• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 247
  • 120
  • 27
  • 20
  • 15
  • 11
  • 7
  • 7
  • 6
  • 5
  • 5
  • 4
  • 3
  • 3
  • 2
  • Tagged with
  • 568
  • 141
  • 117
  • 108
  • 88
  • 59
  • 56
  • 54
  • 52
  • 51
  • 50
  • 46
  • 46
  • 45
  • 42
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Verificação do efeito de injeção de gás através de válvulas submersas multiporos sobre a lingotabilidade e limpeza do aço

Silva Junior, Valter Garcia da January 2009 (has links)
A limpeza dos aços está diretamente associada ao conteúdo de óxidos dos mesmos, sendo que os diferentes tipos de inclusões não-metálicas presentes podem prejudicar desde os processos de fabricação e conformação até as características necessárias para a aplicação do produto final. As inclusões se formam e se modificam ao longo dos processos de fabricação, e estão relacionadas principalmente às práticas de refino secundário e de lingotamento. Essas inclusões estão sempre presentes nos aços, de modo que é impossível se produzir um aço completamente livre das mesmas. Atualmente, existe uma série de pesquisas buscando o desenvolvimento de práticas e de processos para incrementar a limpeza dos aços. Entre essas está o desenvolvimento de novos materiais refratários adequados às diversas etapas de uma Aciaria. Com especial importância na limpeza dos aços estão as práticas e tecnologias aplicadas no lingotamento contínuo. Neste trabalho foi avaliada a influência do uso de nitrogênio injetado através de poros no colo das válvulas submersas sobre a lingotabilidade e limpeza dos produtos laminados a partir de tarugos. Para este estudo foram testadas diferentes vazões de gás e depois mensurado seu efeito. As técnicas utilizadas para a avaliação foram: verificação da abertura dos tampões; índice de sucateamento nas linhas de inspeção; severidade em ultrassom pelo método de imersão; análise dos teores de oxigênio total e nitrogênio e análise pelo método de distribuição de valores extremos da maior inclusão estimada. Os resultados práticos foram então comparados entre os lotes escolhidos para o teste. Verificou-se através dos dados coletados boa compatibilidade entre as diferentes variáveis e coerência dos resultados com os relatos da literatura. O uso de gás nitrogênio se mostrou ser potencialmente benéfico para a melhoria da limpeza e lingotabilidade do aço, apesar de mais testes serem necessários para a validação das hipóteses levantadas. / The steel cleanliness is directly associated to its inclusion content. The different kind of non-metallic inclusion can harm from the manufacturing and forming processes up to the demanding characteristics for the final products. The inclusions are formed and modified along the steel manufacturing process, and they are related mainly to the secondary refining and casting of steel. These inclusions are always present in the steel, so it is hardly possible to produce steels completely free of them. Nowadays, there are several fields of research concerning with the development of practices and processes to improve steel cleanliness. The development of new lining materials which are suitable for each melting shop step is one of these fields. With special importance over the steel cleanliness issue, the practices and technologies applied to the continuous casting process can be cited. In this work, the influence of nitrogen injection though the pores of the submerged entry nozzle over the castability and cleanliness of rolled products was evaluated. For this study, different gas flows were tested and then measured its effects. The techniques used for the evaluation were: stopper rod opening; rejection index during the inspection lines; severity in immersion ultra-sonic inspection; total oxygen and nitrogen content analysis and largest inclusion diameter estimated by extreme values distribution. The practical results for each lot of steel were then compared. It was verified from, the collected data, good compatibility between these different variables and coherency of the results with the experiences reported in the literature. The use of nitrogen gas showed itself to be potentially good for the improvement of cleanliness and castability of steel, though more trials are necessary for the validation of the considered hypothesis.
192

Aplicação do mecanismo de desenvolvimento limpo: o caso Novagerar / Application of Clean Development Mechanism: the case Novagerar

Gleice Donini de Souza 24 August 2007 (has links)
A Convenção-Quadro das Nações Unidas sobre Mudanças Climáticas, que tem como objetivo final a estabilização das concentrações de gases de efeito estufa em um nível que impeça a interferência humana perigosa no sistema climático, estabeleceu o Protocolo de Kyoto. O Protocolo é um instrumento que permite aos Países do Anexo I (aqueles historicamente responsáveis pelas emissões de GEE) os meios de atingirem suas metas de redução de emissões de Carbono. Para que as metas sejam atingidas, o Protocolo instituiu mecanismos de flexibilização, dos quais destacamos o Mecanismo de Desenvolvimento Limpo (MDL). O MDL prevê financiamentos de Países do Anexo I em atividade que resultem em reduções/seqüestro de Carbono em países Não Anexo I. O primeiro projeto de MDL registrado no Comitê Executivo no mundo é o brasileiro NovaGerar, objeto deste estudo. O propósito deste trabalho é discutir o Protocolo de Kyoto, o Mecanismo de Desenvolvimento Limpo e verificar suas oportunidades a partir do projeto NovaGerar. / The United Nation Framework Convention on Climate Change (UNFCCC) has as final target to establish the greenhouse gases concentration on the atmosphere in one level that impedes the dangerous human interference on the climatic system. The UNFCCC established the Kyoto Protocol, one tool which allows Annex I Countries (that ones historically responsible for greenhouse gas emissions) to achieve their reduction targets. The Protocol put in place flexibility mechanisms - to help Annex I Countries to achieve their reduction targets - among them we highlight the Clean Development Mechanism (CDM). The CDM foresees Annex I Countries financings to activities which result in reduction/sequestration of Carbon in non Annex I Countries. The first CDM project registered in the Executive Committee was the Brazilian NovaGerar, subject of this study. The purpose of this text is to discuss the Kyoto Protocol, the Clean Development Mechanism and verify its opportunities based on NovaGerar project.
193

Mecanismo de desenvolvimento limpo e a difusão de tecnologias de fontes renováveis no setor de energia elétrica brasileiro / Clean development mechanism and the diffusion of renewable technologies in Brazilian power sector

Melo, Mariane Queiroz de, 1982- 19 August 2018 (has links)
Orientador: Ruy de Quadros Carvalho / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-19T16:15:10Z (GMT). No. of bitstreams: 1 Melo_MarianeQueirozde_M.pdf: 1651877 bytes, checksum: 96c77fad53d4f0135ad1faf49866e212 (MD5) Previous issue date: 2011 / Resumo: Principal objetivo desta dissertação é estudar o Mecanismo de Desenvolvimento Limpo como uma influência na adoção de práticas e tecnologias mais limpas e sustentáveis no setor de energia elétrica do Brasil A inquietação sobre as mudanças climáticas tem saído do âmbito puramente ambiental e se tornado uma preocupação econômica e social. A discussão sobre a responsabilidade das atividades humanas para o aquecimento global (ações antropogênicas), sobre os efeitos das mudanças climáticas serem ou não iminentes e o que fazer para impedir o agravamento do problema são questões que nos últimos anos tem orientado o debate ambiental em relação às mudanças climáticas. Com a implantação do Protocolo de Kyoto, o mecanismo proposto para auxiliar a mitigação e o desenvolvimento econômico é o Mecanismo de Desenvolvimento Limpo (MDL). Por meio deste mecanismo, os países desenvolvidos e aqueles em desenvolvimento poderão criar projetos, em cooperação, para atingir os objetivos de redução dos gases de efeito estufa. Desta forma, o MDL serviria como motivação econômica às nações que precisam reduzir suas emissões de dióxido de carbono. Para melhor entendimento da contextualização e classificação teórica do Mecanismo de Desenvolvimento Limpo é apresentado as principais características da Economia Ambiental sobre as questões ambientais e uma visão alternativa a esta corrente de pensamento econômico. Mostrando que a influência do desenvolvimento tecnológico em sistemas de energia e meio ambiente permeia as discussões da política energética e ambiental. Após apresentar o referencial teórico é descrito o setor elétrico brasileiro e em seguida as características institucionais do MDL. A última parte da dissertação apresenta a experiência do MDL no Brasil, descrevendo as atividades de projetos e a estrutura e trâmite dos projetos na instituição brasileira responsável pela análise e aprovação dos projetos. Para analisar os projetos de MDL em energia renovável no País foi necessário entender quais são os procedimentos para aprovação dos projetos e os resultados alcançados no desenvolvimento desses projetos. Após a descrição institucional foi feito o estudo e análise dos projetos brasileiros em energia renovável para geração de energia elétrica, para tentar responder à questão proposta neste trabalho, se MDL representa um estímulo efetivo à adoção e difusão de tecnologias e práticas mais limpas e sustentáveis no Brasil, principalmente no setor de energia elétrica / Abstract: This essay's main goal is studying the Clean Development Mechanism as an influence in the adoption of more practical, clean and sustainable technologies in the electrical electric power sector of Brazil. The inquietude on climate changes has left the environmental scope and is becoming an economical and social concern. The discussion on human activity responsibilities over global warming, the climate changing effects being or not imminent and what to do to avoid the escalation of the problem are questions that have being heading and orienting the environmental debate on climate changing. With the implantation of the Kyoto Protocol, the mechanism proposed to contribute the mitigation and economical development is the Clean Development Mechanism (CDM). Through this mechanism, developed and developing countries will be able to create, together or not, projects to achieve the objectives of reducing the amount of greenhouse gases issued. This way, CDM will stand as an economical motivation to all nations that need to reduce its carbon dioxide emissions. For better understanding of the contextualization and theoretical classification of the Clean Development Mechanism, are presented the main characteristics of Environmental Economics on environmental issues and an alternative view to this economics school. Showing that the influence of technological development in energy and environment systems permeate the discussions of energy and environmental policy. After presenting the theoretical reference, the Brazilian electricity sector is described and then the institutional characteristics of the CDM. This essay last part presents the CDM experience in Brazil, describing the project activities, structures and advances on the Brazilian institute responsible for analyzing and approving the projects. To analyze the CDM projects on renewable energy in Brazil, it was necessary to understand which are the procedures for approval and achieved results while developing these projects. After the institutional description, the study and analysis of the Brazilian projects on renewable energy for electric power generation was made to try answering the question proposed in this essay: whether CDM represents an effective spur to the adoption and diffusion of more practical, sustainable and cleaner technologies in Brazil, especially in the electricity sector / Mestrado / Politica Cientifica e Tecnologica / Mestre em Política Científica e Tecnológica
194

Contribuição para o projeto basico de uma celula de combustivel de eletrolito polimerico

Souza, Vinicius Ricardo de 17 October 2002 (has links)
Orientador: Wagner dos Santos Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-02T13:01:07Z (GMT). No. of bitstreams: 1 Souza_ViniciusRicardode_M.pdf: 5087609 bytes, checksum: 86dd0a3a9b59a2601d2f14847b4a419f (MD5) Previous issue date: 2002 / Resumo: Um dos desenvolvimentos atuais mais significativos em sistemas energéticos está na área das células de combustível. Estes dispositivos que geram energia elétrica combinando hidrogênio (ou hidrocarbonetos) com o oxigênio do ar, apresentam-se como fortes vetores de desenvolvimento científico-tecnológico, que apontam no sentido de substituírem os motores à combustão interna na área dos transportes, assim como para gerar energia elétrica de um modo limpo e eficiente, dentro de um novo mercado, o da geração distribuída. O início das pesquisas em células de combustível ocorreu há mais de 150 anos, por William Grove, mas apenas nos últimos 15 anos, com o grande desenvolvimento na área de materiais, foi que a tecnologia em células e pilhas de combustível tomou-se bastante promissora no cenário energético mundial. É nesse contexto que surge o objetivo deste trabalho, levando em conta estudos e o desenvolvimento do Projeto Básico de uma Célula de Combustível de Eletrólito Polimérico (PEMFC), além de mostrar alguns campos de atuação que oferecem, já como dispositivos comercialmente viáveis, e servindo a sociedade. Considerou-se para tal a literatura especializada, com o projeto sendo construído a partir de software gráfico apropriado. Fezse também uma análise crítica dos dados disponíveis na literatura, anexando-se Folhas de Dados contendo especificações dos componentes da célula. Examinou-se a função de cada componente da célula, descrevendo os processos quimicos, e eletroquimicos que ocorrem neste reator assim como, as suas variáveis de projeto e de processo. Os muitos avanços alcançados no desenvolvimento tecnológico das PEMFC, principalmente no decorrer da década de 90, e a partir dela, através do esforço conjunto entre entidades governamentais e a indústria de vários países, demonstraram a viabilidade comercial desses geradores de energia, principalmente nas aplicações móveis. Assim, em um futuro determinista e imediato, as PEMFC se tornarão realidade como geradores de energia de alta eficiência e, de baixa emissão de poluentes, contribuindo para o desenvolvimento de uma sociedade mais comprometida com os impactos ambientais da geração e consumo de energia, posta a seu serviço e bem estar. As pilhas de combustível devem ser o marco inicial da denominada Era do Hidrogênio / Abstract: One of the most significant recent developments in energy systems is in the area from the fuel ceils. These devices that generate electric energy combining hydrogen (or hydrocarbons) with the oxygen of the air as fortresses vectors of scientific-technological development, that aim in the sense of replace the motors to the internal combustion in the area of the transports, as well as for generate electric energy of a way c1ean and efficient, inside a news market, the from the generation distributed. The beginning from the researches from fuel cells occurred there is more of 150 years, by William Grove, but barely in the last 15 years, with the big development in the area of stuff, went that to technology in ceIls and stacks of fuel cells became promising enough in the world energy setting. It is in that context that the objective of this arises work, leading in count studies and the development of the Project Basic of an Proton Exchange Membrane Fuel Cell (PEMFC), beyond show some fields of action that they offer, already as commercially viable devices, and serving to society. For such, to literature specialized is consult, with the project being built from graphic software appropriated. Make also an analysis critic of the data available in the literature, enclosing Data Sheets, contained specifications of the components from the cell. This work examine the function of each component from the ceIl, describing the chemical and electrochemical reaction that occur in this reator as well as, theirs variables of project and of process. The many advancements achieved in the technological development of the PEMFC, mainly in elapse from the decade of 90, and from of the joint effort between govemmental entities and to industry of several countries, showed to commercial feasibility of those generators of energy, mainly in the automobile application. Like this, in a future immediate, the PEMFC will become reality as generators of energy of high efficiency and, of pollutants emission decrease, contributing for the development of a more committed society with the environmental impacts from the generation and consume of energy, places to its service and comfort The stacks of fuel cell should be the initial landmark from the named Age of Hydrogen / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química
195

From Clean Development to Strategic Sustainable Development : Strategic planning for the Clean Development Mechanism

Dyer, Georges, McKay, Michelle, Mira, Mauricio January 2006 (has links)
Under the Kyoto Protocol, the Clean Development Mechanism (CDM) has the dual objectives of facilitating a cost-effective way of meeting greenhouse gas emission reduction targets and contributing to global sustainable development. Due in part to a lack of consensus on definitions of sustainability and sustainable development and a lack of capacity to address these concepts, there is a risk that CDM projects may fail to move the host country towards sustainability. We suggest the use of a scientific, principle-based definition of sustainability to guide project participants in their decision-making process. We propose a user-friendly project planning tool – CDM Select – that can build capacity for project developers to employ a strategic, whole-system approach to sustainable development and increase the likelihood that CDM projects move society towards sustainability. Early review of CDM Select by experts and practitioners in the CDM arena indicate that it has strong potential to assist in these efforts.
196

The development of a green energy sector model for the Southern African Development Community (SADC)

Ramagoma, Mbavhalelo Justice January 2016 (has links)
The Southern African Development Community (SADC) region, like most parts of the African continent, faces significant modern energy services access challenges. It is estimated that less than 45% of the SADC region’s populace have access to reliable modern energy forms and the situation is worse in rural areas where access is approximately 30%. Poor energy security is exacerbated by electricity power cuts and load shedding in almost all of the member states in the region. With the advent of battery storage, all forms of green energy have the potential to contribute to the shortfall in the supply of peaking power required to meet the daily (morning and evenings) and seasonal (winter) peaks when most power is required on the grid network. The region is endowed with vast green (renewables/low carbon or clean) energy resources. The purpose of this study is to expand the empirical body of research and knowledge on factors that contribute to widespread access success to green energy in the SADC region. Investments into green energy resources require an understanding of the unique characteristics of the energy sector in the region. In order to achieve this, a conceptual theoretical model was developed and tested empirically. Factors that influence green energy access success were identified through literature reviews and discussions with energy practitioners. All identified factors were then operationalised by carefully defining them in the context of the study. In order to test the proposed theoretical model and the hypothesised relationships, a structured questionnaire was developed and sent to energy practitioners from various sections of the energy sector in the region. STATISTICA 12 was employed to analyse relationships between variables and responses between identified groups. Pearson Product Moment Correlation (Pearson r) was employed to determine correlations between variables. Conclusions about hypotheses six (6) to fifteen (15) were made based on correlations between variables. T-tests were employed to make inferences about the views of various categories of respondents with regard to the twelve (12) identified variables. Multivariate analysis of variance (MANOVA) and Analysis of variance (ANOVA) examined associations between the dependent and independent variables with the identified categories of respondents and conclusions about hypotheses one (1) to five (5) and sixteen (16) were also made. The study finds that policy and the regulatory environment are still the main driving force behind energy access in the region. Power generation is managed by authorities’ power utility companies. Unbundling of power utilities supported by new energy business and operating models to accommodate mini and off grid power plants is found to be a key to green energy access in the region. The energy market is transforming in favour of independent power producers (IPPs) and consumers will significantly influence energy access decisions in the future. Green energy power storage to overcome intermittency will feature prominently in the success of green energy access in the region. Widespread access success to green energy will be attained when green energy access is reliable, affordable, efficient, and socially acceptable, meet the demand and reduces environmental pollution. The study recommends that strategic green energy planning must incorporate green energy infrastructure development, projects finance and human capacity development as priorities amongst SADC region’s member countries. Regional energy access enabling institutions must be strengthened; energy policies implemented with vigour and private sector participation enhanced in an integrated energy market.
197

Blossoming Bit by Bit: Exploring the Role of Theatre Initiatives in the Lives of Criminalized Women

Merrill, Elise January 2015 (has links)
This thesis explores to role of theatre in the lives of criminalized women. It seeks to better understand the ways in which theatre initiatives can be used as a tool for participants through various means, such as potentially being a form of self-expression, or a way to gain voice. This exploration was facilitated by conducting a case study of the Clean Break Theatre Company, a theatre company for criminalized women in London, England. Data was collected through performance and course observations and interviews with twelve women. The final themes shape the exploration as participants identify the importance of self expression through theatre, and its ability to aid in personal transformation or growth. Theatre initiatives are important because they create a unique lens into the experiences of these women, as well as being used as a tool for change in their lives.
198

Transition to clean household energy in low-income urban settlements of South Africa : safety, health and low carbon

Kimemia, David Kimani 02 July 2015 (has links)
D.Phil. (Environmental Management) / Clean, efficient, and low carbon energy services are crucial to the sustainable functioning of a household unit. Therefore, this study explores a vital query on the best pathway to achieve universal modern energy access in low-income South African households, based on information gathered from interviews in urban settlements. The thesis is based on published papers touching on thematic areas of household energy access – from baseline assessments to appraisal of modern energy programmes. A set of factors that are necessary for successful introduction and uptake of clean energy are identified for consideration by policy makers. Results indicate widespread use of paraffin and solid fuels in inefficient combustion technologies among low-income urban households even in the rich Johannesburg metropolis. In the absence of formal employment, some township residents use the basic fuels and conventional combustion technologies for productive purposes. Growth in the thermal-intensive informal businesses could be achieved faster through provision of efficient and reliable alternative energy technologies and better operational environment. This study has highlighted the undue risk borne by energy-poor households in the performance of the day-to-day energy tasks. The results show that household risk is positively correlated with the quality and quantity of energy used, with paraffin being the most risky fuel and the apparent risk being larger in non-electrified households. The affected communities have expressed a desire to adopt cleaner and safer forms of energy for residential and economic uses. It is incumbent upon the government and relevant role players to create enabling systems for acquisition of the preferred modern energy streams. An LPG intervention project in the City of Tshwane has demonstrated the inherent potential for modern energy to transform the socioeconomics and overall wellbeing of a family. The impact of such energy interventions could be improved through better-designed energy delivery models that cater for residential and productive needs, leading to sustainable communities. Education and income have been shown to be good precursors for modern energy uptake. Therefore, efforts towards sustainable energy for all should not only focus on indigent assistance and expansion of electrification, but also be intertwined with policies addressing skills need and better household incomes.
199

Monitoring of fouling and clean-in-place (CIP) using the Rotoscope and microscopy and monitoring of trihalomethanes (THMs) produced from electro chemically activated (ECA) water during CIP

Mashangoane, Boitumelo Francina 07 February 2012 (has links)
The unwanted occurrence of biofilms in various industries requires critical remedial action in order to prevent their detrimental effects which potentially result in huge economic losses. Adequate monitoring of biofilms is a powerful tool to aid their thorough understanding and ultimate control. The Rotoscope is an instrument based on the principle of light absorption and reflection that was used in this study to monitor and study biofilms. Biofilm development of cocci and bacilli species was monitored using the Rotoscope and microscopy. Light reflectance decreased over time as the biofilm developed. Information on the different stages of biofilm development could also be deduced from light reflectance assays of the Rotoscope. Microscopy validated results which were obtained from light reflectance assays. Information on the morphology of the bacteria, depth of the biofilm as well as the different stages of biofilm development was deduced from EM and CLSM images. The Rotoscope was an easy, effective, on-line monitoring device for the development of biofilms. It was a lso showed to be useful in coll ecting informati on to help characterize bacteria species present within a biofilm The Rotoscope was integrated into a simulated soft drink (SO) production line to monitor biofouling and the efficacy of a clean-in-place (CIP) regime using electrochemically acti vated (ECA) water. During CIF the Catholyte and Anolyte (components of ECA) were effective as detergent and disinfectant respecti vely. This was indi cated by results obtained from microbial analysis of removable slides from the MPD, microscopic analysis, as well as pH, ORP and EC analysis. The absence of microbial growth and soil on microscope slides from the Rotoscope were a good indication of the high efficacy of Catholyte and Anolyte (components of ECA) as detergent and disinfectant respectively in a crp system. In addition, the re latively constant values reported for pH, ORP and EC before and aft er CIP suggests that the Catholyte and Anolyte were effective during CIF. The effect of Anolyte on trihalomethane (THM) formation was observed because of the presence of chl orine compounds. Low levels of THMs were obtained from CIP effluent which provided a good indicati on that Anolyte is an environmentally friendly alternative disinfectant compared to conventional disinfectants currently used in CIP. Increased pH and the presence of bromide resulted in an overall increase of THMs in systems using dissolved organic carbon (DOC) models (Glucose, maltose and phenol). There was however variation in the amount of THM produced using the three DOC models. The differences were attributed to the composition of organic matter in particular the aromacity and the nature and position of the functional groups of the model DOCs. / Dissertation (MSc)--University of Pretoria, 2012. / Microbiology and Plant Pathology / unrestricted
200

Adaptação e avaliação de desempenho de sistema asseptico para leite fluido em garrafa plastica / Adaptation and evaluation of performance of aseptic system for fluid milk in plastic bottle

Petrus, Rodrigo Rodrigues 17 December 2004 (has links)
Orientador: Jose de Assis Fonseca Faria / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-04T01:05:22Z (GMT). No. of bitstreams: 1 Petrus_RodrigoRodrigues_D.pdf: 1772681 bytes, checksum: a2e739a7a3e2168d1c5de3ebe70fed22 (MD5) Previous issue date: 2004 / Resumo: O objetivo desta pesquisa consistiu na adaptação e avaliação do desempenho de um sistema asséptico piloto para leite fluido em garrafa plástica. O sistema foi avaliado através da identificação e monitoração sistemática de pontos de controle do processo, testes de esterilidade comercial, análises sensorial e físico-química do produto e avaliação da embalagem. Os pontos de controle foram monitorados antes e simultaneamente aos processamentos, a saber: tratamento térmico do leite; conformidade operacional da sala de envase, incluindo pressurização, taxa de movimentação de ar, contagem de partículas totais e microrganismos no ar e avaliação de limpeza e sanificação de superfícies; análise microbiológica da água de enxágüe da linha de processamento e envase, análise das embalagens e de sua água de enxágüe. Quatro lotes de 150L de leite com pH próximo a 6,7 foram processados entre 135 a 144ºC durante 10s em um trocador de calor a placas e acondicionados assepticamente em garrafas de polietileno de alta densidade (PEAD) de 500mL, em uma sala limpa ISO classe 7. A assepsia das embalagens foi feita através de aspersão de uma mistura contendo 0,5% de ácido peracético e 0,8% de peróxido de hidrogênio a 30ºC/10s. O leite processado através do sistema asséptico piloto avaliado foi comparado ao leite longa vida comercial em embalagens cartonadas e em garrafas plásticas de PEAD de alta barreira, aplicando-se testes de aceitação sensorial. Os resultados da avaliação dos pontos de controle do processo indicaram um bom desempenho apresentado pelo sistema desenvolvido, justificado pelas baixas contagens ou ausência de microrganismos nos pontos avaliados. Dos 4 lotes processados, 2 atingiram a esterilidade comercial, baseado nos critérios físico-químicos e microbiológicos adotados. A vida útil do produto, estimada através de testes sensoriais, atingiu 4 semanas para os dois primeiros lotes produzidos, 8 semanas para o lote 3 e 11 semanas para o lote 4. A opacidade das embalagens utilizadas na pesquisa foi de 90%, inferior a opacidade das embalagens comerciais, que foi de 100%. Portanto, a barreira à luz foi considerada insuficiente para a embalagem em avaliação, em virtude da elevada sensibilidade do leite à fotoxidação. Concluiu-se que o sistema asséptico piloto avaliado correspondeu às expectativas de desempenho, devendo, entretanto, ser submetido à implementação de melhorias em sua infra-estrutura para que possa ser eventualmente disponibilizado para processamentos em pequena escala, visando a produção de leite comercialmente estéril acondicionado em garrafas plásticas / Abstract: The objective of this research was the adaptation and performance evaluation of a pilot aseptic system for liquid milk filled into plastic bottles. The system was evaluated by identifying and systematically monitoring the process control points, by commercial sterility tests, sensory, physical and chemical analyses of the product and an evaluation of the packaging. The control points were monitored before and during process as follows: heat treatment of the milk; operational conformity during filling in the aseptic room including pressurization, air movement rate, total and viable particle count and evaluation of surface cleanliness and sanitation; microbiological analyses of the rinsing waters used in the process and filling lines and an analysis of the packages and their rinsing water. Four 150L batches of milk with pH values of about 6.7 were heat processed between 135 and 144°C for 10s in a plate heat exchanger and filled aseptically into 500mL high density polyethylene (HDPE) bottles in an ISO class 7 clean room. The aseptic condition of the bottles was obtained by spraying with a mixture containing 0.5% peracetic acid and 0.8% hydrogen peroxide for 10s at 30°C. The processed milk using the pilot aseptic system was compared by sensory analysis with commercial long life milk filled into carton-type packages and plastic bottles. The results of the microbial evaluation of the control points indicated good performance of the system developed based on the low counts and absence of microorganisms at some evaluated points. Of the 4 batches processed, 2 attained commercial sterility based on the physical-chemical and microbiological criteria adopted. The shelf life of the product, estimated according to the sensory tests, was 4 weeks for the first two batches processed, 8 for batch 3 and 11 for batch 4. The opacity of the packaging used was 90%, lower than that of commercial packaging, which was 100%. Thus the light barrier property was considered inadequate considering the high sensitivity of milk to the photooxidation. It was concluded that the pilot aseptic system evaluated corresponded to the performance expectations, however, it should be submitted to some implementations of improvements in its infrastructure in order to be recommended for small-scale commercially ile milk production / Doutorado / Doutor em Tecnologia de Alimentos

Page generated in 0.0549 seconds