AMERICAN INSTITUTE OF CROP ECOLOGY
A RESEARCH ORGANIZATION DEVOTED TO PROBLEMS OF
PLANT ADAPTATION AND INTRODUCTION
WASHINGTON, DC.
AICE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XVIII
PURIFICATION OF GASES THROUGH HIGH TEMPERATURE REMOVAL
OF SULFUR COMPOUNDS
Edited By
M. Y. Nut!
The material presented here is part of a survey of
USSR literature on air polln
conducted by the Air Polk
HJCAN INSTITUTE OF CROP ECOLOGY
OF AIR
*AV >TlTUrr
OALED!
SILVER SPRING, MARYLAND 20910
-------
PUBLICATIONS of the AMERICAN INSTITUTE OF CROP ECOLOGY
Ref.
No.
1
•9
10
II
12
13
14
15
16
17
18
19
20
21
22
23
24
UKRAINE-Ecological Crop Geography of the Ukraine and the
Ukrainian Agro-Climatic Analogues in North America
POLAND-Agricul rural Climatology of Poland and Its Agro-
Climatic Analogues in North America
CZECHOSLOVAKIA-Agricultural Climatology of Czechoilc-
valcia and Its Agro-Climatic Analogues in North America
YUGOSLAVIA-Agricultural Climatologyof Yugoslavia and Its
Agro-Climatic Analogues in North America
GREECE—Ecological Crop Geography of Greece and Its Agro-
Climatic Analogues in North America
ALBANIA-Ecological Plant Geography of Albania, Irs Agri-
cultural Crops and Some North American Climatic Analogues
CHINA—Ecological Crop Geography of China and Its Agro-
Climatic Analogues in North America
GERMANY—Ecological Crop Geography of Germany and Its
Agro-Climatic Analogues in North America
JAPAN (I (-Agricultural Climatologyof Japan and Its Agro-
Climatic Analogues in North America
FINLAND-Ecological Crop Geography of Finland and Its Agro-
Climatic Analogues in North America
SWEDEN—Agricultural Climatology of Sweden and Its Agro-
Climatic Analogues in North America
NOR WAY-Ecological Crop Geography of Norway and Its Agro-
Climatic Apologues in North America
SIBERIA-Agricultural Climatology of Siberia, Its Natural Belts,
and Agro-Climatic Analogues in North America
JAPAN (2)-Ecologlcal Crop Geography and Field Practices of
Japan, Japan's Natural Vegetation, and Agro-Climatic
Analogues in North America
RYUKYU ISLANDS-Ecologicol Crop Geography and Field
Practices of the Ryukyu Islands, Natural Vegetation of the
Ryukyus, and Agro-Climatic Analogues in the Northern
Hemisphere
PHENOLOGY AND THERMAL ENVIRONMENT AS A MEANS
OF A PHYSIOLOGICAL CLASSIFICATION OF WHEAT
VARIETIES AND FOR PREDICTING MATURITY DATES OF
WHEAT
(Based on Data of Czechoslovakia and of Some Thermally
Analogous Areas of Czechoslovakia in the United States
Pacific Northwest)
WHEAT-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMAL AND PHO-
TOTHERMAL REQUIREMENTS OF WHEAT
(Based on Data of North America and Some Thermally Anal-
ogous Areas of North America in the Soviet Union and in
Finland)
A COMPARATIVE STUDY OF LOWER AND UPPER LIMITS OF
TEMPERATURE IN MEASURING THE VARIABILITY OF DAY-
DEGREE SUMMATIONS OF WHEAT, BARLEY, AND RYE
BARLEY-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMAL^AND PHO-
TOTHERMAL REQUIREMENTS OF BARLEY
RYE-CLIMATE RELATIONSHIPS AND THE USE OF PHENOL-
OGY IN ASCERTAINING THE THERMAL AND PHOTO-
THERMAL REQUIREMENTS OF RYE
AGRICULTURAL ECOLOGY IN SUBTROPICAL REGIONS
MOROCCO, ALGERIA, TUNISIA-Physical Environment and
Agriculture
LIBYA and EGYPT-Physical Environment and Agriculture. . .
UNION OF SOUTH AFRICA-Physical Environment and Agri-
culrure, With Special Reference ID Winter-Rainfall Regions
AUSTRALIA-Physicol Environment and Agriculture, With Spe-
cial Reference to Winter-Rainfall Regions
26 S. E. CALIFORNIA and S. W. ARIZONA-Physicol Environment
and Agriculture of the Desert Regions
27 THAILAND-Physical Environment and Agriculture
28 BURMA-Physical Environment and Agriculture
28A BURMA—Diseases and Pests of Economic Plants
28B BURMA-Climate, Soils and Rice Culture (Supplementary In-
formation and a Bibliography to Report 28)
29A VIETNAM, CAMBODIA, LAOS-rhysical Environment and
Agriculture
29B VIETNAM, CAMBODIA, LAOS-Diseasei and Pestsof Economic
Plants
29C VIETNAM, CAMBODIA, LAOS-Climarological Data (Supple-
ment to Report 29A)
30A CENTRAL and SOUTH CHINA, HONG KONG, 1AIWAN-
Physical Environment and Agriculture $20.00'
308 CENTRAL and SOUTH CHINA, HONG KONG, TAIWAN-
Major Plant Pests and Diseases
31 SOUTH CHINA-lts Agro-Climatic Analogues in Southeast Asia
32 SACRAMENTO-SAN JOAQUIN DELTA OF CALIFORNIA-
Physical Environment and Agriculture
33 GLOBAL AGROCLIMATIC ANALOGUES FOR THE RICE RE-
GIONS OF THE CONTINENTAL UNITED STATE
34 AGRO-CLIMATOLOGY AND GLOBAL AGROCLIMATIC
ANALOGUES OF THE CITRUS REGIONS OF THE CON-
TINENTAL UNITED STATES
35 GLOBAL AGROCLIMATIC ANALOGUES FOR THE SOUTH-
EASTERN ATLANTIC REGION OF THE CONTINENTAL
UNITED STATES
36 GLOBAL AGROCLIMATIC ANALOGUES FOR THE INTER-
MOUNTAIN REGION OF THE CONTINENTAL UNITED
STATES
37 GLOBAL AGROCLIMATIC ANALOGUES FOR THE NORTHERN
GREAT PLAINS REGION OF THE CONTINENTAL UNITED
STATES
38 GLOBAL AGROCLIMATIC ANALOGUES FOR THE MAYA-
GUEZ DISTRICT OF PUERTO RICO
39 RICE CULTURE and RICE-CLIMATE RELATIONSHIPS With Spe-
cial Reference to the United States Rice Areas and Their
Latitudinal and Thermal Analogues in Other Countries
40 E. WASHINGTON, IDAHO, and UTAH—Physical Environment
and Agriculture
41 WASHINGTON, IDAHO, and UTAH-The Use of Phenology
in Ascertaining the Temperature Requirements of Wheat
Grown in Washington, Idaho, and Utah and in Some of
Their Agro-Climatically Analogous Areas in the Eastern
Hemisphere
42 NORTHERN GREAT PLAINS REGION-Preliminary Study of
Phonological Temperature Requirements of a Few Varietios
of Wheat Grown in the Northern Great Plains Region and in
Some Agro-Climatically Analogous Areas in the Eastern
Hemisphere
43 SOUTHEASTERN ATLANTIC REGlON-Phenologicol Temper-
ature Requirements of Some Winter Wheat Varieties Grown
in the Southeastern Atlantic Region of the United States and
in Several of Its Latitudinally Analogous Areas of the Eastern
and Southern Hemispheres of Seasonally Similar Thermal
Conditions
44 ATMOSPHERIC AND METEOROLOGICAL ASPECTS OF AIR
POLLUTION-A Survey of USSR Air Pollution Literature
45 EFFECTS AND SYMPTOMS OF AIR POLLUTES ON VEGETA-
TION; RESISTANCE AND SUSCEPTIBILITY OF DIFFERENT
PLANT SPECIES IN VARIOUS HABITATS, IN RELATION TO
PLANT UTILIZATION FOR SHELTER BELTS AND AS BIO-
LOGICAL INDICATORS-A Survey of USSR Air Pollution
Literature
(Continued on inside of back cover)
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AICE-AIR-72-18
AICE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XVIII
PURIFICATION OF GASES THROUGH HIGH TEMPERATURE REMOVAL
OF SULFUR COMPOUNDS
Edited By
M. Y. Nuttonson
The material presented here is part of a survey of
USSR literature on air pollution
conducted by the Air Pollution Section
AMERICAN INSTITUTE OF CROP ECOLOGY
This survey is being conducted under GRANT R 800878
(Formerly R01 AP 00786)
OFFICE OF AIR PROGRAMS
of the
U.S. ENVIRONMENTAL PROTECTION AGENCY
*AMERICAN INSTITUTE OF CROP ECOLOGY
809 DALE DRIVE
SILVER SPRING, MARYLAND 20910
1972
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TABLE OF CONTENTS
Page
PREFACE v
PURIFICATION OF GASES THROUGH HIGH TEMPERATURE REMOVAL
OF SULFUR COMPOUNDS
V. S. Al'tshuler and A. A. Gavrilova
INTRODUCTION 1
I. REMOVAL OF HYDROGEN SULFIDE FROM GASES 5
Review of the Processes and Methods of Removal of
Hydrogen Sulfide from Gases 5
Selection of Reactants for High-Temperature Removal
of Hydrogen Sulfide from Gases and General
Characteristics of the Conditions of Regeneration
of Solid Residue 20
THERMODYNAMICS OF PROCESSES OF HIGH-TEMPERATURE
REMOVAL OF HYDROGEN SULFIDE FROM GASES 22
Thermodynamics of the Process of Hydrogen Sulfide
Removal from Gas Mixtures Using Calcium Oxide 22
Thermodynamics of the Process of Hydrogen Sulfide
Removal from Gas Mixtures Using Iron Oxides 30
Thermodynamics of the Process of Hydrogen Sulfide
Removal from Gas Mixtures Using Manganese Oxides 39
EVALUATION OF THE ACTIVITY OF VARIOUS SOLID REACTANTS
IN THE PROCESS OF HYDROGEN SULFIDE REMOVAL FROM
GASES AT HIGH TEMPERATURES 46
REMOVAL OF HYDROGEN SULFIDE FROM GASES BY MEANS OF
CALCIUM OXIDE 56
REMOVAL OF HYDROGEN SULFIDE FROM GASES BY IRON OXIDES 74
HYDROGEN SULFIDE REMOVAL FROM GASES BY MEANS OF
MANGANESE OXIDES 88
iii
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Page
II. REMOVAL OF SULFUR DIOXIDE FROM GASES 98
SURVEY OF PROCESSES AND METHODS OF REMOVAL OF
SULFUR DIOXIDE FROM GASES 98
THERMODYNAMICS OF THE REACTIONS BETWEEN SULFUR DIOXIDE
AND METAL OXIDES Ill
EVALUATION OF THE ACTIVITY OF SOLID REACTANTS IN THE
COURSE OF REMOVAL OF SULFUR DIOXIDE FROM GASES AT
HIGH TEMPERATURES 116
REMOVAL OF SULFUR DIOXIDE FROM GASES BY CALCIUM OXIDE 119
REMOVAL OF SULFUR DIOXIDE FROM FLUE GASES BY
MANGANESE OXIDES 125
III. USE OF HIGH-TEMPERATURE REMOVAL OF SULFUR COMPOUNDS
FROM GASES IN LAYOUTS OF THERMAL ELECTRIC POWER
PLANTS 129
CONCLUSION 136
LITERATURE CITED 138
APPENDIX 140
IV
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PREFACE
The present volume represents a translation of a Russian monograph*
intended for a broad segment of engineers, technicians, and scientists in
the chemical, power, gas, coal, and metallurgical industries. In the
introduction to the monograph the authors state that in recent years the
problem of recovery of sulfur compounds from industrial waste gases has
become highly important in the area of sanitary protection of atmospheric
air. They point out that sulfur dioxide discharged into the atmosphere
together with the waste gases is harmful to the health of the population,
damages vegetation, and has a corrosive effect on buildings and installations.
The monograph presents the results of the authors' numerous theoretical
and experimental studies which deal with the removal of sulfur compounds
(hydrogen sulfide and sulfur dioxide) from heated gaseous mixtures through
the use of dry methods and without lowering the temperature of the gases.
The authors discuss problems of selection of solid reactants suitable
for the removal of hydrogen sulfide gases at 500-1100°C., and also for the
removal of sulfurous anhydride at 400-800°C. Results of performed thermo-
dynamic and numerous experimental studies are given. Conditions of processes
of high-temperature purification of gases by means of solid reagents are
indicated. Prospects for the -use. of dry methods of removal of sulfur com-
pounds from gases at high temperatures under conditions of combustion of
sulfur fuels at steam power plants are evaluated.
It is hoped that the monograph selected for presentation in this
volume will be conducive to a better appreciation of some of the air pol-
lution investigations conducted in the USSR. As the editor of this volume
I wish to thank my co-workers in the Air Pollution Section of the Institute
for their valuable assistance.
M. Y. Nuttonson
i
November 1972
• -r-sM "*
Ministerstvo Ugol'noy Promyshlennosti SSSR. Ihstitut Goryuchikh Iskopaemykh. Izdatel stvo
Moskva, 148 pages, (1969).
-------
INTRODUCTION
The extraction of sulfur components from gaseous mixtures is an impor-
tant technological process, very common in modern technology. The use of
this process is determined by purely technological needs and by the strin-
gent limitations connected with the sanitary protection of the purity of the
air reservoir. In industry, purification of gases involving removal of
sulfur compounds is required in many cases in order to ensure a normal
course of the main production process. For example, the presence of sulfur
in gases used for the synthesis of ammonia, methanol, and other organic
compounds causes poisoning of the catalysts and brings the process to a
standstill. For this reason, the gas should be thoroughly purified by re-
moving all the sulfur compounds.
Nearly all combustible gases used for the production of power and for
technological purposes are subjected to purification involving removal of
sulfur compounds. Many years of experience have shown that in all cases,
the purification improves the quality of the gas, facilitates the conditions
of its utilization and extends the scope of its application.
In recent years, in the USSR and almost everywhere else in the world,
a special importance has been assumed by the problem of recovery of sulfur
compounds from industrial waste gases, chiefly in the area of sanitary pro-
tection of atmospheric air. The sulfur dioxide discharged into the atmos-
phere together with the waste gases is harmful to the health of the popula-
tion, damages the vegetation, and has a corrosive effect on buildings and
installations.
The chief source of contamination of the air reservoir with sulfur
dioxide are the flue gases of fuel-burning power installations, primarily,
major thermal electric power plants operating on sulfur-containing fuels
(mazuts, coal, and others). It has been calculated, for example, that since
the time when mankind began to burn sulfur mazuts and coal, about 10% of the
world output of metal has been expended in compensating for the losses due
to corrosion.
Considerable damage is also daused by sulfur-containing waste gases of
nonferrous metallurgy (copper- and nickel-smelting plants), sulfuric acid
production, etc. A large number of methods have been proposed for removing
various sulfur compounds (hydrogen sulfide, sulfur dioxide, organosulfur
compounds) from gases, i.e., methods that have been used in an enormous
amount of research and experimental industrial work. In describing the indus-
trial development of these methods, one can note the broad industrial applica-
tion of methods of purification of gases involving only the removal of hydro-
gen sulfide and organic sulfur.
A large number of major installations removing hydrogen sulfide and
organosulfur compounds from gases by different purification methods, primarily
- 1 -
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liquid ones, are operating in the chemical and other industries according
to the composition and amount of the gas being purified and the degree of
purification required. Here the removal of sulfur compounds from gases
is an important part of the technological setup of the entire industry,
and in most cases involves utilization of the recovered sulfur in the pro-
duction of commercial goods.
The situation is much worse in the case of industrial development of
methods of sulfur dioxide removal from gases. Despite the large number
of studies made on the removal of sulfur dioxide from gases, their results
cannot be considered adequate for industrial utilization on the necessary
scale. Actually, there are as yet no processes applicable to large-scale
industrial purposes that would permit an economical extraction of sulfur
dioxide from waste gases.
For this reason, the problem of preventing the discharge of harmful
sulfur-containing gases into the atmosphere is very serious for many branches
of the national economy, primarily for thermal electric power plants. The
chief difficulties in the creation of efficient and economical methods of
removal of sulfur dioxide from the flue gases of electric power plants lie,
on the one hand, in the large volumes of gases subjected to purification
(8000 m^ per ton of reference fuel) and, on the other hand, in the small
concentrations of sulfur dioxide in the gases (0.1-0.4% by volume). The
presence of mechanical particles (soot, ash) in the flue gases also compli-
cates their purification.
The inadequacy, mainly from the standpoint of technical and economic
considerations, of the methods of purification of flue gases proposed thus
far has been responsible for the tendency to use high smokestacks in meeting
the sanitary requirements in modern thermal power engineering. In this case,
the atmospheric concentration of noxious sulfur compounds which is allowed
by sanitary requirements is achieved mainly by increasing the dispersing
capacity of the smokestacks or limiting the output of electric power plants
when the dispersing capacity of the stacks has reached its limit.
However, even though the dispersal of pollutants over large areas and
volumes decreases their concentration, the total discharges into the atmos-
phere are not decreased, and their noxious effect on the environment remains,
being only slowed down in time- All this confirms the fundamental inadequacy
of the existing measures for controlling the pollution of the air reservoir,
particularly in connection with the considerable growth of the unit capaci-
ties of electric power plants, and also in light of the social requirements
of complete elimination of the noxious effects of the discharges.
A graphic description of the method of controlling noxious impurities
by increasing the dispersing capacity of smokestacks may be formulated as
follows: "the higher the stack, the lower and weaker the science". More
- 2 -
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desirable and justified is not the dispersal of sulfur dioxide, but the
prevention of its appearance in the gases being emitted through a smoke-
stack. This may be achieved not only by creating new, efficient methods
of purification of flue gases, but also by removing the sulfur at the
stage of preparation of the fuel for combustion.
In thermal power engineering great interest has been shown in recent
years in solving the problem of recovery of sulfur by first gasifying the
sulfur fuel. This trend specifies a residue-free gasification of the organic
part of the fuel, removal of sulfur compounds from the gas obtained, and its
subsequent use in power production. In this case, the boiler unit is not
exposed to the action of sulfur gases and their mechanical impurities, and
the amount of gases being subjected to purification is about one-half as
much as in the case of purification of flue gases.
The most important condition for the use of gasification in the removal
of sulfur as a stage of preparation of sulfur fuel for combustion is the
achievement of a high energy efficiency of the entire process. Essentially,
this problem consists in a maximum decrease of the fuel loss in the main pro-
cess of gas generation and in the preservation of the physical heat from the
hot combustible gases obtained during their purification involving removal
of sulfur and other undesirable impurities before they are supplied to the
power plant. The decrease of direct fuel loss during gasification is deter-
mined by the characteristics of the gas-generating process. On the whole,
it may be assumed that in gasification, this loss will be equal to that
resulting from incomplete combustion (carryover, loss with slag) during the
direct combustion of the corresponding fuels. Therefore, from this stand-
point, the inclusion of the fuel gasification process in the scheme of an
electric power plant will have little effect on the heat economy of electric
power production.
A more substantial influence on the efficiency of the process may be
exerted by the stage of removal of sulfur compounds from the gases, and
particularly the removal of hydrogen sulfide, which during gasification is the
chief sulfur-containing component of the gas obtained. The methods of
removal of hydrogen sulfide from gases used thus far are carried out at low
temperatures and require considerable, cooling (down to 100°C) with an appre-
ciable loss of physical heat and expenditure of energy on purification and
cooling, resulting in a decrease of the energy efficiency. Within certain
limits, this decrease may be offset by cooling the gases in waste heat
boilers, which are included as an element of the thermal electric power plant.
However, even in this case, when low-temperature gas purification is used,
one must not neglect a certain drop of the total energy efficiency of the
electric power plant. Thus a major importance is acquired by the creation of
dry, high-temperature methods of removal of hydrogen sulfide from gases, the
use of which would permit the preparation of the fuel without any appreciable
heat loss.
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This monograph gives a survey of studies made in this area and pre-
sents the results of theoretical and experimental research conducted by
the authors on the high-temperature purification of gases involving removal
of hydrogen sulfide. Considering certain prospects of creating dry, high-
temperature methods of gas purification with the removal of sulfur dioxide
as well, the monograph classifies the existing material and gives the
results of the authors' studies of this subject. Accordingly, the mono-
graph consists of two main parts: 1) removal of hydrogen sulfide and
2) removal of sulfur dioxide from gases.
The authors take this opportunity to express their gratitude to
M. I. Nedashkovskaya, G. F. Dushin and 0. Ye. Vol'naya, on the staff of
the laboratory of gas processes at the Institute of Mineral Fuels for
their assistance in the compilation of the monograph, and to K. T. Ostrikovaya
for putting it in final shape.
- 4 -
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REMOVAL OF HYDROGEN SULFIDE FROM GASES
Review of the Processes and Methods of Removal of Hydrogen Sulfide from Gases
The process of removal of hydrogen sulfide from gases is widely used in
various branches of industry - chemical, gas, petrochemical, and others. This
process has been used in gas technology for a long time, since the start of the
last century, and historically was first developed in urban illuminating-gas
plants. Later, hydrogen sulfide began to be removed from gases of the coke in-
dustry, natural and technological gases, synthesis gases, and hydrogen.
Initial proposals concerning the removal of hydrogen sulfide from gases
involved its absorption by various absorbents in solid fragments at moderate
temperatures. Processes using slaked lime, iron hydroxide, natural bog ore
and others were applied in industry.
For many years thereafter, the development of the processes of removal of
hydrogen sulfide from gases amounted to many proposals concerning the composi-
tion of the absorbents and to the improvement of the technology of the process-
es involving their use.
A definite breakthrough in the development of the technology of removal
of hydrogen sulfide from gases occurred in the 1930's in connection with the
development in 1921 in the U.S.A. of the so-called Seabord process, based on
the use of an absorbent soda solution.
Since that period until the present time, the removal of hydrogen sulfide
from gases evolved in the direction of the creation and development mainly of
liquid (wet) methods of purification. Liquid processes did not displace dry
ones, which continue to develop, since they have many advantages, for example,
a higher degree of purification.
A classification of the liquid and dry processes is given in flow chart 1.
According to the characteristics of the conditions of utilization of the
hydrogen sulfide being recovered, three groups can be distinguished in each
of these processes. The first group includes processes and methods whose main
purpose is only gas purification, without utilization of the hydrogen sulfide
being recovered.
The products of the main reaction of hydrogen sulfide with any given re-
actants are the waste in this case and are discarded. In the category of
liquid processes, this group includes the above-mentioned soda ("Seabord")
process based on the reaction
NaHS + NaHOV
- 5 -
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Technological flow chart 1. Classification of
processes of removal of hydrogen
sulfide from gases.
Processes of removal
of H S from gases
Liquid (wet)
Without utiliza-
tion of sulfur
Soda
I
ON
I
With formation of
'elemental sulfur
Arsenic-
alkalrne
Iron-alkaline
Cyclic, with util-
ization of sulfur
With formation of
concentrated H S
2
Ethanol-
amine
Ammonia
Carbonate
Xricalcium
phosphate
Phenolate
Alkacid
Rectisol
With formation of
new sulfur-con-
taining chemical
compounds
Formation of
ammonium sul-
fate
Ammonia-
alkaline
Polythionate
Catasulfate
Vacuum-
soda
.Potash
Without .
utilization
of sulfur
Purificar
^ 1C8'
tion with
hyd:
iron
ide
rox-
Dry
Cyclic with util-
ization of sulfur
Purification
with activated
carbon
Purification
with iron'
oxide
Purification
with manganese
oxide
•With forma-
tion of new
sulfur-con-
taining
chemical
compounds.
-------
This process consists in the absorption of hydrogen sulfide in a dilute
solution of sodium carbonate (s;l-3.57o) at 35°C., followed by regeneration
the solution by bubbling air, which carries away the hydrogen sulfide and is
discharged into the atmosphere. An example of a dry process can be the ab-
sorption of hydrogen sulfide by iron hydroxide under conditions where the
spent mass is characterized by a relatively low sulfur content.
Fig. 1. Flow chart of liquid cyclic processes.
1 - gas washer; 2 - pump; 3 - heat exchange;
4 - cooler? 5 - heater; 6 - distillation
column; 7 - boiler; 8 - exit of acid gases;
9 - exit of fresh solution; 10 - exit of
purified gas; 11 - entrance of unpurified
gas.
The low efficiency of the processes of gas purification without utili-
zation of sulfur and the serious sanitary limitations on the discharge of
sulfur-containing products (hydrogen sulfide into the atmosphere and the ab-
sorbent mass into dumps) make such processes unsuitable for broad industrial
application.
The second group includes the so-called cyclic processes and methods by
which either commercial hydrogen sulfide or elemental sulfur is obtained.
Here hydrogen sulfide is recovered from the gases by means of reactants which
are subjected to regeneration and are recycled for subsequent reuse.
A flow chart of liquid cyclic processes for recovering hydrogen sulfide
is shown in Fig. 1. The main units of this scheme are an absorber and a de-
sorber, the designs of which may be of different types: packed, bubbling,
and others. In addition, depending on the composition of the absorber, pur-
pose of the unit and conditions of its operation, additional special devices
and installations are introduced into the scheme. Various solutions have
found applications as absorbers in liquid cyclic processes: alkaline-arsenic,
ethanolamines, acid carbonates (soda, potash), ammonia, and other solutions.
Regeneration of the absorbers in liquid cyclic processes is accomplished by
decreasing the pressure, heating the solution, and blowing air or water vapor
through it.
Hydrogen sulfide recovered from gases in cyclic liquids and dry processes
may be subjected to oxidation directly in the course of purification with forma-
tion of elemental sulfur, or isolated during regeneration of the absorbent in
concentrated form for further use.
- 7 -
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In processes of gas purification involving removal of hydrogen sulfide
with formation of elemental sulfur, the chief end result is the reaction
HsS + 0,502
Dry oxidation processes with formation of elemental sulfur, based on this
reaction, will be discussed below. In order to ensure the oxidation of hydro-
gen sulfide to elemental sulfur, use is made in liquid processes of alkaline
solutions containing chemicals which enter into irreversible chemical reactions
with hydrogen sulfide.
Among such cyclic liquid processes, the arsenic-soda process (the so-
called Phylox process) has been most widely applied. Without discussing the
mechanism of this process, which has been closely studied both in the USSR [1]
and abroad, one can note that the determining reactions in this case are
. ,5O2
Similar determining reactions may take place in the iron-soda process
("ferrox" process), iron-cyanide processes, and others.
The regeneration of absorbing solutions in all these processes is usu-
ally carried out by blowing air through them, so that sulfur is replaced by
oxygen in the molecule of the absorbing reactant, sulfur precipitates out in
finely divided form, and is floated with air. It is essential to note that
in processes where the reactants used are suspensions instead of not readily
soluble substances (iron- alkaline and iron-cyanide processes), the sulfur ob-
tained is highly contaminated with the solid reactant, something that does
not occur in the purification of gases by the arsenic-soda process. The
absorbent solutions used in the purification of gases in this group of pro-
cesses are usually characterized by a low concentration of the main reactants,
this being due to the regeneration conditions of the solutions. Their sulfur
capacity, i. e., the amount of hydrogen sulfide which can be absorbed by
1 nr of solution, is 1.5 kg. For this reason, the absorption process makes
it necessary to use considerable amounts of absorbent solutions.
An important characteristic of the process is the degree of develop-
ment of side reactions. When alkaline solutions of reactants are used, not
all of the absorbed hydrogen sulfide is converted into sulfur. Part of it
enters into a side reaction with the formation of thiosulfate, so that it is
removed from the cycle together with part of the absorbing solution. Accord-
ing to actual data, about 10-20% of the sulfur absorbed from the gas by the
arsenic-soda solution oxidizes to hyposulfite during regeneration of the solu-
tion. In iron-alkaline processes, up to 30-40% of the weight of absorbed
- 8 -
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sulfur is converted into hyposulfite. Let us note in passing that attempts to
modify the iron-alkaline processes by replacing iron with nickel or copper
have not been applied in industry. A technological flow chart of the assembly
for the removal of hydrogen sulfide from gases by the process most commonly
used, the arsenic-soda process, with formation of elemental sulfur, is shown
in Fig. 2. This purification process is selective, i. e., there is a high
selectivity for hydrogen sulfide. The presence of carbon dioxide, even in
amounts up to 20%, has no appreciable effect on the process of hydrogen sul-
fide recovery.
Air
t Sulfur foam
_^
Hyposulfite.
//
To spent residue
To foam collector
Fig. 2. Technicological flow chart of assembly for the removal of hydrogen sulfide
from gases by the arsenic-soda process.
1 - electrostatic precipitator; 2 - absorber; 3 - regenerator; 4 - foam collector;
5 - vacuum filter; 6 - atrt^clave; 7 - settling tank for autoclave liquid; 8 - liquid-
sulfur collector; $ - cooling drum (or pan): 10 - evaporator; 11 - crystallizer; 12 -
centrifuge; 13 - first-stage neutralize:-; l4 - neutralization vacuum filter; 15 - sol-
vent for arsenic sulfide; 16 - second-stage neutralize:-; 17 - filter press or settling
tank; 18 - solution heater; 19 - unit for obtaining colloidal sulfur; 20 - solvent for
j; 21 - saturation scrubber; 22 - tank for soda solution.
Among the liquid cyclic processes of removal of hydrogen sulfide from
gases with formation of elemental sulfur, one can also include a process
using sulfur dioxide. This process is based on the reaction of fi^S with
S(>2 in aqueous solutions with the precipitation of sulfur.
Detailed studies have established that a considerable part of the sulfur
does not precipitate in the free form, but is used up in the formation of thio-
sulfate, polythionates and thioacids. The impossibility of controlling the
course of these reactions, an intensive corrosion of the equipment, and also
- 9 -
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a low rate of the main reaction have caused work on this process to be vir-
tually discontinued.
Cyclic processes involving formation of concentrated hydrogen sulfide,
based on a physic ochemical equilibrium and the reversibility of the absorp-
tion reaction and evolution of hydrogen sulfide have become highly popular
in gas purification techniques.
In such liquid processes, absorption of hydrogen sulfide from gases is
accomplished with the aid of solutions of weak bases (amino derivatives) or
salts of strong bases and weak acids (phenolates, phosphates, soda, and
others). The absorption process is carried out at a low temperature, about
35°C.
The main reaction underlying the proposed processes of sulfur purifi-
cation with formation of concentrated hydrogen sulfide may be expressed as
follows:
Ethanolamine Process
2RNH2 + HaS £ (RNH^S - monoethanolamine (MEA") process,
+ HgS^ (R^IH2)2S - diethanolanine (DBA) process,
H2S J (R NH)2S - triethanolamine (TEA) process.
where R = CH2CH2OH.
Phenolate Process
+ HgS £ CgHjpH + NaHS
Phosphate Process
KHS,
+ KHS.
Carbonate Process
gS J NaHS + NaHCOj - vacuum-soda process
+ HgS J KHS + KHCOj - potash process.
Alkacid Process
R'COOK + HgSj R'COOH + KHS,
where R1 os (CH3)2 N-CH2~ (radical of alkacid DIA).
The regeneration of the absorbing solutions is usually carried out by
heating them to boiling. As a result of the temperature elevation, the
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solubility of hydrogen sulfide decreases, the hydrolysis of its salts with
weak bases (amino derivatives) increases, and the volatile hydrogen sulfide
is displaced from solutions of weak acids of low volatility. Thus the equi-
librium partial pressure of hydrogen sulfide above the solution is consider-
ably increased, and this gas is driven off together with water vapor. The
concentrated hydrogen sulfide obtained after the condensation of water vapor
is then used to produce sulfur or sulfuric acid.
The absorbing solutions (usually of high concentration) used in this
group of processes have a high sulfur capacity, up to 65 kg of hydrogen sul-
fide per m3 of solution, and for this reason a relatively small amount of the
latter is kept in circulation.
The equipment of the individual liquid cyclic processes of gas purifi-
cation with formation of concentrated hydrogen sulfide is very similar and
differs only in the absorbing reactant used. To give a general representa-
tion of the technological design of such processes, Fig. 3 shows a diagram
of an assembly for the process with monoethanolamine purification. Among
the cyclic processes of the second group one can also include the process
of so-called Rectisol purification, based on the absorption of hydrogen
sulfide with methanol cooled down to the range of -30 to -70°C. at pressures
from 5 to 50 atm. In this process, methanol acts only as the solvent, with-
out entering into intermediate chemical compounds with the gas being absorbed.
The third group of processes of gas purification involving removal of
hydrogen sulfide is characterized by the fact that the extraction of hydrogen
sulfide is carried out in a single complex that is used to produce new chemi-
cal compounds. Here the gas purification is associated with the synthesis
of by-products whose value frequently determines the general desirability of
carrying out the given process. The absorbents most frequently used are
chemicals that simultaneously absorb hydrogen sulfide (under conditions of
its oxidation) and ammonia to produce ammonium sulfate. Such processes have
been developed chiefly for the purpose of removing hydrogen sulfide from
coke-oven gas and simultaneously extracting ammonia. Of the processes pro-
posed for this purpose (Fel'd's polythionate process, Burkheiser's sulfite-
bisulfite process and others), the most interesting is the "catasulf" pro-
cess, based on the catalytic oxidation of hydrogen sulfide with oxygen in the
presence of other combustible gases to sulfur dioxide, and the absorption
of NH3 and SOo by sulfite liquors. The ammonium bisulfite and ammonium
sulfite obtained are then oxidized to the sulfate.
However, despite the large number of studies made in this area, this
process has not been developed in industry, chiefly because of its tech-
nological complexity, considerable corrosion of the equipment, and depend-
ence of the course of the process on the ratio of ammonia to hydrogen sulfide
concentrations in the gas.
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Fig. 3. Flow diagram of gas purification assembly using the
ethanolamme process.
1 - absorber; 2 - trap; 3 - level controller; 4 - pump; 5 - heat
exchanger; 6 - cooler; 7 - regenerator; 8 - condensation ves-
sel; 9 - dephlegmator.
The above brief review of the three groups of processes differing in the
conditions of utilization of the recovered sulfur must not be considered as
a complete characterization of the existing processes of removal of hydrogen
sulfide from gases. The majority of these processes have been described in
detail in specialized literature [2-5]. For this reason, we shall hereinafter
dwell only on some general aspects of hydrogen sulfide removal from gases
with reference to the stated problem, i. e., high-temperature gas purifica-
tion. Obviously, primary attention should be focused in this case on the
characteristics of dry purification methods.
The variety of the processes of hydrogen sulfide removal from gases pro-
posed up to the present time is not accidental and cannot be accounted for
solely be the natural development of gas engineering. Apparently, this is
largely due to the variety of the specific conditions under which the removal
of sulfur from gases had to be carried out. Depending on the purpose and de-
gree of gas purification desired, composition of the initial gas, output of
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the installations, possibility of utilizing the recovered sulfur, pressure,
sipply of raw material for the preparation of absorbents, and other factors,
different requirements have appeared with regard to the gas purification pro-
cess, and thus certain other processes were created. It is therefore very
difficult to compare the technical-economic indices according to the existing
methods of sulfur removal, since these indices, even for the same method and
a given output, fluctuate over wide limits depending on many of the above-
mentioned factors.
Nevertheless, as a general argument on the efficiency of gas purifica-
tion processes, it may be noted that the magnitude of capital investment in
all the processes is determined by the gas load and is independent of the
sulfur content of the gas. As far as the operational cost and expenditure
indices are directly proportional to the amount of sulfur being recovered
from the gas. Hence it may be concluded that in the purification of gases
with a low hydrogen sulfide content, particularly in the case of purifica-
tion of power plant gases, the dry gas purification processes will be more
competitive.
Of major importance for ensuring an efficient purification of gases is
the composition of the gas mixture undergoing purification. For example,
cyclic processes in which the carbonates formed are not decomposed during re-
generation are not suited for gases containing carbon dioxide. Among liquid
processes, this applies to the phenolate and phosphate ones. Some liquid pro-
cesses, for example, the ethanolamine and alkacid ones, can be used independ-
ently for the absorption of carbon dioxide from gases. In the case of joint
absorption of H2S and C02, it is necessary to consider only the corresponding
change of the flow coefficients.
The presence of a certain amount of oxygen in the gases being purified is
allowed in almost all dry methods of sulfur removal. In cyclic liquid process-
es, the presence of oxygen in the gases causes the formation of hyposulfite,
and this affects the economics of the process (cost and consumption of addi-
tional absorbent). As is shown by theory and experiment, in all sulfur re-
moval processes, it is desirable to use a higher pressure in order to achieve
a greater efficiency. However, this does not justify the expense involved
ir. compressing the gas if the pressure is used only to improve the sulfur re
moval. For this reason, pressure ife desirable only in cases where this is
dictated by other, technological, considerations.
It is very important to note that almost all of the proposed liquid pro-
cesses of sulfur removal are carried out at moderate temperatures limited by
the boiling points of the absorbent solutions (usually at 30-40°C.).
It is of definite interest to make a comparative evaluation of the
various liquid processes of hydrogen sulfide removal from gases in order to
consider their characteristics in the development of dry high-temperature
processes. Here it should be pointed out first of all that as a result of
- 13 -
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numerous theoretical and experimental studies, serious industrial objections
have been raised to a number of the processes, casting doubt on the desira-
bility of their further development. Thus, for example, in almost all the
processes utilizing hydrogen sulfide to produce new chemicals and in oxida-
tion processes involving formation of elemental sulfur (with the exception of
arsenic processes), an extensive development of side reactions, a slow rate of
the principal reactions, the practical impossibility of maintaining the stoi-
chiometric ratios of the reactants, and a considerable corrosion of the equip-
ment have been established. Arsenic-alkaline processes were found to be more
advantageous as compared with iron-alkaline ones in view of the purity of the
sulfur obtained.
The indices of cyclic phenolate, phosphate and alkacid processes are
clearly inferior to the ethanolamine process of hydrogen sulfide removal from
gases. Therefore, it is possible at the present time to discuss the follow-
ing liquid processes of hydrogen sulfide removal from gases, i. e., processes
having industrial importance and prospects for further development: arsenic-
alkaline, ethanolamine, carbonate (soda and potash) and Rectisol processes.
From the standpoint of the degree of purification of gases, the best of
these processes may be considered to be the ethanolamine process, in which
a purification of up to traces of hydrogen sulfide is attainable.
The arsenic process permits a hydrogen sulfide recovery resulting in a
residue of 0.1-0.5 g/nr in the gas. Carbonate processes give a degree of
purification of about 90%. The ethanolamine process also has advantages over
other liquid processes in the sulfur capacity of the solution (and hence, a
lower consumption of steam) and in the technological simplicity of the process
(absence of a vacuum or deep cooling). Among the advantages of the carbonate
processes is the use of low-pressure waste steam, a point that must not be
disregarded when such processes are used at thermal electric power plants.
As already indicated, all the liquid processes of hydrogen sulfide re-
moval from gases are carried out at moderate temperatures, and therefore
even the best of these processes do not meet the requirements of their utili-
zation for purifying hot gases without preliminary cooling.
In reference to the stated objective, i. e., the creation of high-temper-
ature purification processes, of greatest interest are dry processes of hydro-
gen sulfide removal from gases. The dry gas purification processes are not
as numerous as those involving liquid removal of hydrogen sulfide from gases.
Two processes have been widely accepted in industry: removal of H2S from
gases by iron oxides and by activated carbon.
Removal of HgS from gases by iron oxide. This process has been adequate-
ly perfected and is carried out at 30°C. In recent years, reports have ap-
peared on the development and industrial verification of this process at 350^-
400°C. [6]. The low-temperature process consists in passing the gas slowly
- 14 -
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through the purifying mass, containing ferric hydroxide. The main reactions
of this process may be schematically represented by the following equations:
2Fe (OH)3 + 3HZS = Fe.S3 + 6H.O,
2Fe (OH)S + HSS = 2Fe (OH).. + S + 2HA
Fe (OH)3 + H;S = FeS -f- 2H.O.
These reactions are characteristic of the process when an alkaline ab-
sorbent mass is used. In the absence of an alkali, the reaction follows the
equation
2Fe (OH)3 + 3H-S = 2FeS + S + 6H40.
As the gas is gradually passed through the mass, its content of active
ferric oxide decreases, the content of the reaction products - ferrous sul-
fide and sulfur - increases, the reactivity of the mass diminishes, and break-
through of the unreacted hydrogen sulfide begins.
Regeneration of the spent mass consists in its treatment with a steam-
air mixture. As a result, ferrous sulfide is converted back into ferric
hydroxide, and elemental sulfur separates out, and remains mixed with the mass,
which is ready to react again. This involves the following principal reactions:
2Fe2S8 + 302 + 6HS0 = 4Fe (OH)3 + 6S,
4FeS + 3O2 + 6H40 = 4Fe (OH)3 + 4S.
While absorbing hydrogen sulfide from the gas and undergoing regenera-
tion, the gas-purifying mass becomes increasingly enriched with elemental
sulfur (practically up to 35-50%) before it is completely spent. The re-
activity of such a mass is low, and it is therefore replaced with a fresh
one. Both stages - absorption of sulfur and regeneration of the mass - are
associated with the evolution of heat. When sulfur is absorbed, the evolu-
tion of heat is small, since the concentration of hydrogen sulfide in the
gas is low, but this involves evaporation of a small portion of the moisture
present in the mass. In regenerating the mass, it is necessary to take
special steps to provide for the necessary temperature conditions. The largest
amount of sulfur bound by the mass is evaluated from its Fe203 content, which
should be no less than 50%. However, the content of active modifications of
ferric oxide (a and y) *-s more important in this case.
The first modification (a) is present in bog ore, while the second enters
into the composition of red mud, which is the waste from the production of
alumina from bauxites. Practice shows that the absorbent mass should have a
porosity of 50%. The spent absorbent mass is usually utilized by sulfuric
acid plants as a substitute for pyrite in the production of sulfuric acid.
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Attempts to isolate sulfur from the spent mass by extraction with carbon
disulfide, kerosene and other solvents failed to yield any satisfactory re-
sults from the economic standpoint. On the whole, the process of removal
of H£S from a gas by means of ferric oxides at low temperatures is charac-
terized by a high degree of purification of the gas, and also technological
simplicity and reliability. Disadvantages of this process include its inter-
mittent character and primarily, the bulk of the equipment, whose large size
is due to low reaction rates at moderate temperatures.
These disadvantages are avoided for the most part by carrying out the
process at higher temperatures.
A large number of laboratory and experimental industrial studies aimed
at developing a process for recovering hydrogen sulfide from gases by means
of iron oxides in a stationary and fluidized bed at temperatures up to 400°C.
were recently conducted in England with reference to the purification of coke-
oven gas [6],
Laboratory experiments on the conditions of the reaction between sulfur
coke-oven gas (I^S*!?.) and ferric oxides in a stationary bed were carried
out in a quartz tube 25 mm in diameter with particles up to 1 mm in size
at a gas velocity of 0.05 m/sec.
At 250° C. and a space velocity of 100 hr""1, and also at 400°C. and a space
velocity of 140 hr" , and almost complete recovery of hydrogen sulfide was
achieved. Similar results for the degree of removal of hydrogen sulfide
from the gas were obtained by using iron oxides in a fluidized bed in a re-
action vessel 5 cm in diameter at 400°C. and a space velocity up to 300 hr~^.
Experiments were also carried out on the regeneration of sulfur-containing
iron oxides by firing them in a stream of air at a temperature up to 800°C.
and checking their activity after the firing. The experiments showed the
feasibility of a complete cycle of I^S removal from the gas by means of
ferric oxides at the indicated temperatures, i. e., up to 400°C. On the
basis of results of laboratory studies, a semicommercial assembly with an
output of 3000 nr/hr using sulfur-containing coke-oven gas and a fluidized
bed of iron oxides at 400°C. was installed at the Appleby-Frodingham plant
in 1956. A diagram of the installation is shown in Fig. 4. The operation
of this assembly has essentially confirmed the results of laboratory ex-
periments and shown the practical desirability of an industrial application
of this process.
Of interest from a theoretical and practical standpoint are studies of
the kinetics of the reaction of hydrogen sulfide with ferric oxides at high
temperature, conducted by 0. P. Korobeynichev [7]. He studied'the effect
of temperature; pressure, initial composition of the gas phase, space veloc-
ity of the gas, particle size, and conditions of pretreatment of the re-
actant on the course of the reactions of hydrogen sulfide, carbonyl sulfide,
send carbon disulfide with iron oxides.
- 16 -
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~~i jn
*L^J
Fig. 4. Diagram of assembly at Appleby-Prodingham.
1 - sulfur-containing gas; 2 - gas blower; 3 - heat exchangers;
4 - two-stage adsorber with fluidized bed; 5 - purified gas;
6 - scrubber; 7 - inert gas; 8 - air blower; 9 - regenerator;
10 - gas enriched with sulfur dioxide; 11 - iron oxides.
The kinetics of this reaction of hydrogen sulfide with iron and its
oxides were studied at 150-350°C.
A first order of the reaction with respect to hydrogen sulfide was estab-
lished together with an accelerating effect of hydrogen and carbon monoxide
on the recovery of hydrogen sulfide from the gases.
0. P. Korobeynichev also carried out short-term laboratory experiments
to study the course of the process of removal of l^S from producer gas at
temperatures up to 900°C. using Tikhvin bauxites.
The conditions of the process of H£S removal from gases in a fluidized
bed of iron cinder were also studied by M. Altybayev, Yu. I. Savchenko et
al. [8], They confirmed the possibility of achieving a 100% removal of I^S
from gases at 300°C.
Purification of gases with activated carbon. The process is based on
the property of activating coals to kdsorb hydrogen sulfide and exert a
catalytic effect on its oxidation to elemental sulfur. In this process, the
gas to be purified, mixed with air necessary for the oxidation, is passed
through a bed of activated carbon.
The overall equation of such a process may be expressed as follows:
»2=2HlsO-f-2S.
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To make sure 'that the reaction takes place at a sufficient rate at ordi-
nary temperature, a small amount of ammonia (0.2 g per 1 m^) is added to the
gas being purified. The action of ammonia apparently consists in maintain-
ing the necessary alkalinity of the surface of the activated carbon. The
elemental sulfur being produced obliterates the pores of the coal, gradually
decreasing its activity and thus limiting the duration 'of its continuous
service. Depending on the characteristics of the coal, from 50 to 150% of
sulfur relative to the weight of the adsorbent can be adsorbed before the
breakthrough of hydrogen sulfide. The adsorbent is then subjected to re-
generation. This stage of the process is carried out by treating the coal
with a solution of ammonium sulfide. The latter extracts the sulfur from
the pores of the coal, forming polysulf ides.
The polysulf ide solution formed is subjected to heating, during which
the polysulfides decompose
On cooling, the NHj and l^S evolved, mixed with water vapor, from the
t
starting solution
After washing and steaming, the coal, now free of sulfur, is reused for
gas purification. The physicochemical principles of the process of hydrogen
sulfide removal from gases were developed by Ya. D. Zel'venskiy [9], He
established that the kinetics of this process are of an external-diffusion
character and are therefore independent of the individual properties of the
adsorbent. On the other hand, activated carbons differ substantially in
sulfur capacity, which may be explained by the characteristics of their
porous structure. As a result of studies on the selection of activated
carbons'. with optimum sulfur capacity, a special brand, the "C coal", has
been proposed which is obtained by steam-gas activation of chemically active
and low-ash brown coals in a fluidized bed.
The degree of removal of H2S from the gas on this coal of relatively
high mechanical strength is more than 99% for an average sulfur capacity
equal to 112% of the weight of the coal or 370 g per 1 1 of coal.
In recent years, the removal of hydrogen sulfide from gases by means of
activated carbon has been carried out in a fluidized bed, which permits one
to achieve an uninterrupted operation and to considerably improve the tech-
nical-economic indices .
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Ǥ
Fig. 5. Temperature dependence of the degree of
recovery of hydrogen sulfide from combustible gas
by means of calcium oxide.
WO BOO IZOO
Temperature, °C.
From the standpoint of the objectives of our study, there'is also some
interest in the work of Wickert, published at the end of 1963, dealing with
the gasification of liquid sulfur-containing fuel with high-temperature re-
moval of hydrogen sulfide from the combustible gas, using calcium oxide dust
as the reactant [10], In this study, the author came to the conclusion that
it is possible to achieve a process such that it proves the temperature de-
pendence of the degree of recovery of hydrogen sulfide from a combustible
gas with the aid of CaO (Fig. 5).
Wickert suggests that the regeneration of the spent reactant - finely
dispersed calcium sulfide - be carried out by treating it in the regenerator
with hot water and blowing hot flue gases through it to obtain hydrogen sul-
fide of high concentration and calcium carbonate in the solid phase.
Wickert emphasizes that under fuel gasification conditions, the presence
of CaO will accelerate the reaction between carbon and water vapor, i. e.,
will decrease the content of soot in the gas in the case of gasification of
liquid fuel. The author proposes a process for preparing a sulfur-free gas
from the liquid gas whereby hydrogen sulfide is removed from the gas in a
fluidized bed of calcium oxide particles at high temperatures (Fig. 6).
Of major interest are also the studies made by V. T. Chagunava [16]
on the removal of hydrogen sulfide from coke oven and water gases at room
temperature by means of manganese ore (roasted) and also on the removal of
organosulfur compounds from synthesis gas and benzene by these reactants at
400-450°C.
On the basis of laboratory experiments carried out in 1957 at one of the
nitrogen fertilizer plants, an industrial assembly was built for removing
hydrogen sulfide from coke oven gas with manganese peroxide ore, with an out-
put of 15,000 nr/hr. In 1959, this plant also adopted a manganese method of
removal of organosulfur compounds from synthesis gas. The throughput of the
assembly at a space velocity of 200 hr"^ and a linear velocity of 0.1-0.2
m/sec was 15,000-20,000 m3/hr.
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Fig. 6. Flow diagram of
he production of sulfur-free gas after
Wicfcert.
1 - gas generator; 2 - reactor? 3 - screw conveyers; 4 - stirer;
5 - column; 6 - drum filter; 7 - cyclone.
Flows: I - fuel; II - water; IH_- flue gases from boiler;
IV - gas to boiler.
The service life of the mass for a sulfur capacity of 3-5%, depending on
the content of organosulfur compounds in the gas, ranged from 1 to 3 months.
The spent mass was discarded.
The above survey of the processes and methods of hydrogen sulfide removal
from gases proposed thus far illustrates rather'clearly the extensive develop-
ment of liquid processes and to a lesser extent, processes of dry sulfur re-
moval from gases.
All these processes are carried out at comparatively low temperatures, and
interest in the development of high-temperature processes (above 400°C.) of
hydrogen sulfide removal from gases by means of solid reactant, has grown only
in the last few years.
The high-temperature process of sulfur removal from gases is as yet in-
sufficiently developed, posing major objectives before researchers.
Selection of Reactants for High-Temperature Removal of Hydrogen
Sulfide from Gases and General Characteristics of the
Conditions of Regeneration of Solid Residue
The high-temperature removal of hydrogen sulfide from gases is best car-
ried out by means of solid reactants which should be stable at these tempera-
tures, and after reacting with hydrogen'sulfide, should yield stable forms of
sulfur compounds. 'From this standpoint, of greatest interest are metals ~'
calcium, magnesium, and barium, whose oxides melt at 2500°C., and whose sul-
fates and sulfides are stable at temperatures up to 1200°C. Oxides of these
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metals are present In common inexpensive natural mineral substances such as
lime Ca2CC>3, dolomite CaMg(C03)2, and magnesite MgC03, which can be used as
reactants in the high-temperature purification of gases.
Of great importance in this connection will be their dissociation tem-
perature. It should be below the temperature of the principal process of
purification of gases by these reactants in order to ensure the conversion
of carbonate salts into metal oxides and prevent the formation of such salts
when sulfur gases containing carbon dioxide are used. The dissociation tem-
perature of dolomite is 730°C., lime 970°C., and magnesite-640°C. Hence, when
lime is used, for example, the process should be carried out at temperatures
not below 950°C.
The use of alkaline earth oxides for the removal of hydrogen sulfide from
gases at lower temperatures, 600-800°C., is less effective, particularly in
the case of gas mixtures containing carbon dioxide. The presence of the lat-
ter leads to a wasteful expenditure of reactants on the formation of carbonate
salts, and requires an additional consumption of heat in the course of regener-
ation.
Oxides of iron and manganese can be used to remove hydrogen sulfide from
gases in the 600-800°C. temperature range. Their use as reactants does not
cause the formation of metal acid carbonates. The temperature of dissocia-
tion of iron'carbonate according to the data of many authors ranges from
360 to 450°C., and for manganese carbonate the start of decomposition.takes
place at 300° C. As far as the stability of salts of sulfur compounds is
concerned, particularly iron and manganese sulfides, their decomposition tem-
perature is above 1200°C. When they are used for the removal of hydrogen
sulfide from gases, natural iron and manganese ores can be considered. Thus,
iron and manganese oxides may satisfy the requirements for setting up the
high-temperature removal of hydrogen sulfide from gases (500-800°€.)• Alkaline
earth oxides are fundamentally more suitable at higher temperatures.
To set up an economical process of removal of sulfur compounds from gases,
it is necessary to consider the characteristics of the solid residue obtained
after the reaction. Knowledge of the properties of this residue determines
the conditions of regeneration of th,e solid material and the possibility of
a profitable utilization of the recovered sulfur. These characteristics de-
pend on the set of conditions in which the purification process is carried
out, and primarily on the composition of the gases. In a reducing gaseous
medium, such as is typical of the process of gasification of liquid and
solid fuels, chiefly metal sulfides are formed. Their regeneration can be
carried out by roasting in a medium of atmospheric air with the formation
of metal oxides in the solid residue and sulfur dioxide in the gas.
Regeneration of metal sulfides can also be carried out by use of steam-
air treatment and'in principle, depending on the steam-to-oxygen ratio in
the initial blast, final gas mixtures with different contents of sulfur
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dioxide and hydrogen sulfide can be obtained. Sulfur dioxide or gas mix-
tures with it may be used in the production of sulfuric acid or elemental
sulfur.
Thus, analysis of the general conditions prevailing in the setting up
of processes of high-temperature removal of hydrogen sulfide from gas mix-
tures shows the expediency of using alkaline earth oxides (CaO, MgO, etc.)
and also iron and manganese oxides for this purpose.
The process of regeneration of the solid residue after the reaction
may be carried out by roasting or by steam-air treatment of the sulfides
obtained.
THERMODYNAMICS OF PROCESSES OF HIGH-TEMPERATURE REMOVAL OF
HYDROGEN SULFIDE FROM GASES
The characteristics of the course of low-temperature processes of sul-
fur removal from gases are insufficient for setting up the processes of gas
purification at higher temperatures (500-100°C.)> which have their own spe-
cific features. The analysis and evaluation of these characteristics re-
quires first of all an examination of the thermodynamic properties of such
processes.
Thermodynamics of the Process of Hydrogen Sulfide Removal from
Gas Mixtures using Calcium Oxide
The reaction of calcium oxide with hydrogen sulfide is a complex process
which in addition to the main reaction
HjS^CaS-f H.O —17.25 koal
may involve a reaction of direct thermal decomposition of hydrogen sulfide, and
also other reactions between calcium oxide and the products of the main process.
When calcium oxide reacts with multieomponent gas mixtures containing hydrogen
sulfide, in addition to the indicated reactions there may take place reactions
of the individual components with one another and with calcium oxide. In order
to determine the thermodynamic characteristics of the entire complex process),
it is obviously necessary to have data on the thermodynamics of individually
occurring reactions. To this end, calculations were made on the thermodynamic
equilibrium of the reaction CaO + H2S .«_ CaS + H20 at 600-1400°C.
The calculations were carried out by using standard values of thermodynamic
- 22 -
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functions of the individual components of the system (see Appendix).
Values of the equilibrium constant /Cp=pHj0/pHjS for different tem-
peratures were determined by calculating the values of the free energy of
the reaction from the Temkin-Shvartsman equation
;/r = (AH ln/T) - AS;98 -
where A//°29s and AS°298 are the heat of formation (cal/mole) and entropy
(cal/deg mole) of the components at standard conditions ; Aao, Aah Afl2, Aa_2
are the coefficients of temperature change of the heat capacity of the sys-
tem; MO, MI, M%, and M_2 are coefficients taken from H. I. Temkin and L. A.
Shvartsman's reference table.
The value of Kp was calculated from the equation 'n Kp — ~ &ZT /RT, where
Az is the free energy, cal/mole; R is the universal gas constant, equal to
0.082 1 atm/deg, and T is the absolute temperature in °K.
Fig. 7. Equilibrium degree of conversion of hydrogen
sulfide vs. content of water vapor in gaseous mixture
at different temperatures.
1 - 600"C.; 2 - 900-0.; 3 - 1000°C.; k - IIOO'C.
20
IlO 60 80 /ttO
The degree of conversion of I^S at equilibrium is determined from the
formula a.==-Kpl(1 + Kp). Results of tHe calculations, given below, show that
in the temperature interval of interest to us, the values of K are suffi-
ciently large and a approaches 100%, i. e., the reaction of drf hydrogen
sulfide with calcium oxide proceeds almost completely in the direction of
formation of water with a practically complete consumption of the hydrogen
sulfide supplied:
, /. «C 500 700 800 900 1000 1100 1200 1300 MM
AZ,/r.'. -17,891 -15.76& -13,903 -12,311 -11,190 -10.038-9.010-8.081 -
InJCp. . . . 3.91 3.44 8,04 " 2,69 2.44 2.20 1.97 1.77 1.60
f p==J'HjO//'H,S 8110 2750 1100 490 275 168 x 93 59 40
a, % .... ~100 -100 ~100 ~100 99.5 99.3 99.0 98.5 _ 97.S
- 23 -
-------
The equilibrium degree of conversion of hydrogen sulfide depends on the
content of water vapor in the gaseous mixture.
Figure 7 shows this dependence at various temperatures for different
ratios of partial pressures of water vapor and hydrogen sulfide in the ini-
tial blast. The degree of conversion a in this case was calculated from
the formula
Kn-A
where A — PHIO/PH,S is the ratio of partial pressures of water vapor and hy-
drogen sulfide in the blast.
In setting up processes of high temperature removal of hydrogen sulfide
from gases, it is necessary to consider the possibility of the reaction of
its direct thermal decomposition under certain conditions. For this reason,
values of the constants of thermodynamic equilibrium of the reaction
+'/2 Sa were determined at various temperatures [40]:
Here account was taken of the fact that in the 700-1400°C. temperature
range, which is of interest to us, the sulfur vapor consists mainly of di-
atomic molecules.
The degree of conversion of hydrogen sulfide during thermal decompo-
sition at equilibrium was calculated from the formula
The calculated values of the equilibrium constants of the reaction
Kp= PaJ^'sJpajS and of the degree of conversion of hydrogen sulfide ct at
different temperatures are as follows:
/."C 700 800 900 10CO 1100 1200 .13CO 1-iOC
Kp 0,75.10-«0,50-10-S0,22.10-*0,73.10-*0,020 0,044 0,088 0,162
o 0,040 .0,048 0,054 0,060 0,095 0,140 0,215 0,320
From the above data it follows that the direct thermal decomposition
of hydrogen sulfide is manifested only at temperatures above 1200-1300°C.
- 24 -
-------
Up to 1100°C., the equilibrium degree of conversion during thermal decompo-
sition of hydrogen sulfide does not exceed 10%.
The reaction H2ST*H2+V2 82 is also inhibited when the hydrogen content
of the blast is relatively low. For this reason, in the removal of hydrogen
sulfide from gaseous mixtures containing hydrogen, the reaction of thermal
decomposition of hydrogen sulfide has little effect on the results of the main
process. The results of the complex process of hydrogen sulfide removal from
gaseous mixtures will be affected to some extent by the reduction of calcium
oxide by hydrogen.
In this connection, we calculated the equilibrium constants of the re-
action CaO + H2^tCa + H20 at temperatures from 700 to 1400°C.:
t, "C 700 - goo 900 1000
#P = PH,O/PHI 1,6-10-" 1,0-10'" 5,6-10-" 1.1-10-"
t, °C 1100 1200 1300 1400
9,5.10-" i,6-M-»» 1,3- 10-" 0,8-10-'^
The calculations showed that in the 700-1400°C. range, the effect of the
individual reaction of reduction of calcium oxide by hydrogen is slight.
On the basis of the established characteristics of the thermodynamic
equilibrium of individually occurring reactions, it was possible to perform
a calculation of the equilibrium of the overall process of interaction be-
tween the complex hydrogen sulfide-containing gaseous mixture and calcium
oxide. As a mixture of this type we took power-producing gas from sulfur
mazuts, constituting the mixture "
From a thermodynamic standpoint, the determining reactions of these
gases with calcium oxide in such a system may be considered to be the
following:
CaO + HjS ^± CaS + HiO; H»S s±
COj + H4.
The equilibrium composition of the gas will be determined by jointly
solving a system of equations including equations of equilibrium constants
of the individual reactions and the equation of material balance.
- 25 -
-------
The working equations of the process are
(2)
(3)
OI//>COPH,O: (*)
+ PH, = PH.O + PH, + PH.S' (5)
p = PH.O + PH.S + PH, + Ps, + PN, + Pco + Pco, . (6)
ff ? V tt V fft If ////
where AP • *\P » ^P • Ap are the equilibrium constants of the respective
reactions; p with the corresponding subscripts are the partial pressures of
gases at equilibrium; pb with the corresponding subscripts are the partial
pressures of the gases in the initial blast; P is the total pressure.
Using some simple transformations of equations (1) - (3), one can
readily determine the value of the partial pressure of sulfur vapor
In the 700-1400°C. temperature range, K " changes from 0.75 x 10"^ to
0.162; Kp'", from 1.6 x 10"19 to 0.8 x 10"10; K ', from 2750 to 40.
Consequently, in the indicated temperature range, the partial pressure
of sulfur vapor amounts to a negligibly small value.
In determining the most important index of the process of sulfur re-
moval from a gaseous mixture, i. e., the degree of conversion of hydrogen
sulfide, we shall write A^p&o/PHjs^B^p fi./pfe.s- Then equation (5) may be
written as follows:
whence
PH.S 1 + A + B
Since the quantity K'JK?' entering into the denominator of this ex-
pression represents a large value, the degree of conversion of hydrogen sul-
fide in the course of the reaction of sulfur-containing power-producing gas
with calcium oxide at 700-1400°C. is practically complete.
- 26 -
-------
Thus, thermodynamic analysis showed the possibility of carrying out the
process of removal of hydrogen sulfide from sulfur-containing power-producing
gas by calcium oxide at high temperatures.
Considering the thermodynamic evaluation of the conditions of roasting
of calcium sulfide for the purpose of regenerating the reactants, we can
note that to date this process has not been studied, although a large number
of studies on the roasting of sulfides of the metals, chiefly nonferrous ones,
have been published in the literature.
In this connection, the authors carried out a thermodynamic analysis of
the process of interaction of calcium sulfide with oxygen, the results of
which are presented below. The method of calculation was similar to the pre-
ceding one.
When calcium sulfide is oxidized, the formation of calcium sulfate or
oxide and also free calcium and elemental sulfur is possible, according to
the reactions
CaS + 202 = 0280!; (7)
(S)
(9)
CaS + VA = CaO + '/&. (10)
Data on the probability of the reactions in the course of roasting may
be obtained by comparing the values of the free energy change of these re-
actions .
The calculated values of AZ/T for these four reactions are given below:
Temperature, °C. 600 700 800 900 1000 1100 1200 1300 1400.
Reaction
(7) ..... —174 —148—127— 110 —94 —83 —71 —83 —55
(S) ...... —106 — 9i —83 —75 —68 —62 —57 —52 —48
(9) ...... 56 50 46, 42 38 36 33 31 29
23,6 21,1 19,0 17,4 16,2 15,0 14,0 13,1 12,4
Hence, at 600-1400°C., the reaction of calcium sulfide oxidation pro-
ceeds toward the formation of CaSO4, CaO, SO2 H S2. , Reaction (9) at these
temperatures is possible only from right to left, so that the formation of
metallic calcium according to this reaction is excluded. The probability
of oxidation of calcium sulfide according to reaction (7) with formation of
CaSC>4 is greater than according to reaction (8) with the formation of CaO
and S02, and considerably exceeds the possibility of formation of elemental
- 27 -
-------
sulfur according to reaction (10). At temperatures above 1300°C., the prob-
ability of reactions (7) and (8) is practically the same.
i ->
Since during roasting of the sulfide in the gaseous mixture oxygen is
present together with S02, the possibility of oxidation of SC^ to SO, accord-
ing to the reaction.
SO. + V*0* = SO,. (11)
is not excluded.
Values of the free energy (AZ/7") of reaction (11) at different tem-
peratures are given below:
t, °C 600 700 800 900 1000 1100 1200 1300 1400
—AZ/T 1,1 3,87 6,24 8,22 9,83 11,25 12,52 13,53 14,45
The free energies of reaction (11) have a positive value, so that at
600-1400°C. the reaction may be neglected.
Numerous studies of the oxidation of metal sulfides established that
sulfides in a mixture with sulfates or higher oxides are good reductants for
the latter. Considering this point with regard to the oxidation of calcium
sulfide, one can propose the following course of the reaction:
SCaSO, + CaS = 4CaO + 4SO2. (12)
The calculated values of the free energy of reaction (12) are
t, °C 600 700 800 900 1000 1100 1200 1300 1400
AZ/T 101,1 72,3 49,0 33,3 14,0 0,8 —10,2 —19,7 —27,9
At 1200°C. and above, calcium sulfate is reduced by calcium sulfide to
calcium oxide and sulfur dioxide.
Thus, when calcium sulfide is roasted in the presence of atmospheric
oxygen at temperatures above 1200°C. and in the absence of kinetic inhibition,
the process may be expected to proceed with the predominant formation of S02
and CaO. Under these conditions, the amount of elemental sulfur formed will
be minimal. In addition to the temperature effect, this is also due to the
fact that the roasting is always carried out with a certain excess of air
that promotes the combustion of sulfur to sulfur dioxide.
This can be readily ascertained by analyzing the conditions of simul-
taneous occurrence of reactions (8) and (10). From the equations for the
- 28 -
-------
equilibrium constants of these reactions one can determine the expressions
for the partial pressures: pSo,= Kppo,, Ps,^ (Kp )Vo,, whence
PSO,
i/,
In the 700-1400°C. temperature range, the value of Kp"/(K£)2 is 108-1012,
1/2
and the magnitude of p in the presence of excess oxygen has appreciable
°2
values. Therefore, p__ is many times greater than pg , and the amount of
elemental sulfur evolved during the roasting of sulfides will be minimal.
A slightly different composition of the gases may be obtained by treat-
ing calcium sulfide with steam and air.
First it should be noted that thermodynaraically, favorable conditions are
lacking for the regeneration of the sulfide by its direct steam treatment at
500-1300°C. Actually, the process of high- temperature removal of hydrogen
sulfide from gases here considered is based on the reaction CaS + l^O = CaO +
, which takes place in the opposite direction.
A more favorable thermodynamic picture is obtained for the steam-air
treatment of calcium sulfide (Table 1).
Table 1.
Free
Energy Change for Reactions of Calcium Sulfide with a
iteam-Air Mixture at Different Temperatures.
Steai
Reaction
«J58 + *-<*> +
2CaS + HsO+lV«02=
= 2CaO + HaS+SOs
2 CaS + H«O -J- IVs Oj =
=2 CaO +SO-. + Vt S. + HB
3 CaS + HjO + 2 Ot =
=3 CaO + HjS + SO. + V* S:
3Si?§Wfir
AZ/f at temperature, "C.
.500
1
-63,9
—113,1
.
—96,8
—145,9
-21,1
600
—55,9
—98,0
—84,9
—126,8
-15,7
700
-49,5
-85,9
—75,4
-111,7
-11,5
800
-^44,3
-76,1
-65,7
-99,4
-7,7
900
-40,1
-68,0
-61,3
-89,1
^™^« D
1000
-36,4
-61,1
—55,9
-79,8
-2,1
- 29 -
-------
An evaluation of the possible distribution of sulfur between S0? and lU
based on the formation of elemental sulfur, was made by using the calculated
equilibrium constants of the determining reactions:
. I. CaS + lV?4= CaO +.S02, ^ pSOi/p%',
II.
III.
It may be readily established that
1 Pso.
and
In the 600-1000°C. temperature range, the values of K'/K" change from
28 18 ^
1.6 x 10 to 2 x 10 , which indicates large values of tv' lj(")'(p'^ /pHo)
i. e., a very small content of H2S in the gas at equilibrium.
The amount of elemental sulfur being liberated is also relatively small,
owing to the large values of Kl'/OC1)2 in the 600-1000°C. temperature range
(10 -lO-*-!) and to the relatively lesser effect of the magnitude of the equi-
librium oxygen concentration.
The use of steam-air treatment of sulfides as compared to oxidizing
roasting can provide for the regeneration of calcium oxide at temperatures to
1000°C. with the predominant formation of sulfur dioxide, a slightly higher
yield of elemental sulfur, and a minimum amount of hydrogen sulfide.
Thermodynamics of the Process of Hydrogen Sulfide Removal from
Gaseous Mixtures using Iron Oxides
Thermodynamic studies of the system Fe-S-0-H-C have been conducted mainly
by metallurgists in connection with processes of desulfurization of metals.
The main purpose of these studies was to elucidate the conditions of transfer
of sulfur from solid ferrous sulfide to the gaseous phase and vice versa at
high temperatures.
G. Shenk [11] plotted graphically the regions of existence of pure sub-
stances consisting of two solid phases FegO^-FeS, FeO-FeS, and Fe-FeS at
temperatures of 627-1327°C. for different compositions of the gaseous phase
(02, H2, CO, C02, H2S, S02, S03, S2, H20). Also known are studies dealing
- 30 -
-------
with the thermodynamic equilibrium of a system containing no carbon, Fe-S-O-H
[7, 12, 13].
Some studies give thermodynamic calculations for systems consisting of two
solid phases, Fe^-FeS and FeO-FeS, and the equilibrium constants of the
reactions are determined without calculating the equilibrium composition of
the gas [12, 13].
The most complete study of the equilibrium in the system Fe-S-O-H was
made by 0. P. Korobeynichev [7], who analyzed the following combinations of
two solid phases: Fe203-Fe304-FeS2, Fe30^-FeS-FeS2, Fe30 -Fe-FeS, Fe^-
FeO-FeS, FeO-Fe-FeS, and calculated the equilibrium gas composition for each
of them at temperatures of 300-1200°K.
The published studies, however, do not give a complete picture of the
course of the process of interest to us here, i. e., the removal of hydrogen
sulfide from combustible carbon-containing gases by means of iron oxides at
high temperatures (500-100°C.)« For this purpose it is necessary first of
all to know the thermodynamic characteristics of the course of the many re-
actions in the system Fe-S-0-H-C at these temperatures. We therefore cal-
culated values of the free energy for the possible reactions of iron oxides
with the hydrogen sulfide present in combustible gases, i. e., in the re-
ducing medium (CO, H2, C02, N2) at 500-1000°C. The results of these cal-
culations are given in Table 2. As follows from these calculations, if one
considers the interaction of iron oxides with hydrogen sulfide in the absence
of reducing gases, in the reaction of the lower oxides Fe203 and FeoO/, their
reduction by hydrogen sulfide with the liberation of elemental sulfur in the
gaseous phase is observed [reactions (1) and (2)]. The liberation of ele-
mental sulfur in a reducing medium is rather improbable, since it would be
hydrogenated, for example, by hydrogen according to reaction (5).
Ferrous oxide and iron with hydrogen sulfide form iron sulfide according
to reactions (3) and (4). In a reducing medium, the interaction of iron
oxides with hydrogen sulfide can form only iron sulfide in the solid phase,
or iron and its lower oxides may be obtained along with the iron sulfide. In
the latter case, one solid component is consumed and two other solid phases
are formed. '
There is a high probability of occurrence of reactions between iron
oxides and hydrogen sulfide in a reducing medium with the formation in the
solid phase of a single component - iron sulfide [reactions (6)-(9)]. In
the overall process of removal of hydrogen sulfide from gases in a reducing
medium (H2,CO), it is evident that in addition to the reactions in which
iron oxides combine directly with hydrogen sulfide, the reduction of iron
oxides by hydrogen and carbon monoxide to lower oxides will take place. This
is confirmed by data on the thermodynamic potential change over the entire
range of temperatures from 500 to 1200°C. for reactions (10)-(15). Here the
- 31 -
-------
SS
I
Table 2.
Change of the Free Energy of the Reactions of Iron Oxides with Hydrogen Sulfide in a Reducing Medium.
Reaction
Fe»O8+3H,S:=2FeS + 3H40 + 0,5S, (1)
FesD« + 4HtS = 3FeS + 4H»0 + 0,5Ss (2)
FeO + H»S = FeS + H,O (3)
Fe + HgS = FeS + H, (4)
Hs + 0,5S» = HtS. (5)
Fe*0s + 2 HSS + H» = 2 FeS + 3H2O (6)
Fes04 + 3H8S + Ht = 3FeS + 4HiO (7)
FesOs + 2 HSS + 00 = 2 FeS -J 2 H,O + COs (8)
FesO4 + 3HsS + CO:=3FeS + 3H8O + COs (9)
2 Fe2Os + HjS + H« = Fe$O« + FeS + 2 H8O . (10)
2 FeaO« + H8S + 2 Hs = 5 FeO + FeS + 3 H»O (11)
2FeO + HjS + Hs = Fe + FeS + 2HiO (12)
2 Fe20» 4- HsS + C6 = FesO« + FeS + H*0 +00, (13)
Fe30* + H,S + CO=2 FeO + FeS + HSO+00» (14)
2 FeO + HZS + 00= Fe + FeS + HSO -f GO2 (15)
9 FeaOs + HjS = 6 FesO« + SOg + H8O (16)
3 FesO4 + 10 HSS == 9 FeS + 10 H»O + SOg (17)
FeS. = FeS + 0,5 83 (18)
AZ/T at temperature, °C.
500
-18,38
—23,53
—14,67
—17,18
—16,73
—107,04
—39,56
—37,71
—42,76
—29,91
-6,53
—12,65
— 32j76
—13,11
—15,29
—25,24
—70,24
—96,48
600
-20,26
—25,03
-13,33
—15,27
—13,80
-105,81
—37,92
-35,16
—39,83
—29,13
-10,08
-11,95
-30,59
—12,80
-13,20
—31,59
-73,15
—89,62
700
—21,96
—26,51
—12,43
—13,93
v— 11,50
—105,04
—36,86
—33,36
—37,77
—28,71
—12,59
-11,53
-29,08
—12,50
—11,70
—37,15
—76,27
—84,33
800
—23,40
—27,89
—12,10
—13,41
—9,66
-104,88
-36,57
—32,59
—36,89
—28,72
—13,79
—11,40
—28,41
—12,25
—10,95
—41,43
—79,57
,—81,19
900
-25,06
—29,39
—11,52
—12,48
—8,17
-103,56
—35,91
—31,33
—35,41
—28,02
—15,47
—11,29
—27,40
—11,89
—9,88
—46,83
—82,95
—76,90
1000
—26,52
—30,80
-11,38
-12,16
—6,94
-104,55
—35,83
—30,86
—34,84
—28,85
-16,15
—11,37
-27,03
—11,57
—9,39
—51,32
—86,46
—74,27
1100
—27,93
—32,20
-11,40
—12,03
-5,93
-104,79
—35,96
-30,65
—34,55
—29,24
-16,44
—11,57
—26,91
—11,23
—9,10
—55,65
-90,15
_72,16'i
1200
—29,32
-33,60
—11,54
—12,05
—5,09
—105,19
—36,24
-30,66
-34,49
—29,75
—16/42
—11,86
—26,98
—10,86
-8,97
—59,90
—93,73
—70.47
-------
reduction of iron oxides to pure iron according to reactions (12) and (15)
is observed.
In principle, reactions of iron oxides with hydrogen sulfide with the
formation of iron sulfide and sulfur dioxide in the gaseous phase are also
possible [reactions (16) and (17)]. However, in a reducing medium, these
reactions may by neglected. 0. K. Korobeynichev has estimated the loss of
sulfur in the form of SO in the reduction of iron oxides with hydrogen-
containing gas to iron, and showed that even at a ratio (pjj + p£n)/PHoS
equal to 40, this loss does not exceed 0.4%. He also calculated the equi-
librium composition of the gaseous phase at different stages of the process
for a gaseous mixture of the composition 1% H^S, 10% Hn, and 89% N2, at a
pressure of 1 atm. Results of the calculations are shown in Table 3.
Table 3.
Equilibrium Composition of Gaseous Phase.
Stage
Fe-;Os ;± FesO*
Fe*04 *± Fe, FeS
FesO«*iFeO, FeS
'
FeO+iFeS
Fe«±FeS
Gas
SO,
H.O
H8
HSS
H.S
H4O
HZS
: H..
HiO
HjS
Hs
H»0
H.S
Hs
Concentration of gas (in #) at temperature (°K)
700
1
11
<^1
<^1
io-»
9,5
1,5
800
1
11'
<1
3,3- 10~8
8,35
2,65
Ho stages
1,1-10,
4.4-10"8
11
1000
1
11
No stage
4-10"4
5
5
2f9-10~*
7 ,3
3 ,7
4,4-lQ-8
1.6-10"1
2,1
8,9
1,05-KT1
6,6
4,6
1.7-10'1
In the process of hydrogen sulfide removal from gases by iron oxides in
the solid phase, the formation of only iron sulfide is most probable; as far.
as a pyrite medium (FeS2) is concerned, it is unstable in this temperature
range, as is confirmed by the negative value of the free energy of reaction
(18). Experimental data of a thermographic analysis performed by several
authors [14] also showed that this process takes place vigorously at 520-
530°G. Thus, thermodynamie analysis of reactions between iron oxides and
- 33 -
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hydrogen sulfide in a reducing medium showed that hydrogen sulfide can be
recovered from combustible gases at 500-1000°C.
Considering the thermodynamic evaluation of the conditions of regener-
ation of solid absorbents in the removal of H2S from gases by means of iron
oxides, it is necessary to note the large number of publications devoted to
the process of oxidation of iron sulfide by atmospheric oxygen. The inves-
tigators were chiefly interested in problems connected with the mechanism
of oxidation of iron sulfide by oxygen.
The equilibrium reactions in the system Me-S-0 were studied by G. Shenk
[11], W. Reinders [15], and others. Shenk [11] investigated the equilibrium
conditions of the solid phases Fe2Og-FeS as a function of the composition
of gaseous mixtures containing 62, SO^, SO.,, and also gave a graphical re-
presentation of the regions of existence of the solid phases Fe^O^-FeS,
FeO-FeS, and Fe-FeS in the presence in the gaseous phase of the following
components: S02, SO-j, S2, 02, CO, C02, H2> H20 at 600-1600°C.
Several studies have dealt with the transfer of sulfur from the solid
phase FeS to the gaseous phase by means of the solid components Fe20o,
Fe30^ and FeO according to the reactions.
3 FeA + FeS ;* 10 FeO + SO2,
2FeO+ FeS ^.3 Fe + SO2.
The studies showed that under equilibrium conditions, FeS oxidizes to
Fe^g at a temperature as low as 850°C., and the oxidation of FeoO. occurs
only in the range of 1300-1350°C.; if excess FeS is present, metallic iron
may also be formed. The process of desulfurization of the metal is possible
only at high temperatures.
In order to achieve a rational organization of the process of regener-
ation of the solid reactant for its subsequent utilization in cycles of
hydrogen sulfide absorption from gases, it is necessary to evaluate the
equilibrium of the individual reactions that are possible in the overall
process of oxidation of iron sulfide by oxygen.
Table 4 gives the results of calculations of free energy values under
different conditions for a series of reactions possible during oxidation
of iron sulfide by atmospheric oxygen.
As is evident from the data of Table 4, at 500-1200°C., the reactions
of iron sulfide oxidation by oxygen (l)-(4) proceed mainly in the direc-
tion of formation of iron oxides in the solid phase and sulfur dioxide in
the gaseous phase.
- 34 -
-------
Table 4.
Free Energy Change of the Reactions of Iron Sulfide with Oxygen.
Oi
I
Reaction
FeS + O» = Fe +-SO»_ (1)
FeS + l,5O» = FeO + SO* (2)
3FeS + 5O4 = FesO4 + 3SO» (3)
2 FeS + 3 , 5 O2 = Fe»03 +. 2 SOj (4)
FeS + 2O4=FeSO4 (5)
3 FeSO4 + FeS = 4 FeO + 4 SO, (6)
FeS + 0,5Oz=FeO + 0,5Sj (7)
2 FeS + 1 , 5;0z = FeiOs + Sz (8)
3 FeS + 2OZ = Fes04 + 1 ,5 S« (9)
0,5Sj + Oz = SOi8 (10)
FeS + 2 Ot— FeO + SO, (11)
3 FeS + 6 ,5 Oz = FC8O4 + 3 SO» (12)
2FeS + 4,5O4=FejO3 + 2SO, (13)
FeO + SO3=FeSO4 (14)
&.Z/T at temperature, °C.
500
—120,69
—125,60
-534,25
—318,04
—167,00
—1,96
—91,46
—126,63
—165,83
—54,61
-r!34,72
—472,85
—545,02
—31,82
600
—106,27
—108,50
—386,79
—275,28
—136,94
—24,07
—80,73
—108,72
—142,02
—46,30
—114,28
—400,26
—494,02
—22,14
700
—94,62
-94,71
—336,97
—241,35
—112,80
—41,71
-71,84
—94,34
—109,99
—39,69
—97,90
—342,32
—453,28
—14,33
800
—86,87
—83,36
—304,33
—213,86
—96,95
—56,07
—65,88
—84,93
-93,51
—35,44
—87,18
—304,75
—426,83
—9,16
900
—76,60
—73,80
—262,23
—191,08
—76,36
—68,01
—58,18
—72,56
—81,98
—29,87
—73,12
—255,71
—392,27
—2,49
1000
—69,83
—65,62
—233,34
—171,92
—62,15
—78,09
—52,74
—64,02
—71,91
—26,12
-63,61
—222,36
—368,72
+2,15
1100
—63,69
—58,49
-208,45
-155,58
—49,83
—86,70
—47,96
—56,59
—63,02
—22,92
—55,30
—193,73
—348,46
+6,19
1200
—58,25
-51,24
-186,76
-132,25
—36,60
—107,30
-43,69
-50,01
—55,07
—20, 16
—48,02
—108,85
—330,82
+9.74
-------
Despite the probability of oxidation of iron sulfide by atmospheric
oxygen to metallic iron, the latter in the presence of excess oxygen is
almost completely oxidized to ferrous oxide (FeO). ; This is confirmed by
data of thermodynamic studies carried out by G. Shenk [11].
The formation of iron sulfate in the solid phase according to reaction
(5) is probable at 500-1200°C., and its reduction by iron sulfide to ferrous
oxide is possible according to reaction (6). Numerous investigations of
the oxidation of metal sulfides by oxygen have confirmed the fact of lower-
ing of the decomposition temperature of sulfates in the presence of reduc-
tants, i. e., metal sulfides.
There exist favorable thermodynamic conditions of liberation of ele-
mental sulfur according to reactions (7)-(9), but in the presence of excess
oxygen sulfur will be oxidized by the latter to sulfur dioxide according to
reaction (10). In principle, the formation of sulfur trioxide is also
possible in accordance with reactions (11)-(13) during oxidation of iron
sulfide by oxygen. However, the theory of metallurgical processes notes
that sulfur trioxide is an unstable compound at high temperatures. This
is indicated by positive values of the free energies of the reaction
S02 + %02 = S03 at 600-1400°C.
It is difficult to postulate the possibility of formation of iron sul-
fate in the course of roasting at temperatures above 900°C., as is evident
from the results of calculation of the free energy from reaction (14). It
has been experimentally established that the temperature of the start of
thermal decomposition of iron sulfate is 450-550°C.
Iron sulfate formed by an amorphous oxide is a relatively unstable com-
pound at temperatures above 500°C., which is important for the roasting pro-
cess.
Thus, thermodynamic analysis of the reactions of oxidation of iron
sulfide by oxygen shows that in the course of roasting, iron oxides are
primarily formed in the solid phase and sulfur dioxide in the gaseous phase.
If we now consider the thermodynamic evaluation of the conditions of
steam-air treatment of iron sulfide, we can note first of all that, in the
case of calcium sulfide, direct treatment with water vapor has little effect.
This is illustrated by Table 5, which gives values of the free energies of
different reactions of iron sulfide with water vapor at 500-1200°C.
The necessary regeneration of solid reactants is thermodynamically
possible only in the steam-air treatment of iron sulfide, as is demonstrated
by the results, given in Table 6, of calculations of the free energies of
different reactions between iron sulfide and a steam-air blast of different
compositions at 300-1000°C. Here the formation of metallic iron is rather
improbable, and the process is directed toward the formation of its oxides.
- 36 -
-------
Table 5.
Free Energy Change of the Reactions of Iron Sulfide with Water
Vapor at Different Temperatures.
Reaction
FeS + HS0 =
= FeO + H,S
FeS + 3 HSO =
= FeO + SO2 +
+ 3H2
2FeS+3H2O =
= Fe2O3 +
2FeS+7HtO=
= Fe8Os +
+ 7H2 + 2SO2
3FeS + 4H20=
+ 4H.+ 1.5S,
3FeS+10H20=
+ 10H*+3SOS
AZ/r at temperature, "C..
500
+14,7
+63,3
+«6,7
+131,6
+99,6
+185,1
600
+13,3
+54,2
+59,2
+114,8
+87,3
+158,1
700
+12,4
+47,1
+53,4
+101,6
+78,0
+140,4
800
+12,1
+41,5
+48,9
+90,9
+70,6
+127,8
800
+11,5
+36,9
+45,3
+82,3
+64,8
+111,4
1000
+11,4
+33,1
+42,5
+75,1
*
+60,2
+100,5
1100
+11,4
+30,1
+40,2
+69,1
+56,6
+91,4
1200
+11,5
+27,5
+38,5
+64,1
+53,7
+83,6
An evaluation of the thermodynamically probable distribution of sulfur
between S02» I^S and elemental sulfur in the course of steam-air regeneration
of the sulfide may be approximated by analyzing a system consisting of the
three determining equations of the process which include all the reacting
components :
.2 FeS + 2 O2 + H2O = Fe40s + HzS + S02,
KP = Pso, •PH.S/PH.O'PO,'
3 FeS + Os + HjO = 3 FeO + HgS + S2l
I Kt> = PH.s'Ps./Po, -PH.01'
3 FeS + 2 Oa + 2 H2O = FeaO< + 2 HjS + SO2,
' * =
Using some simple transformations, one can readily show that
PSO.
PH.S ~
Pso, *p PQ,
PS, K*p PH.O
- 37 -
-------
Table 6.
Free Energy Change of Reactions of Iron Sulfide with a Steam-Air Mixture.
CO
oo
Reaction
FeS + V* Og -(- HSO = Fe + SO» + Hg
FeS + O8 + H»O = FeO +SO» + H»
2FeS + VtO» + HtO = 2FeO + S» + Ha
2 FeS + l/*O» + HaO = 2 Fe + H«S + Oa
2FeS + Y»0» + H40 = 2Fe + SOs + VaS, + H!!
2 FeS + O« + H»O = Fe.0a + S8 + Hs
2 FeS + 1 VrOi + H,O = 2 FeO + H,S + SOa
2 FeS + 2 O2 + H40 = FejOs + H,S + SOZ
2 FeS + 2 Oj + HSO = Fe»Os + SO» + V* Si + H»
2 FeS + 3O2 + HiO = FejOs + 2SO« + H»
3 FeS + 0* + H»0 = 3 FeO + H2S + Sa
3 FeS +2Os + 2 H4O = FesO« + 2 H»S + SO*
3FeS+2O4 + HsO = 3FeO + SOa + Ss + Hl
3 FeS + 2»/s O» + H.O *= FeaO4 + SOa + 85,+ ^
3 FeS + 4»/« O8 + H»O = Fe8O« + 3 SO4 + Hz
4 FeS + IVa Os + 3 HaO == 2 Fe»O3 + 3 HZS + Vs Sa
4 FeS + 2Va O« + HSO = 4 FeO + HjS + S0a + Sg
4 FeS + 3»/i 0« + HjO = 2 FesOs + H2S + SO3 + Sa
4 FeS +4VsOt + H,O = 4 Fe + HiS + SO2 + S»
CFeS+2Oa+4H2O = 2Fe30
-------
As was shown by the calculations, the values of K1 in the 300-100°C.
temperature range changed from 10 to 10 , and the values of K" and K"'
P p
from 10 and 10 to 10 and 10 respectively. For this reason the
ratios Psc^/P^S and PS02/'PS2 wil1 be very lar§e» *•• e-> hydrogen sulfide
and elemental sulfur will be obtained in minimum amounts.
Thus, the steam-air treatment of iron sulfide as compared with oxidiz-
ing roasting can be carried out at lower temperatures, but the gas obtained
will contain chiefly sulfur dioxide.
Thermodynamics of the Process of Hydrogen Sulfide Removal from
Gaseous Mixtures Using Manganese Oxides
As was indicated earlier, in principle, manganese oxides are suited for
the removal of hydrogen sulfide from gases at high temperatures. It is evi-
dent that the practical realization of such a process will make it necessary
to utilize natural manganese ores.
The majority of natural manganese compounds consist of complex oxides
of manganese with a valence ranging from two to seven. The most common
natural oxide is manganese dioxide, which is found in the form of the min-
eral pyrolusite. Natural manganite, which contains manganese dioxide and
manganous oxide, is also widely distributed.
Since gaseous mixtures from which hydrogen sulfide is removed contain
active reducing components for metal oxides, the process of purification
may include a varied set of simultaneous reactions - not only the reaction
of hydrogen sulfide with manganese oxides, but also the reduction of these
oxides. Here one may also observe reactions of hydrogen sulfide with higher
and lower manganese oxides resulting in a stable sulfide form of manganese,
and also the reduction of higher manganese oxides to lower ones and to the
pure metal. In addition to these reactions, the possibility of liberation
of elemental sulfur and formation of sulfur dioxide in the gaseous phase
is not excluded. '
Analysis of literature data on this question has shown that no detailed
thermodynamic studies have been made to date on the entire problem of inter-
action of various manganese oxides with hydrogen sulfide in a reducing me-
dium, if one does not consider studies of the thermodynamics of the reaction
between manganous oxide and hydrogen sulfide. Ref. [16] discussed the ther-
modynamics of this reaction at 400-1000°C. for the process of desulfuriza-
tion of benzene with a contact mass consisting of manganous oxide. It was
noted that such a reaction is possible in this temperature interval.
- 39 -
-------
In order to evaluate the course of the entire process as a whole when
manganese oxides are used for the removal of hydrogen sulfide from a com-
bustible gas in a reducing medium, it is necessary 'to determine the proba-
bility of numerous reactions of these oxides with hydrogen sulfide, resulting
in the formation of manganese sulfide. Since the composition of the initial
ore contains mainly manganese dioxide, the initial interaction will obviously
take place in the direction of a reaction of manganese dioxide with hydrogen
sulfide, resulting in the formation of manganese sulfide, and in the simul-
taneous reduction of manganese dioxide by hydrogen and carbon monoxide to
lower manganese oxides.
Subsequently, the lower manganese oxides either will react with hydrogen
sulfide also to form manganese sulfide along with manganous oxide and manga-
nese, or reactions involving only the formation of manganese sulfide will
take place.
In order to obtain a quantitative evaluation of the thermodynamic proba-
bility of the occurrence of reactions between manganese oxides and hydrogen
sulfides in a reducing medium, a comparison of their free energies was made.
Table 7 gives the results of a calculation of the free energies for
numerous reactions of hydrogen sulfide with manganese oxides at 500-1200°C.
On this basis, one can determine the highest probability of reactions of
manganese dioxide with hydrogen sulfide in a medium of hydrogen and carbon
monoxide [reactions (l)-(4) and (13)-(15)], resulting in the formation of
manganese sulfide and lower manganese oxides at 500-1000°C.
Other reactions taking place at these temperatures are (5), (6), (16)
and (17), which represent the interaction of manganese oxide and mangano-
manganic oxide with hydrogen sulfide and result in the formation of lower
oxides of manganes and its sulfide. The occurrence of reactions of manganous
oxide with hydrogen sulfide in a reducing medium, resulting in the formation
of manganese sulfide and pure manganese, is improbable.
The absence of metallic manganese in these reactions is confirmed by
the experimental studies of V. T. Chagunava dealing with the interaction of
hydrogen sulfide with manganese oxides at 300-400°C. Chagunava explains
this by the fact that manganous oxide and manganese sulfide have the same
crystal structure, and therefore the reactions of manganese oxides with
hydrogen sulfide involve sulfidization of manganous oxide without its re-
duction to the pure metal. On the contrary, when iron oxides are used for
the removal o'f hydrogen sulfide from a gas, as was noted earlier, the sul-
fidization of iron is associated with the process of its reduction to the
pure form.
Furthermore, as is evident from Table 7, there is a high probability of
reactions between manganese oxides and hydrogen sulfide in the presence of
- 40 -
-------
hydrogen and carbon monoxide only up to the formation of manganese sulfide
[reactions (8)-(12) and (19)-(21)].
Considering that manganese disulfide may be present in the solid phase
along with manganese sulfide, we calculated the free energies of the reaction
of thermal decomposition of manganese disulfide at the indicated temperatures.
The calculations, whose results are presented in Table 7, revealed a positive
value of this quantity only at 500°C., indicating the thermal stability of
manganese disulfide [reaction (31)]. Starting at 600°C. and higher, the free
energy values are negative, i. e., thermal decomposition occurs. Consequently,
at temperatures above 600°C., the formation of manganese disulfide is excluded.
It was important also to evaluate the probability of liberation of elemental
sulfur in the course of removal of hydrogen sulfide from the gas.
The overall process of interaction of manganese dioxide with hydrogen
sulfide up to the formation of lower oxides of manganese, manganese sulfide
and elemental sulfur is described by reactions (22)-(25).
From the data listed in Table 7 it is evident that the probability of
the indicated reactions is high.
However, it should be pointed out that in the reaction of hydrogen sul-
fide with manganese oxides at room temperature, V. T. Chagunava observed the
liberation of elemental sulfur only in a neutral medium, whereas in a re-
ducing medium this liberation was absent. For this reason, the degree of
recovery of manganese in the neutral medium was lower (93-94%) than in the
reducing medium (97-98%).
As is evident from Table 7, in the indicated temperature range there are
favorable conditions for the occurrence of reaction (29), i. e., hydrogenation
of sulfur by hydrogen with the formation of hydrogen sulfide.
The formation of sulfur dioxide is possible according to reactions (26)-
(28). On the basis of calculation of the free energy values it may be assumed
that no suitable conditions exist for the occurrence of these reactions at
500-1200°C.
It was important to evaluate reaction (30) of thermal decomposition of
manganese carbonate. It is evident from Table 7 that there is a probability
that this reaction will take place at 500-1200°C., i. e., at these tempera-
tures manganous oxide will not react with carbon dioxide.
When hydrogen sulfide is removed from the gas by manganese oxides at
600-800QC., manganese carbonate will not be formed.
Thus, the performed thermodynamic analysis of numerous reactions of
manganese oxides with hydrogen sulfide in a reducing medium showed that the
- 41 -
-------
Table 7.
Free Energy Change of Reactions between Manganese Oxides and
Hydrogen Sulfide in a Reducing Medium.
ts>
I
I
Reaction
3 Mn6» + H»S + 2 Hs = MnzOs + MnS + 3 H2O (1)
4 MnOz + HtS + 3 Hz = Mn80< + MnS + 4 H2O (2)
2MnO» + H2S+2H2 = MnO + MnS + 3 H2O (3)
2 MnO» + H2S + 3H2 = Mn + MnS + 4 H«O (4)
2 Mn.O3 + H. + H2S = Mn3O4 + MnS + 2 H20 (5)
2 MnsO« + HjS + 2 H2 = 5 MnO + MnS + 3 H8O (6)
2MnO+Hs,S+2H8=Mn + MnS + 2HjO. (7)
MnOj+HsS + Ha = .MnS+2HsO (8)
MntO-i + 2 H2S + H2 == 2 MnS + 3 HSO (9)
MhaOa + 3 H2S + Hs = 3 MnS + 4 H2O (10)
MnO + HSS = MnS + HtO (1 1 )
Mn + H.S = MnS + Hs (12)
3 MnOji + H^ + 2 CO *= Mn-i03 + MnS + (13)
+ 2 CO« + H2O
2 MnOi + H2S + 2 CO = MnO + MnS + (14)
2MnO*+H2S + 3CO = Mn + MnS+ (15)
2Mm03 + Hg + CO = Mn301 + MnS+ (16)
?o?;1:So+co=2Mn0+MnS+ (17)
AZ/r at temperature, °C.
500
—128,20
—180,36
—109,21
—71,15
—45,01
—61,16
+57,22
—59,83
—54,76
—130,99
—14,05
—52,48
—135,03
-115,51
—81,50
—49,29
—41,20
COO
-116,66
-163,86
-100,06
—66,80
—42,65
—58,74
+54,15
—54,32
—50,36
—118,54
—12,77
—46,42
—120,94
—103,78
—73,39
—43,83
—38,12
700
-107,43
-157,04
—92,72
—64,48
—39,47
—56,77
+51,78
—49,92
—46,88
—108,66
—11,77
—41,67
-109,75
—94,43
—66,98
—39,48
—35,69
800
—99,91
-139,79
—86,49
—60,93
—36,88
—55,13
+49,90
—44,36
—44,07
-100,68
— 10,98
—37,86
—100,34
— 88,46
—62,92
— 36.,46
-34,19
900
-93,67
-130,79
-81,76
-57,98
—34,73
—53,74
+48,38
—41,96
-43,86
—94,12
—10,35
-34,74
—93,20
—80,58
—57,53
—32,97
—32,14
1000
-88,41
—123,18
-77,55
—55,89
—32,90
—52,54
+47,12
-37,98
—39,38
—88,64
—9,83
—32,14
—86,92
—75,32
—53,95
—30,46
—30,81
1100
-83,92
-116,66
.—73,95
—54,13
—31 ,35
—51,48
+46,06
—36,67
—38,21
—84.0
—9,41
—29,96
—81,65
—70,83
—50,95
—28,29
—29,68
1200
—80,05
—111,03
—70,84
-52,00
—30,0
—49,38
+45,16
—32,99
-36,83
-80,06
-9,06
—28,09
-77,0
—66,98
—18,37
—26,39
-28,72
-------
Table 7 (continued)
Reaction
2 MnO + H»S + CO = Mn + MnS + H,O + CO, (18)
MnO« + H»S + CO = MnS + H»0 + CO» (19)
Mn»O» + 2 HjS + CO = 2 MnS + 2 H»O + CO» (20)
MnaO« + 3 H8S + CO = 3 MnS + 3 H20 +CO2 (21)
3 MnOi + 3 H2S = MnjOs + MnS + 3 H,,O + S» (22)
5 MnO» + 6 H»S = MnA + 2 MnS + 6 H4O + (23)
2Mnol + 3HiS = MnO + MnS + 3H!!p + Si (24)
MnOa + 2 HzS = MnS + 2 H2O + Sa (25
9MniOs+H2S = 6Mni04 + SO2 + H»O (26^
3 MnaOi + 10 H»S = 9 MnS + 10 H»0 + SOt (27)
2 MnO + HtS = 2 Mn + SO* + Hg (28]
0,5S2+.Ha=H4S (29]
MnCOs = MnO + GOa v (30)
MnS4 = MnS + 0,5Sa (31)
AZ/r at temperature, °C.
500
+20,55
—113,36
—30,14
—68,98
—94,96
—176,73
—75,98
—12,89
+116,78
+364,54
+110,51
—16,73
-3,59
+1,32
600
+18,23
-107,72
—24,42
—63,25
—89,34
—165,88
—72,76
—17,46
+120,63
+311,37
+93,08
—13,80
—6,03
-1,17
TOO
+16,35
-100,56
—19,86
—58,76
—84,81
-157,89
—70,12
—21,05
+123,84
+268,89
+79,22
—11,50
—7,55
—3,16
800
+15,06
—95,81
—16,15
—55,19
—81,76
-152,53
—68,31
—23,31
+126,10
+241,24
+70,32
—9,66
—8,39
—4,803
900
+13,43
—91,75
—13,05
—52,24
—77,89
—145,65
-66,01
—26,29
+128,97
+205,40
+58,62
—8,17
—8,72
—6,18
1000
+12,25
—88,25
—10,41
—49,81
—75,19
-140,83
—64,36
—28,25
+131,11
+181,00
+50,74
—6,94
—8,65
—7,37
1100
+11,21
—85,16
-8,15
—44,76
—72,84
—136,61
—62,90
—29,89
+133,03
+160,10
+44,71
—5,93
—8,27
—8,28
1200
+10,28
—82,0
—6,19
—46,01
—70,78
—132,89
—61,59
—31,28
+134,80
+142,00
+38,18
—5,09
—7,64
—9,27
-------
removal of hydrogen sulfide from the gas may be carried out with manganese
oxides at 500-1000"C. with the formation of manganese sulfide in the solid
phase.
In evaluating the conditions of regeneration of manganese sulfide by
its oxidation with oxygen, it should be noted that almost no studies have
been made of this problem. Obviously, this is explained by the absence of
large deposits of manganese sulfide and its limited industrial uses. Only
thermodynamic calculations of the values of the free energy of formation and
dissociation pressure of manganese sulfide at various temperatures have been
published [17, 19].
Metallurgists have been chiefly interested in problems of desulfuration
of slags in steelmaking. As was noted in [11], the process of desulfuration
involves, among other reactions, the reaction Mh + PeS = MnS -t- Fe. G Shenk
[11] discussed the equilibrium conditions of this reaction in the metallur-
gical process. A study of the kinetics and mechanism of the reaction of
manganese sulfide with oxygen at 25-400°C. is discussed in Ref. [18]. A
compound of the composition MnS20g was observed in the solid phase in this
temperature range. Decomposition of this compound begins at 500°C. No
studies have been made on the oxidation of manganese sulfide at tempera-
tures above 500°C.
Table 8 shows the free energies values for some reactions occurring dur-
ing the oxidation of manganese sulfide by atmospheric oxygen. Gas is evident
from this table, there is a distinct possibility of reactions between manga-
nese sulfide and oxygen up to the formation of manganese and lower oxides in
the solid phase, and also sulfur dioxide in the gaseous phase at temperatures
from 500 to 1200°C. [reactions (l)-(5)].
In the solid phase, in the oxidation of manganese sulfide by oxygen, the
formation of manganese sulfate is also possible according to reaction (6).
Manganese sulfate in turn may react with manganese sulfide according to re-
action (7) with the evolution of sulfur dioxide and manganese oxide at 500-
1200°C. The probability of the occurrence of this reaction increases with
rising temperature. When manganese sulfide is oxidized by atmospheric oxy-
gen in the gaseous phase, the evolution of sulfur trioxide may be observed
in the gaseous phase, and of manganese oxides in the solid phase according
to reactions (8)-(10) at the above-indicated temperatures. However, sul-
fur trioxide reacting with manganous oxide according to reaction (11) will
form manganese sulfate. In addition, as we have noted, sulfur trioxide will
be less stable with rising temperature.
The evolution of sulfur is possible according to reactions (12)-(14),
whose occurrence is due to the negative values of the free energy at 500- '
1200°C. Sulfur in turn may burn to sulfur dioxide [reaction (15)] at
500-1200°C.
- 44 -
-------
Table 8.
Free Energy Change of Reactions of Manganese Sulfide with Oxygen.
•e'-
en
Reaction
MnS + 0, = Mn + S08 (1)
2 MnS rf- 3 O» = 2 MnO -f- 2 SO» (2)
MnS + 2 Oa = MnOz + SO,. (3)
3 MnS + 50i = Mn A + 3SOZ ' (4)
2 MnS + 3,5Os = MnzO» + 2SO4 (5)
MnS+2O*=MnSO4 (6)
MnS + 3MnSO« = 4MnO + 4SO« (7)
MnS + 2Os = MnO + SOs '(&)
3 MnS + 6 ,5 O» = MnsO4 + 3 SO3 (9)
2 MnS + 4,5Oj = MntO3-{-2S03 (10)
MnO-i-SOs = MnSO4 (11)
MnS-f 0,5O« = MnO + 0,5Ss (12),
2 MnS + 1 ,5 O» = MnzO» + S, (13)
3MnS +2O2 = Mn3O1 + l,5Sj (14)
P'5Si+0i = SOi (15)
&Z/T at temperature, °C.
500
—26,03
—254,64
—146,48
—172,65
—290,53
—174,96
—73,34
—135,51
—450,63
—506,26
—40,35
—32,47
—100,33
—137,05
—54,61
600
—22,41
—220,42
—123,00
—141,57
—249,03
—144,16
—95,12
—114,97
—381,33
—458,05
—29,93
—27,98
—84,19
—115,28.
—46,30
700
—19,47
^-192,91
-104,20
-116,67
^-215,84
—120,47
—113,02
—99,07
—326,17
—419,56
—22,20
—24,33
—71,21
—97,73
—39,69
800
—17,48
—188,90
—88,29
—96,32
—188,35
—100,88
—126,91
—85,21
—290,96
—388,29
—17,33
—21,84
—62,62
—86,05
—35,44
000
—14,97
—151,83
—75,08
—75,52
—165,87
—84,63
—138,22
—74,09
—244,07
—362,31
—10,84
—18,76
—51,59
—71,10
—29,87
1000
—13,19
-135,99
-63,77
-64,85
—146,88
—70,94
—147,53
-64,72
—212,98
—340,40
—6,55
—16,48
—43,94
—60,69
—26,12
1100
—11,64
-122,42
—53,96
—52,39
—130,59
—59,26
—155,24
-56,71
—185,81
—321,67
—2,90
—14,52
—37,31
—51,64
— 22,92
1200
—10,27
—110,58
-45,37
—41,56
—116,46
—49,17
-161,78
—49,73
—162,58
—305,49
—0,22
-12,79
—31,51
—43,69
—20,16
-------
Table 9.
Free Energy Change of Reactions of Manganese Sulfide with
Water Vapor at Different Temperatures.
D ao f»+- 4 «»»
ASS ct j. on
*— A\nCx ~t~ f"i*"S
MnS+2H.O =
= MnO. +
+ H.S + H.
2MnS + 3H..O=
= Mn.03 +
+ 2HsS+Hj.
3MnS+4H£O=
+ 3H2S4+H.
AZ/r at temperature, "C.
500
+14,1
+59,9
+54,8
+131,0
600
+12,8
+54,3
+50,4
+118,5
700
+11,8
+49,9
+46,9
+108,7
800
+11,0
+44,4
+44,1
+100,7
900
+10,3
+42,0
+43,9
+94,1
1000
+9,8
+38,0
+39,4
+88,6
1100
+9,4
+36,7
+38,2
+84,0
1200
+9,1
+33,0
+36,8
+80,1
On eke basis of a thermodynamic analysis of the numerous reactions oc-
curring in the course of oxidation of manganese sulfide by atmospheric oxygen,
the possibility of formation of manganese oxide in the solid phase and of sul-
fur dioxide in the gaseous phase has been established.
T e steam-air treatment of manganese sulfide is characterized by the same
therraodyiiHinic properties that were revealed for processes of steam-air treat-
ment of calcium and iron sulfide. Direct treatment of manganese sulfide with
w.~.;..er v-por is also ineffective, as indicated by the positive values of the
free e .ergies of the corresponding reactions at 500-1200°C., listed in Table 9.
Thermodynamically, only the steam-air treatment is possible, which in-
cludes a whole group of different reactions of the steam-air blast with man-
ganese sulfide. Values of the free energies of these reactions at different
temperatures are listed in Table 10.
Thermodynamic analysis shows that, as in the case of the steam-air treat-
ment of calcium and iron sulfides, when the steam-air blast reacts with man-
ganese sulfide, the gas obtained will chiefly contain sulfur dioxide and a
minimum amount of hydrogen sulfide and elemental sulfur. The solid residue
will contain chiefly manganese oxides. The formation of metallic manganese
is rather improbable.
EVALUATION OF THE ACTIVITY OF VARIOUS SOLID REACTANTS IN THE PROCESS OF
HYDROGEN SULFIDE REMOVAL FROM GASES AT HIGH TEMPERATURES
Thermodynamic studies have shown that the high-temperature removal of
- 46 -
-------
Table 10.
Free Energy Change of Reactions of Manganese Sulfide with a Steam-Air Mixture.
Reaction
MnS + V* Os + HSO = Mn + SO» +HZ
MnS 4
h O. + H2O = MnO + SO2 + H2
MnS + 1 i/g Og + mo = MnO2 + SOz + H2
2 MnS + i/g Oz + I IsO = 2 Mn + SO2 + H2 + V* Su
2 MnS + V* Og + HsO = 2 Mn + SOg +H2S
2 MnS + O. + H.O = Mii-A, + Sg + H8
2 MnS + I1/. O* + H«O = 2 MnO. + Sj + H2
2 MnS + 1 1/« O- + H«O == 2 MnO + H«S + SO«
2 MnS + 2 O» + H.O = MnaO3 + H2S + S02
2 MnS + 3 O2 + H..O = Mn«O3 + 2 SO* + Ht
2 MnS + 2 a 4- H«O = Mn.,03 + SO. + Hs + V2 S,
2 MnS 4
1- 2i /» O» -4- H»0 = 2 MnO4 + H.S + SO«
2 MnS + 2i'A a + H«O = 2 MnO. + SO2 + VsSt + Hs
3 MnS 4
hO* + H,O=:3MnO + H«S + SS
3 MnS + IVs'Os + HZO = Mn3O4 + I1"/* S-. + Hz
3 MnS + 2 O.. + H«O = 3 MnO + SO. + S» + Hg
3 MnS + 2 O~, 4- 2 H.O = Mn3O, + 2 H£S + SO2
3 MnS 4
h 2i /» O- -t- H.O = 3 MnO» + H2S + S.
3 MnS + 2V, O* 4- H-.O = Mn3O< + SO2 + Sz + Hs
3MnS-
4 MnS -
4MnS-
4 MnS -
4 MnS -
4 MnS -I
r /.I/. oa + H.O = Mn3O4 + 3 SOg + H4
. !/„ 0» + H.O = 4 Mn + HaS + SO* + S2
- li/2 0. + 3 1-UO = 2 Mns08 + 3 HgS + »/t Sg
- 21/8 Os + H.O = 4 MnO + HjS + Sd + S»
- 3Vo O.. + HsO = 2 Mn4O$ + H5S + SOg + Sg
- /,!/., O, 4- H.O = 4 MnO. + HaS + SO» + S2
6 MnS + 2 b» + 4 H»6 = 2 Mu3Q, + 4 H»S + S2
B MnS + 4»/aOs + H4O = 2 Mn3O4 + H»S + SOZ + 2S2
AZ/r at temperature, °C.
300
+52,8
-90,1
—120 7
+163,2
+123,7
-63,7
—59,7
-1621
-421,0
-327,5
-193,5
-223,3
-197,5
— 74 6
—113,5
M On c
— — jO^J Q
-20g;o
-166,4
-503 7
-5348
+317,1
-107,3
—254,6
—368,9
—377,0
—150,6
-478,3
400
+43,5
—75,6
—97,8
+137,3
+103,2
—47,8
—48,1
—135,1
—351,5
-271,0
—159,3
—179,5
—159,1
—62,8
—92,9
—153,8
—170,2
—129,5
—422,5
—446,7
+263,3
—82,9
—213,1
—302,6
—302,3
—117,8
—393,6
500
+36,6
-64,9
—80,9
+118,0
+88,0
—36,1
—39,6
—114,3
—300,0
—229,2
—134,2
—147,0
—130,7
-54,1
—77,6
—132,5
—141,4
—102,1
—363,9
—381,5
+223,5
—65,0
—182,4
—253,5
-246,6
-93,5
—330,9
600
+31,2
-56,7
—68,0
+103,2
+76,4
—27,1
—33,0
— D9,5
—260,3
—197,1
—114.8
—123,0
—108,9
— 47,4
—65,9
—116,1
—119,2
—81,2
—316,1
—331,3
+192,9
—51,2
—158,8
—215,7
—203,9
—74,9
—282,6
700
+26,9
—50,2
-57,7
+91,3
+07,1
—20,1
—27,9
—87,2
—228,7
—171,5
—99,5
—102,2
—91,6
—12,1
—56,7
— 1(0,1
—101,6
-6"., 6
—279,3
—291,3
+168,6
—40,3
—IBS!?
—170,1
— fiO.l
—214,2
800
+23.4
—45,0
-49,4
+81,7
+59,6
—14,4
-23,8
—77,2
—203,2
—151,1
—86,3
-86,1
—77,7
—37,8
—49,2
-92,6
—87,4
-51,5
— 2/i9,4
—259,0
+148,8
—32,0
—12',, 7
—161,4
— 112,6
—48,2
—213,2
900
+20,5
-40,6
-42,6
+73.7
+53,3
-9,7
—20,4
—68,9
-182,0
—133,7
—76,8
—72,9
—66,1
—31/1
— 13,0
— 83,8
—75,6
—40,0
—221,7
—232,1
+132,3
-21,4
-112,0
—141,3
— 119,3
— 3H, 1
— 187,-M
1000
+18,0
—37,0
—36,8
+06,9
+48,0
—5,8
-17,6
—62,0
—161,1
—119,3
—68,2
—61,7
—56,4
—31,5
—37,8
—76,5
—65,7
—30,7
—203,9
—209,0
+118,4
—18,4
—101,3
—121,4
—100,8
—30,2
—105,7
-------
hydrogen sulfide from power-producing gas at 1000°C. and above should be
carried out by use of alkaline earth metal oxides. At 600-800°C., the solid
reactants used may be iron oxides or manganese oxides. In this connection
it became necessary to determine the activity of oxides of the indicated
metals of this group relative to hydrogen sulfide at high temperatures. The
activity of the solid reactants was studied in a medium of pure hydrogen sul-
fide and in its mixture with water vapor.
The study using alkaline earth oxides was carried out on an assembly with
continuous automatic recording of kinetic curves obtained from the change in
the volume of the escaping gas (Fig. 8).
Fig. 8. Diagram of experimental assembly.
The assembly consisted of a quartz reactor 7 18 mm in diameter, a con-
denser 9, with a float device 14 for recording the volume of the gas which
passed through it in reference to time. The unit was first purged with ni-
trogen from which oxygen had been removed by means of copper turnings 2 and
which had been dried with calcium chloride 3. Weighed amounts of different
solid reactants with a particle size of 0.25-0.5 mm were charged on a layer
of porcelain particles of the same fraction. The weight of the charge was
0.825 g. The quartz reactor was heated with a demountable electric furnace
6 to a given temperature, then a Kipp generator 1 was used to supply hydro-
gen Sulfide, obtained by reacting hydrochloric acid with ferrous sulfide.
The temperature of the layer was measured with a platinum/platinum-rhodium
thermocouple connected to a galvanometer. When a steam-gas medium was used,
water vapor was supplied from a steam superheater 5. The unreacted amount
of water vapor was condensed in a condensate collector 10. The amount of
- 48 -
-------
gas leaving the quartz reactor was measured with a flow meter 4. The unre-
acted hydrogen sulfide was absorbed in alkali in a gas-washing Tishchonko
bottle 11, and the remaining gas was collected at different time intervals
into gas-absorption pipets 13 through a U-shaped water manometer 12 with
simultaneous measurement of its amount by a float recorder. The velocity
of the drum was 69.7 mm/min. A 1 mm vertical displacement of the recorder
pen takes place when 9.3 cnr of gas is evolved. A large amount of gas was
collected periodically into gasometers IS.
The degree of conversion of hydrogen sulfide was calculated from the
amount consumed by the reaction. The amount of unreacted hydrogen sulfide
was calculated from the difference between the volumes of the readings of
the flow meter and automatic recorder. Knowing the amount of hydrogen sul-
fide supplied at a given time and the unreacted amount, one can calculate
the amount of hydrogen sulfide consumed in the reaction. The degree of con-
version of hydrogen sulfide was calculated as the ratio of the amount of
l^S consumed in the reaction to the total amount of hydrogen sulfide supplied
during a given period of time.
In order to study the activity of hydrogen sulfide with solid reactants
metal oxides were used: calcuim oxide, magnesium oxide, their mixture (50%
each), and kaolin. Experiments on the comparative activity of different
reactants showed that the most effective reactant with hydrogen sulfide at
1100°C., a linear velocity of 0.099 cm/sec and an actual contact time of
1.56 sec was calcium oxide and a mixture of calcium oxide and magnesium
oxide (50%). For these reactants, the degree of conversion of hydrogen sul-
fide remains a constant equal to 100%, in the course of 30 min (Fig. 9).
- //o
3-
7O
g fff
/O 20 30
lime, min.
"100
g »
• H
g
1 fO
o
tff
W 20 30
Time, min.
Fig. 9. Comparative activity of different
reactants in reactions with pure hydrogen
• sulfide at 1100°G.
Fig. 10. Comparative activity of reactants
in reactions of a mixture of hydrogen sul-
fide with water vapor at 1100°C.
1 - CaO, MgO + CaOj 2 - Kaolin; 3 « MgO.
1 - CaO; 2 - Kaolin; 3 - MgO; 4 - CaO +
MgO
- 49 -
-------
Kaolin and magnesium oxide react less actively with hydrogen sulfide.
The degree of conversion of hydrogen sulfide after 13 min for kaolin is
91.1%, and after 30 min decreases to 84.4%, whereas for magnesium oxide
after 8 min the degree of conversion of hydrogen sulfide reaches 88.5%, then
decreases to 66.0% in the course of 30 min.
A study of the activity of solid reactants with hydrogen sulfide (3.06%)
in excess water vapor at 1100°C., a linear velocity of the steam-gas mixture
equal to 0.032 m/sec and an actual contact time of 0.218 sec shows that cal-
cium oxide is one of the most effective reactants in the reaction with hydro-
gen sulfide.
The degree of conversion of hydrogen sulfide, equal to 100%, lasts for
16-18 min, and after 30 min'drops to 75-78% (Fig. 10). The activity for
kaolin in the reaction with hydrogen sulfide in a medium of water vapor is
very high, equal to 100% for 15 min, and decreases to 64.4% after 30 min.
A mixture of magnesium oxide and calcium oxide (50%), and also magnesium
oxide are less active: a 100% conversion of hydrogen sulfide is observed
only for 5.5 min, and after 30 min decreases to 60-62% for the mixture and
to 48% for magnesium oxide.
Experiments involving the study of the activity of hydrogen sulfide to-
ward alkaline earth metal oxides in a medium of hydrogen sulfide and in a
mixture with water vapor showed that the most effective reactant at 1100°C.
is calcium oxide. This is a relatively cheap reactant, since it can be ob-
tained by roasting from universally distributed natural limestones. The
high reactivity of calcium oxide toward different sulfur compounds is well
known. This property is used in technology: the use of limestone for tying
up sulfur in metallurgical processes during the melting of pig iron has been
widely adopted.
In order to obtain sulfur free metal, the sulfur is converted from iron
sulfides into calcium sulfide, which is practically insoluble in the metal,
but dissolves well in slags, particularly basic slags. The desulfuration of
pig iron with calcium oxide is carried out at high temperatures which cause
the sulfur to be eliminated with the liquid slags [20].
In the technology of removal of sulfur compounds from gases, calcium
oxide has been used relatively little, mainly in the removal of sulfur di-
oxide from gases.
In dry methods of hydrogen sulfide removal from gases by means of bog
ore, lime is frequently used as the active additive to the ore.
All attempts known thus far to use calcium oxide for the removal of hy-
drogen sulfide from gases have been random in character, and there are no
systematic published studies of the conditions under which this reaction
- 50 -
-------
takes place. In this connection, it becomes necessary to make a detailed
study of the kinetics of the reaction between hydrogen sulfide and calcium
oxide, which takes place both independently and together with side reactions
that are possible under such conditions.
As already noted, the use of calcium oxide for purifying sulfur-contain-
ing gases is desirable at 1000°C.
In selecting the reactants for removing hydrogen sulfide from gases at
600-800°C., it is also necessary to point out the stability of salts of sul-
fur compounds and the exclusion of the stability of formation of carbonate
salts from the carbon dioxide present in the gases being purified. Thermody-
namic analyses have shown that oxides of iron and manganese satisfying the
technical requirements of high-temperature purification can be used for re-
moving hydrogen sulfide from gases at 600-800°C. In this respect, various
natural iron and manganese ores and also other minerals available for use on
a large scale are of some interest. The choice of solid reactants is de-
termined by the chemical activity of the interaction of varios ores and min-
erals with hydrogen sulfide at high temperatures.
Fig. 11. Diagram of experiuental assembly for studying the kinetics
reactions of the recovery of sulfur compounds from gases.
A study of the activity of various solid reactants at temperatures to
800°C. was made on a somewhat modified assembly with continuous recording of
the reaction rate in time (Fig. 11). The assembly consisted of a quartz
reactor 6 10-13 mm in diameter heated by a demountable electric furnace 4,
a condenser 7, a gas heater 5, a system of Drechsel gas-washers 8, gas-ab-
sorption pipets 11, an U-shaped water manometer 12, and a gasometer 13.
The experiments used a layer of solid particles of reactants 0.5-1 mm in
- 51 -
-------
size, which were charged on a layer of porcelain particles. The height of the
reactants was 100 ram, and the weight of the charges varied from 7.0 to 38 g
with the density of the reactants used. The hydrogen sulfide necessary for
the experiment was obtained from a Kipp generator by reacting hydrochloric
acid with ferrous sulfide, and was pumped by liquefaction at -60°C. into a
specially prepared flask of 100 cnr* capacity, the maximum pressure in which
was 25 atm. To study the activity of various reactants with hydrogen sul-
fide, an artificial gas mixture similar in composition to power-producing
gas (but without carbon monoxide) was specially prepared at a pressure of
100 atm. Hydrogen sulfide was pumped in first from a samll cylinder. The
composition of the gas in the cylinder was as follows (in %): I^S 0.35-0.5;
C02 5.9; H2 18.9, and N2 74.7-74.85.
The solid reactants used were natural ores and minerals: magnetite of
the Sokolovskiy-Sarbay deposit and from Nizhniy Tagil and Vysokaya Mountain,
pyrolusite and manganite from the Nikopol1 Deposit, KMA (Kursk Magnetic
Anomaly) hematite, chromite, sphalerite (preroasted), siderite (light and
gray) of the Bakal'skiy deposit (Urals), limestone and dolomite (roasted and
unroasted), magnesite (roasted), and sphene.
The order in which the experiments were carried out was as follows:
prior to the experiment, the assembly was purged with nitrogen 1, and after
the desired temperature was reached in the layer of reactant, hydrogen sul-
fide containing gaseous mixture 2 was supplied to the reactor at a certain
rate through flowmeter 3.
Past the reactor, the bulk of the gas which has passed through gas meter
9 and jar with alkali 10 is vented into the atmosphere, and the other part
of the gas for determining its hydrogen sulfide content is passed at a cer-
tain rate amounting to 200 cm^/min through Drechsel gas washers 8 filled
with cadmium acetate. The method of determination of hydrogen sulfide with
cadmium acetate is applicable when the hydrogen sulfide content ranges from
20-30 mg/nr to 10-15 g/iir. After the experiments were carried out, the
weighed samples of reactants were cooled in a stream of nitrogen and sub-
jected to chemical analysis to determine the metal sulfide, sulfate, and
total sulfur content. The degree of conversion of hydrogen sulfide was cal-
culated from its amount consumed in the reaction. Two series of investiga-
tions were carried out to study the activity of the solid reactants with
hydrogen sulfide when the latter was present in concentrations of 0.2 and
0.35-0.5%. The composition of the gas is given above. The experiments
were conducted at 700°C., a linear gas velocity of 0.46-0.48 m/sec, and a
contact time of 0.2-0.22 sec.
The experiments utilized limestone and dolomite roasted for 5 hr at
1000°C.; sphalerite was roasted at 900°C. Unroasted dolomite showed the
highest activity in interaction with hydrogen sulfide. After 40 min of re-
action, the degree of conversion of hydrogen sulfide was 98.1%, and after
80 min, it decreased to 94.87% (Table 11). For roasted dolomite, the degree
- 52 -
-------
of conversion of hydrogen sulfide after 40 min was 96.57%, and after 60
min, 87.65%. Such a decrease in the degree of conversion of hydrogen sul-
fide was obviously due to the conditions of preparation of the surface in
the course of roasting of dolomite.
Siderite (light) during the initial period of its reaction with hydro-
gen sulfide in the course of 40 min has a lower degree of conversion that in-
creases from 82.87 to 95%, and then its value remains constant for 90 min.
This may be due, on the one hand, to the thermal decomposition of siderite
during the initial period of the reaction, and on the other hand, to the re-
duction of the iron oxides obtained by the active components of the gas
(hydrogen) to lower oxides, causing the subsequent increase in the degree of
conversion of hydrogen sulfide. Roasted magnesite is reactive during the
first 20 min, when the degree of conversion of hydrogen sulfide is 91.37-
95.45%, and after 60 min decreases to 49.21-51.25%.
Table 11.
i
Reaction of Hydrogen Sulfide (0.2$) with Different Solid Reactants
(v = 0.47 m/sec; r = 0.21 sec).
Hagnesite
(roasted)
/
20
30
40
50
60
//
95,45
87,14
73,52
65,37
49,21
Light siderite
(Bakal, Orals)
/
10
'20
30
70
90
//
82,87
91,37
93,0
96,64
94,73
Dolomite
(roasted)
7
20
40
50
60
70
II
98,33
96,57
87,33
87,65
77,41
Dolomite
(unroasted)
/
20
40
60
80
—
11
98,93
98,08
95,61
94,87
—
Note. 1 - time, min; 2 - degree of conversion of IUS, %,
Figure 12 gives the results of studies of the reactivity of various
natural ores and minerals with hyddbgan sulfide at 700°C. and a hydrogen
sulfide concentration of 0.35-0.5%. The greatest effectiveness relative
to hydrogen sulfide is shown by pyrolusite Ma02> KMA hematite Fe203> mag-
netite of the SokolovskiySarbay deposit Fe^, siderite (gray) FeC03,
and dolomite CaMg(C03)2. For these reactants, the degree of conversion of
hydrogen sulfide is 97-98% during a long period of purification of the gas.
For example, the indicated degree of conversion of hydrogen sulfide for
pyrolusite remains constant for 120 min of the reaction, 141 min for mag-
netite, 90 min for siderite (gray), and 70 min for dolomite (unroasted).
- 53 -
-------
The removal of hydrogen sulfide from the gas by manganite of the Nikopol1
deposit [Mh02JMh(OH)2 J is 96.66-98.8% in the course of 60 min, then a decrease
to 92.6% is observed after 80 min, and a drop to 66.14% in the course of 100
min of reaction. A lower activity with hydrogen sulfide is shown by magnetite
(Nizhniy Tagil), roasted limestone (CaO) and sphalerite (ZnS), followed by
limestone and chromite, which has almost no purifying effect.
In the study of the activity of various solid reactants, the composi-
tion of the gas in the course of removal of hydrogen sulfide was investigat-
ed. As is evident from Table 12, in the reaction of solid reactants with
hydrogen sulfide, a change occurs in the composition of the gas being puri-
fied, in the direction of a decrease in the carbon dioxide content of the
initial gas, and the appearance of carbon monoxide and water vapor is ob-
served in the final gas. Such a change of the composition is due to the
occurrence of the reaction C02 + E^-CO + KLO.
/00
80
fff
20
I
a
L o
20
fff • SO /DO
Time, min.
'20
Fig. 12. Change in the degree of conversion of hydrogen sulfide
with time in reactions with different substances at 700°C., for
a velocity of 0.48 m/sec, and a time of 0.21 sec.
1 - magnetite of Sokolovskiy-Sarbay deposit; 2 - pyrolusite of
Nikopol1 deposit? 5 - gray siderite; k - unroasted dolomite;
5 - light siderite; 6 - manganite of Nikopol1 deposit; 7 - mag-
netite of Nizhniy Tagil deposit; 8 - roasted limestone; 9 -
roasted sphalerite (ZnS); 10 - limestone; 11 - sphene; 12 -
chromite;
It is evident that at 700°C. the reconversion reaction C02 + H2 takes
place on all the solid reactants used.
- 54 -
-------
Thus, analysis of results of the study of the activity of solid re-
actants with hydrogen sulfide showed that the most effective ones at 700°c.
are pyrolusite, hematite, magnetite, siderite, and dolomite. These re-
actants may be used in the technology of hydrogen sulfide removal from
gases at 600-800°C. In order to obtain a definitive evaluation of the use
of these reactants in the removal of hydrogen sulfide from gases, it is
necessary to study the optimum conditions of recovery of sulfur compounds
from combustible gaseous mixtures. In this regard, iron and manganese
ores, which we shall discuss in more detail below, are of definite interest
for the study.
Table 12.
Change of the Gas Composition during the Reaction of
Hydrogen Sulfide (0.55-0.9$) with Solid Reaotants.
Reactant
Magnetite
Sokolovskiy-Sarbay
Nizhniy Tagil
Nikopol1 pyrolusite
KMA hematite
Manganite
Roasted sphalerite
Siderite
gray
light
Limestone
roasted
unroasted
Unroasted dolomite
initial RBS, VBl» #"»
H,S
0,37
0,34
0,35
0,35
0,32
0,44
0,47
0,46
0,46
6,50
0,50
CO,
5,7
5,4
5,4
5,3
5,3
5,9
5,9
5,9
5,9
5,9
5,9
H,
18,9
18,9
18,9
19,7
19,7
17,7
17,7
17,7
17,7
17,6
17,6
N,
75,33
75,33
75,33
74,58
74,61
75,96
75,93
75,94
75,94
76,00
76,00
Time,
min
141
55
60
60
100
25
40
28
22
30
75
' Final-gas, vol. °f>
CO,
4,63
4,60
3,50
2,80
2,60
5,00
3,70
2,40
2,49
2,50
3,90
CO
2,4
2,1
3,0
2,8
3,0
0,4
1,3
3,6
1,3
2,0
3,0
H,
18,28
16,05
16,10
14,65
17,33
15,58
14,90
14,75
9,35
10,00
14,62
N,
74,67
77,22
77,40
79,75
77,07
79,02
80,70
79,25
86,86
85,50
78,48
- 55 -
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REMOVAL OF HYDROGEN SDLFIDE FROM GASES BY MEANS OF CALCIUM OXIDE
Studies of the activity of various solid rea.ctants have established
that the most effective absorbent of hydrogen sulfide at 1000-1100°C. is
calcium oxide. In order to determine the optimum conditions of the reac-
tion between calcium oxide and hydrogen sulfide at high temperatures, it
was necessary to study a large group of problems involved in the practical
realization of the process as a whole.
An experimental study of the process was carried out by using a method
similar to the one described earlier in experiments designed to evaluate
the activity of solid reactants.
A layer of calcium oxide particles from 0.25-0.5 to 2-3 mm in size
was used for the experiments. The height of the active layer ranged from
4 to 95 mm.
In work with different hydrogen sulfide concentrations (0.3-1%) in
the gaseous mixtures, the latter were obtained by premixing the gases
before sending them into the reactor.
The kinetics of the reaction of hydrogen sulfide with calcium oxide
were studied in a neutral nitrogen medium with different concentration of
hydrogen sulfide in the gaseous mixture.
The study established that as the velocity of the blast increases, the
rate of absorption of hydrogen sulfide by calcium oxide increases linearly
(Fig. 13).
15
10
15
10
S
0
ffj 0.8 1,2 f,f 2,0 Zfy
v, m/sec.
Fig. 13. Rate of reaction of HgS
present in different concentrations
with calcium oxide versus velocity
of the blast (time from start of
experiment 30 min, temperature 1000°C.
fraction 1-2 mm).
1 - 0.2#; 2 - 0.#; 3 - 0.$; * - 0.50!
Under the conditions of the experiments,
which were technically limited by the magni-
tude of the possible velocity of the blast
(2.13 m/sec), we were unable to exclude the
influence exerted on the reaction rate by the
diffusion inhibition associated with the flow
of the reacting mixture to the surface of the
solid material. This indicates that the reac-
tion in question can have a much higher rate
if a kinetic regime of the process is provided
for.
For a hydrogen sulfide concentration in
the gases up to 0.5 vol. %, characteristic of
gaseous hydrogen sulfide-containing mixtures
usually subjected to purification, a nearly
100% removal of hydrogen sulfide from the/ gas
is obtained in one hour at a blast velocity
up to 2.2 m/sec (T = 0.04 sec). As the
- 56 -
-------
W, rag/ndn g
Mr
fff
/O
hydrogen sulfide concentration increases
from 0.2 to 0.5%, its conversion rate in-
creases (Fig. 14), This obviously corres-
ponds to a steady diffusion regime of the
reaction of calcium oxide with hydrogen sul-
fide, which is first order with respect to
the concentration. The degree of conversion
of hydrogen sulfide with increasing blast
velocity at different concentrations (0.2-
-0.5%) remains relatively high and at the
given height of the layer amounts to 99-100%
in the course of one hour.
Fig. 14. Rate of the reaction of
f^S with CaO versus HjS concentra-
tion at different velocities of the
blast (time from start of experiment
30 min, temperature 1000°C., fraction
1-2 ran).
The influence of temperature on the rate
of absorption of hydrogen sulfide by calcium
oxide was studied at a linear velocity of the
gas feed of 2.13 m/sec and a hydrogen sulfide
concentration of 0.3%. The temperature was
varied from 500 to 1000°C. The highest de-
gree of conversion of hydrogen sulfide,
99-100%, in the course of one hour was observed at 500 and 700°C. The decrease
of the degree of conversion of l^S during the same period was respectively
equal to 71.2 and 54.8 (Fig. 15).
1 - 0.32 in/sec; 2 - 1.06 m/sec;
3 - 1.6 m/sec; 4 - 2.13 m/sec.
I
8*
g .fff
c
8
10 20 30 W SO fff 70
Time, min.
Fig. 15. Degree of conversion of F^S
versus temperature (blast rate 2.13
m/sec, contact time 0.039 sec).
1 - 5008C.; 2 - 700°C.; 3 - 1000»C.
The value of the activation energy (Fig. 16) was 3300-4500 cal/mole,
which confirms the diffusional character of the process of sulfur removal
under the conditions of the experiments.
Studies of the influence of the height of the calcium oxide layer on
the reaction rate were conducted in a neutral medium of nitrogen at 1100°C.,
a linear gas velocity of 0.021 m/sec, a hydrogen sulfide concentration of
4.5%, and a particle size of 0.25-0.5 mm. The height of the layer was varied
from 4 to 52 mm. Correspondingly, the amount of calcium oxide in the weighed
sample ranged from one-half the stdichiometric amount to a tenfold excess.
- 57 -
-------
It is evident from Fig. 17 that when the height of the layer h = A mm
(T = 0.185 sec), the degree of conversion of hydrogen sulfide, equal to
100%, is observed only during the initial period of the reaction and as
early as 2.92 min from the start of the reaction drops to 80%. For a layer
height h = 35 mm (T = 1.62 sec), a 100% degree of conversion of IkS is pre-
served for 56 min. Thus, under the conditions of the experiments, in order
to ensure a 100% conversion of hydrogen sulfide, a minimum time of contact
between the hydrogen sulfide-containing gases and pure calcium oxide is
required that at v = 0.02 m/sec amounts to 0.2 sec. Other things being
equal, for a shorter time of contact between the gases and the solid reac-
tant (decrease of the height of the layer) and a longer residence time of
the layer of the indicated height of solid material in the reaction zone
(increase of consumption of CaO from the given charge) , a breakthrough of
hydrogen sulfide is observed, i.e. , there is a low degree of conversion of
hydrogen sulfide.
It is of interest to evaluate the excess calcium oxide over the
stoichiometric amount providing for a 100% conversion of hydrogen sulfide
for different heights of the layer. This quantity was calculated from the
formula
A-gi A
where M is the excess calcium oxide over the necessary stoichiometric amount;
A is the weight of the initial charge, mg; g is the stoichiometric amount of
CaO reacting completely per unit time with all of the I^S supplied, mg/min;
t is the residence time of CaO in the reaction zone from the start of the
reaction, min.
The consumption of calcium oxide at differ-
ent times is shown in Table 13. As is evident
from this table, the minimum excess of calcium
oxide is 10-12, when a 100% conversion of hydro-
gen sulfide is maintained, and below this value
a lower degree of conversion and a breakthrough
of hydrogen sulfide are observed. Hence, for
the indicated minimum excess of pure calcium
oxide, the degree of consumption of the solid
reactant will be 10%. In a process where the
calcium oxide excess is greater, the consumption
of the solid reactant will always be higher, since
the hydrogen sulfide breakthrough in the presence
of a calcium oxide excess of less than 10-12 does not
signify the elimination of the remaining amount :of
calcium oxide from the reaction and indicated only
its operation with a lower degree of conversion of
hydrogen sulfide.
log w.
Fig. 16. Logarithm of the rate
of the reaction of HgS with CaO
versus 1000/1.
1-30 min; 2-40 min;
3-50 min.
- 58 -
-------
%,
° mo
§
•rt
01
| 80
§
o
* ^
Of
OI
50 0,185 see AI « 4 mm; 2 — 1» ~
- 0.32 sec, AI •= 7 mm; 3 — x a - 0.46 sec;
Ai = 10 mm; 4 — f» = 0.85 sec, A, - 18 mm;
5 — ts -» 1.62 sec, *s - 35 mm;
- 2,4 secf A« - 52 mm
At the same time, a 100% conversion of hydrogen sulfide is achieved by
a sufficient layer height. This is demonstrated by data obtained in experi-
ments with 100% absorption of hydrogen sulfide and different layer heights,
where the degree of consumption of calcium oxide reached 30-35%, and the
residence of the solid material in the apparatus was 1 hr.
Table 13.
Consumption of Calcium Oxide Relative to the Stoichiometric
Amount for Different Layer Heights (in mm) and Weights (in g).
line,
nan
1
4
5
10
15
20
30
A, = 0.407.
A, = 4
10,40
1,84
1,28
0,14
.4,^0,815,
ft, = 7
21,80
4,67
3,55
1,28
0,52
0,14
A,= 1.635.
A, = 10
44,60
10,40
8,13
3,58
I 2,04
1,28
0,52
4« = 3.26,
ft. = 18
90,10
21,70
17,20
8,10
5,06
3,55
2,03
Xj = 6.0,
A. = 35
166,50
40,80
32,50
15,70
10,15
7,38
4,58
.4. = 10,0.
A. = 52
279,0
68,7
54,8
26,9
17,6
13,0
8,3
Note. Boldface figures denote values of excess calcium below which
the hydrogen sulfide breakthrough is observed.
- 59 -
-------
The dependence of the degree of consumption of CaO on the layer height
is shown below:
Layer height of CaO, mm 35 60
Sample weight, g 6 10
Contact time T, arb. sec 0,35 0,6
Linear gas velocity, in/sec 0,021 0,021
Degree of consumption of CaO, % 36,0 21,6
Thus, experiments conducted with different heights of the calcium
oxide layer demonstrated the feasibility of a complete conversion of hydro-
gen sulfide in the presence of a minimum excess of the pure solid reactant,
equal to 10-12 as compared with the stoichiometric amount.
Studies of the thermodynamics and kinetics of the reaction of calcium
oxide with hydrogen sulfide showed that this process can be carried out in
practice at high temperatures (about 1000°C.). Th& use of such a process is
of major interest for certain branches of industry (chemistry, metallurgy),
and should be applied to the recovery of hydrogen sulfide from complex gaseous
mixtures containing various active gases (lU, CO, (XL, H~0).
Thus it is necessary to analyze the problem of the effect of the composi-
tion of gaseous mixtures on the removal of hydrogen sulfide from them by means
of calcium oxide at high temperatures.
Thermodynamic analysis showed a possible influence of the main reaction
of water vapor and hydrogen on the results, and also a probable occurrence of
the reversible reaction of conversion of carbon monoxide by water vapor. The
presence of water vapor shifts the equilibrium of the reaction CaO + l^S + CaS +
+ H_0 in the opposite direction, i.e., will inhibit the removal of hydrogen
in sulfide from gaseous mixtures. The presence of hydrogen in the gas will
hinder the reaction of thermal decomposition of hydrogen sulfide HoS ^ H9 +
•* £* £•*
+ i/2 82, which is undesirable in the purification of gases, since it is associ-
ated with the evolution of elemental sulfur.
Experiments on the effect of water vapor on the rate of the reaction CaO +
+ H^S were carried out at 1100°C., with the charging of 0.815 g of calcium oxide
having a particle size of 0.25-0.5 mm, and a linear velocity of the steam-gas
mixture of 0.08 and 0.1 m/sec. The concentration of hydrogen sulfide was 0.94
and 1.26%, and that of water vapor, 98.74-99.06%. To compare the results
obtained, the experiments were conducted under the same conditions, but in a
neutral medium of nitrogen. It is evident from Table 14 that the degree of
conversion of hydrogen sulfide in the neutral medium is 100% during a long,
period of time (70 min). At the same time, in a medium of water vapor in /the/'
presence of the same low concentration of hydrogen sulfide, other conditions
being equal, a 100% conversion is observed only during the initial period
(6 min). After 30 min, the conversion of hydrogen sulfide decreases to 30-60%.
- 60 -
-------
Table 14.
Effect of Water Vapor on the reaction CaO + H.S = CaS + H-0
(f = 1100°C; 0.25-0.5 nun fraction).
H,S. %
1,26
1,26
0,94
0,94
1,00
N,, %
—
—
—
99,0
H,0, %
98,74
98,74
99,06
99,06
—
Linear
velocity,
in/see
0,08
0,08
0,10
0,10
0,10
Contact
time T
, sec
0,09
0,09
0,07
0,07
0,08
Reaction
time, min
6,5
17,0
30,0
6,0
16,0
30,0
6,0
19,0
30,0
6,0
17,0
30,0
3,0
Degree of
conversion
of H2S, %
100,0
87,8
60J
100,0
89,0
60,9
100,0
56,0
28,0
100,0
50,0
31,9
100,0*
Degree of
decomposition
of HgO, %
0,016
0,940
1,050
0,097
0,760
0,860
0,098
0,640
0,820
0,027
0,480
0,790
—
*Under these conditions and for a reaction time of 9-70 min, the degree
of conversion of HjS continued to remain equal to 10036.
The series of experiments performed clearly show that the degree of
conversion of hydrogen sulfide in the presence of a large excess of water
vapor (up to 100-300) may decrease substantially, but in practice, the
purification of gases is usually achieved with a much smaller excess of
steam (20-40).
In the experiments, the degree of decomposition of water vapor was low
and amounted to 0.1-1%. Possible secondary reactions taking place with the
formation of calcium sulfate are almost absent here. This is also confirmed
by chemical analysis of the solid residue.
Thermodynamic analysis showed that the thermal decomposition of hydro-
gen sulfide substantially affects the results of the process only at temper-
atures above 1200-1300°C. Up to 1100°C., the thermal decomposition of hydro-
gen sulfide at equilibrium does not exceed 10%.
The reaction of thermal decomposition of hydrogen sulfide is inhibited
even at a relatively low content of hydrogen in the blast. To confirm this
and to follow the effect of hydrogen on the degree of thermal decomposition
of hydrogen sulfide, the experiments were conducted in a hollow quartz reactor
20 mm in diameter at a linear velocity of the nitrogen-hydrogen mixture of
0.53 m/sec, at 1000°C., and with the following composition of the gas supplied
(in %): H2 15.2, N2 84.43, and H2S 0.37. After the gas mixture was passed
- 61 -
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several times through the heated hollow quartz reactor with porcelain pack-
ing of the 2-3 mm fraction and a height of 35 mm, the hydrogen sulfide con-
tent at the exit from the reactor was the same (0.37%) as at the entrance.
This confirms the thermal stability of hydrogen sulfide in the presence of
hydrogen. The presence of hydrogen in the gaseous mixture excludes the
thermal decomposition of hydrogen sulfide with the liberation of elemental
sulfur and permits one to determine the true rate of the reaction between
calcium oxide and hydrogen sulfide.
Experiments showing the effect of carbon dioxide in a gaseous mixture
on the rate of the reaction of hydrogen sulfide with calcium oxide were
carried out in a quartz reactor 18 mm in diameter with a layer height of
35-41 mm, a particle size of 2-3 mm, at 1000°C. , and at a linear gas velocity
of 0.1 m/sec. The hydrogen sulfide concentration was 0.35-0.5%; the content
of carbon dioxide was 8%, and that of nitrogen, 91.6%.
The results of the study showing the effect of the composition of differ-
ent gaseous mixtures on the rate of the reaction studied are presented in
Table 15. The degree of conversion of hydrogen sulfide was high (99.0%) for
1 hr. This demonstrates that the carbon dioxide present in the gas does not
affect the rate of this reaction. In addition, at 1000°C. and in the presence
of carbon dioxide in the gas, no visible reaction was observed between the
latter and calcium oxide, since the indicated temperature was above the disso-
ciation temperature of calcium carbonate. There is no change in the rate of
the direct reaction of hydrogen sulfide with calcium oxide in the presence of
carbon dioxide.
The second series of experiments were conducted in order to determine the
rate of the reaction with calcium oxide using a hydrogen sulfide-containing
mixture of gases close in composition to the power-producing gas obtained from
the gasification of sulfur-containing mazuts. The experiments were conducted
witha 10-g calcium oxide charge, a layer height of 57 mm, and a particle size
of 2-3 mm, at a linear gas velocity of 0.1 m/sec and a temperature of 1000°C.
A gaseous mixture of the following composition was used (in %): HoS 0.36;
CO 9.8; C02 13.8; H2 13.0; CH4 4.4, and N£ 59.0.
It is evident from Table 15 that under the indicated reaction conditions,
there is a change in the composition of the gas undergoing purification in
the direction of a decrease in the content of carbon dioxide and hydrogen and
an increase in the content of carbon monoxide and water vapor. After purifi-
cation, the gas contained (in %): C02 7.07; CO 17.68; EL 10; CH^ 4.80; and
N2 60.45. Such a change in the gas composition is explained by the occur-
rence of the reaction C02 + H2^CO + HO.
It is well known that calcium oxide is a catalyst in the conversion reac-
tion CO 4- H20. At high temperatures, the reconversion reaction C02 + H takes
place, which is observed under the conditions of the experiments performed.
- 62 -
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Table 15.
Reaction of Hydrogen Sulfide with Calcium Oxide versus Composition of Gaseous
Mixtures (t = 1000'C.; v = 0.11 m/sec; T = 0.57 sec).
Has,
vol. %
0,35
0,36
0,45
0,42
gra&P
gas
CompCH
nent
CO-
No
CO*
CO
H2
C«4
N2
COZ
CO
Hz
CH,
Nz
C02
H2
CH4
N2
Vol.
;P
8,00
91,65
13,80
9,80
13,00
4,40
59,00
6,50
16,45
9,60
4,30
63,10
9,20
13,10
4,30
73,40
Reaction
time,
min
10,00
17,00
26,30
25,00
59,00
5,50
11,50
20,00
38,00
57,83
7,00
14,83
23,00
40,50
62,00
7,00
15,00
20,50
40,30
57,50
Degree
of con-
version
of HaS,
7>
99,63
99,59
99,61
99,63
99,54
97,70
97,60
97,80
97,80
97,50
98,50
98,20
97,50
97,80
97,60
97,50
97,20
96,80
96,70
96,70
Sulfur
residue
ng/m3
19,0
21,0
19,8
18,5
23,4
121,0
126,0
116,0
117,0
134,0
102,5
130,5
173,5
145,5
162,0
163,0
181,0
193,5
203,0
210,0
Composition of final gas, %•
CO,
7,00
8,00
8,00
S,oo
8,00
5,97
6,57
7,07
6,37
6,43
6,55
6,60
6,90
7,10
7,50
4,10
4,10
3,90
6,72
4,50
H,
_
—
—
—
—
7,98
8,38
10,00
9,42
9.28
9,60
8,10
10,90
11,10
10,70
8,70
8,30
10,30
8,38
8,57
CO
_
—
—
—
—
13,98
17,00
17,68
16,63
17,53
16,45
18,50
18,30
18,50
18,20
5,45
5,90
6,40
5,80
6,00
CHi
—
—
—
—
3,42
5,15
4,80
4,68
4,93
4,30
6,60
5,30
4,80
5,10
3,30
4,30
4,00
3,40
3,79
N.
93,00
92,00
92,00
92,00
92,00
68,65
62,90
60,45
62,80
61,83
63,10
60,20
58,60
58,50
58,50
78,45
77,50
75,40
75,70
77,10
To confirm this fact, experiments were carried out with all other condi-
tions being the same, but in the absence of «rbo» «n«ide > .^V'cH
mixture of the following composition (%): H2S 0.42; CO,, 9.2, H2 1J.1, Ui^
L 1 and No 73 4. It is shown that in this case the escaping gas contains up
to 5.6-5.9! of carbon monoxide which obviously resulted from the reconversxon
reaction CC
A change in the composition of the gas obtained in the direction of a de
f r-t! ==•=£ tt r^S e^or
va!ue of the combustible components ^ and GO is approximately the same.
When an inert gaseous medium is used (see Table 15), the degree of conver
sion S hydrogen sulfide of complex gaseous mixtures by calcium oxide remaxns
Mgh (97%) for a long period of time (in experiments longer than 1 hr) .
- 63 -
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Such a high degree of conversion of hydrogen sulfide, obtained in the ex-
periments, indicates a high activity of calcium oxide toward hydrogen sul-
fide in different gaseous media. The presence of hydrogen lowers the rate
of thermal decomposition of hydrogen sulfide and demonstrates a high actual
rate of the main process.
As a result of the development of a method of high-temperature removal
of hydrogen sulfide from gaseous mixtures by means of calcium oxide, it be-
came necessary to determine the conditions of repeated use of solid reactants
in order to determine the possibility of utilizing the recovered sulfur and
reducing the consumption of the reactant.
The main objectives were to determine the optimum characteristics of
calcium sulfide roasting in an oxygen atmosphere and to evaluate the changes
in the indices of the reaction of hydrogen sulfide with calcium oxide ob-
tained after the roasting. It is known that roasting of metal sulfides has
been widely applied in metallurgy [22]. A large number of studies have been
published in the technical literature dealing with the theory and practice
of oxidizing roasting of sulfide ores and concentrates of nonferrous metals
such as lead, copper, nickel, zinc, and others. The problems involved in
the roasting of calcium sulfide have not been studied thus far, obviously be-
cause of a lack of its natural sources.
Thermodynamic analysis established that in the roasting of calcium sul-
fide in atmospheric oxygen medium at temperatures above 1200°C., the process
takes place with the predominant formation of CaO and SC>2. Under these con-
ditions, the formation of CaSO^. and SOg is improbable, and the amount of
elemental sulfur will be minimal because of the presence of excess air.
First of all, it is necessary to determine the optimum roasting tempera-
ture at which the sulfur will be driven out of the solid residue completely,
and to establish the conditions of possible sintering of calcium sulfide, due
to the exothermic character of the roasting process.
Further, it is necessary to establish the optimum consumption of air in
order to obtain the maximum content of sulfur dioxide in the escaping gases
that is necessary for the production of sulfur or sulfuric acid.
The reaction of calcium sulfide roasting in an atmospheric oxygen medium
was studied on the assembly shown in Fig. 11. The solid reactant used was
calcium sulfide that met the RU1061-54 Provisional Technical Specifications
of the Ministry of the Chemical Industry. The sulfur content of the calcium
sulfide ranged from 18 to 25%. Calcium sulfide was first pressed into pellets
with a hydraulic press, then the pellets were ground down to the desired size
and sifted into fractions. Particles 1-2 mm in size were used in the experi-
ments, and the layer height was 50-70 mm.
- 64 -
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As a result of oxidation of calcium sulfide with atmospheric oxygen, sul-
fur dioxide passed into the gaseous phase; the dioxide was caught in Drechsel
gas washers filled with a titrated iodine solution. Preliminary experiments
established that no sulfur trioxide was formed in the gaseous phase.
After the experiment, the weighed sample was cooled in a stream of nitro-
gen down to room temperature and subjected to chemical analysis to determine
calcium sulfide and sulfate and total sulfur in the solid phase.
The reaction of oxidation of calcium sulfide by atmospheric oxygen is
exothermic:
CaS + 1,5 02 = CaO + SO* + 118,5 kcal.
The temperature and air flow rate are determining and interrelated
factors in this reaction.
On the basis of the conditions of high-temperature hydrogen sulfide re-
moval from the gas by calcium oxide and the subsequent repeated use of the
latter, it is desirable to set up the process in such a way as to provide
for a uniform roasting of calcium sulfide in the atmospheric oxygen medium
without sintering, but with a certain hardening of the outer surface of the
fragments.
Studies on the effects of temperature on
the degree of roasting of calcium sulfide in an
oxygen atmosphere were conducted at a linear air
velocity of 0.32 m/sec for a contact time of
0.19 sec (Fig. 18). The starting temperature
of the heating of calcium sulfide ranged from
510 to 900°C.
The most characteristic feature is the
fact that as soon as a given temperature is
reached in the layer and air is supplied,
the temperature rises noticeably and instan-
taneously because of the exothermic nature
of the process, and this causes an increase
in the reaction rate during the first few
minutes of the reaction with subsequent ex-
pulsion of the bulk of the sulfur by roast-
ing. At tin = 510°C., because of the exo-
thermic nature of the reaction, the maximum
temperature in the layer is 1120°C., for
to zo
. lime, mim
Fig. 18. Change in the degree of ex-
pulsion of sulfur by roasting, with
time for various initial temperatures
of the layer.
/ — 5IO«C; 2-600'C; 3 — TOO-KXPC;
<-900«C
t.n=600°C.,
= 800-900°C., t
1180°C., and for tln
= 1400°C. As a result
max
- 65 -
-------
w
Time, min.
A
Fig. 19. Change in the degree
of expulsion of sulfur by
roasting, with time at various
gas velocities.
of unsteady conditions, a nonuniform expulsion of
sulfur takes place.
During the first 3-3.5 min for tin = 510°C.,
the roasting reaches 27-34.4%, and 1.2-4.5% of
sulfur dioxide is evolved into the gaseous phase
(see Fig. 18). The rate subsequently decreases
sharply, and after 30 min the degree of expulsion
amounts to only 35.6%. At t^ = 600-800°C., the
roasting process proceeds much more vigorously;
in 2.5 min, the degree of sulfur expulsion is al-
ready 50-56%. The amount of sulfur dioxide in the
gas reaches 10-15%. Then the rate of the entire
process slows down sharply. At t£n = 900°C., the
maximum temperature rises to 1450-1500°C. , and in
4 min the roasting proceeds to the extent of 79-
80%. In the escaping gas, the sulfur dioxide con-
centration is 13-15%. During the period of the
highest reaction rate, at an excess air coeffi-
; -To, -0.32 m/sec; TI~ o.i9 sec? 2-i>,-cient = 1> the highest sulfur dioxide concentra-
-o,52m/seo, t, - 0,109 sec; J-t-j-tion is observed in the gaseous phase, equal to
-i.06m/sec,T,= 0.056 sec. 15%> and at _, 1>2-1.5, the sulfur dioxide concen-
tration decreases to 10-12.3%. After the expulsion of the bulk of the sulfur
from the solid reactant, the value of the excess air over the stoichiometric
amount increases to 7-10, and the rate of roasting still remains insignifi-
cant. The low reaction rate at the end of the roasting is due to the transi-
tion into the regime of the internal diffusion region.
In a practical realization of the process of roasting of calcium sulfide
in an atmospheric oxygen medium, it is evident that at a slow reaction rate
the amount of air supplied should be decreased.
Studies made on the roasting of calcium sulfide in atmospheric oxygen
show that a vigorous roasting takes place at 1200-1400°C. , which corresponds
to an initial layer temperature of 850-900°C.
The choice of temperature for setting up a steady roasting process for
the purpose of high-temperature removal of hydrogen sulfide from the gas
may be made by considering the entire set of conditions - flow rate of air
and amount of sulfur to be roasted.
In order to study this phenomenon, the experiments were conducted by
using linear air velocities Vi = 0.32 m/sec,
0.52 m/sec, and v,
1.06 m/sec at an initial layer temperature of 900°C. As the air blast ve-
locity increases from 0.32 to 1.06 m/sec and the contact time decreases
from 0.19 to 0.056 sec, the degree of roasting increases, indicating that
the roasting rate is determined by external diffusional factors involved in
- 66 -
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/ /
Pig. 20. Diagram of assembly for high-temperature removal of hydrogen sulfide from gas under pressure.
-------
the migration of the oxidant to the surface of calcium sulfide (Fig. 19).
The increase in the blast rate affects most noticeably the degree of
roasting during the first 1-2 min of the reaction. During this period, the
degree of roasting of calcium sulfide at a blast velocity of 0.32 m/sec is
56%, whereas at 0.52 m/sec it reaches 86%, and at 1.06 m/sec, 95-97%. This
increase in the degree of roasting of calcium sulfide is due to an increase
in the rate of supply of the oxidant to the surface of the reactant and also
to the temperature elevation, resulting from the exothermic character of the
reaction, which determines the rate of expulsion of sulfur. The maximum
temperature in the layer at a blast velocity of 0.32 m/sec is 1160°C.; at
0.52 m/sec it increases to 1200-1300°C., and at 1.06 m/sec, it reaches
1600°C.
The effect of such high temperatures during roasting of calcium sul-
fide in an atmospheric oxygen medium did not cause any appreciable sintering
of the particles; only a certain fusion of the surface was observed, appar-
ently due to the short duration of this action.
During the period of maximum roasting
rate, a considerable amount of sulfur dioxide
is evolved. The sulfur dioxide concentration
in the gaseous phase is 12-15%, which corre-
sponds to an excess air coefficient of 1.2-
1.3. The sulfur dioxide concentration obtain-
ed is sufficient for use in the production of
sulfuric acid.
The roasted calcium oxide can be recycled
into the process of hydrogen sulfide removal
from the gas for multiple use. Thus, the above
experiments on the roasting of calcium sulfide
showed that a degree of roasting of 95-97% may
be achieved at 1200-1400°C. and an excess air
coefficient equal to 1-1.2. The concentration
of the sulfur dioxide formed in the gas reaches
9-15%.
Gas exit.
Fig. 21. Diagram of high-temperature
reactor for operation under pressure.
1 - inner furnace; 2 - outer furnace;
3 - electric, heating.
In order to make a definitive determina-
tion of the conditions of the roasting process
in the removal of hydrogen sulfide from power-
producing gas, it was necessary also to study
the repeated use of the solid reactant follow-
ed by its regeneration, taking into account
the characteristics of the process.
Considering that when a high-temperature
removal of IS from gas is used at thermal
- 68 -
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electric power plants, a pressure of 8 and 20 gauge atmospheres is specified
for the process, it becomes necessary to use the calcium oxide repeatedly in
the course of sulfur removal from the gases under pressure. The study of the
high-temperature removal of hydrogen sulfide from the gas by roasted limestone
under pressure, followed by regeneration of calcium sulfide by air, was con-
ducted by using the assembly shown in Fig. 20.
The assembly consists of gas heater 5, steam superheater 6, reactor ?,
and condenser 8.
Preliminary experiments established that a substantial loss of hydrogen
sulfide from the gas is observed in the hollow reactor, because of metal cor-
rosion. A reactor of special design was constructed for this purpose (Fig. 21),
An alloy spiral 2 was wound on a porcelain tube 17.5 mm in diameter and
1 m long and was placed in a stainless steel jacket with an inner diameter
of 50 mm and outer diameter of 60 mm. Between the porcelain tube and the
steel jacket was packed a layer of grog brick charge with a particle size
of 0.5-0.6 mm, and at the exit from the tubes the ring-shaped charge was
coated with kaolin.
The contacts were brought out by using insulation material teflon (poly-
tetrafluoroethylene), which withstands temperatures up to 350°G. and is cooled
with water.
On the outside, the reactor was heated with a demountable electric fur-
nace. The solid reactant used was calcium oxide obtained by roasting natural
limestone for 5-9 hr at 11000C. The chemical composition of limestone (%) is
given below:
SiOj
A1S09
FeA
CaO
Total . . 99,36
The hydrogen sulfide-containing gaseous mixture was specially prepared
under a pressure of 100-110 g atm. The height of the active layer ranged
from 80 mm to 610 mm. The temperature was measured along the height of the
layer at four points at the center of the layer, and in the upper and lower
parts, the thermocouple entered to a depth of 10-15 mm. The fourth ther-
mocouple measured the temperature of the entering gas from above.
Prior to the experiment, the entire system was purged with nitrogen 1
(see Fig. 20). After the desired temperature was reached in the layer, a
. 1,92
. 0,67
. 0,58-
. 52,6
MgO
SOS
Calcination
loss
... 1,04
. . . 0,11
. . . 42,42
- 69 -
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gaseous mixture 2 was supplied from a cylinder with a hydrogen sulfide concen-
tration of 0.2-0.8% through a DT-150 differential manometer 3, buffer 4, heater
5, and into reactor 7, where the necessary pressure was produced. On leaving
the reactor, the gas was cooled in condenser 8, passed through a gas meter,
gas absorption pipets, and vented into the atmosphere. Another part of the
gas was passed at a certain velocity (200 cnr/min) through Drechsel gas wash-
ers filled with cadmium acetate to determine the hydrogen sulfide concentra-
tion. In work with water vapor, a certain amount of water is supplied from
buret 13 by means of pump 12 into steam superheater 6 and enters together
with the gas into steam heater 5. In the calibration of the boiler, the steam
condenses in condenser 14 and is collected in receiver 9. The bulk of the gas
then passes through gas meter 10 and is vented into the atmosphere, and the
other part is taken up by the gas absorption pipets 11.
•*.
s ffff
§
o
S
1
$ffff
Time, min.
too
Fig. 22. Change 5n the degree of conversion of hydrogen sulfide with
tine in the reaction of CaO and H-^S at different pressures.
1, 2 - pressure respectively 1 abs atm and 20 g atm; v^ 4 m/sec;
Tj = 0.052 sec; 3,4 - respectively 1 abs atm and 20 g atm; V2 = 2.5
m/sec; T^ = 0.13 sec; 5, 6, 7 - respectively 1 abs atm, 8 and 20 g
atm; v, = 2.2 m/sec; T, = 0.22 sec.
The calcium sulfide formed is regenerated by air in the following manner.
The assembly is purged with nitrogen, then the heating is turned on. Simul-
taneously, Drechsel gas washers filled with cadmium acetate for absorption of
the hydrogen sulfide evolved are removed, and the consumption of gas since
the start of heating to a given temperature of the experiment is recorded.
Air is then supplied to the layer at a certain velocity. The concentration
of sulfur dioxide in the escaping gas is determined by passing the latter
through Drechsel gas washers filled with a titrated iodine solution. After
the experiments have been carried out, the charge is cooled in a stream of
nitrogen and subjected to chemical analysis to determine the total sulfur
and the sulfide and sulfite sulfur.
- 70 -
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Initially, it was necessary to observe the effect of pressure on the de-
gree of removal of hydrogen sulfide from the gas at 1000°C. The study of
gas purification with roasted limestone was conducted at a pressure of 1 abs
atm and 8 and 20 g atm. The weight of the charge was 110-115 g, the particle
size, 1-2 mm, and the linear velocity, 2.2, 2.5, and 4 m/sec. The gas com-
position was as follows (in %): H2S 0.53; C02 11.02; H2 18.10; N2 70.35. It
is evident from Fig. 22 that as the pressure increased from 1 abs atm to 20 g
atm at a linear velocity of 2.2 m/sec and T = 0.22 sec, the degree of conver-
sion of hydrogen sulfide increased. At a pressure of 1 abs atm, after 36 min,
it was 93.34%, and toward the end of the cycle, after 63 min, it decreased to
86.76%. At a pressure of 8 g atm during the first 15 min it was 96%, and
after 76 min it decreased to only 92.5%. The highest degree of conversion
of hydrogen sulfide (96.4%) occurred at a pressure of 20 g atm during a long
purification period lasting 93 min.
An increase in the linear velocities of the hydrogen sulfide mixture
supplied and hence a decrease in the contact time leads to a reduction in the
degree of conversion of hydrogen sulfide at pressures of 1 abs atm and 20 g
atm. As the pressure increases, the degree of consumption of the reactant
rises from 17 to 34%.
The experiments performed showed that hydrogen sulfide can be removed
from power-plant gas at pressures of 8 and 20 g atm and at a linear gas ve-
locity of 2.2 m/sec with T =0.22 sec (without considering the pressure and
temperature), with a sufficiently high degree of purification amounting to
93-96% in the course of 1-1.5 hr.
Experiments at pressures up to 20 g atm also established a slight in-
fluence of the water vapor content on the removal of hydrogen sulfide from
moist gas (12-15%). Results of experiments with moist hydrogen sulfide-
containing gas are given in Table 16. The degree of consumption of the solid
reactant was 36.5%.
Table 16.
Removal of Hydrogen Salfj.de from Moist (12$) Power-Plant Gas
(w = 4,25 m/secs T = 0,052 sec).
, H,S = 0,51%
Time, min •
6,00
9,16
11,33
16,16
20,50
25,00
30,00
Degree of
conversion
of HgS, %
100,00
67,84
74,96
58,43
46,33
43,43
43,96
BfCess
CaO.
34,50
9,73
6,00
4,64
3,45
2,77
2,19
H,S = 0,46%
Time, min
3,50
4,66
7,75
12,33'
17,83
22,83
27,00
Degree of
conversion
of Has, .#
100,00
93,75
84,64
73,52
65,38
60,84
49,64
Excess
CaO.
14,10
10,50
6,36
4,02
2,74
2,07
1,75
- 71 -
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Repeated use of calcium oxide in the course of high-temperature removal of
hydrogen sulfide from the gas consisted in the alternate interaction of hydro-
gen sulfide-containing gas with calcium oxide followed by regeneration with
atmospheric oxygen of the calcium sulfide formed.
The determining characteristics of the multiple reuse of calcium oxide
were first determined.
The studies showed that the degree of conversion of hydrogen sulfide
decreases after a triple absorption, due to a change in the initial condi-
tions of the reaction, namely, a decrease in the weight and height of the
change and hence in the contact time.
In order to preserve the initial conditions of the reaction, the charge
used in several experiments was combined for subsequent cycles of multiple
absorption and regeneration. It should be pointed out that during the roast-
ing of calcium sulfide in atmospheric oxygen, as a result of the exothermic
character of the reaction, the temperature in the layer rose to 1600°C. and
higher, causing sintering of the whole charge. In order to keep the charge
from sintering, the initial temperature of the layer should be properly con-
trolled. Under the conditions of the experiments, the initial heating tem-
perature did not exceed 950°C.
The main series of experiments on the repeated use of calcium oxide
(roasted limestone) in the course of high temperature removal of hydrogen
sulfide from a gas (Table 17) were carried out under the following condi-
tions:
h, mm A, g v, m/sec ^.seo \ H»S, %
Absorption _•
1st • • b10 115,0 2,2 0,3 0,40
2nd • . 450 115,3 2,2 0,214 0,G9
3rd • • 450 115;0 2,2 0,214 0,50
4th • • 610 168,0 2,0 0,3 0,54
5th . / 4CO- 146,0 . 2,0 0,2 0,61
6th • • SCO 109,75 2,21 0,23 0,615
The temperature of removal of hydrogen sulfide from the gas was 1000-
1100°C., and the pressure was 8 g etm. The process of gas purification in-
volved the use of a hydrogen sulfide-containing gaseous mixture of the fol-
lowing composition (in %): H2S 0.4-0.6; C02 7.6; 1^ 22.69; N2 70.11.
The calcium sulfide formed was regenerated with atmospheric oxygen at
a linear velocity of 0.7-0.8 m/sec with a contact time of 0.6-0.8 sec at
atmospheric pressure.
- 72 -
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Table 17.
Repeated use of Roastfd Limestone (l-2 mm Fraction) During Hydrogen Sulfide
Removal from Gas under Pressure.
Absorption of HgS
- 1
/
0,5/100,0
10,0/93,3
20,0/93,3
30,0/07,9
40,0/93,0
43,5/93,0
53,0/90,64
9S,5/9S,01
'05,5/85,2?
2
10,0/97,14
20,5/97,0
30,0/97,0
40,0/95.3
50,0/95,0
53,0/76,8
—
3
5,0/93,0
10,0/07,0
15,0/97,0
21,0/96,0
35,0/96,0
50,0/95,0
60,0/95,0
4
5,21/97,0
15,0/96,3
25,0/96,2
34,0/95,8
50,0/95,0
62,0/95,6
5
5,25/99,0
11,33/93,0
18,0/93,0
25,00/97,2
31,50/97,3
51,50/96,3
6
5,0/100-
15/99,3
25/99,2
35,0/93,7
46,0/97,8
00,0/07,3
71,0/95,3
81,0/91,0
90,0/83,3
Note. Numerator - time (min); denominator - degree of conversion of
The air was supplied to a layer heated to an initial temperature of 900°C.,
and subsequently, because of the exothermic character of the reaction, the tem-
perature rose to 1400-1500°C. The roasting of calcium sulfide in atmospheric
oxygen was carried out with a large excess of oxygen, since the purpose was
to obtain the maximum possible removal of sulfur from calcium sulfide in
order to preserve the activity of the latter in the cycle of absorption of
hydrogen sulfide from the gas. The linear velocity of the air was 0.7 m/sec,
and the contact time, 0.7 sec.
It is evident from Table 17 that after calcium oxide was used 6 times,
its activity was preserved. The degree of removal of hydrogen sulfide from
the gas was 98% in the first cycle during 100 min, and in the subsequent
cycles, 95-96% in the course of 60 min. The degree of consumption of cal-
cium oxide in the first cycles was 28-37%, then decreased to 23%. As far
as the composition of the gas being purified is concerned, as was shown
earlier in the case of calcium oxide used as the catalyst, at 1000-1100°C.
a change occurs in the direction of a decrease in the content of carbon
dioxide and hydrogen and increase of carbon monoxide and water vapor. When
calcium oxide is used repeatedly, a similar pattern of change in the gas com-
position is observed during the entire period of the reaction (Table 18).
The process of roasting .of calcium sulfide in an atmospheric oxygen medium
was carried out for a long time, i. e., lasted 3.5-4 hr. Analysis of the
solid residue showed the sulfide sulfur content to be 0.11-0.86%. The de-
gree of roasting reached 95-98%.
- 73 -
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Table 18.
Change in the Composition of Power-Plant Gas after the Removal of Hydrogen
Sulfide with Calciam Oxide (Roasted Limestone).
Exper-
iment
No.
1
2
3
4
5
6
7
S
9
Initial gas, vol. °h
H»S
0,32
0,45
0,53
0,40
0,40
0,69
0,50
0,5i
0,01
CO,
6,00
5,40
11,02
7,60
7,00
4,00
7, CO
7, GO
7, CO
H,
22,79
20,13
18,10
18,90
18, Si
18,30
22,09
22,69
22,09
Mi
70,89
71,02
.70,35
73,10
73,16
77,01
09,21
69,17
69,10
Final gas, vol. %.
CO,
4
9
2,15
2,00
3,90
!,!'3
2,,0
0,70
-i,30
l.CO
2,70.
CO
4,40
6,50
8,03
0,21
5,70
3,20
-i,90
6,20
. 5,00
H,
19,79
13,57
11,05
13,00
13,70
15,52
15,80
16,90 -
16,00
t
N,
73,06
77,93
76,46
78,12
77,90
80,53
76,00
7i,GO
76, cO
During the initial periods of roasting, when the solid residue contains
a substantial amount of sulfur, 6-8% S02 passes into the gaseous phase even
in the presence of a large excess of air. During roasting of calcium sulfide
in an oxygen atmosphere, a cercain fusion of the surface of the reactant is
observed, causing an increase in the mechanical strength of the fragments.
Whereas in the first two cycles of absorption and regeneration after the
dispersal of the charge up to 5% dust is present, this dust is absent from
the following cycles, but 0.5-1 and 0.25-0.5 mm fractions appear that are
preserved until the end of the 5th-6th use. In addition, the specific
gravity of calcium oxide increased after its use in several cycles.
Thus, the above studies of repeated use of calcium oxide in the re-
moval of hydrogen sulfide from power plant gas at a pressure from 1 abs
atm to 20 g atm show its activity to be high after the 6th cycle. At a
linear velocity of the gas being purified of 2.5 m/see and a contact time
of 0.25-0.3 sec, the degree of purification in the first cycles reaches
97-98% during 1.5-2 hr, and decreases to 95-98% in the following ones. The
degree of consumption of calcium oxide is 28.37% and subsequently decreases
to 25%.
REMOVAL OF HYDROGEN SULFIDE FROM GASES BY IRON OXIDES
The study of the activity of various solid reactants at 700°C. showed
that iron oxides and in particular, natural iron ores are effective absorb-
ers of hydrogen sulfide from gaseous mixtures. Of greatest interest for
practical applications are hematite, magnetite, and siderite.
- 74 -
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The reaction of iron oxides with hydrogen sulfide in a reducing medium
is a complex process. In addition to direct reactions between iron oxides
and hydrogen sulfide, it also involves crystallochemical transformations from
higher oxides to lower ones and iron, associated with the reduction of the
gas by active components - hydrogen and carbon monoxide. The overall process
of hydrogen sulfide removal from gases will be determined by the entire set
of physicochemical conditions.
The object of study used was KMA hematite. The first group of experi-
ments were conducted at various blast velocities and at 500°C. The particle
size was 0.5-1.0 mm, and the height of the active layer, 50 mm. The gas
being purified had the following composition (in vol. %): H2S 0.34-0.37;
C02 5.52; H, 20, and N2 74.11-74.14. The linear velocity of the gas sup-
plied ranged from 0.484 to 4.18 m/sec. The studies were conducted by using
the assembly illustrated in Fig. 11.
The experiments showed that at linear velocities above 3.45 m/sec, the
rate of absorption of hydrogen sulfide by hematite was no longer dependent
on the feed velocity of the gas being purified, i. e., the extrakinetic re-
gion of the reaction is reached under these conditions (Fig. 23). The in-
dicated characteristic of the reaction rate was taken for a time of 5-7 min
from the start of the experiment, at which the initial reaction conditions
underwent little change. As the process proceeded further and the initial
conditions changed, there was also a change in the rate of the reaction be-
tween hydrogen sulfide and hematite (Table 19).
W x 1CT , g/min g
7
Fig. 25. Rate of the reaction of hydrogen sulfide with
hematite versus gas feed rate at 500°C. (0.5-1 mo frac-
tion) .
1 - minj 2-7 min.
i 2 3 « S
v, n/secr
\
As the blast velocity increases, the degree of conversion of hydrogen
sulfide decreases. At blast velocities of 0.48 and 1.36 m/sec, it amounts
to 93-96% during 15 min of reaction. At a blast velocity up to 2.18 m/sec,
the degree of conversion of hydrogen sulfide is 93.84% in the course of 5
min, and after 20 min it decreases to 26%.
A further increase in blast velocity to 3.44 m/s.ec leads to a decrease
in the degree of conversion of hydrogen sulfide to 77-92% during 4 min and
to 16-18.5% during 15 min. At a maximum gas feed velocity of 4.18 m/sec,
during 4 min, the degree of conversion of hydrogen sulfide is 87.7%, and
- 75 -
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during 15 m.'.a, 22.14%. The decrease in the degree of conversion of hydrogen
sulfide with increasing velocity of the gas being purified is due to a de-
crease in the time of contact of the gas with particles of the solid reac-
tant.
A study of the effect of temperature on the rate of reaction of hydrogen
sulfide with KMA hematite was conducted under conditions similar to those of
the extrakinetic region at a linear gas velocity of 3.44 m/sec with particles
0.5-1.0 mm in size. The temperature of the process was 350, 400, 450, and
500°C.
As the temperature rose from 350 to 500°C., the degree of conversion of
hydrogen sulfide increased (Fig. 24). At 350°C. it was 41.49% during 2 min
of reaction, and during 15 min dropped to 5.45%. At 400°C. it was 48.72%
during 3 min and decreased to 16.53% during 15 min.
TablH 19.
Effect of Gas Blast Velocity on the Reaction of Hydrogen sulfide with KMA
Hematite (t WC.; flS, = 0.35$; 0.5-1.0 nun Fraction).
Tine, min
Conversion of
H2S, %
t>i = 4,18 m/sec Ti = 0,012 sec.
3-5
5-9
9—15
66,16
31,14
22,14
ff« = 3,46 ai/sec T2 = 0,0145 sec.
0-4
4—7
7-11
11-15
•92,50
57,23
23,60
15,65
V3 = 2,99 ""/sec Tg — 0,0167 sec.
0—5
5—7
7—10
10—15
84,82
51,66
43,48
18,51
»s = 1 ,36 n/sac TS = 0,037 seo .
0-5
5-10
10-15
96,92
95,90
95,80
Tine, min
Conversion of
H^, %
Oi = 4,02 m/sec ti = 0,013 sec.
0—4
4—7
7-10
10—13
87,75
57,68
37,46
28,14
»* = 3,41 m/sec ** = 0,0146 sec.
0-4
4—7
7—10
10—15
75,83
54,05
25,66
18,51
o« = 2,18 m/sec T4 = 0,023 sec.
0-5
5-10
10—15
15—20
93,84
68,68
39,45
26,33
Vt = 0,484 m/sec T6 = 0,103 sec.
0—3
3-6
6—10
10—15
91,98
91,45
93,06
93,36
- 76 -
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A temperature rise to 450°C. caused a certain increase in the degree of
conversion of hydrogen sulfide; during 3 min it was 59-67.65%, then decreased
to 21%. The highest value (89-93.14%) was reached by the conversion of hy-
drogen sulfide at 500°C. in the course of 3 min of reaction, and during 15
min this value decreased to 25%.
Such a decrease in the conversion of hydrogen sulfide with falling
temperature is due to a decrease in the reaction rate under these conditions
(Figs. 25 and 26). The values of the reaction rate were calculated by re-
ducing to unity the weights of the actually reacting charge of Fe3C>4 during
certain periods of time during 3, 10 and 15 min, and were referred to the
average active concentration of hydrogen sulfide at the given time.
The values obtained for the hydrogen sulfide absorption rate at differ-
ent times (from the start of the reaction) and at different temperatures are
shown in Table 20. The logarithm of the rate of hydrogen sulfide absorption
versus the reciprocal absolute temperature is shown in Fig. 27.
so
u
20
lime, min.
t5
Fig. 24. Effect of temperature on
the degree of conversion of hydrogen
sulfide in its reaction with hematite
(b -3,45 m/sec, T =0.015 sec,
0.5-1 mm fraction).
/ — 3SO'C; 2-400°C; 3 — 450*0; 4-500' C
W x 10-3, g/min g.
Pig. 25. Effect of temperature on the
rate of the reaction of hydrogen sul-
fide with hematite.
/ — 3,45 m/sec;* — 0,68 m/sec
The value of the apparent activation energy determined from Fig. 27 for
3, 10 and 15 min, i. e., for the entire period of the reaction, remained al-
most unchanged and equal to 8330 cal/mole.
In order to determine the conditions of purification of gases with a high
degree of recovery of hydrogen sulfide and during a long period of time, experi-
ments were carried out at elevated temperatures and with a longer contact time.
The experiments were carried out at 500, 700 and 800°C. The velocity of the
gas supplied was 0.69 m/sec, the contact time 0.15 sec, and the particle size
- 77 -
-------
0.5-1.0 mm. The composition of the gas used was as follows (in %): H2S
0.34, C02 5.83; H2 19.29, and K2 74.54. From Table 21 it is evident that
a high degree of conversion of hydrogen sulfide was obtained in the experi-
ments at all the temperatures studied,
At 500°C., during the entire period of the reaction (50 min), the gas
purification is 96.64-97.65%. A temperature rise to 700-800°C. leads to a
certain decrease in the degree of purification to 94-95% in 20 min, and
during 60 min it rises to 96-97%. It is obvious that at these temperatures,
the reactions of reduction of iron oxides by hydrogen are predominant dur-
ing the initial period of the process, and thereafter the iron oxides be-
come more reactive with respect to the main process of recovery of hydrogen
sulfide from the gases.
a
8
S /O
Time, min.
fS
Fig. 26. .Change in the rate of
the reaction or hydrogen salf me
with hematite in time at differ-_
ent,temperatures^ _ »°—
3,45 m/sec, T = 0,015 sec, 0.5-1
/ —350*C; 2 —400°C; 3 — 450" C; 4 — 500° C
/./ 1.3 1,3
-V
log '
*
Fig. 27. Logarithm of the rate of
the reaction of hydrogen sulfide
«ith hematite versiis.recipritfaL ab-
solute temperature (» = 3,45m7sec,
T =0,015 sec, ' 0.5—1 m
fraction
1-3 min; 2-10 min; 3-15 min.
This is confirmed by the results of analyses of the change of the gas com-
position with time in the course of purification at different temperatures.
It is evident from Table 22 that the gas composition changes in the direc-
tion of a decrease of carbon dioxide and formation of carbon monoxide and water
vapor. Moreover, considering that carbon monoxide was absent from the initial
gas, such a change in the gas composition may be explained by the occurrence
of reactions in which iron oxides are reduced with hydrogen, and also by the
- 78 -
-------
development of the reaction between carbon dioxide and hydrogen, C02 +
CO + t^O. As the temperature rises, the amount of carbon monoxide in the gas
increases. It is of interest to evaluate the degree of consumption of hydrogen
in reductive reactions of iron oxides and in the reaction of reconversion of
carbon dioxide by hydrogen.
Table 22 shows the degree of consumption of hydrogen in the above-
indicated reactions at different temperatures. In the first 3-4 rain, there
is a predominance of reactions of reduction of iron oxides by hydrogen,
which take place at different rates at different temperatures. As the tem-
perature rises, the degree of reduction of iron oxides and hence the consump-
tion of hydrogen increases from 31.61% at 600°C. to 45.3% at 700°C. and 53.08%
at 800°C. The degree of conversion of hydrogen in the reconversion reaction
at these temperatures is approximately the same and amounts to 8.85-11.0%. In
the next 11 min at 600°C., there is an equal development of the reaction of
reduction of iron oxides by hydrogen, characterized by a hydrogen consumption
of 12.24%, and reactions of reconversion of carbon dioxide by hydrogen, with
a hydrogen consumption of 11.09%.
As the temperature is raised to 700°C., during 11 min of the process, the
reaction of carbon dioxide with hydrogen, characterized by a hydrogen conver-
sion of 18.68%, predominates. There are also reductive reactions of iron ox-
ides with hydrogen, with a degree of conversion of 7.88%. At 800°C., during
the same period of time, 19.05% of hydrogen is consumed in the main reaction,
and 12.38% in the reduction. This shows that a temperature rise promotes
the development of the reaction of carbon monoxide reconversion. At 600,
700 and 800°C. during 33 min, hydrogen continues to be predominantly consumed
(18.89%) in the reaction with carbon dioxide, and an increase in the degree
of consumption of hydrogen in reductive reactions with iron oxides is observed
(up to 8.75%).
Analysis of the solid residue after the removal of hydrogen sulfide from
the gas at 700-800°C. showed that it contains a substantial amount of pyro-
phoric iron, which ignites spontaneously in air. The increase in the re-
ducibility of the solid reactant may substantially affect the increase in
the degree of hydrogen sulfide removal from gases, maintaining it for a
longer period of time than in the case of the experiments described, which
lasted 1 hr. Obviously, this will make it possible to increase the degree
of consumption of the solid absorbent in the course of removal of hydrogen
sulfide from the gases.
The apparent activation energy of the reaction of hydrogen sulfide with
iron oxides was determined for the diffusion regime of reaction, and its
value for a time of 20 and 40 min from the start of the experiment was 1800
cal/mole.
- 79 -
-------
Table 20.
Effect of Temperature on .the Reaction of Hydrogen Sulfide (0.390
with Hematite (v = 5.5 m/sec; 0.5-1.0 mm Fraction; T = 0.015 sec).
lime,
rain
3
10
15
T°, K
773
728
673
623
773
728
673
623
773
728
673
623
jooo/r
1,29
1,37
1,51
1,61
1,29
1,37
1,51
1,61
1,29
1,37
1,51
1,61
4ftS
nan x g
8,91
6,08
4,22
2,55
4,24
2,70
1,99
1,13
2,78
2,33
1,57
0,52
Reduced rate
W x 1CT
1,563
0,889
0,558
0,3258
0,5255
0,3126
0,2220
0,1203
0,3170
0,2607
0,1711
0,0535
log W.
—3,8068
—4,0511
—4,2530
-4,4870
-4,2799
-4,5050
-4,6540
—4,9289
—4,4990
—4,5839
—4,7667
—5,2767
Table 21.
Reaction of Hydrogen .Sulfide with Hematite at Different Temperatures
Cv = 0.69 m/sec; 0.5-1 mm Fraction; T = 0.15 secj.
Time,
min
10
20
30
40
50
60
r = MO* c
Degree
of con-
version
of H2S, %
97,15
96,64
96,84
96,94
97,10
—
g
min x g
0,67
0,63
0,71
0,69
0,74
—
7=700° C
Degree
of con-
version
of HoSf^p
_
93,84
—
96,52
—
97,07
r, _§_.io-«
min x g
0,83
—
0,90
—
0,96
r = 8oo> c ^~~
Degree
of con-
93,48
94,50
_
95,79
__
96,08
W, — * — — lo1
min x g
0,83
0,86
—
0,90
—
0,88
- 80 -
-------
Table 22.
Change in Gas Composition during the Reaction of KMA Hematite with Hydrogen
Sulfide at Different Temperatures (v = 0.69 m/sec; T = 0.15 sec).
Tempera-
ture, °C.
600
700
800
Reaction
time, min
3,33
11,25
33,33
3,80
11,50
33,50
4,33
' 11,75
33,00
Final gas, vol. %
CO,
4,09
3,86
5,04
4,16
2,51
2,52
4,45
2,12
2,43
CO
1,82
2,13
0,21
2,24
3,62
3,63
1,70
3,66
3,65
H,
11,35
14,78
18,38
8,31
14,16
16,15
7,35
13,22
13,93
N,
82,74
79,23
76,37
85,29
79,71
77,70
86,50
81,00
79,99
H2 for re-
conversion,
*
9,54
11,09
1,09
11,59
18,68
18,79
8,85'
19,05
18,89
H2 for re-
duction, °f>
31,61
12,24
3,65
45,38
7,88
2,47
53,08
12,38
8,75
Note. Composition of initial gas (in #): H^ - 0.33 (at 600°), 0.34
(at 700°) and 0.35 (at 800°); C02 - 5.83; H2 - 19.29, N2 74.55 (at 600e),
74.54 (at 700°) and 74.53 (at 800°).
Results of experiments on the reaction of hydrogen sulfide with KMA hem-
atite showed that the removal of hydrogen sulfide from the gas can be carried
out at 500-800°C. with a sufficient degree of recovery of hydrogen sulfide,
amounting to 96-97% during a long period of the reaction.
The experiments also established that when hydrogen sulfide of the gas
containing it reacts with hematite at a linear velocity of 0.53 m/sec and a
contact time of 0.19 sec, a change in particle size from 0.25-0.5 to 2-3 mm
had no appreciable effect on the indices of hydrogen sulfide recovery. This
is explained by the fact that under the given experimental conditions there
was a large excess of the reactant that provided for a sufficient reactive
surface during the entire course of the reaction.
Fig. 28. Change in the rate of the reaction
between hydrogen sulfide and hematite with
time at different gas feed velocities at 700°C.
-0.055 sec.
- 81 -
-------
A large group of experiments were conducted on the removal of hydrogen
sulfide from gases with hematite at elevated temperatures. At high gas feed
velocities, the linear velocities of the gas supplied ranged from 0.27 to
0.66 m/sec at a hydrogen sulfide concentration in the gas of 0.24% and at
linear velocities from 0.53 to 1.81 m/sec, at a hydrogen sulfide concentra-
tion of 0.4% (C02 8.5%, H2 18.2%, N2 72.9%) at 700°C. and a particle size of
0.5-1.0 mm.
As the blast velocity rose from 0.27 to 0.66 m/sec, the rate of the re-
action of hydrogen sulfide with hematite increased. The degree of hydrogen
sulfide removal from the gas under the indicated conditions was 95-98% during
the entire reaction cycle (Ihr). A further increase of the feed velocity of
the gas being purified led to a substantial increase of the reaction rate (Fig.
28). Under the conditions of the experiments, it was impossible to raise the
blast velocity further in order to exclude the diffusion inhibition at 700°C.
On the one hand, this was due to the rather high reaction rate at this temper-
ature (a high degree of recovery of I^S), and on the other, to the large height
of the solid reactant (100 mm), which at high blast velocities caused a com-
paction of hematite and the creation of a large resistance of the layer. Thus
one can expect that at 700°C., the rate of this reaction can be higher if a
kinetic reaction regime is provided for, i. e., if there are no diffusional
inhibitions. Moreover, the experimentally established rate of the reaction
of hydrogen sulfide with hematite is acceptable for setting up a technologi-
cal process of hydrogen sulfide removal from gases at all the blast velocities
studied. This is confirmed by the data of Fig. 29, when the degree of hydro-
gen sulfide conversion at blast velocities of 0.53-1.04 m/sec amounts to
91-94% during 29 min of the reaction, then increases to 94-96% in the course
of 40-60 min. For a blast velocity of 1.81 m/sec the degree of purification
reaches 99% during 10 min, 96.88% during 29 min, then drops to 77.83% in the
course of 45 min. As was already noted in an evaluation of other experiments,
a certain decrease of the degree of conversion of hydrogen sulfide during the
initial period of the reaction at gas feed velocities of 0.53-1.29 m/sec is
due to the reduction of higher iron oxides to lower oxides and iron. Subse-
quently, the rate of the main process of hydrogen sulfide removal from the
gas increases. This is confirmed by data indicating a change in gas composi-
tion during the removal of hydrogen sulfide, listed in Table 23.
s
if
g° so
Is
g".S
j.
\. A/ 0^
* Kj * v
1 1 1 1 1 1
ffO
so
Tine, min
Fig. 29. Change in the degree of conversion of hydrogen sul-
fide during its reaction with hematite at different gas feed
velocities (T = 700°C.; H^ concentration, 0.$).
1 - 1.24 m/sec; 2 - 1.04; ~b - 0.83; 4 - 0.53; 5 - 1.81.
- 82 -
-------
During the initial period of removal of H2S from the gas, i. e., 10
min after the start of the experiment, at a gas feed velocity of 0.27 m/sec,
the hydrogen concumption in the reduction processes was 27.9%, and in the
reaction of carbon dioxide with hydrogen, 18.1%. During the following peri-
od from 30 to 70 min, the predominant role was played by the reconversion
reaction, with a hydrogen consumption of 24%, and in the reduction of iron
oxides, with 3.55%.
At a blast velocity of 0.52 m/sec after 17-27 rain from the start of the
experiment, the reconversion C02 + H2 predominates, with a hydrogen consump-
tion of 23.8 and 29%; in the reduction of iron oxides, 5.95-4.07% of hydrogen
is consumed. At the end of the cycle, after 57 min, only the reaction of
carbon dioxide with hydrogen, with a hydrogen consumption of 18.6 and 24.5%,
takes place. In a reducing medium, no appreciable evolution of elemental
sulfur was observed.
Table 23.
Change of the Gas During the Reaction of KMA Hematite with Hydrogen Sulfide
at Different Blast Velocities (t = 7QO°C., 0.5-1 mm Fraction)
Contact
tine, sec
0,28
0,20
0,15
Linear
velocity,
m/sec
0,27
0,52
0,65
Reaction
time,
min
10
31
70
27
57
17
54
Final gas,. vol. %
CO,
5,07
4,0
4,0
3,2
4,0
3,0
3,9
CO
3,35
4,45
4,45
4,4
4,5
5,4
4,55
H,
10
13,49
13,55
13,0
14,83
12,47
14,95
N,
81,58
78,06
78,00
79,4
76,67
79,13
76,6
Hg for
reconver-
sion, %
18,1
24,0
24,0
23,8
18,6
29,0
24,5
H2 for
reduction,
*
27,9
3,24
3,55
5,95
—
4,07
—
Note. Composition of initial gas (in #): HgS 0.24; CO 8.5; H, 18.5;
N2 72.76. Z
Analysis of the solid residue showed that when hydrogne sulfide reacts
with hematite, all of the sulfur passes into iron sulfide. The sulfur con-
tent of solid residue in the reaction of hydrogen sulfide with hematite at
different gas feed velocities (t = 700°C.) is as follows:
Conditions of gas
l»i = 0,53 m/sec
t;t = 0,83 m/sec
Va = 1,04 m/sec
»«= 1,29 m/sec
ri« — M .fM m/sec
; supply
Ti — 0 19 se"c ....
tj — 0,13 sec. . . .
Ca — 0,096 sec. . . .
P4 — 0 078 sec . . .
T« — 0.055 sec. . . .
. . 9,21
. . 13,81
. . 16,08
. . 17,37
. . 16,52
ssulf
9,12
13, 6i
16,0
17,0
16,18
- 83 -
-------
From the above data it is evident that the total sulfur content of
the solid phase corresponds to that of iron sulfide. As the blast velocity
increases from 0.53 to 1.29 m/sec, the total sulfur content in the solid
reactant rises from 9.21 to 17.37%. At a blast velocity of 1.81 m/sec, it
amounts to 16.52% during a shorter reaction period, 45 min. The degree of
consumption of the purification reactant rises from 23 to 43.4% as the feed
velocity of the gas flow increases from 0.53 to 16.29 m/sec.
The indicated degree of consumption of the absorbent at all the blast
velocities studied is sufficient reason for setting up the process of hydro-
gen sulfide removal from gases.
Thus, the study of the kinetics of the reaction between hydrogen sulfide
and iron oxides showed the practical feasibility of the process of hydrogen
sulfide removal from gases at 600-800°C. with a sufficient degree of recovery
amounting to 95-97% in the course of an hour.
In organizing a complete technological process of removal of sulfur
compounds from gases, in addition to increasing the economy, it is necessary
to plan the conditions of regeneration of the spent reactant and utilization
of the recovered sulfur.
As was shown by chemical analysis of the solid residue, all of the
sulfur passes from the gas into iron sulfide. The latter can be regenerated
by roasting in atmospheric oxygen or by steam-air treatment in which mostly
sulfur dioxide is obtained in the gaseous phase and iron oxides in the solid
phase.
Studies of the roasting of iron sulfide in atmospheric oxygen were
conducted at initial layer temperatures of 600 and 700°C. and a linear air
velocity of 0.060 m/sec (contact time about 1 sec). Natural iron sulfide
with a sulfur content of 22.18% was subjected to roasting.
Table 2k
Roasting of Ferrous Sulfide in Atmospheric Oxygen at Different Temperatures
(v = 0.060 m/see? 1 = 1.0 sec)
Time,
min
•so.,%
legree of
Converr
sion of
S. £
Excess
Air . a
r=60o° c
11,50
17,00
22,00
30,00
45', 00
60,00
4,26
9,06
8,25
5,56
3,47
1,60
4,25
9,12
13,50
18,70
24,40
27,30
2,71
1,22
1,32
2,20
3,47
7,13
line,
min
so,, %
Degree of
Conver-
sion of
Excess
Air a
T = 700° C
10,50
14,00
17,50
21,25
24,66
28,00
4,21
11,95
12,97
13,67
13,42
13,97
4,85
9,58
14,30
19,30
24,10
28,70
2,84
1,00
1,08
1,02
1,04
1,00
- 84 -
-------
It is evident from the data of Table 24 that at 600°C., an average of
3.5-9% of sulfur dioxide is evolved into the gaseous phase, and the degree
of expulsion of sulfur amounts to 27.3% during 1 hour. When the temperature
is raised to 700°C., the process of reaction of ferrous sulfide with atmos-
pheric oxygen is accelerated. The amount of sulfur dioxide evolved reaches
11-12% in the gas, and the degree of expulsion of sulfur increases to 28.7%
after only 28 min.
A major disadvantage of the process of roasting of ferrous sulfide
with air under the indicated conditions is a considerable temperature rise
in the layer because of the exothermic character of the reactions taking
place; this led to sintering of the charge along the layer and consequently
to a decrease in the sulfur expulsion rate.
The process of roasting of ferrous sulfide in the solid phase results
primarily in the formation of iron oxides, this being in accord with the
analyses of the composition of the solid phase conducted by G. S. Frents
[22], who studied the oxidation of iron sulfide by atmospheric oxygen at
600, 700 and 800°C. The main product of the reaction in the residue were
iron oxides and also traces of iron sulfate; at 800°C., an appreciable
amount of metallic iron is observed.
Possible overheating of the solid absorbent can be minimized by regen-
eration with steam-air treatment. Studies of the reaction of ferrous sul-
fide with a steam-air mixture were conducted on the apparatus described earlier,
where additional consideration was given to the saturation of air with water
vapor until a certain content was reached before the air entered the reactor.
The studies were conducted with a blast in which the ratio of steam to
oxygen was 2, 4 and 40 at 600-800°C. The linear velocity of the steam-air
mixture was 0.1 ra/sec (T = 0.61 sec) and 0.42 m/sec (T = 0.14 sec).
It is evident from Table 25 that for a ratio H20/02 = 2 at 600°C., the
process practically does not occur. Raising the temperature to 700°C. leads
to a considerable increase of the roasting of ferrous sulfide, with the evo-
lution of 13% of sulfur dioxide and traces of hydrogen sulfide into the gaseous
phase. The degree of expulsion of sulfur is 44% during 33 min.
A vigorous development of the process of roasting of ferrous sulfide also
continues to be observed at 800°C. with the same degree of expulsion of sulfur.
However, the distribution of the gaseous products of roasting is somewhat dif-
ferent — the content of sulfur dioxide is 11-12% and that of hydrogen sulfide,
up to 2%.
The steam-air treatment of ferrous sulfide makes it possible to conduct
the regeneration process under milder temperature conditions without any
appreciable fusion of the charge.
- 85 -
-------
Table 25
Reaction of Steam-Air Mixture with Ferrous Sulfide at H20/C^ = 2 (v = 0.1
m/sec; T= 0.61-0.64 sec)
Time,
min
HSS. %
so,. %
Degree of
Conver-
sion of
S, %
r = 60o° c
17
30
__
0,27
1,46
0,63
3,35
7 = 700" C
8,50
12,00
15,16
18,67
22,25
26,16
29,50
33,00
—
0,109
—
—
0,071
—
0,310
0,100
6,01
12,89
14,33
13,00
13,56
13,40
13,36
13,37
5,92
11,18
16,26
21,34
27,13
33,56
38,82
44,66
Time,
min
H,S. %
SOS. %
Degree of
Conver-
sion of
S, %
7=800° c
10,00
13,50
17,33
20 ,41
23,58
26,83
29,91
33,00
0,467
1,790
1,620
1,800
1,920
1,810
2,070
1,110
3,92
11,18
11,18
12,05
1 1 ,94
11,52
12,32
12,23
7,86
13,07
18,51
23,23
28,40
33,15
37,80
42,35
To increase the hydrogen sulfide content of the final reaction products,
the experiments were conducted in the presence of a higher content of water
vapor in the blast, H20/02 = 4 at 600, 650 and 700°C.
Table 26
Reaction of Steam-Air Mixture with Ferrous Sulfide at
(v = 0.11-0.12 m/sec; T = 0.48-0.54 sec)
= 4
Time,
min
Has, %
so,, %
Degree of
Conver-
sion of
S, %
r=6oo° c
14,66
22,25
31,00
0,21
0,0068
2,830
1,430
0,999
4,86
6,27
7,33
7 = 650° C
12,75
17,00
21,50
26,00
31,61
39,00
0,45
1
1,80
'2,56
?
2,14
1,96
1
1,37
3,06
7,64
7,37
1
6,91
5,91
4,95
6,10
>
10,03
14,10
18,50
23,70
28,80
Time,
min
49,00
57,00
H,S. %
1,12
0,82
so,. %
3,65
2,20
Degree of
Conver-
sion of
S, %
37,60
40,50
T = 700° C
11,00
15,08
18,25
21,58
25,00
28,58
32,25
37,00
0,44
1,46
2,00
1,56
1,71
3,41
1,71
1,58
4,04
10,13
10,79
11,28
11,65
11,29
11,39
9,61
5,08
9,19
13,12
17,36
21,75 '
25,70
30,44
41,82
- 86 -
-------
It is evident from Table 26 that at 600°C., the process of steam-air
roasting takes place inefficiently. Raising the temperature to 650°C.
causes a considerable increase in the rate of the reaction of the steam-
air blast with ferrous sulfide with the evolution of 3 to 7.64% sulfur
dioxide and noticeable amounts of hydrogen sulfide, from 1 to 2.5%, into
the gaseous reaction products. The regeneration process takes place more
intensively at 700°C., when an average of 10-11% sulfur dioxide and
1.5-2.0% hydrogen sulfide are observed in the gaseous phase. The degree of
expulsion of sulfur from the solid residue reaches 42%.
A tenfold increase in the steam content of the blast during the steam-
air treatment of ferrous sulfide did not result in any appreciable increase
in the hydrogen sulfide content of the end products of the reaction at
700-800°C.; on the contrary, it led to a decrease in the expulsion of sulfur
to 27-36% in the course of 55 min of the reaction (Table 27).
Table 27
Reaction of Steam-Air Mixture with Ferrous Sulfide at
(v = 0.38-0.4? ni/sec; T = 0.126-0,156 sec)
= 40
lime,
iinn
H,S, %
so,. %
Degree oi
Conver-
sion of,
s, %
T = 700° C
7,00
10,33
15,58
23,00
27,00
34,50
39,00
43,25
47,75
54,25
1,180
0,490
0,315
0,344
2,420
2,400
0,320
0,600
0,567
0,385
3,00
7,98
5,04
4,05
6,26
8,52
9,56
11,95
8,20
6,14
1,24
5,96.
8,18
10,06
12,83
17,32
19,67
21,93
24,00
26,66
Tine,
min
H«S, %
SOZ, %
Degree of
Conver-
sion of
S,
r = 8oo° c
8,00
14,00
20,00
25,33
31,58
37,66
43,83
50,50
56,00
1,975
3,960
1,350
1,770
1,665
0,012
0,012
0,011
0,172
2,30
2,04
9,55
9,72
9,70
12,48
13,07
12,54
11,60
2,54
5,43
12,66
16,19
20,18
24,53
28,56
32,40
36,30
The above experiments graphically confirm the conclusions drawn from
thermodynamic analysis to the effect that in the overall process of steam-
air roasting, the gaseous phase chiefly contains sulfur dioxide and minimum
amounts of hydrogen sulfide and elemental sulfur.
The completed study of the regeneration of the solid reactant shows
that a practically feasible process consists of steam-air treatment of
ferrous sulfide at 700-800°C. with a steam-to-oxygen ratio equal to 2, sul-
fur dioxide being chiefly obtained in the gaseous phase.
- 87 -
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HYDROGEN SULFIDE REMOVAL FROM GASES BY MEANS OF MANGANESE OXIDES
Thermodynamic analysis showed that reactions between hydrogen sulfide
and manganese oxides can take place in a reducing medium at 300-900°C.
Moreover, the presence of hydrogen and carbon monoxide in the gas undergoing
purification may lead to the development of secondary reductive reactions
associated with crystallochemical transformations of higher manganese oxides
into lower ones.
We studied the reaction of natural manganese ores with hydrogen sulfide
by using the procedure described earlier. Hydrogen sulfide was removed
from the gases by using an enriched manganese concentrate of grade I of the
Nikopol1 deposit of the following composition (in %) : Mn 44.7; Mn02 50.5;
Si02 16.1; A1203 1.8; ^2Q3 2*1; Ca° 1>5; Mg° 1'0; Na2° °-445 s 0.02; K20
1.19; P 0.22; C02 1.21. The hydrogen sulfide content of the gas being
purified was 0.24%, C02 6.08%, H2 18.0% and N~ 75.68%. The linear velocity
of the gas supplied was varied from 0.435 to 3.81 m/sec.
The effect of the blast velocity on the degree of conversion of hydrogen
sulfide with manganese concentrate is shown in Table 28. As the blast
velocity rises from 0.435 to 3.81 m/sec, the degree of conversion of H^S falls
off.
Starting with a gas feed velocity of 3.15 to 3.81 m/sec, the reaction
rate becomes independent of the blast velocity during the first 3 min of the
reaction. At the indicated gas feed velocities, the diffusional inhibition
of the supply of the reactants to the surface where the reaction occurs has
little effect.
The effect of temperature on the rate of the reaction of hydrogen sulfide
with manganese concentrate was studied at a linear gas velocity of 3.07 m/sec
and a contact time of 0.013 sec. The temperature in the layer was maintained
at 350, 400 and 500°C. The gas being purified contained (in vol. %) H2S 0.38;
C02 5.9; H2 19.05; NZ 74.67.
The degree of conversion of hydrogen sulfide reached its highest value
at 350-500°C. during the first 3 min of the reaction (Fig. 30 a). This
figure shows the presence of a minimum degree of conversion of hydrogen sul-
fide. At 400-500°C. it is observed after 10 min of the reaction, and at
350°C., after 6 min. A similar minimum is noted also in the rate of the
reactions of hydrogen sulfide with manganese oxides (Fig. 30 b).
This type of change in the reaction rate of hydrogen sulfide for manganese
concentrate may be due to the occurrence of reactions involving the reduction
of higher manganese oxides by hydrogen at all the temperatures studied. This
is illustrated in Fig. 31, the data of which were used to determine the value
- 88 -
-------
• Table 28
Effect of Linear Velocity of the Gas Flow on the Rate of the Reaction of
Hydrogen Sulfide with Manganese Concentrate of Grade I of the Nikopol" Deposit
Time,
rain
)egree of Cor
version of
H8S, %
W, T-^- X 105
mm x g
v = 0 , 435 m/sec t = 0 , 092 sec
10
20
30
97,11
93,95
• 95,48
0,94
0,97
1,14
0=2,59 m/sec T = 0,015 sec
5
10
15
18
92,08
71,78
40,23
32,36
6/24
5,16
3,13
2,25
0 = 3, 10 m/sec T = 0,0129 sec
3
6
10
15
95,16
76,58
59,25
40,63
8,10
5,96
4,70
3,43
v = 3 , 74 m/sec T = 0 , 0107 sec
3
6
10
15
87,90
57,72
39,91
22,19
7,99
5,50
4,05
2,32
Time,
min
Degree of
Conversion
of H,S. %
T'ffi^i'105
0 = 1,92 m/sec T = 0.021 seo
5
10
15
20
95,15
84,09
68,53
49,78
4,60
4,35
3,78
2,77
o = 3. 15 m/sec T = 0.0127 sec
3
6
10
15
93,69
73,97
58,08
41,78
7,50
6,44
5,32
3,98
o = 3,81 m/sec,; T = 0,0105 sec
3
6
10
15
89,11
60,69
40,94
29,44
8,10
5,96
4,34
3,12
.
of the apparent activation energy for different periods of the reaction
3, 10 and 15 min.
W x 10~3, g/inin x g
fZ
(0
tff
IS
J /ff // *
line, min
Pig. 30. Effect of temperature in the reaction of f^S with
manganese concentrate.of Grade I of the Nikopol' deposit on
the degree of conversion (a; and reaction rate W {.v = 5 m/.
T = 0.013 sec).
1 - 350°C.; 2 - 400°C.; 3 - WC.; 4 - 500'C.
sec,
- 89 -
-------
Fig. 31. Logarithm of
the rate of the reaction
of I^S with manganese
concentrate of Grade I of
the Nikopol1 deposit ver-
sus reciprocal tempera-
ture, v - 3.0 m/sec,
T = 0.013 sec
For a reaction time of 3 min, the apparent
activation energy was 5078 cal/mole. The reaction
value obtained is similar to the value of the
apparent activation energy for reactions of reduc-
tion of manganese oxides by hydrogen. In the
reduction of the manganese mass with a nitric acid
mixture at temperatures up to 75-400°C., the acti-
vation energy is 6400 cal/mole.
As the reaction time increases from 6 to 15
min, an increase in the apparent activation energy
to 14960 cal/mole takes place. Such a value of the
apparent activation energy characterizes the pro-
cess of hydrogen sulfide removal from the gases by
manganese concentrate of grade I of the Nikopol*
deposit under conditions close to the extrakinetic
region.
To purify the gases with a high degree of
removal of hydrogen sulfide in the course of a
long period of time, the experiments were carried
out at elevated temperatures and with an increased
contact time on the same reactant.
Table 29 gives the results of experimental data on the effect of temper-
ature from 500 to 800°C. on the removal of hydrogen sulfide from the gas by
manganese concentrate at a feed velocity of 0.65 m/sec and a contact time
of 0.15 sec.
Table 29
Reaction of Hydrogen Sulfide with Manganese Ore at Different
Temperatures (v = -.65 a/see; T = 0.15 sec)
Time,
min
Degree of
Conversion
ofH,s. %
W, — S-.x 105
g x nun
T = 500" C
10-
30
50
97,50
98,53
98,24
5,40
6,30
6,50
T = 700e C
• 10
30
50
97,7
93,6
98,5
5,53
6,42
6,58
)egree of
Conversion
of H,S. %
w. -£— x 105
g x min
T = 600° C
93,50
98,00
99,20
5,68
6,34
6,55
T = 800° C
99,03
99,27
98,81 •
5,80 •
6,35
6,60
- 90 -
-------
At all temperatures from 500 to 800°C., the rate and degree of purifi-
cation of the gas were sufficiently high. The degree of purification of
the gas amounted to 97-99% in the course of 50 min. During the first 10 min
of the reaction at 500-700°C., the purification was 97.5%, and subsequently
increased to 98-99%. A certain decrease in the degree of purification during
the initial period of the reaction was due to reactions of reduction of
manganese oxides by hydrogen. This is confirmed by data on the change of the
gas composition, presented in Table 30. During the first 3-4 min of purifi-
cation, the manganese oxides are reduced by hydrogen, and the latter is almost
absent in the outgoing gas. In the course of further removal of hydrogen
sulfide from the gas, carbon monoxide appears, indicating the presence of
reactions of reconversion of carbon dioxide with hydrogen and formation of
carbon monoxide, C02 + H- = CO + H.,0.
Table 30
Change in Gas Composition During the Reaction of Manganese Ore with
Hydrogen Sulfide at Different Temperatures (v = 0.65 m/sec; T =0.15 sec)
Temper-
ature, "C
500
600
700
800
Reaction
Tine, min
3,50
12,33
32,50
3,28
13,08
30,33
3,45
11,66
31,50
3,66
12,50
31,58
Final gas, vol. %
CO,
2,30
0,89
1,29
2,30
1,94
0,47
2,32
1,19
0,95
2,10
0,54
0,32
CO
_
0,55
0,60
—
0,82
0,95
—
0,90
2,43
—
0,97
1,26
H2
1,01
6,25
6,41
0,91
7,82
6,40
—
4,55
5,86
—
5,87
6,55
- N,
96,69
92,31
91,70
96,79
- 89,42
92,18
97,68
93,36
90,76
97,90
92,62
91,87
H2 For
Reconver-
sion, %
5,24
5,24
5,68
—
7,82
9,05
—
8,57
.23,20
—
9,23
12,00
H2 For
Reduction,
*
90,4
35,1
33,4
91,4
17,7
33,2
100,0
48,2
21,1
100,0
38,1
25,8
Mote. Composition of initial gas (in #): H2S 0.27; COg 2.30; H2 10.50}
rtf. rtf
N, 86.93.
In evaluating the degree of consumption of hydrogen in the reaction of
reduction of manganese oxides and in the reaction of reconversion of carbon
dioxide by hydrogen, it was found that in the first 3-4 min of the process
of hydrogen sulfide removal from the gas, approximately 90-91% of the hydro-
gen is expended in reactions of reduction of manganese oxides, and at 700-
800°C., 100% of the hydrogen is consumed in these reactions. Then, during
the period from 12 to 33 min since the start of the gas purification process,
the reaction of reconversion of carbon dioxide by hydrogen takes place
together with the reduction of manganese oxides by hydrogen. As the temperature
- 91 -
-------
rises, the consumption of hydrogen in this reaction increases from 5.24 to
12%.
«u,
The use of natural manganite showed that it is reactive in the extrac-
tion of hydrogen sulfide at 700°C. in the course of 90-120 min, with a
degree of purification of 96-100%. This is clearly evident from the data
below (v = 0.74 m/sec; T = 0.0965 sec):
Time, min 31 60 90 120
Degree of Conversion of H-S, % ... 99,87 97,64 97,23 96,76
Time, inn 9 & 74 90
Degree of Conversion of H,S, % ... 100,00 98,84 97,33 96,66
In a tentative evaluation of the effect of pressure on the course of
the reaction of hydrogen sulfide with manganite, experiments were carried
out at a pressure of 8 g atm at 700°C. with a linear velocity of 2.62 m/sec
and a contact time of 0.057 sec. The hydrogen sulfide removal from the gas
in the course of 45 min was 100%.
In order to expand the raw material base of the solid reactants for the
removal of sulfur from gases and for the use of manganese ores of other
deposits, experiments were conducted in which three grades of manganese con-
centrate of grade II and slime were used.
Sample No. 1 - manganese concentrate of grade II of the Grushevka ore-
dressing plant containing 36.1% Mn; 0.28% P. Sample No. 2 - slime obtained
from Maksimovska ponds containing (in %): 14.2 Mn; 19.2 Mn02; 2.6 MnO; 52.8
Si02> and 3.3 CaO. Sample No. 3 - manganese concentrate of grade II from
the Chkalovsk ore-dressing complex containing 36.3% Ifa and 0.203% P.
It is evident from Fig. 32 that the degree of recovery of hydrogen
sulfide for samples No. 1 and 3 is approximately the same and amounts to
92-97% in the course of 1 hour. Hence, manganese concentrates of grade II
can also be used to remove hydrogen sulfide from gases. As far as manganese
slime is concerned, (sample No. 2), a high degree of gas purification is
obtained only in the course of 30 min to the extent of 96%, after which an
abrupt breakthrough of hydrogen sulfide and a drop of the degree of purifi-
cation to 21% are observed at a linear gas feed velocity of 1 m/sec and a
contact time of 0.1 sec.
A definitive recommendation of the use of manganese slime will require
a further study of the physicochemical characteristics of this process of
hydrogen sulfide removal from gases.
In view of the fact that sample No. 3 of manganese concentrate of
grade II from the Chkalovsk ore-dressing complex was found to be applicable
to the extraction of hydrogen sulfide from gaseous mixtures, the subsequent
- 92 -
-------
experiments on the effect of temperature were conducted by using this reactant:
Degree of conversion of
at temperature (eC)
600
700
800
10 min 20 min .10 min GO min
97,30
93,13
95,7S
90,22
95,07
97, SS
97,16
95,81
98,00
97,22
91, IS
From the data cited it is evident that at 600-700°C., a linear gas ve-
locity of 1 m/sec and a contact time of 0.1 sec, manganese concentrate of
grade II purifies the hydrogen sulfide containing gas to the extent of 96-977.
in the course of 1 hour. At 800°C., during the first 10 min, the hydrogen
sulfide removal from the gas is 98%, then decreases to 94.18% after 60 min.
Fig. 32. Change in the degree of conversion of hydrogen sulfide
during the reaction with manganese concentrate of grade II (samples
No. 1 and 2) and manganese slime (sample No. 3) with time.
In order to set up a complete technological procedure for hydrogen sul-
fide removal from gases by manganese ore, it is necessary to specify the
conditions of regeneration of the spent reactant and of the use of the ex-
tracted sulfur.
As was shown by chemical analysis of the solid residue, all of the sul-
fur from the gas is tied up in manganese sulfide.
The total sulfur content of the reactant was 18-22%, which corresponds to
a degree of consumption of the reactant of 25-26%, but this is not the limit,
since the degree of purification achieved in the experiments, 95-97% in the
course of 1 hour, is still an adequate quantity for subsequent use of the re-
actant.
The regeneration of manganese sulfide can be carried out by roasting in
atmospheric oxygen with the evolution of sulfur dioxide into the gaseous
phase and formation of manganese oxides in the solid phase, or by using the
- 93 -
-------
steam-air treatment, which also results in the formation of manganese oxides
and sulfur dioxide, and partly hydrogen sulfide and gaseous sulfur.
The conditions of roasting of manganese sulfide in atmospheric oxygen
were studied by using a chemically pure reactant at 500, 600 and 700°C.,
at a linear gas feed velocity of 0.061 m/sec and a contact time of 1 sec.
The sulfur content of manganese sulfide was 19.7%. Manganese sulfide was
first made into pellets, which were then crushed to 0.5-1.0 mm.
The temperature change in the layer resulting from the reaction was
recorded by an upper and a lower thermocouple, both of which penetrated the
layer to a depth of 5 mm. At an initial temperature of 500°C., the maxi-
mum temperature briefly reached 940°C., for tj_n = 600°C., t^x = 960°C.,
and for tin = 700°C., t^^ = 1000°C.
A very essential feature was the evolution of sulfur dioxide and of a
minimum amount of hydrogen sulfide (up to 17.) into the gaseous phase during
the unsteady period of heating to the given temperature of the experiment,
and the amount of sulfur dioxide evolved during the heating increased with
rising temperature.
Table 31.
Roasting of Manganese Sulfide (MnS) in Atmospheric Oxygen at Different
Temperatures (v = 0.061 m/sec; f = 1 sec)
Tine,
min
• H ««
Iso*
o
W O
***
2 '
u)c
QO 0
W
in
O tt
w'S
T-=500CC
Heating.
4,50
7,50
10,50
13,50
17,50
21,25
3,85
10,35
15,19
15,12
16,63
13,02
10,80
6,97
16,30
25,40
32,80
40,10
50,50
59,80
—
3,94
1,25
1,00
1,00
1,07
1,11
Time,
min
r.
^s
o
WO
*L
iffi '
in
m
g.5"j ' i g £
<§o.%
£a
7^600'C
Heating.
3,66
6,66
10,25
13,66
17,00
21,00
25,00
3,09
14,20
14,40
14,10
12,70
13,00
12,40
13,10
7,65
18,70
27,40
37,60
46,80
56,20
66,30
77,20
—
1,00
1,00
1,00
1,10
1,07
1,12
1,02
Time, '
min
• H <•
-W CM
>H CO
£53
*s
-------
Roasting with this amount of sulfur dioxide being evolved into the
gaseous phase takes place with an excess air coefficient of 1-1.1. The
roasting may occur in such a way that different oxide forms of manganese
are formed in the solid phase. It has been established that at 500°C.
the oxidation of manganese sulfide involves the formation of manganic ox-
ide 0fei2°3) in the solid phase, and at 600 and 700°C., manganous oxide
(MnO), provided that sulfur is present in the solid residue.
When the solid absorbent is regenerated by using steam-air treat-
ment of manganese sulfide, depending on the ratio of water vapor and air
in the blast mixture, hydrogen sulfide may be obtained in the reaction
product in addition to sulfur dioxide.
The steam-air treatment of manganese sulfide was achieved at a linear
blast velocity of 0.11 m/sec and a contact time of 0.53-0.58 sec with a
steam-to-oxygen ratio of 2 and 4. The sulfur content of the regenerated
mass was 19.7%. The temperature varied from 400 to 800°C.
During feeding of the steam-air mixture, the temperature in the layer
rose as a result of the exothermic nature of the reaction. Nevertheless,
the use of the steam-air blast makes it possible to maintain stable tem-
perature conditions without overheating, thus preserving the original pro-
perties of the material being roasted.
The data listed in Table 32 show that at all the temperatures studied,
a high degree of desulfurization is observed that during 25 min of the re-
action amounts to 80%. The bulk of the sulfur is evolved in the form of
sulfur dioxide (content in the gas, 10-14%), and a slight amount of it is
converted into hydrogen sulfide (content in the gas up to 2%) and elemental
sulfur. The evolution of misty gaseous sulfur that remained practically un-
trapped was observed visually.
In order to increase the hydrogen sulfide content in the end products
obtained, experiments were carried out with a large supply of steam (I^O/^ = 4)
at 500 and 800°C. However, as is evident from the data of Table 33, no sub-
stantial increase of hydrogen sulfide occurred in the gaseous phase, and the
degree of expulsion of sulfur, other conditions being equal, underwent little
change.
The studies made on the steam-air treatment of manganese sulfide con-
firmed the conclusions of the thermodynamic analysis that in a gas at equi-
librium, for the conditions under consideration, the main substance formed
is sulfur dioxide, with smaller amounts of hydrogen sulfide and elemental
sulfur.
In evaluating the conditions of roasting of manganese sulfide, of great
interest are the studies of V. I. Chagunava [16], who carried out studies on
-- 95 -
-------
ON
I
Table 32.
Reaction of Steam-Air Mixture with Manganese Sulfide at I^O/Og = 2 (v = 0.10-0.11 m/sec;T = 0.53-0.58 see)
Tine, ,
min
¥•
s%"
Degree of
Conversio
of s, %
r==4oooc
5,50
10,40
14,00
18,00
21,67
25,25
30,00
50,00
—
0,39
—
—
—
—
—
0,017
9,47
12,01
12,58
12,83
12,64
13,98
9,08
12,81
14,57
30,77
43,31
56,73
69,01
85,94
97,14
100,00
Tuq,
nun
T-
S%"
Degree of
Conv^ai
r=5oo°c
2,50
5,25
8,25
10,50
14,42
18,33
21,42
25,58
0,08
0,57
0,UO
0,80
0,55
0,75
0,59
0,82
8,82
15,27
14,38
12,64
13,36
11,66
12,12
11,14
7,62
18,47
29,27
37,78
52,60
64,82
75,18
87,42
Tiipe,
min
V
3-
Degree of
Conversio
of S. %
r=6ooec
4,16
7,08
10,58
14,33
17,16
20,75
24,33
28,00
0,74
0,49
0,61
1,17
1,22
1,06
0,18
0,62
8,43
13,40
13,29
12,51
12,57
12,84
12,40
12,16
10,34
21,01
33,03
40,46
5«,61
70,22
80,51
90,84
lime,
min
T
so,,
%
Degree of
Conversion
of s, %
r=8oo°c
5,42
8,17
10,59
12,83
14,50
17,00
21,00
25,00
0,29
1,10
1,72
2,02
1,33
1,17
1,24
l.OS
8,71
13,09
14,55
22,09
14,40
13,29
13,53
12,10
10,%
20,05
29,10
38, 40
44,70
53,80
66,72
78,50
-------
the desulfurization of benzene involving removal of organic sulfur and
hydrogen sulfide by a manganese contact mass (MnO), followed by regenera-
tion of manganese sulfide with a steam-air mixture with different air-to-
steam ratios (2:1, 4:1, 7:1) at 600-700°C.
Table 33.
Reaction of Steam-Air Mixture with Manganese Sulfide,
H20/02 = 4 (v = 0.11 in/sec; T = 0.55-0.59 sec.
Tine,
min
n,s. %
so,. %
)egree of
'onversior
of S, %
r=50o° c
5,58"
9,55
12,91
16.581-
20,16
23,36
27,33
31,00
—
—
0,017
0,192
0,081
0,117
0,105
0,0162
10,87
12,40
13,71
12,43
12,92
13,25
12,24
13,18
10,10
18,28
25,90
33,19
42,68
51,04
66,58
76,02
lime,
min
H,S. %
so,. «„
Degree of
Conversion
of S. %
T = 800e C
5,50
9,08
12,91
16,16
19,88
22,91
26,58
30,00
1,05
1,49
1,29
1,14
1,07
1,43
1,48
1,07
8,92
10,90
11,61
11,95
11,61
11,91
11,74
11,57
10,7
23,2
32,2
43,0
54,3
62,8
73,8
83,0
At the indicated temperatures, a high degree of desulfurization is
achieved (90-99%). The activity of the purifying mass changes slightly
after 8 cycles of absorption of sulfur compounds and regeneration. In the
solid phase, the crystalline form of the initial substance after the regen-
eration is preserved. This is confirmed by x-ray structural analysis of
the solid phases.
In addition, thermograms of the sulfide mass and of the same mass after
regeneration and secondary sulfidization were almost identical. Oxidation
of manganous oxide and manganese sulfide by the steam-air mixture takes
place partially before the formation of pyrolusite, as indicated by .the
pyrolusite and 3-kumakite effect at 600-700 and 965-975°C. Endothermic
effects of decomposition of manganese sulfate are absent from the diagrams.
In the course of steam-air treatment of manganese sulfide, no appreciable
amounts of manganese sulfate can be formed in the roasted mass because of
its reduction by the sulfide with the evolution of sulfur dioxide into the
gaseous phase. The absence of SO ions from the regeneration products was
established by chemical and roentgenometric analyses.
- 97 -
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II
REMOVAL OF SULFUR DIOXIDE FROM GASES
Sulfur dioxide, which is present in relatively low concentrations
in the waste gases of industrial enterprises, is the chief cause of pol-
lution of the air reservoir. For this reason, the problem of sanitary
protection of air purity is primarily one of recovery of sulfur dioxide
from the so-called poor sulfur gases discharged into the atmosphere.
This applies primarily to the purification of the flue gases of thermal
electric power plants operating on sulfur-containing types of fuel (mazuts,
coal) containing 0.3-0.6% sulfur dioxide. The amount of these gases is in-
creasing enormously and steadily in connection with the rapid development of
thermal-power engineering.
At the present time, a large number of flue-gas purification processes
are known which have been the subject of numerous studies, and in many cases,
of experimental industrial research, but they do not include methods suitable
for industrial application that would permit an economical recovery of sulfur
dioxide from these gases. In order to solve this problem, which is of major
practical importance, it is necessary to make full use of the results of
p revious s t udies.
SURVEY OF PROCESSES AND METHODS OF REMOVAL
OF SULFUR DIOXIDE FROM GASES
A classification of the processes of sulfur dioxide removal from gases
proposed and studied thus far can be arrived at by using the same criteria
as in the classification of processes of hydrogen sulfide removal from
gases (chart 2).
It is useful first of all to divide all the processes into two main
categories differing in the physical state of the main reactant used for
recovering sulfur dioxide from gases.
The first category includes processes involving the use of a liquid
phase (liquid or "wet" processes) and therefore carried out at relatively
low temperatures.
The second category irfcludes processes and methods based on the reaction
between the gas and a solid phase (processes of "dry" purification). Here
there are no temperature limitations on the main reaction, which is character-
istic of processes of "Vet" purification related to the evaporation temperature
of the liquid phase.
- 98 -
-------
Chart 2. Classification of processes of sulfur dioxide removal from gases.
Processes of S02
removal from gases
Liquid
(wet)
Without utiliz-
ation of sulfur
Water
purification
Lime
-
vo
vo
Cyclic,
utilizing
sulfur
Magnesite
Zinc
Xylidene
Ammonia
Aluminum
sulfate
I
With formation of
sulfur-containing
chemicals
Ammonia-sulfuric
acid
Catasulfate
Acid-catalytic
Formation of
sodium salts
of H2S03
Treatment of
mineral raw
material
with diluted
SO,
Without utiliz-
ation of sulfur
Using ash
with high
Ca content
With neutraliz-
ation of
gaseous NHj
Dry
Cyclic, with
utilization
of sulfur
Using
activated
charcoal
/
Using iron
oxides
Using
manganese
-
With formation of
new sulfur-
containing
chemicals
Contact-
catalytic
-------
Each of these categories can in principle be subdivided into three
main groups differing in the characteristics of utilization of the sulfur
dioxide being recovered.
The first group includes processes whose main purpose is gas purifi-
cation as such, without considering the possibilities of utilization of the
recovered sulfur dioxide. The products of the main reaction of sulfur
dioxide with any given reactants constitute the waste in this case and are
discarded. This group includes the first attempt to actually achieve sulfur
removal from flue gases, i.e., the process of purifying the gases by washing
with water. In this process, the bulk of the SO- dissolves in the water
directly, and a certain amount reacts chemically, in the form of sulfuric
acid thus formed, with the salts Ca(HCO,)2 and Mg(HCO-)2 present in the
water to form CaCO-, MgCO- and carbon dioxide. The main difficulty in
removing SC>2 from gases by means of water lies in the large amount of water
required (5000-6000 m^ at 50°C. per ton of recovered sulfur), which after
washing of the gas acquires an acid reaction. Moreover, the discharge of
the acid water into reservoirs is environmentally just as harmful as the
discharge of sulfur dioxide into the atmosphere.
The removal of sulfur dioxide from gases by dissolution in very dilute
aqueous solutions of alkaline salts has been carried out in England in
installations of the Battersea electric power plants and at Bankside. Here
advantage was taken of the high natural alkalinity of the waters of the
Thames River and of the possibility of discharging the was waters into it.
The degree of removal of SO- from the gas was 90-95% [5].
Nor is the sulfur of flue gases utilized in the lime process of purifi-
cation based on the neutralization of sulfur dioxide with slaked calcium
oxide, which is supplied in the form of lime milk or of a suspension of
finely divided active limestone.
The process is described by the following equations:
Ca (OH>2 + HzSOs = CaSO3 + 2 H20.
The calcium sulfite obtained is poorly soluble in water (0.138 g/1)
and in the course of purification of the gases precipitates out of solution
in the form of fine crystals. A side reaction is the oxidation of sulfite
to sulfate by oxygen
2 CaSO3 + O2 = 2 CaSO4.
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The waste of the process vising the lime method is a slime consisting
of calcium sulfite and sulfate. It is technically undesirable to subject
this slime to regeneration, even though the studies performed established
that it can be used in the production of binders, but it has not been used
in industry thus far. Under laboratory conditions, the lime process has
been tested by the All-Union Heat Engineering Institute im. F. E. Dzerzhinskiy
(VTI) and, on a larger scale, in an experimental unit of the Kashira State
Regional Electric Power Plant [21]. This process is characterized by a
relative simplicity and achieves a practically complete removal of S02.
However, the substantial consumption of the reactants, coupled with the im-
possibility of their regeneration and utilization of sulfur and the lack of
industrial consumers of the slime, make the lime process uneconomical and
unpromising.
The second group includes the so-called cyclic processes and methods,
with the formation of commercial sulfur dioxide or elemental sulfur. Here,
sulfur dioxide is removed from the gases by means of reactants that are
subjected to regeneration and recycled for subsequent reuse.
In dry cyclic processes, which will be discussed in more detail below,
sulfur dioxide is absorbed from the gases by activated carbon or other
solid reactants.
The absorbents used in liquid cyclic processes are various solutions:
ammonia, organic amines (xylidene, pyridine), suspensions of metal oxides
(MgO, CaO, ZnO) and others.
Regeneration of the absorbents in these processes is carried out by
heating the solution and driving off the SO in a stream of water vapor,
or by calcining the filtered sparingly soluble sulfate salts in ovens.
Among the many proposed liquid cyclic processes of extraction of SO^
from flue gases, the greatest interest among researchers and in industry
has been shown in the ammonia, magnesite, zinc and xylidene processes.
The cyclic ammonia process is characterized by the following reactions
of formation of ammonium sulfite and bisulfite:
S02 + 2NH3 + H«0 ?. (NH4)2SO3,
(NH4)oS03 + SO* + H50 -^ 2NHiHS03.
The pressure of S0~ and NH, above the ammonium sulfite and bisulfite
solutions may range over considerable limits and depends on the ratio of
the concentrations of the neutral and acid salts. This ratio can be chosen
so that the partial pressures of S02 and NH3 are negligible. Such a solu-
tion can then be used to absorb S02 almost without losing any NHg.
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Therefore, in absorbing S09 from gaseous mixtures, use is made not
of ammonia water alone, but of a solution containing certain proportions
of (NH,)2S03 and NH^HSOg. The optimum temperature of the purification
process is 30°C. The ammonium bisulfite obtained as a result of absorption
of S(>2 is an unstable compound undergoing regeneration relatively easily
during boiling, with the formation of sulfur dioxide and ammonium sulfite,
which can be used again in gas purification.
In the process, ammonium sulfite is partially oxidized by the oxygen
usually present in the waste gases to ammonium sulfate, which accumulates
in the circulating solution. To extract the sulfate, part of the solution
is continually or periodically brought out of the cycle and evaporated,
causing separation of sulfate crystals, and the solution is returned to the
system. The oxidation of ammonium sulfite can be substantially decreased
by adding inhibitors, for example, paraphenylenediamine (0.05-0.1% of the
weight of the solution), to the solution. The ammonia method of flue gas
purification has been studied in detail in the USSR [24] and the U.S.A. [23].
Operation of an experimental-industrial unit trapping S02 by the ammonia
method at Thermal Electric Power Plant 12 of the Moscow Regional Administra-
tion of the Power Economy showed that the gases emitted into the atmosphere
after the purification contained a certain amount of ash, ammonium salts,
and a mist, causing undesirable sanitary conditions in the area around the
unit. For this reason, the setup also included wet electrostatic precipita-
tors for final purification of the waste gases. The flue gases subjected
to purification by the cyclic ammonia method should be first recooled to
30-35°C. In view of the enormous attendant heat loss (the temperature of
the flue gases is 120-140°C.), and bulk of the unit, and considering the
relatively low indices of the main process, the cyclic ammonia method of
S02 removal from gases holds little promise for industrial application.
The magnesite cyclic process is based on the absorption of sulfur
dioxide by a suspension of magnesium oxide in water. This involves the
formation of magnesium sulfite poorly soluble in water, according to the
reaction MgO + S02 = MgSOg. As it is formed, it precipitates out of the
solution in the form of MgS03'6H20 crystals. After filtering and dehydration,
magnesium sulfite is roasted at 1000°C., and decomposes at this temperature
into the component parts MgS03 = MgO + S02- Sulfur dioxide is thus obtained
with a concentration sufficient for the production of sulfuric acid (8-10%).
Magnesium oxide is reused for the absorption of 862.
During the purification of the gases and also during drying and roasting
of the sulfite, a certain part of the latter is oxidized to sulfate, which
after filtering remains in solution. The recovery from the solution of
crystalline magnesium sulfate, which constitutes a commercial product, is
carried out by evaporating the solution.
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In the USSR, the magnesite method of gas purification was developed
by the "Gazoochistka" trust and VTI and was tested on a large pilot unit
for purifying the flue gases at the Kashira State Regional Electric Power
Plant [21].
The magnesite process is not applicable to the purification of flue
gases of electric power plants because of the complexity of the layout,
the necessity of a complete removal of ash from the gases, and mainly
because of the large heat loss because of the drying and decomposition of
magnesium sulfite, which reaches 4% of the amount of fuel consumed by the
electric power plant.
Very similar to the magnesite process of removal of sulfur dioxide
from flue gases is the cyclic zinc process, based on the production of
zinc sulfate and thermal decomposition of the latter into S0? and ZnO.
The advantage of using zinc oxide over magnesium oxide is the lower dis-
sociation temperature of the acid sulfate salt (260 instead of 650°C.) and
the possibility of obtaining sulfur dioxide of high concentration (up to
100%) by this reaction.
However, the difficulties involved in the regeneration of the zinc
sulfate which is thus inevitably obtained, the complexity of the technolog-
ical flow scheme and the high cost of the main reactant, zinc oxide, have
been responsible for the lack of development of this process.
Cyclic liquid processes based on the adsorption of sulfur dioxide by
aromatic amines, particularly xylidene CgH^(CI^^NHo, ^ave also been
unsuitable for the recovery of sulfur dioxide from flue gases. The adsorp-
tion capacity of xylidene relative to sulfur dioxide is many times that of
water, but its use in the pure form is impossible because of the formation
of crystalline xylidene sulfate, so that the absorbent usually employed is
a mixture of xylidene with an aqueous solution of soda. Xylidene is toxic
and possesses a certain volatility, and therefore the waste gases following
absorption should be washed with sulfuric acid, which greatly complicates
the flow scheme.
The third group of processes of sulfur dioxide removal from gases
includes those in which sulfur dioxide is recovered and utilized in the
production of new chemicals. This group of processes is characterized by
the fact that the absorbent is not recycled into the process, but used in
the reaction with sulfur dioxide.
Dry processes of this group include treatment mainly of the mineral
raw material (phosphorites, ores, salts, and others) with sulfur dioxide.
Among liquid processes of the third group, the most important are
those in which the absorbent used is ammonia, so that the production of
- 103 -
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ammonia fertilizers can be achieved.
For example, practical applications have been found for the ammonia -
sulfuric acid process based on the reaction
2NHjHS03 + H2SO4 = (NH4).SO, -J- 2SO-. + 2 H,O.
A drawback of this process is a substantial consumption of ammonia and
sulfuric acid.
The same group includes the "catasulf" process.
Of practical interest is the process, verified under laboratory condi-
tions [24], of production of sodium sulfates through absorption of SC^ by
solutions of alkalis or carbonates. However, considering the small industrial
demand for sodium salts, this process cannot be widely applied in the removal
of sulfur from flue gases.
Among other liquid processes of this group we can mention the production
of silute sulfuric acid through catalytic oxidation of sulfur dioxide by oxy-
gen in an aqueous medium.
The catalysts used are ions of metals - iron and manganese. This process
requires a thorough removal of ash and catalyst-poisoning impurities from
the gases, and because of the low rate of the principal reactions and large
consumption of the catalyst, it is unsuitable for the purification of flue
gases.
Considering the general and comparative evaluation of the proposed pro-
cesses for removing sulfur dioxide from flue gases, one should note th.at they
do not pertain to processes occurring in boiler units, and for this reason
the problems of corrosion of power plant equipment and contamination of the
heating surfaces of boilers are not at all solved by using just any methods
of sulfur removal. As far as the proposed liquid processes of sulfur removal
from flue gases are concerned, they all require deep cooling to 30-40°C,
since they are based on the use of aqueous solutions or suspensions of certain
reactants. As a result, the buoyancy of the gases discharged from the smoke-
stacks decreases sharply, resulting in a harmful increase of the concentration
of carbon dioxide in the ground layers of the air reservoir. Nevertheless,
from a technical point of view liquid processes do solve in various degrees
the problems of removal of sulfur dioxide from gases. However, on the basis
of technical-economic considerations, present-day liquid processes of sulfur
removal from flue gases do not meet the requirements of thermal power engine-
ering.
This conclusion has been reached both in the USSR and abroad on the
basis of a serious technical-economic study of this problem. Thus, in 1961,
- 104 -
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the institutes "Giprogazoochistka" and "Giprokhim" carried out a detailed
technical-economic study of a few of the most promising processes of
purification of flue gases, i.e., the limestone, magnesite, zinc, and ammonia
processes. It was shown that the construction of sulfur-removing units at
electric power plants is not profitable as compared with the construction of
chemical plants of equivalent output, and can be justified only by consider-
ations of preservation of air purity.
Calculations of the overall effect of the use of the indicated liquid
processes, carried out in recent years, revealed a 3-4% decrease in the
thermal economy of electric power plants as compared with direct combustion
and discharge through high smokestacks, and a substantial increase (up to
20%) in the specific capital investments and operational expenditure. Un-
favorable technical-economic characteristics of liquid processes of sulfur
dioxide removal from flue gases have been responsible for the fact that at
the present time, both in the Soviet Union and abroad, further studies and
development of these processes have been practically discontinued.
The researchers' attention has switched to the development of dry
sulfur removal processes for which some encouraging prospects have been
noted in electric power plants. Here the work is developing in two direc-
tions: development of processes of dry trapping of sulfur dioxide from
the flue gases past the boiler unit and before their entrance into the smoke-
stack, and creation of processes of dry sulfur removal directly in the boiler
unit itself.
A characteristic feature of the methods developed is their development
chiefly as cyclic adsorption processes. They are based on the absorption
of sulfur dioxide by solid adsorbents (activated carbon, silica gel) or
reactants (metal oxides) at moderate temperatures, followed by regeneration
at higher temperatures by driving off the sulfur dioxide through calcination
or blowing hot air or steam.
The absorptive capacity of silica gel (S) and activated carbon (A.c.)
for S02 was studied by G. I. Chufarov [25] and I. N. Kuz'minykh [26]. The
characteristics of these adsorbents are as follows:
S S A.c. A.c.
S02 content of gas, vol. % 2 4 2 4
Absorptive capacity of 80s per100 g
of adsorbent, g
at 0°C 9,5 13,0 19,0 24
at 108C 8,5 11,0 16,0 20
at 20eC 7,0 8,8 12,5 17
In order to drive S02 out of the spent adsorbent, the silica gel must
be heated to 130°C., and the activated carbon to 250°C. In the course of
- 105 -
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removal of SC^ from the gases by activated carbon in the presence of oxygen
and water vapor, coal simultaneously acts as the catalyst in the formation
and then adsorption of sulfur trioxide and sulfuric acid.
I. F. Zemskov [27] studied the purification of flue gases by various
types of activated carbon. According to the experimental data, the sorption
of 1 T of sulfur dioxide requires 5-6 T of activated carbon of type SKTD-1.
Fig. 33. Technological diagram of assembly for the
removal of sulfur dioxide from flue gases by acti-
vated carbon at an electric power plant.
1 - flue gas; 2 - first stage of adsorber;
3 - second stage of adsorber; 4 - purified flue
gas; 5 - cooler; 6 - heater; 7 - desorber;
8 - screens 9 - coke; 10 - coke elevator;
11 - purified flue gas; 12 - enriched S02 gas;
13 - coke.
The process of sulfur dioxide removal from flue gases by activated
carbon is being developed on a large scale in the German Federal Republic
at moderate temperatures (up to 50° Q and relatively elevated ones (100-
160 °C.). Experiments on sulfur removal at moderate temperatures showed that
the process is difficult to carry out technologically even if one neglects
the fact that it produces ash-contaminated sulfuric acid of low concentra-
tion (7-15%) [28].
More promising prospects for the use of activated carbon for sulfur
removal from flue gases were discovered at temperatures of around 160°C.
The sulfur dioxide adsorbed at temperatures above 50°C. can be recovered
from the charcoal in the form of sulfuric acid on heating to 250°C. The
activated charcoal is regenerated at 350-450°C. without access of oxygen.
Such a process, known as the "reinluft" process, was carried out in 1959
on a unit with an output of up to 2000 m.3/hr of flue gases at the Wolfsburg
electric power plant (Fig. 33) [29].
In 1967, a report was published [30] to the effect that the process was
being carried out on a larger installation (near Dortmund). The adsorbent
used in this process may be fine-grained peat semicoke and also semicoke
obtainable from brown or bituminous coal. Additional activation of these
types of adsorbents is carried out directly in the course of sulfur removal
in the presence of S02 and of the sulfuric acid obtained.
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In addition to processes based on the adsorption of sulfur dioxide,
the literature contains material on research on other dry processes of
sulfur removal from flue gases, in particular, by means of iron oxides
and manganese oxides. Laboratory experiments on the purification of gases
using iron oxides [31] showed that at 200-450°C. at a ratio of iron oxides
to SC>2 slightly higher than stoichiometric, in the presence of oxygen,
sulfur dioxide is oxidized to SO-. The process of regeneration takes place
at about 600°C. Judging from the published information, a more advanced
process of sulfur removal from flue gases using manganese oxides was pro-
posed in Japan [32], The main reactant used here is a powder of activated
Mn02, which spreads throughout the stream. On reacting with Mn02, sulfur
dioxide and trioxide form manganese sulfates, which are recovered together
with the unreacted Mh02 in a cyclone and an electrostatic precipitator.
A technological diagram of such a process is illustrated in Fig. 34.
On the basis of the results obtained with an installation operating
according to this process, with an output of 3000 m3/hr of flue gases, a
semi-industrial plant with an output of 150,000 m^/hr is now being constructed
at the electric power plant of lokeiti (Honshu).
Among dry sulfur removal methods, of major interest is a process based
on the catalytic oxidation of sulfur dioxide to the trioxide followed by its
evolution in the form of sulfuric acid.
Essentially, this process is analogous to that of production of sulfuric
acid by the contact method and differs from it in the concentration of sulfur
dioxide in the gaseous mixture (0.2-0.4 instead of 7-8%). A technological
diagram of an installation utilizing such a process is given in Fig. 35.
A contact-catalytic process of purification of flue gases is being
developed with promising results in the German Federal Republic [33] and
U.S.A. [37].
Of considerable interest are the possibilities of recovering sulfur
dioxide from gases directly in the boiler unit. Research by the Perm Phar-
maceutical Institute conducted in collaboration with the Kizel State Regional
Electric Power Plant No. 3 in 1961 showed the feasibility of removing sulfur
dioxide from the flue gases of a thermal electric power plant by introducing
finely crushed limestone into the high-temperature zone of the furnace separ-
ately from the sulfur coal [41].
The experiments were carried out by using Kizel coal, the Gubakha inter-
mediate product, and a mixture of coal with the intermediate product. Lime-
stone of the Vsevolodo-Vil'va quarry, containing 85.2% of calcium carbonate,
was used as the reactant for the absorption of S02. The limestone dust was
blown into the 1000-1200°C. zone through eight nozzles located along the
front and side walls of the boiler at different angles of inclination. The
- 107 -
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s
00
To stage of
crystallization
r—•- of-
Fig. 34. Technological diagram of the process of flue gas purification by means of manganese dioxide.
1 - flue gas blower} 2 - adsorber; 5 - multistage cyclone; 4 - electrostatic precipitator; 5 - dissolver;
6 - filter; 7 - oxidizing column; 8 - stripping column of NHj; 9 - dissolver of NHj; 10 - air compressor.
-------
o
vo
(2000 parts
per million)
SO, (20 parts
• per million)
S0{200
millionF V^ //
Removal of
fly ash
S0{2300
Removal of Parts_
fly ash Per million;
a\
SO,. (200
parts
..per millijon)
SOJ (20 parti?
per . f
million )| I
Fig. 35. Technological diagram of contact catalytic process of sulfur dioxide removal from flue gases.
1 - coal; 2 - coal conveyor; 3 - coal mill; 4 - boiler; 5 - steam collector; 6 - feed water;
7 - mechanical dust collector; 8 - high-temperature electrostatic catcher; 9 - converter;
10 - air heater; 11 - air blower; 12 - electrostatic precipitator for acid; 13 - oxygen pump;
14 - sulfuric acid; 15 - smokestack.
-------
experiments were carried out over the course of nine weeks in order to
determine the effect of the amount of limestone supplied to the boiler
furnace, of arrangement and angle of inclination of the limestone nozzles,
and of working load of the boiler on the degree of purification and tempera-
ture of dew point, fuel of different sulfur contents being used.
Given below are experimental data showing the effect of the amount of
limestone supplied on the degree of removal of SC>2 from flue gases:
Amount of limestone, 0 40 60 80 100 120
% of stoichiometrie
^concentration, * ^ Q^ Q^ 0^2 0,193 0,120
industrial product 0,593 0,451 0,403 0,34 0,252 0,16:',
Degree of purification, %
coal — 22,8 31,0 41,5 51,2 70.S
intermediate product - 24,3 33,1 43,1 57,2 72,0
The industrial tests performed confirmed the fundamental possibility of
removing sulfur dioxide from flue gases by limestone injected separately
from the fuel. However, even this method is characterized by disadvantages,
i.e., a low degree of purification and a high content of limestone dust in
the outgoing gas. A similar study was made in the U.S.A. [28], where a study
was made of the effect of sulfur removal from gases leaving the furnaces
during the combustion of anthracite coal. It was shown that limestone should
not be recommended for introduction into the burning coal, since it may react
with the silica present in the coal dust. Limestone was found to be more
effective than dolomite, and a small amount of iron in the limestone increases
the efficiency of the sulfur trapping.
Positive results with sulfur removal from flue gases during blowing of
dolomite dust into a boiler furnace were obtained in the German Federal
Republic at the Wolfsburg electric power plant, which operates on sulfur
mazut [10]. The study showed the optimum particle size of dolomite to be
10-60 y. The residence time of the flue gases in the boiler was 6 sec.
In addition to the recovery of sulfur compounds directly in the boiler
unit by means of some reactants or others introduced from the outside, of
scientific and practical interest are the studies of N. G. Titov and
L. A. Borozdina, aimed at elucidating the conditions under which the ash of
solid fuels may be a necessary reactant in the sulfur removal process [35].
The authors showed that the presence in the coals of minerals that
are usually present and whose composition includes calcium and magnesium does
not influence the decrease in the content of sulfur compounds in flue 'gases,
since the dissociation of these minerals with the formation of CaO and MgO
proceeds at high temperatures, after the bulk of the sulfur gases have been
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driven out of the furnace. However, in the presence of calcium and magnes-
ium humates in the fuels (lowland peats, some forms of brown coals), the
starting combustion stage is accompanied by the decomposition of these
humates at temperatures of about 200-300°C., with the appearance of calcium
and magnesium oxides capable of binding the sulfur oxides formed into
involatile sulfates.
The degree of conversion of sulfur oxides into sulfates depends not
only on the quantitative relationships of humates and sulfur in the coal,
but also on the mode of combustion of the fuel.
THERMODYNAMICS OF THE REACTIONS
BETWEEN SULFUR DIOXIDE AND METAL OXIDES
The process of removal of sulfur dioxide from gases at high temperatures,
like the high-temperature recovery of hydrogen sulfide from gases, is best
accomplished technically by using solid reactants that are stable at these
temperatures and after reacting with S02 yield stable forms of sulfur com-
pounds. Since flue gases from which sulfur dioxide is to be removed usually
contain a certain amount of oxygen (o>l), the process of sulfur removal will
obviously be carried out in an oxidizing medium, leading to the formation
of sulfates of the reacting metals.
The appearance of sulfites is improbable in this case, since they all
are unstable compounds that in the presence of oxygen at high temperatures
change into the corresponding sulfates.
The removal of sulfur dioxide from gases at high temperatures may involve
the use of solid reactants containing such metals as calcium, magnesium,
manganese, iron, and others. The melting and decomposition points of certain
pure metals, oxides, sulfates, and carbonates {14] of these metals are given
below:
Ca Me Zn Fe Mn
tnelf °c 850 650 1868 1539 1244
tvap. °C 1480 1105 4750 3070 2095
CaO MgO ZnO FcjO, Fc,O« FcO MnO
tmeit- °C 2585 2JOO 2000 1505 1550 1420 1650
^ap, «C 3500 2WO _____
OiSOi MgSO« FeSO, Fc.(SO4), MnSO4
/dec. °C 960 HOD 500 650 850
'uelf'C. •• • • 1420 — — — 700
CaCO, MgCOj *eCO, MnCO,
tdec. °C 910 680 400 300
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The removal of sulfur dioxide from flue gases by means of solid
reactants can in principle be carried out over a wide temperature range,
from 200 to 1000°C. Considering that the flue gases contain a considerable
amount of carbon dioxide, which together with sulfur dioxide may enter into
reactions with the solid absorbents, in order to decrease the consumption
of the reactants, the temperature of the process should be above the disso-
ciation temperature of the carbonates of the metals employed.
The dissociation of anhydrous iron carbonate ("or of tne mineral side-
rite) is described by the following overall equation:
n FeCO3 = m FeO + q FeA + p CO,, + r CO.
According to the data of certain authors [36], the decomposition of
iron carbonate occurs at 400°C., and at 500°C. the dissociation ends com-
pletely. The decomposition of manganese carbonate, taking place in an oxygen
atmosphere according to the reaction MnCOg + 1/2 Q£ = Mn02 + ^2' *s observed
at 300°C. [37].
In a carbon dioxide atmosphere, the dissociation of MnCOg occurs in
stages, MnCOo ^ Mn^ + COo, followed by oxidation of manganous oxide according
to the reaction 3MnO + C02 •* Mn304 + CO at 339-369°C.
A decomposition temperature of about 620-680°C. was determined for the
dissociation of magnesium carbonate MgCO~ = MgO + COo [38]. A large number
of studies [14] have dealt with the process of decomposition of calcium
carbonate.
According to the data of many authors, the dissociation temperature of
calcium carbonate fluctuates depending on its content of impurities (Table 34).
According to the data of 0. A. Yesin and P. V. Gel'd [14], the metal
carbonates considered above form the following series in order of stability:
MnC03, FeC03, MgC03, CaC03. This is also confirmed by the temperature depen-
dence of the dissociation pressure of carbonates (Fig. 36).
An evaluation of the above decomposition temperatures of metal carbonates
shows that in order to purify the flue gases at temperatures of 500°C. and
above, it is desirable to use manganese and iron oxides. A selectivity of
the process with respect to sulfur dioxide is thus achieved.
At purification temperatures above 700°C., magnesium oxide can be used
additionally. Above 900°C. , calcium oxides can be used in addition to the
indicated metal oxides.
In order to obtain a preliminary estimate of the feasibility of reactions
between the indicated metal oxides and sulfur dioxide, the thermodynamic
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Table
Content of Impurities in Calcium Carbonate (in
Carbonate
Chalk
Marble • • • •
Limestone • • • •
CaCO,
9Q 17
i)7 18
9(5 41
90, 51
MCCO,
U U7
0 42
2 90
2,32
RtO,
0,07
0'17
0 Oi
2,40
FcCO,
<> 34
u,M
Insoluble
Residue
0,05
(I 7Q
0 ''*'
•>,&
Decompo-
sition
?3S:r«E
010
Ol/.
f>2l
CuO
equilibrium of these reactions was analyzed. Table 35 gives the values of
calculated free energies (AZ/T) of the individual reactions. As is evident
from this table, for all the metal oxides discussed (Ca, Mg, Fe, Mn), one
can observe a sufficient thermodynamic probability of occurrence of reactions
between these oxides and sulfur dioxide in the presence of oxygen at 300-
1000°C. Some thermodynamic limitations on the maximum temperature in such a
process exist for iron oxides (not above 600°C.) and manganese oxides (not
above 900°C.).
Fig. 36. _Temperature dependence of the
dissociation pressure of carbonates.
HUW'K
Considering the temperatures which are technologically permissible when
metal oxides are used, i.e., the fusion and dissociation temperatures of
metal oxides and sulfates, one can reach the following conclusions: when
iron oxides are employed, it is desirable to carry out the process of removal
of sulfur dioxide from gases at temperatures up to 400°C; when manganese oxides
are employed, the temperature of the process should not exceed 800°C.; calcium
and magnesium oxides can be used in processes of gas removal at temperatures
up to 1000°C.
In setting up a technological process of removal of sulfur dioxide from
flue gases under actual conditions, the preparation of the necessary metal
oxides should obviously be based on the use of natural raw material in the
form of minerals: limestone, chalk, magnesite, dolomite, siderite, and
others. Thus, it is of practical interest to determine the thermodynamic
characteristics of the reaction between sulfur dioxide and carbonates of the
- 113 -
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Table 35
Free Energies of Reactions of Sulfur Dioxide with Metal Oxides.
Reaction
CaO + SO2 + 0,5 Ot ;± CaSO4
MgO + SOs + 0,5 Oj ?i MgSO4
ZnO + SOa + 0,5 Oa «± ZnSO4
Fe2O3 + 2SQ9 + 0,5 O2 ;± 2 FeSO*
FesO4 + 3SOa + O2 15 3 FeSO4
FeO + S0a + 0,5 0* ;± FeS04
Fe + SOz + Oa;±FeSO4
MnOa + SOs;±MnSO4
2 MnjOs + SO. 15 MnS04 + Mn»O4
Mn3O4 + 3 SOS 4- O4 ?± 3 MnSO4
MnO + SOS + 0,5 Oa j± MnSO4
AZ/r at Temperature, °C.
300
—141,27
—201,73
—76,41
-69,03
— 1'34,08
—79,36
•HT73,GO
. —
—
—
—
400
—110,38
—1-61,52
-56,12
—41,82
—85,91
—56,77
—134,65
—
—
—
—
DOO
-87,58
—131,65
—41,20
—21 ,37
—49,67
—39,93
—105,70
—34,78
—19,62
—98,95
—47,71
COO
-70,10
—108,56
—29,82
—5,35
—21,24
—26,87
—83,32
—20,84
—12,91
—70,94
34,56
700
-56,29
-90,13
—20,88
+7,62
+1,81
—10,40
—65,45
—20,59
— 7,(i2
-48,77
—24,15
800
—48,57
-77,94
—15,22
+16,3:5
+ 17,35
-9,56
—53,89
—15,59
-3,:«8
-30,s:t
—17,59
900
—36,04
—62,60
—7,84
+27,51
+37,25
—0,68
—38,70
—1 1 ,49
+0,09
—16,15
—8,86
1 000
—28,44
—52,0!
—2,96
+35,39
+51,33
+5,41
—28,40
—8,10
+2,98
-3,77
—3,09
Table 36
Free Energies of Reactions of Sulfur Dioxide with Metal Carbonates
Reaction
CoC03 + SOz + 0,5 Oa = CaSO4 + CO2
MgCOs + SO2 + 0,5 Oe = MgSO4 + COsi
ZnCOa + SOZ + 0,5 O4 = ZnSO4 + CO2
FeCO, + SOa + 0,5 Ot = FeSO4 + 00S
MnCOa + SO» + 0,.r> O» = MnSO4 + COa
A2/r at Temperature, "C.
300
—107,44
—96,48
—88,20
—155,63
—80,03
400
—88,07
-78,57
—71,99
—118,48
—02,155
500
—73,91
—65,10
—59,93
—105,57
—48,52
600
-63,14
—54,41
—50,57
—95,43
—37,10
700
—54,72
—46,02
-43,04
—87,18
—27,50
SOO
—49,56
—40,28
—38,12
—81,01
— 2u,<;r.
900
—42,58
—32,97
—31,65
—74,42
— 12.20
tooo
—38,10
—27,84
—27,18
—69,34
—5,70
-------
metals considered in the presence of oxygen. Table 36 gives calculated
values of the free energies of these reactions at different temperatures.
The table shows that the removal of sulfur dioxide from gases is
thermodynamically feasible in the presence of oxygen by means of carbonates
of calcium, magnesium, iron, zinc and manganese over a wide temperature
range, from 300 to 1000°C. This range covers temperatures exceeding the
dissociation temperature of the carbonates considered. Hence, actually
above these dissociation temperatures, the laws governing the reactions
between sulfur dioxide and oxides of these metals, not their carbonates,
are applicable. Below the dissociation temperatures of carbonates, the
direction of the reactions toward the formation of metal sulfates instead
of their carbonates is determined by the effect of the joint presence of
sulfur dioxide and salts of weak acids.
Thus, a thermodynamic evaluation of the reaction of oxides and carbonates
of several metals (Ca, Mg, Fe, Mh, Zn) with sulfur dioxide in an oxidizing
medium indicates the probability of their occurrence at high temperatures,
which provides a basis for the development of suitable technological processes
of sulfur removal from flue gases.
In this connection, in order to ensure the necessary technical-economic
effectiveness of such processes, it is necessary to consider the problems of
utilization of the recovered sulfur, i.e., the conditions of processing of
the metal sulfates formed, with the obtaining of commercial products.
A practical solution to the problem of utilization of recovered sulfur
with simultaneous regeneration of the original absorbents can be the thermal
decomposition of metal sulfates by roasting. In this case one can obtain
sulfur dioxide with a concentration in the gaseous phase that is acceptable
for industrial use (up to 10%). Without touching on the technological and
technical-economic evaluation of such a solution, one should note that the
temperature conditions of the process of thermal decomposition of sulfates
will be different for different metals.
The thermal decomposition of iron sulfate should be carried out at
temperatures above 500-600°C., that of manganese sulfate above 700°C., and
that of magnesium sulfate, above 1000-1100°C. Higher temperatures are re-
quired by the roasting of CaSO.. The choice of optimum temperatures for the
roasting process should be made in each specific case by taking into account
the possibilities of ensuring suitable economic indices of the entire process
of removal of sulfur dioxide from the gases.
- 115 -
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EVALUATION OF THE ACTIVITY OF SOLID REACTANTS IN THE COURSE OF REMOVAL
OF SULFUR DIOXIDE FROM GASES AT HIGH TEMPERATURES*
Analysis of the thermodynamic studies shows that a high temperature
process of removal of sulfur dioxide from flue gases is possible and should
be carried out by using oxides and carbonates of calcium, magnesium, iron
and manganese over a wide temperature interval, from 200 to 1000°.
Calcium and magnesium oxides, whose sulfates decompose at temperatures
above 1100°C., are the most acceptable reactants in the removal of sulfur
dioxide from gases. Thus, it is necessary to determine the activity of
oxides of these metals in their reaction with sulfur dioxide and when the
latter is mixed with oxygen at 1100°C. The studies were carried out on a
unit with continuous recording of the rate of the process, as indicated by
the volume of the escaping gas. The procedure was the same as in experiments
involving the removal of hydrogen sulfide from gases described earlier.
The initial reactants used were chemically pure calcium oxide, magnesium
oxide, their mixtures, and kaolin with a particle size of 0.25-0.5 mm. The
calcium and magnesium oxides were first pressed into pellets using a hydraulic
press (pressure of 1.5 T/cm.2), then broken down to the necessary particle
size.
Pure sulfur dioxide was used in the experiments. As a result it was
found (Fig. 37) that the highest activity toward pure sulfur dioxide at
1100°C., a linear gas velocity of 0.11 cm/sec and a contact time of 7.1 sec
is displayed by calcium oxide, followed by a mixture of calcium oxide and
magnesium oxide, kaolin, and pure magnesium oxide. To evaluate the role of
oxygen in the process, experiments were also carried out using a mixture of
sulfur dioxide and oxygen. The volume concentration of sulfur dioxide was
65.3, that of oxygen 7.3, and that of nitrogen, 27.4%. The linear velocity
of the gaseous mixture was 0.157 cm/sec, and the contact time, 4.45 sec.
A considerable decrease in the activity of the metal oxides used was found
in the reaction with sulfur dioxide (Fig. 38).
1*0
70
tog
-------
'SOr
BO
IS fO
01
1
o
o IfO
-------
8
30
SO
fe fff
g*
5"
m
Fig. 39. Reaction of sulfur dioxide with solid
reactants at 700°C. (v = 0.5 m/sec, T = 0.19 sec).
1 - unroasted dolomite; 2 - roasted limestone;
3 - unroasted limestone; 4 - manganite; 5 - pyrolusite;
6 - magnesite; 7 - hematite; 8 - magnetite; 9 - side-
rite; 10 - roasted sphalerite; 11 - sphene;
12 - chromite
When dolomite is used for 40 min, a degree of purification of the flue
gas equal to 98% is obtained; during the next 20 min, a decrease in the
degree of purification to 78.18% is observed. The degree of purification
of the gas with calcium oxide (roasted CaGO,) amounts to 99.23% in the
course of the first 32 min, and during the next 60 min decreases to 72%.
Natural limestone also possesses a high reactivity during the first 30 min
of the reaction, when the purification is 98.45%, after which it decreases
to 89.11% in 40 min and to 22.33% in 60 min.
Comparison of the activity of natural limestone and limestone pre-
roasted to calcium oxide shows that, other conditions being equal, the
removal of sulfur dioxide from flue gas is achieved in the course of a
longer period of time when roasted limestone is used. This is apparently
due to the presence of carbon dioxide in the flue gas.
It is probable that when natural limestone is used to purify the flue
gas, the carbon dioxide present in the latter effects a decrease in the
degree of purification toward the end of the reaction period, shifting the
reaction equilibrium to the opposite side, whereas during the purification
with calcium oxide, the same carbon dioxide leads to the formation of
calcium carbonate and has a lesser effect on the gas purification.
Next in activity in their reaction with sulfur dioxide are manganite
and pyrolusite of the Nikopol' deposit.
The removal of sulfur dioxide from the flue gas by manganite amounts to
96-99% during 32.5 min, then decreases to 52.44% during the following 51 min.
Pyrolusite is much less active than manganite. For pyrolusite, a 96% puri-
fication takes place only during 10 min, then decreases to 66.75% during,
27.5 min.
In the reaction with hydrogen sulfide, pyrolusite is more active than
manganite. This is due to the chemical composition of these ores. Natural
- 118 -
-------
manganite Mn02Mn(OH)2 has the following chemical composition (in %): MnO
40.4; Mn02 49.4; H20 10.2, and small amounts of Si02, Fe203 and other im-
purities. Pyrolusite contains chiefly Mn02, which accounts for 63.2% of Mn,
and the impurities Fe203, Si02, H20. Obviously, the presence of manganous
oxide in manganite is more readily oxidized by sulfur dioxide than the high
oxidized form, i.e. , pyrolusite Mn02%
As was shown by experiments using other reactants, the lowest reactiv-
ity is displayed by roasted magnesite, KMA hematite, magnetite, siderite
(of the Bakal deposit), roasted sphalerite, chromite, and sphene. As far
as the use of iron ores for the removal of sulfur dioxide from flue gases
is concerned, the degree of purification with hematite and magnetite during
the first 5-6 min of the reaction amounts to only 57.9-59%.
The removal of sulfur dioxide from the gas by iron ores was carried
out at 700°C., above the temperature of thermal decomposition of iron sul-
fate. The use of iron oxides for desulfurization of flue gases should be
carried out at up to 400°C., when the iron sulfate formed is stable.
Thus, the completed series of experiments aimed at determining the
activity of natural ores toward sulfur dioxide showed that in the removal
of sulfur compounds from flue gases at 700°C., the following solid reactants
can be used: dolomite, limestone, and manganese ore - manganite and pyro-
lusite.
The possibility of using these ores is also confirmed by thermodynamic
analysis of the reactions between sulfur dioxide and the chief elements
entering into the composition of these ores.
REMOVAL OF SULFUR DIOXIDE FROM GASES BY CALCIUM OXIDE
Considering the great reactivity of calcium oxide toward sulfur dioxide,
it is expedient to make a more detailed study of the physicochemical condi-
tions of purification of flue gases by natural limestone. First of all, it
was necessary to elucidate the effect of the blast velocity on the rate of
sulfur removal from flue gases, the effect of the temperature of the process,
and effect of particle size. Particular attention was given to the result
of binding of sulfur in the solid residue, for the purpose of evaluating
the conditions of regeneration of the absorbent so that it can be used
further in the process of purification of flue gases.
The study of the optimum conditions of recovery of sulfur dioxide from
flue gases was conducted in the same manner as the study of removal of hydro-
gen sulfide from gases on an installation described earlier. Before the
experiment, the limestone used was roasted for 5 hr at 1000°C. The unreacted
sulfur dioxide was determined by passing the gas through an aqueous solution
- 119 -
-------
of iodine and by quantitative evaluation of the results according to the
reaction
, -f- J» •+ 2 1-I.O = HsSOj + 2 H J.
Experiments designed to study the effect of the feed velocity of the
gaseous mixture on the rate of removal of sulfur dioxide from the flue gas
were conducted at 700° C. The linear velocity of the gas supplied was varied
from 0.32 to 1.78 m/sec. The composition of the gas (in %) approximated that
of the flue gas: S02 0.5; C02 14.4; 02 4.0 and N2 81.1. The size of the
absorbent granules was 0.5-1.0 mm. As the blast rate was raised from 0.32 to
1.78 m/sec, the rate of the reaction of sulfur dioxide with calcium oxide in-
creased during the first 10 min. The degree of conversion for this period of
purification of the flue gas was 98-99%. After 15 min, the rate of the
reaction of sulfur dioxide with calcium oxide decreased sharply as the blast
velocity sharply decreased. This is apparently because at high blast veloci-
ties (1.17 and 1.78 m/sec), a large amount of reactant is consumed, and the
layer height and contact time decrease to values that are not conducive to a
high degree of gas purification. In addition, the degree of conversion of
sulfur dioxide at lower gas supply velocities, 0.32-0.43 m/sec, was 97-99%
for 40 min (Fig. 40) . Such a degree of conversion of sulfur dioxide at a
blast velocity of 0.85 m/sec was observed for 20 min, and at a blast velocity
of 1.17 m/sec, for only 10 min. At a blast velocity of 1.78 m/sec, the degree
of conversion falls to 82.77% in 10 min. Under the conditions studied, it
was not possible to exclude the effect of the feed velocity of the gaseous
mixture on the rate of the main process of purification. In this case, the
degree of purification is also substantially affected by the rate of supply
of the reacting gaseous mixture to the surface of the reactant. Nevertheless,
the completed series of experiments clearly show that the removal of sulfur
dioxide from the flue gas (98-99%) in the course of 40 min can be carried out
at a linear velocity of 0.32-0.43 m/sec and a contact time of 0.22-0.24 sec.
The degree of utilization of the solid reactant in the experiments reached
as high as 22%. However, such a degree of utilization did not fully character-
ize the performance of the absorbent, since the duration of the experiment
did not exceed 1 hr. Subsequently, the reactant was able to purify the flue
gas, and thus its degree of utilization may be considerably increased under
actual condi tions .
The study of the effect of temperature on the removal of sulfur dioxide
from flue gas by calcium oxide was conducted both in a medium of pure sulfur
dioxide and in a gaseous medium similar to flue gas in composition.
The study of the effect of temperature during the reaction of calcium
oxide with pure sulfur dioxide was conducted at 310, 570 and 1100 °C. at a
linear gas velocity of 0.11 cm/sec and a contact time of 7.1 sec (without con-
sidering the temperature) .
- 120 -
-------
•00
U
o
&>
-------
Fig. 42. Change in the degree 9f conversion of
sulfur dioxide in the flue gas in thf- reaction
with CaO (SO, 0.5$, v = 0.41 m/sec, T = 0.25 sec)
at different temperatures.
1 - 500°C,; 2 - 600°C.; 3 - 700'C.; 4 - 800°C.
Time, min.
The study performed showed the practical feasibility of the process
of removal of sulfur dioxLde from flue gases by calcium oxide at high temp-
eratures, 600-800eC. Of major importance is the evaluation of the solid
residue for the purpose of regenerating calcium oxide and utilizing the
recovered sulfur.
To determine the phase composition of the wolid absorbent, studies
were conducted on the reaction of sulfur dioxide with limestone at differ-
ent temperatures in a neutral medium of nitrogen containing 0.2-0.3% sulfur
dioxide and 1.0% oxygen. The phase composition of the products of the
reaction of limestone with sulfur dioxide at different temperatures is shown
in Table 37.
Table 37
Phase Composition
SO- content, vol. %
0,20
0,35
0,26
0,25
0,21
temperature, °C
500
6riO
700
800
900
Content of .Sulfur Compounds in
the Solid Phase, wt. %.
CaSO4
_
—
32
89
94
CaSO3
63
31
19
6
4
CaS
37
09
49
o
2
It is evident from the table that up to 700°C., the bulk of the sulfur
is recovered in the form of calcium sulfite and sulfide. As the temperature
is raised, the amount of these salts of sulfur compounds decreases markedly.
The phase analysis of products of the reactions between sulfur dioxide
and limestone depends greatly on the oxygen content of the flue gases. For
the usual oxygen content of flue gases, 3-7%, and a temperature above 600°C.,
chiefly calcium sulfate is formed in the solid residue, and the total amount
- 122 -
-------
Fig. 43. Absorption of S02 by calcium carbonate
at different temperatures.
1 - chalk (0.4-1.6 mo fraction); 2 - limestone
(0.4-1.6 mm fraction).
of sulfide and sulfite does not exceed 2-4% of the amount of sulfate. The
recovery of sulfur dioxide from calcium sulfate requires roasting at 1400-
1500°C., which can hardly be justified. The problems of regeneration of
the absorbents in this process require further study. Of practical interest
is the evaluation of the degree of utilization of the reactants at different
temperatures in the course of removal of sulfur from flue gases by natural
limestone and chalk.
Gas of the following composition was used in the experiments (in %):
S02 0.3-0.4; O>2 7.9; 02 6.55; NZ 85.25. The results of the experiments
are presented in Table 38. It is evident from the latter that the reaction
of natural limestone with sulfur dioxide begins practically at 700°C. and
takes place most completely at 900 and 1000°C. The temperature of the start
of the reaction of chalk with sulfur dioxide is slightly lower, about 600°C.
Chalk is more reactive at reaction temperatures up to 900°C. (Fig. 43).
The high reactivity of chalk as compared with that of limestone is explained
by its large internal surface area.
At 1000°C., the process of absorption of sulfur dioxide takes place at
the same rate on limestone and chalk. The degree of conversion of sulfur
dioxide is substantially determined by the particle size of the absorbent
and increases as the particle size decreases from 3 to 1.6 mm (see Table 38).
As the temperature rises, the degree of utilization of the reactant
increases. For chalk, it rises from 13 to 49% in the 600-900°C. range. For
limestone, it increases from 3.15 to 35% under the same conditions.
. The above study leads to the conclusion that in the removal of sulfur
dioxide from flue gases, chalk can be used side by side with limestone.
For these solid reactants as well as for roasted limestone, effective solu-
tions should be found for the problems of utilization of the recovered sulfur
- 123 -
-------
and repeated use of absorbents in the process.
Table 38
Results of Recovery of Sulfur Dioxide with Limestone and Chalk.
Temperature,
ec.
so2, %
Stot> ™
Solid
Sorbent,
79
Degree of
Absorp-
tion, %
Linear
Velocity,
m/sec
Contact
time,
sec
Utilization
of
Sorbent, %
600
700
800
900
1000
600
700
800
600
700
800
900
1000
600
900
1000
Limestone, 1.6-0.4 mm fraction
0,390
0,390
0,300
0,300
0,300
0,290
0,294
0,315
0,270
0,300
0,345
0,263
0,348
0,275
0,240
0,313
0,73
1,85
3,86
9,40
13,34
4,35
11,10
23,00
48,50
70,00
1,28
1,44
1,58
1,72
1,9)
0,039
0,035
0,032
0,029
0,026
Chalk, 1.6-0.4 mm fraction
3,12
7,17
10,66
12,55
10,55
19,00
45,00
85,00
88,00
6i, 00
1,28
1,44
1,58
1,72
1,83
0,039
0,035
0,032
0,029
0,027
Chalk, 2.5-1.6 mm fraction
4,05
11,87
14,56
17,30
52,10
62,00
1,18
1,38
1,34
0,042
0,038
0,037
Limestone, 5-1.6 mm fraction
2,04
4,60
5,58
8,51
4,50
8,60
15,00
18,20
26,60
17.00
1,27
1,28
1,23
1,75
1,42
0,039
0,039
0,041
0,028
0,0.35
Limestone, 1.6-0.5 mm fraction
1,78
9,16
13,27
8,80
30,90
47,50.
1,25
1,81
1,56
0,040
0,028
0,032
13,20
32,50
47,50
49,00
37,50
17,20
52,00
62,00
8,60
19,60
18,20
26,50
17,00
7,60
31,00
47,00
Note. For the 1.6-0.4 mm fraction, the duration of the experi-
ment was taken as 60 min, and for the 2.5-1.6, 5-1.6 and 1.6-0.5 mm
fractions, 120 min.
- 124 -
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REMOVAL OF SULFUR DIOXIDE FROM FLUE GASES BY MANGANESE OXIDES
The activity of manganite in the reaction of sulfur dioxide with solid
natural materials is noteworthy. Therraodynamic analysis has shown that in
an oxidizing medium, manganese sulfate is formed in the solid residue dur-
ing the reduction of sulfur dioxide. From the standpoint of the conditions
of regeneration of the absorbent, manganese sulfate may prove to be a more
usetul reactant, since it decomposes at temperatures up to 1000°C. , evolving
sulfur dioxide into the gaseous phase.
In our experimental studies, the purification material used for desul-
funzing the flue gases was natural manganite of the Nikopol1 deposit,
Mn02Mn(OH)2. Its chemical composition is MnO 40.4; MnO, 49.4; H.O 10.2%,
and small amounts of Si0, Fe0, and other impurities. The composition
of the gas supplied was as follows (in %) :
No 81 . 86 .
S02 0.44; CO- 3.3; 09 14.4;
^
The experiments were conducted at 700°C. , with a layer height of 150 mm,
a particle size of 0.5-1.0 mm, and linear gas velocities of 0.43, 0.58 and
0.93 m/sec.
tO 20 JO 1(0 SO SO
lime, rain.
Fig. 44. Change in the rate of reaction of
sulfur dioxide with manganite at different
gas flow rates at 700°C.
1 - Vj •= 0.43 m/sec, Tj = 0.31 sec; 2 - v^ =
= 0.58 m/sec, T2 = °«29 se°5 3 - V = 0.93
m/sec,
= 0.16 sec.
W 20
30 W SI SO
Tine, min.
Fig. 45. Change in the degree of conversion
of sulfur dioxide in the reaction with manganite
with time at different gas flow rates (designa-
tion of curves same as in Fig. 44).
- 125 -
-------
l\
a
90
70
SO
JO
I
Fig. 46. Change in the degree of conversion
of sulfur dioxide in the reaction with manga-
nite with time at different gas flow rates
(S0 = 1.92JO.
1 -
*.. j 0.48 m/sec, t^ 0.20 sec; 2 - V2
- 1.79 m/sec, T- = 0.092 sec.
0 W 20 JO W SO fO
lime, min.
An increase in the feed velocity of the gaseous mixture led to an in-
crease in the reaction rate and a decrease in the degree of removal of sul-
fur dioxide from the flue gas (Fig. 44). For a gas feed velocity of 0.43
m/sec, its degree of purification was 95-99.65% during 54 min (Fig. 45),
and at 0.93 m/sec, a 96% conversion of sulfur dioxide was observed in the
course of 34 min. For comparison, experiments were carried out with a gas
having a higher concentration of sulfur dioxide, 1.92%, at blast velocities
of 0.48 and 1.72 m/sec (Fig. 46). Increasing the feed velocity of the gas
being purified also led to an increase in the reaction rate of sulfur dioxide
with manganese oxides during the first 5-8 min of the experiment, and then,
at a higher blast velocity, 1.79 m/sec, it dropped sharply. As the blast
velocity increased, the degree of purification of the gas decreased, owing
to a decrease in the time of contact of the gas with particles of the solid
absorbent.
The degree of consumption of the solid reactant at the lower blast
velocity was 44.7%, and at a velocity of 1.79 m/sec, 33.4%.
A study of the effect of temperature on the rate of removal of sulfur
dioxide from the gases was conducted at 500, 600 and 700°G. with the follow-
ing gas composition (in %) : S02 0.41; 02 14.4; N2 81.89, a linear gas
velocity of 0.42 m/sec and a contact time of 0.3 sec.
W x 10~3, g/min g
Fig. 47. Change in the rate of the reaction
of sulfur dioxide with manganite with time at
different temperatures.
1 - 500°C.; 2 - 600'C.; 3 - 700eC.; 4 - 800°C.
1.0
iff S0 til sa fff
line, Din.
- 126 -
-------
Pig. 48. Change in the degree of conversion
of sulfur dioxide in the reaction with manganite
with time at different temperatures.
1 - 500°C.; 2 - 600'C.; 3 - 700°C.
20 30 IfO 50
Time, rain.
As the temperature rose from 500 to 700°C., the purification rate of
the gas increased (Fig. 47). The highest degree of conversion of sulfur
dioxide was observed at 700°C. and reached 96-99.65% in the course of
54 min (Fig. 48). As the gas purification temperature was lowered, the
degree of conversion decreased slightly. At 500°C., a 98% degree of con-
version of sulfur dioxide lasts only during the first 20 min of the experi-
ment.
4
A study of the reaction of sulfur dioxide with natural manganite at
different temperatures showed that the purification of flue gases may be
achieved at 500-700°C. with a sufficient degree of removal. In addition,
the purification of the flue gas involved the use of other grades of mangan-
ese ore of the Nikopol1 deposit, in particular, ore of the Grushevskiy quarry
(A) and concentrate (B), the chemical composition of which is given below:
Component,% A B
Mn .'.... 29,90 44,70
Mn02 .... 18,60 50,60
SOZ 24,50 16,10
Al20s 4,40 1,80
Fea03 3,80 2,10
CaO 4,38 v 1,50
Component,
MgO . . . .
Na2O .-. . .
KzO ....
P
S
CO2
A
1,98'
0,23
B
1,00
0,44
1,19
0,22
0,21
0,21
The flue gas being purified had the following composition (in %):
SO 0.74-0.86; C02 12.3; 02 4.5; N2 82.34-82.46. The degree of conversion
of sulfur dioxide in the reaction with natural ore of the Grushevskiy quarry
was slightly higher than in the reaction with the concentrate. Apparently,
the degree of conversion is substantially affected by calcium and magnesium
oxides.
A definitive utilization of the indicated natural manganese ores re-
quires further study of the characteristics of the physicochemical reaction.
- 127 -
-------
Analysis of the solid phase during the reaction of sulfur dioxide with
manganese ore showed that the content of sulfide sulfur is negligibly low
(0.014-0.06%), all the sulfur from the gas being bound as sulfate sulfur.
In order to obtain a preliminary evaluation of the possibilities of repeated
use of the reactant, after the cycle of absorption of sulfur dioxide by man-
ganite, thermal decomposition of manganese sulfate was carried out at 900-
1000°C. in a stream of air in the course of 2 hr. The total sulfur content
was determined in the solid material. The absorptive capacity of manganite
decreased somewhat after a quintuple absorption of sulfur dioxide. This is
explained by the fact that in the thermal decomposition of manganese sulfate,
the sulfur absorbed is not completely evolved. Up to 50% of the recovered
sulfur remained in the solid phase, causing a decrease in the degree of
removal of sulfur dioxide from the gas in a later cycle. In order to increase
the rate of thermal decomposition of manganese sulfate, it is necessary to
raise the roasting temperature.
Another variant of the process of regeneration of the solid absorbent
may be the low-temper method of dissolution of manganese sulfate in water
followed by separation of the manganese sulfate solution.
The experiments performed showed the fundamental possibility of setting
up the process of purification of flue gases with the aid of natural manganese
ore at 500-700°C. The problems of regeneration and repeated use of the reac-
tants should be investigated further in order to determine the optimum charac-
teristics of the process as a whole.
- 128 -
-------
Ill
USE OF HIGH-TEMPERATURE REMOVAL OF SULFUR COMPOUNDS FROM GASES
IN LAYOUTS OF THERMAL ELECTRIC POWER PLANTS
As was noted earlier, at the present time, in connection with the
development of high-temperature technology and the widespread use of sulfur
fuel and sulfur-containing raw material, a solution must be found to the
problem of high-temperature removal of hydrogen sulfide and sulfur dioxide
from gases. This is required both from the standpoint of purely technological
considerations and for the purpose of sanitary protection of the purity of the
air reservoir.
In recent years, this problem has acquired a particular importance in
modern thermal-power engineering, where it is necessary to apply an effective
solution to the problem of utilization of sulfur mazuts and coals by major
thermal electric power plants.
A survey of the state of development of this problem revealed a very
scant number of studies dealing with high-temperature removal of hydrogen sul-
fide and sulfur dioxide from gases. In the case of hydrogen sulfide removal
from gases, this involves the process of sulfur removal at 300-400°C. by means
of iron oxides, and in the case of sulfur dioxide removal, the process using
manganese oxides. Promising results in reducing the sulfur content of flue
gases have been obtained by blowing limestone and dolomite into the gas stream
directly into the high-temperature zones of the boiler unit. At lower tempera-
tures (up to 200°C.), the investigators' attention was concentrated on the
development of sulfur removal processes based on the use of activated carbon.
A substantial number of studies and experimental industrial work have
been conducted on the so-called liquid (wet) processes of sulfur removal,
which are carried out at temperatures not above 100°C. Liquid processes of
hydrogen sulfide removal from gases have found extensive applications in the
chemical, gas, petrochemical and other industries. As far as liquid processes
of removal of sulfur dioxide from gases are concerned, despite their adequate
technical foundation, they are not used for the purification of gases with a
low S09 content, particularly in the case of sulfur removal from flue gases,
because of unsatisfactory technical-economic indices.
Considering the clearly inadequate amount of study devoted to problems
of hydrogen sulfide and sulfur dioxide from gases at temperatures that can be
practically employed, i.e., around 400-1000°C., the authors carried out numerous
theoretical and experimental studies with the aim of at least partially filling
this gap.
The results of these studies, presented in the preceding chapters, per-
mit one to draw the sufficiently definite conclusion that the required high-
temperature processes of removal of hydrogen sulfide or sulfur dioxide from
- 129 -
-------
gaseous mixtures are feasible. In addition, the completed studies provide
a basis for a preliminary determination of the prospects and for the formula-
tion of general views regarding the applicability of high-temperature processes
of sulfur removal at thermal electric power plants using sulfur-containing
types of fuels (mazut, coal).
The process of high-temperature removal of hydrogen sulfide from gases
may find applications at thermal electric power plants in the preparation of
sulfur fuel for combustion through its preliminary gasification. In this
case, noxious discharges of ash and sulfur compounds into the atmosphere are
absent. At the same time, the reliability of the operation of boiler units
increases as a result of elimination of abrasive wear by ash and of the effect
of sulfuric acid corrosion. A special importance is assumed by a reliable
operation of modern power units as their unit capacity increases. It has been
calculated, for example, that the total loss involved in incomplete stoppage
of a power unit of 200,000 kW capacity amounts to several tens of thousands of
rubles.
When gasification of solid fuel is included as a stage of its prepara-
tion for combustion at thermal electric power plants, one can exclude the
equipment of units for pulverizing the fuel and also electric precipitators
for removing fly ash from the flue gases and the installation for the removal
of sulfur compounds.
Since the combustion will not involve a solid fuel, but the power-
producing gas obtained from it, one can increase the thermal stress of the
furnaces and heating surfaces by a factor of approximately 2, and hence, de-
crease the outside dimensions of the boiler unit.
For the conditions of high-capacity thermal electric power plants, the
gasification of fuels should be expediently carried out under pressure, and
this will permit a considerable improvement of the technical-economic indices
of this process and will facilitate the creation of high-capacity units corres-
ponding to the scale of utilization of the fuel at the electric power plants.
If the high-pressure gas obtained must be used in furnaces at atmospheric
pressure, the potential energy of the compressed purified gas will be used in
an expansion gas turbine. This turbine actuates an air compressor which com-
presses that part of the air which is removed for gasification from the total
amount of air supplied for the combustion of fuel (~40%). A flow diagram of
such a thermal power plant is shown in Fig. 49.
On the basis of gasification under pressure, the problem of utilization
of sulfur mazuts and low-quality solid fuels is being effectively solved in
new power installations of high-capacity thermal electric power plants, more
economical than steam turbine installations. In the USSR and elsewhere, major
work is being carried out for the purpose of creating electric power plants
with steam-gas and gas-turbine installations where the fuel is burned in furn-
aces under pressure, so that their thermal stress can be increased, the layout
- 130 -
-------
simplified, the reliability increased, and the main indices of the production
of electric power improved.
Fuel
Fig. 49. Flow diagram of steam-turbine electric power plant with
preliminary gasification of fuels.
GPP - gas-producer plant; C - air compressor; H3T - expansion gas
turbine; SB - steam boiler; ST - steam turbine.
According to the data of the TsKTI im. I. I. Polzunov (Central Scientific
Research Institute for Boilers and Turbines) [39], the introduction of the
steam-gas installations developed by this institute in place of steam turbine
installations of equal capacity and of the same steam parameters in gas-mazut
electric power plants can provide the following savings (in %): in fuel, 7-15;
in specific metal consumption, up to 28; in specific capital investments, up
to 25; in labor expended on construction and assembly work, up to 30; in cost
of electric power, up to 15. An even greater effect resulting from the intro-
duction of steam-gas installations is found by comparing these indices of the
installations with thermal steam-turbine electric power plants operating on
solid fuel. The technical-economic indices of steam-turbine plants operating
on solid fuel are known to be less favorable than those of analogous plants
operating on gas.
Steam-gas and gas-turbine electric power plants set high requirements
on the purity of the working substances and therefore on the types of fuel
utilized. The most convenient fuel from this standpoint are combustible gases.
More serious difficulties are involved in the use of mazuts, particularly sul-
fur mazuts, because of the corrosion of the vanes, turbines, air heaters and
other parts of the unit. Despite numerous studies along these lines, no solu-
tions have been found thus far to the problem of direct utilization of solid
fuel in these installations.
The most realistic solution to this problem consists in the preliminary
gasification of sulfur mazuts and solid fuels, involving the use of the purified
gas obtained in the new power installations. Figures 50 and 51 show schematic
diagrams of steam-gas and gas-turbine installations using purified power-
producing gas obtained from gasification of the fuel. A diagram of the operation
- 131 -
-------
of a gas turbine with discharge of the flue gases into the boiler and use of
gasification of the fuels is shown in Fig. 52.
Thus, in modern steam-turbine and new steam-gas and gas-turbine electric
power plants, the gasification of sulfur fuel should be regarded as an impor-
tant preliminary stage of its preparation for combustion.
Objectives arise in connection with the creation of new processes of
gasification of low-quality solid fuels and sulfur mazuts satisfying the
requirements of thermal-power engineering with regard to the total energy
efficiency and a sufficient intensity of the process, i.e., a rate that would
permit the creation of high-output gas producers. These objectives have been
worked on for several years at the laboratory of gas processes of the Institute
of Mineral Fuels, and this has resulted in the proposal of new methods of gasi-
fication of sulfur mazuts and solid fuels [42].
Fuel
Steam
Flue gases
Fig. 50. Diagram of steam-gas electric power plant with
preliminary gasification of fuels.
GT - gas turbine; ST - steam turbine? C - air compressor;
GPP - gas-producer plant.
A characteristic feature of these methods is the removal of soot, fly
ash and sulfur compounds from the gases at 1000-1100°C., which permits one to
increase the total energy efficiency of production of the gas to 94-96% on
mazut and 92-93% on solid fuel. The high-temperature removal of soot and dust
from gases is achieved by combining cyclones (coarse purification) with granu-
lar and ceramic filters (fine purification). In addition, steps have been
developed that permit a maximum reduction of the formation and entrainment of
soot and dust (use of water-mazut emulsions of catalysts, high pressures). The
removal of sulfur compounds (hydrogen sulfide) from gases at high temperatures
is accomplished by means of solid reactants consisting of alkaline earth oxides
of metals. The dissociation temperatures of carbonates of these metals are
below the temperature of the gas purification process (900-1000°C.), and their
sulfides are thermally stable and characterized by a high melting point. 'The
perfected methods of gasification of sulfur mazuts and low-quality solid fuels
are characterized by a high intensity of the main gasification process. Under
laboratory conditions, during the gasification of sulfur mazuts, the thermal
- 132 -
-------
stress of the reaction volume of the gas generator reached 35 x 106 kcal/m3 hr,
or 8000 kg/tn^ hr. During the gasification of fine-grained brown coals (0-10 mm)
in a fluidized bed at a pressure of 20 t atm, a generator-shaft cross-sectional
stress of 10,000-12,000 kg/m2 hr is reached.
Steam
Fig. 53. Diagram of gas-turbine electric power plant
with preliminary gasification of fuels.
PC - final air compressor; GPP - gas-producer plant;
HPCC - high-pressure combustion chamber; HPC - high-
pressure air compressor; HPT - high-pressure gas turbine;
LPC - low-pressure air compressor; LPCC - low-pressure
combustion chamber; LPT - low-pressure gas turbine.
Gas
Fig. 52. Diagram of gas-turbine electric power
plant with discharge into boiler.
CC - combustion chamber; AH - air heater;
EGT - expansion gas turbine; SB^- steam boiler;
remaining designations same as in Figs. 50 and 51.
It is not necessary to emphasize that the use of gasification of fuels
as a preliminary stage of their preparation for combustion can be technically
and economically justified only by ensuring a high total energy efficiency of
the process. For this reason, the use for this purpose of the process of
high-temperature removal of hydrogen sulfide from gases, which in contrast to
other processes makes it possible to conduct the purification without appreci-
able heat loss, is a decisive factor in achieving the necessary indices.
- 133 -
-------
A technological flow diagram of the gasification of sulfur mazuts
according to the method of the Institute of Mineral Fuels is shown in
Fig. 53. The gasification is carried out with a pure air blast using
aqueous emulsions of sulfur mazuts consisting of a monodisperse system in
which water in the form of minute droplets is dispersed throughout the
mazut (water - mazut).
It was established experimentally that the use of a water-mazut emul-
sion creates favorable conditions for atomizing the fuel in the reaction
volume, thus ensuring a uniformity of the process with a minimum formation
of soot. The hot gas obtained during the gasification, with a temperature
of about 1100°C., undergoes high-temperature purification involving the
removal of soot in a cyclone_and in a multilayered heat-stable granular
filter. The layout of a granular soot-removing apparatus specifies the
possibility of changing the filter and its regeneration, followed by the
return of the particle layer into the soot remover. After the purification,
the gas at a temperature of about 1000-1100°C. is led into the sulfur remover,
which contains a layer of calcium oxide particles, obtained by firing natural
limestone. The gas freed from sulfur compounds enters the energy user at a
temperature of 900-1000°C. After the sulfur removal, the solid reactant,
which consists of a mixture of calcium sulfide with unreacted calcium oxide,
is subjected to regeneration by firing in a separate unity. The regeneration
gases, containing about 10% 862, are used for the production of sulfuric
acid or elemental sulfur. In some cases, it is possible also to use a solid
reactant after the sulfur remover for the production of structural materials.
In experiments on the gasification of heavy sulfur mazuts under a pressure of
20 g atm at a high intensity of the process (up to 8000 kg/m^ hr for mazut) ,
a gas with a caloric value of 1100-1150 kcal/m3 was obtained. The yield of
dry gas per 1 kg of anhydrous mazut was 5.75-5.9 m3/kg, and the utilization
of air was 4.3-4.4 m^/kg of mazut. The average composition of the purified
gas obtained was (in %): C02 8-9; CO 15-16; H2 12-13; CH4 2.5-3.3; N2 60.
The flow scheme of gasification of solid fuels by the method of the
Institute of Mineral Fuels differs from that of sulfur mazuts only in the
process by which the hot unpurified gas is obtained. In this case, the gasi-
fication of coals is carried out in a fluidized bed of fine-grained particles
at 900-1100°C. and a pressure of 20 g atm. When the processes are carried
out in a fluidized bed under pressure, this permits the elimination of the
drawbacks characterizing the most modern processes of gasification: the inten-
sity of the process is increased, the outside dimensions of the gas producer
and other equipment are decreased, and the entrainment of solid material is
reduced. The hot gas obtained from the solid fuel in gas producers with a
fluidized bed under pressure is subjected to the removal of dust and hydrogen
sulfide at high temperatures in accordance with a flow scheme analogous to
that of purification of the hot gas from mazuts. In experiments on the gasi-
fication of brown coals (W? = 25%) in a fluidized bed at a pressure of 20 t atm
with a steam-air blast, a gas with a thermal conductivity of 1150 kcal/m3 was
- 134 -
-------
/7
Ui
I
Conveyor of
granular filter
Regeneration
—- gas
to HjSO,,
plant
Transport of
sulfur-re-
moving contact
Fig. 53. Diagram of gasification of sulfur raazuts under pressure with high-temperature removal of soot and sulfur
compounds from the gas.
1 - gas producer; 2 - soot catcher with high-temperature granular filter; 3 - screw washer of granular filter for
removal of soot; 4 - centrifuge; 5 - gas heater; 6 - sulfur remover with high-temperature sulfur-removing contact;
7 - regenerator of sulfur removing contact; 8 - intermediate container [capacity] for sulfur-removing contact;
9 - screen; 10 - limestone conveyor; 11 - screw limestone grinder; 12 - dust catcher; 13 - unit for preparation of
mazut according to the scheme of the All-Union State Planning Institute; Ik - mazut emulsifier of the Khotuntsev-
Pushkin system; 15 - water heater; 16 - pump for water-mazut emulsion; 17 - blast turbocompressor.
-------
obtained with approximately the following composition (in %): CC^ 9-10;
CO 18-20; H 11-13; CH 2-2.5; NZ 54-55. For 1 m3 of the gas obtained,
the utilization of air was 0.7 m3, and that of steam, 0.06-0.10 kg. The
yield of the gas per 1 kg of working fuel was 3.0 m3.
A technical-economic evaluation of the perfected methods of gasification
of sulfur mazuts and low-quality solid fuels showed their high efficiency in
the national economy. At the present time, there are sufficient technical
and technical-economic prerequisites for the development of a high-intensity
gasification of solid fuels and sulfur mazut with a high-temperature purifi-
cation of the gases as the preliminary step of their preparation for combus-
tion at high-capacity electric power plants. This also provides a rational
solution to the problem of sanitary protection of the atmosphere around ther-
mal electric power plants.
Considering the evaluation of the prospects for the use of high-temper-
ature removal of sulfur dioxide from flue gases, one should note that the
studies performed showed only the feasibility of such a process with the aid
of certain metal oxides (CaO, MnOo). However, no adequate solution has been
found for the problems of utilization of the sulfur and regeneration of the
absorbents used.
In order to achieve favorable economic indices of the process of flue
gas purification, it is necessary to envisage combining the production of
electric power with that of commercial chemicals by using the recovered sul-
fur and the absorbents themselves.
An effective solution of these problems will create favorable conditions
for the use of the process of high-temperature removal of sulfur dioxide from
flue gases at thermal electric power plants.
CONCLUSION
At the present time, in the USSR and throughout the world, the problem
of recovery of sulfur compounds (HjS and 802) from industrial gases is assum-
ing a particular urgency, chiefly from the standpoint of sanitary protection
of the air reservoir. Of no less importance is the possibility of utilizing
the sulfur recovered from the gases, since the demand for it is rising
steadily. An examination of the technical publications dealing with this
problem shows that the solution has consisted primarily in the creation of
low-temperature, liquid processes of sulfur removal from gases.
However, new, highly effective technological processes in power engineer-
ing, metallurgy, chemistry and other branches of technology are based on the
use of high temperatures. Their realization depends largely on the feasibility
of using the purification of heated gaseous mixtures by removing the sulfur
- 136 -
-------
compounds (H2S and S02) which they contain without lowering the temperature.
No studies have been made thus far on the creation of high-temperature
processes of sulfur removal from gases. This made it necessary to set up
a series of theoretical and experimental studies in order to find effective
conditions for the removal of hydrogen sulfide and sulfur dioxide from gases
at high temperatures. First, studies were made on the problems of selection
of solid reactants suitable for removing hydrogen sulfide from gases at
500-1100°C. and sulfur dioxide at 400-800°C. These reactants should be ther-
mally stable and after reacting should yield stable forms of sulfur compounds.
When natural substances containing these reactants are used, their dissocia-
tion temperatures should be below the temperature of the main process of
sulfur removal in order to prevent the formation of carbonates in the case of
purification of sulfur gases containing carbon dioxide.
The suitability and practical expediency of using calcium, iron and
magnesium oxides present in such inexpensive natural minerals and ores as
limestone, hematite, magnetite, siderite, pyrolusite, manganese concentrates
of various grades, and others, for the removal of hydrogen, sulfide from gases
was experimentally demonstrated.
Limestone, dolomite, pyrolusite and manganite can be used for the removal
of sulfur dioxide from gases -at high temperatures.
The conditions of sulfur removal from gases by use of selected reactants
were further studied in detail, as well as the problems of their regeneration
with the extraction of the recovered sulfur. Thermodynamic analysis of the
reactions of hydrogen sulfide and sulfur dioxide with selected metal oxides
showed that they could be carried out within the indicated temperature inter-
val. Thermodynamically favorable conditions were also established for the
regeneration of metal sulfides by oxidizing with air or by steam-air treatment
with formation of solid metal oxides and gaseous sulfur products.
Numerous experiments were conducted to study the kinetics of the reactions
of calcium oxide, iron oxides and manganese oxides with hydrogen sulfide, on
the basis of which optimum conditions were established for the removal of sul-
fur from power gases at 500-1100°C.
Suitable experiments on the study of the kinetic conditions were conducted
on the reactions of sulfur dioxide with calcium and manganese oxides at 400-
900°C.
Experimental studies were also made on the course of the regeneration
reactions of calcium, iron and manganese sulfides in connection with the re-
peated use of solid reactants in the sulfur-removal process.
On the whole, the studies performed make it possible to conclude that
the processes of high-temperature removal of sulfur compounds from gases by
means of solid reactants are entirely feasible.
- 137 -
-------
LITERATURE CITED
I. I'. If. IIyen HOD, A. n. Aii,1 p ii a iioB. MunibsiKow.'ii ii;x>necc
xn. OHTH, 1937.
2. H. H. E r o p o B, M. M. R M H T p 11 c D, £. fl. 3 N x o B, IO. H. D p o n. c-
K ii ft. OmicTKa OT ccpu KOKCona.ibiioro H Apyrnx ropiomix rason. McTa.i.iypr-
H3,iaT, 1960.
3. F. H. H y c n H o n, K. C. 3 a p e M 6 o. OMiicTxa, ocyuina H o.aopsisaunn npu-
pojiiibix rasoa. rocToiirexiia.iaT, 1947.
4. M. C. JI n T B n H e H K o. OiiierKa KOKCOBOFO rasa OT cepoBOAopoAa. Mota.n-
^yprns.iaT, 1959.
5. A. JI. K o y ji b, . C. P113 e H - AOKT. aiicc. HTH,
1963.
10. K. \Vickcrt. Versuchc zur Entschweflung vor und hinter dcm Brenner zur
Verringcring SOZ des Auswurfs.— Milt. Vercin. GrosskcssIIbcsiger, 1963,
N83.
11. F. LLleiiK. $H3iiKO-xnMiiJi MeTajiJiyprniecKiix uponeccon. XapLKon, rocii3Aa~-
yCCP 1935
12. B. A. K a p 2< a B n H, A. B. A B jt e e B a. JKXO, 1934, N° 12, 25.
13. B. H. n o n o B.— H3B. nysos. XfiMitn H xiiMimccKan rcxnojionifl, 195S, Jfs 6,61..
14. O. A. ECHH, n. B. fejibfl. H3wiecKaji XUMIIH niipo.MCTa.i.iyprHMecKiix.
npoueccoB, H. I. CscpflJioBCK, McTa.n.iyprnsAaT. 1962.
15. W. Reinders.—Z. anorgan. und allgeni. Chem., 1915, 93, 213; 1923, 126,.
85.
16. B. T. HaryHasa. Hcc/ieaoBaimn no npiiMciicniiio Mapranucuux KoirraKTOD-
B XHMiiiecKOH npoMiiui^ciuiocTH. TCii.incii, USA-BO <:Mcmincpcda», 1965.
17. OcuoBbi MeTa^.nyprHii, T. I, M. I. MeTa.i.iyprnsAaT, 1961.
18. C. C. BauaHou, B. n. KasaxoB, C. C. flep 6eHCBa.— >KHXF.
1967, 12, Bbin. 6, 1417.
19. A. H. BoJibCKHit. OCHOBU Tcopiiu MCTa.i.iypniypamtsi nyryna. MeTajuiyprra/iaT, 19G2.
21. H. F. SajioniH, C. M. IJJyxep. O'IIICTKB AMMonbix raaoo. JI., rocancpro-
II3A3T, 1951.
22. T. C. p e H u. OKiic.ieiii!e cyab4)HAOB MCTaJi^oB. HSA-BO «Hayxa», 1964.
23. II. F. I o h n s t o n e.—Industr. and Engng Chcm., 1935, 27, N 5—6, 587.
24. 3. n. PoseiiKiion. MsBJieqcime AuyoKiicii cepu us ra3OB.
1952.
- 138 -
-------
25. P. II. M y cj> a p o n. A,acopGuiiomioe oGoramcinic Ge.iuux ccpiiiiCTi.ix raaon.—
TpyAM Bccc. cT.03,aa no ocuonaw XIIM. npoM. rocxi!Mii3,aaT, 1932.
20. H. H. KyahMiiiitix. TcxuiiKa H SKoiioMiwa a.acopOmioiiiioro o6oraiuciui!i
6CAHUX cepiuiCThix rasoB.— TpyflLi Bcec. cieaaa no ociiouaM XIIM. npow.
FocxiiMiiSAaT, 1932.
27. Jl. <1>. SCMCKOB.—Han. BVSOB. XHMHH H xiiMimccKan Tcxnojionin, 1965,
Ml, 94.
28. I. J o h s w i s h.~ Brennstoff-Warme-Kraft, 1962, 14, N 3. 105.
29. E. Wahnschafc. Entschwcflung der Rauchgase.—Mitt. Vcrein. Grosskcs-
selbcsizer, 1963. N 83.
30. Coks clians flue gas in Germand process.—Chcm. Eng., 1967, 74, N 22, 94.
31. H. H e i t m a n.— Entschweflung der Rauchgascn. Mitt. Verein. Grosskesscl-
besizer. 1963, N 83.
32: loshimuran T o s h i o.— Electr. World, 1967, 167, N 12, 127.
33. K- G a s i o r o \v s k i. Die Ebgase—Entschweflung nach Dr. Wauling.—
Mitt. VQB, 1963, N 83.
34. C. H. C a B H y K, A. M. T B e p c K o ft.— Ten.iositepreTHKa, 1965, Xs 8, 89.
35. H. T. T n T o B, Jl. A. B o p o 3 A H H a.— XIIMHS TBepjioro Ton^HBa, 1968,
Kt 5, 100.
M. A. A. B a ft K o B, A. C. T y M a p e B.— Has. AH CCCP, OTH, 1937, Ks 4, 565.
37. H. Kossinger, H. Me. Murdie, B. Simpson.—J. Amer. Ceram. Soc.,
1956, 39, 168.
38. H. A. ft e p e p. e p H ft.— CrpOHTejibHwe MaTepna^w, 1937, N° 11, 55.
39. M. H. KopneeB, E. H. OpytKOBCKH fl, A. A. P o M a H o B.—Ten.no-
SHepreiHKa, 1964, J6 9, 7.
40. Cnpaso'iHiiK «TepMowiHaMHMecKHe CBoficTBa HHAHBHaya^bHbix BemecrB>, T. II.
HSA-BO AH CCCP, 1962.
41. A. H. KCTOB. K). M. MapruHOB, B. B. Jlapn HOB, A. C. Ill JiH-
r e p c K H fi. OnwT paCoru SKcnepHMeHiaabHoft ycranoBKH cepoouucTKii TO-
noHHbix raaoB T3U no cyxony H3BCCTKOBOMy cnoco6y.— nepeaoBoft Haymio-
TexHH«iecKHi"i H npoiiscoACTBeHHbift onuT, N 12, rOCHHTH, 1968.
42. C6. «ra30Bbie npoueccw*. M., HSA-BO «HayKa>, 1967.
,- 139 -
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APPENDIX
Heat Capacities (cp = a » bT + cl~2), Temperatures (T^ Entropies (s), Heats
of Formation (-An" and also Temperatures (t) and Heats of Phase Transformations
Co) of Certain Elements and Compounds.
Substance
CO(gas)
CO. (gas)
COS
cs.
CSS
Ca.a
Ca.p
Ca (liquid)
CaO (solid)
CaS
CaSO«
CaSOa.a.p,
Fe, a
Fe, p
Fe, T
Fc, 6
Fe (liquid)
FeO (solid)
FeO (liquid
FesO,,a
FesO«,p
FesOs.a
FezOs.p
FeaOs.T
FeS.a
FeS.p
FeS.T
FcSs
FeS04
FcCOs
Hs(gas).
H2O
HS0
HtS
»S
Si
5: ^
< S
1 •*
26,40
94,05
33,90
__
—21,00
0,0
—
—
151,90
110,00
342,40
288,40
0,0
—
—
—
—
63,50
—
268,00
—
197,00
—
—
22,80
—
—
42,40
220,50
178,70
0,0
68,32
57,80
4,807
a
1
ooS
$5
«!
47,30
51,07
55,30
M
36,20
9,95
— i
—
9,50
13,50
25,50
21,20
6,49
—
—
—
—
14,20
—
35,00
—
21,50
—
—
16,10
—
—
12,70
25,70
22,20
31,20
16,75
45,13
49,20
S»
o
—212
—
—
—
440
850
—
2600
—
1193
-50
906,1401
910
1400
1539
—
1371
—
627
1597
677
777
—
138
325
1195
190
—
—
—25g
0
100
—60
1
Q > cal/mole
—
—
_
—
270
2070
—
12400
—
—
48
326
215
165
3670
—
7490
—
0
33000
160
0
—
570
120
77,30
325
—
—
—
1436
9820
—
Cj,< cal/deg mole
a
6,79
10,55
11,33
18,40
12,45
5,31
1,50
7,40
11,86
10,20
16,78
24,98
4,18
9,00
1,84
10,50
10,00
12,38
16,30
21,88
48,00
23,49
36,00
31,70
5,19
17,40
12,20
17,88
24,03
11,03
6,52
18,03
7,17
7,02
6-101
0,98
2,16
2,18
__
1,60
3,33
7,74
1,08
3,80
23,60
5,24
5,92
—
4,66
_
—
1,62
—
48,20
—
18,60
—
1,76
26,40
—
2,38
1,32
—
26,80
0,78
—
2,56
3,68
c-10-'
—0,11
-2,04
-1,83
__
—1,80
—
2,50
—
—1,66
—
—
—6,20
—
—
—
—
—
-0,38
—
—
—
—3,55
—
—
—
—
-3,05
—
—
0,12
—
0,08
—
Temperature
Interval, °K
298—2500
298—2500
298—1800
293— vaporization
temperature
298—1800
298—713
713—1123
1123—1800
298—2000
273-1000
298—1400
298—1200
298—1033
1033—1181
1181—1674
1674—1812
1812—3000
298—1200
1650—2000
298-900
900—1800
29S— 950
950—1050
1050—1750
298-411
411-598
598—1468
298—1000
—
298—885
298—3000
273—373
298-2500
298—1800
- 140 -
-------
APPENDIX (Cont'd)
Substance
Mg (solid)
MgO
MgS
MgS04
MgCO3
Mn,a
Mn.p
Mn.T
Mn,6
Mn (liquid)
MnO
Mn30j,a
Mn3O4,3
Mn£O3
MnOz
MnS
MnS.
MnS04
MnCOs
Os
S (rhombic)
S (monoclinic)
S (liquid)
SOs (gas)
S2
S03 (gas)
Zn (solid)
Zn (liquid)
•7*iG
ZnS
ZnO»
ZnC03
CO 0)
^1
< CO
' .*
0,0
143,70
81,20
305,50
262,00
0,0
—
—
—
—
92,00
331,40
—
229,40
124,30
49,00
49,50
254,20
213,90
0,0
0,0
-0,07
—
70,95
-31,00
94,32
0,0
83,20
48,20
233,90
194,20
V
1
-g
CD'S
oCy>-*
"3 o
7,77
6,55
0,20
21,90
5,70
7,60
—
—
—
—
14,30
35,50
—
26,40
12,70
18,70
27,30
26,80
20,50
49,02
7,62
7,78
—
59,25
54,40
61,20
9,95
10,40
13,80
30,60
•— __ _
O
*
**
650
2770
—
H30
—
728
1001
1137
1244
—
1785
1172
1560
—
250
1530
—
700
—
—219
95,5
119
—
—76
—
420,00
1975
1020
735
19.70J —
3
5
rH
a
o
Cx
2140
8500
—
—
—
535
545
430
3500
—
13000
4970
—
—
—
—
—
—
—
—
85
335
—
—
—
1765
~—
—
—
_
cp, cal/deg mole
a
5,33
10,83
—
23,01
18,62
5,16
8,33
10,70
11,30
11,60
11,11
34,64
50,20
24,73
16,60
11,40
—
29,26
—21,99
7,16
3,58
3,56
5,40
10,38
8,54
10,70
5,5
7,50
11,71
12,16
21,90
9,33
t-103
2,45
1,74
—
13,80
3,81
0,66
—
—
—
1,94
10,82
—
8,38
2,44
1,80
—
8,92
9,30
1,00
6,24
6,96
5,50
2,54
0,28
6,42
2,40
1,22
1,24
18,20
r-10-<
0,103
-1,48
—
—
—4,16
—
—
—
—
—
—0,88
—2,20
—
-3,23
-3,88
—
—
—7,04
—4,69
-0,40
—
—
—
-1,42
-0,79
-3,12
-2,18
-1,36
33,00 —
Temperature
Interval, "K
298—923
298—2100
— —
298—750
298—1000
1000—1374
1374-1410
1410—1517
1517—2300
298—1800
298—1445
1445—1800
298—1350
298—780
298—1803
—
298-1100
298—750
298-3000
298—368,0
368,6-392
392—1000
298-1800
298—2000
298—1200
298-692,7
692,7—1200
294—1600
208-1200
298 — vaporiz-
ition tefiperature
298—780-
- 141 -
-------
46 THE SUSCEPTIBILITY OR RESISTANCE TO GAS
AND SMOKE OF VARIOUS ARBOREAL SPECIES
GROWN UNDER DIVERSE ENVIRONMENTAL
CONDITIONS IN A NUMBER OF INDUSTRIAL RE-
GIONS OF THE SOVIET UNION-A Survey of USSR
Air Pollution Literature
47 METEOROLOGICAL AND CHEMICAL ASPECTS
OF AIR POLLUTION; PROPAGATION AND DIS-
PERSAL OF AIR POLLUTANTS IN A NUMBER OF
AREAS IN THE SOVIET UNION-A Survey of USSR
Air Pollution Literature
48 THE AGRICULTURAL REGIONS OF CHINA
49 EFFECTS OF METEOROLOGICAL CONDITIONS
AND RELIEF ON AIR POLLUTION. AIR CON-
TAMINANTS - THEIR CONCENTRATION.
TRANSPORT, AND DISPERSAL-A Survey of USSR
Air Pollution Literature
50. AIR POLLUTION IN RELATION TO CERTAIN
ATMOSPHERIC AND ME TO RO LOGI C A L
CONDITIONS AND SOME OF THE METHODS
EMPLOYED IN THE SURVEY AND ANALYSIS
OF AIR POLLUTANTS-A Survey of USSR Air
Pollution Literature
51. MEASUREMENTS OF DISPERSAL AND
CONCENTRATION. IDENTIFICATION, AND
SANITARY EVALUATION OF VARIOUS AtR
POLLUTANTS, WITH SPECIAL REFERENCE TO
THE ENVIRONS OF ELECTRIC POWER PLANTS
AND FERROUS METALLURGICAL PLANTS
-A Survey of USSR Air Pollution Literature
62 A COMPILATION OF TECHNICAL REPORTS ON
THE BIOLOGICAL EFFECTS AND THE PUBLIC
HEALTH ASPECTS OF ATMOSPHERIC
POLLUTANTS - A Survey Of USSR Air Pollution
Literature
53 GAS RESISTANCE OF PLANTS WITH SPECIAL
REFERENCE TO PLANT BIOCHEMISTRY AND TO
THE EFFECTS OF MINERAL NUTRITION - A
Survey of USSR Air Polutlon Literature
54 THE TOXIC COMPONENTS OF AUTOMOBILE
EXHAUST GASES: THEIR COMPOSITION UNDER
DIFFERENT OPERATING CONDITIONS. AND
METHODS OF REDUCING THEIR EMISSION - A
Survey of USSR Air Pollution Literature
55 A SECOND COMPILATION OF TECHNICAL
REPORTS ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS OF
ATMOSPHERIC POLLUTANTS - A Survey of USSR
Air Pollution Literature
56 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL SYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART I) - A Survey of USSR Air
Pollution Literature
67 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL SYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART II) - A Survey of USSR Air
Pollution Literature
58 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL AYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART III) - A Survey of USSR Air
Pollution Literature
59 A THI«D COMPILATION OF TECHNICAL
REPORTS ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS OF ATMOSPHER-
IC POLLUTANTS - A Survey of USSR Air Pollution
Literature
60 SOME BASIC PROPERTIES OF ASH AND INDUS-
TRIAL DUST IN RELATION TO THE PROBLEM
OF PURIFICATION OF STACK GASES - A Survey
of USSR Air Pollution Literature
(Volume XVI)
61 A FOURTH COMPILATION OF TECHNICAL RE-
PORTS ON THE BIOLOGICAL EFFECTS AND THE
PUBLIC HEALTH ASPECTS OF ATMOSPHERIC
POLLUTANTS A Survey of USSR Air Pollution
Literature
(Volume XVII)
62 PURIFICATION OF GASES THROUGH HIGH TEM-
PERATURE REMOVAL OF SULFUR COMPOUNDS
— A Survey of USSR Air Pollution Literature
(Volume XVIII)
63 ENVIRONMENTAL POLLUTION WITH SPECIAL
REFERENCE TO AIR POLLUTANTS AND TO
SOME OF THEIR BIOLOGICAL EFFECTS - A
Survey of USSR Air Pollution Literature
(Volume XIX)
64 CATALYTIC PURIFICATION OF EXHAUST GASES
— A Survey of USSR Air Pollution Literature
(Volume XX)
Reprints from various periodical*.
A INTERNATIONAL COOPERATION IN CROP IMPROVEMENT
THROUGH THE UTILIZATION OF THE CONCEPT OF
AGROCLIMATIC ANALOGUES
(The Uta of Phenology, Meteorology and Geographical
Latitude for the Purposes of Plant Introduction and the Ex-
change of Improved Plant Varieties Between Various
Countries. )
B SOME PRELIMINARY OBSERVATIONS OF PHENOLOGICAL
DATA AS A TOOL IN THE STUDY OF PHOTOPERIODIC
AND THERMAL REQUIREMENTS OF VARIOUS PLANT
MATERIAL
*C AGRO-CLIMATOLOGY AND CROP ECOLOGY OF THE
UKRAINE AND CLIMATIC ANALOGUES IN NORTH
AMERICA
D AGRO-CLIMATOLOGY AND CROP ECOLOGY OF PALES-
TINE AND TRANSJORDAN AND CLIMATIC ANA-
LOGUES IN THE UNITED STATES
• USSR-Some Physical and Agricultural Characteristics of the
Drought Area and Its Climatic Analogues in the United States
: THE ROLE OF BIOCLIMATOLOGY IN AGRICULTURE WITH
SPECIAL REFERENCE TO THE USE OF THERMAL AND
PHOTO-THERMAL REQUIREMENTS OF PURE-LINE VARI-
ETIES OF PLANTS AS A BIOLOGICAL INDICATOR IN
ASCERTAINING CLIMATIC ANALOGUES (HOMO-
CLIMES)
'Out of Print.
Requests for studies should be addressed to th«
American Institute of Crop Ecology, 809 Dole
Drive, Silver Spring, Maryland 20910.
------- |