Halogens, dioxins/furans

Transcription

1 Halogens, dioxins/furans Halogen compounds in fuels and fuel/flue gases Chlorine-related corrosion HCl control in flue gases and fuel gases Dioxins/furans formation and control Other compounds: HF, HBr, brominated organo-halogens see: rzevenho/gasbook

2 Organo-halogen compounds ,3,7,8 tetrachloro dibenzo - p- dioxin PCBs PCDDs PCDFs PCB polychlorinated biphenyls polychlorinated dibenzodioxins polychlorinated dibenzofurans with bromine: PBBs, PBDDs etc. furan 2,3,7,8 tetrachlorodibenzo furan

3 Halogens in fossil fuels (mg/kg) (listed as F, Cl, Br) Coal*, lignite / Light fuel oil / Peat ~ 500 Heavy fuel oil - / < 20 Estonian oil shale ~2000 Orimulsion ~700 Petroleum coke, petcoke ~ 300 Natural gas - * Iodine mg/kg

4 Halogens in biomass and waste streams (mg/kg) (listed as F, Cl, Br) Wood (firewood) Munical solid waste (MSW) / Bark Refuse derived fuel (RDF) / Straw Packaging derived fuel (PDF) / 1-4 Landfill gas ~50 ppmw CCl4 Car tyre scrap Auto shredder residue (ASR) Textile ~ 0.25 Newsprint paper ~ 0.11 Computer circuit boards /2-6 (epoxy or phenolic resins) Leather waste Computer monitor housings ~ 0.1 / ~ 2 Electric & electronic equipment ~ 3.5 / ~ 0.9 (E&E) waste plastics * Sewage sludge Mixed medical waste 1-4 Polyurethane foam ~ 0.7 /~ 8/~ 3 (containing CFC11) PVC ~ 50 Black liquor solids * Polymer market mix 1998

5 Oxidation rate of CO in FBC in presence of HCl 1 CO oxidation rate (mol/m3s) K 1 bar 10% O2 5% CO 10% H2O HCl in gas ( ppm-v)

6 Emission standards for halogen 11 % O2, dry HCl mg/m³stp HF mg/m³stp PCDD/F ng/m³stp STP TEQ Power plant Finland (1990+) MSW incinerator Finland (1994) MSW incinerator EU (2000) Power plant Germany (1999) MSW incinerator Germany (1999) Waste incinerator USA (1995) no standard or 99.5% red. no standard no standard no standard no standard

7 Chlorine-related corrosion #1 Dewpoint of hydrochloric acid Corrosion rate by HCl and Cl 2

8 Chlorine-related corrosion #2 Important for chlorine-related corrosion: HCl,, Cl 2 NaCl, KCl, O 2, SO 2, H 2 O Tube metals Temperature

9 Chlorine-related corrosion #3 Corrosion rate versus chlorine in coal

10 Halogen removal in FGD (with forced oxidation)

11 Removal of HCl (& HF, HBr) from flue gases Conventional, at low concentrations: in wet scrubber for FGD, gives ~70% removal of HCl,, HF. Disadvantages: dissolution of SO 2 and lime/limestone are inhibited HF and fly ash give AlF x complexes in FGD (Inkoo Corrosion, deposits formation upstream Inkoo,, Finland) More suitable methods: (cold) inject alkali and collect salt particles in filter (hot) injection of calcium-based sorbent in upper furnace

12 HELSINKI UNIVERSITY OF TECHNOLOGY Flue gas to SO2 separator Flue gas from dust separator Pump / 3rd stage container 1st stage Water Packing 2nd stage Pump / Packing Salt solution to vaporiser set stage 3 container set stage 2 Water 3-stage HCl scrubber, producing hydrochloric acid gives % HCl, which is further processed to 30-31%

13 Sorbents for HCl,, HF, HBr (i.e. HX) #1 Limestone CaCO 3 Nahcolite NaHCO 3 Lime CaO Hydrated lime Ca(OH) 2 Soda/trona NaHCO 3 Na 2 CO 3 Melting points of halogen salts NaF: 988 C ; NaCl: 801 C ; NaBr: 755 C CaF 2 : 1360 C ; CaCl 2 : 772 C ; CaBr 2 : 730 C KF: 858 C ; KCl: 770 C ; KBr: 734 C

14 Sorbents for HCl,, HF, HBr (i.e. HX) #2 Potassium salts : high vapour pressures for KF, KCl, KBr

15 Removal of HCl and HF from pulverised coal combustion flue gas (Illinois, US, 1993) Hydrated lime injected into a coal-fired boiler at Ca/S=1.66, 3%-wt sulphur in fuel Injected into upper furnace at ~1250 C Chemistry : Ca(OH 2 ) fi CaO + H 2 O CaO + 2 HCl fi CaCl 2 + H 2 O CaO + 2 HF fi CaF 2 + H 2 O Results : HCl 63-86% removal, from 660 ppmw HF 94-99% removal from 49 ppmw

16 Halide removal (HCl( HCl,, HF) from IGCC raw fuel gas at ~400 C Buggenum IGCC HCl ~ 600 ppm HF ~ 220 ppm Texaco IGCC HCl ~ 500 ppm HF ~190 ppm for coal, 0.2 % Cl,, 0.04 % F

17 Removal of HCl from flue gas with various sorbents

18 Formation of dioxins / furans #1

19 Formation of dioxins / furans #2

20 De Novo dioxins / furans formation Depends on 5 major factors : 1. The cooling rate of the flue gas, especially around 300 C 2. The amount of fly ash 3. The presence of trace elements, especially Cu and Pb 4. The carbon and chlorine content of the fly ash 5. The presence of free oxygen Radical reactions Cl + OH fi HCl + O, OH + H fi H 2 O are competing with CO + OH fi CO 2 + H giving apparently lower stoichiometry,, giving more soot and C x H y Deacon reaction : 2HCl + ½ O 2 <=> Cl 2 + H 2 O catalysed by Cu, Pb, Sn,,... ; reaction equilibrium to Cl 2 below ~500 C Cl 2 + O 2 + C x H y C fi PCDDs/Fs

21 Equivalence schemes for PCDD/Fs Dioxin I- TEF Furan I - TEF 2,3,7,8-TCDD 1 2,3,7,8-TCDF 0.1 1,2,3,7,8-PCDD 0.5 1,2,3,7,8-PCDF ,2,3,4,7,8-HxCDD 0.1 2,3,4,7,8-PCDF 0.5 1,2,3,6,7,8-HxCDD 0.1 1,2,3,4,7,8-HxCDF 0.1 1,2,3,7,8,9-HxCDD 0.1 1,2,3,6,7,8-HxCDF 0.1 1,2,3,4,7,8,9-HpCDD ,3,4,6,7,8-HxCDF 0.1 1,2,3,4,6,7,8,9-OCDD ,2,3,7,8,9-HxCDF 0.1 1,2,3,4,6,7,8-HpCDF ,2,3,4,7,8,9-HpCDF ,2,3,4,6,7,8,9-OCDF International Toxic Equivalence Factors (I-TEF) (NATO, 1988) standardize the toxicity of the dioxins and furans, to derive a toxic equivalence as 2,3,7,8-TCDD. The I-TEF for the dioxins and furans without chlorine atoms at the 2, 3, 7, and 8 positions is zero.

22 Rate of de novo PCDD/F formation

23 Effect of calcium-based sorbents on PCDD/F release from an FB waste combustor

24 Emission control for PCDD/Fs Carbon injection* Fixed bed carbon absorption + SNCR SNCR + carbon injection* Lime / char adsorption SCR catalytic oxidation SCR catalytic oxidation + carbon injection* * collected downstream in (a separate) dust control system also for PCBs, brominated compounds (PBBs( PBBs,, PBDD/Fs)

25 Dioxins/furans control for waste incinerators (MSW = municipal solid waste) process PCDD/Fs from furnace ng/m³stp gas clean-up system PCDD/Fs removal efficiency % 5 incinerators for RDF wet scrubber + > 95.7 or MSW fabric filter 3 incinerators for SCR + wet scrubber MSW + fabric filter pilot incinerator for sorbent injection + > MSW fabric filter MSW incinerator 170 wet scrubber + ESP 64.3

26 PCDD/F removal by a bag filter : effect of entrance temperature

27 Other halogens #1: control of HF + HCl Process* Temperature HF removal HCl removal at outlet EC % % dry sorbent injection + fabric filter spray dryer absorber + ESP > 95 spray dryer absorber + fabric filter > 95 spray dryer absorber + dry sorbent ~ > 95 injection + ESP or fabric filter ESP + wet scrubber > 95 spray dryer + west scrubber + ESP or fabric filter > 95 * sorbent = sodium- or calcium- based sorbent

28 Other halogens #2: formation of brominated dioxins/furans (PBDD/Fs) from PBDE flame retardants