&EPA
United States Industrial Environmental Research EPA-600/7-78-089
Environmental Protection Laboratory June 1978
Agency Research Triangle Park NC 27711
Coal Desulfurization
Using Microwave
Energy
Interagency
Energy/Environment
R&D Program Report
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EPA-600/7-78-089
June 1978
Coal Desulfurization
Using
Microwave Energy
by
P.O. Zavitsanos, J.A. Golden, K.W. Bleiler and W.K. Kinkead
General Electric Company
Re-entry and Environmental Systems
P.O. Box 8555
Philadelphia, Pennsylvania 19101
Contract No. 68-02-2172
Program Element No. EHE623A
EPA Project Officer. Lewis D. Tamny
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
A method has been developed which removes pyritic and organic sulfur from
several U.S. coals. The method utilizes microwave energy alone to remove 50%
of the pyritic sulfur; in combination with sodium hydroxide removes more than
9570 of the pyritic sulfur and about 60% of the organic sulfur in exposure times
of the order of one to three minutes at one atmosphere of inert gas. Additional
sulfur is trapped in the ash when coal is burned accounting for almost complete
absence of S02 in the combustion gases. The process temperature is a modest
250°C - 300°C and the associated loss in the heating value of the treated coal
is ins ignificant..
Analysis of the data suggests that microwave heating in the absence of
NaOH converts FeS2 to FeSx (where x£ 1), and gaseous sulfur compounds, thus
accounting for 50% removal of pyritic sulfur. In the presence of NaOH sulfur
is converted to water soluble sulfides (Na2Sx, x^l) at a rate which appears to
follow first order kinetics.
The mechanism by which fast rates of desulfurization are accomplished is
most probably related to the fast (and to some degree selective) in-depth
heating of the bed. The activation of water, FeS2 and NaOH create local
volatilization high temperature and pressure conditions which accelerate sulfur
reactions before the coal has a chance to decompose. It is also quite possible
that local non-equilibrium chemistry as a result of localized discharge sites
plays a beneficial role.
iii
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CONTENTS
Abstract . . „
Figures v
Tables vii
Acknowledgments viii
1. Introduction and Background -.. .1
Statement of Problem . 1
Types of Sulfur in Coal 1
Candidate Desulfurization Processes 2
2. Thermochemistry 5
Thermal Decomposition 5
Reactions of Pyritic Sulfur with Leachants . 5
3. The Use of Microwaves in Coal Desulfurization 13
Theory and Measurements of Dielectric Properties 13
Experimental Approach 18
4. Experimental Results ,. • 32
Sulfur Removal as Observed by Energy Dispersive
X-rays (EDX) and Electron Probe Microanalysis 32
Coal Desulfurization as Evidenced by Sulfur
Chemica1 Analys is 39
Kinetics 46
Ash Content and Calorific Value of Treated Coal 55
5. Schematic Flow Sheet of Proposed Process 59
6. Process Energy Requirements and Economic Projections 61
7. Conclusions 66
References 67
IV
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Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
FIGURES
Mass spectrometric analysis of gaseous products from coal ....
Mass spectrometric analysis of the vaporization of FeS2
Gaseous products from pyrite oxidation
Gaseous products from pyrite reaction with sodium hydroxide . .
Experimental set up for dielectric property measurements
Microwave transmission measurements - Ky. #11 Coal (59%,),
NaOH (9.4%), H20 (31.6%)
Microwave power absorption
Transmissions coefficient vs . frequency
Microwave . power absorption by coal in waveguide (at 8.3 GHz) .
Diagram of microwave desulfurization apparatus, 8.35 GHz and
8.35 GHz microwave equipment and measurement apparatus
Diagram of turntable used in 6 KW 2.45 GHz experiments
Temperature dependence of weight change for coal
(a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of virgin #6 Pennsylvania coal
(pvritic). 300X
Page
6
10
11
12
15
16
17
19
20
22
24
25
26
27
28
31
33
18 (a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of #6 Pennsylvania coal heated 90
seconds with microwaves, 300X 34
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FIGURES (Continued)
Number . Page
19 (a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of #6 Pennsylvania coal heated 90
seconds with microwaves in presence of NaOH, 300X 35
20 Energy dispersive x-ray spectrum for virgin sample PSOC-273-1
(Ky. #11) ..:." 36
21 Energy dispersive x-ray spectrum for PSOC-273-1 coal after 30
second microwave exposure using NaOH leachant (sample washed) .. 36
22 Energy dispersive x-ray spectrum for residue from wash water
from leachant/microwave irradiation treated PSOC-273-1 coal .... 36
23 Iron to sulfur ratio by dispersive x-rays 38
24 Surface temperature of PSOC-255 (L. Kittanning) coal during
microwave exposure in the presence of sodium hydroxide 41
25 Reduction of total pyritic sulfur 44
26 Sulfur reduction as a function of exposure time and water
removal (PSOC-320 Pittsburgh Seam Coal, 4.5% Iron Pyrite
added) 45
27 Reduction of total sulfur for PSOC-257 47
28 Reduction of total sulfur for PSOC-270 48
29 Reduction of total sulfur for PSOC-294 49
30 Sulfur reduction for PSOC-255 50
31 Time dependence of sulfur removal from coal PSOC-294 using
microwave irradiation and double exposure 51
32 Reduction of total (organic) sulfur for PSOC-270, 2.45 GHz 52
33 Reduction of total sulfur for PSOC-273-1 (double treated
samples) 53
34 Reduction of sulfur forms from Ky. #11 coal (PSOC-273-1) ;
(double treated samples) 54
35 Sulfur removal 1st order kinetics PSOC-294 56
. 36 Sulfur removal 1st order kinetics PSOC-255 57
37 Proposed schematic flow sheet for G.E. chemical coal cleaning
process 60
vi
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TABLES
Number Page
1 Measurement of Complex Dielectric Constants at 8.3 GHz 14
2 Microwave Power Absorption by Ky. #11 Coal in Waveguide 21
3 Candidate Coal Samples 37
4 Electron Probe X-ray Microanalysis of Coal Samples 40
5 S, C, H, N, 0, Ash, Moisture, Volatile Matter, and Fixed
Carbon of Sample Coals 43
6 Ash and Energy Content 58
7 Ultimate Analysis 58
8 Process Energy Requirements 62
9 Capital Costs with Microwave Desulfurization 64
10 Operating Costs 65
VLl
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ACKNOWLEDGMENTS
OTHER CONTRIBUTORS
It is with much appreciation and pleasure that we acknowledge the con-
tributions of the following people to this report.
W.G. Browne - Thermochemistry
P.D. Gorsuch - Microstructural Characterization
H. Thai - Dielectric Properties
E.J. Nolan (with Day & Zimmermann Support) - Economic Evaluation
FUNDING SOURCES
The funding for this effort was provided by the Environmental Protection
Agency 'at the 677» level; the balance was funded by the National Science
Foundation under Grant No. AER-7523626.
OTHER SUPPORT
The enthusiastic support of T. Kelly Janes, J.D. Kilgroe, and L.D. Tamny
of EPA, and D.E. Shelor and A. Macek of DOE, as well as the encouraging
involvement of GE/RESD upper management, are great fully acknowledged.
V1L1
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SECTION 1
INTRODUCTION AND BACKGROUND
STATEMENT OF PROBLEM
Coal is a plentiful resource asset in the United States and increased
use of coal is vital to satisfy the nation's energy needs as well as improve
its economic stability and energy self-sufficiency. Despite the vast coal
reserves, however, troublesome environmental problems arise from the con-
stituent high-sulfur which, upon combustion, releases sulfur dioxide into the
atmosphere.
In accordance with the Clean Air Act of 1970, the Environmental Protection
Agency in 1971 promulgated new source performance standards that limited
sulfur oxide emissions from coal combustion to 1.2 Ib 802/10^ Btu. For a
12,000 Btu/lb coal, the above standard limits the coal sulfur content to a
maximum of about 0.770 by weight. Thus, the Clean Air Act virtually eliminates
direct use of most Eastern and Midwestern coals, which tend to have higher
sulfur contents than the Western coals. This becomes a very important con-
sideration because the Eastern and Midwestern coals are closest to the region
of maximum need and represent about 40 percent of total U.S. reserves (1,2).
TYPES OF SULFUR IN COAL
Sulfur exists in coal in the "pyritic", "organic", and "sulfate" form.
The sulfate sulfur is usually in quantities less than 0.05% and therefore is
not an important factor. Pyritic sulfur is present in the form of a dis-
persion of particles that have the chemical composition Fe$2- The size and
form of these particles varies greatly with geographic location, from seam to
seam for a specific geographic location, and even within a chunk of coal. The
organic sulfur is chemically bound to the organic structure of the coal and
accordingly it cannot be removed by conventional cleaning or preparation pro-
cesses, but requires chemical treatment.
Although there is no exact knowledge of the forms in which organic sulfur
is present in the coal matrix, several groups have been suggested. These
include disulfides, mercaptans, thioethers and thiophenes. It is also
believed that a significant portion of organic sulfur is a part of the hetero-
cyclic aromatic ring structure.
-------
In general, the fraction of the sulfur present in the various proposed
forms is unknown. This is indeed unfortunate because the nature of the sulfur
compounds involved plays a significant role in terms of identifying an effec-
tive desulfurization treatment. It is known for example that sulfur present
in the form of ring structures is more difficult to hydrogenate or to remove
by thermal decomposition than other forms of organic sulfur. In fact, when
coal is coked, as much as 45% of the original organic sulfur remains in the
final coke product and it is believed that it is the sulfur in the ring
structure which resists removal even at the high coking temperatures. Based
on this kind of information it is estimated that 40-6070 of the organic sulfur
in U.S. coals is present in ring structure.
CANDIDATE DESULFURIZATION PROCESSES
Many methods have been considered for the removal of sulfur-from coal (3).
Those which have received the most serious attention remove pyritic sulfur
using either density difference or magnetic separation techniques (4,5) and
chemical desulfurization. The former techniques are only partially effective,
limited to inorganic sulfur present largely as iron pyrite, and can result in
large heating losses because much useful coal material is carried over with
the pyrites. Chemical cleaning methods are more effective in sulfur removal,
and fuel value losses can be small; thus, chemical cleaning is now emphasized
as having the potential of providing more effective means for coal desulfur-
ization and opening the road towards wider coal utilization.
Among a number of chemical desulfurization methods that have been pro-
posed, three have been actively developed in recent years. These are the
TRW-Meyers, the Battelle "Hydrothermal", and the Ledgemont Processes. Brief
summaries of these processes are of value.
In the TRW-Meyers process, inorganic sulfur is extracted from small-
particle-size coal with a hot solution of ferric sulfate, which is capable of
oxidizing pyritic sulfur to soluble sulfates and elemental sulfur (6-10).
Since the elemental sulfur is deposited within the coal matrix, a second
treatment stage is required to remove the elemental sulfur, either by extrac-
tion with an aqueous acetone solvent or alternately by heating and vapor-
ization. Since the leaching step reduces ferric sulfate to ferrous sulfate,
the spent leachant is regenerated by re-oxidizing the ferrous sulfate back to
ferric sulfate with air or pure oxygen. It is claimed that this process
removes practically all the pyritic sulfur present without affecting the
heating value of the coal itself. A single batch of homogeneous coal requires
a reaction time on the order of eight hours to remove 807<> of the pyritic
sulfur, although multi-stage leaching can remove considerably more pyrite.
This process is the most developed of the candidate chemical methods. It has
been evaluated extensively through laboratory and bench-scale testing and has
reached the pilot plant demonstration stage.
The Battelle "Hydrothermal" process involves leaching pulverized coal
with hot caustic solutions that extract most of the inorganic sulfur and part
of the organic sulfur in the form of a soluble sodium sulfide (11-13). If
the leached coal is treated subsequently with dilute acid, the ash content is
also reduced. Experiments in small laboratory-scale batch and continuous-flow
-------
reactors indicate needed reaction times of about 30 minutes at temperatures
up to 350°C and pressures of about 200 atmospheres. The main advantage of
this process is the ability to attack both pyritic and organic sulfur without
significantly reducing the calorific value of the treated coal.
The Ledgemont process, announced in 1974 (14-16) by Kennecott Copper
Corporation, involves leaching pulverized coal with a hot aqueous solution
containing dissolved oxygen under pressure. This solution results in oxi-
dation of the iron pyrites and their conversion into sulfuric acid and/or
water-soluble sulfates. The most attractive feature of this process is the
need for only oxygen and water for leaching out large amounts (90%) of pyritic
and modest amounts (20%) of organic sulfur. A major disadvantage, however,
results from the loss of about 1470 carbon during treatment. Also, the treated
coal is significantly inferior in terms of residual heating value (5-157» loss)
(17).
Further tests with this process using compressed air instead of oxygen
in the range of 35 to 100 atmospheres of pressure, and temperatures in the
vicinity of 200°C have been conducted at Pittsburgh Energy Research (DOE-Lab)
with interesting results (18). Most of the pyritic sulfur (9070) and up to
407» of the organic sulfur in coal are converted into sulfuric acid, with an
overall heating value recovery of 93 to 977> in small-scale laboratory experi-
ments. Apparently, the higher temperatures result in the extraction of part
of the organic sulfur.
Even though the Ledgemont-type processes appear promising for chemical
desulfurization, they are limited by relatively slow rates of sulfur extrac-
tion, the presence of relatively corrosive dilute sulfuric acid solutions,
and the need for operation at relatively high pressures.
Other desulfurization methods that deserve mention include the IGT-
Hydrodesulfurization process, the Syracuse Corporation's chemical comminution
process and the Hazen process.
The IGT process (5) uses pre-oxidized coal, hydrogen at modest pressures,
and temperatures as high as 800°C. The process removes 80-907« of pyritic
sulfur and 60-807o of organic, but causes excessive volatilization of the coal
and losses of solids as high as 387° of the original weight. (In order to
satisfy EPA requirements, both gas and solid phases have to be used.)
The Syracuse process, developed by Howard (20), involves chemical com-
minution of coal by use of liquid ammonia at high pressure. It breaks up the
matrix and enhances the detachment of mineral matter; thus, separation by
gravity is improved.
The Hazen process claims a selective chemical reaction of the mineral
component in pulverized coal with gaseous iron pentacarbonyl which converts
the pyritic sulfur into a paramagnetic substance without affecting the
mineral-free coal. The magnetic mineral component is subsequently separated
from the pulverized clean coal by dry magnetic separation methods. The pro-
cess is limited to removal of pyritic sulfur only and severe grinding will be
required for many Eastern coals which contain very fine size pyrites (^50
-------
micron mean diameter). Iron pentacarbonyl [Fe(CO)5j consumption of about 32
Ibs/ton of coal is required (21) as well as severe monitoring requirements
are expected because of the very high toxicity of iron pentacarbonyl. The
distinct advantages of the process are associated with the moderate temper-
ature, low pressure and relatively short retention time requirements.
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SECTION 2
THERMOCHEMISTRY
THERMAL DECOMPOSITION
As previously discussed sulfur in coal is strongly bonded either to iron
(Fe-S) or to carbon (C-S), with bond energies of 115 and 175 kcal/mole respec-
tively. For this reason, it is difficult to break these bonds thermally
without partially decomposing the coal matrix itself.
When coal is heated to temperatures in excess of 400°C it is known to
enter a regime of thermal decomposition which eventually removes most of the
hydrogen in the form of H2 and hydrocarbons and greatly reduces the heat
content of coal. Figure 1 shows mass spectrometric data as a function of
temperature of species emanating from Clarion County, Pa. coal (containing
4.17« sulfur, mostly pyritic). The sample was heated in a tantalum crucible
in a conventional furnace at a heating rate of 10°C/min. using the time-of-
flight mass spectrometer apparatus as described in previous publication (24).
It is apparant from these data that the evolution of sulfur compounds (H2S,
S02» SO, or CH3SH and COS) is essentially coincident with the evolution of
hydrocarbons (all observed species are not shown on this plot). At the end
of such a run, 30-357<> of the weight is lost because of the generation of
volatiles, while a significant portion of the sulfur still remains in the
charred residue. It is for this reason that reactants such as 02> H2 and NaOH
have been considered (for the removal of sulfur) in the hope that sulfur can
engage in reactions which remove it from the coal matrix without seriously
decomposing the coal itself.
REACTIONS OF PYRITIC SULFUR WITH LEACHANTS
Thermochemical Calculations
Nepokrytykh et.al. (22) have treated pyrite with alkali solutions in the
vicinity of 300°C in an autoclave. The sulfur is extracted by the solution
as S= (90-93%) and as S203=, S03= and 804" (total 7-107o). The solid phase
undergoes the following sequence of transformation:
pyrite-- > hematite >maghemite >magnetite
FeS2 Fe2°3 Fe3°4
-------
100.000
80,000 ~
60.000
40,000
20,000
8,000
6,000
4,000
t 2,000
z
3
tr
t ' 40,000
CD
OC
5 30,000
>
H
w 20,000
Z 10,000.
z
o
C2Hg
UJ
CC
400
300
200
100
400
300
200
100
0
CO-
COS
200
400
600
50,000
40,000
30,000
20,000
10,000
20,000
15,000
10,000
5,000
2,000
1,500
1,000
500
4,000
3,000
2,000
1,000
2,000
1,500
1,000
500
0
CH<
800
TEMPERATURE, C
H2S
SO + CH3SH
S02
CAH
6" 6
200
400
600
800
Figure 1. Mass spectrometric analysis of gaseous products from coal,
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FeS2(s) + 4NaOH(sr-* (|f)[(|) Fe203(s) + 2 Na2S(g) + 2H20(1)]
This process can be represented to a first approximation as follows:
(2)
The free energy and enthalpy changes for reaction (2) as a function of temper-
ature using the thermochemical data of Barin (23) are as follows:
400
500
600
AF° (kcal/mole FeS2) 0.7 -2.4 -3.8*
AH° (kcal/mole FeS2) 10.5 11.4 0.4*
It is noteworthy that the heat of solution of Na2S in H20/i\ will alter
the numerical values computed f or AF° andAH°.
From NBS Circular 500 (Part 1 Tables - pp. 456-7), "Selected Values of
Chemical Thermodynamic Properties", (1952), the following considerations help
evaluate the FeS2/NaOH system:
Therefore,
and
Species
Na2S
H20
State
Condensed - 89.2
Condensed -416.9
Liquid - 68.32
-, N
^ (c) '
-89.2 (4%)(-68.32)
. .
(c)
-416.9
-307.44
AH = -416.9 + 396.64
= -20.26 kcal/mole of hydrated Na2S
** f "}9\ / \ I 9 <
AHR = (^1 (-20.26|j^] = -8.22 kcal/mole
* NaOH in a liquid at 600 K
** Change in heat of reaction (2) due to hydration
7
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The exothermic heat of hydration of Na2S should be sufficient to drive the
AF for the pyrite + NaOH reaction negative.
If we assume Na2S hydrates to Na2S(4^H«0) we should add -8.22 kcal/mole
to the previous table which makes reaction (2) exothermic even at 600 K
(327°C).
Finally, 8.6% (3/35) of the hydrogen in the reaction is released as
gaseous hydrogen; it is important to know whether this H2 is reabsorbed in
the coal matrix.
If NaOH is substituted with Na2C03 the corresponding reaction can be
represented, to a first approximation, as follows:
FeS2(s) + 2^0)3^(11) [\ Fe203(s) + 2Na2S(g) + 2C02(g)]
+ (3!) [3 ^Ns) + 2Na2S°4(s) + 2C°(g)]
(3)
The free energy and enthalpy changes for reaction (3) as a function of temper-
ature using the thermochemical data of Barin (23) are as follows:
400 500 600
AF° (kcal/mole FeS2) 56.5 47.4 40.9
AH° (kcal/mole FeS2) 92.4 88.8 88.6
Since the free energy change for reaction (3) is a large positive value the
use of Na2C03 as a leachant (for sulfur) is not favored thermodynamically.
Other candidate reactions of interest include the use of 0~ and H2. In
the case of 02 substantial oxidation of the coal matrix has been observed"
under conditions of sulfur oxidation. The use of H2 produces H2S under con-
ditions of temperature and pressure where considerable amount of coal is
decomposed (5).
Experimental Data on Pyrite Reactions
In an effort to gain some basic understanding on the behavior of FeS2 as
a function of temperature and the presence of reactants (which may hold
promise in coal desulfurization), a series of measurements were made on the
gaseous species using the Knudsen Crucible/Time-of-Flight Mass Spectrometer
apparatus.
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The first series of experiments involved heating FeS2 in the same manner
as coal was heated' in gathering the data shown in Figure 1. The reported ion
intensity as a function of temperature as shown in Figure 2 reveals the
behavior of pyrite. At a temperature close to 400°C under conditions of
equilibrium pyrite begins to decompose and releases gaseous sulfur. The most
abundant vapor species are 82, 83, Sg, 87, So, and Sc.'! The decline in ion
intensity at temperatures above 700°C suggests the depletion of sulfur in the
sample due to the conversion of FeS/? to FeS.
In order to distinguish between Fe$2 vaporization and FeS2 oxidation,
oxygen was added to the crucible. The results of this experiment are shown
in Figure 3. The major peaks observed were mass 64 due to 82 and/or SC^, 48
due to SO, and 80 due to 820. This experiment suggests that the formation of
the sulfur oxides coincides with the evolution of elemental sulfur from the
decomposition of FeS£ and also with the thermal decomposition of coal itself
(see Figures 1 and 2). This in turn suggests that the use of 02 under con-
ditions of equilibrium converts sulfur to its oxides in a temperature range
which is too high in order to achieve desulfurization without the destruction
of coal itself.
The next series of experiments involved heating FeS2 in the presence of
NaOH. The ratio of FeS2 to NaOH was 3.76 (by weight) which resulted in an
excess of FeS2 in terms of the stoichiometry required to form Na2S (i.e.
FeS2 + 4NaOH).
The results of these experiments are shown in Figure 4. The most striking
result from this series is the fact that although FeSo was in excess no gaseous
sulfur was observed until the temperature reached 650°C. This suggests that
FeS2 has reacted with NaOH at a temperature range well below the decomposition
range of FeS2 (or coal itself) to form the bisulfide Na2S, and perhaps poly-
sulfides Na2Sx (where x>l). It also suggests that these compounds are stable
to relatively high temperatures (600°C or higher). This is an important
result because low temperature sulfur reactions are required to bring about
chemical desulfurization of coal.
It is obviously important to make similar runs with H2 as well as re-
placing FeS2 with model organic compounds which have been considered to host
organic sulfur in coal.
Based on the above discussion, it appears that the ideal chemical desul-
furization process is one which maximizes the rates of sulfur removing
reactions, while the chemical attack (and the reduction in heating value) of
the coal matrix is held at a minimum. This is difficult because both the
desulfurization reactions as well as the destruction of coal are favored by
increased temperature and the presence of oxidants. Therefore, a method,
which is capable of selectively heating or chemically activating regions high
in sulfur content and/or selectively heating (or activating) a leachant, is
expected to induce non-equilibrium conditions which accelerate rates of
reactions involving sulfur bonds, shorten the total reaction time, and reduce
energy and pressure requirements. This, in turn, would simplify the process
and eventually reduce process costs. The use of microwave energy, as discussed
in a later section, appears to hold promise in terms of process simplicity and
economics.
85 and 87 were not plotted.
-------
in
Z
W
O
M
W
Oi
100
200
T°C
800
Figure 2. Mass spectrometrLc analysis of the vaporization of
10
-------
itr
CO
a
w
H
2
O
H
10
200
300
400
500
600
700
800
T°C
Figure 3. . Gaseous products from pyrite oxidation.
11
-------
2
2
1Q.
10.
. 10
9
e.
7.
0.
—S2-
. .. A ...sa
.Q1
.-.. S7
100
200
300
400 50
T°C
600
700
800
Figure 4. Gaseous products from pyrite reaction with sodium hydroxide.
12
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SECTION 3
, THE USE OF MICROWAVES IN COAL DESULFURIZATION
THEORY AND MEASUREMENTS OF DIELECTRIC PROPERTIES .
The potential usefulness of microwaves in chemical desulfurizat ion is
supported by the physical nature of microwave energy absorption. Microwave
power dissipation by a medium is proportional to the imaginary part of the
complex dielectric constant (£"") which is a measure of the dissipated power
per unit electric field (squared) according to
P/V = Jf f E £"
*- o s-
where
P is power absorbed
V is volume
f is the applied frequency (I/sec)
£* is the permittivity of free space (3.85 x 10" farads/m)
E is the electric field (V/m)
£" is the imaginary part of the complex dielectric constant
In the case of inhomogeneous mixtures, if £" differs significantly
within the mixture, one would expect different heating rates and pressure rise
within the various regions and most probably a change in the overall chemistry
of the system, as compared to a method of heating based on conduction from
the exterior of the sample. In the case of polar molecules £" " is high and
one can expect a situation whereby the energy is channeled into the medium
primarily via molecules of high dipole moment even though these molecules may
be uniformly dispersed. Under conditions of high power density (or pulsing)
one expects maximum deviations from equilibrium and perhaps the most inter-
esting effects relative to being able to shift reaction rates advantageously.
The work of Ergun and Berman at the Bureau of Mines (25) has demonstrated
that pyrites can indeed be selectively heated by microwaves in the presence of
coal, and partially converted to para-magnetic forms. This conversion, which
takes place in the absence of any observed loss of coal volatiles, was con-
sidered beneficial in terms of increasing the efficiency of subsequent magnetic
separation of pyrites from coal.
13
-------
Further studies at this Laboratory directed towards gaining basic under-
standing of the very complex nature of coal, included measurements on the
dielectric properties of coal and some of its significant sulfur compounds
such as pyrite (Fe$2) > thianthrene (Cj^HgS), dibenzothiaphene (Ci2^8^2^5
potential leachants such as NaOHA^O, as well as mixtures of coal/FeS2 and
coal/NaOH with ^0. The complex dielectric constants were determined from
waveguide measurements. These measurements consisted of completely filling
a known length of the waveguide with the material and measuring the complex
reflected signal, the position of minimum and amplitude of the transmitted
signal. The measurements were repeated for various specimen lengths. The
apparatus used for these measurements is shown schematically in Figure 5.
Typical microwave transmission measurements are shown in Figure 6 for
Ky. #11 coal mixed with a NaOH solution into a slurry. Measurements were made
on transmitted and reflected power; absorption was obtained by subtracting the
sum of the two from the total incident power.
Furthermore, Figure 7 shows the ratio of absorbed/incident power at
8.3 GHz for several materials media of interest. The,,apparent conclusion is
that coal low in pyrites is relatively transparent to microwaves at this fre-
quency while pyrites (FeS2) and NaOH (especially with water) greatly enhance
the level of absorption.
The complex dielectric constant was varied in a computer program to match
the experimental results. Measured dielectric values at 8.3 GHz for compounds
of interest are shown in Table 1.
TABLE 1. MEASUREMENT OF COMPLEX DIELECTRIC CONSTANTS AT 8 . 3 GHz
Material £" (Loss)
Coal (Ky. No. 11; Primarily Organic Sulfur) 0.12
FeS2 1.0
C12H8S2 <0.01
NaOH 0.10
NaOH + Coal (Dry) 0.30
NaOH (9.4%) + Coal (59%) + H20 (31.6%) 1.9
Free Space 0
14
-------
Port #1
Calibration
Reference
Plane1
Extended
Reference
Plane
Coax
Adapter
fl
n r
^
U / L
i
— 1 fi °1 rnr? . '
. r
y
^v;§
^ / 'r< Z >J-
Waveguide
Short
Additional
Length of
Waveguide
Sample Holder
Waveguide
Figure 5. Experimental set up for dielectric property measurements.
15
-------
w
Z
w
Q
I—i
U
2
Z
O
M
H
U
• REFLECTED POWER
X TRANSMITTED POWER
D ABSORBED POWER
THICKNESS IN INCHES
Figure 6. Microwave transmission measurements - Ky. #11 Coal (597=), NaOH (9.47.), H20 (31.67»)
-------
1.04-
N
ac
O
OO
>
<
oi
u
w
CO
o
H
Q
W
cq
o:
o
Cfl
CQ
PL,
O
o
l-l
H
COAL + 20%
NaOH WET
COAL + 20?!
NaOH DRY
0.3 0.4 0.5
THICKNESS OF MEDIUM (IN.)
Figure 7. Microwave power absorption.
-------
These measurements show that: a) dry coal free of mineral matter as well
as dibenzothiaphene (C^^g^) anc* thianthrene (CioHoS) are essentially trans-
parent to microwaves at 8.3 GHz, b) pyrite particles (YeS^) are relatively
good absorbers and c) moist sodium hydroxide is an extremely good absorbing
medium.
Additional measurements on FeS2 and Coal (Ky. #11) were carried out in
the frequency range 0.6 - 4.2 GHz. The transmission data are shown in
Figure 8. Reduced data on the dependence of loss factor (£"") vs. frequency
(0.6 - 8.3 GHz) are shown in Figure 9. It is obvious from these measurements
that in this frequency range the loss in FeS2 is by a factor of ten (or more)
higher than that of coal.
In an effort to identify the behavior of coal/FeS2 or coal/H^O mixtures,
coal samples containing different amounts of FeS2 or ^0 were placed in the
waveguide and the amount of absorbed power was measured as a function of
additive. These data are shown in Table 2 and Figure 10. As expected from
the previous individual measurements the addition of small quantities of FeS2
or H20 increases the lossiness of coal significantly.
EXPERIMENTAL APPROACH
General
Existing GE-RESD facilities were used in this project. These facilities
included: a) microwave sources 2.4 GHz (1 KW, 6 KW) and 8.3 GHz (1 KW) with a
specially designed treatment chamber, b) gas handling and analytical instru-
mentation consisting of several mass spectrometers (time-of-flight and other)
and gas chromatographs adequately equipped to handle compounds of sulfur,
nitrogen, hydrocarbons, H2> CO, and H20, and c) equipment for sulfur analysis
(in coal) as well as a combustion calorimeter for calorific value determin-
ations. In addition, the treatment chamber was instrumented so that net power
absorbed by the sample could be measured.
The data obtained from the experiments included: a) accurate measure-
ments of the microwave energy input, b) the gaseous species generated,
c) extent of desulfurization, d) calorific value of the treated coal,
e) total mass loss during treatment, and f) measurement of surface temperature
with an IR pyrometer and bulk temperature using a thermocouple at the end of
the exposure. These measurements, in combination with the complete proximate
and ultimate analyses, provided by Pennsylvania State University, resulted in
a great deal of information relevant to the removal mechanism of the pollutant-
forming constituents and the economics of the process.
As an adjunct to the studies of the chemistry of the process, some of
the coal types evaluated in the project were subjected to pre- and post-
exposure microstructural and electron probe analyses. These data were used
to: a) help elucidate the microwave coal desulfurization mechanism(s), and
b) aid in explaining any microwave interaction differences between the coals.
18
-------
p
w
H
O
w
p
w
§
o
w
CO
w
(X,
DB 7.
10 90%
8 88%
7
6 75%
5
4
3 507.
2
1 12%
0
FeS
COAL (KY #11)
.6 1 2345
FREQUENCY - GHz
Figure 8. Transmissions coefficient vs. frequency.
19
-------
\
\
\ FeS2
\
\
O \
B \
<
\
$ 3
3
\
\
/"\
\
\
\
\ / \
.2 X
COAL \ /
KY. #11 \^ ' \
V '
.2 .4 .6 1 2 3 .A 6 8
FREQUENCY - GHz
Figure 9. Loss factor variation.
20
-------
TABLE 2. MICROWAVE POWER ABSORPTION BY KY. #11 COAL IN WAVEGUIDE
(Dry)
Coal
Coal
Coal
(Dry)
Coal
Coal
Coal
Coal.
Sample. Reduction
(db)
Coal 3
+ 6.37, Water 7
+ 147, Water 27
+ 25% Water >30
Coal + 1% FeS2 ' 4.5
+ 3% FeS2 5
+ 57. FeS2 5
+ 77, FeS2 5.4
+ 11% FeS0 7
70 Loss
50
60
99
>99
64
68
79
71
80
21
-------
ioo 4-
— WATER
—FeS2
COAL (KY. NO. 11)
I
10
I
12
\
14
I
16
i
18
I
20
i
22
r
26
2 4 6 8 10 12 14 •16 - 18 20 22 24
% OF FeS2 AND WATER ADDITION TO COAL
Figure 10. Microwave power absorption by coal in waveguide (at 8.3 GHz).
i
28
-------
Microwave Facilities
Coal desulfurization experiments have been carried out with several
microwave energy sources. The first was a 1 KW, 8.35 GHz Klystron powered
unit assembled at GE, the second was'a 2 KW, 2.45 GHz magnetron unit and the
third a 6 KW, 2.45 GHz magnetron powered generator. Both 2.45 GHz generators
were manufactured by Cober Electronics Inc., Stanford, Connecticut. All
three are CW units with power level variable from zero to the rated power.
In addition, the units are equipped with dial meter readouts of forward and
reflected power. The 6 KW generator has a chart recorder output as well as
meter recording.
Figure 11-shows a diagram of the experimental set up used with the 8.35
GHz and the 2.5 KW, 2.45 GHz power sources. Microwave energy is transmitted
from the generator via rectangular metal waveguide to an aluminum box appli-
cator (26.7 cm cube). The applicator has a removable lid with a sighting
tube and an extension tube which is used as a vent and gas sampling port.
The sighting tube has a 15 mm diameter quartz window. Coal powder samples
(10-30 g) to be irradiated were placed in a quartz cup (4.5 cm dia. x 7 cm)
held by a foam quartz pedestal as shown in the diagram. Air was removed from
the applicator using a nitrogen or argon purge. All experiments were run at
1 atmosphere. Figure 12 is a photograph of the 8.35 GHz system which shows
the Klystron, the forward 'and reflected power meters and the applicator box.
A photograph of the applicator and box are shown in Figures 13 and 14.
Absorption traces at the top of these figures are read to determine the fre-
quency of greatest absorption. The cavity can be tuned for absorption at
8.3 GHz with the coal sample only.
This system is now upgraded with two 6 KW, 2.45 GHz units. The appli-
cator designed for use with the two 6 KW generator is a steel pressure vessel
45.7 cm dia. x 914 cm length. This unit will provide a facility in which
kilogram quantities of coal samples can be irradiated. A turntable was
designed and constructed to enable rotation of the containerized coal samples
during irradiation in the applicator. This ensures more uniform exposure to
the microwave field. A diagram of the turntable is shown in Figure 15. The
table is a foam quartz disc 21 cm dia. x 2.5 cm which has a pyrex test tube
mounted on the under side as shown in the diagram. The disc rotates on a
pointed teflon rod attached to a foam quartz base. The turntable is rotated
by directing a stream of N2 against grooves cut radially into the under side.
With moderate flows 2-3 rps are produced. Samples to be irradiated are held
in a pyrex petri dish 14 cm dia. x 1.5 deep or in pyrex beakers. This arrange-
ment has been used to treat samples up to 500'g.
Analytical Procedures
One of the sulfur analysis techniques used was adopted from ASTM Procedure
E30 "Sulfur by Direct Combustion - lodate Titration Method." A known weight
of sample of coal to be analyzed is placed in a combustion boat and ignited
in a stream of oxygen at temperatures in excess of 1100°C. The S02 produced
is absorbed in an acidified starch-iodide solution and determined during the
combustion, by titration with a potassium iodate solution. The following
reactions are involved in the process:
23
-------
Coal Sample
NJ
-O
Microwave
Generator
Metal
Wave Guide
Aluminum
Box Applicator
(26-7 cm cube)
Plastic gas sampling
tube for mass spectro-
meter and gas chromato-
graph analyses
'^-Sighting Port
Quartz Cup
.5 cm dia x 7 cm)
Nitrogen
Purge
Foam Quartz
Pedestal
Figure 11. Diagram of microwave desulfurization apparatus, 8.35 GHz and 2.45 GHz experiments
-------
ho
Ui
Figure 12. 8.35 GHz microwave equipment and measurement apparatus
-------
o
D,
M
O
en
Frequency
Figure 13. Treatment chamber and sample holder.
26
-------
c
o
c.
O
10
Frequency
Figure 14. Treatment chamber with coal sample (500g).
27
-------
r
Applicator
26.7 cm Alum.
Cube
n
Wave
Guide
Top View
Side View
Pyrex Petri Dish
14 cm dia. x 1.5 cm
-Foam Quartz Disc
Argon or
"inlet
-Pyrex Tube
-Teflon Post
Figure 15. Diagram of turntable used in 6 KW 2.45 GHz experiments,
28
-------
KI03 + 5 KI + 6 HCI = 3 I2 + 6 KCI + 3 H20
S02 + I2 + 2 H20 = H2 S04 + 2 HI
where the liberated I2, in an aqueous solution, is oxidized by S0? to HI.
This procedure determines only combustible sulfur, which ends up as S02.
Sulfur tied up in the ash is not determined by this technique.
Other analytical techniques used in this work involved use of the LEGO
(IR-33) Sulfur Determinator which burns the sample at a temperature as high
as 1600°C and analyzes for S02 using an infrared detector. This technique
has been shown to detect all sulfur present.
Comparison of results obtained by the above techniques with total sulfur
determinations based on the Eschka method showed good agreement on untreated
samples. In the case of treated samples the Eschka method in some cases
detected sulfur levels one to three tenths of a percent higher than the lower
temperature combustion method thus suggesting some capturing of sulfur in the ash
Mott's method was used for the determination of sulphate and pyritic
sulfur whenever these analyses were deemed necessary. The method is based on
acid extractions of two samples of pulverized coal. One sample is extracted
with hydrochloric acid, the other with nitric acid and the amount of iron is
determined in the extracts. Values thus determined are used to calculate the
pyritic sulfur content of the coal. Organic sulfur cannot be measured directly
and is calculated from the relationship
^° ^organic = stotal " (^pyritic + ^sulphate)
Determinations of C, H, and N were made with a Perkin Elmer Elemental
Analyzer - Model 240. This is an instrument which accurately determines the
C, H, and N content of organic compounds by detecting and measuring their
combustion products (C02> ^0 and N2). The combustion is carried out in pure
oxygen under static conditions with the combustion products being analyzed
automatically in a self integrating steady-state, thermal conductivity
analyzer.
Ash content is determined from the residue of either the lower temperature
combustible sulfur analysis or the C, H, and N analysis.
There is no simple direct method for the determination of oxygen.
Oxygen was calculated from the relationship
70 0 = 100 - (7o N + % C + 7o H + 7o S + 7. Ash)
The proximate analysis of coal consisting of moisture loss, 7» ash, %
volatiles and 7» fixed carbon was determined by a thermogravimetric procedure
developed and recommended by the Perkin Elmer Corporation. In this analysis
the sample is weighed directly into the instrument at room temperature under
a N2 purge. The temperature is then raised to 100°C and the N2 flow rate
29
-------
increased. At the end of five minutes (sufficient time to dry the sample)
the N2 flow rate is reduced to the initial level and the sample is reweighed.
The difference between the initial and the second weight represents the loss
in weight due to moisture. The temperature of the sample is then rapidly
raised to 950°C, while maintaining a constant N£ flow, and is held 5 to 10
minutes. The total weight loss for the sample minus that for moisture loss
is due to volatiles; the 70 fixed carbon is calculated from the relationship
7o C = 100 - (70 Volatiles + % Ash)
The results obtained by the above technique agree quite well with the. results
obtained using the A.S.T.M. procedure D271 - 64. A typical plot of weight
versus time-temperature is shown in Figure 16.
Microstructural Characterization
A series of coal samples were examined before and after exposure to
microwaves using standard scanning electron microscopy (SEM) and energy
dispersive x-ray (EDX) techniques. This provided information as to the
effects of treatment on surface topography and the level and spatial distri-
bution of sulfur as well as other contaminants such as Al, Si, Cu, K and Fe.
Energy dispersive x-ray techniques greatly enhance the analytical value
of the SEM as the characteristic x-rays emitted under bombardment by electrons
provide both qualitative and quantitative information about the nature and
amount' of elements present in the volume excited by the primary electron beam.
For this study, the scanning electron microscope was equipped with a non-
dispersive spectrometer. With this type of equipment, the energy of the x-ray
photons generated is converted into an electrical pulse in a silicon crystal.
A bias voltage applied to the crystal collects the charge, which is proportional
to the energy of the x-rays. The pulse is amplified, converted to a voltage
pulse and fed into a multichannel analyzer. The resulting spectrum for
elements above fluorine (atomic number 9) is subsequently plotted on a chart
after a sufficient period of counting to insure adequate accuracy. Data
plotting was carried out at two levels of sensitivity, namely, 10"+ and
5 x 10 counts for full scale chart deflection. In addition, SEM interfaced
rays can be photographically recorded for the various impurities present.
SEM/EDX studies were conducted on two types of samples. In one set, the
coal particles, approximately 1/8 inch in diameter, were cleaved and the
cleaved surfaces examined for topography and sulfur distribution by SEM inter-
faced mapping. In the other techniques, 100 mesh coal particles were pressed
into a small cavity in standard spectroscopically pure carbon SEM mounts and
the small powder compacts subsequently carbon shadowed to provide appropriate
electrical characteristics. EDX studies on the carbon mount and carbon
shadowing material indicated that they were quite pure and did not have any
significant effect on the apparent compositional characteristics.of the coal
samples.
30
-------
100
o
H
H
1-1
Z
CJ
Pi
Figure 16. Temperature dependence of weight change for coal,
31
-------
SECTION 4
EXPERIMENTAL RESULTS
SULFUR REMOVAL AS OBSERVED BY ENERGY DISPERSIVE X-RAYS (EDX) AND ELECTRON
PROBE MICROANALYSIS
The characteristics of the cleaved surfaces and SEM interfaced EDX sulfur
maps for a high pyritic sulfur coal (Pennsylvania #6 Clarion County with~47» S)
are shown in Figures 17, 18, and 19 for 3 sets of conditions. Figure 17 shows
the smooth cleaved surfaces of the as-received coal with the sulfur map*
indicating a very uniform dispersion of the sulfide particles. Figure 18 is
a similar series of pictures for a sample, heated 90 seconds in the microwave
unit (8.35 GHz) without leachant. These results indicate a reduction in
sulfur content and some fragmentation of the structure due to coupling of the
FeS2 particles and H20 with the microwaves. Figure 19 shows the combined
effects of microwave irradiation and NaOH treatment. It is to be noted that
the structure appears to be uniformly altered by the leachant and has an
apparently much lower sulfur content.
Evidence for the removal of organic sulfur by microwave irradiation in
the presence of sodium hydroxide is provided by the energy dispersive x-ray
spectra for Kentucky No. 11 (PSOC-273-1) coal before and after treatment and
the residue from the wash water obtained after leachant removal. Figure 20
shows a very high ratio .of sulfur to iron and supports the Penn State analysis
of this particular sample showing essentially only organic sulfur (4.8%)
(Table 3). Figure 21 shows a significant reduction in the sulfur peak height
for the microwave/NaOH treated and washed sample. Figure 22 displays the
spectrum for the dry residue obtained from the wash water after evaporation;
sulfur and silicon appear to be the only elements extracted in significant
amounts from the sample.
The attack of pyritic and organic sulfur on the previous two samples
during short exposure periods is demonstrated in .Figure 23 where the reduction
in sulfur is depicted as an increase in the Fe/S ratio.
* In a sulfur map obtained by the EDX microanalytical technique, the density
of white dots at any location is a direct function of sulfur content
whether .present as sulfide particles'or organic compounds.
32
-------
(a)
(b)
Figure 17. (a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of virgin #6 Pennsylvania coal
(pyritic), 300X.
33
-------
(a)
(b)
Figure 18. (a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of #6 Pennsylvania coal heated 90
seconds with microwaves, 300X.
34
-------
(a)
(b)
Figure 19. (a) Scanning electron micrograph and (b) SEM interfaced sulfur
map for a cleaved surface of #6 Pennsylvania coal heated 90
seconds with microwaves in presence of NaOH, 300X.
35
-------
HIGH
SENSITIVITY
LOW SENSITIVITY
LOW SENSITIVITY
LOW SENSITIVITY
ENERGY (KEVI
ENERGY (KEV)
ENERGY (KEV!
Figure 20. Energy dispersive
x-ray spectrum for virgin
sample PSOC-273-1 (Ky. #11)
Figure 21. Energy dispersive
x-ray spectrum for PSOC-273-1
coal after 30 second micro-
wave exposure using NaOH
leachant (sample washed).
Figure 22. Energy dispersive
x-ray spectrum for residue
from wash water from leachant/
microwave irradiation treated
PSOC-273-1 coal.
-------
TABLE 3. CANDIDATE COAL SAMPLES
Sulfur Content,
UJ
•-j
Coal #
PSOC-320
PSOC-257
PSOC-294
PSOC-255
PSOC-353
Pa. #5
Pa. #6
PSOC-273-1
PSOC-273-2
PSOC-270
Geographic Origin
Pittsburgh Seam, Berlin, Pa.
Upper Freeport Seam from Pa.
Pittsburgh Seam from Pa.
Lower Kittanning Seam from Pa.
Clarion Seam from Pa.
Upper Kittanning Seam, Clarion County, Pa.
Upper Freeport Seam, Clarion County, Pa.
Ky. #11 Seam, Sinclair Strip Mine
Ky. #11 Seam
.American Seam, Maxine Mine, Al.
Pyritic
0.45
1.06
2.27
4.49
4.65
2.37
3.8
0.18
2.63
0.02
Organic
0.64
0.56
0.34
0.78
1.21
0.2
0.2
5.71
1.87
2.70
Sulfatic
0.07
0.01
0.03
0.07
0.02
0.14
0.05
Total
1.16
1.62
2.62
5.30
5.93
2.57
4.0
5.91
4.64
2.77
-------
ORGANIC
O SULFUR
Q PYRITIC
• SULFUR
1.6--
1.4--
o
M
H
in
1.0--
g 0.8-t
g
CO
^ 0.64
0.4--
0.2--
D
PYRITIC SULFUR.
TREND
D
1
AS
RECEIVED
ORGANIC SULFUR
TREND
DOUBLE
TREATMENT
(60 SEC. TOTAL)
ASH
Figure 23. Iron to sulfur ratio by dispersive x-rays,
38
-------
In addition to the EDX measurements, electron probe x-ray microanalysis
(wavelength dispersive spectroscopy) was used to look at high pyritic coal
samples from L. Kittanning (PSOC-255, Table 3). Measurements of Fe-Kcx, and
S-K
-------
TABLE 4. ELECTRON PROBE X-RAY MICROANALYSIS OF COAL SAMPLES
Counts for
(100 sec.)
Fe S Sample
73544
72843
15894
21657
7865
182962
190520
'
1109
5317
390
As received
> PSOC-255
(0.25")
PSOC-255
' Exposed in M.W.
Fe/S (Ratio)
0.
0.
14.
4.
20.
41
38
33
07
17
S/Fe
2
2
0
0
0
(Ratio)
.44
.63
.070
.246
.0496
X (in
1.
1.
0.
0.
0.
FeSx)
81
95
052
182
037.
113893 155364
111860 148661
Strd. FeS
0.73
0.75
1.37
1.33
1.01
0.985
40
-------
400,-
300-
o
o
E-i
3
200-
w
rJ
100
IRRADIATION TIME (SECONDS)
Figure 24. Surface temperature of PSOC-255 (L. Kittanning) coal during
microwave exposure in the presence of sodium hydroxide.
41
-------
temperatures between presumably identical runs there was much closer agreement
between the bulk temperature measurements which were consistently below 250°C.
Based on visual observations it appears that hot spots and arcing as well as
sodium line radiation are generated on the surface of the sample during irradi-
ation. These may account for the differences in recorded surface temperatures.
The important thing however (as it will be discussed later) is the fact that at
these low temperatures and short exposure times significant amounts of sulfur
are removed at one atmosphere.
Desulfurization Measurements
Selection of Samples--
In order to maximize the efficiency of this activity the Coal Research
Section of the Pennsylvania State University was used as a source of well
characterized* samples. The coal samples selected for study as shown in
Table 3 range widely in terms of sulfur level and form from high pyritic-low
organic to high organic-low pyritic. Additional characterization data,
proximate, and ultimate analysis of the selected coal samples are shown in
Table 5.
Desulfurization Results Without Leachants--
Experiments using microwave heating (without leachants) were initiated
with 0.25" particles of highly pyritic coals, Pa. #6 (Clarion County) and
PSOC-255 (L. Kittanning). As shown in Figure 25 these coals exhibit extensive
desulfurization 40-607» in short periods of exposure (20-60 seconds); it is
significant to mention that the accompanied mass losses were about 670 and
sulfur compounds (such as H2S and traces of COS and S02) were identified mass
spectrometrically. Another significant observation was the fact that (after
grinding) the treated samples could be further purified with ease by a low
strength (bar) magnet (30) due to the extensive conversion of FeS2 to FeSx
(where x^l) which is much more paramagnetic than its parent FeS2-
Preliminary measurements with coal samples high in organic sulfur failed
to show significant reduction in the sulfur level after similar exposure.
Results on Low Sulfur Coal Enriched with Added FeS2 (PSOC-320, Pittsburgh
Seam, Berlin,Pa. + 5.3% FeS2)--
In an attempt to test the theory that NaOH activated by microwave energy
can react fast with FeS2 in the presence of coal without degrading the coal
structure, a synthetic slurry was made from lOg (-100 mesh) low sulfur coal,
0.53g FeS2, 2g of NaOH and 5g of water. The samples were then exposed to a
microwave cavity (power input 300 watts at 8.3 GHz) for variable periods of
time ranging from 10 seconds to 90 seconds. At the end of each run the total
weight was measured, the sample was then washed to remove the product Na2S
arid the excess NaOH dried and analyzed for total sulfur. The results as shown
in Figure 26 very conclusively demonstrate that before the sample lost all of
the water present, 707» of all the sulfur was removed over a 90 second time
period.
* Characterization was done by Commercial Testing and Engineering, Co.,
Chicago, '111. . .
42
-------
TABLE 5. S, C, H, N, 0, ASH, MOISTURE, VOLATILE MATTER, AND FIXED CARBON OF
SAMPLE COALS
Coal
Pa. #5
PSOC-26
PSOC-252
PSOC-255
PSOC-257
PSOC-270
PSOC-272
PSOC-273-1
PSOC-294
PSOC-296
PSOC-320
D
1 j i
i-H
3
CO
Combustible
2.37
3.08
3.65
4.3
1.60
1.95
2.45
4.78
2.45
1.24
1.16
Nitrogen
1.53
1.72
1.68
.85
1.40
1.33
1.21
2.35
Carbon
78.82
66.11
66.74
62.78
71.48
60.19
62.65
68.23
Hydrogen
5.69
4.40
4.92
3.91
5.02
4.80
4.24
4.99
Oxygen
9.12
10.77
7.57
10.39
11.00
18.62
10.08
8.03
£
en
2.47
9.62
11.24
17.84
10.55
17.4
5.4
12.88
19.94
Moisture
4.3
3.0
0.7
0.7
4.0
M
01
Volatile Mat
37.8
41.0
27.19
34.74
o
CO
0
0)
X
-r-l
52.6
47.8
62.26
45.32
43
-------
100 T-
SO--
2 60.
o
•w
--OS
BS
!D
&-,
40--
.j
..
0 - PA. #6 - CLARION COUNTY
0 - PSOC-255 - L. KITTANNING
O
20 40 60
TOTAL MICROWAVE EXPOSURE TIME (SEC.)
80
Figure 25. Reduction of total pyritic sulfur
44
-------
18--
— TOTAL WEIGHT
— 7° SULFUR
.COAL (4% H20)
/ + NaOH
10 20 30 40 50 60 70 80
90
— 6
— 5
—4
I
— 3
— 2
— 1
IRRADIATION TIME (SEC)
Figure 26. Sulfur reduction as a function of exposure time and water removal
(PSOC-320 Pittsburgh Seam Coal, 4.5% Iron Pyrite added).
45
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Desulfurization of Pyrttic Coals Using Microwaves and Sodium Hydroxide--
This phase of the study involved pyritic coals ranging in sulfur content
from 1.6% (PSOC-257) to 1.95% (PSOC-270) to 2.6% (PSOC-294) to 5.27% (PSOC-255)
The data for these four coals are shown in Figures 27, 28, 29, and 30, respec-
tively. Again the data suggest an impressive level of sulfur reduction 50-75%
during exposure times of 90 seconds or less. All runs were made with 16% NaOH
and at microwave frequencies of 2.45 or 8.35 GHz; the higher frequency in
general appeared to be more effective.
In addition a double exposure to two 30 second periods (with washing
between the exposures) proved to be more effective than a single 60 second
run. Double exposure data on PSOC-294 are shown in Figure 31. It is apparent
that the two steps totaling 60 seconds can remove 70-967=, of the sulfur while a
single 60 second exposure reduces the sulfur level by 537o and prolonged ex-
posure to 90 seconds appears to provide no further reduction (Figure 29).
Desulfurization of Organic Sulfur Coals Using Microwaves and Sodium Hydroxide--
Work to date has been focused on Ky. #11 coals (PSOC-273, 1 and 2) and
Alabama Coal Maxine Mine (PSOC-270). As shown in Table 3 PSOC-270 and PSOC-
273-1 contain essentially only organic sulfur and were selected because of
that.
Desulfurization data on these samples are shown in Figures 32 and 33.
The data show that actual removal of sulfur reaches the.70% level as deter-
mined by Eschka and 80-85% by combustion (LECO-Method) at 1600°C (2912°F).
When the combustion temperature is lowered to a range of 2600°F-2700°F there
is additional reduction in the amount of registered combustible sulfur. This
reduction is due to trapping of sulfur in the ash by small amounts of residual
alkali thus suggesting that as much as 907, of the sulfur present in coal can
be eliminated from the combustion gases by a combination of precombustion
removal and trapping in the ash.
A second batch of Ky. #11 coal PSOC-273-2 contained a total of 4.64%
sulfur, 2.63% pyritic, 1.877o organic, 0.147, sulfatic as shown in Table 3.
Several runs were made under double exposure conditions. Sulfur analyses were
made for total sulfur and sulfur forms; the total was obtained by the Eschka
method. The results as shown in Figure 34 show a high rate of removal of
pyritic sulfur 90-987= during exposure times of the order'of sixty seconds and
removal of 50-60% of the organic sulfur in corresponding exposure periods of
ninety to a hundred seconds.
KINETICS
Global kinetic expressions describing sulfur removal can be very helpful
in designing process conditions. For this reason the data were analyzed and
plotted assuming first order reaction kinetics on sulfur present, i.e.
dx/dt = kj_ (a - x)
46
-------
90
80--
70 --
60--
50 --
40-.
10--
o
i ,1 1 1
10 12 14 16
MICROWAVE TREATMENT TIME (SECONDS)
i
|
i
I
18
: j ::."
20 : . :
Figure 27. Reduction of total sulfur for PSOC-257,
-------
00
Q
CO
90..
80--
70--
60--
50--
40--
30--
20--
10--
20
40
I
I
60 • 80 100
MICROWAVE TREATMENT TIME (SEC.)
120
Figure 28. Reduction of total sulfur for PSOC-270.
-------
• : . 10 •••.; 2(1
30 . . - . 40 50 . . 60 .
._.j- TOTAL. TRKArif-aiNT.T.iMK__(SECPNDSl.
80.
90
Figure 29. Reduction of total sulfur for PSOC-294.
49
-------
Ui
o
90..
80..
70..
6(U
o
H
I 5U4.
|
8
s 40..
30..
20..
10..
0
10
I
I
20 30 40
MICROWAVE TREATMENT TIME (SEC.)
50
60
Figure 30. Sulfur reduction for PSOC-255.
-------
100--
z
o
M
H
U
g
oi
3
§
CO
0
20 JO 40 SO
TOTAL TREATMENT TIME (SECONDS)
GO
Figure 31. Time dependence of sulfur removal from coal PSOC-294 using micro-
wave irradiation and double exposure.
51
-------
80 ; 12!Q . 160
; : t ; !
TOTAL MICROWAVE EXPOSURE; Tlhffi (SEC)
Figure 32. Reduction of total (organic) sulfur for PSOC-270, 2.45 GHz
-------
90 --
: 80 - -
70 --
60 --
H
5 50 --
S
g
t/3
40 4
30 --
20 --
10 --
o
O
6
0
o
<3> - TOTAL SULFUR (ESCHKA ANALYSIS)
Q - COMBUSTIBLE SULFUR
I
40
50 60 70
TOTAL MICROWAVE EXPOSURE TIME (SEC.)
80
90
100
Figure 33. Reduction of total sulfur for PSOC-273-1 (double treated samples):
-------
Figure 34. Reduction of sulfur forms from Ky. #11 coal (PSOC-273-2) (double treated samples)
-------
where
a = sulfur present at time (t) = 0
a-x = sulfur present after time (t)
k-, = rate constant
Data for PSOC-294 and PSOC-255 are shown in Figures 35 and 36. The
observed reasonable fit to a straight line indicates that the removal of
sulfur follows first order kinetics at early times.
ASH CONTENT AND CALORIFIC VALUE OF TREATED COAL
The three coals which were extensively studied in terms of desulfurization
measurements were also analyzed in terms of ash and calorific content. The
results as shown in Table 6 suggest that no significant changes in either are
introduced by the treatment.
Ultimate analysis was carried out on a limited basis. A typical run on
PSOC-273 coal as shown in Table 7 suggests "a modest increase in the oxygen
content but no adverse effects on C or H.
55
-------
1.0-
0.8-
^0.6--
n;
C
0.2--
O
O
Q
0
10
20
30
I T
40 50
TIME (SEC)
60 .70 80 90
Figure 35. Sulfur removal 1st order kinetics PSOC-294.
-------
Ln
0.8--
0.6--
0.4--
0.2--
G
10
I
20
30
TIME (SEC)
40 50
60
Figure 36. Sulfur removal 1st order kinetics PSOC-255.
-------
TABLE 6. ASH AND ENERGY CONTENT
Coal
PSOC-255
PSOC-255.
PSOC-273-1
PSOC-273-1
PSOC-294
PSOC-294
Treatment
As received
Microwave + NaOH
(Figure 30)
As received
Microwave + NaOH
(Figure 33)
Dry Ash Free (DAF)
Microwave + NaOH
Ash Content Calorific Value
(7oWt.) (Btu/lb)
17.5 11,349
18.1 11,711
12.9 10,645
14.3 10,395
13,095
13,522
(DAF - Figure 29)
TABLE 7. ULTIMATE ANALYSIS
Coal
Treatment
7o S
H
0
PSOC-273-1 As received
5.12 1.33 60.19 4.80 15.68
PSOC-273-1 Microwave + NaOH 1.84 1.15 63.34 4.39 20.30
58
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SECTION 5
SCHEMATIC FLOW SHEET OF PROPOSED PROCESS
Although simplifying techniques are now being worked out, a flow diagram
as shown in Figure 37 identifies the .various steps in the Microwave/NaOH
•process.
59
-------
NiOH
SOLUTION
Na OH SOLUTION
MAGNETRON
OR
RF GENERATOR
POWDERED COAL
H
V
DEWATERING
IRRADIATION
CHAMBER
DEWATERING
SULFUP
RECOVERY
N«OH
SOLUTION
MAGNETRON
OR
RF GENERATOR
IRRADIATION
CHAMBER
DEWATERING
DEWATEPING
OPTIONAL
DRYING
COMBUSTION
OR
TRANSPORTATION
Figure 37. Proposed schematic flow sheet for G.E. chemical coal cleaning
process.
60
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SECTION 6
PROCESS ENERGY REQUIREMENTS AND ECONOMIC PROJECTIONS
The desulfurization process steps that our initial experiments have
identified are:
(1) Pulverization of coal to 30-100 mesh.
(2) Mixing with a sodium hydroxide solution to produce a thick slurry.
(3) Partial drying of the slurry.
(4) Microwave irradiation for periods of 30-60 seconds at one atmosphere
(N2).
(5) Wash coal and dry for use.
(6) Convert sulfides to elemental sulfur and recover sodium hydroxide.
The last step, the sulfide conversion, may involve either the use of
carbon dioxide generated by a limestone calciner step or directly from the
stack gases. The carbon dioxide converts the sulfides to sodium carbonate
and hydrogen sulfide; the regeneration of sodium hydroxide from sodium
carbonate is accomplished by reacting it with lime, i.e.:
Na2S + C02 + H20 >Na2C03 + H2S
CaO + H20 > Ca (OH)2
Ca (OH)2 + Na2C03 >CaC03 + 2 NaOH
Further steps involve the use of a Glaus unit which converts hydrogen
sulfide to elemental sulfur; limestone either goes to a calciner to regener-
ate carbon dioxide and lime
CaC03 > C02 + CaO
or to a landfill if stack carbon dioxide is used.
The energy required to carry out the process steps has been estimated
for each individual step and is shown in Table 8 as compared to the energy
content of the coal. These preliminary estimates suggest that 13-24% of the
coal energy is required as input energy into the process.
61
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TABLE 8. PROCESS ENERGY REQUIREMENTS
ESTIMATES
REMARKS
Net Coal Heat Value Loss
Microwave Irradiation
Coal Slurry Dryers
Decant Liquor Evaporator
Limestone Calciner
Auxiliaries
TOTAL
0.041 Btu Lost
Btu (Coal)
0.08 Btu to Irradiate
Btu (Coal)
0.06 Btu (Steam)
Btu (Coal)
0.008 Btu (Steam)
Btu (Coal)
0.043 Btu (Fuel)
Btu (Coal)
0.005 Btu
Btu (Coal)
0. 237 Btu/Btu Coal
Can Be Eliminated
(Heat From Stack Gas)
May Be Eliminated
0. 134 Btu/Btu Coal*
*If Slurry Dryer and Calciner
are not used.
-------
Furthermore, economic estimates by GE-KESD, in consultation with Day and
Zimmermann, Inc. (Philadelphia, Pennsylvania - Architect/Engineers), were
performed on capital and operating costs for this process. The results of
these economic studies are shown in Tables 9 and 10.
The calculations were based on the demand of a 500 MW coal-burning power
plant, with the assumption that the desulfurization portion of the plant is
on-stream 70% of the time and the pulverized coal is available at the power
plant. Although these calculations can only be viewed as preliminary esti-
mates, they do suggest however that the process has high merit and that
further research and development is required.
63
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TABLE 9. CAPITAL COSTS WITH MICROWAVE DESULFURIZATION
DOLLARS-INSTALLED
Costs Common To Scrubbers
• Chemical Storage & Preparation
• Sludge Pond
• Railroad Siding
Coal Washing Tanks
Thickeners
Surge Tanks
Claus (Allied)
Vacuum Filters
Pumps
Evaporators
Microwave Reactor (2, 500 $/KW)
Contingency (20%)
TOTAL
2,800,000
2,700,000
4,560,000
100,000
3,865,000
6,000,000
100,000
3,040,000
17,550,000
40,715,000
8,143,000
48,858,000
97.7 $/KW
64
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TABLE 10. OPERATING COSTS
Electricity
Steam
NaOH
Lime
Operating Labor
Maintenance
Overhead
Taxes
Insurance
TOTAL OPERATING COST:
Amortization (20 years - 10%)
TOTAL ANNUAL COST
DOLLARS/YEAR
1,722,000
2,260,000
2,580,000
680,000
240,000
2,949,400
776,383
1,956,000
150,000
13,313,000
5,745,750
19,058,000
.0062 $/KWH
•$12/tonoflO Btu/% Coal
65
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SECTION 7.
CONCLUSIONS
Based on measurements and interpretation conducted in the course of this
study, the following conclusions have been reached.
1. Pyrites and sodium hydroxide (with small amounts of water) absorb
microwave energy much more efficiently than coal itself.
2. Microwave irradiation of pyritic coal can induce reactions between
pyrite particles and their immediate environment to convert FeS2
to FeS and produce gaseous sulfur compounds such as H2S, COS and
S02- This step removes about 507, of the pyritic sulfur and facili-
tates further removal of pyritic sulfur via physical separation
techniques such as magnetic and density gradient.
3. Microwave irradiation of mixtures of coal/NaOH (1670)/H20 (10-207o).
converts pyritic or organic sulfur into water soluble sulfides
(Na2S, Na2Sx) which can be removed from the coal by washing. The
sulfides can subsequently be converted to elemental sulfur and
NaOH which goes back into the process for continuous use.
4. The required microwave energy is a very modest fraction of the
heat content of the treated coal ('>/370) while the heat content of
the treated coal remains essentially unchanged.
5. The conditions of very short exposure times (in the order of one
minute) and pressure of one atmosphere required to reduce the
sulfur level significantly in combination with being able to
retain the heat content of the coal in combination indicate this
process has great potential for economic coal desulfurization.
6. The mechanism by which fast rates of desulfurization are accom-
plished is most probably related to the fast (and to some degree
selective) in-depth heating of the bed. The activation of water,
FeS2 and NaOH create local volatilization high temperature and
pressure conditions which accelerate sulfur reactions before the
coal has a chance to decompose. It is also quite possible that
local non-equilibrium chemistry as a result of localized dis-
charge sites plays a beneficial role.
7. Present economic estimates suggest that this process has economic
merit as compared with other chemical desulfurization methods.
66
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REFERENCES
1. L. Hoffman, et.al., "Survey of Coal Availability by Sulfur Content,"
Mitre Corporation'MTR-6086, NTIS PB-211505 (May 1972).
2. W.J. Ward, et.al., "Search for General Electric Business Opportunities
in Sulfur Emission Control," Report No. 74CRD189 (October 1974).
3. E.F. Osborn, "Coal and the Present Energy Situation," Science, Vol. 183,
No. 4124, p.477 (1974).
4. S. Frindal and H. Kolm, "Magnetic Desulfurization of Coal," IEEE Trans.
Magnetic, MAG-9310 (1973).
5. D.K. Fleming and R.D. Smith, "Hydrodesulfurization of Coals," presented
at 173rd ACS National Meeting, New Orleans (March 1977).
6. J.H. Gary, et.al., "Removal of Sulfur From Coal by Treatment with
Hydrogen," R&D Report No. 77, Interim Report No. 1 prepared by the
Chemical and Petroleum Ref. Engineering Department, Colorado School of
Mines, March 30, 1973 for the Office of Coal Research, U.S. Department
of Interior.
7. L. Lorenzi Jr., J.S. Lord, L.J. Van Nice, E.P. Koutsoukos, and R.A. Meyers,
"TRW Zeroes in on Leaching Method to Desulfurize Pyritic Coals," Coal Age
22. (H). 76-79 (November 1972).
8. J.W. Hamersma, M.L. Kraft, W.P. Kendrick, and R.A. Meyers, "Chemical
Desulfurization of Coal to Meet Pollution Control Standards,". American
Chemical Society, Division of Fuel Chemistry, Reprints of papers pre-
sented at 167th National Meeting, Los Angeles (April 1-5, 1974).
9. J.W. Hamersma, M.L. Kraft, W.P. Kendrick, and R.A. Meyers, "Meyers'
Process Cuts Out 80% Sulfur," Coal Mining & Processing _11 (8), 36-39
(August 1974).
10. R.A. Meyers, "Desulfurize Coal Chemically," Hydrocarbon Processing j4 (6),
93-95 (June 1975). .,
11. E.P. Stambaugh, J.F. Miller, S.S. Tan, S.P. Chauhan, H.F. Feldman,
H.E. Carlton, J.F. Foster, H. Nack, and J.H. Oxley, "Hydrothermal
Process Produces Clean Fuel," Hydrocarbon Processing 54 (7), 115-116
(July 1975).
67
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12. "Hydrothermal Process Cleans Up Coal," Chemical and Engineering News
_53 (27), 24-25 (July 1, 1975).
13. "New Process Makes Clean Coal," Chemical Week _118 (1), 33-35
(January 7, 1976).
14. J.C. Agarwal, R.A. Giberti, P.P. Irminger, L.J. Petrovic, and S.S. Sareen,
"Coal Desulfurization: Costs/Processes and Recommendations," presented
at American Chemical Society Meeting, Los Angeles (April 1974).
15. J.C. Agarwal, R.A. Giberti, P.F. Irminger, L.F. Petrovic, and S.S. Sareen,
"Chemical D.esulfurization of Coal," Mining Congress Journal _61 (3),
40-43 (March 1975).
16. J.C. Agarwal, R.A. Giberti, and L.J. Petrovic, "Method for Removal of
Sulfur From Coal," U.S. Patent 3,960,513 (June 1, 1976).
17. S.S. Sareen, "Sulfur Removal from Coals: NH3/02 System," presented at
173rd ACS National Meeting (March 1977).
18. S. Friedman, "Oxidative Desulfurization of Coal," presented at 173rd ACS
National Meeting (March 1977).
19. R.W. Fisher and T.D. Wheelock, "Advanced Development of Fine Coal
Desulfurization and Recovery Technology," Quarterly Technical Progress
Report (February 1977).
20. P. Howard, "Chemical Comminution. A Process for Liberating Mineral
•Matter from Coal," presented at 173rd ACS National Meeting, New Orleans
(March 1977).
21. R. Oder et.al., "Technical and Cost Comparisons for Chemical Coal
Cleaning Processes," Bechtel Corporation Report (March 1977).. Also
presented at the Coal Conversion, American Mining Congress, Pittsburgh,
Pennsylvania (May 1977).
22. T.A. Nepokrytykh, S.I. Kuznetsov, N.G. Tyurin, and F.F. Fedyaev, Chemical
Abstracts 82:328464 (1975).
23. I. Barin and 0. Knacke, "Thermochemical Properties of Inorganic Sub-
stances," Springer-Verlag, N.Y. (1973).
24. P.O. Zavitsanos and G.A. Carlson, "Experimental Study of the Sublimation
of Graphite at High Temperatures," J. Chem. Phys. _59, 2966-2973 (1973).
25. S. Ergun and M. Berman, "Separation Method," U.S. Patent 3,463,310
(August 26, 1969).
68
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26. (a) P.D. Zavitsanos and K. Bleiler, "Coal Desulfurization with-Micro-
waves," GE Patent Docket 40-RE-0086 (August 1975); (U.S. Patent Pending).
(b) P.D. Zavitsanos, et.al., "Coal Desulfurization with Microwaves and
Sodium Hydroxide," GE Patent Docket 40-RE-0155 (May 1976).
27. P.D. Zavitsanos, "Coal Desulfurization by Microwave Energy," EPA Monthly
Reports (1976-1977).
28. J.L. Beeson, G.E. Fanslow, and T.S. King, "Using Microwave Power to
Reduce the Sulfur Content of Iowa Coal," Energy and Mineral Resources
Research Institute and Engineering Research Institute, Iowa State
University, Ames, Iowa (November 1975).
29. B. Bak, et.al., "Microwave Spectra of Thiophene," J. Chem. Phys. 25,
892 (1956).
30. P.D. Zavitsanos, "Coal Desulfurization Using Reactive Electromagnetic
Irradiation in Combination with Physical Separation," GE Patent Docket
40-RE-0220 (March 1978).
69
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing/
1. REPORT NO.
EPA-600/7-7 8-089
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Coal Desulfurization Using Microwave Energy
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
P.D. Zavitsanos K.W. Bleiler
J.A. Golden W.K. Kinkead
9. PERFORMING ORGANIZATION NAME AND ADDRESS
General Electric Company
Re-entry and Environmental Systems
P.O. Box 8555
Philadelphia, Pennsylvania 19101
10. PROGRAM ELEMENT NO.
E HE 62 3 A
11. CONTRACT/GRANT NO.
68-02-2172
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 8/76-10/77
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES jERL-RTP project officer is Lewis D. Tamny, Mail Drop 61, 919/
541-2709.
16. ABSTRACT
The report describes the use of microwave energy and NaOH to remove
pyritic and organic sulfur from several U.S. coals. Exposure times on the order
of 1 minute at 1 atmosphere of inert gas can remove up to 85% of the sulfur with little
or no loss in heating value of the coal. Data analysis suggests that sulfur is conver-
ted to water soluble sulfides (Na2S, Na2Sx) in the process and that sulfur conversion
follows first-order reaction kinetics0 The mechanism by which fast rates of desul-
furization are accomplished is most probably related to the fast (and to some degree
selective) in-depth heating of the bed. The activation of water, FeS2, and NaOH
creates local volatilization, high temperature and pressure conditions which accel-
erate sulfur reactions before the coal has a chance to decompose. It is also quite
possible that local non-equilibrium chemistry (as a result of localized discharge
sites) plays a beneficial role.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
C. COSATI Held/Group
Pollution
Coal
Coal Preparation
Desulfurization
Microwaves
Sodium Hydroxide
Pyrite
Pollution Control
Stationary Sources
Pyritic Sulfur
Organic Sulfur
13B
08G,21D
081
07A,07D
20N
07B
3. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
78
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
70
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