feature article
Adiox™ is an innovative material for removing toxic dioxins from combustion
gases, making it an ideal absorbing material for tower packings and
demisters in wet scrubbers. Adiox can also be used as a police filter to
reduce the memory effect, as well as the primary dioxin removal
technology. Sven Andersson, Siegfried Kreisz and Hans Hunsinger discuss
this novel technology for the cleaning of flue gases.
Innovative Material Technology
Removes Dioxins from Flue Gases
ioxins, or polychlorinated dibenzo-p-dioxins and
combined with an oxidation catalyst are also known to be an
polychlorinated dibenzo furans (PCDD/Fs), are a group
effective method to destroy dioxins. This method, however,
D
of persistent and extremely toxic chlorinated organic
requires a costly gas re-heating if used after wet scrubbers
compounds. Major emission sources are known to be processes
(gas-liquid contactors for removing acid components).
like waste incineration, metal production, bio-fuel incineration
Other methods for dioxin removal include catalytic bag
and uncontrolled combustion. Under stable combustion
filters, as well as the injection of activated carbon or tensides in
conditions, dioxins are almost completely destroyed during
wet scrubbers.
incineration, but are re-formed during the cooling of the flue gas
[1] and during dust separation at temperatures above 200 °C by
Memory effect
de-novo synthesis [2]. A review of the formation mechanisms
involved is given by Tuppurainen et al. [3].
Plastics, such as polypropylene (PP), are widely used as
Dioxin concentrations are commonly reported as toxic
construction material in wet scrubbers because of their excellent
equivalents (TEQ), which is the sum of the congener
corrosion resistance and low price. Significant amounts of
concentrations multiplied by their specific TEQ-factors. The
dioxins can initially be transferred from the flue gas to the
extreme toxicity of 2,3,7,8-Tetra-CDD (also known as Seveso-
plastics until an equilibrium loading is reached. However, this
dioxin) is the reference and has a TEQ-factor of one. Dioxins
equilibrium can be disturbed by changes in temperature or
and furans containing higher numbers of chlorine atoms
dioxin concentration. An increase in the temperature or decrease
(including the 2-, 3-, 7- and 8-positions) have lower
in gas concentration will lead to dioxin desorption to the gas
TEQ-factors.
phase. This absorption/desorption behaviour is known as the
‘Memory Effect’ (Figure 1a).
The equilibrium concentration in the plastic is very
State-of-the-art dioxin removal
temperature dependent. An increase in temperature from 65 °C
A number of technologies are available for removing or
to 90 °C increases the desorption rate of dioxins from PP by a
destroying dioxins from gases, but the investment and/or running
factor of ten [4]. Both the vapour pressure [5] and the diffusivity
costs of these technologies are usually very high. Waste
[6] increase with a decreasing degree of chlorination. The
incineration plants commonly use bag house filters (fabric
desorption rates are therefore higher for the lower chlorinated
filters), equipped with activated carbon injection, or fixed bed
dioxins and furans. The lower chlorinated dioxins contribute the
carbon filters in order to fulfil the emission limits for dioxins.
most to the TEQ-value. Subsequently, the Memory Effect can
SCR-catalysts (selective catalytic reduction) for NO x -reduction
contribute significantly to the emission value.
(a)
(b)
Figure 1: Schematic view of (a) absorption/desorption in polypropylene and (b)
absorption/adsorption in Adiox (polypropylene containing carbon particles).
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feature article
Gas outlet
Gas inlet
Adiox tower packing
Quench HCI-scrubber
Test rod assembly
Figure 2: Adiox tower packings in the wet HCl-scrubber of the municipal solid waste
incineration plant in Thisted, Denmark. A test rod assembly is placed downstream of the
quench, below the tower packings.
A typical situation where these phenomena can occur is if an
of a grate-fired furnace, boiler, electrostatic precipitator (ESP),
existing wet flue gas cleaning system is retrofitted with an
an acid scrubber and a neutral scrubber [8]. The flue gas flow is
upstream dioxin removal device. In this case the construction
40 000 m 3 /h (normal, dry gas).
materials downstream of the device may contain large amounts
The wet scrubbers, equipped with PP tower packings, were
of absorbed dioxins, which can be desorbed over a long period
installed in 1991. Normally, the removal efficiency of dioxins in
of time.
wet scrubbers operated over such a long time is not significant
(equilibrium loading) or even negative (Memory Effect) [4]. A
first measurement before replacing the tower packing confirmed
Adiox: carbon filled plastics
these suspicions.
In order to avoid the dioxin release from the polymers, a new
construction material was developed, in which carbon particles
(i) Removal efficiency
are dispersed in a polymer (such as PP). In this new material,
called Adiox (patent pending), the dioxins are first absorbed in
In 2001 the PP tower packings were replaced by Adiox tower
the PP. Then they diffuse to the surface of the carbon particles,
packings (Figure 2). Two dioxin measurements were taken
where they are irreversibly adsorbed (Figure 1b). The PP acts as a
before and two measurements after the scrubbers were carried
selective barrier, which protects the carbon from other
out according to EN1948 during start-up and then after one,
contaminants such as mercury (Hg).
three, six, nine and 12 months of operation. The start-up
The absorption of dioxins in pure PP and in Adiox,
measurement was characterized by a low flue gas flow and low
respectively, was tested in laboratory experiments [7]. Gas
temperatures, resulting in a high removal efficiency. The clean
containing dioxins was passed through a fixed bed of pure PP
gas concentrations was <0.1 ng TEQ/m 3 (n, dg) in spite of
granules at 80 °C. A break-through of the lower chlorinated
elevated raw gas concentration typical for start-up conditions.
dioxins was detected after one month. Upon heating the granules
An almost constant high removal efficiency of 70% was
to 120 °C, a substantial part of the dioxins were desorbed. The
observed at normal operation over the 12 months (Figure 3).
experiment was repeated with Adiox granules. No break-through
No indication of saturation or decreasing removal efficiency
was detected and desorption at 120 °C was negligible.
Several types of components, such as tower packings and
demisters (droplet separators), can be produced from Adiox
material. Adiox tower packings can be applied in existing wet
scrubbers, with a minimum of effort, producing a simple means of
reducing dioxin emissions and avoiding the Memory Effect. The
dioxin removal capacity of Adiox tower packings and demisters is
favoured by the large specific surface area, selectivity for dioxins
and high absorption capacity. It is possible to incinerate the
material after usage: the dioxins are then destroyed.
Adiox has so far been installed at more than ten full-scale
waste incineration lines. The old PP-tower packings in the
existing scrubbers and/or droplet separators were replaced by
new ones made of Adiox material.
First full-scale installation
Figure 3: The removal efficiency of two wet
scrubbers in series equipped with Adiox tower
The first Adiox installation was made at the municipal solid
packings (0 months = start-up).
waste incineration plant in Thisted, Denmark, which consisted
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(a) Dioxin absorption
The concentration of tetra-chlorinated dibenzo furans (TCDFs)
in the test rods is plotted against time in Figure 4. It is obvious
from Figure 4 that Adiox absorbs TCDFs during the entire test
period, while an equilibrium concentration is reached for pure PP
after a few months.
(b) Mechanical properties
The tensile strength, yield strength, E-modulus and Charpy
impact strength were tested for Adiox and pure PP, respectively,
after zero, three, six and 12 months. All measured values varied
within ±10% and no trends indicating degradation could be
seen. Some single tower packings were compressed at a
constant speed between two metal surfaces and the force was
measured. No differences could be detected between new and
old Adiox tower packings in the resulting force-compression
Figure 4: The concentration of
diagram.
tetrachlorinated dibenzo furans (TCDFs) in
the test rods shown in Figure 1 after
different exposure times.
Applications
Adiox allows the design of multifunctional scrubbers, where
could be detected, in spite of the relative high raw gas
HCl, HF, SO 2 and oxidized Hg, as well as dioxins can be
concentrations (typically 6-10 ng TEQ/m 3 (n, dg)). The dioxin
removed simultaneously. Elemental Hg can be oxidized and
concentrations in the gas-phase were much higher compared to
captured in the scrubber using the MercOx process [9]. Extended
the particle phase, both before and after the scrubbers. The
energy recovery by condensation of the flue gas can be integrated
removal efficiencies of the different congeners were practically
into the scrubber as well.
constant during the 12 months. A decreasing removal efficiency
of the lower chlorinated dioxins, typical for pure PP, was not
(i) Wet scrubber
observed.
After the 12-month test period, the ESP was replaced by a
Adiox has been installed in the wet flue gas treatment
bag house filter with carbon injection. The dioxin
downstream of an ESP in order to reduce dioxin emissions (e.g.
concentration of the flue gas entering the wet scrubbers was
in Thisted and Kolding, Denmark).
reduced from 10 ng TEQ/m 3 (n, dg) to <0.1 ng TEQ/m 3 (n, dg),
The use of Adiox tower packing as a police filter in a
i.e. by more than two orders of magnitude. The highly dioxin
scrubber downstream of a primary dioxin removal system, such
loaded Adiox tower packings were, however, not replaced. In
as a bag house filter, will result in additional security to
the case of dioxin loaded PP tower packings, a significant
guarantee low emission values. In this instance, Adiox will
release of low chlorinated dioxins would have taken place in
increase the margins in cases of carbon dosage failure, filter
this situation. Despite the high dioxin loading of the tower
leakage or increased dioxin concentrations during start-up.
packing, the dioxin concentrations of the flue gas were reduced
Adiox has been installed in a scrubber downstream of a bag
from 0.073 ng TEQ/m 3 (n, dg) at the scrubber inlet to
house filter equipped with catalytic bags (hazardous waste
0.028 ng TEQ/m 3 (n, dg) at the outlet. During an additional
incineration in Salaise, France), as well as normal bags in
measurement, the operation of the bag house filter was
combination with carbon injection (e.g. Umeå, Sweden).
disturbed. Under these unfavourable conditions the dioxin
concentrations also fell from 0.25 ng TEQ/m 3 (n, dg) to 0.058
(ii) Primary dioxin removal system
ng TEQ/m 3 (n, dg) over the scrubbers. This demonstrates the
effectiveness of Adiox as a police filter.
The second Adiox installation was made in a two-stage scrubber
after an ESP at the Kolding MSW incineration plant in Denmark.
A pilot scrubber was installed in series with the full-scale
(ii) Material testing
scrubber. The aim of this flexible installation was to demonstrate
The main objective of the first full-scale installation was to
how economical and operational benefits can be gained by a
determine the lifetime of Adiox tower packings, taking into
complete integration of the PCDD/F removal into the wet
consideration the mechanical properties and PCDD/F absorption
scrubbing process downstream of an ESP.
capacity.
The results of the tests clearly demonstrate that the Adiox
A test rod holder (Figure 2) was installed in the acid scrubber
process, in combination with upstream particle removal, can
in order to study the properties of different Adiox material
meet the EU-directive exhaust gas limit requirements on
compositions. It is located in a manhole directly under the
dioxin at 0.1 ng TEQ/m 3 (n, dg). Such a simple air pollution
support grid of the tower packing. The test rods are exposed to
control system can consist of an ESP followed by a
the acid scrubbing liquid, as well as the dioxin concentration of
multifunctional scrubber (Figure 5). The required amount of
the raw gas.
Adiox material is typically larger than for a traditional
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feature article
scrubber, and is determined on the basis
of the dioxin concentration after the
electrostatic precipitator. The first full-
scale installation with this configuration
will go into operation in 2004.
(iii) Dry absorber
Fixed bed carbon filters are sometimes
used as a final dioxin removal stage. There
is a risk of fire in these filters, and
contaminated dust particles may escape
during operation or handling of the
carbon pellets. Using Adiox granules
instead of carbon pellets would overcome
these disadvantages. Earlier experiences
with a fixed bed adsorber showed high
removal efficiencies using PP granules [7,
10]. Based on these findings and taking
the high loading capacity of Adiox into
account, the new material could be an
interesting alternative to fixed bed carbon
Figure 5: Schematic view of a flue gas treatment with ESP for
filters.
dust removal, wet scrubbers for HCl, HF, SO 2 and Hg (oxidised)
removal and Adiox tower packings for dioxin removal. Flue gas
condensation for energy recovery can be integrated in the
Conclusions
system.
Adiox is well suited for selective absorption
of dioxins in wet gas scrubbers. It can be
6.
S Kreisz, H Hunsinger & H Seifert. 2000. PCDD/F Diffusion
integrated in new or existing wet scrubbers without the need for
Velocities in Polypropylene, Organohalogen Compounds ,
additional equipment. The Memory Effect caused by the
Vol. 45, p.435-437.
absorption/desorption equilibrium of dioxins in the tower
7.
S Kreisz, H Hunsinger & H Seifert. 2002. Carbon Doped
packing can be eliminated.
Polypropylene as PCDD/F Adsorber, Organohalogen Compounds ,
The system is passive which makes it robust and reliable. It is
Vol. 56, p.369-372.
effective even during start-up and in unstable operating
8.
S Andersson, S Kreisz & H Hunsinger. 2002. PCDD/F Removal from
conditions where other technologies may not work optimally.
Flue Gases in Wet Scrubbers - a Novel Technique, Organohalogen
The carbon particles are encapsulated in PP, which makes the
Compounds , Vol. 58, p.157-160.
material very easy to handle. After use, Adiox can be
9.
J Korell, H Seifert, H-R Paur, S Andersson & P Bolin. 2003. Flue Gas
incinerated, and thereby destroying the dioxins.
Cleaning with the MercOx Process, Chem. Eng. Technol. , Vol. 26,
p.737-740.
10.
S Kreisz, H Hunsinger & H Seifert. 2000. Polypropylene as
References
Regenerable Absorber for PCDD/F Emission Control, Chemosphere ,
1. H Hunsinger, K Jay & J Vehlow. 2000. Formation and Destruction of
Vol. 40, p.1029-1031.
PCDD/F Inside a Grate Furnace, Organohalogen Compounds ,
Vol. 46, p.86-89.
Contact
2. H Vogg & L Stieglitz. 1986. Thermal behavior of PCDD/F in fly ash
from Municipal Waste Incinerators, Chemosphere , Vol. 15,
*Sven Andersson,
Götaverken Miljö AB, Box 8876,
p.1373-1378.
SE-402 72 Göteborg,
3. K Tuppurainen, I Halonen, P Ruokojärvi, J Tarhanen & J
Sweden.
Tel: +46 31 501960;
Ruuskanen. 1998. Formation of PCDDs and PCDFs in Municipal
Fax:+46 31 229867;
Waste Incineration and Its Inhibition Mechanisms: A Review,
E-mail: info@gmab.se;
Chemosphere , Vol. 36, No. 7,
Website: www.gmab.se
p.1493-1511.
Siegfried Kreisz & Hans Hunsinger,
4. S Kreisz, H Hunsinger & H Vogg. 1996. Wet Scrubbers - a Potential
Forschungszentrum Karlsruhe GmbH,
ITC-TAB, Postfach 3640,
PCDD/F Source, Chemosphere , Vol. 32, No. 1,
DE-76021 Karlsruhe,
p.73-78.
Germany.
5. B Rordorf. 1989. Prediction of Vapor Pressures, Boiling Points and
Tel: +49 7247 822656;
Fax:+49 7247 824373;
Enthalpies of Fusion for Twenty-nine Halogenated Dibenzo-P-Dioxins
E-mail: info@oea.fzk.de;
and Twenty-five Dibenzofurans by a Vapor Pressure Correlation
Website: www.fzk.de
Method, Chemosphere , Vol. 18, No 1-6,
p.783-788.
*Corresponding author.
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