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Enormous amount of protective masks was consumed in connection with the COVID-19 pandemic and they still burden the environment. Therefore, it is necessary to look for possibilities of their disposal in an ecologically acceptable way. This article focuses on particulate matter produced concerning the energy disposal of pandemic FFP2 masks. These masks were processed into small pieces, added to spruce and beech wood (in the weight proportion 5 % and 10 % of FFP2 masks) and formed into pellets. The concentration of particulate matter formed during their combustion was measured by the gravimetric method. The inorganic elements were detected from filters with captured particulate matter by an energy-dispersive X-ray fluorescence spectrometer and verified by inductively coupled plasma-optical emission spectroscopy. It was found that higher concentrations of particulate matter were recorded predominantly with a higher mass airflow. In both airflows (40 % and 50 %), beech pellets had a higher mass concentration than spruce pellets probably caused by the presence of bark in beech wood. Based on the chemical composition, the following elements in small amounts (0–2 mg on a filter) were identified: K, S, Cl and Fe. High concentrations of harmful elements carried in particulate matter have not been detected. FFP2 masks added in a small percentage (up to 10 %) can be used in wood pellets for combustion purposes without significantly affecting the combustion process.

Bio-waste is a source of energy-rich material. Therefore, it can be used in further processes and efficiently utilized. Further processes of waste utilization include compressing them to pellets. However, this type of pellet often has a low bulk density, high ash content, low ash melting temperature, and low calorific value. This research dealt with the energy properties of peanut and pistachio nut shells that were pure or mixed with spruce sawdust in half proportion and compressed into pellets. As a continuation of previous research, the properties of these pellets prepared were measured and compared with pure spruce pellets and with pellets from walnut shells. The tested shell pellets had calorific values similar to wood pellets from spruce. However, mixing nut shells with spruce solved the problems of high ash content and low ash melting temperatures. The amount of wood present in the pellets resulted in increased ash melting temperatures and decreased the ash content.

This experimental study aimed to validate the integration of a gravitational loop heat pipe (GLHP) with respect to a gas fireplace insert. The GLHP was utilized to enhance the efficiency of the fireplace by preheating the combustion air with waste heat from flue gases. The experiment involved monitoring key parameters such as vapor and condensate temperatures and absolute pressure within the LHP. The results demonstrated that a filling volume of 0.1 L of water in the LHP allowed for successful operation, while exceeding 0.2 L resulted in flooding and decreased system efficiency. Challenges related to vapor production and condensate return were identified, suggesting the need for further research and design improvements. The experimental verification confirmed the feasibility of implementing the gravitational LHP in a gas fireplace insert and emphasized the importance of optimizing vapor production and condensate return mechanisms. This study contributes to the advancement of thermal management strategies and provides valuable insights for enhancing the design and performance of such systems.

The objective of this article is to address the challenges associated with visualizing air flow over a heating source in an open laboratory environment. The study uses a combination of experimental visualization and numerical simulation techniques to generate a 3D model of the air flow and heat transfer between the heating source and the environment via natural convection. The Particle Image Velocimetry method is used to experimentally visualize the air flow, which is known for its benefits of high speed and accuracy, and for its ability to avoid disturbing the flow of the fluid being investigated. The data obtained from this experimental method are used as input for numerical simulations using the Ansys Fluent program. The numerical simulations identify air vortices and other elements that disrupt the airflow in the laboratory environment. The resulting 3D model accurately represents the actual situation in the laboratory and could be further optimized by adjusting parameters such as the output of the heater and the heating source temperature. These parameters play a crucial role in ensuring thermal comfort in the laboratory environment, which is of utmost importance for user comfort. In conclusion, the study provides valuable insights into the visualization of air flow over a heating source and demonstrates the effectiveness of combining experimental and numerical simulation techniques to generate accurate 3D models of air flow and heat transfer.

The COVID-19 pandemic brought a period of high consumption of protective masks and an increase in their waste. Therefore, it was necessary to look at possibilities for their disposal. This article is focused on the disposal of FFP2 masks in the form of pellets blended with sawdust. Further, their ash melting behavior was observed. The method of ash preparation can impact the resulting values of melting temperatures. Therefore, this article investigates the resulting values of ash melting temperatures determined during different ash preparations, such as temperatures (550 °C and 815 °C) and ash size (non-sifted, smaller than 50 µm and 100 µm). All measured deformation temperatures were higher than 1100 °C and even higher than 1200 °C for some samples. Moreover, the presence of FFP2 masks in pellets only insignificantly affected the values of melting temperatures compared to pure wood pellets. The measured values also showed that increasing the temperature of ash preparation from 550 to 815 °C can increase the resulting values of melting temperature. The most significant proportion of the fraction size on the resulting melting temperatures was observed for beech with 5% and 10% of masks at an ash temperature of 550 °C and for spruce with 10% of masks at an ash temperature of 815 °C.

Agricultural and other residues are promising renewable energy sources. However, they can cause problems in combustion processes. One of these problems is also low ash melting temperatures. Except, the ash melting behavior can be impacted by many factors, such as ash preparation or used atmosphere. This article deals with comparing different atmosphere conditions during measurements of ash melting temperatures of three agricultural pellets: alfalfa, straw, and hay. The first one was oxidizing with compressed air and nitrogen. The second atmosphere was reduced with the air purge, and the last was only reduced, consisting of 60% carbon monoxide and 40% carbon dioxide. Differences between individual atmospheres were none, up to 9.8%. The most significant differences have appeared between oxidizing and reducing atmospheres. In general, the oxidizing atmosphere presents a less expensive way. More attention should be paid to the use of oxidizing atmosphere for applications in heat sources mainly due to its similarity to the combustion process. However, it would be suitable to realize more comprehensive research regarding ash preparation in different ways and with using of different types of fuel.

INTRODUCTION: Production of emissions from small heat sources burning solid fuels in households inSlovakia is relatively high. At the present time, the operation of such devices are neither controlled norregulated properly and effectively.OBJECTIVES: This work presents a research analysis of current monitoring and maintenance procedures and certified norms for all solid-fuel small-scale heating systems utilized in households.METHODS: The research compared data from over 13 countries in the European Union, evaluatinginformation regarding certified emission limits, efficiency levels, normalized monitoring procedures for both, fuel standards and heating system performance. A proposition is therefore presented for a new monitoring and inspection guide for solid-fuel heating systems in Slovak Republic households, where regulations, such as Ecodesign or the EN 305-5, were integrated.RESULTS: Using a mathematical-statistical model, the implementation of the proposed regulations brings an emission saving of almost 140 tons per 10,000 inhabitants for both central and local heating systems.CONCLUSION: The study demonstrated substantial opportunity in decreasing operation cost, prolongationof product lifetime, and last but not least, the reduction of health risks of local citizens.

There are two thermodynamic models of the closed and vented heat pump drying process described in the paper. The models have been used for optimization of process design parameters with respect to drying rate and energy efficiency, respectively. The optimization was performed in points of parametric space defined by refrigerant and air flow rates. Results of the optimization shows the same maximal drying rate performance for closed cycle and both objective functions. There is higher potential of drying time reduction for vented cycle in comparison to closed cycle. Results of the optimization showed strong correlation of the MER parameter with refrigerant flow rate for both closed and vented heat pump drying cycle. There is same maximal MER value obtained for both MER and SMER optimized cycle parameters.

One of the most important issues in choosing a heating system is the question: What kind of fuel can be burned in given heating system. Modern automatic solid fuel boilers are often specialized only on a narrow range of suitable pellet materials. Pellets from cheaper sources are also beginning to appear on the market. However, many burners are unable to burn these new types of pellets without significant burning problems. The article deals with the influence of the proper construction of the burner on the smoothness of the combustion process and the smooth operation of the combustion equipment. The results of the experiments document the continuity of the combustion plant in the combustion of less quality pellets containing bark using more modern combustion technologies. In fact, less quality pellets cause the formation of ash sinters which cause the continuous combustion process to be interrupted, resulting in fluctuations in equipment performance and the onset of thermal discomfort. The results showed no problem with burning even when making sinters, but also showed a fluctuation in performance and the need for manual control, especially when heating or clogging the supply pipe. They also showed significant damage to pellets in the worm feeder section. These problems, therefore, ultimately require further research to ensure complete, seamless operation.

On the way to reducing emissions released into the atmosphere, there is an obstacle in the form of the emissions of solid pollutants produced by households, namely the burning of solid fuels in small heat sources. In this article, the authors deal with the development of a low-cost electrostatic precipitator, which would be able to significantly reduce the production of particulate matter. This is a tubular precipitator concept, which is enhanced by dividing the precipitation space into four chambers, each of which has an ionization electrode. With the investigated structural arrangement, it is possible to increase the size of the collection area without affecting the external dimensions of the separator. The essence of this article was to focus on the design of an ionization electrode, which, in addition to the function of a negative electrode, would also fulfill the function of a structural element of the proposed geometry. The work contains a technical design for the shape of the ionization electrode, which was subsequently examined using ANSYS Fluent software. The conditions under which a corona discharge will occur on the electrodes and how particulate matter is captured in the separation device were investigated with the help of simulations of the electric field intensity. According to the achieved simulation results, calculations were made for the theoretical efficiency of particle collection, which reached a value of approximately 78%.

Air quality and air pollution are important issues, and thus it is necessary to look at possibilities for how to decrease emissions in the atmosphere affordably and effectively. This article focuses on solid aerosols, specifically particulate matter, and the design of a low-cost solution for their decrease in the atmosphere. The mass concentration of particulate matter with the proposed optimized electrostatic precipitator was measured and compared with measurement without its implementation. Based on the results, it can be concluded that the designed ESP type could catch approximately 71% of solid particles. However, the real ability to capture particulate matter could be expected to be approximately 50–60% due to possible clogging, irregular cleaning and maintenance under normal conditions. Further, the article deals with the application of the village model with this type of electrostatic precipitator in households. Based on this model, the production of particulate matter would be reduced from 12.24 t/year to 6.12 t/year considering 50% separation efficiency and to 5.25 t/year considering 60% separation efficiency by the application to all heat sources for burning solid fuels for all emission classes. However, the reduction in particulate matter would be lower in real conditions.

A membrane-based enthalpy exchanger is a device used for heat and humidity recovery in ventilated buildings. The energy-saving potential of such a device is dependent on the parameters responsible for heat and moisture recovery. The trend is toward composite membranes, which are custom produced, and their parameters can be adjusted for a given application; therefore, the diffusion and sorption characteristics of such membranes are unknown. In order to obtain the values of the water vapor diffusivity of three investigated handmade membranes, a serial resistance model using a Field and Laboratory Emission Cell (FLEC) is proposed. Experiments were conducted to identify the resistance in each step of the moisture transfer process to extract the moisture diffusivity in the membranes. The calculated moisture diffusivities in the membranes were 8.99 × 10−12 (m2/s) for the membranes from cellulose acetate, 1.9 × 10−10 (m2/s) for the microporous PE/PUR membranes, and 1.53 × 10−11 (m2/s) for the PET/PUR microfibrous membranes. The obtained membrane diffusivities were then used in the proposed effectiveness-NTU-based model of an exchanger with a cross-flow arrangement to predict performance under various operating conditions. The results show that the highest latent effectiveness was found for the exchanger core made from the PE/PUR membrane and the lowest was for the one with the PE/PUR membrane core.

Modern food industry concerning meat producers produce high amounts of bone waste. Bones represent biggest portion of zoo-mass waste which must be destroyed for hygienically reasons. Bones also have long durability and it is taken long time to decomposing this material microbiologically. We already know way to destroy this waste by crushing and making meat and bone meal. However, feeding with meat-and-bone meal can cause animal diseases. Because of that we try to prove combustion as a suitable way to get rid of this waste. Everything can be cleansed by flames and combustion also release energy captured in bone tissue. This energy can be used as heat or transformed to electric current also. But the other side, bone burning also has its emission problems that this work is trying to solve.

Spiral plate heat exchangers (SPHEs) are used in industrial applications due to their enhanced thermal performance and tolerance to a soiled stream. The coupling of several SPHEs in series might further improve performance in terms of the effectiveness parameter. In the present study, a compact connection of several SPHE modules is proposed and investigated. For this purpose, a numerical model for the prediction of the effectiveness parameter of a modular SPHE was developed. The model predicted a 2.9% increase in the maximal effectiveness for a two-module SPHE in comparison to a conventional single module SPHE. The temperature profiles of particular streams within the two-module SPHE were predicted. The improved thermal performance and compactness of the modular SPHE configuration observed is advantageous for space-constrained applications.

Capturing particulate matter (PM) is an important issue due to the protection of human health and the quality of their life. This paper describes the innovation of an affordable particulate matter capture device for small heat sources to reduce particulate matter emissions. The design of two investigated variants of the device is based on the principle of a tubular electrostatic precipitator with one charging electrode placed in the chimney. The design of the precipitators is aimed at increasing the area of the collecting electrodes by elements dividing precipitation space, with a simultaneously increased number of charging electrodes. The influence of the elements’ application on the pressure drop and the gas flow velocity through the devices is analyzed by computational fluid dynamics (CFD). The work is further focused on the economic evaluation of precipitators and design adjustments for lower energy consumption. The achieved results show the right direction of efforts to improve the equipment designed to capture PM emissions.

At present, we are still feeling the effects of the COVID-19 pandemic in connection with the huge amount of waste generated. However, the reuse of the produced waste in other processes requires energy consumption. This article deals with the reuse of face masks FFP2, which were added as an admixture to spruce or beech sawdust and then processed into pellets. During the production process of the pellets, energy consumption was measured and further converted to one ton of pellets, and also the consumption was reflected in the price of electricity. After storage, the mechanical durability and dimensions of the individual pellets were measured, and their density was calculated. Based on the results, it can be concluded that spruce pellets with 10% face masks FFP2 (consumption 747.41 kWh; durability 97.53%) and beech pellets with 5% face masks FFP2 (consumption 721.27 kWh; durability 97.38%) achieved higher values of mechanical durability and also consumed more energy than the remaining samples with lower values of durability without considering the sample with spruce sawdust and 5% FFP2 face masks (consumption 872.63 kWh; durability 91.68%). The production of spruce pellets with 5% FFP2 face masks was affected mainly by cold outside weather.

A lot of residual biomass has energy value and can be used for further applications through suitable treatments, such as pelletization. This treatment can improve properties, mainly energy density, but can also lead to problems due to their low ash melting temperatures, high ash content, and the formation of harmful compounds during combustion. This article deals with the energy potential of pellets produced from spruce sawdust, spruce bark, and pine cones in different proportions. The impact of cone and bark contents on pellet properties was also observed. The energy properties of the produced pellets were measured, such as the contents of carbon, hydrogen, nitrogen, moisture, volatile, fixed carbon, and ash, as well as calorific values and ash melting temperatures. Based on the results, it can be concluded that the addition of pine cones and spruce bark to spruce sawdust mainly affected the contents of nitrogen and ash and melting temperatures. Despite this, all produced pellets met the standard EN ISO 17225-2 for the content of nitrogen, ash, and also lower calorific value at least B quality. However, only three pellet samples of five met this standard for A2 and B quality for ash melting behavior. Therefore, they present an alternative fuel with interesting energy potential.

Combustion of biomass-based solid fuels is becoming increasingly popular, especially in small heat sources. A major problem in the combustion of biomass is the increased production of emissions and especially the solid component of PM particles. Currently, the most used solution to this problem is the application of electrostatic chimney separators, which innovations are discussed in our article. Two models of electrostatic precipitators were constructed in this work. The aim of this work was to compare the use of a standard single-pipe chimney electrostatic precipitator with a newer four-pipe variant. Eight measurements were performed on both devices with and without the use of an electrostatic precipitator, on the basis of which the separation efficiency was evaluated for both variants. The results of the measurements showed the initial value of the average PM production in the one-pipe variant decreased from 1012 to 416 mg.m−3 when using the separator, while in the use of the four-pipe variant it decreased from the starting value 342 to only 152 mg.m−3. These results show that the improvement of the classic single-pipe separator by increasing the number of tubes significantly reduced the production of PM emissions and increased the separation efficiency from 66 to 85%.

With the combustion of solid fuels, emissions such as particulate matter are also formed, which have a negative impact on human health. Reducing their amount in the air can be achieved by optimizing the combustion process as well as the flue gas flow. This article aims to optimize the flue gas tract using separation baffles. This design can make it possible to capture particulate matter by using three baffles and prevent it from escaping into the air in the flue gas. The geometric parameters of the first baffle were changed twice more. The dependence of the flue gas flow on the baffles was first observed by computational fluid dynamics (CFD) simulations and subsequently verified by the particle imaging velocimetry (PIV) method. Based on the CFD results, the most effective is setting 1 with the same boundary conditions as those during experimental PIV measurements. Setting 2 can capture 1.8% less particles and setting 3 can capture 0.6% less particles than setting 1. Based on the stoichiometric calculations, it would be possible to capture up to 62.3% of the particles in setting 1. The velocities comparison obtained from CFD and PIV confirmed the supposed character of the turbulent flow with vortexes appearing in the flue gas tract, despite some inaccuracies.

Woody and agricultural wastes are important fuels in many countries, and have the potential of being even more important in the future. The main problems of plant biomass combustion are low ash melting temperatures and increased emissions. The most widely used treatment to solve the problem of low ash melting point is blending a fuel with an additive. In this work, pellets were produced from wheat straw containing wood sawdust and paper sludge in the following proportions 40:40:20 and 45:45:10 (straw/sawdust/paper sludge). The purpose of this work was to study the influence of sludge and dendromass on the straw pellet parameters and combustion process. The highest calorific value of 15.71 MJ kg−1 was registered for a sample with a 10% paper sludge concentration. The effectiveness of paper sludge was proved, and the ash melting temperature was increased from 1025 to 1328 °C for the same sample.

This paper deals with the pyrolysis conversion of synthetic waste materials into noble fuels, i.e., heating oils, gasoline, diesel, and carbon. The following article presents the principle and use of pyrolysis conversion of waste tires and plastics. The core of the paper is the determination of energy properties of noble fuels obtained from pyrolysis conversion and the possibility of their real use in industry. The aim of this paper is a technical-economic evaluation of the use of waste pyrolysis in practice in the Slovak Republic. Unlike various methods of waste management, there are also more efficient methods, which primarily have a positive effect on the ecology of our Earth and at the same time can be effectively used for the production of alternative fuels. One of these methods is the pyrolysis conversion of synthetic waste materials into noble fuels. It is an ecological, waste-free, economical, and economical disposal of waste with a full recovery of its energy and material components with reduced emissions, and therefore this direction of using synthetic waste for the conversion of alternative fuels contributes to sustainable development. A significant advantage of this waste management is considered to be the fact that only waste tires or chlorine-free plastics are used as input materials without other necessary raw materials obtained by other economic activity. Tires and plastics are generated daily as waste in every household.

In this publication the trophy level of Wapienica dam reservoir, based on the composition species of planktonic algae and their biomass, and concentrations of chlorophyll a, was defined. The research was conducted during the vegetative season in 2013 year; the samples were taken from two research points (W1 – the part of river Wapienica inflow to reservoir and W2 – the part of the reservoir dam) by using bathometer. The whole biomass of planktonic algae and concentration of chlorophyll a from two research areas were low and it allowed to classify water of this reservoir to oligo-/ mesotrophic. Only in the part of the reservoir dam, in summer season, an increased trophy level was observed (Heinonen 1980). A similar trophic character (oligo-/ mesotrophic) of the water reservoir was also indicated by algae species: Achnanthes lanceolata (Bréb.) Grun. in Cl. and Grun., Chrysoccoccus minutus (Fritsch) Nygaard. For a temporary increase of the trophy level, the diatom Nitzschia acicularis (Kütz.) W. Sm. could indicate, because it is a typical species in poorly eutrophic water. The green algae (Pediastrum and Coelastrum, which were observed in summer season) could also indicate for a rise of the trophic state, because they are typical for eutrophic water.

The alternative energy sources are more and more used for production of heat. Several new combustion devices allow co-firingof different fuels, like dendromass and phytomass. The article analyses combustion of wood and straw pellets in the same boiler.Measurements were realized in two automatic heat sources – one is adapted to burn pellets made from wood or straw and anotherallows only burning of wood pellets. There are analysed performance and emission parameters of boiler.

The effort of many manufacturers of heat sources is to achieve the maximum efficiency of energy transformation chemically bound in the fuel to heat. Therefore, it is necessary to streamline the combustion process and minimize the formation of emission during combustion. The paper presents an analysis of the combustion air temperature to the heat performance and emission parameters of burning biomass. In the second part of the paper the impact of different dendromass on formation of emissions in small heat source is evaluated. The measured results show that the regulation of the temperature of the combustion air has an effect on concentration of emissions from the combustion of biomass.