Mirjana Stamenic

Nergy efficiency is a key pillar of the Republic of Serbia's contemporary energy policy, and its successful implementation depends on a functional energy management system. In this context, licensed energy advisors play an important role in conducting energy audits and providing professional support to system obligors. This paper analyzes the legal framework, competencies, and practical role of energy advisors in the energy management system, with particular emphasis on energy audit procedures. The Law on Efficient Use of Energy precisely defines the conditions for obtaining the status of licensed energy advisor, and the training system is structured through three areas – mechanical engineering, electrical engineering, and architecture – ensuring a multidisciplinary approach. The program combines theoretical training, practical exercises, and preparation of individual reports under mentorship, while the examination procedure includes testing and oral defense before a commission. In the paper, the role and methodology of conducting energy audits, which are fundamental instruments for evaluating energy performance, are defined. In the energy audit report, licensed energy advisors identify measures that provide economic benefits (reduction of energy and fuel costs) and ecological effects (reduction of emissions of gases that have a negative environmental impact). The paper concludes that the success of the energy management system depends on the synergy of the regulatory framework, professional competencies of energy advisors, and the willingness of obligors to implement recommended measures, thereby contributing to the sustainable development of the energy sector of the Republic of Serbia.

Air in the machine hall of a typical paper mill contains a significant amount of water vapor and is often contaminated with paper fibers and other fine dust particles. The largest amount of water vapor and heat is released during the thermal drying process of paper inside the enclosed hood of the dryer section of the paper machine. The released water vapor partially flows into the machine hall through gaps and openings in the dryer hood. In addition, substantial quantities of water vapor are generated in the wet end of the paper machine, which includes the headbox, forming section, wire section, and press section. Depending on the thermodynamic state of the air, conditions often arise in which water vapor condenses upon contact with cold surfaces within the hall. This phenomenon has a highly adverse effect on the production process and may compromise the quality of the paper being produced. For this reason, a properly designed machine hall ventilation system should capture and remove heat, water vapor, and particulate contaminants at their sources before the warm, humid, and contaminated air is released into the hall environment. The air exhausted from the hall through the ventilation system contains a considerable amount of energy that can potentially be recovered and reused. On the other hand, the fresh air supplied to the machine hall must be preheated, which requires significant amounts of energy during the winter period. This paper presents recommendations and best-practice examples for the design of effective and energy-efficient ventilation systems for machine halls in the paper industry. Such systems ensure optimal indoor air conditions necessary for the reliable operation of paper machines while reducing energy consumption and operating costs.

The alumina, in the form of α-Al₂O₃ tabular balls, considered in this study is a high-purity form of aluminum oxide that has been fired at high temperatures (well above 1900 °C), virtually removing porosity. However, the purity and inertness of the surface of the Al₂O₃ tabular balls minimize the catalytic activity, which is why lithium doping was tried. Thus, the target of this study was the effect of doping with lithium ions in some tabular balls of Al₂O₃ (the crystalline structure is corundum) on the improvement of the catalytic properties of alumina. This study examined the impact of a lithium catalyst on the combustion of various fuels within a porous inert medium (PIM) burner. This study specifically compared low calorific gaseous fuel (e.g., biogas) combustion in a PIM burner with and without the lithium catalyst. The experimental setup comprised a gas preparation unit for mixing CNG and CO₂ to simulate biogas and a PIM burner. The PIM burner comprised Al₂O₃ spheres (13 mm diameter, 45% porosity) in a random packing configuration. Three fuels, varying in composition and lower heating value (LHV ranging from 20.771 to 27.695 MJ/m³), were combusted at air ratios ranging from 1.67 to 1.79. The results indicated that the catalyst increased peak combustion temperatures by 23.2 °C to 51.4 °C, depending on the fuel type and air ratio. Significantly higher carbon monoxide (CO) concentrations were observed without the catalyst, particularly with fuel type F1, while nitrous oxide (NOx) levels remained consistently low. Upstream flame propagation was observed in the presence of the catalyst. These findings demonstrate the potential of lithium catalysts to enhance combustion stability and reduce emissions in porous media combustion burners. Following these studies, it can be stated that Li(I) has the role of promoter of the catalytic process.

The approach flow is the section of a paper machine between the machine chest and the headbox. It is made up of a number of unit operations in order to clean contaminants, refine, deaerate and dilute (control the consistency) stock before it is distributed uniformly over the width of the machine in the headbox. Well-designed approach flow system supply a continuous suspension flow of constant consistency, quality and flow rate at constant pressure to the headbox of the paper machine. Variations of stock flow rates less than 1% from nominal flow rate are preferable. Hydrocyclones play a crucial role in the approach flow system of a paper machine by improving stock cleanliness before the pulp reaches the headbox. They are a type of centrifugal cleaners which remove unwanted particles from the pulp suspension, such as: sand, grit, metal particles, ink residues, plastics. The principle of filtration is based on the high-velocity tangential flow where the pulp slurry is pumped into the hydrocyclone at high speed tangentially, creating a vortex. Centrifugal separation occurs with heavy particles (rejects) that are pushed to the outer wall and exit through the bottom (reject port). Light, clean fiber suspension (accepts) exits through the top (overflow outlet) and continues toward the headbox. In this paper application of hydrocyclones in the paper industry is analized and methodology for their sizing and selection is presended.

Steam boiler blowdown is a necessary process undertaken in steam boilers to control the level of total dissolved solids (TDS) within the boiler. The number of times a boiler is blown down depends mainly on the quality of boiler feed water. The hot water is usually discharged into a flash or expansion vessel which reduces the pressure of the liquid, and results in flash steam and boiler blowdown water. Heat recovery then may take place, both on the flash steam and boiler blowdown water, by means of heat exchangers. The paper presents the possibilities for reducing heat losses caused by desalination and blowdown of industrial steam boilers. Techniques for reducing the amount of hot water discharged for the purpose of desalination and blowdown, as well as the possibility of waste energy recovery, were considered. The paper also presents a methodology for determining the flow rate of hot water from boiler desalination and blowdown where it is not possible to measure the flow rate directly, which can be useful when conducting short energy audits. In the paper feasibility of the application of heat recovery systems is presented, based on the results of analysis that was carried out for an industrial scale system in operation.

The energy audit is a standardized procedure that determines the level of energy consumption for the quantity of manufactured products, the indicators that are important for assessing the energy efficiency of the production process or a specific part of the production process, the efficiency of the system that supplies the production plant with energy sources (heating and cooling energy, compressed air, electricity, etc.). The energy audit defines the substance and heat balance of the entire factory, individual installations, and sometimes individual equipment, depending on the quality and resolution of the data collected, i.e., the requirements of the analyses carried out as part of the energy audit. In addition, the proposed measures will improve the energy efficiency of the process, plant, or factory. The measures are then evaluated regarding their technical feasibility, i.e., financial profitability, and finally ranked. An energy audit is a valuable tool that makes it possible to determine the initial state of energy efficiency, i.e., to quantify the impact after a certain period of implementing measures to improve energy efficiency. On the other hand, the Law on Energy Efficiency and Rational Use of Energy (Official Gazette RS 40/21) and the accompanying regulations prescribe the obligation and frequency of conducting energy audits for the obligated parties of the energy management system. In this paper, the authors will answer the question of whether the energy audit is an obligation and an unnecessary burden for the obligated parties of the energy management system in the Republic of Serbia or whether it is a valuable tool that has significant financial savings on the one hand, and a positive effect on the environment by reducing the consumption of fossil fuels and electricity from non-renewable energy sources and reducing the emission of pollutants into the atmosphere on the other.

The combined production of electricity and thermal energy (combined heat and power or co-generation) is the most efficient and convenient approach to reduce costs for energy at industrial power plants and district heating plants that use natural gas as fuel to produce thermal energy for various needs. This paper analyses the operational characteristics of the combined heat and power plant, which has been operating since January 1, 2021, at the Vozdovac Heating Plant as part of the Belgrade district heating system. The combined heat and power plant consists of three gas engine units with a total nominal electric power of 10 MW and thermal power of 10.1 MW, which use natural gas as fuel. The combined heat and power plant is used for district heating and preparing domestic hot water while electricity is sold to the local electric grid. The analysis in this paper focuses on the plant?s operational characteristics: the number of working hours, the total energy consumption and energy production, the efficiency as well as the operational and maintenance costs. Also, the impact of the drastic changes in the prices of natural gas, electricity, and maintenance costs in the last year on the financial profitability of the combined heat and power plant was analysed in particular.

The aim of this experimental research is to confirm the correctness of the proposed methodology for optimizing atmospheric gas burners. Also, the burner was tested in actual conditions. The object of this experimental optimization is a typical modern atmospheric gas burner for households (required heat output for average households ranges from 8 to 12 kW) to which the proposed methodology will be applied in order to optimize its design characteristics and performance to obtain energy efficient and an environmentally friendly device.