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26
General and regional geology
УДК 622.71
Selivanova T., Pechnikov V., Ken-ichi Itakura
TATYANA V. SELIVANOVA, Candidate of Geological and Mineralogical Sciences, Associate Professor, Sub-Department of Geology, Geophysics and Geoecology, School of Engineering, Far Eastern Federal University, Vladivostok. 8 Sukhanova St., Vladivostok, Russia, 690950, e-mail: [email protected] VLADIMIR S. PECHNOKOV, Candidate of Physical and Mathematical Science, Associate Professor, Sub-Department of of Physics, School of Natural Science, Far Eastern Federal University, Vladivostok. 8 Sukhanova St., Vladivostok, Russia, 690950, e-mail: [email protected]
KEN-ICHI ITAKURA, Professor, Department of Computer Science and System Engineering, Muroran Institute of Technology. 27-1 Mizumoto, Muroran 050-8585, Japan, e-mail: [email protected]
The coal thermo-magnetic analysis of coal samples to evaluate
the resolution of geomagnetic method when monitoring the combusting area
One of the most important problems of coal thermochemical conversion technologies is evaluation of the combustion area in coal seams and rock masses. The modern sensing and control techniques used to monitor the combustion area in coal seams are expensive and technically complicated.
The thermo-chemical conversion of coal mineral components has an effect on magnetic characteristics of coal seam and can be used for a real-time control of combusting area. To specify this, laboratory experiments aimed to investigate the regularities of the magnetic properties of coal in the process of their thermal decomposition were carried out at Far Eastern Federal University. The obtained results were backed up by a theoretical analysis and laboratory measurements. When heating coal samples, thermoremnant magnetisation emerges in them, the magnetic characteristics of coal vary between submagnetic and ferromagnetic ones. The paramagnetic pyrite present in the coal mass converts into magnetite under high temperatures, the smallest quantities of it increases the magnetic properties of coal. So, the magnetometry may be a useful geophysical tool to evaluate the combustion volume and its migration for underground coal gasification.
Key words: coal, laboratory experiment, coal specimen, magnetic behavior, thermal action, thermo-magnetic conversion.
Introduction
Well-known methods for thermochemical conversion of coal under high temperature review prompting suggestions that UCG and underground coal burning are the most promising technologies to largely reducing the coast for coal mining and transportation [1-4, 7] These technologies provide increasing the coal resources available for utilization un-mineable thin or deep coal seams under difficult geological and mining condition, pollution control, especially regarding to emissions of nitrous oxides,
© Selivanova T., Pechnikov V., Ken-ichi Itakura, 2015
mercury and sulfur, eliminates ash disposal after coal. One of the most important problems of thermochemical conversion of coal technologies is evaluation of the combustion area in underground coal seams and rock masses. Employed modern sensing and control techniques for the combustion area control in underground coal seams are expensive and technically complicated.
Thermo-chemical conversion of coal mineral components has an effect on physical characteristics of coal. For example, thermo-chemical conversion paramagnetic coal minerals into ferromagnetic ones make for sharply increasing of nature and remanent magnetization of a coal seam under heating. So, geomagnetic control based on remote sensing of thermochemical processing coal seam magnetic field may be used for evaluation of combustion cavity and its migration in the coal seam under controlled underground coal firing. Primarily, for the purpose interpretability of combusting area by monitoring the geomagnetic activity it is necessary to experimentally evaluate of coal magnetic behavior convention for temperature.
To this guessing check laboratory experiments have been made as an activity of the Far Eastern Federal University. Our investigation based on a theoretical analysis and laboratory simulation tests. Typical results of the laboratory experiments are presented below.
Theoretical basis for coal thermo-chemical conversion
The results of some investigation [3, 8, 10] demonstrated thermo-chemical conversion mechanism of different metamorphic phases and petro-graphical composition coal is based on identical principals. Coal thermo-chemical conversion is complicated multistage process composed of consecutive reactions. Rate and stage of thermo-chemical coal transformation depend on intermediates properties of thermal destruction of coal greater then on initial chemical composition of coal. Temperature, pressure, dispersity of coal grains, presence of reactive liquid and gaseous substances has a significant effect on thermo-chemical coal transformation. Coal thermal effect is an accumulating result of thermal effect of single minerals. Thermosetting minerals can predominate in an accumulating thermal effect of coal. The thermal effect of poly-mineral substance depends on presence of mechanical impurities into a mineral and dispersion degree of its and perfection degree of a mineral.
Coal thermo-chemical conversion in depending on metamorphic phases. Coking fat coal have endothermic effects under heating temperature 400-500 °C according to conversation great bulk of coal into plastic state releasing of volatile components. At the same temperature range forming of semi-coke's structure starting and heat release is fixed. Gas coalhas the same volume if volatile components like fat coal, but has more content of water as opposed to fat coal, so the thermograms of these types of coal are conformed, but the thermogram of gas coal has more intensive endothermic effect under heating temperature 100-200 oC. Intensity of the endothermic effect is sharply increasing for candle and brown coal and decrease for coking and lean coal. Thermogram of anthracite has intermediate behavior.
Increasing of leptynite (liptinite) content (to 50%) determines considerable reinforcement of exothermic effect (250-450 °C) and emergency of endothermic effect (450-500 °C). Such different of leptynite (liptinite) and vitrinite thermograms can be explained by variety of their chemical structures. Vitrinites of starting stage of metamorphism have high content of aromatic structures as opposed to leptynite. Particulate matter process of lignin-cellulose complex of brow coal can be accompanied by increasing of hydrogen and carbon content and decreasing of humic acids content. This process reflects on the thermo-grams by decreasing, at first, and then completes disappearance of exothermic effect under heating temperature 500 °C. At the same time the new exothermic effect is registered under heating temperature 450-500 °C increasing from black-brown to light-brown coal, that according with process of oxidation of humic acids.
Some scientiets (Brodskay (1970), Burov et al. (1979) investigated fine-dispersed goethite contained in a coal as alpha-form is transformed into beta-form attended by dehydration and mineral structure destruction under heating temperature 50-400 C. Under further heating until temperature 1 370-1 400 °C goethite is transformed into magnetite. Hexagonal (Fe1-xS) and monoclonal (Fe7S8) Fe7S8 pyrrotin, at first, monoclinic modification of pyrrotin is polymorphic transformed into hexagonal form
under heating to 300 °C, and then under farther heating to 430-750 °C pyrrotin oxidize and hematite is generated. Under heating to 380-700 °C pyrite contained in a coal oxidize and hematite is generated too. Under heating a coal to 440-600 °C arseno- pyrite contained in a coal oxidize and hematite is generated too.
Experimental
To applicability check of geomagnetic method for control of combustion area location thermo-magnetic investigation of coal samples of the Urgal coal deposit has been executed. Some experimental tests were undertaken to indentify the magnetic susceptibility, remanent magnetization, magnetic moment are changing under high temperature on the coal samples to set up fundamental information for the technology engineering to evaluate the location of the combustion cavity by the geomagnetic activity.
Simulation tests were made in the magnetic field facility of the Sci-education centre "Physics of the Earth, laboratory of magnetism" School of natural Science of Far Eastern Federal University in Vladivostok (Russian Federation).
Coal specimens
The coal samples used in the tests were selected from the Urgal coal deposit which some coal seams advanced for thermochemical conversion. The Urgal deposit pertains to the Bureinskiy coal basin (Khabarovskiy Region, Far Eastern Federal District) [9]. Krapiventzena V.V. demonstrated coal of this basin are a vitrinite type with vitrinite components content more 65% [5, 6]. Coal of the Bureinskiy coal deposit contains some mineral admixture like lens, interbeds and dispersions. Mineral substances of this coal basin generally are represented by clay minerals (kaolin, illite), carbonates (inherit, calcite), oxides (quarts), illites (limonite), sulfides, phosphates, sulfates, silicates, different salts, rare-earth elements. Iron mineral are represented by pyrite and siderite. Usually iron minerals is occurred small-grained, regular-shaped masses, lens spread in the coal filling cracks and plant tissue vesicle located at the coal seam roof. In coal seam structure eggshell (23,7-51,6%) and weak-luster (30-35,7%) coal prevail. Glance vitrain coal of eastern part of the coal basin have high concentration of ferruginous minerals (20,55-20,93%). Percentage volume of ferruginous minerals of semi bright coal of the basin are 2,3-5,94%. Weak-luster coal have some less concentration of ferruginous minerals (0,6-5,23%). Generally coal of Bureinskiy basin are high ash (about 50%), specific weight of 1-1,7 g/cm .
15-th coal samples used in the tests were selected from the top commercial seams of the Urgal coal deposit. Original color of all specimen were brown (Table). The samples had horizontal stratification. Organically and mineral inclusions visually were not determined. The samples had laminated structure. Based on structure-texture specific the samples may be related to large striated lithologic type. The specimen had exogenous and hypergenic fractures crossing the specimen in two orthogonally related planes. Dominant forms of cleavages were stepped, scaly, fission fragment, irregular ones. Fracture forms were varied widely changed from even flat fractures to plagio-clastic and concave fractures, irregular hatched fracture. Fracture surface was homogeneous, smooth, unruffled and parallel hatched. Coal substance was transfixed by macro pores and transitions pores different direction and different depth. Numerous fractures were exogenous; hypergenic fractures practically were not visible. The coal was crumpled and it fell to pieces under weak mechanical pressure. Factor of general fracturing of coal specimen was 2. As shown in photography of coal sample polished section N3 coal persistent pyrite (Fig. 1, a) under heating is transforming into magnetite (Fig. 1, b).
FEFU: SCHOOL OF ENGINEERING BULLETIN. 2015. N 2/23 / ВЕСТНИК ИНЖЕНЕРНОЙ ШКОЛЫ ДВФУ. 2015. № 2 (23)
a) situational analysis b) under thermo activity
Fig. 1. Photography of coal sample polished section (Urgal coal deposit, Khabarovskiy Region, Far Eastern Federal
District)
Analytical samples characteristics
1 thin-short-striated coal (up to 1 mm) eggshell black black large block, chinley coal fine grain concave fracture 2%
2 thin-short-striated coal (up to 1 mm) weak-luster grayish-black black large block, chinley coal fine grain plagio-clastic 1%
3 striated-banded weak-luster black black large block, chinley coal fine grain concave fracture 1%
4 striated-lenticular-banded eggshell black black large block, chinley coal fine grain flat fracture 3%
5 striated-lenticular-banded weak-luster black grayish-black large block, chinley coal fine grain concave fracture 2%
6 striated-banded weak-luster grayish-black grayish-black large block, chinley coal fine grain concave fracture 2%
7 striated-banded eggshell grayish-black black large block, chinley coal fine grain concave fracture 1%
8 striated-lenticular-banded weak-luster black black large block, chinley coal fine grain concave fracture 2%
9 thin-short-striated coal (up to 1 mm) eggshell black black large block, chinley coal fine grain irregular hatched fracture 3%
10 striated-banded weak-luster grayish-black grayish-black large block, chinley coal fine grain concave fracture 1%
11 thin-short-striated coal (up to 1 mm) eggshell black black large block, chinley coal fine grain concave fracture 2%
12 thin-short-striated coal (up to 1 mm) weak-luster black black large block, chinley coal fine grain concave fracture 1%
13 thin-short-striated coal (up to 1 mm) eggshell grayish-black black large block, chinley coal fine grain concave fracture 2%
14 thin-short-striated coal (up to 1 mm) eggshell black black large block, chinley coal fine grain concave fracture 2%
15 thin-short-striated coal (up to 1 mm) eggshell black black large block, chinley coal fine grain concave fracture 1%
Laboratory magnetic measurement methodology of samples is widely known (Fig. 2). Measuring mechanism of the magnetometer-vibrator composed of synchronous motor providing sample holder vibration (30 hz frequency) in exciting solenoid (1).The solenoid is allocated into the Helmholtz coils which filed compensate for the vertical and horizontal magnetic induction earth field components to 0,1%. The solenoid and sensing coils (4) are allocated into "jacket water" cooling system (6). Sensitivity
Q 2
of the magnetometer-vibrator is 1,235x10- Am . Measurements were made under permanent action by external magnetic field (B=125, mTl).
Powdered coal samples were used for the goal active surface area increasing. The powdered coal putted into quartz vessel caliber of it was 3 mm and 10 mm height. The samples tamped down tight and fixed by glass silk. The sample (2) was grappled by the holder (3) of magnetometer-vibrator (Fig. 2). Sample inductive magnetic moment measurement was made after the sample has been keeping into the oven (5) under fix temperature for a 4 minute. Experience has shown that a sample is thoroughly heat-up to set point temperature for a 4 minute.
Results
Carried out research and these results suggest that magnetization of coal specimen are changing under heating and combusting. Combusting coal magnetization have complicated multistage type of change. Fig. 3 presents inductive magnetic moment volume of coal sample T 4(3) change. After the specimen heating until fixed temperature inductive magnetic moment volume Mi (mkAm2) was studied. From this graph, the results show that inductive magnetic moment volume was relativity stable under heating until 490 oC. Furthermore heating Mi sharply increased and then deeply decreased. Formation magnetite as a result of terminal conversation of pyrite according with maximum on inductive magnetic moment curve. Thereupon, traceable sharp minimum of the inductive magnetic moment curve is according with Curie point of magnetite.
Fig. 2. Experimental setup for magnetic measurement
0,2 0,1 0
400
450
500
t m
550
600
Fig. 3. Inductive magnetic moment volume of coal samples T-4(3)
For the purpose of research detail the coal specimens were heated until 350, 400, 450, 500, 600 degree centigrade for 1 hour and after it there magnetic activity were studied. Fig. 4 presents inductive magnetic moment volume of coal sample T-4 Mi (mkAm2).
2
Fig. 4. Inductive magnetic moment volume of coal samples T-4 Mi (мкАм ) for different temperature heating
Based on virgin magnetization curves Mi (mkAm ) presented on the Fig. 4 correlation between magnetic susceptibility and heating temperature of coal sample T-4 was determined (Fig. 5).
t m
Fig. 5. Magnetic susceptibility of coal sample T-4
So, depending on pyrite's form contained in a coal coal's magnetic parameters varieties from anti-ferromagnetic to ferromagnetic. Ferruginous mineral dissociation is starting under heating temperature 450-500 °C. Thermo-chemical decay of pyrite is attending of magnetite forming and progressive oxidation of magnetite into hematite at the same time. Under heating thermoremanent magnetization of pyrite is forming and contribute into full magnetization of coal. So, thermo-chemical conversion
paramagnetic coal minerals into ferromagnetic ones make for sharply increasing of nature and remanent magnetization of a coal seam under heating. Even trace of ferromagnetic magnetite in coal samples cause of a high level of magnetization and remanent magnetization emergence.
Conclusion
So, based on experimental results, geomagnetic is expected to be a useful geomagnetic tool to for evaluation of combustion volume and its migration for underground coal gasification. It is necessary further development of real-time control technology of combusting area location using distant geophysical measurements for UCG. So, for further designing of monitoring technology based on distant geophysical measurements the following investigations are necessary:
- further petro-physical research of different metamorphic phases and petro-graphical composition coal under high temperature;
- applicability check of different geophysical methods based on mathematic and physical simulation.
- development of real-time control technology based on distant geophysical measurements of the combustion area around gasification cavity and guidelines of it practical using.
In the near future, we are planning to develop geophysical monitoring technology for evaluation of the ground combustion area.
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Общая и региональная геология
Т.В. Селиванова, В.С. Печников, Кен-ичи Итакура
СЕЛИВАНОВА ТАТЬЯНА ВАЛЕРЬЕВНА - кандидат геолого-минералогических наук, доцент кафедры геологии, геофизики и геоэкологии Инженерной школы (Дальневосточный федеральный университет, Владивосток). Суханова ул., 8, Владивосток, 690950. E-mail: [email protected]
ПЕЧНИКОВ ВЛАДИМИР СТЕПАНОВИЧ - кандидат физико-математических наук, доцент кафедры физики Школы естественных наук (Дальневосточный федеральный университет, Владивосток). Суханова ул., 8, Владивосток, 690950. E-mail: [email protected]
КЕН-ИЧИ ИТАКУРА - профессор департамента компьютерных наук и инженерных систем (Муроранский технологический институт, Япония). 27-1 Мизумото, Муроран 050-8585, Япония. E-mail: [email protected]
Термомагнитный анализ угольных образцов с целью оценки разрешающей способности геомагнитного метода для мониторинга зоны горения
Наиболее важной проблемой дальнейшего развития технологии термохимической переработки угольных пластов является мониторинг продвижения огневого забоя в реальном времени. Применяемые в настоящее время методы контроля огневого забоя являются дорогостоящими и технически сложными.
В процессе термического воздействия угольная масса и ее минеральная составляющая претерпевают значительные термомагнитные преобразования, что позволяет предположить целесообразность применения магниторазведки для дистанционного мониторинга развития огневого фронта по простиранию пласта в реальном времени. Для уточнения данного предположения на лабораторной базе Дальневосточного федерального университета были выполнены исследования закономерностей магнитных свойств угля в процессе их термической деструкции. Для обоснования разрешающей способности методов магнитометрии для мониторинга продвижения огневого забоя необходимо экспериментально оценить закономерности изменения магнитных свойств угольных образцов под действием высоких температур. Полученные результаты основывались на теоретическом анализе и лабораторных измерениях. Результаты измерения магнитного момента в постоянном поле при различной температуре нагрева угольных образцов Ургальского каменноугольного месторождения Буреинского бассейна с использованием вибромагнитометра и представлены в статье. При нагреве угольных образцов формируется термоостаточная намагниченность, и магнитные характеристики угля изменяются от слабомагнитных до ферромагнитных. Парамагнитный пирит, присутствующий в угольной массе, под действием высоких температур преобразуется в магнетит, присутствие которого даже в малых количествах значительно увеличивает магнитные свойства угля. Следовательно, магнитометрия может рассматривать как возможный геофизический инструмент мониторинга зоны продвижения огневого забоя в реальном времени.
Ключевые слова: уголь, лабораторный эксперимент, угольные образцы, магнитные изменения, термическая активность, термомагнитные преобразования.
