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Spirit of Scientists∣Academician Xian Xuefu: Making unremitting endeavor to safeguard energy security of China

Xian Xuefu (January 1929-), an expert in mine safety technology, academician of Chinese Academy of Engineering, and a pioneer of basic study of coal-bed methane (CBM). For a long time, Xian has devoted himself to the study of coal-bed methane theory and its engineering application. He has managed to solve the problem with gas adsorption bond of much debate through theoretical and practical verification, and established a mechanical method for predicting the potential danger zone of coal and gas outburst. He has been given 3 National Awards for Progress in Science and Technology, the Souvenir Medal for "Celebrating the 70th Anniversary of the People's Republic of China" in 2019 and the title of the "Most Beautiful Striver".

In 1949, Xian was admitted to the Mathematics Department, Sichuan Provincial Educational College. In 1950, in response to the national needs, Xian signed up for college entrance examination again and started to study engineering.

In 1955, when filling in his Graduate Job Assignment Registration Form, Xian wrote "I'm devoting my entire life to coal mine undertaking" in the Aspiration column. Apparently, he did what he promised to do. In the past 40 years since the reform and opening-up of China, Xian has kept close watch on the energy demands of China, and made tremendous contribution to research of areas including mine safety technology and engineering field, coal seam gas mining theory and its engineering application.

Always ahead of others, he became the first to solve an worldwide problem.

In the 1960s, China was in desperate need of engineering technical talents in energy. Xian was sent to the Soviet Union to study the hydraulic coal mining technology, which was quite popular in the Soviet Union back then. Just as Xian was about to make an impression with what he had learnt in Soviet Union, the hydraulic coal mining technology was gradually fading out in China due to its intrinsic defects. There were very few hydro-powered coal pits left. What he had learnt became completely useless.

As the problems with coal mine safety production got increasingly prominent, coal and gas outburst and gas explosion, in particular, become the biggest obstacles hindering coal mine safety production. Xian knew clearly what was happening and started out looking for a solution. Back at that time, when coal and gas outburst occurred, people would exactly copy the experience of the Soviet Union. Xian said that according to Academician Skokzynski of the Soviet Union, the most effective way to tackle coal and gas outburst is to first mine the protective layer in the upper (or lower) part of the coal seam with outburst risk to protect the outburst layer. Protection shall be provided throughout the mining stage where an upper protective layer with an interlayer spacing of less than 60 m and a lower protective layer with an interlayer spacing of more than 10 m are used for mining of dangerous layer. Xian also pointed out that the mining of the protective layer would cause a large amount of gas to burst from the adjacent pressure relief layer to the protective layer, it is necessary to drill a hole to drain and utilize gas. At that time, the mining of lower protective layer of Nantong and Zhongliangshan Coal Mines in Chongqing was afflicted by the problem with mining of protective layer with an interlayer spacing of less than 10 m. However, the risk coefficient of close-distance mining of protective layer was significant, and there was no successful experience in foreign countries to learn from. Xian decided to do something unprecedented.

With this in mind, Xian made his first turning in his academic career. In the early 1960s, Xian Xuefu called upon teachers of the Mining Department of Chongqing University who were then engaged in research on protective layer mining and gas disaster prevention in Nantong Mining Bureau to carried out research on close-distance protection layer mining and gas drainage. Hard work paid off. In the middle 1960s, the scientific research group led by Xian Xuefu made critical technological breakthrough. They successfully implemented the engineering practice of gas drainage for close distance mining of the protection layer at Chongqing Nantong Mining Bureau, and solved the international problem with gas drainage for close distance mining of the protection layer, which posed great risk. China became the first country in the world to successfully implement the technology of gas drainage for close distance mining of the protection layer.

After that, building on the breakthroughs, Mr. Xian carried out study with Sun Peide and established a solid gas coupling seepage calculation method for the overflow of the double-layer and multi-layer systems of the mining protection layer, and solved the problem of dividing the effective protection scope of adjacent layers. In the 1970s, Mr. Xian made the point that the gas in coal seams is not only a disaster causing factor, but also a relatively clean energy and resource. This triggered a shift of the focus of China's coal mine gas safety work from control measures to the combination of prevention and control. According to Mr. Xian, before coal mining, the gas should be extracted first and utilized, so as to prevent and control gas disasters from the source, and make use of gas resources.

Xian and his team have carried out extensive theoretical and practical research of the prevention and control of coal and gas outburst disasters. A project he directed won awards at the National Science Conference of China held in 1978.

As a meticulous researcher, Xian managed to solve international academic disputes.

From March 18 to 31, 1978, the Central Committee of the CPC and the State Council held the National Science Conference of China. The Conference highlighted the basic Marxist thesis that "science and technology are productive forces", made the decision to emancipate people's mind, established the fundamental policy of respecting knowledge and talents, and ushered in a bright spring of science in Chinese history.

These moments still remain fresh in Xian's memory. For Xian and many other scientific and technological workers in China, the golden age of their academic and teaching career started in that spring. After 1978, Xian was eventually able to devoted himself to the research of the prevention and control of coal and gas outbursts again after the research had been suspended for many years.

For the gas drainage engineering practice and the research of the mechanism of coal and gas outburst, it is extremely important to identify the interaction mechanism between methane molecules and coal surface molecules. From the 1980s to the early 1990s, no agreement was reached on this issue at the global level. Most of the researchers held that the force between methane molecules and coal surface molecules equaled Van der Waals' force. However, a few researchers, such as Edingale and Tonic, argued that there might be chemical bonds between them under high pressure, and they were generally metastable.

To resolve the academic dispute, from 1984 to 1995, Academician Xian launched an interdisciplinary research, which was the first of its kind in the world. He took in students of chemical discipline as his team members and used various characterizing and testing means including X-ray scattering, infrared spectroscopy, CT scanning technology to study the adsorption (desorption) process of methane in coal at the molecular level. By doing so, he identified the size and distribution of the interaction potential between coal surface and methane molecules, as well as the characteristics of adsorption state and experimental measurement. Finally he came to the conclusion that the interaction force between coal and methane under non-extreme conditions is Van der Waals' force.

Back at that time, despite the fact that many experimental technologies could be used to study the interaction between molecules and solid surfaces, none of them were suitable for studying the adsorption system of methane and coal. Knowing that the influence of C-H bond in coal could be overcome by isotope replacement (deuterium hydrogen), Mr. Xian and his team tried the use of on-site low-temperature infrared spectroscopy to conduct experimental measurement of methane adsorption in coal. Study of the interaction between coal surface and methane using the quantum chemical calculation method and the field low-temperature infrared spectrum experiment showed that the interaction between methane and coal surface was anisotropic. The lowest energy and the greatest interaction potential were observed when methane was adsorbed on the coal core surface in the form of triangular cone overlap. On this basis, it was drawn that the interaction force between methane and coal surface molecules is the Van der Waals force, and that the adsorption process was a physical process. The dispute over adsorption bond property between methane and coal surface was this way solved theoretically and experimentally. Resolution of the dispute laid a solid foundation for the study of coal and gas outburst mechanism and the development of gas extraction technology.

By thinking out of box, Mr. Xian established a new method for predicting coal and gas outburst disasters.

Data records and incomplete statistics show that since the first coal and gas outburst in the Yi'ak Mine of the Lu'alei Coalfield in France in 1834, some 40,000 coal and gas outburst disasters have occurred in more than 20 countries all over the world, including China. The two most disastrous outbursts respectively happened in Donbas Jiajialin Mine of the Soviet Union in 1969 (involving 14,000 tons of coal and 250,000 cubic meters of gas) and in Tianfu Sanhui No. 1 Mine in Chongqing, China in 1975 (involving 12,780 tons of coal and rock and 1,400,000 cubic meters of gas). For a long time, many scientists all over the world have been studying this scientific problem. Many of them are from Russia and China. Despite the remarkable progress we have made in prevention and control of outbursts, coal and gas outbursts are still happening here and there.

According to Xian Xuefu, the coal and gas outburst is in nature a mine engineering geological disaster. The prevention and control involve identifying the mechanism of outburst occurrence, finding a way to predict it, developing monitoring means and establishing corresponding prevention and control measures. Both the scientific problem at the center of this task and the key technological difficulties lie in mechanism and prediction. This core problem dose relate only to geological and engineering science, but also other discipline related to them, including physics, chemistry, mechanics and mathematics.

The prediction of the potential danger zones vulnerable to coal and gas outbursts is of extreme importance for prevention and control of gas disaster. The study of this problem has been stuck in the qualitative research stage for a long time. The practice of coal mine production shows that coal and gas outbursts are regional and zonal and that most of the coal and gas outburst areas fall within the geological structure change zone of a mine. In order to figure out the underlying reasons of this phenomenon, from the perspective of mechanics, Xian Xuefu and his team found through research that the occurrence of this phenomenon might be attributed to the change of the geometric shape of the coal and rock strata in the geological structural belt, and the corresponding change of the physical and mechanical properties of the coal and rock masses in the geological structural belt.

Xian Xuefu believed that the numerical method of mechanics could be used to predict the potential danger zones of coal and gas outburst in the mine if detailed geological data could be obtained before the construction and during the production of the mine, the in-situ stress test is carried out from the perspective of mechanics, and specific physical and mechanical properties of coal and rock are obtained.

Based on the idea, Xian brought up a method to measure in-situ stress using Kaiser effect and used this experimental method to prove that the stress-strain law of composite rock and gas bearing coal is consistent with that of single rock and coal. This provided a basis for the selection of constitutive equation for numerical calculation of gas bearing composite coal. Based on the experiment results, Xian established the stress intensity and strain intensity criterion for the fracture failure of gas filled coal and rock on the basis of the Drucker-Prager strength criterion, and brought forward the method of dividing the outburst potential danger zones by the stability coefficient.

In the research, Xian Xuefu was never content with the general theoretical derivation, however strict the derivation is in logic, and insisted in carrying out repeated verification through numerical calculation and comparison with indoor experiments and field application results. On that basis, Xian proposed a method to predict potential danger zones of coal and gas outburst in underground mining of coal mines, which was applied in many coal mines, such as Yutianbao Coal Mine, Yanshitai Coal Mine, and Shuijiang Coal Mine in Nantong, Chongqing, Xunchang Coal Mine and Lyushuidong Coal Mine in Furong, Sichuan and Pingdingshan No. 8 Coal Mine in Henan. The areas in which outbursts occurred were consistent with those predicted using this method, which verified the reliability of the method.

Always taking the lead, Xian launched the world first field test of supercritical carbon dioxide fracturing.

Along the journey of scientific research, Xian is always driven by his relentless pursuit of truth and sensitivity to the academic frontier. In the 21st Century, in response to China's growing dependence of on foreign countries for natural gas, which posed serious threats on China's energy security, Xian Xuefu and his team shifted their focus of scientific research to the field of shale gas development, and launched one of the first researches of shale gas development in China, leveraging the geographical advantages of Chongqing as the center of China's shale gas development.

In view of the geological occurrence conditions of shale gas in China, and in order to solve problems including heavy consumption of water resources and prominent environmental pollution facing the traditional hydraulic fracturing, Xian initiated cooperation with scientific research institutions at home and abroad in 2009, and became the first to put forward the academic idea of strengthening the integration of shale gas development and geological storage with supercritical carbon dioxide by using supercritical carbon dioxide instead of water as fracturing fluid to transform the reservoir and replace shale gas at the same time. This way, the oil recovery was increased and underground storage of carbon dioxide was finally realized. The Project "Use of Supercritical Carbon Dioxide to Strengthen the Foundation for Efficient Development of Shale Gas " under the 973 Program recommended by Xian based on the above idea was successfully approved. Research under this Project has by now resulted in success of the first field test of supercritical carbon dioxide fracturing in the world, which provided substantial support for the high-efficiency development of shale gas and large-scale carbon dioxide emission reduction in China.

According to Xian Xuefu, scientific researchers should always remain neutral and objective and never stop seeking the truth. In recent years, in order to tackle potential environmental and geological disaster risks in the large-scale development of shale gas, Xian repeatedly called upon researchers to study the problems with an objective and neutral attitude, and provide basis for environmental risk and disaster prevention and control in the process of shale gas development based on scientific facts.

Xian is always humble and cautious toward scientific and academic research. In his opinion, everyone has limitations and has something that they don't know or are not good at. He is reluctant to express opinions on any problem out of his expertise. A researcher once came to him and ask him to write a preface for a book. Xian refused, saying that this book was not related to his research area and he was unable to judge the scientificity and rigorousness of the book. He then recommended a professor in that research area to write a preface for the book.

When deciding whether to attend an academic conference, Xian has established his own rules. He only attends conferences related to his research areas. If he is to deliver an academic report, he would ponder on the content of the report and verify any related data. He never deliver the same academic report for the second or repeats the content of a report in another one.

As a teacher, he lays particular emphasis on students' character and civic virtue.

Xian has been teaching in Chongqing University since 1956. In the 60 years, he has trained a great number of outstanding graduates, who are now academicians, members of the Central Committee, provincial and ministerial officials, department and bureau officials, as well as academic leaders and key technical members in various areas.

"What I like the most about CQU is its down to earth style of study, which is quite important. Science is the pursuit of the truth. To pursue the truth, we must be down to earth." Xian is very proud that people often describe his students as down to earth.

Already at the age of 90, Xian is still supervising student. When reviewing students' papers, he would use a pencil to write down his revision suggestions on structural adjustment and use of punctuation marks. The whole page will be covered by his handwritings, and sometimes he would change some of the revision suggestions several times...This shows that Xian is careful about every suggestion he gives.

Xian said: "Young people are successors of construction of China. As their teachers, besides teaching and preaching, we have to set up an example for them. For me, teaching by example is more important than verbal instruction."

His office in the Mining Experiment Building located on the campus of Chongqing University was decorated in 1999 when Xian was selected as an academician of the Chinese Academy of Engineering. He divided it into two compartments, and used one of them as the secretary workshop and the other as his reading room. On top of the table there is an old spectacle case and a half-used pencil and an eraser. A piece of scratch paper is fully covered by his neat handwritings on both sides.

This office is not quite spacious. The doorplate has already been taken down by someone as instructed by Xian. According to the secretary, Xian removed the doorplate because he did not want to be interrupted often. This room is mostly filled by books. A pile of old books are sitting on the window sill by the office desk. More than a decade ago, after hearing Chongqing University Library was disposing of old books, Xian immediately sent two students to get two boxes of old books for him. These old books are mostly professional books written in Russian. When in his young age, Xian learned a lot from and was greatly inspired by these books. He recovered these books because he believed that he still could learn something from them. Xian reorganized the old books in his office, and translated some of the important lines extracted from the books into Chinese for fear that his students could not understand.

The stacked pile of the note papers is now more than half a meter high. They are precious wealth Xian leaves behind for his students.

His students said that everything had changed after decades but Mr. Xian remained literally unchanged.

His students recalled that Mr. Xian was always the first to arrive at the Experiment Building. His driver would pick him up from his home at 7:00 every morning. Xian would always get ready before that time so as not to keep the driver waiting. On weekends, Xian would walk to the office on his own so that the driver could take two days off.

For many years, Xian would only take a leave from the Chinese New Year's Eve to the third day of the first month of the Chinese calendar every year. At other times, Xian would start reading books immediately after arriving in the office. Sometimes he would translate Russian materials regardless of the weather. After turning 80, besides teaching and scientific research, Xian would spend some time writing poems. In one of his inscriptions, he wrote: "Past events have faded like a puff of smoke, true friendship stands out in difficult times. How wonderful everything is. It is great fun to find it out. Life is but a span. Luckily the glow of the setting sun is splendid.” Xian gave this inscription to his students and encouraged them to stay curious about everything and enjoy doing scientific researches.

Xian hardly ever talked about his life goals with others. A couple of years ago, he wrote the following lines in his personal summary: "Knowledge is boundless but life is limited. So we should treasure our time and work hard to serve the country. This is what I keep telling myself throughout my journey of study, and is where my life goals lie." This is what Xian has been practicing in his entire life.

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