combustion kinetics (4) - nccrdnccrd.in/iciwsindia2015-assets/docs/ranzi4.pdf · combustion...

Winter Combustion School Madras December 15, 2015

Combustion Kinetics (4)

Solid Fuel Combustion

Eliseo Ranzi

Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”Politecnico di Milano


Outline 2

Combustion of solid fuels, characterization of solid fuel (plastics, coal, biomass, RDF), multistep kinetics of devolatilization and pyrolysis, secondary gas phase reactions, particle and reactor scale.


3Solid Fuel Pyrolysis, Gasification and Combustion

Yin, C , Rosendahl , LA , Kaer , SK Prog. Energy Comb. Science 34 (2008) 725

A complex multi-componentmulti-phase

and multi-scale problem.

Biomass Travelling Grate Combustor


AbstractDetailed chemistry of thermal treatments of solid fuels (large numbers ofspecies and reactions) requires careful simplifications.This multi-component and multi-phase problem requires to apply

chemical lumping procedures at four different levels:

1- Characterization of the Solid Fuel in terms of Reference Components2- Multistep Kinetic Models of Devolatilization of Reference Components3- Heterogeneous Gas-Solid Reactions of Char with O2/H2O/CO2

4- Secondary Gas-Phase Reactions of Tars and Volatile Components

The comprehensive description of coupled transport and kinetic processes, bothat particle and reactor scale, increases the mathematical complexity of solid fuelgasification and combustion.

Two application examples at the reactor scale:Countercurrent Coal or Biomass GasifierBiomass Combustor on a Travelling Grate

illustrate the viability of this approach.

A compromise needs to be found between computation efforts and prediction accuracy.

4


5Mathematical Modeling of a Travelling Grate Combustor

Requires at least to analyse the three following features:- Solid Fuel Characterization- Kinetics

Pyrolysis of Solid Fuel (release of volatile components)Heterogeneous Reactions (char gasification and combustion)Homogeneous Reactions of gases and tars

- Mathematical Model Balance EquationsParticle and Reactor Scale

Courtesy Garioni-Naval_2012


Solid Fuel Combustion 6

Coal

Plastics

Biomasses

MSW and RDF

Fuel Characterization

Kinetic schemes ofSolid Fuel DevolatizationChar GasificationSecondary Gas Phase Reax

Balance equations at the particle and reactor scale


Outlines

•Solid Fuels Characterization•Biomass (Cellulose, Hemicellulose, Lignins, and Extractives)•Coal, Plastic and Refuse Derived Fuels

•Kinetic Models•Solid Fuel Pyrolysis and Devolatilization•Char Gasification and Combustion•Secondary Gas-Phase Reactions

•Comprehensive Multi-Scale and Multi-Phase Model •Balance Equations at Particle and Reactor Scale

•Application Examples•Countercurrent Coal and Biomass Gasifier •Biomass Combustor on a Travelling Grate

7


8SOLID FUELS

Coal Plastics Biomasses

MSWMunicipal Solid

Wastes

Solid fuels

Mechanical selections

Refuse Derived Fuel (RDF)

Plastics(PE, PP, PET, PS)

Biomass(Wood, Tissue and Lignocellulosic..)


straw

cellulosehemicellulose

agriculturalresidues

miscanthus

lignins

0 0.25 0.5 0.75 10

0.5

1.5

1

2

O/C atomic

H/C

atom

ic

Anthracite

lignitebituminous

coals

After: R.H. Hurt (1998) "Structure, properties, and reactivity of solid fuels." 27th Symposium on Combustion. 2887-2904

Solid Fuels in Van Krevelen Diagram.

MSWRDF

PMMA

PE/PP

PS

ABS

naylon-6

Plastics

9


Solid Fuels in Van Krevelen Diagram. 10

0

0.5

1

1.5

2

0 0.2 0.4 0.6 0.8

H/C

Ato

mic

Rat

io

O/C Atomic Ratio

Van Krevelen Diagram

RDF

Coal

BiomassPlastics


11

Physical structure of Biomass spans several orders of magnitude, from the atomic level of biopolymers (10-10 to 10-9 m) to the microstructured cellular network (10-5 to 10-3 m) to the macrostructures of thick particles and pellets (10-3 to 10-2 m) and finally to trees and grasses.

Multi-Scale Nature of Biomass.

Mettler et al., Energy Environ. Sci., 2012, 5, 7797


Himmel et al., Biomass Recalcitrance: Engineering Plants and Enzymes for Biofuel Production. Science 2007 (2) 315; 804-807

Multi-Scale Nature of Cellulose.

Corn stover (scale 1 m) Scanning electron micrograph of the cross section of maize stem

(scale 50 μm)

Atomic force micrograph of the cellwall surface. The diameter of microfibril is 3-5 nm (scale 50 nm)


Biomass composition:Cellulose, Hemicellulose and Lignin

Cellulose is the structural component of the primary cell wall of green plants. Cellulose is a linear polymer of up to 10,000 D-glucose molecules (C6H10O5)n

13

H-bonds between polymer chains


Microfibril of Cellulose Cristallyte

Himmel et al., Biomass Recalcitrance: Engineering Plants and Enzymes for Biofuel Production. Science 2007 (2) 315; 804-807

Pectin (poly-galacturonic acid)forms a gel that glues the cell-wall components together.


Biomass composition:Cellulose, Hemicellulose and Lignin

15

Hemicellulose is a complex mixture of different sugar monomers (xylose, mannose, galactose, arabinose,..)being xylose the most abundant. It is the biomass component with a high char formation tendency


16Molecular Composition of Biomass

http://digital.library.okstate.edu/oas/oas_image_files/v72/p51_56Fig1.jpg

Cellulose and hemicellulose chains are embedded in lignin.


Building blocks of lignin 17

lignin structure:chemical bonds and functional groups

Custodis, V. B., Bährle, C., Vogel, F., & van Bokhoven, J. A. (2015). Phenols and aromatics from fast pyrolysis of variously prepared lignins from hard-and softwoods. Journal of Analytical and Applied Pyrolysis, 115, 214-223.

There are three main alcohol monomers, with different methoxylation degree.

Coniferyl Synapyl Coumaryl

Lignin is a complex macromolecule with a high molecular mass (>10,000 uma)

It confers mechanical strength to the plant.


18

F. Streffer (2014) Lignocellulose to Biogas and other Products. JSM Biotechnol Bioeng 2(1): 1023


19

Wood species Cellulose Hemicellulose Lignin

SoftwoodsPicea glauca 41 31 27Abies balsamea 42 27 29Pinus strobes 41 27 29Tsuga canadensis 41 23 33Norway spruce 46 25 28Loblolly pine 39 25 31Thuja occidentalis 41 26 31

HardwoodsEucalyptus globulus 45 35 19Acer rubrum 45 29 24Ulmus americana 51 23 24Populus tremuloides 48 27 21Betula papyrifera 42 38 19Fagus grandifolia 45 29 22Agricultural residuesCorn stover 40 17 25Wheat straw 30 20 50

Switchgrass 45 12 30

Fengel D, Wegener G. Wood. Chemistry, ultrastructure, reactions. Walter de Gruyter: Berlin, 613 pp (1984).Zhang YP. Reviving the carbohydrate economy via multi-product lignocellulose biorefineries. J Ind Microbiol Biot 35:367-375 (2008).

Biochemical Analysis of Biomasses

Extractives:The biomass material that is soluble in either water or ethanol during exhaustive extraction.


Extractives 20


Water soluble extractives Phenolic Compounds

-H2O

Flavonoids

Condensed Tannins

Phenolic Acids

-H2O

Hydrolysable Tannins

+ Sugar


Resin Acids

Fatty acids

-H2O

Water insoluble extractives

Resins

+ Glycerol

Fats/OilsTriglycerides

Terpens Monoterpens

Carotenoids


Biomass Characterization: Proximate Analysis and TGA23

TGA is a recording of mass changes, as a function of a combination of temperature with time.

Devolatilization(300-600 °C)

100

80

60

40

20

0

Ashes

Time/Temperature

100

80

60

40

20

0

100

80

60

40

20

0

Drying(100°C)

Char Gasificationor Combustion(800-1200 °C)

Volatiles

Fixed Carbon and Ash

Humidity

Proximate Analysis is derived from Thermo Gravimetric Analysis (TGA)

The proximate analysis gives moisture, volatile content VM (when heated to 950 C), the remaining fixed carbon FC , the Ash (mineral) together with the high heating value (HHV).


Biomass: Proximate and Ultimate Analysis24


Proximate Analysis of typical Biomasses

25

A. Williams, J.M. Jones, L. Ma, M. Pourkashanian ‘Pollutants from the combustion of solid biomass fuels’ Progress in Energy and Combustion Science 38 (2012) 113-137


Biomass Composition and Proximate Analysis 26

http://www.ieabcc.nl/workshops/task32_Lyon/full%20page/04%20David%20Baxter.pdf

The proximate analysis gives moisture, volatile content VM (when heated to 950 C), the fixed carbon FC remaining at that point, the Ash (mineral) together with the high heating value (HHV).

Proximate Analysis

Wt%

Coal

Biomass


27Biomass Composition

http://www.ieabcc.nl/workshops/task32_Lyon/full%20page/04%20David%20Baxter.pdf

The ultimate analysis gives the composition of the biomass in weight percentage of Carbon, Hydrogen and Oxygen as well as Sulfur and Nitrogen.

Ultimate /Elemental Analysis (wt%)

Coal

Biomass


Proximateand Ultimate (Elemental) Analysis

of typical Biomasses

28

A. Williams, J.M. Jones, L. Ma, M. Pourkashanian ‘Pollutants from the combustion of solid biomass fuels’ Progress in Energy and Combustion Science 38 (2012) 113-137

C/H/O atomic balances allow to define biomasscomposition in terms of three Reference Components


Ultimate Analysis allows to derive

Biomass composition in terms of

Cellulose, Hemicellulose and Lignins Cotton

% Cellulose % Lignins

% Hemicellulose

Birch Bark

Biomass Characterization

Biomass is considered as a linear combination of Cellulose, Hemicellulose and Lignins

29

Ranzi, E., Cuoci, A., Faravelli, T., Frassoldati, A., Migliavacca, G., Pierucci, S., & Sommariva, S. (2008).Chemical kinetics of biomass pyrolysis. Energy & Fuels, 22(6), 4292-4300

http://images.google.it/imgres?imgurl=http://www.lineasecondaria.it/images/tronco-betulla.jpg&imgrefurl=http://www.lineasecondaria.it/&h=309&w=250&sz=25&tbnid=YSIBB7QOiC4J:&tbnh=112&tbnw=90&hl=it&start=18&prev=/images?q=betulla&svnum=10&hl=it&lr=


http://image.excite.it/www/blog/excite/foto/d109_0986.jpg




5 reference species

3 elemental balances (C, H, O)

3 reference mixtures

BIOMASS


Ultimate Analysis allows to derive

Biomass composition in terms of

Cellulose, Hemicellulose and Lignins Cotton

% Cellulose % Lignins

% Hemicellulose

Birch Bark


Biomass is considered as a linear combination of Cellulose, Hemicellulose and Lignins

31

Ranzi, E., Cuoci, A., Faravelli, T., Frassoldati, A., Migliavacca, G., Pierucci, S., & Sommariva, S. (2008).Chemical kinetics of biomass pyrolysis. Energy & Fuels, 22(6), 4292-4300

Weight fraction of reference components:(daf basis)

Cellulose -C6H10O5- 0.329Hemicellulose -C5H8O4- 0.179LIGH -C22H28O9- 0.253LIGO -C20H22O10- 0.175LIGC -C15H14O4- 0.064

The biomass is described as a linear combination of 5 reference species.

It is then necessary to describetheir pyrolysis behavior






Biomass Characterization 32

P. Debiagi et al (2015) Energy & Fuels, 22(6), 4292-4300.

Hydrophilic (Tannins) and hydrophobic (triglycerides)

extractives allow to extend the applicability of the

characterization method.


Pyrolysis and Devolatilization of Biomass33

http://www.biomasstorrefaction.org/torrefaction/

Torrefied biomass has several benefits over untreated biomass:•Higher calorific value•More homogeneous product•Higher bulk density•Excellent grindability•Durability•Hydrophobic nature/water resistance•No biological activity


Torrefaction 34

Torrefied biomass shows better transportation characteristics (lower handling and storage costs) compatible properties to coal (bulk energy density , heating value) grindability, and hydrophobicity.

Torrefaction reduces investment for co-firing application

Thermal pre-treatment technology, which produces a solid biofuel product with a superior handling, milling and co-firing capabilities compared to other biomass fuels.


35

http://news.mongabay.com/bioenergy/2008/07/torrefaction-gives-biomass-20-energy.html


Van Krevelen diagram for coals, biomass and torrefied biomass.

T.G. Bridgeman , J.M. Jones , I. Shield , P.T. Williams (2008 ) ‘Torrefaction of reed canary grass, wheat straw and willow to enhance solid fuel qualities and combustion properties’ Fuel 87(6) 844 - 856

Torrefaction is the first step of Biomass Pyrolysis Process

Torrefied biomass devolatilises and burns over a shorter temperature range.

Devolatisation profiles of untreated and treated reed canary grass (RCG).

Torrefied biomass has a higher combustion heat (higher fixed carbon).

The advantages are more pronounced at higher torrefaction temperatures.

36


Torrefaction and Pyrolysis are the first steps in Thermal Treatments of Solid Fuels.

MSW

straw

cellulosehemicellulose

agriculturalresidues

miscanthus

lignins

0 0.25 0.5 0.75 10

0.5

1.5

1

2

O/C atomic

H/C

atom

ic

Anthracite

lignitebituminous

coals

RDF

PMMA

PE/PP

PS

ABS

naylon-6

Plastics

It is thus necessary to describethe chemical evolution of the solidfuels (i.e. the reference species )

towards the residual Char

37


Cellulose Pyrolysis.Concerted Reactions and Mechanism of Glucose Pyrolysis and Implications for Cellulose Kinetics

38

V. Seshadri and P. R. Westmoreland ‘Concerted Reactions and Mechanism of Glucose Pyrolysis and Implications for Cellulose Kinetics’ J. Phys. Chem. A 2012, 116, 11997−12013

Formation of levoglucosan from β-D-glucose by dehydration.

Retro-aldol condensation of xylose


Mechanism of formation of C1–C6 organic compounds from glucose

39

Intermediates produced from glucose via concerted reactions in the condensed phase. Glucose is short-lived and rapidly transforms to various melt phase and vapor phase species.

R. Vinu and L. J. Broadbelt (2012) ‘A mechanistic model of fast pyrolysis of glucose-based carbohydrates to predict bio-oil composition’ Energy Environ. Sci., 2012


Ab initio molecular dynamics simulations are performed with α-cyclodextrin to reveal the pathways of cellulose pyrolysis.Homolytic cleavage of glycosidic linkages and furan formation directly from cellulose without

any small-molecule (e.g., glucose) intermediates are obtained.

M. S. Mettler, S. H. Mushrif, A. D. Paulsen, A. D. Javadekar, D. G. Vlachos and P. J. Dauenhauer ‘Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates’ Energy Environ. Sci., 2012, 5, 5414-5424

Contrary to previous pyrolysis work using mm-scale cellulose samples, thin-film pyrolysis enables the study of condensed-phase pyrolysis chemistry under isothermal conditions and minimizes the breakdown of volatile products.

This work combines thin-film technology with first-principles computations to elucidate major condensed-phase pyrolysis paths.

Conversion of cellulose to furans and small oxygenates

α-cyclodextrin is an appropriate surrogate of cellulose.

40


Reaction Pathways of α-cyclodextrin Pyrolysis.

M. S. Mettler et al., Energy Environ. Sci., 2012, 5, 5414-5424

41


Oxygenated species from pyrolysis of cellulose and hemicellulose

42

Shen, D., Jin, W., Hu, J., Xiao, R., & Luo, K. (2015). An overview on fast pyrolysis of the main constituents in lignocellulosic biomass to valued-added chemicals: Structures, pathways and interactions. Renewable and Sustainable Energy Reviews, 51, 761-774.


Average values are shown for thin-film pyrolysis at 500 C with 90% mean confidence intervals.

Compounds from thin-film pyrolysis experiments 43


44

Shen, D., Jin, W., Hu, J., Xiao, R., & Luo, K. (2015). An overview on fast pyrolysis of the main constituents in lignocellulosic biomass to valued-added chemicals: Structures, pathways and interactions. Renewable and Sustainable Energy Reviews, 51, 761-774.

Primary Reaction Paths of Cellulose Pyrolysis

Levoglucosane

5-hydroxy-methyl-furfural

hydroxy-acetaldehyde


Multistep Kinetic Model of Cellulose Pyrolysis

Cellulose

Levoglucosane

DecompositionProducts

Active Cellulose

Char + H2OReaction Kinetic constant

[s-1]Reaction

Heat [kj/kg]

Cellulose → Active Cellulose 8×1013 exp (-45000/RT) 0

Active Cellulose → Acetic Acid + 0.2 Glyoxal + 0.2 CH3CHO + 0.25 HMFU + 0.2 C3H6O + 0.22 CO2 + 0.16 CO + 0.83 H2O + 0.1 CH4 + 0.01 HCOOH + 0.01G{H2} + 0.61 Char

1×109 exp (-30000/RT)

650

Active Cellulose → Levoglucosane 4×T exp (-10000/RT) 490

CELL → 5 H2O + 6 Char 8×107 exp (-31000/RT) -1800

45

Bradbury, A. G., Sakai, Y., & Shafizadeh, F. (1979). A kinetic model for pyrolysis of cellulose. Journal of Applied Polymer Science, 23(11), 3271-3280.Ranzi, E., Cuoci, A., Faravelli, T., Frassoldati, A., Migliavacca, G., Pierucci, S., & Sommariva, S. (2008). Chemical kinetics of biomass pyrolysis. Energy & Fuels, 22(6), 4292-4300. Energy & Fuels, 2008, 4292-4300

These reactions not only describe the residual char (Broido-Shafizadeh model), but also give a guess

of the composition of released tar and gases.


Validation of Cellulose Pyrolysis ModelComparisons with experimental TG data

Temperature °C300 400 500 600

0.1

0.2

0.3

0.4

0.5

.

Levoglucosano

HAA

300 400 500 600

0.1

0.2

0.3

0.4

0.5

Mol

e Fr

actio

n

Levoglucosane

C2H4O

Dati: Radlein D., Piskorz J. (1991)

Low Heating Rates

Antal M.J. et al.(1995-1998)

High Heating Rates

Milosavljievic I., Suuberg E.(1995)

46

250 300 350 400 450 500 550

0.2

0.4

0.6

0.8

1

Resi

duo

• Exp.Modello

1°C/min 80°C/min

10°C/min

250 300 350 400 450 500 550

0.2

0.4

0.6

0.8

1

Resi

duo

• Exp.Modello

1°C/min 80°C/min

10°C/min

600

• ExperimentalPrediction

250 300 350 400 450 500 550

0.2

0.4

0.6

0.8

1

Temperatura °C

Resi

duo

100°C/min

1000°C/min

• Exp.Modello

600



250 300 350 400 450 500 550

0.2

0.4

0.6

0.8

1

Temperatura °C

Resi

duo

100°C/min

1000°C/min

250 300 350 400 450 500 550

0.2

0.4

0.6

0.8

1

Temperatura °C

Resi

duo

100°C/min

1000°C/min

• Exp.Modello

Similar multistep kinetic models are alsodeveloped and validated for

hemicellulose and lignins.


47Multistep Kinetic Model of Cellulose Pyrolysis

Ranzi, E., Cuoci, A., Faravelli, T., Frassoldati, A., Migliavacca, G., Pierucci, S., & Sommariva, S. (2008). Chemical kinetics of biomass pyrolysis. Energy & Fuels, 22(6), 4292-4300. Energy & Fuels, 2008, 4292-4300

The peculiarity of this pyrolysis scheme is the attempt to describe not only solid residue, but also a detailed

composition of released gas and tar species.


48

Validation of Biomass Pyrolysis ModelComparisons with experimental TG data

Biomass devolatilization is then the combination of the pyrolysis of cellulose,

hemicellulose, and lignin


From Biomass to Coal 49

The same approach is used for:

- Coal Characterization

- Multistep Kinetic Model of Coal Devolatilization


50

Nine ‘Reference’ Coals wereselected in a narrow area

by Zhao et al. (1994)

Zhao, Y., Serio, M. A., Bassilakis, R., & Solomon, P. R. (1994). A method of predicting coal devolatilization behavior based on the elemental composition. ‘25th Symposium on Combustion’ 25(1): 553-560. Elsevier.Sommariva, S., Maffei, T., Migliavacca, G., Faravelli, T., & Ranzi, E. (2010). A predictive multi-step kinetic model of coaldevolatilization. Fuel, 89(2), 318-328.

Three reference coals are selected: COAL1 anthraciteCOAL2 bituminousCOAL3 lignite

Again, Elemental Analysis and C/H/O balances allow to define actual coal as a

mixture of three Reference Coals

Coal Characterization


Characterization of the Solid Fuel

5 reference species

3 elemental balances (C, H, O)

3 reference mixtures

BIOMASS COAL

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

60 65 70 75 80 85 90 95 100Carbon (wt %)

Hydr

ogen

(wt%

)

Tomita

Solomon

Fletcher

IFRF

References

COAL3

COAL2

COAL1

CHAR

H

CHARc

COAL


Multistep Kinetic Model of Coal Devolatilization 52

Sommariva, S., Maffei, T., Migliavacca, G., Faravelli, T., & Ranzi, E. (2010). A predictive multi-step kinetic model of coal devolatilization. Fuel, 89(2), 318-328.

A multistep kinetic model was alsodeveloped and validated for the three

reference coals.

Initially the coal forms a metaplastic phase, then, with different mechanisms at low and high temperatures, gas and tar species are released.


53

Pittsburg TARS

0.00

0.10

0.20

0.30

0.40

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg H2O

0.00

0.04

0.08

0.12

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg CO2

0.00

0.01

0.02

0.03

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg CO

0.00

0.01

0.02

0.03

0.04

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg TAR

0.0E+00

2.0E-02

4.0E-02

6.0E-02

8.0E-02

1.0E-01

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Pittsburg TG

0.40

0.60

0.80

1.00

0 10 20 30 40 50(min)

Wei

ght l

oss

300

600

900

1200

T (K)

Pittsburg C2H4

0.000

0.002

0.004

0.006

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg H2O

0.0E+00

5.0E-03

1.0E-02

1.5E-02

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Pittsburg CH4

0.00

0.02

0.04

0.06

0 10 20 30 40 50(min)

Wei

ght f

ract

ion

Pittsburg CO2

0.0E+00

1.0E-03

2.0E-03

3.0E-03

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Pittsburg CO

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Pittsburg C2H4

0.0E+00

4.0E-04

8.0E-04

1.2E-03

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Pittsburg CH4

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

0 10 20 30 40 50(min)

Evol

utio

n ra

te (w

t/min

)

Extensive Validation of Coal Pyrolysis ModelTG Experiments of Solomon et al. (1990)

Solid residue, Tar , COx , H2O, CH4 , C2H4 and their evolution rates

Sommariva, S., Maffei, T., Migliavacca, G., Faravelli, T., & Ranzi, E. (2010). A predictive multi-step kinetic model of coal devolatilization. Fuel, 89(2), 318-328.


From Biomass and Coal

to Plastics and RDF/MSU

54


55


56

https://www.google.it/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwij2q7G067JAhXHXhoKHR08B24QjRwIBw&url=http%3A%2F%2Fepthinktank.eu%2F2013%2F11%2F07%2Fplastic-waste%2Fplastics-production-plastic-waste-treatment-of-plastic-waste%2F&psig=AFQjCNHVE6nw8_4TJWLDrSwD97a0J6KNRw&ust=1448646520408459


57

0

0.2

0.4

0.6

0.8

1

250 300 350 400 450 500 550 600

PS PP PE

Temperature °C

Resi

due

Pyrolysis of Plastic PolymersTG depolymerization of Poly-Styrene (PS), Poly-Propylene (PP), and Poly-Ethylene (PE)follows the Bond Dissociation Energies. Residual char is negligible.

PVC

Dehydrochlorination of Poly-Vinyl-Chloride (PVC) is the fastest step.The formation of (-CH=CH-)n is the reason for the successive residual char.Ranzi, E., Dente, M., Faravelli, T., Bozzano, G., Fabini, S., Nava, R., ... & Tognotti, L. (1997). Kinetic modeling of polyethylene and polypropylene thermal degradation. Journal of Analytical and Applied Pyrolysis, 40, 305-319.


Elemental H/C/O Characterization of RDF

4

6

8

10

12

14

50 60 70 80 90% C [w/w]

% H

[w/w

]

RDF elemental composition

LigninCellulose

Plastics

H2O

240

4

6

8

10

12

14

50 60 70 80 90% C [w/w]

% H

[w/w

]

RDF elemental composition

LigninCellulose

Plastics

H2OH2O

240

RDF (on daf basis) are simply characterized in terms of Plastics, Cellulose and Lignin on the basis of H/C/O balances and heating value.

58

Sommariva, S., Grana, R., Maffei, T., Pierucci, S., & Ranzi, E. (2011). A kinetic approach to the mathematical model of fixed bed gasifiers. Computers & Chemical Engineering, 35(5), 928-935.


59

Sommariva, S., Grana, R., Maffei, T., Pierucci, S., & Ranzi, E. (2011). A kinetic approach to the mathematical model of fixed bed gasifiers. Computers & Chemical Engineering, 35(5), 928-935.

Effect of Particle Size on RDF pyrolysis

Plastic content is higher in coarse particlesand it is responsible of the seconddevolatilization step at 400–500 ◦C.Ash and inert materials are moreabundant in fine particles.(Buah et al., 2007)

This dependence of RDF composition on the particle size was also observed in terms of different heating value by Skodras et al. (2008).

coarseparticles

(dp=1-35mm)

fineparticles

(dp<.5mm)


Solid Fuels and Reference (Lumped) Species 60

The peculiarity of this approach is that all these schemes consist of a limited number ofdevolatilization reactions, which are able to describe not only the solid residue, but alsothe detailed composition of released gas and tar species.

A few lumped or reference species, togetherwith their pyrolysis models, allow to describe

the devolatilization process of the different fuels

The overall kinetic model of Solid Fuel Pyrolysis is simply the combination of the multistep kinetic models of Biomass , Plastics, and Coals.


61

Importance of Secondary Gas-Phase Reactions

in Solid Fuel Pyrolysis Process.


Transport Phenomena and Gas Phase Kinetics in Biomass Pyrolysis.

6262

The pyrolysys of biomasses occurs through the thermal degradation of solid cellular wall material to form an intermediate liquid (metaplast).

Subsequent high temperature decompositions generate volatile organic compounds (VOCs -Tar ) which exit the particle, through the wood pore (cellular lumen).

Gas-Phase Reactions need to be considered

Mettler et al., Energy Environ. Sci., 2012, 5, 7797


M. S. Mettler, S. H. Mushrif, A. D. Paulsen, A. D. Javadekar, D. G. Vlachos and P. J. Dauenhauer ‘Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates’ Energy Environ. Sci., 2012, 5, 5414-5424

The initial thermal decomposition of coal and biomass generates a short-lived liquid phase (metaplast). Further heating of the liquid intermediate produces tar/bio-oil species which can further react in the gas phase.

Multi-Component and Multi-Phase Nature of Coal and Biomass Pyrolysis Process.

Thousands of solid, liquid, gas-phase reactions are involved in

Coal and Biomass pyrolysis.

They deoxygenate and volatilize solid fuel to generate liquids and

gases.

It is then necessary to account for Gas-Phase Secondary ReactionsHeterogeneous Char reactions

63


Secondary Gas Phase Reactions : PAH and Soot Formation in Coal Pyrolysis (Sarofim et al., 1987)

64

Mitra, A., Sarofim, A. F., & Bar-Ziv, E. (1987). The influence of coal type on the evolution of polycyclic aromatic hydrocarbons during coal devolatilization. Aerosol science and technology, 6(3), 261-271.

Similarly, it is necessary to account for the successive pyrolysis and oxidation reactions of all the volatiles

(gas and tar) released by the solid fuels.


65

T.F. Lu, C.K. Law ‘Toward accommodating realistic fuel chemistry in large-scale computations’Progress in Energy and Combustion Science 35 (2009) 192–215

65

Methyl decanoateis a biomass fuel surrogate. Detailed kinetic mechanism consists of 3036 species and

8555 reactions.

Automatic Generation of kinetic mechanisms easily produces

Large Kinetic Models

Size of Gas-Phase Kinetic Mechanisms

POLIMISemi-detailedlumped


66Gas Phase Reactions

Detailed Kinetics of Pyrolysis and Combustion(hundreds of species and thousands of reactions)

Hierarchy and Modularityare the main features of Detailed Kinetic Schemes

• GRI Kinetics for Gases

• PRF and additives for Gasolines

• Diesel and Jet Fuels

•Tar and Oxygenated Species• NOx

• PAH and Soot formation

CO-CO2

Ethers

CH4C2-C4

nC7-isoC8

H2 - O2

Heavy FuelsMe-Esters

Alcohols

Due to the hierarchical and modular structure of detailed kinetic schemes, the extension to new

tars or released species only requires the additionof their primary propagation reactions.


67

Tran, L. S., Sirjean, B., Glaude, P. A., Fournet, R., & Battin-Leclerc, F. (2012). Progress in detailed kinetic modeling of the combustion of oxygenated components of biofuels. Energy, 43(1), 4-18.

Oxygenated components of biofuels


68

Liu, D., Togbé, C., Tran, L. S., Felsmann, D., Oßwald, P., Nau, P., ... Battin-Leclerc,F. and Kohse-Höinghaus, K. (2014). Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography, Combustion and flame,161(3), 748-765.

Decompositions of dihydrofuryl radicals(C4H5O-2 and C4H5O-3)


Secondary Gas-Phase Reactions: 2,5-dimethylfuran Pyrolysis (Lifshitz et al., 1998)

69

Fi 5 Di h lf l i i 99 5% A 3 C i f

2,5-dimethylfuran pyrolysis in 99.5% Ar at 3 atm.

Lifshitz, A., Tamburu, C., Shashua, R., ‘Thermal Decomposition of 2,5-Dimethylfuran. Experimental Results and Computer Modeling’, J. Phys. Chem. A 102: 10655-10670 (1998)

Comparisons of model predictions and experimental data


70Cellulose Pyrolysis Products (Norinaga et al. 2013)

Norinaga, K., Shoji, T., Kudo, S., & Hayashi, J. I. (2013). Detailed chemical kinetic modelling of vapour-phase cracking of multi-component molecular mixtures derived from the fast pyrolysis of cellulose. Fuel 103 (2013) 141–150.

Volatile released by cellulose pyrolysis


71

Vapour-phase cracking of molecular mixtures derived from the fast pyrolysis of cellulose

Secondary Gas-Phase Reactionsof Cellulose Pyrolysis Products at 700-800 °C

Norinaga, K., Shoji, T., Kudo, S., & Hayashi, J. I. (2013). Detailed chemical kinetic modelling of vapour-phase cracking of multi-component molecular mixtures derived from the fast pyrolysis of cellulose. Fuel 103 (2013) 141–150.


Norinaga lignina 72


Secondary Gas-Phase Reactionsof Levoglucosane

73


74

Heterogeneous Gas-Solid Reactions

Multi-Phase Model at the Particle Scale


Heterogeneous Gas-Solid ReactionsMulti-Phase Model at the Particle Scale (Wen, 1968)

75

Particle Model consists of mass and energy balances for solid and gas phase

Wen, C. Y. (1968). Noncatalytic heterogeneous solid-fluid reaction models. Industrial & Engineering Chemistry, 60(9), 34-54.

Two asymptotic regimes are usually defined:a kinetic controlled regime for low temperatures and small particles

(Heat and Mass Transport are faster than Kinetics)a transport controlled regime for high temperatures and big particles

(Transport rates become lower than the kinetic rates)

Shrinking Model (unreacted core)General Model (reacting volume)


76Particle Model 76

,,

,1, 1 , ,

, ,1

1 1 1 1, 1, , ,1 1

Sj i

j j i

j ij i j j i j j j i

NCPS Sj i p j i j NCP NCP

ij j j j j j i j i j j i j i j j

i i

dmV R

dtdm

J S J S V Rdt

d m c TJC S JC S S J h S J h V HR

dt

− −

=− − − − −

= =

= ⋅ = ⋅ − ⋅ + ⋅ = ⋅ − ⋅ + ⋅ − ⋅ + ⋅

∑∑ ∑

Particle Model consists of mass and energy balances

Rj,i is the net formation rate of ith species in the jth sector

Conduction Diffusion Reaction

The density distribution is the sum of the densities of different species in each particle sector.Similarly, the shrinking and porosity of each sector inside the particle is calculated.


Thermally Thick Particles: Biot and Pyrolysis Numbers

Py Numbers decrease with increasing temperatures

Paulsen et al. Energy Fuels 2013, 27, 2126−2134

Biot relates conduction and convection times.

Pyrolysis Numbers relate thermal and kinetic times.

77


78Pyrolysis of Thermally Thick Biomass Particle‘Exotic’ behavior of the center temperature profile

Wood sphere at 688 K.

dp=2.54 cm

Experimental center temperature overshoots the external temperature,due to the exothermic reactions of char formation

Park, W. C., Atreya, A. and Baum, H. R. (2010) 'Experimental and theoretical investigation of heat and mass transfer processes during wood pyrolysis', Combustion and Flame, 157(3), 481-494.

The flat Temperature plateau at ~650 K is due to endothermic tar devolatilization.

Comparisons of experimental and predicted (red lines) results.


Pyrolysis of Thick Biomass Particle

Park, W. C., Atreya, A. and Baum, H. R. (2010) 'Experimental and theoretical investigation of heat and mass transfer processes during wood pyrolysis', Combustion and Flame, 157(3), 481-494.

The ‘endothermic’ release of tar component and ‘exothermic’ charification process are responsible

for this behavior of the temperature profiles

Comparisons of experimental and predicted (red lines) Center Temperature Profiles.

79


Pyrolysis of Thick Biomass Particle:time-resolved gas phase composition (Bennadji et al., 2013)

80

648 K

*Acetic Acid (CH3COOH) and Hydroxy-Acetaldehyde (CH2OH-CHO) are lumped together

Bennadji, H., Smith, K., Shabangu, S., & Fisher, E. M. (2013). Low-temperature pyrolysis of woody biomass in the thermally thick regime. Energy & Fuels, 27(3), 1453-1459.

Secondary gas phase reactions are not important in these conditions.


Secondary Gas-Pase Reactions at the

Elemental Reactor Scale

81

Reactor LayerReactor Layer

Gas Stream

The dynamic model of the ideal Gas-Solid Reactor accounts for the

exchanges and for kinetics both in the solid and the gas phase.

Fuel Particle

Particle Model consists of mass and heat balances

Secondary Gas-Phase Reactionstake place in the elemental reactor


Elemental Reactor Model (Gas-phase) 82


Gas Stream

The dynamic Mass and Energy Balances of the Perfectly Stirred Reactor accounts for

Gas-Solid exchanges

Devolatilization Kinetics Heterogeneous Combustion/Gasification

Secondary Gas-Phase Reactions

, ,

, , , ,

1, , , ,

1 1 1

i

IN i OUT i

iIN i OUT i N i R g i

NCP

i p g NCP NCP NCPi

IN i g OUT i g N i N i N RAD gi i i

dg G G J V Rdt

d g C TG h G h J h JC J HR

dt

η

η η=

= = =

= − + + ⋅

= ⋅ − ⋅ + + + +

∑∑ ∑ ∑

ConvectionGas-Solid Exchange

RadiativeHeat Flux

ReactionHeat

η is the number of fuelparticles in the reactorvolume (VR)


83

Without considering secondary gas-phase reactions, the model

overestimate the production of tars above

500 °C (dashed line)

Effect of Secondary Gas-Phase Reactions


0%

20%

40%

60%

450 650 850 1050Temperature [°C]

Corbetta, M., Frassoldati, A., Bennadji, H., Smith, K., Serapiglia, M. J., Gauthier, G., Melkior, T., Ranzi, E., & Fisher, E. M. (2014). Pyrolysis of centimeter-scale woody biomass particles: kinetic modeling and experimental validation, Energy & Fuels.

Effect of Secondary Gas-Phase Reactions

BIO-OIL(TAR) GAS

RESIDUE

Without considering secondary gas-phase reactions, the model

overestimate the production of tars above

500 °C (dashed line)

84


BIO OIL from Fast Pyrolysis of Biomass 85

Bridgwater, A. V. (2003). Renewable fuels and chemicals by thermal processing of biomass. Chemical Engineering Journal, 91(2), 87-102.Calonaci, M., Grana, R., Barker Hemings, E., Bozzano, G., Dente, M., & Ranzi, E. (2010). Comprehensive kinetic modeling study of bio-oilformation from fast pyrolysis of biomass. Energy & Fuels, 24(10), 5727-5734.

Optimal temperature for bio-oil production Reactor LayerReactor Layer

Gas Stream


86

The heat needed for the pyrolysis is provided by the CHP plant fluidized-bed boiler by feeding hot sand to the CFB pyrolysis unit (800oC). Cold sand together with the char (at around 500oC) is send back to the fluidized-bed boiler, in which also the non-condensablesare fired. The combination allows lower investment costs when integrating into existing boilers


Biomass Thermochemical Conversion Processes 87

European Biomass Industry Association http://www.eubia.org


Gasification Regime of Thick Particles 88

A single reactor layer is fed with thick Fuel particles and Air at 300 K and a nominal Φ = 3.

Below a critical contact time there is a sudden shut down of the system.

Gasification regime requires high contact times to homogeneously heat

up the biomass particle.Volatiles form CO and H2.

At low contact time of solid particles a combustion regime

can prevail on gasification. Gas phase temperature rises,

while the center of the particle remains unreacted.

There is only a partial release of tar and volatiles, and the complete combustion to CO2

and H2O.


Multi-Phase Model at Particle and Reactor Scale

89

Gas Stream

Grate

Gas Stream

Grate

Gas Stream

Grate

A fixed bed of solid particlesis considered as a cascade of several Elemental Reactors


Gas Stream

The dynamic model of the ideal Gas-Solid Reactor

accounts for the exchanges and for kinetics both in the solid and the gas phase.

Fuel Particle

Particle Model consists of mass (solid and gases) and

heat balances


Gasifier is a Stack of Elemental Reactor Layers(counter-current and co-current configuration)

90

syngas

solid fuel

SteamAir/Oxidizer Ash

Fuel

ash

Syngas

Steam/Oxidizer

Top

Bottom

Temperature


91

Fuel Particle


Gas Stream

Gas Stream

Solid Particles

Solid Particles

PARTICLE SCALE REACTOR LAYER SCALE

COUNTERCURRENT GASIFIER REACTOR SCALE

Multi-Scale Nature of Solid Fuel Gasifier


92

15-30 solid phase species, 100-200 gas-phase components,

5-10 reactor layers, and 3-5 discretization sectors in the solid particle.

Several Thousands of Balance Equations

The resulting Stiff System of Differential Algebraic Equations (DAE) is solved by using the BZZMATH Library.

The Jacobian matrix is structured in Sparse Diagonal Blocks.

Mathematical Model of the Counter-Current Gasifier

Buzzi-Ferraris, G. (1993). Scientific C++; Building Numerical Libraries the Object-Oriented Way. Addison-Wesley Longman Publishing Co., Inc..Buzzi-Ferraris, G., & Manenti, F. (2010). Fundamentals and linear algebra for the chemical engineer: Solving numerical problems. Wiley-vch.


93

Solid speciesGas-solid

interactions

Sector 1

Sector N

Migration of gas species

Layer 1

Layer NR

Migration of gas species

PARTICLE SCALE REACTOR LAYER SCALE REACTOR SCALECOUNTERCURRENT GASIFIER

∼30 elements

∼100 elements

∼30 elements

Solid species (NCS)

Gas-solid interactions

(NCg)

∼30 elements

∼30 elements

Gas-phase species(NCG)

Solid Fuel GasifierBlock Sparse Structure of the Jacobian

External Sector

Internal Sector


94


95Counter-Current Coal Gasifier

Empirical correlations are required to account for the morphological changes of the coal particles and the fixed bed.

Shrinking and swelling, porosity and density, diffusivity….


96

2D Models: Anisotropic particles

Comminution of fuel particleduring conversion

Gómez-Barea, A., & Leckner, B. (2010). Modeling of biomass gasification in fluidized bed. Progress in Energy and Combustion Science, 36(4), 444-509.

Anisotropy and Morphological Changes


Counter-Current Coal Gasifier 97


300 800 1300 1800Temperature [K]

solid

gas

exp

Leucite Sub-bitum.

Validation of the Coal Gasifier Model

AIR

/H2O

SYN

GAS

FUEL

RESID

UE

PYROLYSIS

GASIFICATION

CHAR COMBUSTION

DRYING

ASH ZONE

Grieco, E. M., & Baldi, G. (2011). Predictive model for countercurrent coal gasifiers. Chem. Eng. Sci., 66(23), 5749-5761.

C78%

H5%

O14%

N2%

S1%

Leucite Sub-bitum.

Moisture 17.4 %

F = 0.1 kg/s/m^2

F = 0.25 kg/s/m^2xO2 = 16.5 %xN2 = 63 %xH2O = 20.5 %

Steady-stateTemperature

Profiles

Steady-stateSyngas

Composition

98


99Simplified Structureof a Travelling Grate Combustor


100

The biomass bed on the grate is assumed as several stacks of elemental reactor layers.

The grate movement determines the effective contact times of the biomass on the grate.

The steady problem is thus transformedinto a dynamic problem of a travelling ‘Slice’ of the fuel bed.

Steady and Dynamic Problem


101

Decomposition and CombustionReactions in the Freeboard

Integral closure of mass and energy balances :Pyrolysis products with primary and secondary air are involved in gas-phase reactions.Flue gases heat up the radiating walls of the furnace.

Travelling Grate Biomass Combustor


102

Top LayerIgnition

CharCombustion

Front

E. Ranzi, S. Pierucci, P. C. Aliprandi, S. Stringa (2011)‘Comprehensive and detailed kinetic model of a traveling grate combustor of biomass’ Energy & Fuels 25:4195 - 4205

Detailed predictions of Temperatures and Reactivityinside the Travelling Grate Combustor.


103Detailed simulations allow to derive a Control Model of the Travelling Grate Combustor.


0

1

2

3

4

13 14.75 16.5 18.25 20

Posi

tion

on th

e tr

avel

ing

grat

e [m

]

Grate velocity [m/h]

Ignition

Combustion front

0

1

2

3

4

0.12 0.14 0.16 0.18

Posi

tion

on th

e tr

avel

ing

grat

e [m

]

Bed thickness [m]

Ignition

Combustion front

Grate velocity and bed thicknesseffect on ignition and combustion front.

Similarly, the effect of Biomass Composition, Fuel Size, Radiating Temperature, Primary and Secondary Air Flowrate

is investigated.


104Control Model of the Travelling Grate Combustor.(12 MW biomass combustor operating in Belgium)

Summary of operating conditions, biomass characteristics, and model predictions.



105

• Solid fuel pyrolysis and combustion processes are intrinsically more difficultto describe than gas-phase processes on a fundamental mechanistic leveland present major challenges to combustion scientists.

• The morphological changes during fuel conversion require to account forcontinuous modifications of physical and transport properties.

• For this reason, lumping procedures need to be applied at different levels.• Once lumped models are available, it is always feasible and useful to increase

the description level and to improve model predictions

• For several solid fuels, the simple knowledge of the C/H/O content issufficient to understand their pyrolysis and combustion behavior.

• Of course, the catalytic effect of ashes is only one of the further complicatingaspects of this problem

Conclusion


106

CRECK Modeling Group at Politecnico di Milano

Thanks for the attention


107

Thanks for the attention

The financial support of CNR/MSE ‘Clean Coal Project’ is gratefully acknowledged.

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