Dissertations / Theses on the topic 'Biogas generation electricity'

The world´s future energy generation needs to be sustainable without negative impact on people´s health or on our nature. Within present trends to develop energy scenarios with diminishing use of fossil fuels, nuclear power etc. it seems difficult to meet an increasing need for energy. Incorporation of renewable energy sources within the energy sector could mitigate future energy crises in a sustainable way. Bangladesh is a south Asian developing country with great prospects of renewable energy resources. Severe energy crisis such as shortage on electricity generation over the decades is one of the major problems in the country. This problem could be reduced by introducing renewable energy resources at a large-scale within the power sector. Renewable energy sources are increasingly used due to its availability and it has little negative impact on the environment. Solar energy and biomass are great and valuable resources in the green energy field. In this thesis, a feasibility study of a hybrid renewable energy system, HRES, including biogas fueled internal combustion engines, driving an electrical generator and solar PV in vicinity to urban areas in Bangladesh was analyzed using HOMER software. The HRES system was designed for electricity generation in a community near Dhaka city in the Gazipur district where great resources of solar and biomass are available. In the proposed hybrid system, a 40-kW biogas electric generator is integrated with 80 kW of PV panels and the analysis shows an energy price of €0.1435/kWh.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
From the duration of the Kyoto Protocol, there has been a renewed interest in technology of bio-digesters. As they allow a reduction in the emission of greenhouse gases compared to other waste treatment methods, their deployment can permit the marketing of carbon credits, resulting in money. The present study aims to analyze the process of dissemination of this technology in Santa Rosa, situated in the northwestern of Rio Grande do Sul state, especially powered by private companies. The profile properties that have these installed equipment, in addition to an examination of possible difficulties encountered by land owners, towards the deployment and use of this technology, with the contribution of biodigesters, on the energy issue and mitigation of environmental pollution in these areas. Through a revision of the existing literature and application of questionnaires some information about the installation of bio-digesters were taken, noticing if they contribute as alternatives in order to add value to the breeding properties and as viable alternative to the solution of environmental problems involved in the process. This study revealed that 33.33% of installed equipment is disabled. The work also presents a case study of isolated electric power generation using biogas as a fuel in an internal combustion engine of Otto cycle, in conjunction with CDM project, installed in a midsize property of pig breeding. The generation plant consists of a stationary Otto cycle engine, adapted to operate with biogas, coupled to an electric generator nominal 30 kVA three-phase. Through the study of the economic and financial feasibility, it was concluded that the application for generating electricity is viable and the overall efficiency of the system is satisfactory. Through another point of view, it presents a second case study, on the insertion of a property in a project of clean development mechanism (CDM) in pig production.
A partir da vigência do Protocolo de Kyoto, houve um interesse renovado pela tecnologia dos biodigestores. Como eles permitem uma redução na emissão de gases do efeito estufa, em relação a outros métodos de tratamento de dejetos, a sua implantação pode permitir a comercialização de créditos de carbono, resultando em valores monetários. O presente trabalho tem como objetivo analisar o processo de disseminação desta tecnologia na microrregião de Santa Rosa, situada na mesorregião do Noroeste Riograndense, impulsionada, especialmente, por empresas privadas. Estudou-se o perfil das propriedades que possuem estes equipamentos instalados, além de uma análise das possíveis dificuldades encontradas pelos proprietários rurais, no sentido de implantação e utilização dessa tecnologia, verificando-se a contribuição dos biodigestores, referente à questão energética e minimização da poluição do meio ambiente nessas áreas. Através da revisão da literatura existente e aplicação de questionários, foram levantadas diversas informações acerca da instalação de biodigestores, observando se contribuem como alternativa de agregação de valor às propriedades criadoras e como alternativa viável para a solução dos problemas ambientais envolvidos no processo. O presente estudo revelou que 33,33% dos equipamentos instalados encontram-se desativados. O trabalho também apresenta um caso prático de geração de energia elétrica isolada, utilizando biogás como combustível em um motor à combustão interna do Ciclo Otto, em conjunto com projeto de MDL, instalado em uma propriedade de médio porte, para criação de suínos. A planta de geração consiste de um motor estacionário de Ciclo Otto, adaptado para operar com biogás, acoplado a um gerador elétrico trifásico de 30 kVA nominal. Através do estudo da análise de viabilidade econômico-financeira, concluiu-se que a aplicação para a geração de energia elétrica é viável e a eficiência global do sistema é satisfatória. Numa outra visão, apresenta-se um segundo caso prático, na inserção de uma propriedade em um projeto de mecanismo de desenvolvimento Limpo (MDL) na suinocultura.

Bioenergy is increasingly being used a means of combatting the effects of anthropogenic climate change in sectors such as the power industry. Problems can exist in utilising biomass fuels however such as high moisture contents and low calorific value when compared with fossil fuels. Torrefaction is a pre-treatment process that aims to address some of these issues. In this pre-treatment step, solid biomass is heated in an inert atmosphere to between temperatures between 200 and 300°C resulting in the loss of low-energy volatiles and moisture improving fuel chemical and physical properties and is the focus of this thesis work. Firstly, the effect of changing torrefaction temperature and residence time is investigated. Results show that torrefaction increases the calorific value of fuels via reduction in moisture and volatiles contents as a result of degradation of some of the lignocellulosic components- this also improving the grindability characteristics of torrefied materials- with these change more pronounced as conditions become more severe. Results further show that with increasing torrefaction severity, the solid product yields decrease while the liquid and gaseous products increase. The combustion properties of torrefied biomass is also investigated, with results showing that torrefaction reduces the reactivity of biomass fuels and that upon rapid devolatilisation, chars from torrefied fuels differ morphologically to those of untreated biomass and undergo a lesser degree of burnout. Results also show that promotion of nitrogen to the gas phase during rapid devolatilisation may be fuel dependent after torrefaction has been performed. Finally, the effect of torrefaction of supply chain GHG emissions is investigated where it was found that GHG savings can be made as a result of increased calorific value in torrefied materials. Emissions savings are maximised where heat integration of the combustion of the volatiles gases evolved during torrefaction is implemented and wood chips are used as utility fuel. Results also indicate that torrefaction favours long distance transport as a result of improved fuel properties.

Bangladesh, where only 20% of the total population are connected to grid electricity, has a promising scope to utilise biomass for decentralised electricity generation. In this study, sustainable biomass electricity generation model was developed for the country, by combining tech no-econometric and optimisation modelling techniques. The developed model addresses the biomass generation and availability, feasible technologies, cost and efficiency correlations, economic plant size, plant economics and sensitivity, and environmental and social impacts. In 2003, the national total annual available biomass energy potential in Bangladesh varies from 183.848 to 223.776 TWh. The feasible technologies are: gasification based ICE-generator, anaerobic digestion based ICE-generator and direct combustion based steam turbine or Stirling engine-generator. Correlations of capital investment costs and overall conversion efficiencies with the plant electricity generating capacity have been developed. Direct combustion technology shows the highest electricity generation potential of 20.21 TWh/year; followed by gasification, of 14.30 TWh/year. Economic radius of biomass collection and size of the plants has been determined for maximum profitability. The biomass electricity plants economics have been estimated and compared with the diesel and dual-fuelled plants. Analysis shows that, anaerobic digestion and gasification-based electricity generation plants are economically feasible. Biomass electricity plant is highly sensitive to changes in biomass price, selling price of electricity, investment cost, plant lifetime, conversion efficiency and operating hours. The employment of the biomass electricity instead of diesel generator saves significant amount of the greenhouse gas emissions. It creates more employment than conventional and presents other socio-economic benefits as well. Due to the combination of electricity generation potential, promising economics and low greenhouse gas emissions; gasification-based biomass electricity plant is recommended for the country. Biomass availability and plant economics vary between districts to districts. Computer programmes have been developed for district wise biomass electricity plant analysis.

With the increasing need for renewable energy technologies in the world, biomass fuel transformation technology is growing towards meeting that need, among others. Challenges remain certain and new innovations are being tested in bid to overcome them with the application of biomass as energy source. This report presents some studies carried out into understanding the potential and challenges associated with utilization of biomass fuel, especially for technologies that are appropriate for rural applications.  Utilization of biomass gasification technologies is in the focus of this study.   The great potential biomass fuel provide to Uganda for possible energy production in small scale application is presented. This study was carried out to understand the possibility of using biomass as fuel in electricity power generation in Uganda. It takes into consideration the use of biomass gasification technology in energy production. Challenges related to the application of biomass fuels are discussed, mostly with tar and alkali metal compounds in the gas stream.   Suggested methods to combat some of the challenges with biomass fuels are pointed out in this study. Application of externally fired gas turbine (EFGT) system is a particular approach discussed and its technical performance analyzed.  The analysis revealed that efficiency of the EFGT system is greatly dependent on the heat exchanger effectiveness and on turbine inlet temperature. Optimum performance can be realized with air compression ratio of 3.4. It is also noted that fouling and deposition in the heat exchanger can affect its performance.   A related study carried out was on the retention of alkali metals in an updraft gasifier. The gasifier was chosen for possible integration with the EFGT system. Finding was that about 99% of the alkali metals are retained in the gasifier. It is anticipated that this would reduce on the deposition in the heat exchanger, reducing on maintenance time. A need is identified to determine the level of deposition mentioned. A simple thermodynamic modeling of the alkali metals condensation reaction on a high temperature heat exchanger surface was conducted. The results showed that with appropriate quantity of S in the raw fuel, alkali metals bounding with Cl are greatly reduced. Cl is passed out as gaseous HCl, leaving deposition of none corrosive sulphates. Recommendation is made to study this phenomenon in an experimental setting.   Biomass gasification technology integration with an internal combustion (IC) engine is also studied. Here requirements for the producer gas quality have been discussed. Some tests carried out with wood pellets and wood cylinders compared the yield of tar from the two physically different fuels.  Wood pellets were found to yield more tar than wood cylinders.   Economic analysis of biomass gasifier integrated with an IC engine running a generator of 100 kWe was carried out. Comparison with a diesel electricity generator of similar capacity was made for a scenario in Uganda over a project life of 20 years. Different Plant Capacity Factors (PCF) and fuel costs including subsidies were considered. The analysis showed that over long period of time biomass power plant was more beneficial than the diesel power plant at PCF over 40%. This is more pronounced with unsubsidized diesel fuel.
QC 20111206

Access to energy is crucial to human welfare; no residential, commercial or industrial activity can be conceived without energy supply. At the same time, current dependence on fossil fuels and their negative effects on global climate claim for urgent alternatives. The situation in Sub-Saharan Africa is poignant: over half of the population, mainly in rural areas, live without access to electricity services. Crop residues from farming communities in those areas are unused; while technology for electricity production from agricultural biomass is progressing, managing decentralised rural electricity projects is still a challenge, especially in developing countries like Ghana, given the variety and complexity of the factors conditioning biomass to energy supply chains. Such complexity has been previously formulated in academic exercises, but with limited practical applicability for energy planners, practitioners and investors. This research has deployed a holistic approach to biomass-to-energy planning, yet flexible to adapt to different regulatory scenarios and energy supply configurations. A qualitative framework has been developed, taking into consideration four critical components: social development, organisational/institutional, technical, and financial, with their respective metrics. Then, the framework has been applied to three real case study configurations in Ghana, involving primary data collection, sustainability modelling and discussion of the techno-economic feasibility results with policy makers and practitioners. The first configuration consists in decentralised power generation using crop residues from clustered smallholder farms in 14 districts in Ghana; the number of clustered farms, reference residue yields, and residue densities are determined to assess the distances within which it would be feasible to supply feedstock to biomass power plants. The findings show that a minimum of 22 to 54 larger (10 ha) farms would need to be clustered to enable an economically viable biomass supply to a 1000 kWe plant. Financial analyses indicate that such investment would not be viable under the current renewable feed-in-tariff rates in Ghana; increased tariff by 25% or subsidies from a minimum 30% of investment cost are needed to ensure viability using internal rate of return as an indicator. Carbon finance options are also discussed. The second configuration focuses on co- and tri-generation from clustered crop residues. Techno-economic results show that 600 kW and 1 MW biomass fuelled plants to generate power, heating (for cassava or maize drying) and cooling (to refrigerate tomatoes) are feasible, considering a minimum 20% yearly profit for investors’ equity. Additional income between 29 and 64 US $/tonne of crop residue would be possible for farmers if a minimum of 60% of the heat produced can be traded. The consideration of carbon financing under the most common traded prices has little impact on the project results; if more favourable schemes (like the Swedish carbon tax) are considered, the viability of co- and tri-generation plants run on agro residue can be possible even with a low level of residual heat sales. The third configuration analyses minigrid electricity generation and services based on biomass gasification in five Ghanaian communities. Results show that the projected electricity demand compares favourably with the potential supply from available crop residues. Project financing via 100% private funding would not be viable under current national uniform tariffs; however, by applying an end-user tariff equal to the current expenditure on electricity-equivalent uses in the communities, a subsidy of about 35% on initial investment would enable a private entrepreneur an internal rate of return of 15%, whereas a 60% subsidy could enable internal rate of return of 25%. The outcomes of this research have triggered the interest of Ghanaian and international policy makers, developers and private investors.
L'accés a l'energia és crucial per al benestar humà, no es pot concebre cap activitat residencial, comercial o industrial sense subministrament d'energia. Alhora, la dependència actual dels combustibles fòssils i els seus efectes negatius sobre el clima global reclamen alternatives urgents. La situació a l'Àfrica Subsahariana és punyent: més de la meitat de la població, principalment rural, viu sense accés a serveis elèctrics. Tanmateix, en aquestes zones abunden les restes agrícoles. Tot i que la tecnologia per a la producció d'electricitat a partir de biomassa agrícola avança, la promoció de l’electrificació rural descentralitzada continua sent un repte, especialment en països en desenvolupament com Ghana, atesa la varietat i la complexitat de factors que condicionen l’aprofitament energètic de la biomassa. Aquesta complexitat s'ha tractat en exercicis acadèmics, però amb poca aplicabilitat pràctica per a planificadors d'energia, promotors i inversors. A fi de contribuir a una millor planificació i presa de decisions, aquesta Tesi desplega un marc integral d’anàlisi tenint en compte quatre components (desenvolupament social, organitzatiu/institucional, tècnic, i financer), flexible per adaptar-se a diferents configuracions de subministrament d'energia i escenaris reguladors. Aquest marc s'ha aplicat a tres casos reals a Ghana, recollint dades de camp, modelitzant la viabilitat tecno-econòmica i debatent els resultats amb promotors públics i privats. La primera configuració consisteix en la generació elèctrica a partir de restes agrícoles de petites plantacions rurals, en 14 districtes a Ghana, on s?ha determinat la biomassa disponible i la seva localització per calcular les distàncies màximes que permetrien la rendibilitat de petites centrals elèctriques. Els resultats indiquen que un mínim de 22 a 54 plantacions (de 10 ha. cadascuna) haurien d'agrupar-se per permetre un subministrament de biomassa econòmicament viable a una planta de 1000 kWe. Financerament aquesta inversió no seria viable amb les tarifes actuals d’injecció a xarxa; un increment d’aquesta tarifa en un 25%, o bé una subvenció mínima del 30% del cost d'inversió són necessàries per garantir la viabilitat. La segona configuració se centra en la co- i la tri-generació a partir de restes agrícoles. Els resultats de l’anàlisi tècnic-econòmica mostren que centrals de 600 kW i 1 MW per autogenerar electricitat, calor (per assecar mandioca o de blat de moro) i fred (per refrigerar tomàquets) són factibles, fins i tot aportant un retorn anual mínim del 20% per a inversors externs. A més de l’electricitat, en cas de poder vendre com a mínim un 60% de la calor produïda, es podria pagar entre 29 i 64 USD per tona de biomassa. La consideració de bons de carboni a preus habituals de mercat internacional té poc impacte en els resultats del projecte; si es consideren esquemes més favorables (com els bons de carboni a Suècia), la viabilitat de les plantes de co-i tri-generació a partir de restes agrícoles seria possible fins i tot amb un baix nivell de vendes de calor residual. La tercera configuració tracta el servei elèctric amb microxarxes basades en la gasificació de restes agrícoles de comunitats rurals. Els resultats de l’anàlisi en 5 comunitats mostren que el potencial de generació elèctrica a partir de la biomassa disponible supera la demanda elèctrica projectada. El finançament només a partir d’aportacions privades no seria viable amb les tarifes nacionals de consum elèctric actuals; en canvi, si s’aplica una tarifa de consum igual a la despesa actual en usos equivalents a l’electricitat (p.ex. llanternes i piles, bateries de cotxe), una subvenció del 35% sobre la inversió inicial permetria una taxa interna de retorn del 15% a inversors privats, mentre que un 60% la subvenció permetria una taxa interna de retorn del 25%.Els resultats d'aquesta investigació han estat considerats pels grups d'interès de Ghana dins de la formulació de polítiques i regulacions d'electrificació rural, i perspectives de trigeneració i els minigresos de biomassa també han desencadenat l'interès dels inversors privats internacionals i ghanesos

Remotely located and sparsely populated areas often do not have access to an efficient grid connection for electricity supply. However, plenty of biomass is normally available in such areas. Instead of employing island solutions such as small diesel generators or large battery stacks for power provision, a flexibly operating microscale biomass power plant using locally available and renewable feedstock is not only an efficient way of providing those areas with competitive and reliable electricity, but also a step towards energy self sufficiency for a large share of areas worldwide, and towards mitigating the looming high costs of grid infrastructure upgrading and extension. A novel power plant design combining thermo chemical and biochemical biomass treatment was developed in this research. This system consists of a small scale gasifier and an anaerobic digester unit, both coupled to a gas storage system and a micro turbine as the generation unit. This design is suitable to continuously provide reliable electricity and accommodate fluctuating residential power demand, and it can be scaled to a level of around 100kWe, which is a fitting size for a group of residential customers, such as in a remote village. The project covers a review of available technology; the choice of suitable technology for such a plant and the design of the system; the set up of a detailed plant model in chemical engineering software; extensive simulation studies on the basis of load profiles to evaluate and optimise operation; and feedstock sourcing, efficiency and economic analyses. It will be shown that such a system is a feasible and economic solution for remote power supply, and that it can overcome many of the current obstacles of electrifying rural regions.

The main aim of this master's thesis is innovative approach to design of self propelled sprayer with technical, esthetic, ergonomic and economic demands. The final design with it's modern and functional look should be an attractive element of agrotechnics. Another aim is also to fulfill social and psychological functions and address the public about protection of cultivated crops with emphasis on alternative energy and other uses of agricultural machinery.

Electrification of households in rural area and isolated regions plays a significant impact on the balanced economic development. Brazil grows with a high population growth rate, but still parts of rural area and isolated regions do not have the accessibility of electric power. This study focuses on the feasibility study of a hybrid PV-wind-biomass power system for rural electrification at Nazaré Paulista in southeast Brazil. This study was performed by using the hybrid renewable energy system software HOMER. The wind and solar data was collected from Surface meteorology and Solar Energy-NASA, and the biomass data was collected and estimated from other previous studies. The result shows, the hybrid PV-wind-biomass renewable system can meet 1,601 kWh daily demands and 360 kW peak load of the selected rural area. The power system composed of 200 kW PV panels, 200 kW biomass generator, 400 battery banks, and 200 kW converter. All the calculations were performed by Homer and the selection were based on the Net Present Cost (NPC) and Levelized cost of energy (COE). Because of the fossil fuels’ negative impacts on human health and environment, all the energy sources for this system are renewable energies which have less pollution.

Thesis (MBA)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: The goal of this study was to investigate the feasibility of a small-scale biomass gasification system within the context of a cooperative wine cellar operation in the Western Cape of South Africa. Central to this goal was the questions whether the time for the implementation of such small-scale renewable energy technologies in South Africa has arrived, in light of the status quo which has changed drastically from the days of abundant and cheap coal-based electricity, and whether the new opportunities afforded by the CDM can help foster financial feasibility. There are various macro-drivers contributing to the current-day emphasis on renewable energy and cogeneration projects. The first and most pressing driver is the global climate change imperative, while the others include the increased aspiration of countries towards energy security, the realization of the importance of sustainable development and the subsequent renewable energy policies that falls within the ambit of sustainable development. Small-scale biomass gasification technology still poses some challenges, particularly when it comes to the gasification of agricultural residues, as with grape residues in the case of this project. The most important technical feasibility problem to overcome is the low ash agglomeration temperature of grape residues reported in the literature. Although the local equipment manufacturer foresees no problem in this regard with their system design - since they have conducted tests on sunflower seed residues, which have similar ash properties, without experiencing any agglomeration problems - the seriousness of this aspect will be confirmed during pilot trials. In order to be eligible for emissions reduction trading under the CDM, the project must adequately demonstrate that the emissions reductions are additional to the business-as-usual scenario, in both the environmental and financial sense. The project will satisfy the environmental additionality requirement, since in its absence the wine cellar will continue its full reliance on coal-based electricity from the grid. Financial additionality, in its strictest sense, requires for the project to be infeasible if it does not pursue CDM participation, which the financial feasibility modeling results indicated to be true in this case. A feasibility model was developed to - subject to the input parameter values assumed and basic assumptions made - be able to assess the financial viability of the project. The main assumptions were that the private feed-in into the national electricity grid was available to all IPPs, in spite of the fact that in its Medium Term Power Purchase Program me (MTPPP) of May 2008 Eskom had only requested expressions of interest from IPPs that had a generating capacity of 5MW and higher to install private base load capacity. This assumption is commensurate with the country's renewable energy targets and the official government aim of achieving a 30% contribution from IPPs to the national electricity mix. The second assumption was that the 65 to lOOclkWh offered by Eskom in its MTPPP will be applicable to sub-SMWe IPPs as well (Creamer, 2008), and that this lower bound electricity price of 65clkWh can be applied over the whole project lifetime. Inherent to this assumption is the further supposition that the progressive decline of electricity prices to an eventual level of 35clkWh by 2018 foreseen by Eskom will not materialize, due both to the sustained pressure an expanding South African economy will put on the considerable but time-consuming supply-side initiatives launched by Eskom, and the likelihood for price premiums to be introduced for clean electricity in order to meet the country's renewable energy targets. From the assumed input parameter values the initial capital and COM expenditures, operating revenues and costs over the project lifetime were determined, and then used to calculate the net cash flows, where after the NPV was computed to serve as the deciding criterion on financial feasibility. A discount rate of 18% was assumed, corresponding with the subjectively judged risks that the project posed as a small-scale renewable energy system within the wine cellar operations. In the case where the project excluded all CDM aspects, the NPV was negative at - ZAR342 573, but this improved to ZAR325 193 if the project participated in the CDM. Thus it was concluded that the project will only be financially feasible if it includes CDM participation, and that this positive contribution can be leveraged by pursuing a programmatic CDM approach. This entails the development of this project as part of a larger program in which similar projects are implemented as they arise, up to the official UN limit of 15MWe in total to still qualify as a small-scale program. The nature of the assumptions that form the backbone of this study indicate that the positive financial feasibility result in the case where the project includes COM participation will become practically relevant only over the short- to medium-term as these assumptions become reality in South Africa. Therefore, although the time for such small-scale renewable energy projects has clearly not arrived as yet, it would seem that it is indeed around the corner.
AFRIKAANSE OPSOMMING: Die mikpunt van die navorsing was om die lewensvatbaarheid van 'n klein-skaal biomassa vergassing sisteem binne die konteks van 'n kooperatiewe wynkelder in die Wes-Kaap van Suid-Afrika te ondersoek. 'n Sentrale aspek was die vrae of die tyd aangebreek het om klein-skaal volhouhare energie projekte in Suid-Afrika tot uitvoering te bring, gesien in die lig van 'n status quo wat drasties weg beweeg het van die tydperk toe elektrisiteit volop en goedkoop was, en of die geleentheid wat die CDM bied sulke projekte finansieel lewensvatbaar kan maak. Daar is verskeie eksterne makro-drywers wat bydrae tot die huidige fokus op sulke volhoubare energie projekte. Hieronder tel globale klimaatsverandering as die dringendste drywer, terwyl die res onder andere die hernuwe strewe van lande tot verbeterde energie-sekuriteit, die besef van die belangrikheid van volhoubare ontwikkeling en die daaropvolgende volhoubare energie beleid stappe insluit. Daar bestaan nog etlike tegniese uitdagings tot die toepassing van klein-skaal biomassa vergassing tegnologie, spesifiek met betrekking tot die vergassing van afval landbou byprodukte, soos wat die geval is met druiwe afval in hierdie projek. Die belangrikste tegniese uitvoerbaarheids-aspek wat aandag verg is die lae smeltpunt van druifafval-as wat in die literatuur rapporteer word. Alhoewel die plaaslike toerustings-vervaardiger nie enige probleme in hierdie verhand voorsien nie, aangesien toetse met sonneblom afval - met as-eienskappe rofweg identies aan die van druiwe-afval - geen smelting van die as getoon het nie, sal dit tog nogsteeds aan verdere toetse onderwerp word. Vir die projek om te kwalifiseer as geskik vir verhandeling in kweekhuisgas vermindering deur middel van die COM, moet dit voldoende bewys kan word dat alle uitlaatgas vermindering addisioneel is tot wat die geval sou wees in die gewone gang van besigheid. Hierdie addisionaliteit is relevant in beide 'n omgewings- en finansiele sin. Hierdie projek sal orngewings-addisionaliteit bevredig deurdat die wynkelder in sy afwesigheid volkome afhanklik van die steenkool-gebaseerde elektrisiteit vanaf die nasionale netwerk sou bly, terwyl finansiele addisionaliteit bewys is deur die finansiele lewensvatbaarheids-model wat getoon het dat die projek slegs ekonomies uitvoerbaar sal wees indien dit CDM deelname insluit. Die lewensvatbaarheids-model is ontwikkel om die ekonomiese uitvoerbaarheid van die projek te evalueer, onderworpe aan die aangenome inset parameter waardes en basiese aannames in die studie. Die hoof-aanname was naamlik dat privaat terugvoer in die nasionale elektrisiteits-netwerk vir alle grootte IPPs moontlik is, ten spyte van die feit dat Eskom se MTPPP van Mei 2008 slegs kapasiteite van 5MW en groter aanvaar bet. Hierdie aanname is gebaseer op Suid-Afrika se volhoubare energie teikens en die regering se offisiele mikpunt om 30% van alle krag-voorsiening vanaf IPPs te bekom. Die tweede hoof-aanname was dat die 65 tot 100clkWh wat Eskom in sy MTPPP aangebied het, ook van toepassing sal wees op sub-SMW IPPs (Creamer, 2008), en dat die laer prys-limiet van 65c/kWb oor die hele projek-leeftyd toegepas kon word. Inherent tot hierdie aanname is die verdere veronderstelling dat die progressiewe daling in elektrisiteits-pryse tot 'n eventuele vlak van 35clkWh voorsien deur Eskom nie sal realiseer nie, beide as gevolg van die volgehoue druk wat die groeiende Suid-Afrikaanse ekonomie op die aansieniike, maar tydrowende, opwekkings-kapasiteit uitbreidings van Eskom behoort te plaas, en ook die hoe waarskynlikheid dat prys premiums vir skoon elektrisiteit ingestel word sodat Suid-Afrika sy volboubare energie telkens kan bereik. Die aanvanklike kapitaal en CDM uitgawes, en bedryfsuitgawes en - inkomstes oor die projekleeftyd is vanaf die aangenome inset parameter waardes afgelei, waarop die NPV van die projek uitgewerk is om te dien as die beslissende maatstaf van ekonomiese haalbaarheid. 'n Diskontokoers van 18% is gebruik, ooreenstemmend met die subjektief beraamde risikos wat die projek inhou as 'n klein-skaal volhoubare energie sisteem. Die resultate van die finansiele lewensvatbaarheids-model het getoon dat in die geval waar die projek geen CDM aspekte bevat nie, die NPV hoogs negatief sou wees met 'n waarde van -ZAR342 573, terwyl dit verbeter na ZAR325 193 as die projek CDM deelname insluit. Die gevolgtrekking is dus gemaak dat die spesifieke projek slegs ekonomies haalbaar sal wees indien dit wel CDM deelname insluit, en dat hierdie positiewe finansiele bydrae van die CDM geoptimaliseer kan word deur 'n programmatiese CDM benadering te volg. Dit behels die ontwikkeling van die projek as deel van 'n groter program waarin soortgelyke projekte mettertyd geimplementeer word soos hulle ontstaan, tot by die offisiele VN limiet van 15MWe om sodoende nog te kwalifiseer as 'n algehele klein-skaalse program. Die aard van die hoof-aannames in hierdie studie is indikatief dat die positiewe finansiele lewensvatbaarheid in die geval waar die projek CDM deelname insluit, eers oor die kort- tot medium-termyn prakties relevant sal word soos die aannames bevredig word. Dus, alhoewel die era van klein-skaalse volhoubare energie projekte nog nie aangebreek het in Suid-Afrika nie, lyk dit tog asof dit om die draai is.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The main goal of this study is the generation of electricity using a modern open top biomass gasifier, (having a water gas cleaning system) imported from India, and a 36 kVA engine-generator. The engine, originally a Diesel MWM D229-4 was converted at the Laboratório de Inovação da UFPB to run just with poor gas from the gasifier. The fact that the imported gasifier had been designed to feed a dual engine to generate at the maximum 20 kWe, caused some difficulty when associated with the converted engine which ran just with gas. Therefore, drastic changes needed to be introduced at the original gasifier because when the engine was running at levels of power greater than 8.4 kWe, a sudden interruption occurred due to flooding of the gas cleaning water. Upon the required modifications, the gasifier was able to produce sufficient poor gas to generate 26 kWe of power. The engine was tested for different ignition advance angles: 22°, 20°, 16° e 9° and for two different types of wood. It was noted that the angle adjustment had a great influence not only over the engine performance itself, but also on the efficiencies of the gasifier and consequently of the system composed by the gasifier and the electrical generator. In this adjustment the ignition advance angle of 9° stood out as one that could guarantee economic advantages and better performance for the system, when the entire experimental range of power is considered. Taking into account that in our experiments an additional of 6 kWe was obtained as compared to the designed value for the Indian system operating with a dual engine, running with diesel and poor gas, we can conclude that the present results and considerations point to the importance of using a biomass gasifier as a successful means of solving the electrical energy dilemma in Brazil.
O principal objetivo deste estudo é a geração de eletricidade usando um sistema formado por um gaseificador de biomassa, moderno, topo aberto (com um sistema de lavagem do gás), importado da Índia, e um grupo gerador de 36 kVA. O motor, originalmente a diesel MWM D229-4 foi convertido no Laboratório de Inovação da UFPB, para funcionar com gás pobre. O gaseificador foi projetado para alimentar um motor do tipo dual, com capacidade máxima de geração de 20 kWe. Foi usado, todavia, para alimentar um motor a diesel convertido para funcionar apenas com gás. Nestas condições não gerava potências superiores a 8,4 kWe, uma vez que ocorria parada brusca do motor, decorrente do seu encharcamento pela água de lavagem do gás. Este fato fez com que drásticas modificações no projeto original, fossem introduzidas. As alterações efetuadas possibilitaram a produção de gás suficiente para gerar 26 kWe. O motor foi testado com diferentes ângulos de ignição, 22°, 20°, 16° e 9°, e o gaseificador com dois diferentes tipos de rejeitos de madeira. Verificou-se que o ajuste do motor tinha grande influência nos desempenhos, do motor, do gaseificador e, consequentemente, no do sistema gaseificador/grupo gerador. Neste ajuste destacou-se o ângulo de ignição de 9° que permitiu maiores vantagens econômicas e melhores condições de funcionamento, quando todo o intervalo de potência ensaiado foi considerado. Levando em conta que a potência elétrica produzida com a biomassa residual foi 6 kW acima da estipulada para o sistema que funcionaria com o motor dual, isto é, com diesel e gás pobre, e tratando-se de um sistema ecologicamente correto, pode-se concluir sobre a importância do uso de gaseificadores de biomassa como sendo uma opção para resolver o dilema da energia elétrica no Brasil.

Este trabalho analisa a possibilidade de plantio sustentável de dendê (Elaeis guineensis) e o uso de sua biomassa residual como combustível em uma usina termelétrica para o provimento de energia elétrica em parte do Sistema Isolado, ao sul do Estado de Roraima. Para isso são conjugadas: a análise financeira, os aspectos sociais e as questões ambientais. Parte-se da definição das áreas necessárias para o plantio do dendê e para a instalação da indústria de extração dos óleos de palma e palmiste, associada a uma usina termelétrica movida à biomassa residual de dendê. Em seguida, procede-se a análise financeira, na qual é considerada a venda dos óleos de palma e de palmiste para a indústria alimentícia e de cosméticos, enquanto a biomassa residual (cachos de frutas vazios, cascas e fibras) é utilizada como combustível um uma usina termelétrica de 10MW de potência. A análise conjunta destas atividades indica que é possível obter uma taxa interna de retorno próxima a 16,71% ao ano e um valor presente líquido de R$ 46,9 milhões quando utilizada uma taxa de desconto de 15% ao ano, para um investimento total de R$ 491,5 milhões. Pelo fato de a região analisada estar localizada no Sistema Isolado, foi incorporado ao fluxo de caixa a sub-rogação dos benefícios da Conta Consumo de Combustível. Além de provar-se economicamente viável, no quesito ambiental, o trabalho realiza uma análise quantitativa da redução de emissões de gases de efeito estufa decorrente da substituição das termelétricas a óleo Diesel prevalentes na região pela biomassa residual do dendê. Tal plantio resulta em uma redução de aproximadamente 444 mil toneladas de CO2, assim como promove a recuperação de 28.888 mil hectares de terras degradadas. A análise social, por sua vez, indica que o plantio de dendê permite que cerca de 2.888 famílias permaneçam próximas às suas terras de origem, trabalhando em atividades apropriadas para o bioma amazônico e com uma geração de renda anual de R$ 5.800 somente com o plantio do dendê.
This study examines the viability of a sustainable project with the production of palm (Elaeis guineensis) to supply oil to food or cosmetic industries and the use of the residual biomass as a biofuel by a power plant. The biofuel side of the project aims the provision of electricity in part of the so called Isolated System, in southern Roraima. The analysis combines a financial approach, with social and environmental concerns. The starting point is the definition of the area size for planting the crop and fitting the assumptions of the industries (palm oil mill and biomass-fired power plant). In the procedures it is considered the palm oil and palm kernel oil sales for the food and cosmetics industries, while the residual biomass (empty fruit bunches, shells and fiber) is used as a fuel in a thermoelectric power plant. The analysis points to an internal rate of return close to 16,7% and a net present value of US$27.6 million, using a discount rate of 15% per year, for an investment of US$ 280 million. In environmental perspective, the quantitative analysis points to the reduction in emissions of greenhouse gases from the displacement of the Diesel powered plants, quite common in the region, by residual biomass powered one. Such displacement results in a reduction of approximately 444 thousand tons of CO2, as well as the recovery of 28,888 hectare of deforested areas. In social perspective, the project allows approximately 2,888 families to remain close to their homeland, working in appropriated activities for the local biome, obtaining US$3,400 per year only with palm plantation.

碩士
國立交通大學
機械工程學系
98
This study carried out the 30kW-generator experiments on a small biogas plant in a swine farm to collect data to serve as a preliminary study for constructing a 300-KW power plant of a bigger scale biogas plant in the near future. Firstly, the effects of fuel supply rate together with corresponding different excess air ratio on power generation were studied. Secondly, the effect of oxygen-enriched combustion for engine was tested. Finally, a heat exchanger was installed to recover waste heat from the engine exhaust gas to increase the usage of the energy. The economic benefits were also estimated by the data obtained by this research. The experimental results showed that the optimum biogas flow rate to the present engine is around 240 to 260L/min, and the maximum power generation, the corresponding thermal efficiency and the percentage of consumed CH4 is 26.8kW, 28.7% and 95.4%, respectively, at biogas supply rate of 260L/min. With 3% oxygen-enriched air, the maximum power generation, thermal efficiency and the percentage of consumed CH4 are increased up to 28.2kW, 30.2% and 100% approximately for 260 L/min, and the engine can operate normally at a lower limiting fuel supply rate at 220 L/min. The heat exchanger can recover 923kJ/min of heat leading to an overall efficiency of 47.3% at the biogas supply rate of 240 L/min. With the total swine population (around 4.3 million heads) from the farm scale of over 1000 heads of pigs in Taiwan, the estimation based on data from this study shows the economic benefits of using biogas: Per year, electricity generation of 2.67 × 108 kWhe (corresponding to electricity charge saving of 800 million NT$), nature gas charge saving of 260 million and carbon dioxide reduction of 170 thousand tons.

Energy is an important input for various activities that provide impetus to economic, human and social development of any country. Among all the energy carriers, electricity is the most important and sought after energy carrier for its quality, versatility and ability to perform various technology driven end-use activities. Therefore access to electricity is considered as the single most important indicator determining the energy poverty levels prevailing in a country. Demand for electricity has increased significantly, especially in the developing countries, in recent years due to growth in population and intensification of economic activities. Therefore, providing quality and reliable electricity supply at low-cost has become one of the most pressing challenges facing the developing world. Although sufficient efforts have gone into addressing this issue, little progress has been made in finding a satisfactory solution in alleviating this problem. Currently, electricity supply is mostly dependent on centralized large-scale power generation. These centralized systems are strongly supply focused, fossil-fuel intensive, capital intensive, and rely on large-distance transmission and distribution systems. This results in electricity cost becoming unaffordable to the majority poor which comprises more than 70% of the total population in developing countries like India and the benefits of quality energy remaining with the rich, giving rise to inequitable distribution of energy. Continuous exploitation of fossil fuels has also contributed to local and global pollution. Therefore it is necessary to explore alternate means of providing energy access such that the energy carriers are clean, easy to use, environmentally benign and affordable to the majority of the rural poor. India is at a critical juncture of passing through the path of development. India is also in a unique position that its vast majority of rural population is energy poor which is disconnected from the electricity grid. In this context, the proposed research is an attempt towards developing a greater understanding on the issue of rural energy access and providing a possible solution for addressing this gap. This has been proposed to be achieved by adopting a decentralized energy planning approach and distributed energy systems mostly based on renewable energy sources. This is expected to reduce dependence on imported energy, promote self-reliance, provide economically viable energy services for rural applications and be environmentally safe. The focus is limited to biomass energy route which has many advantages; it is a geographically equitably distributed resource, geographical advantage of having potential to setup energy systems at any location where vegetation is present and not seasonal like other renewable energy technologies. A mathematical model-based approach is developed to assess the feasibility of such a proposal. Models are developed for performing biomass resource assessment, estimating end-use-wise hourly demand for electricity, performing capacity and location planning and assessing economic feasibility. This methodological framework was validated through a case study developed for the district of Tumkur in the state of Karnataka (a state in southern region of India). The literature survey was conducted exhaustively covering the whole span of supplyside and demand-side management of electricity systems, and grid-connected and stand-alone power generation systems, their technical, economic and environmental feasibilities. Literature pertinent to GIS applications in biomass assessment, facility location planning and scheduling models were also reviewed to discern how optimal capacity, location and economic dispatch strategy was formulated. Through the literature survey it was understood that there were very few attempts to integrate both demand-side management and supply-side management aspects in the rural energy context. GIS based mathematical models were sparsely used in rural energy planning and decision making. The current research is an attempt to bridge these gaps. The focus in this study is on effectively utilizing the locally available biomass resource. Assessment of Biomass Potential for Power Generation As a first step, the supply option was studied at village level by overlaying LULC (land use land cover) and village boundary GIS maps of Tumkur district. The result was fortified by the NDVI results from remote sensing images of land use pattern in Tumkur district. A detailed village-level assessment of wasteland potential was made for the entire district. The result showed which shows that in Tumkur district, roughly 17.3% of total geographical land was under exploitable wasteland. Using secondary data and literature, biomass potential indices were prepared for different wasteland types to determine the total biomass potential for power generation. The results based on the GIS data the assessment shows that Tumkur has roughly 17.3% of exploitable wasteland. A complete village-level annual power generation potential was assessed considering both energy plantations from wasteland, existing degraded forests and crop residues. Assessment of end-use-wise hourly Demand for Electricity at Village Level Household survey was conducted for 170 sample households randomly chosen from 15 villages, again randomly selected to represent different socio-economic categories. Using statistical tools like k-means clustering, one-way ANOVA and Tukey’s HSD test, first the households were classified into three economic categories to study the distribution of the households in each sample village. Later based on the number of households of each type in a village, the villages were further classified into five groups based on their socio-economic status. This was done to select the right representative per-household power demand for a village of any particular socioeconomic category. The representative per household power demand in each economic category along with secondary data helped in deriving the electricity daily load profiles for all the villages. Representative demand profiles were generated for different seasons across different sectors namely domestic, agriculture and industry sectors at the end-use level comprising of activities like home lighting, appliances, irrigation pump sets operation and small industry operations. Mathematical Modeling for Optimal Siting of Biomass Energy Systems Since the power has to be generated through biomass route, biomass may have to be transported over a large geographical area which requires efficient design of logistic systems. Apart from that, a major component of cost of biomass power is the cost of transportation of biomass from source to the power plant. Therefore it is important to determine the optimal siting of biomass energy systems to minimize the cost of transportation. Since these optimal locations are based on minimizing Euclidian distance, installing the power generation systems at these locations would also minimize total cost of local transmission and distribution. In order to locate the biomass energy system, K-medoid clustering algorithm was used to determine the optimal number of clusters of villages to minimize the Euclidean distance between the medoid of the cluster and the villages within the cluster, and minimize the total installed capacity to meet the cluster demand. The clustering algorithm was modified in such a way that the total capital cost of the power generation system installation was minimized. Since the total project cost not only depended on capital cost alone, but also on biomass transportation and power transmission costs, these costs were also included in the analysis. It was proposed to locate the energy systems at the medoids of the clusters. Optimal Capacity Planning Installing biomass power systems requires large investments. It is therefore necessary to reduce the peak demand to bring down the installed capacity required. This was achieved by developing heuristics to arrive at an optimal scheduling scheme of the end-use activities that would minimize the peak demand. The heuristics procedure was demonstrated on five representative villages, each from different economic category. The optimal demand profile was used as input in HOMER micro-energy system simulation software to perform a techno-economic analysis. The simulation facilitated a thorough economic feasibility study of the system. This included a complete analysis of the cash inflows and outflows, capital cost of the system, operation and maintenance cost, cost of fuel and estimation of total GHG emissions. There are many limitations in planning at village-scale. The results indicated that capacity planning done at the village level was prone to over-estimation of installed capacity of the system increasing the investment requirement, under utilization of the capacity and suffered from supply scarcity of biomass. This emphasized the need for looking at a bigger conglomerate of villages in other words cluster of villages. In the next step, the optimal capacity planning was performed for one of the clusters formed using the K-medoid clustering algorithm with the power generation system located at the medoid. For demonstrating the practical feasibility of extending the methodology to cluster level, a cluster with maximum number of villages was chosen from the optimal cluster set in the k-medoid algorithm output. The planning was conducted according to the socioconomic category of the villages in the cluster. Economic implications of Stand-alone (SA) vs Grid-connected (GC) Mode of Operation Other important question that was answered in this analysis was a comparison of GC systems with SA systems. Since extension of grid to a village that is not electrified involved drawing high voltage transmission lines from the nearest grid point, installation of distribution transformers and low transmission lines within the village for distribution. Since these involve high costs it was necessary to study whether or not it is feasible to extend the grid or install a stand-alone system. This question was answered by the breakeven distance for which grid extension becomes more economical than a SA system. For each village breakeven distance varied with the total installed capacity and the operational costs. This helped to compare the GC systems vis-à-vis SA systems from the point of view of economic feasibility. Summary It is necessary that planning and strategies be rational and reasonable for effectively assuaging the rural electrification imbroglio. The current study has highlighted the importance of integrating both demand-side-management and supply-sidemanagement of energy systems in the context of planning for power generation and distribution in rural areas. The key findings in the current study are: • The study showed the feasibility of biomass power systems in meeting the rural electricity needs. • Biomass assessment results showed that, if the power demand could be brought down by replacing the existing appliances with efficient ones (ex. compact fluorescent lamps and improved irrigation pump set valves), Tumkur district has enough biomass potential to meet both the current as well as increased future demands for electricity. • The optimal number of clusters minimizing total capital cost of biomass energy systems, transportation cost of biomass and distribution cost of power, was 96 for Tumkur district. For Kunigal block, the optimal number of clusters was 37 and 32 for supply and demand scenarios 1(BAU -Business As Usual) and 2 (with 10% increase in cropland and 20% increase in demand). • The optimal capacity planning emphasized the importance of clustering of villages for minimizing the total installed capacity. The result also showed that the breakeven distance was the determining factor about the choice of GC vs SA systems. The main contributions of this thesis are: i. Hourly demand pattern was studied to estimate the aggregate demand for electricity at village level for different sectors across various seasons. ii. Village-wise biomass resources potential for power generation was assessed iii. Optimal locations for siting biomass energy systems were identified using k-medoid clustering algorithm iv. An optimal scheduling of end-use activities was planned using heuristics method to minimize the installed capacity v. Optimal location, scheduling plan of end-use activities and optimal capacity were determined for individual villages as well as village clusters vi. The economic implications of grid extension vis-à-vis stand-alone mode of operation of the installed biomass energy systems were studied The generalized, multipronged approach presented in this thesis to effectively integrate both demand-side management and supply-side management in rural energy planning can be implemented for any rural region irrespective of the location. The results emphasized that for efficient demand-side and supply-side management, it is important to plan for clusters of villages than at the individual village level. The results reported in this thesis will help the policy and strategy makers, and governments to achieve rural electrification to a satisfactory extent to ensure continuous, uninterrupted and reliable power supply by determining the clustering strategy, optimal cluster size, optimal scale and siting of decentralized biomass power generation systems.

Dissertação de Mestrado Integrado em Engenharia do Ambiente apresentada à Faculdade de Ciências e Tecnologia
Devido à necessidade de reduzir as emissões de gases de efeito de estufa, em linha com o cumprimento das metas estabelecidas pela União Europeia, é necessário explorar opções para a geração de eletricidade com base em fontes renováveis. Em Portugal, está previsto que as duas centrais termoelétricas de geração de eletricidade a partir de carvão sejam descomissionadas até 2030. Em particular, a conversão da central do Pego para operar a biomassa está a ser equacionada. Esta dissertação tem como objetivo principal avaliar os impactes ambientais de ciclo de vida (CV) associados à geração de eletricidade na central termoelétrica do Pego após a sua conversão para operar exclusivamente com biomassa florestal. A análise foi feita considerando a geração média anual prevista para a central, de 10 % da capacidade atual, e máxima de 25 %. Foram desenvolvidos modelos e inventários de ciclo de vida para cada um dos cenários de geração. Para a geração anual média da central, o modelo inclui os processos de extração e recolha, transporte, destroçamento, secagem e torrefação, arrefecimento, moagem e combustão de biomassa e geração de eletricidade para a unidade funcional de 1 kWh de energia gerada. Foi considerado o abastecimento a partir de biomassa endógena e foram analisadas diferentes condições de torrefação, diferentes consumos energéticos no processo de secagem e diferentes fontes de energia para estes processos. Para o funcionamento da central na sua capacidade máxima foram analisados diversos cenários de importação de biomassa: importação de biomassa do Uruguai, importação de biomassa do Canadá, importação de péletes de biomassa do Canadá e importação de péletes torrificadas do Canadá. Através dos métodos ReCiPe e Cumulative Energy Demand foram avaliados os impactes nas categorias alterações climáticas, depleção da camada de ozono, acidificação terrestre, eutrofização de água doce e requisitos de energia fóssil primária. Os resultados mostram que os processos que apresentam maiores impactes ambientais são o transporte (até 55 %), a secagem e torrefação (até 33 %) e a combustão e geração de eletricidade (até 48 %). Verificou-se que com a utilização de biomassa como fonte de abastecimento para os processos de secagem e torrefação, as condições de torrefação de 250 ºC; 30 minutos se apresentam como as mais favoráveis. No caso da utilização de gás de torrefação, juntamente com biomassa, para o fornecimento de energia para a secagem e a torrefação, verificou-se que as condições de 300 ºC; 30 minutos são as que apresentam menores impactes ambientais. Verificou-se que aumentando as distâncias de transporte para recolha de biomassa para o abastecimento da central em 46 % resultou num aumento de impactes ambientais entre 2 e 29 %. No cenário de geração anual máxima verificou-se que a importação de biomassa do Uruguai e a importação de péletes do Canadá são os cenários de importação de biomassa que apresentam os menores impactes ambientais. No entanto, o transporte é responsável por 55 a 91 % dos impactes ambientais. Os diferentes cenários de geração máxima anual de eletricidade (utilização de biomassa endógena e importada) foram comparados com o cenário de geração média anual (utilização de biomassa endógena) e com outros sistemas de geração de eletricidade em Portugal (carvão e gás natural). Concluiu-se que um aumento da geração de eletricidade na central superior ao valor médio (10 % de capacidade) que necessite de biomassa importada, resulta em impactes ambientais superiores à utilização de carvão ou gás natural na maioria das categorias de impacte. A possível conversão da central para operar a biomassa florestal deve, por isso, ter em conta a disponibilidade de biomassa endógena de modo a minimizar os impactes ambientais.
Due to the need to reduce greenhouse gas emissions in line with meeting the targets set by the European Union, options for renewable sources for electricity generation need to be explored. In Portugal, the two coal-fired thermoelectric power plants are expected to be decommissioned by 2030. In particular, the conversion of the Pego power plant to operate with biomass is being equated. The main objective of this dissertation is to evaluate the life cycle (LC) environmental impacts associated with electricity generation in the Pego thermoelectric power station after its conversion to operate exclusively with forest biomass, based on the Life Cycle Assessment (LCA) methodology. The analysis was made considering the expected annual average generation for the plant of 10% of the current capacity and maximum of 25%. Life cycle models and inventories were developed for each of the generation scenarios. For the average annual generation of the plant, the model includes the processes of extraction and collection, transport, shredding, drying and torrefaction, cooling, milling and combustion of biomass and electricity generation for the 1 kWh functional unit of energy generated. It was considered the supply from endogenous biomass and different torrefaction conditions, different energy consumption in the drying process and different energy sources for these processes were analyzed. In order to operate the plant at its maximum capacity, several scenarios for biomass importation were analyzed: biomass importation from Uruguay, biomass importation from Canada, importation of biomass pellets from Canada, and importation of torrified pellets from Canada. Using the ReCiPe and Cumulative Energy Demand methods the impacts on climate change, ozone depletion, terrestrial acidification, freshwater eutrophication and primary fossil energy requirements were assessed. The results show that the processes with the greatest environmental impacts are transportation (up to 55%), drying and torrefaction (up to 33%) and combustion and electricity generation (up to 48%). It was verified that with the use of biomass as a source of supply for the drying and torrefaction processes, the torrefaction conditions of 250 ºC; 30 minutes are presented as the most favorable. In the case of torrefaction gas, together with biomass, for the supply of energy for drying and torrefcation, the conditions of 300 ° C were found to be; 30 minutes are the ones with the lowest environmental impacts. Increasing the transport distances for biomass collection to power plant supply by 46% resulted in an increase in environmental impacts ranging from 2 to 29%. In the scenario of maximum annual generation it was found that the importation of biomass from Uruguay and the importation of pellets from Canada are the biomass import scenarios with the lowest environmental impacts. Howevwe, transportation is responsible for 55 to 91 % of the environmental impacts. The different scenarios of maximum annual electricity generation (use of endogenous and imported biomass) were compared with the scenario of average annual generation (use of endogenous biomass) and other electricity generation systems in Portugal (coal and natural gas). It was concluded that an increase in power generation at the plant higher than the average value (10% capacity) requiring the use of imported biomass results in higher environmental impacts than the use of coal or natural gas in most impact categories. The possible conversion of the plant to operate forest biomass should therefore take into account the availability of endogenous biomass in order to minimize environmental impacts.

H ιδέα της παρούσας μεταπτυχιακής ερευνητικής εργασίας βασίζεται στην παραγωγή ηλεκτρικής ενέργειας με φωτοαποικοδόμηση οργανικών ρύπων, μέσω φωτοηλεκτροχημικών κυψελίδων(PECs). Mε τον τρόπο αυτό επιτυγχάνεται η κατανάλωση των οργανικών ουσιών και η μετατροπή της ηλιακής ακτινοβολίας σε ηλεκτρική ενέργεια. Ο σκοπός της εργασίας ήταν η παρασκευή, ο χαρακτηρισμός, η μελέτη φωτοευαίσθητων ηλεκτροκαταλυτών και η μορφοποίηση τους σε ηλεκτρόδια, των οποίων εξετάστηκε και αναλύθηκε η φωτοηλεκτροχημική τους συμπεριφορά. Η φωτοηλεκτροχημική κυψελίδα αποτελείται από τα ηλεκτρόδια ανόδου και καθόδου, τα οποία φέρουν το φωτοκαταλύτη και τον ηλεκτροκαταλύτη αντίστοιχα. Εξαιτίας του n-τύπου ημιαγωγού που φέρει η φωτοάνοδος καθώς και της πρόσπτωσης της ηλεκτρομαγνητικής ακτινοβολίας πάνω στον ημιαγωγό, παρατηρείται η απορρόφηση φωτονίων και ο σχηματισμός ζεύγους ηλεκτρονίων-οπών. Η διαδικασία απορρόφησης ενός φωτονίου,για τη δημιουργία φωτοφορέων,απαιτεί το ποσό ενέργειας του φωτονίου να είναι μεγαλύτερο ή ίσο από/με το ενεργειακό χάσμα του ημιαγωγού. O ρυθμός επανασύνδεσης των φωτοπαραγόμενων ηλεκτρονίων και οπών περιορίζεται, με τη χρήση «θυσιαζόμενων ενώσεων», οι οποίες μπορεί να είναι δέκτες ή δότες ηλεκτρονίων. Με τον τρόπο αυτό προκαλούνται στην επιφάνεια του ημιαγωγού μη αντιστρεπτές αντιδράσεις, όπως οξείδωση των φωτοπαραγόμενων οπών, ώστε οι διαθέσιμοι φορείς φορτίου να ξεκινήσουν τις οξειδοαναγωγικές αντιδράσεις. Παράδειγμα, τέτοιων θυσιαστήριων ενώσεων αποτελεί η μεθανόλη, η οποία χρησιμοποιήθηκε στη συγκεκριμένη ερευνητική εργασία. Ως φωτοκαταλύτες χρησιμοποιήθηκαν η νανοκρυσταλλική τιτανία, TiO2 και ο σύνθετος ημιαγωγός TiO2/CdS, ο οποίος και παρασκευάστηκε με τη μέθοδο SILAR. Συγκεκριμένα το διοξείδιο του τιτανίου είναι η εμπορικά διαθέσιμη Degussa P-25, με αναλογία ανατάση:ρουτηλίου 3:1. Ως ηλεκτροκαταλύτης χρησιμοποιήθηκε ο εμπορικός καταλύτης Pt (30%)/C, πάνω σε αγώγιμο ύφασμα άνθρακα (Carbon Cloth). Η μελέτη των ηλεκτροδίων πραγματοποιήθηκε σε κατάλληλους φωτοηλεκτροχημικούς αντιδραστήρες, που σχεδιάστηκαν και κατασκευάστηκαν από τον κ. Λιανό για το σκοπό αυτό, ενώ έγινε χρήση λαπτήρα προσομοίωσης ορατής και υπεριώδους ακτινοβολίας. Η νανοκρυσταλλική τιτανία (ΤiO2) ως φωτοκαταλύτης, έχει ενεργειακό χάσμα 3,2eV και απορροφά φωτόνια μόνο στο υπεριώδες φάσμα της ηλεκτρομαγνητικής ακτινοβολίας. Για την αντιμετώπιση του ζητήματος αυτού, τοποθετήθηκε ευαισθητοποιητής θειούχου καδμίου (Csd) του οποίου το ενεργειακό χάσμα είναι 2,42eV και ενεργειακά έχει υψηλότερη στάθμη, από το διοξείδιο του τιτανίου, με αποτέλεσμα την αύξηση της απόκρισης στο ορατό φάσμα. Η ορατή ακτινοβολία απορροφάται από τον φωτοευαισθητοποιητή, ο οποίος διεγείρεται και εφόσον το ενεργειακό επίπεδο του διεγερμένου ηλεκτρονίου είναι ηλεκτραρνητικότερο από τη στάθμη αγωγιμότητας του TiO2, μεταπηδά στο TiO2 και συμμετέχει στην φωτοηλεκτροχημική διαδικασία. Η οπή που διαχωρίζεται από το διεγερμένο ηλεκτρόνιο, παραμένει στον φωτοευαισθητοποιητή και συμμετέχει σε αντιδράσεις οξείδωσης. Η ποιότητα και η αποτελεσματικότητα της καθόδου, παίζει εξίσου σπουδαίο ρόλο με εκείνη της ανόδου. Η απόδοση των φωτοηλεκτρικών κυψελίδων ελέγχεται μέσω του συντελεστή πληρότητας (Fill Factor), ο οποίος φαίνεται να παρουσιάζει μεγαλύτερη τιμή όσο αυξάνονται οι επιφάνειες των ηλεκτροδίων της ανόδου και της καθόδου, ενώ βέλτιστη απόδοση της φωτοηλεκτροχημικής κυψελίδας έχει επιτευχθεί με τη χρήση ηλεκτροδίου Carbon Cloth εμπλουτισμένου με νανοσωματίδια Pt (0.5mg Pt/cm2). Οι κυριότερες κατηγορίες των οργανικών ενώσεων που χρησιμοποιούνται ως οργανικοί ρύποι είναι οι αλκοόλες, οι πολυόλες και τα οξέα, ενώ στην παρούσα εργασία πιο αποδοτική φάνηκε να είναι η χρήση της μεθανόλης.
The idea behind this master’s degree thesis is based on the production of electrical energy through photo-degradation of organic emissions using photo-electrochemical cells. This way the consumption of the organic emissions and the conversion of the solar power to electricity are achieved. This thesis was aiming at the production, the characterization and the study of photosensitive electrocatalysts and turning them into electrodes, whose electrochemical behavior was studied and analyzed. The photo-electrochemical fuel cell is composed of the anode and cathode electrodes, who bare the photocatalyst and electrocatalyst respectively. Due to the n-type semiconductor on the photo-anode and its exposure to electromagnetic radiation, consumption of photons is observed and hole-electron pairs are formed. The energy of the incoming photon needs to be higher than the band gap of the semiconductor, for it to be absorbed and carriers to be created. The recombination rate of those carriers is reduced by using sacrificial agents or hole scavengers, which can be donors or acceptors of electrons. This way non- reversible reactions are achieved. Example of those is methanol, which was used in the present thesis. As photo-catalysts nanocrystals of titanium oxide and the composite semiconductor TiO2/CdS were used. The electro-catalyst Pt/C on carbon cloth was utilized. The study of the electrodes was performed used photo-electrochemical reactors designed by Prof. Lianos in combination with lamps simulating the solar spectrum. The nanocrystals of titanium oxide have a band gap of 3.2eV (in the UV region) which is the reason why CdS was deposited on top. The later has a band gap of 2.42eV and so increases the absorption in the visible region of the spectrum. The visible radiation is absorbed by the CdS layer and since the excited electron in more electronegative than the conduction band of the titanium oxide, it lowers its energy by hopping to the titanium oxide layer and participates in the photo-electrochemical procedure. The hole that’s left behind in the CdS layer is participating in the oxidation reactions. The performance of the photoelectrical cells was calculated through the fill factor and has an increasing value for increasing area of the electrodes. The optimum performance of the photoelectrochemical fuel cell was achieved by using a carbon cloth electrode enriched with Pt (0.5mg Pt/cm2). The primary categories of organic compounds used as organic emissions are alcohols, polyols and acids. The optimum performance was achieved by using methanol.