Thermodynamic modeling of biomass combustion and ash chemistry applications

Daniel Lindberg1

Rainer Backman2, Patrice Chartrand3,Mikko Hupa1

1. Åbo Akademi University, Finland2. Umeå University, Sweden

3. Ecole Polytechnique de Montreal, Canada

1

Source: European Commission’s Market Observatory data for 2008

Solar1.1%

Hydro18.6%

Wind6.7%

Biomass and wastes

69.7%

Geothermal 3.8%

EU-27, gross inland energy consumptionPrimary raw materials

2

Biofuels – Waste derived fuels – “Opportunity fuels”

Woodchips Saw dust Bark

Forest residues Annual crops Prunings Shells, husks & hulls Olive stones

Biorefinery residues Pulp & paper process by-

products

Refuse derived fuels (RDF)

Waste sludges Recovered waste wood Meat and bone meal Chicken litter

3

Figure courtesy: Mälarenergi Ab & Foster Wheeler

Ash Forming Matter in Biomass Combustion –Research Topics

Characterization of AFM Release of AFM in furnace Fly Ash Formation Bed/Grate Reactions Fouling Superheater Corrosion Understanding Fuel Mixtures

4

Fouling and corrosion due to unsuitable fuel mix

5

Thermodynamic modeling & Ash chemistry

Ash deposition

Superheatercorrosion

Bed agglomeration

Traceelement

emissionsBlack liquor combustion

Furnaceslagging

6

ExampleBlack liquor recovery boiler

7

+

Black Liquor

Wood

LigninFibre

WhiteLiquor

(NaOH + Na2S)

Fibre

Kraft Pulping Process

155oC900 kPa

A 1000 t/d Kraft Pulp Mill

0

500

1000

1500

2000

2500

3000

Chemicals

Wood

DissolvedOrganics

Fibre

Chemicals

t/d BlackLiquor

Pulp

8000 ~ 10,000 t/d weak black liquorproduces 1500 t/d BL d.s.

As-Fired Black Liquor Composition (750 liquor samples; All Wood Species)

Typical RangeSolids content, % 72 65 – 85HHV, MJ/kg 13.9 12.5 – 15.5

C, wt% d.s. 33.9 30 – 40H 3.4 3.2 – 4.0O 35.8 34 – 38Na 19.6 17 – 22S 4.6 3.6 – 5.6K 2.0 1 – 3Cl 0.5 0.1 – 4

Com

posi

tion

Deposition (Na2SO4,KCl)

Corrosion

Molten salts in the recovery boiler

800-1000°C

1000-1300°C

800-1000°C

200-450°C 500-800°C

Smelt: Na2S+Na2CO3

Smelt bed

Smelt Spout

Na2CO3 + Na2S

Smelt

Equilibria with Molten Phases:Black Liquor Recovery Boiler and Alkali

Salts

Lars Pejryd & Mikko Hupa (1984) Bed and furnace gascomposition in recovery boilers – advancedequilibrium calculations. Tappi Pulping Conference

Equilibrium modeling of furnace gas and smelt bedof a kraft recovery boiler

Non-ideal interactions for liquid Na2CO3-Na2Soptimized by Gunnar

Thermodynamic databases for alkali saltsThermodynamic properties of alkali salts Na-K-S-C-O-Cl-H system re-evaluated

Lindberg (2007) Thermochemistry and meltingproperties of alkali salt mixtures (PhD thesis)

Lindberg, Backman & Chartrand. (2007) Journal of Chemical Thermodynamics. Thermodynamic evaluation and optimization of the (NaCl + Na2SO4 + Na2CO3 + KCl + K2SO4 + K2CO3)

Covers all Na-K components from reducing to oxidizing conditions

FTPulp database in Factsage

15

16

My PhD defense in 2007

0102030405060708090

100

400 600 800 1000

Mel

t fra

ctio

n [W

t%]

T [°C]

T0 T15

T70 T100

T0, First melting temperature: Corrosion T15, Sticky temperature: Deposition T70, Flow temperature: Deposit buildup T100, Complete melting temperature: Flow properties

Melting properties of alkali salts & characteristic temperatures

500

520

540

560

580

600

620

500 520 540 560 580 600 620Measured

Cal

cula

ted

FrederickSingbeilWalsh

Solidus temperature (T0) of superheaterdeposits from BL recovery boilers

Solidus measured withDTA

Deposits containNa+,K+/SO4

2-,CO32-,Cl-

Thermodynamic modelpredicts solidus (T0) within±10°C

18

0

20

40

60

80

100

120

140

(Na,K)2SO4 + 1.3% Cl, T0=522°C

Cor

rosi

on la

yer t

hick

ness

, m

(Skrifvars et al. 2008)19

Liquidus temperatures (T100) of Na+,K+/Cl-,SO42-,CO3

2-

mixtures

500

600

700

800

900

1000

500 600 700 800 900 1000T (meas.) / °C

T(ca

lc.)

/ °C

Sementsova 1956

Bergman 1958

20

Stickiness of Partially Molten ParticlesEntrained Flow Reactor Tests in Toronto

0

0.02

0.04

0.06

0.08

0.10

0.12

0 10 20 30 40 50 60 70 80 90 100

Fraction molten phase (wt-%)

Dep

ositi

on (m

g/g-

cm2 -

min

)

(Tran et al. 2002)21

Åbo Black Liquor Recovery Boiler Advisor

Rainer Backman, Gunnar Eriksson, Kaj Sundström: The Recovery Boiler Advisor - Combination of Practical Experience and Advanced Thermodynamic Modelling, Proceedings: 3rd Colloquium on Process Simulation, June 12-14, 1996

An application of ChemApp on the chemical processes in the kraft recovery boiler

Windows-based program for boiler designers and operators to predict chemical processes in the furnace and in flue gas channels

One-dimensional, multi-stage chemistry model using chemical equilibrium calculations, physical models for deposit behavior and experimental information for combustion characteristics

Why thermodynamic modeling is useful for BL combustion

Well-defined ”ash” chemistry (Na-K salts) Alkali salts have good contact in smelt

bed High liquid content in inorganic particles

down to 500 °C + molten phase has lowviscosity fast reactions

Concepts T15 and T70 work for recoveryboilers

25

ExampleBiomass and waste boilers

26

100

90

80

70

60

50

40

30

20

10

0

80

70

60

10

20

30

40

50

90

100 00 10 20 30 40 50 60 70 80 90 100

CaO+MgO

K2O+Na2O SiO2

FossilPeat

WoodForest residueBarkWaste wood

woo

wood derived fuels

Agricultural residue

ÅA fuel database

Major ash-forming elements in different fuels

Ash phases

Silicates Minerals in fuels Polymeric phases Ex. KAlSi3O8

High viscosity liquid Quasichemical or

associate models for thermodynamics

Salt-like phases Various formation

reactions Simple ionic phases Examples KCl, CaSO4

Low viscosity liquid Sublattice models for

thermodynamics

28

800 900 1000 1100 1200 1300 1400 15000

2

4

6

8

10

12

14

16

Temperature, °C

g/kg

fuel

Ca3(PO4)2-s

(CaOMgO)SiO2-s

CaOMgO-sCaCO3-s

K2SO4-l

K2CO3-lLiquid

K2(

CO

3,SO

4)-s

Fly Ash Composition of SalixMulticomponent Multiphase Thermodynamic Calculation

(Hupa et al. 1999)29

Availability of thermodynamic dataAccurate existing data Low-alkali silicates (coal,

peat)

Alkali salt mixtures (black liquor)

Selected Na-K-Ca-Mg-Zn-Pb salt mixtures (on-going) (biomass, waste)

Improvements needed K2O-rich silicates (straw)

Phosphate mixtures (on-going) (agricultural fuels)

Unified database for heavy metals

30

Molten saltsOn-going and future developments Addition of Ca-Mg-Pb-Zn-P to Na-K-S-C-O-

Cl-H system underway to cover all major salt-like phases in biomass and wastecombustion

New approach to include phosphorus in the liquid phase

31

32

(Na,K)Cl(ss) + CaSO4(s) + K2Ca2(SO4)3(s2)

Liquid + (Na,K)Cl(ss) + CaSO4(s)

Liquid + CaSO4(s)

Liquid

Experimental data by Rubleva & Bergman (1956) J. Gen. Chem. USSR

CaSO4 - (NaCl+KCl)

mole CaSO4/(CaSO4+NaCl+KCl)

T(C

)

0.0 0.2 0.4 0.6 0.8 1.0500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

Liquid contains Ca2+, K+, Na+//SO42-, Cl-

Quaternary reciprocal systemNo additional model parameters

Phosphate chemistry – new results

33

615

K3P

O4

K4P

2O7

Liquid

KP

O3

615 645

1074

1620

1104

811740709

K2O - P2O5

n(K2O)/(n(K2O)+n(P2O5))

T(o C

)

0.5 0.6 0.7 0.8 0.9 1.0400

600

800

1000

1200

1400

1600

Liquid

Liquid + K3PO4

KCl + K3PO4

733

1620

771

Liquid

Liquid + K3PO4

KCl + K3PO4

n(K3PO4)/(n(K3PO4)+n(KCl))

T(o C

)0.0 0.2 0.4 0.6 0.8 1.0

400

600

800

1000

1200

1400

1600

731-733 °C

K3PO4-KCl mixtureModel vs experiment

35

Example for biomass boilers

Mueller, Skrifvars, Backman, Hupa (2003) in ”Progress in CFD”

36

More of Gunnar’s contributionsto combustion applications

37

38

Thermodynamic modeling of ashchemistry in combustion

Useful tool for modeling alkali salt melting and reactions in BL recovery boilers Bed behavior, corrosion, deposit formation

Useful tool for predicting ash chemistry in biomassand coal combustion Well-defined databases for coal ashes and slags Database for salt phases including Ca, Mg, Pb, Zn, and

P is being developed Databases for alkali-rich silicates need development Limitations of kinetics, fuel speciation, combustion

techniques need to be addressed for proper use of thermodynamic modeling

Gratulerar Gunnar

önskaralla vänner vidÅbo Akademi