Relationships Between Coal Chemistry and … Between Coal Chemistry and Decomposition Products...
Transcript of Relationships Between Coal Chemistry and … Between Coal Chemistry and Decomposition Products...
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!