Introduction to basic mechanism of mercury removal from flue gas downstream incineration plants

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flue gas downstream incineration plants Building

1 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/

2 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/ Basics of mercury removal 2

K or 357 C Atomic number 80 Groupe 12 Period 6 1) highly toxic 1) Hazardous to the environment 1)

3 Mercury properties Natural sources: Liquid in pure form as a mineral, called cinnabar HgS Speciality: Liquid at ambient temperature Mercury Atomic mass Hg 200,592 g/mol Melting point 234,32 K or - 38,83 C Boiling point 630,20 K or 357 C Atomic number 80 Groupe 12 Period 6 1) highly toxic 1) Hazardous to the environment 1) EU-Gefahrstoffkennzeichnung aus EU-Verordnung (EG) 1272/2008 (CLP) Margot Bittig Lima, June 20/ Basics of mercury removal 3

4 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 Margot Bittig Lima, June 20/ Basics of mercury removal 4

5 Mercury species in raw gas Elemental mercury Hg(0) Hg metallic monoatomic gas Mercury (II) Halides Hg(II) e. g. Cl Hg Cl Cl Hg Cl covalent linear molecules Mercury (I) Halides Hg(I) e. g. Cl Hg Hg Cl Hg Cl Hg Cl not stable in gases Margot Bittig Lima, June 20/ Basics of mercury removal 5

6 Mercury species in raw gas SO x Halides (HCl, HBr, HI) Hg(0) Hg(II) Sewage sludge, coal, lignite Municipal waste, high caloric waste Margot Bittig Lima, June 20/ Basics of mercury removal 6

7 Specialities Mercury the removal from flue gases is a special challenge Hg(0), Hg(II) e. g.hgcl 2, HgBr 2 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 Margot Bittig Lima, June 20/ Basics of mercury removal 7

8 Techniques for flue gas treatment Techniques for flue gas treatment Particle removal techniques Particular for mercury Adsorptive treatments Adsorbent + bag house filter or fixed bed Absorptive treatments Scrubber Katalytic treatments plus Oxidation Hg(0) Hg(II) Margot Bittig Lima, June 20/ Basics of mercury removal 8

9 Oxidation Catalytic Denitrification: Further development of SCR catalysts leads to Oxidation of Hg(0) high dust or low dust or tail end Combustion/ Boiler S C R Dust removal Removal of sour components S C R Precision cleaning S C R Stack Addition of Halides: Bromide containing additives are given into the combustion zone Oxidation of Hg(0) Margot Bittig Lima, June 20/ Basics of mercury removal 9

10 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/ Basics of mercury removal 10

11 Adsorption entrained flow system with carbon based sorbent agent is a treatment with a good performance but 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 Margot Bittig Lima, June 20/ Basics of mercury removal 11

12 Absorption Flue gas ccrubber Absorption of Hg = Equilibrium gas liquid Henrys Law Impact: T Hg(II) (gas) as HgX 2 (Hg 2+ ) (Hg X + ) Hg(II) (aq) = HgXX 2 Hg 3 - X X Hg 4 2- Cl - Br - I - SO 3 2- CN - OH - Gas Complex reaction Impact: T, K, C T: Temperature K: Stability constant C: Concentration Margot Bittig Lima, June 20/ Basics of mercury removal 12

13 Absorption Henrys Law Impact: T (Hg 2+ ) Henrys Law Impact: T (HgX + ) Hg(II) (gas) Hg(II) (aq) = HgX 2 Hg(0) (aq) as HgX 2 HgX 3 - Hg(0) (gas) Complex reaction Impact: T, K, C HgX 4 2- Gas Redox reaction (aq) Impact: T, E, K T: Temperature K: Stability constant C: Concentration E: Standard electrode potential Margot Bittig Lima, June 20/ Basics of mercury removal 13

14 Absorption Flue gas scrubbers are units with a good performance but 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 Controlling the washing water conditions Hg/ligands Oxidizing/reducing Margot Bittig Lima, June 20/ Basics of mercury removal 14

15 Defining the mercury sink Combustion Boiler Evaporation in flue gas Denitrification / dioxin removal Oxidation Hg(0) Hg(II) Re-emission solid/dissolved gaseous? Precipitation in WWT DISPOSAL Adsorption at particles DISPOSAL Water conditioning / evaporation of effluent water Dust removal / dry adsorption Scrubber Absorption = Hg (aq) Waste Water Treatment (WWT) Denitrification / dioxin removal Oxidation Hg(0) Hg(II) Precision cleaning Stack Margot Bittig Lima, June 20/ Basics of mercury removal 15

16 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 Margot Bittig Lima, June 20/ Basics of mercury removal 16

17 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/ Basics of mercury removal 17

18 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? SO x Halides (HCl, HBr, HI) Development of innovative measurement systems for low mercury concentrations < 1 µg/m³ std.dry Margot Bittig Lima, June 20/ Basics of mercury removal 18

19 Dr.-Ing. Margot Bittig Margot Bittig Lima, June 20/ Basics of mercury removal 19

Topsøe Catalysis Forum 2009

Topsøe Catalysis Forum 2009 Mercury Behaviour in Combustion Flue Gases Topsøe Catalysis Forum 9 Munkerupgaard 7 th -8 th of August 9 Dr. Harald Thorwarth Energie braucht Impulse Introduction clean gas Cr Co Ni Cd As Cu Pb Hg Input