Topsøe Catalysis Forum 2009

Transcription

1 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 ash ESP ash gypsum waste water 1

2 Trace Element Classification Theoretical Equilibrium Calculations 1 Mole Fraction (Mol-%) 8 6 Hg(g) HgO(g) HgCl (g) Temperature (ºC)

3 Example: Coal fired Power Station 9 Hg(g) [µg/m³] elemental ionic 5 1 downstream eco downstream SCR Example: Waste Incineration Plant Hg(g) [µg/nm³] Test #1 Test # Hg elemental Hg ionic 1 raw gas clean gas raw gas clean gas 6

4 Impact of Fuel Technical Scale one Catalyst Layer 5 Hg elemental Hg ionic Hg(g) [µg/m³] 9 % 6 % % Coal SCR in % Coal + Straw SCR in Impact of SCR DeNOx Catalysts Technical Scale one Catalyst Layer 5 Hg elemental Hg ionic Hg(g) [µg/m³] 9 % 7 % % Coal - SCR in % Coal - SCR out

5 Competition of Mercury and Ammonia at Catalyst Lab Scale - one Catalyst Layer Hg [µg/m³] NH addition Hg out Hg tot out NO out NO [ppm] τ NH [s] 9 Competition of Mercury and Chlorine at Catalyst Lab Scale one Catalyst Layer ] Hg(g) [µg/m ] low HCl concentration no HCl high HCl concentration Hg(g) dosed to the catalyst Hg(g) breaktrhough released Time [Hocquel ] 1 5

6 Mercury oxidation across catalyst Technical Scale one Catalyst Layer 11 ionic mercury share γ [%] upstream SCR downstream SCR no NH injection downstream SCR NH injection,5,1,15 Cl in fuel [wt.-%,daf] Catalyst Zone Model NH injection dummy layer mercury reduction zone NH injection dummy layer mercury reduction zone mercury neutral zone mercury oxidation zone mercury neutral zone mercury oxidation zone catalyst layers catalyst layers new catalyst monoliths deactivated catalyst 1 6

7 Impact of fly ash and precipitation technologies Technical Scale ESP and Fabric Filter Relative Enrichment (RE) 8 6 Element: Hg 5 C 18 C EC /. EC+straw /. EC+MSS /. 1 C 11 C BA APH ESP 1 ESP ESP FF µm 5 µm No direct correlation between particle size and Hg concentration in ash Temperature ( C and 1 C) and precipitation technique of importance 1 Sorption Capacity of Fly Ash Laboratory Scale - Impact of Temperature 1 Hg(g)-breackthrough [µg/m ] sewage sludge fly ash sample 75 glass wool 5 empty reactor tube increasing sorption capacity 158 C 5 17 C 1 C time after start of dosing [s] [Hocquel ] 7

8 Sorption Capacity of Fly Ash Laboratory Scale - Impact of Carbon in Ash and Calcium 1 Hg(g)-breakthrough [µg/m ] T = 1 C 75 glass wool 5 5 empty reactor tube bituminous coal Probe Probe 1 sewage sludge c[rest-c] =,7% c[cao] =,9% c[rest-c] = 1,9% c[cao] = 7,7% c[rest-c] =,% c[cao] = 9,5% time after start of dosing [s] sewage sludge / coal mixture c[rest-c] = 7,% c[cao] = 6,% [Hocquel ] Impact of CaO in Ash on Mercury Speciation Laboratory Scale - Sorption of HgCl (g) and Hg (g) 16 HgCl (g) Group I: T SR SR no impact of HCl and SO Group II: no sorption Hg (g) Group I: no sorption Group II: no sorption no impact of HCl sorption rate SR [%] sorption rate SR [%] Group I: MgO, CaO, TiO CaO gas 1 gas gas gas CaO gas 5 1 sorption rate SR [%] sorption rate SR [%] Group II: Al O, Fe O, SiO Fe O 1 Temperatur [ C] Fe O gas 1 gas gas gas 6 blank gas 5 1 8

9 Impact of CaO in Ash on Mercury Speciation Lab Scale - Reduction of HgCl (g) and Oxidation of Hg (g) Reduction Group I: T RR RR no impact of HCl and SO Group II: no impact reduction rate RR [%] Group I: MgO, CaO, TiO gas 1 gas gas gas CaO 1 reduction rate RR [%] Group II: Al O, Fe O, SiO gas 1 gas gas Fe O 1 Oxidation Group I: no impact Group II: no impact oxidation rate OR [%] 8 6 CaO gas 5 oxidation rate OR [%] 8 6 Fe O gas 5 gas Hg Behaviour in wet FGDs 1% 75% Removal Across FGD 5% 5% % removal -5% -5% Hg() Hg(+) re-emission 18 9

10 Hg Behaviour in wet FGDs treated gas outlet spray nozzles II droplet separator spray nozzles I treated gas absorption of SO contact zone untreated gas inlet absorber sump Air 19 SO removal in wet FGDs H O + + CaCO (liq.) HCO - + Ca + + H O SO HSO - HCO - Ca + SO - HSO - CaSO (liq.) SO - O (liq.) CaSO 1

11 Mercury removal in wet FGDs Hg HgCl Cl HgCl - HgCl - Hg-CaSO (s) 1 Parameters influencing Mercury Behaviour in wet FGDs Redox Potential? SO? ph? flue gas Cl - / Br -? O? Hg temperature? 11

12 Ongoing FGD Research Different research projects ongoing studying the impact of different parameters like: - fuel composition - flue gas composition - FGD parameters: - temperature - ph value - redox potential learn to adjust parameters to optimise Hg separation Summary Mercury Behaviour in Combustion Flue Gases 11 C 8 C 1 C 7 C Fuel, e.g.: waste; coal boiler DeNOx DeDust FGD Cl Br F ash S 1 HgH HgS HgSO Hg(CH ) Hg Catalytic Oxidation HgO Condensation / Sorption HgBr Hg Hg Cl HgCl Removal of Hg + / Reemission of Hg [Hocquel ] 1 conversion Hg(p) Fly ash HgCl precipitation gypsum Filter cake Hg Hg stack Waste water 1

13 Summary Mercury Behaviour in Combustion Flue Gases 5 Hg is totally vaporised during combustion to Hg (g) at furnace exit Due to kinetic limitations Hg (g) not completely oxidised during cooling process Applied Air Pollution Control Devices (APCD) and fuel composition important for Hg behaviour and removal prior to stack SCR DeNOx catalysts can have a significant positive effect on Hg, supporting the oxidation of Hg (g) to HgCl (g) which is relevant for Hg removal in the FGD Depending on the fly ash removal efficiency, the temperature and the composition of the fly ash, mercury can be removed with the fly ash in a dust filter In an FGD removal of Hg (g) is usually very poor and the removal of HgCl (g) is very good. Even though Hg removal in an FGD is very good, the removal in general and the important factors in detail are subject to ongoing research activities Depending on the combination of the already applied APCDs, the Hg removal can be very good E.g. in Germany, no additional specific Hg removal technologies required 1