In this review paper described are possible chemical reactions and their thermodynamic analysis during direct reduction. The sticking mechanism during direct reduction in the fluidized bed was analysed, and the reasons for the sticking appearance explained. The most important parameters on the sticking were analysed. The ways for prevention and observation were considered. The plan for experimental investigations was proposed. The investigations could be performed in fluidized bed reactor. Coal will be used as inert material. Separately, the influence volatile content in the coal on the reduction process and sticking appearance, will be analysed. As results of these investigations would be some improvements of the method direct reduction of iron ore in the fluidized bed.

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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.

This paper investigates the environmental impacts and energy benefits of the cultivation of Miscanthus (Miscanthus × giganteus Greef et Deu.), in order to initiate its use in sustainable household heating in the Republic of Serbia. Based on the analysis of available data regarding the use of agricultural machinery in Serbia, a Miscanthus supply chain is constructed and examined in detail, scrutinizing all relevant operations—from planting of rhizomes to thermal energy production. Results of the life cycle assessment identify the briquetting process as the most environmentally burdensome operation due to high electricity consumption and low productivity. It is concluded that an average yield of 23.5 t dry matter (d.m.) year−1 obtained from 1 ha of chernozem soil would have energy output:energy input (EO:EI) ratio of 51:1, and would release 365.5 gigajoules (GJ) of heat during combustion in a boiler. With this amount of energy, around 383 m2 of a free-standing family house in Serbia can be heated annually. The same amount of energy is obtained by the combustion of 22 t of lignite or 23 t of wood logs. The substitution of lignite and wood with Miscanthus briquettes would lead to significant reduction of CO2 equivalents (eq), SO2 eq, P eq, N eq, 1,4 dichlorobenzene (1,4-DB) eq, Non-methane volatile organic compound (NMVOC), PM10 eq and U235 eq emissions. This designates Miscanthus as a more sustainable energy solution for household heating. In instances where more modern agricultural machinery is used, emission reduction is higher, except for CO2 eq due to higher emission factors predicted for more powerful engines. Depending on Miscanthus’ annual yield, the replacement of set-aside land with Miscanthus plantations result in carbon (C) sequestration from 0.08 t C ha−1 year−1 to 0.91 t C ha−1 year−1. In a modern machinery scenario, C sequestration is only attainable when maximal Miscanthus yield is obtained. The combined use of machinery with different engine power is the best option for Miscanthus cultivation in Serbia.

The paper presents results of an experimental investigation of convective drying of apples "var. Idared," potatoes "var. D esir ee" and bananas "var. Grand Nein," in full recirculation laboratory-scale dryer. The experiments were conducted with cubeshaped apple samples (side length 10 and 13 mm), potato chips (slice thickness 2 and 3 mm) and banana cylinders (slice thickness 6 and 7 mm), without pretreatment. The drying experiment was conducted at fully controlled air temperature (35-45-558C), relative humidity (10-20-30%) and air velocity (1-1.5-2 m/s). Results are discussed through their comparison with other heat pump drying system scenarios in order to find the most efficient one. The efficiency of the heat pump drying (HPD) system was analyzed using the several indicators: specific moisture extraction rate (SMER), specific energy consumption (SEC), heat pump dryer efficiency (HPDE) and moisture extraction rate (MER). The average values of the full air recirculation HPD system efficiency indicators were obtained in range: SMER HP 5 0.030-1.317 kg/kWh, SMER HPD 5 0.047-0.651 kg/kWh, SEC 5 0.211-9.358 MJ/kg, HPDE 5 0.426-20.7 MJ/kg and MER 5 1.362-17.194 kWh/kg. The results were evaluated in order to provide better information about the benefits of full air recirculation usage in HPD systems in regards to the other similar dryer configurations. PRACTICAL APPLICATIONSThis study uses full air recirculation to provide better control of the main drying parameters and to minimize impact of the surroundings. The novelty of this study lies in the fact that RH of the drying air was precisely controlled during all experiments. The evaluation of the relevance of full air recirculation HPD system is rare in literature and therefore the present study is directed toward quantification of influence of HPD system configuration on drying process efficiency. Dependence of several energy efficiency indicators of HPD system performance: SMER, SEC, HPDE and MER on HPD system air recirculation rate were investigated. The results were evaluated in order to provide better information about the benefits of full air recirculation usage in HPD systems in regards to the other similar dryer configurations.

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