Experimental Study of Ignition and Combustion Characteristics of

Dec 21, 2017 - Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia. ‡ Key...
1 downloads 14 Views 659KB Size
Subscriber access provided by READING UNIV

Article

An Experimental Study of Ignition and Combustion Characteristics of Single Particles of Zhundong Lignite Zhezi Zhang, Mingming Zhu, Jianbo Li, Kai Zhang, Gang Xu, and Dongke Zhang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03145 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 23, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

An Experimental Study of Ignition and Combustion Characteristics of

2

Single Particles of Zhundong Lignite

3

Zhezi Zhang1*, Mingming Zhu1, Jianbo Li1,3, Kai Zhang2, Gang Xu2 and Dongke Zhang1

4

1

5

Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia

6 7

2

Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China

8 9

3

Key Laboratory of Low-grade Energy Utilization Technologies and Systems of the Ministry of Education of China, Chongqing University, Chongqing 400044, China

10 11 12 13 14 15 16 17 18

(A manuscript offered to the “6th Sino-Australian Symposium on advanced coal and biomass

19

utilisation technologies” Special Issue of “Energy & Fuels”)

20 21 22 23 24 25 26

* Corresponding author:

27

Zhezi Zhang

28

Email: [email protected]

29

Phone: +61 8 6488 7602

30

Fax:

+61 8 6488 7622

31 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

32

Abstract

33

The ignition and combustion behaviour of single particles of Zhundong lignite was experimentally

34

investigated. Single particles of Zhundong lignite with diameter varying from 2 to 3 mm were

35

suspended on a SiC fibre and their burning in air in a horizontal tube furnace operating at 1023,

36

1073, 1123, 1173 and 1223 K observed, aided with a CCD camera at 25 fps. By analysing the

37

captured images, the ignition delay time, flame displacement, volatile flame duration, volatile

38

extinction time, total burnout time and the ignition mechanism were determined. The typical

39

ignition and combustion process of Zhundong lignite consisted of four sequential but overlapping

40

stages: 1) pre-ignition stage involving drying, devolatilisation and oxidation at the particle surface;

41

2) heterogeneous ignition and combustion; 3) ignition and combustion of volatile matter in the gas

42

phase; and 4) combustion of the remaining char residue. Surprisingly, the ignition of Zhundong

43

lignite followed a joint hetero-homogeneous mechanism under all conditions studied. Upon the

44

volatile matter ignition, a soot-free yellowish translucent flame was formed surrounding the particle

45

and the volatile flame duration was noticeably long-lasting. The high sodium content in Zhundong

46

lignite was believed to be responsible for such a phenomenon. The ignition and combustion

47

characteristics, such as ignition delay time, volatile flame extinction time and the total combustion

48

time of Zhundong lignite, decreased with increasing furnace temperature and decreasing particle

49

size.

50

Keywords: Char combustion; Devolatilisation; Ignition; Single particles; Soot-free flame;

51

Zhundong lignite

52

2 Environment ACS Paragon Plus

Page 2 of 26

Page 3 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

53

1. Introduction

54

As the major coal production base in China, Zhundong lignite plays a vital role in China’s energy

55

security1. A scientific understanding of the ignition and combustion behaviour of this low-rank coal

56

is crucial for more efficient utilisation of this resource2-4. While an enormous amount of attention

57

has been paid to the understandings of ash slagging, fouling and corrosion problems due to the high

58

sodium content in Zhundong lignite1, 5, 6, information on its fundamental ignition and combustion

59

characteristics is very scarce. Weng et al.

60

characteristics of Zhundong lignite using the thermogravimetric technique, focusing on the effect of

61

sodium and alkali metals. They reported that ignition and combustion behaviour of Zhundong

62

lignite was affected by removing the water-soluble and organically bonded alkali metal in the

63

lignite. It was concluded that the water-soluble and organically-bonded alkali metal had some

64

catalytic effects, promoting ignition and increasing burning rate of the lignite. However,

65

contradictory results were reported by Chen et al9 , who found that only the organically-bonded

66

sodium promoted the combustion of Zhundong lignite in their TGA experiments. Nevertheless, the

67

slow heating rates used in TGA experimentation were considerably different from the actual

68

combustion process in a boiler. Therefore, the understanding of the fundamental ignition and

69

combustion behaviours of Zhundong lignite in an environment that simulates the real heating rate in

70

the boiler is essential.

7

and Wang et al.

8

studied the ignition and combustion

71 72

Our previous studies focussed on the understanding of the effect of washing treatment10 on the

73

ignition and combustion characteristics of Zhundong lignite. As a continuation effort of these

74

studies, the present study examined the effect of furnace temperature (1023 – 1223K) and particle

75

size (2 – 3 mm) on the ignition mechanisms and combustion phenomena of Zhundong lignite using

76

the suspended single particle experimentation approach11-13. The selected furnace temperature and

77

particle size represented typical fluidised bed combustion conditions 14.

78 79 3 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

80

2. Experimental

81

The proximate, ultimate and ash composition data of the Zhundong lignite used in this study are

82

shown in Tables 1 and 2. The surface functional groups of Zhundong lignite were analysed using

83

FTIR (Nicolet 6700, Thermofisher) with the results presented in Figure 1. The as-received lignite

84

was first crushed into small chunks, which were then carefully filed into spherical particles of 2, 2.5

85

and 3 mm in diameter. A small hole (ca. 0.25 mm in diameter) was carefully drilled into the centre

86

of the particle for attaching the particle to a SiC fibre. The samples were then dried in an oven at

87

378 K overnight and stored in a desiccator prior to experimentation.

88 89

Figure 2 shows the schematics of the experimental setup of the single particle ignition and

90

combustion 12. It consisted of a horizontal tube furnace (800 mm in length and 40 mm in diameter)

91

to provide a hot air environment, a particle suspension system, a linear stepper - motor for

92

delivering the lignite particle into the furnace and a CCD camera (Basler PIA-210gc) for capturing

93

the combustion process. A LED backlight was used to illuminate the lignite particle before the start

94

of each experiment to identify the time at which the particle arrived at the centre of the furnace. To

95

start the experiment, the linear stepper motor, the data acquisition card, the backlight and the CCD

96

camera were triggered simultaneously, using a Programmable Logic Controller, after the furnace

97

reached the desired temperatures (1023, 1073, 1123, 1173 or 1223K).

98 99

Key ignition and combustion characteristics, such as ignition delay time, volatile ignition time (tvi),

100

surface ignition time (thi), volatile flame duration (tf), volatile flame extinction time (tve), burnout

101

time (tb), total combustion time (tt), the flame displacement (xf), ignition mechanism and temporal

102

variation of the particle size, were obtained by processing the images captured by the camera. The

103

definitions of the aforementioned ignition and combustion characteristics were schematically shown

104

in Fig. 3 and more details can be found in authors’ previous publication10. In the present work, the

105

flame displacement was determined using the following method. Firstly, a vertical line (488 pixel 4 Environment ACS Paragon Plus

Page 4 of 26

Page 5 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

106

length and one pixel width) was drawn passing through the centre of the particle. Then the pixel

107

greyscale intensity along the line was taken using Matlab and plotted against the number of pixels

108

along the line as shown in Figure 4 (a). Secondly, the first derivative of the pixel greyscale along

109

the line was calculated and plotted as shown in Figure 4(b). It is evident that there were two

110

distinctive peaks, namely, peaks 1 and 2, which indicate the volatile flame front and the particle

111

surface, respectively. Thus, the distance between these two peaks was taken as the flame

112

displacement.

113 114

3. Results and Discussion

115

Figure 1 shows the FTIR spectra of the Zhundong lignite. The peaks at 2920 cm-1 and 2850 cm-1

116

correspond to CH3 and CH2 (stretching in the aliphatic group)15-18. The peaks near 1435 cm-1 and

117

1370 cm-1 correspond to the absorption of the methyl group (–CH3)15-18. In the region from 1300 to

118

1000 cm-1 various oxygenated compounds are responsible, including aliphatic ethers/alcohols in

119

1100 - 1000 cm-1 region, C-O stretch and O–H bend in phenoxy structures in 1300 – 1100 cm-1

120

region16-18. The peak at 3060 cm-1 corresponds to an aromatic C-H stretching absorption band and

121

the peaks near 910, 810 and 750 cm-1 are related to the C-H bending adjacent to an aromatic ring16-

122

18

123

peak at 1576 cm-1 is related to the carboxyl group in the salt from (–COOM)16. This is also in

124

agreement of the ash chemistry data presented in Table 2 and literature findings that a large portion

125

of the sodium in the raw Zhundong lignite exists as carboxylate sodium salts6, 19, 20.

. The peak at 1700 cm-1 corresponds to the C=O stretches in carboxylic groups (-COOH)15-18. The

126 127

Figure 5 shows the typical time sequenced images of ignition and combustion of Zhundong lignite

128

in air. It is clear that the ignition of Zhundong lignite conformed the joint hetero-homogeneous

129

ignition mechanism, with the ignition on the surface occurred prior to the ignition of the volatile

130

matter. As shown in Figure 5, the ignition and combustion processes of Zhundong lignite consisted

131

of four distinctive stages: (1) Pre-ignition stage: when the particle arrived at the centre of the 5 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

132

furnace, a rapid increase in the particle temperature was induced by radiation heat transfer from the

133

furnace wall and, to a lesser extent, conduction and convection heat transfer from the hot air. Once

134

the heterogeneous ignition criterion was met, the ignition occurred on the ignite surface; (2)

135

Heterogeneous ignition and combustion stage: as can be seen in Figure 5, at 6.7 s a bright dot

136

appeared on the surface of the particle, indicating the heterogeneous ignition of the particle. Upon

137

ignition, the combustion of the particle continued as demonstrated by the development of the bright

138

area on the particle surface; (3) Volatile ignition and combustion stage: as combustion continued, at

139

9.02 s, a yellowish translucent flame surrounding the particle was observed. This suggests that the

140

volatile matter had ignited and was burning. The yellowish translucent flame also indicated that the

141

burning of the volatile matter was almost soot-free

142

noticeably long-lasting, ca. 54 s, which was unusual compared with the combustion phenomena of

143

other low rank coals with low sodium contents as reported in the literature 11-13, 22. It is believed that

144

the water-soluble form of sodium (e.g. NaCl) and the organically-bonded form of sodium (e.g.

145

sodium carboxylic functional groups) in Zhundong lignite are converted to carbon matrix anchored

146

sodium containing surface complex during the particle heating, devolatilisation and combustion

147

processes 23, 24. Some of the large fragments of volatile matter are deposited on to these active sites,

148

via condensation, recombination and/or polymerisation reactions, and become catalytically cracked

149

25

150

to the formation of smaller particles. On the other hand, due to the metal-induced catalytic cracking,

151

the OH radical concentration is increased by the presence of Na species. As a result, the flame

152

temperature is increased, further accelerates the oxidation of the soot precursors and nascent soot

153

particles

154

after the volatile flame extinguished. The brightness of the burning char decreased towards the end

155

of the combustion and finally extinction occurred at 77.06 s.

21

. In addition, the volatile flame duration was

. The release of the sodium species into the gas phase suppresses particulate amalgamation leading

26-28

; and (4) Residue char combustion stage: the burning of the char residue continued

156

6 Environment ACS Paragon Plus

Page 6 of 26

Page 7 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

157

The four-stage combustion phenomena were observed for all particles examined in the present

158

study. However, the behaviour of volatile matter combustion was significantly affected by

159

temperature and particle size. As shown in Figure 5 (b) and (c), in the first a few seconds following

160

ignition, the volatile matter flame was seen to consist of two layers, namely, a luminous yellowish

161

inner layer and a translucent outer layer. This dual layer flame structure became more profound at

162

either a higher furnace temperature or for a smaller particle and only lasted for a very short period,

163

in the order of a few seconds. The bright yellowish flame was an indication of the formation of soot

164

particles. The ignition process of large lignite particles is generally controlled by the external heat

165

transfer to the particle29, 30. The external heat transfer to the particle can be expressed in terms of Eq

166

(1), according to which the external heat transfer is significantly enhanced at a higher furnace

167

temperature and for a smaller particle, leading to a higher heating rate of the particle. The higher

168

heating rate would lead to more intense volatile release into the boundary layer which was also

169

deprived of oxygen. As a result, a greater amount of soot was formed for smaller particles at higher

170

furnace temperatures.

λc 171

∂Tp ∂r

r=

D 2

= εσ (Tw4 − Tp4 ) +

2λa  ln(1 + B )  (T∞ − Tp )  D B  

(1)

172

where λc and λa are the thermal conductivity of lignite and air (kWm-1·K-1), r is the radial distance

173

from the particle center (m), D is the diameter of the lignite particle (m), ε is the lignite particle

174

emissivity, σ is the Stefan-Boltzmann Constant (5.6703×10-8 Wm-2K-4), Tw, T∞ and Tp are the

175

furnace wall temperature, gas temperature and particle temperature (K) and B is the Spalding heat

176

transfer number.

177 178

Figure 6 shows the time-dependent variation in the volatile flame displacement for the burning

179

particle that is presented in Figure 5(a). It can be seen that the flame front initially expanded to ca. 2

180

mm once the flame was formed but then quickly contracted back to ca. 0.8 mm from the particle

181

surface at around 14 s. During the ignition delay period, a large amount of volatile matter was 7 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

182

released and accumulated around the particle, which, upon ignition, demanded a great amount of

183

oxygen, resulting in a rapidly increasing flame size to reach more oxygen. Once the flame was

184

stabilised, the flame size remained almost constant till about 63 s.

185 186

Figure 7 shows the d2–t plots31 for the burning of Zhundong lignite for a) 3 mm single particles at

187

various furnace temperatures and b) 2, 2.5 and 3 mm single particles at a fixed furnace temperature

188

of 1123 K. It is evident that the particle sizes remained invariant from arrival at the furnace centre

189

till the ignition of volatile matter. This indicates that the release of volatile matter from the particles

190

and particle surface reactions did not cause noticeable changes to the particle size prior to ignition

191

for Zhundong lignite. After ignition, the particle size decreased almost linearly as a function of time,

192

suggesting the char oxidation process followed the classic d2-law 32 , controlled by oxygen diffusion

193

in the boundary layer to the particle surface

194

combustion process, an ash shell was observed while the char oxidation continued within the shell.

195

The particle size became almost constant while the char oxidation continued, suggesting that the

196

burning of the residue char in this period followed the classic shrinking core model30, 33.

197

The tvi, thi, tve and tt of Zhundong lignite as a function of furnace temperature and particle size are

198

shown in Figures 8 and 9. Under all test conditions, the heterogeneous ignition consistently

199

occurred before the ignition of volatiles in the boundary layer. As expected, tvi, thi, tve and tt all

200

decreased with increasing furnace temperature and decreasing particle size. The trends for

201

variations in the heterogeneous ignition time and homogeneous ignition time are in agreement with

202

the theoretical calculations that the ignition process of large lignite particle is controlled by the

203

external heat transfer from ambient to the particle29, 30. The external heat transfer was enhanced at

204

higher temperature and smaller particle size and ultimately reduced the time required for ignition.

205

As the combustion process is controlled by the diffusion of oxygen to the particle surface as

206

discussed above, at the same furnace temperature, the time required for the complete combustion of

207

single particles decreased with decreasing particle size. However, an increase in the furnace

32

. However, in the final few seconds of the char

8 Environment ACS Paragon Plus

Page 8 of 26

Page 9 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

208

temperature only induced a small decrease in the total combustion time for particles of the same

209

size.

210 211

4. Conclusions

212

As a continuation effort of our previous studies, the effect of particle size and furnace temperature

213

on the ignition and combustion characteristics of single particles of Zhundong lignite were studied

214

in the present paper. Under the tested conditions, the ignition of Zhundong lignite followed the joint

215

hetero-homogeneous mechanism and the combustion of the Zhundong lignite consisted of pre-

216

ignition heating, heterogeneous ignition and combustion, volatile matter ignition and combustion,

217

followed by the combustion of solid residue. The particle size was almost constant during the pre-

218

ignition and the heterogeneous ignition and combustion stages while decreased almost linearly with

219

time upon the volatile matter ignition. The volatile flame was virtually soot-free and lasted a

220

lengthy period of time. However, at higher temperatures, a layer of sooty flame was formed close to

221

the particle surface but only lasted a very short period. In the final stage of the combustion of solid

222

residue, the particle size decreased with time initially but then remained invariant towards the end

223

of the combustion, following the shrinking core model. Generally speaking, the key ignition and

224

combustion characteristic times decrease with increasing furnace temperature and decreasing

225

particle size.

226 227

Acknowledgement

228

Financial and other supports have been received from the Australian Research Council under the

229

ARC Discovery Project scheme (DP110103699) and the ARC Linkage Project scheme

230

(LP100200135).

9 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

231

References

232

1.

233

combustion by phase-selective laser-induced breakdown spectroscopy. Proc. Combust. Inst. 2015,

234

35, (2), 2339-2346.

235

2.

236

from three different ranks in O2/N2 and O2/CO2 atmospheres. Combustion and Flame 2012, 159,

237

(12), 3554-3568.

238

3.

239

single particles from three different coal ranks and from sugar cane bagasse in O2/N2 and O2/CO2

240

atmospheres. Combustion and Flame 2012, 159, (3), 1253-1271.

241

4.

242

combustion phenomena at the particle level. Combustion and Flame 2016, 164, (Supplement C),

243

22-34.

244

5.

245

Zhundong coal ash in oxy-fuel combustion atmosphere. Fuel 2015, 150, (0), 526-537.

246

6.

247

sodium during combustion of Zhundong coals. Journal of the Energy Institute 2016, 89, (1), 48-56.

248

7.

249

Combustion Characteristics in Zhundong Coals. Journal of Fuel Chemistry and Technology 2014,

250

20, (3), 216-221.

251

8.

252

emission of Zhundong coals. Journal of the Energy Institute 2016, 89, (4), 636-647.

253

9.

254

of sodium in high sodium coals form Xinjiang and its effect on combustion process. Journal of Fuel

255

Chemistry and Technology 2013, 4, (7), 832-838.

Yuan, Y.; Li, S.; Yao, Q., Dynamic behavior of sodium release from pulverized coal

Khatami, R.; Stivers, C.; Levendis, Y. A., Ignition characteristics of single coal particles

Khatami, R.; Stivers, C.; Joshi, K.; Levendis, Y. A.; Sarofim, A. F., Combustion behavior of

Khatami, R.; Levendis, Y. A., An overview of coal rank influence on ignition and

Zhou, B.; Zhou, H.; Wang, J.; Cen, K., Effect of temperature on the sintering behavior of

Li, G.; Wang, C. a.; Yan, Y.; Jin, X.; Liu, Y.; Che, D., Release and transformation of

Weng, Q.; Wang, C.; Che, D.; Fu, Z., Alkali Metal Occurrence Mode and Its Influence on

Wang, C. a.; Liu, Y.; Jin, X.; Che, D., Effect of water washing on reactivities and NOx

Chen, C.; Zhang, S.; Liu, D.; Guo, X.; Dong, A.; Xiong, S.; Shi, D.; Lv, J., Existence form

10 Environment ACS Paragon Plus

Page 10 of 26

Page 11 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

256

10.

Zhang, Z.; Zhu, M.; Zhang, Y.; Setyawan, H. Y.; Li, J.; Zhang, D., Ignition and combustion

257

characteristics of single particles of Zhundong lignite: Effect of water and acid washing.

258

Proceedings of the Combustion Institute 2017, 36, (2), 2139-2146.

259

11.

260

effect of convection on the ignition behaviour of single coal particles under various O2

261

concentrations. Fuel 2014, 116, (0), 77-83.

262

12.

263

Single Coal Particles Prior to Ignition Using a Monochromatic Imaging Technique. In Australian

264

Combustion Symposium, Perth, 2013; pp 283-286.

265

13.

266

coal particle in a hot furnace under normal- and micro-gravity condition. Proc. Combust. Inst. 2009,

267

32, (2), 2029-2035.

268

14.

269

fluidised-bed. Fuel 2000, 79, (8), 873-883.

270

15.

271

Reactivity and Aromatic Structure of Coal. Energy & Fuels 2000, 14, (3), 646-653.

272

16.

273

Fourier transform interferometry. Fourier Transform Infrared Spectroscopy 2012, 4, 169-240.

274

17.

275

groups in macerals across different coal ranks via micro-FTIR spectroscopy. International Journal

276

of Coal Geology 2012, 104, (Supplement C), 22-33.

277

18.

278

Analytical Chemistry, John Wiley & Sons, Ltd: 2006.

279

19.

280

Transformation of Sodium during Pyrolysis of Zhundong Coals. Energy & Fuels 2015, 29, (1), 78-

281

85.

Liu, B.; Zhang, Z.; Zhang, H.; Yang, H.; Zhang, D., An experimental investigation on the

Zhang, Z.; Liu, B.; Zhu, M.; Zhang, H.; Zhang, D., Temperature Measurement of Large

Zhu, M.; Zhang, H.; Tang, G.; Liu, Q.; Lu, J.; Yue, G.; Wang, S.; Wan, S., Ignition of single

Ross, D. P.; Heidenreich, C. A.; Zhang, D. K., Devolatilisation times of coal particles in a

Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S., Relationship between Pyrolysis

Painter, P. C.; Starsinic, M.; Coleman, M. M., Determination of functional groups in coal by

Chen, Y.; Mastalerz, M.; Schimmelmann, A., Characterization of chemical functional

Coates, J., Interpretation of Infrared Spectra, A Practical Approach. In Encyclopedia of

Wang, C. a.; Jin, X.; Wang, Y.; Yan, Y.; Cui, J.; Liu, Y.; Che, D., Release and

11 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

282

20.

Li, X.; Bai, Z.-Q.; Bai, J.; Han, Y.-N.; Kong, L.-X.; Li, W., Transformations and Roles of

283

Sodium Species with Different Occurrence Modes in Direct Liquefaction of Zhundong Coal from

284

Xinjiang, Northwestern China. Energy & Fuels 2015, 29, (9), 5633-5639.

285

21.

286

in air and different oxy-fuel atmospheres”. Applied Thermal Engineering 2015, 74, (0), 61-68.

287

22.

288

particle in a fluidized bed under O2/CO2 and O2/N2 atmospheres: A combination of visual image

289

and particle temperature. Applied Energy 2014, 115, 301-308.

290

23.

291

Alkali and Alkaline Earth Metallic Species on the Char Ignition Temperature of a Loy Yang Coal

292

under O2/N2 Atmosphere. Energy & Fuels 2012, 26, (1), 112-117.

293

24.

294

brown coal char particles during combustion. Combust. Flame 2011, 158, (12), 2512-2523.

295

25.

296

metals during the pyrolysis of a Victorian brown coal. Fuel 2000, 79, (3–4), 427-438.

297

26.

298

diffusion flames. Combust. Flame 1982, 46, 301-314.

299

27.

300

diffusion flames. Combust. Flame 1987, 67, (2), 179-184.

301

28.

302

C2H4/O2/N2/Ar premixed flame. Fuel 1991, 70, (12), 1403-1411.

303

29.

304

Combustion 1982, 19, (1), 1045-1065.

305

30.

306

large to be controlled by heat transfer. Combustion and Flame 2006, 146, (3), 553-571.

Marek, E.; Świątkowski, B., Reprint of “Experimental studies of single particle combustion

Bu, C.; Liu, D.; Chen, X.; Pallarès, D.; Gómez-Barea, A., Ignition behavior of single coal

Wu, L.; Qiao, Y.; Gui, B.; Wang, C.; Xu, J.; Yao, H.; Xu, M., Effects of Chemical Forms of

van Eyk, P.; Ashman, P.; Nathan, G., Mechanism and kinetics of sodium release from

Li, C. Z.; Sathe, C.; Kershaw, J. R.; Pang, Y., Fates and roles of alkali and alkaline earth

Ndubizu, C. C.; Zinn, B. T., Effects of metallic additives upon soot formation in polymer

Bonczyk, P. A., The influence of alkaline-earth additives on soot and hydroxyl radicals in

Bonczyk, P. A., Effects of metal additives on soot precursors and particulates in a

Smith, I. W., The combustion rates of coal chars: A review. Symposium (International) on

Chern, J.-S.; Hayhurst, A. N., A model for the devolatilization of a coal particle sufficiently

12 Environment ACS Paragon Plus

Page 12 of 26

Page 13 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

307

31.

Law, C. K., Recent advances in droplet vaporization and combustion. Progress in Energy

308

and Combustion Science 1982, 8, (3), 171-201.

309

32.

310

Particles. Journal of Engineering for Power 1963, 85, (3), 183-188.

311

33.

312

Combustion and Flame 2007, 151, (3), 426-436.

Essenhigh, R. H., The Influence of Coal Rank on the Burning Times of Single Captive

Mitchell, R. E.; Ma, L.; Kim, B., On the burning behavior of pulverized coal chars.

313

13 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

314

Figure Captions

315

Figure 1

FTIR spectrum of Zhundong lignite

316

Figure 2

Schematic diagram of the single particle ignition rig

317

Figure 3

A schematic diagram showing the definitions of key ignition and combustion characteristics of single lignite particles

318

319

Figure 4

(a) greyscale intensity and (b) first-order derivative of the greyscale intensity as a

320

function of the numbers of vertical pixels of a burning 3 mm Zhundong lignite particle

321

at 1073 K.

322

Figure 5

Typical sequences of images of (a) 3 mm Zhundong lignite burning at 1073 K, (b) 2.5

323

mm Zhundong lignite burning at 1123 K and (c) 3 mm Zhundong lignite burning at

324

1273 K in air

325

Figure 6

5(a)

326

327

Figure 7

Temporal size variations of (a) 3 mm particles burning at various furnace temperatures and (b) 2, 2.5 and 3 mm particles burning at the fixed temperature of 1123 K.

328

329

Temporal variations of the flame displacement of the burning particle shown in Figure

Figure 8

Variations of the heterogeneous ignition time, homogeneous ignition time, volatile

330

flame extinction time and the total combustion time of single Zhundong lignite particles

331

of 3 mm in diameter burning in air as a function of furnace temperature

332

Figure 9

Variations of the heterogeneous ignition time, homogeneous ignition time, volatile

333

flame extinction time and the total combustion time of single Zhundong lignite particles

334

of 2, 2.5 and 3 mm in diameter burning in air at 1123 K

335

14 Environment ACS Paragon Plus

Page 14 of 26

Page 15 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

336

Energy & Fuels

Figure 1

337 338

Figure 1

FTIR spectra of Zhundong lignite

339

15 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

340

Page 16 of 26

Figure 2

Linear Stepper Motor

Coal Particle

Backlight

CCD Camera PLC

Motor Controller

Temperature Controller

SiC fibre Furnace Computer

341 342

Figure 2

Schematic diagram of the single particle ignition rig

343

16 Environment ACS Paragon Plus

Page 17 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

344

Energy & Fuels

Figure 3

345

346 347 348

Figure 3

A schematic diagram showing the definitions of key ignition and combustion characteristics of single lignite particles

349

17 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

350

Figure 4

351 352

Figure 4

(a) greyscale intensity and (b) first-order derivative of the greyscale intensity as a

353

function of the numbers of vertical pixels of a burning 3 mm Zhundong lignite

354

particle at 1073 K.

355

18 Environment ACS Paragon Plus

Page 18 of 26

Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

356

Energy & Fuels

Figure 5

Ignition

(a)

Image No.

1

2

3

4

5

6

7

(Time, s)

(t=0)

(t=6.7)

(t=9.02)

(t=11)

(t=63)

(t=77)

(t=77.06)

Ignition

(b)

Image No.

1

2

3

4

5

6

7

(Time, s)

(t=0)

(t=4.54)

(t=4.84)

(t=6)

(t=50)

(t=60)

(t=60.4)

Ignition

(c)

Image No.

1

2

3

4

5

6

7

(Time, s)

(t=0)

(t=4.24)

(t=4.76)

(t=6.5)

(t=52)

(t=69)

(t=69.3)

357 358

Figure 5

Typical sequences of images of (a) 3 mm Zhundong lignite burning at 1073 K, (b)

359

2.5 mm Zhundong lignite burning at 1123 K and (c) 3 mm Zhundong lignite burning

360

at 1273 K in air

361

19 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

362

Figure 6

363 364 365

Figure 6

Temporal variations of the flame displacement of the burning particle shown in Figure 5(a)

366

20 Environment ACS Paragon Plus

Page 20 of 26

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

367

Energy & Fuels

Figure 7

368

369 370 371

Figure 7

Temporal size variations of (a) 3 mm particles burning at various furnace temperatures and (b) 2, 2.5 and 3 mm particles burning at the fixed temperature of 1123 K.

372

21 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

373

Figure 8

374 375

Figure 8

Variations of the heterogeneous ignition time, homogeneous ignition time, volatile

376

flame extinction time and the total combustion time of single Zhundong lignite

377

particles of 3 mm in diameter burning in air as a function of furnace temperature

378

22 Environment ACS Paragon Plus

Page 22 of 26

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

379

Energy & Fuels

Figure 8

380 381

Figure 8

Variations of the heterogeneous ignition time, homogeneous ignition time, volatile

382

flame extinction time and the total combustion time of single Zhundong lignite

383

particles of 2, 2.5 and 3 mm in diameter burning in air at 1123 K

384

23 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

385

Table Caption

386

Table 1

Proximate and ultimate analyses of the Zhundong lignite

387

Table 2

Ash chemistry of the Zhundong lignite

388

24 Environment ACS Paragon Plus

Page 24 of 26

Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

389

390

Energy & Fuels

Table 1

Proximate and ultimate analyses of the Zhundong lignite Proximate analysis

Ultimate analysis

(wt% d.b.1)

(wt% d.a.f.2)

Ash

Fixed carbon

Volatile matter

C

H

O3

N

S

3.4

59.7

36.9

70.5

2.6

25.3

0.6

1.0

Note: 1. dry basis; 2. dry ash free basis; 3. oxygen content was calculated by difference.

391

25 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

392

Table 2

Page 26 of 26

Ash composition of the Zhundong lignite Ash composition (wt%) SiO2

Al2O3

CaO

Fe2O3

K2O

MgO

Na2O

P2O5

TiO2

5.42

6.39

40.7

3.06

0.55

7.62

6.08

0.048

0.30

393

26 Environment ACS Paragon Plus