Filip Kokalj

• Doctor of Engineering
• Associate Professor at University of Maribor

This paper examines sustainable industrial practices in Serbia, particularly in the mining and energy sector, focusing on the potential of flotation tailings and fly ash, as materials with the largest share in disposed waste in Serbia in 2023 (95%). It highlights the environmental challenges of mining waste and explores innovative approaches to was...

Waste-to-energy (WtE) is a key part of modern waste management. In the European Union, approximately 500 WtE plants process more than 100 million tons of waste yearly, while globally, more than 2700 plants handle over 500 million tons. Roughly 20% of the waste processed is bottom ash (BA). However, this ash can contain heavy metals in concentration...

The circular economy is more than just a concept; it represents a powerful mechanism for converting linear value creation into a circular model through a comprehensive and systemic approach to sustainable development. This model can contribute to the transformation of the economy by shaping production, consumption, and disposal processes to close m...

This article examines the impact of financial support mechanisms and geopolitical factors on the profitability of investments in solar power plants within Slovenia. The European Union’s energy policy prioritizes increases in renewable energy sources, aiming to reduce dependency on unstable and volatile fossil fuel markets. Solar power plants play a...

Contemporary societies, whether they have reached advanced levels of economic and social development or are still developing, need to prioritise the implementation of circular economy practices. This will facilitate the shift towards regenerative, sustainable, and closed-loop industrial systems. For now, there are some efforts to encourage patterns...

Practically all residential and commercial gas appliances installed within the EU today were designed for operation with natural gas. A clean and efficient solution for heating and hot water generation is the combustion of hydrogen in case of a gas condensing boiler. Safe and stable combustion of hydrogen is a complex issue, and several influence p...

Wood biomass fuels have become increasingly important in terms of achieving future sustainability targets regarding RES, especially to reduce GHG and the use of domestic energy sources, on other hand with these fuels the pulutant air emissions have to be addressed with great attention. Nowadays, air staging and flue gas recirculation are often used...

This work is aimed at determining the impact of Secondary Air (SA) boundary conditions on CFD combustion simulation results in a small-scale wood pellet boiler. Two sets of boundary conditions are considered: (1) The SA inflow boundary conditions (i.e., the temperature, mass flow and turbulence distribution), and (2) The SA diffuser wall boundary c...

An effective air staging strategy is of great importance for achieving low emissions and sensible heat losses through flue gas extraction. In cases where a commercially available system needs to be optimised, often the only viable measure is the modification of process parameters. In this work, the aim is to (1) Discover a combination of the most s...

Optimal geometric and process parameters related to air staging which ultimately lead to lower pollutant formation and a higher thermal efficiency can be found by utilisation of the CFD simulation method. Simplified and computationally efficient methods for the simulation of complex phenomena which occur in a biomass boiler can therefore be of grea...

Lead-acid batteries are the most frequently used energy storage facilities for the provision of a backup supply of DC auxiliary systems in substations and power plants due to their long service life and high reliability. It is possible to define the load in these systems, therefore the IEEE 485 Standard can be used for the selection of batteries ac...

The applicability is studied of a simplified equilibrium model for prediction of the composition and quality of producer gas from gasification of different waste. A simplified equilibrium model of stoichiometric type based on system thermodynamic equilibrium has been developed in the form of a stand-alone computer application. Standard numerical me...

This paper presents the most appropriate numerical approach for investigation of the ignition phenomena of the premixed confined combustion in a condensing boiler. A transient simulation with the coupling of the burning velocity model was sufficient enough to describe fully the phenomena that are responsible for the ignition sequence and the flame...

Grate-fired boilers are commonly used to burn biomass/wastes for heat and power production. In spite of the recent breakthrough in integration of advanced secondary air systems in grate boilers, grate-firing technology needs to be advanced for higher efficiency and lower emissions. In this paper, innovative staging of combustion air and recycled fl...

Renewable energy production, storage and utilization has been studied in connection with fluctuating renewable power production and demand. The coupling has been considered of surplus renewable power with sewage sludge gasification and renewable syngas storage. High quality syngas produced with power support can be introduced into a gas distributio...

Waste water treatment is a standard process in developed countries. It is intended to minimize the influence of waste water on the environment. The treatment process produces various remains that are generally called sewage sludge. In general, the remaining material is treated physically to dewater the sludge to reduce the volume and mass before di...

Each year, the modern society produces more waste. Domestic habits and economic standard place Slovenia next to the other progressive countries. Statistically speaking, every person produces around a kilogram of waste per day. Taking into account the average heating value of waste, this equals around a quarter of a liter of heating oil or almost on...

The purpose of the research work in the presented article was to find a solution, by means of a mathematic model, to the problem of how to prepare solid fuels from non-hazardous waste that can be processed into solid fuels according to the national law in force. Non-hazardous waste is defined by the DIRECTIVE 2008/98/ES of the European Parliament a...

Nowadays, a part of Municipal Solid Waste (MSW) of higher calorific value is usually used as a fuel in Waste-To-Energy-Plant (WTEP) which uses bed combustion process in a grate furnace. The properties and structure of MSW are very variable, so the complete combustion and emissions on the reasonable level are often very hard to achieve. The Computat...

The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output par...

The combustion process for using municipal solid waste (MSW) as a fuel within a waste-to-energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as MSW proximate and ultimate analysis, the season of the year, primary and secondary air-inlet velocity and, secondly, on ou...

The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output par...

The combustion process, using municipal solid waste (MSW) as a fuel in waste to energy plant, calls for a detailed understanding of these phenomena On the one hand, this process depends on many input parameters, like MSW proximate and ultimate analysis, the season of the year, primary and secondary inlet air velocity, and on the other hand on the o...

A numerical analysis of combustion in the secondary chamber (thermoreactor) of a two-stage pilot scale incinerator using computational fluid dynamics (CFD) is presented in detail. Various versions of the CFD program package CFX were used, which offer different combustion models for specific types and forms of combustion processes. The present study...

Waste incineration still seems to be an essential technology in the concept of integrated waste management. However, the desirable quantity of waste incineration residue needs to be as low as possible. Therefore, related optimization of two-stage waste incineration technology has been performed with the main goal of producing lower amounts of boile...

The average annual overall and specific fuel energy consumptions of the passenger car (PC) country fleet in the Republic of Slovenia during the years 1992 – 2020 have been analyzed. The mathematical model REMODIO has been used to calculate and predict the annual energy consumption. The governing expression is presented including the total number of...

Waste incineration is still an essential technology in the concept of integrated waste management. Most of the combustion residues are incinerator bottom ash. It has been discovered that incinerator bottom ash from the incineration of separated waste in the primary chamber of the modular two-stage incinerator mainly consists of metal oxides, especi...

The impact of errors of the variable input data on the error of motorized passenger car road CO2 emission prediction is investigated. The Institute emission computation model REMODIO is used for these tests as an example. The orthogonal composition design 33 (OCD 33) is used to vary the input data of the three variables: the number of registered pa...

A numerical analysis of the combustion in the secondary chamber (thermoreactor) of a two-stage pilot-scale incinerator using computational fluid dynamics (CFD) is presented. The focus of the research was on those physical conditions that ensure complete combustion, i.e., temperature, residence time and turbulent mixing. Various versions of the CFD...

The numerical simulations of combustion in secondary combustion chamber of pilot scale waste incinerator using computational fluid dynamics are analyzed. State-of-the-art commercial software packages enable reliable and accurate simulation of combustion processes including the ultimate analysis of the physical complete combustion conditions. Result...

Abstract The aim of this paper is to evaluate the contribution of vehicular fuel and IC engines on CO2 emission. Definitions of mass and volumetric emission indexes and emission factor are given, and the calculated values for mostly used CnHm fossil fuels are presented. The scenario of European carmaker voluntary agreement to reduce the specific CO...

Abstract Acid sludge or gudron is oily waste that forms in the process of acid rafination inter products of crude oil or waste oil with concentrated sulphur acid. There are several old dump sites for acid gudron in Slovenia. Recently was made a decision to start the remedial process of these old unsolved ecological problems. After the recent invest...

Abstract The interdependence between IC engine development and fuel/lubricant quality has existed, ever since the first engine was born. In fact the first engine was invented and designed for using explicitly only a definite type of fuel. This has required a continuous and strong cooperation between engineers, researchers and other experts of both...