Effect of Na2O in Ash Composition on Petroleum Coke Ash

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Effect of Na2O in Ash Composition on Petroleum Coke Ash Fusibility Jiazhou Li, Jiansheng Zhang, Jiantao Zhao, and Yitian Fang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b02317 • Publication Date (Web): 30 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019

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Energy & Fuels

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Effect of Na2O in Ash Composition on Petroleum Coke Ash Fusibility

2

Jiazhou Li,a, Jiansheng Zhang,*, a Jiantao Zhao,b Yitian Fangb

3

a

4 5 6

Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China

b

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001, China

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ABSTRACT: Petroleum coke (petcoke) ash fusibility is closely related to the ash-

8

related fouling and slagging, which have significant effects on the clean and efficient

9

utilization of petcoke. Sodium (Na) element in petcoke ash is considered as an

10

inducement for ash fouling and slagging. In this paper, we investigate the effect of Na2O

11

on the petcoke ash fusibility from the perspectives of atmosphere, Na2O content, and

12

temperature. The crystalline minerals and surface morphologies of high-temperature

13

ashes were determined by X-ray diffraction (XRD) and scanning electronic microscopy

14

(SEM), respectively. Thermodynamic software FactSage was applied to calculate the

15

ash melting process. The results show that ash fusion temperature (AFT) of petcoke ash

16

exhibits the continuous decline with the addition of Na2O at both oxidizing and

17

reducing atmospheres, which is ascribed to the mineral transformation behaviors of

18

high-temperature ashes. Under oxidizing atmosphere, the low-melting Na-bearing

19

albite (NaAlSi3O8) formed at high-temperature ash with the addition of Na2O decreases

20

the AFT, and the decomposition of high-melting anorthite (CaAl2Si2O8) and quartz

21

(SiO2) further leads to the decline of AFT. Under reducing atmosphere, another low-

22

melting Na-bearing nepheline (NaAlSiO4) is found in high-temperature ash. Moreover,

23

mullite and anorthite disappear with Na2O content increasing, which can both

24

contribute to the progressive decline of AFT. The high-temperature ash samples with 1

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high Na2O content have higher melting extent at oxidizing and reducing atmospheres.

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These ash particles present more smooth surface and denser layer structure.

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1. INTRODUCTION

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With industrialization process of the world, the demands for crude oil and oil-

29

related products increase continuously. Petcoke, as a primarily waste by-product

30

produced during crude bitumen or heavy oil refining, its production is steadily

31

expanding [1-3]. The advantages of high carbon content, high heat value, low ash

32

content, and abundant availability make petcoke a very attractive raw material.

33

Although petcoke has a remarkably low level of ash, it plays an important role in the

34

process of thermal conversion. The ash behaviors at high temperatures can cause many

35

key issues in boilers and gasifiers such as fouling, slagging, and deposition. Ash fouling

36

and deposition lower not only the efficiency of heat exchangers but also the lifetime of

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equipments [4,5]. Furthermore, ash fusion behaviors impact the continuous slag tapping

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process [6]. Therefore, it is imperative to deeply understand the ash fusion behaviors.

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Many experimental methods such as ash fusion temperature test, sintering strength test,

40

thermomechanical analysis (TMA), and high-temperature processing microscope

41

(HTPM) have been developed to investigate the ash fusibility [7-11]. Ash fusion

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temperature defined by the certain shape of an ash cone is most widely used to evaluate

43

the ash fusion behaviors. AFT gives an indication of ash softening and melting

44

behaviors. Moreover, it also provides an information of the progressive melting of ash

45

to slag [12].

46

The ash fusibility has been correlated with the ash chemical composition and

47

mineral transformations. van Dyk [13] found that the acidic components SiO2, Al2O3,

48

TiO2, as well as the SiO2-Al2O3 ratio all have a significantly increasing effect on the

49

coal ash flow temperature. Liu et al. [14] studied the influences of ash composition CaO, 2


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Fe2O3, K2O, and SiO2/Al2O3 (S/A) ratio on coal ash fusion temperature. It was found

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that AFT decreased with increasing Fe2O3 content and S/A ratio, but showed no

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significant change as K2O content varied. For the effect of CaO, AFT reached a

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minimum value and then followed an increase. Vassilev et al. [15] pointed out that the

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addition of SiO2, Al2O3, and TiO2 increased the AFT, whereas CaO, MgO, and Fe2O3

55

resulted in the decline of AFT. van Dyk [16] studied the variation of AFT via three-

56

component Al2O3-Na2O-SiO2 system. The liquid temperature dropped from above 1500

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oC

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indicated that AFT initially decrease to a minimum value and then began to increase

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with the addition of CaO, Fe2O3, and MgO. Besides, AFT increases with S/A ratio

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increasing. Chen et al. [18] found that Na2O had a positive effect on the decrease of

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AFT because of the formation of fusible Na-bearing aluminosilicates. These researches

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mentioned above are focused on the relationships between ash fusion temperature and

63

coal ash chemical composition.

to 1200 oC when the Na2O content increased from 0.5 to 10%. Song et al. [17]

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The ash chemistry of petcoke indicates that the ash composition resembles coal

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except for the presence of V and Ni whose concentrations, in some case, account for

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above 20 wt.% and 10 wt.% respectively [19]. These differences between petcoke ash

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and coal ash may lead to the different and unpredictable behaviors of mineral in ash at

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high temperatures [20]. The effects of ash composition V2O5, NiO, Fe2O3, CaO, and

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S/A and (SiO2+Al2O3) ratios have been investigated in many works [21-25]. However,

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the influence of Na2O in petcoke ash components has not drawn enough attention. Na

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is considered as one of the most concerned elements because it can cause ash-related

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corrosion and fouling problems of boilers firing petcoke. The condensation of Na2SO4

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decreases the melting temperature of solution by forming vanadates [26]. Thus, this

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work mainly investigates the effect of Na2O on petcoke ash fusibility under different 3


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atmospheres. In general, the AFT obtained at oxidizing (air) and reducing (CO/CO2

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volume ratio=6/4) atmospheres is considered to be valuable guides for the ash slagging

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of combustion and gasification, respectively [27].

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Many researchers have attempted to simplify the ash system by using synthetic

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ash rather than real ash because of the presence of complex phases and impurities in

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ash [14,28-31]. The property of synthetic ash at high temperatures might resemble that

81

of real ash [28]. Therefore, the synthetic ash composed of primary oxides SiO2, Al2O3,

82

V2O5, CaO, Fe2O3, NiO, and Na2O is selected as the experimental samples in this work.

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The four characteristic temperatures including initial deformational temperature (DT),

84

softening temperature (ST), hemispherical temperature (HT), and flow temperature (FT)

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are measured by automatic analyzing system. The mineral composition and

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microstructure of high-temperature ash samples are identified by XRD and SEM.

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Moreover, thermodynamic software package FactSage is applied to analyze the

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potential multiphase equilibria during the ash melting process.

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2. EXPERIMENTAL SECTION

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2.1. Synthetic Ash Samples.

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Five petcoke samples (Shanxi local oil refinery, Wuhan Petrochemical Co.,

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Zhenhai Petrochemical Co., Zibo Qilu Petrochemical Co., Ltd., and Daqing Oilfield)

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were ashed at 700 oC for 24 h [32]. The chemical composition of five petcoke ashes is

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listed in Table 1. Based on these ash compositions, synthetic ash samples were prepared

95

by V2O5, NiO, SiO2, Al2O3, Fe2O3, CaO, and Na2O. These seven constituents account

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for more than 95 wt.% of petcoke ash. The Na2O content ranges from 0 to 9.0 wt.%.

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Note that, Na2CO3 was selected in synthetic ash rather than Na2O because Na2CO3 was

98

more thermodynamically stable. Also, it should decompose into Na2O and CO2 at high 4


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temperature [33]. Seven analytical reagents were blended evenly by ball milling for 1

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h. The chemical composition of synthetic ash samples is shown in Table 2.

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2.2. AFT Test.

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The AFT of synthetic ash samples was measured by an AFT automatic analyzer

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from KY Company, China following the Chinese standard procedure GB/T219-2008

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[34]. The measurements were performed under an oxidizing (air) atmosphere and a

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reducing (CO/CO2 volume ratio=6/4) atmospheres, which were widely used as the

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guides for ash slagging of combustion and gasification, respectively [27]. The ash cones

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were heated initially to 900 °C at 15 °C/min and then decreased to 5 °C/min. The four

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characteristic temperatures were identified and recorded automatically in the heating

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process.

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2.3. Quenching Experiments.

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The quenched high-temperature ashes were prepared in a horizontal electronic

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furnace with the maximum temperature of 1600 oC. Figure 1 shows the schematic

113

diagram of furnace apparatus. About 1.0 g synthetic ash was filled in corundum crucible

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and then heated to the target temperature under oxidizing and reducing atmospheres.

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The thermal profile is set according to the AFT test. When the sample reached the

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scheduled temperature and then kept for 15 min, it was quickly taken out and quenched

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in ice-water.

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2.4. Characterization and Testing.

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The petcoke ash chemical composition was analyzed by X-ray fluorescence (XRF)

120

spectrometry (XRF-1800, Shimadzu, Japan) with a Rh target X-ray tube (50 kV, 40

121

mA). The X-ray power diffractometer (RIGAKU D/max-rB) with Cu Ka radiation (40

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kW, 100 mA, Ka1=0.15408 mm) was used to identify the mineral components of

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quenched ash. The ash sample was scanned over the 2θ range of 10°-80° with a step 5


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size of 0.01° at 4° 2θ/min scanning speed. In addition, the surface morphologies of

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minerals and the microanalysis of ash particle were observed by JSM-7001F scanning

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electron microscope.

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2.5. Thermodynamic Equilibrium Calculations

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Thermodynamic software FactSage 6.4 based on the Gibbs free energy

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minimization can be used to analyze multiphase equilibria, proportions of liquid and

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solid phases, and phase transitions under specified atmospheres and temperatures

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conditions. In this work, the multiple components system of SiO2-Al2O3-V2O5-CaO-

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Fe2O3-NiO-Na2O was established in Equilib to calculate the mineral transformations of

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ashes with different Na2O content at high temperatures. FToxid and FactPS database

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were selected for the possibly formed solution species. The calculations were

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performed under 0.1 MPa at oxidizing (air) and reducing (CO/CO2 volume ratio=6/4)

136

atmospheres, respectively. According to the theory of Gibbs free energy, all

137

homogeneous and heterogeneous reactions with negative Gibbs energy may occur.

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Moreover, the lower Gibbs free energy indicates that the reaction has the higher priority

139

[35].

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3. RESULTS AND DISCUSSION

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3.1. Effect of Na on Ash Fusibility.

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The experimental AFT of synthetic ash samples with different Na2O content under

143

oxidizing atmosphere is given in Figure 2a. It can be seen that AFT shows a staged

144

decline with the addition of Na2O. It decreases sharply as the Na2O content increases

145

up to 1.5 wt.%, which indicates that the formation of low-melting fluxing minerals

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occurs under oxidizing atmosphere. AFT drops slightly in the Na2O content range of

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1.5-7.0 wt.%, while it follows a rapid decrease with the Na2O content further increasing. 6


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Figure 2b shows the AFT of synthetic ash samples with different Na2O content

149

under reducing atmosphere. The ash without Na2O has a higher AFT compared to that

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at oxidizing atmosphere. The reasonable explanation may be as follows: the high-

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melting V2O3 (1940 oC) is the stable form of V at reducing atmosphere, which plays a

152

key role for the high AFT. However, V is present mainly as the low-melting V2O5 (690

153

oC)

154

almost unchanged. With the Na2O content further increasing, it follows a continuous

155

and impressive decline, of which DT decreases from 1430 oC (Na2O content is 1.0 wt.%)

156

to 1185 oC (Na2O content is 9.0 wt.%). Apparently, the low-melting minerals and

157

eutectics are formed under an appropriate Na2O content at high temperatures, which

158

leads to the decline of AFT.

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3.2. Effect of Na on Mineral Transformations at Oxidizing Atmosphere.

at oxidizing atmosphere. When the Na2O content is less than 1.0 wt.%, AFT keeps

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The interactions among minerals in high-temperature ash can influence the

161

mineral composition, and then change the variation trend of AFT. Therefore, the

162

mineral components of high-temperature ash were identified by XRD to investigate the

163

variation mechanism of AFT. Figure 3 shows the XRD patterns of synthetic ashes with

164

varying Na2O content at different temperatures under an oxidizing atmosphere.

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According to the variation trend of AFT (Figure 2a), the heating temperature of ash

166

with 0.5 wt.% Na2O is between 1000 and 1300 oC, and that of ash with 1.5, 3.0 and 9.0

167

wt.% Na2O is from 1000 to 1200 oC. When Na2O content is 0.5 wt.%, as shown in

168

Figure 3a, the major crystalline minerals are anorthite (CaAl2Si2O8), calcium

169

pyrovanadate (Ca2V2O7), quartz (SiO2), and spinel (NiAl2O4) at 1000 oC. These

170

minerals keep thermodynamically stable until the temperature reaches up to 1300 oC,

171

where the diffraction peaks of calcium pyrovanadate disappear due to its relatively low

172

melting point of 1288 oC. A small amount of Na may form amorphous minerals at high 7


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temperatures. Both anorthite and spinel have high melting point (>1500 oC), but the

174

molten V2O5 and calcium pyrovanadate may decrease the AFT effectively.

175

When Na2O content is 1.5 wt.% (Fig. 3b), the diffraction peaks of anorthite,

176

calcium pyrovanadate, quartz, and spinel are found in XRD patterns at 1000 oC. Also,

177

the formation of Na-bearing species albite (NaAlSi3O8) occurs in ash. However, albite

178

melts at 1200 oC because of its low melting point of 1118 oC, which may be responsible

179

for the decline of AFT, as shown in Figure 2a. Other four crystalline minerals anorthite,

180

calcium pyrovanadate, quartz, and spinel are stable in the temperature range of 1000

181

oC-1200 oC.

182

mineral phases of ash with 3.0 wt.% Na2O basically resemble those of ash with 1.5

183

wt.% Na2O. The existing difference between two ashes is that the diffraction peaks of

184

quartz are not found in ash with 3.0 wt.% Na2O. The formation of anorthite and albite

185

may contribute to the disappearance of quartz following the reactions:

As Na2O content increases to 3.0 wt.% (Fig. 3c), it can be seen that the

186

CaO+Al2 O3 +2SiO 2 =CaAl2Si 2 O8

(1)

187

Na 2 O+Al2 O3 +6SiO 2 =2NaAlSi3O8

(2)

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When Na2O content is 9.0 wt.% (Figure 3d), calcium pyrovanadate, spinel, and albite

189

are the main crystalline minerals between 1000 and 1100 oC. The diffraction peaks of

190

albite disappear at 1200 oC. Both quartz and anorthite are not generated within the

191

whole ash melting process, which may be ascribed to the following reaction [29]:

192

Na 2 O+CaAl2Si 2 O8 +4SiO 2 =2NaAlSi3O8  CaO

(3)

193

This reaction consumes a large amount of high-melting anorthite and quartz. In contrast,

194

the content of low-melting albite increases to some extent with increasing Na2O content.

195

All these can lead to the further decrease of AFT.

8


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In order to verify the crystalline minerals formed in high-temperature ash slag, the

197

phase assemblage of synthetic ashes with varying Na2O content at different

198

temperatures is calculated by thermodynamic equilibrium calculations FactSage, as

199

shown in Figure 4. When Na2O content is 0.5 wt.%, the minerals spinel, calcium

200

pyrovanadate, quartz, calcium metavanadate, anorthite, and albite are predicted to form

201

at low temperature (1200 oC),

202

calcium metavanadate, anorthite, and albite begin to disappear. The predicted minerals

203

in ash slag include spinel, calcium pyrovanadate, quartz, and vanadium dioxide.

204

However, according to the XRD patterns, the formations of calcium metavanadate and

205

vanadium dioxide do not occur between 1000 and 1300 oC. As Na2O content increases

206

from 0.5 to 9.0 wt.% in phase assemblage, the content of low-melting albite and calcium

207

pyrovanadate increases progressively, while that of high-melting quartz and spinel

208

declines accordingly, which may contribute to the decrease of AFT (Fig. 2a).

209

3.3. Effect of Na on Mineral Transformations at Reducing Atmosphere.

210

The XRD patterns of four synthetic ash samples (Na2O content is 0.5, 1.5, 3.0, and

211

7.0 wt.%, respectively) heated from 1200 to 1500 oC in a reducing atmosphere are

212

shown in Figure 5. When Na2O content is 0.5 wt.% (Fig. 5a), the high-melting minerals

213

mullite (1850 oC) and vanadium trioxide (1940 oC) are formed, and can keep

214

thermodynamically stable within the whole ash melting process. Also, the diffraction

215

peaks of anorthite and quartz appear at 1200 oC until the temperature reaches up to 1500

216

oC,

217

coulsonite (FeV2O4) is found between 1200 and 1300 oC. In comparison to the

218

crystalline minerals of ash with 0.5 wt.% Na2O obtained under an oxidizing atmosphere

219

(Fig. 3a), Ni is present in the form of elemental nickel (Ni) under a reducing atmosphere

220

rather than spinel (NiAl2O4) between 1200 and 1300 oC. As Na2O content increases to

where both minerals are converted into amorphous. Another V-bearing species

9


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1.5 wt.% (Fig. 5b), the diffraction peaks of high-melting mullite do not appear from

222

1200 to 1500 oC, which may be ascribed to the formation of albite (Eq. 2). Albite may

223

transform into amorphous since its melting point is 1118 oC. The formations of

224

anorthite, quartz, coulsonite, vanadium trioxide, and nickel occur between 1200 and

225

1300 oC. The diffraction peaks of coulsonite and nickel disappear at 1400 oC. With

226

temperature further increasing to 1500 oC, vanadium trioxide is the only crystalline

227

mineral. No Na-bearing crystalline species are formed from 1200 to 1500 oC.

228

When Na2O content is 3.0 wt.% (Fig. 5c), another Na-bearing species nepheline

229

(NaAlSiO4) is formed at 1200 oC in comparison to the crystalline minerals of ash with

230

1.5 wt.% Na2O content (Fig. 5b). The formation of nepheline may follow the reactions

231

[27]:

232 233

Na 2 O+Al2 O3 +2SiO 2 =2NaAlSiO 4 NaAlSi3O8 +CaAl2Si 2 O8 +Na 2 O=3NaAlSiO 4  CaO+2SiO 2

(4) (5)

234

Nepheline disappears at 1300 oC due to its low melting point of 1254 °C. Also, it is

235

found that the diffraction peaks of quartz do not appear in XRD patterns. Apparently,

236

the formation of low-melting nepheline and the disappearance of high-melting quartz

237

can lead to the decrease of AFT. With Na2O content increasing to 7.0 wt.% (Figure 5d),

238

another high-melting mineral anorthite does not form in high temperature ash slag,

239

which may effectively verify the Eq. 5. The content of nepheline increases with the

240

addition of Na2O, all of which further decrease the AFT, as shown in Figure 2b.

241

Figure 6 shows the phase assemblage of synthetic ashes with different Na2O

242

content at reducing atmosphere. When Na2O content is 0.5 wt.%, albite, wollastonite,

243

coulsonite, anorthite, nickel, and vanadium trioxide are the dominant minerals at high

244

temperatures, which are basically consistent with the crystalline minerals in XRD 10


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patterns. As Na2O content increases to 1.5 wt.%, albite is converted into nepheline.

246

With Na2O content further increasing, the content of low-melting nepheline increases

247

gradually, while that of high-melting anorthite, coulsonite, and vanadium trioxide

248

declines progressively. Anorthite disappears when Na2O content is 7.0 wt.%. All the

249

minerals transformations mentioned above can validate the variation trend of AFT (Fig.

250

2b).

251

3.4. Effect of Na on Surface Morphologies of High Temperature Ash Samples.

252

In addition to mineral transformations, the variations in surface morphologies of

253

high-temperature ash also reflect the ash fusibility [36,37]. The quenched ash is

254

considered to keep the morphology of high-temperature ash well and prevent the crystal

255

segregation [27]. Figure 7 shows the SEM photomicrographs of synthetic ashes with

256

different Na2O content, which were quenched in ice water from 1200 oC at oxidizing

257

atmosphere (Fig. 7a) and 1400 oC at reducing atmosphere (Fig. 7b), respectively. All

258

the high-temperature ashes are magnified 3700 times. It is well known that the high

259

melted ash particles have the smooth surface and dense layer structure [14]. When the

260

addition of Na2O is 0.5 wt.%, the high-temperature ash samples consist of irregular and

261

fine particles at both oxidizing and reducing atmospheres. These particles have rough

262

surface and loose structure. With the addition proportion increasing to 3.0 wt.%, it is

263

found that some fine particles have been agglomerating into large particles. When Na2O

264

content reaches to 9.0 wt.% (Fig. 7a) and 7.0 wt.% (Fig. 7b), respectively, the ash

265

particles have been further agglomerated and have molten surface. Moreover, some

266

protuberances are formed on the molten surface. The ashes have more smooth surface

267

and denser layer structure. Therefore, it is concluded that the ash with high Na2O

268

content has the high melted extent at both oxidizing and reducing atmospheres, which

269

is consistent with the variations of AFT (Fig. 2). 11


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4. CONCLUSIONS

271

The effect of Na2O on petcoke ash fusion characteristics was investigated in this

272

work from different perspectives including atmosphere change, Na2O content variation,

273

and temperature rising. The main conclusions could be summarized as follows.

274

(1) The AFT of petcoke ash samples is closely related to the addition of Na2O

275

content. AFT shows continuous decline with increasing Na2O content at both oxidizing

276

and reducing atmospheres.

277

(2) The mineral transformations during ash fusion process contribute to the

278

variations of AFT. With Na2O content increasing, the formations of low-melting albite

279

at oxidizing atmosphere and nepheline at reducing atmosphere decrease the AFT

280

markedly. Moreover, the decomposition of high-melting anorthite and quartz further

281

leads to the decline of AFT.

282

(3) Under oxidizing and reducing atmospheres, the high-temperature ash samples

283

with high Na2O content have higher melting extent. These ash particles present more

284

smooth surface and denser layer structure.

285

AUTHOR INFORMATION

286

Corresponding Author

287

E-mail address: [email protected]

288

ACKNOWLEDGEMENTS

289

The authors gratefully acknowledge the financial support of the National Key

290

Research and Development Project (No. 2017YFB0602602).

291

REFERENCES

292

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Energy & Fuels

Table 1. Ash Composition of Five Real Petcoke (wt.%) Petcoke

V2O5

NiO

SiO2

Al2O3

Fe2O3 CaO

MgO

TiO2

SO3

K2O

Na2O

P2O5

Shanxi

33.89 7.55

13.92 1.18

0.83

0.75

0.76

1.74

0.54

Shengli

33.89 10.92 16.11 8.84

5.92

15.92 3.03

0.85

0.75

0.76

3.20

0.55

Zhenhai

29.82 12.37 25.44 7.60

10.12 8.79

1.21

0.35

1.35

0.96

0.98

0.32

Daqing

32.35 9.75

17.74 7.04

5.35

21.35 0.74

0.64

0.97

1.35

1.05

0.61

Yangzi

27.32 11.87 21.32 9.72

9.43

8.84

0.46

0.98

0.83

5.75

0.46

20.20 10.54 7.40

1.53

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Page 18 of 26

Table 2 Chemical Composition of Synthetic Ash Samples composition (wt.%) sample

SiO2

Al2O3

V2O5

CaO

Fe2O3

NiO

Na2O

1

22.60

11.30

34.00

13.10

8.00

11.00

0.00

2

22.54

11.27

33.80

13.02

7.95

10.92

0.50

3

22.48

11.24

33.60

12.94

7.90

10.84

1.00

4

22.40

11.20

33.45

12.85

7.84

10.76

1.50

5

22.30

11.15

33.30

12.78

7.78

10.69

2.00

6

22.00

11.00

33.00

12.69

7.71

10.60

3.00

7

21.50

10.75

32.20

12.49

7.61

10.45

5.00

8

21.00

10.50

31.40

12.31

7.51

10.28

7.00

9

20.40

10.20

30.70

12.15

7.43

10.12

9.00

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Energy & Fuels

Figure 1. The schematic representation of the furnace apparatus.

19


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386

Figure 2. Effect of Na2O content on AFTs at different atmospheres (a) air; (b) CO/CO2 volume ratio=6/4.

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Energy & Fuels

Figure 3. XRD patterns of synthetic ashes with different Na2O content at oxidizing atmosphere (a) 0.5 wt.% Na2O; (b) 1.5 wt.% Na2O; (c) 3.0 wt.% Na2O; (d) 9.0 wt.% Na2O

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387

388

Figure 4. FactSage calculation of synthetic ashes with different Na2O content at oxidizing atmosphere (a) 0.5 wt.% Na2O; (b) 1.5 wt.% Na2O; (c) 3.0 wt.% Na2O; (d) 9.0 wt.% Na2O

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Energy & Fuels

389

390

Figure 5. XRD patterns of synthetic ashes with different Na2O content at reducing atmosphere (a) 0.5 wt.% Na2O; (b) 1.5 wt.% Na2O; (c) 3.0 wt.% Na2O; (d) 7.0 wt.% Na2O

23


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391

Figure 6. FactSage calculation of synthetic ashes with different Na2O content at reducing atmosphere (a) 0.5 wt.% Na2O; (b) 1.5 wt.% Na2O; (c) 3.0 wt.% Na2O; (d) 7.0 wt.% Na2O

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Energy & Fuels

0.5 wt.% Na2O

0.5 wt.% Na2O

3.0 wt.% Na2O

3.0 wt.% Na2O

9.0 wt.% Na2O

7.0 wt.% Na2O

(a)

(b)

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Figure 7. SEM photomicrographs of synthetic ashes with different Na2O content (a) 1200 oC at oxidizing atmosphere; (b) 1400 °C at reducing atmosphere

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Effect of Na2O in Ash Composition on Petroleum Coke Ash

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