Experimental study on the removal of PAHs using in-duct activated carbon injection

Article abstract of DOI:10.1016/j.chemosphere.2004.11.022

This paper presents the incineration tests of municipal solid waste (MSW) in a fluidized bed and the adsorption of activated carbon (AC) on polycyclic aromatic hydrocarbons (PAHs). An extraction and high performance liquid chromatography (HPLC) technique was used to analyze the concentrations of the 16 US EPA specified PAHs contained in raw MSW, flue gas, fly ash, and bottom ash. The aim of this work was to decide the influence of AC on the distribution of PAHs during the incineration of MSW. Experimental researches show that there were a few PAHs in MSW and bottom ash. With the increase of AC feeding rate, the concentrations of three- to six-ring PAHs in fly ash increased, and the concentration of two-ring PAH decreased. The total-PAHs in flue gas were dominated by three-, and four-ring PAHs, but a few two-, five-ring PAHs and no six-ring PAHs were found. PAHs could be removed effectively from flue gas by using in-duct AC injection and the removal efficiencies of PAHs were about 76-91%. In addition, the total toxic equivalent (TEQ) concentrations of PAH in raw MSW, bottom ash, fly ash, and flue gas were 1.24 mg TEQ kg^-1, 0.25 mg TEQ kg^-1, 6.89-9.67 mg TEQ kg^-1, and 0.36-1.50 μg TEQ N m^-3, respectively.

Full text of DOI:10.1016/j.chemosphere.2004.11.022

Chemosphere 59 (2005) 861–869
www.elsevier.com/locate/chemosphere
Experimental study on the removal of PAHs using
in-duct activated carbon injection
*
Hong-Cang Zhou , Zhao-Ping Zhong, Bao-Sheng Jin, Ya-Ji Huang, Rui Xiao
Department of Power Engineering, Key Laboratory of Clean Coal Power Generation and Combustion Technology of
Ministry of Education, Thermal Energy Engineering Research Institute, Southeast University, Sipailou 2,
Nanjing, Jiangsu 210096, PR China
Received 2 March 2004; received in revised form 4 November 2004; accepted 17 November 2004
Abstract
This paper presents the incineration tests of municipal solid waste (MSW) in a fluidized bed and the adsorption of
activated carbon (AC) on polycyclic aromatic hydrocarbons (PAHs). An extraction and high performance liquid chro-
matography (HPLC) technique was used to analyze the concentrations of the 16 US EPA specified PAHs contained in
raw MSW, flue gas, fly ash, and bottom ash. The aim of this work was to decide the influence of AC on the distribution
of PAHs during the incineration of MSW. Experimental researches show that there were a few PAHs in MSW and bot-
tom ash. With the increase of AC feeding rate, the concentrations of three- to six-ring PAHs in fly ash increased, and
the concentration of two-ring PAH decreased. The total-PAHs in flue gas were dominated by three-, and four-ring
PAHs, but a few two-, five-ring PAHs and no six-ring PAHs were found. PAHs could be removed effectively from flue
gas by using in-duct AC injection and the removal efficiencies of PAHs were about 76–91%. In addition, the total toxic
ꢀ
1
,
equivalent (TEQ) concentrations of PAH in raw MSW, bottom ash, fly ash, and flue gas were 1.24 mg TEQ kg
ꢀ
1
ꢀ1
ꢀ3
0
.25 mg TEQ kg , 6.89–9.67 mg TEQ kg , and 0.36–1.50 lg TEQ N m , respectively.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Polycyclic aromatic hydrocarbon; Municipal solid waste; Fluidized-bed incinerator; Activated carbon; In-duct injection;
TEQ
1
. Introduction
cant advantages over other methods of waste disposal:
mass/volume reduction, bacteria die off and energy
recovery. But the major disadvantage of incineration
processes is the emissions of toxic air pollutants,
including polycyclic aromatic hydrocarbons (PAHs),
polychlorinated biphenyls, and polychlorinated dibenzo-
With the expansion of the city scale and the popula-
tion explosion, the output of municipal solid waste
MSW) is increasing rapidly in China. The total yield
(
of MSW had been reached 0.165 billion tons in China
in 2001 (SEPA, 2002). Incineration of wastes is expected
to further increase in the future due to its three signifi-
p-dioxins/polychlorinated
dibenzofurans
(PCDDs/
PCDFs) (Wang et al., 2002). PAHs are harmful to the
environment and the health of people due to their high
degree of mutagenicity and carcinogenicity when they
enter the human body through breathing, eating, and
drinking.
*
Corresponding author. Tel.: +86 25 83794744; fax: +86 25
83795508.
E-mail address: zhouhongcang@163.com (H.-C. Zhou).
0
045-6535/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2004.11.022

862
H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
At present, the researches on PAHs during the incin-
the experiments warrant the need for seeking better tech-
nologies for disposing MSW in the future.
eration of MSW lie in two aspects. One studied the im-
pact of the composition of MSW and operating
parameters (such as the bed temperature, excess air
ratio, and residence time.) on the PAH formation during
MSW incineration (Khalfi et al., 2000; Li et al., 2001;
Wey et al., 2001), the other investigated the influence
of the vapor pressure of PAHs, the ambient tempera-
ture, and the concentration of PAHs and particles in
the gaseous phases on the distribution of PAHs between
gaseous and solid phases (Halsail et al., 1994; Kamens
et al., 1995; Wey et al., 2000; Lee et al., 2002). However,
a few studies have investigated the removal of PAHs in
flue gas (Liu et al., 2002; Mastral et al., 2002a).
2. Experimental
2.1. Experimental material
According to the typical components of MSW in
China, a simulated MSW was used in this experiment.
The MSW was dried and crushed to the size of less than
1.5 mm. The analytical results of MSW in this test are
shown in Table 1.
The removal of volatile organic compounds (VOCs)
by adsorption has been paid more attention at present.
A number of studies on the removal of VOCs, such as
PCDDs/PCDFs, by the injection of activated carbon
2.2. Experimental rigs and procedure
Fig. 1 shows a schematic of the fluidized-bed inciner-
ator system for MSW in this study. The system was com-
posed of a start-up subsystem, an air supply subsystem,
a MSW feeding subsystem, a fluidized-bed incinerator, a
measurement and control subsystem, an AC feeding
subsystem, among others. The fluidized-bed incinerator
was made of a stainless steel cylinder of 100 mm inside
diameter, 4.4 m total height and 4 mm thickness. The
MSW feeding system consisted of a frame, a hopper
and a drive system of an electric motor and a speed con-
troller. The cold air from the blast blower was divided
into two path-ways, one supplied the oxygen for the
combustion of diesel oil in the start-up burner and then
entered the interlayer to heat the incinerator, the other
was preheated by the heat exchanger placed into the
start-up burner and entered the incinerator to fluidize
the bed materials and supply oxygen for MSW incinera-
tion. At the top of the incinerator, the primary cyclone
and the secondary cyclone would remove the larger size
particles. The AC injecting system was placed between
cyclone and bag house. AC was fed into the flue gas
by a spring feeder driven by a motor. The temperature
probes and the pressure gauges were placed along the
height of the incineration furnace and flue gas pipes.
The sampling positions of flue gas, fly ash, and bottom
ash are shown in Fig. 1.
(
AC), have been reported in literature. A powered AC
injection system could adsorb PCDDs/PCDFs and re-
moved them effectively at low temperature, but it did
not destroy them and required disposal of larger
amounts of solid residue, which was more highly con-
taminated with PCDDs/PCDFs (Bonte et al., 2002).
The removal efficiencies of PCDDs/PCDFs were up to
9
5% when AC was injected in front of electrostatic pre-
cipitator. Sprayed dryer absorber/bag filter had high
removal efficiency (99%) of PCDDs/PCDFs when a mix-
ture of lime and AC was sprayed into sprayed dryer
absorber (Kim et al., 2001). Tejime et al. (1996) have
studied the reduction of PCDDs/PCDFs in exhaust
gases from MSW incineration plants using a fabric filter
(
FF) with/without AC injection and found that the injec-
tion of a small amount of AC into the duct allowed the
removal efficiency of 97–99% to be obtained when the
exhaust gas temperature at the FF inlet was maintained
at 190 °C or less. Smolka and Schmidt (1997) also
thought the activated-carbon-filters were an effectively
technology to remove PCDDs/PCDFs from the flue
gas of waste incineration plants. But no research work
on the removal of PAHs in flue gas from MSW inciner-
ation in a fluidized bed using in-duct AC injection has
been reported in literature.
Each run was started with the filling of the bed of
quartz sand up to the required height. The screw feeder
was turned on and the minimum fluidized air flow rate
The aim of this paper was to investigate the influence
of AC on the distribution of PAHs during MSW incin-
eration in a bench-scale fluidized bed. The concentra-
tions of 16 US EPA specified PAH species were
determined by high performance liquid chromatography
3
ꢀ1
(8 N m h ) required to fluidize the bed material in
the incinerator was supplied through the diesel oil
start-up burner. The start-up period is necessary to pre-
heat the bed up to the required temperature before the
commencement of fuel feeding. When the bed tempera-
ture reached 500 °C, MSW was screwed into the fluid-
ized-bed incinerator, MSW feeding rate could be
adjusted to allow a certain excess air in order to achieve
complete combustion of MSW. When the bed tempera-
ture of incinerator reached the desired temperature of
the experiment, i.e. about 850 °C, the AC feeding system
(
(
HPLC), including naphthalene (NaP), acenaphthylene
AcPy), acenaphthene (AcP), fluorene (Flu), phenan-
threne (PhA), anthracene (AnT), fluoranthene (FluA),
pyrene (Pyr), benzo(a)anthracene (BaA), chrysene
(
Chr), benzo(b)fluoranthene (BbF), benzo(k)fluoranth-
ene (BkF), benzo(a)pyrene (BaP), indeno(1,2,3,-cd)pyr-
ene (In(1,2,3-cd)P), dibenzo(a,h)anthracene (DbA), and
benzo(ghi)perylene (BghiP). The results obtained from

H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
863
Table 1
The analytical results of MSW
ꢀ1
C
ar (%)
H
ar (%)
Oar (%)
Nar (%)
Sar (%)
Aar (%)
M
ar (%)
V
daf (%)
Qnet.ar (kJ kg
)
29.26
3.68
18.53
0.73
0.15
31.47
16.18
44.11
6172
Fig. 1. Schematic of a fluidized bed incinerator for MSW.
was run to inject AC into flue gas to adsorb PAH. The
flow rate and temperature of flue gas were about
tion tube packed with 5 g XAD-2 resin and an absorp-
tion bottle filled with dichloromethane. All samples
containing PAHs were refrigerated at 4 °C before their
extracting.
3
0 N m h (including the air flow rate of AC injection
ꢀ1
1
3
ꢀ1
of 1.5 N m h ) and 110–120 °C in all runs, respec-
tively. The pressure drops and temperatures were moni-
tored and registered at 10 min intervals. After the bed
temperature stabilized, the samples of raw MSW, flue
gas, fly ash and bottom ash were collected for analy-
sis. When all sampling and data recording was com-
pleted, MSW feeding system was stopped. The whole
fluidized-bed incineration system for MSW was shut
down after the temperature dropped below the safe
temperature.
All samples containing PAHs were first extracted for
8 h by Soxhlet extraction and condensed to 1 ml by
Kuderna–Danish (K–D) concentrator, respectively.
Then, the concentrated solution was made to pass
through a purifying tube packed with activated silica
gel. The purifying tube was then eluted to obtain PAHs
in the purifying solution. Further, the purified solution
was condensed to 1 ml by using a K–D concentrator
and a gentle stream of pure nitrogen. Finally, the ex-
tracted samples were put into brown vials and stored
at 4 °C for HPLC analysis.
2
.3. Sampling and analysis methods
The samples were analyzed by the Waters Alliance
HPLC system coupled with a Waters 2695 Seperations
Module, a Waters 2475 Multi k Fluorescence Detector,
and a Waters 2996 PDA Detector. Injections of 1 ll
The samples of PAH were collected from raw MSW,
bottom ash, fly ash, and flue gas. The sampling train for
PAH in flue gas is shown in Fig. 2. The flue gas contain-
ing PAHs was sampled using a stainless sampling probe
and passed through the glass fiber filter, which removed
the fine particles that escaped from the bag house. Then
it was passed through a cooling tube, which condensed
the light molecular weight PAHs into the liquid phase,
and the remaining PAHs were captured using an adsorp-
samples were made onto
a C18 column (length
250 mm, 4.6 mm i.d.) containing 5 lm particles for
ꢀ1
PAHs. The mobile phase, flowing at 1.2 ml min , was
programmed to hold, firstly held a mixture of 60:40
(v/v, %) acetonitrile and water for 12 min, secondly fol-
lowed by an 11 min ramp to a composition of 100% of

864
H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
Fig. 2. The sampling train for PAH in flue gas.
acetonitrile, and finally held a mixture of 60:40 (v/v, %)
acetonitrile and water for 7 min. The excitation and
emission wavelength of fluorescence detector were
The toxic equivalent factor (TEF) to assess the harm
of the different PAH to the human health from the
health-risk assessment view of point was shown by Tsai
et al. (2002). The toxicity of PAH was expressed as a
TEF in relation to the most toxic PAH, BaP. The TEFs
of 16 PAHs specified by US EPA were shown by Tsai
et al. (2002). In this study, the concentration of each
PAH species was converted to the toxic equivalent
(TEQ) concentration based on the TEF like PCDDs/
PCDFs. The TEQ concentration of PAH compound i
in the samples was calculated as following:
2
24 nm and 330 nm, respectively. The wavelength of
PDA detector was 254 nm. The concentrations of the
6 PAHs recommended by US EPA were determined
1
from naphthalene to indeno(1,2,3-cd)pyrene. The HPLC
was calibrated with a diluted standard solution of 16
PAH compounds (PAH Mixture-610M from Supleco)
recommended by US EPA. The recovery efficiencies of
16 PAH compounds ranged from 60% to 117%, and
the method detection limit (MDL) of them ranged from
TEQ ¼ CPAHi  TEFPAHi
;
i
1
.92 pg to 233 pg. The recovery efficiency (RE) was de-
Q3ꢀQ1
fined as RE ¼
 100%, where Q
1
is the amount
i
where TEQ is the TEQ concentration of the ith PAH
Q2
ꢀ
1
ꢀ3
of PAH to be measured in sample without standard
solution, Q is the amount of PAH to be added into
sample in standard solution, Q is the amount of PAH
to be measured in sample with standard solution.
(mg TEQ kg
,
or lg TEQ N m ),
C
PAHi is the
ꢀ3
ꢀ
1
concentration of the ith PAH (mg kg , or lg N m ),
TEFPAHi is the TEF of the ith PAH.
Hence, the total TEQ concentration of 16 PAHs
2
3
specified by US EPA was calculated as following:
X
2.4. Calculations for PAH removal efficiency and TEQ
value
TEQ ¼
ðTEQ Þ;
i
where TEQ is the total TEQ concentration of the 16
ꢀ
1
ꢀ3
One of the main aims in this study is to research the
specified PAH (mg TEQ kg , or lg TEQ N m ).
removal efficiency of PAH in flue gas emission from
MSW incinerator using in-duct AC injection. The calcu-
lation of removal efficiency of PAH in flue gas by mea-
suring PAH before and after AC injection is a good idea
and also easy to do. However, in order to know the dis-
tribution and concentration of PAH in fly ash and min-
imize the cost of PAH analysis, the amounts of PAH in
fly ash collected by bag house and in flue gas after AC
injection were determined while PAH in flue gas before
AC injection was not measured in this study. Thus, the
removal efficiency of PAH in flue gas could be calculated
by the following formula:
3. Results and discussion
3.1. Concentrations of PAH in raw MSW, fly ash,
bottom ash, and flue gas
After having been pretreated, the samples were ana-
lyzed by the HPLC. The analytical results of all samples
collected from the MSW fluidized-bed incinerator are
shown in Table 2. It can be found that only four- and
five-ring PAHs were detected in raw MSW and bottom
ash, and the concentration of total-PAH in bottom
ash was lower than in raw MSW. The longer residence
time (>2 s) of PAH in high temperature zone could
make the unburned organic materials of bottom ash be
destroyed, reduce the formation of PAH, and decom-
pose the formed PAH in bottom ash through the high
temperature section due to the secondary pyrolysis of
g ¼ ½C
1
Q =ðC
1
Q þ C
2
Q Þꢁ Â 100%;
1
1
2
where g is the PAH removal efficiency (%), C
PAH concentration of fly ash (mg kg ), Q is the yield
1
is the
ꢀ
1
1
ꢀ
1
of fly ash (kg h ), C is the PAH concentration of flue
2
ꢀ
3
gas (mg N m ), Q
2
is the flow rate of flue gas
3
N m h ).
ꢀ1
(

Table 2
The distributions of PAHs in raw MSW, fly ash, flue gas, and bottom ash
PAHs
Raw MSW
)
Run 1 AC concentration:
ꢀ3
Run 2 AC concentration:
ꢀ3
Run 3 AC concentration:
ꢀ3
Run 4 AC concentration:
ꢀ3
Bottom ash
ꢀ1
ꢀ
1
(
mg kg
1.0 g N m
1.3 g N m
1.6 g N m
2.0 g N m
(mg kg
)
Fly ash
mg kg
Flue gas
(lg N m
Fly ash
(mg kg
Flue gas
(lg N m
Fly ash
(mg kg
Flue gas
(lg N m
Fly ash
(mg kg
Flue gas
(lg N m
ꢀ1
ꢀ3
ꢀ1
ꢀ3
ꢀ1
ꢀ3
ꢀ1
ꢀ3
(
)
)
)
)
)
)
)
)
NaP
AcP
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
4.79 ± 0.24
0.09 ± 0.01
1.97 ± 0.09
1.05 ± 0.08
18.49 ± 0.92
57.56 ± 2.30
67.61 ± 3.04
<MDL
2.73 ± 0.14
0.05 ± 0.01
4.60 ± 0.21
2.66 ± 0.20
23.98 ± 1.32
8.20 ± 0.53
24.7 ± 1.11
5.93 ± 0.36
16.97 ± 0.93
3.83 ± 0.31
4.81 ± 0.36
7.35 ± 0.57
2.96 ± 0.25
3.89 ± 0.27
0.50 ± 0.05
0.54 ± 0.05
20.15 ± 1.03
38.00 ± 1.54
48.00 ± 2.16
<MDL
2.48 ± 0.12
0.09 ± 0.01
2.38 ± 0.11
1.10 ± 0.03
25.02 ± 1.38
6.79 ± 0.44
26.62 ± 1.20
7.31 ± 0.44
18.38 ± 1.01
4.25 ± 0.34
5.37 ± 0.40
7.30 ± 0.51
2.71 ± 0.23
4.89 ± 0.34
0.54 ± 0.05
0.60 ± 0.06
3.28 ± 0.16
7.15 ± 0.29
11.70 ± 0.53
2.90 ± 0.22
28.38 ± 1.57
10.37 ± 0.67
22.44 ± 1.01
5.54 ± 0.33
5.91 ± 0.33
1.05 ± 0.03
1.04 ± 0.03
2.67 ± 0.19
0.78 ± 0.07
<MDL
4.16 ± 0.21
0.14 ± 0.02
3.14 ± 0.14
1.38 ± 0.10
30.33 ± 1.67
9.94 ± 0.65
28.59 ± 1.29
9.03 ± 0.54
12.88 ± 0.71
2.77 ± 0.22
1.98 ± 0.15
6.67 ± 0.47
1.96 ± 0.17
3.41 ± 0.24
0.40 ± 0.04
0.52 ± 0.05
5.98 ± 0.30
16.61 ± 0.66
19.78 ± 0.89
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
AcPy
Flu
PhA
23.37 ± 1.31
3.28 ± 0.54
22.55 ± 1.01
6.69 ± 0.40
18.92 ± 1.04
4.00 ± 0.32
3.95 ± 0.30
6.67 ± 0.47
2.56 ± 0.22
2.90 ± 0.20
0.41 ± 0.04
1.17 ± 0.18
15.7 ± 0.86
2.12 ± 0.14
12.74 ± 0.57
1.64 ± 0.10
7.94 ± 0.44
1.89 ± 0.15
1.93 ± 0.15
<MDL
5.04 ± 0.28
1.70 ± 0.11
4.86 ± 0.22
0.71 ± 0.04
3.99 ± 0.22
1.01 ± 0.03
0.82 ± 0.06
<MDL
7.20 ± 0.40
3.27 ± 0.21
12.41 ± 0.56
2.08 ± 0.12
4.54 ± 0.25
0.83 ± 0.07
2.44 ± 0.18
<MDL
AnT
FluA
Pyr
Chr
BaA
8.69 ± 0.48
0.22 ± 0.02
<MDL
0.75 ± 0.06
<MDL
BbF
BkF
11.3 ± 0.80
<MDL
<MDL
1.75 ± 0.12
<MDL
<MDL
BaP
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
DbA
In(1,2,3,-cd)P
BghiP
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
<MDL
MDL: the method detection limit.

866
H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
PAH at high temperature. From Table 2, it can also be
seen that the total-PAH in fly ash and flue gas were
mainly dominated by three- and four-ring PAH, the
concentrations of two-, five- and six-ring PAH were
lower than the others. In particular, no six-ring PAH
was detected in flue gas for all runs. Table 2 also shows
that the concentrations of total-PAH in flue gas and
the solid samples, such as raw MSW, fly ash, and bot-
tion. There was also no obvious effect on distribution
of PAH in fly ash when the AC concentration increased.
The reason may be that MSW incineration in a bench-
scale fluidized-bed incinerator was tested at a constant
temperature (about 850 °C) to investigate the influence
of AC concentration on the distribution of PAH. Dur-
ing these experiments, the operating parameters of
MSW incineration, such as air flow rate and MSW feed-
ing rate, were fixed. Therefore the total yields of PAH
varied in a small range for all runs. In order to study
the distribution of PAH during MSW incineration, the
weights of bottom ash and fly ash were weighed out
and the flow rate of flue gas was also measured in all
runs. The increase of total weight of fly ash captured
by bag house due to the injection of AC and the con-
stant concentration of PAH in flue gas before bag house
would reduce the concentration of PAH in fly ash, while
AC injection could effectively removal PAH from flue
gas and increase the amounts of PAH in fly ash. There-
fore, the concentration of PAH in fly ash depended
on two actions mentioned above. In generally, the con-
centrations of PAH in fly ash from MSW incineration
in this study increased slowly with a rise of AC
concentration.
ꢀ
3
tom ash, were about 75.20–188.00 lg N m and 2.49–
ꢀ
1
17.00 mg kg , respectively.
1
3.2. Effect of AC concentration on distributions of
PAH in fly ash and flue gas
The effect of AC concentration on distributions of
PAH in fly ash and flue gas is presented in Fig. 3. From
Fig. 3a, it can be concluded that there were mainly three-
to five-ring PAH in fly ash, and the amounts of two- and
six-ring PAH were tiny. The concentrations of PAH in
ꢀ
1
fly ash were the same amount of 105 mg kg for four
different AC concentrations. An increase of AC could
remove more PAH from flue gas and increase the
amounts of PAH in fly ash. But the increase of the con-
centration of PAH in fly ash was not obvious due to the
increase of the mass of fly ash with a rise of AC injec-
The correlation of the amounts of different rings
PAH and total-PAH and AC concentration in flue gas
are shown in Figs. 3b and 4. It can be observed that
the total PAH in flue gas was dominated by the low
and medium molecular weight PAHs, especially the
three-ring PAH. In addition, the six-ring PAH was not
been found in flue gas. The reason may be that the high
molecular weight PAH has high boiling point and low
vapor pressure, which usually exist in the form of solid
phase at low temperature and are easy to deposit or be
adsorbed on fly ash and AC through nucleation, con-
densation and adsorption (Liu et al., 2002; Mastral
Fig. 3. Effect of AC concentration on the distributions of
different rings PAH in fly ash and flue gas.
Fig. 4. Effect of AC concentration on the concentration of
total-PAH in flue gas.

H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
et al., 2002b). Therefore, there was few high molecular
867
weight PAH in flue gas. In other words, the medium-
and high-ring PAHs were more abundant in fly ash.
The action of in-duct AC injection lay in three aspects
before the PAH vapor formed into the particulates of
PAH. Firstly, it could enhance the non-homogeneous
adsorption reaction between PAH vapor and the AC
particulates. Secondly, it could make PAH vapor adsorb
onto the surface of AC through the action of nucleation,
condensation and adsorption. Finally, it could provide
enough large physical adsorption force to adsorb PAH
in flue gas. Thus many PAHs were removed effectively
from the flue gas with the increase of AC concentration.
The concentration of total-PAH in flue gas was in re-
verse proportion to the AC concentration (shown in
Fig. 4).
3.3. Effect of AC concentration on PAH removal
efficiency from flue gas
The performance of in-duct AC injection depends
primarily on the AC concentration in flue gas, AC prop-
erties, and flue gas temperature. In the absence of AC
injection, the amount of PAH captured depended on
the amount of carbon in fly ash, when the fly ash carbon
content was low which means lower adsorption specific
surface area of fly ash, or when PAH concentration in
flue gas was high, poor removal efficiencies were ob-
tained. When the fly ash carbon content was high which
means higher adsorption specific surface area of fly ash,
and the PAH concentration in flue gas was low, high re-
moval efficiencies were obtained. Injection of AC into
the flue gas could be used to increase solid-phase carbon
concentration. Increasing the AC concentration in flue
gas, there was generally sufficient adsorption specific
surface area to capture low or high levels of PAH. The
amount of excess carbon need for continuously high lev-
els of capture would depend on the variation of PAH
concentration in flue gas (Kilgroe, 1996).
Fig. 5. Effect of AC concentration on the removal efficiency of
PAH from flue gas.
The results show that the removal efficiency of total-
PAH was direct proportion to the concentration of
AC in flue gas. An increase of AC concentration not
only increased the adsorption surface area of AC, but
also enhanced the collision between PAH and AC, and
the probability of nucleation, condensation and adsorp-
tion for PAH vapor on the surface of AC. Therefore,
PAHs in flue gas, especially those PAHs with high car-
cinogenic characteristic and high molecular weight,
could be removed effectively from MSW incinerator by
using in-duct AC injection.
The effect of AC concentration on the removal effi-
ciencies of PAH in flue gas during MSW incineration
in a fluidized bed is shown in Fig. 5. Fig. 5a shows that
the removal efficiencies of two- and three-ring PAH were
lower than four- to six-ring PAH. It is obviously due to
the low-ring PAH existed in the gaseous phase was dif-
ficult to be removed by AC injection, while PAH with
medium and high molecular weight was mainly existed
in particulates and easy to be adsorbed by AC. At the
same time, through the mechanisms of nucleation, con-
densation and adsorption, the medium and high molec-
ular weight PAH tended to the solid phase. In Fig. 5a, a
rise of AC concentration led to the removal efficiency of
three-ring PAH increase, but the change of the removal
efficiencies of five- and six-ring PAH was not obvious.
Fig. 5b shows the correlation of the removal effi-
ciency of total-PAH in flue gas and AC concentration.
3.4. Effect of AC concentration on PAH TEQ
concentration
The TEQ concentrations of PAH in raw MSW and
bottom ash are shown in Fig. 6a. It is mentioned that
the total TEQ concentrations of PAH were mainly dom-
inated by five-ring PAH in raw MSW and bottom ash.
The percents of the TEQ concentration of the five-ring
PAH in raw MSW and bottom ash were 91.2% and
70.1%, respectively. Therefore, the bottom ash from
MSW incineration must be disposed before the reuse
of them.
Fig. 6b shows the effect of AC concentration on the
TEQ concentration of PAH in fly ash. It can be found
that the five-ring PAH was the main contributor of the

868
H.-C. Zhou et al. / Chemosphere 59 (2005) 861–869
From Fig. 6a–c, it can be concluded that the total
TEQ concentrations of PAH in raw MSW, bottom
ꢀ
1
ash, fly ash, and flue gas were 1.24 mg TEQ kg
,
.25 mg TEQ kg , 6.89–9.67 mg TEQ kg , and 0.36–
ꢀ ꢀ1
1
0
1
ꢀ3
.50 lg TEQ N m , respectively. In addition, the high
toxicity PAH, such as four- to six-ring PAH, could be
removed effectively from MSW incinerator by using in-
duct AC injection. Therefore the TEQ concentrations
of four- to six-ring PAH in fly ash were very high, espe-
cially the five-ring PAH.
4
. Conclusions
Under our test conditions, MSW incineration in a
fluidized bed formed a large amount of PAHs. The four-
and five-ring PAHs dominated in raw MSW and bottom
ash while the total PAHs in fly ash and flue gas were
dominated by three- to five- ring PAH and three- and
four-ring PAH, respectively. There was no six-ring
PAH in flue gas for all runs. With increasing the concen-
tration of AC, the concentration of PAH in flue gas de-
creased apparently, while the concentration of PAH in
fly ash increased. This indicated that the in-duct AC
injection could effectively reduce the concentration of
PAH in flue gas during MSW incineration. The total
TEQ concentrations of PAH in raw MSW, bottom
ꢀ
1
ash, fly ash, and flue gas were 1.24 mg TEQ kg
,
.25 mg TEQ kg , 6.89–9.67 mg TEQ kg , and 0.36–
ꢀ ꢀ1
1
0
1
ꢀ3
.50 lg TEQ N m in this experiment, respectively.
Fig. 6. The TEQ distributions of PAH in raw MSW, fly ash,
bottom ash and flue gas.
Acknowledgments
This study was supported by the Doctoral Founda-
tion of Ministry of Education of China (20030286005)
and Shanghai Tongji Gao TingYao Environmental Sci-
ence and Technology Development Foundation.
total TEQ concentration in fly ash. This result was dif-
ferent from Fig. 3 due to the different TEF of PAH.
The maximum TEF of PAH was nearly higher 1000
times than the minimum TEF. Though some PAHs,
such as BaP, had a lower concentration, their TEQ con-
centrations were higher. The higher concentration of
PAH in the samples did not mention the higher TEQ
concentration of PAH. Hence, when the PAHs emission
from MSW incineration or the others emission sources
were assessed, both the concentration of PAH and the
total TEQ concentration of PAH must be done.
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