Exploring coal spontaneous combustion by bibliometric analysis

Exploring coal spontaneous combustion by bibliometric analysis

Process Safety and Environmental Protection 132 (2019) 1–10 Contents lists available at ScienceDirect Process Safety and Environmental Protection jo...

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Process Safety and Environmental Protection 132 (2019) 1–10

Contents lists available at ScienceDirect

Process Safety and Environmental Protection journal homepage: www.elsevier.com/locate/psep

Exploring coal spontaneous combustion by bibliometric analysis Fuqiang Yang ∗ , Dongyang Qiu College of Environment and Resources, Fuzhou University, Fuzhou 350116, China

a r t i c l e

i n f o

Article history: Received 26 May 2019 Received in revised form 31 July 2019 Accepted 16 September 2019 Available online 18 September 2019 Keywords: Coal spontaneous combustion Bibliometric analysis CiteSpace

a b s t r a c t Coal spontaneous combustion (CSC) is a serious problem and remains a global safety concern in coal industry. In this paper, bibliometric analysis of the worldwide scientific publications on CSC was conducted to understand the characteristics and research trends in the Science Citation Index Expanded (SCI-Expanded) database. CiteSpace was adopted to evaluate the relationship among different countries/territories, authors, and keywords. In total, 829 documents on CSC were indexed, covering 1752 authors, 197 journals, 53 countries, and 591 institutes between 1984 and 2018. The studies related to CSC have been growing from 3 in 1984 to 126 in 2018. China, Australia, and the USA lead scientific production on CSC research, while more international collaboration should be strengthened in future. Wang DM, Qin BT, and Deng J are the most active researchers in this field. Fuel, International Journal of Coal Geology, and Energy and Fuels are the major sources of CSC publications. In addition, China holds three academic entities among the national-wide top 10 active institutions, with China University of Mining and Technology as the most productive research institutes. According to the frequency of keywords, low temperature oxidation, kinetics, mechanism, model are the dominant topics in CSC research. Similarly, there are new research hotspots appearing in recent years, related to 3 phase foam, fire extinguishment, and foam preparation. © 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.

1. Introduction As an important fossil fuel, coal has been widely utilized in various industries over a long period of time, covering power generation, steel industry, chemical production, etc. (Zhou et al., 2019). In view of the global industrial growth, coal is regarded as the principal energy source over the world and will continue to maintain in high demand in a lot of countries (Liu et al., 2019; Ren et al., 2019; Wang et al., 2019). In China, it is reported that coal has accounted for almost two-thirds of national energy sources in the past 40 years (Chai et al., 2019). The corresponding coal consumption of China will achieve 4.43 billion tons/year in 2020, with an increasing rate of 7.8% per year (Deng et al., 2018). Coal is a flammable black soft rock, composed of organic matter and a quantity of inorganic matter (Bhowmick et al., 2017). When exposed to the air, coal can react with oxygen and causes an exothermic reaction (Nimaje and Tripathy, 2016). In a specific environment, coal temperature will rise up to the ignition point and the spontaneous combustion takes place due to continuous accu-

∗ Corresponding author at: 2 Xueyuan Road, University Town, Fuzhou, Fujian Province, China. E-mail address: [email protected] (F. Yang).

mulation of heat from oxidation (Nimaje and Tripathy, 2016; Cui et al., 2018a, 2018b). In general, CSC is a complex dynamic process which is mainly determined by chemical reactions between oxygen molecule and functional groups on the coal surface (Shi et al., 2018a, 2018b; Zhang et al., 2019). The whole process involves low-temperature oxidation, self-heating and combustion (Cui et al., 2018a, 2018b). Meanwhile, CSC is influenced by internal and external factors, including chemical compositions, particle size, and pore structure, as well as environmental temperature, oxygen concentration and moisture (Li et al., 2018; Shi et al., 2018a, 2018b). It is well known that CSC is one of the principal disasters during coal mining, storage, transportation, and utilization (Wu et al., 2018; Tang, 2018). This long-standing phenomenon can result in a series of serious problems associated with safety concerns, environmental pollution, and economic loss (Wang et al., 2003a, 2003b; Carras et al., 2009; Ma et al., 2017; Qin et al., 2018; Liang et al., 2019). Accordingly, it is of great significance to conduct investigations to prevent and control CSC hazard, referring to reaction mechanism(Wang et al., 2003a, 2003b; Zarrouk and O’Sullivan, 2006; Li et al., 2018; Zhang et al., 2019), Physical technologies such as grouting and liquid foam (Shi et al., 2018a, 2018b; Shi and Qin, 2019), chemical inhibitors (Ma et al., 2017; Cui et al., 2018a, 2018b; Deng et al., 2018; Tang, 2018; Wu et al., 2018; Xi et al., 2019), numerical simulation (Yuan and Smit, 2009; Huang et al., 2018;

https://doi.org/10.1016/j.psep.2019.09.017 0957-5820/© 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.

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Wu et al., 2019), forecasting technology (Song and Kuenzer, 2014; Peng et al., 2017; Liang et al., 2019), thermal analysis (Qi et al., 2017; Mohalik et al., 2018; Yang et al., 2019a), and liability assessment (Avila et al., 2014; Arisoy and Beamish, 2015; Nimaje and Tripathy, 2016), etc. Although a large number of publications on diverse aspects of CSC have been achieved, no bibliometric analysis is adopted to carry out the research associated with CSC, resulting in a lack of comprehensive understanding in this field. As a quantitative statistical analysis technique, the bibliometric method is widely applied to provide an overview of extensive publications and grasp the present status quo in a specific research domain (Chen et al., 2016; Li et al., 2017a, 2017b, 2017c; Boudry et al., 2018; van Nunen et al., 2018; Mao et al., 2018; Peng et al., 2018; Yang et al., 2019b). The corresponding conclusions are of great importance for researchers to determine the hotspots of study subjects, explore proper future research fields, and pursue collaborations with other countries or institutes (Boudry et al., 2018; Geng et al., 2017). Many software tools (Pan et al., 2018) can be utilized to investigate CSC from the viewpoint of bibliometric analysis, including CiteSpace, VOSViewer, Bibexcel, HistCite, CitNetExplorer, and Network Workbench Tool, etc. As a powerful and efficient scientometric tool, Citespace is developed by Chen at Drexel University (USA) in 2004 (Chen, 2004, 2006), which is a freely accessible Java application for depicting large bibliometric maps in scientific literature conveniently. Some detailed information about CiteSpace can be obtained by the official website (http://cluster.cis.drexel.edu/∼cchen/citespace/). Also, it has updated some editions, compring Citespace II and Citespace III (Chen et al., 2016). Accordingly, Citespace has been applied by scholars in various fields, such as energy security (Zhou et al., 2018), hospitality research (Li et al., 2017a, 2017b, 2017c), emergy research (Chen et al., 2016), nonpoint source pollution research (Xiang et al., 2017), carbon emissions trading (Yu and Xu, 2017). Although CiteSpace is quite popular in knowledge mapping, no attempt has been made to utilize it analyzing CSC literature. Due to the increasing number of publications on CSC researches, it is necessary to summarize the current status and the evolution trend in CSC. In this paper, all the documents associated with CSC are retrieved from Web of Science (SCI-Expanded) database via CiteSpace. In terms of annual outputs, authorship, countries, mainstream journals, leading institutions, keywords, and citation performance, the related tables and figures are given for future researchers to understand the overall status of CSC studies and indicate some ideas about the research directions (Zhang et al., 2017; Peng et al., 2018). Meanwhile, the gap between bibliometric analysis and CSC research is filled in this study.

2. Methodology Bibliometrics is a statistical method applied to evaluate and quantify the number and increase trend of a specific subject (Mao et al., 2018; Soosaraei et al., 2018). As one of the most frequently utilized software tools in library and information science, CiteSpace is adopted to visualize the authorship, geographical distribution, and keywords in scientific literature related to CSC (Pan et al., 2018; Ouyang et al., 2018), and provide a comprehensive picture on the development trends of knowledge, theories and research topics in this area. The research was carried out on 9 April, 2019. English publications referring to coal spontaneous combustion, coal self-heating, coal spontaneous heating, coal low-temperature oxidation in the titles, abstracts, and keywords from 1984 to 2018 were extracted from the Science Citation Index Expanded (SCI-Expanded) database via

Table 1 Document type of literature reports during.1984–2018. No.

Document types

Number of total articles

Proportion

1 2 3 4 5 6 7

Article Proceedings paper Review Meeting abstract Editorial material Letter Correction

757 45 15 6 3 2 1

91.31% 5.43% 1.81% 0.72% 0.36% 0.24% 0.12%

Fig. 1. Number of CSC publications and cumulative number of CSC by year.

the Web of Science (WoS). Additionally, manual techniques were utilized to exclude the results not related to CSC researches. 3. Results and discussion 3.1. Publication output and growth With the terms of “coal spontaneous combustion” OR “coal spontaneous heating”, OR “coal self-heating”, OR “coal lowtemperature oxidation”, 829 publications associated with CSC were obtained in SCI-Expanded database. As shown in Table 1, there are seven document types in the publications. Journal articles (757) were the most frequently applied document type taking up 91.31% of the total publications. They were followed by proceeding papers (45; 5.43%), reviews (15; 1.81%), with the remainder of less than 1% including meeting abstracts (6), editorial materials (3), letters (2), and corrections (1). As displayed in Fig. 1, the number of yearly CSC publications fluctuated from 1984 to 2008, while a remarkable rising phenomenon appeared since 2009. Meanwhile, it can be found that the cumulative publication output of CSC follows an exponential growth. This situation may be attributed to the great rise of coal consumption due to the rapid industrial development, and a large number of researchers contributed to coal fires. There were only 3 publications related to CSC in 1984. In 2018 alone, 126 documents linked to CSC were published. 3.2. Geographical distribution of CSC researches Based on the addresses and affiliations of authors, the CSC contribution of different countries/territories and institutions was analyzed. There was a large geographic range of academic articles on CSC, covering 53 countries. Accordingly, the top ten countries were responsible for more than 91% of the total publications. Table 2 lists the top ten most productive countries ranked by the num-

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Table 2 The top 10 productive countries/territories of CSC during.1984–2008. Country

TP(%)

SP R(%)

CP R(%)

FP R(%)

RP R(%)

H-index(R)

China Australia USA India Poland Turkey Japan South Africa Spain Canada

348 (41.98) 96 (11.58) 92 (11.10) 45 (5.43) 39 (4.70) 38 (4.58) 30 (3.62) 27 (3.26) 22 (2.65) 21 (2.53)

1(30.64) 3(4.95) 2(6.63) 5(4.22) 4(4.46) 6(3.50) 7(2.65) 8(2.53) 10(1.08) 9(2.17)

1(11.34) 2(6.63) 3(4.46) 5(1.21) 10(0.24) 6(1.08) 7(0.96) 8(0.72) 4(1.57) 9(0.36)

1(40.89) 3(6.03) 2(7.12) 4(5.19) 5(4.70) 6(4.46) 7(3.02) 8(2.90) 9(2.29) 10(2.17)

1(39.81) 3(7.60) 2(7.72) 4(5.07) 5(4.70) 6(4.46) 8(2.89) 7(3.34) 9(2.29) 9(2.29)

27(2) 27(2) 29(1) 14(4) 10(8) 13(5) 15(3) 12(6) 13(5) 11(7)

TP: Total publications; SPR: Single country publication rank; CPR: International collaborative publication rank; FPR: First author publication rank; RPR: Corresponding author publication rank.

ber of total publications with other information: single country, international collaborative, the first author, as well as corresponding author. Obviously, China (348, 41.98%) is the most productive country with the largest number of publications during this period, followed by Australia (96, 11.58%), the USA (92, 11.10%), India (45, 5.43%), Poland (39, 4.70%), Turkey (38, 4.58%), Japan (30, 3.62%), South Africa (27, 3.26%), Spain (22, 2.65%), and Canada (21, 2.53%). Similarly, China ranked first with regards to single country and international collaborative publication, as well as first author and corresponding author publication. In respect to the influence, the USA ranked first with a H-index up to 29, while China and Australia ranked second with a H-index 27. The annual CSC publications from the top three countries are given in Fig. 2. It can be found the number of documents published by China have been rising up greatly, from 6 papers in 2011 to 95 papers in 2018. In contrast, the annual publications on CSC of Australia and the USA fluctuate between 1 and 11, without a stable increase trend. Evidently, Australia and the USA are far behind China in the annual number of publications on CSC since 2011. Meanwhile, Fig. 2 presents annual coal productions in the three top countries. In China, the coal production each year shows an increasing trend from 2008 to 2013. Subsequently, a slight reduction appears until 2016, and then the coal production has been going up due to the large energy consumption. Correspondingly, the overall trend of annual coal production in Australia has been rising up slowly in recent ten years, while the production in the USA has been decreasing slightly since 2008. Furthermore, the annual coal production in China far exceeds those of Australia and the USA. In China, coal plays a primary role in the energy structure (Cui et al., 2018a, 2018b; Zhu et al., 2019), accounting for more than 60% of national energy consumption during the 13th Five-Year Plan Period (Liu et al., 2019). Also, CSC is a serious problem in China’s mines, and almost all coal seams are liable to spontaneous combustion (Zhang et al., 2011; Huang et al., 2018), resulting in about 400 annual fires in China (Wu et al., 2018). Therefore, extensive literature on CSC have been published in China. According to statistics (BP, 2019), the coal reserves of China, Australia, and the USA are 138,819, 147,435, and 250,219 billion tons in 2018, respectively. It can be inferred that a large number of papers on CSC will be published by the three countries in the future, especially China. The cooperation relation among the countries/territories in the field of CSC were also investigated by using social network analysis (see Fig. 3). The size of the circles represents the amount of related publications, and the thickness of links denotes the degree of international collaborations (Li et al., 2017a, 2017b, 2017c). In other words, the larger the circle is, the more important the country is. Similarly, the thicker line indicates closer cooperation between countries/territories. Obviously, China, Australia, and the USA play the key roles in CSC research. Meanwhile, the USA has plenty of

cooperation with Japan, Canada, and Australia. The collaboration between South Africa and England is also close. Whereas, China has little exchanges and cooperation with other countries in CSC studies. In general, more international collaboration in CSC field should be strengthened in future. The contribution of different institutions (591) was analyzed according to the institute of the authors’ affiliation. The top ten institutions that contribute to the majority of documents on CSC are given in Table 3. It can be seen that China University of Mining and Technology (196, 23.64%) is the leading institution related to CSC over the world, followed by Xi‘an University of Science and Technology (China) with 33 publications. Other three institutions, i.e. Taiyuan University of Technology (China), Council of Scientific Industrial Research CSIR (India), and Indian Institute of Technology (India), have published 30(3.62%), 24(2.90%), and 21(2.53%) documents associated with CSC, respectively. In addition, China University of Mining and Technology also published the most documents in respect to single country, international collaborative, the first author, as well as corresponding author. 3.3. Journals analysis There were 197 journals publishing CSC research from 1984 to 2018. Table 4 presents information of the top 10 most productive journals which have published almost half of all CSC publications (49.7%; n = 412/829). The key journals in this field refer to Fuel (144, 34.9%), International Journal of Coal Geology (60, 14.56%), Energy & Fuel (47, 11.41%), and Fuel Processing Technology (38, 9.22%), with 144, 60, 47, and 38 articles on this topic, respectively. In the top-10 most active journals, the subject category Engineering and Energy & fuels appears 8 and 6 times, respectively. Additionally, Fuel, Combustion and Flame, International Journal of Coal Geology, have high impact factor (IF) value of 4.908, 4.494, and 4.130, respectively. In addition, Fig.4 indicates the annual number of research documents on CSC published in the top three journals. It can be seen that overall trend of paper quantities published by Fuel has been increasing since 2010, with exception in 2013. Similarly, a stable growth of papers appears in Energy & Fuels, with exceptions in 2015 and 2018. However, the annual publications related to CSC in International Journal of Coal Geology fluctuates in recent ten years, reaching the minimum in 2012. Obviously, Fuel, as the dominant source of main study work in fuel science, is drawn more attention in CSC researches. 3.4. Authors and their cooperation Aaccording to the statistics, there were 1752 authors publishing CSC researches. Table 5 shows the top-10 authors that have published the most papers on CSC. It is evident that Wang DM, from China University of Mining and Technology, is the author with the largest number of 37 CSC articles, followed by Qin BT (China Univer-

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Fig. 2. Annual publications on CSC and the coal production in the top three countries (Mtoe: Million tons of oil equivalent).

Fig. 3. Countries and territories cooperation network in CSC research.

Table 3 The top 10 of most contributing institutions publishing on CSC research. Institutes

TP(%)

SP R(%)

CP R(%)

FP R(%)

RP R (%)

China Univ Min & Technol, China Xi’an Univ Sci Technol, China Taiyuan Univ Technol, China CSIR, India Indian Inst Technol, India CSIRO, Australia Natl Yunlin Univ Sci & Technol, China Univ Witwatersrand, Australia Univ Queensland, Australia Univ Newcastle, Australia

196(23.64) 33(3.98) 30(3.62) 24(2.90) 21(2.53) 20(2.41) 19(2.29) 17(2.05) 17(2.05) 15(1.81)

1(18.70) 7(0.72) 3(1.08) 6(0.84) 8(0.36) 8(0.36) 10(0) 3(1.08) 5(0.96) 2(1.45)

1(4.95) 2(3.26) 3(2.53) 6(2.05) 5(2.17) 6(2.05) 4(2.29) 9(0.97) 8(1.09) 10(0.36)

1(21.95) 2(3.74) 3(3.62) 4(2.65) 8(1.21) 9(0.84) 10(0.12) 6(1.57) 5(1.69) 7(1.45)

1(21.35) 3(3.38) 2(3.62) 4(2.65) 8(1.21) 8(1.21) 10(0.72) 5(1.69) 6(1.57) 6(1.57)

TP: Total publications; SPR: Single institute publication rank; CPR: Inter-institutionally collaborative publication rank; FPR: First author publication rank; RPR: Corresponding author publication rank.

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Table 4 The top 10 of most active journals publishing on CSC research. No. Journal title

Number of publications

Percentage (%) Impact factor in 2017

Subject category of the journal

1 2 3 4 5

144 60 47 38 36

34.95 14.56 11.41 9.22 8.74

4.908 4.130 3.024 3.956 1.982

Energy & fuels Engineering Energy & fuels Geology Energy & fuels Engineering Chemistry Energy & fuels Engineering Engineering

22 20 15 15 15

5.34 4.85 3.64 3.64 3.64

1.132 3.441 4.494 2.209 0.555

Thermodynamics Energy & fuels Engineering Engineering Thermodynamics Energy & fuels Engineering Thermodynamics Chemistry Energy & fuels Engineering Environmental sciences & ecology

6 7 8 9 10

Fuel International Journal of coal geology Energy & Fuels Fuel Processing Technology Journal of Loss prevention in the process industries Combustion Science and technology Process safety and environmental protection Combustion and Flame Journal of Thermal Analysis and Calorimetry Energy Sources Part A-Recovery Utilization and Environment

Fig. 4. Annual publications on CSC from top three journals during.2008–2018.

Table 5 The top 10 prolific authors in CSC research. Author

Country/Institute

Number

Average citations per publication

H-index

Wang DM Qin BT Deng J Li ZH Xin HH Tang YB Qi XY Yang YL Dou GL Shu CM

China/China University of Mining and Technology China/China University of Mining and Technology China/Xi’an University of Science and Technology China/China University of Mining and Technology China/China University of Mining and Technology China/Taiyuan University of Technology China/China University of Mining and Technology China/China University of Mining and Technology China/China University of Mining and Technology China/ Natl Yunlin Univ Sci & Technol

37 32 26 25 23 22 20 19 16 16

12.19 7.88 9.35 6.16 10.7 6.68 10.35 6.26 13.25 6.63

13 9 10 8 8 6 8 7 7 7

sity of Mining and Technology, 32 articles), and the third is Deng J (Xi’an University of Science and Technology, 26 documents). Interestingly, all the ten-top authors come from China. In other words, Chinese researchers attached significant emphasis to CSC studies due to serious coal fires. Furthermore, the relationships between authors in this field were obtained using cooperation network (see Fig. 5). The number of publications is denoted by the size of the circles, while the cooperation can be represented by the line between two authors. The colors indicates the collaboration clusters. It can be seen that

the major researchers in the cooperation network are Wang DM, Qin BT, Deng J, and Li ZH. Other scholars are connected with one of these main researchers. For example, Wang DM developed his close collaborations with Dou GL, Qi XY, and Xin HH.

3.5. Cited analysis The cited analysis indicates the number of times of the publications on CSC has been cited by other publications listed in Web of Science. Table 6 shows the twenty most frequently cited

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Fig. 5. Authors cooperation network in CSC research.

Table 6 The top 20 most most frequently cited publications. No.

Author

Journal

Country/Institute

Citations

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Wang et al., 2003a, 2003b Stracher and Taylor, 2004 Karthikeyan et al., 2009 Bell et al., 2001 Carras and Young, 1994 Pone et al., 2007 Querol et al., 2008 Clemens et al., 1991 Cheng et al., 2017 Song and Kuenzer, 2014 Nugroho et al., 2007 Wang et al., 2003a, 2003b Kucuk et al., 2003 Yuan and Smith, 2008 Carras et al., 2009 Krishnaswamy et al., 1996a, 1996b Krishnaswamy et al., 1996a, 1996b Beamish et al., 2001 Itay et al., 1989 Singh et al., 2007

Progress in Energy and Combustion Science International Journal of Coal Geology Drying Technology International Journal of Coal Geology Progress in Energy and Combustion Science International Journal of Coal Geology International Journal of Coal Geology Fuel Fuel International Journal of Coal Geology Fuel Combustion and Flame Combustion and Flame Fuel International Journal of Coal Geology Fuel Fuel International Journal of Coal Geology Fuel Processing Technology International Journal of Coal Geology

Australia/Univ Newcastle USA/Univ Syst Georgia Singapore/Natl Univ Singapore South Africa/Univ Natal Australia/CSIRO South Africa/Univ Witwatersrand Spain/CSIC New Zealand/DSIR China/Shandong Univ Sci & Technol China/China Univ Min & Technol England/Univ Leeds Australia/Univ Newcastle Turkey/Ataturk Univ USA/NIOSH Australia/CSIRO USA/Univ Wyoming USA/Univ Wyoming Australia/Univ Queensland South Africa/Univ Witwatersrand India/CSIR

314 263 180 164 162 155 150 123 122 110 105 104 103 100 99 94 89 86 84 83

publications in the field of CSC with basic information: authors, journal title, total citations, and the country/institutions during 1984–2018. The most cited paper is titled “Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modeling”, authored by Wang et al. (2003a, 2003b) in Progress in Energy and Combustion Science, with total 314 times. “Coal fires burning out of control around the world: thermodynamic recipe for environmental catastrophe” (Stracher and Taylor, 2004) and “Low-rank coal drying technologies current status and new developments (Karthikeyan et al., 2009)” published by International Journal of Coal Geology and Drying Technology, are ranked second and third most highly cited articles, with respectively 263 and 180 citations. Compared with the twenty most frequently cited publications, Australia is best denoted as country of first author with five publications, followed by the USA with four publications. Wang, Carras, and Krishnaswamy are appearing twice as the first author in the list. The journal International Journal of Coal Geology is best repre-

sented with eight articles, followed by Fuel with six publications. In addition, eight of the publications refer to “low temperature oxidation” by checking up the content of the twenty most frequently cited articles. Nowadays, the Essential Science Indicators (ESI) database is frequently applied to evaluate scientific productions. Highly cited papers (HCPs) included in ESI database are regarded as high quality in a scientific field (Liao et al., 2019). Therefore, Table 7 presents the ESI-HCPs in CSC field via SCI-E database. Overall, there are only 7 HCPs on CSC, mainly published in recent five years. Kong as the first author published two HCPs in this field, focusing on the effect of electromagnetic radiation on coal spontaneous combustion. 3.6. Keywords analysis Considering keywords associated with the core content of the publications, the analysis of keywords is helpful to recognize significant research topics in CSC studies. Fig. 6 indicates the overview

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Table 7 ESI highly cited papers in CSC researches. Title

Journal

Author

Institutes

Low-rank coal drying technologies current status and new developments An intelligent gel designed to control the spontaneous combustion of coal: Fire prevention and extinguishing properties Coal fires in China over the last decade: A comprehensive review

Drying Technology Fuel

Karthikeyan et al. (2009) Cheng et al. (2017)

Singapore/National University of Singapore China/Shandong University of Science and Technology

International Journal of Coal Geology

Song and Kuenzer (2014)

Recent developments in drying and dewatering for low rank coals An experimental study for characterization the process of coal oxidation and spontaneous combustion by electromagnetic radiation technique

Progress in Energy and Combustion Science Process Safety and Environmental Protection

Rao et al. (2015)

The effect of high temperature environment on rock properties-an example of electromagnetic radiation characterization

Environment Science and Pollution Research

Kong et al. (2018)

Effects of igneous intrusions on the structure and spontaneous combustion propensity of coal: A case study of bituminous coal in Daxing Mine, China

Fuel

Shi et al. (2018a, 2018b)

China/China University of Mining and Technology; Germany/ German Aerospace Centre China/China University of Mining and Technology China/Shandong University of Science and Technology; China University of Mining & Technology; China/Zhongyuan University of Technology China/Shandong University of Science and Technology; China University of Mining & Technology China/China University of Mining and Technology; China/Tiefa Coal Ltd, Daxing Mine

Kong et al. (2018)

Fig. 6. Keyword co-occurrence network of CSC.

Table 8 The most frequent keywords in CSC research. Keywords

Frequency

Keywords

Frequency

Keywords

Frequency

Low temperature oxidation Coal spontaneous combustion Coal Mine fire Bituminous coal Kinetics Moisture content Mechanism Coal self-heating Stockpile Model Temperature Low rank coal China Pyrolysis

353 302 169 137 82 80 77 69 64 63 55 50 49 48 45

Oxygen Lignite Particle size Prevention Product Air Self ignite Propensity Prediction Environmental impact Gas Mine Seam fire Thermal analysis Coal storage

43 42 41 37 32 29 27 27 26 25 22 21 19 17 16

Pore structure 3 phase foam Activation energy Combustion characteristics Inorganic matter Coalfield Inhibitor Parameter Fly ash Coal waste dump DSC Callide coal TG-FTIR Foam preparation Different sulfur content

15 14 13 12 12 10 7 7 7 6 6 4 4 2 2

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of the keyword co-occurrence network with 176 nodes and 565 links. A node denotes one key term obtained from the publications related to CSC. The size of each node is corresponding to the cooccurrence frequencies of the related keywords (Li et al., 2017a, 2017b, 2017c). In Table 8, there are top 45 terms with a total of 2442 co-occurrence frequencies, which take up more than 90% of all keyword frequencies. Table 8 indicates “low temperature oxidation” is the most frequently used keyword with 353 times. It is well known that CSC is aroused by the heat accumulation due to coal oxidation at low temperatures. Therefore, a lot of researchers focus on the chemical reactions between coal and molecular O2 at low temperatures (Wang et al., 2003a, 2003b). At the same time, “kinetics (80)”, “mechanism (69)”, “model (55)”, “prevention (37)”, “prediction (26)”, and “thermal analysis (17)” are also specific research hotspots in CSC field. Among the top 45 keywords, three of them are associated with coal types, including bituminous coal (82), low rank coal (49), and lignite (42) due to their strong spontaneous

combustion propensity. CSC is determined by various factors, so some researchers devote themselves to understanding the effects of moisture content (77), temperature (50), oxygen (43), particle size (41), and pore structure (15) on CSC. The time-zone visualization is used to present the keywords in chronological order and reveal the co-occurrence relations between pairs of keywords (Zeng and Chini, 2017). Fig. 7 describes the time-zone visualization in CSC study. The lines linking with keywords are co-occurrence connections for each pair of keywords. The colors of lines denote the year of the first co-occurrence. The early emerging interest on keywords such as low temperature oxidation, coal spontaneous combustion is rising, which is indicated by more lines being associated with these keywords. In recent three years, there were new research hot spots appearing, such as 3 phase foam, fire extinguishment, and foam preparation. Keywords burst detection is related to recognize keywords that show a high frequency of occurrence within a certain period (Zeng and Chini, 2017). In other words, the observed keywords are drawn

Fig. 7. The keywords time zone distribution map of CSC.

Fig. 8. Top 11 keywords with the strongest citation bursts.

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more attention by researchers during a given period of time. Fig. 8 gives a keyword burst detection result on CSC, starting from the first literature retrieval year in 1991. It can be seen that thermal analysis, low temperature oxidation, bituminous coal, and coal stockpile were bursting from 1991 to 2001, 1991–2002, 1992–2003, and 1994–2011, respectively. Subsequently, the keywords kinetics, model prediction, and coal waste dump were observed as bursting from 1996 to 2011, 1996–2003, and 2000–2010, respectively. In addition, environmental impact and 3 phase foam attracted great interest from 2007 to 2013, and 2015–2018, respectively. In general, the attention in the embodied CSC field has changed from earlier discussions of oxidation mechanism, test methods, and model prediction to the practical extinguishment in preventing and controlling the CSC disaster. 4. Conclusions A review of the publications on coal spontaneous combustion (CSC) was presented with the information involving document types, countries, institutions, journals, authorship, citation, and keywords. Overall, the number of researches on CSC has risen up greatly during 1984 and 2018. China, Australia, and the USA are the top three countries with large productivity in CSC publications. According to social network analysis, the USA has plenty of cooperation with Japan, Canada, and Australia. However, there is still large space for contributing to international cooperation in this field. China University of Mining and Technology takes the leading position of institutions in total articles on CSC and has the highest H-index. Fuel, International Journal of Coal Geology, and Energy & Fuel are the top three journals publishing the most CSC articles. Wang DM is the author with the largest number of CSC publications. The keyword analysis indicates low temperature oxidation, mechanism, model, moisture content, fire extinguishment are the prevalent topics. Also, the attention in the embodied CSC has shifted from earlier topics of oxidation mechanism to the present extinguishment in preventing and controlling the CSC disaster. The results in this study can provide significant information for future researchers to better understand the hotspots associated with CSC. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 51874100 & 51741402); the State Scholarship Fund of China Scholarship Council (No. 201806655019). References Arisoy, A., Beamish, B., 2015. Reaction kinetics of coal oxidation at low temperatures. Fuel 159, 412–417. Avila, C., Wu, T., Lester, E., 2014. Petrographic characterization of coals as a tool to detect spontaneous combustion potential. Fuel 125, 173–182. Beamish, B.B., Barakat, M.A., George, J.D.S., 2001. Spontaneous-combustion propensity of New Zealand coals under adiabatic conditions. Int. J. Coal Geol. 45 (2), 217–224. Bell, F.G., Bullock, S.E.T., Halbich, T.F.J., Lindsay, P., 2001. Environmental impacts associated with an abandoned mine in the Witbank coalfield, South Africa. Int. J. Coal Geol. 2-3, 195–216. Bhowmick, T., Nayak, B., Varma, A.K., 2017. Chemical and mineralogical composition of Kathara Coal, East Bokaro Coalfield, India. Fuel 208, 91–100. Boudry, C., Baudouin, C., Mouriaux, F., 2018. International publication trends in dry eye disease research: a bibliometric analysis. Ocul. Surf. 16, 173–179. BP, 2019. Statistical Review of World Energy 2018 Underpinning Data. http://www. bp.com/statisticalreview. Carras, J.N., Young, B.C., 1994. Self-heating of coal and related materials: models, application and test methods. Prog. Energy Combust. Sci. 1, 1–15. Carras, J.N., Day, S.J., Saghafi, A., Williams, D.J., 2009. Greenhouse gas emissions from low-temperature oxidation and spontaneous combustion at open-cut coal mines in australia. Int. J. Coal Geol. 2, 161–168. Chai, J., Du, M.F., Liang, T., Sun, X.J.C., Yu, J., Zhang, Z.G., 2019. Coal consumption in China: how to bend down the curve? Energy Econ. 80, 38–47.

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