1,721,025 research outputs found
Modellazione ed ottimizzazione di sistemi avanzati per la produzione di energia elettrica da biomassa lignocellulosica
No full textLo sfruttamento a fini energetici della biomassa è un tema di grande interesse nel panorama energetico italiano. I motivi preponderanti di questo interesse sono l’abbondante disponibilità ben distribuita sul territorio, il buon grado di efficienza ed affidabilità delle tecnologie di conversione e la generosa incentivazione economica dell’energia elettrica prodotta dettata dai recenti decreti ministeriali. In questo contesto, una tecnologia di grande interessante risulta essere la gassificazione di biomassa lignocellulosica. La tecnologia in questione è in grado di convertire la biomassa solida in un vettore gassoso che può essere a sua volta convertito in energia elettrica attraverso sistemi quali macchine a fluido o dispositivi elettrochimici. La gassificazione è ad oggi la tecnologia più efficiente per convertire biomassa lignocellulosica in energia elettrica, inoltre risulta sostenibile per quanto riguarda il bilancio ambientale della CO2. Questo lavoro di tesi risulta quindi incentrato su sistemi tecnologicamente avanzati che gassificano biomassa lignocellulosica al fine di alimentare generatori stazionari di energia elettrica. La prima parte dell’elaborato è focalizzato sulla caratterizzazione chimico-fisica delle biomasse impiegate. Successivamente viene trattata la gassificazione sia da un punto di vista chimico-analitico sia tecnologico, sono presentate e discusse le tipologie di gassificatori più diffuse nel panorama scientifico con particolare dettaglio in merito alle più idonee a processare biomassa lignocellulosica. Si è poi trattata la modellazione dei reattori di gassificazione a letto fisso in cui sono illustrati tre diversi approcci modellistici di completezza e complessità crescente. Per ogni modello, sviluppato partendo dalla letteratura di riferimento, è illustrata la validazione sperimentale ed il campo di applicabilità. Nel seguito sono descritti e simulati al calcolatore alcuni sistemi di generazione compresivi dello stadio di filtraggio/purificazione del gas, eventuale stoccaggio del gas e sua conversione in energia elettrica. Sono presi in considerazione alcune applicazioni d’avanguardia: sistemi di stoccaggio ad assorbimento attivo della CO2 tramite zeoliti, sistemi di riduzione dell’azoto nell’aria intesa come agente gassificante e sistemi elettrochimici con celle a combustibile ad ossidi solidi per la generazione elettrica. A conclusione dell’indagine analitica sulla tecnologia si è effettuata un’analisi economica costi-benefici di alcuni impianti commerciali a gassificazione lignocellulosica di piccola taglia. Sono descritti i guadagni derivanti dalla vendita dell’energia elettrica prodotta secondo il programma d’incentivazione nazionale vigente ma anche i costi legati alla manutenzione degli impianti e allo smaltimento dei sottoprodotti quali carbonella, catrami e condensati. Per completezza viene illustrata un interessante applicazione della gassificazione: un impianto per la generazione distribuita di biodiesel ed energia elettrica partendo da coltivazioni energetiche in cui la gassificazione svolge un ruolo fondamentale nel processo di produzione del biodiesel.Biomass utilization for energy purposes is a topic of great interest in the Italian energy scenario. The predominant reasons of this issue are the abundant availability well distributed in the area, the good degree of reliability and efficiency of conversion technologies and the generous subsidies for the yield electricity dictated by recent government rule. In this context, a technology of great validity is the gasification of wood biomass. This technology is able to turn solid biomass into a gaseous carrier called syngas which can be converted into electrical energy through systems such as fluid machines or electrochemical devices. The gasification is currently the most efficient technology to convert wood biomass into electricity and it is also sustainable in terms of the environmental balance of CO2. Therefore, the thesis is focused on technologically advanced systems that gasify wood biomass in order to feed stationary generators of electricity. The first part of the thesis is focused on the physical-chemical characterization of wood biomass. Subsequently, gasification is described from the chemical-analytical point of view and some technological applications are introduced. The most common types of gasifiers in the scientific field are presented and discussed with more details about the fixed bed gasifiers which are the most suitable reactors able to process wood biomass. The modeling of fixed bed gasifier is presented and three different modeling approaches of increasing complexity and completeness are discusses. For each model, adopted from literature, the experimental validation and applicability domain are shown. In the following, some biomass generation system are described and simulated. The filtration, purification and storage of the syngas and its conversion into electrical energy are taken into account. Some advance applications are also considered: storage systems with absorption of CO2 using zeolite, reduction of nitrogen in the inlet air considered as gasifying agent and electrochemical solid oxide fuel cell for electrical generation. An economical cost - benefit analysis of some commercial small size wood gasification plants are made. The gains from the sale of yielded electricity are reported according with the national subsidies but also the costs related to the plant maintenance and the disposal of by-products such as charcoal, tars and condensates are discussed. Finally, an interesting application of gasification is described: a plant for distributed generation of biodiesel and electricity starting from energy crops in which the gasification plays a fundamental role in the process of production of biodiesel
Modeling and investigation of the channeling phenomenon in downdraft stratified gasifers
No full textDowndraft stratified gasifiers seem to be the reactors which are most influenced by loading conditions.
Moreover, the larger the reactor is, the higher the possibility to stumble across a channeling phenomenon.
This high sensitivity is due to the limited thickness and superficial placement of the flaming pyrolysis
layer coupled with the necessity to keep all the zones parallel for a correct running of this kind of
gasifier. This study was aimed at modeling and investigating the channeling phenomenon generated
by loading condition variations on a 250-kWe nominal power gasification power plant. The experimental
campaign showed great variations in most of the plant outputs. These phenomena were modeled on two
modified mathematical models obtained from literature. The results of the models confirmed the capability
of this approach to predict the channeling phenomena and its dependency on the loading method
Modelling and simulation of a wind-hydrogen CHP system with metal hydride storage
No full textThis paper describes the modelling and simulation of a wind-hydrogen system aimed at supplying electrical and thermal residential loads, where the thermal load is in part supplied by a catalytic hydrogen combustion device with hydrogen stored in a metal hydride system composed of a cluster of five metal hydride tanks equipped with a metal foam heat exchanger.The complete mathematical model has been developed from models available in literature and describing the different sub-systems that constitute the overall wind-hydrogen system. It has been laterimplemented in a multi-domain software environment to simulate system operations.Results over a year-long simulation show complete stand-alone capabilities, with an electrical efficiency and a combined heat and power efficiency of 8.2% and 12.5% respectively. At the end of thesimulation period, a hydrogen annual surplus of 110.5 kg is left over which can, for instance, be used to feed a hydrogen powered car for about 9500 km
Effects of upgrading systems on energy conversion efficiency of a gasifier - fuel cell - gas turbine power plant
Full text linkThis work focuses on a DG-SOFC-MGT (downdraft gasifier - solid oxide fuel cell - micro gas turbine) power plant for electrical energy production and investigates two possible performance-upgrading systems: polyphenylene oxide (PPO) membrane and zeolite filters. The first is used to produce oxygen-enriched air used in the reactor, while the latter separates the CO2 content from the syngas. In order to prevent power plant shutdowns during the gasifier reactor scheduled maintenance, the system is equipped with a gas storage tank. The generation unit consists of a SOFC-MGT system characterized by higher electrical efficiency when compared to conventional power production technology (IC engines, ORC and EFGT). Poplar wood chips with 10% of total moisture are used as feedstock. Four different combinations with and without PPO and zeolite filtrations are simulated and discussed. One-year energy and power simulation were used as basis for comparison between all the cases analyzed. The modeling of the gasification reactions gives results consistent with literature about oxygen-enriched processes. Results showed that the highest electrical efficiency obtained is 32.81%. This value is reached by the power plant equipped only with PPO membrane filtration. Contrary to the PPO filtering, zeolite filtration does not increase the SOFC-MGT unit performance while it affects the energy balance with high auxiliary electrical consumption. This solution can be considered valuable only for future work coupling a CO2 sequestration system to the power plant
Aige conference: A kinetic model for a stratified downdraft gasifier
No full textA model for a stratified downdraft gasifier has been developed. It has been adapted from two different models from literature with appropriate modifications and improvements. The new “interacting” model is able to predict the syngas composition, input and output flow rates and the gasifier cold efficiency under different working condition and with different biomass input. It works assuming a constant biomass consumption. The results of the model has been compared to experimental data taken from a downdraft gasifier power plant system with nominal power output of 200 kWel. The plant has been set at 160 kWel in order to avoid system instabilities related to high power runs.A model for a stratified downdraft gasifier has been developed. It has been adapted from two different models from literature with appropriate modifications and improvements. The new "interacting" model is able to predict the syngas composition, input and output flow rates and the gasifier cold efficiency under different working condition and with different biomass input. It works assuming a constant biomass consumption. The results of the model has been compared to experimental data taken from a downdraft gasifier power plant system with nominal power output of 200 kWel. The plant has been set at 160 kWel in order to avoid system instabilities related to high power runs
Biodiesel and electrical power production through vegetable oil extraction and byproducts gasification: Modeling of the system
No full textAim of this work is to introduce an alternative to the standard biodiesel production chain, presenting an innovative in situ system. It is based on the chemical conversion of vegetable oil from oleaginous crops in synergy with the gasification of the protein cake disposed by the seed press. The syngas from the gasifier is here used to produce electrical power while part of it is converted into methanol. The methanol is finally used to transform the vegetable oil into biodiesel. Through a coupled use of ASPEN PLUS (TM) and MATLAB (TM) codes, a rapeseed, soy and sunflower rotation, with a duration of three year, was simulated considering 15 ha of soil. This surface resulted sufficient to feed a 7 kW(el) power plant. Simulation outputs proven the system to be self-sustainable. In addition, economical NPV of the investment is presented. Finally the environmental, economical and social advantages related to this approach are discussed
Energy and biochar co-production from municipal green waste gasification: A model applied to a landfill in the north of Italy
Full text linkThis work discusses the advantages that can be obtained from the integration of landfill gas with biomass gasification. The case study presented consists of a landfill located in the province of Reggio Emilia, in the north of Italy. Landfill gas from municipal-waste fuels four internal combustion engines with overall nominal power of 2 MW, the electricity is sold back to the grid, while the thermal power is used for the heating of an industrial greenhouse compartment for basil production. Within the same facility, green waste is collected from the surrounding municipalities then chipped and sieved. Fine particles are disposed into a composting plant close by, while the sieved fraction is sold to the market for electricity production in large-scale boiler-based power plants. The idea here presented and discussed consists of the implementation of a gasifier to convert the sieved fraction of green waste into a syngas fuel directly on site. Syngas is blended with the landfill gas and then fed to the gas engines. In this work green waste gasification is tested in a commercial small-scale gasifier, proving that sifted green waste is a suitable fuel for this application. A specific consumption of 1.2 kg/kWh and a total electrical efficiency of 16.22% were measured. The sizing of the full-scale gasification facility is based on both the experimental results and data about the local availability of green waste. The economic return of the investment is then discussed. Finally, a further level of integration between gasification and the existing site is proposed: gasification-derived biochar is investigated as soil amendment for the on site company at the landfill that grows basil commercially. Results of 55 days in vivo tests show an increase in the biomass production of the basil of 53% compared to the control test group
Easy to implement ventilated sunspace for energy retrofit of condominium buildings with balconies
No full textEnergy retrofit of the facade of condominium buildings may be a difficult task because thermal bridges such as those due to balconies, common elements in the architecture of many countries, are often arduous to correct by added insulation due to several constraints. An alternative retrofit approach is therefore analyzed, easy to implement and relatively inexpensive. It consists in changing a balcony into a ventilated sunspace during the cold season, exploiting solar gains to compensate heat loss. More specifically, transparent plastic roll-up sheets are installed along the balcony perimeter, removable in the hot season, to enclose the volume between two superposed balcony slabs. The obtained sunspace is then used as a pre-heating chamber for a single-flow ventilation system that ensures the air changes required indoors. Heat gain to the indoor environment can thus be increased with respect to a simpler sunspace without ventilation, and possibly modulated along the day by proper control of the flow rate. In this work, the proposed approach and a small-scale physical model are presented. The model will serve to validate analyses aimed to forecast and optimize the performance of ventilated sunspaces built around balconies
Experimental assessment and modeling of energy conversion effectiveness in a gasification power plant
No full textNational and international energy scenarios seem to be rediscovering a new confidence in gasification power plants as a valuable technology for biomass conversion. Their adaptability, in both direct power production and biofuels synthesis, has been manifested into the development of wide varieties of reactor models and sizes. An appropriate modeling of the system, supported by experimental analysis, is necessary to achieve the high level of efficiency of the gasifier and the proper effectiveness of the entire energy plant conversion. This work is aimed at studying a stratified downdraft gasifier coupled to two IC engines with the total nominal power of 250 kWel. The model of the system is based on mass and energy balance; the model outputs are compared here with those coming from the experimental campaign. All the major thermo-chemical parameters are monitored, these include: air and gas flow rate, biomass moisture content, consumption and ultimate analysis, reaction zones temperatures, tars and char production. In this paper, the model outputs have been compared with the data to evaluate the sensitivity of the model. Moreover, the difference between the theoretical data and the experimental data have been exanimate
Integration of biological waste conversion and wastewater treatment plants by microalgae cultivation
No full textIn this study, growth performance and lipid content of two microalgae species Neochloris oleoabundans and Chlorella vulgaris are monitored by using three different types of sludge waste feedstocks obtained from the water treatment plants located in Bedonia, Borgotaro and Fornovo (Montagna2000 Spa, Province of Parma, Italy). The sludge waste is optimized in order to achieve microalgal growth media and dispose of the sewage sludge produced at the wastewater treatment facilities. Both photoautotrophic and heterotrophic growth conditions are applied to the microalgal cultivations. The growth parameters of microalgae strains such as cell concentration, growth rate, optical density, cell biovolume, photosynthetic pigments and lipid contents are monitored. The amounts of total dried lipid biomass, obtained by the biological conversion of the wet sludge waste, are determined. Lipid production of microalgal cells grown in the medium optimized from sludge waste from the Fornovo site provides the highest amount of microalgal lipid content for N. oleoabundans and C. vulgaris photoautotrophic cultivations, while sludge waste from the Bedonia site provides for N. oleoabundans heterotrophic cultivation
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