Browsing by Author "Silva, D."
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- Biomass quality in a thermoelectric plant along one yearPublication . Silva, D.; Tarelho, L.; Silva, J. Figueiredo; Freire, M.; Lopes, HelenaABSTRACT: The biomass quality is an important issue for the operation of a thermoelectric plant. Independently of the combustion technology, the biomass fuels and its characteristics are responsible for some operating problems during the thermochemical conversion of the biomass in thermal energy. These operation problems are related to the boiler and heat exchangers, dedusting technologies (e.g., electrostatic precipitator). Some studies show the phenomena of corrosion and incrustation on the walls of the boiler (named as fouling phenomenon) and on the walls of superheater, economizer, and equipments for flue gas treatment (named as slag phenomenon). When the biomass presents high levels of alkaline metals, like herbaceous and agro-industrial residues, these problems will be intensified. For example, the potassium and sodium decrease the melting point of the ashes, causing the incrustations and slag formation. On the other hand, magnesium and calcium in the biomass lead to the increase of the melting point of the ashes. The influence of the biomass quality on the bottom and fly ashes properties is related with the quantity of inert material, unburned carbon content and chemical composition. Thus, the main goal of this research work is focused on the characteristics of the forest biomass residues used as fuel in a Portuguese thermoelectric plant equipped with grate furnace technology. The results obtained allow the evaluation of the influence of some physical-chemical characteristics of the biomass on the produced ashes, and in the overall power plant performance.
- Hydrogen production and storage from hydrolysis of sodium borohydride : study of the regeneration of sodium borohydride [Resumo]Publication . Silva, D.; Nunes, H. X.; Rangel, C. M.; Pinto, A. M. F. R.
- Hydrogen production and storage from hydrolysis of sodium borohydride: study of the recyclability of the by-product of reaction [Resumo]Publication . Silva, D.; Nunes, H. X.; Rangel, C. M.; Pinto, A. M. F. R.ABSTRACT: Hydrogen is one of the most valuable alternatives to fossil fuels to produce energy. However, although it is abundant in the universe and has the highest gravimetric density, it is difficult to obtain and store in its molecular form and in safe conditions. One alternative to the conventional hydrogen storage is to use the high hydrogen content (10.66 wt. %) of sodium borohydride to, simultaneously, produce and store it.
- Innovative reactor prototype for Hydrogen production in a stationary application using sodium borohydridePublication . Barbosa, Rui; Ferreira, V.; Silva, D.; Condes, J.; Ramos, S.; Amaral, V.; Pinto, A. M. F. R.; Figueiredo, A.; Rangel, C. M.Hydrogen storage has proved to be the greatest obstacle preventing hydrogen from replacing fossil fuels. Hence, a safe, efficient and economical method of storing hydrogen must be available to turn viable a hydrogen economy based on renewable resources [1]. Hydrogen can be stored in chemical hydrides such as sodium borohydride (NaBH4), with large theoretical H2 content of 10,9 wt%. With the aid of catalysts, and at room temperatures, the alkaline hydrolysis of NaBH4 can be enhanced [2]. In this work, a 100 L innovative reactor for hydrogen production was designed, based on the optimized layout of a laboratorial scale reactor [3], as part of a project financed by the Portuguese financial support program NSRF. The developed system has the capability to feed a 5 kW PEM fuel cell with a maximum hydrogen consumption of 75 slpm. The NaBH4 solution is stored in a 50 L reservoir from where seven consecutive 7,0 L injections to the reactor are possible. The Ni-Ru based catalyst applied can be re-used several times without losing its performance [1] and because of this capacity its replacement will be done, manually, every seven NaBH4 solution injections (simultaneously with the residual solution removal and the reactor cleaning). The catalyst should then be recovered for further utilization. Additionally to the reactor, a 400 to 500 L reservoir was also designed to be used as the system buffer since the reactor works in batch mode and it is desired that the PEMFC operates continuously. The system was conceived for stationary applications and eventually to be installed in remote areas, reason why the systemś monitoring and control are fully automatized. Its hydropneumatic circuit layout is characterized by four parts: injection system, reactor, valves bloc and buffer. It is assumed that the designed system can operate continuously throughout 15 hours with a medium hydrogen consumption of 10 slpm, which can supply a daily household energy power demand.
- LUCIS:a learning experience to improve lifetime and operating strategies in low power PEM fuel cellsPublication . Barbosa, R.; Travassos, Maria Antónia; Rangel, C. M.; Sá, R.; Silva, D.; Magalhães, A.; Ferreira, V.LUCIS, a demonstration project co-financed by the Innovation Agency in Portugal (AdI), was carried out in the framework of the DEMTEC Programme (Incentives to Technologically Innovative Pilot Systems). Its main goals were: Validate the reliability of proton exchange membrane fuel cells (PEMFC) when used in practical situations and the competitive advantages that these solutions can represent compared to conventional solutions; Evaluate impacts associated with the use of hydrogen and the benefits to business competitiveness. This project allowed a learning experience in real applications of low power PEMFC. Demonstrations were grouped in two large categories that covered several applications of PEMFC. The prototypes used were produced by SRE (Portugal) and were specifically designed to be used in small power applications, portable, traction or stationary. In this work, the technological validation was carried out for different stacks with power from 10 to 100W. Hydrogen was supplied by compressed gas bottles and metallic hydrides. All the fuel cells were previously characterized in specialized laboratories. Recommendations were drawn for every application in order to improve fuel cell lifetime and operating strategies.
- Primeiro registo de trilobites no Silúrico de Portugal (Sinclinal de Moncorvo)Publication . Pereira, Sofia; Silvério, Gonçalo; Colmenar Lallena, Jorge; Moreira, Noel; Silva, D.; Sá, ArturRESUMO: A ocorrência de fósseis de trilobites em Portugal é conhecida desde há mais de 150 anos, mas permanecia por comprovar a presença deste grupo nas litologias do Silúrico. Reporta-se agora o primeiro registo de trilobites no Silúrico de Portugal, numa sucessão de intercalações de argilitos e calcários da Formação Campanhó do Sinclinal de Moncorvo. As trilobites são raras, estando a associação amplamente dominada por equinodermes scyphocrinitídeos, com cefalópodes nautiloides ortocónicos, tendo ainda sido registado um único fóssil de bivalve, Panenka?, constituindo também o primeiro registo do grupo no Silúrico da região. Do ponto de vista sistemático, foi possível identificar o encrinurídeo Cromus sp. e os phacopídeos Ananaspis? e Denckmannites?. Não obstante a identificação em nomenclatura aberta, o material português apresenta maior semelhança com as espécies-tipo destes géneros, respetivamente Cromus intercostatus, Denckmannites volborthi e Ananaspis fecunda, as três identificadas na Formação Kopanina do Ludlow da Chéquia, sugerindo a mesma idade para os níveis estudados. Os novos dados estreitam a relação deste setor da Zona Centro-Ibérica com as faunas bentónicas silúricas de afinidades boémicas, já reconhecidas no NO de Espanha, Pirenéus, Catalunha e na Zona de Ossa Morena, sendo distintas da restante Zona Centro-Ibérica e semelhantes ao norte de África e Boémia.