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UNDERGROUND COAL GASIFICATION (UCG): AN INNOVATIVE TECHNOLOGY FOR EMISSIONS REDUCTION AND ENVIRONMENTAL MANAGEMENT

07 June 2015
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Authors: Дарья Алонцева
Category: Energy

Introduction

Underground coal gasification (UCG) technique, which is a method of converting deep-seam coal into a combustible fuel used for power generation, as a feedstock for the manufacturing of hydrogen, chemicals or transport fuels. Underground coal gasification (UCG) has significant advantages and can be categorized as a clean coal technology to produce syngas in-situ [1]. However, it suffers from lack of a comprehensive understanding of the process because it takes place deep underground and consists of multi-phenomena. Hence, UCG modelling can be employed to investigate different aspects of this process. While small scale processes can be mechanistically informative, large scale processes may behave quite differently and mechanistic description for them is not formative [1,2]. Underground coal gasification (UCG) is a potential method for economically recovering stored energy in coal formations, especially from coal deposits that cannot be mined using conventional methods. A well-developed UCG technology has the potential to increase the world’s coal reserve substantially [3], it also is an environmentally friendly technology [4].

The goal of this research is to increase our understanding of the key physical processes and the capability to predict with high level of confidence and certainty the underground processes involved in UCG.

Research objectives:

-  This work will assess physical data which are important for processing and making the modelling more robust. As a result, literary and patent search will be held, demonstration sites will be selected for the study and ​​sampling will be made (samples of Kazakh coal);

  - to identify the most valid and reliable in terms of modeling physical and chemical phenomena that affect the dynamics of the UCG reaction. As a result, most modern methods of analytical study will be used to carry out a comprehensive analysis of the specific features of the structure and some properties of coal samples, as well as the study of the geological structure of the selected demonstration sites;

-  to develop a model of the physical and chemical processes that accompany the UCG process against the established features of the structure and properties of coal and geology sites. This will result in a mathematical model of the UCG process in relation to a particular field;

 - to collect data on the demonstration sites and develop a database for the UCG operating model. This will be used to create a unique database for the computer simulation of the UCG process at demonstration sites;

 - to carry out testing and validation of the model using the obtained data in real time mode. This will try out the model applied to actual Kazakhstan deposits.

- to perform the analysis of the results and the selection of the optimum UCG process conditions for maximum performance and reduced emissions. As a result, we will provide the scientific bases of an innovative UCG technology with reduced emissions and environmental management;

The study in the Project framework will lay a necessary and scientific theoretical foundation for further quantitatively studying the process of underground coal gasification and forecasting the change patterns in the scale of the Republic of Kazakhstan.

 

Description of Innovative Technology UCG for Emissions Reduction and Environmental Management in Frame of Joint Research Project

The world is facing a major challenge to meet future energy supplies. Coal continues to be the world’s leading source of energy, with coal-fired power accounting for about 30% of the electricity produced in the world. With global energy demand projected to rise by up to 55% by 2030 (International Energy Agency, 2010) [5], fossil fuels will continue to hold a dominant share of the world’s energy mix with the demand for coal projected to 70% in absolute terms by 2030 [6]. With fossil fuels remaining the main source of energy for decades to come, reducing carbon dioxide (CO2) emissions using carbon capture and storage (CCS) technology is seen as one of the best solutions in combating climate change [7].

The latest technologies for the clean use of coal will help to meet the challenges of our energy future. In the context of Kazakhstan, environmental pollution from coal is well recognised and recently, the mining and the use of coal has been identified as harmful to nature and the environment and as a consequence [8], the Kazakhstan President Nursultan Nazarbayev has instructed its government to develop a plan through 2050 that would result in at least 50% of the country’s electricity being generated from renewable resources [9].

The Republic of Kazakhstan has the second largest coal  reserves as well as the second largest oil production among the former Soviet republics after Russia with estimated total liquids production was 1.64 million barrels per day (bbl/d) in 2013 (US, Energy Information Administration, 2013) [6]. According to US, Energy Information Administration, 2013), Kazakhstan consumed a total of 2.3 quadrillion Btu of energy in 2010, with coal accounting for the largest share of energy consumed at 64%, followed by oil and natural gas at 19% and 14%, respectively [7]. In addition, the vast majority of Kazakhstan's power generation comes from coal-fired power plants, concentrated near the coal producing regions (e.g., anthracite reserves from Karaganda, Ekibastuz and Tengiz-Korzhankolskogo basins and the brown coal which is concentrated mainly in the Maikuben basins) [10].

According to IHS (2013) [10], Kazakhstan's total installed generating capacity was approximately 19.5 gigawatts (GW) in 2011, 85% of which was coal-fired power and the remaining 15% was hydropower. As of 2011, Kazakhstan's net generation was totalled approximately 81.2 billion kilowatthours (kWh) of electricity (Kazakhstan Geological Committee) [11]. Figure 1 shows the typical Kazakhstan’s energy consumption by fuels (2010) showing that 64% is from coal.

Furthermore, the Republic of Kazakhstan has become  the tenth largest coal producer in the world  over the past recent decades. It is significant that in the East Kazakhstan region (EKR), where the execution of this project is planned, 1052.8 mln tons of balance coal are concentrated [12], i.e., East Kazakhstan is on the 4th place in Kazakhstan on coal resources after Pavlodar, Karaganda and Aktobe regions. The expected coal resource in East Kazakhstan is 1.6 billion tons [12], i.e. East Kazakhstan takes the 5th place among the regions of the Republic of Kazakhstan, which makes the project studies in the region attractive and justified. Kazakhstan has steadily increased coal production levels to satisfy the growing energy demand, producing 126 Mt of coal in 2012 [11].

Figure 1 - Kazakhstan’s Energy consumption by fuels, 2010 [10]. At the current rate of production, Kazakhstan has enough coal for the next 250 years. In terms of production, the country occupies eighth place with mines currently produce a little more than 120 million metric tons per year (mtpy) of which 97 million mt are consumed domestically and 22 million mt are exported. Currently, Kazakhstan has 4% of known world reserves with 33.6 Bt of proven coal reserves as at the end of 2012. Among the countries of the Commonwealth of Independent States (CIS), Kazakhstan occupies third place in terms of largest reserves and first place in terms of coal production per capita [5,6]. At present, the coal industry provides 78% of the electricity in the Republic of Kazakhstan, almost 100% of coke production and it fully meets the needs of the domestic sector.  Underground coal gasification (UCG) offers great promise to revolutionise the way coal is used and consumed. Figure 2 below shows the schematic of the basics if the underground coal gasification technology.

A basic UCG process consists of two boreholes drilled into a coal seam some distance apart, one for the injection of oxidants and the other for the production of synthetic gas (syngas). Depending on the deliverability of the coal seam mainly to gas flow, the distance between the wells may need human interference to increase the connectivity of the injection and production points. This can be done using well developed methods from the oil and gas industry, such as directional drilling, hydraulic fracturing, and reverse combustion.

 

 

 

Figure.2 -  Schematic of underground coal gasification basics. The development of UCG as part of clean coal technologies is essential, enabling the Republic of Kazakhstan and the UK to remain competitive with other nations that are also developing these technologies. When one looks globally, the estimate of the reserve is in excess of 800 billion tonnes and here reserve means coal accessible with existing technology and current plans for extraction. The potential impact of clean coal technology on a global scale cannot be overstated. The present reserves-to production ratio based on conventional mining is 122 years [12]. This would only increase if humankind was able to exploit more coal and do it cleanly.  To access these reserves without significant environmental impact requires clean coal technology. 

This research project will take forward the Republic of Kazakhstan’s response to the challenge from fossil-fuel power plants at a time when it has a significant need to replace its ageing power generation assets. The benefit of this research project to the Republic of Kazakhstan economy is overwhelming and it will always help the Republic of Kazakhstan to minimise its dependence on imported oil and gas.

Additionally, in an ever increasingly energy hungry global economy whose emerging environmental conscience continues to steer generation technologies away from traditional carbon intensive means, forecast increases in demand for clean energy fuels such as uranium are extremely exciting for uranium rich countries such as Kazakhstan. Kazakhstan’s mining industry would benefit in particular from improving procedures to prevent contamination from tailings, waste rock dumps and smelters. The UCG technology development within the framework of this project also contributes to the ecologically clean intensification of coal development and the improvement of measures to protect the environment.

The project is aimed at using by the Republic of Kazakhstan of the most advanced integrated technologies of materials research and modeling of reaction mechanisms and process dynamics of the reaction of underground coal gasification, providing insight into and forecasting the key UCG processes. This work focuses on the acceleration of technological progress and the development of UCG technology in Kazakhstan through the use of highly developed and advanced modeling techniques.

The scientific novelty of the project lies in the fact that for the first time:

- will  carry out a comprehensive analysis of structural features (at the nanoscale) and some properties of the Kazakh coal samples, as well as the study of the geological structure of the selected demonstration areas, on the basis of which will be offered models of the physical and chemical processes that accompany UCG the process, taking into account the established features of coal and sites;

- a database for the computer simulation of UCG process applied to specific fields in Kazakhstan, taking into account their unique characteristics, will be formed;

- the UCG process model applied to actual deposits in Kazakhstan will be tried  out;

- on the basis of mathematical modeling the regularities of the UCG process will be established, and its optimum conditions for maximum performance and reduced emissions will be recommended.

The studies carried out within the Project will provide the necessary scientific and theoretical foundation for further quantitative study of the process of underground coal gasification and forecasting models of its change in the scale of the Republic of Kazakhstan.

The main differences of the technology being developed from existing analogues:

- the use of mathematical computer modeling allows predicting the key UCG processes;

- the modeled is as applied to specific fields in Kazakhstan, taking into account their unique features. The use of such technology is very specific, and requires a careful study of the material features and geology of the site. It is not possible to simply extrapolate the data obtained by calculations of another model, it is necessary to develop an individual model with the account of a specific material and site, which defines the character of the process;

- the whole UCG process will be environmentally clean. While UCG may cause surface subsidence in shallow tests, overall it presents fewer negative environmental effects than other known ways of coal deposit development.

High-technology UCG methods have a steady and ever growing market demand for new high technology and environmentally-friendly technologies in the Republic of Kazakhstan and abroad. The demand for the technology being developed across the Republic of Kazakhstan is defined as the prospect of growth in exports of energy sources, and the orientation of Kazakhstan at the “green economy.” We offer basic research in the field of new at the global level clean UCG technologies, and at the same time further substantiate the possibility of applied use of the developed technology.

Besides accelerating the technical progress in Kazakhstan, the project will actively involve young people, increase the capacity of Kazakhstan science that provides the solution of the three main objectives set by the President of the Republic of Kazakhstan in his message of January 17, 2014 to the people of the Republic of Kazakhstan [13].  

Basic research methods: mathematical computer modeling, High-Resolution Transmission Electron microscopy (HR-TEM)/ Energy Dispersion Spectroscopy (EDS) analysis, and Scanning Electron Microscopy (SEM)/ Energy Dispersion Spectroscopy (EDS), STEM, X-ray diffraction (XRD), light microscopy, mass spectrometry, in-situ experiment testing. Parallel application of the most modern analytical methods like nano-mineralogy studies using an integrated application of advanced characterisation techniques such as mathematical computer modeling will provide increased accuracy, reliability and predictability of the results of the study.

Mathematical modelling of processes: in the developing and exploration of new research, experiment is undoubtedly is a very important means, however, recently the combination of experiment, numerical simulation and modelling has gained popularity [14-16]. Latest modelling software will be purchased to carry out the modelling aspect of this work which will include advanced, steady and dynamic states modelling of the underground processes. Basic and advanced equilibrium together with reaction model will be carried out in the modelling experiments. The overall approach to mathematical modelling will be based on comprehensive numerical models using the fundamental equations of mass/energy balance, chemical kinetics, etc. The proposed research work will include the experimental validation of the models, generally through the data collected from the existing field/pilot scale-field testing. The results of the simulation and modelling studies will provide, for the first time, a mechanistic subsurface gasification at various depths into underground coal gasification models and for assessing the effects of predicted changes in gasification conditions/parameters on syngas quality and quantity.

During the project implementation, there are two kinds of risks associated with the research work:

• breakdown of the main equipment;

• the human factor - incapability of participation of one or more of the leading researchers due to unforeseen circumstances.

In case of unforeseen failure of the main equipment the research group has at its disposal reserve equipment close to the characteristics of the basic equipment to conduct the study. In addition, the policy of the organization provides the opportunity to use the equipment of other divisions.

The research group was formed on the principle of interchangeability. The qualifications of the participants allow others to replace an absent participant. In addition, some reserve is foreseen in case of replacement of a responsible officer.

 In the course of the project scientific ethics will be respected; it will be provided by authored publications and certificates, following the principles of scientific novelty and validity of the proposed ideas and technical solutions. New scientific and technological solutions will be protected by patents and copyright certificates. All ethical issues will be resolved in the course of the project according to ethical and legal standards. All significant results of the research project will be presented annually at conferences on the theme of the project and published in the form of research papers. Public presentations of the project results exclude the possibility of plagiarism and false co-authorship. Research in the framework of the project is implemented by the research team of employees of one structural unit of a large organization that excludes the use by individual participants of data and findings of the study without the consent of the other members.

According to the executive organization’s system, the results of work of the research group belong to the organization. When publishing the results the authorship is distributed in proportion to the contribution of the researcher in the task solving, and the reference to the grant with the indication of its number is indicated.

Key international communications, participation in the project of foreign scientists: Dr Liadi (Kola) Mudashiru is a research manager of the Project. Dr Mudashiru  is a Research Fellow at Newcastle University, UK where he received his PhD (in geochemistry) and MSc (in Environmental Biogeochemistry) degrees respectively with his Executive MBA. Dr Mudashiru is an international research scientist with international reputation having worked in Canada, China, the Netherlands, Australia, India and in the UK (where he has lived for over a decade). Dr Mudashiru has a solid background in geochemistry with distinguished track record of academic excellence and achievements. He had over five years of research experience as a young researcher working in multidisciplinary research environment involving laboratory experiments, conventional and unconventional energy, climate change, reservoir modelling and environment. Dr. Mudashiru is a prolific writer with over 20 publications, contributions to two published books, numerous honours /awards for research and academic excellence and achievements and over 50 conference presentations as an invited/a guest speaker. His research interests include coal chemistry, sustainable use of coal, underground coal gasification technology, coal to liquid, coal to gas, fossil fuels and unconventional energy recovery. Dr Mudashiru’s scientific research has been concentrated on processes of energy production from unconventional resources; clean use of fossil fuels [4] underground coal gasification [1, 2, 17] Chemical reactions, equation of states, compositional, kinetics, thermodynamics, CO2 sequestration and fingerprinting; CO2 sequestration in saline aquifers, depleted gas reservoirs and coal seams; Environmental chemistry and geochemistry [18-21]; Computational fluid dynamics, geochemical and environmental modelling; Laboratory, experimental and instrumentation, structural elucidation and characterization using a wide range of analytical facilities including spectroscopic and microscopic techniques. His official website: http://www.ncl.ac.uk/sustainability/staff/profile/liadi.mudashiru

Dr Grigorios Itskos has earned his PhD (2012) at the National Technical University of Athens/School of Chemical Engineering. He is a young researcher with particular expertise in coal fly ash science & utilization engineering and coal/biomass co-firing & gasification, with 16 ISI-journal publications and more than 200 citations (Scopus) in this field over the last 5 years, from them the relative publications [22-26]. He has been Research Fellow at the Centre for Research and Technology Hellas (CERTH) for 7 years and during his tenure there he has participated in multiple EU-, SME-, and industrially funded projects, mainly referring to solid fuels science & technology. His current h-index = 9 (Scopus) with a clear upward potential. As of January 2014 he serves NU/School of Engineering as Assistant Professor at the School of Engineering.

 

Expected Results

Under this project:

- a comprehensive nano-mineralogical analysis of samples of Kazakh coal, the geological structure of the selected demonstration sites will be conducted and a unique database will be established;

- models of physical and chemical processes of UCG with regard to specific structure and properties of coal and geology sites will be developed;

- a mathematical model of the UCG process for a particular field will be created and tested;

- on the basis of mathematical modeling of the UCG optimal process conditions for maximum performance and reduced emissions will be determined;

- scientific basis for innovative UCG with reduced emissions and environmental management will be developed; and the methodology patent application (European) will be made.

The study within the Project will provide the necessary scientific and theoretical foundation for further quantitative study of the process of underground coal gasification and forecasting models of its change in the scale of the Republic of Kazakhstan, as well as allow Kazakhstan to develop innovative, efficient and environmentally friendly technologies, as opposed to traditional aging technologies for fossil fuel extraction.

The results and findings of the project will be widely presented and thoroughly discussed at conferences and exhibitions. Participation in prestigious conferences will allow testing the results of the research project at the international level, acquiring new scientific connections, publishing research results in journals with impact factors, as only the papers presented at the conference are accepted for consideration in a particular journal.

Participation in prestigious international conferences and exhibitions, publications in leading foreign and domestic journals provides a wide dissemination of the results of the Project among potential users, a community of scholars and the general public.

We also recognise that this work may have direct relevance to a number of policy issues and organisations including the Kazakhstan Ministry of Science and Technology, Ministry of Oil and Gas, Department of Energy and Climate Change (DECC), Committee on Climate Change (CCC), the Coal Authority, Environment Agency, European Commissions, SET-energy-plan, International Energy Agency (IEA) and energy providers. We will therefore, actively disseminate our work through appropriate media channels and to relevant policy organisations and stakeholders. We will also work with the Technology Transfer Office located in the Business Directorate at the University of EKSTU to identify paths to future commercialisation of any potential commercial opportunity.  Upon completion of the project we plan to apply for National Agency for Technology and Development for the commercialization of this technology

Participation in the Project of Dr Liadi Mudashiru, one of the leading scientists in the UK (in the field of UCG research), as a co-manager makes it particularly attractive. The focus of the Project is the development of joint fundamental research with great applied potential of the technology being developed. Thus, we come to the world level of scientific development strategically planning its implementation not only in Kazakhstan, but also at  the EU level by increasing the presence and visibility of Kazakhstan scientists at international level. The implementation of the Project will also provide an opportunity for young researchers from the Republic of Kazakhstan to undergo research trainings in the UK, and have consultations with  world-renowned scientists on their PhD projects. Therefore, the implementation of the Project will make a significant contribution to the implementation of the "Kazakhstan-2050" Strategy and the state program of industrial-innovative development of Kazakhstan for 2015-2019 in the field of education and science, ensuring the acquisition of international experience in the preparation of highly qualified and integrated into the world labor market of the engineering staff; acquaintance, exchange views and experiences with the developers of innovative technologies; presentation and search for potential partners to implement own achievements in the educational and research activities.

Through this joint research funding application between Newcastle University and the University, (if successful), participating Kazakhstan researchers will:

  • Gain access to state-of-the-art research, analytical and computational resources;
  • Be able to consult and network with a wide range of academics across many relevant disciplines with potential for future research collaboration(s);
  • Access other stake-holders in complementary business areas;
  • Utilise Newcastle University’s market research, and technology transfer services;
  • Have a fast-track to consortia building and grant applications;
  • Develop a range of products including technologies in modelling and management of sub-surface processes and products, methodologies for measurement, monitoring and verification of subsurface processes;
  • Strengthen research collaboration and partnership with international reputable university;
  • Library of information about UK coal (characteristics, quality & quantity) and the potential use of syngas for full scale commercial operation of UCG-CCS in the NE England-(preliminary findings from the "Project Ramsay") funded by the One North East- this information is worth- £100K;
  • Access to the latest state-of-the-art modelling and simulation softwares for the risk assessment of the potential environmental impact of UCG with CCS (output from a PhD research work). This information is worth- £75K;
  • Access to modern and brand new "Thermal Laboratory" equipped with the state-of-the-art facilities for syngas analysis, CO2 emissions monitoring and profiling. This is access to facility suitable for this project worth-£100K.
  • The funding (if successful) will make the Republic of Kazakhstan a world leader in the clean coal research;
  • It will take forward the Kazakhstan President’s initiative on clean energy;
  • It will strengthen the Kazakhstan interactions with UK academics and researchers.

 

The importance of developing clean coal technologies to accelerate and promote business exploitation of these technologies and its potential contributions to the local, regional, national and international economy cannot be underestimated. Kazakhstan will need to quickly develop these opportunities in order to remain competitive with this sector and to militate against climate change phenomenon.

The insight gained through this research work will broaden and widen our knowledge and expertise in the field and lead to improved understanding of clean coal technologies such as UCG and generate experimental data leading to new process insight and commercial scale operations.

Potential beneficiaries: mining companies of Kazakhstan, relevant Kazakhstan ministries, the United Kingdom, and the International Energy Agency (IEA) etc.

 

Acknowledgment

This research is funded for 2015-2017 by the Scientific Committee of the Ministry of Education and Science of the Republic of Kazakhstan for the project “Underground Coal Gasification (UCG): An Innovative Technology for Emissions Reduction and Environmental Management”.

 

Bibliography and references
1 Roddy, D.J., and Mudashiru, L.K. Underground coal gasification with CCS // Cambridge: Royal Society of Chemistry. – 2009. 2 Mudashiru, L.K., and Roddy, D.J. Project Ramsay: Potential for Underground Coal Gasification with Carbon Capture and Storage (UCG-CCS) in North East England, UK // Proceedings of the International Pittsburgh Coal Conference. – USA, 2009. 3 Younger, PL., Roddy, DJ., and Gonzalez, G. King Coal: Restoring the monarchy by underground coal gasification coupled to CSS // In: Seventh Petroleum Geology Conference. – 2009. 4 Kola, L.Mudashiru. Keynote Seminar on: Carbon Capture and Storage: Reducing emissions from power generation // Proceedings of the Westminster Energy Environment and Transport Forum (WEET). – London, 2009. – № 1 (2009). – P. 64. 5 Key World Energy Statistics // International Energy Agency. – 2012. 6 World Coal Statistics // International Energy Agency. – 2013. 7 BP Statistical Review of World Energy // British Petroleum (BP). – 2013. 8 Country profile: Kazakhstan // U.S. Energy Information Administration (IEA). – 2013. 9 “Kazakhstan - 2050” Strategy [Electronic resource]. – Access mode: http://strategy2050.kz/ru/page/gosprog4/ 10 Kazakhstan Prepares to Grow Coal Production // Coal Age News. – 2013. 11 Prospects for coal and clean coal technologies in Kazakhstan // IEA Clean Coal Centre. – 2011. 12 The concept of the development of the coal industry of the Republic of Kazakhstan for the period until 2020 (in Russian). – 2008. - № 644, (June 28). 13 Vorotnikov, V. Emerging CIS nation uses coal to provide affordable power to its citizens while exporting coking coal to neighbouring markets. – 2013. 14 “Kazakhstan's Way - 2050: The common goal, common interests, common future” Message of Nursultan Nazarbayev, the President of the Republic of Kazakhstan to the people of Kazakhstan of January 17, 2014 [Electronic resource]. – Access mode: http://www.akorda.kz/en/category/gos_programmi_razvitiya 15 Yang, L., and Liu, S. Numerical simulation on heat and mass transfer in the process of underground coal gasification // Numerical Heat Transfer. – 2005. – P. 437-557. 16 Paterson, L. et al. Numerical modelling of pressure and temperature profiles including phase transitions in carbon dioxide wells // In: Society of Petroleum Engineers Technical Conference. – 2008. 17 Yang, L. Study on the model experiment and numerical simulation for underground coal gasification // Fuel. – 2004. – P. 573-585. 18 Mudashiru, L.K., and Roddy, D.J. Project Ramsay: Potential for Underground Coal Gasification with Carbon Capture and Storage (UCG-CCS) in North East England, UK [Electronic resource] // In: Twenty-Sixth Annual International Pittsburgh Coal Conference. – 2009. – Access mode: http://www.engr.pitt.edu/pcc/2009%20Past%20Conferences.html 19 Mudashiru, L.K, Aplin, A.C., and Horrocks, B.R. Voltammetric methods for the determination of dissolved, colloidal and particulate iron in mine-water discharge // The Analyst. - 2009. 20 Mudashiru, Liadi K., Horrocks, Benjamin R., Aplin, Andrew C. Importance of colloidal iron in mine waters revealed by differential pulse voltammetry // Geochimica et Cosmochimica Acta. – 2008. - № 72(12). – A659. 21 Mudashiru, L.K., Horrocks, B.R., Aplin, A.C. Importance of colloidal iron in mine waters revealed by differential pulse voltammetry // In: 8th Annual V M Goldschmidt Conference, Date: JUL. – Vancouver, Canada, 2008. 22 Itskos, G., et al. Characterization of solid residues from high temperature gasification of olive kernel // Waste and Biomass Valorization. – 2014. - № 5. – P.893-901. 23 Itskos, G., et al. A comparative characterization study of Ca-looping natural sorbents // Applied Energy. – 2013. – № 108. – P.373–382. 24 Itskos, G., et al. The outcomes of the 2-decade monthly monitoring of fly ash-composition in a lignite-fired power station // Waste and Biomass Valorization. – 2010. - №1 (4). – P.431-437. 25 Itskos, G., et al. Size fraction characterization of highly-calcareous fly ash // Fuel Processing Technology. – 2010. - № 91 (11). – P.1558-1563. 26 Itskos, G., et al. Comparative uptake study of toxic elements from aquatic media by the different particle size fractions of fly ash // Journal of Hazardous Materials. – 2010. - №183 (1-3). – P. 787-792.

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