Dioxin emissions after installation of a polishing wet ... - BVSDE

Chemosphere 61 (2005) 405–412
www.elsevier.com/locate/chemosphere
Dioxin emissions after installation of a polishing wet
scrubber in a hazardous waste incineration facility
Carl-Johan Löthgren * , Bert van Bavel
Department of Natural Sciences, Man-Technology-Environment Research Centre, Örebro University, SE-701 82 Örebro, Sweden
Received 22 December 2003; received in revised form 10 January 2005; accepted 15 February 2005
Available online 13 April 2005
Abstract
Dioxin levels measured after wet scrubbing systems have been found to be higher than levels measured before the
scrubber. It is believed that there is an adsorption of PCDD/Fs on plastic materials in the scrubber. The PCDD/F levels
after a polishing wet scrubber were followed continuously for 18 months using long-time sampling equipment at a hazardous
waste incineration facility in Sweden. Each sampling period lasted two weeks. It was found that the levels during
and shortly after start-up periods were elevated. The decline was very slowly, which supports a memory effect in the
scrubber. Further, a multivariate model showed that the relation between different homologues changed over time,
which is in agreement with a desorption model, taking into account the vapour pressures for different congeners.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: PCDD/PCDF; Memory effect; Flue gas cleaning; MVDA; Incineration
1. Introduction
Dioxin formation from incineration is known since
1977 when dibenzo-dioxins and dibenzo-furans were
found in fly ashes and flue gases (Olie et al., 1977). Their
toxic effects are well known and dioxins have been in
focus in the environmental discussions for almost 20
years (Van den Berg et al., 1998). Throughout these
years efforts have been made to minimize the formation
and emission of dioxins from incineration facilities, both
by means of primary measures, i.e. combustion control
and by secondary measures such as the supply of additives
or catalysts to the flue gas treatment system. One
* Corresponding author. Tel.: +46 1930 5100; fax: +46 1957
7027.
E-mail address: carl-johan.lothgren@sakab.se (C.-J. Löthgren).
of the most used methods is the injection of activated
carbon into the flue gas channel just before a bag house
filter, where the carbon together with the fly ash form an
adsorption layer on the bag on which dioxins are adsorbed.
Emissions after such an installation are known
to be well below the EU emission limit of 0.1 ng/m 3
(Chang and Lin, 2001).
According to the EU directive 94/67/EG and EU
directive 2000/76/EC emission measurements of
PCDD/Fs only have to take place once or twice yearly
and such measurements are made under normal, i.e.
good operation conditions. Typical CO levels are well
below the stipulated 50 mg/m 3 normal dry gas. The
emission levels under other operating conditions have
been poorly studied until recently, when Belgian MSW
incinerators started continuous flue gas sampling for dioxin
analyses. Blumenstock et al. (2000) found an increase
in PCDD/F levels after a period with bad
operating conditions in a pilot scale incinerator. This
0045-6535/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2005.02.015

406 C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412
was later confirmed by several other authors (Gullett
et al., 2000; Zimmermann et al., 2001; Gass et al., 2002).
Gass et al. (2002) investigated the emissions from a full
scale incinerator and obtained the same results as earlier
were shown in pilot scale.
Wet scrubbing, i.e. the physical or chemical absorption
of gases in a liquid, has been used for a long time
for the removal of acid components in flue gases from
incineration facilities because of its good removal efficiency
(Onnen, 1972; Korell et al., 2003). High dioxin
emissions have, however, been found after wet scrubbers
when they have been placed as the final step in a flue gas
cleaning system. It has further been shown that this is
caused by the so called memory effect, where dioxins
are adsorbed on plastic details such as scrubber fillings
when the formation and emission from the incinerator
is high. The adsorbed dioxins are then desorbed slowly
when the plant is running under more stable conditions.
A comparative study using a pilot scale scrubber made of
glass showed no such increased emission levels (Hunsinger
et al., 1998). This memory effect can be distinguished
from high emissions caused by bad combustion
through its different congener pattern (Kreisz et al.,
1996; Gass and Neugebauer, 1999; Adams et al., 2001;
Giugliano et al., 2002).
To comply with the hazardous waste incineration
directive (EU directive 94/67/EG), which came in force
on the first of July 2000 in Sweden, a hazardous waste
treatment facility in Kumla, Sweden was equipped with
an enhanced flue gas cleaning. A wet scrubber was installed
after the existing semi-dry system, which consisted
of a spray dryer and a fabric filter with activated
carbon injection. Already five weeks after the new scrubber
was taken into operation, elevated PCDD/F emissions
were observed. In order to learn more about the
dynamic behaviour of the scrubber as to dioxin emissions
a continuos sampling device was installed in July
2001. The results from these measurements are presented
in this article.
2. Material and methods
The hazardous waste treatment facility studied
mainly consists of an incineration line with a rotary kiln,
secondary combustion chamber, boiler and a flue gas
cleaning system. The flue gas cleaning consists of a
semi-dry absorber, a fabric filter and the new wet scrubber.
In the absorber lime milk is injected to neutralize
the main part of HCl and SO 2 present in the flue gas. Between
the absorber and the fabric filter activated carbon
is injected for dioxin removal. The incineration temperature
in the rotary kiln is above 1100 °C. Outlet temperature
from the boiler is 280 °C. In the semi-dry flue gas
cleaning system the temperature is lowered to 160 °C
and in the scrubber the temperature is 70 °C.
The scrubber consists of a quench and a 28 m high
scrubbing tower, 5.5 m in diameter, filled with filling
material of polypropylene (Rauschert hiflow rings type
50–6). The scrubber and quench shell are made of
glass fibre reinforced plastic (GRP) Derakane 470.
After the scrubber the flue gas fan is situated and the
gases leave the plant through a 60 m high chimney,
which interior surface also is made of GRP. A schematic
sketch of the plant and the sampling points are shown in
Fig. 1.
Fig. 1. Schematic sketch of the plant and indication of sampling points for dioxins. The layout of the Amesa sampling system is shown
in the bubble.

C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412 407
The purpose of the wet scrubber is to polish the emission
levels of HCl and SO 2 to comply with the 1/2-hour
averages prescribed by the Swedish implementation of
the European Hazardous Waste incineration directive.
This is achieved by introducing H 2 O 2 to the scrubber
liquid, the so called MercOx-process. The H 2 O 2 content
in the scrubber liquid also increases the removal efficiency
for mercury. The MercOx process has been described
in detail by Korell et al. (2003).
Five weeks after the first start-up of the plant with
the new scrubber, dioxin levels were measured before
and after the scrubber. High concentrations were found
after the scrubber even though the concentrations before
the scrubber were low. Further measurements during the
autumn 2000 confirmed these results. In order to learn
more about the dynamic behaviour of the scrubber as
to dioxin emissions a continuos sampling device was installed
in July 2001. Since then samples have been taken
continuously whenever the plant has been in operation.
The commercial sampling equipment used has been described
by Funcke and Linnemann (1992) and Mayer
et al. (2000) and consists of a titanium probe, a XAD-
2-cartridge and a control cabinet. (Fig. 1). Flue gases
are taken out isokinetically, pass the cartridge and are
transferred to the control cabinet where flue gas volume
and water content is measured.
The sampling period for each analysis has varied between
one to two weeks. Sample preparation and analyses
have been made by Eurofins GfA-laboratories in
Germany according to EN1948. Eurofins GfA is accredited
according DIN EN ISO/IEC 17025:2000 and is
participating on a regular basis in international intercalibration
studies.
3. Multivariate data treatment
Multivariate data analysis (MVDA) has been used
successfully in a number of investigations where complex
data sets are to be evaluated, also in the field of dioxin
research (Pitea et al., 1994; Buekens et al., 2000;
Wang et al., 2003). Multivariate data analysis (MVDA)
consists of several methods to extract information from
large data matrices. In MVDA the samples (objects k),
in our case the weekly dioxin measurements, are seen
as points in a multidimensional space with as many
dimensions as variables (i) measured on the samples.
In principal component analysis (PCA) the points in
the multidimensional space are projected down onto a
line, a plane or a hyperplane to give the best low-dimensional
representation of the data. The data matrix (X) is
now approximated by a systematic part (the loading and
the score vectors) and a random part (the residuals)
which consists of errors in the measurements and imperfections
in the approximation. The dimension of PCA is
determined by cross validation.
The visualisation of the PCA is normally done in diagram
form. The variables are plotted in a diagram with
the loading vectors as the axes. The greater the absolute
value (positive or negative) of a variable is, the greater
impact it has on its loading vector. Variables correlated
with a specific vector can thus be identified. The objects
are plotted in a diagram with the score vectors as the
axes. Objects that have similar patterns will be located
near each other and objects with different patterns will
be more apart.
Before MVDA was performed on the data set, all
data were centered and scaled to unit variance. The calculations
were performed on a PC with the software program
Simca 7.01 (Umetri AB, Umeå, Sweden). PCA is
described in detail elsewhere (Wold et al., 1983; Wold
et al., 1984).
4. Result and discussion
The sum of the different homologues for all measurements
performed in the flue gas since 1998 are shown as
series of time in Fig. 2. The first part shows the measurements
made before the wet scrubber and the second part
shows the measurements made after the wet scrubber,
both short-time and long-time samplings. Each sampling
is named according to the time when it was performed
with the year and the consecutive week number of that
year in the form yyww. When two measurements have
been accomplished the same week, the individual measurements
have been denoted a and b. Two maintenance
stops in April and October 2002 are also indicated in the
figure. The TEQ values for the measurements before the
wet scrubber varied between 0.003 ng/m 3 (W9839a) and
0.033 ng/m 3 (W9935). A significant higher level of TeC-
DDs (0.19 and 0.5 ng/m 3 ) explains much of the rise in
1999. No further investigations have been made in this
study as to the cause of the results before the wet scrubber.
The values shall be seen in comparison to the results
from the measurements performed after the wet
scrubber.
In the year 2000 when the wet scrubber was installed,
sampling was performed simultaneously before and after
the wet scrubber. The results before the wet scrubber as
to TEQ values were 0.010, 0.006 and 0.005 ng/m 3 , which
are in the same range as earlier results, i.e. well below
0.1 ng/m 3 . The TEQ-values after the wet scrubber in
the sampling campaigns in year 2000 were much higher,
0.18, 0.10, 0.36 and 0.45 ng/m 3 . During the first sampling
campaign in May (W0021), the difference between
the TEQ value before and after the scrubber is about
one order of magnitude, 0.01 ng/m 3 before the scrubber
compared to 0.18 and 0.10 ng/m 3 after the scrubber. In
the campaign in October (W0040) this difference has increased
to almost two orders of magnitude, 0.006 and
0.005 ng/m 3 before the scrubber compared to 0.36 and

408 C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412
Measurements
100
before scrubber
Measurements
after scrubber
Maintenance
stop spring
2002
Maintenance stop
autumn 2002
10
ng/m 3
1
0.1
0.01
0.001
9839a
9839b
9934
9935
0021
0040a
0040b
0021a
0021b
0040a
0040b
0127
0131
0136
0137
0138
0139
0140
0141
0146
0147
0148
0149
0150
0151
0152
0201
0202
0203
0204
0205
0206
0207
0209
0211
0213
0215
0218
0220
0222
0224
0226
0228
0230
0232
0234
0235
0236
0237
0238
0240
0242
0244
0247
0249
0251
0252
Sum TeCDD
Sum PnCDD
Sum HxCDD
Sum HpCDD
OCDD
Sum TeCDF
Sum PnCDF
Sum HxCDF
Sum HpCDF
OCDF
TEQ
Fig. 2. Results of dioxin measurements 1998–2002 for all homologues and the TEQ value. To the left of the dotted line the results
before the scrubber installation are shown. Maintenance stops are indicated with solid lines. Each sampling period is named with year
and week number in the form yyww.
0.45 ng/m 3 after the scrubber. It is clear that the differences
in TEQ values before and after the scrubber above
all can be explained by the drastically higher levels of
low-chlorinated homologues after the scrubber. For
example TeCDD increased from the range 0.02 to
0.14 ng/m 3 before the scrubber to 0.1–0.7 ng/m 3 after
the scrubber, TeCDF increased from the range 0.01 to
0.07 ng/m 3 before the scrubber to 3.5–5.7 ng/m 3 after
the scrubber and PnCDF increased from the range
0.02 to 0.07 ng/m 3 before the scrubber to 1.54–3.11
ng/m 3 after the scrubber. OCDD, on the other hand,
was in the range 0.03–0.15 ng/m 3 before the scrubber
and 0.01–0.04 ng/m 3 after the scrubber. The same
applies for OCDF, which was in the range 0.02–0.19
ng/m 3 before the scrubber and 0.01–0.05 ng/m 3 after
the scrubber.
This change in composition is illustrated in the fingerprint
plots in Figs. 3 and 4. Especially the fraction
levels of TeCDFs have risen. Before the scrubber the
average fraction of TeCDF is 8% and after the scrubber
it is 49%. The somewhat deviating pattern for the measurements
in 1999 can also be seen. At this time the
TeCDD fractions are the most deviating homologue
with values of 44% and 52% compared to 5–14% for
other measurement periods before the scrubber.
The fingerprint plot in Fig. 4 shows clearly decreasing
values with the degree of chlorination. For the PCDFs
the average level of the TeCDF is 49% and that is
approximately double the amount of the PeCDFs,
which is 23%, i.e. more than the double of HxCDFs
(9%). HpCDFs have an average fraction of 2% and
OCDFs have an average fraction of 0.2%. For PCDDs
the trend is similar but to a lesser extent (TeCDD 6%,
PeCDD 6%, HxCDD 4%, PnCDD 1% and OCDD
0.2%).
In August 2000, as soon as the results from the measuring
campaign in May 2000 were available, an electrostatic
precipitator (ESP) used as by-pass for the fabric
filter during start-up and shut down was closed since it
was suspected that PCDD/Fs were loaded into the
scrubber during its operation periods and slowly released
afterwards, the ‘‘so called’’ memory effect described
in the literature by Kreisz et al. (1997); Wevers
and De Fré (1998); Giugliano et al. (2000); Adams

C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412 409
Fig. 3. Homologue fingerprint for the measurements made before the wet scrubber. This includes both measurements made before and
after the scrubber installation. In the years 1998–2000.
Fig. 4. Homologue fingerprint for the measurements made after the wet scrubber in the period May 2000 to July 2001. High ratio of
low chlorinated congeners can be observed due to memory effects in the wet scrubber.

410 C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412
et al. (2001). When the ESP was in operation no carbon
could be injected so it seemed logical that dioxins were
transported to the wet scrubber during these periods.
As can be seen in Fig. 2 the dioxin levels were elevated
also in the measuring campaign in October 2000 (0.36
and 0.45 ng/m 3 TEQ in W0040). When the continuous
sampling equipment was installed in July 2001 the
TEQ-value after the scrubber was 0.52 ng/m 3 , which is
in the same range as in the October measurement. In
Fig. 2 it can be seen that all the homologues except
OCDF and OCDD fell from this high level to a level
comparable to the levels measured before the scrubber
(0.003–0.03 ng/m 3 ). This decline took almost 15 months
from the shut down of the ESP. In W0147, which is in
the beginning of November 2001 the first result below
0.1 ng/m 3 TEQ after the scrubber was obtained. The result
was 0.06 ng/m 3 TEQ and two weeks later the level
had decreased further to 0.04 ng/m 3 .
During the period of continuos sampling presented
here, two dramatically risings of TEQ levels were observed,
both in the period just after a maintenance stop
of the plant. At the first occasion (W0215) the TEQ
value increased from 0.02 ng/m 3 to 0.25 ng/m 3 and at the
second occasion (W0240) the TEQ-value increased from
0.03 to 0.15 ng/m 3 . It is believed that during the start-up
periods high levels of dioxins are generated which normally
is not recognized since sampling normally takes
place only during stable operating conditions.
The high concentrations just after start-up and the
somewhat exponential decline afterwards indicate that
dioxins are adsorbed on the olefin plastics in the scrubber
and released slowly. Otherwise a sharp peak would
be expected just after start-up. It is also typical that
the concentrations of OCDD/F do not vary over time
since it is known that the absorption for these homologues
are much stronger than for the others, (Kreisz
et al., 1996). The different absorption pattern for different
congeners can be explained by their different vapour
pressures. The strong dependence on vapour pressures
with the degree of chlorination has been described by
Rordorf (1989).
The change in composition can be seen even better
when the data is studied using multivariate statistics.
The concentrations of the 17 congenes that are used in
the calculation of the TEQ value and the results in
Fig. 2 were evaluated using PCA. At first a general
PCA analysis of the data was made. This model gave little
information as to the memory effect, since most of the
variation in the data set was used to explain the changes
in concentrations between the different sampling periods.
If, however, the individual results for every congener
was divided by the total amount of all dioxins and
furans in that sample, the influence from variations in
concentration could be eliminated.
A new PCA model was calculated using the new variables
and it was found that principal components 1 and
3 of this model best described the variations in congener
pattern that had been observed. The score and loading
plots for these vectors are shown in Figs. 5 and 6
respectively.
7
6
5
4
3
4
3
2
t [3]
1
0
-1
-2
-3
2
1
10
8
50
45 44
49
4743
46 48 40
3536 29 32 33 4239
38
31
20 26 34
24 25 30
41 37
55
56
53
57 22
9
1119
52
21 181716
5
23 27 51 1314
54
12 15
7
28
-4
-5
6
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
t [1]
Fig. 5. Score plot vector 1 vs vector 3. Observations 1, 2, 3, 4, 6, 8, 10 are measurements before the wet scrubber. Maintenance stops
are between obs. 36–37 and obs. 50–51. The ellipse indicates the Hotelling T2 95% confidence interval.

C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412 411
0.40
totdioxin
TEQ
TCDD
0.30
0.20
2378TCDD
HxCDD
PnCDD
0.20
p [3]
0.00
-0.10
-0.20
HpCDD
1234678hpCDD
1234789hpCDF
HpCDF 123789hxCDF
OCDD OCDF
1234678hpCDF
123789hxCDD
123478hxCDD
123678hxCDD123478hxCDF
23478pCDF
HxCDF
123678hxCDF
12378pCDD
2378TCDF
234678hxCDF
12378pCDF
PnCDF
TCDF
-0.30
TotFuran
-0.30
-0.20 -0.10
0.00
p [1]
0.10
0.20
Fig. 6. Loading plot vector 1 vs vector 3. Low-chlorinated congeners are situated to the right and PCDDs are situated to the top,
PCDFs to the bottom of the diagram.
To the left in Fig. 5, with low values in score vector 1,
all the measurements before the scrubber are located
(obs. nos 1,2,3,4,6,8,10) and the measurements after
the scrubber are located more to the right. Two maintenance
stops are located between obs. nos 36 and 37 and
between nos 50 and 51. A rapid shift in score vector 1
can be observed during the two maintenance stops. Further
it is visible how the observations at the beginning of
the continuos sampling period (obs. nos 12–16) are all
located close together. During a transition period of
four weeks the observations have moved to a new point
in the diagram, indicating a new composition in the
emission pattern. The emission pattern is then relatively
stable until the maintenance stop between observations
36 and 37 occurs.
Observation 12, which is the first measurement with
the continuos sampling device, and observation 37 almost
have the same score in vector 1 but differ in vector
3. From observation 37, which is the first observation
after one of the maintenance stops, the process again
moves from high values in vector 1 to lower values over
a couple of weeks. The same shift can be seen even better
between observations 50 and 51 which is the second
maintenance stop during the period covered in this study.
The loading plot (Fig. 6) shows a tendency that the
degree of chlorination is described by loading vector 1
and the ratio of PCDD to PCDF is described by loading
vector 3. Low-chlorinated congeners have higher loadings
in vector 1 and PCDFs are situated toward lower
values in loading vector 3. Implementing this in the
score diagram it seems that just after a maintenance stop
there is a big loss of dioxins and furans with four chlorine
atoms. The difference in score vector 3 for the observations
12 and 37 would then indicate that the ratio
PCDD/PCDF is higher after the maintenance stop than
it was when the continuos samplings were started. The
PCA model also shows that there is a shift between
PCDDs and PCDFs over time since the loadings for
total-PCDD and total-PCDF are situated on one of
the diagonals in Fig. 6.
5. Conclusions
• The high PCDD/F emissions found after the installation
of the wet scrubber was caused by memory
effects due to high formation in the incinerator during
start up of the plant.
• The homologue pattern after the wet scrubber differs
significantly from the pattern before the scrubber. A
relation between the degree of chlorination, the
vapour pressure and the emission level for a specific
congener was found with the use of multivariate
statistics.
• Start-up periods, e.g. after maintenance stops, are the
main cause of elevated dioxin emissions from an
incinerator. This can only be shown by continuos
monitoring where all modes of operation are covered.

412 C.-J. Löthgren, B. van Bavel / Chemosphere 61 (2005) 405–412
Acknowledgments
The authors would like to thank the staff at Sydkraft
SAKAB for their assistance and acknowledge the analyses
work of Eurofins, Münster Roxel.
This study was financially supported by the Swedish
Knowledge foundation and SAKAB Kumla
Miljöstiftelse.
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