This work presents Combined Heat and Power (CHP) gas engine factory as one of the possible solutions for cogeneration in the industry which has high values of electrical and total efficiency, and the ...electrical efficiency relatively changes little with the change in power of the plant. The cost‐effectiveness of such a plant is significant to the supply of industrial consumer electricity from the grid, and heat from the factory boiler. A problem in assessing the cost‐effectiveness of using such a plant is that it uses more fuel here than in the case of energy supply from the boiler room factory and electrical distribution networks. In this case, the price of fuel and electricity as well as the level of placement of thermal energy, as shown here, determines the cost‐effectiveness of the plant. The final decision on the application of the CHP plant must be preceded by a careful technical analysis of the plant and energy system as well as a financial analysis of the selected case. Due to errors that occurred in practice, this paper aimed to point out the basic problems in choosing the power and mode of operation of these plants.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The folowing article considers the process of determining the working temperature of the workpiece in the cutting zone when machining the machine plastic on the lathe. Maintenance of the processing ...temperature of the workpiece in the limits of less than 100 °C is possible with the application and programming of the fuzzy logic controller (FLC) for the required processing conditions.
Programming is established for three inputs and one output and the experimental results refer to generating the value of the acceptable temperature value for the polytetrafluoroethylene (PTFE) processed material, better known as teflon.
Fuzzy logic controller adaptation based on Mamdani rules in this paper is supposed to regulate the number of revolutions of the main CNC machine spindle so that the workpiece temperature could be kept below 100 °C without using a coolant to avoid chemical reactions between the coolant and the base material.
The input parameters for the fuzzy controller are the temperature of the machined material, feed speed and depth of cut and the output is the number of revolutions of the main spindle. Acceptable temperature of the workpiece ranges between ∼20 °C and 100 °C, of the feed speed between 0,05 and 0,089 mm/rev and of depth of cut between 1 and 5 mm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigated the solar power potential and performance in Serbia, a country with favorable solar conditions but limited resource utilization. The principal objectives of the investigation ...were to analyze the performance ratio (PR) and assess the electricity production of simulated solar power plants in different distribution areas. The Photovoltaic System software (PVsyst 7.3) was employed to simulate five grid-connected solar power plants, each with a capacity of 10 MW, in five distribution areas of the Serbian Public Electric Utility Company. The study found that the PR values varied from 81.7 % to 84 %, indicating favorable conditions for harnessing the solar potential. The simulations projected an annual electricity delivery to the grid of 64.41 GWh. According to the study’s estimates, installed solar power plants would be capable of meeting 0.22 % of the electricity needs in Serbia.
This paper aims to enhance the efficiency of biogas plants for the production of electrical and thermal energy by optimizing substrate selection and digester heating techniques. The study presents a ...comprehensive project of a biogas plant, including all necessary installations and a detailed methodology for equipment selection. Specific substrates used include animal flour, corn silage, and molasses, each chosen for their high dry matter content and biogas production efficiency. The digester heating technique was analyzed to maintain optimal fermentation temperatures, ensuring a stable and efficient biogas production process. The projected daily biogas production is estimated to be 5688 m3. The analysis shows that maintaining a constant digester temperature significantly improves biogas yield. Seasonal variations in thermal energy requirements were identified, highlighting the need for effective insulation and heating mechanisms, particularly during colder months. Additionally, the implementation of advanced heating techniques demonstrated a reduction in overall energy consumption for maintaining the desired digester temperature. This research provides valuable insights for the design and operation of efficient biogas plants. By optimizing substrate mixtures and digester heating, the study contributes to sustainable energy production, reduced greenhouse gas emissions, and enhanced biogas plant efficiency, supporting both environmental protection and economic development.
The paper presents results of experimental research and simulation of the main parameters of crude oil pipeline transport. In Serbia, 70 % of the produced oil belongs to a paraffin type, of which ...over 25 % has a high content of paraffin. High-content paraffin oil usually has a high pour point. The paraffin content in crude oil from Vojvodina, Serbia, is in the range 7.5 to 26 %, and the oil pour temperature varies from 18 to 36?C. The imported crude oil has a flow point max. 8?C. Homogenization, i.e. mixing of domestic and imported crude oil, improves the transport properties and decreases the pour point. After homogenization, the crude oil is pre-heated, and then transported by a pipeline to the refinery for further processing. Heating induces modification of crude oil physical properties, especially flow properties so to prevent wax formation within the oil pipeline. The aim of this paper was to determine operating parameters and flow characteristics for a particular oil pipeline (428 mm inner diameter, 91,000 m length) under real operating conditions. By heating in the range of 20 - 50?C, the viscosity of crude oil was reduced, approaching the viscosity of water. The pipeline is isolated (100 mm thick isolation) and buried into in the ground (1 m depth). It is found that the heat transfer coefficient has a dominant influence on the cooling rate of the oil in the pipeline. The heat transfer coefficient is mainly determined by the isolation thickness so that it was determined as 0.60 W m-2 K-1 for + 100 mm thickness, while it was 2.20 W m-2 K-1 for the non-isolated pipeline. Heat losses through the main pipeline ranged from 36 - 110 kJ m-1 h-1 (10 - 30 W m-1). The difference between the starting and the ending temperature of crude oil ranged from 10 to 12?C. Such a decrease of ?t = 10 oC and, consequently, the increase in viscosity induced a noti-ceable increase in the pressure drop and pump power by 3 to 4 %, at the maximum flowrate of 0.194 m3 s-1 (700 m3 h-1). The cooling rate during transportation under stationary thermal and hydraulic conditions is in the range 0.52 ? 0.5 oC h-1. In the case of domestic oil (Vojvodina, Serbia) transport, the downtime should not exceed 24 h, since stopping and cooling of the oil would result in formation of solid paraffin particles followed by oil gelation.
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The spray dryer is very often applied in chemical and food - processing industries. This drying method includes suspension - spraying with the contents about 30 to 65% of dried substance. The drying ...period in most cases is only several seconds. The drying agent is the warm air. A model of momentum, heat and mass transfer in the atomization - swirler zone was proposed. To verify the model an extensive experimental investigation was performed on water evaporation at different initial air temperatures, feed rates, flow rates of the drying agent and different parameters of atomization and initial particle size distribution. Good agreement between experimental results and theoretical data was achieved. The model was verified experimentally on the basis of results of investigations on drying of a 40% mass solution of starch and water.
This study examines the impact of cutting regimes on determining cutting resistance in the processing of polypropylene (PP) using the CNC lathe EMCO F5. The rationale for this research stems from ...polypropylene’s rarity among thermoplastics in possessing structural stability, allowing for its comparison to metals and practical application in products replacing metal parts. Leveraging its favorable mechanical properties, polypropylene finds utility in producing parts subject to dynamic loads, boasting high resistance to impact loads—particularly undesirable in machining. An advantageous characteristic of polypropylene is its affordability, rendering it an economical choice across numerous applications. Despite these merits, polypropylene’s exploration in cutting processing remains limited, underscoring the novelty of this research endeavor. The main method for determining cutting resistance involves measuring electric current strength during processing. This direct measurement, facilitated by input cutting regime parameters, is recorded by the PLC controller, with the current value extracted from the machine tool’s ammeter. The experimental approach entails varying cutting regime parameters—cutting speed (v), feed rate (s), and depth of cut (a)—across minimum and maximum values, recognized as pivotal factors influencing cutting force development and the attainment of the desired machined surface quality.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This paper discusses the process of increasing the effectiveness of CNC lathe for carrying out the appropriate experiments. Experiments are related to the plastics processing machine and programming ...fuzzy logic controller (FLC) for the requirements of machining. Input parameters of the FLCare obtained as a result of previous experimental parameters set by experience and with a great subjective impact of technologists. Expected results of FLC's settings are based on the complete autonomy of the process and eliminating subjective errors.
In modern life conditions, when emphasis is on environmental protection and sustainable development, fuels produced from biomass are increasingly gaining in importance, and it is necessary to ...consider the quality of end products obtained from biomass. Based on the existing European standards, collected literature and existing laboratory methods, this paper presents results of testing individual thermal - chemical properties of biomass energy pellets after extrusion and cooling the compressed material. Analysing samples based on standard methods, data were obtained on the basis of which individual thermal-chemical properties of pellets were estimated. Comparing the obtained results with the standards and literature sources, it can be said that moisture content, ash content and calorific values are the most important parameters for quality analysis which decide on applicability and use-value of biomass energy pellets, as biofuel. This paper also shows the impact of biofuels on the quality of environmental protection. The conclusion provides a clear statement of quality of biomass energy pellets.
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