Análisis del comportamiento medioambiental de aceros y fluídos de transferencia de calor implicados en centrales termosolares con tecnología cilindro-parabólica y almacenamiento térmico

El presente trabajo de investigación está desarrollado en el entorno de las energías renovables y, particularmente, centrado en las centrales solares térmicas de concentración con arquitectura cilindro-parabólica.La energía termosolar presenta numerosas ventajas entre las que destaca su gestionabilidad gracias a la inclusión del almacenamiento térmico de energía, que se realiza en tanques de acero ocupados por sales fundidas. Es sabido que el contacto entre acero y sal produce problemas de degradación de materiales que se deben subsanar con el avance de la técnica. A su vez, las centrales termosolares cilindro-parabólicas históricamente se han dotado de un circuito primario compuesto por tubos absorbedores de la radiación solar, fabricados en acero, por los que circula el fluido de transferencia de calor, que se trata de un aceite térmico. Es lo que se conoce como un sistema indirecto.El aceite térmico presenta un techo tenológico en su temperatura de operación máxima lo que supone que para obtener mejores eficiencias en los ciclos de potencia se deben buscar nuevos materiales que lo sustituyan, como pueden ser las propias sales fundidas ya que alcanzan temperaturas de operación superiores. Si se contempla el uso de sal fundida simultáneamente como fluido de transferencia de calor y de almacenamiento térmico, se denomina sistema directo y, actualmente, están desarrollándose estudios que fomentan esta tipología.Todo ello, sumado a la necesidad de mejora de las propiedades de aceros y sales previamente indicados, enmarca esta tesis doctoral en un análisis de materiales. Sin embargo, no se trata de un análisis y selección de materiales desde el punto de vista convencional, en el que se estudian las propiedades mecánicas, químicas, térmicas, etc. de los mismos, sino de un análisis medioambiental. De hecho, esto es la principal novedad y aporte de este trabajo..

Análisis y evaluación de las emisiones de mercurio procedentes de las centrales térmicas españolas

Actualmente la mayor parte de la producción de electricidad es dependiente de los combustibles fósiles. Su combustión lleva asociada una problemática medioambiental relativa a emisiones contaminantes. No sólo los grandes contaminantes como los gases de efecto invernadero provocan la citada problemática, es necesario atender a otro tipo de contaminantes como los metales pesados, tales como el mercurio que daña gravemente los ecosistemas por ser bioacumulativo y biomagnificarse en la cadena trófica. En la actualidad la mayor fuente de emisiones de mercurio a la atmósfera es la combustión de combustibles fósiles por lo que se hace necesario un estudio de los sistemas para monitorizar y reducir las emisiones procedentes de las centrales térmicas que queman éstos. Estudios de la Agencia de Protección Medioambiental de los Estados Unidos han determinado que, de las tecnologías actuales para el tratamiento de gases de combustión en centrales térmicas, la combinación de caldera de lecho fluidizado circulante seguida de filtro de mangas es la que reduce las emisiones de mercurio en mayor medida. También surgen nuevas líneas de investigación para actuar directamente sobre el mercurio como agente contaminante aunque a día de hoy se encuentran en fase de desarrollo. Una muestra de veintiuna centrales térmicas de España ha servido como base para analizar el panorama nacional en lo que a emisiones de mercurio se refiere, para una planta tipo. Conociendo la cantidad de mercurio real que emite cada una de estas centrales, gracias a la base de datos PRTR, y usando el modelo ISC3 de dispersión del aire se obtuvieron las concentraciones de inmisión a las que se ven expuestas las poblaciones en un radio de 50km a la redonda de la central. Se obtuvieron como conclusiones que el relieve orográfico es fundamental a la hora de decidir el emplazamiento de una central térmica ya que, por ejemplo, los valles provocan repuntes de contaminación. También se apreció como una atmósfera inestable favorece la dispersión de contaminantes y que factores de diseño tales como la altura de chimenea son así mismo determinantes.Ingeniería Técnica en Mecánic

Comparative environmental assessment of two materials suited to central tower CSP technology

Compatibility of containment materials with molten salt thermal storage media is a significant technical challenge for Concentrating Solar Power plants. Metal alloys in contact with molten salt must have a specific behavior, mechanical properties and resistance to degradation processes that allow them to operate at temperatures above 500 °C, being both respectful to the environment. Firstly, this study presents two types of specific materials to operate at raised temperatures in Concentrating Solar Power plants, particularly the central tower technology. The materials are AISI 347H stainless steel and the Ni-based alloy HRSA INCONEL 617. Then, a Life Cycle Assessment shows the influence and contribution to different impact categories from the elements that compose both metals, demonstrating that materials that provide better mechanical properties could have environmental shortcomings. This paper aims to contribute to an improved understanding of the environmental implications of these materials and which is the best choice in terms of sustainability. The results showed better environmental behavior in the AISI 347H case against INCONEL 617.Publicad

Life Cycle Assessment of heat transfer fluids in parabolic trough concentrating solar power technology

The majority of parabolic trough concentrating solar power plants consist of an indirect system where the heat transfer fluid (typically synthetic oil) exchanges energy with a secondary circuit which is connected to the power cycle. Synthetic oil has a technical limitation by the maximum operating temperature. This results in the search for new fluids. On the other hand, with the aim of having energy when there is no sun shining, it has increased the use of thermal storage. Thermal energy storage systems are composed of molten salts and presents higher operating temperatures than synthetic oil. Thus, direct systems, in which thermal storage and heat transfer fluid are unified and normally molten salts, emerge to improve the power cycle performance. To determine the future potential of direct systems, this paper evaluates the environmental damage of two types of molten salts and synthetic oil in order to decide whether the use of salts is better than synthetic oil, from an environmental point of view by using the Life Cycle Assessment (LCA) techniques. LCA results showed greater impacts in the syntheticoil case than the molten saltsPublicad

Influence of elemental composition in environmental impacts of steel

The environmental behavior of four steels was analyzed. In the operation phase of concentrating solar power plants, steels withstand high temperature because of its contact with molten salts. Hence, choosing the steel type for the molten salt tanks remains a great challenge. In the cold tank, carbon steel is usually used although an approach with low chromium content steel is being studied for these applications. Likewise, in high temperature applications, such as hot store tank, austenitic stainless steel is the most frequent choice. However, ferritic steel is being considered as a promising material in these applications. As many researchers studied the steel technical properties without considering their environmental damages, this work aimed to introduce the environmental aspects into the material choice by using the life cycle assessment technique. On one hand, the results showed the environmental adequacy of carbon steel against low chromium content steel. On the other hand, the results obtained in those steels suitable in high temperature application revealed significant environmental benefits from the ferritic steel instead of the austenitic steel

Waste tyres valorisation through gasification in a bubbling fluidised bed: An exhaustive gas composition analysis

Waste tyres gasification in a bubbling fluidised bed reactor is evaluated by means of a complete characterisation of the product gas. The experiments are carried out at two temperatures, 700 and 850 degrees C, and various equivalence ratios (ER) while using air as a gasifying. Additionally, the effect of steam is also studied at 850 degrees C. High temperature and low ER increase the production of H2, CH4, and C2H4. Steam addition mainly affects H2 and CO production. Low carbon conversion (CC) into gas and cold gas efficiency (CGE) are obtained, increasing with temperature and ER. The lower heating value (LHV) of the gas decreases with the ER because of the higher partial combustion rates. LHV values range between 12 MJ/Nm3 with steam addition at ER = 0.13 and 850 degrees C to 5.3 MJ/Nm3 at ER = 0.33 and 700 degrees C using air only. Along with a major permanent gas (CO2, CO, H2, CH4, and C2Hn), up to 25 short-chain hydrocarbons (non-aromatic hydrocarbons ranging from C3 to C6+) and two light aromatics are present in the product gas. Among short-chain hydrocarbons, C3 and C4 compounds are present in the highest yields. All these minor hydrocarbon species (i.e., C3 to C6+), not usually reported in biomass or waste gasification studies, yield up to 13 %vol. on a N2-free basis. Their contribution to the gasification performance is important because they account for half of the energy content in the product gas. Therefore, it is important to consider them in the gasification process, not only for energy purposes but also for the chemical industry.This research has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731101 (BRISK II project: Biofuels Research Infrastructure for Sharing Knowledge II). Funding for APC: Universidad Carlos III de Madrid (Read & Publish Agreement CRUE-CSIC 2022)

Recycling CO2from flue gas for CaCO3nanoparticles production as cement filler: A Life Cycle Assessment

CaCO3 nanoparticles as filler have received considerable attention for the mechanical improvement that they provide to cements. However, their life-cycle impact on the environment remains almost unexplored, even if the cement industry is considered one of the largest CO2 emitters. In this perspective, this research work assessed a novel method for using CO2 from cement flue gases to produce nanoCaCO3 as cement filler within the cradle to cradle thinking. For this purpose, two routes of CO2 capture were assessed followed by the study of the synthesis of CaCO3 through a mineral carbonation. Three scenarios for the synthesis of CaCO3 nanoparticles were assessed targeting the use of waste or by-products as raw materials and recirculation of them to reduce any kind of emission. The three scenarios were evaluated by means of the Life Cycle Assessment methodology. Once the best considered route for nanoCaCO3 production was determined, this research work examined the environmental effect of including 2 wt% of CaCO3 nanoparticles into the cement. Closing the loop follows a circular economy approach since the CO2 is captured within the same cement factory. The results were compared with conventional Portland cement. Regarding nanoCaCO3 results, the scenario with simultaneous production of NH4Cl, and using as calcium source CaCl2 deriving from the soda ash Solvay process, proved to be the best option. Moreover, when cement was filled with 2 wt% of this nanoCaCO3, the benefit in terms of emission reductions in the Climate Change category was higher than 60 % compared to the conventional Portland cement.This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement No. 768583- RECODE project (Recycling carbon dioxide in the cement industry to produce added-value additives: a step towards a CO2 circular economy, https://www.recodeh2020.eu/). This paper reflects only the author's view and the content is the sole responsibility of the authors. The European Commission or its services cannot be held responsible for any use that may be made of the information it contains.Publicad

Sustainable management of peel waste in the small-scale orange juice industries: A Colombian case study

Appropriate waste management in emerging economies like Colombia should be an asset for the overall sustainability. In the Orange Peel Waste case, incineration and Anaerobic Digestion are challenging solutions for the orange juice agro-industrial sector for avoiding the landfill, which is the conventional practice. However, these alternatives should be assessed in order to determine their feasibility. This paper aims to understand if incineration and Anaerobic Digestion are potential alternatives to landfill form a techno-economic and environmentally perspective. To this aim, a comparative Life Cycle Assessment was carried out in four scenarios. In the first scenario coal and landfill are used as source of energy and landfill disposal in the actual orange juice process. In the second scenario, the peels are incinerated to avoid landfill and reduce the need for coal. The third scenario includes the valorization of the peels by means of Anaerobic Digestion which produces biogas for the plant energy requirements. In the fourth scenario, apart from the energy from biogas, the digestate becomes a fertilizer for use in the orange crops. The results revealed that scenario III and IV are environmentally friendly options compared to Scenario I, but they incur higher costs than Scenario II. Carbon footprint found that 1.55 kg of CO2 are saving when coal substitution is reduced from 0.493 kg in SI to 0.279 kg in SII. Therefore, Scenario II is more suitable for the Colombian socioeconomic reality since Scenario II is not only techno-environmentally achievable, but also economically feasible. The methodology used in this case study could be applied to other countries or small and medium scale technologies and could also be useful for the scientific community, enterprises and policy-makers.The authors wish to acknowledge the financial support of the Fondo Regional de Tecnología Agropecuaria FONTAGRO [Contract:ATN/RF 16111RG, 2016] and of the Departamento Administrativo de Ciencia, Tecnología e Innovación, Doctorados Nacionales [Contract:727, 2015]. Also this article is the result of the work developed through the "Programa de investigación reconstrucción del tejido social en zonas de pos-conflicto en Colombia" [SIGP 57579] withthe research project "Competencias empresariales y de innovación para el desarrollo económico y la inclusión productiva de las regiones afectadas por el conflicto colombiano" [SIGP 58907]. Finally, the authors would like to express their appreciation to FLP Procesados Company for providing the data for the case study

Jamaican bioethanol: an environmental and economic life cycle assessment

E10 is a blend of 10% bioethanol and 90% gasoline that can be used in the engines of most cars without causing damage. Currently for the E10 blend, Jamaica imports gasoline from Trinidad & Tobago and bioethanol from Brazil because the bioethanol production in Jamaica is at an early stage. However, the country has great potential for bioethanol production. In order to assess the environmental and economic feasibility of bioethanol in Jamaica, this paper presents an economic and environmental life cycle assessment for a case study in Jamaica in two different scenarios. The Baseline Scenario represents the use of E10 in the current conditions in which bioethanol comes from Brazil and gasoline from Trinidad & Tobago. Scenario I represents the use of E10 with bioethanol from Jamaica and gasoline from Trinidad & Tobago. The comparative environmental life cycle assessment revealed that the Baseline Scenario had better results than Scenario I in ten environmental categories. The economic assessment results in Scenario I were 7% higher than in the Baseline Scenario. Hence, the current context (Baseline Scenario) was identified as the scenario with the best economic performance. Therefore, the current situation in Jamaica (Baseline Scenario) scored better results than Scenario I from an environmental and an economical point of views. It is recommended to increase the bagasse cogeneration of Scenario I to lower the environmental impacts. To improve their productivity, it is necessary to improve the Jamaican sugar infrastructure by combining molasses and cane juice to produce bioethanol.Publicad

Sustainability assessment of electricity cogeneration from sugarcane bagasse in Jamaica

Cogeneration from sugarcane bagasse in Jamaica represents a significant opportunity to reduce CO2 emissions and its dependence on a fossil fuel-based energy matrix. Generation of electricity through cogeneration is a huge opportunity in countries where the sugarcane industry is in decline. This article draws on the findings of a case-study on electricity generation through cogeneration in Jamaica to provide some key messages that may be useful for policy-makers and the private sector to make electricity generation by cogeneration a more competitive option the for investors. To this end, this article analyses two scenarios: the first is a Baseline Scenario that assesses the impact of cogeneration technology already installed in a Jamaican sugarcane company where the cogeneration stage produces 2,2 MW; the second one considers that the cogeneration technology is changed to a new biomass based power plant upgrading the cogeneration stage in order to produce 5 MW of power from bagasse. The assessment was carried out by using a complete Life Cycle Assessment, Life Cycle Costing and Social Life Cycle Assessment. The results revealed that generation of electricity from cogeneration derived from bagasse is a suitable alternative adding economic, environmental and social value.Publicad