coal gasification reactivity

Coal Gasification Reactivity:Measurement and ApplicationMeasurement and Application

David HarrisCSIRO Energy TechnologyResearch Program Leader, Low Emissions TechnologyPittsburgh Coal Conference, September 2007 Johannesburg, South Africa

Outline

• The science and technology associated with coal gasification and its emergence as a key component in low emissions power technologies is very broad and complexis very broad and complex

• Many R&D programs aimed at technology development and demonstration• Objective of this presentation is to provide some insights into recent

research on one important aspect of coal use in gasification systems:p p g y• Coal gasification ‘reactivity’

• Research tools and capabilities to assist in technology development, implementation and optimisation

• Strategy of ‘deconstructing’ the gasification process• Provide flexible, fundamental knowledge and data to understand coal

behaviour in complex gasification systems• The use of model frameworks to ‘reconstruct’ the complex process• The use of model frameworks to reconstruct the complex process• Reduce the reliance on empirical, situation specific testing and develop

flexible, predictive capabilities• Understand the impact of coal type and reaction conditions on gasification

CSIRO. Coal Gasification Reactivity: Measurement and Application

processes

Research Team

• David Harris• Combustion and gasification reactionsCombustion and gasification reactions

• Daniel Roberts• Heterogeneous reaction kinetics

• John Stubington (University of NSW)• John Stubington (University of NSW)• Pyrolysis and thermal processing reactions, student leadership

• San Hla G ifi ti i d lli• Gasification conversion modelling

• Liz Hodge• PhD student, high temperature char/gas kinetics


Key R&D Partnerships – Clean Coal Technologies

CSIRO Energy Technology’s work is fully embedded in collaborative initiatives. CSIRO is a key research provider for many research centres.

Cooperative Research Centres• CRC for Coal in Sustainable Development• CRC for Clean Power from Lignite (concluded 2006)• CO2CRC (CO2 capture and storage)

Centre for Low Emissions Technology (cLET)• Qld Govt, CSIRO joint venture – generators, ACARP, UQ partners• Enabling Technologies – gas cleaning, processing, separation

Australian Coal Association Research Program (ACARP)

COAL21 - Industry, Government, Research groups• Development of technology and policy action plan and roadmap• COAL21 Fund – support demonstration & implementation

CSIRO E T f d Fl hi


CSIRO Energy Transformed Flagship• broad strategy – specific GHG targets

Low Emissions Power Generation

E

Post-combustion captureCapture ofEnergy

Conversion

ASU

Energy / Power

Capture of CO2

Capture ofCoal Energy

ASUOxy-fuel combustion

Storage/Usef COCO2

Coal

Pre-combustion decarbonisationEnergy /

Conversion of CO2

Gasification COShift

Energy / Power

or H2 / COCO2/H2

separationSyngas (CO+H2)


Source: adapted from IEA Clean Coal Centre

Gasification based polygeneration processes

CSIRO. Coal Gasification Reactivity: Measurement and Application Source: US DoE Oak Ridge Laboratories – UT- Batelle

CSIRO R&D focus

Coal Gasification


Gasification processes

• Gasification is a flexible core technology with many applications • Steelmaking

P• Power• Chemicals, liquid fuels production• Active carbon• Biomass utilisation …..

Gasification is the ke enabling technolog in f t re lo emissions• Gasification is the key enabling technology in future low emissions power and Hydrogen energy systems

• IGCC ‘polygeneration’ of power, chemicals and hydrogen, NOx, SOx greatly reducedG C ff• IGFC – increased efficiency

• “Zero Emission” technologies• CO2 separation and sequestration• Hydrogen based energy

• Current gasification research builds on a strong R&D base developed from extended use of combustion technologies

• Flash pyrolysis/hydrogenation (1970s)• Combustion kinetics, ash formation, gas cleaning (1970-1990s)


Combustion kinetics, ash formation, gas cleaning (1970 1990s)• Coal gasification ‘reactivity’ (1980’s, 1990’s, current)

‘Strategic Science’ and Experimental Design

• Need to identify the appropriate issues• Isolate the issue from the processIsolate the issue from the process

• ‘Deconstruct’ the process• Practical coal and technology performance models need

flexible ‘fundamental’ data and understandingflexible fundamental data and understanding• ‘Reconstruct’ the system• Predictive rather than purely empirical capability • Not an academic ‘indulgence’• Not an academic indulgence

• Cooperation between industry, universities and research organisationsto ensure relevance

• Necessary depth and rigour through PhD and postdoc programs

• Its not all about simulating the industrial process!


Gasification Research in AustraliaTo improve the understanding of coal performance in gasification technologies, supporting:

• Use of Australian coals in new technologies

• High pressure, high temperature coal i t

g• Implementation of advanced clean coal technologies in Australia.

conversion measurements• Effects of reaction conditions and coal type• Development of coal test procedures

• Fundamental investigations of coal• Fundamental investigations of coal gasification reactions

• Reaction mechanisms and kinetics, model development.

• Slag formation and flow for entrained-flow gasification

• Syngas cleaning & processing


• Gas separation (H2/CO2)• Technology performance models

Coal Conversion in Gasification

Coal gasification is a multi-stage process• Coal pyrolysis

• Rapid volatile release• Determines char yield and morphology

• Combustion• Limited, fast. O2 consumed early in process• Exothermic, provides heat for endothermic

ifi ti ti

O2

CO/CO2

gasification reactions

• Char Gasification• Slow, rate determining. Endothermic

CO d H O t d t CO d H

CO2 and H2O

CO + H2

• CO2 and H2O converted to CO and H2.

• Slag formation and flow• Flux may be required to achieve adequate

viscosity


viscosity fluxslag

Interrogating the Gasification Process

PEFR I ti ti• Using laboratory-scale apparatus it is

PEFR: Investigating gasificationbehaviour under controlled and

possible to understand in some detail the important processes that combine to convert coal under gasification conditions.

O2

CO/CO2

Pilot testing – generating real gasification conditionsto test overall coal

co t o ed a dmeasurable conditions• Larger-scale testing allows us to test

how such information can be ‘recombined’ under process conditions, leading to a good knowledge of what

CO2 and H2O

CO + H2

to test overall coal performance

High pressure wire-mesh reactor:

happens in a gasifier.• This allows us to confidently assess

coals for specific gasification technologies, provide design g

Pyrolysis behaviour under high pressuresand high heating ratesChar gasification kinetics: high pressureTGA and fixed-bed reactorsSlag viscosity measurements

tec o og es, p o de des ginformation for gasifier construction, and a sound basis for troubleshooting gasification processes.


fluxslagGas AnalysisTGA and fixed bed reactorsg y

Direct Measurement of CoalDirect Measurement of Coal Gasification Conversion

Behaviour


High Pressure Entrained Flow Reactor (PEFR)

Feeder

Preheating and mixingg

Three-section reaction zone

• Capable of 20 bar pressure 1500°C wall

reaction zone

W t h• Capable of 20 bar pressure, 1500 C wall temperature

• Coal feed rate of 1-5 kg/hr • Gas mixtures of O2, CO2, H2O and N2• Adjustable sampling probe - char and gas

Water quench

Sampling probe and gas analysis


Adjustable sampling probe char and gas samples collected at different residence times (0.5-3s) Gas Analysis

Coal Conversion Rates20bar, 2.5% O2, C:O ~ 100%

100

%) (b) 1400°C

100

(%) CRC274(a) 1100°C

40

60

80

Con

vers

ion

(%

CRC252

CRC274

CRC298

CRC26340

60

80

Con

vers

ion CRC310

CRC299

CRC358

CRC281

Char conversion

ease

0

20

40

Car

bon

C CRC263

CRC358

0

20

40

Car

bon

C CRC281

Pet Coke

Vol

atile

rele

• Initial rapid conversion (up to 0.5s) is indicative of the contribution of devolatilisation

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Residence Time (s)

0.0 0.5 1.0 1.5 2.0 2.5 3.0Residence Time (s)

devolatilisation• Rate of increase of conversion following this is due to the influence of char

reactivity.• CRC310 has high volatile yields and low char reactivity• CRC281 has low VY but higher char reactivity


• CRC281 has low VY but higher char reactivity• Note - conversion data is for complex reactant gas mixture – current work

considers individual reactants

Evaluation of Coal Gasification Behaviour

100

120

%) CRC274

60

80

cy' (

%)

CRC2741400°C, 2.5% O2

40

60

80

n Co

nver

sion

(% CRC298CRC299CRC281CRC252CRC263

40

60

tion

'Eff

icie

nc CRC298CRC281CRC299CRC252

0

20

40

Carb

on CRC263CRC358

1400°C, 2.5% O2

0

20

Gas

ifica

t

CRC263CRC358

0 50 100 150 200 250

Stoichiometry (%)

Trends expected due to increased amount of O available

0 50 100 150 200 250Stoichiometry (%)

• Trends expected, due to increased amount of O2 available• Higher volatile coals achieve greater conversion than lower volatile coals

• Exception is CRC299 – indicates that char reactivity is also significant (agrees with TGA testing of same coal suite)


• Coals differentiated on the basis of different char reactivities

Gasification conversion drives gas phase composition

CRC274 – 1300°C, 5%O2VM (daf) = 32.6%6

7

(mol

%)

4

5

mpo

sitio

n (

COPoints = measuredLines = equilibrium

2

3

um G

as C

om

CO2

steam

O2

0

1

Equi

libri

u

H2

2

0 20 40 60 80 100

Carbon Conversion (%)• Demonstrates the strong effect of carbon conversion on CO/H2 in product gas


• Earlier work (1atm) shows that when char gasification kinetics are known, we can ‘predict’ conversion (by different reactions) in complex flow system

Deconstructing theDeconstructing the Process: Char Structure and

R ti it

O2

CO/CO2

ReactivityCO2 and H2O

CO + H2


fluxslag

Volatile Yield at Elevated Pressure

60% Open symbols = DTFCl d b l WMR

40%

50%

f coa

l (da

f)

AnthonyArendtGibbinsSuubergGriffin

60

al (d

af)

Coal C

Closed symbols = WMR

30%

40%

Yiel

d, w

t% o

f GriffinA (31.7%)B (34.8%)C (35.7%)D (36.2%)E (50 4%)

20

40

ld, w

t% o

f co

Coal B

20%0 10 20 30

Pyrolysis Pressure (atm)

E (50.4%)

00 5 10 15 20 25

Pyrolysis Pressure (atm)

Yie

• Volatile yield decreases with increasing pressure• Not correlated with Prox. VM• General agreement between wire mesh and high P drop tube results


g g p• flow methods expensive and complex for volatile yield measurement,

difficult for volatiles and tar composition measurement

Carbon-Gas Reactions

Char-CO2: Char-H2O:

Cf + H2O C(O) + H2

C(O) → CO + Cf′

Cf + CO2 C(O) + CO

C(O) → CO + Cf′

Key issues:• Competing reactions

Cf + H2 → C(H2)

• Competing reactions • Complex kinetics• Rate controlling mechanism changes with

reaction conditions• Coal properties affect char reactivity


Heterogeneous Reaction of Porous Particles

d

CO2

2CO CO + 1/2 O2 = CO2

Cg

CO2

I

0III

II

• More complex for full gasification system

Cs


More complex for full gasification system• Multiple reactions – may be operating in different regimes

Reaction RegimesTemperatures where pf combustion & gasification technologies operate

R i II R i IRegime III Regime II Regime I

η =1Low-temperature ‘intrinsic’ measurements

1

measurements

η << 1 η < 0.5

1/T


External mass transfer control

Chemical + porediffusion control

Chemical ratecontrol

Gasification Kinetic Models

• Two approaches to describing gasification kinetics at high pressuresp

• nth order rate equation, power law, ‘global’ rate expression• Langmuir-Hinshelwood rate expression

1 - nth order E ⎞⎛1 nth order• Approximation of multiple rate equations• valid over limited (defined) ranges of temperature, pressure etc.• Useful for integration of specific data into specific models

ng

ag P

RTEA ⋅⎟

⎠⎞

⎜⎝⎛ −= expρ

Useful for integration of specific data into specific models2 - Langmuir-Hinshelwood

• Derived from accepted rate equations for overall reaction• Therefore applicable generally over wider ranges of conditions• Therefore applicable generally over wider ranges of conditions• Useful for integrating chemical (intrinsic) kinetics into gasification

(and) process models.


‘Intrinsic’ Reaction Kinetics at High Pressure

• High Reactant Pressures•Increasing reactant pressure increases rate but not infinitely

16

20

/s) x

10

5

H2O

rate, but not infinitely•Limits application of nth order rate equation over wide ranges of partial pressure

•Well-described by LH kinetics and ‘surface i ’ d l

4

8

12

Spec

ific

Rat

e (g

/g/

CO2saturation’ model

D G Roberts and D J Harris (2000). Char Gasification with O2, CO2 and H2O: Effects of Pressure on Intrinsic Reaction Kinetics, Energy & Fuels 14(2), 483-489.

00 10 20 30

Reactant Pressure (bar)

S

• Total Pressure Effect• ‘Dilution’ effect• Insignificant effect on ‘intrinsic’ low 3.E-05

4.E-05

5.E-05

e (g

/g/s

)

Char D

Char Y

Char B

CO2 = 5 atm

• Insignificant effect on intrinsic , low-temperature reaction kinetics

D G Roberts, D J Harris and T F Wall (2000). Total Pressure Effects on Chemical Reaction Rates of Chars in O2, CO2 and H2O F l 79(15) 1997 1998

1.E-05

2.E-05

Spec

ific

Rat

e


H2O, Fuel 79(15), 1997-1998.0.E+00

0 10 20 30Total Pressure (bar)

Surface Effects at High Pressurem

p. (°

C) 1100

8002.0

2.5

ak A

rea 0.8

1.0(a) CO2

Tem

30 atm20 atm

500

800

0 5

1.0

1.5

Nor

mal

ised

TPD

Pea

0.2

0.4

0.6

Thet

a

TPD Peak

Des

orpt

ion

Rat

e

20 atm10 atm1 atm 0.0

0.5N

0.0

Theta

1.4

a 1 0

1.2

(b) H2O

0 1000 2000 3000 4000

Time (s)

D

0.6

0.8

1.0

1.2

lised

TPD

Pea

k A

rea

0.4

0.6

0.8

1.0

Thet

a

Temperature-programmed desorption 0.0

0.2

0.4

0 10 20 30 40

Reactant Pressure (bar)

Nor

ma

0.0

0.2TPD Peak

Theta


D G Roberts and D J Harris (2006). A Kinetic Analysis of Coal Char Gasification Reactions at High Pressures, Energy & Fuels 20(6), 2314-2320.

( )

Competition Between Reactants

1. CO2 reaction intermediates effectively reduce the available active surface area for

22)]([][][ COtOHt OCCC −=

reduce the available active surface area for H2O reaction

2. LH kinetic model can be used, with a reduced available site concentration, to arrive at an ‘inhibited’ reaction rate

3. Net reaction rate is CO2 reaction plus the ‘inhibited’ H2O reaction

inhibited reaction rate

=1 MPa steam, 900°C= 0.5 MPa steam, 900°C

( )( ) ⎟

⎟⎠

⎞⎜⎜⎝

⎛

+−⋅+=

2

2

2231

31

11

CO

COOHCOmixture Pkk

Pkkρρρ

2=1 MPa steam, 850°C= 0.5 MPa steam, 850°C

Lines represent model calculations (i.e. ) mixtureρ


D G Roberts and D J Harris (2007). Char Gasification in Mixtures of CO2 and H2O: Competition and Inhibition, Fuel, DOI:10.1016/j.fuel.2007.1003.1019.

Describing ‘Intrinsic’ Gasification Kinetics

• Utilisation of the reaction surface is key to application of kinetics

• Impacts on choice of kinetic model• Impacts on how reactivity data are applied to systems containing

more than one reactant• Langmuir-Hinshelwood Model works well over relevant ranges

of pressure• Works in pure gases and in mixtures of reactantsp g• Being tested at high pressure in presence of products• Still to be applied to high temperatures


Application of Intrinsic Rate Data

T (K)

20 atm Pressure, 50% Reactants • Assumptions:

• Average pore size

-5

-3

s)

5000 2400 1400 1000 800

mass transfer limit

e age po e s e(5 nm) (measured)

• Rates normalisedto external surface area

-13

-11

-9

-7

Rat

e, g

/cm

2 /s

O O

area• Uniform particle

size (100 μm)• Single point in

b ff hi t

-19

-17

-15

13

ln(

CO2

H2O O2

burnoff history

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

1000/T (K-1)

• Need to be able to ‘predict’ rate at high T, P on basis of ‘intrinsic’ reactivity


• Char physical structure (pore size, particle size, morphology…) key to high T reaction behaviour

Moving up the Arrhenius Curve: HighCurve: High Temperature Rates

sion

rate

) Regime IRegime IIRegime III

ln (c

onve

rs

~800-900°COver 1000°C ??Very high!


Inverse Temperature

Can Char Structures be adequately Modelled?

High vol sub bituminous char Semi-anthracite char

• Need at least some reasoned correlations between coal and char types• Initial work with empirical correlations


Classification of char types (high pressure chars)

80100

510

15

020406080

Perc

ent

Pressure (atm)

Gro

up I

Gro

up II

Gro

up II

I (atm)

• High pressure increases population of Group 1 (fluffy) chars

• Correlated to coal petrography


Correlated to coal petrography• Impact on reactivity and modelling

Wu H, Bryant GW, Benfell KE, Wall TF. Energy Fuels 2000; 14:282.

High Temperature Ch /CO R tChar/CO2 Rate Measurements


Gas Analysis

CO2/char reaction rate at ‘high’ temperature

Coal Whigh VM

Coal Ylow VM0 8

1.0

on

1400 °C1300 °C

20 bar total pressure, 5 bar CO2 partial pressure

high VMlow VM

0.6

0.8

al c

onve

rsi 1300 °C

1200 °C1100 °C

0.2

0.4

fract

iona

• PEFR operated with controlled gas atmospheres (fix PCO2, Ptotal, T, t), Char produced in-

0.0 1.0 2.0 3.0

residence time (s)

0.00.0 1.0 2.0 3.0

residence time (s)p g p ( 2, total, , ), p

situ • Conversion measured along length of reactor (t ≤ 3s)• Char samples taken for thorough analysis

• Morphology, structure, surface area pore size distribution…


• ‘Intrinsic’ reactivity• Density and particle size

Char/CO2 reaction rates: Integration of intrinsic and ‘apparent’ rates

• Activation energy at high temperature ~ half that

20 bar total pressure, 5 bar CO2 partial pressure0

obtained at low temperature• Consistent with a transition

to ‘regime II’ at approximately 1373K)

-2

0

E ~100 kJ mol-1

approximately 1373K• First of a kind data for high

pressure char/CO2 and char/steam reactions

, g

g s-1

bar

-n)

-6

-4

• Still need integration of gasification rate & char structure during conversion

• topic of current PhD

ln (k

,

-10

-8 E ~200 kJ mol-1

• topic of current PhD program

10000/Particle Temperature (K-1)

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5-12


Understanding the high temperature system

• Regime 1 Kinetics• Lots of work has been done in understanding rates at highLots of work has been done in understanding rates at high

pressure• This research is ongoing….

• Diffusion theoryy• Well developed

• High temperature kinetics• Measurements presented hereMeasurements presented here

• Particle morphology and microstructure• Complicated and variable with conversion as well as reaction

conditionsconditions• How does all this come together in a gasification system?

• Traditionally used an ‘effectiveness factor’• How can this be used within the constraints of a complicated char


• How can this be used within the constraints of a complicated char gasification system?

Measured and Calculated Pore Diffusion Effects (Combustion)

• Entrained Flow (Regime II) and Fixed bed (Regime I) data obtained at same conversion level

• Diffusion co-efficient measured directlydirectly

• small particles and f(T)• Intrinsic rate data can be

accurately extrapolated toaccurately extrapolated to practical temperatures

• Need to extend this approach to high temperature, high pressure gasification reaction systems

CSIRO. Coal Gasification Reactivity: Measurement and Application (Harris, Valix et al 1992)

Reconstructing the Process: Modelling of Flow ReactorsModelling of Flow Reactors


Model validation: application to PEFR experimental program

vers

ion

(%)

60

80

100

ol%

)

2.0

3.0CRC-358 (Expt)CRC-274 (Expt)CRC-252 (Expt) CRC-358 (Model)CRC-274 (Model) CRC-252 (Model)

6 (a)

Car

bon

conv

0

20

40 CRC-358 (Expt) CRC-274 (Expt) CRC-252 (Expt) CRC-358 (Model)CRC-274 (Model)CRC-252 (Model)

6 (b)

CO

2 (m

0.0

1.0

Distance from reactor top (m)

0.0 0.5 1.0 1.5 2.0

5.0

6.0

7.0CRC-358 (Expt)CRC-274 (Expt)CRC-252 (Expt)CRC-358 (Model) CRC-274 (Model)CRC-252 (Model)

3.0

CRC-358 (Expt)CRC-274 (Expt)CRC-252 (Expt) CRC-358 (Model)CRC-274 (Model) CRC-252 (Model)


0.0 0.5 1.0 1.5 2.00.0

CO

(mol

%)

1.0

2.0

3.0

4.0

H2

(mol

%)

1.0

2.0

• Model calculations differentiate between initial rapid devolatilisation/combustion processes and the slower char gasification.

6 (c)


0.0 0.5 1.0 1.5 2.00.0

1.06 (d)

Distance from reactor top (m)0.0 0.5 1.0 1.5 2.0

0.0


• Model is able to predict well the profile of carbon conversion and gas composition for different types of Australian coals.

• Still need to ‘overlay’ char surface area and structure dataHla, Harris & Roberts, 5th International Conference on CFD in the Process Industries - December 2006

Gasification modelling

0.80.9

s) 70

80

%)

C+O2 C+CO2 C+H2O Carbon conversion

0.30.40.50.60.7

ion

rate

(kg/

kg/s

30

40

50

60

on c

onve

rsio

n (%

Gas TParticle flow

0.00.10.20.3

0.0 0.5 1.0 1.5 2.0 2.5

Di t f t t ( )

Rea

cti

0

10

20

Car

bo Gas T flow

• Model needed for interrogation and application of measurements• Integration of fundamentals with system and technology models


Integration of fundamentals with system and technology models• relationships with international programs (REI, USA), Pilot and demo plant

operators• Australia has no pilot or commercial scale gasification plant


• Collaboration is essential to apply knowledge and to ‘validate’ outcomes• Pilot scale test program conducted August 2007 (Siemens, Germany)

Where are we now?

• Benchmark experimental data have been obtained on the gasification performance of a wide range of Australian coals at high pressures and temperatures

• There are clear effects of volatile yield and char gasification reactivity on gasification performance

• The rate of the heterogeneous char gasification reactions is critical in• The rate of the heterogeneous char gasification reactions is critical in determining coal conversion levels.

• Gas phase composition can be relatively well understood using equilibrium considerations. However…

• Conversion rate drives the gas phase reactions• Fundamental kinetic data for important char gasification reactions at

are now emerging for application at appropriate reaction conditions. d d f th d l t f di ti d l th t b d f l• needed for the development of predictive models that can be used for coal

and technology assessment.• Current work is producing data under conditions where coal/char-specific

processes (e.g. char reaction rates) can be separated and interpreted and


re-constructed to produce an overall gasification conversion model

What is required?

• Reliable kinetic measurements need to be extended to all key reactions at elevated pressure

• Product inhibition competing/parallel reactionsProduct inhibition, competing/parallel reactions• Char surface area and porosity development

• Still need measurements of rate and structure from high T, P conditions l i i i d ifi ito apply intrinsic rate data to gasification systems

• Missing links and challenges!• Ability to predict:• Ability to predict:

• Volatile yield and char structure from high pressure pyrolysis • Char structure and morphology evolution during gasification

Need to apply to pilot and practical systems• Need to apply to pilot and practical systems • Models validated for simple flow system • First pilot scale trial program now complete for a well characterised set of

Australian coals


• Are issues that differentiate coals in the laboratory significant at practical scale?

CSIRO Energy TechnologyCSIRO Energy TechnologyDr David HarrisResearch Program Leader,Low Emissions Technology

Phone: +61 (7) 3327 4617Email: [email protected]: www.csiro.au/science/energy

Thank youThank you

Contact UsPhone: 1300 363 400 or +61 3 9545 2176

Email: [email protected] Web: www.csiro.au

coal gasification reactivity

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