The release of nitrogen and sulphur during the combustion of chars derived from lithotypes and maceral concentrates

The release of nitrogen and sulphur during the combustion of chars derived from lithotypes and maceral concentrates John

C. Crelling,

K. Mark

Thomasi

and H. Marsh

Coal Characterization L aboratory, Department of Geology, Southern Carbondale, IL 62901 USA t Northern Carbon Research Laboratories, Department of Chemistry, Newcastle upon Tyne, Newcastle upon Tyne, NE? 7RU, UK (Received 16 April 1992)

Illinois University

University, of

This paper describes an investigation of the variation of nitrogen and sulphur composition in macerals and their release during combustion. A whole-seam-channel coal sample and hand-picked blocks of vitrain and fusain were collected for detailed investigation. These samples were separated into their maceral components by density gradient centrifugation. The raw coal sample and lithotypes and the maceral fractions derived from these materials were characterized in detail. The char reactivities and nitrogen/sulphur release were studied in 20% oxygen/argon in a thermogravimetric analysis/mass spectrometer system. The results showed that there were marked differences in the nitrogen and sulphur contents of the maceral fractions. Nitrogen was retained in the chars relative to the coal precursor under the conditions used in the EFR pyrolysis step. The nitrogen oxide released during combustion of the EFR chars reached a maximum at a higher temperature than the corresponding CO and CO, peaks for all the maceral concentrates studied. The variations in maceral reactivity are discussed in relation to carbon burn-out in combustion systems.

(Keywords: combustion; litbotypes; macerals)

power stations are responsible for of tons of NO, and N,O per year Not only do the emissions contribute to the acid-rain problem, but N,O is also a ‘greenhouse gas’ and takes part in upper-atmosphere chemistry to enhance the ozone-layer problem. A better understanding of how coal nitrogen, with different chemical structures, influences the generation of nitrogen oxides during combustion, can lead to reductions in emissions. The release of nitrogen during the combustion of coal involves two main stages: (i) the volatilization and combustion of small molecules, some of which contain nitrogen; and (ii) the slower gasification in the solid char particles derived from the coal which contains nitrogen bound in the carbon structure. Three main mechanisms for the formation of oxides of nitrogen have been proposed: Modern coal-burning emissions of millions into the atmosphere.

1. from the reaction of atmospheric nitrogen with oxygen at temperatures above about 1200°C: 2. from the reaction of radicals such as OH with nitrogen in the same temperature range; and 3. from the reaction of nitrogen in coal with oxygen during combustion at temperatures as low as 700°C. In coal combustion, the major proportion of the oxides of nitrogen are formed by reaction of nitrogen chemically bound in the fuel rather than by oxidation of atmospheric Presentedat ‘Environmental Aspects of Coal Utilization and Carbon Science Conference’, 31 March-2 April 1992, University of Newcastle upon Tync. UK 001&2361/93/030349%09 I’ 1993 Butterworth-Heinemann

Ltd.

nitrogen’. The origins and states of nitrogen in coal remain uncertain. The paucity of information on this element is in contrast to that available for sulphur and oxygen. The fate of coal nitrogen has been studied by several authors2-5 leading to the present conclusion that there is no simple relationship between coal nitrogen and oxides of nitrogen released during combustion. Burchil16 recently found a relationship between coal rank and nitrogen content for two suites of coals from Indonesia and the UK. Nitrogen contents reach a maximum at about 85 wt% (dmmf) carbon content. The technique of X-ray photoelectron spectroscopy proved to be useful. The nitrogen was found to be essentially heterocyclic: 5-membered pyrrolic nitrogen was found in the bituminous range with 6-membered, pyridinic nitrogen increasing with increasing coal rank7. Distributions of nitrogen in the maceral constituents of coals have not been studied, although Burchil16 suggests that most nitrogen is found in the vitrinite. No information exists for ‘Gondwana’ southern hemisphere coals. Coal extracts and volatile products have been examined by differential pulse voltametry, FT-i.r. and size-exclusion chromatograpy’ but the chemistry of these processes may have changed the functionality of the nitrogen from that in the original coal. Pohl and Sarofim’ indicated that. given sufficient time, all nitrogen can be volatilized from the coal/char system. However, during combustion the process is so rapid that nitrogen remains in the char. In a study of nitrogen behaviour in different coals, not only does the nitrogen differ in terms of quantity and chemical bonding with coal rank, but other very relevant

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Release of nitrogen

and sulphur: J. C. Crelling et al.

coal properties change as well. In particular, coal is a very heterogeneous material composed of macerals and minerals which vary in their occurrence, properties and distribution. Hence the coal properties studied should include: (i) variations in the properties of macerals and microlithotypes which are relevant in the combustion of small particles, e.g. reactivity, nitrogen content and functionality etc.; and (ii) variations in mineral matter content, components of which may act as pyrolysis/gasification/combustion catalysts. The objective of this study was to examine the release of nitrogen and sulphur compounds from coal lithotypes and macerals under strictly controlled experimental conditions.

EXPERIMENTAL Samples Field collection. Three coal samples of the Herrin no. 6 coal seam were collected from an active surface mine in Perry County, southern Illinois, USA. One, designated 2140A, was a whole-seam-channel sample representing the entire seam. A second, designated 2140B, consisted of hand-picked blocks of coal featuring numerous and prominent vitrain layers which were later concentrated manually. The third, designated 2140D, consisted of blocks of massive fusain. Samples 2140B and 2140D were collected from the same locality as the channel sample and, indeed, are lithotypes of that same seam. Laboratory preparation of maceral concentrates. In the density gradient centrifugation (DGC) technique’0-‘3 the coal sample is reduced to micrometre size in a fluid energy mill. The sample is put into a vessel that is filled with an aqueous CsCl density gradient commonly ranging from 1 to 1.6gml-‘. The vessel is then centrifuged and the particles move to the appropriate density level. At present the largest vessel in use has a capacity of 2 1 and can process a maximum sample size of 2 g of coal. After centrifugation the sample solution is fractionated by pumping, then filtered, weighed and dried. The density and weight of each fraction are measured and plotted. The resulting density profile accurately reflects the maceral composition of the sample and specific density fractions are composed virtually exclusively of single macerals. Micrometre-sized particles were too small to be used in the pyrolysis experiments, therefore the three original samples were sieved to the range of - 200 to + 325 mesh (- 74 to +44 pm) and then processed in the DGC apparatus to concentrate maceral groups. The following fractions were separated: from the channel sample, a vitrinite (2140Avit) and an inertinite (2140Ainert) fraction; from the vitrain, a single vitrinite fraction (2140Bvit); from the fusain, a semifusinite (2140DJ and a fusinite (2140D,) fraction. Characterization The chemical composition of all coal and char samples was determined with micro-ultimate analysis

with either a standard proximate analysis or a modified thermogravimetric analysis that gave moisture, volatile matter and ash values. The petrology of the coal samples and the morphology of the chars were analysed. The

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surface areas of the chars were determined from adsorption of carbon dioxide at 273 K interpreting the isotherm by the Dubinin-Radushkevich (D-R) equation. Extrapolation of the D-R plot to log’ (p/p’) = 0 (where p is pressure and p” is the saturation vapour pressure) gives a maximum surface area value for the microporosity. As the adsorption isotherms are of type 1, the isotherm gives a minimum value at the maximum gas uptake. Pyrolysis All eight samples with particle size 4474pm were pyrolysed under nitrogen in an entrained flow reactor (EFR) at the Northern Carbon Research Laboratories at the University of Newcastle upon Tyne. The pyrolysis took place in nitrogen at 1273 f 5 K with a heating rate of 104-IO5 K s-l and with a residence time of approximately 1 s in an isothermal reaction zone of 1.66 m. The resulting chars were collected and stored under argon gas. Gasification

studies

The samples were all gasified in a Thermal Sciences 1SOOSTAthermogravimetric analyser with a gas analysis probe situated directly above the sample connected to a VG quadrupole (300 amu) mass spectrometer. Temperature-programmed oxidative gasification was carried out in a mixture of 20% oxygen/argon at a heating rate of 15 K min- I. The weight loss during gasification was monitored and the evolved gases were sampled with a 1 mm diameter probe which transported them to the mass spectrometer, where the type and rate of gas evolution during gasification were monitored. Reactivity measurements were obtained by isothermal gasification at 500°C in 20% oxygen/argon. The reactivity measurements were calculated by the-method described previously. RESULTS

AND DISCUSSION

Samples

The DGC density profile of the channel sample (2140A) is shown in Figure 1. The peak represents the vitrinite content of the sample and the area under the high density tail represents the inertinite content. The shaded areas under the peak and the tail are the density ranges that were concentrated to give, respectively, a vitrinite

1.00

1.10

1.20

1.30 Density

1.40

1.50

1.60

(6lmL)

Figure 1 Density profile of the whole-seam-channel sample (2140A). The shaded area under the peak indicates the density range of separated vitrinite and the shaded area under the tail indicates the density range of separated inertinite

Release of nitrogen

concentrate (2140Avit) and an inertinite concentrate (2140Aint). Figure 2 shows the DGC profile of the hand-picked vitrain (2140B) which features a central peak and virtually no inertinite tail. The sample under the shaded area was concentrated to give a refined vitrinite sample (2140Bvit). The DGC profile of the hand-picked

1.00

1.10

1.20

1.30

1.40

1.50

Characterization

Figure 2 Density profile of the hand-picked vitrain sample (2140B). The shaded area under the peak indicates the density range of separate vitrinite

100 r

t

(2140DJ A

1.10

1.20

1.30

1.40

1.50

1.60

1.70

Dsnaity (s/mL)

Figure 3 Density profile of the The shaded area under the left separated semifusinite (2140D,) peak indicates the density range

Figure 4

Comparison

hand-picked fusain peak indicates the and the shaded area of separated fusinite

of the morphology

fusain sample (2140D) features two distinct peaks, which are shaded in Figure 3. These two density ranges were concentrated to give a semifusinite sample (2140D,, lower density peak) and a fusinite sample (2140D2, higher density peak). The maceral composition of these samples was verified by petrographic analysis. The chars of these samples resulting from the pyrolysis experiments in the entrained flow reactor were also examined using optical microscopy. Comparisons of the petrology of the channel sample, maceral concentrates and hand-picked lithotypes together with the morphology of the EFR chars derived from these samples are shown in Figures 4-6, respectively. The vitrinite-rich samples showed a predominantly thin-walled open cenosphere morphology. The semifusinite showed a thicker-walled honeycombed network morphology while the fusinite had a mostly unfused morphology. As expected, the channel sample showed a proportional mix of these three char morphologies.

1.60

Density (6lmL)

1.00

and sulphur: J. C. Crelling et al.

sample (2140D). density range of under the right (2140D,)

of (a) the channel

The proximate

and ultimate analyses are given in analysis of the whole coal sample (2140A) is typical for the Herrin no. 6 seam, except for the ash content which is different from its vitrinite concentrate. This is not surprising because the vitrinite maceral group makes up about 85-90 wt% of this seam and the low ash content is a result of the DGC process. The inertinite concentrate shows slightly reduced volatile matter and increased fixed carbon contents. However, this fraction has a similar ash content to the raw coal and therefore may have some contamination. The vitrain sample (2140B) and its DGC concentrate (2140Bvit) have similar analytical data to each other and to 2140A and 2140Avit discussed above. The fact that the vitrain (2140B) was hand picked accounts for its lower ash content compared with the raw coal. The fusain samples are remarkable for their much lower volatile matter and much higher fixed carbon contents. These trends are at their extreme in the fusinite DGC concentrate (2140D,), with less than half of the volatile matter and almost 30% more fixed carbon than the whole-coal sample (2140A). It is important to note that all of these samples come from the same locality in the same seam and thus represent at least part of the Tables I and 2, respectively. The proximate

coal sample (2140A) and (b) the EFR char derived

from the coal

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Release of nitrogen

352

and sulphur: J. C. Crelling et al.

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Release of nitrogen

and sulphur: J. C. Crelling et al.

Figure 5 Comparison of the morphology of the DGC maceral concentrates and EFR chars derived from these concentrates: (a) vitrinite concentrate (2140Avit); (b) EFR char (2140Avit); (c) inertinite concentrate (2140Aint); (d) EFR char (2140Aint); (e) semifusinite fraction (2140D,); (f) EFR char (2140D,); (g) fusinite fraction (2140DJ; (h) EFR char (2140AD,); (i) vitrinite concentrate (2140B); (i) EFR char vitrinite concentrate (2140B)

Figure 6

Comparison

of the morphology

of the lithotype

samples: (a) vitrain (2140B); (b) EFR char (2140B); (c ) fusain(2140D);(d)EFRchar(2140D)

range of chemical variation found in individual coal particles from the same seam. The trends in the proximate analyses are also evident in the ultimate analyses, with the ultimate carbon analyses following the fixed carbon and the hydrogen following the volatile matter. The sulphur contents of the vitrain (2140B) and vitrinite (2140Bvit) samples are similar to the vitrinite (2140Avit) in the whole-coal vitrinite. The high sulphur content of the whole coal is typical of much of the Herrin no. 6 seam in Illinois, USA. The decrease

in sulphur content in the DGC samples is due to the removal of pyrite. The lowest sulphur contents are in the fusain samples, which are known to contain less organic sulphur than other macerals. Interestingly, the nitrogen contents of the fusain samples are approximately half of the values of the other samples. Only ultimate analyses were run on the char samples because of their pyrolysed nature and low volatile matter content; the results are given in Table 3. The ash content increases during pyrolysis due to loss of volatile matter

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Release of nitrogen and sulphur: J. C. Crelling et al. Table 1

Results of proximate

analyses

of coal

(wt%)

Sample

Ash”

Vol. Matter’

Fixed C”

Vol. Matte?

Fixed Cb

2140A

16.9

35.6

41.5

42.9

57.1

2140Avit

4.6

38.5

56.9

40.3

59.7

2 140Aint

15.4

33.8

50.8

39.9

60.1

2140B

6.4

38.0

55.6

40.6

59.5

2140Bvit

3.5

38.5

51.7

40.2

59.8

2140D

15.1

23.5

61.4

23.6

12.7

2140Dr

2.8

23.8

13.5

24.5

75.5

2140D,

2.4

12.1

85.5

12.4

87.6

“Dry b Dry ash free

Table 2

Results

Sample

of ultimate c

analyses

of coal (wt% daf)

H

N

s

Table 4

78.9 11.2 11.3

6.2 6.3 6.0

4.7 2.5 3.5

1.5 1.5 1.4

8.7 8.7 11.8

2140B 2140Bvit

78.8 17.2

5.9 6.3

2.2 2.3

1.5 1.5

11.6 12.7

2140D 2140D, 2140D,

85.0 80.5 81.0

2.4 4.4 2.6

0.2 1.1 0.6

0.6 0.7 0.4

11.8 13.3 15.4

Results of ultimate

analyses

area analyses

of char (m’ g-r)

Sampie

Surface area maximum (from D-R plot)

Surface area minimum (from isotherm)

2140A 3140Avit 2140Aint

300 330 280

190 230 190

2140B 2 140Bvit

280 300

210 210

2140D 2140D, 2140DZ

250 450 280

170 290 190

0

2140A 2140Avit 2140Aint

Table 3

Results of surface

of char (wt%)

Sample

C

H”

N”

Ash”

2140A 2140Avit 2140Aint

95.0 92.2 94.1

1.0 0.9 0.7

1.9 1.9 1.8

21.9 1.1 26.3

2140B 2140Bvit

94.7 91.2

0.8 0.8

2.0 1.9

13.7 6.3

2140D 2140D, 2140D,

96.9 93.6 96.4

1.0 0.6 0.6

1.0 1.2 0.7

17.8 3.2 2.2

‘*I

“Dry ash free b Dry

0 200

and this is usually marked for the vitrinite-rich samples. The carbon contents range from about 91 to almost 97 wt%, and hydrogen is 1 wt% or less. However, the semifusinite ash only increases slightly and the fusain ash does not increase at all. The nitrogen is also increased in the pyrolysis chars, by about 25530% compared with the whole coal and vitrain samples and by about 65-75% in the fusain samples. The latter is surprising bearing in mind the lower volatile matter of fusain. This suggests that the volatile matter evolved during pyrolysis contains very little nitrogen. The results of the surface area analyses, given in Table 4, show that the surface areas of the chars are in the range of 170-290 m2 g-r minimum and 25&450 m2 g- ’ maximum. Gasijicationlcombustion The gas evolution profiles from the temperatureprogrammed oxidative gasification of the coal, lithotype and maceral concentrate samples in 20% oxygen/argon

354

FUEL, 1993, Vol 72, March

250

300

350

400

450

500

550

600

650

700

TEMPERATURE t

Figure 7 of sample

co2

+

co

*--

NO*1 00

Temperature-programmed gas evolution 2140A - whole-seam-channel sample

--t---- so**1

00

profile of EFR char

are given in Figures 7-13. The intensity values plotted are based on the partial pressure values detected in the mass spectrometer for the m/z of the various gases. For clarity, ail signals were reduced to a common baseline and some have been scaled as indicated. While a number of gases were actually detected, only those gases of special interest (CO,, CO, NO and SO,) are plotted in the figures. The early sharp peak due to CO, that appears only for data from chars of the raw whole coal and the raw hand-picked fusain (Figures 7 and 9) is assumed to be due to the catalytic effect of mineral matter because the peak is not seen in any of the DGC samples in which the mineral matter has been reduced. The lower reactivity

Release of nitrogen

and sulphur: J. C. Crelling et al.

1

0 200

250

300

350

400

450

500

550

600

650

0 200

700

250

300

350

-

co

TEMPERATURE + Figure 8 of sample

co2

+

--H-- NO*100

co

Temperature-programmed 2140B - hand-picked

-+--

gas evolution vitrain

SO2*100

+

profile of EFR char

co2

400 450 500 550 TEMPERATURE --t---- NO’,00

Figure 11 Temperature-programmed char of sample 2140Bvit - vitrain

600

-+-

650

7OC

so2*100

gas evolution profile DGC vitrinite fraction

of EFR

10

25

9 6 7 k?

6

2 fi g

5 4 3 2 1

0 200

250

300

350

400

450

500

550

600

650

700

1

250

300

350

400 450 500 TEMPERATURE

TEMPERATURE -+Figure 9 of sample

co2

+

.-w-- NO*100

co

Temperature-programmed 2140D - hand-picked

.-+--

gas evolution fusain

SO2*100

t

profile of EFR char

+

co2

._+.._ NO*,

co

Figure 12 Temperature-programmed char of sample 2140Aint ~ channel

550

00

600

650

70( 1

+... SO2*,0

gas evolution profile of EFR sample DGC inertinite fraction

2 1

1 0 200

t

250

co2

300

*

350

400 450 500 TEMPERATURE

co

Figure 10 Temperature-programmed char of sample 2140Avit ~ channel

+-.

NO*100

550

600

--+

650

700

SO2*100

gas evolution profile of EFR sample DGC vitrinite fraction

0 200

l-A-CO2

250

300

350

+

co

400 450 500 TEMPERATURE --x---- NO*100

550

600

--+--

650

70

SO2’lOO

Figure 13 Temperature-programmed gas evolution profile char of sample 2140D, - fusain DGC peak 1 (semifusinite)

of EFR

FUEL, 1993, Vol 72, March

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Release of nitrogen

and sulphur: J. C. Crelling et al.

2 1 0 200 +

250 co2

300 -s-

350 co

400 450 500 TEMPERATURE --+--. NO*100

550

600 f--

650

700

so2*100

Figure 14 Temperature-programmed gas evolution profile char of sample 2140D, - fusain DGC peak 2 (fusinite)

of EFR

of the intertinite group of macerals is also apparent. For the fusain samples (2140D, D, and D,, Figures 9, 13 and 14) the major CO, evolution in these samples occurs from 550 to 6OO”C, while it occurs at lower temperatures for all other samples. Also, in all samples the CO2 and CO peaks have a similar shape. Except for some of the fusain samples, which start with a very low sulphur content, the SO, evolution begins early in the gasification process. In Figures 7 and 8 there are large SO, peaks well before the CO, peak. This peak is believed to be due to the gasification of pyrites because it was not found in the DGC samples where pyrite was removed. The nitrogen-evolved during the gasification of these chars as NO, which accounts for approximately half of the nitrogen evolved, peaks after the CO, in all cases. In most samples the NO gas evolution profile is asymmetric with a definite shoulder on the low-temperature side. Furthermore the NO peak reaches a maximum at a higher temperature than the corresponding CO, peak. This bimodal nature suggests that there may be at least two mechanisms or types of functionality for NO release. This conclusion is supported by results obtained in the gasification of model carbons derived from polynuclear aromatics containing pyrrolic and pyridinic functionalityi4~“. The fact that various macerals behave differently during the temperature-programmed gasification is very evident in the profiles of these samples. Vitrinite and inertinite macerals usually have distinctly different patterns. The gas evolution profile of the raw vitrain (which is mostly vitrinite, see Figure 8), the vitrinite separated from the vitrain (Figure II). and the vitrinite separated from the whole-coal sample (Figure IO) all have similar shapes. The CO, evolution profile rises sharply at the start of combustion and decreases less rapidly on the high-temperature side. The raw vitrain CO, profile reaches a maximum at a slightly higher temperature. In contrast, the inertinite profiles are broad and fairly symmetrical. Figure 14, the fusinite separated from the fusain sample, shows this typical form. The profile of the separated semifusinite (Figure 13) shows some additional structure, a small secondary peak and a slight shoulder both on the low-temperature side, on this basic form. The profile of the raw fusain (Figure 9) which has high

356

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semifusinite content, is similar to the semifusinite profile (Figure 13). However, the former has a small, sharp initial peak which is probably due to some catalytic effects and exothermicity producing a small temperature increase. The results of the isothermal combustion experiments at 500°C are given in Table 5. The reactivity measurements are highest for the vitrinite-rich samples (2140A, 2140B, 2140Avit and 2140Bvit). It is noteworthy that the purest vitrinite (2140Bvit) has the highest reactivity within the small range of values observed. All of the inertinite-rich samples (2140D, D, and D2) have considerably lower reactivities than vitrinite-rich samples and, indeed, the lowest reactivity sample is fusinite (2140D,), which is approximately half of the reactivity of the vitrinite-rich samples and has the highest density. The semifusinite (2140D,) is intermediate in reactivity between the fusinite and vitrinite. The inertinite separated from the whole coal sample (2140Aint) is slightly more reactive than the inertinite obtained from fusain (2140D) but is intermediate between the fractions obtained from fusain (2140D, and D2). It is apparent that the variations in inertinite reactivities are due to the petrographic variations in the inertinite macerals. CONCLUSIONS While all of these samples come from the same locality in the same seam, they show a considerable variation in chemical composition, which represents at least part of the range of chemical variation found in individual coal particles. It is apparent that variations in both lithotype and maceral composition give large variations in nitrogen content, char morphology and char reactivity. Furthermore, under the conditions used in the EFR, the nitrogen is retained in the char compared with the original coal, lithotype or maceral precursor. The disappearance of a sharp peak in the CO, evolution profiles in all of the samples that have been processed to reduce mineral matter suggests that there is some catalytic gasification effect due to the mineral matter. In all cases the NO evolution profile reaches a maximum at a higher temperature than the corresponding CO, peak. The SO, gas evolution profile has two peaks, one before and one just after the start of the CO, peak. The early peak is seen only in the raw channel and vitrain samples; the other samples have been separated by density gradient centrifugation and therefore have had their mineral matter greatly reduced. It is proposed that the initial peak is due to pyritic sulphur and the second peak is due to organic sulphur. The data represent the typical variations in the gasification/combustion behaviour of pulverized fuel. The variations in reactivity and nitrogen and sulphur release during the combustion of macerals can be quite large. It Table 5

Results of isothermal

oxidation

reactivity

studies of chars

Sample

Ash W)

Reactivity (h ’ a.f.)

2140A 2140B 2140D 2140D, 2140D, 2140Aint 2140Avit 2140Bvit

28.8 12.0 20.0 6.0 2.0 29.0 8.3 7.8

15.9 14.4 8.8 11.1 7.8 10.2 15.2 16.3

Release of nitrogen

is apparent that the variation in the reactivity of macerals may be a major factor in carbon burn-out. The fusinite macerals show no evidence for the generation of thermoplasticity during pyrolysis in the EFR and are significantly less reactive than the semifusinite and vitrinite macerals. These results are therefore relevant to the selection of coals for combustion processes and the design and operation of furnaces for electricity power generation. ACKNOWLEDGEMENTS The authors thank the SERC for supporting this research. This research was carried out while J. C. C. was on sabbatical leave at the University of Newcastle upon Tyne (grant no. SERC GR/G/59622). The Thermal Sciences/VG Quadrupoles Thermogravimetric AnalysisMass Spectrometer was purchased under grant no. SERC GR/F/64302. REFERENCES 1

Wendt. J. 0. L., Pershing, D. W.. Lee, J. W. and Glass, J. W. 17th Symposium on Combustion, The Combustion Institute.

2

3 4 5 6

7 8

9 10 11 12 13 14 15

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