Abatement of Fine Particle Emission by Heterogeneous Vapor

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Abatement of fine particle emission by heterogeneous vapor condensation during wet limestone-gypsum flue gas desulfurization Hao Wu, Danping Pan, Rongting Huang, Guangxin Hong, Bing Yang, Ziming Peng, and Linjun Yang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00673 • Publication Date (Web): 16 Jun 2016 Downloaded from http://pubs.acs.org on June 19, 2016

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Energy & Fuels

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Abatement of fine particle emission by heterogeneous vapor condensation

2

during wet limestone-gypsum flue gas desulfurization

3

Hao Wu 1, Danping Pan 1, Rongting Huang 1, Guangxin Hong 2, Bing Yang 2, Ziming Peng 2, Linjun

4

Yang 1,*

5

1

6

Energy and Environment, Southeast University, Nanjing 210096, Jiangsu Province, China

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2

8

China

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ABSTRACT

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of

Jiangsu Ruifan Environmental Protection Limited Company, Nantong 226200, Jiangsu Province,

10

The fine particles in desulfurized flue gas comprise coal-fired fine particles from combustion and

11

generated fine particles from desulfurization. The abatement of fine particle emission by

12

heterogeneous vapor condensation during wet flue gas desulfurization (WFGD) is experimentally

13

investigated in this paper. A supersaturation atmosphere, which is necessary for heterogeneous

14

vapor condensation, is established by increasing the humidity and reducing the temperature of the

15

flue gas before WFGD. The improvement of the removal of coal-fired fine particles and the

16

inhibition of generated fine particles formation in desulfurization process by heterogeneous vapor

17

condensation were studied, and the influences of inlet flue gas parameters on the emission of total

18

fine particles, including coal-fired fine particles and generated fine particles during desulfurization,

19

are examined. The results indicate that the total emission of fine particles in desulfurized flue gas

20

can be significantly decreased via heterogeneous vapor condensation. This decrease in the emission

21

of coal-fired fine particles is mainly related to the removal of fine particles via heterogeneous vapor

22

condensation, and the generation of fine particles from desulfurization is abated because of both the

23

decrease in the inlet flue gas temperature and heterogeneous vapor condensation. Higher inlet flue 1

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gas humidity can adequately reduce the emission of generated fine particles from desulfurization.

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The reduction in the flue gas temperature before WFGD is the main factor that inhibits the

26

formation of fine particles and removes coal-fired fine particles during desulfurization.

27

Key words: WFGD; Fine particles; Heterogeneous vapor condensation; Emission; Abatement

28

1. Introduction

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Fine particles that are emitted from coal-fired power plants are considered a great threat to the

30

ecological environment and human health because of enrichment in heavy metals, organic

31

pollutants and viruses

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particles from power plants [3]. Traditional de-dusting systems, such as bag-type dust collectors and

33

electrostatic dust collectors, have trouble collecting fine particles because of the Greenfield Gap [4].

34

However, this removal can be significantly improved if the size of fine particles can be increased

35

before entering the traditional de-dusting systems

36

to increase the size of fine particles

37

being nucleation centers, has been exploited and has proven to be a promising technique. When the

38

vapor pressure in the flue gas is higher than the corresponding saturated vapor pressure, a

39

supersaturation atmosphere is established

40

condenses onto the surfaces of fine particles, forming condensational droplets with larger sizes. The

41

removal performance of conventional de-dusting systems can be enhanced for these larger droplets.

[1, 2]

. Recently, more attention has been paid to reducing the emission of fine

[5]

. Hence, many techniques have been proposed

[6-10]

. Heterogeneous vapor condensation, with fine particles

[11,12]

. Supersaturation is metastable, so the vapor

42

At present, increasing numbers of wet flue gas desulfurization (WFGD) systems have been

43

installed in coal-fired power plants to control the emission of SO2. Reportedly, the concentration of

44

fine particles increases after limestone-gypsum desulfurization in the coal-fired power plants [13, 14],

45

and these fine particles were deemed to be formed by entrainment and the evaporation of

46

desulfurization slurry

[15]

. Therefore, a process that combines heterogeneous vapor nucleation and 2


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desulfurization has been proposed and developed to decrease the emission of fine particles [16]. Yan

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[17]

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and noted that inlet flue gas with higher humidity and lower temperature was beneficial for the

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formation of supersaturation. Bao

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fine particles can be significantly enhanced by adding steam into the flue gas before desulfurization,

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achieving a removal efficiency of approximately 30-40%.

investigated a supersaturation atmosphere that was established in the desulfurization scrubber

[18]

reported that the removal performance of desulfurization for

53

According to previous research results, supersaturation can be obtained in a desulfurization

54

scrubber, and heterogeneous vapor condensation can be used in WFGD systems to limit the

55

emission of fine particles. However, previous research has focused on limiting the total amount of

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fine particles (including coal-fired fine particles and generated fine particles) during WFGD with

57

heterogeneous vapor condensation. Any improvements in the removal of coal-fired fine particles

58

and the inhibition of the formation of fine particles by heterogeneous vapor condensation during

59

desulfurization process are still not very clear. Therefore, investigating the removal and formation

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characteristics of fine particles during desulfurization with heterogeneous vapor condensation is

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very important.

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In the present work, the characteristics of fine particles before and after limestone-gypsum

63

desulfurization are examined. Improvements of the removal of coal-fired fine particles and the

64

inhibition of the formation of fine particles by heterogeneous vapor condensation during

65

desulfurization are investigated experimentally. Furthermore, the influences of inlet flue gas

66

parameters on these improvements of the removal of coal-fired fine particles and the inhibition of

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the formation of fine particles are studied.

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2. Experimental system and measurement technique

3


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2.1 Experimental facility

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The experimental facility consisted of three sections, including a flue gas simulation section,

71

desulfurization section and slurry circulation section, as shown in Fig. 1. The flue gas simulation

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section included an aerosol generator (SAG-410, Germany), a vortex gas pump, an SO2 gas cylinder,

73

a steam generator and a heater. The flue gas (approximately 15 Nm3·h-1) was generated by the

74

vortex gas pump, and the temperature, humidity, SO2 concentration, and concentration of coal-fired

75

fine particles could be adjusted to a stable value in the flue gas simulation system. The

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desulfurization system was a three-level desulfurization scrubber, and the top of desulfurization

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scrubber contained a demister to eliminate entrained slurry droplets from flue gas. The slurry

78

circulation section was used for slurry preparation and feeding, including a desulfurization slurry

79

tank, a stirrer, a heater, pumps and corresponding pipelines. In the experimental facility,

80

heat-insulating material was used for heat preservation, and the temperature distribution in the

81

experimental facility was similar to that in an actual power plant.

82

Two experimental strategies were designed, denoted as case 1 and case 2, to investigate the

83

removal characteristics of coal-fired fine particles and the formation characteristics of generated

84

fine particles during desulfurization. For both cases, supersaturation might be attained via regulating

85

the flue gas temperature and humidity before WFGD [19]. In the case 1, water was sprayed into the

86

desulfurization scrubber to avoid the formation of fine particles from the entrainment and

87

evaporation of desulfurization slurry. In this case, the decreasing of coal-fired fine particles was

88

mainly caused by the effect of liquid scrubbing. In case 2, desulfurization slurry was sprayed into

89

the desulfurization scrubber, and the flue gas consisted of particle-free air. In this case, the increase

90

in the generation of fine particles from desulfurization was mainly caused by the entrainment and

91

evaporation of the desulfurization slurry. 4


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In addition, the liquid-gas (L/G) ratio was set to 15 L·Nm-3, and the desulfurization slurry

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temperature or spraying liquid temperature was kept at 50 oC during the experiment.

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2.2 Measurement method

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An electrical low pressure impactor (ELPI, Finland) was used to measure the fine particles size

96

distribution and concentration before and after desulfurization. The measurements ranged from

97

0.023 to 9.314 µm (aerodynamic diameter). The sample gas was withdrawn from the flue gas and

98

heated to avoid vapor condensation. The sample gas flowed through a cyclone to a dilutor and then

99

into the ELPI. Particles that were larger than 9.314 µm were removed by a cyclone. The flue gas’

100

temperature and humidity were determined by means of temperature-humidity transmitter

101

(HMT337, Finland).

102

3. Results and discussion

103

3.1 Size distribution and number concentration of fine particles in the flue gas

104

The fine particles in the inlet flue gas were provided by an aerosol generator. The fine particles

105

concentration and size distribution were measured by the ELPI before and after desulfurization. For

106

the case without vapor condensation, the inlet flue gas temperature and humidity were set as 120 oC

107

and 60 g·Nm-3, respectively. For the case of vapor condensation, the temperature and humidity of

108

the flue gas before WFGD were set as 60 oC and 120 g·Nm-3 [19], respectively.

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Fig. 2 shows the concentration of fine particles before and after desulfurization. The

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concentration of fine particles was approximately 3.7×106 1·cm-3 before WFGD. When the flue gas

111

passed through desulfurization system, the concentration of fine particles increased to 4.1×106

112

1·cm-3 without heterogeneous vapor condensation and decreased to 2.4×106 1·cm-3 with

113

heterogeneous vapor condensation. Thus, many new fine particles were generated via 5


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desulfurization, and heterogeneous vapor condensation during desulfurization limited the emission

115

of fine particles. Although some coal-fired fine particles were removed by desulfurization without

116

heterogeneous vapor condensation, some fine particles were still generated. These fine particles that

117

were generated by desulfurization were deemed to be sulfates, sulfites and unreacted limestone [20].

118

For the case with heterogeneous condensation, on the one hand, some coal-fired fine particles

119

would become condensation droplets in a supersaturation atmosphere via heterogeneous vapor

120

condensation, so these condensation droplets would be separated more easily by the effect of slurry

121

scrubbing and demister interception

122

could also cause many slurry droplets to increase in size, thus allowing them to be separated by a

123

demister. As the amount of entrained slurry droplets decreased, the emission of generated fine

124

particles also decreased.

[21]

. On the other hand, heterogeneous vapor condensation

125

Fig. 3 presents the size distribution of fine particles in the WFGD inlet and outlet flue gas. The

126

size distribution indicated that the fine particles in the flue gas were mostly in the submicron range

127

with a peak at approximately 0.1 µm. These results are similar to those from coal-fired flue gas in

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power plants

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heterogeneous vapor condensation, which indicates that the mean size of the fine particles became

130

smaller. However, the peak of the size distribution further shifted to the left after desulfurization

131

with heterogeneous vapor condensation, which indicates that the number of large fine particles

132

decreased during desulfurization.

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3.2 Improving the removal of coal-fired fine particles by heterogeneous vapor condensation

[22, 23]

. Additionally, the peak shifted slightly to the left after desulfurization without

134

Clean water was sprayed into the desulfurization scrubber to investigate the removal

135

characteristics of coal-fired fine particles during desulfurization with heterogeneous vapor

136

condensation. During the experiments, the flue gas temperature before WFGD was set to be 60 or 6


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120 oC, and the humidity was set to be 120 or 60 g·Nm-3. In addition, the removal efficiency was

138

used to describe the removal of fine particles via desulfurization. The removal efficiency was

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defined as follows:

η=

140 141 142

N inlet − N outlet × 100% N inlet

(1)

where η is the removal efficiency, N inlet is the concentration of coal-fired fine particles before WFGD, and N outlet is the concentration of coal-fired fine particles after WFGD.

143

Figs. 4 and 5 depict the concentration and removal efficiency of coal-fired fine particles from the

144

interception effect of the demister and with scrubbing effect of liquids and without heterogeneous

145

vapor condensation. The removal efficiency of coal-fired fine particles was approximately 37%

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under the typical operating conditions of power plants (Tg,in = 120 oC, Hg,in=60 g·Nm-3). As the

147

temperature ranged from 120 oC to 60 oC at the same humidity, the removal efficiency increased

148

slightly from 37% to 41% because a lower inlet flue gas temperature would have decreased the gas

149

velocity in the desulfurization scrubber. Accordingly, the gas residence time in the desulfurization

150

scrubber would have increased, which would improve the removal of coal-fired fine particles.

151

However, the contribution from the flue gas temperature reduction for the improvement of removal

152

performance was limited, and the flue gas temperature could not be continuously reduced under

153

power plant actual conditions. The removal efficiency significantly improved to 72% with

154

heterogeneous vapor condensation, which can be explained by the increasing size of the coal-fired

155

fine particles. In a supersaturation atmosphere, many coal-fired fine particles could become larger

156

condensation droplets via heterogeneous vapor condensation, which are more easily separated by

157

using liquid scrubbing and a demister.

158

Figs. 6 and 7 present the stage removal efficiency and coal-fired fine particles size distribution.

7


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The temperature reduction of the flue gas before desulfurization improved the removal performance

160

of coal-fired fine particles of all sizes, but the Greenfield Gap still existed. On the contrary, the

161

Greenfield Gap almost disappeared when heterogeneous vapor condensation occurred during

162

desulfurization, and the removal performance of fine particles in all stages significantly improved.

163

These phenomena can be explained as follows. When the gas temperature decreased without

164

heterogeneous vapor condensation, the gas residence time in the desulfurization scrubber increased.

165

That is, the flue gas was scrubbed by more liquid and the collision probability between liquid

166

droplets and coal-fired fine particles was enhanced. Thus, the removal of fine particles of all sizes

167

slightly improved. However, the particles size distribution remained unchanged, and coal-fired fine

168

particles that were smaller than 0.1 µm were still removed by diffusive force, while fine particles

169

that were larger than 1 µm were separated by inertia force

170

of fine particles in the range of 0.1-1 µm was inefficient, and the Greenfield Gap still existed. With

171

heterogeneous vapor condensation, the fine particles sizes could be increased in a supersaturation

172

atmosphere. In other words, fine particles with sizes of 0.1-1 µm might become larger droplets with

173

sizes above 1 µm, and then inertia force would be the primary force that removes these droplets.

174

However, fine particles with sizes below 0.1 µm would remain almost unchanged because the

175

supersaturation that formed in the desulfurization scrubber was not sufficient enough

176

improvement in the removal efficiency of these particles was mainly related to the enhancement of

177

thermophoresis and diffusiophoresis from phase transitions.

178

3.3 Inhibiting the formation of fine particles with heterogeneous vapor condensation

[24]

. Therefore, the removal performance

[25]

. The

179

An experiment to study the formation characteristics of fine particles during desulfurization was

180

conducted with particle-free air as the inlet gas. The desulfurization slurry that was sprayed into the

181

desulfurization scrubber was derived from coal-fired power plants. During the experiments, the inlet 8


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gas temperature was set to be 60 or 120 oC and the humidity was set to be 120 or 60 g·Nm-3. In

183

addition, the reduction rate was used to describe the inhibition of the formation of fine particles

184

during desulfurization. The reduction rate was defined as follows:

ϕ=

185

N1 − N 2 × 100% N1

(2)

186

where ϕ is the reduction rate, N1 is the concentration of fine particles that are generated after

187

WFGD under typical operating conditions (Tg,in = 120 oC, Hg,in = 60 g·Nm-3), and N 2 is the

188

concentration of fine particles that are generated after WFGD under experimental operating

189

conditions.

190

The concentration of generated fine particles in desulfurized flue gas is shown in Fig. 8, and the

191

reduction rate of these fine particles through different approaches is presented in Fig. 9. The

192

concentration of generated fine particles in desulfurized flue gas was approximately 2.69 × 106

193

1·cm-3 when the humidity of inlet gas was 60 g·Nm-3 at the temperature of 120 oC. When the

194

temperature decreased from 120 oC to 60 oC at a humidity of 60 g·Nm-3, the concentration

195

decreased to 2.25 × 106 1·cm-3 and the reduction rate was 16.4%. When the inlet gas humidity

196

improved from 60 to 120 g·Nm-3 at a temperature of 60 oC, the concentration further decreased to

197

1.32 × 106 1·cm-3 with a reduction rate of 50.9%. Pan [15] found that these generated fine particles in

198

desulfurized flue gas are derived from the entrainment of slurry droplets. When the gas temperature

199

before WFGD decreased from 120 to 60 oC, the gas temperature in the desulfurization scrubber

200

would also decrease. Therefore, the evaporation of slurry droplets in the desulfurization scrubber

201

decreased at relatively low temperatures. Partial slurry droplets that could evaporate into smaller

202

droplets and then be entrained from the desulfurization scrubber under typical operating conditions

203

would have barely changed in these circumstances. That is, many droplets that would escape from

204

the desulfurization scrubber under typical operating conditions would be separated by a demister or 9


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slurry scrubbing. Accordingly, the concentration of generated fine particles in the desulfurized flue

206

gas decreased as the amount of entrained slurry droplets decreased. In the course of the inlet flue

207

gas humidity increased from 60 to 120 g·Nm-3 at 60 oC, supersaturation would be established in the

208

desulfurization scrubber. Many slurry droplets that would have previously been entrained from the

209

desulfurization scrubber grew into larger condensational grown droplets, which could be more

210

easily separated by a demister or slurry scrubbing. Thus, the amount of entrained slurry droplets

211

decreased in the desulfurized flue gas, thereby decreasing the emission of generated fine particles.

212

Additionally, the reduction in the emission of generated fine particles because of the lower inlet

213

gas temperature was inconspicuous compared to that from heterogeneous vapor condensation

214

because of the different mechanisms of these two processes. Figs. 10 and 11 show that a reduction

215

in the flue gas temperature before scrubber would decrease the generation of fine particles of all

216

sizes. The main reason for this phenomenon was the inhibition of slurry droplet evaporation

217

because of the temperature reduction of the flue gas. Although the evaporation of slurry droplets

218

was inhibited, some slurry droplets could still evaporate into smaller droplets and escape from the

219

desulfurization scrubber. In contrast, supersaturation would be achieved via adjusting the inlet flue

220

gas humidity to 120 g·Nm-3. According to the heterogeneous vapor condensation theory

221

droplets can be regarded as pure liquid droplets, so the critical supersaturation degree is much lower

222

than that fine particles from coal combustion. Given the same supersaturation degree, most slurry

223

droplets could be enlarged by heterogeneous vapor condensation. Hence, more slurry droplets

224

would be separated by a demister or slurry scrubbing, further decreasing the amount of entrained

225

slurry droplets.

226

3.4 Effect of the parameters of inlet flue gas on the emission of fine particles

227

3.4.1 Effect of the temperature of the inlet flue gas on the emission of fine particles 10


[11]

, slurry

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The effect of the inlet flue gas temperature on the emission of fine particles after desulfurization

229

is shown in Fig. 12. During the experiments, the inlet flue gas humidity was always kept at 120

230

g·Nm-3. As shown in Fig. 12, the total emission of fine particles decreased as the inlet flue gas

231

temperature decreasing. The total concentration of fine particles decreased from 4.2×106 1·cm-3 to

232

3.9×106 1·cm-3 as the inlet flue gas temperature decreased from 140 to 100 oC. During this process,

233

the concentration of coal-fired fine particles only changed slightly, while the emission of generated

234

fine particles more obviously decreased. According to the results of previous research

235

supersaturation would not be formed under these circumstances, and the removal and formation

236

mechanisms of fine particles would remain almost unchanged. Hence, the reduction in the total

237

emission of fine particles was mainly related to the decrease in generated fine particles. However,

238

this situation changed when the inlet flue gas temperature decreased to 80 oC. During this process,

239

the total concentration of fine particles obviously decreased because supersaturation was established

240

in the desulfurization scrubber as the inlet flue gas temperature decreased to 80 oC. According to

241

previous calculation results

242

obtained in this case. Any generated fine particles could be considered to have been derived from

243

the entrainment and evaporation of slurry droplets. On the one hand, many larger slurry droplets

244

would be activated before becoming condensation droplets, which might be separated through

245

demister interception and slurry scrubbing. On the other hand, many smaller slurry droplets that

246

should escape from the desulfurization scrubber change only slightly because the supersaturation

247

degree is not sufficiently high. Nevertheless, the amount of entrained slurry droplets would decrease.

248

Correspondingly, the emission of generated fine particles in the desulfurized flue gas was abated.

249

The critical supersaturation degree for coal-fired fine particles, which were insoluble, was higher

250

than that for slurry droplets

[19]

,

[16]

, a supersaturation degree of approximately 1.05-1.10 could be

[11]

. Although supersaturation could 11


be formed in the desulfurization

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251

scrubber, the supersaturation degree was not high enough to reach the critical supersaturation

252

degree of most coal-fired fine particles. Therefore, only small amounts of coal-fired fine particles

253

with larger sizes could be activated and then removed. The coal-fired fine particles in the flue gas

254

most in the submicron range, so the decrease in larger fine particles only slightly affected the

255

emission of coal-fired fine particles. When the inlet gas temperature further decreased to 60 oC, the

256

total emission of fine particles significantly decreased. The same variation trends appeared for the

257

concentration changes of coal-fired fine particles and generated fine particles. These phenomena

258

can be explained as follows. The further reduction in the inlet flue gas temperature decreased the

259

flue gas temperature in the desulfurization scrubber. Correspondingly, the saturation vapor pressure

260

of the flue gas reduced. The definition of the supersaturation degree

261

could increase. On the one hand, a higher supersaturation degree could cause additional small slurry

262

droplets and coal-fired fine particles to become condensation droplets. On the other hand, a higher

263

supersaturation degree would also increase the amount of condensable water vapor, which can

264

increase the final size of the condensation droplets

265

particles significantly decreased.

266

3.4.2 Effect of the humidity of the inlet flue gas on the emission of fine particles

[11]

suggests that this value

[26]

. For these reasons, the total emission of fine

267

Fig. 13 presents the effect of the inlet flue gas humidity on the emission of fine particles after

268

desulfurization. The inlet flue gas temperature was always kept at 60 oC during the experiments. As

269

seen in Fig. 13, the total concentration of fine particles changed slightly as the humidity of the inlet

270

flue gas improved from 60 to 90 g·Nm-3. On the contrary, the total concentration of fine particles

271

significantly decreased when the humidity continuously improved to 120 g·Nm-3. Subsequently, the

272

total concentration of fine particles continuously decreased as the humidity further increased, but

273

this decreasing rate slowed down. The same variation trend can also be observed for the 12


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concentrations of coal-fired fine particles and generated fine particles.

275

No supersaturation atmosphere formed as the inlet flue gas humidity improved from 60 to 90

276

g·Nm-3. The removal of coal-fired fine particles was still related to the effect of liquid scrubbing

277

and the demister. Hence, the changes in the emission of coal-fired fine particles were not significant.

278

However, the higher humidity of the inlet flue gas meant higher water vapor partial pressure in the

279

desulfurization scrubber, which inhibited the evaporation of slurry droplets. In this case, many

280

slurry droplets that could have evaporated into smaller droplets and then escape from the

281

desulfurization scrubber before were separated by the demister, decreasing the amount of entrained

282

slurry droplets. Therefore, the total concentration of fine particles after desulfurization was

283

decreased slightly under these conditions. A supersaturation atmosphere was formed as the humidity

284

increased to 120 g·Nm-3. On the one hand, many larger coal-fired fine particles were activated first

285

and became condensation droplets, which could be removed more easily. On the other hand, the

286

evaporation of slurry droplets was greatly restrained, and many slurry droplets were activated and

287

enlarged in this supersaturation atmosphere, decreasing the amount of entrained slurry droplets.

288

Correspondingly, the concentration of generated fine particles decreased, and the total amount of

289

fine particles significantly decreased. The total emission of fine particles further decreased as the

290

humidity increased because higher humidity increases the supersaturation degree and the amount of

291

condensable water vapor. A higher supersaturation degree could activate additional small coal-fired

292

fine particles and slurry droplets, and more abundant condensable water vapor would cause larger

293

condensation droplets to form. Thus, more coal-fired fine particles would be removed and fewer

294

fine particles would be generated in this case.

295

4. Conclusions

296

Improvements of the removal of coal-fired fine particles and the inhibition of the generation of 13


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

297

fine particles during WFGD by heterogeneous vapor condensation were experimentally investigated

298

in this paper. The influences of the inlet flue gas temperature and humidity were also presented. The

299

results showed that the fine particles concentration after desulfurization increased because of the

300

formation of fine particles under typical operating conditions. When a supersaturation atmosphere

301

was formed in the desulfurization scrubber, the emission of fine particles, including coal-fired fine

302

particles and generated fine particles, obviously decreased because of heterogeneous vapor

303

condensation. The decrease in the concentration of coal-fired fine particles was mainly related to

304

heterogeneous vapor condensation. Coal-fired fine particles activated under a supersaturation

305

atmosphere, and then vapor condensed onto the surface of these activated coal-fired fine particles,

306

forming larger condensation droplets. These larger condensational droplets were separated more

307

efficiently via liquid scrubbing and demister interception. The decrease in the concentration of

308

generated fine particles was mainly related to simultaneous effects from the temperature reduction

309

of the inlet flue gas and heterogeneous vapor condensation. This lower inlet flue gas temperature

310

weakened the evaporation of slurry droplets, and heterogeneous vapor condensation increased the

311

size of the slurry droplets. This simultaneous effect decreased the amount of entrained slurry

312

droplets, which then decreased the emission of generated fine particles. In addition, lower

313

temperature and higher humidity limited the emission of fine particles.

314

Acknowledgments

315

The project was financially supported by the Science and Technology Support Program of

316

Jiangsu (NO. BE2014856), the National Natural Science Foundation of China (NO. 21276049), and

317

the National Basic Research Program of China (973 Program NO.2013CB228505).

318

References

319

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[2] Atkinson, R.W.; Mills, I.C.; Walton, H.A. Anderson HR. Fine particle components and health - a systematic

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review and meta-analysis of epidemiological time series studies of daily mortality and hospital admissions. J.

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Expo. Sci. Environ. Epidemiol. 2015, 25 (2), 208-214.

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[3] Yao, Q.; Li, S.; Xu, H.; Zhuo, J.; Song, Q. Studies on formation and control of combustion particulate matter in China: a review. Energ. 2009, 34 (9), 1296-309.

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[4] Seinfeld, J.H.; Pandis, S.N. Atmospheric Chemistry and Physics; John Wiley: Hoboken, NJ, 1998; p 1326.

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[5] Vogt, U.; Heidenreich, S.; Büttner, H.; Ebert, F. An extensive study of droplet growth and separation of

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submicron particles in packed columns. J. Aerosol Sci. 1997, 28(Suppl 1), S395-S396. [6] Ji, J.; Hwang, J.; Bae, G.; Kim, Y. Particle charging and agglomeration in DC and AC electric fields. J. Electrost. 2004, 61 (1), 57-68. [7] Tammaro, M. Heterogeneous condensation for submicronic particles abatement. Ph.D. Dissertation, University of Naples Federico II, Naples, Italy, 2010.

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[8] Lind, T.; Kauppinen, E. I.; Srinivasachar, S., Porle, K.; Gurav, A.S.; Kodas, T.T. Submicron agglomerate

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particle formation in laboratory and full-scale pulverized coal combustion. J. Aerosol Sci. 1996, 27(Suppl 1),

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361-362.

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[9] Rodríguez-Maroto, J. J.; Gomez-Moreno, F. J.; Martín-Espigares, M.; Bahillo, A.; Acha, M.; Gallego, J. A.;

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Riera, E.; Hoffmann, T. L.; Rodríguez, G. Acoustic agglomeration for electrostatic retention of fly-ashes at

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pilot scale: influence of intensity of sound field at different conditions. J. Aerosol Sci. 1996, 27(Suppl 1),

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621-622.

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[10] Li, Y. W.; Zhao, C. S.; Wu, X.; Lu, D. F.; Han, S. Aggregation mechanism of fine fly ash particles in uniform magnetic field. Korean J. Chem. Eng. 2007, 24(2), 319-327. [11] Fletcher, N. H. The Physics of Rainclouds; Cambridge University Press: London, 1962. 15


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[12] Gorbunov, B.; Hamilton, R.; Clegg, N.; Toumi, R. Water nucleation on aerosol particles containing both organic and soluble inorganic substances, Atmos. Res. 1998, 47(2), 271-283.

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[13] Meij, R.; Winkel, H. The emissions and environmental impact of PM10 and trace elements from a modern

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coal-fired power plant equipped with ESP and wet FGD. Fuel Process. Technol. 2004, 85(S6-7), 641-656.

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[14] Nielsen, M. T.; Livbjerg, H.; et al. Formation and emission of fine particles from two coal-fired power plants.

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Combust. Sci. Technol. 2002, 174(2), 79-113. [15] Pan, D. P.; Guo, Y. P.; Huang, R. T.; Sheng, Y.; Yang, L. J. Formation of fine particles in flue gas desulphurization process using limestone-gypsum, J. CIESC. 2015, 66(11), 4618-4625. [16] Wu, H.; Yang, L. J.; Yan, J. P.; Hong, G. X.; Yang, B. Improving the removal of fine particles by heterogeneous condensation during WFGD processes. Fuel Process. Technol. 2016, 145, 116-122. [17] Yan, J. P.; Study on fine particles removal from coal combustion improved by vapor condensational growth. Ph.D. Dissertation, Southeast University, Nanjing, China, 2009. [18] Bao, J. J. Study on improving the removal of fine particles by heterogeneous condensation in WFGD system. Ph.D. Dissertation, Southeast University, Nanjing, China, 2012.

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[19] Wu, H. Pan, D. P.; Bao, J. J.; et al. Improving the removal efficiency of sulfuric acid droplets from flue gas

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using heterogeneous vapor condensation in a limestone-gypsum desulfurization process. J. Chem. Technol.

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Biotechnol. 2016, in press. (DOI: 10.1002/jctb.4974)

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[20] Yang, L. J.; Bao, J. J.; Yan, J. P.; Liu, J.H.; Song, S. J.; Fan, F. X. Removal of fine particles in wet flue gas desulfurization system by heterogeneous condensation. Chem. Eng. J. 2010, 156(1), 25-32. [21] Bao, J. J.; Yang, L. J.; Song, S. J.; Xiong, G. L. Separation of fine particles from gases in wet flue gas desulfurization system using a cascade of double tower. Energ. Fuel, 2012, 26(4), 2090-2097.

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[22] Quann, R. J.; Sarofim, M. N. A. F. A laboratory study of the effect of coal selection on the amount and

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composition of combustion generated submicron particles, Combust. Sci. Technol. 1990, 74 (1), 245-265. 16


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[23] Yan, L.; Gupta, A. R.; Wall, T. Fragmentation behavior of pyrite and calcite during high-temperature processing and mathematical simulation. Energ. Fuel, 2001, 15(2), 389-394. [24] Bao, J. J.; Yang, L. J.; Yan, J. P.; Xiong, G. L.; Lu, B. Xin, C. Y. Experimental study of fine particles removal in the desulfurated scrubbed flue gas. Fuel. 2013, 108(11), 73-79. [25] Fan, F. X. Study on growth mechanisms of inhalable particles in acoustic field and in supersaturated vapor environment, Ph.D. Dissertation, Southeast University, Nanjing, China, 2008. [26] Chen, C. C.; Tao, C. J. Condensation of supersaturated water vapor on submicrometer particles of SiO2 and TiO2. J. Chem. Phys. 2000, 112(22), 9967-9977.

17


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374

List of Figures and Tables Captions

375

Fig.1 Schematic diagram of the experimental rig

376

Fig.2 The number concentration of fine particles in flue gas

377

Fig.3 The number size distribution of fine particles in flue gas

378

Fig.4 Number concentration of coal-fired fine particles in desulfurized flue gas for case 1

379

Fig.5 Total removal efficiency of coal-fired fine particles for case 1

380

Fig.6 Number size distribution of coal-fired fine particles in desulfurized flue gas for case 1

381

Fig.7 Stage removal efficiency of coal-fired fine particles for case 1

382

Fig.8 Number concentration of generated fine particles in desulfurized flue gas for case 2

383

Fig.9 Total reduction rate of generated fine particles for case 2

384

Fig.10 Number size distribution of generated fine particles in desulfurized flue gas for case 2

385

Fig.11 Stage reduction rate of generated fine particles for case 2

386

Fig.12 Number concentration of fine particles after desulfurization as a function of inlet flue gas

387

temperature

388


389

humidity

18


Page 18 of 31

Page 19 of 31

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

390

Energy & Fuels

Fig.1 Schematic diagram of the experimental rig

391

19


Energy & Fuels

392

Fig.2 The number concentration of fine particles in flue gas 6

6x10

-3

Number concentration / 1⋅cm (STP)

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

Page 20 of 31

6

5x10

6

4x10

6

3x10

6

2x10

before desulfurization after desulfurization without heterogeneous condensation after desulfurization with heterogeneous condensation

6

1x10

0 0

393

50

100

150

Time / s

200

20


250

300

Page 21 of 31

394

Fig.3 The number size distribution of fine particles in flue gas 7

1x10

6

1x10

-3

dN/dlogDp / 1⋅cm (STP)

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

5

1x10

4

1x10

3

1x10

2

1x10

before desulfurization after desulfurization without heterogeneous condensation after desulfurization with heterogeneous condensation

1

1x10

395

0.0

0.1

Dp / µm

1.0

21


10.0

Energy & Fuels

396

Fig.4 Number concentration of coal-fired fine particles in desulfurized flue gas for case 1 6

3.0x10

6

2.5x10

1

1

2

-3


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

Page 22 of 31

2

6

2.0x10

6

1.5x10

3

6

1.0x10

o

-3

1: Tg,in=120 C, Hg,in=60 g ⋅Nm o

5

-3

2: Tg,in=60 C, Hg,in=60 g ⋅Nm

5.0x10

o

-3


0.0 0

500

1000

1500

2000

Time / s

397

22


2500

3000

Page 23 of 31

398

Fig.5 Total removal efficiency of coal-fired fine particles for case 1 100 o

-3

1: Tg,in=120 C, Hg,in=60 g ⋅Nm Total removal efficiency / %

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

80

-3

o

-3

3: Tg,in=60 C, Hg,in=120 g ⋅Nm 60

40

20

0

399

o


1

2

23


3

Energy & Fuels

400

Fig.6 Number size distribution of coal-fired fine particles in desulfurized flue gas for case 1 7

10

6

10

5

10

-3


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

Page 24 of 31

4

10

3

10

2

10

Inlet flue gas o

-3

Outlet flue gas (Tg,in=120 C, Hg,in=60 g ⋅Nm ) 1

10

o

-3

Outlet flue gas (Tg,in=60 C, Hg,in=60 g ⋅Nm ) o

0

10 0.01

401

-3

Outlet flue gas (Tg,in=60 C, Hg,in=120 g ⋅Nm )

0.1

Dp / µm

1

24


10

Page 25 of 31

402

Fig.7 Stage removal efficiency of coal-fired fine particles for case 1 100

o

-3

Tg,in=120 C, Hg,in=60 g ⋅Nm o

Stage removal efficiency / %

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

80

o

-3

Tg,in=60 C, Hg,in=120 g ⋅Nm 60

40

20

0 0.01

403

-3

Tg,in=60 C, Hg,in=60 g ⋅Nm

0.1

1

Dp / µm

25


10

Energy & Fuels

404

Fig.8 Number concentration of generated fine particles in desulfurized flue gas for case 2 6

3.0x10

1 2.5x10

1

2

6

2.0x10

6

1.5x10

3

6

1.0x10

o

-3


-3


5

5.0x10

o

-3

3: Tg,in=60 C, Hg,in=120 g ⋅Nm 0.0 0

405

1

6

-3


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

Page 26 of 31

500

1000

1500

2000

2500

Time / s

26


3000

Page 27 of 31

406

Fig.9 Total reduction rate of generated fine particles 60 o

50

Total reduction rate / %

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

-3


-3


40 30 20 10 0

407

1

2

27


Energy & Fuels

408

Fig.10 Number size distribution of generated fine particles 6

10

-3


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

Page 28 of 31

5

10

4

10

3

10

2

10

1

10

o

-3


-3


0

10 0.01

409

-3

Tg,in=60 C, Hg,in=120 g ⋅Nm 0.1

Dp / µm

1

28


10

Page 29 of 31

410

Fig.11 Stage reduction rate of generated fine particles for case 2 100 o

T g,in=60 C, H g,in=60 g ⋅Ν m

Stage reduction rate / %

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

80

T g,in=60 C, H g,in=120 g ⋅Ν m

−3

60

40

20

0 0.01

411

o

−3

0.1

1

Dp / µm

29


10

Energy & Fuels

412


413

temperature 6

5x10

-3


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

Page 30 of 31

6

4x10

6

3x10

6

2x10

Total fine particles Coal fired fine particles Generated fine particles

6

1x10

0 60

414

80

100

120

o

Inlet flue gas temperature / C

30


140

Page 31 of 31

415


416

humidity 6

5x10

-3


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

Total fine particles Coal fired fine particles Generated fine partices

6

4x10

6

3x10

6

2x10

6

1x10

0 60

417 418

90

120

150

-3

Inlet flue gas humidity / g⋅Nm

419

31


180

Abatement of Fine Particle Emission by Heterogeneous Vapor

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