Energy & Fuels 2000, 14, 597-602
597
The Effect of Sulfur Dioxide on the Formation of
Molecular Chlorine during Co-Combustion of Fuels
Ying Xie, Wei Xie, Kunlei Liu, Laura Dicken, Wei-Ping Pan,* and John T. Riley
Combustion Laboratory, Department of Chemistry, Western Kentucky University,
Bowling Green, Kentucky 42101
Received August 9, 1999
This project was designed to evaluate the combustion performance of and emissions from a
fluidized bed combustor during the combustion of mixtures of high sulfur and/or high chlorine
coals and municipal solid waste (MSW). The effect of sulfur dioxide on the formation of molecular
chlorine during co-combustion of fuels was examined in this study. Sulfur dioxide was shown to
be an effective inhibitor for the formation of molecular chlorine through the Deacon Reaction
and, subsequently, the formation of chlorinated organics. Theoretically, co-firing high sulfur coals
with MSW will decrease the possibility of polychlorodibenzodioxin/furan (PCDD/F) formation
during the combustion process. A mixture of coal and PVC pellets was burned in a 0.1 MWth
bench-scale fluidized bed system at WKU and no detectable amounts of chlorinated organics
were found in the flue gas and bed ash. The results from this study indicated the practical effects
of using coal as a combustion support fuel when burning MSW.
Introduction
The amount of municipal solid waste produced in the
United States each year continues to rise. The total
MSW produced in 1993 rose to 187.5 million tons
(equivalent to nearly 2.0 kg per day per person) from
179 million tons in 1988, and will reach approximately
200 million tons in the year 2000.1-3 However, the
rapidly declining availability of sanitary landfills has
forced most municipalities to evaluate alternative waste
management technologies in order to reduce the volume
of waste sent to landfills. Waste-to-energy technologies
are receiving more and more attention as landfill costs
and environmental concerns rise.
Incineration of MSW, or refuse-derived fuels (RDF)
processed from MSW and consisting of combustible
material, is one of the alternative waste management
strategies to replace landfilling. Such waste-to-energy
technology has already displayed a few advantages over
conventional methods. In 1993, nearly 30 metric tons
(Mt) of MSW generated in the United States was burned
in 151 plants, of which 125 were operated as waste-toenergy plants.4 However, extra care needs to be taken
in burning RDF and the operating conditions need to
be optimized so that combustion can take place in an
environmentally acceptable manner. The development
of MSW combustors has slowed significantly in recent
years, resulting from apprehension over possible emis* Corresponding
author.
Fax:
(270)745-5361.
Email:
Wei-Ping.Pan@wku.edu.
(1) Ekmann, J. M.; Smouse, S. M.; Winslow, J. C. Co-firing of Coal
and Waste, IEA Coal Research, IEACR/90, 1996.
(2) Steuteville, R. What is New in the Waste Stream? Biorecycle
1992, 33 (10), 10.
(3) Dichristina, M. How We Can Win the War Against Garbage.
Popular Sci. 1990, 237 (10), 57.
(4) Strong Waste-to-Energy Growth Predicted. Air Waste 1994, 44
(2), p 122-123.
sions of hazardous chlorinated organics, especially the
harmful polychlorinated dibenzo-p-dioxins (PCDDs) and
polychlorinated dibenzofurans (PCDFs). The emission
of PCDD/Fs from incineration processes were first
reported in 1977 by Olie and co-workers.5 A number of
measurements and evaluations have been carried out
in a variety of combustion systems since then. Trace
quantities of PCDD/Fs have been detected in many
combustion systems involving the burning of organic
materials, such as MSW, paper industry wastes, motor
vehicle exhausts, etc.6
Fluidized bed combustion (FBC) technology is characterized by intense mixtures between solids and gases
during combustion, as well as long residence times for
fuel particles in the high-temperature zone, resulting
in very little active carbon being produced during the
combustion process. Therefore, the possibility of the
occurrence of a de novo synthesis is minimum. As
indicated in the study by Dickson,7 in the presence of
sufficient phenol and chlorine sources, fly ash catalyzed
the formation of PCDDs using chlorophenol as precursors. Laboratory evidence demonstrates that transition
metal ions of Cu and Fe are capable of catalyzing
PCDD/F formation reactions, which take place on the
fly ash particles. The small organic molecules can be
adsorbed onto the fly ash and subsequently converted
to PCDD/Fs.8 The total synthesis involves the Deacon
Reaction and is represented by the following steps:
(5) Olie, K.; Vermeulen, P. L.; Hutzinger, O. Chemosphere 1997, 6,
455.
(6) Buckland, S. J.; Hannah, D. J.; Taucher, J. A.; Allison, R. W.
Organohalogen Compd. 1990, 3, 219.
(7) Dickson, L. C.; Lenoir, D.; Hutzinger, O. Chemosphere 1989, 19,
77.
(8) Born, J. G. P.; Louw, R.; Mulder, P. Organohalogen Compd. 1990,
3, 31.
10.1021/ef990173d CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/22/2000
598
Energy & Fuels, Vol. 14, No. 3, 2000
Xie et al.
PVC (in MSW) f HCl (thermal decomposition) (1)
4HCl + O2 f 2H2O + 2Cl2 (Deacon Reaction)
C6H5OH (in fuels) + Cl2 f chlorophenols
(2)
(3)
condensation of chlorophenols f
PCDDs and PCDFs (4)
Molecular chlorine produced from the Deacon Reaction
is considered as a key intermediate step in the above
mechanism. The occurrence of the Deacon Reaction in
the MSW incineration process can be supported by
numerous studies regarding the effect of oxygen on
PCDD/Fs production.9-11
Coal as a co-firing energy source for municipal solid
wastes, is able to suppress the formation of chlorinecontaining organic compounds. Scheidle and co-workers
demonstrated that adding lignite coal as an auxiliary
fuel to paper recycling residues decreased the levels of
dioxins in fluidized-bed incinerator emissions.12 Similar
results can be inferred from the studies13-16 which
showed that co-firing MSW with 60% coal drastically
reduced the formation of PCDD/Fs. Ohlsson and coworkers observed that despite the enhancing level of
HCl due to the addition of RDF, no PCDD/Fs have been
detected when co-firing high sulfur coal and RDF
pellets.17 Frankenhaeuser and others also reported the
adverse effects of SO2 in the formation of organic
chlorides during the co-combustion of plastics with
coal.18 On the basis of thermodynamic evaluation and
published test data, Griffin proposed that as long as the
Cl/S ratio is high, chlorine formation for the elevated
production of chlorinated aromatics and PCDD/Fs is
prevalent, but in the presence of substantial amounts
of sulfur, chlorine production and consequently PCDD/
Fs formation is suppressed.19 Co-combustion seems to
have the dual advantage of being a source of energy and
having the potential of reducing the formation of
chlorinated species in combustor emissions.
Several different mechanisms are proposed for the
inhibition of PCDD production involving the sulfur
species, one of which suggests that in coal combustion
the role of sulfur interference with the chlorination step
(and hence the formation of PCDDs) is critical. When
sulfur is present in excess over chlorine, in any system,
the forward reaction predominates:
(9) Vogg, H.; Metzger, M.; Stieglitz, L. Waste Manage. 1987, 5, 285.
(10) Sakai, S.; Hiraoka, M.; Takeda, M.; Nie, P.; Ito, T. Formation
and Degradation of PCDDs/PCDFs in a Laboratory Scale Incineration
Plant; Presented at The Kyoto Conference on Dioxins, Problem of MSW
Incineration, 1991; Kyoto International Community House, 1991.
(11) Gullet, B. K.; Bruce, K. R.; Beach, L. O. Chemosphere 1990, 20
(10-12), 1945.
(12) Scheidle, K.; Wurst, F.; Kuna, R. P. Chemosphere 1986, 17,
2089.
(13) Gullett, B. K.; Bruce, K. R.; Beach, L. O. Waste Manage. Res.
1992, 8, 203.
(14) Grochowalski, A.; Wybraniec, S. Chem. Anal. (Warsaw) 1996,
41 (27), 27.
(15) Lindbauer, R. L. Chemosphere 1992, 25 (7-10), 1409.
(16) Banaee, J.; Larson, R. A. Waste Manage. 1993, 13, 77.
(17) Ohlsson, O. O.; Shepherd, P. In Combustion Modeling, Cofiring
and Nox Control; FACT-Am. Soc. Mech. Eng. 1993, 17, 173.
(18) Frankenhaeuser, M.; Manninen, H.; Virkki, J.; Kojo, I. The
Effect of the Chlorine/Sulfur Ratio on Organic Emissions from the
Combustion of Mixed Fuels; NESTE Final Report: Porvoo, Finland,
1992.
(19) Griffin, R. D. Chemosphere 1986, 15, 1987.
SO2 + Cl2 + H2O T SO3 + 2HCl
(5)
Thus the chlorinating agent, chlorine, is converted
into HCl, which is very unlikely to undergo aromatic
substitution reactions to form PCDD and PCDF precursors. In the study reported in this paper, this reaction
was examined by conducting experiments in a tube
furnace. The results indicate the apparently inhibiting
effect of sulfur on the Deacon Reaction.
The combustion and thermal decomposition processes
of other materials that comprise MSW and their blends
were examined in our study using TG/FTIR/MS and GC/
MS trapping techniques. The combination of TG/FTIR
and TG/MS offers complementary techniques for detection and identification of evolved gases. The major
advantages of these techniques lie in their abilities to
obtain information concerning combustion products on
line at the elevated temperatures.
On the basis of the static results from TG/FTIR/MS,
two coals with different chlorine contents were co-fired
with PVC in a bench scale 0.1 MWth FBC system. The
effects of temperature, with and without limestone, and
S/Cl mole ratios on PCDD/Fs formation in ash were
investigated.
Experimental Section
TGA/FTIR/MS System. To study the combustion performance of MSW co-fired with coal, a small amount (about 1020 mg) of sample (coal or PVC or the blend of coal and PVC)
was placed in the TGA and heated to 1000 °C at different
heating rates in an air atmosphere. The gaseous products were
analyzed by the TGA/FTIR/MS system, and the FTIR spectra
and MS profiles were recorded.20 The three major components
of this system are a Model 951 Thermogravimetric Analyzer,
a Model 1650 Fourier Transform Infrared Spectrophotometer,
and a VG Thermolab Gas Analysis System.
The TGA is interfaced to the FTIR using an insulated Teflon
tube which is heated to a temperature of 150 °C by a Powerstat
variable autotransformer in order to prevent possible condensation of the gaseous products. The mass spectrometer is
coupled with the TGA by means of a fused silica capillary
sampling inlet that is heated to approximately 170 °C.
Studies with a Tube Furnace. This series of tests were
performed in a quartz reaction tube inserted into a horizontally
mounted electric Lindberg furnace. Prior to the introduction
of samples into the reactor, the furnace was preheated to the
desired temperature. To simulate the conditions used in the
AFBC system, a mixture of flue gas atmosphere including CO2
(15%), CO (0.2%), O2 (5%), and H2O vapor (5%) in N2 was
adopted. The compositions of the process gases were adjusted
by calibrated Teflon flow meters. The reaction products were
swept into a cooled trap containing a chosen absorbent. After
the reaction was complete the trapping solution was concentrated and then subjected to GC/MS analysis.
A Shimadzu QP 5000 system with a NIST/EPA/NIH 62,000
compound database was used for GC/MS analysis. Aliquots of
2 µL of sample were injected in the splitless mode onto a RTX-5
fused silica capillary column (60 m × 0.32 mm and a stationary
phase thickness of 1.0 µm). Helium was used as the carrier
gas. The surrounding temperature for injector, interface, and
detector was 230 °C. The mass spectrometer was operated in
the selected ion monitoring (SIM) mode. The identification of
compounds was accomplished by using a computerized library
search and by comparison with literature mass spectra.
Moreover, comparison to the GC retention time for pure
(20) Lu, R.; Purushothama, S.; Yang, X.; Hyatt, J.; Pan, W.-P.; Riley,
J.; Lloyd, W. G. Fuel Process. Technol. 1999, 59, 35.
SO2 Effect on Cl2 Formation during Fuel Combustion
Energy & Fuels, Vol. 14, No. 3, 2000 599
Figure 1. Profiles of HCl and Cl2 evolved during the combustion of PVC.
compounds was also used to confirm the identification of
unknowns. Standard materials were tested to establish the
detection limits for the experimental setup, for calibration, and
determination of the quantitative working range for the
compounds. The detection limit is 0.1 ppb when the selected
ion monitoring (SIM) mode is chosen.
Bench Fluidized Bed Combustion. The inner diameter
of combustor21 is 0.3 m and the height is 4.4 m. The freeboard
zone of the combustor is 2.5 m high, providing adequate
residence time for the combustion of fine particles which may
be entrained in the gases. The fuel (coal and PVC) is injected
into the combustor through a pressurized underbed feed
mechanism. To determine if any chlorinated organic compounds were formed during the combustion reactions, three
samples each of flue gas, fly ash, and bed ash were obtained
for each run condition. The combustion gases were collected
in a Tenax trap and glass fiber filters for 24 h with a 300 mL/
min flow rate. The line between combustor and adsorption
tubes was heated to 450 °C to minimize any condensation. The
collected samples were Soxhlet extracted with CH2Cl2 for 6 h.
Extracts were then concentrated in micro Kuderna-Denish
apparatus to 0.5 mL before GC/MS analysis through the
selected ion monitoring (SIM) mode.
Results and Discussion
Characterization of Raw Materials and Their
Blends. To understand the fundamental processes and
mechanisms of thermal decomposition, the thermal
behavior of coal, MSW, and their blends were investigated using TGA/FTIR/MS at a fast rate of 100 °C/min.
Part of the results have been presented by Lu and coworkers.20 These results are important to the analysis
and control of the performance of a FBC system. Upon
interpretation of the MS spectrum obtained from the
combustion of PVC, one finds a very notable result, that
is the production of molecular chlorine accompanies the
release of a large amount of HCl during the combustion
of PVC. As illustrated from Figure 1, masses 36 and 38
(21) Xie, W.; Pan, W.-P.; Riley, J. Energy Fuel 1999, 13, 585.
are formed at the same time, and the integrated ratio
of their ion intensity strongly suggests the presence of
isotopes of H35Cl and H37Cl. Furthermore, three additional m/z peaks appear at exactly the same point,
with apparent masses of 70, 72, and 74 corresponding
to 35Cl2, 35Cl37Cl, and 37Cl2. This is strong evidence
suggesting that some fraction of the abundant HCl may
be undergoing a thermal Deacon Reaction to produce
molecular chlorine. Following the in-situ generation of
Cl2, the aromatic compounds can be readily attacked to
form the chlorinated organics such as chlorobenzene,
which corresponds to masses of 112 and 114. It is a
plausible starting point for the formation of chlorinated
organics from the combustion of chlorine-rich fuel
mixtures. When changing the atmosphere from air to
nitrogen, chlorine is not identified in the products from
the thermal decomposition of PVC. This can be ascribed
to the absence of oxygen, a necessary reactant in the
Deacon Reaction. However, instead of Cl2, HCl is still
the major product from the combustion of PVC, even in
air.
As determined from the FTIR data, as shown in
Figure 2, the chlorine and hydrocarbon species formed
during the combustion of blends are released at the
same time. In fact, the heating rate in an AFBC system
is much higher than 100 °C/min. Thus, one can expect
there are greater possibilities for the production of
chlorinated organic compounds during co-firing coals
with RDF in an AFBC system.
Mechanism for the Formation of PCDD/Fs during the Combustion of MSW. Four grams of different
raw materials (newspaper, cellulose, and RDF) were
burned in air in a tube furnace. The furnace was
preheated to a temperature of 850 °C before the sample
was introduced. The gaseous products were trapped in
chilled CH2Cl2 and analyzed by GC/MS. In summary,
the results of replicate analyses show phenol as one of
the major organic products released during the combus-
600
Energy & Fuels, Vol. 14, No. 3, 2000
Xie et al.
Figure 2. 3D FTIR spectra of combustion products of PVC heated at a fast heating rate.
Table 1. Chlorination and Condensation Reactions of Phenol
run
temperature (°C)
time (min)
tentative product identification
1
2
3
4
5
6
7
250
425
600
600
700
800
800
30
30
15
30
30
15
30
dibenzofurans, mono-, di-, and trichlorophenols
chlorinated phenols and dibenzofuran
dibenzofurans, no chlorophenols
dibenzofurans, mono-, di-, and trichlorophenols
dibenzofurans, mono-, di-, and trichlorophenols
dibenzofurans, no chlorophenols
dibenzofurans, mono-, di-, and trichlorophenols
Table 2. Products from the Study of the Condensation Reactions of Chlorophenols
sample
temperature (°C)
tentative product identification
2,4-dichlorophenol
700
2,4-dichlorophenol
400
4-chlorophenol
2-chlorophenol
700
700
tetrachlorodibenzodioxin, tetrachlorofuran,
dibenzodioxin, 2-chlorophenol, 2,6-dichlorophenol,
2,4,6-trichlorophenol, dichlorobenzene
trichlorobenzene, dichlorodibenzofuran
trichlorodibenzodioxin, tetradichlorodibenzofuran,
dichlorodibenzodioxin
dichlorodibenzofuran, benzene, chlorobenzene
dichlorodibenzofuran, phenol
tion of newspaper, cellulose, and RDF. From the GC/
MS data, chlorophenol was determined to be a major
product when blends are burned.22
To examine the gas-phase chlorination of phenol, as
illustrated by eq 3, 100 mg portions of phenol were
placed in a heated tube and evaporated in the presence
of a constant flow of 0.5% Cl2 in nitrogen. The reaction
products were cooled by liquid nitrogen and condensed
upon exiting from the reaction tube, carefully washed
by methylene chloride, and analyzed by GC/MS. The
test results is listed in Table 1. The chlorination of
phenol began at a temperature around 250 °C and
produced 2-chlorophenol, 4-chlorophenol, and 2,4-chlo(22) Pan, W. P.; Riley, J. T. Co-Firing High Sulfur Coal with Refuse
Derived Fuels; Final Report, Project No. DE-FG-94PC94211, Nov, 1997.
rophenol. At higher temperatures, dibenzofuran was
produced.
The combustion of chlorinated phenols, which may
lead to the reaction illustrated by eq 4, was examined
by heating 100 mg portions of 2,4-chlorophenol in the
presence of air in the tube furnace. The results of the
analysis of the reaction products are presented in Table
2. The GC/MS results show the products from the
combustion of 2,4-dichlorophenol include 2,4,6-trichlorophenol, tetrachlorodibenzofuran, and dichlorodibenzodioxin. Tetrachlorodibenzofuran and dichlorodibenzodioxin were also formed below 400 °C. The results
from this series of experiments strongly suggest the
possibility that PCDD/Fs form from the condensation
of combustion products of chlorophenol.
SO2 Effect on Cl2 Formation during Fuel Combustion
Energy & Fuels, Vol. 14, No. 3, 2000 601
Table 3. Proximate and Ultimate Analysis Data for Raw
Materials
Figure 3. Relative yield of chlorinated phenols as a function
of S/Cl ratio.
The Effect of Sulfur Species on the Deacon
Reaction. In a study conducted by Gullet and coworkers, it was reported that the reaction of Cl2 with
SO2 to form HCl (reaction 5) is not measurable below
800 °C.23 These results are not apparent from thermodynamic calculations of the free energy change. Although equilibrium calculations suggest that the reaction is favored over the full range of temperatures
tested, the kinetics of the reaction may prevent observation of measurable product until the higher temperatures are reached.
The possible effect of SO2 upon the formation of Cl2
through the Deacon Reaction was examined at 800 °C.
The flow rate of HCl (1% in nitrogen), SO2 (4.86% in
nitrogen), and air were adjusted using calibrated Teflon
flow meters. The evolved gas was trapped by an
absorbent, which was prepared by dissolving 50 mg of
phenol in 25 mL of methylene chloride. The amount of
phenol in the trapping solution was accurately controlled to within (0.0001 g. After each experiment the
trapped solutions were concentrated to 1 mL and
injected into the GC/MS system for analysis. In this
quantitative study, the concentrations of HCl (250 ppm)
and O2 (5%) in the gaseous mixtures were fixed and only
the concentration of SO2 was changed in the range from
0 to 1230 ppm. The results of tests under varying
conditions are summarized in Figure 3, and all data
points presented are an average of at least three runs.
As clearly shown in this figure, without SO2 in the
reaction system the relative yield of chlorinated phenol
(represented by Chlorinated Phenol/Phenol) is significant. With the addition of SO2 the production of
chlorinated phenol, which results from the production
of molecular chlorine, decreases. When the S/Cl ratio
approached 2.5/1, the chlorinated phenol production was
reduced to less than 8% of that produced in the absence
of SO2. Before the S/Cl reaches 2.5/1, the yield of
chlorinated phenols versus S/Cl ratio shows a linear
relationship. After that point the extra addition of
sulfur, even doubled, has no apparent influence on the
chlorine species formation, as shown by the plateau in
Figure 3. The results shown in this figure indicate that
the molecular chlorine produced through the Deacon
Reaction in this reaction system was depleted by SO2,
as indicated by reaction 5.
(23) Gullet, B. K.; Bruce, K. R.; Beach L. O. Environ. Sci. Technol.
1992, 26, 1938.
parameters
95010
95031
PVC
Wood
coal seam
rank of coals
moisturea
ash
vol. matter
fixed carbon
carbon
hydrogen
nitrogen
sulfur
oxygen
chlorine, ppm
cal. value (Btu/lb)
blend
A
2.32
7.22
39.97
52.82
79.38
5.31
1.63
0.67
5.69
1039
14077
IL No. 6
B
8.32
10.78
37.21
52.02
72.61
4.82
1.54
2.38
7.57
3065
12842
0.00
0.36
99.64
0.00
38.71
4.2
0.07
0.22
0
54.65b
8556
4.71
1.14
80.6
14.3
49.9
6.13
0.08
0.12
42.55
748
8343
a Moisture is as-determined. All other analyses are reported on
a dry basis. The rank of each coal is high volatile A, B, or C
bituminous. b The unit for chlorine in PVC is percent.
Griffin, from a study of co-incineration of coal and
municipal solid wastes, suggested that dibenzodioxins
would not form when the S/Cl ratio was greater than
10, and proposed increasing the sulfur of the wastes in
co-combustion with coal in order to decrease dioxin
formation.19 However, in the study reported in this
paper in which the S/Cl ratio was less than 2.5/1,
dramatic decreases in the major chlorine-containing
products of combustion were observed.
Co-Combustion of PVC with Coal in a FBC
System. Based on the laboratory studies concerning the
PCDD/Fs formation, mixtures of coal and major components of MSW were burned in a 0.1 MWth AFBC
facility in order to investigate co-combustion performance. The effects of the S/Cl molar ratio and the kinds
of coal on PCDD/Fs formation were studied under the
same combustion temperature, gas velocity and excess
air rate. PVC and wood pellets were selected as cocombustion fuels for this study, since they are the major
source of chlorine during MSW incineration.
The experimental run conditions were: Fuel compositions: (1) 100% coal; (2) 89% coal, 1% PVC, and 10%
wood pellets; (3) 86.7% coal, 3.3% PVC, and 10% wood
pellets. Fuel feed rates: 9.94 kg/h; Ca/S ratio: 3.0; bed
temperature: 850 °C; gas velocity:1.25 m/s; excess air
ratio: 1.25. The analytical values for the raw materials
used in this study are shown in Table 3.
The results from the combustion run showed that no
chlorinated organics were detected in the flue gases and
the bed ashes under all co-firing experimental conditions
in this study. The effects of the PVC/fuel weight ratio
on the PCDD/Fs concentration in the fly ashes are
presented in Figures 4 and 5. It can be seen from these
figures that the amount of PCDD/Fs in fly ash increases
with an elevated PVC/fuel ratio, and the yield of PCDD
is always higher than that of PCDF. This fact provides
additional evidence for the importance of chlorine
content in fuel on the PCDD/Fs formation. Figure 4 is
a comparison of tetrachlorodibenzodioxin (TCDD) concentration in fly ash for two different kinds of coal. As
shown in the figures, with an increase of the PVC/fuel
ratio the TCDD concentration in the fly ash is enhanced
for both coals. TCDD emission from the combustion of
coal 95031 increased gradually, whereas the TCDD
emission from the combustion of coal 95011 remained
relatively constant as the PVC/fuel ratio is increased.
However, for tetrachlorodibenzofuran (TCDFs), the
602
Energy & Fuels, Vol. 14, No. 3, 2000
Xie et al.
Table 4. The Effect of Limestone on the Distribution of
2,3,7,8-TCDD and 2,3,7,8-TCDF
2,3,7,8-TCDD
gas phase
fly ash (ng/kg)
bed ash
2,3,7,8-TCDF
gas phase
fly ash (ng/kg)
bed ash
Figure 4. The effect of PVC/fuel ratio on 2,3,7,8-TCDF
content in fly ash.
Coal 95010 with 3.3 wt
% PVC
Coal 95031 with 3.3 wt
% PVC
with
limestone
no
limestonea
with
limestone
no
limestonea
b
2009
b
b
5171
b
b
1200
b
b
3733
b
b
1533
b
b
2491
b
b
1241
b
b
3755
b
a No new limestone was fed with fuel, the original bed material
is limestone. b Under detection limit.
chloride in flue gas are also revealed. The effects of
limestone on PCDD/Fs content in fly ash were listed in
Table 4. With more limestone being injected into
combustor, more hydrogen chloride was captured by
limestone. HCl concentration in flue gas decreases
significantly. Thus, the production of PCDD/Fs were
reduced remarkably as shown in Table 4.
Conclusions
Figure 5. The effect of PVC/fuel ratio on 2,3,7,8-TCDD
content in fly ash.
trend for the two coals is the same, as is shown in Figure
5. Since coal 95010 has a higher sulfur content then coal
95031 has, these results indicate the promising future
for co-firing MSW with high sulfur coal. On the basis
of different trends obtained for TCDD and TCDF
emissions for two coals, the different mechanisms for
PCDD and PCDF formation in the presence of excess
In a tube furnace, chlorophonel was identified as a
major organic product when blends are burned and SO2
is an effective inhibitor of the formation of molecular
chlorine through the Deacon Reaction. There is no
evidence to identify gas-phase PCDDs and/or PCDFs in
this study under the bench fluidized bed combustion
system. The other parameters (such as the amount of
limestone, the concentration of SO2 in the flue gas, bed
temperature, and fluidized velocity) may also influence
the formation of chlorinated organic compounds in the
fly ash.
Acknowledgment. The authors thank the U.S.
Department of Energy for the financial support through
grant number DE-FG-94PC 94211.
EF990173D