About dioxin removal and wet scrubber.

Feature

Filtration+Separation December 2 0 0 5

Dioxin removal:

Adiox for wet

scrubbers and

dry absorbers

diox is an innovative technology for removing toxic dioxins from

gases. Tower packings, droplet separators and fixed bed fillings

can be made of this dioxin absorbing material. Sven Andersson,

Siegfried Kreisz and Hans Hunsinger discuss the use of this

novel technology under wet and dry conditions.

Innttrroodduuccttiioonn I

Addiiooxx:: ccaarrbboonn ffiilllleedd ppllaassttiiccss A

incomplete flue gas burnout. The dioxins

are absorbed in the construction materials

There are a number of technologies available

The background for inventing Adiox resulted

of the flue gas cleaning system during the

for removing or destroying dioxins from

from an observation that plastics can absorb

start-up phase, but are desorbed during the

gases, such as baghouse filters and catalysts.

large amounts of dioxins from gases*; these

following period of normal operation. This

The investment and/or running costs of these

can later be desorbed.

desorption can lead to increased emissions

technologies are usually very high.

This absorption/desorption equilibrium is

over a very long time range.

Adiox (patent pending) is a new dioxin

known as the Memory Effect ( see figure 1a ).

Adiox was developed to avoid the dioxin

removal technology that has established itself

as an efficient and economic way to reduce

A situation where the Memory Effect plays

desorption described above*. The Adiox

dioxin emissions, and is marketed and sold by

an important role is during the start-up of

material consists of a polymer, such as

Götaverken Miljö AB as material deliveries,

an incineration unit, when large amounts of

polypropylene (PP) - containing carbon

package units or turn key flue gas treatment

dioxins are formed due to unstable

particles. The dioxins are first absorbed in

systems.

combustion conditions characterised by an

the polymer. Then they diffuse to the surface

Figure 1(a): Schematic view of absorption/desorption in plastic

Figure 1(b): Schematic view of absorption/adsorption in Adiox (plastic containing

carbon particles)

Feature

Filtration+Separation December 2 0 0 5

The use of Adiox tower packing as a

“police” filter in a scrubber - downstream of

a primary dioxin removal system such as a

baghouse filter - results in additional

security to guarantee low emission values.

In this case, Adiox increases the margins in

the case of, for example, carbon dosage

failure, filter leakage or increased dioxin

concentrations during start-up.

Adiox has been installed in scrubbers with

additional carbon injection ( at AVR Avira,

Netherlands ) as well as in a MercOx-

scrubber, downstream of a baghouse filter

with carbon injection ( at a hazardous

waste incineration facility at Sakab,

Sweden ).

At Måbjergværket ( see figure 2 on page 23 ),

wet Adiox scrubbers in combination with one

electrostatic precipitator (ESP) per line have

Figure 2: Adiox has been in operation as a primary dioxin removal system at Måbjergværket (Denmark)

acted as the main dioxin filter since the fall

since the fall of 2004. All measurements are far below the 0.1 ng TEQ/Nm3.

of 2004. The eleven dioxin measurements

performed so far show that the

concentrations in the stack are permanently

of the carbon particles, where they are

different modifications of Adiox to the high

far below the emission limit of 0.1 ng

irreversibly adsorbed ( see figure 1b ). The

dioxin concentration of 8 ng TEQ/m3 (n.,

TEQ/m3 (n., d.g.).

polymer acts as a selective barrier, which

dry gas). The high absorption capacity of

protects the carbon from adsorption by other

Adiox was thereby demonstrated.

Flue gas condensation for energy recovery is

contaminants such as Mercury (Hg.)

also integrated in the system. The required

Further research was done at a second

amount of Adiox material is typically larger

Several types of components, such as tower

installation in Kolding (Denmark) , where a

than for a traditional scrubber, and is

packings, demisters (droplet separators) and

pilot Adiox scrubber was operated to develop

fixed bed fillings can be produced from Adiox

and demonstrate the concept of using Adiox

determined on the basis of the dioxin

material. By applying Adiox tower packings in

as the main dioxin filter.

concentration after the electrostatic

existing wet scrubbers (gas-liquid contactor)

precipitator.

The impressive results of this pilot plant

the dioxin emissions are efficiently reduced

have lead to the first full scale installation

and the Memory Effect is almost completely

at Måbjergværket (Denmark) , using only

avoided.

What are Dioxins?

Adiox for dioxin reduction ( see below .)

The dioxin removal capacity of Adiox tower

Dioxins, or polychlorinated dibenzo-p-

Adiox is particularly well suited for removing

packings and demisters is favoured by the large

dioxins and -dibenzo furans

dioxins from gases including municipal solid

(PCDD/Fs), are a group of persistent

specific surface area, selectivity for dioxins and

waste incineration, hazardous waste

and extremely toxic chlorinated organic

high absorption capacity.

incineration, chemical and biomass

compounds. Major emission sources

The expected life time of the Adiox material is

industries; Adiox has been successfully

are known to be processes like waste

2-4 years, depending on the application. After

installed in all of these application fields.

incineration, metal production, bio-fuel

usage, the dioxins are destroyed by incinerating

incineration and uncontrolled

Another application area is the metal

the loaded material.

combustion. Under stationary effective

industry, where several potential installations

combustion conditions, dioxins are

have been identified and are currently being

355 iinnssttaallllaattiioonnss iinn 44 yyeeaarrss 3

almost completely destroyed during

discussed.

incineration, but are re-formed during

Adiox has been installed at more than 35 full

the cooling of the flue gas* and during

scale incineration lines within three years,

Addiiooxx iinn wweett ssccrruubbbbeerrss A

dust separation at temperatures above

since its market introduction in 2002. The

200 °C by de-novo synthesis*. A review

Adiox allows the design of multifunctional

gas flows of these plants range from 5,000 to

of the formation mechanisms involved

wet scrubbers, where HCl, HF, SO

2 and

is given by Tuppurainen et al*.

180,000 m3/h (normal, wet gas).

oxidised Hg as well as dioxins can be

removed simultaneously. Elemental Hg can

Dioxin concentrations are commonly

The first full-scale test installation was

be oxidised and captured in the scrubber

reported as toxic equivalents (TEQ),

performed at the municipal solid waste

which is the sum of the congener

incineration plant of Thisted (Denmark) in

using the MercOx process*, which can also

concentrations multiplied by their

2001, where the existing tower packings were

be combined with Adiox .

specific TEQ-factors. The extreme

replaced with the Adiox material.

Extended energy recovery using

toxicity of 2,3,7,8-Tetra-CDD (also

A constant removal efficiency of 70% was

condensation of the flue gas can be

known as Seveso-dioxin) is the

reference and has a TEQ-factor of one.

maintained for one year, after the limited

integrated into the scrubber as well.

Dioxins and furans with larger numbers

amount of Adiox tower packing had been

Adiox is easy to install in existing wet

of chlorine atoms (including the 2-, 3-,

installed in the existing scrubbers*.

scrubbers. The circulation of the scrubber

7- and 8-positions) have lower TEQ-

A material optimisation program was carried

liquid keeps the material clean from dust

factors.

out in parallel at the plant, by exposing

deposits.

Feature

Filtration+Separation December 2 0 0 5

Using Adiox material instead

of carbon pellets would not

have these disadvantages.

The design of the absorber

can be kept simple, since no

material dosing systems are

required. Granular beds

have porosities around 30%.

If the gas contains particles,

parts of the bed may be

clogged, leading to

channelling and increased

pressure drop. Tower

packings, originally designed

for the use in wet scrubbers,

can be used instead. The

porosity is typically 95%,

which reduces the risk for

clogging. Intermittent

rinsing may be used to clean

the surface during operation.

A simple, cost-effective

pollution control system

can be obtained by

Figure 3: A compact state-of-the-art air pollution control system consisting of ESP, wet scrubber and dry Adiox absorber.

combining an ESP, a

multi-functional wet Adiox

scrubber and a dry Adiox

Addiiooxx iinn ddrryy aabbssoorrbbeerrss

efficiency per installed amount is higher,

absorber ( see figure 3 above ).

since the water film in a wet scrubbing

Using Adiox in a dry absorber instead

A dry pilot absorber, using Adiox tower

process poses a mass transfer limitation for

would have the effect of making the

packings, was installed at line 1 of the Renova

the dioxins. Less material is thereby

installation more compact. The initial

municipal waste incinerator in Göteborg

required for the same removal efficiency.

laboratory tests with Adiox were performed

(Sweden) . The flue gas treatment consists of

Fixed bed carbon filters are sometimes used

with dry gas. The full-scale installations

an ESP, two wet scrubbers, reheater and a

as a final dioxin removal stage.

made so far, however, have been carried out

baghouse filter as seen in Figure 4 .

in wet scrubbers.

There is a risk of fire in these filters, and

The second scrubber is used for enhanced

If Adiox is employed in a dry absorber

contaminated dust particles may escape during

energy recovery with flue gas condensation

instead of a wet scrubber, the removal

operation or on handling of carbon pellets.

by cooling the gas from 60 to 40°C using

heat pumps during the cold

season. The gas is reheated

to typically 60-80°C. The

pilot absorber operates with

a fraction of the total gas

flow (approximately 3000

m3/h) extracted after the

reheater. Today, SO

2 and

dioxins are removed in the

baghouse filter.

The pilot experiments

demonstrate the possibility

of removing the dioxins in

a dry Adiox absorber instead

of a baghouse filter. In such

a case, SO

2 could be

removed in the wet

scrubbers.

The inlet concentrations

ranged from 0.7 to 2.0 ng I-

TEQ/m3 (n, d.g., 11% O2),

and the clean gas

concentrations ranged from

0.002 to 0.02 ng I-TEQ/m3

Figure 4: Pilot Adiox absorber at the Renova municipal waste incineration plant in Göteborg, Sweden. The dry Adiox absorber is

located downstream of an ESP, wet scrubbers and re-heater. The removal efficiency was higher than 97.5% in all measurements

(n, d.g., 11% O

2). No

with this configuration.

trend of decreasing removal

Feature

Filtration+Separation December 2 0 0 5

efficiency with time could be seen. All

Coonncclluussiioonn

*Contact author or the editor for details of

measured particle associated dioxins were

references

Adiox is very well suited for selective

<<0.1 ng TEQ/Nm3 in this plant.

absorption of dioxins and has a high loading

capacity.

Coonnttaacctt

The highest temperature during the tests

Sven Andersson (corresponding author)

was 90 °C Initial tests have been made with

It can be integrated in new or existing wet

Götaverken Miljö AB

glass fibre filled Adiox in order to guarantee

scrubbers without the need for additional

Box 8876, SE-402 72 Göteborg

equipment.

dimensional stability of the packings at

Sweden

Tel: +46 31 501960

even higher temperatures.

Using the material in a dry absorber can

Fax: +46 31 229867

decrease equipment sizes due to the higher

One important consideration for the pilot test

E-mail: sven.andersson@gmab.se

efficiency per volume.

Website: www.gmab.se

was to assess the amount of fly ash collected on

It is effective even during start-up and in

the Adiox surface during operation. No rinsing

stationary operating conditions, where other

Siegfried Kreisz & Hans Hunsinger

of the tower packings was therefore made

Forschungszentrum Karlsruhe GmbH

technologies may not work optimally. Other

during the test.

advantages are:

ITC-TAB, PO Box 3640

DE-76021 Karlsruhe

After 9 months, the Adiox tower packings

• Ease of installation;

Germany

were covered by a thin, porous layer of

Tel: +49 7247 822656

• A reduction (or even avoidance) of the

Fax: +49 7247 824373

particles, which could easily be removed by

Memory Effect

E-mail: info@oea.fzk.de

rinsing with water. No change in pressure

Website: www.fzk.de

• Multifunctional HCl, HF, SO2 removal,

drop or decrease in removal efficiency with

and condensation;

time could be seen during the whole period.

Caallll ffoorr PPrroodduucctt RReevviieeww AArrttiicclleess aanndd

• A high porosity - low clogging risk;

Feeaattuurreess::

The aim of this pilot installation was to

• Clean handling and no “hot-spots”;

If your company’s products have been

demonstrate how the complete dioxin

tested by an independent, objective

removal can be achieved in a static,

• No final residue (PCDD/Fs are destroyed

source, we may be interested in

by incineration);

compact and robust piece of equipment

publishing the results. Email details to

downstream of a conventional flue gas

• A simple, static system with high

d.hopwood@elsevier.com

cleaning system.

availability.

•

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