Dispositivo automatizado para a limpeza da superfície refletora de heliostato em sistemas de energia solar concentrada – CSP
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Data
2017-05-19
Autores
Lampkowski, Marcelo [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A possibilidade de redução na oferta de combustíveis convencionais aliada ao crescimento da demanda por energia e a crescente preocupação com o meio ambiente impulsionam a pesquisa e desenvolvimento de fontes alternativas de energia menos poluentes, renováveis e que produzam menor impacto ambiental. Dentre estas alternativas, destaca-se a energia solar, fonte disponível e passível de ser explorada a partir de todas as suas potencialidades. Atualmente, uma das vias tecnológicas de aproveitamento da fonte solar para geração de energia é a heliotermia, também conhecida como energia solar concentrada ou Concentrated Solar Power (CSP), baseada na utilização de superfícies espelhadas que refletem e concentram a radiação solar direta com o objetivo de convertê-la em energia térmica, a partir da qual se gera vapor d’água que irá acionar um ciclo termodinâmico reversível que converte calor em trabalho, conhecido como Rankine. O soiling consiste no depósito de diferentes tipos de sujeiras em uma superfície exposta em um dado ambiente. No caso de usinas CSP de torre central, o acúmulo gradativo de poeira, sujeira ou até mesmo de excremento de pássaros nas superfícies refletoras dos heliostatos causa uma redução significativa na quantidade de radiação solar que atinge o receptor posicionado no alto da torre e diminuição da eficiência de todo o sistema. Assim, faz-se necessário manter um alto fator de refletividade nas superfícies espelhadas dos heliostatos por meio de uma limpeza regular. Este trabalho apresenta a proposta de um mecanismo automatizado para efetuar a limpeza de superfícies refletoras de heliostatos. O desenvolvimento deste dispositivo, desde sua concepção, passando pelas fases de construção, instalação e funcionamento, respeita padrões de eficiência da limpeza, visa o baixo custo de produção, facilidade de instalação e minimização dos impactos ambientais pertinentes, como, por exemplo, baixo consumo de água na operação. Por meio de experimentos realizados em situações reais de aplicação, utilizando para tal um heliostato de 8 m2 localizado no Departamento de Engenharia Rural da Faculdade de Ciências Agronômicas da UNESP, campus de Botucatu, constatou-se que o dispositivo proposto é uma opção operacionalmente e economicamente viável de solução ao soiling quando aplicado na região de Botucatu, principalmente se comparado a outras propostas de métodos de limpeza de heliostatos apresentadas nos cenários internacional e nacional. Além disso, por meio de estudos sobre os impactos ambientais de usinas heliotérmicas, foi possível sugerir melhorias no processo de licenciamento ambiental de usinas CSP no Brasil.
The possibility of reduction in the supply of conventional fuels, the continuous growing demand for energy and the current concern with the environmental scenario influence the development of researches regarding alternative, renewable and less polluting energy sources, which produces less environmental impact. Among these alternatives, it is worth mentioning the solar energy, available source and that can be explored from all its potentialities. Nowadays, one of many the technological process that uses solar energy for electricity generation is the solar thermal one, also known as Concentrated Solar Power (CSP), based on the use of mirrored surfaces that reflect and concentrate the direct sunlight in order to convert it into thermal energy, from which it generates water vapor that will initiate a reversible thermodynamic cycle which converts heat into energy (Rankine cicle). The phenomenon known as soiling consists in the depositing of different types of dirt on a surface exposed in a given environment. In the case of power tower CSP plants, the gradual accumulation of dust, dirt or even bird's excrements on the reflective surfaces of heliostats causes a significant reduction in the amount of solar radiation that reaches the receiver located at the top of the tower and decreases the efficiency of the entire system. Thus, it is necessary to maintain a high reflectivity factor in the mirrored surfaces of the heliostats through a regular cleaning. This work presents a proposal of an automated mechanism to clean up the reflective surfaces of heliostats. The development of this device, from its conception, through the stages of construction, installation and operation, regarding the cleaning efficiency standards, aimed at low production cost, ease of installation and minimizing the relevant environmental impacts, such as, low consumption of water during its operation. Through experiments in real situations, using a 8 m2 heliostat located in the Department of Rural Engineering of UNESP's Faculty of Agronomic Sciences, Botucatu campus, it was verified that the proposed device is an operationally and economically option for the solution to soiling when applied at Botucatu's region, especially if compared to other proposed methods of heliostats cleaning presented in the international and national scenarios. In addition, through studies on the environmental impacts of heliothermic plants, it was possible to suggest improvements in the environmental licensing process of CSP plants in Brazil.
The possibility of reduction in the supply of conventional fuels, the continuous growing demand for energy and the current concern with the environmental scenario influence the development of researches regarding alternative, renewable and less polluting energy sources, which produces less environmental impact. Among these alternatives, it is worth mentioning the solar energy, available source and that can be explored from all its potentialities. Nowadays, one of many the technological process that uses solar energy for electricity generation is the solar thermal one, also known as Concentrated Solar Power (CSP), based on the use of mirrored surfaces that reflect and concentrate the direct sunlight in order to convert it into thermal energy, from which it generates water vapor that will initiate a reversible thermodynamic cycle which converts heat into energy (Rankine cicle). The phenomenon known as soiling consists in the depositing of different types of dirt on a surface exposed in a given environment. In the case of power tower CSP plants, the gradual accumulation of dust, dirt or even bird's excrements on the reflective surfaces of heliostats causes a significant reduction in the amount of solar radiation that reaches the receiver located at the top of the tower and decreases the efficiency of the entire system. Thus, it is necessary to maintain a high reflectivity factor in the mirrored surfaces of the heliostats through a regular cleaning. This work presents a proposal of an automated mechanism to clean up the reflective surfaces of heliostats. The development of this device, from its conception, through the stages of construction, installation and operation, regarding the cleaning efficiency standards, aimed at low production cost, ease of installation and minimizing the relevant environmental impacts, such as, low consumption of water during its operation. Through experiments in real situations, using a 8 m2 heliostat located in the Department of Rural Engineering of UNESP's Faculty of Agronomic Sciences, Botucatu campus, it was verified that the proposed device is an operationally and economically option for the solution to soiling when applied at Botucatu's region, especially if compared to other proposed methods of heliostats cleaning presented in the international and national scenarios. In addition, through studies on the environmental impacts of heliothermic plants, it was possible to suggest improvements in the environmental licensing process of CSP plants in Brazil.
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Palavras-chave
Energia heliotérmica, Espelhos, Sujidade, Heliothermic energy, Mirrors, Soiling