Table of contents

Preface

Dear Ladies and Gentlemen,

Between 19^th and 21^st of June 2017 in Andrychów (Poland) took place the national conference entitled 'Role of Polish coal in the national and European energy sector'. The conference gathered over 120 participants and among them major figures from the mining and energy sector in Poland both from academia and industry. Poland with its largest hard coal mining reserves in European Union struggles with carbon emission limits which in the near future will cause a significant problem for the energy sector and as a consequence – to the mining industry. This meeting was a place of exchange of ideas and views on the future of energy and coal industry in Poland. The following subjects were within the scope of this meeting:

• Brown and hard coal sector market analysis.

• Energy market analysis.

• Mining and energy sector development scenarios for Poland.

• Mining and energy production costs.

• Health and safety in mining industry.

• Modern methods of power generation from coal.

• Coal in the heating sector.

• Energy storage.

• Carbon capture and storage.

The conference series is a result of selection of the most important articles. All articles were peer reviewed through process administrated by the Editors.

All papers published in this volume of IOP Conference Series: Materials Science and Engineering have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Polish energy sector is facing a number of challenges, in particular as regards the reconstruction of production potential, diversification of energy sources, environmental issues, adequate fuels supplies and other. Mandatory implementation of Europe 2020 strategy in terms of "3x20" targets (20% reduction of greenhouse gases, 20% of energy from renewable sources, and 20% increase of efficiency in energy production) requires fast decision, which have to be coordinated with energetic safety issues, increasing demands for electric energy, and other factors. In Poland almost 80% of power is installed in coal fired power plants and energy from hard coals is relatively less expensive than from other sources, especially renewable. The most of renewable energy sources power plants are unable to generate power in amounts which can be competitive with coal fires power stations and are highly expensive, what leads o high prices of electric energy. Alternatively, new generation of coal fired coal power plants is able to significantly increase efficiency, reduce carbon dioxide emission, and generate less expensive electric power in amounts adequate to the demands of a country.

National energy security is of fundamental importance for economic development of a country. To ensure such safety energy raw material, also called primary energy sources, are necessary. Currently in Poland primary energy sources include mainly fossil fuels, such as hard coal, brown coal, natural gas and crude oil. Other sources, e.g. renewable energy sources account for c. 15% in the energy mix. Primary energy sources are used to produce mainly electricity, which is considered as the cleanest form of energy. Poland does not have, unfortunately, sufficient energy sources and is forced to import some of them, mainly natural gas and crude oil. The article presents an insightful analysis of energy raw material reserves possessed by Poland and their structure taking account of the requirements applicable in the European Union, in particular, those related to environmental protection. The article also describes demand for electricity now and in the perspective of 2030. Primary energy sources necessary for its production have also been given. The article also includes the possibilities for the use of renewable energy sources in Poland, however, climatic conditions there are not are not particularly favourable to it. All the issues addressed in the article are summed up and ended with conclusions.

That aim of this paper is to compare trends in global, European use of coal with tendencies in Poland, one of heavy coal dependent countries. Polish power generation is unique among OECD countries, the share of both hard coal and lignite in power generation reaches 81% [1]. Climate policy of European Union is to phase out intensive greenhouse gases sectors, thus to transform Polish power generation into less carbon intensive. Although such policy is generally accepted in Poland, the paste and practically proposed regulation that excludes coal generation from capacity mechanisms, is considered as threat to energy security. Coal is the base for generation for one simple reason, abundant in European scale hard coal reserves and significant capacities in lignite. Natural gas reserves allow to supply about 1/3 of consumption, but prices and supplies dependent hitherto on contracts with GAZPROM did not allow to develop significant generation capacities. Renewable resources are limited, there is not much possibilities for hydro, wind and solar. Poland is also one of the countries of poor air quality, traditional coal based space heating systems plus obsolete car fleet generate vast emissions, especially during the winter. Only recently this became top priority of environmental authorities. This situation is subject to transformation, government, managers are aware that the role of coal needs to be decreased, but there are two main questions, the paste of transformation and the future energy mix. The paper attempts to answer the question whether the expected changes in Polish energy mix are comparable or differ from the global and European tendencies.

Poland's accession to the European Union has reduced the remnants of import barriers. Moreover, the consolidation and commercialization of the energy sector, the implementation of climate package elements and a whole host of other determinants have caused hard coal mining to begin functioning in a highly competitive market, and its negotiating position, as well as the possibility of survival, depends not only on the level of coal prices in international markets, but also on internal competition.

This paper discusses the position of power coal on international markets and presents some current problems concerning the functioning of particular segments of the hard coal market in the European Union and Poland in terms of opportunities and threats that are a result of climate and energy policy.

One of the ways to protect objects exposed to the influences of mining exploitation is establishing protective pillars for them. Properly determined pillar provides effective protection of the object for which it was established. Determining correct dimensions of a pillar requires taking into account contradictory requirements. Protection measures against the excessive influences of mining exploitation require designing the largest possible pillars, whereas economic requirements suggest a maximum reduction of the size of resources left in the pillar. This paper presents algorithms and programs developed for determining optimal dimensions of protective pillars for surface objects and shafts. The issue of designing a protective pillar was treated as a nonlinear programming task. The objective function are the resources left in a pillar while nonlinear limitations are the deformation values evoked by the mining exploitation. Resources in the pillar may be weighted e.g. by calorific value or by the inverse of output costs. The possibility of designing pillars of any polygon shape was taken into account. Because of the applied exploitation technologies the rectangular pillar shape should be considered more advantageous than the oval one, though it does not ensure the minimization of resources left in a pillar. In this article there is also presented a different approach to the design of protective pillars, which instead of fixing the pillar boundaries in subsequent seams, the length of longwall panels of the designed mining exploitation is limited in a way that ensures the effective protection of an object while maximizing the extraction ratio of the deposit.

Compressed Air Energy Storage (CAES) is one of the methods that can solve the problems with intermittency and unpredictability of renewable energy sources. The storage is charged by increasing air pressure with the use of electrically driven compressors, which convert the electric energy into potential energy. The pressurized air is stored in compressed air storage volumes (caverns, voids, porous structures etc.) of any kind and can then be released upon demand to generate electricity again by expansion of the air through an air turbine or gas turbine. Limited availability of salt caverns in Europe creates difficulties in the implementation of this concept on larger scale. This paper deals with underground storage part in CAES concept and lists benefits related to the storage of air in abandoned coal mines. Examples of natural gas storage in abandoned coal mines are given and compared with the compressed air storage. The study shows an example of coal mine volume calculation. The non-exhaustive list of problems and solutions associated with this idea is given in order to develop this concept at larger scale.

The article refers to methane presented in hard coal seams, which may pose a serious risk to workers, as evidenced by examples of incidents, and may also be a high energy source. That second issue concerns the possibility of obtaining methane from liquidated coal mines. There is discussed the current methodology for determination of methane resources from hard coal deposits. Methods of assessing methane emissions from hard coal deposits are given, including the degree of rock mass fracture, which is affected and not affected by mining. Additional criteria for methane recovery from the methane deposit are discussed by one example (of many types) of methane power generation equipment in the context of the estimation of potential viable resources. Finally, the concept of "methane resource exploitation from coal mine" refers to the potential for exploitation of the resource and the acquisition of methane for business purposes.

A range of preventive works has been presented based on the example of one of the exploited longwalls and the costs borne by the coal mine have been exhibited. Further, the paper presents the costs of preventive aerological practices conducted for the improvement of work safety, borne by one of the coal mining companies. The paper also includes the calculation of cost indices. Based on these cost indices, an analysis of costs of the applied aerological preventive practices was conducted for the longwalls driven in years 2014-2015 by one of the coal mining companies.

The article presents methods of calculating costs of workplace accidents incurred by an employer, and the influence of the number and severity of accidents on changes in the amount of accident insurance contribution paid by an employer within the framework of the social security system.

The situation in the hard coal industry in Poland is forcing the identification of effectual and practical indicators of the effectiveness of machinery and equipment. In the article, the authors discuss the possible use of the OEE indicator for the evaluation of production processes in hard-coal mines. In summary, recommendations are made to enable efficiency assessment of mining machinery using the OEE.

This article presents the results of studies regarding the physical properties of selected combustion by-products (CCPs) currently produced in the energy production industry. These properties have been compared with the requirements of the technologies applied in the Polish underground mines. The article gives special consideration to the application of the products in the hydraulic backfill technology. The possibility of using bottom-ashes and slags was considered. The amount of CCPs disposed in Polish hard coal mines is approximately 1.1 million Mg and the tendency is decreasing. In the past two years, approximately 100-150 thousand Mg of CCPs was used in the hydraulic backfill technology. The percentage of the fraction smaller than 0.1 mm is determining for the possibility of using a given type of CCPs in the backfill material. This practically excludes the possibility of using any fly ashes in that technology. In slags from conventional boilers and bottom ashes from fluidized bed boilers the fraction below 0.1 mm constitutes 25% of the total at maximum, which allows for their use in the materials used in hydraulic backfill as a component comprising from 30% to 60%, respectively. Slags (10 01 01) are characterized by the lack of bonding properties, which, in case of open backfill systems that are exposed to atmospheric conditions, constitutes an advantage in comparison to bottom ashes (10 01 24), which in turn definitely exhibit bonding properties. The solution of the problem of using bottom ashes is their supply and application on a current basis.

Polish hard coal mines commonly use hydromixtures in their fire prevention practices. The mixtures are usually prepared based on mass-produced power production wastes, namely the ashes resulting from power production [1]. Such hydromixtures are introduced to the caving area which is formed due to the advancement of a longwall. The first part of the article presents theoretical fundamentals of determining the parameters of gravitational hydraulic transport of water and ash hydromixtures used in the mining pipeline systems. Each hydromixture produced based on fine-grained wastes is characterized by specified rheological parameters that have a direct impact on the future flow parameters of a given pipeline system. Additionally, the gravitational character of the hydraulic transport generates certain limitations concerning the so-called correct hydraulic profile of the system in relation to the applied hydromixture characterized by required rheological parameters that should ensure safe flow at a correct efficiency [2]. The paper includes an example of a gravitational hydraulic transport system and an assessment of the correctness of its hydraulic profile as well as the assessment of the impact of rheological parameters of fine-grained hydromixtures (water and ash) produced based on laboratory tests, depending on the specified flow parameters (efficiency) of the hydromixture in the analyzed system.

This publication concerns the problems of occupational safety and health in hard coal mines, the basic elements of which are the mining hazards and the occupational risk. The work includes a comparative analysis of selected provisions of general and industry-specific law regarding the analysis of hazards and occupational risk assessment. Based on a critical analysis of legal requirements, basic assumptions regarding the practical guidelines for occupational risk assessment in underground coal mines have been proposed.

The paper presents the results of the conducted research using the questionnaire. Based on published categories of motives present in the work situation, 12 questionnaires were sent directly to the salvage miners' professional group. On the basis of the results obtained, 12 categories of importance of motives present in the life of the rescuer were proposed. After identifying the categories, a scheme of motives for the meaning of work in the life of the rescuer was proposed, which distinguishes six basic motives of the significance of the work of a lifeguard.

The article presents statistical data regarding the evacuation of miners affected by underground fire hazards. The data indicates that the hazard remains considerable. Due to the increasing lengths of escape routes, measures should be introduced in the longwall regions, which shall improve the safe evacuation of miners, especially in conditions of highly limited visibility or the lack thereof. Within the research project No. 12, entitled: 'The development of orientation systems and systems for signalling the direction of crew withdrawal for escape routes in longwall gates', which is a part of the Strategic Research Project entitled 'The improvement of work safety in mines' financed by the National Centre for Research and Development, a 'lifeline' was designed – that is, a measure that is very effective in the evacuation of staff. Subsequently, tests of time of passage were conducted in the 'Krupiński' coal mine in conditions of lack of visibility. The tests have confirmed the suitability of the 'lifeline' as the measure used for orientation towards the correct direction of evacuation, which increases the pace and the confidence while travelling through the escape route. The mean speed of passage through the heading with an upwards inclination of 11° was 22 m/min, while in case of a nearly horizontal longwall gate, it was 39 m/min.

This paper presents the characteristics of methane hazard and prevention undertaken in the N-6 longwall of seam 330/2 in "Krupiński" coal mine. On the basis of methane concentration measurements conducted with the use of telemetric system, time series of the average and maximum methane concentration at the outlet of the longwall area were generated. It was ascertained that they exhibit a strong autocorrelation. Based on a series of the average methane concentration, a time series of ventilation methane content was created and a total methane content was calculated with the use of methane flow rate measurements in the demethanization system. It was ascertained that dependence between methane concentration and output on the examined day and on the previous day is weak and also that the dependence between methane concentration and air flow rate is very weak. Dependencies between ventilation methane content, total methane content and demethanization efficiency were also investigated. Based on forecasting models [1] developed earlier by H. Badura, forecasts have been made to predict the average and maximum methane concentrations. The measured values f methane concentration show a high level of accordance with forecasted ones.