HELSINKI UNIVERSITY OF TECHNOLOGY ENE-47.153 Trace ...

HELSINKI UNIVERSITY OF TECHNOLOGY ENE-47.153

Trace elements and alkaliTrace elements and alkali•• Trace elements in fuels and wastesTrace elements in fuels and wastes

•• Emission standards for trace elementsEmission standards for trace elements

•• Trace elements (excluding mercury) emission controlTrace elements (excluding mercury) emission control

•• Mercury emission controlMercury emission control

•• Alkali in fuels and wastesAlkali in fuels and wastes

•• Removal of alkali from fuel gases and flue gasesRemoval of alkali from fuel gases and flue gases

see: www.hut.fi/~see: www.hut.fi/~rzevenhorzevenho//gasbookgasbook


Most important trace elements Most important trace elements ** and alkali and alkali ##

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Emission standards for trace elementsEmission standards for trace elementsfrom combustion and incineration plantsfrom combustion and incineration plants

mg/m³STPSTP

@ 11 % O22, dry

Powerplant

Finland(1990+)

MSWincinerator

Finland(1994)

MSWincinerator

EU *(2000)

Powerplant

Germany(1999)

MSWincineratorGermany

(1999)

Wasteincinerator

USA(1995)**

Hg no standard 0.05 0.05 no standard 0.03 0.06/0.061or 85% red.

Cd only 0.03/0.015

Cd + Tl no standard 0.05 0.05 no standard 0.05

As+Co+Cr+Cu+Mn+Ni+Pb+Sb+Sn+V

nostandard

0.5 0.5 nostandard

0.5

Pb only 0.37/0.15* Includes waste co-firing in cement kilns ** Two values: existing / new


Gas turbine inlet specifications for trace elementsGas turbine inlet specifications for trace elements

Element Regulation 1 (1990) (ppmw)

Regulation 2 (1997) (ppmw)

Motivation

Na + K 0.06 0.03 hot corrosion

Pb 0.12 1 hot corrosion

V 0.06 0.05 hot corrosionCa 1.3 1 fouling

Zn 0.24 affects additives against Vanadium corrosion


Trace elements in fossil - and waste-derived fuelsTrace elements in fossil - and waste-derived fuelsCoal Peat Heavy

fuel oilPet

cokeMSW RDF Wood Waste

woodWastepaper

Scraptyres

Sew.sludge

Hg 0.02-3 ~0.07 < 0.01 < 15 1 - 10 0.01-0.2 ~0.08 0.5 - 10

As 0.5 - 10 1 - 3 1 - 2 0.5-500 ~3 ~0.2 0.1-100B 5-100 < 0.5 ~ 0.5

Be 0.1 - 10 ~ 0.1 ~ 0.01 1 - 40 ~1 ~ 0.8Cd 0.05-10 0.1-0.3 < 100 1 - 10 ~ 0.5 ~ 0.7 5 - 10 1 - 10

Co 0.5 - 20 1 - 2 ~0.5 < 20 ~ 0.1 ~5

Cr 0.5 - 60 0.5 - 2 ~ 0.5 5 - 104 < 1500 50-250 ~ 1 1 - 4 ~ 6 ~ 100 ~ 100Cu 5 - 60 ~ 10 < 0.1 < 2500 < 1000 0.5 - 3 ~ 15 ~ 18 200-700

Mn 5 - 300 30-100 0.5 - 1 < 1000 ~250 10-1000 ~27 ~ 200Ni 0.5-100 5 - 10 20 - 50 ~ 300 < 5000 10-100 ~0.5 < 20 ~7 ~ 75 ~ 50

Pb 1-300 1 - 5 1 - 5 6-100 < 2500 100-500 1 - 20 < 50 ~ 8 60-760 100-300

Sb < 1 < 80 < 5 ~ 5 100-500

Se 0.2 - 3 ~ 1 ~ 0.1 < 10 3 - 6 ~ 0.2 ~ 0.08Sn < 10 3 - 100 ~500 ~ 8

Tl ~ 1 0.04-3 ~ 0.25V 1-100 5 - 50 100-200 ~2

Zn 1-1000 ~20 ~ 10 ~ 2 % 300-800 5 - 150 < 30 ~ 150 1-2 % ~1000

unit :ppmw =mg/kg,

dry


Vanadium corrosion by oil ashVanadium corrosion by oil ash

Oxidation of iron viaOxidation of iron via

NaNa22O.6VO.6V22OO55 + Fe <=> + Fe <=>NaNa22O.VO.V22OO44 .5V .5V22OO55 + + FeO FeO

NaNa22O.VO.V22OO44.5V.5V22OO5 5 + ½ O+ ½ O22

<=> Na<=> Na22O.6VO.6V22OO55

NaNa22SOSO44 + yV + yV22OO55 <=> <=>NaNa22O.yVO.yV22OO55 + SO + SO33

(y = 1, 3 or 6) (y = 1, 3 or 6)Inhibition by magnesium:Inhibition by magnesium:

3MgO + V3MgO + V22OO55 <=> 3MgO.V <=> 3MgO.V22OO55


Behaviour of trace elements in coalBehaviour of trace elements in coalcombustion flue gasescombustion flue gases

(FGD = flue gas(FGD = flue gas desulphurisation desulphurisation, PM = particulate matter), PM = particulate matter)

Typical emissions (Typical emissions (µµµµg/MJ) :g/MJ) :

MercuryMercury HgHg 0.5 - 140.5 - 14

Antimony Antimony SbSb < 0.1 - 2.4< 0.1 - 2.4Arsenic Arsenic AsAs 0.1 - 4.20.1 - 4.2BerylliumBeryllium BeBe < 0.1 - 1.4< 0.1 - 1.4CadmiumCadmium CdCd < 0.1 - 3.0< 0.1 - 3.0CobaltCobalt CoCo < 0.1 - 6.8< 0.1 - 6.8ChromiumChromium CrCr < 0.1 - 51< 0.1 - 51LeadLead PbPb 0.6 - 290.6 - 29ManganeseManganese MnMn 1.1 - 221.1 - 22NickelNickel NiNi 0.3 - 400.3 - 40SeleniumSelenium SeSe <0.1 - 130<0.1 - 130


Trace elements partitioning during combustionTrace elements partitioning during combustionor or gasificationgasification: Class I,II,III elements: Class I,II,III elements


Relative enrichment factor (RE)Relative enrichment factor (RE)

Bottom ashBottom ash Fly ashFly ash

Class IClass I RE ~ 1RE ~ 1 RE ~ 1RE ~ 1

Class IIClass II RE ~ 0.7RE ~ 0.7 RE 1.3 ~ 4RE 1.3 ~ 4

Class IIIClass III RE << 1RE << 1 RE >> 10RE >> 10

100100

fuelfuel inin ashash %% xx

fuelfuel inin ionionconcentratconcentrat elementelementashash inin ionionconcentratconcentrat elementelement

RERE =


Effect of chlorine on trace element volatilityEffect of chlorine on trace element volatilityIncineration 0 % chlorine Incineration 10 % chlorine

Principal species

Volatilisationtemperature

°C

Principal species

Volatilisationtemperature

°CChromium CrO2/CrO3 1613 CrO2/CrO3 1611

Nickel Ni(OH)2 1210 NiCl4 693Beryllium Be(OH)2 1054 Be(OH)2 1054

Silver Ag 904 AgCl 627Barium Ba(OH)2 849 BaCl2 904

Thallium Tl2O3 721 TlOH 138Antimony Sb2O3 660 Sb2O3 660

Lead Pb 627 PbCl4 - 15Selenium SeO2 318 SeO2 318Cadmium Cd 214 Cd 214Osmium OsO4 41 OsO4 41Arsenic As2O3 32 As2O3 32Mercury Hg 14 Hg 14


Partitioning of class I, II, III trace elementsPartitioning of class I, II, III trace elementsduring pulverised coal combustionduring pulverised coal combustion


Trace elementTrace elementpartitioning duringpartitioning during

pulverised coalpulverised coalcombustioncombustion

0

2

4

6

8

As B Cd Cr Hg Ni Pb Se

% in

pu

t b

esid

es c

oal

fu

el

limestone

FGD water

0

2

4

6

8


% in

pu

t b

esid

es c

oal

fu

el

limestone

FGD water

0

20

40

60

80

100


% o

utpu

t

flue gas

FGDresiduefly ash

bottom ash

0

20

40

60

80

100


% o

utpu

t

flue gas

FGDresiduefly ash

bottom ash

↑↑↑↑ output output

→→→→ input input

StudstrupStudstrup 3, Denmark 3, Denmark


Effect of fuel type and furnace type onEffect of fuel type and furnace type ontrace element emissionstrace element emissions

Process Heavy fueloil spray

combustion

Pulverisedpeat

combustion

Grate peatcombustion

Pulverisedcoal

combustion

CirculatingFBC peat

Particles controlefficiency, %

- 98.7 - 99.5 59 - 81 95.6 - 99.5 99.5 - 99.8

Emissions µg/MJ

Hg 0.0011 0.11 0.10 0.12 0.03

As 1.5 < 1.5 - 2.3 2 - 10 2 - 39 < 0.1 - 1.6

Be < 0.004 0.05 0.1 - 1.5 5 0.01 - 0.3

Cd 0.008 < 0.002 - 0.13 0.8 - 4 0.5 -1.8 0.1 - 0.4

Co 3 0.3 - 1.2 0.06 - 0.2 1 - 22 0.3 - 4Cr 3 3 - 79 0.6 - 3 8 - 230 0.7 - 1.3

Mn < 14 10 - 26 17 - 31 2 - 230 0.6 - 6

Mo 3 < 1 - 11 < 0.07 - 0.9 < 1 -41 < 1.5 - 2.3Ni 310 - 540 < 33 - 54 < 1 - 5 < 15 - 170 9 - 13

Pb 5 3 - 4 40 - 200 20 - 120 1 - 11

V 1300 4 - 6 0.7 - 7 10 - 88 9Zn 15 < 6 - 12 7 - 37 20 - 220 1 - 11


Controlling trace elements emissionsControlling trace elements emissions

Most concern:Most concern: Hg, Se, B, As,Hg, Se, B, As, Cd Cd,, Pb Pb class III/IIclass III/IILess concern: Less concern: CrCr, Cu, , Cu, NiNi, V, , V, ZnZn class II/ Iclass II/ I

Class I and II in bottom ash and (enriched) in fly ashes: Class I and II in bottom ash and (enriched) in fly ashes: →→→→removal depends mainly on dust control system (and itsremoval depends mainly on dust control system (and itsefficiency for 0.1 - 1 efficiency for 0.1 - 1 µµµµm fines)m fines)

Class II and III can be (more) effectively removed by the Class II and III can be (more) effectively removed by theflue gas flue gas desulphurisation desulphurisation system (Hg ~ 40%, Se ~70%)system (Hg ~ 40%, Se ~70%)

Specific methods based onSpecific methods based on sorbents sorbents can be used, such ascan be used, such asactivated carbon, clays and activated carbon, clays and aluminum aluminum silicates.silicates.

For coal combustion / For coal combustion / gasificationgasification not (yet) widely used, for not (yet) widely used, forwaste incinerators often used for Hg and As, waste incinerators often used for Hg and As, CdCd, , PbPb


Trace element removal by wet FGDTrace element removal by wet FGDdownstream of particulate controldownstream of particulate control

Removal efficiency % Outlet concentration µg/m³STPSTP

Hg ~ 50 ~ 1.5

Se ~ 60 ~ 10Be ~ 80 ~ 250

Fly ash 90 ~ 99 1000 ~ 10000


Sorbents Sorbents forforheavy metalsheavy metals

Sorbent Element Temperature range

Based on zeolites- impregnated with sulphur- impregenated with iodides- Ag and Hg ion exchanged

Hg low temperatures,up to 400EC

Based on activated carbon- activated carbon

- activated carbon impregnated withsulphur, chlorine, iodides

- oxidised activated carbon

Hg

at highertemperatures also

Cd, Pb

low temperatures,up to 300EC

Siliceous materials- Mg, Ca, Al silicates

- Mixed silicates, silicate -fly ashmixtures, impregnated siliceous

materials

V, Pb, Ni, Zn

at low temperaturesalso Hg, Cd

high temperatures 600-1000EC

low temperatures e.g. < 100EC

Based on alumina- activated alumina gel,

- alumina coated steel wool, - alumina impregnated with alkali

carbonate or phosphate

Pb at up to 700EC

Calcium compounds- hydrated lime/fly ash

- limestone/fly ash, limestone/silica- hydrated lime + Sn, limestone,

calcium chloride

Hg, Zn, V, Ni at low temperature

As at hightemperature

Hg at up to 300-400EC,

V, Ni, As at high temperatures

Other materials- MgO, Mg(OH)2,

- Cr, Ni compounds- Fe compounds, e.g. blast furnace

dust

Hg, V, Ni, Pb, As V, Ni at up to 550EC

As at high temperatures


MercuryMercury (from coal) (from coal)partitioningpartitioning


MercuryMercuryemissions fromemissions from

coal fired boilerscoal fired boilers(US)(US)

unit: mg/GJ,1 GJ ~ 300 m3

STP flue gas

Mercury in US coalMercury in US coal::


Mercury species transformationsMercury species transformations during pulverised coal combustion during pulverised coal combustion


Mercury emissions controlMercury emissions controlFilter + wet scrubber Filter + wet scrubber versusversus ESP + wet scrubber ESP + wet scrubber


Mercury emissions controlMercury emissions controlInjection of activated carbon and hydrated lime at filter inletInjection of activated carbon and hydrated lime at filter inlet

HgClHgCl22

Hg°Hg°


Control of mercury emissions - #1 of 2Control of mercury emissions - #1 of 2•• Low temperaturesLow temperatures

–– ad-/ad-/abab-sorption on activated carbon-sorption on activated carbonHgClHgCl22: : physisorptionphysisorption, Hg: , Hg: chemisorptionchemisorption, more efficient, more efficientwith a sulphur, chlorine or iodine - impregnated with a sulphur, chlorine or iodine - impregnated sorbentsorbent

–– injection of Na injection of Na22SS44 and removal of and removal of HgS HgS in acid scrubber : in acid scrubber :

•• HgClHgCl22 + Na + Na22SS44 →→→→ HgSHgS + 3 S + 2 + 3 S + 2 NaClNaCl

•• HgHg°° + + NaNa22SS44 →→→→ HgSHgS + Na + Na22SS33

•• NaNa22SS44 + 2 + 2 HClHCl →→→→ HH22S + 3 S + 2 S + 3 S + 2 NaClNaCl

•• HgClHgCl22 + H + H22SS →→→→ HgS HgS + 2 + 2 HClHCl

•• HgHg°° + S + S →→→→ HgSHgS


Control of mercury emissions - #2 of 2Control of mercury emissions - #2 of 2

•• (..... Low temperatures: (..... Low temperatures: ))–– sodium chlorite (NaClOsodium chlorite (NaClO22) in acid scrubber for ) in acid scrubber for HClHCl–– SOSO22 + activated carbon (for Hg°) + TMT (for Hg + activated carbon (for Hg°) + TMT (for Hg2+2+))–– aluminium silicatesaluminium silicates–– oxidation by Hoxidation by H22OO22 and wet scrubbing and wet scrubbing

•• High temperatures:High temperatures:–– Ca/Mg-basedCa/Mg-based sorbents sorbents, fly ash, Ca(OH), fly ash, Ca(OH)22++SnSn–– some metals:some metals: Cr Cr,, Ni Ni, Fe-compounds, Fe-compounds


Removal of mercury with activated carbonRemoval of mercury with activated carbon(140°C, inlet 20 (140°C, inlet 20 µµµµg/mg/m³³ Hg) Hg)

Effect of particle size and contact timeEffect of particle size and contact time Effect of particle size and C/Hg ratioEffect of particle size and C/Hg ratio


Akali Akali in fuels in fuels (mg/kg, dry)(mg/kg, dry)

Coal Lignite Peat Orimul-sion™

Woodsawdust

Straw RDF Autoshred-der res.

Scraptyres

Sew.sludge

Blackliquorsolids

Na 100 -1500

100 -300

~ 400 ~ 2000 ~ 40 100 -5000

3000 -5000

~ 10000 200 -600

~ 2000 15 - 20 %

K 50 -3000

100 -1000

~ 700 ~ 300 ~ 500 5000 - 10000

2000 -3000

~ 3000 200 -600

~ 6000 ~ 1 %


Natrium Natrium in coal :in coal :�� release of release of NaNa during heat-up during heat-up�� relation between relation between Na Na & & ClCl,,�� NaNa-vapour in PFBC flue gas-vapour in PFBC flue gas

��

��

illinois coal


Sodium / ash interactions in furnacesSodium / ash interactions in furnaces


Vapour pressuresVapour pressures

of alkali speciesof alkali species

↑↑ Saturated vapour pressureSaturated vapour pressure

of alkali chlorides of alkali chlorides NaClNaCl, , KClKCl

→→ Alkali saturation pressures Alkali saturation pressuresand concentrations in coal-and concentrations in coal-derived gasderived gas


Vapour phase alkali in PFBCVapour phase alkali in PFBC((OtaniemiOtaniemi, Finland, 770-920°C, 10 bar), Finland, 770-920°C, 10 bar)

unit : weight-ppb


Alkali in flue gas/Alkali in flue gas/gasifiergasifier product gas product gas

•• In In gasifiergasifier product gas product gas chlorides, hydroxides, sulphidechlorides, hydroxides, sulphideIn flue gasIn flue gas <1000°C : chlorides <1000°C : chlorides + SO2+ SO2 →→ sulphates sulphates

•• Comparison PGBC / PFBG of peat, 900Comparison PGBC / PFBG of peat, 900°°C :C :alkali ~2 orders of magnitude higher in fuel gas than in flue gasalkali ~2 orders of magnitude higher in fuel gas than in flue gas

•• Maximum alkali for expansion turbine inlet:Maximum alkali for expansion turbine inlet: 24 24 ppbppbassuming air ratio 2.5 for for gas turbine:assuming air ratio 2.5 for for gas turbine: 84 84 ppb ppb in fuel gasin fuel gas

•• 90 - 99% of the alkali has to be removed90 - 99% of the alkali has to be removed


•• Species and concentrations:Species and concentrations:350°C350°C 600°C600°C 1227°C 1227°C

PotassiumPotassium KK -- KClKCl K > K > KCl KCl > KBO> KBO22SodiumSodium NaNa -- NaClNaCl Na Na > > NaCl NaCl > NaBO> NaBO22

•• NaNa+K in +K in gasifier gasifier gas, gas, ppmwppmw ~10~10-5-5 ~0.8+~1~0.8+~1 for Shell for Shell gasifiergasifier•• Below 530-570°C: alkali concentrations below turbine inlet limitsBelow 530-570°C: alkali concentrations below turbine inlet limits

•• Temperature below 600°C:Temperature below 600°C: all alkali as chlorides and sulphates all alkali as chlorides and sulphatesparticles, which will be collected with the particles, which will be collected with the fly ashfly ash

•• Temperature above 600Temperature above 600°°C:C: ¬¬ Cooling and removal as particles Cooling and removal as particles Absorption using Absorption using aluminumaluminum

silicates (600-1000silicates (600-1000°°C)C)

Alkali removal from flue gas/Alkali removal from flue gas/gasifiergasifier product gas product gas


•• SorbentsSorbents:: KaoliniteKaolinite, Bauxite, , Bauxite, EmathliteEmathlite

•• Reductions achieved: close to 100%Reductions achieved: close to 100%

•• Chemical fixation in the material. Chemical fixation in the material. E.g.E.g. for bauxite: for bauxite:AlkCl AlkCl + H+ H22O + AlO + Al22OO33.xSiO.xSiO22(s) (s) →→→→ AlkAlO AlkAlO22.xSiO.xSiO22 + 2HCl + 2HCl

•• Sorption can be combined with hot gas particulate controlSorption can be combined with hot gas particulate controlin moving granular bed filters, allowing 2-5% alkaliin moving granular bed filters, allowing 2-5% alkali

Alkali removal from flue gas/Alkali removal from flue gas/gasifiergasifier product gas product gasby solid by solid sorbents sorbents at 600-1000°Cat 600-1000°C


Alumina Alumina silicate silicate sorbentssorbents for alkali for alkali600-1000°C600-1000°C

SiO22

%-wtAl22O33

%-wt(Na,K)22O

%-wt(Ca,Mg)O

%-wtP22O55

%-wtOthers%-wt

Emathlite ~ 69 ~ 8 ~ 1 ~ 9 ~ 3 ~ 10

Kaolinite ~ 51 ~ 44 ~ 0 ~ 0 ~ 0 ~ 5

Bauxitic kaolinite ~ 36 ~ 58 ~ 0 ~ 0 ~ 0 ~ 6Attapulgite ~ 62 ~ 10 ~ 1 ~ 10, ~ 5 ~ 1 ~ 2

Ca-montmorillonite ~ 54 ~ 18 ~ 2 ~5, ~ 13 ~ 0 ~ 8

Procedure :Procedure :inject inject sorbentsorbent into gas and collect into gas and collect sorbent sorbent in particulatein particulate

control systemcontrol system

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