Integração de Sistemas de Energia - ISE
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- Estudo experimental e numérico de um queimador de gás naturalPublication . Azevedo, PedroNeste trabalho pretendeu-se demonstrar a aplicabilidade da modelação de dinâmica de fluidos através de um código computacional (Fluent/UNS), para a previsão de escoamentos de fluidos e respectiva combustão, numa fornalha horizontal. Foi introduzido o gás natural como combustível, através da utilização de uma mistura com características idênticas à do gás natural. Foram realizados ensaios cromatográficos ao combustível para verificação da composição elementar. Para a construção da malha computacional utilizada no modelo numérico, tornou-se necessária a utilização de dois programas, por forma a permitir a integração dos 37 injectores, respeitantes ao queimador, na face da fornalha. Foi escolhida uma malha com cerca de 78000 células, que garante a indepedência dos resultados. Para modelação do escoamentofoi utilizado o modelo de turbulência k-ε, por se adequar melhor ao escoamento em causa, bem como pelas exigências computacionais. A transferência de calor por radiação no interior da fornalha, é calculada através da utilização do Modelo de Radação de Transferência Discreta (DTRM). Os resultados numéricos foram validados por ensaios experimentais, realizados com um queimador protótipo montado numa fornalha horizontal, cujos resultados foram analisados juntamente com os homólogos numéricos.
- Short-Term scheduling of a polymer compounding plantPublication . Castro, Pedro; Barbosa-Póvoa, Ana Paula; Matos, Henrique A.This paper addresses the optimal short-term scheduling of a three parallel production line plymer compounding plant, whose equipments require cleaning between product changeovers. A very effective user-friendly software tool was developed, which consists of a general scheduling model coupled with capabilities of Microsoft Excel for data handling and analysis. The scheduling model is based on a Resource Task Network discrete time formulation and leads to Mixed Integer Linear Programming problems. As outputs the user can access the optimal schedules for a number of different objectives.
- Analysis of processing systems involving reaction and distillation : the synthesis of ethyl acetatePublication . Filipe, Rui M.; Castro, Pedro; Matos, Henrique A.; Novais, Augusto Q.The integration of reaction and separation into a single process unit, i. e., reactive destillation, may offer several advantages over conventional systems that use a reactor followed by a distillation column. In this paper we explore the operational characteristics of reactive distillation and highlight some of this potential benefits, using the production of ethyl acetate as an illustrative example. With this aim, the two types of system are compared employing different reactor types and a number of performance indicators, such as yield, conversion, purity, specific energy consumption and residence time. A sensitivity analysis is carried out on some variables and parameters, in order to explore and define the distillation columns operating conditions. As expected, results point to a clear advantage of reactive distillation allowing for the azeotrope to be surpassed and for the overcoming of chemical equilibrium, favouring an increase in conversion and product purity, along with reduced operating costs.
- LP-based heuristic procedure for the optimal design of water using networks with multi-contaminantsPublication . Teles, João P.; Castro, Pedro; Barbosa-Póvoa, Ana Paula; Novais, Augusto Q.This paper proposes a new strategy for the optimal design of water-using networks in industrial systems featuring possibly more than a single water source and multiple contaminants. The model formulation is supported on a superstructure that exploits reuse opportunities and gives rise to a non-convex nonlinear which often leads to local optimal solutions. To overcome this, the new approach generates multiple initialization points, one for each possible sequence of operations, where a particular starting point is obtained by the sequential solution of a small set of related linear programs. The best solution of the several non-linear problems that are solved is then assumed to be the global optimal solution. The results obtained for a set of case studies have shown that the best initialization point is often the global optimal solution and that the procedure as a whole is efficient in escaping local optima.
- Resultados do inquérito às empresas spin-offs de investigação: relatório do projecto REBASPINOFFPublication . Rodrigues, Cláudia; Videira, Pedro; Fontes, Margarida
- Estudo da formação e destruição de óxidos de azoto em chamas de hidrogénio e /ou hidrocarbonetos com ou sem presença de compostos azotadosPublication . Azevedo, PedroIn the nineties, the World Health Organization updated their “Air Quality Guidelines for Europe” (WHO, 2000) with the objective to provide detailed information on atmospheric pollutants and their adverse effects on human health. Consequence of exposure to compounds as the nitrogen oxides, volatile organic compounds (VOC), peroxyacetylnitrates (PAN) and aldehydes, upon reacting with solar light, produce the photochemical smog along with the formation the tropospheric ozone. Among other undesirable consequences, the nitrogen oxides act as main harmful precursors for the formation of the photochemical smog (Broekhuizen, 2002). This work aims at studying the formation of nitrogen oxides and their subsequent destruction in hydrogen and/or hydrocarbon flames with or without seeding with nitrogen compounds, hence producing conditions for a reduced kinetic mechanism that can be used in CFD software. This research work was carried out involving both experimental and numerical studies. The experimental work studied the influence of the parameters for hydrocarbons combustion and NOx formation and destruction. The parameters varied were the temperature, equivalence ratio, fuel composition and the presence of nitrogen compounds artificially added. The main reactants used were hydrogen, methane, oxygen and argon and there was seeding of flames with ammonia or nitrogen oxide, varying between 500 and 1000 ppmv. The experimental runs were carried out using a test bench specially built for this work and used laminar flames with equivalence ratios ranging from 0.8 to 1.2. The results were obtained through flue gas monitoring inside the flame and this was achieved by placing a probe with extraction of gases at several axial distances ranging from 10 to 30 mm above the burner. Temperature and velocity of burnt gases were calculated. The concentration of some combustion products, namely oxygen, hydrogen, carbon oxides was determined on a gas chromatograph, the nitrogen oxides were measured using an on line gas analyzer with an electrochemical cell and the levels of both hydrogen cyanide and ammonia were quantified with selective electrodes in aqueous solution. The use of detailed kinetic mechanisms for a 3 D reactive computational fluid dynamics flow as the one representing a flame is very difficult. So a reduced kinetic mechanism was employed and estimation methods were utilised for the calculation of physical properties of chemical species. The reduced kinetic mechanism was compared with three more detailed mechanisms and one reduced kinetic mechanism in one-dimensional chemical kinetic package, Chemkin, employing reaction parameters like flue gas composition distribution, temperature and velocity profiles along burner axial distance and residence time. The results were found to be in good agreement. The reduced kinetic mechanism was then integrated in the computational fluid dynamics package, Fluent, together with physical properties of chemical species for a reactive flow in 3 D. The numerical calculations were then compared with experimental data and there was a good agreement with respect to the overall combustion mechanism of methane. However, the results for nitrogen oxides, though demonstrating the same tendency as experimental work, suggest that some improvements in the model are needed in order to obtain more satisfactory correlation. Based on the validation results, a reduced kinetic mechanism involving 50 reactions integrating nitrogen chemistry was developed that could represent H2 and/or CH4 flames with nitrogen chemistry. The extension of this work to more complex hydrocarbons could be achieved without significantly increasing the chemical reactions or species quantity involved.
- Return mobility of scientists and knowledge circulation : an exploratory approach to scientists attitudes and perspectivesPublication . Fontes, MargaridaThe paper addresses the international mobility and return of scientists and its implications for regions/countries with weaker scientific and technological systems. It focuses on the “return dilemma” and, using the Portuguese case as empirical setting, discusses the conditions for return, the “diaspora” alternative and the role of policies in minimising the impacts of mobility flows. Despite the growing importance assumed by scientific mobility, our understanding of mobility flows, in particular of return mobility, is still deficient. Data about the level of mobility and mobility paths is scarce and difficult to obtain and the knowledge about expatriate scientists’ motivations and strategies, namely their attitudes towards the home country and their perspectives concerning career and return mobility, remains limited. The research presented in this paper is a preliminary contribution to attend to some of these issues. A method is proposed to address some methodological problems in empirical research on scientific mobility. It permits to delimit a sample of “scientifically productive” expatriate scientists in specific fields, to locate these scientists and to trace their professional trajectories, thus making possible to collect information on their mobility behaviour as well as to gain some preliminary insights on their attitudes and perspectives. This methodology is experimentally applied to the Portuguese case. Notwithstanding its exploratory nature, the empirical research provides some insights into the behaviour of a younger generation of “scientifically productive scientists” in a field with a strong international mobility pattern (biotechnology), which can be relevant for policy making
- Acciones para el desarrollo de las energias renovablesPublication . Pinto, Filomena; Rodrigues, Carlos; Viana, Susana; Marques, Isabel PaulaO parque experimental de energias renováveis da Herdade da Mitra, em Évora integra um sistema de microgeração de abastecimento eléctrico em Portugal, através da integração de diferentes unidades utilizadoras de fontes renováveis: fotovoltaica, eólica, gasificação e digestão anaeróbica. Neste capítulo serão abordadas estas diversas tenologias referindo os princípais conceitos teóricos que suportam cada uma delas, antes de descrever cada uma das instalações projectadas no âmbito do projecto PETER. Na instalação de gasificação a biomassa florestal existenet na Zona do Parque é utilizada para a produção de um gàs. O gasificador de leito fluidizado tem uma capacidade térmica de 350 kW e um consumo de cerca de 80 kg/h de biomassa. Após as operações de limpeza do gás obtido para melhorar as respecivas características, este é convertido em enrgia através de um grupo gerador, que é constituído por um motor de combustão interna "dual-fuel" acoplado a um gerador eléctrico de 70kWe. A instalação de digestão anaeróbica do parque destna-se à conversão da matéria orgânica da biomassa húmida em biogás, tendo como fonte os efluentes agro-pecuários e industriais que são produzidos na herdade e/ou na região Alentejana. A unidade de digestão anaeróbia é um protótipo de demonstração que corresponde a um digestor híbrido de fluxo ascendente com 15 m3 de capacidade. As unidades de digestão anaeróbica e de gasificação partilham os sitemas de colecta e de tratamento do gás produzido e da sua conversão em energia eléctrica e térmica. A energia eléctrica é, por seu turno injectada no circuito de microgerção e a energia térmica é valorizada através da manutenção da temperatura de digestão da unidade anaeróbica. Assim, a gestão integrada de diversas tecnologias, vocacionadas para a remoção da carga poluente contida nos efluentes agro-pecuários e para a reutilzação dos fluxos obtidos, apresenta-se como um sistema de valorização energética e agrícola de recursos endógenos da região onde são produzidos. O sistema fotovoltaico tem uma potência de pico de 10 kW, permitindo a demonstração de diferentes tecnologias de conversão. O sistema fotovoltaico encontra-se ligado à rede eléctrica da herdade da Mitra.
- Building new indicators for researchers’ careers and mobility based on electronic curriculum vitae: the case of the DeGóis platformPublication . Fontes, Margarida; Assis, José; Araújo, Emília; Bento, Sofia; Henriques, Luísa; Pirralha, André; Santos, LeonelThere are currently two main databases in Portugal regarding researchers’ electronic CVs: • the FCT-SIG (Council for Science and Technology-Information and Management System) – hereafter called the FCT Information System, and • the DeGóis Platform Although this report will be concentrated on discussing the DeGóis Platform, since the latter will prevail in the medium/long term, replacing the former one, we believe it is useful to shed some light on the FCT Information System, as it still comprises the bulk of researchers’ electronic CVs in Portugal.
- Interdisciplinary approach to automated negotiation: a preliminary reportPublication . Lopes, Fernando; Novais, Augusto Q.; Coelho, HelderAutonomous agents with negotiation competence are becoming increasingly important and pervasive. This paper follows an interdisciplinary approach to build autonomous negotiating agents by considering both game-theoretic techniques and bargaining procedures from the social sciences. The paper presents a generic model that handles bilateral multi-issue negotiation, describes equilibrium strategies for the bargaining game of alternating offers, and formalizes important strategies used by human negotiators. Autonomous agents equipped with the model are able to negotiate under both complete and incomplete information, thereby making them very compelling for automated negotiation.