a curve with a steep slope over the temperature range of
interest. The sorption reaction with a lesser slope would
require much less heat but a greater temperature change for
thermal regeneration than would a reaction whose equilibrium
constant increases rapidly with temperature. Regeneration by
altering the chemical conditions, e.g., reducing atmospheres,
will also be considered.
The purpose of this study is to use approximate
thermodynamic calculations for identifying metal oxides for
which S03 sorption-regeneration is favored. The approach is
to eliminate some of the metal oxides from consideration as
potential sorbents. If a metal oxide is "on the borderline",
it is not eliminated, since the data used in screening are
-45-
-------
approximate. A factor of 10 in S03 partial pressure (one
logarithmic unit) is not significant for this screening study,
and a potential sorbent would not be screened out on that
basis. In summarizing the criteria described above, the most
promising candidates are those whose log K plots lie less
than five logarithmic units below the log Pgo curve. The
type of regeneration used will depend on the slope over the
temperature range from 750 to 1200°C.
Based on the above criteria, the metal oxides having
the greatest potential as SOZ sorbents in a fluidized bed com-
bustion system are listed in Table IV. The temperature range
over which the criteria hold are included for each compound.
As seen in Table IV, the only single metal oxides
having any potential are strontium oxide and calcium oxide
since sodium and barium oxides are feasible only over very
narrow temperature ranges. Calcium oxide appears feasible
over the lower region of the temperature range of interest,
while strontium oxide has potential only in the upper region
of the temperature range considered. Several binary metal
oxides containing aluminum, titanium, or iron(III) also appear
promising. Of these LiA102 and Li2Ti03 meet all criteria over
the whole temperature range considered in this investigation.
-46-
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TABLE IV
MOST PROMISING SORBENTS
BASED ON THERMODYNAMIC SCREENING RESULTS
Temperature Range
Sorbent 1C
NaaO 1100-1200
CaO 750-1090
SrO 950-1200
BaO 1080-1200
LiA10a 750-1200
LiFeOa 750-950
LiaTi03 750-1200
NaAlOp 750-820
NaFe08 750-1020
CaAla04 750-950
SrAla04 750-1000
SrTi03 750-920
BaAls04 750-1000
BaTi03 750-1000
-47-
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4.0 BIBLIOGRAPHY
PA-016 Parsons, Terry, Gary D. Schroeder, and David DeBerry,
Applicability of Metal Oxides to the Development of
New Processes for Removing S02 from Flue Gases,
Two Volumes, Austin, Texas, Tracer, Inc., 1969.
VO-034 Vogel, G. J., et al., Reduction of Atmospheric
Pollution by_ the Application of Fluidized-Bed
Combustion and Regeneration of Sulfur-Containing
Additives. EPA-R2-73-253, Argonne, 111., Argonne
National Lab., 1973.
-48-
-------
RADIAN CORPORATION
APPENDIX
FIGURES A-l THROUGH A-53
-49-
-------
LIST OF FIGURES
Figure
A-l Log K Versus T for the Reaction
LiaS04 ?» Li80 + S03
A-2 Log K Versus T for the Reaction
NaaS04 2 NaaO + S03
A-3 Log K Versus T for the Reaction
KaS04 ji KgO + S03
A-4 Log K Versus T for the Reaction
BeS04 2 BeO + SQg
A-5 Log K Versus T for the Reaction
CaS04 2 CaO + SO,
A-6 Log K Versus T for the Reaction
SrS04 «» SrO + S0a
A-7 Log K Versus T for the Reaction
BaS04 T* BaO + S03
A-8 Log K Versus T for the Reaction
NiS04 i> NiO + S03
A-9 Log K Versus T for the Reaction
ZnS04 i* ZnO + S03
A-10 Log K Versus T for the Reaction
CdS04 j» CdO + S03
A-ll Log K Versus T for the Reaction
1/3 Cea(S04)3 S 1/3 Ce803 + S03
A-12 Log K Versus T for the Reaction
%Ce(S04)8 £ %Ce08 + Spg
A-13 Log K Versus T for the Reaction
LiaS04 + Ala03 ? 2LiA10a + S03
-50-
-------
Figure
A-14 Log K Versus T for the Reaction
Lis04 + Cr03 «» LiaCr04 + S03
A-15 Log K Versus T for the Reaction
LiaS04 + Cr803 2 LiaCr804 + S03
A-16 Log K Versus T for the Reaction
Li8S04 + Fe803 «» 2LiFeOa + S03
A-17 Log K Versus T for the Reaction
LiaS04 + TiOa «* LisTi03 + S03
A-18 Log K Versus T for the Reaction
LiaS04 + Va05 «» 2LiV03 + S03
A-19 Log K Versus T for the Reaction
NaaS04 + Ala03 «» 2NaA10a + SOS
A-20 Log K Versus T for the Reaction
NaaS04 + Cr03 «* NasCr04 + S03
A-21 Log K Versus T for the Reaction
NaaS04 + Cra03 ;» NaaCra04 + S03
A-22 Log K Versus T for the Reaction
Na3S04 + Fea03 «i 2NaFeOa + SOs
A-23 Log K Versus T for the Reaction
NaaS04 + Ti08 2 NagTiO^ + S03
A-24 Log K Versus T for the Reaction
NaPS04 + VaO^ ^ 2NaV03 + S03
A-25 Log K Versus T for the Reaction
KpSC^ + Ala03 j» 2KA10a + SOb
A-26 Log K Versus T for the Reaction
KaS04 + Cr03 f K^ Cr04 + S03
A-27 Log K Versus T for the Reaction
KaS04 + Cra03 # ^^04 + S03
-51-
-------
Figure
A-28 Log K Versus T for the Reaction
KaS04 + Fea03 f 2KFeOa + S03
A-29 Log K Versus T for the Reaction
KaS04 + Ti08 «• KgTiOg + S03 .
A-30 Log K Versus T for the Reaction
KgS04 + VaOs
-------
Figure
A-41 Log K Versus T for the Reaction
CaS04 + Vaq. 4* CaVaOs + S03
A-42 Log K Versus T for the Reaction
SrS04 + Ala03 rf SrAla04 + S03
A-43 Log K Versus T for the Reaction
SrS04 + CrOj j» SrCr04 + S03
A-44 Log K Versus T for the Reaction
SrS04 + Cra03 rt SrCra04 + S03
A-45 Log K Versus T for the Reaction
SrS04 + Fea03 j» SrFeB04 + S03
A-46 Log K Versus T for the Reaction
SrS04 + TiOa ;» SrTi03 + S03
A-47 Log K Versus T for the Reaction
SrS04 + VS05 ;» SrVaOs + S03
A-48 Log K Versus T for the Reaction
BaS04 + Ala03 t BaAla04 + S03
A-49 Log K Versus T for the Reaction
BaS04 + Cr03 «> BaCr04 + S03
A-50 Log K Versus T for the Reaction
BaS04 + CrB03 4 BaCra04 + S03
A-51 Log K Versus T for the Reaction
BaS04 + Fe803 2 BaFea04 + S03
A-52 Log K Versus T for the Reaction
BaS04 + TiOa ^ BaTi03 + S03
A-53 Log K Versus T for the Reaction
BaS04 + Va05 «» BaVa06 + S03
-53-
-------
LI2S04 * LI20 + S03
CT
V-
a
LU
o
Ol
-Si.
-10
-15
-•2CL.
60S
'-•*. RUG 7.!
700
LOG P
S03
• ii n i i i i i LI iijliiiiiiiiil
J
QOO
900
1000
1100
1200
1300
1 400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-l
Log K Versus T for the Reaction
LiaS04 2 LisO + S03
-------
NH2S94 « Nfl20 + 503
OL
LT
•Z
CD
LJ
—« u_
^» o
a
LU LJ
-J
— O
o n
^ Dl
O (jj
CD Q_
Ul
Ul
I
I I I I I I I I I I I J 11 I I I I I I I I 11 I I I I I I I 1 I I I I
700
000
900
1000
1100
1200
noo
1400
TEMPERflTURE - DEGREES CENTlGRftOE
FIGURE A-2
Log K Versus T for the Reaction
Na2S04 f. Na20 + S03
-------
K2S04 * K20 + S03
-s
•z.
cc
V—
in
C.J
-15
C5
UJ UJ
_J
•— CD
O El
t— •
-> o:
O UJ
- DEGREES
TPTCURE A-
1300
1400
RUG 74
-------
BES04 « BEG + S03
or
H-
CO
2
CD
CJ
CD
=3
-------
CRS04 * Cfl0
S03
a:
v-
co
z
o
o
t— . CD
O
UJ LU
o
o
I
Ln
00
I
-s
-10
-15
-20LJL
600
nn f MR 74
i I i i i i i t i i i I i i i i i i i i i I i i i i i t i i i I i i i i t i i i i I i i i i i i i i t i t i i i i i i t i I i i i t i i i i i
700
GOO
900
TOGO
1100
1200
1300
1400
TEMPERATURE - DEGREES CENTIGRRDE
FIGURE A-5
Log K Versus T for the Reaction
CaS04 it CaO + S03
-------
SRS04 * SR0 + S03
a:
r—
GO
-z.
CD
i— « CQ
a
LJ UJ
o
^
o
CD
VO
-5
-10
-IS
-20
600
07 fllJG 74
LOG P
I
700
800
900
1000
1100
1200
1300
1400
TEMPERRTURE - DEGREES .CENTIGRRDE
FIGURE A- 6
Log K Versus T for the Reaction
SrS04 ;» SrO
S0
-------
BRS04 * Bfl0 + S03
CO
•z.
CD
O
tr
CD
o
LU
O
O 21
CD
_J
o
I
-s
-10
-15
-20
600
nn nun 71
700
LOG P,
S03
iiiiliiiiiiiiiliiiiiitii
800
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-?
Lou K Versus T for the Reflation
BaS04 # BaO + S03
-------
10
-10
NIS04
NI0 + S03
-5
-1 si i 111111 1111
I I I I
I ' 111 I 11 I I I I I I I I 11 I I I... I ..... I
600
700
GOO
900
1000
I 100
1200
1300
1400
i n
J
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-8
Log K Versus T for the Reaction
NiS04 «» NiO + S03
-------
ZNS04 « ZN0
S03
0
CJ
Ql
CD
•— li.
^ o
a
UJ LLJ
_J
" CD
C±) LJ
O n ,
10
i
10
-5
-10
-IS
I I I I I I I I 1 I I
600
700
BOO
900
1000
1100
1200
1300
1400
07 RUG 74
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-9
Log K Versus T for the Reaction
ZnS04 j! ZnO + S03
-------
CDS04 « CD0 + S03
a:
i—
en
CD
CJ
CD
a
LJ
to
fe
O UJ
O Q_
ON
10
-5
-10
15L-
600
06 RUG 7-1
' I
700
' ' ' ' ' '
' '
800
900
1000
1100
JL
1200
1300
1400
TEMPERflTURE - DEGREES
FIGURE A- 10
CENT I GRflDE
Log K Versus T for the Reaction
CdS04 f CdO + S03
-------
0.33C£2(504)3 - S83 + 0.33CE203
.—i CD
— ' L_
33 CD
O
UJ UJ
O LU
CD O_
10
-5
-10
-IS
600
700
i i i
300
900
1000
'''''''''•'''ill'
I 100
1200
1300
I40i
OQ RUG 74
TEMPERflTURE - DEGREES CENTlGRflOE
FIGURE A- 11
Log K Versus T for the Reaction
1/3 Ce3(S04)3 j! 1/3 Cea03
S0
-------
0.5CEIS0412 = S03 + 0.5CE02
or
\-
to
CD
LJ
in 0"1
,— CD
^) o
o
LU LJ
_J
^ CD
O Qj
(D Q_
_J
i
ON
in
10
-s _
-JO
-IS
600
i_l_J_
08 flUG 74
• i
I i
700
800
900
» » » * *
1000
J_l_
I 100
1200
1300
1400
TEMPERflTURE - DEGREES CENTlGRflDE
FIGURE A-12
Log K Versus T for the Reaction
%Ce(S04)8 j» %CeOs + S03
-------
1I2S04 + flL203 * S83 * 2Ufll02
-------
L12S84 + CR83 « L12CR04 + S03
a:
»—
tn
CD
o
O3 tO
i=I CD
i £0
=D CD
O
UJ LJ
~ o:
o uj
CD Q_
-s
-10
-15U.
600
I..
700
800
900
1000
1100
1200
1300
1400
TEMPERRTURE - DEGREES
FIGURE A-14
CENTIGRflDE
07 flUG 74
Log K Versus T for the Reaction
LisS04 + Cr03 «» LisCr04 + S03
-------
LI2S04 + CR203 * LI2CR204
S03
10
CD
LJ
CD
13
LJ LU
CD Uj
-------
LI2S04 + FE203 « S03 + 2UFE02
a:
v—
in
o
zi
ID
ca tn
~ u_
LiJ LJ
_J
(±1 LU
O Q_
10
-s
-10
VO
I
-isLi.
600
no nuc,
I
I
700
000
900
1000
1 100
1200
1300
1400
TEMPERflTURE - DEGREES CENTlGRflDE
; FIGURE A-16
Log K Versus T for the Reaction
LiaS04 + Fea03 tf 2LiFe03
S0
-------
LI2S04 + TI02 * U2TI03
S03
a:
v—
to
:z
a
CD
en
ZD CD
a
LU UJ
_J
— o
o zi
o
I
^1
o
10
-s
-10
-isL.
600
flUG 74
700
LOG P,
000
900
1000
1100
1200
noo
1400
TEMPERflTURE - DEGREES
FIGURE A- 17
CENTIGRflOE
Log K Versus T for the Reaction
LiaS04 + Ti02 S LiaTi03 + S03
-------
L12S04 + V205 « S83 + 2LIV83
a:
v-
tn
•2.
CD
u
OQ in
•—i CD
_j 10
- LL.
±) CD
O
IJJ UJ
_l
•^ CD
O 2=
«—i
CJ LU
CD Q_
10
-S
-10 _
-IS
600
' i
?00
000
1 I I 1 I I
900
1000
1
100
1
1200
1300
400
TEMPERflTURE - DEGREES CENUGRflDE
FIGURE A- 18
Log K Versus T for the Reaction
08 flUG 74
LiaS04 + V805 «» 2LiV03
S03
-------
Nfl2S04 + flL203 * S03 + 2Nflfll_02
G:
v-
in
-2.
CD
LJ
OQ
-------
NFI2S04 + CR03 « NR2CR04 + S03
o
CJ
5 «•>
« CD
_l «
•— U_
Z3 O
O
UJ UJ
O 21
— cc
O UJ
O Q_
CO
i
3 P-JG
10
-5
-10
-isL.
600
oolu
700
LOG P
S03
' ' i i i i ii i i i I
800
900
1000
I ' '
1100
1200
1300
1 400
TEMPERflTURE- DEGREES CENTIGRflDE
FIGURE A- 20
Log K Versus T for the Reaction
NaaS04 + Cr03 2 NaaCr04
S0
-------
NR2S04 + CR203 * Nfl2CR204 + S03
-2.
CL.
*—
(D
•z
CD
O
en ^
j °
•— u_
ID CD
C3
LU LU
O ZI
— a:
C3 LU
CD Q_
40
30
25
600
700
GOO
400
08 RUG 74
TEMPERATURE - DEGREES CENTIGRflOE
FIGURE A-21
Log K Versus T for the Reaction
Na3S04 + Crs03 2 Na8Cra04 + S03
-------
NR2S04 + FE203 * S03 + 2NRFE02
•2L
o:
\—
tO
-z.
o
LJ
£D CO
_ O
cn
O
UJ LJ
O 21
O LU
O 0_
i
•vj
Ln
-5
-10
-15
-20L.
600
700
QOO
900
1000
MOO
1200
1100
1400
TEMPERflTURE - DEGREES CENTlGRflOE
FIGURE A- 22
Log K Versus T for the Reaction
OR PUG 71
Fea()3 ?. 2NaFeOa
S0
-------
ID *">
, , (D
IS
a:
v-
tn
LJ
10
Nfl2S04 + T182 * Nfl2Tl83
S03
Z> CD
O
LU LJ
O 21
— DC
O LJ
(D Q_
0 _
LOG P
S03
en
10
600
i.
700
QOO
$00
-LJ.
1
1000
1 100
1200
1300
1400
TEMPERflTURE - DEGREES CENTlGRflOE
FIGURE A-23
Log K Versus T for the Reaction
NaaS04 + Ti08 2 NaaTi0
S0
-------
Nfl2S04 + V205 * S03 + 2NHV03
a:
i—
to
-2.
&
LJ
QQ CO
*-* a
o z:
r-^
— ct:
o LJ
O Q_
I
•vj
-5
-10
15
600
08 flUG 74
111
700
000
900
1000
I 100
1
1200
1300
1400
TEMPERflfURE - DEGREES CENHGRflOE
FIGURE A-24
Log K Versus T for the Reaction
NaaS04 + V80S i» 2NaV03 + S03
-------
K2S04 + flL203
2KflL82
or
4—
CD
~2.
CD
OQ P">
_ CD
_j CO
o
LU
^ cc
O LU
O Q_
oo
IS
10
-5
LOG P
503
-10L.
600
700
000
900
1000
100
1200
1300
400
TEMPERflTURE - DEGREES
FIGURE A-25
CENTIGRflOE
Log K Versus T for the Reaction
A1803
2KA10
-------
K2S04 + CR03 * K2CR04 + S03
QC
t—
(O
CD
£0
LJ LJ
_J
-^ O
o z:
VO
t
10
-S
-10
-15
GOO
' I I I I I I I I
/-. ~j >-* i n •-> i
•_ • f" _' b ' 'T
I I I I I I I I I I I I I I I I I I I I I I I I I i I I I I I i I I I i I i i i I i i i i I I i I I I t I I I I I t I t I I t I I
700
800
900
1000
1100
1200
1300
i i i i.
1400
TEMPERRTURE - DEGREES CENTIGRflDE
FIGURE A-26
Log K Versus T for the Reaction
+ Cr03 «» KaCr04 + SO3
-------
K2S04 + CR203 * K2CR204 + S03
CD
CD
=> &
C9
LU LJ
C£D
oo
o
45
40
35
30
20,
600
» » ' ' ' ' » ' ' »
)7 flUG 74
700
.1 I...
800
900
1000
i i i 1 i i i i i i i i i i i i i i i i i i i I i i
1100
1200
.1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-27
Log K Versus T for the Reaction
KgS04 + Cr803 «» KaCr804 + S03
-------
K2S04 + FE203 * S03 + 2KFE02
-z.
CL
*—
to
•z
o
IS
10
OQ
CD
UJ
_J
O
2Z
CD 0_
-s
LOG P
S03
i
CO
-10
600
700
C3 P'JG 74
I
QOO
900
1000
I 100
1200
, 1300
1400
TEMPERflTURE - DEGREES CENTIGRRDE
FIGURE A-28
Log K Versus T for the Reaction
+ Fea03 4* 2KFeOa + S03
-------
K2S04 * TI62 * K2T103 + S03
o
21
CD
LJ LJ
_J
^ C3
o z:
#— i
CD uj
o a.
00
10
10
-5
-10
LOG P
S03
600
i i i i i i
.1 I I I I I
700
QOO
900
1000
1 100
1200
1 I I I I I I I I I I
1300
1400
C7 RUG 74
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-29
Log K Versus T for the Reaction
KgS04 + Ti08 «* KgTiO^ + S03
-------
K2S84 + V285 » S03 + 2KV03
en
-------
BES04 + fll_203 * BEHL204 + S03
a:
s-
(D
~2.
CD
(_)
§ s
,— CD
l£ <0
CD u_
•— « CD
_J
1 1 I
C3
LU
o
CD
i
00
-S
-10
-IS!
€00
07 flUG 74
LOG P
S03
i I i i i i i i i i i I i i i i i i i t i I i i i i i i i i i 11 i i i i i i i i i i i i i i i i i i I i i i i I
700
QOO
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTlGRflDE
FIGURE A-31
Log K Versus T for the Reaction
BeS04 + AlaO, t BeAla04 + S03
-------
BES04 + CR03 « BECRG4
S03
10
a:
i—
to
o
o
GO
O
LJ
CD
-5
o
*- cc
CD Q_
_J
-10
00
Ln
i
LOG
S03
-15U
600
I
700
800
900
1000
1100
1200
1300
1400
TEMPERATURE - DEGREES
FIGURE A-32
CENTIGRflOE
07 PUG 74
Log K Versus T for the Reaction
BeS04 + Cr03 2 BeCr04 + S03
-------
BES04 + CR203 * BECR204 + S03
CE
V-
to
-z.
CD
U
CO
3 fe
o
LU UJ
O 21
-5
I
CO
-IS
600
LOG P
503
i I • • j •
700
QOO
900
1000
1100
I
1200
1300
1400
07 flUG 74
TEMPERATURE - DEGREES CENHGRflOE
FIGURE A-33
Log K Versus T for the Reaction
BeS04 + Cr20a «» BeCrs04 + S03
-------
BES04 + FE203 * BEFE204
S03
-2.
CC
S—
tD
LJ
to cn
•—, CD
_
=> CD
o
LJ LJ
_J
"» CD
o 5
O Q_
00
10
-5
-IS
600
LOG P
S03
-La
''''I i i i i I i i i i i i i i i I i i
700
QOO
900
* * *
1000
I I I t 1 1 I
1100
1
1200
1300
1400
07 flUG 74
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-34
Log K Versus T for the Reaction
BeS04 + Fea03 2 BeFe804
-------
BES04 + TI02 * BETI03
S03
-2.
CL
CD
LJ
Z)
t—€
DO
co
^ 0
o
UJ LJ
_l
"- O
O 2=
•—*
— cc
CD iij
i
00
CO
I
10
-5
-10
IS
600
« '
i t i . I • i •
700
07 flUG 74
LOG P
S03
QOO
' » ' *
900
i i i i
1000
1
I 100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRRDE
FIGURE A-35
Log K Versus T for the Reaction
BeS04 + TiOa
BeTiO
-------
BES04 + V205 * BEV206
S03
CD
a
UJ
CD
CD
O LU
CD Q_
00
vo
10
-S
-10
-15
600
07 flUG 74
700
LOG P,
S03
i I i i i I i i i i i i i i i I i i i i i i i i i I
800
900
1000
1100
1200
''''''''''
1300
1400
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-36
Log K Versus T for the Reaction
BeS04 + Va05 i» BeV306 + S03
-------
C8S04 + HL203 * CflflL204
S03
a:
s-
to
-2.
O
LJ
— CO
a: o
CD in
^fe
LJ
LJ
O
•—«
CD
LJ
Q-
i
VO
O
10
-5
15
600
H7 PUG 71
JLJL
700
000
* * * • ' i i
900
1000
I 100
1
1200
1300
1400
TEMPERflTURE - DECREES CENTIGRflDE
FIGURE A-37
Log K Versus T for Lho Reaction
CaS04 h Ala03 ;» CaAla04 + SO,
-------
CflSG4 + CR03 w CRCR04
S03
CD
O
C3
UJ .
CQ
U_
CD
LU
_J
CD
— cc
CD uj
CD n
vo
10
-5
-10
-15
600
J_L.
07 flUG 74
LOG P
503
700
800
i i I i i i i i i i i i I i i i i i
900
1000
1100
1200
1 I I I I I
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A- 38
Log K Versus T for the Reaction
CaS04 + Cr03 ;» CaCr04
S0
-------
Cfl£04 + CR203 * CflCR204 + S03
a:
»—
CO
~Z.
CD
O
a:
CD
a
LU uj
_j
*~" O
O 21
O LU
CD Q_
-5
vo
to
-IS
600
07 RUG 74
LOG P
S03
' ' • •
700
800
'''*'•'
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-39
Log K Versus T for the Reaction
CaS04 + Cr203 # CaCra04 + S03
-------
CflS04
FE203
CHFE204
S03
a:
t—
to
CD
LJ
zz
ZD
*—«
CO
o
UJ
o
CD
O LU
CD Q_
i
vo
10
-5
-10
600
0*7 PUG 74
LOG P
S03
700
QOO
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-40
Log K Versus T for the Reaction
CaS04 + Fea03 f CaFea04 + S03
-------
CRS04 + V205 « CRV206 + S03
CE
I—
CO
z
CD
o
CC
CO
O
CO
(D
O 21
O uj
CD Q_
so
4»
i
10
-5
-10
-IS
600
<-< 1 j-k -7
f ^b /
» »
700
800
900
i i i i i i i I i i i i i i i t i I i i i i i i
10GO
1 100
1200
1300
1400
TEMPERRTURE - DEGREES CENTIGRflDE
FIGURE A-41
Log K Versus T for the Reaction
CaS04 + V805 ^ CaVa06 + S03
-------
SRS04 + RL203 * SRflL204
S03
a:
CO
o
ZI
« ro
§ <«
ID UJ
LJ O
o o:
-« LJ
^ Q_
O
CD
-5
-10
-IS
VO
V -20
600
17 PUG 74
700
I
I
800
900
1000
1100
1200
, 1300
1400
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A- 42
Log K Versus T for the Reaction
SrS04 + Ala03 -f. SrA1aOa + S03
-------
SRS04 + CR03 « SRCR04 + S03
10
CO
2
CD
LJ
CD
~ CD
o z:
O LJ
CD Q_
-S
i
vo
IS
600
LOG P,
S03
i 1 i i
700
GOO
i i
900
1000
1100
1200
1300
400
P.
P. v« p ;j a -7 j
TEMPERflTURE - DEGREES CENTlGRflDE
FIGURE A- 43
Log K Versus T for the Reaction
SrS04 + Cr03 j* SrCr04 + S03
-------
SRS04 * CR203 a SRCR204 •» S03
O
LJ
13
CD W
_l CD
i—i
ID UJ
LU CD
z:
o ct
— UJ
CD
IS
10
-5 „
-10
600
"5 f i <"* "i '
. £ r- J 'j i -
M..I
LOG P
S03
i i i i i
700
800
900
111 J I i i i i i
1000
I 100
1200
1300
TEMPERflTURE - DEGREES CENTIGRRDE
FIGURE A- 44
Log K Versus T for the Reaction
SrS04 + Cra03 f SrCra04 + S03
1400
-------
SRS04
FE203 * SRFE204
S03
IT
t-
to
•z
o
LJ
o:
OQ tn
>-i CD
_i in
O
LU LJ
C3 tu
(D O.
i
SO
CO
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
700
QOO
900
1000
1100
1200
1300
1400
G7 RUG 74
TEMPERflTURE - DEGREES CENTlGRflOE
FIGURE A- 45
Log K Versus T for the Reaction
SrS04 + FegOj # SrFea04 + S03
-------
SRS04 + T[02 » SRTI03
S03
o
LJ
(Q C^
i— i O
_J in
•—• u_
^ CD
CD
LJ LJ
_J
~ CD
CD Q_
_J
NO
I
-5
-JO
-isL.
600
I
700
000
900
1000
1100
1200
1300
1400
lEMPERflTURE - DEGREES CENTlGRflDE
FIGURE A- 46
Log K Versus T for the Reaction
07 HUG 7<1
SrS04 + TiOa t- SrT103
S0
-------
SRS04.+ V205 * SRV7.06 + S03
a:
v—
CO
z
CD
O
CO |TJ
;=! o
i CO
C3
LU UJ
CD uj
-------
BflS04 + HL203 * BflflL204 + S03
CD
CJ
OC
CD ^
~
-------
BHS04 + CR03 * BRCR04 + S03
a:
»—
CO
2
CD
O
CD
±3 (D
C3
LU UJ
-- a:
(±1 UJ
-------
BflS04 + CR203 * BHCR204 + S03
a:
v-
to
-z.
CD
O
CD CO
i—i CD
a
LU
CD
"~~ CD
O 21
r-^
O
CJ
i
15
10
-5
-10
600
C~ RUG 74
LOG P
S03
700
800
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-50
Log K Versus T for the Reaction
BaS04 + Cr803 # BaCra04 + S03
-------
BRS04 + FE203 * BflFE204
S03
10
z
CE
t—
CO
CD
CJ
z:
ID
CD ^
_ CD
=3
-------
BflS04
TI02 * BflTI03 + S03
or
v—
-------
BflS04 + V285 * BRV206 + S03
a:
t—
CD
O
CO ^
,-« CD
ID CD
a
CD
— cc
CD LU
O Q
10
-s
-10
-15
600
' »
RUG 74
"700
.M.I
1300
I I I I I I I I I I I I I I I I 1 I 1 I I I I
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-53
Log K Versus T for the Reaction
BaS04 + V80S ;» BaVsOs + S03
-------
Section 5.2
TECHNICAL NOTE 200-045-10-02a
THE THERMODYNAMICS OF CHEMICAL REGENERATION
OF METAL OXIDE S02 SORBENTS
25 April 1975
Prepared by:
Philip S. Lowell
Terry B. Parsons
-107-
8500 Shoal Creek Blvd./PO Box 9948/Austin, Texas 78766/(512)454-4797
-------
ABSTRACT
This technical note gives the results of an
investigation of the thermodynamics of chemical regeneration
of spent metal oxide S02 sorbents. The goal was to identify
conditions under which metal oxides could be regenerated by
reductive decomposition of metal sulfate sorption products.
Six reducing atmospheres were considered. Three steps were
used in thermodynamic analysis of the reaction between reduc-
ing agents and metal sulfates. First, the products of
reaction between the reducing agent and S03 were predicted
using an equilibrium model to calculate product stream compo-
sitions. Next, the temperature range in which it is thermo-
dynatnically feasible to reduce the metal sulfate to the oxide
with each reducing agent was predicted. Finally, metal oxides
for which there is a tendency to form sulfides during sulfate
decomposition were identified. The results are a list of
oxide-reducing agent combinations and the temperatures at
which the sorption-regeneration processes are predicted to be
thermodynamically favored.
-108-
-------
TABLE OF CONTENTS
Page
ABSTRACT 108
1.0 INTRODUCTION 110
2.0 REACTIONS OF REDUCING AGENTS WITH S03 AND PREDIC-
TION OF EQUILIBRIUM PRODUCT STEAM COMPOSITIONS 114
2.1 Method for Predicting Composition of Product
Mixtures 114
2.2 Composition of Product Mixtures at Equilibrium....118
3.0 IDENTIFICATION OF CONDITIONS AT WHICH REDUCTIVE
DECOMPOSITION OF METAL SULFATES OCCURS 126
3.1 Methods of Thermodynamic Analysis of Sulfate
Reduction Reactions 127
3.2 Results of Thermodynamic Analysis of Sulfate
Reduction Reactions 129
4.0 INVESTIGATION OF THE POSSIBILITY OF METAL SULFIDE
FORMATION 134
4.1 Method of Thermodynamic Analysis of the Sulfide
Formation Reaction 134
4.2 Results of Thermodynamic Analysis of the Sulfide
Formation Reaction 137
5. 0 RESULTS 142
5.1 Summary of Results for Each Metal Oxide 143
5.2 Conclusions 153
BIBLIOGRAPHY 166
APPENDIX - FIGURES A-l THROUGH A-30 1S7
-109-
-------
1.0 INTRODUCTION
This technical note gives the results of an
investigation of the thermodynamics of chemical regeneration
of spent metal oxide 802 sorbents. The work was done under
EPA Contract No. 68-02-1319. It is part of a study of the
feasibility of using metal oxides as S02 sorbents in fluidized
bed combustion of coal.
Radian Technical Note 200-045-10-01, "Thermodynamic
Screening of Dry Metal Oxides for High Temperature S02 Removal",
describes the identification of metal oxides which are pre-
dicted to react with sulfur oxides in combustion gas to form
metal sulfates. These candidate sorbents were identified by
comparing the vapor pressure of S03 over the corresponding
metal sulfate with the partial pressure of S03 in combustion
gas. If the partial pressure of SO3 in combustion gas is
greater than the S03 vapor pressure over the metal sulfate,
this provides driving force for sorption. Table 1-1 lists
both single and binary metal oxides for which the SO3 vapor
pressures over the corresponding sulfate are of the desired
magnitude. The high temperature at which sorption can occur
for the flue gas condition chosen is also listed. It should
be noted that higher pressures, higher mole percent SOX, or
higher 02 mole fraction would raise the maximum stated tempera-
ture.
Further screening of the fourteen candidate S02
sorbents listed in Table 1-1 was done in this study. Simple
thermal decomposition according to Equation 1-1 would be a
desirable method of regenerating the metal oxide.
MeSO., -f MeO + S03 (1-la)
A
MeSO,, -»• MeO + S02 4 %02 (1-lb)
A
-110-
-------
TABLE 1-1
POTENTIAL SORBENTS FOR S02 REMOVAL FROM FLUE GASES
Maximum Sorption
Sorbent* Temperature (°C)
Na20 1380
CaO 1090
SrO 1260
BaO 1380
LiA102 1200
LiFe02 950
Li2Ti03 1200
NaA102 820
NaFe02 1020
CaAl2Ou 950
SrAl2Ou 1000
SrTiOs 920
BaAl20,, 1000
BaTi03 1000
Potential sorbents were selected on the basis of the
vapor pressure of S03 over the metal sulfate. If the
S03 vapor pressure was less than the partial pressure
of SO3 in the flue gas, then a driving force for
sorption was said to exist. See Technical Note 200-
045-10-01 for details. Conditions were 100 ppm SOX,
5% 02, and 1 atm total pressure.
-Ill-
-------
Table 1-1 indicates that the sorption temperatures
are extremely high. Thus, thermal regeneration temperatures
would be prohibitively high (for example, see Vogel, page 11,
VO-034).
The goal of this study was to identify the conditions
under which these metal oxides could be regenerated by reduc-
tive decomposition of the metal sulfate sorption products.
The feasibility of chemical regeneration was investigated using
the model shown in Equation 1-2.
MeSOi, + Reducing Agent ->• MeO + Products of Reaction
between Reducing Agent
and SO3
d-2)
Six reducing agents were considered. The thermodynamics of
reactions in the form of Equation 1-2 were considered for
each reducing agent-metal sulfate combination. The following
individual steps were used.
The products of reaction between the
reducing agent and S03 were calculated as
a function of temperature assuming Equa-
tion 1-2 proceeded as written. The method
and results are described in Section 2.
The temperature range in which it is
thermodynamically feasible to reduce the
metal sulfate to metal oxide with each
reducing agent was predicted. Section 3
describes the method and results of this
analysis.
-112-
-------
Metal oxides for which there is a
thermodynamic tendency to form sulfides
by reaction with S03 reduction products
were identified. Section 4 gives the
method and results in detail.
The results of this study are summarized for each candidate
metal oxide sorbent in Section 5.
-113-
-------
2.0 REACTIONS OF REDUCING AGENTS WITH S03 AND PREDICTION
OF EQUILIBRIUM PRODUCT STEAM COMPOSITIONS
One of the objectives of this study was to regenerate
the sorbent in one step to the oxide. Production of SOa,
elemental sulfur, etc., would be done with the resulting gas.
The six reducing agents considered for this evaluation were
hydrogen (H2), carbon monoxide (CO), synthesis gas (CO + %H2),
coal (which has a carbon to hydrogen ratio of approximately
one), char (C) , and methane (CHi,) . The reducing agents were
evaluated in terms of their tendency to produce an S02 product.
MeSOu + Reducing Agent •* MeO + S02 + Other Products
(2-1)
To accomplish this, the reducing agent must remove one gram
atom of oxygen from S03. This can potentially be accomplished
with one gram mole of CO or H2 (C02 or H20 product) or one-half
gram atom of C (one-half C02 product). Additional reducing
agents will result in a stronger reducing atmosphere. The
reducing atmospheres used and their oxygen sorbing potentials
are listed in Table 2-1.
The first step was to determine the products of
reaction between the reducing agents and 80$. The method
used is described in Section 2.1 and the results are given
in Section 2.2.
2.1 Method for Predicting Composition of Product Mixtures
If Equation 1-2 is assumed to proceed as written,
the equilibrium mixture for the gas phase may be described
by considering Equation 2-2.
Reducing Agent + S03 •»• Products (2-2)
-114-
-------
TABLE 2-1
REDUCING ATMOSPHERES
Name
Hydrogen
Carbon Monoxide
Synthesis Gas
Char
Coal
Methane
Composition per
Mole of SOj
H2
CO
CO + %H2
C
C + H
Oxygen Sorption
Capacity,
gram atoms
1.0
1.0
1.5
2.
2.5
4.
-115-
-------
Compounds which may exist in the gas phase system
containing hydrogen, oxygen, carbon, and sulfur are listed
in Table 2-2. The interaction of these compounds may be
described by Equations 2-3 through 2-11.
H20 + CO •» H2 + C02 (2-3)
3H2 + CO + H20 + CHu (2-4)
CO + %02 + C02 (2-5)
2CO + S2 •* C02 + CS2 (2-6)
CO + %S2 * COS (2-7)
2H2S + 02 * S2 + 2H20 (2-8)
S02 + %02 •*• S03 (2-9)
2S02 * S2 + 202 (2-10)
H2 + %02 * H20 (2-11)
In order to predict compositions, a model of the gas phase
H-O-C-S system at equilibrium was used. It is based on a
set of non-linear equations derived from thermodynamic expres-
sions for equilibrium constant-activity relationships and
mass balances for the species and reactions described in
Equations 2-3 through 2-11. The solution of this set of
non-linear equations yields the mole fraction and activity
of each component at equilibrium at a given temperature.
Fugacity coefficients were set equal to one.
-116-
-------
TABLE 2-2
COMPOUNDS ASSUMED IN THE GAS PHASE
H20 CH, COS
H2 02 H2S
CO S2 S02
C02 CS2 SO 3
-117-
-------
2.2 Composition of Product Mixtures at Equilibrium
The gas phase equilibrium model described in Section
2.1 was used to predict the products of reaction between SO3
and each of the six reducing agents at temperatures of 600,
1000, and 1400°C. The resulting gas phase compositions are
given in Tables 2-3 through 2-8. The product compositions
indicate which species predominate at the temperatures of
interest. For instance, Table 2-3 shows that the products
of the reaction between one mole of SO3 and two gram atoms of
hydrogen are approximately 50 mole percent S02 and 50 mole
percent H20. The S03 and H2 react essentially to completion
and 82 and H2S are not produced in significant quantities.
Table 2-9 lists the major products formed at 600 and 1400°C
with each reducing agent. Note that S02 is the sulfur product
formed most frequently. The undesirable products COS and CSa
are never formed in amounts greater than 0.2%.
Some product distributions vary with a change in
temperature; for instance, methane produces a regeneration
product of 100% H2S at 600°C and 86% S02 - 14% H2S at 1400°C.
Product distributions also vary with a change in reactant
stoichiometry. The amount of various reduced species increases
with an increase in reducing agent. The interaction between
the products is rather complex. The total pressure was taken
as one atmosphere with no diluents. A lower total pressure or
addition of diluents would lower the regeneration temperature.
-118-
-------
TABLE 2-3
REDUCING AGENT: HYDROGEN (H2)
GASEOUS PRODUCTS OF THE REACTION BETWEEN ONE MOLE
OF SO3 AND TWO GRAM ATOMS OF HYDROGEN
Component
H2
02
H20
H2S
S2
S02
S03
COMPOSITION AT EQUILIBRIUM
Mole Fraction at 1 Atmosphere
T = 600°C
0.118396X10'5
.245294x10-12
.499998
.326662x10-'
.917765x10-X1
.499998
.235055x10-*
T = 1000°C
0.481968x10-"
.339883x10-6
.499952 *
.134609x10-6
.192453x10-9
.499952
.479374x10-"
T = 1400°C
). 551022x10"3
.199154x10-3
.499349
. 133200x10-5
.674711xlO-e
.499743
.156752x10"3
-119-
-------
Component
CO
02
C02
S2
CS2
COS
S02
SO 3
TABLE 2-4
REDUCING AGENT: CARBON MONOXIDE (CO)
GASEOUS PRODUCTS OF THE REACTION BETWEEN ONE
MOLE OF SO3 AND ONE MOLE OF CARBON MONOXIDE
COMPOSITION AT EQUILIBRIUM
Mole Fraction At 1 Atmosphere
T = 1400°C
T = 600"C"
.513035xlO~5
.183394xlO'1A
.499994
.164187xlO"6
.123942xlO~14
.499079x10"7
.500000
.203246xlO"6
T = 1000"C"
.612247x10"*
.535616xlO"6
.499939
.774918xlO"10
.303624xlO~19
.263125xlO"9
.499940
.601762xlO"4
.116270-02
.462035-03
.498606
.125249-08
.320641-17
.276169-08
.499530
.238655-03
-120-
-------
TABLE 2-5
REDUCING AGENT: SYNTHESIS GAS (CO + %H2)
GASEOUS PRODUCTS OF THE REACTION BETWEEN ONE MOLE OF
Component
H20
CO
H2
C02
CH,,
02
S2
CS2
COS
H2S
SO 2
SO 3
SO 3, ONE MOLE OF
ONE GRAM ATOM
COMPOSITION
Mole
T = 600°C
.153228
.776387xlO~4
.759325xlO"4
.427168
.107080xlO"15
.584507xlO"17
.796167xlO"2
.161107xlO"7
.166316xlO'3
.604023X10"1
.350920
.805311xlO"8
CARBON MONOXIDE AND
OF HYDROGEN (H)
AT EQUILIBRIUM
Fraction At 1 Atmosphere
T = 1000°C
.164597
.734461xlO"2
.176317xlO'2
.417200
.208966xlO"5
.259192xlO"10
.159053X10"1
.107468xlO"6
.452219xlO'3
.461350X10'1
.346600
.290216xlO"6
T = 1400°C
.135788
.376903X10'1
.436810xlO"2
.359935
.339941X10"1
.229132xlO"6
•354527xlO"2
.132114xlO"7
.150616xlO"3
.774064xlO~2
.416784
.443430xlO"5
-121-
-------
TABLE 2-6
REDUCING AGENT: CHAR (C)
GASEOUS^PRODUCTS OF THE REACTION BETWEEN
ONE MOLE OF S03 AND ONE MOLE OF CARBON
COMPOSITION AT EQUILIBRIUM
Mole Fraction at 1 Atmosphere
Component
CO
02
CO 2
S2
CS2
COS
S02
SO 3
T = 600"C"
.234833xlO"3
.113495xlO~17
.569342
.141274
.196226xlO"5
.211906xlO"2
.287028
.290251xlO"8
T = 1000"CT = 1400^5
.178657X10"1
.756482X10"11
.548256
.135454
.412089xlO"5
.321014xlO"2
.295210
.133540xlO"6
.118337
.337866x10
.433955
.107185
.326585x10
.260020x10
.337918
.138056x10
-7
-5
-2
-5
-122-
-------
TABLE 2-7
REDUCING AGENT: COAL (C:H = 1:1)
GASEOUS PRODUCTS OF THE REACTION BETWEEN
ONE MOLE OF SO3. ONE MOLE OF CARBON.
AND ONE GRAM ATOM OF HYDROGEN (H)
Component
H20
CO
H2
C02
CHU
02
S2
CS2
COS
H2S
S02
SO 3
COMPOSITION
Mole
T = 600UC
.761338x10'1
.188428xlO~3
.799368xlO~4
.489312
.610229xlO"15
.130206xlO"17
.562874X10'1
.585686xlO'6
.107325xlO"2
.169073
.207852
.225128xlO"8
AT EQUILIBRIUM
Fraction at 1 Atmosphere
.108435
.161235X10"1
.228384xlO"2
.465814
.151332xlO~4
.670468X10"11
.768056X10"1
.223997xlO"5
.218155xlO"2
.131319
.197020
.839037xlO"7
T = 1400UC
.469918X10"1
.777471X10"1
.332204xlO"2
.337852
.891323X10"1
-. 474441x10" 7
.610661X10"1
.103159xlO~5
.128945xlO"2
.244324X10"1
.358164
.173398xlO'5
-123-
-------
Component
H20
CO
H2
CO 2
CH,,
02
S2
CS2
COS
H2S
S02
S03
TABLE 2-8
REDUCING AGENT: METHANE (CH,)
GASEOUS PRODUCTS OF THE REACTION BETWEEN
ONE MOLE OF SO3. ONE MOLE OF CARBON.
AND FOUR GRAM ATOMS OF HYDROGEN (H)
COMPOSITION AT EQUILIBRIUM
Mole Fraction at 1 Atmosphere
T = 600UC"
.332826
.688416xlO"3
.188172xlO"2
.331990
.665248xlO~n
.449050x10"19
.390023xlO"3
.798397xlO"7
.326399xlO"3
.331301
.596700xlO"3
.120023X10"11
T = 10000CT = 1400°C
.335427 .240288
.240621X10"1 .208380X10"1
.163271X10'1 .122353X10"1
.300795 .125719
.266753xlO'2 .233412
.125529xlO~U
.784554xlO"2
.789156xlO"6
.104053xlO"2
.300044
.117894X10'1
.217244xlO'8
.914511xlO
"7
.411506xlO
"7
~3
.157099xlO
.409046X10"1
.313826
210937xlO
"5
-124-
-------
TABLE 2-9
MAJOR PRODUCTS OF THE REACTION OF
SO3 WITH REDUCING AGENTS
Sulfur Bearing
Products Other Products
Reactants 600°C 1400°C 600°C 1400°C
S03 + H2 100% S02 100% S02 100% H20 100% H20
SO3 + CO 100% S02 100% S02 100% C02 100% C02
SO3 + CO + H 83% S02 100% S02 75% C02 63% C02
17% H2S 25% H20 24% H20
6% CH.,
7% CO
SO3 + C + H 50% S02 86% S02 88% C02 66% C02
40% H2S 14% S2 12% H20 16% CH.,
10% S2 9% H20
14% CO
SO3 + C 66% S02 75% S02 100% C02 80% C02
34% S2 25% S2 20% CO
SO3 + CH,, 100% H2S 86% S02 50% C02 20% C02
14% H2S 50% H20 40% CH,,
40% H20
-125-
-------
3.0 IDENTIFICATION OF CONDITIONS AT WHICH REDUCTIVE
DECOMPOSITION OF METAL SULFATES OCCURS
This section describes the use of thermodynamic data
to predict the temperatures at which reductive decomposition
of metal sulfates can occur with the six reducing agents.
Methods of data generation and analysis are described in
Section 3.1 and results are given in Section 3.2.
There are several computational schemes by which
the answer may be obtained. One is, for a given compound
and temperature, to choose a stoichiometry for which the
Pgo of the gas exactly balances that of the solid. This
would require an iterative calculation of several stoichiome-
tries at each temperature. Or, by choosing a fixed stoichi-
ometry at three temperatures the actual regeneration tempera-
ture may be interpolated.
From a process point of view the temperature
conditions correspond to that of the exit gas. Since the
activity of solid is unity, this analysis would be applicable
to a cocurrent reactor. The reacting gas could be in contact
with the last trace of solid sulfate if a stoichiometric
amount of solid sorbent were circulated. The gas could be
in contact with a considerable amount of excess sulfate if
more than stoichiometric sorbent were circulated. This
analysis would also be applicable to the exit gas/inlet
solid of a countercurrent reactor. As the gas exits after
picking up the required amount of sulfur there still must be
a slight driving force available.
-126-
-------
3.1 Methods of Thermodynamic Analysis of Sulfate
Reduction Reactions
The feasibility of reduction of metal sulfates to
metal oxides was determined by comparing the equilibrium
partial pressure of S03 in the six reducing gases to the
equilibrium vapor pressure of S03 over the metal sulfate.
At temperatures where the S03 vapor pressure over the sulfate
is greater than PSQ in the reducing gas, there is driving
force for the sulfate to give up S03, or decompose to the
oxide.
The data needed for this analysis were SO3 partial
pressures in the reducing gases as a function of temperature
and vapor pressures of S03 over metal sulfates as a function
of temperature.
Section 2.1 described how the equilibrium
compositions of six reducing gases were calculated as a
function of, temperature. Tables 2-3 through 2-8 gave the
detailed composition in mole fraction for each reducing gas
at 600, 1000, and 1400°C at one atmosphere total pressure.
The mole fraction (activity) of S03 is equal to the partial
pressure at one atmosphere total pressure. The logi0Pso
for each reducing gas taken from Tables 2-3 through 2-8 is
plotted in Figure 3-1.
Both Radian Technical Note 200-045-10-Ola and pre-
vious work (PA-016) describe the methods used to calculate
metal sulfate S03 vapor pressures as a function of tempera-
ture. Briefly, the equilibrium constant for metal sulfate
decomposition reaction is described in Equation 3-1, where
an is the activity of the n— product or reactant.
-127-
-------
00
Reducing
Gas
600
700
800
900
1000
1100
1200
1300
TEMPERflTURE - DEGREES CENTIGRflOE
1400
FIGURE 3-1 - LOG Pcn IN SIX REDUCING GASES AS A FUNCTION OF TEMPERATURE
10 SO 3
-------
„
ea
eq
Since activities of solids are equal to 1, the equilibrium
constant is numerically equal to the activity of S03 at
equilibrium (or the mole fraction at one atmosphere) when
the reaction is normalized to one mole of S03. Graphs of
logioK (equal to logioPgQ ) for metal sulfate decomposition
reactions from 600 to 1400°C are given in the Appendix of
Technical Note 200-045-10-Ola. An example for the calcium
sulfate decomposition reaction is shown in Figure 3-2.
3.2 Results of Thermodynamic Analysis of Sulfate
Reduction Reactions i
———————————— g
Using data such as those shown in Figures 3-1 and
3-2, the vapor pressure of S03 over metal sulfates may be
compared to the partial pressure of S03 in reducing gases in
the temperature range from 600 to 1400°C. This comparison is
facilitated by plotting both the S03 vapor pressure and the
reducing gas S03 partial pressure data on the same set of
coordinates. An example is shown in Figure 3-3 for calcium
sulfate. Figure 3-3 shows that the line representing the SO3
vapor pressure over calcium sulfate intersects the line
representing the equilibrium partial pressure of SO3 in a gas
containing a mole of methane and a mole of SO3 at a tempera-
ture of about 730°C. Below 730°C there is driving force for
the sulfate to absorb SO3 from the reducing gas, and above
730°C there is driving force for the sulfate to give up 80s
to the gas or decompose. Figure 3-3 shows that the corres-
ponding decomposition temperature for a reducing gas produced
by coal or char is 960°C. For CO + %H2 reducing gas the mini-
mum decomposition temperature is about 1025°C. For one mole
-129-
-------
o
I
a:
\—
CD
2
0
O
oc
CD
^> CD
C3
UJ UJ
_J
~ o
LU
n
-S
-10
-is
-20L-
600
I
I
I
I
I
700
800 900 1000 MOO 1200 1300
TEMPERflTURE - DEGREES CENTIGRflDE
1400
FIGURE 3-2 - LOG K VERSUS T FOR THE REACTION
CaSOi, * CaO + S03
-------
I
I-1
10
Symbol
Reducing
Gas
H2
CO
CO + H
C + H and C
CHU
-5
H2
-?nl i i 11 ..... I..
por pressure over CaSOu
600
700
i 11 i i i i i i i i 11 11 i i 1 i i i 11 .I I
800
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE 3-3 -
COMPARISON OF CaSO, VAPOR PRESSURE WITH P IN REGENERATION CASES
-------
of carbon monoxide or one mole of hydrogen (H2) the minimum
temperatures for reductive decomposition of sulfate are approx-
imately 1340 and 1320, respectively. Graphs such as those
shown in Figure 3-3 comparing sulfate vapor pressures with
reducing gas S03 partial pressures were prepared for each poten-
tial metal oxide sorbent. They are included in the Appendix.
Table 3-1, taken from Figures A-l through A-14 in the Appendix,
lists the minimum temperatures for reductive decomposition at
one atmosphere pressure for each metal sulfate listed in Table
1-1 in each reducing gas.
-132-
-------
TABLE 3-1
MINIMUM TEMPERATURES
Reducing
Sulfatea
Na2SO»
CaSO*
SrSO,
BaSO*
LizSOi,
Na2SO»
Na2SO*
A120,
Fe203
Ti02
A120,
FejOj
CaSO* + A120S
SrSO,, + A120S
SrSOn + Ti02
BaSO* +
BaSO* + T102
[ WHICH METAL SULFATES ARE REDUCED BY SIX REDUCING AGEN1
Temperature
Hydrogen
H2
>UOO
1320
>UOO
>1400
>1400
1110
>UOO
830
1220
1180
1250
1020
1230
1190
Carbon
Monoxide
CO
>1AOO
1340'
>UOO
>1400
>1400
1160
>1400
800
1245
1220
1290
1040
1290
1220
Synthesis
Gas
CO + %H2
>1400
1025
1310
>1400
1400
825
1350
670
930
840
900
775
890
910
CO
Coal
C/H °_l
>1400
960
1240
>1400
960
775
1140
645
B75
790
840
735
840
850
Char
C
>1400
960
1210
>1400
960
7B5
1140
655
890
800
860
7W
850
860
Methane
CH>
>1400
730
1060
>1400
<600
660
<600
670
600
640
<600
630
630
* Minimum temperature for Which the vapor pressure of SOj over the metal
aulfate is greater than the partial pressure of SOB in the reducing gas.
-133-
-------
4.0 INVESTIGATION OF THE POSSIBILITY OF METAL SULFIDE
FORMATION
The model used for thermodynamic analysis of
potential S02 removal processes includes reactions for 802
sorption with metal sulfate formation and regeneration of
the metal oxide by reductive decomposition of the metal
sulfate. Other possible reactions include reduction of the
metal oxide all the way to the elemental state (metal) or the
formation of metal sulfide through reaction of the metal oxide
with sulfur species present in the reducing gas. Reduction
of the sulfate to the metal by the reducing gas has been
reported by Shell to occur during reduction of copper oxide
S02 sorbent by hydrogen (PO-001). This was not a serious
problem for Shell since formation of the oxide occurs readily
in the oxidizing atmosphere of the combustion gas. Formation
of metal sulfide would require an additional processing step
of a solid at high temperature. This is to be avoided if
possible. Therefore, this study included identification of
the conditions under which sulfide formation might be expected
during reductive sulfate decomposition. The methods of data
generation and analysis for this investigation are given in
Section 4.1, and the results are given in Section 4.2.
4.1 Method of Thermodynamic Analysis of the Sulfide
Formation Reaction
One reaction which describes formation of metal
sulfides from the oxide is given in Equation 4-1.
2MeO + S2 -»• 2MeS + 02 (4-1)
-134-
-------
Since the gas mixture is an equilibrium mixture the exact
reaction path is not important. All reaction paths would
give the same results at the same equilibrium temperature.
The equilibrium constant for the reaction is described in
Equation 4-2, where an is the activity of the n— product or
reactant.
Ke<(T> = ^eO^sT
Since the activities of solid species are equal to one, the
equilibrium constant for such a reaction is numerically equal
to the ratio of oxygen and sulfur activities at equilibrium
for the reaction normalized to one mole of 02 and 82 . As
described in Section 3.0, the equilibrium constant for a
reaction may be calculated from standard state thermodynamic
properties. As an example, the equilibrium constant for the
calcium oxide-sulfide conversion reaction is shown in Figure
4-1.
The ratio of oxygen and sulfur activities for the
oxide-sulfide conversion reaction at equilibrium may be
compared with the ratio of oxygen and sulfur activities that
actually exist in the reducing gases. The temperature at
which the aQ /ag in the reducing gas is equal to aQ /ag for
the oxide sulfide conversion reaction at equilibrium is the
transition temperature. The region where the aQ /ag of the
gas is greater is the region of oxide stability. The other
region is the sulfide stable range.
-135-
-------
10
o\
I
cc
en
z
o
cc
OQ CM
—« O
ZD O
UJ UJ
_J
*— O
a z:
*— cc
C5 LJ
O 0.
-5
-10 _
i i i i i i i i i I
600 700
..i I
800
900
1000
1100
1200
1300
1VQQ
TEMPERflTURE - DEGREES CENTJGRflDE
FIGURE 4-1 -
07 NOV 7U
LOGARITHM OF THE EQUILIBRIUM CONSTANT FOR THE REACTION
2CaO + S2 * 02 + 2CaS
-------
Activities of oxygen and sulfur in the reducing gases
at 600, 1000 and 1400°C were calculated using the gas phase
equilibrium model as described in Section 2.0. Figure 4-2,
taken from Tables 2-3 through 2-8 in Section 2.0, shows logj 0
aQ /ag in the reducing ga.se s from 600 to 1400°C.
4.2 Results of Thermodynamic Analysis of the Sulfide
Formation Reaction
Using data such as those shown in Figures 4-1 and
4-2, the oxygen-sulfur activity ratios in reducing gases were
compared with the ratios for oxide-sulfur conversion reactions
at equilibrium. Again, the comparison was done by plotting
both sets of data on one set of coordinates as shown in
Figure 4-3 for calcium oxide-sulfide conversion. Figure 4-3
indicates that at 1250°C the line representing logio a02/a
-------
10
CO
I
-s
CM! M
O en
ca I co
oo
O
-10
-IS
-20
Reducing
Symbol Gas
CO
CO + H
CH,
Coal
Char
..——"
-^*sf-
...— ^.-&f--~~
+ H
Coal
600
700
800
900
1000
1100
1200
1300
TEMPERflTURE - DEGREES CENTIGRflDE
1400
FIGURE 4-2 - VARIATION OF THE LOGARITHM OF THE OXYGEN-SULFUR ACTIVITY
RATIO WITH TEMPERATURE IN FIVE REDUCING GASES
-------
10 _
Reducing
Symbol Gas
H»
CM I CM
O CO
CO led
vo
X L°8io a0
8QQ 9QQ 1000 1100 1200
TEMPERflTURE - DEGREES CENTIGRflDE
37 NOV 7U
FIGURE 4-3 - COMPARISON OF OXYGEN-SULFUR ACTIVITY RATIOS IN REGENERATION GASES
WITH THE RATIO FOR THE REACTION 2CaO + S2 •»• 2CaS + 02
-------
is very stoichiometry dependent (see Table 2-2). For coal
or char the minimum temperature for calcium oxide stability
is greater than 1400°C. Graphs such as the one in Figure 4-3
were prepared for all of the metal oxides considered in this
study and are included in the Appendix, Figures A-15 through
A-30. Table 4-1 summarizes data from the graphs for the
minimum temperature of stability of the metal oxides in each
of the six reducing gases.
These calculations correspond to the physical
situation in a cocurrent reactor. The gas phase would be
in contact with the solid phase of interest, i.e., the
solid exiting the regenerator. A counter current reactor
does not have the exiting solid in contact with the gas phase
composition here. The solid of interest will "see" a stronger
reducing atmosphere. It would be expected that sulfide for-
mation would be more of a problem in a counter current than
a cocurrent reactor.
Other considerations are that the regeneration
pressure is one atmosphere and there are no diluents present.
Low pressure operation or diluents could lower the decomposi-
tion temperature. An inspection of the log plots can indicate
the changes involved.
-140-
-------
TABLE 4-1
MINIMUM
TEMPERATURE OF STABILITY OF METAL OXIDE WITH RESPECT TO
FORMATION OF METAL
SULFIDE IN
REDUCING
GAS*
Temperature (°C)
—- -^^^^ Reducing
Metal "— — -^ Agents
Oxide — -^^
Na20
CaO
SrO
BaO
LiA102
LiFe02
A120,
Ti02
NaAIOz
NaFe02
CaAl20»
SrAl20»
SrTiOa
BaAl2Ok
BaTiOs
Li2T103
Hydrogen
H2
970
<600
<600
<600
<600
<600
<600
600-1190
<600
<600
<600
<600
<600
<600
<600
<600
Carbon
Monoxide
CO
955
<600
590
700
<600
<600
<600
880-1325
<600
<600
<600
<600
<600
<600
<600
<600
Synthesis
Gas
CO + %H2
>1400
1250
>1400
>1400
<600
750
<600
>1400
<600
820
740
<600
<600
<600
<600
<600
Coal
C/H = 1
>1400
>1400
>1400
>1400
<600
1100
<600
>1400
<600
1175
1360
<600
<600
<600
<600
<600
Char
C
>1400
>1400
>1400
>1400
<600
975
<600
>1400
600
1030
970-1350
<600
<600
<600
<600
<600
Methane
CH»
>1400
1370
>1400
>1400
<600
890
<600
>1400
<600
980
890
<600
<600
<600
<600
<600
Minimum temperature at which the ratio of oxygen activity to sulfur activity
in the reducing gas is greater than the ratio of oxygen to sulfur activities
at equilibrium for the reaction 2MeO + S2 •* 2MeS + 02.
-141-
-------
5.0 RESULTS
Using thermodynamic analysis, three types of
predictions have been made for each candidate metal oxide
sorbent:
1. the temperature range in which there is a
driving force for S02 sorption with sulfate
formation,
2. the temperature range in which there is a
driving force for reductive decomposition
of the sulfate with six reducing agents of
varying reduction potentials,
3. the temperature range in which metal oxide
formation is favored over metal sulfide
formation during sulfate reduction with the
six reducing agents.
A temperature range of 600 to 1400°C was selected for this
analysis on the bases of the operating temperature of fluidized
bed combustion processes and the physical properties of con-
struction materials.
An estimate of the heat of reaction is advisable since
heat transfer should be minimized where possible. The heat re-
quirement for regeneration of calcium sulfate with CO may be
considered from the following simplified scheme (see Table 2-4).
CaSO,, - CaO + S03 (5-1)
S03 + CO -»• S02 + C02 (5-2)
-142-
-------
The heats of formation at 25°C may be used to estimate the heat
of reaction at other temperatures. Heats of formation are
given in Table 5-1.
Reaction 5-1 is endothermic with an enthalpy change
of +94.1 Kcal. Reaction 5-2 is exothermic with an enthalpy
change of -44.1. The overall reductive decomposition of the
sulfate is the sum of these reactions. It is endothermic at
+50.0 Kcal.
If hydrogen were the reducing agent, then the gas
phase reaction could be approximated by 5-3 (see Table 2-3).
S03 + H2 -»• S02 + H20 (5-3)
Reaction 5-3 is exothermic at -34.3 with the overall reaction
being endothermic at +59.8 Kcal. This will have process
implications for minimizing heat transfer.
5.1 Summary of Results for Each Metal Oxide
The following paragraphs summarize the results for
each candidate metal oxide sorbent. Figures 5-1 through 5-14
show the predicted temperature ranges for sorption with sul-
fate formation for each metal oxide and the temperature ranges
at which sulfate decomposition and oxide stability are predicted
for each metal oxide-reducing agent combination. Again the
basis for these calculations must be kept in mind. Changes
in the design basis would alter the temperature ranges somewhat.
The temperature range in which sorption, regeneration,
or oxide stability are predicted is indicated in the figures
by cross-hatching. For an example, please see Figure 5-1. Sorp-
tion of SQz by sodium oxide to form sodium sulfate is predicted
to occur from 600 to 1380°C, so the diagram shows cross-hatching
on the bottom line from 600 to 1380 on the temperature scale.
-143-
-------
TABLE 5-1
HEATS OF FORMATION AT 25"C
AH,
Compound Kcal/gmole
CaO -151.7
CaSO,, -340.2
S02 -70.9
S03 -94.4
CO -26.4
C02 -94.0
H20(g) -57.8
-144-
-------
01
I
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen
600
800 1000
Temperature, °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide- Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-1 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR Na20
-------
Sodium Oxide
Figure 5-1 summarizes the data for a sodium oxide
sorption-regeneration process. The first (lowest) line
indicates that sorption to form sodium sulfate occurs up to
about 1375°C. The second line indicates that sodium oxide
rather than sodium sulfide would be formed at temperatures
above 970°C if hydrogen were used as the reducing gas, but
that regeneration does not occur with hydrogen up to 1400°C.
In fact, Figure 5-1 shows that sodium sulfate is so stable
that it cannot be reduced by any of the six reducing agents
below 1400°C
Calcium Oxide
Figure 5-2 shows that sorption can occur up to
1100°C. Regeneration is possible with stoichiometric hydrogen
above 1320°C. It is possible with stoichiometric CO above 1340°C.
The oxide will be formed. Increasing the reducing agent strength
to synthesis gas (CO + %H2 per mole S03) lowers the potential
regeneration temperature to about 1020°C. One would expect
calcium sulfide formation below 1250°C. Regeneration with
the greater stoichiometries will produce the sulfide.
Strontium Oxide
Figure 5-3 shows that there is no temperature
between 600 and 1400°C at which regeneration and oxide stabil-
ity occur simultaneously. For those reducing agents which
are predicted to be effective regenerators, strontium sulfide
formation can occur. Strontium sulfide formation would not
be predicted in stoichiometric carbon monoxide or hydrogen,
but sulfate decomposition does not occur at temperatures
below 1400°C with these reducing agents. (An increase in the
-146-
-------
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
\v\\\\v\
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
600
800 1000
Temperature, °C
1200
1400
FIGURE 5-2 - TEMPERATURE REGIONS IN WHICH SORPTION. REGENERATION. AND OXIDE
STABILITY ARE FAVORED FOR CaO
-------
00
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
I- -i-
800 1000
Temperature, °C
K\\
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1200
1400
FIGURE 5-3 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR SrO
-------
CO or H2 stoichiometry or a change in pressure might lower
the strontium sulfate reduction temperature and make this
process feasible.)
Barium Oxide
Figure 5-4 shows that barium sulfate, like sodium,
cannot be reduced by any of the six reducing agents between
600 and 1400°C.
Lithium Aluminum Oxide
Figure 5-5 indicates that the lithium-aluminum
binary oxide can be regenerated by the stronger reducing
agents. Neither formation of lithium nor aluminum sulfide is
predicted. Synthesis gas (CO + %Ha) could be used as the
reducing agent with no sulfide formation in a process in
which sorption takes place up to 1200°C and regeneration
occurs around 1400°C. Since the regeneration reaction is
probably endothermic the lower regeneration temperature may
be attractive.
Lithium-Iron(III) Oxide
Figure 5-6 shows that the lithium-iron(III) binary
oxide could be regenerated by all of the reducing agents.
Formation of lithium sulfide could be a problem. Due to lack
of thermodynamic data for iron(III) sulfide no analysis could
be made of the possibility of conversion of iron(III) oxide
to the sulfide. Coal, char, carbon monoxide or hydrogen could
all be used as reducing agents in processes which employ
sorption up to about 930°C and a higher temperature for either
regeneration or conversion of lithium sulfide to lithium
oxide.
-149-
-------
Reducing Agent
Predicted Temperature
in
O
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
i- • : . i
i
i
i
• 1 . " ' i ' ' ' '•
: ! ' !
i i ,
i . ,
I ' . r • "•; ;
i . .
v////Y/////\^////z////
,.;'•'
/ / / // f s sy/ / \/ /S S*/ ////// SS
1 i i •
/ / / / / /// / / ////// //////t/A
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stabilitv
Regeneration
Sorption
600
800 1000
Temperature, °C
1200
1400
FIGURE 5-4 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR BaO
-------
I
M
Ln
M
I
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
800 1000
Temperature. °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-5 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR LiAl02
-------
01
to
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
77777777
ZZZZZZZZZZ
600
800 1000
Temperature, °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-6 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION. AND OXIDE
STABILITY ARE FAVORED FOR LiFe02
-------
Sodium Aluminum Oxide
Figure 5-7 shows that sodium aluminate can be
regenerated with no formation of sodium or aluminum sulfide
using all of the reducing agents.
Sodium-Iron(III) Oxide
Figure 5-8 indicates that all reducing agents have
a region of regeneration temperature where no formation of
sodium sulfide is predicted. Again, the possibility of iron
sulfide formation could not be assessed.
Calcium-Aluminum Oxide
Figure 5-9 shows that calcium aluminate can be
regenerated by the four strongest reducing agents with no
formation of calcium or aluminum sulfide in the upper
temperature regions. Carbon monoxide and hydrogen are also
effective reducing agents, but the regeneration step requires
a higher temperature than the sorption step.
Strontium Aluminum Oxide
Figure 5-10 indicates that all reducing agents could
be used to regenerate strontium aluminate without formation of
strontium or aluminum sulfide. The extreme stability of the
oxide looks promising.
-153-
-------
Ul
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
800 1000
Temperature, °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-7 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR UaA102
-------
Ln
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
77777
///A
600
800 1000
Temperature, °C
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1200
1400
FIGURE 5-8 - TEMPERATURE REGIONS IN ;WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR NaFe02
-------
01
cr>
i
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
\\N\\\\\
NNNNNS
ZZZZZZZZZZ
600
800 1000
Temperature, ° C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-9 - TEMPERATURE REGIONS IN WHICH SORPTION. REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR CaAl20^
-------
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen
600
/
800 1000
Temperature, °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-10 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR SrAl20,,
-------
Strontium-Titanium Oxide
Figure 5-11 shows that strontium titanate could be
difficult to regenerate without sulfide formation. Sulfide
formation would not be predicted in carbon monoxide or hydro-
gen based decomposition processes above about 1040 or 1020°C,
respectively.
Barium Aluminum Oxide
As indicated in Figure 5-12 barium aluminate could
be regenerated by a strong reducing agent without sulfide
formation.
Barium Titanium Oxide
Figure 5-13 shows that prevention of titanium sulfide
formation is possible only with the use of carbon monoxide or
hydrogen as reducing agents. A process employing these
reductants would involve a sorption step below 1000°C and a
higher temperature regeneration step.
Lithium Titanium Oxide
Figure 5-14 shows that lithium titanate cannot be
regenerated below 1400°C without sulfide formation.
-158-
-------
Reducing Agent
Predicted Temperature
Range
01
vO
I
Methane
. Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
\\\
600
800 1000
Temperature, °C
1200
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-11 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR SrTi03
-------
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
/ //
800 1000
Temperature, °C
1200
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-12 - TEMPERATURE REGIONS IN WHICH SORPTION. REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR BaAl20,»
-------
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
kXXXXXXXXXXXXXX
\r-
XX
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
800 1000
Temperature, °C
1200
1400
FIGURE 5-13 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION. AND OXIDE
STABILITY ARE FAVORED FOR BaTi03
-------
ro
Reducing Agent
Methane
Coal and Char
Synthesis Gas
(CO + %H2)
Carbon Moxoxide
Hydrogen (H2)
600
i
f"
•+-
ZZZZZZZZZZZH
800 1000
Temperature, °C
1200
k\
Predicted Temperature
Range
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Oxide Stability
Regeneration
Sorption
1400
FIGURE 5-14 - TEMPERATURE REGIONS IN WHICH SORPTION, REGENERATION, AND OXIDE
STABILITY ARE FAVORED FOR LizTi03
-------
5.2 Conclusions
The thermodynamic conclusions are of two types.
First is the definition of the temperature range in which the
sorbent will perform. Second is the regenerability of the
sorbent. The most desirable regeneration is one in which the
sulfated sorbent is decomposed to yield gaseous products and
the original oxide sorbent. A.less desirable process is one
that yields a sulfide solid, which would require regeneration
in a second step to yield the oxide form of the sorbent for
recycle.
These results are theoretical calculations to be
used as an aid in making decisions. They are based on data
that have associated experimental errors. Furthermore, some
of the data are estimated. This means that a margin for
error should be considered in making decisions based upon
these data.
Table 5-2 presents the temperature ranges for
processes in which the oxide is the predicted regeneration
product. Table 5-3 presents the temperature ranges of
applicability of the sulfide producing (two-step) regenera-
tion processes.
Many of the sorbents presented in Table 5-2 look
promising. The selection of materials upon which to base a
process should begin with these. Factors such as melting
and softening point, possibility of flux formation with ash
constituents, unusual properties such as the piezoelectric
characteristics of BaTi03, and reaction kinetics must be
considered in a process development program.
-163-
-------
TABLE 5-2
SORPTION-REGENERATION PROCESSES IN WHICH OXIDE FORMATION IS PREDICTED
Maximum Sorpclon
Temperature
Sorbent (°C)
CaO 1090
LlAlOi 1200
LIFeOa- 950
NoAlOa 820
NaFeOj- 1020
CaAliO, 950
SrAl,0» 1000
SrTiO, 920
BaAlaOt 1000
BaTIO, 1000
I. Formula Reducing Agent
CH, Methane ^
C + %Hi Coal
C Char
CO + %H, Synthesis Gas
CO Carbon Monoxide
HI Hydrogen
Temperature Range for
Regeneration with
. Oxide Formation
Reducing Agenc-i CO
Hi 1320-1400
CO 1340-1400
CO + fcHi 1250-1400
CH. 1370-1400
Coal and Char 960-1400
CH. 600-1400
R> 1110-1400
CO 1160-1400
CO + %Hj 825-1400
Coal 1100-1400
Char 1020-1400
Methane 890-1400
H, 830-1400
CO 800-1400
CO + %H, 670-1400
Coal and Char 650-1400
Methane 600-1400
Hi 1220-1400
CO 1245-1400
CO + %Ha 930-1400
Coal 1030-1400
Char 1175-1400
Methane 980-1400
Ha 1180-1400
CO 1220-1400
CO + %Hi 840-1400
Char 970-1350
Coal 1360-1400
Methane 890-1400
Ha 1250-1400*
CO 1290-1400
CO + %Hi 900-1400
Coal and Char ".850-1400
Methane 640-1400
Hi 1020-1400
CO 1040-1320
Ha 1230-1400
CO + %Ha 1290-1400
Coal and Char 850-1400
Methane 630-1400
H, 1190-1400
CO 1220-1320
One mole of reducing agent per mole
1 of SOi was assumed.
2.
Possibility of Iron sulfide formation not Investigated due to lack
of thermodynamic data.
-164-
-------
TABLE 5-3
SORPTIOH-REGENERATION PROCESSES IN WHICH SULFIDE FORMATION IS PREDICTED
Serbent
CaO
SrO
LlFeOj 2.
NaFeOi
Maximum Sorpcion
Temperature
1090
1260
950
1020
950
Reducing Agent-
CO + Wt
Coal and Char
Methane
CO + %Ha
Coal and Char
Methane
Coal
Char
Methane
Coal
Char
Methane
Char
Coal
Methane
Temperature Range for
Regeneration with
Sulfide Formation
1030-1250
960-1400
725-1370
1310-1400
1240-1400
1060-1400
775-1100
775-1020
600-890
875-1030
875-1175
670-980
800-970
800-1360
600-890
SrTIO,
BaTlOi
920
1000
CO
CO + %H2
Coal and Char
Methane
CO
CO + %H,
Coal and Char
Methane
1320-1400
775-1400
740-1400
600-1400
1320-1400
910-1400
850-1400
630-1400
LljTiOi
.1. Formula
CH»
C + %H,
C
CO + %Hj
CO
H,
1200 CO + %H2 1350-1400
Coal and Char 1140-1400
Methane 660-1400
Reducing Agent
Methane
Coal
Chai
Synthesis Cas
Carbon Monoxide
Hydrogen _,
One mole of reducing agent per
, mole of SO] was assumed.
thermodynamt^datT
lnve«1*«e* to lack of
-165-
-------
BIBLIOGRAPHY
PA-016 Parsons, T. B., Gary D. Schroeder, and David DeBerry,
Applicability of Metal Oxides t£ the Development of
New Processes for Removing S02 from Flue Gases,
2 volumes, Austin, Texas, Tracer, Inc., 1969.
PO-001 Pohlenz, J. B., "The Shell Flue Gas Desulfurization
Process", presented at the Environmental Protection
Agency Flue Gas Desulfurization Symposium, Atlanta,
Georgia, November 4-7, 1974.
-166-
-------
APPENDIX
FIGURES A-l THROUGH A-30
-167-
-------
LIST OF FIGURES
Figure
A-l COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER Na2SOi*
A-2 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH 80s VAPOR PRESSURE OVER CaSOi,
A-3 COMPARISON OF SO3 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER SrSO.,
A-4 COMPARISON OF 80s PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER BaSOw
A-5 COMPARISON OF SO3 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER Li2SOi, + A1203
A-6 COMPARISON OF SO3 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER Li2SOu + Fe203
A-7 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER Na2SO.» + AI203
A-8 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER Na2SO., + Fe203
A-9 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER CaSO., + A1203
A-10 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER SrSO., + A1203
A-11 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER SrSO., + Ti02
A-12 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER BaSOu + A1203
A-13 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH S03 VAPOR PRESSURE OVER BaSOu + Ti02
A-14 COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING
GASES WITH SO3 VAPOR PRESSURE OVER Li2SO^ + Ti02
-168-
-------
LIST OF FIGURES (cont.)
Figure
A-15 COMPARISON OF a02/agz IN REDUCING GASES WITH a02/ag2
FOR THE REACTION: 2Na20 + S2 "• 02 + Na2S
A-16 COMPARISON OF aQ2/ag2 IN REDUCING GASES WITH a02/ag2
FOR THE REACTION: 2CaO + S2 + 02 + 2CaS
A- 17 COMPARISON OF a^/agz IN REDUCING GASES WITH aQ2/agz
FOR THE REACTION: 2SrO + S2 + 02 + 2SrS
A-18 COMPARISON OF aQ /agi IN REDUCING GASES WITH aQ2/ag2
FOR THE REACTION: 2BaO + S2 + 02 + 2BaS
A-19 COMPARISON OF aQ /ag IN REDUCING GASES WITH a02/ag2
FOR THE REACTION: 4LiA102 + S2 * 02 + 2Li2S + 2Al2Oa
A-20 COMPARISON OF a^/a^ IN REDUCING GASES WITH aQ2/ag2
FOR THE REACTION: 4LiFe02 + S2 + 02 + 2Li2S + 2Fe2Oa
A-21 COMPARISON OF aQ /ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION* 2A1203 + 3S2 + 302 + 2A12S3
A-22 COMPARISON OF aQ /ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION^ Ti02 + S2 -»• 02 + TiS2
A-23 COMPARISON OF aQ 7ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION^ 4NaAl02 + S2 -»• 02 + 2Na2S + 2A1203
A-24 COMPARISON OF aQ /ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION? 4NaFe02 + S2 -*- 02 + 2Na2S + 2Fe203
-169-
-------
LIST OF FIGURES (cont.)
Figure
A-25 COMPARISON OF a^/a^ IN REDUCING GASES WITH aQ2/aS2
FOR THE REACTION: 2CaAl20,, + S2 * 02 + 2CaS + 2Al2Os
A-26 COMPARISON OF aQ /a^ IN REDUCING GASES WITH a^/a^
FOR THE REACTION: 2SrAl2Oi» + S2 -•• 02 + 2SrS + 2A1203
A-27 COMPARISON OF ag /ag IN REDUCING GASES WITH a^/a
FOR THE REACTION: 2SrTi03 + S2 * 02 + 2SrS + 2Ti02
A-28 COMPARISON OF aQ /ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION: 2BaAl20,, + S2 * 02 + 2BaS + 2A1203
A-29 COMPARISON OF aQ /aSz IN REDUCING GASES WITH a^/a
FOR THE REACTION? 2BaTi03 + S2 •*• 02 + 2BaS + 2Ti02
A-30 COMPARISON OF aQ /ag IN REDUCING GASES WITH a^/a^
FOR THE REACTION: 2Li2Ti03 + S2 + 02 + 2Li2S + 2Ti02
-170-
-------
LOGio P
S03
0 _
SO, vapor pressure over sulfate:
S03 partial pressure in H2:
SO3 partial pressure in CO:
SO3 partial pressure in CO +
SO3 partial pressure in coal or char:
SOj partial pressure in CH*:
I . . . i . . i i i I i i i . • . t
GOO
700
QOO
900
1000
1100
TEMPERflTURE - DEGREES CENTlGRftOE
FIGURE A-l - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Na2SO,
-------
LOG10 P
S03
SO3 vapor pressure over sulfate:
SO3 partial pressure in H2:
SO3 partial pressure in CO:
SO3 partial pressure in CO + %Hz:
SO3 partial pressure in coal or char:
SO3 partial pressure in CHi,:
H2
SO3 vipor pressure over CaSOi,
-IS
-20
1. 111111 I • i 1 i 11111 1111111 t 11111111 I ll
« » «
600
700
000
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-2 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER CaSO,
-------
LOGi
S03
SO3 vapor pressure over sulfate:
SO3 partial pressure in H2:
SOj partial pressure in CO:
S03 partial pressure in CO + %Hz:
SO3 partial pressure in coal or char:
SOj partial pressure in CH*:
-10 _
-1
-20
1
1
1
• « •
..... i i i i I i i i i
i i
1400
600 700
FIGURE A-3 -
800
900
1000
1100
1200
1300
TEMPERflTURE - DEGREES. CENTIGRflDE
COMPARISON OF SO 3 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER SrSO,,
-------
LOG10 P
SO 3
SOS vapor pressure over sulfate:
S03 partial pressure in H2:
SO3 partial pressure in CO:
S03 partial pressure in CO + %H2:
S03 partial pressure in coal or char:
S03 partial pressure in CH»:
800
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-4 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER BaSO,
-------
LOG,0 P
10
i
M
•vl
I
-10
-IS
SOj vapor pressure over sulfate:
S03 partial pressure in Hz:
SO3 partial pressure in CO:
SO3 partial pressure in CO + %Hz:
SOj partial pressure in coal or char:
SO 3 partial pressure in CHi>:
I I
I
I
I
600
700
QOO 900 1000 1100 1200 1300
TEMPERflTURE - DEGREES CENTlGRflOE
1400
FIGURE A-5 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Li2SO,, + A1203
-------
LOG10 P
10—
SO 3
I
I-1
-J
I
-10
SO3 vapor pressure over sulfate:
SO3 partial pressure in H2:
SO3 partial pressure in CO:
SO3 partial pressure in CO + %H2:
SO3 partial pressure in coal or char:
SO3 partial pressure in CH«,:
isL_
600
i i i i
1
i
JL
700
QOO 900 1000 1100 1200 1300
TEMPERflTURE - DEGREES CENTIGRflDE
MOO
FIGURE A-6 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Li2SO,, + Fe203
-------
-J
I
LOGio
10
S03
SOS vapor pressure over sulfate:
80s partial pressure in H2:
SOS partial pressure in CO:
S03 partial pressure in CO + %H2:
S03 partial pressure in coal or char:
SOS partial pressure in CH*:
-1 sLi 11111111111111111111111111111.11.•11..I.i....... I......... I......... I
600
700
BOO
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-7 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Na2S04 + A1203
-------
LOGio P
5"
S03
oo
i
-10
-IS
-20
SOS vapor pressure over sulfate:
S03 partial pressure in H2:
S03 partial pressure in CO:
S03 partial pressure in CO + %H2:
S03 partial pressure in coal or char:
S03 partial pressure in CHt,:
I
I
I
I
I
I
600
700
QOO 900 1000 1100 1200 HOO
TEMPERflTURE - DEGREES CENTlGRflOE
MOO
FIGURE A-8 - COMPARISON OF SO 3 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Na2SOu + Fe203
-------
LOGio P
10
SO;
SO
-IS
S03 vapor pressure over sulfate:
SO3 partial pressure in H2:
SO3 partial pressure in CO:
S03 partial pressure in CO + %H2:
SOj partial pressure in coal or char:
SO3 partial pressure in CH«:
I
I
I
I
600
700
QOO 900 1000 1100 1200 1300
TEMPERflTURE - DEGREES CENTlGRflOE
1400
FIGURE A-9 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER CaSOq + A1203
-------
LOGio F
SO 3
CO
o
-1
-20
SOj vapor pressure over sulfate:
SO3 partial pressure in Hz:
SO3 partial pressure in CO:
SO3 partial pressure in CO + %Ha:
SO3 partial pressure in coal or char:
S03 partial pressure in CH*:
1
111 1111111 111111 I 111 I I I 111111
600
700
QOO 900 1000 MOO 1200 1300
TEMPERflTURE - DEGREES CENTIGRflOE
140C
FIGURE A-10 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER SrSO,, + A1203
-------
LOGio
I
»-•
CO
-10
SOj vapor pressure over sulfate:
SOj partial pressure in Hz:
SO3 partial pressure in CO:
SOS partial pressure in CO + %H2:
80s partial pressure in coal or char:
SO3 partial pressure in CH*:
- 1 SI i i i i i i i i i I i i . i i i i . i I ..... i i i i I
600
700
QOO
900
1000
1100
L.
1200
1300
1400
lEMPERflTURE - DEGREES CENTIGRflOE
FIGURE A-H - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER SrSO,, + Ti02
-------
LOGio P
10—
S03
00
N>
I
1 S
600
S03 vapor pressure over sulfate:
S03 partial pressure in H2:
S03 partial pressure in CO:
SO3 partial pressure in CO + %H*:
SOS partial pressure in coal or char:
SO, partial pressure in CH»:
i i t i i I .
700
i I i i i i i t i i i I i i
800
900
.Mill.
1000
1100
1
1200
1300
1400
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-12 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH SO 3 VAPOR
PRESSURE OVER BaSO,, + A1203
-------
LOG10 PS03
CO
co
-10
SO3 vapor pressure over sulfate:
SO3 partial pressure in H2:
SO3 partial pressure in CO:
SO3 partial pressure in CO -I- %H2:
SO3 partial pressure in coal or char:
SOa partial pressure in CH*:
-1SI i i i i i i i i i i i i i i i i t i i 1 I ......... i I ......... I .
600
700
000
900
1000
1100
1200
1300
1400
TEMPERflTURE - DEGREES CENTlGRflOE
FIGURE A-13 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER BaSOu + Ti02
-------
LOG,o P
SO,
SO3 vapor pressure over sulfate:
S03 partial pressure in H2:
SO3 partial pressure in CO:
SO, partial pressure in CO + %H2:
SO, partial pressure in coal or char:
SO, partial pressure in CH*:
i
M
CO
I
-1 Sill I Illl II III
» 1 1 ' ' I
600
700
GOO 900 1000 1100 1200 1100
TEMPERflTURE - DEGREES CENTIGRflDE
1400
FIGURE A-14 - COMPARISON OF S03 PARTIAL PRESSURE IN REDUCING GASES WITH S03 VAPOR
PRESSURE OVER Li2SOu + Ti02
-------
LOG
i o
0^ ao2/as, inH"
c 80»'aSi for °Kide-sulfide conversion:
a / M J _ f*r\
00
V1 -5
-10
-15
ao,/as2 ln C0:
S02^aS ^n *® +
aoz/as! in Coal=
aO,/aS2 in Char:
'-^
l
1
_L
60(1
100
800 900 1QQQ 1100 1200
TEMPERflTURE - DEGREES CENTJGRflDE
1300
moo
FIGURE A-15 - COMPARISON OF an /ac IN REDUCING GASES WITH an /aQ FOR THE REACTION
t>2 o2 O2 b2
2Na20 + S2 * 02 + 2Na2S
-------
LOG10
10
M -5
oo
o>
I
-to —
-2l ao,/as, tn H»!
S2 aOj/aSj for oxide-sulfide conversion
— BQ /8g in CO:
ao2/as! in co +
a02/as in Coal:
ao.'a
-------
LOG1
a02/aS2
10 _
aOi'8
Si
for
conversion:
-5
CO
-J
I
in CO:
ao!/asl ln C0 +
aoa/asz ln OT»:
in Coal
a02/aS2 ln Char
-10 _
.•••
--
»!•*
10t)
1
1 I | i t 1.
• i • I t i i i i i i i i I i • t . t i i • . I i i « i i i i i i I i i i i i I I I i
BOO 900 1000 1100
TEMPEflflTUBE - DEGREES CENTIGRflOE
1300
IIIQO
FIGURE A- 17 - COMPARISON OF a^/a^ IN REDUCING GASES WITH
2SrO + S2 * 02 + 2SrS
FOR THE REACTION
-------
LOG
i o
00
oo
•to
-IS
eon
ao2/as,
in
aO»'aSi for oxide'8ulfide conversion:
52 ao2/as2 ln C0:
a02/aS2 in C0 +
a0j/aSj in CH*:
a02/aS2 in Coal:
&n /«e in Char:
"700
1
«*
• 1 I i I . I 1 I 1 I 1 I L
BOO
900
1QQQ
1100
1200
1300
, 11,111
1400
TEMPEPflTUnE - DEGREES CENTIGRflOE
FIGURE A- 18 - COMPARISON OF an /ac IN REDUCING GASES WITH an /a
U2 J>2 U2
2BaO +S2 - 02 + 2BaS
FOR THE REACTION
-------
oo
NO
a02/aS2
-5
X
-10
-is
-20
for oxi«te-sulfide conversion:
In CO:
xx
/
a02/aS2 in C0 +
aOa/aS» in CH»!
ao,/asa ln Coal:
ao»/as, in Char:
1QQ
8QQ
900
11QQ
1200
1300
man
TEMPEPflTURE - DEGREES CENTJGPflOE
FIGURE A- 19 - COMPARISON OF an /ac IN REDUCING GASES WITH an /a
t>2 02 »2 £
FOR THE REACTION
4LiA102
2Li2S + 2A1203
-------
VO
o
aOi'aS» for oxl-de-Bulfide conversion:
ln C0:
coa
•JQQ
803
SQQ
1GOU 1100 12CQ
- DEGREES CEMTIGfWOE
FIGURE A-20 - COMPARISON OF
4LiFe02 + S2
13QQ
14QQ
IN REDUCING GASES WITH aQ /ag FOR THE REACTION
02 + 2Li2S + 2Fe203
-------
-10
-IS
vo -20
-25
-30
aOi'aS» for oxide-sulflde conversion:
a02/aS8 in C0:
" ln C0 + %»^
"0»/aS2 ln Coal:
aa ln Char:
6QQ
fen
300
900
1QQQ
noo
1200
1300
14QQ
TEMPERflTURE - DEGREES CENTJGRflOE
FIGURE A- 21 . COMPARISON OF a^/a^ IN REDUCING GASES WITH
2A1203 + 3S2 -»• 302 + 2A12S3
FOR THE REACTION
-------
VO
ao,/as
LOGio 5—
10-. aS2
in H2:
for
conversIon:
•10
•IS
ear
'02'BS2 in C0 + *H*:
ao2'as2
ao2/a:
ao2/as2 inCH» =
ao2/as2 in Coal:
ao2/as2 in Char:
^••Z**n^\
100
BQO
9QQ
•'•'*''*
1QQO
I. ji....... I......... I
....
f.. I ... . .. i.
1SQQ
1400
- DEGREES CEMTJGPflOE
FIGURE A-22 - COHPARISON OF aQ2/aS2 IN REDUCING GASES WITH
Ti02 + S2 * 02 + TiS2
FOR THE REACTION
-------
I
l-»
VO
LOG1
-10
-IS
-20
BQ /Sg for oxide-sulfide conversion:
aQ /as* in CO:
a0*/ag* in CO + %H2:
an fac in CH«:
Oz Sa
ao2/as, in Coal:
aO»/aSj ln Char:
aQ /ag in H2:
i
I
I
CuQ
100
BQQ
900
1QQQ 11QQ tTQQ
- OEG8EES CENTJ6RPOE
tSOQ
14QQ
FIGURE A- 23 - COMPARISON OF a^/a^ IN REDUCING GASES WITH a
4NaA102 + S2 + 02 + 2Na2S + 2A1203
FOR THE REACTION
-------
LOGi
-s
NO
-P-
•to
-IS
a02/aS2 inH*:
for oxide-sulfide conversion:
ao,'as2
a02/aS2 in CO:
a0j/aSz in CO + %H2:
a- /BC in CH«:
aQ /a- in Coal:
a« /a- in Char:
. i f ...... . « «
•00
TOO
TOO
1000
HOB
WOO
FIGURE A-24 - COMPARISON OF a02/aSa IN REDUCING GASES WITH
ANaFe02 + S2 -»• 02 + 2Na2S + 2Fe203
1300
FOR THE REACTION
-------
VO
Ul
LOG.o 2-
5_aS2
-10
-15
-20
a02/aS2 inH"
afl /as for oxide-sulfide conversion:
a0[/ag| in CO:
*0 'aS2 in C0 + %H* :
"O.^S, in
in Coal:
in Char:
I
\
\
\
\
\
600
700
POO 900 1000 1100 1200
TEMPERflTURE - DEGREES CENTIGRflDE
FIGURE A-25 - COMPARISON OF aQ /ag IN REDUCING GASES WITH aQ
2CaAl20,, + S2 * 02 + 2CaS + 2A1203
1300
1400
FOR THE REACTION
-------
NO
LOG10
5
-5
-10
-IS
-20
. /ac for oxide-sulfide conversion:
Jl at
ao»/as2 in C0:
«02'aS2 ln C0 •
ao2/as2 in m* ••
in Coal:
in Char:
a0l/as!inHz:
ao,/asa
GQQ
7QQ
• i.....
iiiii.ii.i.... I...
BOO 900 1QOQ I1QQ 1200
TEMPERflTURE - DEGREES CENTIGRflOE
11»1111 ^_
1300
1.11 11 i.
1400
FIGURE A-26 - COMPARISON OF a^/a^ IN REDUCING GASES WITH a
2SrAl2Ou + S2 * 02 + 2SrS + 2A1203
FOR THE REACTION
-------
LOG.o T-
S|- 82
-5
-10
VO
-15
-20
a02/aS2 for °*ide-sulfide conversion-
a02/aS2 ln C0:
ao2/as2 ln co +
*Ot/aSt in ca"-
HOj'aS *n Coal:
802'aS2 in Char:
ao2/as2 lnHi:
-^;
6QQ
7QQ
13QQ
1'tQQ
BOO 9QQ 1QQQ 1100 1200
TEMPERflTURE - DEGREES CENTJGRflOE
FIGURE A- 27 - COMPARISON OF an /ac IN REDUCING GASES WITH an /ac FOR THE REACTION
(J2 OJ U2 &2
2SrTi03 + S2 * 02 + 2SrS + 2Ti02
-------
LOGi
a
02
, -10
09
I
-IS
a04/as2 for oxide-sulfide conversion:
&Q /as in CO:
a02/aS2 in C0 + %Hz!
ao>'as tn ^H*:
"Oj^'Si in Coal:
aOa/aS. ln Char:
an /a- in H2:
-20
CQQ
7QQ
BOO
9QQ IQQQ UQQ 12QQ
TEMPEPflTURE - DEGREES CENTJGRflDE
13QQ
1(100
FIGURE A- 28 - COMPARISON OF a^/a^ IN REDUCING GASES WITH aQ /ag FOR THE REACTION
2BaAl2Ou + S2 -^ 02 + 2BaS + 2A1203
-------
LOG,
a.
^ -10 -
SO
VO
-IS
-20
600
aO*/aSz for oxifle-sulfide conversion:
- ' in CO:
in CO + %H2:
in CH»:
in Coal:
in Char:
in H2 .-
700
11111 i 1111... |.........
' • * * •
L
L
BOO 9QQ 1QQQ IIQQ 12QQ
TEMPEfiflTURE - DEGREES CENTJGRflOE
1300
1400
FIGURE A-29 - COMPARISON OF a^/a
2BaTi03 + S2
IN REDUCING GASES WITH aQ /ag FOR THE REACTION
> 02 + 2BaS + 2Ti02
-------
LOG1
-5
ro
o
o
i
-10
-IS
-20
aOi/8S2 for °xide-sulfide conversion:
*- '" in CO:
in CO +
in CH»:
in Coal:
aoi/asl in Char:
an /Be
02 aa
lnH2:
600
700
BOO
900 1QQQ 1100 1200
- DEGREES CENTIGRADE
1300
mot
FIGURE A- 30 - COMPARISON OF a^/a^ IN REDUCING GASES WITH a0a/as FOR THE REACTION
2Li2Ti03 + S2 * 02 + 2Li2S + 2Ti02
-------
TECHNICAL REPORT DATA
uttricnuns OH Ilie rc\ trsi before completing)
1 REPORT NO.
E PA; 650/2- 75-065_
4 TITLE'AND'SUBTITLE
Identification of Regenerable Metal Oxide SO2
Sorbents for Fluidized-Bed Coal Combustion
3 RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
July 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHOHIS)
P.S. Lowell and T.B. Parsons
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
P. 0. Box 9948
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
1AB013: ROAP 21ADD-042
11. CONTRACT/GRANT NO.
68-02-1319, Task 10
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Control Systems Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD O
Task Final: 6/74 - 4/75
COVERED
14. SPONSORING AGENCY CODE
IS SUPPLEMENTARY NOTES
16. ABSTRACT
The report briefly summarizes results of an analysis to identify regenerable metal
oxide 802 sorbents for fluidized-bed coal combustion. It recommends continued
investigation. It discusses both the approach used for the theoretical study of
sorption/regeneration processes and implications of the results. The Appendix
contains two technical notes that are major products of this effort: Technical Note
200-045-10-Ola, 'Thermodynamic Screening of Dry Metal Oxides for High Tempera-
ture SO2 Removal,' giving complete details of the thermodynamic analysis of the
sorption process; and Technical Note 200-045-10-02a, 'The Thermodynamics of
Chemical Regeneration of Metal Oxide SO2 Sorbents,' giving detailed methods and
results of the identification of sorbents that can be regenerated by reductive decom-
position of the sulfate.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Air Pollution
Desulfurization
Metals
Oxides
Regeneration
(Engineering)
Thermndvnamins
Sulfur Oxides
Sorption
Coal
Combustion
Fluidized Bed
Processing
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Flfld/Croup
Air Pollution Control
Stationary Sources
Metal Oxides
13B
07A, 07D
11F, 07 B
21B
13H
21D
3. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report I
Unclassified
31. NO. OF PAGES
204
20 SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
-201-
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