Margot Bittig
Institut für Energieund Umwelttechnik e.V.
Introduction to basic mechanism of mercury removal
from flue gas downstream incineration plants
Building capacities for the improvement of the air quality
Lima, June 20/21 2016
Content
Introduction
Mercury input in incineration plants
Crash course in chemical and physical properties
Mercury removal in flue gas treatment systems
Definition of the mercury sink
Research and Development – next steps
Margot Bittig
Lima, June 20/21 2016
Basics of mercury removal
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Mercury properties
Natural sources:
Liquid in pure form
as a mineral, called cinnabar HgS
Speciality:
Liquid at ambient temperature
1)
Mercury
Hg
Atomic mass
200,592 g/mol
Atomic number
Groupe
Period
80
12
6
highly
toxic
1)
1)
Melting point
234,32 K or - 38,83 °C
Boiling point
630,20 K or 357 °C
Hazardous
to the
environment
EU-Gefahrstoffkennzeichnung aus EU-Verordnung (EG) 1272/2008 (CLP)
Margot Bittig
Lima, June 20/21 2016
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Input in Incineration Plants
Mercury in coal
lignite
sewage sludge
raw mix:
Mercury is a natural component of coal, lignite, ore
Mercury content varies due to the mining area
Analysis of the mercury content in input materials
helps to identify necessary measures for Hg removal
Mercury in waste:
Sources are not known / diffuse
Often the wrong waste comes to the incineration
- Paint containers/tubes
- pharmaceuticals
Primary measures:
Waste separation
significant reduction of mercury in waste incineration plants
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Lima, June 20/21 2016
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Mercury species in raw gas
Hg
Elemental mercury Hg(0)
metallic
monoatomic
gas
Mercury (II) Halides Hg(II)
Cl
covalent
linear
molecules
Hg
e. g.
Cl – Hg – Cl
Cl
Mercury (I) Halides Hg(I)
Cl
Hg
e. g.
Cl – Hg – Hg – Cl
Hg
not stable in
gases
Cl
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Lima, June 20/21 2016
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Mercury species in raw gas
SOx
Hg(0)
Halides
(HCl, HBr, HI)
Hg(II)
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Lima, June 20/21 2016
Sewage sludge,
coal, lignite
Municipal waste,
high caloric waste
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Specialities
Mercury – the removal from flue gases is a special challenge
 Hg(0), Hg(II)
e. g. HgCl2 , HgBr2
 Adsorptive und absorptive behavior is different
 The oxidation state of mercury can change along the flue
gas treatment system
 Most of the mercury stays volatile
 Mercury is very affine to surfaces at low temperatures
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Lima, June 20/21 2016
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Techniques for flue gas treatment
Techniques for flue gas treatment
Particular for mercury
Particle removal techniques
Adsorptive treatments
Adsorbent + bag house filter or fixed bed
Absorptive treatments
Scrubber
Katalytic treatments
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Lima, June 20/21 2016
plus
Oxidation
Hg(0)  Hg(II)
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Oxidation
•
Catalytic Denitrification:
high dust
Combustion/
Boiler
•
S
C
R
or
Dust
removal
Addition of Halides:
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Further development of SCR catalysts
leads to Oxidation of Hg(0)
Removal
of sour
components
low dust
or
tail end
S
C
R
Precision
cleaning
S
C
R
Stack
Bromide containing additives are given into
the combustion zone  Oxidation of Hg(0)
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Adsorption
Carbon based sorbent agent:
activated carbon or activated coke
Provided that the activation is adapted to mercury characteristics

Adsorption of Hg(II) is very good

Adsorption of Hg(0) needs doped material (S, Br, I)
Used in fixed bed for precision cleaning
Used as adsorption additive in entrained flow systems
in combination with sorbent agent to reduce sour flue gas components

Caution: good intermixture between flue gas and sorbent agent and

Sufficient time of contact is essential

Benefit: very low dust concentration in the clean gas
Margot Bittig
Lima, June 20/21 2016
Basics of mercury removal
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Adsorption
entrained flow system with carbon based sorbent agent
is a treatment with a good performance

High removal efficiency,

Technical simple,

Cost-saving

in case of mercury concentration peaks a raw
gas measurement is highly recommended

Activation of the coal/coke must be adapted to
mercury characteristics
but
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Lima, June 20/21 2016
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Absorption
Flue gas ccrubber
Absorption of Hg
=
Equilibrium gas
liquid
Henrys Law
T
(Hg2+)

Impact:

(Hg X +)
Hg(II)(gas)

HgX2
Hg X3-
BrICNOHSO32-

as
Hg(II)(aq) = Hg
HgX
X22
Cl-
Hg X42-
Gas
T: Temperature
K: Stability constant
C: Concentration
Complex reaction
Impact:
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T, K, C
Lima, June 20/21 2016
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Absorption
Henrys Law
Henrys Law
Impact:
(Hg2+)
T
T

Impact:

(HgX+)
Hg(II)(gas)
Hg(0)(gas)

Hg(0)(aq)
HgX2
HgX3
as
Hg(II)(aq) = HgX
HgX22
Gas
HgX42-
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Complex reaction
Redox reaction (aq)
Impact:
Impact:
T, K, C
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T, E, K
Basics of mercury removal
T: Temperature
K: Stability constant
C: Concentration
E: Standard electrode
potential
13
Absorption
Flue gas scrubbers
are units with a good performance

High efficiency in case of mercury peaks

High hold up for Hg(aq)

Risk of re-emission

In most scrubber systems mercury removal is not the
main subject but a co-benefit

Mercury must be separated from the washing water in a
water treatment system
but
Controlling the washing water conditions • Hg/ligands
• Oxidizing/reducing
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Lima, June 20/21 2016
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Defining the mercury sink
Combustion
Boiler
Denitrification / dioxin removal
Water conditioning / evaporation of effluent water
Dust removal / dry adsorption
Scrubber
Evaporation
in flue gas
Denitrification / dioxin removal
Precision cleaning
Oxidation
Hg(0)  Hg(II)
Stack
Re-emission
solid/dissolved  gaseous?
Adsorption at particles
Oxidation
DISPOSAL
Hg(0)  Hg(II)
Absorption = Hg(aq)
Waste Water Treatment (WWT)
Precipitation in WWT
DISPOSAL
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Lima, June 20/21 2016
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Research – next steps
Investigation of mercury absorption into liquids
Kinetics of the different reactions in comparison
(complex reactions, redox reactions)
Investigation of mercury precipitation
Stability of the precipitation products during unit standstill periods
Impact of varying process parameters caused by
start-ups and shut-downs
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Lima, June 20/21 2016
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Research – next steps
Investigation of mercury adsorption
Adsorption in fixed bed filters / impact of
• varying concentrations
• varying flue gas volumes
Which mercury species are formed?
How high is the desorption rate from the filter?
Investigation of intelligent filters
Margot Bittig
Lima, June 20/21 2016
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Research – next steps
Investigation of mercury oxidation
Mechanism of mercury oxidization after combustion and along
the boiler system is still not fully understood yet
Concentration rate,
key component or sum?
SOx
Halides
(HCl, HBr, HI)
Development of innovative measurement systems
for low mercury concentrations < 1 µg/m³std.dry
Margot Bittig
Lima, June 20/21 2016
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Dr.-Ing. Margot Bittig
[email protected]
+ 49 2065 418 300
Margot Bittig
Lima, June 20/21 2016
Basics of mercury removal
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