The combustion rate of large coal particles in a fluidized bed is to a large extent controlled by the external diffusion. This rate will depend on the particle diameter. There are several processes that affect this diameter: the combustion process itself; attrition; fragmentation; and swelling. The last two processes can cause large diameter changes in a relatively short period, mainly during devolatilization. The experiments reported in this paper are aimed at finding a simple relationship between some properties of the parent coal particles, and the fragmentation and swelling during devolatilization.

The combination of temperature gradient and volatile release has been identified as the main cause for primary fragmentation (breakage of fuel particles during devolatilization). A mathematical model of the primary fragmentation in a fluidized bed has been developed, incorporating both causes. It takes into account the type of the coal, size of the coal particles, and the fluidized bed temperature. The model simulates fragmentation of a batch of coal particles. For each particle in the batch, the model follows propagation and merging of cracks, starting from randomly distributed pre-existing pores, leading to possible breakage of the particle. The model calculates volume of the fragmented particles and volume diameters, classifying them into size classes. For each size class, the number of particles is counted, and the mass fraction is calculated. The results are the distribution of mass and number of char particles after the devolatilization and the primary fragmentation parameters.

Although the countries of the Western Balkans are mostly electrified, there are still regions which do not have access to the electricity network or where the network capacity is insufficient. For the most part such areas are under special care of the state (i. e. underdeveloped, devastated by war, depopulated), on islands or in mountainous regions. Since the decentralized energy generation covers a broad range of technologies, including many renewable energy technologies that provide small-scale power at sites close to the users, such concept could be of interest for these locations. This paper identifies the areas in Western Balkans where such systems could be applied. Consideration is given to geographical locations as well as possible applications. Wind, hydro, solar photovoltaic, and biomass conversion systems were taken into consideration. Since the renewable energy sources data for Western Balkans region are rather scarce, the intention was to give a survey of the present situation and an estimate of future potential for decentralized energy generation based on renewable energy sources. The decentralized energy generation based on renewable energy sources in Western Balkans will find its niche easier for the users that will produce electricity for their own needs and for the users located in remote rural areas (off-grid applications).

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There is a growing need for the use of alternative and renewable energy sources, in terms of sustainable energy development. One of the potentially biggest renewable energy sources in Serbia is agricultural biomass, quite available and cheap at the moment. For many years, the Vinca Institute of Nuclear Sciences, Laboratory for Thermal Engineering and Energy, has been working on the development of clean technologies for efficient utilization of biomass, and as a result utilities and equipment (boilers and furnaces) with wide range of use have been developed. These devices have complete combustion control and primarily burn baled biomass with no adequate utilization. The results of the development and of the tests of an experimental demonstrativel boiler burning small bales of soya straw have been presented in this paper. In the boiler, the combustion has been organized on the 'cigarette burning' principle, and fuel feeding has been done by gravity. The technical scheme of the boiler and the results of preliminary tests carried out in real operation conditions have been given.

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Harmonization of environmental protection and the growing energy needs of modern society promote the biomass application as a replacement for fossil fuels and a viable option to mitigate the greenhouse gas emissions. For domestic conditions this is particularly important as more than 60% of renewables belongs to biomass. Beside numerous benefits of using biomass for energy purposes, there are certain drawbacks, one of which is a possible high emission of NO x during the combustion of these fuels. The paper presents the results of the experiments with multiple biomass types (soybean straw, cornstalk, grain biomass, sunflower oil, glycerin and paper sludge), using different combustion technologies (fluidized bed and cigarette combustion), with emphasis on the emission of NO x in the exhaust gas. A presentation of the experimental installations is given, as well as an evaluation of the effects of the fuel composition, combustion regimes and technology on the NO x emissions. As the biomass combustion took place at temperatures low enough that thermal and prompt NO x can be neglected, the conclusion is the emissions of nitrogen oxides primarily depend on the biomass composition -it is increasing with the increase of the nitrogen content, and decreases with the increase of the char content which provides catalytic surface for NO x reduction by CO.