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Sorbentes de bajo coste para el control de las emisiones gaseosas de mercurio

Otros títulosLow-cost sorbents for control of gaseous mercury emissions
AutorFuente Cuesta, Aida
DirectorDíaz Somoano, Mercedes ; López Antón, María Antonia
Palabras claveSorbents
Coal combustion
Combustión de carbón
Fecha de publicación19-jun-2014
Resumen[EN] Mercury is a highly toxic element which is found both naturally or as a contaminant introduced into the environment (anthropogenic emissions). Coal-burning power plants are one of the largest sources of mercury emissions related to human activities. Reducing mercury emission to the air is becoming a mandatory issue due to its toxicity and persistence in the environment. Devices for particle, sulfur dioxide or nitrogen oxide control available in coal-fired power plants contribute to reducing mercury emissions. In addition control technologies specifically designed to reduce mercury emissions from coal-fired power plants are being developed and tested but have not yet been deployed on a commercial scale. Among these specific technologies, sorbent injection appears a very promising technology, activated carbon being the most frequently used material for this purpose. However, due to economical and operational problems alternative solid sorbents must be found for the implementation of this technology. The aim of this work is to evaluate biomass gasification chars – a byproduct of the thermal processing of organic materials- as mercury sorbents in coal combustion processes. The chars were obtained from the gasification of sunflower husks, poultry litter, clean wood, wood wastes and a mixture of plastic-paper wastes. An exhaustive characterization of the materials was carried out. Mercury retention and oxidation experiments were performed in a laboratory-scale device. The influence of the physicochemical characteristics of the chars, the flue gas composition and the presence of fly ash particles on mercury capture and oxidation processes were determined. In order to propose an interaction mechanism additional kinetic studies and post-retention characterization (programmed temperature desorption and leaching tests) of the resulting solids were carried out. These results will contribute to improving our knowledge about mercury capture behavior and to determining the possible risks of leaching from gasification chars after disposal. The results show that the chars obtained from the gasification of plastic-paper wastes are promising sorbents which exhibit similar retention capacities to those of the commercial activated carbon used as reference material. In general, mercury retention was observed to increase significantly in the presence of reactive species in gas phase. It was found that not only a high carbon content and a well developed microporosity, but also high chlorine and aluminum contents, improved the mercury retention capacity of the chars. A novel method based on the utilization of an ionic exchange resin was employed to determine gaseous mercury speciation. The results show that mercury oxidation in gas phase was mainly promoted by NO2 and, to a certain extent, by SO2+O2. The highest heterogeneous mercury oxidation capacities were observed in the presence of the chars with the highest mercury retention capacities, suggesting that the sorption process also involves the capture of oxidized mercury species. The presence of fly ash particles clearly influenced heterogeneous oxidation but did not affect the mercury retention capacities of the chars. From the kinetic models studied, it can be inferred that the intraparticle diffusion and adsorption steps are important for the global process of mercury adsorption on the chars. The results point to a chemical mercury-char interaction. The leachable concentration of mercury present in the post-retention chars was found to be below the values established as a limit for their disposal as inert wastes on landfill sites by the European Landfill Directive (2003/33/EC).
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