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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 as a primary emission reduction measure in large scale biomass fuel fired boilers, but their combined application in small scale commercial wood pellet boilers is not so common. The implementation of this approach to the small scale burning devices can enable further development of small boilers, in order to achieve a more complete combustion and reduction of pollutant emissions, especially CO, NOx, and PM. In the presented work a comprehensive numerical and experimental study on the combustion parameters is performed, in order to determine the overall combustion properties. A commercial 32 kW small-scale hot water wood pellet boiler was modified numerically from the operating point of view. The findings of this study, like different combinations of recirculated flue gases and secondary air amount, can serve as useful guidelines for the new innovative design and optimisation of the air and recirculated flue gas injection process parameters. The scenarios of this study, where recirculated flue gas was added to the secondary air, were beneficial. Optimally, a CO reduction of 63% was achieved by adding 30% of recirculated flue gas to the secondary air stream, and a 22% reduction was achieved for the NO emissions.

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 suitable process parameters based on a multi-criteria decision-making method and (2) To unveil relevant correlations between the two process parameters under study (PA/SA ratio and excess air), emissions and combustion temperatures. A modified commercial small-scale hot water wood pellet boiler was installed into a laboratory heating system. Nine different cases have been addressed within a parametric study, differing in the PA/SA ratio and overall excess air. Emissions, temperatures inside the combustion chamber and the flow rate of air entering the combustion chamber were measured. A low PA/SA ratio of 0.53 (54.7% reduction from factory settings), combined with a low O2 concentration in the flue gases of 5.26% (39.8% reduction from factory settings), and the elimination of infiltration air resulted in a simultaneous reduction of NOx and CO emissions by 14.4% and 93.9% respectively and a flue gas sensible heat loss reduction of 31.6%.

The common combustion disturbances in the fuel bed in a grate-fired boiler pose a great challenge to accurate modelling of the fuel bed conversion. Therefore, it is difficult to describe the lengthwise profiles of the combustibles leaving the fuel bed into the freeboard accurately. This paper investigates how different fuel bed models or grate inlet profiles will affect the Computational Fluid Dynamics simulation of combustion in the freeboard in industrial grate boilers. Two grate inlet conditions, which are very different in the profiles along the grate but yield the same total mass, momentum, species and energy fluxes into the freeboard, are used in the freeboard simulation of a 13 MWth grate boiler, respectively. The key findings from the comparison between the simulation results and measurement data are as follows. Firstly, the fuel bed model or grate inlet condition accounting for the realistic lengthwise biomass conversion pattern can be used reliably for the simulation of a grate boiler and simulation-based boiler optimisation. Secondly, the impacts of different fuel bed models or different profiles of the grate inlet conditions are virtually restricted only to the vicinity of the fuel bed or in the primary combustion chamber. After the secondary combustion chamber in which up-flowing gas is mixed well with the secondary and tertiary air jets, the simulation results are close to each other. For more general and reliable applications, a comprehensive bed model resolving the mixing, reactions, heat and mass transfer in the fuel bed, is needed and under development.

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 methods have been implemented for solving the mathematical problem formulation. The model`s predicted results have been compared with the published results for biomass and some waste types - municipal solid wastes and refuse derived fuels. Results are included for a bubbling fluidized bed and downdraft fixed bed allothermal gasification, also for catalytic supported gasification. Producer gas predictions by calibrated and non-calibrated versions of the simplified equilibrium model have been studied. The accuracy of these predictions has been evaluated. The results obtained by the simplified equilibrium model have confirmed that such model is a very useful tool for studying the gasification process for municipal solid wastes and refuse derived fuels process parameters for two mostly implemented gasifier types.

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 stabilization, representing most of the actual ignition problems in general. Detailed simulation investigation with the ignition model leads to better comprehension of the whole flame stabilization process and, as a consequence, it facilitates the optimization potential of the global ignition process in boilers. Four different ignition power loads were observed in the investigation. Also, the ratio between oxidizer (air in our case) and the fuel (Methane) was based on the normal combustion process for the described condensing boiler. The numerical results were validated with the experimental set up and testing. Results comparison shows very good correlation of numerical simulation with the experimental case. The ignition times both tested and simulated, that have a significant impact on flame stabilization, are in very good correlation. Also, very good correlations were obtained between the pressure profiles of the numerical and experimental studies.

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 distribution network or stored and utilized on site. Both systems enable gas consumption at power and heat demand periods. The efficiency of power conversion to syngas produced from high moisture sewage sludge has been studied using a developed equilibrium thermodynamic model for the gasification process providing the calculated prediction of the syngas amount and composition. Furthermore, the total energy efficiency has been studied of the syngas production and utilization system. The results show that the optimum scenario to get syngas suitable to introduce into a natural gas distribution network would be to gasify sewage sludge with 35–40 wt.% moisture, while the optimal parameter for syngas to be valorized onsite is, in terms of efficiency, with SS dried to 20 wt.% of moisture content. In the first scenario, a little more power is produced from stored gas in a natural gas distribution network than consumed, and almost twice as much is produced with on-site production, storage and utilization. The study has showed a technically feasible management option for energy production, storage and consumption with available technologies and infrastructure.

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 according to the conventional method of selection. Special attention is paid in the paper to the technical selection of a lead-acid battery, which depends on its operational reliability that decreases with battery aging. It is defined by the extent of maintenance during its service life. A cost analysis was also carried out, which took into consideration maintenance and procurement costs, as well as the costs of the related air conditioning that keeps the prescribed temperature and ventilates the battery room. The impact is shown of selecting a lead-acid battery on the battery room&rsquo, s operating safety when charging. The final selection of lead-acid battery is performed using an optimization algorithm of differential evolution. Using the optimization process, the new battery selection method includes the technical sizing criteria of the lead-acid battery, reliability of operation with maintenance, operational safety, and cost analysis. Two cases of selection of lead-acid batteries for the backup supply of a DC auxiliary system in a transmission substation are presented in the paper, where the input data were determined based on measurements in an existing substation. A comparison is made between the existing conventional and new lead-acid battery selection method based on optimization.

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 great use, provided they offer reliable and reasonably accurate predictions. A previously developed and validated Computational Fluid Dynamics combustion simulation methodology for large-scale waste to energy grate-fired boilers is modified and implemented for the case of a commercial 32 kW wood pellet hot water boiler. An experimental investigation is performed in order to determine process parameters used in the fuel conversion modelling, case setup and, finally, to enable the validation of the numerical modelling approach. The solid fuel conversion is modelled by a coupled empirical 1D bed model which predicts the composition of the combustible gas mixture released from the fuel bed into the freeboard. Compared to the originally proposed fuel bed conversion model, the modified model includes partial char and volatile oxidation, and relies on gas temperatures measured above the fuel bed. Using the modified fuel bed conversion model, several cases were simulated in order to find the most appropriate parameters of the combined finite rate – eddy dissipation combustion model. Results show that by implementing the modified fuel bed conversion model that relies on measurements, reasonably accurate predictions can be achieved of the gas temperature in the combustion chamber and CO concentration at the flue gas outlet.

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 flue gas in a 13 MW th waste wood-fired grate boiler is comprehensively studied based on a numerical model that has been previously validated. In particular, the effects of the jet momentum, position and orientation of the combustion air and recycled flue gas streams on in-furnace mixing, combustion and pollutant emissions from the boiler are examined. It is found that the optimized air and recycled flue gas jets remarkably enhance mixing and heat transfer, result in a more uniform temperature and velocity distribution, extend the residence time of the combustibles in the hot zone and improve burnout in the boiler. Optimizing the air and recycled flue gas jet configuration can reduce carbon monoxide emission from the boiler by up to 86%, from the current 41.0 ppm to 5.7 ppm. The findings of this study can serve as useful guidelines for novel design and optimization of the combustion air supply and flue gas recycling for grate boilers of this type.

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 disposal. This treated sewage sludge has around 25% of dry solids. The chemical and physical properties of the sewage sludge have to be monitored to determine the correct method of disposal. If the sewage sludge contains higher concentrations of heavy metals the only method for the disposal is thermal treatment. This article will present possible technologies for sewage sludge thermal treatment and the experience of Slovene waste thermal treatment plant that incinerates sewage sludge.

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 Computational Fluid Dynamics (CFD) with different CFD codes is often used to analyse the situation in the WTEP. In this paper, the CFD simulation within ANSYS 13.0 software package and in WORKBENCH 2.0 environment is used and supplementary optimisation’s methods are employed by using design explorer approach to achieve the target - optimised values of the input and output parameters which have been defined in order to indicate the complete combustion in the furnace. Furthermore, input and output parameters interaction can be found and presented and measured. On this basis, the optimal operating conditions and optimal combustion chamber dimensions are established through decision support systems in order to assure the complete combustion process with minimal emissions on the environment. Moreover, these requirements should be taken into account to enhance the operation conditions in the existing furnace or in research, development or project phase. In this way, the costs and time in these activities can be reduced. This approach has benefits because it can be used in other furnaces which use other fuels such as biomass, waste-oils or coal.

Institute for power, process and environmental engineering, Laboratory for combustion and Environmental engineering, Faculty of Mechanical Engineering, University of Maribor, Republic of Slovenia 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 parameters such as the temperatures or mass-flow rates of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieving optimal combustible conditions with minimal pollutant emissions, during the plant-design phase. in order to meet these goals, a waste-to-energy plant with bed combustion was investigated by using computational fluid-dynamics approach. The adequate variable input boundary conditions based on the real measurement are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion, or heat transfer models. The operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the combustible products were predicted and visualized. Finally, the response charts and matrix among the input and output parameters during the optimization process are presented, which monitored the dependence among these parameters.

A numerical analysis of combustion in the secondary chamber (thermoreactor) ofa 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 was focused on those physicalconditions that assure complete combustion, that is, temperature, residence time, and turbulent mixing. The selection of an appropriate combustion model was based on a comparison of the numerical results and experimental values of some combustion macro parameters in a thermoreactor. Combustion models based on one-step bimolecular chemical reaction and models based on multistep reactions were used. These models enabled a more detailed prediction of the combustion process in the secondary chamber of a pilot-scaleincinerator. The products of incomplete combustion that are significantly important for the designing and optimization of combustion devices can be predicted by applying multistep reaction models more accurately, especially in a transient regime of combustion.

The average MSW in developed countries has a calorific value between 8 and 12 MJ/kg. Based on this property the MSW can be compared with the fresh wood or lignite, which is low grade coal. The amount of waste generated is still slightly rising over the years with some fluctua‐ tions, due to general economy reasons (at the time of writing – recession) and technical measures in waste management in recent years. The amount of deposited MSW at landfills is getting lower in recent year despite the rise of total generated MSW due to better separate collection and treatment technologies utilized.

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, especially SiO2 and CaO, in proportions that are quite similar to those in cement and so the feasibility of its application as a substitute for cement in concrete was investigated. It was found that after 28 days, the flexural and compressive strengths of the binder using bottom ash were practically comparable with those of a pure cement mixture. The results show that it is reasonable to use a binder containing incinerator bottom ash for applications in which an early-stage lower strength of concrete element is acceptable.

Sažetak Prikazan je utjecaj motornih goriva i pogonskih motora osobnih vozila na emisiju ugljičnog dioksida CO2. Definirani su maseni i volumetrijski indeks i faktor emisije fosilnih goriva i izračunate njihove vrijednosti za najvažnija fosilna motorna goriva. Predstavljen je trend smanjenja specifične emisije CO2 [g CO2/km] osobnih vozila za razdoblje 1995.–2020. koji su predložili proizvođači vozila. Analizirani su procesi pretvaranja primarne energije goriva u pogonskim motorima vozila i njihov utjecaj na stupanj iskorištenja motora i emisiju CO2 vozila. Na osnovi rezultata statističke obrade podataka o deklariranom – tvorničkom i cestovnom specifičnom utrošku goriva [l/100 km] triju grupa vozila s benzinskim motorom, grupiranih po stapajnom obujmu motora, zbirno je ocijenjen utjecaj emisije CO2 na okoliš., 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 CO2 emission [g CO2/km] over the years 1995 through 2020 is discussed. The role of fuel energy conversion process in vehicle engines is analyzed and its effect on fuel consumption [l/100 km] and CO2 emission is summarized. Average values of standardized (ECE) and road (test) fuel consumption performances of vehicles with SI engines have been calculated and associated CO2 emissions are presented. The requisite approaches to reduce vehicle CO2 emission are discussed.

Sažetak Međusobna ovisnost razvoja motora s unutarnjim izgaranjem i kvalitetom goriva/maziva postojala je sve od rođenja prvog motora. Upravo je prvi motor bio izumljen i konstruiran za korištenje samo određene vrste goriva. To je zahtijevalo neprekidnu i tijesnu suradnju između inženjera, istraživača i drugih eksperata iz obje grane industrije. U članku je dat prvo kratak pregled razvoja motora s unutarnjim izgaranjem (MUIZ) u toku prošlog stoljeća i navedeni su zahtjevi za performance motora u bližoj budućnosti. Dalje su analizirana i prodiskutirana neka najvažnija fizička i kemijska svojstva goriva koja određuju kvalitetu goriva za motore: oktanski i cetanski broj, kemijski sastav, prisutnost elementarnog S, N, P i kemijski vezanog N u gorivu, prvenstveno s gledišta njihovog utjecaja na efektivne parametre, radne performance motora i emisiju polutanata., 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 branches of industries. In this paper a short review of IC engine development during the last century is presented first, and the requirements on IC engine performance in the near future are listed. In continuation only a few of most important physical and chemical properties determining the quality of vehicular engine fuels have been analyzed and discussed: octane and cetane number, fuel chemical composition, fuel S, N, P and N, mainly from the stand point of their influence on IC engine effective parameters, operating engine performance and pollutant emissions.

Sažetak Kiseli gudron je zauljena otpadna tvar, koja nastaje prilikom kisele rafinacije međuprodukata nafte odnosno rabljenih ulja koncentriranom sumpornom kiselinom. U Sloveniji postoji nekoliko starih deponija kiselog gudrona. Nedavno se odlučilo pristupiti projektu saniranja tih starih nerješenih ekoloških problema. Poslije ispitivanja i nekih drugih postupaka sanacije, sada se odlučilo isprobati mogućnost spaljivanja gudrona. Za naš rad je bilo odlučeno, da se naprave kemijske analize gudrona sa dvije najveće deponije na području grada Maribora, dakle s deponija na Studencima i u Pesnici. Ove dvije lokacije, kao i neke druge manje bi trebale biti idućih godina sanirane. Gudron je dospio na te deponije prije više od 20 godina. Nastao je pri preradi starih ulja postupkom rafinacije sa sumpornom kiselinom, pri čemu se izvuku nezasičeni ogljikovodici, spojevi metala i organski kloridi. Količina otpadnog materijala pri takvoj preradi iznosi od 3 do 10 % od ulaznih količina.Vidi se da postoji razlika između uzoraka, pogotovo glede koncentracije klora, cinka i olova. Kalorične vrijednosti i koncentracije sumpora su slične i one će najodlučnije utjecati na proces izgaranja te na tvorbu produkata. Najprije je bila obavljena teoretsko - tehnička studija mogućih i za okoliš sigurnih postupaka spaljivanja neobrađenog gudrona. Zbog karakterističnog kemijskog sastava i fizikalnih svojstava gudrona opredijelili smo se za spaljivanje na osnovi dvije različite tehnologije s različitim postupcima obrade dimnih plinova, koje su neophodno potrebne, radi dostizanja nižih emisijskih koncentracija polutanata u odnosu na propisane dozvoljene emisije od EU. Dobrim planiranjem svih pokusa, dobrim izborom tehnologije spaljivanja i tehnologijom prečišćavanja dimnih plinova te kvalitetnim izvođenjem pokusa uspjeli smo izvesti spaljivanje gudrona, koji je dao veoma povoljne rezultate. Pogotovo smo zadovoljni, što smo uspjeli sniziti koncentraciju SO2 ispod dozvoljinih granica. Koncentracije SO2 su bile u dimnim plinima pred čišćenjem na nivou 10g/Nm3, što pokazuje da je gotovo sav sumpor izgorio i napustio primarnu komoru s dimnim plinovima. Sniženje njegove koncentracije se obavilo u dva odnosno tri koraka. Koncentracije teških metala u šljaki pokazuju da je samo manji dio napustio primarnu komoru, što je olakšalo rad naprava za čišćenje plinova., 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 investigation of some other remedial processes, a decision was made to investigate the incineration of acid sludge. In order to conduct the investigation, chemical analyses of acid sludge from two biggest dump sites in area of the city of Maribor, located in the city suburbs of Studenci and Pesnica was made. These two locations and several smaller will be in remedial process in the course of next years. Gudron was transported there more then 20 years ago. It was produced while processing old oils with the process of rafination with sulphur acid. With this process the unsaturated hydrocarbons, metal parts and carbon chlorides are removed. The amount of waste material in such a process is between 3 and 10 percent of input quantity. There is a difference between the two samples, especially in concentration of chlorine, zinc and lead. Calorific value and concentration of sulphur are similar and they are the most influential in the process of combustion and formation of combustion products. In the very beginning, the theoretical-technical study of possible and environmentally safe processes of incineration of unprocessed acid sludge was conducted. Due to specific chemical composition and physical properties of acid sludge the decision was made to perform test incineration of acid sludge by using two different technologies with variety of flue gas treatment systems, which are indispensably necessary for reaching the flue gas emission levels set by the European Community Directive. Appropriate planning of all test trials with correct selection of incineration technology and technology of flue gas treatment together with precise execution of tests shows, that it is possible to incinerate acid sludge with very good results. The concentration of SO2 was the hardest to get under the legislative value. The SO2 concentration in raw gases was around 10 g/Nm3, showing that all sulphur has been burnt and has left the primary combustion chamber with flue gases. The reduction of its concentration was undertaken in two or in three steps. The concentration of heavy metals in slag shows, that only smaller part of them has left the primary chamber, adding to the eased work of flue gas treatment devices.