Milica Mladenović

Although biomass fuels are widely recognized as a viable alternative to fossil fuels, their uncontrolled and uncritical use can also have negative consequences for the environment. The quality of the biomass used for combustion is a very important issue, as residential heating systems generally do not have flue gas cleaning systems. One of the biggest threats to the environment is the emission of heavy metals contained in the fuels into the atmosphere. If the biomass, i.e. its ash, is also deposited on the heating surfaces, which reduces the efficiency of the combustion system, this problem is exacerbated. Considering the fact that air pollution is constantly increasing during the heating season in Serbia, and a large part of the pollution source are appliances that are not equipped with flue gas purification systems (mainly households), this issue is of particular importance. Wood pellets are becoming increasingly popular as a heating fuel, as they have a higher energy density compared to other types of biomass and are easier to handle. Since the production and use of wood pellets in Serbia is increasing year by year, this study investigated the physico-chemical properties of wood pellets (by partial proximate and ultimate analysis, heating value of the fuel, and heavy metal content). In addition, the characteristic melting points of the ash were determined, which serve as indicators of the fuel’s tendency to form deposits on heating surfaces. The heavy metal content was also used to assess the impact of wood pellets on the environment and thus on human health. In order to compare the results obtained and assess the impact, the same analyzes were carried out on a sample of domestic coals. This study confirms the beneficial properties of upgraded wood biomass – wood pellets – compared to coal.

Phase change materials (PCMs) integrated into lightweight building envelopes were experimentally evaluated to assess their impact on indoor thermal performance. A PCM test house and a reference test house were examined under two conditions: without ventilation and with night ventilation. The experiments were conducted under the climatic conditions of the Republic of Serbia, in Belgrade, at the Vinca Institute of Nuclear Sciences. Two observation periods were defined to evaluate the thermal behaviour of the test houses, with four thermal cycles monitored in each period. Results indicate that, on hot sunny days, the PCM test house achieved maximal indoor air temperature reduction of 3.5-4.8 ?C during the non-ventilated period and 4.2-5.9 ?C during the night-ventilated period, while reducing thermal load levelling (TLL) by 64.1-72.5% and 45.5-49.5%, respectively. The average indoor temperature reduction (AITR) ranged from 0.03-6.12% in the first period and from 3.19-6.54% in the second, confirming the potential of passive PCM application for improving indoor thermal stability. These findings show the practical benefits of PCMs in enhancing energy efficiency and indoor thermal comfort in lightweight buildings.

In addition to the grains as the main agricultural product, the agricultural production of soybean also produces large quantities of plant residues in the form of soybean straw. The article focuses on the primary trends in soybean production worldwide, and Serbian's current position in global production. The paper analysis the dynamics and structure of sown areas, gross harvest volumes and soybean yields in the world for the period 2006-2023 in the context of leading producing countries. Soybean straw is an agricultural leftover that yields up to 1.5 kg per kg of soybeans. The existing literature demonstrates the vast potential of soybean straw as an environmentally friendly source of carbon to produce chemicals, materials, fuels and energy similar to oil refineries. The possibility of using untreated soybean straw for the synthesis of building materials was considered. Different types of common cement were used as starting raw materials for synthesis. The characterization of two test samples was performed using X-ray diffraction analysis (XRD), light microscopy (LM), thermal conductivity and heat capacity measurement.

In the discussion on biomass as a renewable energy source, its benefits are repeatedly recognised: - reducing greenhouse gas emissions by substituting fossil fuels; - increasing energy security by diversifying the energy mix and reducing dependence on imported fuels; - creating economic prospects by promoting rural development, job creation and valorisation of waste streams. However, the utilisation of biomass in combustion processes faces some challenges. This article emphasises one of them: the ash problem due to the pronounced tendency to form deposits on the heating surfaces. In order to properly design or select a biomass combustion system, the indicators of the tendency of biomass ash to form deposits on the heating surfaces must be adequately determined. Determining ash melting temperatures for biomass is crucial for understanding combustion behaviour and potential problems such as slagging and fouling. Biomass ash melting temperatures are typically determined at 550 °C for biofuels and 815 °C for solid mineral fuels. Some established certification schemes and national regulations favour the preparation of biomass samples by ashing at 815 °C. In this paper, the question is answered whether and how the ashing temperature of the biomass sample influences the characteristic points of the ash melting temperatures. The characteristic ash melting temperatures were determined for different types of biomass (wood chips, soybean and maize straw), where the ash sample was obtained by ashing at three different temperatures (550, 710 and 815 °C).

Mercury is a highly toxic trace element that poses a serious global environmental threat due to its mutagenic properties, persistence in ecosystems, and its capacity for bioaccumulation. Combustion of fossil fuels, particularly coal, is one of the primary sources of atmospheric mercury emissions, prompting many countries to implement stringent regulatory limits. In response, this study aims to investigate and compare the mercury content in various types of coal and biomass fuels (wood chips and pellets) to evaluate their environmental suitability for energy production. The results demonstrate a clear and substantial difference in mercury concentrations between the two fuel groups. All analyzed coal samples contain significantly higher levels of mercury compared to biomass fuels. This variation is strongly influenced by sulfur content and other key fuel quality parameters, including calorific value, ash content, and elemental composition. These findings are essential for understanding how intrinsic fuel properties affect mercury emissions during combustion. Ultimately, the study aims to inform cleaner energy production practices by guiding fuel selection and optimizing combustion technologies to minimize environmental mercury release.

The EU has recognised the issue of rural depopulation and has taken political measures to solve it. Smart rural communities, organised in cooperatives using indigenous biomass for energy purpose , are considered an effective solution to alleviate this problem by providing smart services to the local population, leading to higher economic competitiveness. The experience of Austria, Italy, Denmark, the Netherlands, and other countries that are leaders in this field, are valuable and can be implemented in our country as well. Restarting the agricultural village cooperative and directing them to produce, in addition to traditional crops, more profitable ones (medicinal plants, fruits, vegetables), to then process, store and market them at the most favorable time, for that and for animal breeding, using their autochthonous energy resources – biomass, is a way to organize sustainable production even on small rural farms. In addition to the above, all thermotechnical equipment and installations can be produced in domestic small and medium enterprises. In this approach, the country’s reindustrialization can begin while also reducing the decline of villages. The paper presents an overview of the steps that can lead to implementation of the above activities, noting that some parts of this work have already been presented before.

Exploring alternative options to address the impending global energy crisis while taking into account environmental concerns and climate change mitigation and addressing the sky-rocketing energy demand has become urgently essential. This need is further highlighted by the significant reliance of the Republic of Serbia on imported energy sources so that the focus of its energy sector strategy is rational use of energy resources, use of renewable energy sources (RES), and waste management with satisfying environmental regulations. The use of low-calorific and waste materials in conjunction with fluidized bed combustion technology is a method to achieve all the above goals synergistically. This paper presents experimental results of combustion of several solid wastes (coal mining waste from the ?RB Kolubara? complex, Serbia, paper sludge and hazelnut shells), conducted in an industrial prototype and experimental bubbling FB boiler (capacity up to 500 kW). Burning these wastes has a variety of advantages, including recovering substantial energy remaining in the waste and minimizing the overall waste volumes. The work focused on determination of furnace temperature profiles, composition of the flue gas at the furnace outlet as well as fluidization air and fuel flowrates, the minimum fluidization rate, fluidization number, maximum heat output and the transferred heat of the tested fuels. Based on the obtained results, potentials of FBC of waste fuels and the possibility of utilization of their energy potential are evaluated.

Energy costs are rapidly rising around the world and it is important to find a way to reduce energy consumption. Energy consumption in buildings can account for up to 40% of total energy consumption in developed European countries due to an increase in living space per person, an increase in the need for air conditioning, an increase in the number of appliances used in households, and other factors. Due to the increasingly frequent high temperatures during the summer and the increase in electricity consumption, it is very important to find a way to decrease indoor temperatures in urban residential buildings without using more energy, given the severe energy crisis that has engulfed Europe and the high percentage of energy and electricity consumption in the residential sector. Installation of phase changeable materials is one method for improving the thermal envelope of a building by increasing the thermal capacity of the envelope and thus affecting the reduction of indoor temperature oscillations and, consequently, reduction of summer electricity consumption. In this study, the TRNSYS software package was used to simulate and compare the indoor air temperature in typical detached houses built in period 1946 and 1970 in the Belgrade area, for both, the case without and the case with installed phase change (PCM). It was shown that incorporating a PCM with a melting temperature of 25?C into the inter-floor construction of the house could significantly improve comfort conditions by reduce indoor temperature fluctuations during the warm period without consuming additional energy. When the temperature outside is around 30?C, the maximum air temperature in the house drops by about 2?C.

Despite many benefits of agricultural biomass utilization as an energy source, there are certain disadvantages such as the possible high emission of NOx. The NOx emission represents one of the key challenges for agricultural biomass use as a fuel. The experimental denitrification chamber was used to evaluate the impact of initial NO content, NH3:NO molar ratio, flue gas temperature, and the temperature difference between two denitrification chamber sections on NOx reduction using ammonia aqueous solution. The optimization of experimental conditions was done in the NO concentration range from 200-800 ppm, NH3:NO molar ratios from 0.31-3 and second chamber section temperature range from 770-67?C. The denitrification process under controlled conditions is the starting point for the optimization of the secondary denitrification technique of selective non-catalytic reduction SNCR process on real-scale plants combusting biomass or any other fuels with increased NOx emission.

In the context of the current geopolitical situation and energy uncertainty, the aim of the paper is to affirm the use of biomass as a domestic energy source and to point out guidelines for its proper and efficient use. According to the official data of the Ministry of Mining and Energy of the Republic of Serbia, biomass represents by far the greatest potential for renewable energy in the country. Over 60% of the estimated potential of renewable energy in the Republic of Serbia belongs to biomass (not counting large hydropower plants). The possibility of energy use of biomass, further, does not depend on weather conditions, time of day or season, unlike other renewable energy sources such as wind and solar energy. In addition to this and other advantages that biomass as the only carbon - CO2 - neutral renewable fuel has, it should be noted that facilities for the conversion of energy from biomass through combustion are relatively technologically simple and can be produced entirely in our country. If these facilities were used in district heating systems with the possibility of using thermal energy for technological processes in the cultivation and processing of agricultural products even out of the heating season, the potentials and effects of biomass utilization would increase. Facilities for processing and finishing agricultural products (such as dryers) can also be largely produced in the Republic of Serbia. Advantages and the degree of utilization of biomass as a renewable energy source are even more pronounced when used in cogeneration plants. When all the above is considered, it can be concluded that the use of biomass can take a significant place in the overall reindustrialization of our country, which will be discussed in more detail in this paper. The paper also points out some of the obstacles to the realization of these efforts as well as examples of good practice.