Моделирање и оптимизација процеса пиролизе кукурузног окласка

Развој енергетике је снажан модификатор привредне структуре и погонски фактор технолошког и економског развоја. Стални и све виши пораст потрошње енергије, условљених како због повећања становништва тако и због повећања нивоа и стандарда живота у свим земљама света, наговестила је чињеницу да се залихе фосилних горива исцрпљују. Паралелно са суочавањем ограничености извора фосилних горива јавља се и проблем нагомилавања CO2 у атмосфери и ефекат „стаклене баште“ и „киселих киша“. Дакле енергија и заштита животне средине представљају „два лица истог новчића“. У циљу задовољења свих захтева, како по погледу задовољења енергетских потреба тако и испуњење услова задатих правилима заштите животне средине, потребно је интензивније користити обновљиве изворе енергије (ОИЕ). Енергија биомасе представља акумулирану сунчеву енергију којом се енергија трансформисала у хемијску енергију процесом фотосинтезе. С обзиром да је енергија акумулирана сунчева енергија у биомаси хемијског порекла, њеном експлоатацијом нема периода прекида рада, као у случају других ОИЕ (енергија ветра, сунчева енергија, итд.). Биомаса као се сматра за CO2 неутрално гориво. Наиме, угљеник из атмосфере се потхрањује у биљке током њиховог раста, да би се током њиховог разлагањем та иста количина угљеника вратила у атмосферу, у облику CO2. Биомаса садржи мале количине сумпора и азота, који су главни елементи у формирању „киселих киша“. Из наведених разлога потпуно је јасно да се у оквиру било које политике одрживог развоја као један од основних постулата мора предвидети и коришћење биомасе за потребе генерисања енергије...The need for energy and fuels is one of the common threads throughout human history. Energy, in its many useful forms, is a basic element that influences and limits human’s standard of living and technological progress. The sustainable provision of energy that meets the needs of the present without compromising the ability of future generations to meet their needs, did not receive much attention until the middle of the twentieth century, that is, the fossil fuel era, and then usually only in crisis situations of one kind or another. The rapid worldwide increase in the consumption of fossil fuels in the twentieth century to meet energy demand, mostly by industrialized nations, suggests that the time is not too distant before depletion begins to adversely affect oil and natural gas reserves. Also, the greenhouse effect and acid rains are mainly associated with the use of fossil fuels. The carbon cycle in nature is basically balanced, but the artificial emission of CO2 by the use of fossil fuels is the cause of the increase in CO2 in the air. Other gases like methane, nitrous oxide, and ozone also can be the cause of the greenhouse effect, but their weight is smaller compared to CO2. Energy and environment currently are two sides of one coin. To separate one from another, the world needs to increase usage of alternative biomass energy resources. Biomass energy is considered to be CO2 neutral in so far as its production and consumption are balanced. Biomass is also noted for less S content and, thus, less likely to cause acid rain. Biomass has historically supplied human needs for food, fibre, energy and structural material. The potential for biomass to supply much larger amounts of useful energy with reduced environmental impacts compared to fossil fuels has stimulated substantial research and development of systems for handling, processing, and converting biomass to energy..

Numerical modeling of Nomex honeycomb core composite plates at meso scale level

Kompozitne ploče sa saćastom ispunom se sve više koriste pri izradi primarnih vazduhoplovnih struktura. Ovi materijali koriste se pri konstrukciji oplata trupova letelica, centralnih i spoljnih torzionih kutija krila, oplata pogonskih grupa, vrata stajnih trapova, komandnih površina kao što su spojleri i eleroni. Da bi se odredila polja napona i deformacija opterećene strukture neophodno je poznavanje svih elastičnih koeficijenata. U ovom radu, metod za određivanje svih potrebnih elastičnih koeficijenata ispune i ploča je predstavljen. Koristeći se eksperimentalno dobijenim rezultatima za papir NOMEH (tip 410 ) kao i fenolnu matricu materijalni model je predstavljen, izrađen je model konačnih elemenata kompozitne ploče sa saćastom ispunom i numerički je simuliran test savijanja u tri tačke. Dobijeni rezultati upoređeni su sa rezultatima dobijenim eksperimentom. Primećeno je dobro slaganje između predloženog modela materijala i eksperimentalno dobijenih vrednosti.Honeycomb core composite plates are becoming more important in the construction of primary aerospace structures. Nowadays, these types of materials are used for construction of fuselage skins, central and outer wing boxes, engine tail cones, landing gear doors, command surfaces like spoilers and ailerons etc. To determine the stress strain field in loaded honeycomb plates elastic coefficients are required. In the present work, a method for determining all required elastic coefficients for the core and plates is presented. Using experimentally obtained values for Nomex paper (type 410) and phenolic resin material model is presented and FEA model of composite plate with honeycomb core is created and three point bend test is simulated. Numerically obtained stress and strain values are compared to the experiment. Good agreement between proposed material model and experimentally obtained values is observed

Numerical modeling of Nomex honeycomb core composite plates at meso scale level

Kompozitne ploče sa saćastom ispunom se sve više koriste pri izradi primarnih vazduhoplovnih struktura. Ovi materijali koriste se pri konstrukciji oplata trupova letelica, centralnih i spoljnih torzionih kutija krila, oplata pogonskih grupa, vrata stajnih trapova, komandnih površina kao što su spojleri i eleroni. Da bi se odredila polja napona i deformacija opterećene strukture neophodno je poznavanje svih elastičnih koeficijenata. U ovom radu, metod za određivanje svih potrebnih elastičnih koeficijenata ispune i ploča je predstavljen. Koristeći se eksperimentalno dobijenim rezultatima za papir NOMEH (tip 410 ) kao i fenolnu matricu materijalni model je predstavljen, izrađen je model konačnih elemenata kompozitne ploče sa saćastom ispunom i numerički je simuliran test savijanja u tri tačke. Dobijeni rezultati upoređeni su sa rezultatima dobijenim eksperimentom. Primećeno je dobro slaganje između predloženog modela materijala i eksperimentalno dobijenih vrednosti.Honeycomb core composite plates are becoming more important in the construction of primary aerospace structures. Nowadays, these types of materials are used for construction of fuselage skins, central and outer wing boxes, engine tail cones, landing gear doors, command surfaces like spoilers and ailerons etc. To determine the stress strain field in loaded honeycomb plates elastic coefficients are required. In the present work, a method for determining all required elastic coefficients for the core and plates is presented. Using experimentally obtained values for Nomex paper (type 410) and phenolic resin material model is presented and FEA model of composite plate with honeycomb core is created and three point bend test is simulated. Numerically obtained stress and strain values are compared to the experiment. Good agreement between proposed material model and experimentally obtained values is observed

Kinetics of Corncob Pyrolysis

Two different corncob samples from different continents and climates were studied by thermogravimetry at linear and nonlinear heating programs in inert gas flow. A distributed activation energy model (DAEM) with three and four pools of reactants (pseudocomponents) was used due to the complexity of the biomass samples of agricultural origin. The resulting models described well the experimental data. When the evaluation was based on a smaller number of experiments, similar model parameters were obtained which were suitable for predicting experiments at higher heating rates. This test indicates that the available experimental information was sufficient for the determination of the model parameters. The checks on the prediction capabilities were considered to be an essential part of the model verification. In another test, the experiments of the two samples were evaluated together, assuming more or less common kinetic parameters for both cobs. This test revealed that the reactivity differences between the two samples are due to the differences in their hemicelluloses and extractives. The kinetic parameter values from a similar earlier work on other biomasses (Varhegyi, G.; Bobaly, B.; Jakab, E.; Chen, H. Energy Fuels, 2011, 25, 24-32) could also been used, indicating the possibilities of a common kinetic model for the pyrolysis of a wide range of agricultural byproduct

Gasification of wastes and residues for electricity production

Gasification technology presents one of the promising options for converting biomass energy into electricity. Gasification process converts carbonaceous materials into carbon-monoxide, hydrogen, carbon-dioxide, and gaseous hydrocarbons (producer gas). Producer gas can be supplied as fuel to the internal combustion engines and power generators. In order to maximize the efficiency of biomass conversion, producer gas should be utilized not only for power generation but also for thermal production from the producer gas sensible heat. In this paper, one of common types of agricultural residues, in Serbia, corn cob and corn stalks, were compared with wood chips and analysed in order to evaluate their possible utilisation for electric and thermal energy production. Plant consists of downdraft gasification unit coupled with gas engine. Modelling results show that for 1000kg of dry biomass can be produced: 1566 kWe and 1016 kWth (for wood chips material with HHV=19.70 MJ/kg); 11142 kWe and977.8 kWth (for corn cob HHV=19.25 MJ/kg); 1399 kWe and 960.4 kWth (for corn stalks with HHV=17.31 MJ/kg)

Air duct modification towards outlet pressure drop and vibration level reduction

U ovom radu prikazana je metodologija proračuna strujanja vazduha u vazdušnim kanalima koji su modifikovani dodavanjem specijalnih usmerivača vazduha segmentnog oblika poprečnog preseka aeroprofila. Modifikacija vazdušnog kanala izvršena u cilju smanjenja pada pritiska na izlazu samog kanala kao i u cilju smanjenja vibracija koje se javljaju tokom strujanja radnog fluida kroz kanal. Predstavljena metodologija proračuna strujanja zasnovana je na savremenim numeričkim metodama proračuna strujanja (CFD) odnosno metodi konačnih elemenata (FEA) za proračun vibracija i čvrstoće konstrukcije.In this work complete methodology for calculation and analysis of fluid flow in air ducts is presented. In order to minimize outlet pressure drop and to reduce the duct vibrations the plates with airfoil cross sections are added to duct critical zones. It was observed that airfoil stream plates efficiently contribute to outlet pressure drop, duct vibration and noise reduction. Modern methods such as CFD and FEA can be efficiently deployed in numerical treatise of flow and vibration analysis in air ducts

Modelling of selected waste biomass downdraft gasification

Gasification of waste biomass has double benefit since it presents an efficient and environmentally friendly procedure to produce energy. Modelling of gasification of demolition wood and coffee waste, and their mixtures, in downdraft gasifier is investigated. Air is exclusively used as a gasification agent. A model for waste biomass gasification has been developed using “Engineering Equation Solver” (EES). The downdraft gasification model, prepared within this study, is an analytical semi-empirical model that can be used as a tool to analyse the general trends of biomass downdraft gasification. The main characteristic and advantage of this model are that involves main gasification sub-processes (drying, pyrolysis, gasification). Also, the model is capable of dealing with a wide variety of biomasses (based on elemental and ultimate analysis) and to predict its behaviors during a gasification process (yield and composition of the products - producer gas, charcoal, and tar). Different gasification process parameters (temperature, equivalence ratio, air preheating) are varied and discussed in order to define the optimal (qualitative and quantitative) yield of producer gas for each biomass and their mixture

Modeling devolatilization process of Serbian lignites using chemical percolation devolatilization model

Different mathematical models can describe coal devolatilization as the part of combustion process. Some models are simple, while others are more complex and take into account coal's complexity and heterogeneity of structure. A chemical percolation devolatilization model for describing the devolatilization process of two Serbian lignites from Kostolac and Kolubara open coal mines was studied. Results of the model were compared to devolatilization measurements obtained from two experimental methods - a wire mesh reactor and thermogravimetric analysis. Two coal samples with four different granulations were investigated for each lignite under different experimental conditions (different maximum temperatures and heating rates). Total volatile yields obtained from the wire mesh reactor and thermogravimetric analysis together with results predicted by the chemical percolation devolatilization model are presented and compared with literature data. For thermogravimetric analysis simulation, the chemical percolation devolatilization model yielded better results in cases where the kinetic parameters obtained under experimental conditions were used rather than kinetic parameters derived from predefined values in the model itself. For wire mesh reactor, the chemical percolation devolatilization model predictions of devolatilization were mixed and were dependent on temperature

Air duct modification towards outlet pressure drop and vibration level reduction

U ovom radu prikazana je metodologija proračuna strujanja vazduha u vazdušnim kanalima koji su modifikovani dodavanjem specijalnih usmerivača vazduha segmentnog oblika poprečnog preseka aeroprofila. Modifikacija vazdušnog kanala izvršena u cilju smanjenja pada pritiska na izlazu samog kanala kao i u cilju smanjenja vibracija koje se javljaju tokom strujanja radnog fluida kroz kanal. Predstavljena metodologija proračuna strujanja zasnovana je na savremenim numeričkim metodama proračuna strujanja (CFD) odnosno metodi konačnih elemenata (FEA) za proračun vibracija i čvrstoće konstrukcije.In this work complete methodology for calculation and analysis of fluid flow in air ducts is presented. In order to minimize outlet pressure drop and to reduce the duct vibrations the plates with airfoil cross sections are added to duct critical zones. It was observed that airfoil stream plates efficiently contribute to outlet pressure drop, duct vibration and noise reduction. Modern methods such as CFD and FEA can be efficiently deployed in numerical treatise of flow and vibration analysis in air ducts

Modeling devolatilization process of Serbian lignites using chemical percolation devolatilization model

Different mathematical models can describe coal devolatilization as the part of combustion process. Some models are simple, while others are more complex and take into account coal's complexity and heterogeneity of structure. A chemical percolation devolatilization model for describing the devolatilization process of two Serbian lignites from Kostolac and Kolubara open coal mines was studied. Results of the model were compared to devolatilization measurements obtained from two experimental methods - a wire mesh reactor and thermogravimetric analysis. Two coal samples with four different granulations were investigated for each lignite under different experimental conditions (different maximum temperatures and heating rates). Total volatile yields obtained from the wire mesh reactor and thermogravimetric analysis together with results predicted by the chemical percolation devolatilization model are presented and compared with literature data. For thermogravimetric analysis simulation, the chemical percolation devolatilization model yielded better results in cases where the kinetic parameters obtained under experimental conditions were used rather than kinetic parameters derived from predefined values in the model itself. For wire mesh reactor, the chemical percolation devolatilization model predictions of devolatilization were mixed and were dependent on temperature