This paper presents R&D project of multi fuel concept (MFC) for future coal-based power plants, demonstrated on example of cofiring Middle-Bosnia brown coal with waste woody biomass and natural gas. Pulverised Combustion (PC) lab-scale furnace has been used for the cofiring tests, varying up to 20%w portion of biomass and up to 10%th portion of natural gas in the fuel mix. Tests were purposed to optimize the combustion temperature, air distribution, including Over Fire Air System (OFAS), fuel combination and fuel distribution, including reburning concept, as function of emissions and combustion efficiency estimated through the ash deposits behaviours and unburnt. Considering application of proposed MFC in case of TPP Kakanj unit 6 (118 MWe) set here as a referent power plant, temperature levels and fuel distributions for lowest emissions of CO2 and NOx were found during lab tests, provided that combustion efficiency is at an acceptable level. Derived research results yield input data for calculation sustainability indicators of MFC for the referent power plant, considering 6 fuel options - different combinations of coal, biomass and natural gas. Single criteria analysis and multicriteria sustainability assessment have been done, giving an advantage to the options of cofiring coal with woody biomass and natural gas in the case demonstrated.

Small modular district heating/cooling grids can be fed by different heat sources, including solar collectors, biomass systems and surplus heat sources (e.g. heat from industrial processes or biogas plants that is not yet used). Especially the combination of solar heating and biomass heating is a very promising strategy for smaller rural communities due to its contribution to security of supply, price stability, local economic development, local employment, etc. On the one hand, solar heating requires no fuel and on the other hand biomass heating can store energy and release it during winter when there is less solar heat available. Thereby, heat storage (buffer tanks for short-term storage and seasonal tanks/basins for long-term storage) needs to be integrated. With increasing shares of fluctuating renewable electricity production (PV, wind), the Power-to-Heat conversion through heat pumps can furthermore help to balance the power grid. The objective of the CoolHeating project, funded by the EU’s Horizon2020 programme, is to support the implementation of "small modular renewable heating and cooling grids" for communities in South-Eastern Europe.

This paper describes full lab-scale investigation of Middle-Bosnia coals launched to support selection an appropriate combustion technology and to support opti- mization of the boiler design. Tested mix of Middle-Bosnia brown coals is pro- jected coal for new co-generation power plant Kakanj Unit 8 (300-450 MWe), EP B&H electricity utility. The basic coal blend consisting of the coals Ka- kanj:Breza:Zenica at approximate mass ratio of 70:20:10 is low grade brown coal with very high percentage of ash - over 40%. Testing that coal in circulated fluidized bed combustion technique, performed at Ruhr-University Bohum and Doosan Lentjes GmbH, has shown its inconveniency for fluidized bed combustion technology, primarily due to the agglomeration problems. Tests of these coals in PFC (pulverized fuel combustion) technology have been performed in referent laboratory at Faculty of Mechanical Engineering of Sarajevo University, on a lab-scale PFC furnace, to provide reliable data for further analysis. The PFC tests results are fitted well with previously obtained results of the burning similar Bosnian coal blends in the PFC dry bottom furnace technique. Combination of the coals shares, the process temperature and the air combustion distribution for the lowest NOx and SO2 emissions was found in this work, provided that combus- tion efficiency and CO emissions are within very strict criteria, considering spe- cific settlement of lab-scale furnace. Sustainability assessment based on calcula- tion economic and environmental indicators, in combination with Low Cost Planning method, is used for optimization the power plant design. The results of the full lab-scale investigation will help in selection optimal Boiler design, to achieve sustainable energy system with high-efficient and clean combustion tech- nology applied for given coals.

Keywords:Energy efficiency, CO2 emission, coal-based power plants, decarbonisation. ABSTRACT This paper describes measures which are being undertaken by EPBiH power utility, largest public electricity utility in Bosnia and Herzegovina, to improve its energy efficiency and keep on the track of the European targets outlined in the EU strategic documents and laid down by new energy efficiency Directive 2012/27/EU. By modernization its existing power plants performed in last 10 years, EPBiH improved net efficiency and reduced its CO2 emission for 30% compared to 1990 levels. Plan till 2030 is further increasing the net efficiency up to 40.2%. With introducing Energy Management System, energy efficiency has been involved into all sectors of the company; from coalmines, generation and distribution, to the energy supply, to comply the business model with EU energy efficiency targets and legislation.

This paper presents the findings of research into cofiring two Bosnian cola types, brown coal and lignite, with woody biomass, in this case spruce sawdust. The aim of the research was to find the optimal blend of coal and sawdust that may be substituted for 100% coal in large coal-fired power stations in Bosnia and Herzegovina. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial runs on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated and entrained pulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and 80:20% by weight were tested. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided the blend volume was 7% by weight sawdust and the process temperature did not exceed 1250oC. It was observed that in addition to the nitrogen content in the co-fired blend, the volatile content and particle size distribution of the mixture also influenced the level of NOx emissions. The brown coal-sawdust blend generated a further reduction of SO2 due to the higher sulphur capture rate than for coal alone. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station, Unit 5 (110 MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of brown coal was replaced with sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%wt of sawdust in combination with coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome.

This paper deals with optimization of coal combustion conditions to support selection a sustainable combustion technology and an optimal furnace and boiler design. A methodology for optimization of coal combustion conditions is proposed and demonstrated on the example of Bosnian coals. The properties of Bosnian coals vary widely from one coal basin to the next, even between coal mines within the same basin. Very high percentage of ash (particularly in Bosnian brown coal) makes clear certain differences between Bosnian coal types and other world coal types, providing a strong argument for investigating specific problems related to the combustion of Bosnian coals, as well as ways to improve their combustion behavior. In this work, options of the referent energy system (boiler) with different process temperatures, corresponding to the different combustion technologies; pulverised fuel combustion (slag tap or dry bottom furnace) and fluidized bed combustion, are under consideration for the coals tested. Sustainability assessment, based on calculation economic and environment indicators, in combination with common low cost planning method, is used for the optimization. The total costs in the lifetime are presented by General index of total costs, calculated on the base of agglomeration of basic economic indicators and the economic indicators derived from environmental indicators. So, proposed methodology is based on identification of those combustion technologies and combustion conditions for coals tested for which the total costs in lifetime of the system under consideration are lowest, provided that all environmental issues of the energy system is fulfilled during the lifetime. Inputs for calculation of the sustainability indicators are provided by the measurements on an experimental furnace with possibility of infinite variation of process temperature, supported by good praxis from the power plants which use the fuels tested and by thermal calculations of the different options (different temperature in the boiler furnace) of the referent energy system.