Controls on Hydrogen Sulfide Formation and Techniques for its

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Controls on Hydrogen Sulfide Formation and Techniques for its Treatment in the Binchang Xiaozhuang Coal Mine , China Chao Zhang, Renhui Cheng, Shugang Li, Lei Qin, Chao Liu, Jie Chang, and Hua Liu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03614 • Publication Date (Web): 04 Dec 2018 Downloaded from http://pubs.acs.org on December 4, 2018

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Energy & Fuels

1

Controls on Hydrogen Sulfide Formation and Techniques for its

2

Treatment in the Binchang Xiaozhuang Coal Mine , China

3

Chao Zhang a,b, Renhui Chenga,b, Shugang Li a,b, Lei Qin a,b, Chao Liu a,b, Jie Chang a,b*, Hua Liu a,b

4

a. College of Energy Science and Engineering, Xi’ an 710054 China,

5

b. Key laboratory of Western Mine Exploitation and Hazard Prevention of the Ministry of Education,

6

Xi’ an 710054 China.

7

Abstract: To determine the main factors controlling hydrogen sulfide enrichment in coal mines,

8

the #4 coal seam in the Binchang Xiaozhuang coal mine, China, was investigated. A new

9

hydrogen sulfide control method was also tested on this seam. Using coal petrography, X-ray

10

diffraction, and other techniques, the reactions that generated the hydrogen sulfide in the

11

Xiaozhuang coal were investigated. The main controlling factors that affect the physical and

12

chemical properties of coal and its H2S are analyzed from the perspectives of thermal evolution

13

temperature, gas adsorption, pore characteristics, total sulfur content, and the coal’s reducibility

14

index. In addition, the degree of correlation for each factor was determined quantitatively using

15

gray system theory to construct a generalized gray relational degree evaluation model. Finally, a

16

high-pressure circulating pulsed alkali treatment technique was proposed to cope with the

17

dangerous levels of hydrogen sulfide found in coal mines. The treatment technique was applied in

18

the field. The results of the investigation on hydrogen sulfide formation show that the H2S in the

19

#4 coal seam was generated by biological sulfate reduction. When the concentration of hydrogen

20

sulfide increased from 0.8 ppm to 6 ppm, the ranges of the thermal evolution temperature, the

21

adsorption constant, the Brunauer–Emmett–Teller (BET) specific surface area, the total sulfur

22

content, and the reducibility index increased from 96°C to 113 °C, 28.8 to 36.2, 0.4125 m2·g–1 to

23

0.9864 m2·g–1, 0.21% to 0.88% and 3.1 to 8.5, respectively. The correlation coefficients of the

24

main controlling factors, in descending order, were: reducibility index> adsorption constant> total

25

sulfur content> thermal evolution temperature> BET specific surface area. The high-pressure

26

circulating pulsed alkali treatment method tested can effectively control the high concentrations of

*

Corresponding author: Tel: +8615513616924 (Jie Chang). Email address: [email protected]

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hydrogen sulfide and prevent hydrogen sulfide related mine shutdowns.

28

Keywords: coal-mine hydrogen sulfide; main controlling factors; generalized gray correlation

29

analysis; hypobaric circulation vapor treatment technology.

30

1. Introduction

31

The possibility of high concentrations of hydrogen sulfide occurring in the coal mines in

32

China is increasing as the resource of minable low sulfur coal decreases 1-4. Hydrogen sulfide is a

33

highly toxic and corrosive gas that cause air pollution

34

can not only corrode mining equipment but also cause eye irritation, breathing problems, damage

35

the nervous system, and increased risk of respiratory diseases.

36

amounts of hydrogen sulfide is a serious threat to mine personnel and to the coal mining industry

37

in general

38

reactions responsible for its formation and these studies can help to prevent hydrogen-sulfide

39

related disasters 7, 11, 20-23. Hydrogen sulfide abundance in mines is far lower than it is in the field.

40

Based on a study of geological condition, the abundance of sulfur-bearing minerals, e.g. pyrite and

41

sulfates, and the vitrinite reflectance, Meng et al proved that sulfate can be used to form hydrogen

42

sulfide 4, 24, 25. Much of the pyrite and organic sulfur was produced via biological sulfate reduction

43

(BSR) below 120 °C

44

demonstrated that the δ34S of mine produced by BSR was commonly negative, and even reached

45

−50‰. In contrast, the δ34S of mine produced by thermal sulfate reduction (TSR) was commonly

46

greater than +10‰, which is similar to the δ34S of sulfides in the field 27, 28. Liu et al. and Machel

47

H G et al. found that anaerobic environments with temperature of 60 °C to 80 °C had an effect on

48

the type of sulfate-reducing bacteria (SRB) present

49

ash index can indicate the trend of the reducing capacity for sedimentary environments hosting

50

coal seams containing hydrogen sulfide

51

coal, the salinity index, and the retention index to determine the hydrodynamic condition of the

52

coal’s formation, their studies further revealed the effects of the reducing sedimentary

53

environment on the formation of hydrogen sulfide 2. Fu et al. studied the excess sulfur in the

54

Zaozhuang Bayi coal mine, China, and reached the conclusion that magmatic heat led to abnormal

14, 16-19.

4-9.

The hydrogen sulfide from coal seams

10-15.

Exposure to even small

Hydrogen sulfide has been studied to analyze the physical and the chemical

26.

By measuring hydrogen sulfide and pyrite δ34S abundances, Liu et al

29, 30.

21, 27.

Yan et al. and Jiang et al. noted that the

After Deng et al. used the acid-base index of the


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enrichment of hydrogen sulfide 31.

56

Previous work on controlling hydrogen sulfide in mines mainly focused on spraying lye and

57

improving ventilation. Researchers in the Soviet Union used a series of adaptive and advanced

58

methods to prevent hydrogen sulfide-related disasters after studying hydrogen sulfide in the

59

Makaev coal mine 27, 28, 32. In 1958, Chinese researchers started to study and effectively control the

60

hydrogen sulfide in the Xishan coal mine in XinJiang and the Fourth mine operated by the Hebi

61

Mining Bureau

62

mine

63

ferrous iron, can be used to absorb water-soluble hydrogen sulfide in mines. Special experiments

64

investigating monocomponent dosages of Fe3+ and H2O2 in Fenton’s reagent, PH values, reaction

65

times, rotation speeds, and reaction temperatures were conducted to find optimal reagent

66

formulae. Studies on the absorption kinetics of Fenton’s reagent for hydrogen sulfide

67

neutralization have also been carried out

68

mesoporous silica, which has a good adsorption effect on hydrogen sulfide 35.

31, 32.

11, 18, 24.

Wang and Fu et al proposed a method to control hydrogen sulfide in a

Lin and Wei et al noted that Fenton’s reagent, a solution of hydrogen peroxide with

33, 34.

Zhang developed Mn2O3 adsorbent loaded with

69

The above investigators all conducted meaningful research on the formation and enrichment

70

of hydrogen sulfide. In this study, hydrogen sulfide formation in the Binchang Xiaozhuang coal

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mine in Shaanxi province, China, was studied using X-ray diffraction (XRD) and geological

72

analysis. Physical and chemical properties of the coal such as its petrography, thermal evolution

73

temperature, hydrogen sulfide adsorptive capacity, pore characteristics, reducibility, and total

74

sulfur content were studied. The dominant factors concerning abnormal H2S enrichment in the #4

75

coal seam in the Binchang Xiaozhuang mine were studied and the relations of the dominant

76

factors were quantitatively studied using the generalized gray correlation analysis method. In this

77

paper, a high-pressure circulating pulsed alkali treatment method for hydrogen sulfide is proposed.

78

Compared with the traditional alkali injection technology, this method can connect more pores in

79

the coal seam, has a larger range of action, and has a larger penetration range of lye. In addition,

80

the effect of coal mine site management was investigated. The results show that after using this

81

method, the hydrogen sulfide concentration of 40202 working face is always controlled below

82

6.6ppm. Therefore, the high-pressure pulsed alkali injection technology has better hydrogen

83

sulfide treatment effect.


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

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2. Hydrogen sulfide formation mechanisms

85

2.1 Formation mechanism

86 87

It is universally acknowledged that formation and preservation of hydrogen sulfide in a mine mainly results from the following reactions and processes.

88

1). Biological sulfate reduction (BSR). In an oxygen-free environment, sulfate in coal seam is

89

absorbed by SRB. These bacteria oxidize organic material and absorb energy to reduce sulfate and

90

produce hydrogen sulfide. The reaction of sulfur and Fe2+ produces pyrite and organic sulfur with

91

the help of the SRB 36. The reaction can be written as:

92

∑CH [or C]+CaSO4→H2S→FeS2+So

93

2). Thermal Sulfate Reduction (TSR). Through oxidation and chemical reactions between

94

sulfate and solid organic matter or hydrocarbons, sulfate will reduce to sulfur and carbon dioxide

95

31, 37.

These reactions can be expresses as:

96

2C+CaSO4+H2O→CaCO3+H2S↑+CO2

97

∑CH+CaSO4→CaCO3+H2S↑+H2O

98 99

3). Inorganic processes. Because of diastrophism and gas movement, it is hard to preserve and enrich hydrogen sulfide 37.

100

The appearance of relatively large amounts of organic sulfur and pyrite is the direct evidence

101

for BSR reaction by chemical mechanism of BSR. However, because of the complexity of the

102

processes that generate coal, hydrogen sulfide from TSR will be a part of subsequent BSR

103

reactions to produce organic sulfur and pyrite. In a coal seam, hydrogen sulfide is more reactive

104

than carbon dioxide or methane and this means it is more involved in chemical reactions. It is

105

therefore less enriched and less of it is preserved. Thus the possibility of hydrogen sulfide being

106

present in a seam is low. For significant H2S to be present, similarities must have existed between

107

hydrogen sulfide and the movement and preservation of another gas (particularly methane). In

108

coal seams, there are also differences in microscopic surface structures, adsorption, and total

109

sulfur content.

110

2.2 Geological conditions in the Binchang Xiaozhuang coal mine

111

The structures in the coal seam of interest are simple and there are no faults. There are


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Energy & Fuels

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aquifers in these coal measures but there are also many impervious mudstones with low porosity

113

and permeability. The average thickness of the seam is 15.23 m so it is an extraordinarily thick

114

seam. The mine and seam geology are very conducive for the enrichment and preservation of

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hydrogen sulfide.

116

The #4 seam contains many phytoliths and the coal reflects a marsh lithofacies. An aquifer

117

with a few gypsum beds directly overlies the coal and it is enriched in SO42−. Figure 1 shows

118

obvious picture can be found in fracture surface of coal, which is one of presentation of, an

119

indication that BSR has taken place. The depth of the #4 coal seam ranges from 350 m to 850 m;

120

this is rather shallow and would allow BSR. The average temperature gradient in this region is

121

4.56 °C/100 m so the seam temperatures range from 16 °C to 39°C, temperatures in which SRB

122

can easily survive. The hydrogen sulfide content of seam #4 is commonly below 0.1%, which

123

make is a low H2S coal seam. However, BSR will only proceed under anaerobic conditions.

124

Although only a little hydrogen sulfide is produced, the conditions for H2S accumulation and

125

preservation are excellent. Taken together, the above factors imply that BSR may be the reason for

126

the hydrogen sulfide in the #4 coal seam.

127 128 129

Fig 1. Fracture surface of coal

2.3 Mineralogy and redox conditions

130

The XRD patterns in Fig 2. show that the four groups of coal samples analyzed are similar.

131

The X-ray spectra show that pyrite (a moderate peak at 28.26°, a weak peak at 33.16°), gypsum

132

(weak peaks at 14.67° and 54.77°) and quartz (strong peaks at 21.11° and 26.70°, a weak peak at

133

46.11°) are present in all the samples. The gypsum in the mine provided SO42− for H2S formation

134

and the pyrite is an indication of BSR. The considerable Fe3+ present in the coal seam was


Energy & Fuels

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removed from the sediments as colloform Fe(OH)3 and with the help of HA, was incorporated in

136

the coal. The Fe3+ was reduced into Fe2+ and then reacted with sulfur to produce FeS·nH2O.

137

Eventually, FeS2·nH2O derived from reaction between FeS·nH2O and S was dehydrated to form

138

pyrite.

CQ

Q

Q-quartz P-pyrite C-gypsum

P

C P

Q C

C

Q

P

XR-1

I/(CPS)

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

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XR-2 XR-3 XR-4

0 139 140 141

10

20

30

40

50

2θ/(°)

60

70

80

90

Fig 2. Picture of X-ray diffraction

3. Analytical methods and results

142

Because space is limited, only the following parameters of the coal were investigated for this

143

paper: coal petrography, thermal evolution, adsorption, pore morphology, total sulfur content, and

144

reducibility index. Other important factors, such as preservation conditions, will be explored in

145

future work.

146

3.1 Coal petrography

147

Figure 3 show that the appearance of the coal depends on the hydrogen sulfide concentration.

148

Low porosity corresponds with lower hydrogen sulfide concentrations as shown in Fig 3(a). In

149

Figs 3(b) and (c), the complexity of the surface and the specific surface area increase with the

150

number of sampling points, which demonstrates the enrichment in hydrogen sulfide.


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Energy & Fuels

Coal A

151 152 153

Coal B

3000×

a)CH S=0.4ppm a) CH2S2 =0.4ppm

Coal C

3000×

b)CH S=2.5ppm b) CH2S2 =2.5ppm

3000×

c)CH2S=5ppm c) CH2S =5ppm

Fig 3. SEM images of the surfaces of coal sample at imaged at 3000 times enlargement

154

In Fig 4(f), has the most micropores and fissures and the largest specific surface area. In

155

addition, the relationship between H2S enrichment and external structure is demonstrated by the

156

observation that situation where external appearance is more compact and fewer microfissures at

157

point (d). Coal A

158 159

Coal B

10000×

S=0.4ppm a) d)CH CH2S2=0.4ppm

Coal C

10000× b)e)CH CH22SS=2.5ppm =2.5ppm

10000×

f)CH c) CH2S=5ppm 2S =5ppm

160

Fig 4. SEM images of coal surface of 10000 times enlargement using electron microscopy

161

The integral fractal dimension was calculated by using Fractal Fox 2.0 on SEM images of

162

specific surface areas.

163

As listed in Table 1 and shown in Fig 5, the higher the concentration of hydrogen sulfide is,

164

the higher the specific surface area integral fractal dimension. A higher integral fractal dimension

165

reflects more pores and a larger number of fissures in the coal. These would allow the coal to

166

adsorb more hydrogen sulfide.

167 168 169 170 171


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Table 1. Surface area integral fractal dimension Magnification times ×3000

×10000

Density of H2S/ppm

R-Squared

SE-1

0.4

0.962

2.58

SE-2

2.5

0.968

2.66

SE-3

5

0.962

2.74

SE-1

0.4

0.963

2.46

SE-2

2.5

0.967

2.6

SE-3

5

0.962

2.65

2.80

2.80

×3000上

2.75

2.70

2.70

Fractal dimension 分形维数

2.75

2.65 2.60 2.55 2.50 2.45 2.40

173 174 175

Fractal

NO.

Fractal dimension 分形维数

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

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dimension

×10000上

2.65 2.60 2.55 2.50 2.45

0

1

2 3 4 5 C(H2S)/ppm

6

2.40

0

1

2 3 4 5 C(H2S)/ppm

6

Fig 5. Surface area integral fractal dimension

3.2 Thermal evolution

176

The effect of the coal seam’s thermal evolution and its temperature on the formation of

177

hydrogen sulfide and their effect on determining the specific formation process is well known.

178

Vitrinite reflectance is the method most commonly used to determine maximum coal

179

temperatures.

180

The vitrinite reflectance (Ro) from eight groups of coal samples were measured for this work.

181

A linear regression equation proposed by Barker and Pawlewicz, which is apparently burial time

182

independent, was used to determine Tmax for the samples tested. The temperature, Tmax, can be

183

calculated from 32:

184 185

ln R0  0.0078Tmax  1.2

（1）

Where, T𝑚𝑎𝑥is the maximum thermal evolution temperature and R0is vitrinite reflectance.


Page 9 of 25

186

The Ro,max values determined from our samples were concentrated in the

187

0.728%~0.639%.range.

188

From Fig 6, it can be seen that the maximum vitrinite reflectance and hydrogen sulfide

189

concentrations correlate with thermal evolution temperatures. As shown in Fig. 6(a) and (b), the

190

Ro,max values increase from 0.639% to 0.728% and the H2S concentrations increase from 0.8 ppm

191

to 6 ppm as the temperature increases from 96 °C to 113 °C.

7 6 5

0.65

3 上 96上 0.639上 b

2

0.75

上 113上 0.728上 0.70

a

4

0.60 0.55

1 0

192

0.80 上Concentration 上上上上 of H2S 上 113上 6上上Rmax 上上上上上上上

上上上上Rmax 上上上上 /%

Concentration of /ppm H2S (ppm) 上上上上上

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

上 96上 0.8上 96

100 104 108 112 116 120 Thermal (℃）上 evolution 上上上上temperature /°C

0.50

193

Fig 6. Relationship between vitrinite reflectance and ancient geographical temperature

194

Higher temperatures cause higher vitrinite reflectances. From their names, it is obvious that

195

BSR and TSR are reduction reactions and these reactions produce hydrogen sulfide. The highest

196

evolution temperature that the coal in the #4 seam has undergone is below the 120 °C critical

197

temperature. This means the BSR and TSR reactions can generate high concentrations of

198

hydrogen sulfide.

199

3.3 Hydrogen sulfide adsorption

200

The coal’s adsorptive capacity greatly affects hydrogen sulfide enrichment in the same way it

201

affects methane adsorption. As mentioned previously, hydrogen sulfide is more reactive than

202

methane. Therefore, under ideal conditions, the effects of the adsorption parameters are more

203

pronounced in hydrogen sulfide than they are on methane. The correlations between hydrogen

204

sulfides’ adsorption parameters and temperature are shown in Fig 7.


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205 206

Fig 7. Relationship between adsorption characteristics and the concentration of hydrogen

207

sulfide

208

Figure 7(a), (b), and (c) illustrate the relationships between H2S concentration and its

209

adsorptive capacity (Q), adsorption constant (A), and porosity (P), respectively. When the

210

concentration of H2S increases from 0.8 ppm to 6 ppm, Q, A, and P increase from 20.3 m3/t to

211

24.7 m3/t, 28.8 to 36.2, and 2.33% to 2.67%, respectively. It can be seen that the adsorption

212

constant, porosity and maximum adsorption amount are proportional to hydrogen sulfide

213

concentration. The concentration of hydrogen sulfide increases with the increase of adsorption

214

constant, porosity and maximum adsorption.

215

3.4 Pore characteristics

216

Experiments on different pore diameters, specific surface areas, and integral fractal

217

dimension were conducted to study the effect of the pores on hydrogen sulfide enrichment. The

218

results are shown in Table 2.

219

Table 2. Relationship between pore characteristics and hydrogen sulfide concentration in coal Intrusion

Proportion of intrusion volume

Density

Fractal

of H2S

dimension

/ppm

/D

XZ-1

6

2.82

0.0241

0.9864

45.4

XZ-2

4

2.74

0.0202

0.8214

38.1

XZ-3

3.5

2.71

0.0194

0.7646

XZ-4

3

2.68

0.0191

XZ-5

2

2.64

0.0187

XZ-6

1

2.62

0.0184

No.

volume of

BET

BJH

/（m2·g-1）

Proportion of BET /%

/% ＜10nm

10~1

10~100

＞100nm

＜10nm

44.6

10

34.3

43.8

21.9

43.2

18.7

32.7

41.3

26.0

29.8

48.1

22.1

28.7

44.6

26.7

0.7135

33.2

47.6

19.2

31.1

39.3

29.6

0.6827

35

52.6

12.4

31.9

39.0

29.1

0.6289

35.9

51.1

13

28.8

42.9

28.3

/（cm3·g-1）

00nm


nm

＞100nm

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XZ-7

0.88

2.6

0.0174

0.4832

34.3

48.5

17.2

25.4

45.1

29.5

XZ-8

0.8

2.59

0.0168

0.4125

28.6

46.4

25

20.2

47.6

32.2

220

From Table 2, it can be seen that most of the pores in these samples of coal are small and

221

medium-sized pores; the total pore volume and specific surface area are large. The hydrogen

222

sulfide concentration increases with the Brunauer–Emmett–Teller (BET) specific surface area

223

(0.4125–0.9864 m2·g–1) and Barrett–Joyner–Halenda (BJH) pore volume (0.0168–0.0241 cm3·g–

224

1).

225

methane adsorption isotherms and the Frenkel–Halsey–Hill (FHH) equation. These values meet

226

the condition that value should be between two and three. Therefore, larger pores could lead to a

227

greater pore volume and larger specific surface area, which will allow higher hydrogen sulfide

228

abundances.

229

3.5 Reducing index

230 231

Calculations to determine the integral fractal dimension returned values from 2.59 to 2.82 using

In this section, the reducing index (K) is used to evaluate the geochemical reductive capacity, which can be used to study hydrogen sulfide reactions. The equation is:

232

K=I%×0.8+O%-AI-H%×2

233 234

（2）

where K is the reducing index; I% is what?; O% is oxygen content; AI is ash index. As shown in the Table 3, K value increases with reducing index, theoretically.

235

From Table 3, it can be seen that there is a positive correlation between H2S concentration

236

and ash index (0.286 to 0.347) and reducing index. The critical value for the reducing capacity to

237

reducing index ratio is 1. The higher the AI is, the stronger the reducing capacity. Calculations

238

using Eq. (2) show that the reducing capacity of the coal samples is low, and K for these samples

239

is between 3.1 and 8.5. The above factors and other physical properties, such as the depth of the

240

coal seam and the seam’s simply structure, contribute to this phenomenon resulting in the

241

hydrogen sulfide concentration being low.

242

Table 3. Relationship between hydrogen sulfide concentration and reducing index of coal Density No.

of H2S /ppm

Ash composition/% Fe2O3+CaO+MgO

SiO2+Al2O3

Oxygen

Hydrogen

content

content

（O）/%

（H）/%

Inertinite /%

Ash component index AI

Reducing index K

1

6

24.12

69.56

13.8

3.7

46.1

0.347

8.5

2

4

22.56

65.39

15.7

4.6

43.8

0.345

7.1

3

3.5

23.38

68.44

12.6

4.1

45.7

0.342

6.8


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4

3

21.78

67.85

12.5

5.2

45.6

0.321

6.4

5

2

22.31

71.24

12.8

5.2

43.2

0.313

5.7

6

1

21.24

69.14

11.2

4.4

41.5

0.307

4.7

7

0.88

22.76

76.63

11.8

6.2

42.2

0.297

3.4

8

0.8

21.35

74.65

10.3

7.2

44.7

0.286

3.1

243

In Fig 8, it is apparent that, visually, the higher the H2S concentration is, the higher AI and K

244

are. Higher AI and K values will result in a stronger reducing capacity and the possibility that

245

BSR will occur and produce more hydrogen sulfide.

0.34

A

0.32

8 A

A

b

7

A

0.31

6

A

0.30

246

5

A

0.29

0.27

248

A

a

0.33

4

0.28

247

9

index 上Ash 上上上上AIAI index 上Reducing 上上上上 K K

上上上 index 上上 KK Reducing

0.35

Ash index AI (%) 上上上上上 AI/%

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 12 of 25

A A

0

1

2 3 4 5 Concentration of 上 H2/ppm S (ppm) 上上上上

6

3

Fig 8. Relationship between hydrogen sulfide concentration and reduction of coal seam

3.6 Sulfur species

249

Total sulfur consists of the sulfate sulfur, pyrite sulfur, and the organic sulfur. Different areas

250

containing sulfur were sampled in order to determine the abundances of the different forms of

251

sulfur. A graph showing sulfur type versus concentration is shown in Fig 9.


Page 13 of 25

b) Sulfate sulfur Ss,ad

Total Sulphur content (%) 上上上上 /%

1.0

上上Sulphur 上上 /%content (%) Total 上 6,0.88上 y=0.103x+0.135

0.8 0.6 0.4 0.2

(0.8,0.21)

0.0 0

1

2 3 4 5 6 上上上上of 上 /ppm Concentration H S (ppm)

7

0.30

Sulfate sulfur content (%) 上上上上上上 /%

a) Total Sulphur St,ad

0.20 0.15 0.10

y=0.0015x+0.0198 0.05上 0.8,0.02上上 6上 0.03上 0.00 0

2

3

4

5

6

7

0.30 Pyrites 上上 Sulfur 上上上content 上 /%(%)

0.6 0.5

上 6,0.62上

0.25 0.20

y=0.076x+0.065

0.4

Organic sulfur content (%) 上上上上上 /%

0.7

Organic 上上上sulfur 上上content /% (%)上 6,0.23上

y=0.025x+0.054

0.15

0.3

0.10

0.2

0.05 上 0.8,0.08上

上 0.8,0.11上

0.0 0

252

1

上上上上 Concentration of上H/ppm 2S (ppm)

d) Organic sulfur So,ad

c) Pyrites Sulfur Sp,ad

0.1

Sulfate 上上上sulfur 上上 content 上 /% (%)

0.25

2

Pyrites Sulfur content (%) 上上上上上上 /%

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 2 3 4 5 6 7 上上上上上 Concentration of /ppm H2S (ppm)

0.00 0

1 2 3 4 5 6 上上上上of 上 /ppm Concentration H2S (ppm)

253

Fig 9. Relationship between total sulfur content and sulfur content and hydrogen sulfide

254

concentration

7

255

Correlations between total sulfur content and concentration of sulfur hydrogen are illustrated

256

in Fig 9. The change of total sulfur content from 0.21% to 0.88% corresponds to the change of

257

hydrogen sulfide from 0.8 ppm to 6 ppm. This is because the hydrogen sulfide is produced from

258

sulfate sulfur, organic sulfur and pyrite sulfur. Figure 9(b) shows the relationship between sulfate

259

sulfur and sulfur hydrogen. Sulfate sulfur ranges from 0.02% to 0.03% but there is no correlation

260

between the two. Figure 9(c) shows the relationships between pyrite sulfur and sulfur hydrogen,

261

whereas Fig 9(d) shows organic sulfur and sulfur hydrogen. Higher concentration of hydrogen

262

sulfide corresponds to higher contents of total sulfur, sulfate sulfur (0.11% to 0.62%), and pyrite

263

sulfur (0.08% to 0.23%). The reason for these correlations is that biochemical coalification and

264

some sulfur concentrating reactions result from SRB. Reactions between SO42− and

265

hydrocarbons or organic material produce more sulfur hydrogen. Then, pyrite is produced from

266

Fe2+ and sulfur hydrogen. In addition, sulfur hydrogen reacts with organic materials to produce


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

267 268

sulfur-bearing organic compounds.

4. Gray correlation analysis

269

Gray correlation analysis, based on the similarity of tendencies in systems, was used to

270

quantify the correlation between internal factors including generalized gray absolute correlative

271

degree, generalized gray relative correlative degree, and comprehensive gray correlative degree.

272

Experiments to quantify the correlative degree via generalized gray correlation analysis method

273

were conducted to affirm the importance of each factor.

274

4.1 Contrast and reference sequence quantification

275

Determination of contrast sequence (xi (k)) and reference sequences (x0(k)) is the first step. in

276

grey analysis. For this analysis, there are no

277

follows 26, 38:

contrast sequences composed of m factors as

278

xi (k )  {xi (1)，xi (2)......xi (m)}

279

x0 (k )  {x0 (1)，x0 (2)......x0 (m)}

280

In this work, the concentration of hydrogen sulfide was defined as the reference sequence and

281

the rest of the impact factors were defined as the contrast sequence. Eight groups of data were

282

obtained to study the mechanism; the data are listed in Table 4.

283

4.2 Modification of factor sequence

284

（i=1，2……n，k=1，2……m）

The reference and contrast sequences were modified as shown below: xi0 (k )  {xi0 (1)，xi0 (2)......xi0 (m)}

285

={xi (1)  xi (1), xi (2)  xi (1),......xi (m)  xi (1)}

x00 (k )  {x00 (1)，x00 (2)......x00 (m)} 286

={x0 (1)  x0 (1), x0 (2)  x0 (1),......x0 (m)  x0 (1)}

287 288 289 290 291 292


Page 14 of 25

Page 15 of 25 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

293

Table 4. Original data sequence of the influence factors Consensus

Compare sequence

sequence No.

294 295 296

297 298

Total

Thermal

sulphur

evolution

content/%

temperature/°C

0.98

0.88

113

8.5

35

0.82

0.46

110

7.1

3.5

34.6

0.78

0.41

109

6.8

4

3

32.3

0.71

0.37

107

6.36

5

2

30.7

0.68

0.33

106

5.7

6

1

29.8

0.63

0.32

97

4.86

7

0.88

29.1

0.55

0.28

97.5

3.4

8

0.8

28.8

0.41

0.21

96

3.1

Density of

Adsorption

H2S/ppm

constant

1

6

36.2

2

4

3

BET

/（m2·g-1）

The generalized grey absolute correlation coefficient determines the general correlation using the areas under the curves . The sequence matrix was modified to take the following form:  F0  0   2   2.5 Z   3   4  5   5.12  5.2 

F1 0 1.2 1.6 3.9 5.5 6.4 7.1 7.4

F2 0 0.16 0.2 0.27 0.3 0.35 0.43 0.57

F3 F4 F5  0 0 0  0.42 3 1.4   0.47 4 1.7  0.51 6 2.14   0.55 7 2.8  0.56 16 3.64   0.6 15.5 5.1  0.67 17 5.4 

The coefficient ε can be calculated from Eqs. (3)–(6):

1+ s 0  si 1+ s 0  si  si  s 0

 oi =

300

si   xi0 (k )dk 

302

index

4.3 Grey absolute correlation coefficient ε

299

301

Reduction

m

1

m

s0   x00 (k )dk  1

si  s0 

m 1

m 1

（3）

1

 x ( k )  2 x ( m) k 2

m 1

0 i

1

0 i

（4）

 x ( k )  2 x ( m) k 2

0 0

1

0 0

 ( x (k )  x (k ))  2 ( x (m)  x (m)) k 2

0 i

0 0


0 i

0 0

（5）

（6）

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

303

Page 16 of 25

4.4 Grey relative correlation coefficient γ

304

The grey relative correlation coefficient stands for the relationship between sequences and the

305

rate of change at the initial point. Non-dimensionalization of non-time sequences is the first step

306

necessary to compare the average method, the initial data method, and the interval method . The

307

initial data method was used in this study and returns:

308

xi' (k )  {

xi (1) xi (2) x ( m) , ,...... i } xi (1) xi (1) xi (1)

309

x0' (k )  {

x0 (1) x0 (2) x ( m) , ,...... 0 } x0 (1) x0 (1) x0 (1)

310 The second step is to modify the sequences to obtain:

311

312 313

314 315

 F '0   0  0.33   0.42 Z   0.5   0.67  0.83   0.85   0.87

F '1 0 0.03 0.04 0.11 0.15 0.18 0.2 0.2

F '5   0  1.65  2  0.25  0.33 0.43  0.6   0.58 0.76 0.15 0.64 

F '2 0 0.16 0.2 0.28 0.31 0.36 0.44

F '3 0 0.48 0.53 0.58 0.63 0.64 0.68

F '4 0 0.03 0.04 0.05 0.06 0.14 0.12

Those sequence matrixes and the corresponding correlation coefficient can be expressed as:

 0i =

1+ s '0  si' 1+ s '0  si  si'  s '0

4.5 Grey comprehensive correlation coefficient δ The grey comprehensive correlation coefficient has obvious advantages for presenting the

316

similarity of two sequences and the adience

317

point. This comprehensive correlation coefficient is defined as:

318

（7）

of sequences to the rate of change at the initial

    (1   )

（8）

319

where, ρ is the distribution coefficient in the grey absolute and relative correlation

320

coefficient, which depends on the rate of change of sequences and the similarities of both

321

sequences. In most instances, ρ is 0.5, which signifies randomness. The distribution coefficient

322

was determined by the maximizing deviation method.

323

The total deviations of the grey absolute and relative correlation coefficients are


Page 17 of 25 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

324

Energy & Fuels

m

D i    0i   0 k k 1

325

13,

m

,

D i    0i   0 k k 1

, respectively, These can be combined with Eq. (8) to give

20, 22

: 326

327 328



D i D i  D i

（9）

4.6 Gray correlation analysis results The above calculations are shown in Table 5.

329

Table 5. Calculation of correlative degree of main controlling factors Total

Thermal

sulphur

evolution

content /%

temperature /°C

29.42

29.42

29.42

29.42

36.8

2.57

4.12

77

24.88

︱Si -S0︱

7.38

26.86

25.31

47.58

4.44

ε

0.9

0.55

0.58

0.69

0.93

︱S’0︱

4.47

4.47

4.47

4.47

4.47

︱S’i︱

0.91

2.33

4.3

0.61

2.61

︱S’i- S’0︱

3.59

2.29

1.44

4.22

1.98

γ

0.64

0.77

0.87

0.59

0.8

ρ

0.61

0.67

0.55

0.49

0.68

δ

0.8

0.62

0.71

0.64

0.89

Ranking

2

5

3

4

1

Main controlling

Adsorption

BET /

factor

constant

（m2·g-1）

︱S0︱

29.42

︱Si︱

Reduction index

330

Note: ε: Absolute relationship; γ: Relative relationship; ρ: Partition coefficient; δ: Comprehensive

331

correlative degree.

332

With reference to Table 5, it is worth noting that the reducing index (0.89) is the dominant

333

factor for the grey comprehensive correlation coefficient and the weakest factor is the BET

334

specific surface area (0.62). Figure 10 shows the influence factors for hydrogen sulfide enrichment

335

in descending order . As the figure shows, the order is reducibility factor > adsorption constant >

336

total sulfur content > thermal evolution temperature > BET specific surface area. The grey

337

comprehensive correlation coefficient has both advantages

338

absolute correlation coefficient is suitable for the same dimension or close dimensions and the

in the sorting sequence. The grey


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

339

Page 18 of 25

grey relative correlation coefficient is also one-dimensional.

340

The reducing index (K) and the possibility of a whole system reaction present comprehensive

341

characteristics, which show the same inclination for both. The adsorption constant and adsorptive

342

capacity of the coal for sulfur hydrogen have a significant influence on H2S enrichment.

343

Fundamentally, the element (sulfur) in sulfur hydrogen comes from different sulfur species in

344

other sulfur compounds.

345

abundance of sulfur hydrogen. However, the coal’s thermal evolution is the power for BSR at low

346

temperatures and for TSR at high temperatures. Thermochemical sulfate reduction produces more

347

hydrogen sulfide than BSR. In most cases, TSR, or even TDS at higher temperatures, mainly

348

occurs in oil and gas reservoirs. Hence, there is much less hydrogen sulfide in coal mines than in

349

oil and gas fields. The BET specific surface area is important for preservation.The larger the BET

350

specific surface area, the greater the possibility of hydrogen sulfide adsorption.

Total sulfur content is a dominant factor controlling the original

Adsorption 上上上constant 上 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50

上上上index 上上 Reducing

351 352 353

上上上上evolution 上 Thermal temperature

上上上 Correlation

BET specific BET上上上上 surface area

上Total 上上Sulphur 上 content

Fig 10. Radar chart of factors correlation

5. New method for hydrogen sulfide control

354

Traditional technologies for H2S control, like spraying lime or lye, are in many cases

355

ineffective and may lead to accidents after their application. Adsorption efficiency can be

356

improved by injecting alkali . However, these hydrogen sulfide remediation efforts are expensive

357

and they may only move the hydrogen sulfide to another area in the mine . Here, a high-pressure,

358

pulsed alkali treatment technology is proposed to resolve those issues.


Page 19 of 25 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

359

Energy & Fuels

5.1 The high-pressure pulsed alkali method

360

This method employs two new techniques and one new substance. They are a high-pressure

361

pulsed alkali injection system, a pulsed alkali drilling and sealing technique, and a superior alkali

362

oxidizing agent. These three developments are described in more detail below.

363

(1) High-pressure pulsed alkali injection

364

Figure 11 shows this procedure works by increasing surface area. Pulse water injection

365

pump(Chongqing zhaowei mining machinery manufacturing co.,2BZ-125/20) turn water into

366

high-pressure water and it extends fractures. After the pores in the coal seam are connected, the

367

surface area of the crack is greatly increased compared to the conventional alkali injection

368

method. The lye can penetrate into the deeper coal seam more fully, the scope of action becomes

369

larger, and the treatment effect is obviously improved. Water tank

Pulse water injection pump

Guiding hole

Excess flow valve

Pressure gauge

Flowmeter Globe value check valve

Fracturing hole

Guiding hole

370 371

Fig 11. System of high pressure pulsed inject alkali

372

(2) Pulsed alkali drilling and sealing

373

Figure 12 shows this system is composed of a hole hop-pocket, capsule hole packer, PVC

374

pipe, manual pressure pump, injection pipe, and cement grout. The procedure is as follows: first,

375

the hole hop-pocket PVC pipe is put into a drill hole. Then, cement is injected to fill the gap

376

between pipe and drill hole wall to fix the pipe in place. Finally, the hole packer is set at a

377

predetermined position in the hole and the pressure pump is used to expand the packer. This

378

method has better sealing performance. In addition, it has the advantages of reusable, cost saving


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

Page 20 of 25

379

and efficiency improving. After use, large diameter PVC pipe can also be used as gas extraction

380

pipe.

3胶囊封孔器 3 Capsule hole Packer

Globe value Manual pressure pump

2水泥浆液 2 Cement grout

Injection pipe

1抽放管Pipe 1Drainage

Slurry retaining bag

hole packer

PVC pipe

Fracturing hole

Fracturing pipe Return pipe

381 382

Fig 12. System of pulsed injecting alkali drilling and sealing

383 384

(3) The superior alkali

385

A superior alkali oxidizer was developed by conducting experiments on oxidizing agents and

386

surfactants to be added to the alkali solution. These experiments quantified the proportions of the

387

additives in order to overcome the deficiencies of ordinary alkali oxidizers.

388

5.2 Field test overview

389

When the 40202 working face in the Binchang Xiaozhuang coal mine was being mined,

390

hydrogen sulfide emissions were high. After spraying lime to control the H2S, this gas problem

391

was only partially resolved. The new high-pressure pulsed alkali treatment system was tested by

392

using it on portions of the 40202 working face and comparing its effects to the 40201 working

393

face where no control methods were used.

394

5.3 Field tests results

395

Concentrations of hydrogen sulfide higher than prescribed safety limits were discovered in

396

the 40202 return airway. The maximum H2S concentration there was 15 ppm, higher than the 6.6

397

ppm allowed by Chinese Standards . The 40202 working face was divided into two sections to test

398

the new H2S control method. The first 600 m section was treated by spraying and injecting

399

ordinary alkali; the new control method was used on the rest of the working face. After treatment,

400

the hydrogen sulfide concentrations

401

statutory limit remained. The changes in hydrogen sulfide concentrations in the upper corner and

402

the return airway are shown in Fig 13.

were much lower. Only a few concentrations higher than the


Page 21 of 25

a) 0-300m

b) 300-600m

10 上Down-corner 上上上上上 angle 上Return 上上上air roadway上上上上

9

Upper corner Alert levels

7

CH2S/ppm

CH2S/ppm

8 6 5 4 3 2 1 0

0

30

60

90 120 150 180 210 240 270 300

16 15 Down-corner angle 上上上上上上 14 上Return 上上上air roadway上上上上 13 Upper corner 12 11 Alert levels 10 9 8 7 6 5 4 3 2 1 0 300 330 360 390 420 450 480 510 540 570 600

Face上advanced 上上上上 distance 上上 /m (m)

Face上advanced distance 上上上上上上 /m (m)

d) 900-1300m

c) 600-900m 10 8

10 Down-corner angle 上上上上上上上上上上air roadway上上上上 Return

7


9 8

Pyrites Sulfur content (%) CH2S/ppm

9

CH2S/ppm

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

6 5 4

angle 上Down-corner 上上上上上上Return 上上上 air roadway 上上上上

Organic sulfur content (%)

7 6 5 4

3

3

2

2

1

1

0 600 630 660 690 720 750 780 810 840 870 900

0 900

950 1000 1050 1100 1150 1200 1250 1300

上上上上上distance 上上 /m (m) Face advanced

403


上上上上上distance 上上 /m (m) Face advanced

404

Fig 13. Concentration contrast of 40202workstation versus distance

405

Figure 13(a) shows the change in H2S concentrations in the first 300 m of the working face. It

406

is worth noting that H2S concentrations in the down corner are universally low, but they are a little

407

higher in the return airway and the upper corner. This is because the coal seam has a low sulfur

408

content and produces little hydrogen sulfide.

409

Figure 13(b) shows the change in hydrogen sulfide concentrations in the 300–600 m section

410

of the 40202 working face. It is clears that the H2S concentrations in the down corner are slightly

411

increased but the overall is low .But the concentrations in the return airway and the upper corner

412

are above statutory limits (most are 15 ppm).

413

Figure 13(c) shows the H2S concentrations in the 600–900 m section of the working face, the

414

first section to be treated with the new alkali solution and the new application procedures. It is

415

easy to see that the hydrogen sulfide concentrations in the down corner is at a very low level.

416

while the concentration in the return air road and upper corner is slightly higher ,but still below the

417

safety limit.


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

418

Figure 13(d) shows the change in H2S concentrations in the final section of the 40202 face,

419

the section from 900 m to 1300 m. It can be seen that the concentrations in the down corner are

420

similar to the concentrations in the 600–900 m section and that they are far lower than the 15 ppm

421

hydrogen sulfide previously recorded in the return airway. These results show that this new H2S

422

control technology is very effective.

423

424

Fig 14. Comparison of concentration in upper corner of both workstations

425

The contrast between hydrogen sulfide concentrations at the 40201 and 40202 working faces

426

is shown in the Fig 14. The over-limit H2S readings at the 40201 face are common and some

427

worst-case measurements are as high as 15 ppm. In contrast, after the new alkali solution and

428

control methods were used at the 40202 face, over-limit hydrogen sulfide concentrations are rare.

429

6. Conclusions

430

1). Vitrinite reflectance measurements indicate a maximum thermal evolution temperature for

431

the coal samples studied of 96 °C to 113 °C. The degree of maturation increases with the

432

increasing temperature and this has a positive effect on BSR and TSR and causes these processes

433

to produce more hydrogen sulfide.

434

2). There is a positive correlation between the adsorption constant, the BET specific surface

435

area, and hydrogen sulfide concentrations. The changes in H2S concentration in coal from 0.8 ppm

436

to 6 ppm corresponds to the change in adsorption from 28.8 to 36.2, the growth in the BET

437

specific surface area from 0.4125 m2·g–1 to 0.9864 m2·g–1, and the increase in the integral fractal


Page 22 of 25

Page 23 of 25 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

438

dimension from 2.59 to 2.82. Greater adsorption corresponds to higher porosity and this results in

439

more adsorbed hydrogen sulfide.

440

3). The total sulfur content, the reducing index (K), and the ash index also have positive

441

correlations with the hydrogen sulfide concentrations. The total sulfur ranges between 0.21% and

442

0.88%, the reducing indexes are in the 3.1–8.5 range, and ash index ranges from 0.286 to 0.347.

443

The weak reducibility of coal seam #4 results in it having a relatively low hydrogen sulfide

444

content.

445

4). The correlative degree of dominant factors as determined by generalized gray correlation

446

analysis are, ranked in descending order, reducing index > adsorption constant > total hydrogen

447

sulfide > thermal evolution temperature > BET specific surface area.

448

5). When a new method for H2S suppression was tested in the Binchang Xiaozhuang

449

underground coal mine, the hydrogen sulfide concentrations in the area tested, particularly in the

450

upper corner of the working face, were effectively controlled.

451

Acknowledgement

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We thank David Frishman, PhD, from Liwen Bianji, Edanz Group China (www.liwenbianji.cn/ac),

453

for editing the English text of a draft of this manuscript.

454 455 456

This work was financially supported by the Special Fund for Basic Research on Scientific Instruments of National Natural Science Foundation of China (Grant No. 51327007) and National Natural Science Foundation of China (Grant No. 51504189，51674192).

457

References:

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Controls on Hydrogen Sulfide Formation and Techniques for its

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