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ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace elements and alkali • Trace elements in fuels and wastes • Emission standards for trace elements • Trace elements (excluding mercury) emission control • Mercury emission control • Alkali in fuels and wastes • Removal of alkali from fuel gases and flue gases see: www.hut.fi/~rzevenho /gasbook www.hut.fi/~rzevenho/
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Most important trace elements * and alkali #
## ##
**
**
** ** ** ** **
** ** ** ** ** ** ** ** ** ** ** **
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Emission standards for trace elements from combustion and incineration plants mg/m³STP STP @ 11 % O22, dry Hg
Power MSW MSW Power MSW Waste plant incinerator incinerator plant incinerator incinerator Finland Finland EU * Germany Germany USA (1990+) (1994) (2000) (1999) (1999) (1995)** no standard
0.05
0.05
no standard
0.03
Cd + Tl
no standard
0.05
0.05
no standard
0.05
As+Co+Cr+Cu+Mn +Ni+Pb+Sb+Sn+V
no standard
0.5
0.5
no standard
0.5
Cd only
Pb only * Includes waste co-firing in cement kilns
0.06/0.061 or 85% red. 0.03/0.015
0.37/0.15 ** Two values: existing / new
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Gas turbine inlet specifications for trace elements Element Regulation 1 Regulation 2 (1990) (ppmw) (1997) (ppmw) Na + K 0.06 0.03 Pb 0.12 1 V 0.06 0.05 Ca 1.3 1 Zn 0.24
Motivation hot corrosion hot corrosion hot corrosion fouling affects additives against Vanadium corrosion
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace elements in fossil - and waste-derived fuels Coal
Heavy Pet fuel oil coke Hg 0.02-3 ~0.07 < 0.01 As B Be Cd Co Cr Cu Mn Ni Pb Sb Se Sn Tl V Zn
0.5 - 10 5-100 0.1 - 10 0.05-10 0.5 - 20 0.5 - 60 5 - 60 5 - 300 0.5-100 1-300 <1 0.2 - 3 < 10 ~1 1-100 1-1000
Peat
1-3 ~ 0.1
1-2 ~ 0.01 0.1-0.3
1-2 ~0.5 0.5 - 2 ~ 0.5 5 - 104 ~ 10 < 0.1 30-100 0.5 - 1 5 - 10 20 - 50 ~ 300 1-5 1-5 6-100 ~1
~ 0.1
MSW < 15 0.5-500 < 0.5 1 - 40 < 100 < 20 < 1500 < 2500 < 1000 < 5000 < 2500 < 80 < 10 3 - 100
RDF
Wood Waste Waste Scrap Sew. wood paper tyres sludge 1 - 10 0.01-0.2 ~0.08 0.5 - 10 ~3
~0.2
~1 1 - 10
0.1-100
~ 0.5 ~ 0.1 ~1 0.5 - 3 10-1000 ~0.5 1 - 20
50-250 < 1000 ~250 10-100 100-500 <5 3-6 ~ 0.2 ~500
1-4 ~ 15 < 20 < 50
~ 0.5 ~ 0.8 ~ 0.7 ~6 ~ 18 ~27 ~7 ~8 ~5 ~ 0.08 ~8
0.04-3 5 - 50 100-200 ~20 ~ 10
5 - 10
1 - 10 ~5 ~ 100 ~ 100 200-700 ~ 200 ~ 75 ~ 50 60-760 100-300 100-500
~ 0.25 ~2 ~ 2 % 300-800 5 - 150
< 30
~ 150
1-2 %
unit : ppmw = mg/kg, dry
~1000
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Vanadium corrosion by oil ash Oxidation of iron via Na2O.6V2O5 + Fe <=> Na2O.V2O4 .5V2O5 + FeO Na2O.V2O4.5V2O5 + ½ O2 <=> Na2O.6V2O5 Na2SO4 + yV2O5 <=> Na2O.yV2O5 + SO3 (y = 1, 3 or 6)
Inhibition by magnesium: 3MgO + V2O5 <=> 3MgO.V2O5
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Behaviour of trace elements in coal combustion flue gases
(FGD = flue gas desulphurisation, desulphurisation, PM = particulate matter) Typical emissions (µ (µg/MJ) :
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury
Hg
0.5 - 14
Antimony Arsenic Beryllium Cadmium Cobalt Chromium Lead Manganese Nickel Selenium
Sb As Be Cd Co Cr Pb Mn Ni Se
< 0.1 - 2.4 0.1 - 4.2 < 0.1 - 1.4 < 0.1 - 3.0 < 0.1 - 6.8 < 0.1 - 51 0.6 - 29 1.1 - 22 0.3 - 40 <0.1 - 130
ENE-47.153
Trace elements partitioning during combustion or gasification: Class I,II,III elements
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Relative enrichment factor (RE) RE =
element concentrat ion in ash % ash in fuel x element concentrat ion in fuel 100 Bottom ash
Fly ash
Class I
RE ~ 1
RE ~ 1
Class II
RE ~ 0.7
RE 1.3 ~ 4
Class III
RE << 1
RE >> 10
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Effect of chlorine on trace element volatility Incineration
Chromium Nickel Beryllium Silver Barium Thallium Antimony Lead Selenium Cadmium Osmium Arsenic Mercury
0 % chlorine
Incineration
10 % chlorine
Principal Volatilisation Principal Volatilisation species temperature species temperature °C °C CrO2/CrO3 1613 CrO2/CrO3 1611 Ni(OH)2 1210 NiCl4 693 Be(OH)2 1054 Be(OH)2 1054 Ag 904 AgCl 627 Ba(OH)2 849 BaCl2 904 Tl2O3 721 TlOH 138 Sb2O3 660 Sb2O3 660 Pb 627 PbCl4 - 15 SeO2 318 SeO2 318 Cd 214 Cd 214 OsO4 41 OsO4 41 As2O3 32 As2O3 32 Hg 14 Hg 14
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Partitioning of class I, II, III trace elements during pulverised coal combustion
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
100 100 80 80
40 40
FGD FGD residue residue fly fly ash ash
20 20
bottom bottom ash ash
60 60
00 As As
B B
Cd Cd Cr Cr Hg Hg Ni Ni Pb Pb Se Se
↑ output → input Studstrup 3, Denmark
% input input besides besides coal coal fuel fuel %
% output output %
Trace element partitioning during pulverised coal combustion
flue flue gas gas
88 66
limestone limestone
44
FGD FGDwater water
22 00 As As
B B
Cd Cd
Cr Cr
Hg Hg
Ni Ni
Pb Pb
Se Se
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Effect of fuel type and furnace type on trace element emissions Process Particles control efficiency, % Emissions µg/MJ Hg As Be Cd Co Cr Mn Mo Ni Pb V Zn
Heavy fuel Pulverised Grate peat Pulverised Circulating oil spray peat combustion coal FBC peat combustion combustion combustion 98.7 - 99.5 59 - 81 95.6 - 99.5 99.5 - 99.8
0.0011 1.5 < 0.004 0.008 3 3 < 14 3 310 - 540 5 1300 15
0.11
0.10
< 1.5 - 2.3 2 - 10 0.05 0.1 - 1.5 < 0.002 - 0.13 0.8 - 4 0.3 - 1.2 0.06 - 0.2 3 - 79 0.6 - 3 10 - 26 17 - 31 < 1 - 11 < 0.07 - 0.9 < 33 - 54 <1-5 3-4 40 - 200 4-6 0.7 - 7 < 6 - 12 7 - 37
HELSINKI UNIVERSITY OF TECHNOLOGY
0.12
0.03
2 - 39 5 0.5 -1.8 1 - 22 8 - 230 2 - 230 < 1 -41 < 15 - 170 20 - 120 10 - 88 20 - 220
< 0.1 - 1.6 0.01 - 0.3 0.1 - 0.4 0.3 - 4 0.7 - 1.3 0.6 - 6 < 1.5 - 2.3 9 - 13 1 - 11 9 1 - 11
ENE-47.153
Controlling trace elements emissions Most concern: Hg, Se, B, As, Cd, Cd, Pb Less concern: Cr, Cr, Cu, Ni, Ni, V, Zn
class III/II class II/ I
Class I and II in bottom ash and (enriched) in fly ashes: → removal depends mainly on dust control system (and its efficiency for 0.1 - 1 µm fines) Class II and III can be (more) effectively removed by the flue gas desulphurisation system (Hg ~ 40%, Se ~70%) Specific methods based on sorbents can be used, such as activated carbon, clays and aluminum silicates. For coal combustion / gasification not (yet) widely used, for waste incinerators often used for Hg and As, Cd, Cd, Pb
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace element removal by wet FGD downstream of particulate control
Hg Se Be Fly ash
Removal efficiency % ~ 50 ~ 60 ~ 80 90 ~ 99
HELSINKI UNIVERSITY OF TECHNOLOGY
Sorbents for heavy metals
Outlet concentration µg/m³STP ~ 1.5 ~ 10 ~ 250 1000 ~ 10000
ENE-47.153
Sorbent Element Temperature range Based on zeolites Hg low temperatures, - impregnated with sulphur up to 400EC - impregenated with iodides - Ag and Hg ion exchanged Based on activated carbon Hg low temperatures, - activated carbon up to 300EC - activated carbon impregnated with at higher sulphur, chlorine, iodides temperatures also - oxidised activated carbon Cd, Pb Siliceous materials V, Pb, Ni, Zn high temperatures 600-1000EC - Mg, Ca, Al silicates - Mixed silicates, silicate -fly ash at low temperatures low temperatures e.g. < 100EC mixtures, impregnated siliceous also Hg, Cd materials Based on alumina Pb at up to 700EC - activated alumina gel, - alumina coated steel wool, - alumina impregnated with alkali carbonate or phosphate Calcium compounds Hg, Zn, V, Ni at Hg at up to 300-400EC, - hydrated lime/fly ash low temperature - limestone/fly ash, limestone/silica V, Ni, As at high temperatures - hydrated lime + Sn, limestone, As at high calcium chloride temperature Other materials Hg, V, Ni, Pb, As V, Ni at up to 550EC - MgO, Mg(OH)2, - Cr, Ni compounds As at high temperatures - Fe compounds, e.g. blast furnace dust
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury (from coal) partitioning
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury emissions from coal fired boilers (US) unit: mg/GJ, 1 GJ ~ 300 m3STP flue gas
Mercury in US coal:
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury species transformations during pulverised coal combustion
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury emissions control Filter + wet scrubber versus ESP + wet scrubber
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury emissions control Injection of activated carbon and hydrated lime at filter inlet
HgCl2
Hg°
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Control of mercury emissions - #1 of 2 • Low temperatures – ad-/ab -sorption on activated carbon ad-/ab-sorption HgCl2: physisorption, physisorption, Hg: chemisorption, chemisorption, more efficient with a sulphur, chlorine or iodine - impregnated sorbent – injection of Na2S4 and removal of HgS in acid scrubber : • HgCl2 + Na2S4 → HgS + 3 S + 2 NaCl • Hg° → HgS + Na2S3 Hg° + Na2S4 • Na2S4 + 2 HCl → H2S + 3 S + 2 NaCl • HgCl2 + H2S → HgS + 2 HCl • Hg° → HgS Hg° + S
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Control of mercury emissions - #2 of 2 • (..... Low temperatures: ) – sodium chlorite (NaClO2) in acid scrubber for HCl – SO2 + activated carbon (for Hg°) + TMT (for Hg2+) – aluminium silicates – oxidation by H2O2 and wet scrubbing • High temperatures: – Ca/Mg-based sorbents, sorbents, fly ash, Ca(OH)2+Sn – some metals: Cr, Cr, Ni, Ni, Fe-compounds
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Removal of mercury with activated carbon (140°C, inlet 20 µg/m³ g/m³ Hg)
Effect of particle size and contact time
Effect of particle size and C/Hg ratio
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Akali in fuels (mg/kg, dry) Coal Lignite Peat Orimul- Wood sion™ saw dust
Straw
RDF
Auto Scrap Sew. Black shred- tyres sludge liquor der res. solids
Na
100 1500
100 300
~ 400 ~ 2000 ~ 40
100 5000
3000 - ~ 10000 200 - ~ 2000 5000 600
K
50 3000
100 1000
~ 700
15 20 %
~ 300 ~ 500 5000 - 2000 - ~ 3000 200 - ~ 6000 ~ 1 % 10000 3000 600
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Natrium in coal : • release of Na during heat-up ‚ relation between Na & Cl, Cl, ƒ Na-vapour Na-vapour in PFBC flue gas •
illinois coal
‚
ƒ
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Sodium / ash interactions in furnaces
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Vapour pressures of alkali species ↑ Saturated vapour pressure of alkali chlorides NaCl, NaCl, KCl → Alkali saturation pressures and concentrations in coalderived gas
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Vapour phase alkali in PFBC (Otaniemi, Otaniemi, Finland, 770-920°C, 10 bar)
unit : weight-ppb
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alkali in flue gas/gasifier product gas • In gasifier product gas In flue gas
chlorides, hydroxides, sulphide <1000°C : chlorides + SO2 → sulphates
• Comparison PGBC / PFBG of peat, 900° 900°C : alkali ~2 orders of magnitude higher in fuel gas than in flue gas • Maximum alkali for expansion turbine inlet: assuming air ratio 2.5 for for gas turbine: • 90 - 99% of the alkali has to be removed
24 ppb 84 ppb in fuel gas
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alkali removal from flue gas/gasifier product gas • Species and concentrations: Potassium K Sodium Na • Na+K Na+K in gasifier gas, ppmw
350°C ~10-5
600°C KCl NaCl ~0.8+~1
1227°C K > KCl > KBO2 Na > NaCl > NaBO2 for Shell gasifier
• Below 530-570°C: alkali concentrations below turbine inlet limits • Temperature below 600°C: all alkali as chlorides and sulphates particles, which will be collected with the fly ash • Temperature above 600° 600°C: ¬ Cooling and removal as particles - Absorption using aluminum silicates (600-1000° (600-1000°C)
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Alkali removal from flue gas/gasifier product gas by solid sorbents at 600-1000°C • Sorbents: Sorbents:
Kaolinite, Kaolinite, Bauxite, Emathlite
• Reductions achieved: close to 100% • Chemical fixation in the material. E.g. for bauxite: AlkCl + H2O + Al2O3.xSiO2(s) → AlkAlO2.xSiO2 + 2HCl • Sorption can be combined with hot gas particulate control in moving granular bed filters, allowing 2-5% alkali
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alumina silicate sorbents for alkali 600-1000°C
Emathlite Kaolinite Bauxitic kaolinite Attapulgite Ca-montmorillonite
SiO2 %-wt ~ 69 ~ 51 ~ 36 ~ 62 ~ 54
Al22O33 %-wt ~8 ~ 44 ~ 58 ~ 10 ~ 18
(Na,K)22O (Ca,Mg)O %-wt %-wt ~1 ~9 ~0 ~0 ~0 ~0 ~1 ~ 10, ~ 5 ~2 ~5, ~ 13
P22O5 %-wt ~3 ~0 ~0 ~1 ~0
Others %-wt ~ 10 ~5 ~6 ~2
~8
Procedure : inject sorbent into gas and collect sorbent in particulate control system
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace elements and alkali • Trace elements in fuels and wastes • Emission standards for trace elements • Trace elements (excluding mercury) emission control • Mercury emission control • Alkali in fuels and wastes • Removal of alkali from fuel gases and flue gases see: www.hut.fi/~rzevenho /gasbook www.hut.fi/~rzevenho/
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Most important trace elements * and alkali #
## ##
**
**
** ** ** ** **
** ** ** ** ** ** ** ** ** ** ** **
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Emission standards for trace elements from combustion and incineration plants mg/m³STP STP @ 11 % O22, dry Hg
Power MSW MSW Power MSW Waste plant incinerator incinerator plant incinerator incinerator Finland Finland EU * Germany Germany USA (1990+) (1994) (2000) (1999) (1999) (1995)** no standard
0.05
0.05
no standard
0.03
Cd + Tl
no standard
0.05
0.05
no standard
0.05
As+Co+Cr+Cu+Mn +Ni+Pb+Sb+Sn+V
no standard
0.5
0.5
no standard
0.5
Cd only
Pb only * Includes waste co-firing in cement kilns
0.06/0.061 or 85% red. 0.03/0.015
0.37/0.15 ** Two values: existing / new
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Gas turbine inlet specifications for trace elements Element Regulation 1 Regulation 2 (1990) (ppmw) (1997) (ppmw) Na + K 0.06 0.03 Pb 0.12 1 V 0.06 0.05 Ca 1.3 1 Zn 0.24
Motivation hot corrosion hot corrosion hot corrosion fouling affects additives against Vanadium corrosion
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace elements in fossil - and waste-derived fuels Coal
Heavy Pet fuel oil coke Hg 0.02-3 ~0.07 < 0.01 As B Be Cd Co Cr Cu Mn Ni Pb Sb Se Sn Tl V Zn
0.5 - 10 5-100 0.1 - 10 0.05-10 0.5 - 20 0.5 - 60 5 - 60 5 - 300 0.5-100 1-300 <1 0.2 - 3 < 10 ~1 1-100 1-1000
Peat
1-3 ~ 0.1
1-2 ~ 0.01 0.1-0.3
1-2 ~0.5 0.5 - 2 ~ 0.5 5 - 104 ~ 10 < 0.1 30-100 0.5 - 1 5 - 10 20 - 50 ~ 300 1-5 1-5 6-100 ~1
~ 0.1
MSW < 15 0.5-500 < 0.5 1 - 40 < 100 < 20 < 1500 < 2500 < 1000 < 5000 < 2500 < 80 < 10 3 - 100
RDF
Wood Waste Waste Scrap Sew. wood paper tyres sludge 1 - 10 0.01-0.2 ~0.08 0.5 - 10 ~3
~0.2
~1 1 - 10
0.1-100
~ 0.5 ~ 0.1 ~1 0.5 - 3 10-1000 ~0.5 1 - 20
50-250 < 1000 ~250 10-100 100-500 <5 3-6 ~ 0.2 ~500
1-4 ~ 15 < 20 < 50
~ 0.5 ~ 0.8 ~ 0.7 ~6 ~ 18 ~27 ~7 ~8 ~5 ~ 0.08 ~8
0.04-3 5 - 50 100-200 ~20 ~ 10
5 - 10
1 - 10 ~5 ~ 100 ~ 100 200-700 ~ 200 ~ 75 ~ 50 60-760 100-300 100-500
~ 0.25 ~2 ~ 2 % 300-800 5 - 150
< 30
~ 150
1-2 %
unit : ppmw = mg/kg, dry
~1000
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Vanadium corrosion by oil ash Oxidation of iron via Na2O.6V2O5 + Fe <=> Na2O.V2O4 .5V2O5 + FeO Na2O.V2O4.5V2O5 + ½ O2 <=> Na2O.6V2O5 Na2SO4 + yV2O5 <=> Na2O.yV2O5 + SO3 (y = 1, 3 or 6)
Inhibition by magnesium: 3MgO + V2O5 <=> 3MgO.V2O5
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Behaviour of trace elements in coal combustion flue gases
(FGD = flue gas desulphurisation, desulphurisation, PM = particulate matter) Typical emissions (µ (µg/MJ) :
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury
Hg
0.5 - 14
Antimony Arsenic Beryllium Cadmium Cobalt Chromium Lead Manganese Nickel Selenium
Sb As Be Cd Co Cr Pb Mn Ni Se
< 0.1 - 2.4 0.1 - 4.2 < 0.1 - 1.4 < 0.1 - 3.0 < 0.1 - 6.8 < 0.1 - 51 0.6 - 29 1.1 - 22 0.3 - 40 <0.1 - 130
ENE-47.153
Trace elements partitioning during combustion or gasification: Class I,II,III elements
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Relative enrichment factor (RE) RE =
element concentrat ion in ash % ash in fuel x element concentrat ion in fuel 100 Bottom ash
Fly ash
Class I
RE ~ 1
RE ~ 1
Class II
RE ~ 0.7
RE 1.3 ~ 4
Class III
RE << 1
RE >> 10
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Effect of chlorine on trace element volatility Incineration
Chromium Nickel Beryllium Silver Barium Thallium Antimony Lead Selenium Cadmium Osmium Arsenic Mercury
0 % chlorine
Incineration
10 % chlorine
Principal Volatilisation Principal Volatilisation species temperature species temperature °C °C CrO2/CrO3 1613 CrO2/CrO3 1611 Ni(OH)2 1210 NiCl4 693 Be(OH)2 1054 Be(OH)2 1054 Ag 904 AgCl 627 Ba(OH)2 849 BaCl2 904 Tl2O3 721 TlOH 138 Sb2O3 660 Sb2O3 660 Pb 627 PbCl4 - 15 SeO2 318 SeO2 318 Cd 214 Cd 214 OsO4 41 OsO4 41 As2O3 32 As2O3 32 Hg 14 Hg 14
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Partitioning of class I, II, III trace elements during pulverised coal combustion
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
100 100 80 80
40 40
FGD FGD residue residue fly fly ash ash
20 20
bottom bottom ash ash
60 60
00 As As
B B
Cd Cd Cr Cr Hg Hg Ni Ni Pb Pb Se Se
↑ output → input Studstrup 3, Denmark
% input input besides besides coal coal fuel fuel %
% output output %
Trace element partitioning during pulverised coal combustion
flue flue gas gas
88 66
limestone limestone
44
FGD FGDwater water
22 00 As As
B B
Cd Cd
Cr Cr
Hg Hg
Ni Ni
Pb Pb
Se Se
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Effect of fuel type and furnace type on trace element emissions Process Particles control efficiency, % Emissions µg/MJ Hg As Be Cd Co Cr Mn Mo Ni Pb V Zn
Heavy fuel Pulverised Grate peat Pulverised Circulating oil spray peat combustion coal FBC peat combustion combustion combustion 98.7 - 99.5 59 - 81 95.6 - 99.5 99.5 - 99.8
0.0011 1.5 < 0.004 0.008 3 3 < 14 3 310 - 540 5 1300 15
0.11
0.10
< 1.5 - 2.3 2 - 10 0.05 0.1 - 1.5 < 0.002 - 0.13 0.8 - 4 0.3 - 1.2 0.06 - 0.2 3 - 79 0.6 - 3 10 - 26 17 - 31 < 1 - 11 < 0.07 - 0.9 < 33 - 54 <1-5 3-4 40 - 200 4-6 0.7 - 7 < 6 - 12 7 - 37
HELSINKI UNIVERSITY OF TECHNOLOGY
0.12
0.03
2 - 39 5 0.5 -1.8 1 - 22 8 - 230 2 - 230 < 1 -41 < 15 - 170 20 - 120 10 - 88 20 - 220
< 0.1 - 1.6 0.01 - 0.3 0.1 - 0.4 0.3 - 4 0.7 - 1.3 0.6 - 6 < 1.5 - 2.3 9 - 13 1 - 11 9 1 - 11
ENE-47.153
Controlling trace elements emissions Most concern: Hg, Se, B, As, Cd, Cd, Pb Less concern: Cr, Cr, Cu, Ni, Ni, V, Zn
class III/II class II/ I
Class I and II in bottom ash and (enriched) in fly ashes: → removal depends mainly on dust control system (and its efficiency for 0.1 - 1 µm fines) Class II and III can be (more) effectively removed by the flue gas desulphurisation system (Hg ~ 40%, Se ~70%) Specific methods based on sorbents can be used, such as activated carbon, clays and aluminum silicates. For coal combustion / gasification not (yet) widely used, for waste incinerators often used for Hg and As, Cd, Cd, Pb
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Trace element removal by wet FGD downstream of particulate control
Hg Se Be Fly ash
Removal efficiency % ~ 50 ~ 60 ~ 80 90 ~ 99
HELSINKI UNIVERSITY OF TECHNOLOGY
Sorbents for heavy metals
Outlet concentration µg/m³STP ~ 1.5 ~ 10 ~ 250 1000 ~ 10000
ENE-47.153
Sorbent Element Temperature range Based on zeolites Hg low temperatures, - impregnated with sulphur up to 400EC - impregenated with iodides - Ag and Hg ion exchanged Based on activated carbon Hg low temperatures, - activated carbon up to 300EC - activated carbon impregnated with at higher sulphur, chlorine, iodides temperatures also - oxidised activated carbon Cd, Pb Siliceous materials V, Pb, Ni, Zn high temperatures 600-1000EC - Mg, Ca, Al silicates - Mixed silicates, silicate -fly ash at low temperatures low temperatures e.g. < 100EC mixtures, impregnated siliceous also Hg, Cd materials Based on alumina Pb at up to 700EC - activated alumina gel, - alumina coated steel wool, - alumina impregnated with alkali carbonate or phosphate Calcium compounds Hg, Zn, V, Ni at Hg at up to 300-400EC, - hydrated lime/fly ash low temperature - limestone/fly ash, limestone/silica V, Ni, As at high temperatures - hydrated lime + Sn, limestone, As at high calcium chloride temperature Other materials Hg, V, Ni, Pb, As V, Ni at up to 550EC - MgO, Mg(OH)2, - Cr, Ni compounds As at high temperatures - Fe compounds, e.g. blast furnace dust
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury (from coal) partitioning
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury emissions from coal fired boilers (US) unit: mg/GJ, 1 GJ ~ 300 m3STP flue gas
Mercury in US coal:
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury species transformations during pulverised coal combustion
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Mercury emissions control Filter + wet scrubber versus ESP + wet scrubber
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Mercury emissions control Injection of activated carbon and hydrated lime at filter inlet
HgCl2
Hg°
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Control of mercury emissions - #1 of 2 • Low temperatures – ad-/ab -sorption on activated carbon ad-/ab-sorption HgCl2: physisorption, physisorption, Hg: chemisorption, chemisorption, more efficient with a sulphur, chlorine or iodine - impregnated sorbent – injection of Na2S4 and removal of HgS in acid scrubber : • HgCl2 + Na2S4 → HgS + 3 S + 2 NaCl • Hg° → HgS + Na2S3 Hg° + Na2S4 • Na2S4 + 2 HCl → H2S + 3 S + 2 NaCl • HgCl2 + H2S → HgS + 2 HCl • Hg° → HgS Hg° + S
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Control of mercury emissions - #2 of 2 • (..... Low temperatures: ) – sodium chlorite (NaClO2) in acid scrubber for HCl – SO2 + activated carbon (for Hg°) + TMT (for Hg2+) – aluminium silicates – oxidation by H2O2 and wet scrubbing • High temperatures: – Ca/Mg-based sorbents, sorbents, fly ash, Ca(OH)2+Sn – some metals: Cr, Cr, Ni, Ni, Fe-compounds
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Removal of mercury with activated carbon (140°C, inlet 20 µg/m³ g/m³ Hg)
Effect of particle size and contact time
Effect of particle size and C/Hg ratio
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Akali in fuels (mg/kg, dry) Coal Lignite Peat Orimul- Wood sion™ saw dust
Straw
RDF
Auto Scrap Sew. Black shred- tyres sludge liquor der res. solids
Na
100 1500
100 300
~ 400 ~ 2000 ~ 40
100 5000
3000 - ~ 10000 200 - ~ 2000 5000 600
K
50 3000
100 1000
~ 700
15 20 %
~ 300 ~ 500 5000 - 2000 - ~ 3000 200 - ~ 6000 ~ 1 % 10000 3000 600
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Natrium in coal : • release of Na during heat-up ‚ relation between Na & Cl, Cl, ƒ Na-vapour Na-vapour in PFBC flue gas •
illinois coal
‚
ƒ
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Sodium / ash interactions in furnaces
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Vapour pressures of alkali species ↑ Saturated vapour pressure of alkali chlorides NaCl, NaCl, KCl → Alkali saturation pressures and concentrations in coalderived gas
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Vapour phase alkali in PFBC (Otaniemi, Otaniemi, Finland, 770-920°C, 10 bar)
unit : weight-ppb
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alkali in flue gas/gasifier product gas • In gasifier product gas In flue gas
chlorides, hydroxides, sulphide <1000°C : chlorides + SO2 → sulphates
• Comparison PGBC / PFBG of peat, 900° 900°C : alkali ~2 orders of magnitude higher in fuel gas than in flue gas • Maximum alkali for expansion turbine inlet: assuming air ratio 2.5 for for gas turbine: • 90 - 99% of the alkali has to be removed
24 ppb 84 ppb in fuel gas
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alkali removal from flue gas/gasifier product gas • Species and concentrations: Potassium K Sodium Na • Na+K Na+K in gasifier gas, ppmw
350°C ~10-5
600°C KCl NaCl ~0.8+~1
1227°C K > KCl > KBO2 Na > NaCl > NaBO2 for Shell gasifier
• Below 530-570°C: alkali concentrations below turbine inlet limits • Temperature below 600°C: all alkali as chlorides and sulphates particles, which will be collected with the fly ash • Temperature above 600° 600°C: ¬ Cooling and removal as particles - Absorption using aluminum silicates (600-1000° (600-1000°C)
HELSINKI UNIVERSITY OF TECHNOLOGY
ENE-47.153
Alkali removal from flue gas/gasifier product gas by solid sorbents at 600-1000°C • Sorbents: Sorbents:
Kaolinite, Kaolinite, Bauxite, Emathlite
• Reductions achieved: close to 100% • Chemical fixation in the material. E.g. for bauxite: AlkCl + H2O + Al2O3.xSiO2(s) → AlkAlO2.xSiO2 + 2HCl • Sorption can be combined with hot gas particulate control in moving granular bed filters, allowing 2-5% alkali
ENE-47.153
HELSINKI UNIVERSITY OF TECHNOLOGY
Alumina silicate sorbents for alkali 600-1000°C
Emathlite Kaolinite Bauxitic kaolinite Attapulgite Ca-montmorillonite
SiO2 %-wt ~ 69 ~ 51 ~ 36 ~ 62 ~ 54
Al22O33 %-wt ~8 ~ 44 ~ 58 ~ 10 ~ 18
(Na,K)22O (Ca,Mg)O %-wt %-wt ~1 ~9 ~0 ~0 ~0 ~0 ~1 ~ 10, ~ 5 ~2 ~5, ~ 13
P22O5 %-wt ~3 ~0 ~0 ~1 ~0
Others %-wt ~ 10 ~5 ~6 ~2
~8
Procedure : inject sorbent into gas and collect sorbent in particulate control system
