Application of analytical and CFD models of liquid fuels combustion in a fluidized bed

In Laboratory for Thermal Engineering and Energy of Institute Vinca, University of Belgrade, a 2-D CFD modeling procedure of numerical simulation of unconventional liquid fuel combustion in bubbling fluidized bed has been developed. This procedure is based on a two-fluid Euler-Euler approach modeling a fluidized bed with the determination of the velocities field of gas and particulates in two-phase, granular flows, analog to the kinetic theory of gases. This model describes in detail the unsteady motion of gas and solid phases, the formation and movement of bubbles with the combustion process in the fluidized bed, but temperature profiles calculated by the bed height differ to some extent from the experimentally obtained profiles. This discrepancy is probably due to the inability of a two-fluid CFD model to give a realistic simulation of the liquid fuel mixing in a fluidized bed. Therefore, an analytical model has been developed, where one of the basic assumptions is that the particles are mixed in the vertical direction of fluidized bed mainly by the bubble wakes. The proposed zonal type of calculating procedure is based on Davidson and Harrison two-phase model of the bubbling fluidized bed, where fluidized bed is divided into zones within which material and energy balances are set

Polycyclic aromatic hydrocarbons emission from cigar burner combustion system and comparison of their content in fly ashes

Agricultural biomass is considered a preferred RES in Serbia because of its availability and suitability to limit the use of fossil fuel resources and reduce GHG emissions. Therefore, constant work has been done to develop technologies that enable its utilization for energy purposes. As an example of these efforts, in the Agricultural Corporation PKB, the soybean straw cigarette-type combustion system has been applied for greenhouse heating for over a decade. However, many volatile and semivolatile organic compounds are emitted directly into the atmosphere or concentrated in ash particles during agricultural biomass combustion. Since some of the emitted compounds, such as polycyclic aromatic hydrocarbons (PAHs), are toxic, monitoring their concentrations in fly ash is recommended. Literature data regarding PAHs content in agricultural biomass ashes are insubstantial, especially in Serbia. For that purpose, PAHs contents in the cyclone and stack fly ashes of soybean straw were investigated and compared. In addition, the emission factors, toxicity, carcinogenicity and benzo[a]pyrene equivalence concentrations were determined and used to estimate the potential environmental impact of these ashes. As a result, stack ash has been shown to have a higher potential environmental risk than cyclone ash. Hence, an assessment of using soybean straw as a feed fuel in a real cigarette-type combustion plant regarding PAHs emission is given. These results provide important information for optimizing combustion conditions and assisting the local entities in managing air pollution and control policies in Serbia

The Removal of Ni2+ and Cd2+ -ions onto Synthetic Mineral Based Composite Functionalized by Polyethylenimine

This study presents the synthesis of porous cordierite- based ceramics and its surface activation by polyethylenimine/nano-CeO2 for the heavy metal removal. The synthesis was carried out by the addition of following powders: MgO, Al2O3, and SiO2 in 2:2:5 molar ratios, respectively. The oxide(s) mixture was further processed in two sequential stages: i) ball milled in the ethanol for 40 minutes and palletized under the pressure of 3 t/cm2, as a pre-sintering process, and ii) the pallets were further sintered for 2h in the air atmosphere at 1350 oC, under a heating rate of 20 oC/min. The sintered mineral composite was crashed and sieved, and mixed with 20 wt % of nanocellulose, as a pore forming agent. Nanocellulose mixture was pressed into pallets under 5 t/cm2 and sintered at 700 oC, under a heating rate of 5 oC/ min. The obtained synthetic cordierite was further tested as the adsorbent activated by polyethylenimine/ nano-CeO2 for the removal of Ni2+ and Cd2+ -ions. The adsorption isotherms, kinetics models, and thermodynamic parameters were also analyzed, manifesting that the adsorption is a spontaneous and endothermic process. The phase composition of the pristine and activated cordierite was analyzed by the X-ray diffraction method (XRD), Fourier transformation infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). This work has shed light on the mechanism of heavy metals removal from the aquatic medium using the novel hybrid (nano)synthesized material

Experimental determination of the swirl burner laboratory models hydraulic resistance

Performed investigation of pulverized fuel combustion in swirl flows has shown that there are two important groups of influential parameters: fuel and burner characteristics. The most important conclusion of these investigations is that each type of fuel needs a defined burner for its combustion and concrete operating parameters for its optimal work. Optimal operating parameters can be determined only by performing the appropriate experiments. Selection of optimal swirl burner design is dependent on energy loss which is used for air transport through burner. Increasing of swirl intensity is convenient for fuel ignition and flame stability, but energy loss for air transport increases, too. Swirl economy is estimated using hydraulic resistance parameter which represents energy loss due to swirling. In the paper are presented the methods and experimental data of hydraulic resistance determination for three laboratory models of swirl burners for pulverized fuel combustion. In the tangential burner the swirling is accomplished by tangential inflow of secondary air and fuel/air mixture. Axial-blade burner of type 1 enables swirling by a set of 18 blades. Axial-blade burner of type 2 is with a central lead of gas and coaxial lead of fuel/air mixture, primary air and recirculating gases. In movable swirl block burner the secondary air swirling is enabled by 8 stationary and 8 movable blocks fixed at movable and stationary plate. (C) 2012 Published by Elsevier Ltd.20th International Congress of Chemical and Process Engineering CHISA, Aug 25-29, 2012, Prague, Czech Republi

Two-dimensional mathematical model of liquid fuel combustion in bubbling fluidized bed applied for a fluidized furnace numerical simulation

Lately, experimental methods and numerical simulations are equally employed for the purpose of developing incineration bubbling fluidized bed (BFB) facilities. The paper presents the results of the 2-D CFD model of liquid fuel combustion in BFB, applied for numerical simulation of a fluidized bed furnace. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The proposed numerical model comprises energy equations for all three phases (gas, inert fluidized particles, and liquid fuel), as well as the transport equations of chemical components that are participating in the reactions of combustion and devolatilization. The model equations are solved applying a commercial CFD package, whereby the user submodels were developed for heterogenic fluidized bed combustion of liquid fuels and for interphase drag forces for all three phases. The results of temperature field calculation were compared with the experiments, carried out in-house, on a BFB pilot facility. The numerical experiments, based on the proposed mathematical model, have been used for the purposes of analyzing the impacts of various fuel flow rates, and fluidization numbers, on the combustion efficiency and on the temperature fields in the combustion zone

Characterization of potential probiotic strain, L. reuteri B2, and its microencapsulation using alginate-based biopolymers

In this study, Lactobacillus reuteri B2was isolated fromthe feces of C57BL/6 mice and assessed on probiotic activity.L. reuteri B2was identified by 16S rDNA sequencing, which the cell viability in acidic conditions at pH 2.0was64% after 2 h, and in the presents of 0.30% of the bile salts, after 6 h, was 37%. Antimicrobial assay with L. reuteri B2showed maximumdiameters against Klebsiela oxytoca J7 (12.5±0.71mm).Wefurther hypothesized if L. reuteriB2 strain in the free form can survive all conditions in the gastrointestinal tract (GIT) then the utilization of theappropriate biomaterials would ameliorate its stability and viability in GIT. L. reuteri B2 was microencapsulatedinto sodium alginate-(Na-alg) and different content of Na-alg and sodium maleate (SM) beads. Characterizationmaterials enveloped their thermal characteristics (TGA/DTA analysis) and structure using: scanning electron microscopy(SEM), FTIR, and particle size distribution. The high survival rate of L. reuteri B2 at lowpH from2.0 to 4.0and in the presence of the bile salts, at concentrations up to 0.30%, was obtained. L. reuteri B2 showed strong antimicrobialactivity and the best protection microencapsulated with Na-alg + SM in simulated gastric juices(SGJ).This is the peer-reviewed version of the article: Popović, M., Stojanović, M., Veličković, Z., Kovačević, A., Miljković, R., Mirković, N.,& Marinković, A. (2021). Characterization of potential probiotic strain, L. reuteri B2, and its microencapsulation using alginate-based biopolymers. International Journal of Biological Macromolecules, Elsevier, 183, 423-434. [https://doi.org/10.1016/j.ijbiomac.2021.04.177]Published version: [https://cer.ihtm.bg.ac.rs/handle/123456789/4594]Supplementary material: [https://cer.ihtm.bg.ac.rs/handle/123456789/4596

Supplementary material for the article: Rusmirović, J.D., Obradović, N., Perendija, J., Umićević, A., Kapidžić, A., Vlahović, B., Pavlović, V., Marinković, A.D., Pavlović, V.B., 2019. Controllable synthesis of Fe3O4-wollastonite adsorbents for efficient heavy metal ions/oxyanions removal. Environ Sci Pollut Res 26, 12379–12398. https://doi.org/10.1007/s11356-019-04625-0

Related to: [http://dais.sanu.ac.rs/handle/123456789/5764]Supplementary material for: [http://dx.doi.org/10.1007/s11356-019-04625-0

Dioksini i njihova toksičnost za ljude

The term dioxins usually refers to polychlorinated dibenzo-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). As 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) has the highest toxic potential, the toxic potentials of other PCDDs and PCDFs are defined in comparison with it. Human exposure to dioxins can be environmental (background), occupational, or accidental pollution. In the human body, dioxins are in part metabolised and eliminated, and the rest is stored in body fat. People vary in their capacity to eliminate TCDD, but it is also dose-dependent; the elimination rate is much faster at higher than lower levels. The liver microsomal P4501A1 enzyme oxygenates lipophilic chemicals such as dioxins. It is encoded by the CYP1A1 gene. Cytosolic aryl hydrocarbon receptor (AhR) mediates their carcinogenic action. It binds to dioxin, translocates to nucleus and together with hydrocarbon nuclear translocator (ARNT) and xenobiotic responsive element (XRE) increases the expression of CYP1A1. Dioxins are classified as known human carcinogens, but they also cause noncancerous effects like atherosclerosis, hypertension, and diabetes. Long-term exposures to dioxins cause disruption of the nervous, immune, reproductive, and endocrine system. Short-term exposure to high levels impairs the liver function and causes chloracne. The most sensitive population to dioxin exposure are the foetuses and infants. A large number of health effects have been documented in the scientific literature, and they all place dioxins among the most toxic chemicals known to man.Dioksini su skupina kemijskih spojeva koji obuhvaćaju poliklorirane dibenzo-dioksine (PCDD) i poliklorirane dibenzo-furane (PCDF). Najveći toksični potencijal (faktor ekvivalentne toksičnosti) ima 2,3,7,8-TCDD, dok su toksični potencijali drugih PCDD i PCDF određeni u odnosu na njega. Izloženost dioksinima može biti izravna: izloženost dioksinima emitiranim u okoliš kao posljedica nesreće, profesionalna izloženost te neizravna, tzv. pozadinska. Nakon ulaska u ljudski organizam dioksini se djelomično metaboliziraju i eliminiraju, a ostatak se pohranjuje u adipozno tkivo. Postoji određena varijabilnost između ljudi u kapacitetu eliminacije TCDD. Eliminacija TCDD ovisna je o dozi – kod veće izloženosti (izloženost višim koncentracijama) brzina eliminacije je viša nego kod manje izloženosti (izloženost nižim koncentracijama). Enzim P4501A1 najvažniji je u oksigenaciji lipofi lnih supstrata poput dioksina. Kodiran je genom CYP1A1. AhR je stanični receptor koji djeluje kao transkripcijski faktor koji posreduje u njihovu karcinogenom učinku. AhR veže dioksin te se premješta u jezgru gdje zajedno s ARNT (engl. aryl hydrocarbon nuclear translocator) i XRE (engl. xenobiotic responsive element), smještenim u promotorskoj regiji gena za CYP1A1, uzrokuje povećani izražaj CYP1A1. Dioksini su karcinogeni spojevi, ali imaju i nekarcinogene učinke poput ateroskleroze, hipertenzije, dijabetesa, poremećaj živčanog, imunosnog, reproduktivnog i endokrinog sustava, posebice kod kronične izloženosti. Akutna izloženost uzrokuje oštećenja jetre i klorakne. Najosjetljivija skupina izloženosti dioksinu je dojenčad u prenatalnom i postnatalnom razdoblju. U znanstvenoj i stručnoj literaturi dokumentirani su brojni zdravstveni učinci kao posljedice izloženosti dioksinima te ih svi ističu kao jedne od najtoksičnijih kemijskih spojeva

Denitrification techniques for biomass combustion

In order to achieve the main Applicable combustion control systems in grate-fired bogoals of sustainable development through the harmonization of rising energy needs with environmental protection, modern society promotes the use of biomass as a renewable energy source. Biomass, like any taother fuel, emits certain pollutants from combustion, nitrogen oxides (NOx) being one of them. Control of NOx emission, originated in biomass combustion, is becoming a very significant technical challenge due to the imposition of increasingly strict emission limits. The experimental research and industrial experiences (that are not always easily available) were analyzed in order to make an overview of proven and prospective technical solutions, as well as directions for practical applications for reducing NOx emissions originating from biomass combustion. The denitrification techniques according to the broadest classification (pre-combustion, combustion control and post-combustion) have been analyzed. As the NOx emission is more strongly influenced by the nitrogen content of biomass fuels (especially of those with significant nitrogen content) rather than the operating conditions, the emphasis is placed on the post-combustion (secondary denitrification) measures and the most successful among them - selective catalytic (SCR) and non-catalytic reduction (SNCR). The SCR catalysts, as well as commonly used amine-based reagents (in both SCR and SNCR), are analyzed in accordance with various parameters (activity temperature domain, the location of installation and structural configuration). The special challenges for SCR and SNCR application were considered, and a comparative overview of advantages and disadvantages are given, in accordance with several different criteria. In addition, the applicability of deNOx techniques from the aspect of individual biomass combustion technology is given. Guidelines for the selection of denitrification measures are created, depending on the biomass combusted, combustion technology used, and the installation capacity

Distribution of PAHs in coal ashes from the thermal power plant and fluidized bed combustion system; estimation of environmental risk of ash disposal

The comparison of fly ash generated from lignite combustion in a thermal power plant Kolubara A (Veliki Crljeni) and bottom and fly ash from coal waste combustion in a semi-industrial fluidized bed boiler (Vinča) was performed as the function of particle size. The average total concentrations of the 16 EPA priority PAHs in ash fractions are 0.49 mg kg−1 of ash (thermal power plant) and 17.48 mg kg−1 of ash (fluidized bed boiler). The sum of 3- and 4-ring PAHs accounts for more than 93% of overall PAHs concentration, and the most abundant among them is fluoranthene. The portions of PAHs groups defined based on their physico-chemical properties, as obtained from quantitative structure-activity relationship (QSAR) models included in the Vega platform, were determined. These portions, emission factors, and benzo[a]pyrene equivalence concentrations were further on used to estimate the potential environmental impact of ash disposal. The PAHs emission factors are higher compared to values in the air pollutant emission inventory guidebook of the cooperative program for monitoring and evaluation of the long-range transmission of air pollutants in Europe (EMEP/EEA). The overall emission factors of 16 PAHs for combustion of lignite and coal waste are determined to be 0.15 and 249.97 mg kg−1 of fuel, respectively. Based on the ratios of benzo[a]pyrene equivalence concentrations of each ash and correspondent fuel, the disposal of fly ash from the cyclone of fluidized bed boiler represents the highest risk to the environment among tested ashes