Relationships Between Coal Relationships Between Coal Chemistry and Decomposition Chemistry and Decomposition

ProductsProducts

Thomas H. FletcherChemical Engineering Department

Brigham Young University

GCEP MeetingMarch 15, 2005

Provo, UT

Outline

• What is coal?• Simple descriptions of coal reaction• Coal chemistry• Lattice models• Secondary reactions• Light gas• Nitrogen evolution

Coal Decomposition

Coal Volatilesheat

Char

Tar

Light gas

Soot

Primary Devolatilization Secondary Devolatilization

Definition: Tar = Volatiles that condense at room T and P

0 .1 0

0 .0 8

0 .0 6

0 .0 4

0 .0 2

0 .0 0

H/C

Rat

io

0 .50 .40 .30 .20 .10 .0

O /C R a tio

1507 lign ite14 45 sub b itu

m .

1 45 1h va

b itum

.

1508

lvb i

tum

.

1 4 93 hvbb itu

m .

Coalification

Graphite

lignitesubbituminousbituminous

lv bituminous

anthracite

Moderate Temperature Pyrolysis0.10

0.08

0.06

0.04

0.02

0.00

H/C

Rat

io

0.50.40.30.20.10.0

O/C Ratio

1507 lignite

1445 subbitum.

1451

hva b

itum.

1508

lv b

itum

.

1493

hvb b

itum.

Early Char Combustion 0.10

0.08

0.06

0.04

0.02

0.00

H/C

Rat

io

0.50.40.30.20.10.0

O/C Ratio

CCL, 0% post-flame O2, 47 ms CCL, 6% post-flame O2, 47 ms CCL, 6% post-flame O2, 72 ms

1507 lignite

1445 subbitum.

1451

hva b

itum .

1508

lv b

itum

.

1493 hvb bitum.

Coal Structure

Pyrrolic Nitrogen

Pyridinic Nitrogen

Bridge Structures

Side Chain

Loop Structure

Aromatic Cluster

Mobile Phase Group

Bi-aryl Bridge

H

C

H2

HO C

H2

N

R

C

R

O

H

SH2

OH

C

H2

H2 OH

H2

OH

CH2

O

O

CH3

C OH

O

R

C

H2

NH

HH

H

HH

H2

H2

H2

OH2

OCH3

C

HH2O

H

H2

C

HH

HH

Primary Coal Pyrolysis

H

N

R

OH

C

CH3

H2

H2

H2

R

CH3

H

O

C HH

CH3

SO

C

CH3

O

H2 OH

H2H2

H2

N

CH3

HH

Tar

R

CO2

H2O

H2O

CO2

CH3

Tar

Lattice Devolatilization Models

• Coal molecule description– 13C NMR spectroscopy

• Rates of bridge breaking– Aromatic clusters remain intact– Kinetics are coal independent

• Lattice statistics– Amount of liberated fragments

• Vapor-liquid equilibrium– Light fragments vaporize

• Crosslinking– Stable bridges form, making char

Types of Lattices

HON E Y COM B L A TTI CE TRI GON AL BE THE L ATTI CE

DI A M ON D L ATTI CE TE TRA GON A L BE THE L A TTI CE

A. Coordination number = 3

B. Coordination number = 4

Lattice Statistics

•45% bridges broken,•~10% fragments liberated•Fragments include monomers,dimers, trimers, etc.

•20% bridges broken,•0.3% fragments liberated

Closed-Form Solution of Percolation Lattice Statistics

1.0

0.8

0.6

0.4

0.2

0.0

Frac

tion

of F

inite

Clu

ster

s

1.00.80.60.40.20.0

Fraction of Intact Bridges (p)

4

126

σ + 1 = 3

Vapor-Liquid Equilibrium and Crosslinking

Finite Fragments (Metaplast)

Infinite Coal Matrix

Tar Vapor

Reattached Metaplast

Crosslinking

Vapor-Liquid Equilibrium

Labile Bridge Scission

MW

f

MW

f

MW

f

Generalized Hydrocarbon Vapor Pressure Correlation for the CPD Model

0.01

0.1

1

10

100

Vapo

rPre

ssur

e(a

tm)

3.02.52.01.5

1000/Temperature (K-1)

110MW = 315 285

258

218

237212

188 158 140127 116

(500 K)(667 K) (400 K) (333 K)

( )TMWccP ci

vapi /exp 3

21 −=

Data taken from Gray et al. (Ind. Eng. Chem. Process Des. Dev., 1985) for12 narrow boiling point fractions of coal liquids from a Pittsburgh seam coal

Input Parameters Required by the CPD Model

• Number of attachments per cluster (σ+1) (i.e., coordination number)

• Fraction of attachments that are bridges (p0) (bridges/bridges+side chains)

• Molecular weight per aromatic cluster (Mcl)• Molecular weight per side chain (Mδ)

Measured w

ith 13C N

MR

Spectoscopy

• Fraction of bridges that are stable (c0)Not measured

Do Structure Parameters Correlate?6.5

6.0

5.5

5.0

4.5

4.0

3.5

Coor

dinat

ion N

umbe

r (σ

+1)

10090807060

%C in daf coal

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

Frac

tion

of In

tact

Bridg

es (P

0)

10090807060

%C in daf coal

700

600

500

400

300

200

100

0

Molec

ular W

eight

per C

luste

r

10090807060

%C in daf coal

80

60

40

20

0

MW p

er S

ide C

hain

(Mδ)

10090807060

%C in daf coal

Lattice Model Capabilities

Can Predict:• Tar yield

– MW distribution• Light gas yield

– Speciation• Char yield

– Elemental composition

As a Function of:• Coal type

– Coal structure• Residence time

– Kinetic rates• Particle heating rate

– Distributed activation energies

– Competing reactions• Temperature

– Kinetic rates• Pressure

– Vapor-liquid equilibrium

Using Correlations for Coal Structure Parameters

60

50

40

30

20

10

0

% Y

ield

(daf

)

95908580757065

% Carbon (daf)

limit of data used to make correlations

CPD mass release measured mass release CPD tar yield measured tar yield

17 non - U.S. coals, 3000 K/s to 1037 K, (Xu & Tomita) No 13C NMR data available, from Genetti et al., E&F 1999

Light Gas Speciation is Empirical

From Solomon et al., E&F, 1988.All E’s are distributed!

19 s

peci

es, n

eedi

ng y

ield

fact

ors

and

rate

coe

ffici

ents

!

Sample Predictions of Gas Species

1.0

0.8

0.6

0.4

0.2

0.0Li

ght G

as C

ompo

sition

95908580757065

Percent Carbon in Parent Coal (daf)

Water

Carbon dioxideMethane

Carbon monoxide

Other gases0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

H/C

Mola

r Rat

io

0.280.240.200.160.120.080.040.00

O/C Molar Ratio

1

2

10

6

8

39

75

4

12

11

Coals Studied by Solomon et al. Coals Studied by Chen

Interpolation matrix for gas species(based on coalification diagram)

Application to Xu and Tomita data(non-U.S. coals)

From Genetti et al., E&F (1999)

Nitrogen Release

• All nitrogen in coal is contained in the aromatic structure– Pyridinic, pyrrolic, and

quartenary

Nitrogen release highly dependent on tar release

Argonne Premium Coals, XPS data from Kelemen et al. (1993), XANES data from Mitra-Kirtley et al. (1993)

100

80

60

40

20

0

% o

f Nitr

ogen

in P

aren

t Coa

l

959085807570% Carbon (daf) in Parent Coal

Pyrrolic

Pyridinic

Other Forms

XPS XANES

Tar Does Not Contain All PyrolyzedNitrogen, Especially for Low Rank Coals

Pulverized coal particles in a radiant drop tube reactor (Chen, Stanford University, 1991)

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Coa

l-N fr

actio

n in

tar/o

ils

0.60.50.40.30.20.10.0

Coal-N fraction released

Dietz subbituminous Illinois No. 6 hv bituminous Pittsburgh #8 hv bituminous Lower Kittanig lv bituminous

Nitrogen Release Models

• Initial N release w/tar• Subsequent N release

from char as HCN at higher T

• Secondary tar reactions– Soot formation from tar– Light gas formation (HCN

and then NH3)

• Additional N release at extremely high T’s– 100% nitrogen release

possible!

stablechar N

coal N + light gas N

soot N

light gas N

T<1000 K T<1600 K

tar N

T>1600 K (long residence t imes)

tar N

light gas N

+

+

char N

+

C (slow)

B (fast)

A

From S. Perry, PhD Dissertation, BYU, 1999

Sample Nitrogen Release Predictions

50

40

30

20

10

0

Mass R

elease (% of daf coal)

200015001000500

Temperature (K)

1.0

0.8

0.6

0.4

0.2

0.0 F

ract

ion

N R

etai

ned

in C

har

Pohl BYU Mass Release N remaining in char

E4=75 kcal/mol, σE4=3 kcal/mol

CPD model

A. Flat-flame burner (high T and dT/dt) • matches volatiles yield and• nitrogen release)

B. High temperature crucible data• volatiles reaches constant value • nitrogen is totally released!

13C NMR data used for coal structure parameters

0.70

0.60

0.50

0.40

0.30

0.20

0.10

Frac

tion

Relea

sed

95908580757065

daf % C in parent coal

16 ms, 1650 K

78 ms, 1650 K

Measured mass release Predicted mass release Measured nitrogen release Predicted nitrogen release

(from Perry et al., E&F, 2000)

Nitrogen Structural Parameters Modeled Correctly!

40

35

30

25

20

15

10

5

0

% de

cay o

f Nsit

e in

char

908580757065

daf % C in parent coal

• Australian, Japanese, and American coals• Pyrolyzed at 1100 K in N2 (drop tube)• Based on 13C NMR analysis and

elemental composition

(from Perry et al., E&F, 2000) 1.0

0.9

0.8

0.7

Nsit

e, ch

ar/N

site,

coal

1.00.90.80.70.60.5

Mcl, char/Mcl, coal adjusted

Beulah Zap

1.0

0.9

0.8

0.7

Nsit

e, ch

ar/N

site,

coal

1.00.90.80.70.60.5

Mcl, char/Mcl, coal adjusted

Pittsburgh #81.0

0.9

0.8

0.7

Nsit

e, ch

ar/N

site,

coal

1 . 00 . 90 . 80 . 70 . 60 . 5

Mcl, char/Mcl, coal adjusted

Illinois #6

1.0

0.9

0.8

0.7

Nsit

e, ch

ar/N

site,

coal

1 . 00 . 90 . 80 . 70 . 60 . 5

Mcl, char/Mcl, coal adjusted

Blue #1

1.0

0.9

0.8

0.7

Nsit

e, ch

ar/N

site,

coal

1 . 00 . 90 . 80 . 70 . 60 . 5

Mcl, char/Mcl, coal adjusted

Pocahontas #3

Structural N parameter as reaction proceeds

Soot Formation

• Soot forms from coal tar, not acetylene

Coal Char + Light Gases + Tar

Tar

Primary Soot Soot agglomerates

Light Gases

Devolatilization

Formation

Gasification

Agglomeration

• Soot model developed and implemented– Uses predicted tar from CPD

model– Soot formation, oxidation, and

growth included– Predicts up to 300 K lower

near-burner temperature in CFD model

Conclusions

• A lot of good scientific research performed on coal pyrolysis

• Lattice models capture much of the chemistry• Models tuned to match existing data

– Mass release vs. t, T, dT/dt, Ptot, coal type– Tar yield (and MW, composition)– Gas species– Nitrogen release– Soot formation

• These models are good tools to explore new concepts!