Finding order in coal pyrolysis kinetics

Prog. Energy Combust. Sci. 1983, Vol. 9, pp. 323--361.

0360 1285/83 $0.00 +.50 Copyrighl © 1984 Pergamon Press Ltd.

Printed in Great Britain. All righ!,~reserved.

F I N D I N G ORDER IN COAL PYROLYSIS KINETICS* PETER R. SOLOMON a n d DAVID G. HAMBLEN

Advanced Fuel Research, Inc., 87 Church Street, East Hartford, CT 06108, U.S.A. Al~traet--A number of experiments have suggested that the rate constants for the release of tar and for the thermal decomposition of the various functional groups in coal pyrolysis depend on the nature of the bridging bond or of the functional group, but appear relatively insensitive to coal rank for lignites, subbituminous and bituminous coals. The principal variation of pyrolysis behavior with rank is due to variations in the concentrations of functional groups and hence, the amount of each pyrolysis product. If the insensitivity of coal pyrolysis kinetics to coal rank can be generally demonstrated, it represents an important simplifyingassumption in, any general theory of coal pyrolysis. But the rank insensitivity of rate constants is controversial. There are two major questions. What species exhibit rank insensitive kinetics? Quantitatively, what does insensitivity mean, variations less than factors of two, ten, hundred, etc.? This paper considers whether pyrolysis data in the literature support the hypothesis of rank insensitive kinetic rate constants. The experiments considered vary in duration from 1.4 msec to 12 hr and in temperature from 350°C tb 1800°C. Considering the available data, it appears that the decomposition of aliphatic, methyl and aromatic functional groups and the evolution of tar and hydrocarbon species have rates which are relatively insensitive to rank variation. The rate varies by at most a factor of five between lignite and bituminous coals. Oxygen species are somewhat more rank sensitive.The factor of five variation in rate due to coal rank is substantially less than the factors of 100--10,000in variation typical of reported rates. Rank variation appears therefore to be a minor cause for these differenceswhich consequently must be attributed to the effects of heat and mass transfer and to the assumptions used in deriving a kinetic rate. The observation that pyrolysis rates are insensitive to rank over such a wide range of conditions suggests that using this approximation in a pyrolysis theory can have wide applicability.

I . INTRODUCTION

Coal pyrolysis is important since it is the initial step in most coal conversion processes and is the step which is most dependent on the properties of the coal. Recent reviews of the pyrolysis literature~ -4 present a complicated profusion of results in which it is difficult to identify any simplifying order. At present, there is no generally accepted theory of coal pyrolysis. In an attempt to develop a coal pyrolysis theory, the thermal decomposition of a variety of coals has been examined in vacuum flash pyrolysis using a heated grid 5-1° and is currently being examined at one atmosphere using an entrained flow reacto& 1- t 6 and a programmed temperature heated grid apparatus. ~3 One outcome of this work has been the elucidation of a relationship between the coal organic structure and the products of thermal decomposition. The relationship has been incorporated into a kinetic model of thermal decomposition which views coal as an ensemble of functional groups organized into tightly bound aromatic ring clusters connected by weaker aliphatic and ether bridges. Thermal decomposition of the coal releases large fragments of the coal molecule (tar) by depolymerization due to rupture of weak bridging bonds. The tar molecules contain a representative sampling of the coal's functional groups. Simultaneously, light gas species are competitively released from the thermal decomposition of the individual functional groups. The rate constants for the

various functional groups depend on the nature of the bridging bond or of the functional group, but appear relatively insensitive to coal rank for lignites, subbituminous and bituminous coals. The principal variation of pyrolysis with rank is due to variations in the concentrations of functional groups and hence, the amount of each pyrolysis product. The theory which

is presented in several previous publications5-16 is currently using the kinetic rate parameters presented in Table 1. The theory considers heat transfer to the particles and mass transfer limitations but not temperature gradients within particles. Since the latter effects are not important for the small particles and moderate heating rates which have been considered, the rates are believed to be chemical kinetic rates. If the insensitivity of coal pyrolysis kinetics to coal rank can be generally demonstrated, it represents an important simplifying assumption in any general theory of coal pyrolysis. But the rank insensitivity of rate constants is controversial. There are two major questions. What species exhibit rank insensitive kinetics ? Quantitatively, what does insensitivitymean, variations less than factors of two, ten, hundred, etc.? The case that can best be documented is that, excluding anthracites, the rates for decomposition of certain functional groups (aliphatic, aromatic, methyl and hydroxyl hydrogen, and ether oxygen) and the primary evolution (excluding secondary reaction) of light gas species (CO, CO 2, HeO, HCN, CH,, C2H~, C2H4 and other light paraffins and olefins) are inrelease of tar and for the thermal decomposition of the sensitive to coal rank. Insensitivity means within factors of two to five not factors of 102-10 a which * Work supported under DOE Contract #DE-AC21-FE- are typical for variations of reported rate constants. Although it might be expected that some variations 05122. 323

324

PETER R. SOLOMONand DAVID G. HAMBLEN TABLE 1. Kinetic rate coefficients

k

yo yo yo

CO2--extra-loose CO2 --loose CO2--tight

yo

H2 0

yo yo yo yo yo Y°o Yt°t Yt°2 Yt°a Yt°4 Y°s

CO--ether loose CO--ether tight HCN--loose HCN --tight NH3 CH~--aliphatic Methane--loose Methane--tight H--aromatic C--non-volatile S--organic

= A(sec-t)exp(-B/T(Kelvins)

= 0.10E + 15exp [ k2 = 0.10E+ 15 exp [ k 3 = 0.10E + 15 exp [ k 4 = 0.17E + 15 exp [ ks = 0.17E + 12exp [ k6 = 0.10E + 19exp [ %7 = 0.54E + 04 exp [ 0.70E + 08 exp [ *k 8 k 9 -- 0.12E + 13 exp [ klo -- 0.17E+ 15exp I 0.17E + 15 exp [ kll 0.17E + 13exp [ kl3 -- 0.16E +08 exp I"k14 0 kl

(23900 + 2500)/'T] (27900 _ 1400)/T] (32900 + 3300)/T] (30000 + 1500)/'T] (25000 + 2500)/T] (54900 + 5000)/T] (8850)/T] (32000)/T] (27300 + 3000)/T] (30000 + 1500)/T] (30000 + 1500)/T] (30000 _ 3000)/T] (23000 + 2300)/T]

=

Total

X° Tar Cracking rates: Paraftins-Olefins Olefin-Acetylene

kr

=

0.45E + 14exp [ - (26400 + 1500)/T]

koL = 0.15E+ 12exp [ - (27600)/T] kAc ffi 0.21E +08 exp [ - (22000)/T]

* Distributed rates have not yet been determined.

should be expected because of rank variations in the average ring size and their effect on the bond strengths of attached functional groups, the data suggest that assuming rank independent kinetic rates is a good first approximation. The most controversy centers on the use of rank insensitive kinetics to describe tar evolution. The evolution of tar is far more complicated than light gas evolution from thermal decomposition of functional groups (for example, the decomposition of methyl groups to form methane). Tar is not a single product; it is a collection of heterogeneous "oligomers" formed from "depolymerization" of the coal "polymer". Its elemental and functional group composition, its yield and its molecular weight distribution depend strongly on the transport properties, pressure, bed geometry, coal particle size and coal type even when the timetemperature history of the coal particle is held constant. This behavior can he understood with a model which treats the depolymerization in conjunction with transport (e.g., vaporization and diffusion). 17-t9 The transport processes are expected to be drastically different depending on whether the coal is swelling or non-swelling. There is little data on tar evolution rates. Kinetic data obtained in this laboratory for nine coals pyrolyzed in 1 atm. of nitrogen by heating in a grid apparatus at 30°C/rain show a systematic 40°C variation (490-530°C) in the temperature of peak tar evolution between low and high rank coals, la This corresponds to a factor of approximately five in the rate constant between the lowest temperature decomposition of a lignite and the highest temperature decomposition of a bituminous coal. There are also data on weight loss, where even for lignites, tar dominates the initial weight loss. Analysis of weight loss data when coal type alone is varied (all other

conditions are held constant) does not indicate a wide variation in tar evolution rates. Certainly, rank dependent rate constants cannot explain the 102-104 variation in reported rate constants. This paper considers whether pyrolysis data support the hypothesis of rank insensitivekinetic rate constants.

The paper concludes that with few exceptions, the kinetic rate constants for individual species evolvedfrom coals pyrolyzed under the same conditions show little variation with rank. The paper also considers why, if the hypothesis is correct, there appears to he such diversity in the "apparent kinetic rates" in the literature. Considering the insensitivity to coal rank, the variations must be due to differences in other factors such as heat and mass transport and the assumptions made in the data analyses.

2. THE BASIS FOR COMPARING PYROLYSIS KINETICS AMONG COALS

The problem of finding order for kinetic rate constunts in coal pyrolysis is illustrated in Fig. I adapted from Ref. 2. The figure presents a summary of reported rate constants x3'2°-36 for weight loss assuming a simple first order process

dW/dt = k(Wo - W) where k is the temperature dependent rate constant, W is the weight loss at time t and Wo is the ultimate weight loss at infinite time. (Witte and Gat 3° assume a pair of rate constants using the model of Kobayashi et al. z6) Figure I shows that at any given temperature, there is between a two and four order of magnitude variation in reported rate constant. To understand such a wide variation, it is necessary to consider the possible causes. These have been discussed extensively

Finding order in coal pyrolysis kinetics

1800

,oJ

I

I

1200 I

I

TEMPERATURE, "C 800 600 500 ~

I

I

I

400 I

I

lo z

Io i

tn

.Ig IZ

~z Iv" O t~

,o-2

,o'3

)0-4 0.4

0.6

O.B

1.0

1.2

1.4

1.6

RECIPROCAL ABSOLUTE TEMPERATURE, 10"3*K "1

325

result from variations in reactor conditions. As an example, consider the weight loss from an entrained flow reactor presented in Fig. 2. The coal is reacted in a hot gas stream within a hot 5 cm diameter alumina tube. Similar conditions were employed by Badzioch and Hawksley, 3s Maloney 33 and Kobayashi et al. 26 Assuming that the coal is at the isothermal furnace temperature when the rapid weight loss occurs this will give the apparent rate constant labeled 13a and 33a in Fig. 1. If, however, weight loss occurs during heat up, the measured kinetic rate constant should be plotted at a lower temperature. Figure 3 (which presents particle temperatures computed by considering convective and radiative heat transfers 13) illustrates that the heating rate can vary substantially with panicle size (Fig. 3a) and sample fce~i rate (Fig. 3b). It can also vary with ambient gas composition which may affect thermal conductivity and radiative absorption, turbulence which can affect the effectiveness of particle-ambient gas mixing, particle swelling which affects particle surface areas, absorptivity, heat capacity, beats of reaction and possibly other effects as well. When appropriate panicle heating rate calculations are performed for the data in Fig. 2, the results may be fit (lines in Fig. 2) using the kinetic rate constant labeled 13b in Fig. 1. Similar considerations were applied by Maloney in deriving the rate labeled

FIG. I. Comparison of kinetic rates for weight loss (or tar loss). (Adapted from Anthony, D. B. and Howard, J. B., Coal Devolatilization and Hydrogasification, A I C h E J. 22, 625 (1976) with permission.)

8 O

in Refs 2 and 3. For coal pyrolysis in the absence of external reacting gases, the possible causes are:

o

-0

1. Coal type. 2. Reaction condition (reaction time, pressure, particle size, heating rate, final temperature and mass transfer rates). 3. The assumptions used for deriving a kinetic expression. In this paper we compare only raw data for coals pyrolyzed under identical conditions. That is, we consider the variations in pyrolysis behavior resulting from variations in coal rank, holding reaction conditions constant and eliminating possible variations introduced in deriving kinetic rates. Comparing the data in this way is necessary because both the reaction conditions and assumptions used for determining a kinetic rate constant appear to cause larger variations than do coal type. Consider, for example, that among the six data sets in Fig. 1 which include more than one coal, 13'23"26"3°'3s'36the variations due to coal type in four of them Â3.26,3s.36 is less than a factor of three. In fact. there is no rate difference between a lignite and a bituminous coal reported by Kobayashi et al. 26 What then is the cause for the two to four orders of magnitude variation in rate constants? Substantial variations in "'apparent kinetic rate constants" can

o o o

°.0

~6.o zLo s6.o ~ 6 . o s6.o i NJE:TOR PO~ZTION CH

~'.o

~6.o z6.o

6 6 . o ~o.o

E

36.o ~6.o s6.o 86.o 7o.o C~

INJECTOR POS!TION

FIG. 2. Weight loss from pyrolysis of a North Dakota lignite in an entrained flow reactor in nitrogen at (a) 820°C and (b) 1000°C.

326

PETERR. SOLOMONand DAVIDG. HAMBLEN 2000

1600

-;12oof

_, r / / , / /

0

"I

100

200

300

400

500

TIME (milliseconds)

1600

1200

~°°t 0

.

100

200

500

~00

500

TIRE (ml I 1 Iseconds)

FIG. 3. Simulation of entrained flow reactor. 13 •14 Variation of heating rate with (a) particle size and (b) coal feed rate.

33b. It is possible that such considerations could shift liner 21, 26, 31, 35 and 36 to a lower temperature as well. This approach cannot be taken with data labeled 28, 30 and 34, since in these experiments, particle surface temperatures were measured. So, unexplained discrepancies still exist which may be caused by nonisothermal conditions within the particle allowing the surface to be at a higher temperature than the region where pyrolysis occurs. This could be caused by high temperature soot surrounding the particle or by mass transfer limitations. Another cause for variations in "apparent rate constants" is the assumptions used for deriving kinetic rates in coal. Most investigators have assumed a first

order process and a rate constant with an Arrhenius temperature dependence, k = ko e-E/RT where k 0 is the frequency factor, E the activation energy, R the gas constant and T the absolute temperature. This assumption is troublesome because of the coal's variety of similar but not identical chemical structures. This typically produces a distribution of rates rather than a single sharp rate for any chemical reaction. The use of a distributed activation energy model was introduced by Pitt, 37 and subsequently employed by Hanaba, 3s Juntgen and van H o c k , 39 Anthony e t al. 36 and Weimer and Ngan. 4° Such

Finding order in coal pyrolysis kinetics 0.3

a

'

I

J

I

energy, Eo and a distribution parameter a) are required has contributed to wide variation in published rates. Examples of the variability in reported kinetic rate constants which can result from the assumptions of the analysis are illustrated in Fig. 4, which shows numerical fits to the pyrolysis data of Campbell43 for CO2. The data are for the evolution rate for CO2 measured as the coal sample was heated at a constant rate. A single first order process would produce a single peak. Campbell assumed the observed double peaks were due to two distinct sources (which we have designated loose and tight) and fitted each source (Fig. 4a) as a simple first order process using a rate constant which follows the Arrhenius temperature dependence. The low activation energy indicated in Fig. 4a is required because the peaks are wide. But suppose the wide peaks are caused by a distribution in activation energy. The simulations of Fig. 4b and c are performed assuming a source W(E) with a Gaussian distribution in activation energies E

I

u

0.2 ,.1

0

0.1 0

0.3 b

I~ r'l

I

I

I

O'~lt

0.2 .J 0 us

W(E)

t~

0.1 0 Lu

o 0.3

Ir-I I=1 c

I

I

I

~0 P~

I¢ 0

0.2

,J

0 ,.>,

O.I 0

11-II-I

0

500

700

900

1100

327

1300

TF.H~r.RATURE ( K )

FIG. 4. Effect of variations of distribution parameter, a, on the kinetic rates. (Data of Campbell43 for a beating rate of 0.055 k/sec.} ~aj a = 0;kioo~= 550exp(-9815/T); ktl~h t = 230 exp ( - 11582T). (b) Medium a: kloo~-- 1.44x 101+exp[- (28600 ___2000)/T]: ktith, = 1.39 x 106 exp[-- (19000 + 500)/T]. (c) Large a: k~oo~= 1,0 x 1021exp [ - (40100 -P4000)/T]. ]':ti,~ht = 2.42 x 1011exp [ - (30100 + 1000).'T]. distributions can be understood from the work of Stein et al. +1 and Vernon+2 which suggests a variation in bond energies with the degree of ring condensation. Using a two parameter fit to define the rate when three parameters Ie.g.. frequency factor, ko. activation

=

w0 o.xf~ exp [ - (E-Eo)2/2~23

where a is the width of the distribution and Eo is the average activation energy. 11'16 Reasonable fits to the data can be obtained with arbitrary values of a. The assumed value of a changes Eo and ko substantially. It is therefore obvious that the experimental data from one constant heatin.q rate experiment are insufficient to uniquely determine the rate constants. Such ambiguities can lead to wide variations in slopes of the lines in Fig. 1. Eliminating such ambiguities can only be done by considering additional experiments which provide sufficient variations in heating rate and final temperature. For these reasons, comparing published values of "apparent kinetic rate constants" is typically not useful. Work is continuing to define meaningful kinetic rates by separating out the effects of heat and mass transfer and by using a distributed activation energy model to fit a wide variety of coals and experimental conditions.13.1+ For this paper, however, data will only be compared for cases where rank is the only variable, that is for cases where more than one coal was run under identical conditions. 3. COMPARISON OF PYROLYSIS DATA AMONG COALS

The hypothesis being tested is that the kinetic rate constants which describe the thermal decomposition of functional groups in the coal to produce volatile species are dependent on the functional group but are insensitive to coal rank for lignite, subbituminous and bituminous coals. This assumption appears to be invalid for anthracite. The best data to consider are therefore the functional group concentrations in the char or the evolution of primary gas species. Other data such as elemental composition of the char, is also useful since its change can be related to the behavior of the functional groups

328

PETERR. SOLOMONand DAVIDG. HAMBLEN

O N

SYNTHESIZED SPECTRUH

I~LIPH~ITIC C-H

j~

FIROHI:ITIC C-H

ETHER C-0 C-O-C

CRRBONYL C=O

A NITROGEN

-N

HISCELLANEOU5

8 ~c ~o

ssbo

szbo

zebo

z4bo zobo tebo NRVENUMBERS(CM-I)

Izbo

ebo

~oo

FIG. S. Synthesis of FT-IR spectrum. during pyrolysis. Overall weight loss is less useful since it is the sum of all the processes together, but the initial rapid weight loss reflects the rapid loss of tar and hydrocarbons and so can also be useful. The following sections compare data for different coals pyrolyzed under identical conditions. 3.1. Char Composition Quantitative FT-IR spectra have been obtained for chars reacted for increasing distances in the Advanced Fuel Research entrained flow reactor. 11,1s-ls The methods for preparing quantitative spectra are described in Refs 5, 44 and 45. With careful sample preparation, variations among replicated samples of coal are within 5 ~o and of char, within 10 ~ (because of smaller sample size). The synthesized spectrum illustrated in Fig. 5 shows the contribution of the individual functional groups to the overall spectrum. The position (in wavenumbers) of the peaks remain constant, but the amplitudes change with the functional group concentration. Figures 6-9 illustrate the results for a lignite, a sub-bituminous coal and two bituminous coals pyrolyzed in helium at 800°C for the indicated distances with a gas velocity of 1.5 m/sec. 13"1s The spectra show rapid removal of aliphatic hydrogen and about one half of the hydroxyls, an increase in aromatic hydrogen and retention of C - O bonds. It is interesting to note that the peak at 1600 wavenumbers (which is believed to be due to aromatic ring stretch enhanced by an attached hydroxyl) does not diminish substantially even when the hydroxyl peak is reduced by a factor of two. The fact that all four coals

of varying rank exhibit almost identical changes in relative functional group composition, supports the concept that kinetic rates for functional group decomposition are insensitive to coal rank. Figure 10 shows the aliphatic, aromatic and methyl hydrogen peak heights at 2960, 800 and 1375 cm-1. respectively for the four coals in Figs 6-9 normalized by the respective peak heights in the parent coal. Given the accuracy of preparing quantitative FT-IR

ILL]NOI~ ee I! 800 C,

~

s8 •

~obo

!

~ .

~

S8

~bo

2RbO zzbo tSbO ~ObO NAVENUHBER5 (CH- ! I

~bo

FIG. 6. FT-IR spectra of chars from Illinois #6 bituminous coal pyrolyzed at 800°C in helium. A scattering baseline correction has been applied and the spectra have been scaled to 1 mg/cm2 dry coal. ~s (© 1983, Electric Power Research Institute, EPRI Report #RP 1654-8, "Measurement and Theory of Coal Pyrolysis Kinetics in an Entrained Flow Reactor", reprinted with permission.)

Finding order in coal pyrolysis kinetics

329

JACOB'5 RANCH P 800 C.

PITTeBURG SERH ~ 800 C,. ° f=3 L~

s'-

8$

~J U

.

W

58

C~

C~

30

s~bo

zebo

zzbo

~ebo

tobo

~bo

NRVENUHBER~ I C M - 1 1

FIG. 7. FT-IR spectra of chars from Pittsburgh seam coal pyrolyzed at 8000C in helium. A scattering baseline correction has been applied and the spectra have been scaled to 1 mg/cm 2 dry coal. 15 (© 1983, Electric Power Research Institute, EPRI Report # RP 1654-8, "Measurement and Theory of Coal Pyrolysis Kinetics in an Entrained Flow Reactor", reprinted with permission.)

30

8,,bo

2ebo

2213o 1 8 b o lobo

NAVENUI~ERS

[CM-I

,,bo

1

FIG. 9. FT-IR sp~tra of chars from Jacob's Ranch subbituminous coal pyrolyzed at 800°(2 in helium. A scattering baseline correction has been applied and the spectra have been scaled to 1 mg/cra2 dry coal ts (© 1983, Electric Power Research Institute, EPRI Report # R P 1654-8, "Measuremere and Theory of Coal Pyrolysis Kinetics in at, Entrained Flow Reactor", reprinted with permission.)

reactor at Combustion Engineering x2 and at 1100°C in nitrogen in an entrained flow reactor at Advanced Fuel Research.13 At higher temperatures, the aliphatic peak is removed more quickly and the aromatic peak reaches a maximum and then decreases. Figure 11 compares hydrogen functional group concentrations for an Illinois # 6 and a Utah bituminous coal pyrolyzed at 1100°C. Again the results appear to be insensitive to coal rank within the accuracy of the measurement. The lines are theoretical predictions using the rates of Table 1. 9AVRGE P 800 C. To test the sensitivity of the data to variations in kinetic rate, computations were made for the Jacob's Ranch sub-bituminous coal at 800°C (Fig. I0) and for the Utah bituminous coal (Fig. 11) assuming factors of ten higher and factors of ten lower rates. These are presented in Fig. 12. Consider first the experiments at 1100oc. The rate Z for H(al) decompositions is very fast and so this .: j m product is evolved during heat up. Consequently, the predicted decomposition varies only slightly as the rate is varied. These conditions can provide a lower bound to the rate for H(al) decomposition, but are not particularly good for accurately defining the rate. The H(ar) decomposition rate, however, is much slower and at 1100°C is comparable to the reciprocal of the experiment time. Varying the rate makes noticeable changes. Using a factor of ten slower rate, almost no ~obo s~bo zebo zzbo zebo ~obo ~bo ~FWENUHBEAS CCM- 11 loss of H(ar) is predicted, while for a factor of ten PIG. 8. FT-IR spectraof chars from Savage, Montana lignite higher rate, there is substantially more decomposition pyrolyzed at 800°C in helium. A scattering baseline correc- predicted than is observed. At these experimental tion has been applied and the spectra have been scaled to conditions the behavior is thus sensitive to rate varial mg cm-' dr)' coal./-~ I© 1983. Electric Power Research tions for H(~ar). The rate reported in Table 1 appears Institute. EPRI Report #RP 1654-8. "'Measurement and to be the best fit for all coals tested at this temperature. Theory of Coal Pyrolysis Kinetics in an Entrained Flog The scatter in the methyl data is too large to do more Reactor". reprinted with permission. I

Samples for char, an accuracy of 10-20 % should be achieved for the normalized data. The lines are predictions of the theory employing the rank independent kinetics presented in Table 1. F o r cases where there is a large interfering mineral contribution, the aromatic hydrogen concentration is determined by difference. The agreement between theory and experiment is good. Other sets of chars were obtained at 1000°C in helium flowing at 0.5 m/sec in an entrained flow

330

PETER R. SOLOMONand DAVIDG. HAMBLEN .p

0

~ N ( RII )

#8,

Pittsburgh

~N( Lit, ) Q

LM~TNTL

+H(¢¢)

Bituminous

~"

0

:g ~J

+

cl

0

lO. 0

z6.o

~.o

..~c,o.

,,~.o

,oSiZlO.

~.o

~.o

vo.

:6.o

c~

36.o

I N.JF'CTOR

~6.o

POS [ T | ON

s6.o

,6.o

7o.

CH

8-

Oa~ aa ) ~II¢.. 4-m a¢ )

J a c o b ' s Ranch, Subbltumlnous

Savage, Montana Lignite~

AM(INIn.

0

i! ,

qo

0

,

10.0

,

ZO,O

30.0

,

qO.O

,

SO.0

,

,

60,0

70.

IN,JECToIq POSITION C]q

'i{ '

ZO,O | N.,~[c'r(~R

POS|TION

FIG. 10. Char functional group composition (DAF) normalized to parent coal functional group composition (DAF) for pyrolysis in helium with a furnace temperature of 800°C. (Note that the aromatic hydrogen for Pittsburgh seam coal and the Montana lignite is determined by difference because of interference of large mineral peaks in the FT-IR spectraJ s) (© 1983, Electric Power Research Institute, EPRI Report # R P 1654-8, "Measurement and Theory of Coal Pyrolysis Kinetics in an Entrained Flow Reactor", reprinted with permission.)

aa

N b OH(RR )

~ ) H ( AR ) o

~I,METHYI..

i

=

AI'IETHYL

•.~.-H( RL )

,

~ -

-f-H( RL )

O

.2O

O

04

=z 2.

O

.-

O

O

O

t-

8 .w-

10 0

20 O

30 0

q0 0

50 O

60 0

70 0

q ~

~0,0

Z0.0 50.0 q0.0 50.0 INJECTOn P0SIT~ON C~

60.0

FIG. 11. Char functional group composition (DAF) normalized to parent coal functional group composition (DAF) for pyrolysis in nitrogen with a furnace temperature of 1100°C. (a) Illinois # 6 bituminous coal (Run #9) and (b) Utah bituminous coal (Run # 10). (Note that the aromatic hydrogen is determined by difference because of interference of large mineral peaks in the FT-IR spectra. '5) (© 1983, Electric Power Research Institute, EPRI Report # RP 1654-8, "Measurement and Theory of Coal Pyrolysis Kinetics in an Entrained Flow Reactor", reprinted with permission.)

70,0

Finding order in coal pyrolysis kinetics

a

" "

.l,.~41~&)

Base Rate xO.1

~j"

331

0

!

Base Rate xO.1

4.-~,

~" f.D

® t¢

-F

O

N

i"

?.

."

+

+ 0

16.o z6.o ~6.o ,6.0 s6.o ~6.o ~o.o INJECTOR

POSI TI~w

~T~mL

{R,

~6.o z6.o- a6.o INJECTOR

CM

b

Base Rate Table I

,6.o~ sfi.o s6.o-'- 7o.c

POSITION

~J

Base Rate Table I

c

i°

(D ~)

,%.

I

(~

n.~..

:O.C

, ~0.0

30.0

INJECTOR

*0.0

POSITION

50.0

SO.O

70.[

~'0

~.~.C

C~

,

±

,

.

~

20.0 ~0.0 ~0•0 INJECTOR PO~tTION

,

~0, n

,

'~r

60.n

70.0

j.

c

I'd

4-w(Jw. |

Base Rate x I0

N~d"

~,NN)

BaSex lORate O

I

O

~J

O O

¢D,

'+

O" O......

~0.0

A

z6.o ~6.o ,6.0 s6.o s6.o 7o.o I NJECTOI~ POSIT ION

~6.o z6.o 3o•o ,6.o-s6.o INJECTOR

POSITION

,6.o" vo.o

CM

FIG. 12. Sensitivity of theoretical predictions for hydrogen functional groups to variation in kinetic rates. (a-c) Jacob's Ranch sub-bituminous coal in helium at 800"C. (d-f) Utah bituminous coal in nitrogen at 1100°C. than provide a lower bound for H(methyl) at this temperature. At 800°C the rate for H(ar) decomposition is too slow for appreciable H(ar) loss during the experiment. The increase in H(ar) is controlled by the other rates (e.g. H(al) and tar). These conditions provide only an upper bound for the H(ar) rate. The conditions allow the rates for H(methyl) and H(al) to be determined and the rate of Table 1 provides a better fit than the rates which differ by factors of ten. The conclusion is

that kinetic rate variation can be accurately observed only when the time of the experiment is of the order of the reciprocal of the rate constant at the experimental temperature. Even when these conditions are achieved, appreciable rank variations in experimental rates are not observed. Char elemental compositions cannot be interpreted as directly as functional group composition since the former is a sum over the latter• But in many cases, the functional group changes occur at different reaction

PETER R. SOLOUO~;and DAVIDG. HAMBLEN

332

b

~CRRBON AHYOROGEH XO RNO S +HITR

!. N

(.,)OXYCEN ~NITROCEN

d'

!-.

N

~.:

N

0".o

| ~. (.1

z6.o

s&.o ~ . o

[ NJECTOn

POSI

1 ION

, ~o.o

6~.o

,~

Q

i 7o.o

".o

to.o

CH

zo.o

no.o

IN..~CTOR

°

,

[]CRRBON OHYOROGEN AOXYGEN +NITROGEN

N

~.o

r~.o

PO'HTION

e~.o

7o.o

CH

LLILHRuu~ C)HYOROGEN AOXYGEN -I-NITROGEN

N

+

~

NN

N t-

I-

o ÷

+ o oo~,,,, ~ .

+

$

\

en

kO0.0

6~.0 O~.0 I~.0 IZ~.0 I~.0 PYfl~YSI$ TE~EMTUR( ~C C

I~.0

18~

~oo.o e~o.o e6o.o ,~oo.o t~oo.o ,;oo.o ,~oo.o teoa e . a . v s , s Tt~.¢eaTURt oeo c

FIG. 13. Char composition normalized to parent coal composition for coal pyrolysis. (a) Kentucky #9 bituminous coal in entrained flow reactor with nitrogen at 1100°C. (b) Beulah, North Dakota lignite in entrained flow reactor with nitrogen at ll00*C. (c) Pittsburgh bituminous coal in heated grid in vacuum for 10 see (data from Ref. 2). (d) Beulah, North Dakota lignite in heated grid in vacuum for 10 see (data from Ref. 13).

conditions and so can be distinguished in the elemental composition, The elemental composition has advantages over functional group composition in accuracy which is typically better than 5 ~ for microanalysis of chars. Figure 13 presents the elemental composition of chars produced in an entrained flow reactor in nitrogen at ll00*C (13a and b) and-in a heated grid by pyrolyzing for 10 sec at the indicated temperature (13c and d). x3 The data for a lignite and a bituminous coal. The char compositions are normalized to the composition in the parent coal. Both coals show similar trends. Hydrogen r a p i d l y disappears as a result of aliphatic and hydroxyl evolution followed by slower disappearance from aromatic hydrogen decomposition. Oxygen shows initial loss due to hydroxyl, carboxyl and some ether evolution, followed by a slower reduction from loss of the remaining ethers. The carbon increases, showing the greatest gains in the lignite which start out at a low carbon

value. Nitrogen first increases due to removal of more volatile species and then decreases at longer residence time or higher temperatures as a result of HCN formation. The lines in the figures are theoretical predictions using the kinetic rates in Table 1. The predictions are in good agreement with the data except for nitrogen at high temperature. Figure 14 shows data for char elemental compositions for the Utah bituminous at l l00°C and the Jacob's Ranch sub-bituminous at 800°C. The data are simulated using the rates of Table 1 and also rates increased and decreased by factors of ten. Where the experimental conditions are sensitive to rate variations, the rates of Table 1 are best and factors of ten variations are typically less suitable. Elemental composition data obtained by Kobayashi 46 are presented in Fig. 15. The chars were produced by pyrolysis in a crucible at I atmosphere at the indicated temperature. Pyrolysis times ranged from 5 rain at 1750°C to 12 hr at 600°C. The trends

Finding order in coal pyrolysis kinetics

333

m,

OCIII~ ~ N ,,s O

~,,;'

d

~NI TIIK~I*

~FLII T INIT,i I ~ X 0 ~ |

Base Rate xO.l

~ g.

Z

Base Rate xO.l

XONO I

--

~y

~..:.

! i-

O 4-

m

m.

i

PO$ I T ! ON

INJECTOR

~rt

,iP

e~m •~.,,,,~o¢,~ xouos

b Base Rate Table

,,.,,tTnv.ta,

T

cd" x o

Base Rate Table I

*No s

.2" p.

,7

t-

t0 .~,

~'0.0

3 0 , F7

~*0.0

POE ! T I ON

INJECTOR

5 0 . C,

60.0

70.0

CH

= ,~

'~.C

ZO,O

30.0

1NdECTOR

~0.0

P0C./TZ0N

50.0

80,n

70,0

C'H

¢

~axlOm

•~.atT~0Ctt

Base Rate x I0

XO dulO I

Base Rate

x 10

xoL~$

(0

z6.o

so.o

[ N JIF'C'TOR

,~.o

PO~[T[0N

so.o

so.o

7o.c

C'H

=' o

1o.0

zo.o

30.0

I N,.J£ C'I"OIR

,~o.o so.o

P O S I T I OIq

so.o

7o.o

L'~

FIG. 14. Sensitivity of theoretical predictions for elemental composition to variations in kinetic rates. (a-c) Jacob's Ranch sub-bituminous coal in helium at 800°C. (d-f) Utah bituminous coal in nitrogen at 1100*C.

are similar to those presented in Fig. 13 except that events happen at lower temperatures because of the longer time of pyrolysis•

3.2. Gas Erolution Gas evolution data from pyrolysis in vacuum for 10 sec in a heated grid 4~ are presented for four coals in Figs 16 and 17. In Figs 18 and 19, data from the heated grid experiment "" are compared to data from pyrolysis in an entrained flog' reactor in nitrogen at JPECS ~ : ~ - E

1100°C. 13 While the amounts of the gas species vary from coal to coal (e,g. lignites have more oxygen containing species, bituminous coals, more methane and other hydrocarbon), the temperature at which the evolution of a species begins, reaches a m a x i m u m rate, and is completed, is insensitive to coal rank. The most variation occurs for CO (Fig. 16) which appears to evolve at a higher temperature in the Rosa coal compared to the lower rank coals. The evolution of the species can be correlated with the elemental and functional group changes occurring in the char. High

334

PETERR. SOLOMONand DAVIDG. HAMBLEN l

.J

i

!

,1

!

l

l

)I

B*lum*nous Cool

g.o

o

<

c

.

M&XIMUM TEMP(It:IATUR(. eC

~)00[

.....

--_ _~::~ ~ 80~" ~ t l - ' ~

-)¢ni** ~1

,

'

n

' C

,

'-=' ,/ ..-. o ~

,

~

,~ ~

,,~ ,30o , ~

, , ~ , ~ - - z,~

MAXIMUM T£MIq[RATUR[, eC

Flo. 15. Variation of elemental composition and weight of char with maximum temp¢rature attained coal pyrolysis in a crucible.46 (Reproduced from Kobayashi, H., Devolatilization of Pulverized Coal at High Temperatures, Ph.D. Thesis, MIT (1976), with permission.)

temperature CO evolution (Fig. 16), is related to the high temperature oxygen loss (Fig. 13), and the high temperature retention of ether linkages (Figs 6-9). The evolution of hydrocarbon gases in heated grid pyrolysis .7 and in an entrained flow reactor ~3 is illustrated in Figs 17-19. Low temperature evolution of methane and paraffins can be correlated with low temperature loss of hydrogen (Fig. 13), and methyl groups and aliphatics (Figs 6-11). Formation of olefins appears to result from the cracking of paraffins. and formation of acetylene appears to result from the cracking of olefins (see Fig. 18). The lines in Figs 18 and 19 are the predictions of the pyrolysis theory using the rates of Table 1. Figure 20 illustrates the effect of varying the kinetic rates by factors of 10 for the simulation of methane, paraffins, olefins and acetylene. The simulations with the base case rate constants of Table 1 provide the best fit to the data for paraffins and olefins. For acetylene the simulation is basically inaccurate due to soot formation. For methane the base rate x 10 is no good but the base rate x 0.i provides as good a fit as the base rate. Gas evolution data for slow constant heating rate experiments t3'a9'*°'*3'*8 are illustrated in Figs 21-33. Each gas species appears to have a characteristic evolution pattern which is insensitive to rank. Ethane, propane, ethylene and higher paraffins and

ROSA

I0.0

BEULAH

0 ¢1 0 Cml / J - 4 sec Hold at: T e m p e r a t u r e

35.0

-~ ¢e O ¢e|

5.0

6 mr. 8

.,=

% ~ ~ b ~ - -.cc;~.

~" 0

. ~ ,,(

PITTSBURGH BITUMINOUS

~VAGE

1oo

35.0

"el ell " o~

s a

m 5.0

300

600

900

1200

1500

1800

o ~ 3OO

600

900

t200

DEVOLATILIZATION TEMPERATURE (°C).

FIG. 16. CO and CO 2 evolution from pyrolysis in heated grid for I0 sec in vacuum.47

1500

1800

Finding order in coal pyrolysis kinetics

ROSA

335

BEULAH

5.0

-ex tll'l)~'~l HETItA.qE

x~,..,~d

@, C21t2

d

O

"

.

.

.

.

|

X

J

SAVAGE

"e,X . H~t HETILANE •C2H2 DROGEI~

600

900

"4) X. I.O tIET CIYDROGEIq 2•H2I-IANE

6

x

0 300

oX

O

•

PITTSBURGHBITUMINOUS 5"01

1200

1

-@ HYDROGEN'/ x HETH.~E

2 r= 14 sec Hold a4)t C.,?.H "reBpersture

1500

e

IS00

300

600

900

1200

t

e

1500

1800

DEVOLATILIZATION TEIqPERATURE (°C)

FIG. 17. Hydrogen, methane and C2H2 evolution from pyrolysis in heated grid for 10 sec (or 4 sec/~ ) in v a c u u m . 47

olefins evolve in a narrow temperature region slightly above the tar evolution. Methane peaks at a temperature just above the light hydrocarbons and continues evolving at higher temperatures. CO2 and CO each show at least two distinct peaks characteristic of at least two distinct sources for each species. H 2 evolves at the higher temperature over a wide temperature range. Where more than one coal has been run in the same apparatus, the evolution peaks have similar shapes and occur at roughly the same temperatures, indicating rank insensitive kinetics. In Figs 21 and 22, 39 the peak location for almost all the species vary by less than + 15°C among the four coals. The temperatures at which the peaks occur are summarized in Table 2. While the peak positions are rank insensitive, the amounts of species evolved vary with rank. In Figs 23 and 24,40 the data are more scattered but the conclusions are the same. The peak positions for five coals are shown in column 3 of Table 2. For most species the peak positions are within __20°C for the five coals. As seen in Table 2, the order of the peaks is the same as for Ref. 39 but corresponding peaks occur at lower temperatures. This is unexpected in view of the higher heating rate. In view of the small variations among coals for each experiment, the difference is most likely due to temperature measurement or heat transfer differences.

The data from Campbell 43 (Fig. 25) and column 4 of Table 2 exhibit a similar order of peaks but occur at a slightly higher temperature than the corresponding data of Juntgen and van Hook. 39 Data for vitrinite from van Kreveien 4s (Fig. 26 and column 5 of Table 2) also follows the normal order of peaks. The exinite and mieronite (Fig. 27) exhibit weight loss at a slightly lower temperature than the vitrinites. Data for 10 coal samples from Solomon e t a l . 13 are presented in Figs 28-33 and column 6 of Table 2. The elemental analyses for the coals are presented in Table 3. The data include one repeated experiment for a Pittsburgh seam bituminous coal experiment with samples of this coal which oxidized after 13 and 504 hr of drying at ll0°C in vacuum. Pyrolysis was carried out by heating the coal in a wire grid rapidly to 150°C and then at 30°C/min to 900°C. The grid is located within an infrared ceU swept by 0.7 liter/rain of nitrogen at 1 atm. Infrared spectra of the evolving products are obtained every 3 sec with a Nicolet 7199 FT-IR. Specific regions of the spectra are integrated to give the amounts of a particular gas in the cell as a function of time. The scale of the ordinate is in uncalibrated units which are proportional to the evolution rate. The tar amounts are indicated by scattering of the IR beam. While this method is not quantitative, it does indicate the onset, peak and con-

336

PETER R. SOLOMONand DAVID G. HAMBLEN o

o

ao P!=mFI N O

=_..

'2- 130 m v x . o X OI.I[FtN

X CLFFIN +' CZMZ

+ C2HZ

,.,

~o.

J

t

i - "~°

0 {: •. Q

+

to.0

Zr,.O 3Q.O ~o.a INJIEC'I'I~I

So.O " ~ . 0

÷

-7c.0

P~$1TION O1

IK,.ECI"~I

tl~JITIflN

~'q

O

"

m d~3~m

/

i:1 +

a

/

e>m.eF m

,- ~. .cz.z

/

/

/

,i! 2 Q

~ . o 7~.o K,m.Bfim.o In.O I ~

~.o-~..

pvm.vsls t m . e m ~

~QO.O 8QQ.O I~0.0

nc~- c

IOQQ.OIZOQ.O I~OQ.O 1800.0 tOO0

PYI~LYSIS TI~IqPI~I~ITUI~

~G

C

FIG. 18. Paraffin,olefinand acetyleneas weight percent of D A F coal for coal pyrolysis.(a) Pittsburgh bituminous coal in entrained flow reactor with nitrogen at 1100°C. (b) Beulah, North Dakota lignitein entrained flow reactor with nitrogen at 1100°C. (c) Pittsburgh bituminous coal in heated vacuum for I0 sec (datafrom Ref.2). (d) Beulah, North Dakota lignitein heated grid in vacuum for I0 sec (datafrom Ref. 13).

TABLE 2. Summary of species of evolution data for slow heating experiments Reference Heating rate (K/rain) Number of coals Species

Peak #

H20 CO: H20

Tar or weight loss Light hydrocarbons CO CH, CO2 CH4 CO H2 N2

CO * Excluding anthracite.

1 1 2 1 1 1 I 2 2 2 1 1 3

(39) 0.0025 3

(39) 1 4

(40) 3-6 5

(43) 3.3 I

(48) 1.8 2

(13) 30 9

Peak temp. (°C)

Peak temp. (°C)

Peak temp. (°C)

Peak temp. (°C)

Peak temp. (°C)

Peak temp. (°C)

460 ± 10 480 ± l0 525 _+10

390 ± 20

507

420 ± 10 370 ± 10" 575 ± 15 670 ± 15 660+15 710 ± 10 700 + 30 910 ± 15

480 + 20 530 + 10 620 ±20 660±60 700 ±30

527 537 587 637 677 747 767

520 ± 30 450 ± 15 470 ± I0 500 ± I0 560 ± 20 700

510 +20 520 +20 530 +20 610 + I0 760 ±40 710 ± I0 840 ±40

Finding order in coal pyrolysis kinetics 0 f~J.

337

0

mOc~ o

o o w.

i:

i! ".0

0

ii 1o.o z,.o

~.o

I ~C'Yb"~q

,~d.o ~ . o

~31'Yl~

ed.o

'm.o

0

-td.o

J

m.o

~.o

,,,:,.o sd.o ed.o

"/~.0

O

'!do cm

COc~ m

O O,

d

i:

O m

il

o O

O

4

o °.

o

A

¢o

~A

A

A A

A

i

liO0,O llO0,O I 0 0 0 , 0 1200,0 IqeO0,O llO0.O 1900 PYI~OL.YSl9 TEHPEIRITnJR( DEG C

|

FIo. 19. Methane as weight percent of DAF coal for coal pyrolysis. (a) Pittsburgh bituminous coal in entrained flow reactor with nitrogen at 1100°C. (b) Beulah, North Dakota lignite in entrained flow reactor with nitrogen at 1100°C. (c) Pittsburgh bituminous coal in heated vacuum for 10 sec (data from Ref. 2). (d) Beulah, North Dakota lignite in heated grid in vacuum for10 sec (data from Ref. 13). clusion of tar evolution. The points in Figs 28-33 are data from individual FT-IR spectra. The order and shape of peaks for tar, light hydrocarbons, methane, CO and CO2 is roughly the same as for other reported data. 39,4°'43,4s The peaks for hydrocarbons vary by no more than 40°C (roughly a factor of five in kinetic rate constant). With reference to the figures, there is a systematic variation in position. with the low rank coals decomposing at the

lowest temperature and the high rank coals at the highest temperature. Figure c in Figs 28-33 shows a simulation for the constant heating rate experiment for the Gillette subbituminous coal using the kinetic rate constants and composition parameters of Table 4. Some modifications in the theory and adjustments to the rates were made in accord with the new constant heating rate data. The adjusted rates are also consistent with the

TABLE3. Elemental analyses of coals used in programmed pyrolysis (DAF) Coal

C

H

N

0 and S

Kentucky #9 Pittsburgh fresh Pittsburgh repeat Pittsburgh dried (13 hr) Pittsburgh dried 1504hr) Utah bituminous Illinois #6 Gillette sub-bituminous Big brown Texas lignite Beulah. North Dakota lignite

81.7 80.9 80.9 77.4 73.6 75.9 75.9 71.5 72.4 70.3

5.6 5.5 5.5 5.5 5.0 5.4 5.5 5.3 5.4 4.9

1.9 1.4 1.4 1.4 1.2 1.3 1.5 1.2 1.4 1.1

10.8 12.2 12.2 15.7 20.2 17.4 17.1 22.0 20.8 23.7

338

PETER R. SOLOMON a n d DAVID G . HAMBLEN

0 +

×

I

r~

+

X

©

o

z

z

OX+

O'Zt

O'Ot

0:~ £3rlooUJ

0:9 0:~ 0:~ LNg3blgJ LH0I 3rt

O'Z!

0"01

O'g 13n0og,,I

0'9

0"~

O'Z

0""

/.HO1:grs

£Ng3IJg,I

._~

o.

.o g

i

4) ,t.J C~ 4J~ cn co ~:

~g

O 0 O (:

0

O o'21

Le'OI

O'g 131"M~1~

o .o

0"9 O'V, 0:2 J.Ng"J~3J J.HOI ~'1

0";]!

0"01

O'g

13rlOl~d

0"9

0"1,

llsl]3U=J

O'Z

o

0 "°

IHO i

o 0

.i.Jb.4 o

0

o

o

m

o

o •

IL

I.I~. i.J 7.

0

Q

o

0

o'z[

o'ol

o:g t:~'couJ

o:g

0:~

.LNg3~Ig,I

0'2 LHOI:~I

0""

0

o"2t

o'ol

o:g £:Jnooua

0:9 J.Ng:~lga

o:e,

0'2 Ix'31~rt

0""

Finding order in coal pyrolysis kinetics

339

:: Hleinflch Dtckebonk Deckel~onk Gustov

~[g~K]

V0 • 9.Ocn~/g Vo= 13.'7cm3/g

Gustov vo• 16.3cm-Vg Furst Leo~d Vo,30.3cm3/g

%/0"3 97 cm31g Vo. 378 cma/9

FOrst t,,~:~ld re,3'-? c~/9

I/,~\

1.6"

,~°

1.21.0

o

0.5

0.4

4;o 600

800 I'ooo ~

• He,nr,¢h • D,cket~onk • Gustov ,Furs! i.toDo~

400

86o

600

Er~ATIYRE °C

VO, 2.79 cm~/g V0, 3.35 cm.lyg %--5.28 cm*/g Vo:7.57cm3/g

•, I..leintlch Vo--12.7 cm3/g • Dckebonk Vo= 13.6 cm3/g • Oustov V0• 15.5 cm3/g • FORM LeoDold VoZ25.2 cm3/g

/

/ / / // / /

,, r~-_eJ

• r t~ KJ

1.5F

M,

'

CO

/

i: 400

°

600

800

I000

0

I

400

600

I

!

800

J

l

I000

TEM'PERATURE °C ,,I.~,nr ,:h • D,ckebonk

COa

.02

V0.3,2 cm~/g VO: 3.6 cm3/g ° Gustav Vo: 3.8 cm~'g Agurst LeODO~ Vo--t..1 cm3/g

.01 ,

,

400

Ik~

600

800

TEAl?ERATI.FRE °C Fu3. 21. Emission rates of non-hydrocarbons during pyrolysis of coals of different rank ra = 1 K/rain.39 (Reproduced from Juntgen, H. and van Hock, K. H., An Update of German Non-Isothermal Pyrolysis Work, Fuel Processing Technol. 2, 261 (1979), with permission.)

high temperature entrained flow reactor data as well. In addition, computations were made with rates ten times higher and ten times lower. The slow heating rate experiment is sensitive to rate variations for all species. A factor of ten in rate results in about a 65°C shift in peak position. Tar evolution (Fig. 28) exhibits the narrowest peak. The data can be modeled nicely with a single source (Fig. 28c). The rate parameters in Table 4 for the base case are the same as in Table 1. The rank variations in the temperature of the peak evolution is small. The lignites peak at about 490°C while the highest rank bituminous coals peak at about 530°C. This corres-

ponds to about a factor of five in rate. The base rate fits the bituminous and sub-bituminous coals. The simulations for a factor of ten higher rate is about 20°C too low for the lowest temperature peak (Texas lignite). The simulation using a factor of ten lower rates clearly does not fit the data. The evolution data for heavy aliphatics arc presented in Fig. 29. The peaks are slightly wider than for tar. The high temperature tail on the peak may be an artifact of the experiment which is caused by gas not immediately swept from the cell. This tail is not modeled. The rate for the base case is the same as in Table 1. Rank variations in the data are small. The

340

PETER R. SOLOMONand DAVIDG. HAMBLEN

/

QO~ 03~

iA,m~ ~ m n e • m-2-~ne

t~m

b ,,

el.l.

¢

C,H.

u=

g= ° l

3OO

4O0

$00

600

7OO"C

(A)

(B)

(a) Rates of emission of some saturated (A) and unsaturated (B) gaseous hydrocarbons for a Fiirst Leopold coal with 39.5 % VM (daf), m -- 2.6 x 10-2 K/min. (The values for methane have to be multiplied by 10.)

d a0~

I'F 0gaa

/ Joo

~00

s/¢

"c

(b) Rates of propane formation for different coals at very tow rates of heating, m = 2.5 x 10- 3 K/min. (a) Heinrich coal 10 % VM mar; (b) Dickebank coal, 19.5% VM mat'; (c) Gustav coal, 29 % VM maf; (d) Fiirst Leopold coal, 39.5 % VM mar. x represents measured values. Curves are calculated according to eq. (3). FIG. 22. Evolution of hydrocarbon gases. 39 (Reproduced from Juntgen, H. and van H e e l K. H., An Update of German Non-Isothermal Pyrolysis Work, Fuel Processing Technol. 2, 261 (1979), with permission.)

lowest peak at 500°C is for a lignite and the highest at 540°C is for a high rank bituminous. Rank variations, therefore, can produce a factor of five variations in kinetic rate for heavy aliphatics. The simulations for factors of ten higher and ton lower rates do not fit the data. Tar and heavy aliphatic typically account for 5075 9/o of the volatiles and up to 90 ~o of the initially released volatiles. Thus, on the basis of the above results, rank variation in initial volatile release must be small. The evolution of methane is presented in Fig. 30. The peak is wider than that for tar and is fit with two sources, methane-loose and methane-tight. The methane rates of Table 4 are a factor of five to ten

lower than those in Table 1. As can be seen in Fig. 20, the Table 1 rate × 0.1 provides a good fit to the data for pyrolysis in the entrained flow reactor at 1100°C, so this change appears consistent with the high temperature pyrolysis data. Additional simulations must be performed to validate the fit for other cases. The variations by factors of ten from the Table 4 rates can clearly be rejected. Data for ethylene evolution are presented in Fig. 31. Evolution starts at the same temperature as for the heavy aliphatics but the peak is broader. This is not surprising since ethylene appears to be formed both as a primary product and as a secondary product of cracking of heavier paraffins and olefins. The peak position varies from about 550°C to about 5900C.

Finding order in coal pyrolysis kinetics

lV03 lVlllgltJ0 J0 IIOIZ~llt

341

"UA

q

,me

c¢

| Id.I >O'J

m+

z

,.J O OC >. 41,.

.C i,q t l I n ' l l l t - ' l Y 0 ~ l I1V11911OII "II01,L~IOA) | 0 ] A f t

W 0 3 l V l I I g l M 0 i l l II01L~+IIJ 'Ull

:+

o 4~

+< <

u)

o CL

O¢ Id,. rlJ ~s +_1 I,kl 1,4 __l C) n,. Ib

iplll • "lllW- I¥0~) i l Y l l O / 1 0 N ' l i 0 1 J r l l 0 A | :10 | l V l l

342

PETER R. SOLOMONand DAVID G. HAMBLEN

--O-

N!

--o--

CN4

--O-- ¢0 •--O-. TOTALW'r.

'1,

;

i l.I

--I.I

o

I

I

Ill

i

411 NI TIMOI[llATUII|.IC

I

I

*

Im

PYROLYSIS YIELOS FROM A WYOOAK COAL

b

12

I

.F--+., ~

"-

CN4

"--I

..-

"

~

L., |

- %

-M I

1~

\IUO

I

+

Ne

II

T|IIM~TURI, ~

PYROLYSIS YIELDS FROM AN ILLINOIS NO. 6 COAL

IA a C

-,.,-

~

,.,

•

5'

_/\ :

I

..+..._

+.

+

m:: z £0

+

+

/

~,-..~_

~

I -/.t/ ~]

TOTALWT. I _____.J

//

-'-*

\~

~,

\

I

~

I

"

-,."

+ E

S

.~._

'

I |R

I l

I I TIWIRATURI,eC

I I

i 1114

PYROLYSIS YIELDS FROM A PITTS8URGH SEAM COAL

FIG. 24. Pyrolysis yields from three coals. 4° (Reproduced from Weimer, R. F. and Ngan, D. Y., ACS Div. F,Jel Chem. Preprints, 24, # 3, p. 129 (1979), with permission.)

Finding order in coal pyrolysis kinetics

°0

+'+

o.3

.~

'+

343

I

I

..YJ"

./

."

-

I-0

I0

~0"5

.~

O, 2 D

0.!

0.3

'

i I

I

'

I

0

|

400

9OO

o 700

100

Tm~=mlhre

*¢

b

(a) Rate of gas flow vs teml~rature for vitrinite of coking coal E at 1.8°C/min. Dashed line represents rate of weight loss against temperature, referring to right-hand ordinate.

Argon 0.2

~'~/"~~~---co.

t(2_

1"5

j/'x, / Total

0.!

, ~ J

'~1.0

i

//

+j

,

.

10

J

H1

0"$

I

0.06

'

I

'

c

•

.~A/ -m,r--'~t

/,oo

0.04

[/" ~(.------(thylene

900 "=(' 1100 Temperature (K)

~

*.

5oo Temperature

-

.

60O

0 7OO

"C

FIG. 26. Pyrolysis of two vitrinites.48 (Reproduced from Fitzgerald, D. and van Krevelen, D. W., Fuel, 38, 17 (1959), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©.)

0.02

700

..~ ,

(b) Rate of gas flow vs temperature for the vitrinite By of high volatile coal B at 1.8°C/rain. Dashed line represents rate of weight loss against teml~rature, referring to right-hand ordinate.

Ethane

°~oo

J

1300

F1G. 25. Rate of gas evolution vs temperature during pyrolysis of Roland seam coal at a heating rate of 0.055 K/sec. The rates are given in cm a K: to convert to time units. multiply the heating rate. The solid curves represent numerical computer fits to the experimental data. The dashed line gives the constant flow rate of Ar through the system. 43 (Reproduced from Campbell, J. H.. Fuel, 59, 102 (1980). with permission by Butterworth & Co. (Publishers) Ltd.. publisher ©.)

The simulation uses the same parameters as for the aliphatics in Fig. 29. The simulation appears to model the initiation of ethylene formation, but not the high temperature tail. The data appear to fall between the Table 4 rate and 0.1 x the Table 4 rate. D a t a for C O are presented in Fig. 32. C O has two distinct sources designated CO-loose and CO-tight in Tables 1 and 4. Both sources produce broad peaks. All ranks of coal have CO-tight whose source is probably aryl ether linkages which may be in the coal originally or may be formed from phenolic O H during water formation. The peak varies between 800°C for

344

PETER R. SOLOMONand DAVID G. HAMBLEN ,

~

IS

11

1.0

i

,

,

r Total

1.0

I.

)

i s

io!+- "' -

./

1

.

//

io.,

/

J

),

:

CH4 -

too

/'

|

:

i

//

s00 T*mp~li~e

600

700 *C

(a) Rate of gas flow vs temperature for the exinite Be of high volatile coal B at 1.8*C/min. Dashed line represents rate of weight loss against temperature, referring to right-hand ordinate. Note double maxima in CO flow.

o~ ~00

~o h~durw

600

o

700

(b) Rate of gas flow vs temperature for the micrinite Bm of high volatile coal B at 1.8°C/rain. Dashed line represents rate of weight loss, referring to right-hand ordinate.

FIG. 27. Pyrolysis of an exinite and micrinite."s (Reproduced from Fitzgerald, D. and van Krevelen, D. W., Fuel, 38, 17 (1959), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©.)

the Gillette s u b - b i t u m i n o u s a n d 880°C for the Pittsb u r g h s e a m coal. T h e d a t a fall between the simulations for the T a b l e 4 rate a n d 0.1 x the T a b l e 4 rate. C O - l o o s e a p p e a r s p r e d o m i n a n t l y in the low r a n k coals. T h e peaks o c c u r at a b o u t 530"C + 20"C. T h e

d a t a are best simulated using the T a b l e 4 rate with factors of ten higher or lower rates n o t fitting the data. D a t a for CO2 are presented in Fig. 33. CO2 evolution is the m o s t r a n k sensitive of the species presented. W a t e r (not presented) is also r a n k sensitive. T h e

TAaLE 4. Kinetic rates and functional group compositions Composition parameter

Gillette coal (WT ~ DAF)

C H N S (organic) O

0.720 0.047 0.012 0.005 0.216

Kinetic rate constants (see- 1)

1.000 Yt° Y10 Ya°

CO2--extra-loo~ CO l-lOOse CO2--tight

Y~

H20

Ys° yo Y7° Ys° yo Yt°o Yt°t Y°2 Yt°3 Yt°4 Y°5

CO--ether loose CO--ether tight HCN--loose HCN--tight NH 3 CHx--aliphatic Methane--loose Methane--fight H - - aromatic C--non-volatile S--organic

Total X ° Tar Cracking rates: Parafflns-Oieflns Olefin-Acetylene

0.0080 0.0240 0.0080 0.0503 0.0900 0.1589 0.0071 0.0154 0.0000 0.1447 0.0130 0.0130 0.0126 0.4500 0.0050 1.0000 0.2500

k 1 = 0.10E + 15 exp [ - (21700 + 2000)/T] k 2 = 0.10E + 15 exp I"- (28400 -t-3000)/T] k 3 = 0.10E+ 15exp [ - ( 3 6 0 0 0 +3300)/7"] k 4 = 0.17E + 15 exp [ - (30000 + 1500)/T] k s -- 0.17E + 12 exp I"- (25000 + 2500)/T] k 6 = 0.10E + 15 exp [ - (40500 + 6000)/T] k7 = 0.17E+ 13 exp [ - (30000 + 1500)/T] *k s = 0.70E +08 exp [ - (32000)/T] k 9 = 0.12E + 13 exp [ - (27300 + 3000)/T] kto = 0.17E + 15 exp [ - (30000 + 1500)/T] kll = 0.15E + 14 exp [ - (30000 ± 2000)/T] k]2 -- 0.34E + 12 exp [ - (30000 ± 2000)/T] kt 3 = 0.16E + 08 exp [ - (23000 ± 2300)/T] k14 = 0

kx = 0.45E + 14exp [ - (26400 + 1500)/T] koL = 0.15E + 12 exp [ - (27600)/T] kxc = 0.21E + 08 exp [ - (22000)/T]

* Distributed rates have not yet been determined.

Finding order in coal py.rolysis kinetics

345

a

• Kentucky Utah + Pitt - 13 • Pitt - 0 -Pitt - 0

,

"" "+" e.4-

P

.....

,

-r ......

'

,

,

"';cizz,tt,

~

N Z l 1 :l.no '11e

*Beulah .Pitt

.....

,'~;'~'~;~':~',

......

-

II

"~'

-

$04

Texs8

" '

•

.FJ'+

C

]0 Base

IV

Rate-Table

xO.l

............. ........... i"~"'.......... 7",, zo5

~ob

-6oh

eo,

~ooo

T[~[ i 150

i

i

200

~flO

i ~

i

i

i

500

600

1an

I tl~[

IL41UII~

t~bo

tzoo

t&m

leoo

(S[CI ] I1~

i 900

I°()

FIG. 28. Evolution of tar for 10 coal samples pyrolyzed in 1 arm. of nitrogen, flowing at 0.7 liter/min. The coal is heated rapidly to 150 o C and at 30°C/min to 900 o C.

346

PETEg R. SOLOMONand DAVID G. HAMBLEN 24.000 ,; K e n t u c k y Utah ÷

..

Pitt

-

13

• Pitt

-

0

16.000

I!. 000

• 000

•

t"

,

"

I

!

i

|

I

I

24. 000

b

-Gillette Illinois .*Beulah •P i t t - 5 0 4 -- Texas

== 16.000

p

g

8. 000

,..I 0

.000

24.000

x 10 ~dABase

16.000

I

R a t e - Table IV

,,l'I/

!°ii

8. 000

Q

• 000

,- .......

0

200

qO0

600

IlO0

1000

7 ....... 7

IZO0

lqO0

11~10

11100

TIME tS[CI I

l~

!

2OO

I

3OO

I

*m0

!

e

S00 t00 ; [ ~ M T t n l t°¢)

I

100

e

NO

i

N0

FIG. 29. Evolution of aliphatic gases for 10 coal samples pyrolyzcd in 1 arm. of nitrogen, flowing at 0.7 liter/rain. The coal is heated rapidly to 150o C and at 30 o C / m i n to 900 o C.

Finding order in coal pyrolysis kinetics Z .~oo

347

a!

I •

Kentucky Utah . P i t t - 13 • Pitt - 0 -- Pitt - 0

•

I. 200

•

i

i

I

i

i

• Gillette x Illinois * Beulah • Texas mPitt - 504

,"4

i, t

% "

0

.000

. . . . . . .

w

w

. . . .

J !

w

i

i

1 . ZOO

C • ~te-Table

IV

.800

.~00

. t'lt~

Zoo

'tO0

8t~

8t~

ltXX3

IL~O

lttDG

1800

1800

TIME (SECI |

,

150 200

l

|

~0

llO0

!

l

!

600 700

500 TENIE~TUIE (oc)

!

~

l

900

30. Evolution of m e t h a n e for 10 coal samples pyrotyzed in 1 arm. of nitrogen, flowing at 0.7 liter/rnin. The coal is heated rapidly to 150°C and at 30°C/min to 900°C.

348

PETER

R. SOLOMON

and

KentucKy Utah

•

÷ Pitt

DAVID

G. HAMBLEN

4~

- 13

_.Pitt :

0

P it t

0

..~~

.{~lO

.';.

w. + • 02G

~;~ •

~

•060

Gillette

s

w

.....

-e%,

u

°

°

!

"

.

u

"%"

b

x Illinois • + Beulah • . • Texas , xx -- Pitt - 504 ."

-j

.0~0

.M

'.

G -s

P. p

.0~

;

'*

./,~

"~.

•b: ÷

.'.

,..,,,

.....

~'~

"4,#

r

,

•

-

"..~ '~¢

'k.

!

i

...

":i..~.';"

'"

~,~.w.s~

l

!

!

•060

6

I0

x

.0~0

•

OZO

"**'.,%.°~..o'~,°.** N '-

.000

...~-.

o

~

°%°°*%.

zob

~ob

cob

sob

~obo

TIrll[ i

150

u

200

i

|

300

~00

i

i

lzbo

1~5o

lsbo

zemo

(SECI !

500 600 700 T(~NDiERATUflE(°C)

!

~

!

900

FIG. 31. Evolution of ethylene for 10 coal samples pyrolyzed in 1 atm. of nitrogen, flowing at 0.7 liter/rain. The coal is heated rapidly to 150°C and at 30°C/min to 900°C.

Finding order in coal pyrolysis kinetics

349

I . 200

a

• Kentucky + Pitt • Pitt -- Pitt

-

13 0 0

.800

.qO0

•

L

OOO

i

D

i

;

•

!

;

!

i

g.~oo ,1 - G i l l e t t e

I--Texas

g m

b

I ~ Illinois I *Beulah ] .Pitt - 504 I,

600

m v

o

o

~

~

,,

.800

• 000

/

Z . ~,OO .

1. BOO 1

[

.^

~ - B a s e

Rate-

*l

.800

.(300 0

ZOO

BOO

~00

~

1000

1200

lqO0

IBO0

liD0

TIIqE ( S E C I ! 150

! 200

. 500

. ~00

i 500

i 600

I 700

! 800

i

TEIPEItATIJE C°O

FIG. 32. Evolution of CO for 10 coal samples pyrolyzed in 1 atm. of nitrogen, flowing at 0.7 liter/min. The coal is heated rapidly to 150 oC and at 30°C/min to 900°C. JPECS ~ :-,-F

350

PETER R. SOLOMONand DAVIDG. HAMBLEN 12. OOO

•

•

.

a

Ken tuc'ky Utah Pitt - 13

• Pitt -- Pitt

- 0 - 0

8. 000

/~++

""

N

m

u

+

4. OOtJ

;

/ ÷

•

+++

/

.

". ~,,~.

.

.',~;.

i.,,""..,..-'~---~

a .

oo0

24.000

b

,.Gillette ~ Illlnolm

*Beulah

.Pitt -

~ % ~

-

504

~

~.~.

Texa,

".+++++.

16.000 o~

8.000

•

000

w

!

!

!

!

i

i

24.000

C •

Rate-

Table

IV

16.000

8. 000

•

000 0

zoo

q,oo

ira6

e~

,~o

z~

l~

16OO

i~Q

T|MF. tSEC! e

150

|

2m

|

l~

!

m

i

SM

|

i

i

!

im

nO

am

lm

lzmq[Mnmz ¢~1

FIG. 33. Evolution of CO 2 for 10 coal samples pyrolyzed in 1 atm. of nitrogen, flowing at 0.7 liter/rain. The coal is heated rapidly to 150°C and at 30°C/rain to 900°C.

Finding order in coal pyrolysis kinetics

experiment 3s'51 are presented in Figs 37-40 for CH4, C,H4, Hs and C O , respectively. The data show roughly similar trends in the lignite and bituminous coals with evolution from the higher rank coal occurring at about 50°C higher temperature. In Fig. 40 the CO s data have been simulated with a distributed rate model using the same kinetic constants for both the lignite and bituminous coal.l 6 Pyrolysis data at very high heating rates, obtained in a shock tube s~ are presented in Fig. 41. These are for very rapid pyrolysis at high temperature. The data for the two coals vary only in the amount of light hydrocarbons produced. If the particles are assumed to be at the gas temperature for the nominal 1.4 msec, the kinetic rate constant would be 7.1 x 10' at 1120°C which is in reasonable agreement with the data of Badzioch and Hawksley a5 as illustrated in Fig. 1.

tO

e'72"c

-

I0 tilth t

/

c-t~ 06

.\

17

~6-cha,

~

~a.: ,~o~

Fiu*d,ling gos:Nlot

*0: 0,

-" CO

0~-

~'

2

z

,

~-

~

,~l~._~._.~...._~,

T,me offer coal oadit~on [ s} a

Devoietilization of Ind;Ina high.volItilI C bituminous

coil 10

w

] ]

/

i

!

~

g?2"C 10Itm COO! $,][e: I.SSmm Bid-char Size ; 1 " 2 0 ~ Fluid*zing got: Nzlt $OI/ff.n COol weight: 0'2¢Sg

/~CH~, [ ~ c* o O!

i

~

3.3. Weight Loss

E

g 0~ c~

;

2

6

s

,o

,~

,',

~llme otter c~t oddition ( s )

b Devoiatflizstion of Pittsburgh bed ¢oa! ~'C

o

06

.S 04, -

w

~

,

!

!

,

s?2'c

r'H6 \ ~,,\

I0 I t m CMi Sile : t'SS mm Ik.d- char s*le : 1"20mm

~

Coot w,~t

/ ~ ~ ' , ~

\\

: 0.2?0 ~1

FluiOizlng giiL: Nalt

0"2

S

2

6 8 10 12 Time ofier ¢0~| Iddition ( | |

1~

351

16

C Devolitilizetioq~ of Wyoming subbituminous C cost

FIG. 34. Pyrolysis of three coals in a fluidized char bed.49 (Reproduced from Morris, J. P. and Keairns, D. L., Fuel, ,58, 465 (1979), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©3

results may be complicated by CO2 evolution from minerals and possible oxidation of the sample. C O , appears to evolve from two major sources designated CO2-1oose and CO,-tight and one minor source, CO2-extra loose. The data for the low rank coals appear reasonably rank insensitive and well simulated by the Table 4 rates. The COs evolution for high rank coals exhibits much wider variation which has not been elucidated. Gas evolution from coal pyrolyzed in a fluidized char bed 49 or a fluidized sand bed 5° are presented in Figs 34-36. The evolution curves for different coals look almost identical except for variations in the species amounts. Data for coal pyrolysis in a rapid heating rate

Weight loss data is the least useful to compare because it results from contributions from all the species, each with a different kinetic rate. As the mix of species varies, so does the "apparent kinetic rate". Tar, hydrocarbon gases, some CO2 and CO species evolve with rapid rates while CO and H2 evolve at lower rates. This trend is illustrated in Fig. 42 which shows the total volatile yield vs temperature for a 10 sec pyrolysis in a heated grid in vacuum. 47 The bituminous coals show rapid weight loss at low temperature due to high tar and aliphatic gas yields. The lignites show rapid weight loss at the same temperature but also substantial weight loss above 1000°C due to CO evolution. To the extent that the tar and aliphatic gas evolution dominate initial rapid weight loss, the comparisons among coals are usdul. Additional weight loss data for the experiments already considered appears in Figs 23, 24, 26 and 27. For any given experiment, the temperature at which the most rapid weight loss occurs, appears insensitive to rank. This is consistent with the observation that the maximum rates for tar and aliphatic gas evolution appear insensitive to rank (see Figs 28 and 29). A recent pyrolysis study 5s compared the weight loss for 5 bituminous coals, an anthracite and a lignite (Fig. 43). Excluding the anthracite (line 1) and lignite (line 7) weight loss for 126 micron particles heated to the final temperature in 1 sec is initiated at 460°C + 15°C. The lignite weight loss appears to start at 500°C and the anthracite at 600°C. Thermograms of three additional coals sa are presented in Fig. 44. Measuring the initiation of pyrolysis weight loss as the intersection of the extrapolated weight loss curve to the initial moisture free weight, gives a temperature of 430 + 10°C for a heating rate of 160°C/min. Weight loss data for 20 min pyrolysis experiments s" for 5 coals are present in Fig. 45. Initial weight loss below 2000C is from moisture loss. The temperature for initial weight loss is 290 + 10°C except the anthracite (500°C).

352

I ~ T ~ R. SOLOMONand DAVID G. HAMBLEN

",~

i

I#1 .~ -~l i.

0

/ii

0

,-~

~0 ~

"\.

¢1

-=-

,

,

,

,

~

o

o

o

¢1

o-~f

(IOOO

lop

~/~

%)

~ _~

-~

splo!~

~y~'~

i

' ,

,

0

o

(lOOO

lop

~?'i ~

-o-"

Ot j

I,,,,

,,,,,, ~

.~ i."

$1i 0 ,q/,qli % )

¢1

o'l

.~

I

I"I'1 ,,,,~ i l

Splll!l

×

~11

i! ~ "

Iii 0

"i!

nn ~ . C

G . -~ g

v

.o

!

~f-I~

"/:

I~.-~ o o._~I

~eg _u

• o

I

¢1 ul

'

I

¢i *tl

(IO0~l

I ¢Ii .,,I

l O P ~ll~q % 1

I

I

iii *~l

ill i~l IPlIIA

.x

I o ~

0

Finding order in coal pyrolysis kinetics

I

U

I

I

•

353

I .

,,~

+

~D

i |

O

<"

~?.°"

=m+

c~

,..+~

~m

= ,.,, =.*.-,

".

"~

o~.-.. + + + m gm.+ z ~ u.~-~

•

~R+ + "++ ~o'~,~

,,+,,

, , ~ ,

,,

J,,,~,

-

,+_+,~+°'"++ --

- - o ,,oo+ ,°,, . , . . , . ,

!

!

i

l

i

,+

+.+~ .-;+.+

,,,,.,

i

'

I

C~

/t,

i

r~

~,~

Cmt~--

C+,?.

~<~

.\ !

I

m0.~ "+8~ I

I

I

I

I

I ,,,11

(100:)

lop

~IA*'I.)

$1DIm!A

,,_ore _~+.+._

.o

i

'

I

~ ~

i

8

o "dp

:[4

PETER R. SOLOMON and DAVID G. HAMBLEN

354

J • 2~

(1.8

~N

0.6

!

_-. 1.2

12 ~ 0,~ i

=~

Jff

~"~

2.0

~

O ttlntt.

:o

t.

I

600

[

1

I

1

.6

[

I ,00

I ^ ~-,I 600

~ [ x [ 800

[ i000

I

0,~

N

°

~

Thesis, MIT (1977), with permission.)

There are a number of properties which are clearly coal rank dependent. These include: I. 2. 3. 4.

db

5. 6. 7. 8. 9.

_

• • •

Io

o

~x~x

4. RANK D E P E N D E N T P H E N O M E N A

7= ~ 1 . 0 -

:i=

-o

~

Fro. 39. Hydrogen evolution in pyrolysis of a lignite and a bituminous coal. 51 (Reproduced from Suuberg, E. M., Ph.D.

I

1,2--

,8-

0.8

x

PEAK TEMPERATURE. Oc.

1.q

~- -J

0.~

0 20(]

I000

FIG. 37. Methane evolution in pyrolysis of a lignite and a bituminous coal. 5t (Reproduced from Suubcrg, E. M., Ph.D. Thesis, MIT (1977), with permission.)

1,6

1.2

x

r

I

800

0.6

0.2

PEAK TEPI~RATUAE, Oc.

4oo

.

1.4~

~

1.2

~

1.0

•

I

600 I

5 I

[

800 I

I 1000.

I

[

I

i

N

__.~

__

oo x

0.~

2OO

~

2.8

1.6 ~

0.2

~

i

stt~tna..

2.0

1.0 i

~, ~

2,8

Ltgnttl Stt~lz~.

.e -

~_'-2

A A

/'.

A w

0 ^ 400

t

I

t

I

I

I .

600 -~ 800 i000 PEAK TEMPERATURE, OC.

FIG. 38. E t h y l e n e e v o l u t i o n in p y r o l y s i s of a lignite a n d a b i t u m i n o u s coal. 5t ( R e p r o d u c e d f r o m S u u b e r g , E. M., P h . D . Thesis, M I T (1977), with p e r m i s s i o n . )

Weight loss data for a bituminous coal and a lignite pyrolyzed at high temperature in an entrained flow reactor 46 are presented in Fig. 46. The weight loss data are remarkably similar. Weight loss data from another heated grid experiment 55 are presented in Fig. 47. The lignite weight loss is slightly slower, possibly from slower CO evolution.

Elemental composition. Functional group composition. Plasticity. Size of aromatic ring cluster or molecular weight of tars. Variations in bridging material. Porosity. Hydrogen bonding. Catalytic constituents. Guest constituents such as methane and other hydrocarbons not chemically bound.

While these properties affect the amounts of volatile constituents, the physical properties, the reactivity of chars and the molecular weight distribution of tars, they do not appear to strongly influence the primary product kinetic rate constants. The elemental and functional group composition (items 1 and 2) are most clearly manifested in the total yields of pyrolysis species as can be seen from the data presented. The coal's plasticity (item 3) may have important consequences for pyrolysis. For example, in an entrained flow reactor, coal particles have been observed to swell substantially, The swelling can drastically change the heat transfer by radiation and the fluid mechanical properties. Melting and swelling will also change the coal's pore structure and the pressure of volatiles in the pores. These effects are expected to have a strong influence on the molecular weight distribution of the pyrolysis products xT- t9 but may have only a minor effect on the kinetic rate constants. ~s The size of the aromatic ring clusters (item 4) will clearly have an effect on the transport of the tar. Tar from high rank coals will be heavier and therefore less volatile. This will have an effect on tar release which may be the cause for the systematic increase in the peak tar yield temperature with rank in Fig. 28. The transport of tar will also be affected by pressure as discussed by Anthony, 36"55 Suuberg, 51"19 Unger and Suuberg 17 and Solomon. ~s

Finding order in coal pyrolysis kinetics

355

10 •

Lignite

@

Bituminous

~

~

./"

6

• / @ ,@

mi

~oo

600 80o TF..~PERATURE (D£GREE$ C. }

m

m iooo

m

FIo. 40. CO, evolution in rapid pyrolysis of a bituminous coal and a lignite. Data points are from Suuberg. 51 Lines are simulations of Solomon et al. 1~ (Reproduced from Suuberg, E. M., Ph.D. Thesis, MIT (1977), with permission.) $a

/

/

O0 w

Montana lignite and slightly lower for the Beulah lignite. Another explanation for lower temperature volatile release in lower rank coals may be variations in the bridge material (item 5) linking the aromatic clusters. Oxymethylene bridges (possibly in low rank coals) should break at lower temperatures than ethylene bridges. Very low temperature evolution of tar from lignhe was recently reported by Suuberg and Scelza. 56 Results illustrated in Fig. 49 show up to 5 ~o weight loss below 700 K. The lignite data in Figs 28, 37-41 also show some lower temperature evolution not seen for the bituminous coals. Recent experiments on oxymethylene bridged napthalene and tetralin polymers show tar release beginning at these temperatures.18 Secondary heterogeneous gasification and combustion reactions will depend strongly on the porosity of the char (item 6). Large variations are possible depending on the swelling of the coal. Such effects will have a rank dependence. Variations in behavior from items 7-9 are expected, but the effects on pyrolysis rates do not appear strong.

/

/

/

1000

I~,oo

I 16o0

laoo

,

I I~

I 2o0o

r(K)

FIG. 41. Light hydrocarbon yields, based on the total mass of coal, for Pittsburgh seam (A) and Illinois # 6 (O) coals. Reaction dwell time is nominally 1.4msec in nitrogen. 27 (Reproduced from Wegener, D. C., M.S. Thesis, Kansas State University (1978), as reported in Lester, T. W., Polavarapu, J., Merklin, J. F., Fuel, 61, 493 (1982), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©.) Another possible effect due to ring cluster size (item 4) may be the retention of nitrogen in the char. Figure 48 shows nitrogen in the char after a 10 second pyrolysis in vacuum in a heated grid. a7 Compared to the two bituminous coals, the nitrogen appears to be significantly lower at high temperature for the Savage,

5. CONCLUSION This paper considered the rate of thermal decomposition of individual functional groups and the evolution of individual species (tars and gases) during coal pyrolysis. When data are considered from experiments in which different coals were pyrolyzed under identical conditions, there is little variation from coal to coal in the behavior of most species. The amounts of species vary from one coal to another, but when yields are normalized by the maximum yield, the temperature or time dependence of the evolution is insensitive to coal rank. A study was performed to determine the sensitivity

356

1~

R. Sor~oMo~ and DAVID(3. HAMBLEN ~ ~

_

_

•

•

'°

~

_

8 .

°o

~

I

o

g

,L~ZIIIO~I ,I .LN~IDN3 ~

1°

o

0

I~ A

_

Finding order in coal pyrolysis kinetics

357

tOO O

.7.s

e? S

Dakota

?S.O

I-I L~ 0

S0"0

S'O.O

i

)?.S

)?.S ,o 25'0

11.S

• Heohng role 160*Clmln • Heottng role &O'Clmin

I1.$

,

n~ 0 v

i ,. IT0

i 3&0

i St0

Temperature

i SIX) I'C)

i |S0

170 I010

(a) Thermogram comparison for two different heating rates in helium. Coal sample is Pittsburgh seam # 8 bituminous; sample mass is 2 rag; sample particle size is 170 x 270 US std mesh; gas purge rate is 40 cm3/min.

,

,

l&O

~IO

e

(b) Thermogram comparison for two different coals heated in helium. Sample mass is 4 mg; sample particle size is 200 x 230 US std mesh; coal heating rate is 160=C/min; gas purge rate is 40 cm3/min.

FIG. 44. Weight loss for three coals, s3 Ciuryla, V. T., Weimer, R. F., Bivans, A. and Motika, S. A., Fuel, 58, 748-54 (1979), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©.)

I

X = 0 = iN= O= ~=

80

I

I

I

I

BEULAH ZAP NORTH DAKOTA LIGNITE WESTERN K E N T U C K Y ~ I I NORTH BARBER ~PB NEW MEXICO MONTANA R O S E B U D S U B B I T U M I N O U S BOTTOM RED A S H A N T H R A C I T E x

•tR= 2 0 . 0 m i n u t e s

~t

El 60

g

x o

J

40 /

°--

__)(. . . .

D

~

/

--o--

-

I IO00

I 1200

/

-

_~___

0

8

/

/

zo

G

J

.x

_._~/

200

400

I010

lemperalure [ *C }

600 Temperature

I 800

1400

(°C)

F1G. 45. A.R. weight loss in equilibrium batch experiments, s4 (Reproduced from Agreda, V. H., Felder, R. M. and Ferrell. J. K.. Measurement of Coal Devolatilization and Elemental Release in Batch and Laminar Flo~v Furnace Reactors. 72nd Annual Meeting of the AIChE, San Francisco, Ca, November 25-29 (1979). with permission.)

358

PETER R . SOLOMON a n d DAVID G . HAMBLEN

I

80 m

I

I

I

LIGN ITk"

I

I

I

I

I

2100 K ~

.0

o,j~'O

7" o

oIF

,

~ O - - L 1940K

/

0

I

I I I I I L..,

F'URN&CE Tr MPrRATURC 0 2100K 0 1940 g 0 1740 K O 1510 K ~' 1260 g AIO00 K

o

,,,o

g°

o

/

:

IOK

o

-

W

80

~

I

I

I

[

I

I

I

1

I

I

J

I

I

I

B| r UMINOU$ COAl=

60 m --

40

i

I

I

FmuRNAC[ 0 2100 0 1940 0 1740 Q 1510 ~ 12E0 A 1000

m

;~

t

)..)

I t I ~

~'l

I I I [__

TrMPI[R&TUR[ g x K I( K g

0

ul

~I

V

20 ) 1

0

W

O

V

~_

0

A

0

I

I

I

I

I

I

I

I

)

10

20

30

40

50

60

70

80

90

Rr'ACTION

TIIE;

L) I~

I )1 140 180

I 220

! ms)

FIG. 46. Weight loss vs residence time at different furnace temperatures. '6 (Reproduced from Kobayashi, H., Howard, J. B. and Sarofim, A. F., Coal Devolatilization at High Temperatures, 16th Symposium (International) on Combustion, p. 411, The Combustion Institute, Pittsburgh, Pa (1977), with permission by Combustion Institute, publisher.)

of some of the experiments considered to variations in the pyrolysis kinetics. For experiments conducted at high heating rates to high temperatures, the events with high rates (such as aliphatics or tar evolution) occur during the heat up. The evolution rates were heating rate limited and the experiments were not sensitive to variations in kinetic rate. When species or experimental conditions were sensitive to kinetic rate variations, significant rank variations were not observed. The most sensitive experiment to rate variations is the slow constant beating rate experiment. Data obtained at Advanced Fuel Research show a systematic rank variation in the temperature of maximum evolution rate for tar and hydrocarbon species of 40°C, from lignite to bituminous coals. This corresponds to a factor of five in rate. There is somewhat greater

variation for oxygen containing species and CO2 has some substantial variations with rank. Considering all the available data, it appears that the decomposition of aliphatic, methyl and aromatic functional groups and the evolution of tar and hydrocarbon species have rates which are relatively insensitive to rank variation. Oxygen species are somewhat more rank sensitive. Since the rank insensitive reactions dominate pyrolysis weight loss, the use of rank independent rates appears to be valid to provide prediction within +20°C. For greater accuracy a systematic variation with rank can be included. The factor of five variation in rate due to coal rank is substantially less than the factors of 100-10,000 in variation typical of reported rates. Rank variation appears therefore to be a minor cause for these differences which consequently must be attributed to

359

Finding order in coal pyrolysis kinetics I

I

I

i

A

50

I

1 0 . 2 SEC.

o 9 . 8 SEC

4,

~b0

¢d I-4

30

U t,.1

?

•

1:0 ATH HELIUM- L]CNITE

O 1 . 0 ATM HELIUM - BITUMINOUS COAL

1,0 ATM NITROGEN- BITUMINOUS COAL ...I

20

~O~U~L

r~ I.=I

t~TZ~;G ItAT~

650°C/S~C

FINAL TDIPEI~ATURE I000°(:

t ~ T I C ~ DIAMETnt 70~ (He)

so~ (.z)

10

I 1.0

0

I 2.0

I 3.0

I 4.0

[ 6.0

I 5.0

I 7.0

It£SIDDIC£ TIl~ (SEC) FIG. 47. Weight loss with time for a bituminous coal and a lignite. 5~ (Reproduced from Anthony, D. B., Rapid Devolatilization and H ydrooasification of Pulverized Coal, Ph.D. Thesis, M IT (1974), with permission.) ROSA

BEULAH _

2.0 •

CNAM N -

=, ~ . DN~t

,tu¢

El

N

0\0.

I • .

==

o

.

.

.

.

•

,

•

.

.

SAVAGE

PITTSBURGH BITUMINOUS ~2.o

B m m

Bcwel

m

0 D

•

0 300

600

900

1200

1500

1800

300

600

900

1200

DEVOLATILIZATION TEMPERATURE (°C)

Flo. 48. Nitrogenchar from pyrolysisin heatedgridfor l0 sec in vacuum.4~

1500

1800

360

PErEX R. SOLOMONand DAVIDG. HAMBLEN draft of this paper. Support for the work was provided by the Morgantown Energy Technology Center of the Department of Energy under Contract #DE-AC21-FE05122. |

. l ,,~

I

P

REFERENCES

lO

2~b

,I

_io.6

It .It 0.4 )0.2

04

•

0.~ J

:

I

~-

I

I/ t 3o d

I 2Q II

/

o

S

| lo

m

I o 400

~

l 600

@ • • • •@It • 700

800

900

FIG. 49. Yields of gases during initial phase of pyrolysis. (a) CO; (b) CO2; (c) C2H,+C2He+C3He+C3Hs; (d) CH,; (e) Weight loss.se (Reproduced from Suuber8, E. M. and Sceiza, S. T., Fuel, 61, 198 (1982), with permission by Butterworth & Co. (Publishers) Ltd., publisher ©.)

the effects of heat and mass transfer and to the assumptions used in deriving a kinetic rate. Continued work is necessary to calculate the effects of heat and mass transfer and to find a kinetic description which will allow consistency in applications over the range of conditions used in pyrolysis. The experiments considered vary in duration from 1.4 msec to 12 hr and in temperature from 350°C to 18000C. The observation that pyrolysis rates are insensitive to rank over such a wide range of conditions suggests that using this approximation in a pyrolysis theory can have wide applicability. Acknowledgement--The authors would like to acknowledge the able technical assistance of James Markham and Marie DiTaranto in obtaining the new entrained flow reactor data and programmed pyrolysis data. Preparation of the manuscript and illustrations were ably performed by Margaret Lane and Sally Solomon. The authors wish to thank Clarence Karr, Gary Friggens, Sandy Webb, Eric Suubcrg, Stephen Niksa, lan Smith, Richard Neavel, Douglas Smoot and Scott Hill for thoughtfully reviewing and commenting on the first

1. AN'n-IONY,D. B. and HOWARD,J. B., Coal Devolatilization and Hydrogasification, AIChE d. 22, 625 (1976). 2. HOWARD,J. B., PETERS,W. A. and SERIO, M. A., Coal Devolatilization Information for Reactor Modeling. Final Report, EPRI Project No. 986-5 (1981). 3. HOWARD,J. B., Chemistry of Coal Utilization, Chap. 12, John Wiley & Sons, New York (1981), Elliot, M. A. 4. GAVXLAS,G. R., Coal Pyrolysis, Coal Science and Technology 4, Elsevier Scientific Publishing Co., The Netherlands (1982). 5. SOLOMON,P. R., Adv. Chem. 193, 95 (1981). 6. SOLOMON,P. R. and COLKET, M. B., 17th Symposium (International) on Combustion, p. 131, The Combustion Institute, Pittsburgh, Pa (1979). 7. SOLOMON,P. R. and HAMBLEN,D. G., Understanding Coal Using Thermal Decomposition and Fourier Transform Infrared Spectroscopy, Proceedings of the Conference on the Chemistry and Physics of Coal Utilization, Morgantown, Wv (1980). 8. SOLOMON,P; R., Fuel, 60, 3 (1981). 9. SOLOMON,P. R., Honns, R. H., HAMBLEN,D. G., CHEN, W. Y., LX CAVA, A. and GamE, R. S., Fuel, 60, 342 (1981). 10. SOLOMON,P. R. and COLKET,M. B., Fuel, 57, 749 (1978). I1. SOLOMON,P. R., HAMBLEN,D. G., Cm,XNGELO, R. M. and KRXUSE,J. L., Coal Thermal Decomposition in an Entrained Flow Reactor: Experiments and Theory, 19th Combustion Symposium, p. 1139, The Combustion Institute, Pittsburgh. PA (1982). 12. SOLOMON,P. R. and H.~mLEN, D. G., Characterization of Thermal Decomposition of Coal in Experimental Reactors, Final Report, EPRI Project No. 1654-7 (1982). 13. SOLOMON,P. R. and HAMBLEN,D. G., Coal Gasification Reactions With On-Line In-Situ FT-IR Analysis,' Quarterly Reports, DOE Contract # DE-AC21-FE05122 (1981). 14. SOLOMON,P. R. and HAMBLEN,D. G., An Investigation of Vaporization and Devolatilization of Coal/Water MAtures, Second Quarterly Report, DOE Contract # DE.AC22.82PCS0254 (1982). 15. SOLOMON,P. R. and HAMBLEN,D. G., Measurement and Theory of Coal Pyrolysis Kinetics in an Entrained Flow Reactor, EPRI Final Report for Project RP 1654-8 (1983). 16. SOLOMON,P. R., HAMeLEN,D. G. and CAXANGELO,R. M., Coal Pyrolysis, AIChE, Symposium on Coal Pyrolysis (1981). 17. UNGER,P. E. and SUUBERG,E. M., Modeling the Devolatilization Behavior of a Softening Bituminous Coal, 18th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, Pa (1981). 18. SOLOMON,P. R., The Synthesis and Study of Polymer Models Representative of Coal Structure, Final Report for GRI, Contract # 5081-260-0582, Phase I (April 1983). 19. SUUm~RG,E. M., PE~RS, W. A. and HOWARD, J. B., Product Compositions and Formation Kinetics in Rapid Pyrolysis of Pulverized Coal-Implications For Combustion, 17th Symposium (International) on Combustion, p. 117, The Combustion Institute, Pittsburgh, Pa (1979). 20. SHAP^aaNA,E. A., KALYUZHNV[,V. V. and CrrOKnANOV, Z. F., Technological Utilization of Fuel for Energy, 1--Thermal Treatment of Fuels (1960). (Reviewed by BADZIOCH,S., Br. Coal Util. Res. Assoc. Mort. Bull. 25, 285 (1961). 21. HOWARD,J. B. and ESSENHIGri,R. H., Pyrolysis of Coal Particles in Pulverized Fuel Flames, Ind. Engng. Chem., Process Des. DeE. 6, 74 (1967). 22. STONE,H. N., BATCHELOR,J. D. and JOHNSTONE,H. F.,

Finding order in coal pyrolysis kinetics Lower Temperature Carbonization Rates in a Fiuidized Bed, Ind. Enono. Chem. 46, 274 (1954). 23. VAN FOU~V~LEN,D. W., v^N HEERDEN,C. and HUNTJENS, F. J., Physiochemical Aspects of the Pyrolysis of Coal and Related Organic Compounds, Fuel, 30, 253 (1951). 24. BOYER, A. F., Assoc. Tech. Ind. du Gaz en France Congres (1952). 25. Wxs~, W. H., HILL, G. R. and KERT^MUS,N. J., Kinetic Study of the Pyrolysis of a High-Volatile Bituminous Coal, Ind. Engn 0. Chem. Proc. Des. Dev. 6, 133 (1967). 26. KOB^YASm,H., HOWARD,J. B. and S~d~OnM,A. F., Coal Devolatilization at High Temperatures, 16th Symposium (International) on Combustion, p. 411, The Combustion Institute, Pittsburgh, Pa (1977). 27. WEG~EI~, D. C., M.S. Thesis, Kansas State Univ., 1978 (as reported in Lv.s~R, T. W., POL^V~PU, J. and Mr~KI.IN, J. F.), Fuel, 61, 493 (1982). 28. BALI~AN3"YNE,A., CI~OU,H. P., OROZVO,N. and STICKt~P,, D., Volatile Production During Rapid Coal Heating, Presented at the DOE Direct Utilization AR & TD Contractors Review Meeting, Pittsburgh, Pa (1983). 29. FREIHAUT,J. D., A Numerical and Experimental Investigation of Rapid Coal Pyrolysis, Ph.D. Thesis, Pennsylvania State University (1980). 30. W~yr~, A. B. and GAT, N., Effect of Rapid Heating on Coal Nitrogen and Sulfur Release, Presented at the DOE Direct Utilization AR & TD Contractors Review Meeting, Pittsburgh, Pa (1983). 31. KENNEDY,J. M., G ~ N , A. R., PV.SSA~NO,S. L. and KIULL, W. V., Kinetics of NO, Formation During Early Stages of Pulverized Coal, Presented at the DOE Direct Utilization AR & TD Contractors Review Meeting, Pittsburgh, Pa (1983). 32. Suuav.~G, E. M., PETERS,W. A. and HOWARD,J. B., lnd. Enono. Process Des. De~. 17, # 1, p. 37 (1978). 33. M^LO~Y, D. G., Ph.D. Thesis, PennsylvaniaState Univ., 1983, and MALONEY,D. G. and JENKINS,R. G., Effects of Preoxidation on Pyrolysis Behavior and Resultant Char Structure of Caking Coals, ACS Div. Fuel Chem. 27, # 1, p. 25 (1982). 34. SEEKER, W. R., SAMUELSEN,G. S., HEAP, M. P. and TROLING~R,J. D., Eighteenth Symposium (International) on Combustion, p. 1213 (1981). 35. B^DZ~OCt~, S. and H^WKSI.EY, P. G. W., Kinetics of Thermal D~omposition of Pulverized Coal Particles,

361

Ind. EnonO. Chem. Process Des. Dec. 9, 521 (1970). 36. ANTONY, D. B., HOWARD,J. B., Ho'rr~, H C. and M~SSN~, H. P., Rapid Devolatilization of Pulverized Coal, 15th Symposium (International) on Combustion, p. 1303, The Combustion Institute, Pittsburgh, Pa (1975). 37. PITt, G. J., Fuel, 41, 267 (1962). 38. HAN^BA,P., Ph.D. Thesis, Aachen (1967). 39. J~TGEN, H. and VAN H~K, K. H., An Update of German Non-lsothermal Pyrolysis Work, Fuel Processino Technol. 2, 261 (1979). 40. W ~ , R. F. and NG^N, D. Y., ACS Div. of Fuel Chemistry Preprints, 24, # 3, p. 129 (1979). 41. STEIN,S. E., GOLDEN,D. M. and BENSON,S. W., J. Phys. Chem. 81, 314 (1977). S'I~N, S. E. and BARTON,B. D., Thermochem. Acta, 44, 265 (1981). 42. V~NON, L. W., Fuel, 59, 102 (1980). 43. C ~ B E L ~ J. H., Fuel, 57, 217 (1978). 44. SOloMON, P. R. and C ~ N G ~ l o , R. M., Fuel, 61, 663 (1982). 45. SOLOMON,P. R., HAMBLEN,D. G. and C~ANOr~lo, R. M., Applications of FT-IR in Fuel Science, ACS Symposium Series 205, p. 77 (1981). 46. KOBAY~m, H. Devolatilization of Pulverized Coal at High Temperatures, Ph.D. Thesis, MIT (1976), corrected as in Ref. 3. 47. SOLOMON,P. R., The Characterization of Coals During Thermal Decomposition, Fifth EPA Fundamental Combustion Research Workshop, Newport Beach, Ca (1980). 48. FITZGERALD,D. and VAN I(JtEVELEN, D. W., Fuel, 38, 17 (1959). 49. MORRIS,J. P. and KrodltNS,D. L., Fuel, 58, 465 (1979). 50. TYI_~, R. J., Fuel, 59, 218 (1980). 51. SUUBF-~G,E. M., Ph.D. Thesis, MIT (1977). 52. D~sYp~S, J., Mum~-~-I, P. and WILLIAMS,A., Fuel, 61, 807 (1982). 53. Q u R ~ , V. T., W l ~ t , R. F., Bxv^Ns, A. and Mo~r~, S. A., Fuel, 58, 748-54 (1979). 54. A o ~ A , V. H., FvzJ3~ R. M. and F ~ ¢ ~ I . , J. K., Measurement of Coal Devolatilization and Elemental Release in Batch and Laminar Flow Furnace Reactors, 72nd Annual Meeting of the AIChE, San Francisco, Ca, Nov. 25-29 (1979). 55. ANTHONY,D. B., Rapid Devolatiltzation and Hydrooasification of Pulverized Coal, Ph.D. Thesis, MIT (1974). 56. SUUeERG,E. M. and SC~LZA,S. T., Fuel, 61, 198 (1982).